Thermal Technology · applications (e.g. Hangzhou DADI). Stoker grate WIPs typically have a daily capacity of 1,000 to 1,500 t/d, each line having a maximum throughput of 500 t/d

International Conference on Solid Waste 2011 Moving Towards Sustainable Resource Management

Thermal Technology

Proceedings of the International Conference on Solid Waste 2011- Moving Towards Sustainable Resource Management,

Hong Kong SAR, P.R. China, 2 – 6 May 2011 309

STATUS AND PERSPECTIVES OF WASTE INCINERATION IN CHINA M. Nelles 1*, T. Dorn 1, K. Wu 2, J. Cai 2

1 University of Rostock, Rostock, Germany 2 University of Hefei, Hefei, China

* Corresponding author. Tel: +49 381 498 34 00, Fax: +49 381 498 34 02, E-mail:[email protected]

ABSTRACT Municipal waste incineration in China is currently playing a minor role in the whole waste disposal segment. Primarily, this is caused by the very high specific treatment costs due to costly machinery investments. On the other hand the large amount of biodegradable fractions in the waste and resulting high water content does not promote incineration either. Today more than 60 Waste Incineration Plants (WIP) are in operation in china. Due to the low heating value of the municipal solid waste in China, incineration either requires co-firing of other combustibles or an elaborate pre-drying mechanism. Usually, coal-firing is applied to support a complete combustion. All WIPs do meet with operational problems and offer sample possibilities for optimization and efficiency enhancements. Current plans show that approximately 400 new incineration plants are envisaged over the next ten years. This will also require adaptation of technology and suitable pre-treatment of the biodegradable fractions.

Keywords: Waste incineration, Organic waste, China, Germany

Introduction Global warming, acid rain, depletion of the ozone layer, ocean pollution, and other forms of environmental pollution are influencing human life on a global scale. Along with greater affluence, mass production and consumption since the opening up policy 30 years ago have brought this problem to China. Now, 16 of the world’s 20 most polluted cities are located in China. Pollution came to China; today, Chinese pollution affects the world. According to World Bank and other publications, China is spending 3 to 10 % of its GDP on dealing with environmental pollution. In 2004, China overtook the US to become the world’s largest generator of waste [1]. This was largely a result of a more affluent population, predominantly located in China’s first and second tier cities, copying a newly attainable Western lifestyle. Today, approximately 660 cities in China generate in excess of 225 million tons of MSW per year.

The present paper provides an overview of the state of MSW management in China with the focus on waste incineration. The current waste management process in China is focussed on land-filling and includes waste collection, transfer and separation, as well as recycling and final disposal. Key characteristics of China's municipal waste composition and generation are identified, leading to propositions on enhancing the current situation of MSW incineration in China. Based on the own case study “Waste Incineration in China” in 2009, additional analysis 2010 in China and the long term experience in Germany, some proposals for a sustainable role of the thermal waste treatment in the circular economy of China are made in the conclusions.

Generation, Composition and Disposal of MSW in China

Economic and social progress, leading to new consumption highs, have also brought growth and increasing diversity – of waste. The total volume of municipal waste collected in 1981 amounted to 26.1 mill. Tonnes. By 2002, more than 20 years later, that figure had quadrupled to 110 mill. Tonnes. That is an annual growth of 8.2 %, compared to an annual population growth of around 4.4 %. In 2002 the statistical parameters of the waste collection database were changed, so historical comparisons cannot be accurately made, however they show a 4.6 % growth in municipal waste from 2003 (148 mill. tonnes) to 2005 (155 mill. tonnes) and a decrease in real terms by 2007 (148 mill. tonnes), showing that the propagation of “3R” has made a noticeable entry. From 2003 to 2006 the number of waste treatment and disposal facilities also shrunk (by 27 %) to 419 facilities. Total capacity however, rose by 17.5 % to 258,000 tonnes a day, indicating that more modern and efficient disposal units were put into operation [2]. Research in that field showed, that the current statistics only cover the large municipalities whereas the rural backcountry is not accounted for. United Nations and World Bank estimate the rural waste generation to 0.8 to 1 kg/person and day, adding some 360 kg to each head of the rural population. Considering that still 52 % of Chinas populace lives on

310 Proceedings of the International Conference on Solid Waste 2011- Moving Towards Sustainable Resource Management,

Hong Kong SAR, P.R. China, 2 – 6 May 2011

the countryside, this adds to another pile of 65 million tons per year. Thus the total waste volume that should be dealt with in a sanitary way is more than 225 million tonnes per year.

Waste composition studies have shown, that the organic fraction of municipal solid waste (OFMSW) is above 60 % after sorting of recyclables (plastics, wood, glass and paperetc.) The results are serious environmental burdens caused by landfill gas and leachate emissions. As an example, results of waste sorting studies of the Tongji University for Shanghai and own investigations for Hefei are shown in figure 1.

Figure 1. Residual waste composition in Shanghai [3] & Hefei

The relevant government authorities have acknowledged that the environmental protection and a modern waste management system hold key roles in sustainable and responsible development. To drive this on, China is actively pursuing an exchange of experience and know-how with the developed world. Against this background China made in the last years great efforts to establish the waste incineration. A number of incineration facilities were build and operating experience gained.

Case Study

Incineration of (Organic) Waste in China

The University of Rostock investigated the status of waste incineration in China. In the following, the main results of 2009 and 2010 are represented [4, 5]. Though waste incineration does not yet play a major role in China’s disposal strategy, currently 16 % of MSW is combusted while more than 80 % still goes into landfills. The limitation of land resources, water table contamination, fire- and explosion hazards as well as residential unrest due to foul odors lead to a growing number of WIPs. The combustion of MSW through incineration plants offers several advantages over landfilling: volume is drastically reduced to 10 to 30 % of initial values; the material is rendered inert; and, provided high-calorific material is burnt, the resultant energy can be recovered and transformed into heat and electricity. The major drawbacks are the high investment costs for the incineration plant; the need for trained manpower; and the need to treat flue gas, bunker leakage water and ash, as these contain highly toxic elements.

Within the framework of a study of Chinese WIPs, 30 plants were shortlisted for visits in April and May of 2009. Telephone calls and direct contact to operators during the annual convention of the WIP Association in Shenzhen showed that many of the plants do not allow visitors. As a result, only 15 of the 77 plants currently in operation (19.5 %) could be visited (Table 1). Many of the plants that do not allow visitors and thus could not be viewed belong to operators who have reference plants which they proudly display. Operators are quite selective about whom to show which plant, because most of the plants are run with a much higher coal co-firing content than officially admitted.

China currently has 77 waste incineration plants (WIPs) in operation, using three main technologies. Most large cities use the stoker grate technology, which was imported at the end of the 1980’s. As an innovative response to implementation problems (further described below) China adapted fluidized bed furnaces to



implement waste-co-firing. Stoker grate hold an approx. 60 % market share and fluidized bed furnaces hold an approx. 33 % market share, with rotary kiln technology accounting for the final 7 %. Where implemented, rotary kilns tend to have a capacity under 100 t/d and are used in hazardous waste applications (e.g. Hangzhou DADI). Stoker grate WIPs typically have a daily capacity of 1,000 to 1,500 t/d, each line having a maximum throughput of 500 t/d. Fluidized bed furnaces have a smaller capacity ranging between 100 to 500 t/d. Interestingly the larger stoker grate plants do not generate more electric power. Indeed, early plants faced a series of operational troubles, which in turn led to a series of adaptations.

Table 1. Waste incineration plants for MSW in China 2009/2010 [4]

Discussions with plant operators gave valuable insight into operational methodology as well as problems and solutions. Most of the plants were designed for a calorific value of 5 to 7 MJ/kg. In actual practice only a value of < 5 MJ/kg is achieved due to the high water and organic content. Research showed even today, due to the high content of wet organic fractions, the average lower heating value of Chinese MSW ranges from 3 to 5 MJ/kg, as opposed to the 6 to 7 MJ/kg typically required to obtain a smooth combustion process. MSW bunkers are therefore crucial to pre-dry waste. Within 5 to 7 days, up to 20 % of water content is lost to leakage, which puts an enormous strain on the water treatment facility, where installed. Other developments to combat the challenges presented by the high water content of the MSW are an extension in length of the stoker grates, to allow for further drying and combustion time. Last but not least, insulation walls have been reinforced to keep losses at a minimum. Despite these measures, most of the waste’s heat value is used to evaporate the MSW’s high water content, rather than superheating the turbine’s steam circles. Given that water reduction during firing accounts for 80 % of weight and volume loss, it is not surprising that fluidized bed technology came into favour. By co-feeding MSW into the coal-fired combustion process, power generation units can claim ‘renewable energy status’ and receive the subsidized energy price of 0.55 RMB/kWh, as opposed to the standard 0.33 RMB/kWh paid to wholly coal-fired power stations. District heating is unknown, as heating is not common in southern China (south of the Yangtze River) and tariff and supply regulations are missing.

All plants cover their costs through tipping fees and co-generation fees. With regards to problems mentioned during WIP operation, these were corrosion within the flue gas system (40 % of plants), treatment of leakage water of the bunker (20 % of plants), internal energy consumption (electric efficiency: 20 % of plants), service and maintenance (13 % of plants) and problems caused by the high water/organic content (grate furnaces).

Bottom ash and slag residues from incineration are used as road and construction materials. Typically slag is first sifted for any remaining metals and then sold on to construction companies. Fly ash from the exhaust gas stream is considered to be hazardous waste, which the Chinese State Environmental Protection Agency guidelines require to be stabilized (through cement) and disposed of in secure landfill sites. This rule is however still in the implementation stage, which means that plants are not yet all in compliance. In terms of



air pollution and residues, most Chinese WIPs use air pollution control systems (APC) comprising of an active carbon adsorption system, dry or semi-dry scrubbers, and textile filters [4]. These should be sufficient to properly treat exhaust gases, however due to the corrosive and abrasive materials, they require frequent servicing and maintenance. As maintenance is generally neglected, many plants operate without the required filtering equipment, or with only limited (and insufficient) results.

One of the major problems of all WIPs is the large amount of biodegradable fractions in the waste and resulting high water content does not promote incineration either two solution options are here possible: Either the separate collection of the biodegradable waste and utilization in compost and/or biogas plants, as is done successfully for example in Germany. Or the mixed wet residual waste is treated by pre-drying and mechanical conditioning, which allows an optimized thermal utilization. Foreign entrants promoting pre-drying technology in combination with existing coal-fired power stations, using the hot flue gases to reduce the water content, achieve an RDF quality near to lignite characteristics. Such RDF can then be used to substitute costly primary fossil fuel. Technologies are available, however prior to being transferred to and implemented in China, they need to be carefully evaluated to match local conditions, which may greatly differ from the parameters at the technology’s inception in Europe or America.

Conclusions

The study outcome showed that the China is making great efforts to establish incineration plants for the MSW treatment, while still at the beginning stage. There were few technical and organizational problems to resolve and to realize an ecological useful operation of WIPs in China. To mentioned are here among others the urgently required improvement of the flue gas cleaning systems and the disposal of the solid incineration residues. The main problem is, that the most WIPs combust waste with high organic and water content, which is ecologically and energetically unrewarding.

References [1] World Bank (WB). 2005. Waste management in China: issues and recommendations.

http://siteresources.worldbank.org/INTEAPREGTOPURBDEV/Resources/China-Waste-Management1.pdf

[2] Figures from the China Statistical Yearbook 2010, http://www.stats.gov.cn [3] Sorting results of Prof. Chen (10/2003-9/2004), Tongji University, Shanghai [4] Dorn, T.; Nelles, M.; Flamme, S.: State and development of the waste incineration in China, in

Bilitewski, B.; Faulstich, M.; Urban, A. (eds.): Proceedings 15. Conference Thermal Waste Treatment, march, 9.-10. 2010 in Dresden/Germany, ISBN 978-3-934253-57-5, pp. 13-33, in German.

[5] Dorn, T.; Flamme, S.; Nelles, M.: Conditions to a successful Technology Transfer explained on samples of Waste Disposal Sector, in Nelles, M., Cai, J, Wu, K. (Eds.): Proceedings ICET 2010, 3. International Conference on Environmental Technology & Knowledge Transfer 13.-14 May 2010 Hefei, Anhui, P.R. China, pp. 27- 37, ISBN 978-3-86009-066-4.



AN EXPERIENCE SHARING FROM JAPAN – ADVANCED WASTE-TO-ENERGY TECHNOLOGY FOR CLEAN ENVIRONMENT

H. Fukai *, T. Aoki, A. Okamoto

JFE Engineering Corporation, Yokohama, Japan * Corresponding author: E-mail: [email protected], Tel: +81-45-505-7821

ABSTRACT Waste management is one of the important roles for the society to maintain our living environment clean and healthy. In Japan, Thermal Treatment has been the major technology for hygienic MSW (Municipal Solid Waste) treatment for log period. In this paper, how the thermal treatment developed to Waste-to-Energy is described. The current overall situation of MSW management is presented as well. Several major thermal treatment processes are introduced with technical countermeasures against environmental impact.

Keywords: Waste-to-energy, Solid waste, Gasification, Hong Kong, Japan

Introduction

Japan has a history of treating wastes thermally for more than a century, with learning experience of not only the technical aspects but also management approaches. This does not mean only thermal treatment is adopted in Japan as MSW solution, but other activities like recycling or reducing waste are also developed. Now thermal treatment developed Waste-to-Energy as a power source in Japan and sharing the above experience serve as a good reference in locating the most suitable solution for the MSW management.

History of Thermal Treatment of MSW in Japan

Back in 1880s, before thermal treatment is adopted, epidemics such as cholera and typhus became widespread in Tokyo. Direct dumping of waste caused lots of flies with germs. To improve the situation, the government enacted "Waste material cleaning act" in 1890.

This act set important concepts. One is local government responsibility of city cleansing including waste collection and disposal. The other is that the wastes shall be incinerated to a maximum extent.

These still remain in the current law in Japan and now each local government owns and operates their own thermal treatment plant, and the number of plants in operation is more than 1,300 plants.

Facts & Figures of Waste Management

Figure 1 illustrates the trend of total MSW generation and daily amount per person. MSW generation increased drastically during 1985 to 1990, when “bubble economy”, and started to reduce from 2000, when “3R”(Reduce, Reuse and Recycle) policy was announced by Japanese government. As a result, Figure2 shows that landfill remaining lifetime is increasing, although landfill remaining capacity is decreasing. However, 3R is not only a reason to extend landfill lifetime, but the development of thermal treatment is still working as a very important roles.

Thermal processes applied in Japan

The most widely adopted technology as Waste-to-Energy is “Stoker” type furnace in Japan, and now 75 percent out of 1,300 thermal treatments have Stoker type technology. And “Gasification” technologies are emerging in rather smaller capacity of Waste-to-Energy plants.

Stoker Type

Stoker type is highly matured technology for thermal treatment of wastes with more than 40 years operation history in Japan, and because of well-proven records, stoker type is now suitable for rather large capacity of Waste-to-Energy facility, i.e. 500 ton per day in a single furnace or more.Recently, ash melting furnaces are incorporated with this type of furnaces, e.g. stoker or fluidized bed, to extend capability of recycling ash. Ash changes into molten slag in the ash melting furnaces by heat from electricity of fossil fuel. Molten slag is recycled as a material for road construction.



Figure 1. Trends of total MSW generation and Per Capita Disposal Rate of MSW

Figure 2. Trends of remaining capacity and life of landfills for MSW

Gasification Type

Even “Gasification” is a conventional technology, its application for MSW was not so common and is now emerging in Japan. Lots of Japan-origin gasification technologies for MSW are proposed.While the technical characteristics are different in each type, the main objective of developing the gasification process is to reduce the mass volume of residues, i.e. gasification furnace does not discharge ash, but can produce molten slag that can be recycled. On the other hand, conventional Stoker needs ash melting furnace to produce recyclable slag. In fact, industrial standards for the slag utilization for road construction are established and slag from the MSW gasification facility has been already used in a market.

Pollution Control Technology

During operation of Waste-to-Energy, emission control is very important and its major effluents are flue gas, ash and wastewater. Their countermeasure technologies have been highly developed to meet with each local or international regulation to protect environment. In this paper, dioxins emission is referred, as it is the latest item of emission and frequently discussed.

800

900

1,000

1,100

1,200

1,300

1,400

1,500

25,000

30,000

35,000

40,000

45,000

50,000

55,000

60,000

1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

Per C

apita

Dis

posa

l Rat

e of

MSW

(g

/day

/per

son)

MSW

Gen

erat

ion

( ,0

00t/y

ear)

Fiscal Year

Annual MSW Generation ( ,000tons/year)Per Capita Disposal Rate of MSW (g/day/person)

Source : Ministry of Environment (Japan)



Dioxins

Dioxins emission from MSW thermal treatment has been a major issue that people concerns. Figure 4 describes the typical methods for suppressing the formation and removal of dioxins in recent Waste-to-Energy plant. Dioxins are generated in the furnace where waste is burning, so the first and most important countermeasure to reduce dioxins is controlling stable combustion in the furnace, especially keeping 3T’s are most important. Second countermeasure is quick quenching of flue gas after the furnace as Dioxins

Table 1. Features of Stoker and Gasification Furnaces

Stoker High Temperature Gasification

& Direct Melting Furnace

- Wide range of Capacity - Well Proven with 40 years operations - Less energy consumption - Discharge Ash to final disposal

- Very wide range of accepting waste - New proven technologies - Need supplementary agent; cokes and lime - Less discharge without Ash

Total waste generation

48.11

Group Collection

2.93

Planned Treatment

45.18 (100%)

Reclamation w/treatment

4.51 (10.0%)

Final Disposal

5.53 (12.3%)

Recycling

9.78

Treatment Residue

9.22 (20.4%)#2

Final Disposal

w/treatment 4.71

(10.4%)#3

Direct Recycling

2.34 (5.2%)

Intermediate Treatment

41.97 (93.0%)#1

Direct Final

Disposal 1.20

(2.9%)

Reduction w/treatment

32.76 (72.6%)

Domestic Self-disposal

0.05

by local community

Unit: million tons

by local government

Figure 3. MSW treatment flow of fiscal year 2008 in Japan

can be generated around 300 degree C as well. To secure dioxins emission, further treatment for flue gas can be applied with activated carbon injection before dust collection or SCR (catalyst) after dust collection.These recent development of the preventive technologies has made it possible to reduce the amount of dioxins to the level of public acceptance even in densely populated urban areas in Japan. And the emission level of dioxins measured at stack is far less than 0.1 ng-TEQ/m3N, which is the common emission standard in most of countries.



Figure 4. Dioxin countermeasures in Waste-to-Energy

Conclusions

Even 3R activities have been more and more active in Japan, there still be amount of MSW that should be sent to Waste-to-Energy facility for thermal treatment. The effect of the facility is obvious; generating power from waste, reducing amount of waste for final disposal and extend lifetime of landfill consequently. As such, Japan is always developing technology like gasification, or making effort to minimize environmental impact from these facilities. Based on these experiences for long time period, we are sure to contribute developing countries environmental circumstances with these technologies.

References [1] Annual Report on the Environment. 2004. the Sound Material-Cycle Society and the Biodiversity in

Japan 2010, Ministry of the Environment (2010) [2] Waste Report 2010, Clean Association of Tokyo 23 (2010) [3] Encyclopedia of waste treatment, N. Kojima et.al, Maruzen (2003)



REVIEW OF MSW THERMAL TREATMENT TECNOLOGIES K.C.K. Lai 1, I.M.C. Lo 2*, T.T.Z. Liu 3

1 Environmental Protection Department, The Government of the Hong Kong SAR, China 2 The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China

3 Harbin Institute of Technology, Shenzhen Graduate School. Xili, Shenzhen, China 518055. * Corresponding author: E-mail: [email protected], Tel: +852-2358 7157

ABSTRACT Thermal technologies currently available for MSW treatment include incineration, gasification and pyrolysis technologies. Plasma gasification and pyrolysis technologies for mixed MSW treatment are still limited in small-scale. In addition, rotary kiln incineration systems are mainly used for sludge, industrial or hazardous waste treatment and their applications for mixed MSW are rare because of operation and maintenance issues/limitation. Among the moving grate incineration, fluidized bed incineration and gasification technologies, moving grate incineration is the most favorable technology to be adopted for a large-scale mixed MSW treatment since it is the only thermal technology which has been adopted for treating over 3,000 tonnes per day of mixed MSW. It has the longest track record of operation and shows the highest capability to tolerate fluctuation of MSW characteristics with robust nature when handling mixed MSW, whereas the other two are less robust and usually require pretreatment of MSW.

Keywords: MSW, Incineration, Gasification, Pyrolysis

Introduction

Review of the municipal solid waste (MSW) management practices worldwide indicates that thermal treatment technology is playing an important role in MSW treatment. In some regions/ countries such as Germany (data provided by Eurostat), Japan (Ministry of the Environment), Netherlands (Eurostat), Singapore (Ministry of the environment and water of Singapore) and Taiwan (Department of Waste Management & Recycling Fund Management Board), thermal treatment technology is the core part of their MSW treatment systems. In pursuance of Directive 1999/31/EC on landfill of waste, European Union (EU) members tend to treat or reduce the MSW by alternative solutions (i.e., thermal treatment technology, recycling or composting) so as to reduce the organic waste delivered to landfills. Hence, the amount of MSW being treated by thermal technology in EU 27 countries, on average, increased from 14% in 1995 to 20% in 2007 (Eurostat). In the of view of significant role of thermal treatment technology for MSW treatment, this paper reviews the latest development as well as pros and cons of different types of thermal treatment technologies including incineration, gasification and pyrolysis.

Review of MSW Thermal Treatment Technologies

Moving grate Incineration Technology

Moving grate incineration involves the combustion of mixed MSW on a moving grate consisting of a layered burning on the grate transporting MSW through the furnace (Niessen, 2002), as shown in Fig. 1a (EC, 2006). The waste is first dried on the grate and then burnt at high temperature (850 to 950 oC) with a supply of air. Because of the application of the grate system, moving grate incineration technology does not need prior MSW sorting or shredding and it can also accommodate large variations in MSW composition and calorific value. In addition, moving grate incineration is a very robust and forgiving technology in terms of waste inputs. Recent review of the information obtained from the associated main suppliers including Hitachi Zosen (Hitachi), JFE Engineering Corporation (JFE), Kawasaki, Mitsubishi Heavy Industries Ltd. (Mitsubishi) and Takuma Co. Ltd (Takuma) indicates that over 93% of their MSW thermal treatment plants installed worldwide adopts moving grate incineration systems. Similar phenomenon is also reported by other main suppliers in Europe. It was also reported that at least 106 moving grate incineration plants were built worldwide for MSW treatment since 2003.Moving grate incineration system has a long track record of operation for mixed MSW treatment and has over 100 years operation experience. It is currently the main thermal treatment facility being adopted for mixed MSW treatment. In comparison with other thermal treatment technologies, the unit capacity and plant capacity of the moving grate incineration system is the highest, which range from 10 to 920 tpd and 20 to 4,300 tpd, respectively. Nowadays, moving grate incineration system is the only system which has been thoroughly proven to be capable of treating over



3,000 tpd of mixed MSW without requiring any pretreatment or preprocessing steps. One of the largest moving grate incineration plants was installed by Mitsubishi in 2000 in Singapore and its total capacity is 4,300 tpd composed of six lines of furnaces.

Figure 1. Schematic diagram of (a) moving grate, (b) fluidized bed, and (c) rotary kiln incineration systems

(EC, 2006)

Fluidized Bed Incineration Technology

Fluidized-bed incineration system (Fig. 1b) is an alternative design to conventional combustion system in which the moving grate is replaced by a bed of granular materials fed by an air distribution system. Bubbling and circulating bed types are the main types of fluidized beds used in the incineration system. The incineration process is controlled by varying the waste feed rate and the air flow to the furnace. If the process is shut down for short duration, the temperature of sand bed is typically be maintained at 450-550oC for quick recovery back to 850-950oC (Niessen, 2002). In comparison to moving grate incineration system, the fluidized-bed incineration system generally offers more intense mixing, longer residence time and better residue burnout and is generally used for treatment of wastes with relatively homogeneous composition and small size. Its application for waste combustion began in early 1960s. Since then, more than 100 commercial plants have been installed in the U.S. and there are over 300 plants worldwide. Its application is mainly to municipal sewage sludge, industrial and hazardous wastes such as plastics, waste oil, paper, paper pulp, waste tire, etc. It is recently reported that about 75% (weight) of the wastes currently being treated by JFE and Mitsubishi fluidized-bed incineration systems are either sewage sludge or industrial/hazardous wastes; while mixed MSW only occupies 25%. Moreover, as recently reported by Hitachi, JFE, Kawasaki, Seghers, Mitsubishi and Takuma which had installed over 850 MSW incineration plants worldwide, only about 2% of their MSW incineration plants adopt fluidized-bed incineration systems. Thus, it is generally recognized not a common technology for mixed MSW treatment probably due to its poor performance on treating highly heterogeneous MSW. In fact, pre-treatment of MSW into homogenous feedstock is a pre-requisite prior to feeding of MSW in a fluidized bed incinerator.

Operation problems typical to fluidized bed incinerators include: (1) methods of charging waste to the furnace to ensure good distribution; (2) bed agglomeration; (3) deposit formation and (4) bed erosion. The fluidized bed incineration plants currently in operation have the much lower unit capacity (10-80 tpd) and plant capacity (10-200 tpd) than the moving grate incineration plants. As reported by Hitachi, two fluidized bed incineration plants with a total capacity of 30x2 tpd and 50x2 tpd were installed in Japan in 1999. For JFE, the plant capacity of their fluidized bed incineration plants for mixed MSW treatment was reportedly ranging from 26x1 tpd and 82.5x2 tpd. Although a fluidized bed incineration plant with a total capacity of 514x3 tpd was installed in Allington Quarry, UK in November 2006, material recovery facility are required to remove the recyclables from the mixed MSW and homogenize the MSW size.

Rotary Kiln Incineration Technology

Rotary kiln system was originally designed for processing basic building materials (e.g. cement). Because of its unique capability to achieve a more complete combustion, it has been further developed to apply for



industrial and hazardous wastes incineration (Niessen, 2002), but its application for MSW is rather limited. Generally, a rotary kiln incineration system has 2 chambers: a primary and secondary chamber (Fig. 1c). The primary chamber is an inclined refractory lined cylindrical tube for conversion of solid fraction to gases, through volatilization, destructive distillation and partial combustion reactions. The secondary chamber is to complete gas phase combustion reactions. A rotary kiln incineration system normally does not require prior sorting or shredding, and can accommodate large variations in waste characteristics. It provides good and uniform interaction of waste and combustion areas as well as is easily controlled the residence time of waste in combustion chamber, generally resulting in a more complete combustion than other incineration systems.

The downside of a rotary kiln incineration system includes the relatively high capital cost and land requirement in comparison with other incineration technologies. High heat loss from the kiln shell also leads to its low energy efficiency. Another disadvantage is that the inherent construction of a kiln emphasizes the suspension of particulate in the gas stream and tends to limit mixing of pyrolyzed waste combustible matter with combustion air, resulting in high particulate and hydrocarbon concentrations in the flue gas. The following technical problems may also appear when treating MSW:

Erosion of the refractory materials - MSW is quite abrasive and may lead to significant erosion of the refractory lining materials throughout the operation;

Plastics deposition - At the colder feed end of the rotary kiln furnace, plastics can melt, but not combust leading to a layer of plastic coating onto the internal refractory lining surface;

Clinkering - Clinkering is the formation of solid aggregates through fusion of the MSW ash that adhere onto the refractory-lined surface. It can block the air ports which further reduces air cooling effect, thereby leading to a higher temperature and further clinkering; and

Kiln length - If the kiln is too long, the end of the kiln could get lower temperature because of an insufficient heat released from the combusted waste, thereby resulting that any slag will solidify and form aggregates in this area.

Nowadays, most of the rotary kiln incineration systems installed are used for sludge, industrial or hazardous waste treatment and their applications for MSW treatment are rare. For instance, none of the 50 rotary kiln incineration systems installed by JFE, Kawasaki, Mitsubishi and Takuma are for MSW treatment. According to our research, Hitachi and B&W Volund are the only suppliers currently reporting that their rotary kiln incineration systems have been used for MSW treatment, but their systems are actually not a pure rotary kiln and usually combined with moving grate incineration unit to avoid formation of clinker.

Gasification Technology

Gasification is a process that converts carbonaceous materials into gaseous mixtures by reacting raw materials at a high temperature with a limited amount of oxygen and/or steam. The resulting gas mixture consisting of various energy-rich gas products, such as CO, H2 and CH4, is called syngas. For MSW treatment, development of gasification technologies has been via air, oxygen or steam gasification. The operating temperatures for air, oxygen and steam gasification generally range from 700 to 1,400 oC. The main systems available for waste gasification include updraft, downdraft, fluidized-bed, entrained flow and rotary kiln gasification systems. The characteristics of the gasification systems, waste composition and operational conditions can result in tars and hydrocarbon gases, which are the undesired products from incomplete gasification. Utilization of syngas is often by direct combustion in a boiler or furnace. The heat energy is used either for process heat or to produce steam for electricity generation.

The major waste types currently being treated by the gasification technologies include municipal wastes (i.e. mixed MSW, refuse-derived fuel (RDF), and sewage sludge), industrial and hazardous wastes, and agricultural wastes. The current gasification plants in operation have a much lower unit and plant capacity than the moving grate incineration plants for mixed MSW treatment in which their unit capacity and plant capacity generally range from 20 to 150 tpd and 30 to 405 tpd, respectively. One of the advantages of the gasification technology over the incineration technologies is that it generally generates less volume of the flue gas and less amount of gas pollutants, thereby resulting in requiring less expensive gas cleaning equipment for off-gas treatment. However, pretreatment of MSW to produce fine granules is normally required since gasifier is less robust for mixed MSW treatment. The track record and operating experience



of the gasification technology for MSW treatment is also very limited especially for large-scale treatment. Up to 2008, there were only approximately 90 gasification plants installed worldwide for MSW and RDF treatment (Archer et al., 2008), which are small number in comparison to 900+ moving grate incineration plants installed. All the recently installed gasification plants by Hitachi, JFE and Nippon Steel are limited to the plant capacity ranging from 19x2 to 135x2 tpd.

Plasma Gasification Technology

Plasma gasification is an advanced waste treatment technology. It involves transformation of carbon-based materials of the waste under oxygen-starved environment using an external high heat source (i.e. plasma). The temperature of plasma gasification can be as high as 2,700-4,400ºC or even up to 10,000oC (McKenna, 2009). At such high temperatures, any metals will melt and any inorganic materials such as soil and gravel will be transformed into a vitrified glass. There is no ash remaining to go back to landfills. Any organic matter present will form the syngas, which can be used for subsequent heat energy or electricity generation. The gas composition coming out of a plasma gasification system is lower in trace contaminants than with any kind of thermal treatment system. There are usually no tars or furans in the syngas. Since plasma gasification of MSW requires significant amounts of energy for creating ultra high temperature condition within the furnace, the energy being recovered from the MSW is usually low. A review of the latest development of the plasma gasification indicates that this technology is mainly adopted for some specific uses, such as treating industrial and hazardous wastes, and even low-level radioactive wastes because of the high temperature condition created by the plasma. Phoenix Solutions Corporation (Phoenix), PyroGenesis Inc. (PyroGenesis), and Westinghouse Plasma Corporation (Westinghouse), the key manufacturers/suppliers of the plasma gasification systems for waste treatment, reported that the main waste types currently being treated by the plasma gasification systems mainly include sewage sludge, auto shredder residues (ASR), MSW ash, PCBs-contaminated wastes, dioxin-contaminated soils, medical wastes, etc. Its application for municipal waste treatment is rare and mainly limited to RDF treatment.

PyroGenesis had recently reported that they had installed a pilot plant at PyroGensis’ facilities in January 2002, which was capable of treating between 0.5 and 2.5 tpd of mixed MSW, hazardous flammable waste and ASR. Pheonix reported that 2 plasma gasification plants were installed in Panama (200 tpd) in 2008 and in Poland in 2006 (300 tpd) for MSW treatment, but their systems require mechanical and biological pre-treatment of mixed MSW to produce RDF. As informed by Westinghouse, the demonstration plant with a plant capacity of 85 tpd of mixed MSW installed at Ottawa, Canada in 2007 is the only plasma gasification plant for MSW (alone) treatment, but it adopts a combination of gasification process followed by plasma gasification of the products of incomplete treatment. Other Westinghouse’s plasma gasification plants are installed for the treatment of industrial/ hazardous wastes or mixture of MSW and industrial wastes.

Pyrolysis Technology

Pyrolysis is theoretically a zero-air indirect-heat process in which organic waste is decomposed to produce oil, carbonaceous char and combustible gases. Since no air is required, there would be less volume of flue gas generated for treatment in comparison to incineration and gasification process. Unlike incineration and gasification systems which are self-sustaining and use air or oxygen for waste combustion, an external source of heat is required to drive the pyrolysis reactions. Also, relatively low temperatures, in the range of 400 to 800oC, are required for pyrolysis. Examples of pyrolysis systems generally for waste treatment include fluidized-bed, fixed-bed, rotary kiln and entrained flow systems. Pyrolysis offers the benefit of using the generated oil, which could be used directly in fuel applications. The solid char may be used as a solid fuel, carbon black or upgraded to activated carbon. The combustible gas produced may contain sufficient energy to supply the energy requirements of the waste pyrolysis systems themselves. Generally, most of the waste pyrolysis systems are still at pilot-scales in which sewage sludge and hazardous waste are the main feedstocks. It is less robust than moving grate incineration technology so that its application for mixed MSW treatment is limited and not suitable for large scale uses. If applied, preprocessing of mixed MSW into RDF is usually required. A review of the latest development of the pyrolysis technology indicates that there is still very little track record of the pyrolysis plant for MSW treatment. Up to 2008, there were approximately 30 pyrolysis plants for MSW or RDF treatment worldwide (Archer et al., 2008). According to the information provided by Hitachi which is one of the key pyrolysis suppliers, the typical unit capacity



and plant capacity of a pyrolysis plant for MSW treatment usually fall within 60 to 80 tpd and 130 to 160 tpd, respectively.

Conclusions

Review of various types of thermal technologies for MSW treatment indicates that moving grate incineration system is the most favorable technology for large-scale treatment of mixed MSW since it has been fully proven for the large-scale application without requiring preprocessing of MSW and has the longest track record of operation. It also shows the highest capability to tolerate fluctuation of MSW characteristics with robust nature. For the other incineration technologies, gasification and pyrolysis technologies, they are either limited in small-scale, limited for industrial/hazardous waste treatment, requiring preprocessing of mixed MSW before feeding, which make them not suitable for large-scale mixed MSW treatment.

References [1] W. R. Niessen. 2002. Combustion and Incineration Processes – Third Edition, Revised and Expanded,

Marcel Dekker, Inc., New York. [2] EC 2006. Integrated Pollution Prevention and Control - Reference Document on the Best Available

Techniques for Waste Incineration, European Commission. [3] Y. Nie. 2008. Development and prospects of municipal solid waste (MSW) Incineration in China.

Frontiers of Environmental Science and Engineering in China 2: 1-7. [4] E. Archer. K. Whiting. J. Schwager. 2008. Briefing Document on the Pyrolysis and Gasification of

MSW, Juniper Consultancy Services Limited, Gloucestershire, England. [5] P. McKenna. 2009. Into thin air. New Scientists 25: 33-36.



HYDROTHERMAL TREATMENT OF INCINERATION FLY ASH: THE EFFECT OF IRON OXIDES

D.Z. Chen *, Y.Y. Hu, P.F. Zhang

Thermal & Environmental Engineering Institute, Tongji University, Shanghai, China *Corresponding auther.Tel:+86 15800446445, E-mail:[email protected]

ABSTRACT The effect of iron oxides on decomposition of PCDD/Fs contained in incineration fly ash during hydrothermal process was investigated. Experimental results indicated that iron oxides formed from mixture of ferrous sulphate and ferric sulphate in the hydrothermal reactor enhanced PCDD/Fs decomposition, especially for the decomposition of 2378-TCDD and 2378-TCDF at the reaction temperature of 290ºC. The decomposition rate of PCDD/Fs was increased to 89.6% by I-TEQ when iron was added as mixture of ferrous and ferric sulphates at 3% (wt/wt); while without active spike of iron salts, the decomposition rate of PCDD/Fs was only 46.17% by I-TEQ. When iron oxides were formed from mixture of ferric and ferrous sulphates, cooling procedure after hydrothermal process becomes more flexible, and longer reaction time was helpful to increase decomposition rates.

Keywords: Incineration fly ash, Iron oxides, Hydrothermal process, PCDD/Fs, Decomposition rate

Introduction

The cheap iron oxides (FexOy) have been reported to have a positive effect on catalytic oxidation of gaseous dioxins (PCDD/Fs) at temperatures below 200ºC, in the presence of ozone[1]. It is reasonable to believe iron oxides might also have catalytic effect on decomposition of PCDD/Fs contained in municipal solid waste (MSW) incineration fly ash during hydrothermal process.

Hydrothermal process for incineration fly ash provides a relatively milder condition compared to high-temperature refractory conditions and it is less energy consuming due to its moderate operating temperatures [2]. Elimination of the PCDD/Fs in fly ash under hydrothermal condition has been explored by Yamaguchi et al. [3] and they showed that PCDD/Fs would decompose when the hydrothermal reactions took place under 573K for 20 minutes in 1N NaOH solution containing 10% (vol/vol) methanol, and that toxicity of PCDD/Fs in the treated fly ash decreased to 0.03 ng-TEQ/g. Although good results were obtained in their work, the reagent, methanol that they used was poisonous and the caustic alkaline conditions would not be acceptable in practice under high pressure.

Under hydrothermal conditions iron added in form of Fe(II) would generate FeOOH or FeO oxides that bind to heavy metals [4]; and these newly formed iron oxides could act as potential catalysts for PCDD/Fs decomposition also. The objective of this study is to prove this effect.

Materials and Methods

Materials

MSWI fly ash was sampled from a full-scale operating incinerator in southeast of China, which adopts spray-dry flue gas scrubbing system followed by a bag filter. The total PCDD/Fs concentration of raw fly ash was 11463.3ng/kg and its toxicity was 628.8ng-TEQ/kg. Its original iron content was 1.42%, so it was pre-treated to remove soluble iron content. Ferrous sulphate and a mixture of ferrous and ferric sulphate were introduced during hydrothermal process. Both ferrous sulphate and ferric sulphate used here were of analytical purity.

Experimental Methods

The autoclave used for the hydrothermal process is reported in Xie et al.[2]. For each experimental batch, pre-treated fly ash and twice-deionised water were mixed, ferrous and ferric salts were dissolved into the suspension according to special dosages as given in Table 1. Afterwards the suspension was pumped into the autoclave to be heated to 563K (with corresponding pressure of 7.44MPa) and kept mixing at that temperature for 0.5 to 3 hours, in this process new iron oxides were formed. After hydrothermal treatment,



the samples were sent to an authorized dioxin laboratory for analysis of PCDD/Fs concentrations with help of HRGC-HRMS method.

Table 1. List of experimental scenarios with different Fe(III)/Fe(II) addition ratio (wt % of fly ash)

Scenario 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Fe (II) (wt%) 1.0 4.0 0.33 0.33 0.33 0.33 0.33 6.0 5.0 0.66 1.33 0 0 0 Fe (III) (wt%) 2.0 0 0.67 0.67 0.67 0.67 0.67 0 0 1.34 2.66 0 0 0 Reaction time 1h 0.5h 1 h 2h 3h 1h 2h

Ending procedure Cooling slowly Cooling

quickly Cooling slowly Cooling quickly

Results and Discussion

Effect of Cooling Procedure

The influence of cooling procedure after hydrothermal thermal treatment is shown in Table 2. For Scenarios (12), (13) and (14) there was no addition of Fe. For Scenario (4) and (5) the same iron was added except for the difference in cooling procedures adopted after hydrothermal treatment. It can be seen that fast cooling after hydrothermal treatment is preferable if no iron is added. When iron was added as a mixture of Fe (II) and Fe (III), cooling slowly was better for reducing the toxicity of the final PCDD/Fs. Usually the fast cooling cannot be ensured in practice, so addition of iron is preferable.

Table 2. Concentration of PCDD/PCDFs after hydrothermal thermal treatment (I-TEQ ng/g)

PCDD/Fs Scenario (12) (13) (14) (4) (5)

2378TCDD 0.115968 0.152708 0.119956 0.038292 0.035450 2378TCDF 0.007716 0.009067 0.006463 0.004531 0.003408 Total I-TEQ 0.300384 0.237185 0.195197 0.103560 0.143741

Influence of Iron Dosage

The changes in the decomposition rates of PCDD/Fs with Fe dosage, when .the reaction time was 1h and slow cooling was adopted for the ending procedure is shown in Fig. 1. The decomposition rate was defined as the ratio of the reduced concentration of the 17 toxic isomers’ to their original concentrations; or the ratio of the reduced I-TEQ value to its original I-TEQ value. When no iron was added, (Scenario (12)) decomposition rates were 80.0% for the 17 toxic isomers and I-TEQ was reduced by 46.17%. While for this treated fly ash the total concentration of PCDD/Fs including all non-toxic isomers was 47.54ng/g.

In Fig. 1. it is shown that when ferric/ferrous sulphate was added, decomposition rate of total 17 toxic isomers (marked as C in Fig.1) increased in general compared to Scenario (12), and decomposition rate in I-TEQ value increased dramatically with its maximum reaching 89.59% at 3%wt (Scenario (1)). Fe addition did not only improve the decomposition rates of the 17 toxic isomers but also enhanced the destruction of the total PCDD/Fs by reducing their concentration from 47.54 ng/g for Scenario (12) to less than 20 ng/g. As Fe addition rose to 4wt% through mixture of ferrous and ferric salts (Scenario (11)) the decomposition rates decreased and concentration of PCDDs/Fs increased (Fig. 1). But as Fe was added in the form of Fe (II) at 4wt% (Scenario (2)) the decomposition rates were higher again, showing different iron oxides act differently. From the data in Fig.1 it can be seen that the best results for I-TEQ value reduction are at iron supplementation at 3%wt as a mixture of Fe (II) and Fe (III).

Influence of Iron Addition on 2378-TCDD Concentration

Concentration of 2378-TCDD is most important for reducing PCDD/Fs toxicity in fly ash. Some scenarios are compared in Table 3 for their 2378-TCDD and 2378-TCDF concentrations. It can be seen that iron added as mixture of Fe (II) and Fe (III) results in much lower 2378-TCDD and 2378-TCDF concentrations,



showing that iron oxides formed from mixture of Fe (II) and Fe (III) is more effective for reducing the most toxic 2378-TCDD; therefore iron oxides formed from mixture of Fe (II) and Fe (III) are preferable.

Figure 1. Decomposition rates of PCDD/Fs vs. Fe dosage (Fe(2.3): iron added as a mixture of Fe(II) and Fe(III) salts; Fe(2): iron added in form of Fe(II))

Table 3. Comparison of 2378-TCDD concentration after treatment with different Fe addition mode

PCDD/F content

Scenario (ng/g) (12) (2) (9) (8) (4) (10) (1) (11)

2378TCDD 0.115968 0.05598 0.049 0.0866 0.03829 0.02749 0.02125 0.009775 2378TCDF 0.07716 0.01535 0.049 0.036 0.04531 0.03454 0.02097 0.02878 total I-TEQ 0.30038 0.096 0.143 0.121 0.10356 0.10702 0.05811 0.10426

Influence of Reaction Time

Table 4 shows 2378-TCDD/F data of some scenarios with different reaction times but the same iron concentration. It can be seen that longer reaction time is more favorable when a mixture of Fe (II) and Fe (III) was added.

Table 4. Comparison of dioxin concentrations after undergone different treatment time

PCDD/F content (ng/g)

Scenario /time (h) (3) /0.5 (4) /1 (6) /2 (7) /3

2378TCDD 0.085317 0.03829 0.089675 0.026513 2378TCDF 0.14433 0.04531 0.03832 0.03223 Total I-TEQ 0.2388 0.10356 0.1537 0.0903

Conclusion

Iron oxides formed from hydrothermal process were investigated to check for their effects on decomposing of PCDD/Fs in MSWI fly ash. Experimental results show that iron oxides formed from a mixture of ferric and ferrous salts were more effective to enhance dioxins’ decomposition than iron oxides formed from ferrous salt alone, especially to reduce concentrations of 2378-TCDD/F. The best result was obtained for scenario with iron addition of 3%wt, and longer reaction time is preferable.

Acknowledgements

The work is financed by China National Hi-Tech Project (Grant No.2008A A06Z340) and NSFC project (Grant No. 50708068).



References [1] C.W. Hou, H.C. Shu, C.H. Pao, F.H. Jyh, B.C. Moo. 2008. Catalytic oxidation of gaseous PCDD/Fs

with ozone over iron oxide catalysts. Chemosphere, 44: 388–397. [2] J.L. Xie, Y.Y. Hu, D.Z. Chen, B. Zhou. 2010. Hydrothermal treatment of MSWI fly ash for

simultaneous dioxins decomposition and heavy metal stabilization. Front. Environ. Sci. Engin. China 3: 108-115.

[3] H. Yamaguchi, E. Shibuya, Y. Kanamaru, K. Uyama, M. Nishioka, N. Yamasaki. 1996. Hydrothermal decomposition of PCDDs/Fs in MSWI fly ash. Chemosphere, 32: 203-208.

[4] Y.Y. Hu, D.Z. Chen, T.H. Christensen. 2007. Chemical stabilization of incineration fly ash with FeSO4 under hydrothermal conditions. Environmental Pollution & Control, 4-8 (in Chinese).



THERMAL TREATMENT FOR BIOSOLIDS – ANOTHER BREAKTHROUGH? K.R. Tsang 1*, F. Sapienza 2

1 CDM, Raleigh, North Carolina, USA 2 CDM, Cambridge, Massachusetts, USA

* Corresponding author. Tel: +1 9197875620, Fax: +1 9197815730, E-mail: [email protected]

ABSTRACT In the U.S. there have been considerable interests in recent years on alternative thermal treatment processes. Conventional thermal treatment processes include thermal combustion, wet air oxidation, and thermal pre-treatment. A number of alternative thermal processes have emerged in recent years. These processes include thermal hydrolysis (Cambi, Biothelys), modified wet air oxidation processes for sludge conditioning and to produce carbon source for wastewater treatment (Athos, Minerals), sludge conditioning processes such as SlurryCarb and ThermoFuel, as well as various gasification processes. Most of these processes are not new and had been tried in the past, some with limited success, and others with failures. Other processes, such as gasification, thermal hydrolysis, and the SlurryCarb process have attracted a lot of attention in the past few years. A review of these processes indicates that thermal processing may offer some needed alternatives for residuals management.

Keywords: Sludge, Biosolids, Thermal treatment

Introduction

Sludge management continues to post a significant challenge as environmental agencies around the world tackle water quality issues by imposing higher wastewater treatment standards. The traditional practice of reusing treated sludge (biosolids) through land application has frequently been challenged by the public and environmental interest groups. The concerns about the negative impacts of sludge reuse on land have driven a number of European countries towards thermal treatment. In the U.S., beneficial use of biosolids has long been advocated. Despite major public education and information efforts by municipalities and professional organizations in the U.S., land application of biosolids continues to meet resistance. While research results continue to show that biosolids reuse on land is safe and beneficial, emerging pathogens and contaminants such as pharmaceutical products continue to raise concerns. As these concerns will not be easily addressed, biosolids reuse on land will continue to face challenges. Most European countries have already moved away from biosolids land application in favour of thermal treatment. Instead of utilizing the nutrient contents of sludge, interest is shifted toward the beneficial use of the fuel content.

Thermal treatment of sludge is not new. Conventional thermal treatment processes include thermal oxidation (incineration) and wet air oxidation, which have been practiced for some time. Although incineration is a well-established and widely practiced technology, it has not been favourably viewed by the public in the past. Ash disposal is also of concern. In addition, a large amount of flue gas is required to be treated before discharging to the atmosphere. In comparison, for gasification utilizing pure oxygen, the amount of flue gas released per kilogram (kg) of dried sludge processed can be reduced by more than 10 times (Werther, 1999). This may have significant cost impacts as air quality requirements will continue to demand higher levels of flue gas treatment. The recent ongoing effort by the U.S. Environmental Protection Agency (EPA) to reclassify municipal sludge as solid waste provided additional fuel for sludge incineration opponents. However, recently a more favourable perception of incineration has been noted when it is combined with energy recovery.

Thermal Treatment Processes

Thermal processing of biosolids (other than incineration) appears to be gaining favour in the last couple of years as the concerns on land application remains and the promise of energy recovery by these processes make them compatible with the popular theme of sustainability, energy efficiency, and carbon reduction. Thermal processes can be grouped into several categories as follow:

� Low temperature thermal treatment � Thermal conditioning � Wet oxidation � Pyrolysis/gasification



� Combustion/incineration � Vitrification/melting

Low Temperature Thermal Treatment

These processes involve heating the sludge to below 100oC, primarily for disinfection purposes such as the Bio Pasteur process. Low temperature treatment has also been proposed as a process to solubilise COD, resulting in less sludge yield.

Thermal Conditioning

Thermal conditioning processes include thermal hydrolysis such as Cambi, Biothelys, and Exelys processes which treat the sludge at around 150-175oC, at pressure of 6-15 bars. These processes aim to condition the sludge for enhanced anaerobic digestion, including higher organic loading, increased volatile solids reduction and gas yield, as well as improved dewaterability post digestion. Thermal hydrolysis has gained popularity in the past decades, with over 20 plants operating primarily in Europe, and a number being planned over the world.

Besides thermal hydrolysis, other hydrothermal processes also aim at changing the characteristics of sludge using elevated temperature and pressure. Examples of these processes are SlurryCarb and Thermofuel. SlurryCarb is a carbonization process operating at around 230oC and 27 bar pressure. The first commercial facility in the U.S. is currently going through final start-up. This process renders the sludge rheology such that dewaterability of the treated sludge is markedly improved. After dewatering and thermal drying, a product with calorific value matching coal can be obtained. A rich side-stream produced requires separate treatment. The process is claimed to be more energy efficient than conventional thermal drying (Enertech, 2008). The Rialto, California facility receives dewatered primary and waste activated sludge for treatment. ThermoFuel operates at 276oC and 82 bar pressure, and only targets waste activated sludge. Both processes produce a dried fuel for use.

Wet Oxidation

Wet oxidation has been used to treat sludge and other organic wastes. It is a thermal process which takes place in an aqueous phase at temperature of 150-330oC and pressure of 10-220 bar using pure oxygen or air. High pressure is used to maintain sludge in liquid phase. Organic matter is converted to carbon dioxide, water, and nitrogen in the process. Most of the processes involve oxidation at subcritical condition (below 374oC and at pressure of 100 bar). These include the Zimpro and Athos processes. For sludge treatment, the Zimpro process operates around 220oC and 35 bar pressure whereas Athos operates at 235oC and 44 bar pressure. VerTech is a deep well technology proposed to achieve the high pressure through a below ground reactor. While wet oxidation under sub-critical condition can convert the sludge successfully, the resultant side stream and emissions are laden with offensive odour and high organic loads. Wet oxidation can also take place under supercritical conditions (above 374oC, and 220 bar pressure). Under these conditions all organics will be converted to minerals, water, and carbon dioxide.

Pyrolysis/Gasification

Pyrolysis is a thermal decomposition of organic substances in the absence of oxygen at temperatures ranging from 300 to 900oC. A series of complex chemical reactions lead to the breakdown of organics and separation into individual gases. The products are pyrolysis gas, char, and oil. The gas, char, and oil can all be burned as fuel. Pyrobuster, one of the technologies marketed by Eisenmann, has two operating facilities in Europe. The Italian facility has been operating since 2006. The technology employs two rotary reactor chambers with pyrolysis taking place in the first chamber, and the combustion of the pyrolysis product in the second chamber.

Gasification is the thermal conversion of carbonaceous solids to combustible gas and ash in a net reducing environment [1] Oxygen is added in a controlled manner at sub-stoichiometric level. Organic compounds are turned into gaseous compounds (syngas) that can be combusted for energy. Gasification has recently been touted as a promising process to manage sludge. The basic principles of biomass gasification have been understood for centuries. Gasification of sludge has the potential benefits of incineration, including



complete sterilization of sludge and reduction of the mass to the minimum amount of ash for disposal. Technical challenges of sludge gasification include the varying feed sludge characteristics, relatively high tar content in the syngas, and potential emission of heavy metals and other compounds.

Combustion/Incineration

Sludge incineration has been practiced for many years and is an established technology. While a number of technologies can be applied, predominant technologies are multiple hearth furnaces and fluidized bed furnaces, with the fluidized bed technology regarded as “state-of-the-art”. Sludge incineration requires excess air which results in costly flue gas cleaning systems as nitrogen, chlorine, sulphur, mercury, dioxin, and furans, etc. are released as gaseous pollutants during sludge combustion. Recent emphasize in the U.S have been on energy recovery systems for sludge incinerators.

Vitrification/Smelting

While a number of incineration plants have been operating successfully, ash disposal remains a challenge. Sewage sludge has a relatively high ash contents. In addition, ash contains most of the contaminants not removed or stabilized during the combustion process. When incineration occur above the melting point of the ash (1250-1300oC), in addition to achieving complete thermal destruction of the organic substances in the sludge, a molten ash having a density two to three times that of incinerated sludge ash is formed. The molten ash has glasslike characteristics, bounds heavy metals and other contaminants remaining, and is suitable to be used in construction. A number of smelting plants were constructed in Japan. In the U.S., a plant was constructed in Illinois employing the Minergy technology. Unfortunately, this facility is no longer operating due to persistent operating issues.

Comparisons of Processes

Given the mixed history of success for various thermal processes, it is important to consider a number of factors when making technology assessments. Basic questions related to the nature of the process from the technical, environmental, and economic perspectives will need to be asked and answered. A comparison of these thermal processes is made by considering the following factors:

� New or re-emerged technology � Net energy producer or consumer � Side-stream production and characteristics � Operational challenges � Odor, emissions, and other environmental impacts

A summary of this comparison is presented in Table 1.



Table 1. Comparison of Thermal Processes

Processes Status Energy Side Streams and operation challenges Other Impacts

Thermal Hydrolysis

Proven Enhances energy production in anaerobic digestion system.

Nutrient rich sidestream from dewatering downstream of digestion must be dealt with.

Odour potential from pressure relief valves and other areas remain.

Wet Oxidation

Emerging Producer For operation in super critical conditions, a number of operating challenges remains, including handling of liquid oxygen, and preventing the coating of pipe interior surface.

Commercialization of the first U.S installation continues to be a challenge.

Pyrolysis/

Gasification

Emerging Neutral Facilities usually coupled with a dryer to produce the feed. Syngas cleaning and slagging are challenges.

First sludge gasifier in the U.S. is still going through startup and continued process modifications.

Incineration Proven Energy producer if dewatered cake > 26-28%

Fluidized bed technology is well established.

More stringent air emission requirements in future.

Smelting Proven Energy consumer While a number of plants have been operating in Japan, a recent full-scale plant in the U.S. has failed.

Operating costs reportedly to be high.

Conclusions

A number of thermal processes have re-emerged as potential candidates to provide an alternative biosolids management strategy to municipalities. While some of these processes promise benefits including renewable energy, reduced carbon footprint, and sustainable management strategy, realization of these benefits are site and process specific. Thermal hydrolysis coupled with anaerobic digestion appears to be gaining popularity. Pyrolysis and gasification are also making progress although more operating experience must be gained from these facilities to ascertain operating cost and issues.

References �1� B. McAuley, J. Kunkel, S.E.Manahan. 2001. A new process for the drying and gasification of sewage

sludge. Water Engineering and Management, 18-23. �2� Enertech presentation, 2008. �3� J. Werther, T. Ogada. 1999. Sewage sludge combustion. Progress in Energy and Combustion Science,

25: 55-116.



PRODUCTION AND PROPERTIES OF GLASS-CERAMICS FROM SEWAGE SLUDGE RESIDUE BY MICROWAVE MELTING METHOD

Y. Tian 1,2*, D. Chen 1, D. Wu 1, W. Zuo 1 1 School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090,

China 2 State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology

(SKLUWRE, HIT), Harbin 150090 ,China * Corresponding author Tel: +86 451 8608 3077/+86 138 0458 9869, Fax: +86 451 8628 3077, E-mail:

[email protected]

ABSTRACT This paper described an advisable method to produce glass-ceramics using sewage sludge residue by the microwave melting method. In a microwave oven, the sewage sludge residue was prepared by pyrolyzing sewage sludge in an inert atmosphere, and then mixed with CaO 10.47wt% and SiO2 10.48wt% to achieve the powder. The quenched glass was obtained by melting the powder in a corundum crucible at about 900 for 10min by the microwave radiation. The two-layer structure was used to improve the microwave absorbing capabilities of the glass powder in the experiment of the microwave melting. The nucleation and crystallization experiments, which were 820 for 1h and 900 , 950 1000 , 1050for 2h respectively, were carried out on the basis of differential thermal analysis (DTA). X-ray diffraction (XRD) analysis of the produced glass-ceramics revealed that the main crystalline phase was anorthite. The prepared glass-ceramics were characterized by physical, mechanical and chemical measurements. From the result of the toxicity characteristic leaching procedure (TCLP) it was found that the glass-ceramics prepared from sewage sludge residue had a strong fixing capacity for the heavy metals such as lead (Pb), zinc (Zn), cadmium (Cd) etc.. All results showed that the glass-ceramics prepared from sewage sludge residue by microwave melting method could be widely used in some applications, especially as the construction material. At the same time, it showed that the microwave sintering was found to be economically charming owing to reduction in melting time and energy consume based on fast heating and volumetric heating of samples.

Keywords: Glass-ceramics, Sewage sludge residue, Microwave melting, Heavy metal, TCLP

Introduction

A large amount of sludge is produced in a sewage treatment plant per day. At present, methods used for the treatment of sewage sludge are landfill and incineration, none of which are of no defects[1]. Meanwhile, people have paid considerable attention to the pyrolysis of sewage sludge[1-4]. However, pyrolysis gives rise to the same collateral products (sewage sludge residue) as the incineration. Plenty of municipal waste incineration fly ash is currently used in road [1], in cement-based products [1] and as an aggregate in concrete [1]. Moreover, sewage sludge residue, which was obtained by microwave pyrolysis, contains a great amount of SiO2, Al2O3 and CaO, which are the key glass network formers, hence it could be taken as a raw material source of the glass-ceramic production.

Recently, a number of reports have been published on glass-ceramics using fly ash from municipal solid wastes(MSW) incineration plants by the electric furnace[1-3]. Compared with conventional sintering, the most fascinating effects during microwave heating are the higher density and the shorter time [4]. The microwave sintering of calcium phosphate ceramics is found to be economically exciting because of substantial reduction in processing time and energy expenditure due to volumetric heating of samples [4]. Therefore, it is possible to produce glass ceramics from sewage sludge residue by the microwave sintering.

The aim of this paper is to produce the glass by microwave melting technology and establish a better understanding of the viability of utilizing the sewage sludge residue to fabricate the glass ceramics for the construction usage. The produced glass-ceramics were characterized by toxicity characteristic leaching procedure (TCLP) for leachability test and X-ray diffractometry (XRD) for crystal structure determination. Moreover, other properties, such as water absorption rate, volumetric density and hardness were also examined.




An aerobically digested sewage sludge obtained from the wastewater treatment plants in Harbin was used. The solid residue was produced by pyrolyzing sewage sludge in a microwave oven. The chemical composition of the residue was determined by X-ray fluorescence spectrometry (Axios PW4400, PANalytical), as shown in Table 1. CaO was added in sewage sludge residue to lower the melting temperature. SiO2 was intercalated in sewage sludge residue to form the target crystalline phase.

The mixture which contained sewage sludge residue 79.05wt%, CaO 10.47wt% and SiO2 10.48wt%, was pressed under uniaxial pressure (1.5MPa) to form cylinders (Φ10×5mm cylinder).The formed body was melted in a corundum crucible by the microwave sintering. In order to improve the microwave absorbing capabilities of the sample, the double-layer structure composed of wave-absorbing powder and wave-transparent powder was used in the experiment of the microwave melting. The powder of wave-absorbing layer had a composition of 90wt% of active carbon and 10wt% of Al2O3, the ratio of the wave-transparent powder mixed with active carbon and Al2O3 was 5:5. The formed body was subsequently sintered and heat treated at certain temperatures, then cooled to room temperature.

Table 1. The main chemical composition of sewage sludge ash by microwave pyrolysis

Composition SiO2 Al2O3 CaO MgO P2O5 Fe2O3 K2O Na2O TiO2 ZnO others

(%) 47.616 18.343 7.908 2.504 7.158 8.292 2.740 1.333 0.814 0.165 0.421

Powder X-ray diffraction (XRD) patterns for main crystalline phases in glass-ceramics were recorded on a P|max-γβ X-ray diffractometer with 50mA and 40kV CuKα radiation (Japan). The leached properties of Zn, Pb and Cd from the glass ceramics were evaluated according to the China Leachability Toxicity Standard method (GB/T 15555.1-15555.11). The concentrations of heavy metals in the leaching solution were determined by a PerkinElmer Optima 5300DV Inductively Coupled Plasma-Atomic Emission spectrometer (ICP-AES, Waltham, MA). Physical properties such as density and water adsorption were measured according to the Archimedes principle using water as a medium.


Thermal properties such as the transition temperature and crystallization temperature were analyzed by differential thermal analysis (DTA, TGA/SDTA85IE) and the results are shown in Fig.2. An endothermic peak with a onset of 690 was the glass transition temperature. And two exothermic crystallization peaks occurred at 801 and 852 . The melting endothermic peak was at about 1210 , and heat treatment experiments proved that the produced sample had molten completely at 1210 . Therefore, the nucleation temperature selected for heat treatment in this study was 820 for 1 h. The crystallization temperature was 900 , 950 , 1000 and 1050 for 2 h.

Figure 1.The temperature and DTA curve of the quenched glass by microwave melting.

The X-ray diffraction patterns of the glass and the glass ceramics are given in Fig.2. For the glass sample, no significant crystalline phases could be detected by XRD, as it was expected. As shown in Fig.2, the

0 2 4 6 8 10 12

300

400

500

600

700

800

900

1000

600 700 800 900 1000 1100 1200 1300-3.0-2.5

-2.0-1.5

-1.0-0.5

0.0

�� 1210

852801

690



glass-ceramic after heat treatment had the crystalline phases. However, there were no apparent crystalline phases at 900 for 2h owing to the lower temperature. From 950 to 1050 for 2h, it was found that the major phase of the glass-ceramics was anorthite. It was obviously beneficial for the application of the residue as the raw material.

The toxicity characteristic leaching procedure (TCLP) results of the sewage sludge residue and glass-ceramics are shown in Table 2. The solid residue generated in the process of the microwave pyrolysis had a relatively low concentration of the heavy metals. Table 2 depicts that the concentrations of heavy metals leached from the sample were far lower than the limits specified in the Chinese standards. The results established that glass-ceramics had a high immobilization capacity for heavy metals such as Cu, Pb, Zn, Cd, Cr and As. Physical and mechanical properties of the produced glass-ceramics are summarized in Table 3.

In this study, a dense material can be obtained in a much shorter time by the microwave sintering. Fig.1 depicts that the quenched glass was sintered in the microwave furnace for 3min from room temperature to 900 and then 10min soaking time at about 900 . If using the traditional sintering, it needed about 45min at the maximum rate of 20 /min to 900 . Furthermore, the heat power of a muffle furnace is 6000W and the microwave power is 2000W. Results showed that the microwave heating was more economic than the traditional sintering at the heating time and the power. It indicates that the whole process is economical.

Figure 2. X-ray diffractograms of glass-ceramics after the heat treatment.

Table 2. Results from TCLP leaching test of the selected samples. ND: not detectable

Table 3. Properties of the selected glass-ceramics

20 40 60 80 1000

600

1200

1800

2400

3000

3600�

�

�

�� anorthite

as-quenched glass

Inte

nsity

(cps

)

2theta (deg.)



Conclusions

Glass-ceramics were produced using sewage sludge residue, CaO and SiO2. The parameters for producing the glass-ceramics were melting at 900 for 15min by the microwave radiation, nucleating at 820 for 1h, and crystallizing at 1000 for 2h. Under these conditions, the sintered glass-ceramics showed good mechanical properties and bending strength. The leaching of heavy metals from glass-ceramics was far lower than the specified limits in the Chinese standards. Meanwhile, microwave sintering was charming owing to reduction in sintering time and energy consume due to fast heating of samples.

Acknowledgements

This study was supported by the National High-tech R&D Program (863 Program) of China (No. 2009AA064704).

References [1] J. Werther, T. Ogada. 1999. Sewage sludge combustion. Prog Energy Combust Sci. 25: 55-116. [2] J.A. Menéndez, M. Inguanzo, J.J. Pis. 2002. Microwave-induced pyrolysis of sewage sludge. Water

Res. 36: 3261-3264. [3] M. Inguanzo, A. Domínguez, J.A. Menéndez, C.G. Blanco, J.J. Pis. 2002. On the pyrolysis of sewage

sludge: the influence of pyrolysis conditions on solid, liquid and gas fractions. Journal of Analytical and Applied Pyrolysis. 63: 209-222.

[4] A.Domínguez, J.A. Menéndez, M. Inguanzo, J.J. Pis. 2005. Investigations into the characteristics of oils produced from microwave pyrolysis of sewage sludge. Fuel Processing Technology .86: 1007-1020.

[5] M.M.C. Alkemade, M.M.Th. Eymael, E. Mulder, W. de Wijs. 1994. Environmental aspects of construction with waste materials, Elsevier Science, B.V., Amsterdam. p. 863.

[6] P. Filipponi, A. Polettini, R. Pomi, P. Sirini. 2003. Waste Manage. 23:145. [7] J. Pera, L. Coutaz, J. Ambroise, M. Chababet. 1997. Cem. Concr. Res. 27:1. [8] J. Yang, B. Xiao, A.R. Boccaccini. 2009. Preparation of low melting temperature glass-ceramics from

municipal waste incineration fly ash, Fuel. 88: 1275-1280. [9] R.C.C. Monteiro, S.J.G. Alendouro, F.M.L. Figueiredo, M.C. Ferro, M.H.V. Fernandes. 2006.

Development and properties of a glass made from MSWI bottom ash, Journal of Non-Crystalline Solids. 352:130-135

[10] G. Qian, Y. Song, C. Zhang, Y. Xia, H. Zhang, P. Chui. 2006. Diopside-based glass-ceramics from MSW fly ash and bottom ash. Waste Manage. 26: 1462-1467.

[11] S. Mahajan, O.P. Thakur, D.K. Bhattacharya, K.Sreenivas. 2008. A comparative study of Ba0.95Ca0.05Zr0.25Ti0.75O3 relaxor ceramics prepared by conventional and microwave sintering techniques, Materials Chemistry and Physics. 112: 858-862.

[12] A. Chanda, S. Dasgupta, S. Bose, A. Bandyopadhyay. 2009. Microwave sintering of calcium phosphate ceramics, Materials Science and Engineering C 29:1144-1149.



PHASE TRANSFORMATION OF METALS IN REUSING THE INCINERATION ASH OF CHEMICALLY ENHANCED PRIMARY TREATMENT SLUDGE AS CERAMIC RAW

MATERIALS K. Shih

Department of Civil Engineering, The University of Hong Kong, Hong Kong, HKSAR, China Tel: +852 28591973, Fax: +852 25595337, E-mail: [email protected]

ABSTRACT This study provided the possible solid state reactions when reusing the sludge incineration ash generated from the chemically enhanced primary treatment (CEPT) as the ceramic raw materials. Nickel and copper oxides were used to simulate the hazardous metal phases in the raw materials, and the ash iron content was found to act as a beneficial role to incorporate the hazardous metals into the metal ferrite phases (NiFe2O4 and CuFe2O4). Experimental results of sintering the NiO+Fe2O3 and CuO+Fe2O3 systems further confirmed the potential of high metal incorporation efficiencies by having iron-containing precursor in the ceramic sintering process. Both ferrite phases were examined by a prolonged leaching experiment modified from the widely used Toxicity Characteristic Leaching Procedure (TCLP) to evaluate their long term metal leachability. The leaching results indicate that both NiFe2O4 and CuFe2O4 products were superior to their original oxide forms (NiO and CuO) for the immobilization of hazardous metals.

Keywords: Sludge, Incineration ash, Spinel, Ceramic

Introduction

Wastewater sludge ash may contain hazardous metals, such as Cd, Cr, Pb, Ni, Cu, Zn, Mn [1, 2]. Its disposal into landfill is not environmentally sustainable because of the additional consumption of non-renewable resources, including material, space and energy. To be more sustainably transforming waste to resource, opportunities of reusing or recycling incineration ash need to be sought to promote the “cradle-to-cradle” design in the waste management plan. Merino et al. [3] studied the ceramic characteristics of using sludge ash alone or mixing with additives (kaolin, montmorillonite, illitic clay, powdered flat glass). Studies of mixing incinerated sewage sludge ash into clay-based building products have concluded no adverse effect on final fired body or ceramic texture [4, 5]. Results obtained by Li et al. [6] showed that when mixed with ashes and/or clay minerals, finely ground glass may act as a flux reducing the leaching by inertization of hazardous constituents. Shih et al. successfully stabilized nickel into its mineral phases by sintering nickel oxide with alumina (Al2O3), hematite (Fe2O3), and kaolinite (Al2Si2(OH)4) as the ceramic raw materials [7-9]. They pointed out that leachability of nickel dropped dramatically in its alumina and ferrite spinel phases when compared to that of nickel oxide. Copper has also been investigated through the incorporation experiment, and the result demonstrates a great reduction of leachability of copper when it was incorporated into CuAl2O4 spinel structure [10].

In Hong Kong, the majority of municipal wastewater sludge is generated from the chemically enhanced primary treatment (CEPT). And the major metals within the bottom ash of incinerating CEPT sludge are Fe, Si, Ca and Al. In this paper, we will discuss the possible solid state reaction when reusing such sludge incineration ash for the ceramic raw materials. Nickel and copper oxides were used to simulate the existence of potential hazardous metals in the ceramic raw materials for the purpose of exploring the product safety during the beneficial use of incineration ash. The effect of incorporating nickel and copper into crystal structures was observed under a 3 h sintering scheme with temperatures ranging from 650 °C to 950 °C. A modified toxicity characteristic leaching procedure (TCLP) was carried out to evaluate the nickel and copper leachabilities of NiO, CuO and their corresponding product phases.


Fe2O3 was used to simulate the major components of ferrite bottom ash through incinerating CEPT sludge. NiO and CuO were used to simulate the phases of potential hazardous metals in the ash. The Fe2O3 and NiO (or CuO) were mixed to a total dry weight of 60 g at the Ni/Fe (or Cu/Fe) molar ratio of 1:2, together with 500 mL of deionized water for ball milling of 18 h. the slurry samples were then dried at 95 °C for 3 d and homogenized again by mortar and pestle. After that, the powder samples were pressed into 20 mm diameter under 640 MPa pressure. The pelletized samples were then heat treated at a rate of 10 °C/min in a top hat



furnace (Nabertherm) and sintered at temperature range from 650 °C to 950 °C for 3 h. The fired samples were air-quenched and ground into powders for XRD analysis and leaching test.

The X-ray powder diffraction data were collected using D8 Advanced Diffractometer (Bruker AXS) operating at 40 kV and 40 mA with Cu Kα radiation. Phase identification was conducted using the Bruker software Diffrac-plus EVA supported by the Powder Diffraction File database of the International Centre for Diffraction Data (ICDD). The modified toxicity characteristic leaching procedure (US EPA SW-846 Method 1311) was used to evaluate the leachability of the product phase. The pH 2.9 acetic acid solution was prepared as the leaching agent from 5.7 mL glacial acetic acid and dilution with MilliQ water to a volume of 1 L. Each leaching vial was filled with 10 mL of leaching agent. The vials were rotated end-over-end at 60 rpm for agitation periods of 0.75-22 or 26 days. At the end of each agitation period, the leachates were filtered with 0.2 μm syringe filters, and the concentrations of Ni (or Cu) were derived from ICP-AES (Perkin-Elmer Optima 3300 DV).


Formation of NiFe2O4

In 2010, Raghavan [11] organized the phase diagrams in the Fe-Ni-O system, and the reaction between NiO and Fe2O3 was indicated as follows:

NiO + Fe2O3 (hematite) → NiFe2O4 (trevorite) (1)

Fig. 1(a) suggests that there are three phases present in the samples sintered at the temperature range 750 to 950 °C, i.e., NiFe2O4 (PDF # 54-0964), NiO (PDF # 73-1519 ), and Fe2O3 (PDF # 86-0550). Though it is difficulty to identify NiO phase from qualitative analysis since all the reflections of NiO overlay those of NiFe2O4, we can estimate the existence of NiO due to the remaining of Fe2O3. From the computed phase diagram of Fe2O3- NiO [12], the formation temperature of NiFe2O4 should be lower than 600 °C. However, NiFe2O4 was found only at temperature at 750 °C or higher in the 3 h sintering (Fig.1(a)). Such result indicates that the diffusion between Fe2O3 and NiO should be an important factor needed to be considered. The solid state reaction is not only determined by thermodynamic constraints but also by the diffusion process. As the heating temperature increased, the peak intensity of the (220) plane of NiFe2O4 increased (Fig. 1b). On the contrary, the peak intensity of the (104) plane of Fe2O3 phase decreased with the increasing temperature. Since no amorphization has been reported in the phase diagram, the above result indicates that the formation of NiFe2O4 spinel phase increases with the increasing sintering temperature.

Figure 1. (a). XRD results of sintering Fe2O3 and NiO mixtures at different temperatures for 3 h, (b) selected peaks between 29° and 35°to represents NiFe2O4 (S), Fe2O3 (H), and NiO (N)



Formation of CuFe2O4

When sintering the mixture of CuO and Fe2O3, the potential reaction can be provided as follows:

CuO + Fe2O3 (hematite) → CuFe2O4 (2)

CuFe2O4 has two crystallographic structures: cubic phase with a lattice parameter of 8.38 Å, and tetragonal phase with lattice parameters of a=8.126 Å and c= 8.709 Å. The tetragonal-to- cubic transition temperature can be influenced by the atomic iron-to-copper ratio as well as by the oxygen deficiency in copper ferrite [13].

Fig. 2(a) shows the XRD patterns of samples sintered at different temperatures (650, 750, 850, 950 °C) for 3 h. At 650 °C, only the reflections of CuO and Fe2O3 phases were observed, and no signal attributable to CuFe2O4 compound (cubic or tetragonal) was observed. Such result indicates that there was no reaction between CuO and Fe2O3 at such temperature within the sintering scheme. However, Lu et al. [14] reported a different result, i.e. tetragonal CuFe2O4 was formed when sintering at 600 °C for 1 hour. The difference may arise from the different types of raw materials. Lu et al. used the sludge as the reactants, and some components in the sludge may further initiate the catalytic reaction between Fe2O3 and CuO. When the treatment temperature was increased to 750 °C, tetragonal CuFe2O4 (PDF #72-1174) was detected, together with the CuO (PDF # 45-0937) and Fe2O3 (PDF # 86-0550) phases. When the temperature was increased to 950 °C, the tetragonal CuFe2O4 (PDF # 72-1174) was the only observable copper ferrite phase.

As illustration Fig. 2(b), the increase of sintering temperature up to 950 °C was followed by a significant increase in the intensity of the selected X-ray diffraction peak of CuFe2O4 phase. In contrast, the intensities of the selected X-ray patterns of both CuO and Fe2O3 phase decreased with the increasing temperature. Such results can be concluded that the formation of CuFe2O4 is strongly affected by the sintering temperature can be effectively enhanced by increasing the sintering temperature to 950 °C.

Figure 2. (a). XRD results of sintering the Fe2O3 and CuO mixture at different temperatures for 3 h; (b) The selected diffraction peaks between 32.5° and 39.5° to represent CuFe2O4 (Ct), Fe2O3 (H), and CuO (C)

Leaching Behavior of NiFe2O4, CuFe2O4, NiO and CuO

Fig. 3 shows that the concentrations of nickel and copper leached from NiO and CuO were much higher than those from NiFe2O4 and CuFe2O4. Within the first few days, the increase of nickel and copper concentrations in leachates were much greater than those for the remainder of the experiment. The metal leaching behavior is generally associated with the proton-cation exchange mechanism as described in Eqs. (3), (4), (5) and (6). Therefore, the much less Ni or Cu leachability has indicated the relatively superior resistance in the acidic attack, such as in the cases of NiFe2O4 and CuFe2O4.

NiO(s)+2H(aq)+ → Ni(aq)

2++H2O (3)



CuO(s)+2H(aq)+ → Cu(aq)

2++H2O (4)

NiFe2O4(s)+8H(aq)+ → Ni(aq)

2++2Fe(aq)3++4H2O (5)

CuFe2O4(s)+8H(aq)+ → Cu(aq)

2++2Fe(aq)3++4H2O (6)

Figure 3. Nickel and copper concentrations in the leachates of NiO, CuO, NiFe2O4 and CuFe2O4. Each leaching vial was filled with 10 mL extraction fluid and 0.5 g powder and then tumbled end-over-end at 60

rmp

Conclusions

The results indicate that the incorporation of nickel and copper ions into NiFe2O4 and CuFe2O4 phases is an environment-friendly strategy to reduce their environmental hazard. This study also suggests a reliable mechanism of further immobilizing hazardous metals during the beneficial use of the waste incineration ash of CEPT sludge as a part of the ceramic raw material.

References [1] C. Wang, X. Hu, M.L. Chen, Y.H. Wu. 2005. Total concentrations and fractions of Cd, Cr, Pb, Cu, Ni

and Zn in sewage sludge from municipal and industrial wastewater treatment plants. J. Hazard. Mater. 119: 245–249

[2] D. Marani, C.M. Bragulia, G. Mininni, F. Maccioni. 2003. Behavior of Cd, Cr, Mn, Ni, Pb, and Zn in sewage sludge incineration by fluidized bed furnace. Waste Manage. 23: 117–124.

[3] I. Merino, L.F. Arevalo and F. Romero. 2007. Preparation and characterization of ceramic products by thermal treatment of sewage sludge ashes mixed with different additives. Waste Manage. 27: 1829–1844.

[4] M. Anderson. 2002. Encouraging prospects for recycling incinerated sewage sludge ash (ISSA) into clay-based building products. J. Chem. Technol. Biotechnol. 77:352-360.

[5] M. Anderson and R.G. Skerratt. 2003. Variability study of incinerated sewage sludge ash in relation to future use in ceramic brick manufacture. Br. Ceram. Trans. 102: 109-113.

[6] C.T. Li, Y.J. Huang, K.L. Huang and W.J. Lee. 2003. Characterization of Slags and Ingots from the vitrication of municipal solid waste incineration ashes. Industrial & Engineering Chemistry Research. 42: 2306-2313.

[7] K. Shih, T. White and J.O. Leckie. 2006. Nickel stabilization efficiency of aluminate and ferrite spinels and their leaching behavior. Environ. Sci. Technol. 40:5520–5526.

[8] K. Shih and J.O. Leckie. 2007. Nickel aluminate spinel formation during sintering of simulated



Ni-laden sludge and kaolinite. J. Eur. Ceram. Soc. 27:91–99. [9] K. Shih, T. White and J.O. Leckie. 2006. Spinel formation for stabilizing simulated nickelladen

sludge with aluminum-rich ceramic precursors. Environ. Sci. Technol. 40:5077–5083. [10] Y.Y. Tang, K.M. Shih and K. Chan. 2010. Copper aluminate spinel in the stabilization and

detoxification of simulated copper-laden sludge. Chemosphere. 80: 375-380. [11] V. Raghavan. 2010. Fe-Ni-O. Journal of Phase Equilibria and Diffusion. 31: 369-371. [12] M.A. Rhamdhani, P.C. Hayes, and E. Jak. 2008. Subsolidus phase equilibria of the Fe-Ni-O system.

Metall. Mater. Trans. B. 39B: 690–701. [13] S.C. Schaefer, G.L. Hundley, F.E. Block, R.A. McCune and R.V. Mrazek. 1970. Phase equilibria and

X-ray diffraction investigation of the system Cu-Fe-O. Metall. Trans. A 1: 2557-2563. [14] H.C. Lu, J.E. Chang, P.H. Shih and L.C. Chiang. 2008. Stabilization of copper sludge by

high-temperature CuFe2O4 synthesis process. J. Hazard. Mater. 150: 504-509.



EVALUATION ON EFFICIENCY OF ENERGY YIELD IN CATALYTIC GASIFICATION OF PAPER-REJECT DERIVED FUEL

K.Y. Chiang *, C.H. Lu, K.L. Chien, S.S. Ton

Department of Environmental Engineering and Science, Feng-Chia University, Tai-Chung, Taiwan * Corresponding author: E-mail:[email protected] Tel: +886-4-24517250 ext 5216,

ABSTRACT This study investigated the feasibility of the enhancement efficiency of energy yield in catalytic gasification of paper-reject derived fuel. The experiments were conducted by controlling the temperature in the range of 600 to 900 and adding mineral catalyst (Aluminum silicate, clay) in varying ratios of between 10 to 20% by weight. According to the experimental results, increasing gasification temperature will enhance the lower heating value (LHV) of syngas in gasification of paper-reject derived fuel. The LHV of syngas increased from 8.65 MJ/Nm3 to 18.23 MJ/Nm3 with increased the temperature from 600 to 900 . The energy density of syngas was also increased from 1.73 to 3.40 as gasification temperature operated between 600 and 900 . This implied that the energy utilization of syngas produced by gasification could increase approximately 2 times the energy content of paper-reject derived fuel. Besides, the energy yield efficiency in gasification will be enhanced by tested mineral catalyst. In case of gasification temperature operated from 600 to 900 , the LHV of syngas was increased significantly from 12.02 MJ/Nm3 to 19.76 MJ/Nm3 by tested mineral catalyst. The experimental results of this research confirm that it is possible to improve the efficiency of tar reduction and energy yield using tested mineral catalyst and promote the potential renewable energy application of paper-reject derived fuel.

Keywords: Biomass, Gasification, Catalyst, Energy density

Introduction

In recent years, the biomass gasification has been the focus of most of countries for renewable energy production and also for the reduction of greenhouse gases emissions. Catalytic gasification technology has been received attention throughout the world due to the following advantages: (1) enhancing of gasification reaction rate; (2) increasing of syngas production; (3) reducing of tar production and promoting the tar transformation. The mineral-based, alkali and alkali earth metal-based and precious metal catalyst were applied widely in previous researches. However, considering the catalyst influenced on syngas production, purchasing cost, availability and reutilization, the mineral catalyst becomes a fantastic material which was including olivine, dolomite, calcium oxide, kaolin and zeolite [1-10]. Although catalytic gasification performed successfully in energy conversion from biomass, the catalysts could occur that were deposited by char and poisoned by sulfur resulting in their lifetime and the energy conversion efficiency decreased. In recognition of the trend toward increased use of various mineral materials as catalysts for biomass gasification, the objective of this study was to investigate the feasibility of enhancement efficiency of energy yield in catalytic gasification of paper-rejected sludge by a mineral aluminum silicate (clay) catalyst. The main objectives of this research were: (1) to establish the optimum operational characteristics in a catalytic gasification of paper-rejected sludge; (2) to analysis the syngas compositions in a catalytic gasification of paper-rejected sludge; (3) to evaluate the energy yield efficiency in gasification of paper-rejected sludge by an aluminum silicate catalyst.


Materials

The paper-rejected sludge was waste generated from a recycled paper manufacturing plant in Tai-Chung County, Taiwan. The sludge was a pelletized derived fuel produced by drying and pelletizing. The tested catalyst was aluminum silicate (clay) and the amount of addition were 10% and 20% (by weight) compared to the feedstock.

Experimental Apparatus and Procedure

The experimental apparatus used in this study was composted of an electric-heated fixed bed gasifier and a sampling train of impinges for trapping of the tar. The effect of a mineral catalyst on synthesis gas



production during paper-rejected sludge gasification was investigated by performing a series of experiments at different gasification temperatures with a varied catalytic amended ratio. For each batch, the gasification temperatures were 600 , 700 , 800 , and 900 . The gasification air was supplied with an air compressor, which corresponded to 30% of the amount of theoretical air supply; that is, the equilibrium ratio (ER) was controlled at 0.30. The synthesis gas residence time is approximately 1 second or more. The experimental residence time is 22 minutes that is predetermined by a heating process known as the gasification time. After the gasification of each batch, the residues in the quartz boat and the condensed gas or particulates trapped by the sampling train were collected separately as char and tar samples. The synthesis gases collected in the sample bag were measured off-line by gas chromatography equipped with thermal conductivity detector (GC 1000-TCD, China Chromatography CO., Ltd.).

Characterization of Materials

The moisture content of the paper-rejected sludge samples were determined by heating for 24 hours at 105 . The volatiles, fixed carbon, and ash fraction of the samples were determined in triplicate using regulation tested procedures of the Taiwan Environmental Protection Administration (EPA)(NIEA R203 and R205). The ultimate analysis on the combustible in the tested biomass was also analyzed in triplicate using an elemental analyzer (Elementary Vario ELIII, Varian Inc.). The energy content of tested biomass was determined using a laboratory bomb calorimeter (Parr 1341 calorimeter). Elemental and proximate analyses and energy content of paper-rejected sludge samples are shown in Table 1.

Table 1. Characteristics of paper-rejected sludge

Properties Proximate analysis (wt. %) Moisture 3.79 Fixed Carbon (d.b.) 10.13 Volatiles (d.b.) 81.69 Ash (d.b.) 8.18 Ultimate analysis (wt %) C 59.17 H 9.73 N 0.23 S 0.23

O 18.98 Cl 0.34

Lower heating value (kcal/kg)

7010


The Influence of Gasification Temperature

According the results of syngas evolution, an increase in reaction rates and gasified gas production will follow an increase in gasification temperature (as shown in Table 2). The maximum synthesis gas production was obtained at gasification temperature 900 and initial reaction time was 2 minutes in duration. In the case of the gasification temperature that ranged from 600 to 900 , the total amount of hydrogen (H2), carbon monoxide (CO), and methane (CH4) increased with the temperature from 3.74% at 600 to 19.31% at 900 , from 3.94% at 600 to 8.54% at 900 , and from 3.89% at 600 to 22.97% at 900 , respectively.

The Influence of a Tested Mineral Catalyst

As the gasification temperature increased from 600 to 900 , the concentration of H2, CO, and CH4 increased significantly from 3.17% to 13.85%, from 4.97% to 8.10%, and from 3.20% to 13.11%, respectively. In the catalytic gasification process, the high gasification temperature will accelerate the gas



production rate and extend the reaction time. Meanwhile, compared to the gas composition in non-catalytic gasification, the tested catalyst could enhance the production of synthesis gas operated at lower gasification temperature. However, it seems that the concentration of H2, CO, and CH4 were slightly increased when the clay addition ratio was increased from 10% to 20%. That is, in the presence of a clay catalyst, there was no significant increase in the concentration for the above mentioned gases with the increasing catalyst addition. However, due to the paper-rejected sludge containing sulfur or chlorine content, could affect the catalytic activity of clay resulting in the poison of catalyst. Therefore, decreasing the activity of clay with decreasing the H2 production due to the thermal destruction of pores and surface areas presented in clay by cracking or poisoning in high gasification temperature [4, 11]. In summary, due to the presence of a catalyst this could extend the gasification reaction time and increase the reaction rate for gas production, the tested catalyst can help to enhance the efficiency of gas production in paper-rejected sludge gasification.

Table 2. The maximum gas composition in paper-reject sludge gasification

Gas composi

tion (vol. %)

Without catalyst With catalyst(10% clay) With catalyst(20% clay)

600 700 800 900 600 700 800 900 600 700 800 900

H2 3.74 7.11 11.23 19.31 3.17 5.30 13.73 13.85 3.50 5.11 9.34 10.80

CO 3.94 7.68 9.11 8.55 4.97 5.82 8.17 8.10 4.33 4.97 8.21 8.28

CH4 3.89 11.47 15.26 22.97 3.20 8.32 12.59 19.11 4.26 7.25 13.68 15.15

CO2 9.93 6.21 7.17 5.56 4.09 5.71 6.02 8.30 6.34 9.73 7.81 7.64

Energy yield Efficiency in Paper-rejected Sludge Gasification

Heating Value of Synthesis Gas

The lower heating value of synthesis gas increased with an increase in gasification temperature (as shown in Figure 1). In the case of non-catalytic gasification, the lower heating value increased with the temperature from 8.64 MJ/Nm3 at 600 to 18.23 MJ/Nm3 at 900 . In the case of the catalytic gasification temperature of 600 , as shown in Figure 2, the lower heating value increased significantly with an increase of the clay addition that ranged from 0% to 20%, which caused the lower heating value to increase from 8.64 MJ/Nm3

(non-catalytic test) to 12.01 MJ/Nm3 (10% clay addition test). It can be concluded that the clay catalyst will enhance the energy content of synthesis gas in lower gasification temperature. However, we have found that increasing the catalytic gasification temperatures to 900 , that the catalyst effect on the increased energy content of synthesis gases was insignificant. The lower heating value of synthesis gases was increasing from 18.23 MJ/Nm3 to 19.76 MJ/Nm3, which produced at gasification temperature of 900 and without/with 10% clay addition, respectively.

Energy Density of Syngas Produced from Biomass

Energy density was defined as maximum lower heating value of synthesis gas compared with lower heating value of tested biomass. Energy density is a useful index for comparing the energy yield efficiency produced by various biomass gasification processes. In this research, as shown in Figure 2, the energy density increased with the temperature from 1.73 at 600 to 3.4 at 900 , when no tested catalyst was used in the experiment. This means that the energy yield efficiency of synthesis gas produced by gasification was 1.73~3.4 times the energy content of the tested biomass. That is, the efficiency of energy utilization of paper-rejected sludge would be enhanced effectively by the gasification.

With the 10% and 20% clay addition, the energy densities were 2.41 and 2.98 at 600 , respectively. Compared to the above mentioned non-catalytic gasification, the clay catalyst has proved to be a good performer for enhancing energy yield efficiency in lower gasification temperatures. However, due to the lower activity and char deposits of clay occurring at 900 , the energy density increased slightly between



3.04 and 3.68. In summary, all the results of the energy density and heating value indicated that a tested catalyst used in this research could enhance energy utilization in gasification of paper-rejected sludge.

Conclusions

This study examined the results of energy efficiency of paper-rejected sludge in a catalytic gasification process. This has led to the following conclusions.

(1) Increasing the gasification temperature increased significantly synthesis gas production and decreased the paper-rejected sludge gasification reaction time. The maximum synthesis gas production was obtained at gasification temperature 900 . The maximum yield of CO, H2, and CH4 increased with an increase in gasification temperature from 3.74% at 600 to 8.54% at 900 , from 3.94% at 600 to 19.31% at 900 , and from 3.89% at 600 to 22.97% at 900 , respectively.

(2) In the case of lower catalytic gasification temperature, the aluminum silicate catalyst could enhance the production of synthesis gas operated at lower gasification temperature. However, in higher catalytic gasification temperature, the surface areas and matrixes of tested clay may be destroyed by thermal cracking resulting in H2 production and this shall increase insignificantly.

(3) According to the results of lower heating value and energy density of synthesis gas, the lower heating value of synthesis gas increased significantly from 12.01 MJ/Nm3 to 19.76 MJ/Nm3 operated between 600



and 900 by the aluminum silicate catalyst. Consequently, the energy density was approximately increased from 1.73 to 3.68. It can conclude that the tested mineral catalyst could enhance effectively on energy utilization in tested biomass gasification process.

Acknowledgements

The authors would like to thank the Environmental Protection Administration (EPA), Taiwan, ROC for financially supporting this work.

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Engineering Chemistry Process Design and Development. 23: 627-637. [2] D. Sutton. B. Kelleher. J.R.H. Ross. 2001. Review of literature on catalysts for biomass gasification.

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NREL/TP-510-32815. [4] Z. Abu El-Rub. E.A. Bramer. G. Brem. 2004. Review of catalyst for tar elimination in biomass

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Catalytic decomposition of biomass tars: use of dolomite and untreated olivine. Renewable Energy. 30: 565-587.

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A LIFE CYCLE EVALUATION OF WOODY BIOMASS GASIFICATION FOR DISTRICT HEATING IN BRITISH COLUMBIA

A. Pa 1, X.T. Bi 1*, S. Sokhansanj 2 1 Clean Energy Research Centre for University of British Columbia, Vancouver, BC, Canada

2Environmental Sciences Division,Oak Ridge National Laboratory Oak Ridge TN 37831,United States * Corresponding author: E-mail: [email protected], Tel: +604-822-4408

ABSTRACT In order to investigate the GHG reduction potential, the replacement of natural gas combustion for district heating by wood waste and wood pellets gasification systems with or without emission control has been investigated by a streamlined LCA. While stack emissions from controlled gasification systems are lower than the applicable regulations, the human health impact associated with stack emissions is expected to increase by 12% and 133% from its current value for wood pellets and wood waste gasification, respectively. With controlled gasification, GHG emission can be reduced by 83% on average. Between wood pellets and wood waste, wood pellets appear to be the better choice as it requires less primary energy and has lower impact on the local air quality.

Keywords: District heating, Woody biomass gasification, Life cycle analysis (LCA), Wood pellets

Introduction

The district heating facility in the University of British Columbia (UBC) generates 99% of its heat from natural gas and the rest from fuel oil. Given UBC's strong motive to become carbon-neutral, it is interesting to investigate the complete replacement of fossil fuels in its boiler house with bio-based fuels. Wood pellets, made of sawmill residue and burn cleaner than unprocessed biomass residue, are being considered in this study because they are produced in large quantity in BC but are usually exported. Finding domestic applications for these pellets would also result in less transportation-related GHG emissions. The replacement of UBC's current natural gas boiler house with a woody biomass gasification system is evaluated by streamlined life cycle analysis (LCA). For this study, the current operation, wood waste gasification and wood pellet gasification and gasification systems with emission controls will be investigated. The overall impacts on human health, ecosystem quality and primary energy consumption in addition to GHG reduction resulting from using wood waste and wood pellets are compared to demonstrate the pros and cons of wood waste and wood pellet utilization when replacing natural gas.


A total of five scenarios will be investigated. The base case is the current operation and the four woody biomass gasification systems are wood waste, wood pellets and each of these two systems equipped with electrostatic precipitators (ESP) with 99% particulate matters (PM) removal efficiency and selective catalytic reactors (SCR) with 80% NOX removal efficiency based on the typical removal efficiencies for these units [1,2]. The material and energy consumptions data are obtained for all scenarios and the energy consumptions are further converted to pollutant emissions based on emission factors (EFs). Note that emissions from infrastructures and land use changes are not included in the database.

Base Scenario

The current facility configuration utilizes natural gas and fuel oil to heat up the entering water stream to produce steam. The production, transportation or transmission of the fuels, along with the end usage emissions are all included in the LCA. The EF for natural gas and fuel oil production and transmission are obtained from GHGenius v3.17 [3] and are referred to as "upstream EF" (not shown here). The combustion EFs are listed in Table 1 and are obtained from various reports [4,5]. In 2008 the boiler house generated 350 kt of steam at 165 psig (1,138 kPa), translating to 974 TJ of heat produced [6]. This heat output is the definition for annual operation and is the functional unit for this study.

Woody Biomass Gasification Scenarios



The proposed woody biomass gasification system is a retrofitted air gasification system. The syngas produced is combusted in the existing combustor to heat up water to generate steam. For the emission-controlled scenarios, the flue gas will be treated with ESP and SCR unit.

The life cycle stages for the wood waste gasification scenarios include the production of two types of wood residues [10, 11], their transportation (utilizing both train and heavy HDV) [11-13], and their final usage at UBC. The two types of wood residues are forest harvesting residues and sawmill residues. The gasification EFs utilized for the wood waste scenarios were based on wood waste gasification in a commercial fixed bed gasifier [14].

Table 1. Estimated wood pellet gasification EF and air emission limits for biomass boilers in Vancouver, Canada in kg per MJ of fuel input

Pollutant Base scenario combustion EF

Wood waste gasification EF from industry

Estimated pellet gasification EF

Vancouver air emission limit for biomass boilers

CO2, fossil 4.92E-02 0 0 CO2, biogenic 0 9.17E-02 a 8.36E-02 CH4

d 9.95E-08 0 0 CH4, biogenic 0 9.03E-06 b 3.00E-07 c N2O 1.59E-06 5.59E-06 b 2.50E-06 c CO d 3.30E-06 0 0 1.59E-04 CO, biogenic 0 1.46E-05 1.20E-06 1.59E-04 NMVOC 3.09E-06 4.30E-06 3.39E-07 NOX 1.31E-05 7.31E-05 b 6.56E-05 4.10E-05 SOX 1.68E-06 0 e 0 e PM 1.14E-07 4.00E-05 1.53E-05 5.13E-06 a calculated based on the carbon content of wood b estimated by the emissions of wood waste combustion in boiler from US AP42 document [7] c estimated using pellet combustion EF from the US-EI database [8] d may include biogenic emission as that source of data does not distinguish between the origin of emission e SOX is set to zero since SOX emission depends mostly on the S content of the fuel and wood contains negligible sulfur [9].

For the wood pellet scenarios, an in-house BC wood pellet life cycle inventory database [15] that was previously developed is utilized. Wood pellet gasification EFs are not available in the literature thus are estimated using the ratios of published wood waste and pellet combustion EFs and the wood waste gasification EFs from the industry. Table 1 summarizes the combustion and gasification EFs for the base and uncontrolled scenarios, also including the current air emission limits for biomass boilers and heaters in Metro Vancouver [16].

Life Cycle Impact Assessments of the Scenarios

The EFs and energy consumption data are imported into a LCA software, SimaPro, for life cycle impact assessment using various methods. The method IMPACT 2002+ [17] version 2.06 is selected for this study. One extra indicator is added to keep track of the primary energy consumption. The overall impacts on human health, ecosystem quality, and climate change are also calculated. Note that IMPACT 2002+ was developed in Europe so the values of parameters used for the compilation of human toxicity are at a continental level for Western Europe. Due to this reason, the final values to be presented here only serve as indicators for scenario comparisons as the absolute values may not be so meaningful due to the geographical and geological differences. Lastly, since health impact depends heavily on the emission location, the health impact associated with stack emission alone is calculated separately as UBC is heavily populated compared to where upstream processing take place.




The annual emissions from UBC boiler house for all five scenarios are presented in Table 2. Other than generic CH4 emission and CO2 emission of fossil origins, all other emissions would increase when the boiler is switched from natural gas to woody biomass gasification.

Figure 1 compares each of the five scenarios' impacts on human health, ecosystem quality and climate change, as well as a breakdown of these impacts into different stages to signal out hot-spots throughout their life cycles. By switching to woody biomass, both impacts on human health and ecosystem quality would increase significantly, even with emission control units in place. Moreover, impact on climate change can be reduced by roughly 83% when switched to woody biomass. Furthermore, to generate 974 TJ of usable heat annually, the current natural gas scenario consumes 1,284 TJ of primary energy while the pellet and wood waste scenarios consume 1,516 TJ and 1,725 TJ, respectively.

Table 2. Annual air emissions from current and wood pellet scenarios in tonnes per year

Base scenario

Uncontrolled gasification Emission-controlled gasification

a Wood waste Wood pellet Wood waste Wood pellet All CO2 55,997 154,205 121,552 154,205 121,552

CO2, fossil 55,911 8,629 8,877 8,629 8,877 CO2, biogenic 86.30 145,575 112,676 145,575 112,676

All CH4 75.70 27.18 17.52 27.18 17.52 CH4 75.70 12.85 16.36 12.85 16.36 CH4

b, biogenic 0.00 14.33 1.17 14.33 1.17 N2O 1.79 9.81 4.63 9.81 4.63 All CO 9.65 47.73 47.60 47.73 47.60

CO b 9.65 21.62 23.43 21.62 23.43 CO, biogenic 0.00 26.10 24.17 26.10 24.17

NMVOC 5.40 17.01 11.79 17.01 11.79 NOX 38.04 219 203 127.00 137.56 SOX 8.22 27.04 11.64 27.04 11.64 All PM 0.56 72.55 43.55 10.18 24.63

PM 0.56 72.06 43.52 9.69 24.59 PM2.5

c 0.00 0.49 0.03 0.49 0.03 a SCR has a removal efficiency of 80% while ESP has a PM removal efficiency of 99%. b may include some biogenic emissions as well. c from “steam generation” only as no PM EF was available for this process.

Figure 1.Stage-wise impact analysis in terms of a) human health, b) ecosystem quality, and c) climate change for all scenarios



Lastly, even with emission control units, the health impact linked to stack emissions would increase by 133% and 12% from its current value for wood waste and pellet gasification, respectively. As a result, it is strongly recommended that both the ESP and SCR be installed.

Conclusions

Replacing fossil fuels with biomass may not always be desirable and the decision would depend heavily on the priorities of the specific project. Natural gas combustion outperforms emission-controlled woody biomass gasification scenarios in primary energy consumption and all impact categories considered other than climate change. Both ESP and SCR are required for woody biomass gasification to satisfy the applicable air emission limits. For emission controlled gasification scenarios, pellet is superior as it has lower primary energy consumption and, compared to the base scenario, the end stage health impact would only increase by 12% as opposed to 133% for wood waste.

References [1] P. Forzatti. 2001. Present status and perspectives in de-NOX SCR catalysis. Appl. Catal. A. 222:

221-236. [2] N. De Nevers. 2000. Air Pollution Control Engineering, McGraw-Hill, Boston. [3] M. Delucchi, Levelton. 2010. GHGenius. v3.17. From: <http://www.ghgenius.com/>. [4] Northwest Instrument Systems Inc. 2009. UBC Powerhouse Combustion Test Report (Prepared for

UBC Utilities). [5] European Environment Agency. 2007. Group 1: Combustion in energy and transformation

industries. From: <http://www.eea.europa.eu/publications/EMEPCORINAIR5/group_01.pdf>. [6] UBC Utilities. 2009. UBC Power House 2008 Year End Report. [7] U. S. Environmental Protection Agency. 1995. AP 42: Compilation of Air Pollutant Emission

Factors. From: <http://www.epa.gov/ttn/chief/ap42/>. [8] Swiss Centre for Life Cycle Inventories et al. 2008. US-EI (Ecoinvent processes with US

electricity). v1.6.0. From: <http://www.ecoinvent.ch/>. [9] L.S. Johansson, B. Leckner, L. Gustavsson, D. Cooper, C. Tullin and A. Potter. 2004. Emission

characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmos. Environ. 38: 4183–4195.

[10] J. Nyboer. 2008. A Review of Energy Consumption and Related Data in the Canadian Wood Products Industry: 1990, 1995 to 2006. From: <http://www.cieedac.sfu.ca/CIEEDACweb/pubarticles/Industry%20-%20Forest%20Products/Wood%20Products%20Report%202007%20_2006%20data_%20Final.pdf>.

[11] S.M. Sambo. 2002. Fuel consumption for ground-based harvesting systems in western Canada. Advantage. 3: 1-12.

[12] Natural Resources of Canada. 2003. Productive Forest Land Use. From: <http://atlas.nrcan.gc.ca/auth/english/maps/environment/forest/useforest/proforlanduse>.

[13] Natural Resources of Canada. 2003. Sawmills Map. From: <http://atlas.nrcan.gc.ca/auth/english/maps/environment/forest/useforest/sawmills>.

[14] D. Sparica. 2009. Personal communication. [15] A. Pa, J. Craven and T. Bi. 2009. Streamlined LCA of Exported Wood Pellets from Canada to

Europe. 8th World Congress of Chemical Engineering (WCCE8). August 23 to 27, 2009. Montréal, Canada.

[16] Metro Vancouver. 2008. Proposed Amendments to the Air Quality Management Bylaw. From: <http://www.metrovancouver.org/boards/bylaws/BylawReview/PropAmendAQBylaw.pdf>.

[17] O. Jolliet, M. Margni, R. Charles, et al. 2003. IMPACT 2002+: A new life cycle impact assessment methodology. Int. J. Life Cycle Assess. 8: 324-330.



CHARACTERIZATION OF STEAM EXPLODED SOFTWOOD PELLETS P.S. Lam 1*, S. Sokhansanj 1,2, X. Bi 1, C.J. Lim 1, A.K. Lau 1

1 Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC, Canada

2 Environmental Sciences Division, Oak Ridge National Laboratory, Tennessee, TN, USA * Corresponding author. Tel: +1 6048273413, Fax: +1 6048026003, E-mail: [email protected]

ABSTRACT The quality of the wood pellets not only affects the ease of handling, but also affects the end-user application performance. A wood pellet must be durable, water repellent and biologically stable for safe handling during transporting and storage. In this work, soft wood powder that was previously treated with saturated steam at 200-220oC for 5-10 minutes along with untreated powder were pelletized. The pellets were characterized in terms of mechanical strength and moisture sorption behaviour. The results demonstrated that pellets treated with steam explosion increased in hardness 6.6 and 3.3 times of maximum breaking force for untreated pellets. A reduced equilibrium moisture content by 6 – 10% was reached at 90% relative humidity and 30oC. The treated pellets experienced a lesser expansion after pelletization than the pellets made from untreated wood powder. There was also a slight increase in high heating value (HHV): 18.94 and 20.09 MJ/kg for the treated samples. Steam treated pellets were more brittle (i.e., higher elastic modulus) and higher rigidity (i.e., lower asymptotic modulus) was observed with increasing steam treatment. Treated pellets required 81% higher energy to densify and to be extruded from the die as compared to untreated pellets. It was postulated that the formation of solid bridge by pseudolignin after steam explosion treatment became a good binder between wood fibers as revealed by scanning electron microscopy.

Keywords: Wood pellet, Steam explosion, Hardness, Moisture sorption, Pseudolignin



PREDICTING THE HEATING VALUE OF WOOD BIOMASSS USING NEAR INFRARED SPECTROSCOPY

J. Doublet *, A. Ponthieux, C. Laroche, M. Poitrenaud, J. Cacho 1 VEOLIA Environnement – Research and Innovation, Limay, France

* Corresponding author. E-mail: [email protected], Tel: +33 1 34 77 88 42

ABSTRACT One of the most important parameters for the design and control of power plants is the heating value of the biomass. The application of near infrared spectroscopy (NIRS) as an alternative method to predict the higher heating value of wood biomass and also the C, H, N and ash content was investigated. A total of 85 samples, collected from different power plants, were used for NIRS calibration and validation. The NIRS prediction was satisfactory (R²P = 0.77 and RMSEP = 216 J.kg-1 DM) and in the range of the error of measurement by the conventional method in bomb calorimeter. An increase of the validity range of the elaborated model remains nevertheless necessary for an industrial use. This should be done by including more variability in the data sample set used for calibration

Keywords: Near infrared spectroscopy, Heating value, Wood biomass, Predicting model

Introduction

The use of wood biomass for the generation of heat or power is increasing. One of the most important parameters for the design and control of the power plants is the heating value of the biomass, defined as the amount of heat released from its combustion. It depends on the biomass composition leading to different performances during combustion. Conventional laboratory measurements of heating value with bomb calorimetric method is time consuming and expensive. Their use by operators for industrial monitoring is therefore limited. Several studies proposed prediction models of heating value based on chemical analysis such C, N, H or O content [1]. However, chemical analysis remains necessary. New technologies providing fast characterisation become thus quite necessary.

The Near Infrared Spectroscopy (NIRS) is a spectroscopic method using the infrared region of the electromagnetic spectrum (800-2500nm). It has been demonstrated that NIR spectroscopy is a suitable method for fast prediction of a wide range of organic parameters for plant biomass, waste, or soil. The prediction by NIRS of the reference value is only based on spectral data and thus do not need any chemical analysis. Moreover, a huge advantage of the NIRS is that many parameters, including complex or composition dependant, can be successfully predicted by one simple measurement. The suitability of NIRS for the predicting value has been evidenced for rice and wheat straw [2]. In case of forest fuels, Gillon et al. [3] indicated that NIRS is less accurate than conventional methods but it can be used to quickly determine the heating value when a large number of measurements are required.

The aim of our study was to develop a NIRS calibration model for the prediction of the heating value of a wide range of wood biomass.


Data Set

Eighty-five samples used for heat or power generation were collected: 60 mixtures of different wood fuels or wood materials (crushed pallets, different of wood chips, refuse from compost screening, tree pruning collected in city area, poplar pruning…), 10 wood pellets, 11 agro-industrial samples (coffee grounds, soybean cake, malt powder, barley residues, energy crops…) and 4 municipal solid waste.

Chemical Determination

All samples were oven-dried at 40°C during 10 days and then grounded at 1mm. The high heating value (HHV) was determined according to the French standard NF-M-03-005, equivalent to the ISO standard 1716. The total organic carbon (TOC), H and N content were determined by elementary analysis whereas the ash content was measured from mass loss on ignition at 550°C.



NIRS Analysis

The NIR spectra was recorded on a Fourier-transform NIR spectrophotometer Antaris II (Thermo electron, USA) at a resolution of 0.4nm. Two different spectra were recorded for each sample and both absorbance spectra were averaged. All spectra were transformed by Standard Normal Variety and Detrend procedures [4]. A first derivative procedure using the Savistsky and Golay algorithm with smoothing was calculated over eleven points on both sides [5]. Preliminary tests showed better results with the described spectra treatment than with MSC procedure or second derivative algorithm. All transformations were performed with The Unscrambler 9.8 software (CAMO Software AS, Norway).

NIRS Calibration, Cross Validation and External Validation

Sixty six samples were randomly selected for calibration of measured parameters. The other 19 samples were used for external validation. Calibration was performed by Partial Least Square (PLS) regression on transformed absorbance spectra with leave-one-out cross validation procedure. The outliers were discarded as in Peltre et al. [6]. Finally, the non-significant wavelengths, with high degree of uncertainty of coefficients during cross validation, were discarded [7]. The accuracy of prediction and robustness of models were then evaluated by the validation sub-set. The quality of models and predictions were evaluated by the coefficient of determination (R²), the root mean square error for predicted values during (RMSE) and the ratio of performance to deviation (RPD).


Chemical Characteristics of Data Sample Set

Most of the higher heating values (HHV) ranged between 18,262 and 19,517 j.kg-1 MS (Table 1), due to the numerous samples of wood and fuels mixtures in the data sample set and the measurement of the HHV on dried samples. In the case of N measurement, the values obtained for 18 samples were below detection limit; therefore no calibration was performed for that parameter.

Table 1. Main characteristics of samples used for calibration models

Quality of NIR Predictions

Good calibration and validation results were obtained for the HHV and the ash content (Table 2 and Figure 1). The prediction of TOC and H was not sufficiently accurate, probably due to the very low values of H measured and in both cases due to the low range of variability. The NIRS seems therefore to be suitable for the prediction of HHV (RMSEP = 216 J.kg-1 DM; RPD = 2.1). Seventeen samples, mainly the non woody materials (agro-industrial and waste samples), were discarded as outliers during calibration. However, good performance was evidenced for wood pellets indicating therefore a suitable accuracy for all woods materials of the data sample set (Figure 1). With a RMSEP of 216 J.kg-1 DM, the accuracy of the model is moreover in the range of the error of measurement by conventional bomb calorimeter method [3].



Table 2. NIRS calibration and validation statistics for the prediction of HHV (J.kg-1MS), TOC, H and Ash content (% DM)

Finally, the validity range of the elaborated model varied between 17,500 and 20,500 J.kg-1 DM. It remains lower than the HHV of biomasses that could be used in heat power plants. Indeed, most the values included in our data sample set that were outside that range were discarded as outliers, mainly due to the scarcity of data. The introduction of samples with high or low values of HHV in our calibration data set appears as a way to improve the range of model validity (wood fuels, woody materials under pellets forms, agro-industrial samples, energy crops…).

Figure 1. Predicted vs. measured values of HHV (J.kg-1 DM)

Conclusions

The prediction of the higher heating value of wood biomass by Near Infrared Spectroscopy appears as a promising and suitable method. The prediction of the higher heating value of wood biomass by NIRS can be determined with a sufficient accuracy (RMSEP = 216 J.kg-1 DM and RPD = 2.1) and without any laboratory or chemical analysis. An increase of the global variability of the data sample set remains nevertheless necessary to improve the range of model validity. This should be done by increasing the number of woody samples under a pellet forms or more globally with samples originated from other sources (agro-industries, energy crops, etc.)



References [1] A. Friedl, E. Padouvas, H. Rotter, K. Varmuza. 2005. Prediction of heating values of biomass fuel

from elemental composition. Ana. Chim. Act. 544: 191-198. [2] C. Huang, L. Han, Z. Yang, X. Liu. 2009. Ultimate analysis and heating value prediction of straw

by near infrared spectroscopy. Bioresource Technol. 29: 1793-1797. [3] D. Gillon, C. Hernando, J.C. Valette, R. Joffre. 1997. Fast estimation of the calorific value of forest

fuels by near infrared reflectance spectroscopy. Can. J. For. Res 27: 760-765 [4] R. Barnes, M. Dhanoa, J. Lister. 1989. Standard Normal Variate transformation and de-trending of

near infrared diffuse reflectance spectra. Appl. Spectrosc. 43:772-777. [5] A. Savitsky, M.J.E Golay. 1964. Smoothing and differentiation od data by simplified least squares

procedures. Anal. Chem. 36:1627-1639. [6] C. Peltre, L. Thuriès, B. Barthès, D. Brunet, T. Morvan, B. Nicolardot, V. Parnaudeau, S. Houot.

2011. Near Infrared reflectance spectroscopy: A tool to characterize the composition of different types of exogenous organic matter and their behaviour in soil. Soil Biol. Biochem. 43: 197-205.

[7] M. Martens, H. Martens. 2000. Modified Jack-Knife estimation of parameter uncertainty in bilinear modelling by partial least squares regression. Food Qual. Preference. 11:5-16.



WASTE-TO-ENERGY INDUSTRY IN THE PEARL RIVER DELTA: LESSONS FOR HONG KONG

V.F.S. Sit 1*, Z.H. Xu 2

1 Advanced Institute for Contemporary China Studies (ACCS), Hong Kong, China 2Advanced Institute for Contemporary China Studies, Hong Kong, China

* V.F.S. Sit Tel: +852 34112105, Fax: +852 34112104, E-mail: [email protected]

ABSTRACT Hong Kong is falling behind other cities in the Pearl River Delta (PRD) in the development of green energy, especially waste-to-energy. With a high population density, limited land and rapid social and economic development, Hong Kong has to consider replacing the traditional method of landfill with incineration for sustainable development. To tackle the problem of urban solid waste, Hong Kong should formulate policies to support the advancement of clean energy. The Delta’s rich experience in waste-to-energy incineration is invaluable and relevant for Hong Kong. This paper aims at examining the current status of solid waste treatment in Hong Kong, analysing its methodologies, successes and drawbacks, and provides advices on the introduction of waste-to-energy incineration technology in Hong Kong, drawing lessons from the experience of the Delta region.

Keywords: Pearl River Delta, Solid waste, Incineration, Landfills, Hong Kong

Introduction

As Hong Kong has been facing serious urban waste problems, it is necessary to review its existing approach and look for new policies. Hong Kong should follow the example of most cities in the developed economies to abandon landfill as the major means of waste disposal, as it is costly, difficult to maintain, and detrimental to the environment. Among the regions facing mounting solid waste problem, the PRD, which is near to Hong Kong, is a good example of a rapidly urbanizing region that has been ardently developing its incineration technology as a primary method to resolve its urban solid waste problem.

Incineration Industry in the PRD

Guangdong is the most economically developed province in China and has a rapidly developing economy accompanied by rapid urbanization. Its per capita GDP reached 37,589 RMB in 2008 and its per capita consumption has also increased rapidly in the past ten years. The population of Guangdong is now 95.44 million, with a population density of 531 persons per km2.

With a high population density, a rapid growing economy and a shortage of land, incineration is considered as an appropriate waste treatment technology for the PRD. In the past decade, through attracting foreign investments and advanced technologies, governments in the PRD had overtaken other provinces in China in the development of the waste-to-energy industry.

Issues Concerning Waste-to-energy Development in the PRD

Over the past decade, the waste incineration industry in the Delta region has been growing rapidly, yet in operation and planning of the plants, local governments are facing problems similar to those in many foreign countries, i.e. to achieve consensus and balance of interests in the community to support the industry.

First, there has been a lack of understanding of the incineration technology by the general public. Since there has been a history of old incinerators in the area that had generated serious pollution, people in the region are quite skeptical to the incineration technology. Due to objection by nearby residents, some incineration plant projects were put on hold or cancelled. Moreover, the volumetric capacity of some incineration plants is far larger than the demand, resulting in the problem of overcapacity. The Macau Incineration Centre is one example. Its utilization rate has been around 50% only, causing much wastage.

Implications of the PRD’s Incineration Industry Development on Hong Kong

Cities in the PRD has already adopted incineration as its primary means of urban solid waste disposal, solving their urban solid waste problems and providing renewable energy and other useful materials for local residents. For example, the currently-constructing Second Phase of the Shenzhen Baoan



Waste-to-Energy Plant (will be operational in 2011) can process over 3,000 tons of urban solid waste every day, or one-fourth of the total urban solid waste produced in the city. It will be equipped with two 64MW generators. Utilizing the “deDiNOx” system of the Belgian company Keppel Seghers, the Dioxin and Furan emission of the plant will be well below 0.1 µg I-TEQ/Nm3, or the limit applicable in China, Singapore and the European Union. Hong Kong, with its dense population, land shortage and rapid economic development, should consider replacing landfill by advanced incineration technology. It should look deeply into the application of science and technology, consider seriously PRD’s experience in municipal waste incineration, and actively encourage the use of waste-to-energy technology.

Figure 1. The distribution of the major incineration plants in PRD

Municipal Waste Problem in Hong Kong

As a world metropolis in Asia-Pacific, Hong Kong has 7 million residents despite its small size of merely 1100 km2. Its continuous development has resulted in the growth of solid waste, which had increased by 34.1% in the past decade. The traditional approach of landfill has failed to tackle the problem, and it takes time for recycling to develop. As all the Strategic Landfills in Hong Kong will reach their full capacity by 2015 and the proposals to convert Country Parks into new landfills have been rejected by the public, the introduction of advanced incineration technology as an effective alternative has thus become crucial.

Strategy on Waste-to-energy Technology in Hong Kong

The experiences of the PRD are summarized below as strategic references for Hong Kong to develop its incineration technology.

Following the example of the PRD, Hong Kong should encourage and import advanced foreign and mainland incineration technologies that meet its needs. There are locally competent technical personnel and abundant management expertise that can help master and utilize foreign engineering and technical skills of the industry.

Furthermore, the government should play a leading role in developing incineration. Most of the local authorities in the Delta region have adopted Build, Operate and Transfer (BOT) to develop their incineration plants. This can motivate private enterprises in the early stage of development and improve their operational efficiency. Hong Kong may consider adopting a modified BOT approach by first funding the construction, and then calling for tenders to build, install and run these plants. However, it is important for the government to prioritize the community’s interests and refrain from bearing too much of the operational costs that may result in a waste of public funds.



It is also crucial to transform the public’s negative attitude towards incineration. Opposition towards incineration has prevented some projects from starting or operating effectively in the PRD. It shows that people’s attitudes can often affect the implementation of a good policy. To develop incineration power generation plants in Hong Kong, the Government must seriously take this public view into account. Only through strengthening communication with the public could the government help to develop their confidence in incineration technology and cater to the interests of all parties of the community.

To strike a balance between economic efficiency and environmental protection, the government should learn from the experiences of other incineration plants such as the Macau Incineration Centre regarding the problem of overcapacity or under-use. In the initial phase, Hong Kong can consider building small and medium-sized incineration plants in one or two locations. When the development has reached maturity, then the government can consider expanding the existing plant or find new locations to meet future needs.

In the 2005 “Municipal Solid Waste Management Policy Framework (2005-2014)”, the government had selected the two sites of Tsang Tsui Ash Lagoons and Shek Kwu Chau, as possible locations to develop integrated waste management facilities, with incineration as its core technology. These two sites are suitable for developing the facilities in the first phase as they are located on the coast, and small or medium sized incineration plants should be considered in the early stage.

In the medium term, Hong Kong needs to consider building one incineration plant in each of the Legislative Council’s election districts. This will be politically more acceptable and can save transportation and administrative costs and improve overall operational efficiency. As community interest in incineration has been aroused recently, it is opportune for the Government to set a timetable and device a comprehensive facility blueprint and to engage public discussion on the matter as soon as possible.

Conclusions

The problem of solid waste in Hong Kong has grown to a scale that imminent new solution has to be in place soon. Hong Kong government must act on its environmental pledge through learning from experiences of other nations and regions. It should be less reliant on landfills, with a major policy shift towards the waste-to-energy approach. In such a process, it should also take due consideration of its own developmental needs and to balance the interests of all parties in the community.

Hong Kong and the cities in the PRD are interdependent. Therefore, when implementing a new strategy of waste-to-energy technology, Hong Kong should consider the PRD as a partner not only for its experience but also the feasibility of joint-venturing with its governments and enterprises.

Lastly, when implementing the waste-to-energy technology to solve Hong Kong’s solid waste problem, the government should stress "promoting green living and sustainable development” as the keynote to cultivate public understanding on the incineration technology and its economic and environmental usefulness to support related projects.

Acknowledgements

This paper utilizes the materials derived from the “Feasibility Study of Energy-from-Waste (EfW) in Hong Kong” of the ACCS. We would like to express our gratitude to the support provided by the institutions.

References [1] Abraham Shu, Rosalia Hsieh. 2008. Using Energy-from Waste (EfW) for managing municipal solid

waste (MSW) in Asia, Seminar on Thermal Waste Treatment, Hong Kong [2] Zhao Qianming, Zhang Shuai. 2008. An Analysis of Waste-to-energy Industry, State Securities,

Shanghai.



TESTING OF BRIQUETTE PRODUCTION FOR HOUSEHOLD USE BY INFORMAL WASTE WORKERS AT THE CALAJUNAN DUMPSITE IN ILOILO CITY,

PHILIPPINES A.R.D. Romallosa 1*, K.J.C. Hornada 1, N. Ravena 2, J.G. Paul 3

1 Central Philippine University, Jaro, Iloilo City, Philippines 2 General Service Office, City Hall Annex Building, Plaza Libertad, Iloilo City, Philippines

3 AHT GROUP AG, GIZ-AHT Project Office, c/o DENR-EMB, Region 6, Iloilo City, Philippines * Corresponding author: E-mail: [email protected], Tel: +63 33 3291971 local 1071

ABSTRACT Three recommended mixtures for briquette production were tested by eight identified informal waste workers within a 10-day briquette production test at the Calajunan dumpsite in Iloilo City, Philippines. The test revealed that Briquette 1 utilized a total of 127.50 kg dry waste paper; Briquette 2 was produced out of 183.80 kg of paper and sawdust while Briquette 3 was formed using 152.00 kg of paper, carbonized rice husk and sawdust. Briquette 2 produced the highest dry briquettes at 175.50 kg per 4.27 hr/day briquetting time followed by Briquette 3 at 142.74 kg for 4.18 hr/day and Briquette 1 at 122.25 kg for 4.19 hr/day. When all briquettes produced per day would be sold by the local waste worker’s association at a rate of Php15 (US$0.34) per kg, Briquette 2 would give the highest approximate daily earnings of Php263 (US$6). Heating value of the pillow-shaped briquettes produced ranged from 6,500 to 7,000 Btu/lb.

Keywords: Household briquettes, Charcoal substitution, Informal sector integration, Waste to energy

Introduction

The proposed conversion of Iloilo City’s dumpsite in Calajunan into a controlled sanitary landfill would mean that the usual activities of the informal waste workers such as recovery of resources through collection and separation of specific wastes would become impossible [1]. To augment this foreseeable predicament, alternative livelihoods have to be initiated for the waste workers. With the integration and registration of the informal waste pickers into Uswag Calajunan Livelihood Association, Incorporated (UCLA) in May 2009, they can now enter official contracts with project partners. Briquetting was identified as one of the alternative livelihoods for the informal waste workers. Five different types of briquettes utilizing a household briquette molder were initially tested to determine the most viable mixtures from biomass and urban wastes that would be assessed further for production by the informal waste workers of the dumpsite. To further verify the three recommended mixtures [2], briquette production for household use was tested by the informal waste workers at the Calajunan dumpsite in Iloilo City, Philippines. Specifically, it aimed to: (a) Conduct a 10-day actual production test to determine the technical requirements and output in producing briquettes; (b) Determine the quality of the briquettes produced; (c) Analyze the socio-economic implications of the production test as to the potential gross earnings when sold in the market by UCLA; and (d) Determine options on the improvement of operation in briquette production.


Preparation of Materials

Waste papers, carbonized rice husk (CRH) and sawdust were prepared for this study. The papers used were shredded waste papers generated from Central Philippine University while others were wastes coming from the different offices and establishments in Iloilo City that were delivered at the dumpsite for disposal. The biomass wastes in the form of CRH and sawdust from nearby areas were also delivered to UCLA Centre for testing.

Production of Briquettes

Production of briquettes was done for 10 days and was test wise conducted by 8 workers (2 males and 6 females) of UCLA. Two members were assigned each for mixtures that use pure paper (100%); paper (50%) + sawdust (50%); and paper (50%) + CRH (25%) + sawdust (25%) while the other two were responsible for supervising the operation. Production was done at UCLA’s Center located just 100 m across Iloilo City’s dumpsite. Operation started at 8 AM, in which the members would prepare and weigh all the necessary dry



materials needed for the whole day testing. The papers were then pulped using a 1-Hp electric-motor pulping machine after which, these were mixed in plastic containers by hand. Smaller sizes of balled materials were placed in each of the molder of the machine for compaction by closing and pressing down the movable upper half portion of the molder. The briquettes produced were then taken out and placed on an improvised platform for sun-drying. Production would briefly stop at lunchtime and continue around 1 PM then ended between 4 to 5 PM. The dried briquettes were later on subjected for heating value test at the laboratory facility of Victorias Milling Company, Inc. at Victorias City, Negros Occidental.


Results in Table 1 show that more input materials were utilized during the 10 days test by Briquette 2 with 183.80 kg. It also numerically produced the highest total dry weight of fuel at 175.50 kg at an average briquetting time of 4.27 hr/day. Based on this rate, more income could be generated by Briquette 2 at Php263 (US$6) compared to that of Briquette 3 at Php213.75 (US$5) or that of Briquette 1 at Php184 (US$4). This would reveal differences in terms of the estimate of potential gross earnings done at initial production [2] because Briquettes 2 and 3 would only have Php233 (US$6) and Php188 (US$4), respectively – a value which is numerically less if compared with production done on an actual scenario. For the 10-day production, the involved waste worker could only operate for about 6 hours. Four hours for briquetting while the remaining time was needed for material and equipment preparation and clean-up of the work area.

Table 1. Technical requirements and output in briquette production

Parameters Measured Briquette 1

(Paper) Briquette 2

(Paper + Sawdust)

Briquette 3 (Paper + CRH +

Sawdust) Total weight of materials, kg 127.50 183.80 152.00 Ave. dry weight per briquette, g 16.55 16.62 18.38 Total dry weight of all briquettes, kg 122.25 175.50 142.74 Ave. briquetting time, hrs/day 4.19 4.27 4.18 Briquettes produced, pcs/hr 256 250 184 kg/day 12.23 17.56 14.25 Approx. earnings per day (@Php15/kg), Php 184.00 263.00 213.75

The three briquettes produced were pillow-shaped and had an approximate length and width of 5 cm and a height close to 4 cm. Bulk density [3] of the fuels was similar to those in previous studies [2], indicating that manual mixing and application of pressure to the molder during compaction are very comparable. A heating value (HV) of about 5,000 Btu/lb or greater is needed to sustain combustion [4]. Results of laboratory analysis revealed that the three fuels have numerically similar HV that ranged from 6,500 to 7,000 Btu/lb. This would imply a promising potential for the briquettes as substitute fuel since charcoal has an HV of 8,627 Btu/lb [5] whereas bituminous coal, a commonly used fuel in industries, has an HV ranging from 10,500 to 15,500 Btu/lb [6].

Table 2. Quality of briquettes produced

Parameters Measured Briquette 1

Paper Briquette 2

Paper + Sawdust Briquette 3

Paper + CRH + Sawdust Briquette size, cm (≈) 4.86L x 5.10W x 4.17H 5.09L x 5.12W x 4.19H 4.96L x 5.22W x 4.20H Bulk density, g/cc 0.20 0.14 0.17 Heating value, Btu/lb 6,500 6,683 7,061

Socio-Economic Implications of Briquette Production

The earnings (Php263/US$6) that two members of UCLA could potentially gain from the production of briquettes made of paper and sawdust can even be increased if all the provided eight units of briquette



molders already available at the UCLA Centre could be utilized for this purpose. In terms of production rate, it would also imply that more briquettes can be produced since the members of UCLA are becoming inclined and familiar with the process of briquette production. The 227 kg waste paper recovered daily at the dumpsite so far [7] would double its value if fully utilized for briquette production by adding sawdust. This would result in an estimated daily earnings of Php6,000 (US$148) when marketed at Php15 (US$0.34) per kg. When sold as plain paper at a current rate of Php1.50 (US$0.03) per kg, UCLA would only earn Php338 (US$7) daily.

Options for Improvement of Production

The established UCLA Centre needs to enlarge its drying facilities in order to increase production, process efficiency and product quality, especially moisture content. To further enhance production of briquettes, the acquisition of equipment such as bigger pulping machine and mechanized mixer are also recommended.

Conclusions

It was concluded that Briquette 2 is the most viable mixture due to ease in preparation and maximization of material leading to high production rate and consequently higher daily earnings. The 227 kg waste paper partially recovered daily at the dumpsite can double its value if maximized as an add-on material to sawdust giving estimated daily earnings of Php6,000 (US$148). The briquettes have promising potential as fuels due to its high HV. It is recommended to subject the fuels to further chemical analysis such as determination of volatile compounds, fixed carbon content, and to clarify the elementary composition and quality of these alternative fuels.

Acknowledgment

The Authors wish to express their sincerest thanks to Central Philippine University, German International Cooperation, General Service Office of the City Government of Iloilo City and all members of the Uswag Calajunan Livelihood Association, Inc. for providing technical, financial and manpower support in the conduct of this study.

References [1] E. Gunsilius and S. Garcia Cortes. 2010. Waste and Livelihoods: Support of the Iinformal Recycling

Sector in Iloilo, the Philippines. Report for the Sector Project “Recycling Partnerships”. [2] A.R.D. Romallosa, K.J.C. Hornada, K.J.C., and J.G. Paul. 2011. Production of briquettes from

biomass and urban wastes using a household briquette molder. In: M. Alamgir, Q.H. Bari, I.M. Rafizul, S.M.T. Islam, G. Sarkar, and M.K. Howlander (eds) Proceedings of Executive Summary of the 2nd International Conference on Solid Waste Management in the Developing Countries. 13 - 15 Feb. 2011. Khulna, Bangladesh. pp. 249-250.

[3] V.M. Faires. 1970. Thermodynamics, MacMillan Company, New York, p. 9. [4] C.C. Lee. 2007. Handbook in environmental engineering calculations. McGraw-Hill, USA. [5] Retrieved from http://erdb.denr.gov.ph/publications/denr/denr_v10.pdf. [6] Retrieved from http://www.ket.org/Trips/Coal/AGSMM/agsmmtypes.html. [7] J.G. Paul, D. Jaque, R. Kintanar, J. Sapilan, and R. Gallo. 2007. End-of-the-pipe” materialrecovery to

reduce waste disposal and to motivate the informal sector to participate in site improvements at the Calahunan Dumpsite in Iloilo City, Panay, Philippines. 11th International Waste Management and Landfill Symposium. Sardinia, Italy. 16 pp.



EXPERIMENTAL AND THERMODYNAMIC INVESTIGATION ON TRANSFER OF ZINC INFLUENCED BY CHLORINE, SULFUR AND PHOSPHOR DURING THERMAL

TREATMENT OF SEWAGE SLUDGE R. Li *, Y. Li, Z. Chen, H. Zhang

Institute of Clean Energy and Engineering and Liaoning Key Laboratory of Clean Energy, Shenyang Aerospace University, Shenyang, China

*Corresponding author: E-mail:[email protected], Tel: 86-24-89724818

ABSTRACT The impact of chlorine, sulfur and phosphor on transfer of Zn during thermal treatment of sludge was investigated by two approaches: experiments using a tubular furnace reactor and thermodynamic prediction. The results indicate that: Zn was mainly bonded with phosphate form in solid phase between 500 and 1200 ; however, Zn existed as the forms of its gaseous metal simple substance at high temperature (>1300 ); Zn in phosphate form was also detected by XRD in slag at 900 . The volatility rate of Zn was all below 10%, and increased slowly with the combustion time and temperature increasing. It also increased a large scale with the chlorine addition. However, the sulfur and phosphor addition inhibited the volatilization of Zn.

Keywords: Sewage sludge, Thermal treatment, Zinc, Transfer, Cl/S/P

Introduction

Compared with other methods sludge incineration has obvious advantages, significantly reducing the volume of sludge, killing organic micro-organisms, saving energy and reducing the use of land resources [1]. But heavy metals will not die out during sludge incineration, just form gaseous metal compound or submicron grain, and eventually release into the environment. Zinc is the most abundant content heavy metal in sewage sludge in China [2], so it is necessary to study the migration and transformation of Zn during thermal treatment of sludge.

Thermodynamics simulation was widely used to study migration and transformation of heavy metals in waste burning systems [3, 4]. However, it should be indicated that these calculations do not give the reaction time, it is necessary to be calibrated by experiment study. G. Fraissler simulated the migration and transformation of Zn during thermal treatment of sludge, and the influence of CaCl2 was also investigated [5]. The objective of this study was to experimentally quantify the impact of chlorine, sulfur and phosphor on the partitioning of Zn under thermal treatment of sewage sludge and to understand its speciation from thermodynamic calculations.


Materials

The sludge was taken from Kunshan. Elementary analysis of the sludge and heavy metals contents of the sample is shown in Table 1. Synthetic sludge with 2.0%,4% and 8.0% (dry weight) chlorine and sulfur addition were prepared by adding NH4Cl and (NH4)2SO4 to the initial sludge; sludge with 5%, 10% (dry weight) phosphor addition were also obtained by adding (NH4)3PO4.

Experimental Method

The apparatus used in this study was composed of an electric-heated tube furnace and impinger train. The impinger train was prepared to absorb Zn in the flue gas. The effects of incineration time (20, 40, 60, 90, 120min) and temperature (900,950,1000 ) on Zn partitioning were first determined for the sludge without chlorine, sulfur or phosphor addition. Three levels of chlorine, sulfur or phosphor addition were then tested to study their impact of Zn volatilization. Most of the experiments were conducted at 900 . Combustion air was supplied by air compressor at a total flow rate of 3L/min.

At the end of each batch experiment, the residues in the quartz boat were collected as slag; combustion gas samples were taken from the impingers. Zn contents of the slag and volatile Zn absorbed in the solutions were determined by atomic absorption spectrophotometer (AAS), after digestion (if necessary) following



the standard procedures [6]. The qualitative analysis on the form of Zn was conducted using the X-ray diffraction (XRD), and the qualitative elemental analysis of sludge was conducted using the energy dispersive X-ray spectroscopy (EDS) technique.

Table 1. Elementary analysis of the sludge and heavy metals contents of the sample (dry basis)

Thermodynamic Equilibrium Simulation

The method of element chemical potentials combined with atom population constraints was operated on HSC-Chemistry 5.0. The system was set up to represent the thermal treatment of sludge in atmosphere. It main considers the basic elements C, H, O, N, Si, Cl, S, P and Zn. The elements contents have been given in Table 2. The calculations were performed in a combustion atmosphere (α=1.4) and temperature (100–1500 ). “s” represents solid phase and “g” represents gas phase.

Table 2. HSC-Chemistry inputs elements and its amount


Impact of Incineration Time and Temperature

Fig.1c shows that ZnSO4(s) is the dominant species at temperatures below 400 , however, Zn was mainly bonded with phosphate in solid phase at temperature between 500 and 1200 . At temperature above 1300 , Zn existed as its gaseous metal simple substance. Zn in phosphate form was also detected by XRD in slag at 900 . Fig.1a and 1b show that the fractions of Zn in slag are all above 90% and decreased gradually with incineration time and temperature increasing.

Impact of Chlorine Compounds

The volatility rate of Zn in the presence of 2.0-8.0% chlorine addition in the forms of NH4Cl after incineration of sludge is shown in Fig.2a. It shows that the volatility rate of Zn increased a large scale with Cl addition, was up to 45.7% when the chlorine addition was 8%. Compared of Figs.2 b and c, the equilibrium calculation results show that Cl significantly increases the fraction of ZnCl2 (g).

Impact of Sulfur Compounds

Fig.3 a shows the volatility rate of Zn in the presence of 2.0-8.0% sulfur addition in the forms of (NH4)2SO4 after incineration of sludge. It shows that the sulfur in the forms of (NH4)2SO4 adding to the sludge may play a role in controlling Cd volatilization during incineration. The volatility rate of Zn decreased from 6.4% to 3.2% with 8% sulfur addition.

Impact of Phosphor Chlorine Compounds



The influence of phosphor addition in the forms of (NH4)3PO4 on the volatility rate of Zn after incineration of sludge is shown in Fig.4 a. Compared with Fig.4 c, it shows that the phosphor addition in the forms of (NH4)3PO4 inhibited the volatilization of Zn through formation of Zn3(PO4)2 under local oxidative environment in the furnace during sludge incineration. The volatility rate of Zn decreased from 6.4% to 4.0% with 10% phosphor addition.

Figure 1. Effect of incineration time and temperature on Zn partitioning: experiment result (a), (b);

thermodynamic simulation result (c); (d) XRD analysis of Slag (900 , 60min)

Figure 3. Effect of sulfur addition on Zn partitioning: experiment result (a); (b) phase diagram for Zn speciation without the presence of sulfur, and (c) in the presence of sulfur (4.0 %)



Figure 4. Effect of phosphor addition on Zn partitioning: experiment result (a); (b) phase diagram for Zn speciation without the presence of phosphor, and (c) in the presence of phosphor (10.0 %)

Conclusions

According to the experimental results, elemental phosphor could increase the retention of Zn on slag through formation of Zn3(PO4)2 under local oxidative environment in the furnace. Sulfur in the forms of (NH4)2SO4 also obviously increased the immobilization of Zn in slag. However, Chlorine was observed to significantly increase Zn volatilization during sludge incineration, the volatility rate was up to 45.7% when the chlorine addition was 8%.

The chemical equilibrium calculations indicate that: ZnSO4(s) is the dominant species at temperatures below 400 , however, Zn was mainly bonded with phosphate in solid phase at temperature between 500 and 1200 ; at temperature above 1300 , Zn existed as its gaseous metal simple substance. Zn in phosphate form was also detected by XRD in slag at 900 .

Comparison of equilibrium calculation results with those from experimental investigation shows that this approach gives a good qualitative view of the Zn behavior during sludge incineration.

Acknowledgements

This work was supported by National Basic Research Program of China (2011CB201500), Program for New Century Excellent Talents in University (NCET-07-0564) and National Natural Science Foundation of China (51077141).

References [1] Y.H. Sun. 2009. Heavy metals concentration in sewage sludge of Yangtze River Delta.

Environmental Protection Science, 35: 26-29. [2] J. Yang, G.H. Guo, T.B. Chen, et al. 2009. Concentrations and variation of heavy metals in

municipal sludge of China. China Water and Wastewater, 25:122-124. [3] Z.S. Liu. 2007. Control of heavy metals during incineration using activated carbon fibers. J. Hazard.

Mater. 142: 506-511. [4] Y. Zhang, Y. Chi. 2005. An Experiment Study on Distribution of Heavy Metals in the Incineration

of Sludge. Power System Engineering, 21:27-29. [5] G. Fraissler, M. Joller, T. Brunner, I. Obernberger. 2009. Thermodynamic equilibrium calculations

concerning the removal of heavy metals from sewage sludge ash by chlorination. Chemical Engineering and Processing: Process Intensification, 48:152-164.

[6] U.S.Environmental Protection Agency (USEPA).1996. Method 29—Determination of Metal Emissions from Stationary Sources, Office of Air Quality Planning and Standards, Washington, D.C.,1996.



STUDY EFFECTS OF CEMENT REPLACED BY BURNED JOSS PAPER ASH D.F. Lin 1, H.L. Luo 1*, L.S. Huang 2, R.S. Weng 1

1 Department of Civil and Ecological Engineering, I-Shou University, 84001, Taiwan, ROC 2 Department of Logistics Management, Shu-Te University, 82445, Taiwan, ROC

* Corresponding author: E-mail: [email protected], Tel: +886-7-6577711 ext 3318

ABSTRACT In Taiwan, joss papers are burned in more than 11,731 registered shrines or temples in traditional Chinese deity or ancestor worship ceremonies during special holidays or occasions. Instead of placing this large amount of burned joss paper ash (BJPA) in landfills, this study proposes recycling BJPA by replacing some cement with BJPA in mortar specimens. Four different amounts of BJPA, 0, 10, 20 and 30%, are proposed to replace cement. Tests like setting time and compressive strength were performed for macro-analyses; the microstructure and chemical composition analyses were carried out. Test results showed that the compressive strength of specimens decreased as the amount of BJPA replacement increased. In addition, as the curing time increased, strength gains for specimens with different amounts of BJPA replacement decreased. Moreover, the expected strength improvement from the pozzolanic reaction provided by the BJPA replacement was not observed in specimens with BJPA replacement.

Keywords: Compressive strength test, Joss paper ash, Pozzolanic reaction

Introduction

Taiwan has a unique human geographic environment with temples or shrines as religious and local area development centers. The total number of temples and shrines registered with the government was 11,731 in 2008. Burning joss paper is a routine religious activity for these temples and shrines, especially in traditional Chinese deity or ancestor worship ceremonies during special holidays or occasions. After burning, joss paper ash is usually directly discarded into landfills or treated by methods that are not environmentally protective. Because the quantity of burned joss paper ash (BJPA) is large and produced at a steady rate, proper recycling or reuse is an important environmental issue in Taiwan. Yang [1] studied the addition of sewage sludge ash with other stabilized materials such as cement, fly ash, and lime to improve soft subgrade soils and suggested future engineering applications. Pan et al. [2] replaced cement with different weight ratios of waste newspaper ash to make mortar specimens. To identify whether part of the cement and fine aggregate can be replaced by BJPA, Lian et al. [3] studied the strength of mortar using BJPA as an additive or replacement in specimens. In this study, the authors propose replacing cement with BJPA to evaluate possible future engineering applications.


Materials

The BJPA samples were obtained from a temple at Kaohsiung County in southern Taiwan. The samples were collected immediately after the joss papers were burned and brought back to the lab for experiments. The specific gravity was 0.31, and the results obtained from XRFanalysis showed that the chemical compositions of BJPA were mainly Ca, Al, Si, S, and K at 38.64, 7.69, 11.31, 0.93, and 0.18%, respectively. Type I Portland cement with a specific gravity of 3.15 was used. Ottawa sand was selected to be the fine aggregate with a specific gravity of 2.64, and the ratio of the cement to sand was 1:2.75.

Methods

After the BJPA samples were brought back to the lab, the samples were left in the lab to cool down to the temperature of the ash. Then, sieve analysis was performed to obtain the particle distribution of the BJPA. Samples with a particle size smaller than #50 were applied to replace part of the cement with the following ratios: 0, 10, 20, and 30%. The water cement ratio was set to 0.485, and the size of the mortar specimens was 5×5×5 cm3. Mortar specimens with no BJPA replacement were used as a control. The flowability test was first carried out. Both the initial and final setting times were measured with a Vicat needle. Specimens were cured at 3, 7, 14, and 28 days. Compressive strength tests were carried out at each designated curing age. After each compressive strength test, a part of the specimens was broken off and left in a bottle with alcohol



to terminate the hydration reaction. Then, microstructure observations were performed to study the micro structural changes.


Flowability

Table 1 shows the results of flowability and setting time for mortar specimens with different amounts of joss paper ash replacement. The flowability for the control group was 46.89% and 36.66, 16.86, and 1.8% for specimens with 10, 20, and 30% replacement, respectively, which implies that the workability of mortar specimens decreased as the amount of BJPA replacement increased. It also suggests that 10% BJPA replacement is the optimum amount to add to mortar specimens when workability is the main concern.

Table 1. Flowability and setting time for mortar specimens with different amounts of BJPA replacement

Setting Time (min) Flow ability (%) Initial Final 0% 248 375 46.89

10% 119 242 36.66 20% 25 75 16.86 30% 17 27 1.80

Figure 1. Results of the compressive strength and mortar specimens with various amounts of BJPA replacement cured at different ages

Compressive Strength

Fig. 1 shows the relationships between the compressive strength and mortar specimens with various amounts of BJPA replacement cured at different ages. When cured for 3 days, the compressive strengths for specimens with 0, 10, 20 and 30% were 31.91, 29.24, 28.86, and 28.48 MPa, respectively, which imply that the compressive strength of specimens was slightly reduced with increasing amounts of BJPA replacement. However, as the curing time was extended, the reduction in compressive strength increased with increasing amounts of BJPA replacement compared to the control group.



Figure 2. XRD results for specimens with 0 and 30% BJPA replacements cured at 7 and 28 days

XRD Analysis

Fig. 2 shows the XRD results for specimens with 0 and 30% BJPA replacements cured at 7 and 28 days. As seen in the figure, the chemical compositions of CH, C-S-H gel, C2S, and C3S were observed for 2θ angles at 29o and 34o at two peak values. As the peak height increases, amounts of these components also increase. Moreover, products like SiO2, CH, and C3S were observed for 2θ angles at 43o and 47o. When comparing the peak values, the intensities of specimens with 0% BJPA replacement were higher than those of 30% BJPA replacement after curing for both 7 and 28 days, which implies that the early and later strengths of specimens were better for specimens with 0% BJPA replacement.

(a) 0% (b) 30%

Figure 3. Results of TGA for specimens with 0 and 30% BJPA replacements when cured at 7 days

TGA/DTA Analysis

The results of TGA showed sharp drops for temperatures ranging from 35 to 100oC, as shown in Figure 3, for specimens cured at 7 days. These decreases were due to the evaporation of water, which resulted in weight loss. Slower drops with smooth curves were seen in the temperature range from 100 to 400oC. These phenomena were caused by the gradual evaporation of pore water in the C-S-H gel of the cement paste. Moreover, other small sharp drops were observed for temperatures between 400 and 450oC, in which the calcium hydroxide became dehydrated. In the same range of temperatures, an endothermic reaction was observed in the DTA analysis. In the temperature ranged from 440 to 650oC, smooth TGA curves were observed again, in which only gases evaporated, which resulted in less weight loss. These losses were the



result of the carbonation of calcium hydroxide and the dehydroxylation of the C-S-H gel. Considering the effects of BJPA on the TGA/DTA analysis, a longer endothermic section was seen for specimens with 30% BJPA replacement at temperatures ranging from 35 to 100oC. This phenomenon was caused by the fact that BJPA can absorb a large amount of water, thus, more heat was needed to evaporate the absorbed water. However, for temperatures between 100 and 400oC, a 5.5% weight loss was noticed for the case of 0% BJPA replacement and a 3% weight loss was observed for 30% BJPA replacement. When the temperature reached 400 to 450oC, there was 3% weight loss for specimens with 0% BJPA replacement and 2% weight loss for 30% BJPA replacement. As stated previously, specimens with 0% BJPA replacement had a greater amount of calcium hydroxide.

Conclusions

In this study, the influences of burned joss paper ash on the physical properties and microstructures of mortar were investigated. The flowability of mortar specimens decreased with increasing amounts of burned joss paper ash replacement. When cement was replaced by 30% paper ash, the flowability only reached 1.8%, which was far less than that obtained from the control group. This study suggests that the amount of cement replaced by the paper ash should not be more than 10%. Moreover, as the amount of cement replaced by burned joss paper ash in mortar specimens increased, the compressive strengths of the specimens were reduced. Among the three amounts of ash replacement, the compressive strength of specimens with 10% replacement was close to that of the specimens with no ash replacement. In conclusion, the authors suggest that it is applicable to use burned joss paper ash as a cement replacement and that the optimal replacement amount is about 10%.

References [1] C.C. Yang. 2004. A study of the sewage sludge applied with the stability treatment in weak pavement

subgrade soil. Master thesis, National Kaohsiung University of Applied Science, Kaohsiung, Taiwan. [2] W.Y. Pan, D.F. Lin, H.W. Huang and H.Y. Liao. 2008. Effects of waste paper ash on the properties

mortar. The 8th Conference on recycling of pavement materials, Jhongli City, Taiwan. [3] Y.J. Lian, G. Qiu, L.A. Chen, Y.Y. Ye, D.Y. He, and Y.J. Luo. 2007. Test performances of using joss

paper ash to make mortar. The 47th Chinese scientific exhibition for the elementary and middle schools, Taiwan.



FUEL PRODUCTS FROM CATALYTIC CO-GASIFICATION OF PULP SLUDGE MIXED WITH BLACK LIQUOR IN FIXED BED REACTOR

C. Sirinawin 1,2, D. Atong 3, S. Thassanaprichayanont 3, V. Sricharoenchaikul 4* 1International Postgraduate Programs in Environmental Management, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand

2National Center of Excellence for Environmental and Hazardous Waste Management (NCE-EHWM), Chulalongkorn University, Bangkok 10330 Thailand

3National Metal and Materials Technology Center, Pathumthani 12120, Thailand 4Department of Environmental Engineering, Faculty of Engineering,

Chulalongkorn University, Bangkok 10330, Thailand * Corresponding author. E-mail: [email protected], Tel: +662 2186689, Fax: +662 2186666

ABSTRACT In this study, product distribution and energy efficiency from co-gasification of the mixed wastes from pulp mill were evaluated using a fixed bed reactor. The operating parameters including temperature of 700-900°C, equivalence ratio (ER) of 0.2, 0.4 and 0.6, ratio of pulp sludge to black liquor of 50:50 at feeding rate of 5 g/min were examined. In addition, 10Ni5La2O35MgO/Al2O3 catalyst was mixed with raw material to study its effect on the conversion reaction. The results of non-catalytic cases indicated that the optimal condition was temperature of 900°C and ER of 0.2 with gas yield of 61.16%, H2 to CO ratio of 1.21, lower heating value of 5.51 MJ/m3 and cold gas efficiency of 79.13%. For catalytic cases, it was found that the catalyst can improve the percentage of gas yield around 8%. Lower heating value and cold gas efficiency of catalytic cases were 3.78-6.73 MJ/m3 and 46.02-90.13% while those obtained from non catalytic trials were 3.37-5.51 MJ/m3 and 34.63-79.13%, respectively. From these results, co-gasification process can be considered as alternative option for conversion pulp sludge mixed with black liquor to usable fuel products.

Keywords: Catalyst, Co-gasification, Pulp sludge, Black liquor

Introduction

Pulp sludge and black liquor are significant biomass wastes from pulp and paper industry. The essential components of black liquor are the remaining substances from the digestive process where the cellulose fibers have been cooked out from the wood such as alkali lignin, polysaccharides, wood extractives, and residual inorganic pulping chemicals [1]. As for the sludge from wastewater treatment system, it generally consists of the solid residue recovered from the wastewater stream of pulping and paper making process [2]. Normally, pulp and paper plant treats pulp sludge by dumping into the landfill and manages black liquor via chemical recovery process. Though variety of treatment processes can be used to manage black liquor and sludge, co-gasification of pulp sludge mixed with black liquor has been suggested as a viable option. This process can convert black liquor and sludge into more valuable products and offers several advantages over combustion process and disposal into the landfill such as NOx, SOx, CO2 and H2S reduction and superior separation sulfur and sodium in black liquor [3]. In this research, fuel products from co-gasification of pulp sludge mixed with black liquor was studied in a fixed bed reactor. The effect of temperature, equivalence ratio (ER), ratio of pulp sludge to black liquor and 10Ni5La2O35MgO/Al2O3 catalyst were examined to determine the optimal condition and the performance of catalyst on the conversion process.


Pulp sludge and black liquor were obtained from pulp and paper manufacturer utilizing Camaldulensis eucalyptus as raw material. They were dried and crushed by fine grinder and sieved to 10 meshes. 10Ni5La2O35MgO/Al2O3 catalyst was prepared by co-impregnation method. Prior to each trial, prepared catalyst was mixed with raw material at 20 %wt. for feeding into the reactor. The gasification experiment was carried out in a fixed bed reactor at reaction temperature of 700-900°C. Gas product was analyzed by online gas analyzer (MRU GmbH, SWG200-1) which capable of continuous real time qualification of CO2, CO, H2 and CxHy (as CH4).




Elemental analysis of pulp sludge mixed with black liquor yielded 32.76% carbon, 4.57% hydrogen, 2.28% nitrogen, and 1.68% sulfur while proximate analysis indicated 19.66% moisture content, 67.04% volatile matter, 12.64% fixed carbon, and 0.66% ash content. The surface area of 10Ni5La2O35MgO/Al2O3 catalyst was 7.74 m2/g. This surface area is relatively small because of limited surface area of Al2O3 supporter (7.39 m2/g). Fig. 1 showed SEM analysis of catalyst. From this image found that this catalyst has irregular shape and small particle size less than 1 μm.

Figure 1. SEM analysis of 10Ni5La2O35MgO/Al2O3 after reduction.

Effect of Temperature and Equivalence Ratio (ER) on Product Distribution

Major products from gasification of mixed raw material are CO2, CO, CH4 and H2 as showed in Fig. 2. Results indicated that product yields improved at higher temperature and lower ER (Fig. 3a). At higher temperature, gas yields increase while solid and liquid yields decrease. Increasing temperature results in more volatile matter released from biomass particle. Also, tar can be cracked and reformed at greater temperature. For the effect of ER on product yields, gas yields decrease with increasing ER because more oxygen is available in the system. Thus, primary water-gas, secondary water-gas and water-gas shift reaction reverse to produce less gas yield but more liquid yield at raising ER. At higher temperature, CO, CO2 and H2 formation increase due to Boudouard, primary water-gas and secondary water-gas reactions. Moreover, water-gas shift, methanation reactions also reverse to form CO and H2. The ratio between H2 and CO also increases with temperature. Increasing ER from 0.2 to 0.6 leads to higher carbon conversion and lower hydrogen conversion (Figs. 4a and 5a). The ratio between H2 and CO also decrease depends on carbon and hydrogen conversion. Results showed that larger of CO2 occur when increasing ER which enhances partial combustion of various gaseous components whereas CO and H2 decreased with raising equivalence ratio and CH4 also decrease gradually.

Figure 2. Typical gas distribution during co-gasification of pulp sludge mixed with black liquor.



Effect of 10Ni5La2O35MgO/Al2O3 Catalyst on Product Distribution

Addition of catalyst enhances gas yield for approximately 10%wt. This catalyst helps reduce liquid yields while solid yields are relatively stable (Fig. 3b). As expected, products distributions were improve at 800°C more than that of 700°C. Adding catalyst causes carbon and hydrogen conversion increase especially for CO and H2 conversions while CO2 conversion decreases (Figs. 4b and 5b). This can be explained by water-gas shift, steam reforming and CO2 reforming reactions. From this reason, the ratio between H2 and CO also approved as well. It should be noted that catalytic process can improve gas quality and tar removal.

Figure 3. Product yields for (a) non catalytic cases and (b) catalytic cases

Figure 4. Carbon conversion for (a) non catalytic cases and (b) catalytic cases

Energy Efficiency

Higher temperature and smaller ER enhance heating value of gas products. Heating values of gas products depend on the kind of gaseous components and the quantity of gas yield. Heating values of gas products is increased when CO, H2, CH4 and gas yield increased and especially on greater portion of CH4 because of its high heating value. LHV of catalytic cases were 3.78-6.73 MJ/m3 while those obtained from non catalytic trials were 3.37-5.51 MJ/m3. These low to medium heating values indicated that produced gas can be used in several industrial processes. Cold gas efficiency defined as the ratio of total LHV of gas products to the LHV of raw material fed. Increasing temperature and decreasing ER caused greater cold gas efficiency. Cold gas efficiency ranges of catalytic cases were 46.02-90.13% while those obtained from non-catalytic trials were 34.63-79.13%. At equivalence ratio of 0.6, cold gas efficiency decreased because more O2 fed leads to larger CO2 production which does not contribute to LHV of product gas. Generally, the data suggest that good energy efficiency may be achieved at temperature around 800 and 900°C.



Figure 5. Hydrogen conversion for (a) non catalytic cases and (b) catalytic cases

Conclusions

The study on co-gasification of pulp sludge mixed with black liquor for product distributions and energy efficiency with non catalytic and catalytic cases by vary temperature and equivalence ratio was performed. The results of non catalytic cased indicated that the optimal condition was temperature of 900°C and ER of 0.2. When 10Ni5La2O35MgO/Al2O3 catalyst was added, improvement of the gasification performance may be achieved, especially at 800°C. From these results, co-gasification of pulp sludge mixed with black liquor could be considered as an interesting option to convert pulp sludge and black liquor into fuel products and also alternative route for waste management in pulp and paper industry.

Acknowledgements

This work was financially supported by the National Metal and Materials Technology Center (MTEC), the National Center of Excellence for Environmental and Hazardous Waste Management (NCE-EHWM), the National Research University Project of CHE and the Ratchadaphiseksomphot Endowment Fund (EN1189A) and Graduate School, Chulalongkorn University.

References [1] V. Sricharoenchaikul, A.L Hicks and W.J. Frederick. 2001. Carbon and char residue yields form rapid

pyrolysis of kraft black liquor. Bioresource Technology. 77: 131-138. [2] G.M. Scott and A. Smith. Sludge characteristics and disposal alternatives for the pulp and paper

industry. Proceeding of the 1995 Intl. environment conference. 7-10 May 1995. Atlanta, GA. p. 269-279.

[3] D. Hammond. 2002. Gasification of black liquor with the addition of secondary sludge. 6190 Independent Research Final Report. Institute of Paper Science and Technology. Atlanta, GA, USA.



AIR GASIFICATION OF CASSAVA RHIZOME IN A FIXED BED GASIFIER P. Sornkade 1, D. Atong 2, S. Thassanaprichayanont 2, V. Sricharoenchaikul 3*

1 Program in Environmental Science (Interdisciplinary Program), Graduate School, Chulalongkorn University, Thailand

2 National Metal and Materials Technology Center, Thailand Science Park, Thailand 3 Department of Environmental Engineering, Faculty of Engineering,

Chulalongkorn University, Thailand *Corresponding Author: E-mail: [email protected], Tel. +662-2186689

ABSTRACT Air gasification of cassava rhizome for thermal and catalytic cases 600–800°C and ER of 0.2–0.6 were performed in this work. In thermal case, the results indicated that the reaction temperature of 800°C and ER of 0.4 yielded the highest gas product. Addition of Ni/α-Al2O3 catalyst improved lower heating value (LHV), carbon and hydrogen conversions, and cold gas efficiency (�CGE) from 3.60 to 6.52 MJ/Nm3, 18.14 to 27.73%, 8.37 to 10.31% and 37.96 to 59.60%, respectively. Moreover, Ni/α-Al2O3 can reduce tar and char in the product as much as 18.16% and 6.31%, respectively. The catalytic gasification of cassava rhizome was optimal at ER of 0.4 and temperature of 700°C.

Keywords: Biomass, Cassava rhizome, Gasification, Nickel catalyst

Introduction

Cassava rhizome is a biomass which is the neck between stalks and tube of this plant. It is a short woody part connected the tube to the rest of the plant. It is typically burnt or land filled by farmer which creates not only the adverse effect to the environment but also resulted in loss of potential energy. According to the FAO estimates, 25 million tonnes per year of cassava was produced in Thailand. Large quantities of cassava rhizome are generated by cassava plants about 8-10 million tonnes. Cassava rhizome could be used for energy production by combustion process or transformed into gas by gasification technology. Among catalysts used in biomass gasification, Ni based ones are noted to be very efficient not only for tar reduction, but also for decreasing the amount of nitrogenous compounds such as ammonia [1]. Based on previous works e.g. García et al. [2] and Pengmei et al. [3] used Ni-based catalyst, studied gasification with steam agent of pine sawdust. Nickel-base catalyst has been found to be active for tar cracking in the primary reactor, at temperature ranging 700–800°C [3-4]. The main objective of this work is to optimize the conditions of cassava rhizome gasification to produce fuel gas.


Biomass Sample

Cassava rhizome (CR) sample was first grinded to about 0.2–2.0 mm size. The moisture, ash, fixed carbon and volatile matter contents of CR were 8.60, 0.74, 15.96 and 74.70 %wt, respectively. The elemental compositions of carbon, hydrogen, oxygen, and nitrogen were found to be 37.60, 5.41, 55.93, and 0.37 %wt, respectively, which can be formulated as C3.13H5.2O3.52N0.03. The lower heating value (LHV) was around 15.37 MJ/kg.

Catalyst Preparation

The 10Ni/α-Al2O3 catalyst was prepared by impregnation method. The catalyst was calcined in air at 850°C for 3 h and reduced in H2 at 700°C for 2 h and sieved to particle size of 15 µm. In any trials, catalyst was mixed with the cassava rhizome at 20 %wt.

Gasification Setup

In this work, an atmospheric pressure, laboratory scale, stainless steel updraft gasifier was used. Reaction temperature was regulated by PID temperature controller from 600–800°C. Oxygen was mixed with nitrogen to achieve equivalence ratio (ER) of 0.2–0.6. The ER is defined as the oxygen-to-fuel weight ratio divided by the stoichiometric oxygen-to-fuel ratio needed for complete combustion. CR was fed into the system at a rate of 3.0 g/min for 30 minutes.



Sampling and Gas Analysis

Gas product first passed through cyclone to collect any entrained char and ash particles. The liquid products such as tar and other heavy hydrocarbons as well as water are retained in a system of four condensers and two gas washers. Gas product was analyzed by online gas analyzer (MRU GmbH, SWG200-1) which capable of continuous real time qualification of CO2, CO, H2 and CnHm (as CH4). The diagram of gasification system is illustrated in Fig. 1.

Figure 1. A schematic of gasification system: (1) feeder (2) fixed bed reactor (3) electric furnace (4) oxygen (5) carrier gas (6) gas pre-heater (7) chiller (8) cyclone (9) condensers (10) gas analyzer


The Effect of Temperature

Generally, temperature is an important parameter in biomass gasification. Gas yield and LHV obtained at reaction temperature of 600-800°C with ER of 0.2 were depicted in Figure 2. The influence of temperature on total gas product, the hydrocarbons and tar were cracked into gas yields when higher temperature. The maximum gas yield was 800°C. Thermal cracking reaction in the Eq. (1), carbon formation in the Eq. (2) and hydrolysis reaction in Eq. (3), which were verified with Le Chatelier’s principle; higher temperatures favour the reactants in exothermic reactions and the products in endothermic reactions.

pCnHm � qCnHm + rH2 (1)

CnHm � nC+ m/2H2 (2)

CO + 2H2O � CO2 + 2H2 (3)

Figure 2. Gas yield and LHV at different temperatures.

The LHV of product gas increase due on the yields of CO and species of permanent gas (hydrocarbons gaseous). Let LHV be the gas yield calculated by the Eq (4).



LHV = (0.126×CO) + (0.108 ×H2) + (0.358×CH4) (4)

where, CO, H2, and CH4 are volume (molar) percentage of these gas species. Maximum LHV of 3.51 MJ/Nm3 and 7.00 are obtained at 800 °C in thermal and catalytic case, respectively as showed in Figure 2. LHV at 800 °C gives maximum heating value.

Estimated cold gas efficiency (ηCGE) is defined as the ratio of the energy in the desired product to the total energy entering the process. �CGE is defined in terms of the volume flow rate (Vg) as:

(5)

where, Vg is gas volume flow rate (Nm3/min), LHVg is lower heating value of gas yield (MJ/Nm3), Mrw is rate of raw material supplied to gasifier (kg/min). The maximum �CGE was 61.56% at 700°C and minimum was 13.68% at 600°C. The �CGE increased proportion to the temperature, comparison between two ranges overall ER 0.2-0.6, temperature 600°C to 700°C and 700°C to 800°C, were improved 1.7 and 1.3 times, respectively.

The heating value of the char (CV) is calculated from Eq. (6), from %wt of C, H and O from the element analysis of the char.

CV = 0.34× [%C] + 1.4× [%H] – 0.16× [%O] (6)

By using an Eq. (6), after the completion of the gasification process, the char of cassava rhizome is varied in proportional to the temperatures where the CVs of 16.07, 15.27, and 11.56 MJ/kg are obtained at 600, 700, and 800 °C, respectively. The elementals were analyzed by CHNS analyzer (Perkin Elmer PE2400 series). The result noted that CV was lower, while the temperature was higher. In general, the CV of char is moderate, ranging between 16–20 MJ/kg which is recommended for further energy production.

The Effect of Equivalence Ratio (ER)

The results of varying ER on char and tar yields are presented in Figure 3. ER has significant influence on the gasification products. On increasing ER, gas yield increased, while char and tar yields decreased. The minimum char and tar contents of 4.40 and 8.20% respectively are obtained at ER of 0.6. Comparison, ER 0.2 and 0.6, gas product roughly increased average about 15.60%, tar decreased by 18.16% and char decreased by 6.31%.

Figure 3. Char and tar content at ER 0.2-0.6



The Catalytic Activity of Ni/α-Al2O3

The surface area of catalyst measured by Brunaur–Emmett–Teller (BET) method was around 7.74 m2/g. Comparison among three different temperatures for both thermal and catalytic cases, the carbon conversion to CO is improved greatly, from 13.83% to 18.58%, from 18.13% to 27.73% and from 23.22% to 28.50% when ER’s change from 0.2–0.6, respectively. Little improvement on hydrogen conversion was obtained, that is from 6.67% to 8.52%, 8.37% to 10.31%, and 10.48% to 11.81% when ER’s changed between 0.2 and 0.6,. Noted that the measurement was conducted from the observation at 700 °C as shown in Figure 4. Comparing the thermal and catalytic cases, carbon and hydrogen conversions increased significantly for 13.57% and 6.51%, respectively. Results indicated that the temperature of 700 °C appeared as favourable for catalytic activity. Based on previous literatures, Pengmei et al. [3] and Miguel et al. [4], it was found that the catalyst can significantly increases total gas production and performance. The conversion of carbon and hydrogen were proportional to the temperature and addition of a catalyst. In catalytic case, % carbon and % hydrogen conversion to CO, H2 and CH4 increased while CO2 decreased. Because of 10Ni/α-Al2O3 catalyst performs very well when comparing with non-catalytic case. The content of H2 increased, while the hydrocarbon was consumed resulting in the reduction of CH4 content [3].

Figure 4. Carbon and hydrogen conversion to CO and H2 for thermal and catalytic cases

Conclusions

This research investigates products obtained from the gasification of cassava rhizome with thermal and catalytic case at ER 0.2–0.6 under different temperatures from 600–800 °C. In thermal case, the result was obtained at 800 °C and ER of 0.4. A higher temperature favoured gas yield, LHV and cold gas efficiency of 79%, 3.51 MJ/Nm3 and 53.97%, respectively. ER had effects on biomass gasification. On improving ER 0.2–0.6, gas yield increased while char and tar yields were decreased. In catalytic case, 10Ni/α-Al2O3 catalyst was used to improve the gasification performance. The LHV, cold gas efficiency, carbon and hydrogen conversion to CO and H2 were 7 MJ/Nm3, 61.56%, 13.57% and 6.51%, respectively. These were added by catalyst, the optimal temperature of 700 °C and ER of 0.4. Therfore, the study further confirmed that the 10Ni/α-Al2O3 catalyst performs well for gas production and quality on cassava rhizome gasification. This works suggests that cassava rhizomes were quite suitable for conversion by gasification process and suitable for power production.

Acknowledgments

Authors would like to thank the National Research University Project of CHE and the Ratchadaphiseksomphot Endowment Fund (EN1189A), National Metal and Materials Technology Center (MTEC), and Program in Environmental Science (Interdisciplinary Program) Graduate School, Chulalongkorn University for financial support.



References [1] L. Devi, K. J. Ptasinski, F.J.J.G. Janssen. 2003. A review of the primary measures for tar elimination

in biomass gasification processes. Biomass and bioenergy. 24: 125-140. [2] L. García, M. L. Salvador, J. Arauzo and R. Bilbao. 1999. Catalytic steam gasification of pine

sawdust. Effect of catalyst weight/biomass flow rate and steam/biomass ratios on gas production and composition. Energy & Fuels. 13: 851 – 859.

[3] Lv. Pengmei, J. Chang, T. Wang, Y. Fu, Y. Chen, and Y. Zhu. 2004. Hydrogen – rich gas production from biomass catalytic gasification. Energy & Fuel. 18: 228–233

[4] C.A. Miguel, C. José, A. María-Pilar and G. Javier. 2000. Biomass gasification with air in fluidized bed. Hot gas cleanup with selected commercial and full-size nickel-based catalysts. Ind. Eng. Chem. Res. 39: 1143 - 1154.



STEAM REFORMING OF TAR MODEL COMPOUND USING PD CATALYSTON ALUMINA TUBE

J. Nisamaneenate 1, D. Atong 2, V. Sricharoenchaikul 1* 1Department of Environment Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok

10330, Thailand 2National Metal and Materials Technology Center, Thailand Science Park, Pathumthani 12120, Thailand

*Corresponding author: E-mail: [email protected], Tel: +662 218 6689 Fax: +662 218 6666

ABSTRACT Gasification process of biomass as a renewable energy source generates tar in product gas. In this study, palladium catalyst on alumina was used in steam reforming of benzene as tar model compound. Pd/Al2O3 showed high efficiency of benzene decomposition and enhanced the formation of syngas. Hydrogen and carbon conversions increased with reaction temperature. The catalytic performance at 600°C and 800°C was similar, i.e., 1%wt > 0.5%wt > 1.2%wt > w/o catalyst. 1%wt Pd/Al2O3 showed excellent catalytic activity with the highest hydrogen and carbon conversions of 83% and 81%, respectively at 800°C. This result is attributed to smooth surface of palladium as noticed from SEM image. Steam to carbon ratio of 2 provided the highest conversion. Addition of catalyst from 4 and 7 tubes did not display much different in term of benzene cracking efficiency. 4th cycle usage of 1%wtPd/Al2O3 exhibited a higher conversion than that of 0.5%wt.

Keywords: Al2O3, Benzene, Biomass gasification, Tar, Palladium

Introduction

Gasification transforms solid fuel to synthesis gas via thermo chemical conversion process [1]. Main problem of biomass gasification process is the presence of tars in produced gas. Tar lead to fouling of process equipments such as lines, filters and turbines by corrosion and deposit formation [2]. General component of tar from biomass gasification process is benzene (37.9%), toluene (14.3%), other one-ring aromatic hydrocarbons (13.9%) as well as multi-ring species such as naphthalene (9.6%), and others [3]. Catalytic steam reforming is probably the best way to utilize and reduce tar. In this work, palladium catalyst for tar destruction is prepared by electroless plating method on alumina tube support as composite membrane. In addition, palladium has ability to selectively separate hydrogen because of the high solubility and diffusivity of this gas in their lattice. Benzene was selected as tar model compound as it represents a more stable structure which is difficult to disintegrate. The efficiency of the catalyst was evaluated on different operating conditions such as temperature, metal loading, concentration of benzene, number of tube, steam to carbon ratio and the catalytic stability.


The alumina tube supports were made of α-alumina was activated by the procedure which may be found elsewhere [4]. After several activation cycles, palladium was deposited by electroless plating with the use of a plating bath containing 0.011 M palladium chloride, 0.167 M ethylenediamine tetra acetic acid disodium salt, 5.56 M ammonia, hydrazine as the reducing agent. The catalyst loading was prepared in various amounts of 0.5, 1 and 1.2%wt. The steam reforming of benzene to syngas was carried out in a tube reactor (25 mm diameters, 400 mm long). Seven of catalyst tubes were placed of the center of reactor. The concentrations of benzene were fixed at 2000 and 5000 mg/l. Benzene and water were fed by syringe pump then evaporated in the furnace (200°C) before entered into the reactor. The produced gases were sampled every ten minutes and analyzed by gas chromatography for H2, CO, CO2, and CH4.


Effects of Temperature and Metal Loading

Experiment of steam reforming of benzene (2000 mg/l) over the different palladium loading at 600°C and 800°C are given in Fig. 1. The produced gas was not stable during first 60 min because feed material had



passed through many joints and voids. At 600°C the hydrogen and carbon conversion were 55% and 51%, respectively. When temperature was above 800°C, conversion increased quickly. The reforming performance at 600°C and 800°C were similarly as followed: 1%wt > 0.5%wt > 1.2%wt > w/o catalyst. Lower conversions with 0.5%wt is probably due to a decrease of specific surface area because the grain has not grown enough for reaction as showned in SEM of Fig. 2. Interestingly, the 1% wt catalyst showed the highest activity. This may due to specific surface area deacreasing from palladium deposited to smoother surface at 1.2%wt as previously discussed.

Figure 1. Conversion of C, H at (a) 600°C (b) 800°C and S/C ratio 2

Figure 2. SEM of surface palladium catalyst (a) 0.5%wt (b) 1%wt (c) 1.2%wt, after reaction at 600°C (d) 0.5%wt (e) 1% wt (f) 1.2%wt and after reaction 800°C (g) 0.5%wt (h) 1%wt (i) 1.2%wt

Effect of Numbers of Pd Catalyst Tube The result of changing number of Pd catalyst tubes (0, 2, 4, 7) for reaction with benzene are given in Fig. 3. The amount of produced gas related to increasing the number of catalyst tubes to some degree. At two catalyst tubes, conversion of hydrogen and carbon were 61%, 52% (2000 mg/l) and 64%, 59% (5000 mg/l). When the number of tubes increased from four to seven, hydrogen conversion at 2000 mg/l increased from 80% to 84% while hydrogen conversion at 5000 mg/l increased from 79% to 85%. Increase catalyst tubes from four to seven were not greatly influence benzene cracking efficiency.

Effect of Concentration of Benzene

When benzene concentration increased from 2000 to 5000 mg/l, the catalytic performance at 600°C and 800°C exhibited similar results. Hydrogen and carbon conversions with 1%wt at 800°C were 79% and 75%



respectively. The comparison between four and seven palladium catalyst tubes at 800°C showed that the hydrogen and carbon conversion at seven tubes were a little more than four tubes.

Figure 3. Conversion of C, H at 800°C (a) 2000 and (b) 5000 mg/l with 1%wt Pd/Al2O3, S/C ratio 2

Figure 4. Conversion of C, H at (a) 600°C (b) 800°C with %wtPd/Al2O3, S/C ratio at 2, residence time at 1 second and benzene 5000 mg/l

Effect of Steam to Carbon Ratio

The effect of steam to carbon molar ratio on the reaction performance of benzene over 1%wtPd/Al2O3 at 800°C is shown in Fig. 5. From the results, it was demonstrated that H2 and CO2 yields increased when the S/C ratio increased. The H2 yield at S/C ratio of 2 and 3 were not significantly different, while the CO yield reduced as S/C ratio increases from 0.9 to 3. It can be explained by water gas shift reaction, at high values of S/C ratios, a high steam partial pressure pushed the water gas shift equilibrium toward hydrogen formation. An adsorbed organic molecule reacts with water on the catalyst surface until all carbon atoms are converted to CO or CO2. Methane is not occurred by intermediate reaction and primary product, but is probably formed through the methanation [3].

Experiments with Used Catatysts

To study the catalytic stability, used catalysts (seven tubes) were rerun for several times. Conversion on reforming of benzene (2000 mg/l) was studied with 0.5%wt and 1%wtPd/Al2O3 at 800°C (in Fig. 5). Slightly decreased of the hydrogen conversion was observed for 1%wtPd/Al2O3 compared with 0.5%wtPd/Al2O3 after 2nd cycles and 4th cycle. At 4th cycle at 800°C with 0.5%wt catalyst, carbon and hydrogen conversions were reduced to 33%, 33% after for fourth cycle. Whereas, for 1%wt catalyst of 4th cycle, carbon and hydrogen conversions were reduced to 50% and 61%, respectively as active site decreased from sintering of catalysts in each cycles. The palladium deposit on 0.5%wt catalyst also peeled off from support during some particular runs. The damage of catalyst might occur from thickness of palladium; the lower amount of palladium loading of 0.5%wt catalyst contributed to the thinner layer which vulnerable to long term thermal reaction.



Figure 5. Effect of steam to carbon molar ratio at 800°C with 1%wt Pd/Al2O3, residence time at 1 second and benzene 5000 mg/l (a, b) C or H Conversion

Conclusions

Pd/Al2O3 catalytic tubing showed good efficiency on benzene decomposition to H2 in the produced gas. The results at higher temperature indicated greater conversion. The performance of catalytic benzene reforming reaction at 600°C and 800°C were in the same trend where 1%wt catalyst at 800°C showed the most pronounced catalytic performance. The reaction at steam to carbon molar ratio of 2 displayed the highest conversion. There was not much different in term of efficiency between installing 4 and 7 catalyst tubes. The activity of catalyst was gradually declined from 1st run to 4th runs. The deactivation of catalyst mainly caused from the sintering of catalyst and did not occur from carbon deposit.

Acknowledgements

Authors would like to thank Cooperation on Science and Technology Researcher Development Project by Office of the Permanent Secretary Ministry Science and Technology, National Metal and Materials Technology Center, and the National Research University Project of CHE and the Ratchadaphiseksomphot Endowment Fund (EN1189A) for their support.

References [1] P. McKendry. 2002. Energy production from biomass (part 3): gasification technologies, Bioresource

Technol. 83: 55–63. [2] J. Han and H. Kim. 2008. The reduction and control technology of tar during biomass

gasification/pyrolysis: An overview. Renewable and Sustainable Energy Reviews. 12: 397-416. [3] R. Coll, J. Salvado, X. Farriol and D. Montane. 2001. Steam reforming model compounds of biomass

gasification tars:conversion at different operating conditions and tendency towards coke formation. Fuel Processing Technol. 74: 19–31

[4] D.A. Pacheco Tanaka, M.A. Liosa Tanco, S.i. Niwa, Y. Wakui, F. Mizukami, T. Namba and T.M. Suzuki. 2005. Preparation of palladium and silver alloy membrane on a porous via simultaneous electroless plating. J. Membr. Sci. 247: 21-27.



PYROLYSIS AND GASIFICATION OF PLASTIC WASTES FROM LANDFILL WITH NI–MG–AL CATALYST

P. Kaewpengkrow 1, D. Atong 2, V. Sricharoenchaikul 1*

1Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330 Thailand

2National Metal and Materials Technology Center, Thailand Science Park, Pathumthani, 12120 Thailand

*Corresponding author: E-mail: [email protected], Tel: +662 2186689 Fax: +662 2186666

ABSTRACT Pyrolysis and gasification processes were utilized in order to study the feasibility on production of value added fuels from landfilled plastic wastes. Plastic wastes were converted in a gasifier at 700-900°C. Equivalence ratio (ER) was varied from 0.4–0.6 with or without addition of Ni–Mg–Al catalyst. Methane was found to be the major gaseous products. The pyrolysis and gasification of plastic wastes without Ni–Mg–Al catalyst resulted in relatively low H2 and CO was low with energy content ranged from 6.10–8.80 MJ/m3. The presence of the Ni–Mg–Al catalyst significantly enhanced H2 and CO production as well as increased gas energy content to 15.76–19.26 MJ/m3. Higher temperature resulted in more H2 and CO, higher carbon conversion and product gas yield which ranged from 87.23–94.29% while solid and liquid decreased. The maximum gas yield was achieved when Ni–Mg–Al catalyst was used at 900°C. The results suggest that the prepared catalyst has favorable effect on waste plastic conversion to H2 and CO as well as other product gas which can be applied to the management of landfill wastes.

Keywords: Catalyst, Gasification, Landfill, Plastic wastes, Pyrolysis

Introduction

Thermoplastics contribute to the total plastic consumption by around 80 %. They were used for typical plastics applications such as packaging [1]. Since most of these plastic wastes are still disposed of by landfill and open dumping, about 65% of collected municipal solid wastes in Thailand are being disposed in open dumpsites [2, 3]. Thus, recycling of plastic wastes is highly encouraged. Incineration of plastics is not an efficient way to manage these wastes as most of useful components are converted to CO2 and released into the atmosphere [4]. Chemical recycling of the waste plastics via pyrolysis and gasification to generate useful hydrocarbons has been a promising alternative for the management of plastic wastes. Gasification is similar to pyrolysis but limited amount of oxidizing agents in reacting atmosphere are allowed and the products contain higher gas fraction than pyrolysis. These processes convert carbon based material into gaseous products containing CO2, CO, H2, CH4 which can be used as sources for heating, power generation as well as generate useful fuels or petrochemical feedstocks [5]. Typically, catalysts are required in order to achieve satisfactory carbon conversion from pyrolysis and gasification processes, Nickel-based catalysts are commonly used by researchers for hydrogen production from the thermal processing of biomass or plastics [6]. The purpose of using catalyst was to crack of tar and increase product gas yield. The main objective of this research is to study the effects of pyrolysis and gasification temperatures, equivalence ratios, addition of a Ni–Mg–Al catalyst on the quality and quantity of produced gas from landfilled plastic wastes.


In this work, plastic wastes were obtained from a landfill in the south of Thailand. Wastes were fed into a rotary trommel screen to separate plastic and soil-like materials. Most of separated plastic wastes were found to be plastic hold bags which were further shredded into small pieces (about 3–5 mm). Thermogravimetric analysis was performed in order to determine the thermal degradation data of the plastic wastes samples. For catalyst preparation task, the support material (Al2O3) is impregnated with the aqueous solution of Ni. The loading amount of Ni catalyst was 10 wt% which was prepared using the aqueous solution of Ni(NO3)2.6H2O and Mg(NO3)2.6H2O as a promoter. The gasifier system consists of a fixed bed reactor made of stainless steel with an inside diameter of 1.85 cm and 110 cm height. Nitrogen and oxygen were used as carrier gas and oxidizing gas, respectively. During each trial, the material was continuously fed from the top of the reactor at a rate of 1 g/min. The pyrolysis and gasification temperature was varied from 700–900°C and equivalence ratio (ER) was varied from 0.4–0.6 for gasification. For the catalytic



experiment, 1 g of plastic wastes was mixed with 0.5 g of catalyst. The catalytic gasification temperature was varied from 700–900°C and equivalence ratio was 0.4. The composition of the product gas was analyzed by online gas analyzer for CO, CO2, CxHy (as CH4) and H2. The solid and liquid fraction yields were directly calculated from measured weight, while the total gas yield was evaluated by difference.


From TGA data, thermal decomposition range of plastic wastes was from 350–700°C. Relatively wide decomposition range followed by a rapid drop around 650°C indicated that plastic waste sample contains several combustible materials with a dominated plastic specie. The separated plastic wastes were low moisture of only 0.01 wt. %, this might be due to natural decomposition of biodegradable organic parts that took place over several years after their disposal, leaving only non-biodegradable plastics in the landfill [2]. The high volatile content of 98.1 wt. % suggests that the waste mainly consists of various organic compounds. Low ash content is an indicator that plastic wastes should be promising sources for the production of fuel via thermochemical process. Elemental composition of plastic wastes revealed 66.7, 12.5, 20.2, 0.0, and 0.6% of C, H, O, N, S, respectively. High carbon content, low sulfur and absent of nitrogen suggest that the sample is suitable for production of fuel gas with high energy content and low NOx and SOx.

Effect of Gasification Temperature and ER on the Gas Composition

The pyrolysis and gasification processes yielded three different product phases: solid (char), liquid, and gas. The product gas yield was mainly ranged from 62.25–82.69% and the gas fractions increased with temperature and equivalence ratio while solid and liquid decreased were shown in Fig. 1(a). The gas composition from the pyrolysis and gasification of plastic wastes at different gasification temperatures were shown in Fig. 1(b). The produced gas contained mainly of hydrocarbon gases (reported as CH4). This decomposition reaction is initiated by depolymerization at higher temperatures to generate gaseous fraction containing CO, CO2, H2 and hydrocarbons. Relatively high hydrocarbon gases in this work may result from high carbon and hydrogen content in raw material as well as high heat transfer rate to plastic wastes. As a consequence, their molecular structures were rapidly decomposed and hydrocarbon gases were formed quickly. It can be observed that hydrocarbons decreased significantly with temperature and equivalence ratio. Gasification runs yielded higher CO and CO2 than pyrolysis process because of additional oxygen in the reactions. From these results, it was found that H2 increased slightly when the gasification temperature was increased. Calorific value is important parameter for direct heat and power utilization of the product gas. In this case, calorific value of the gas product varied from 6.11–8.80 MJ/m3 which is mainly dependent on the amount of methane. The highest calorific value of 8.80 MJ/m3 obtained from 800°C and equivalence ratio of 0.4 is suitable for further usage as quality fuel gas. The maximum cold gas efficiency of 81.59% occurred at 700°C and equivalence ratios of 0.4. Since calorific value of product gases were not significantly change with temperature, it would be more economical to gasify this plastic waste at lower temperature of 700°C.

Effect of Ni–Mg–Al Catalyst on the Gas Composition

The gasification temperatures of 700–900°C and equivalence ratios of 0.4 were investigated for the production of H2 and CO from the catalytic gasification of waste plastics. The catalyst to plastic ratio in this work was maintained at 0.5 g/g. The gas yield increased from 62.25–82.69 % to 87.23–94.29 %. The gas composition from the catalytic gasification of plastic wastes at different gasification temperatures were shown in Fig. 2(b). In the presence of the Ni–Mg–Al catalyst, the content of syngas (H2 and CO) were increased, ranging from 0.51–5.94 vol. % to 5.34–26.11 vol. % with the highest H2 and CO contents were obtained at the highest temperature of 900°C. Moreover, higher temperature resulted in higher carbon conversion, calorific value, cold gas efficiency and product gas yield. Wu et al. [4] found that the promoted water gas reaction would enable more water to react and convert to H2. Hydrocarbons are found to increase with addition of Ni–Mg–Al catalyst which indicating that the generation of these products is dependent on the presence of Ni–Mg–Al catalyst and higher temperature. The calorific value of the produced gas was range from 15.76–19.26 MJ/m3 mainly depending on the quantity of methane. The maximum cold gas efficiency of 97.42% occurred at 900°C were shown in Fig. 2(a). Since calorific value of product gases were



not significantly change with temperature, it would be more economical to gasify at lower temperature of 700°C. It is suggested that a presence of the Ni–Mg–Al catalyst improved the gasification of plastics for product gas yield, H2 and CO production and no significant effect on reduction of hydrocarbon.

Figure 1.(a) Effect of temperature and ER on product distribution (b) Effect of temperature and ER on produced gas and calorific value from pyrolysis and gasification process

Figure 2. (a) Effect of a presence of the Ni–Mg–Al catalyst on cold gas efficiency (b) Effect of temperature

on gas produced with calorific value from catalytic gasification

Conclusion

Plastic wastes from landfill were subjected to pyrolysis and gasification processes at different temperatures and equivalence ratio. Gas product increased with temperature and equivalence ratio, hydrocarbon gases were main products along with CO and H2. The increase of the equivalence ratio leads to lesser formation of tars and char. The calorific value and cold has efficiency of product gas obtained at lower gasification temperature was significantly higher which suggested the optimal operating condition of around 700°C and ER of 0.4. In the presence of the Ni–Mg–Al catalyst, the highest H2 and CO was achieved at the temperature of 900°C, it was significant effects on product gas yield, H2 and CO production, calorific value and cold gas efficiency and no significant effect on reduction of hydrocarbon production. Thus, thermochemical treatment of landfilled plastic wastes using pyrolysis and gasification as a very attractive alternative for sustainable waste management.

Acknowledgments

This work was financially supported by The National Research University Project of CHE and the Ratchadaphiseksomphot Endowment Fund (EN1189A), National Metal and Materials Technology Center (MTEC), and Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University.

References [1] S.M. Al-Salem, P. Lettieri and J. Baeyens. 2009. Recycling and recovery routes of plastic solid waste

(PSW): A review. Waste Management. 29: 2625–2643.

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[2] C. Chiemchaisri, B. Charnnok, and C.Visvanathan. 2010. Recovery of plastic wastes from dumpsite as refuse-derived fuel and its utilization in small gasification system. Bioresource Technology.101: 1522–1527.

[3] T. Kaosol. 2009. Sustainable Solutions for Municipal Solid Waste Management in Thailand. World Academy of Science, Engineering and Technology 60.

[4] C. Wu and P. T. Williams. 2010. Pyrolysis–gasification of plastics, mixed plastics and real-world plastic waste with and without Ni–Mg–Al catalyst. Fuel. 89: 3022–3032.

[5] C. Wu and P. T. Williams. 2 0 1 0. Pyrolysis–gasification of post-consumer municipal solid plastic waste for hydrogen production. International journal of hydrogen energy. 35: 9 4 9-9 5 7.

[6] C. Wu and P.T. Williams. 2009. Investigation of Ni-Al, Ni-Mg-Al and Ni-Cu-Al catalyst forhydrogen production from pyrolysis–gasification of polypropylene. Applied Catalysis Environmental. 90: 147–156.



CATALYTIC DECOMPOSITION OF BIOMASS FUEL GAS OVER LA1-XCEXCOO3 WITH TOLUENE AS MODEL COMPOUND

K. Soongprasit 1,2, D. Aht-Ong 1,2, V. Sricharoenchaikul 3, D. Atong 4* 1Department of Materials Science, Faculty of Science, Chulalongkorn University, Thailand

2Research Unit of Advanced Ceramics and Polymeric Materials, National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Thailand

3Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Thailand 4National Metal and Materials Technology Center, Thailand Science Park, Pathumthani,Thailand

*E-Mail: [email protected] Tel.: +662-564-6500; Fax: +662-564-6447

ABSTRACT Perovskite-type mixed oxides La1-xCexCoO3 were synthesized by sol-gel method. Introduction of Ce tended to decrease crystal size of catalyst from 22.18 to 13.38 nm. Particle size and specific surface area were in the range of 9.58-13.72 µm and 6.03-9.23 m2/g, respectively. Catalytic activity of synthesized catalysts was investigated by steam reforming of toluene as tar model compound. The presence of Ce in catalyst solid solution did not improve activity of catalyst significantly but enhanced stability by promoting the formation of filamentous carbon on the surface. The suitable catalyst for steam reforming of toluene is La0.6Ce0.4CoO3 at 800 °C which carbon conversion as CO and hydrogen conversion as H2 are raised to 64.42% and 63.23%.

Keywords: Steam reforming, Perovskite, Sol-gel, Toluene

Introduction

The main products of thermochemical conversion of biomass are char, gas, and condensate. Condensable products are mostly tar which is a complex of mixture of condensable hydrocarbon that are difficult to deal with in the downstream process because its plugged in the filter and gas line. Catalytic tar removal is the most interesting method to overcome this problem. The efficiency of the process can be increased by reforming hydrocarbon to value added products especially hydrogen. Co is generally used as active site of catalyst for cracking process due to its high activity with hydrocarbon chain end. Nevertheless, Co is easily deactivated by coke deposition. The development of perovskite-type oxides catalyst with high activity is of interest to inhibit coke deposition under low steam/carbon ratio. The problem of perovskite-type oxide for oxidation reaction is the low surface area [1]. From literatures, La substitution by Ce can improve surface area and promote oxidation reaction of steam reforming. Performances of Ce containing catalysts were reported by several researchers such as high oxygen storage capacity, disperse the active metal efficiently, inhibit sintering, inhibit char formation and good promoter in perovskite catalyst [2]. Furthermore, water-gas shift reaction as products is CO2 and H2 was accelerated by Ce that makes it suitable for hydrocarbon reforming to syngas. In this work, toluene was used as tar model compounds to investigated the catalytic activity of sol-gel derived La1-xCexCoO3 (x=0, 0.2, and 0.4) catalyst on steam reforming reaction at 500-800 ºC. Catalyst activity was interpreted in term of carbon and hydrogen conversion to CO2, CO, H2, and hydrocarbon as CH4. The suitable catalyst composition and operating parameters for synthetic gas production was reported.

Experimental

Perovskite-type Catalyst Synthesized by Sol-gel Method

Metal nitrate including La(NO3)3�6H2O, Ce(NO3)3�6H2O, and Co(NO3)2�6H2O were applied as precursors. Metal nitrate precursors were distilled and refluxed until temperature rose to 90 ºC. Then, polyvinyl alcohol (PVA, 98-88% hydrolyzed, MW = 850,000-146,000) 5% solution was added as design metal ion to PVA molar ratio 1:1 and continued refluxed for 2 hrs to ensure the formation of metal complex. The precursor solution was stirred on the hot plate to form gel and dried at 110 ºC overnight. The foam-like structure were obtained and subsequently calcined at 700 ºC for 5 hrs. Crystal structure, crystal size, phase and morphology of synthesized catalysts were investigated using XRD (JEOL, JDX-3530), SEM (JEOL, JSM-5410) and TEM.(JEOL, JEM-2010) Particle and specific surface area were estimated using Mastersizer 2000 instrument and BET method.



Catalytic Steam Reforming of Toluene

Catalytic activity of perovskite structure catalyst was performed via fixed bed quartz reactor at 500-800 ºC. Distilled water was fed continuously using peristaltic pump into evaporator to generated steam while toluene was fed continuously into quartz reaction as design steam to carbon molar ration of 2. Carrier gas flow rate was controlled at 2 L/min using rotameter. Permanent gas such as CO2, CO, H2 and hydrocarbon as CH4 were analyzed by online gas analyzer (MRU; GmbH SWG 200-1). Activity of catalyst was interpreted as carbon and hydrogen conversion of materials (toluene) to gas products (CO2, CO, H2 and hydrocarbon as CH4).


Perovskite Catalyst Prepared by Sol-gel Method

Fresh La1-xCexCoO3 (X=0, 0.2, and 0.4) catalysts were synthesized successfully as illustrated in Figure 1. LaCoO3 phase was observed in all catalysts while the La(OH)3 which is an intermediate phase of perovskite-phase transformation at lower temperature was not detected. In the case of Ce substitution La, Ce was inserted into LaCoO3 structure which appeared as cubic structure of CeO2 according to JCPDS 65-5923 (2θ of 27.96, 33.13, 46.48 and 58.64). This result is corresponded well with Cui et al [2]. Nevertheless, when Ce was added at x=0.4, the Co3O4 cubic structure was observed which maybe affected oxidation of Co in as-prepared catalyst during calcinations. Substitution of La by Ce tended to decrease crystal size of synthesized catalyst from 22.18 to 13.38 nm and decreased particle size from 13.72 to 9.58 μm. The specific surface area of LaCoO3 catalysts was 6.03 m2/g and progressively increased to 9.95 m2/g with greater amount of Ce.

Figure 1. XRD pattern of La1-xCexCoO3 of (a)fresh catalyst and (b) used catalyst at various operating

temperature (� LaCoO3 � CeO2 � Co3O4, � Ce7O12, � La2O2C2, � Ce4O7, � La(OH)3, � Co)

Catalytic Activity

To evaluate performance of prepared catalyst, carbon and hydrogen conversion of toluene to CO2, CO, H2 and CH4 were calculated. (Figure 2). Carbon and hydrogen conversion significantly increased at 700 ºC and 800 ºC which indicated that La1-xCexCoO3 catalysts are active at temperature higher than 700 ºC. The reforming reaction (C7H8 + 7H2O � 7CO + 11H2 and C7H8 + 14H2O � 7CO2 + 18H2) and reverse water-gas shift reaction (CO + H2O � CO2 + H2) can be take place and mainly affected to the increasing of CO and H2. These reforming reactions become thermodynamically occurred at temperature higher 435 ºC and 350 ºC [3]. Good stability of prepared catalyst was displayed in Figure 2 (c). Conversion of toluene was kept in the range of 70% and 60% for La0.6Ce0.4CoO3 and LaCoO3, respectively after 6 hrs.LHV of product gases were increased with temperature and the highest value was 4.22 MJ/Nm3 when La0.6Ce0.4CoO3 was used at 800 ºC. H2/CO ratio of produced gas was in the range of 2.06-5.67. If consider both qualitative and quantitative, the best catalyst for steam reforming of toluene is La0.6Ce0.4CoO3 at operation temperature of 800 °C which carbon conversion as CO and hydrogen conversion as H2 are raised to 64.42% and 63.23%, respectively. LHV and H2/CO (2.91) are acceptable without supplementary fuel and hydrogen and enough for methanol synthesis and Fischer-Tropsch synthesis to produce synthetic diesel.



Figure 2. C and H conversion to CO2, CO, H2 and CH4 from steam reforming of toluene for 1 hr. with (a)

thermal, (b) La0.6Ce0.4CoO3 catalyst and (c) 6 hrs experiment at 800 ºC.

Crystal Structure and Morphology of used Catalyst

Diffractogram revealed that crystal structure of fresh La0.6Ce0.4CoO3 catalyst was changed (Figure 1 (b)) which is strongly related with their operating temperatures. At 700 ºC and 800 ºC, La2O3 was reduced by steam in the process, then La(OH)3 was formed at 2θ of 15.60, 27.95, and 39.48 according to JCPDS 83-2034 [4]. Moreover, appearance of Co0 at 2θ of 44.23 and 51.44 according to JCPDS 15-0806 confirmed that Co3+ in perovskite structure was reduced by active gas, generally H2. Morphology of used catalyst was observed using TEM technique as illustrated in Figure 3. Interestingly, LaCoO3 shows encapsulating carbon on the surface after tested at 800 ºC while both encapsulating and filamentous carbon can be observed on the surface of La0.8Ce0.2CoO3 and La0.6Ce0.4CoO3. Alonso and co-worker [5] discussed the effect of carbon on activity and stability of catalyst. Encapsulation of catalyst particles loses their activities because active site, in this case is Co, cannot access to reactive gas. In contrast, Co encapsulated on the top of the filament is accessible to active gas that make it keeps the catalytic activity. Particle size and specific surface area of used catalysts at 800 ºC were evaluated. It is very clear that particle of used catalysts were smaller than agglomerated fresh catalysts except for La0.6Ce0.4CoO3. This catalyst had high activity as coke formation occurred simultaneously with reforming and reverse water-gas shift reaction. The filamentous carbon deposited on the surface did not affect much to its activity but could cause particle size enlargement (from 9.58 to 44.51 μm) and increase of the surface area (from 9.23 to 16.57 m2/g).

Figure 3. TEM images of used catalyst after steam reforming of toluene at 800 ºC for 1 hr

Conclusions

La1-xCexCoO3 (x=0, 0.2, and 0.4) catalysts were synthesized by sol-gel method successfully. Steam reforming of toluene has shown clearly favorable of La1-xCexCoO3 catalyst for reforming and reverse water-gas shift reaction. The suitable condition for syngas production from toluene at 800 ºC is with La0.6Ce0.4CoO3 catalyst which carbon and hydrogen conversion increased to 64.42% and 63.23%, respectively. LHV and H2/CO of produced gas are 4.22 MJ/Nm2 and 2.91 and acceptable without

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supplementary fuel and hydrogen. Addition of Ce on the LaCOO3 did not improve activity significantly but could enhance stability by promoting the formation of filamentous carbon on the catalyst surface.

Acknowledgements

This research was supported by the National Metal and Materials Technology Center (Project No. MT-B-52-CER-07-249-I). K. Soongparsit thanks The Chulalongkorn University Graduate Scholarship to Commemorate the 72nd Anniversary of His Majesty King Bhumibol Adulyadej and Research Unit of Advanced Ceramic and Polymeric Materials for financial support.

References [1] M. Mori, Y. Iwamoto, M. Asamoto, Y. Itagaki, H. Yahiro, Y. Sadaoka, S. Takase, Y. Shimizu, M.

Yuasa, K. Shimanoe, H. Kusaba, Y. Teraoka. 2008. Effect of preparation routes on the catalytic activity over SmFeO3 oxide. Catalysis Today, 139: 125-129.

[2] Y. Cui, V. Galvita, L.R. Struckmann, H. Lorenz, K. Sundmacher. 2009. Steam reforming of glycerol: The experimental activity of La1-xCexNiO3 catalyst in comparison to the thermodynamic reaction equilibrium. Applied Catalysis B. 90: 29-37.

[3] D. Świerczyński; S. Libs, C. Courson. A. Kiennemann. 2007. Steam reforming of tar from biomass gasification process over Ni/olivine catalyst using toluene as a model compound. Applied Catalyst B: Environmental. 74: 211-222.

[4] V.R. Choudhary, B.S. Uphade, A.A. Belhekar. 1996. Oxidative conversion of methane to syngas over LaNiO3 perovskite with or without simultaneous steam and CO2 reforming reactions: Influence of partial substitution of La and Ni. Journal of Catalyst. 163: 312-318.

[5] D. San-José-Alonso, J. Juan-Juan, M.J. Illán-Gómez, M.C. Román Martínez. 2009. Ni, Co and bimetallic catalysts for the dry reforming of methane. Applied Catalysis A: General. 371: 54-59.



PLASMATRON PYROLYSIS OF MUNICIPAL SOLID WASTE FROM STEAM MECHANICAL HEAT TREATMENT FOR BIOENERGY PRODUCTION

J.L. Shie 1*, L.X. Chen 1, K.L. Lin 1, Y.S. Li 1, C.H. Lee 1, H.K. Ma 2, C.Y. Chang 3 1Department of Environmental Engineering, National I-Lan University, 260, I-Lan, Taiwan 2Department of Mechanical Engineering, National Taiwan University, 106, Taipei, Taiwan

3Graduate Institute of Environmental Engineering, Nation Taiwan University, 106, Taipei Taiwan *Corresponding author: Tel: + 886 39353563, Fax: + 886 39353563, E-mail: [email protected]

ABSTRACT The aim of this work was to study the feasibility and operation performance of plasmatron (plasma torch) pyrolysis of municipal solid waste mixed with raw wood (MSW/RW) from Steam Mechanical Heat Treatment (SMHT) as the target material (MRM). The SMHT is one of the alternatives of pretreatment of municipal solid waste (MSW) before its further separation and reutilization. After SMHT, the properties of constituents of MSW would be significantly changed. The productions of syngas (CO and H2) are the major components in the plasmatron pyrolysis of MRM with relatively high reaction rates. The maximum concentrations of gaseous products occurring times were between 15 to 45 seconds. Almost 90% of gaseous products were appeared in 2 min reaction time. The yields of syngas of plasmatron pyrolysis of MRM are between 78-89.96 wt.%. The recovery of syngas of MRM is 28.7-29.97 wt.%. Residual char or lava is between 16.51-26.87 wt.%. It is proved that MSW can be converted into bioenergy completely using SMHT followed by plasmatron pyrolysis. All the information obtained in this study is useful for the rational design and proper operation of plasmatron pyrolysis system for treating MSW.

Keywords: Syngas, Plasmatron, Pyrolysis, Municipal solid waste, Steam mechanical heat treatment

Introduction

Energy from waste (EfW) can compensate parts of the deficit of municipal solid waste (MSW) disposal. Transformation of waste into energy can be efficiently achieved by applying thermochemical techniques such as combustion, pyrolysis, partial oxidation, gasification and synthesis [1-9]. Papageorgiou et al. found that the green house gas (GHG) impact highly depends on the MSW treatments and the end market of the solid recovery fuel (SRF) [10]. If the MSW is treated by mechanical heat treatment (MHT), the fiber and flocs can be easily separated as SRF. Garg et al. reported that the SRF has the high calorific value of about 15-18 MJ/kg (or 3585-4302 kcal/kg) and is the suitable co-combustion fuel to coal power plant or cement kiln [11]. Its use contributes less GHG impact than mass burn incineration (MBI) [11].

The pyrolysis/gasification of biomass to produce syngas offers an alternative supply of energy to fossil fuels. Because the syngas essentially contains molecular hydrogen and carbon monoxide, it has the potential for use as a high-quality fuel. Moreover, after purification, it becomes an important source of hydrogen which is important in the context of fuel cell technology [12]. Notably, the use of plasmatron pyrolysis or gasification which offers unique advantages for biomass conversion, such as providing high temperatures and heating rates and low emissions of CO2 in comparison to conventional pyrolysis or gasification methods.

In this study, the treatment of MSW mixed with raw wood (MSW/RW) from Steam Mechanical Heat Treatment (SMHT) using a thermal plasmatron reactor as the heat source was further examined. The waste in the view of sustainable material management (SMM) is regarded as the used material. The ultimate goal of SMM is toward total recycling and reuse without waste, achieving the green environment. To match the appeal of SMM, the performance of MHT of MSW/RW aimed at the feasibility of its recovery and reutilization. The SMHT is one of the alternatives to pre-treat the MSW/RW before its further reutilization. After the SMHT, the properties of constituents of MSW /RW would be significantly changed. For example, the mass decreases while the volume density increases. The biomass of MSW/RW from SMHT (MRM), compost-like and primary refuse derived fuel (RDF) or bio-char, becomes easy for torrefaction or pyrolysis. The main objective of this article is to assess the plasmatron pyrolysis of MRM with different temperatures and to examine the effects of operation parameters on the performance. It is the aim of this work to examine the pyrolysis of MRM with the notion of providing product distribution at different contents. The pyrolysis was performed using a plasmatron system in a nitrogen atmosphere with a 10 kW power capacity. The residual materials and non-condensable gases were collected and analyzed using an



elemental analyzer, gas analytical instruments, and gas chromatography analyzers with thermal conductivity detectors (GC-TCD).


Materials

The biomass used in this study was MRM. The MRM was taken from the MSW/RW after the pretreatment of SMHT which was performed and operated in one Fertilizer Company in I-Lan, Taiwan. The sample of MRM was dried in a recycling ventilation drier for 24 h at 378 K before use. The results of the proximate analysis were 57.21, 4.12, 38.05 and 0.62 wt.% for moisture, ash, volatile matter and fixed carbon, respectively, and shown in Table 1. After the removal of moisture, the volatile matter, ash and fixed carbon increased to 88.91, 9.63 and 1.46 wt.%, respectively. The contents of C, H, N, O, S and Cl of dry MRM were 53.13, 7.34, 36.77, 1.49, 0.37 and 0.9 wt %, respectively (Table 1).

Plasmatron operational procedure

The pilot-scale apparatus used and the experimental procedures for the plasmatron steam gasification were similar to previous studies [6-7] and shown in Fig. 1. A 10 kW plasmatron was used for the pyeolysis procedure. For batch feeding, a sample of known mass of about 10 g was placed on the sample apparatus for feeding the sample material. The flow rate of carrier gas N2 (99.99 %) (QN) was adjusted to the desired value, i.e., 10 L min-1 at 101.3 kPa (1 atm) and 293 K, and was controlled by a rotameter. The power supply control unit (chopper) (Taiwan Plasma Corp.) for the plasmatron reactor was set at 2.59 to 4.56 kW (PL) for the temperatures (T) from 573 to 873 K, respectively. For the analysis of gas products, a Gas Chromatograph GC-TCD (Thermo Scientific FOCUS GC) with a Supelco packing column (60/80 carbonxen-1000, 15 ft long, 2.1 mm i.d.) was used. The operation conditions were the same as the previous study [6-7] and set as follows: injector temperature 453 K, detector temperature 513 K, column temperature (following the sampling injection) was held at 513 K for 10 min, helium carrier gas flow rate was 30 mL min-1 for A and B columns, and sample volume was 2 mL. Several duplicate experimental runs were performed in order to verify the values.


Effects of Temperature in the Instantaneous Gaseous Products

Carbon Monoxide and Hydrogen (syngas)

In this study, gaseous samples were collected via the instantaneous sampling method and detected using GC-TCD. The instantaneous concentrations of CO [CO], H2 [H2], CH4 [CH4] and CO2 [CO2] in gaseous products at 573, 773 and 873 K and reaction times (trsf, = reaction time of the solid sample in the furnace after loading) are shown in Figs. 1(a), 1(b) and 1(c), respectively. From Fig. 1(a), the maximum instantaneous concentrations and the corresponding trsf of H2 and CO occur at 1) 92,528 ppmv at 1.25 min and 2) 110,772 ppmv at 0.75 min, respectively, for 573 K with 0.5 min sampling intervals. Fig. 1(b) shows that the maximum instantaneous H2 and CO occurs at 0.75 min with [H2] of 138,198 ppmv, and with [CO] of 176,426 ppmv for 773 K, respectively. For 873 K, Fig. 1(c) shows that the maximum instantaneous H2 and CO occurs at 0.75 min with [H2] of 198,180 ppmv, and with [CO] of 118,058 ppmv, respectively. CO and H2 (syngas) are the major components in the gaseous products with the temperatures yielding maximum concentrations of 316,238 ppmv at 873 K with relatively high reaction rates. The maximum concentration of syngas increases with the increase of temperature. Nevertheless, the maximum concentration of CO and H2 occur at 773 and 873 K, respectively. The formation of H2 is more vigorous than the conversion of C to CO as indicated in Figs. 1(a) and 1(b) with [H2] higher than [CO] only at 873 K. Almost 90% of gaseous products appeared within a 2 min reaction time. Therefore, compared to conventional thermal gasification, the reaction time of 2 min is considerably shorter. Thus, the elevated heating rate of the plasmatron allows the reaction to reach maximum product concentration quickly. The plasmatron can be characterized with its elevated energy density, such that it allows the treatment of solid waste such as MRM faster than conventional gasification methods.



Methane and Carbon Dioxide

Fig. 1 also shows that the maximum instantaneous concentrations of CH4 occur at 11,397 ppmv for 573 K, 21,610 ppmv for 773 K, and 10,843 ppmv for 873 K, respectively, at 0.75 min with 0.5 min sampling intervals. It is clear that the maximum concentration of CH4 is occurring at 873 K. However, the maximum concentrations of CH4 for these three temperatures are still far lower than those of syngas. From Fig. 1, the maximum instantaneous concentrations of CO2 appear at 10,075 ppmv and 0.25 min for 573 K, 15,586 ppmv and 0.75 min for 773 K, and 7,279 ppmv and 0.75 min for 873 K, respectively, with 0.5 min sampling intervals. Shie et al., (2008) [3] pointed out that there are still some other pollutants appearing in the effluent gases, such as SO2, NOx, and HCl, and that their maximum instantaneous concentrations are between 2.61 and 11.42 ppmv for the plasma pyrolysis of sunflower-oil cake. Therefore, an analysis of these pollutants is left out and no data is shown detail in this study. As regards the suppression of pollutants emitted and the reduction of the power consumption, the reaction temperature may be controlled at certain temperature, specifically, below 973 K [3, 6-7].

Figure 1. Instantaneous concentrations in gaseous products from the pyrolysis of MRM using a plasmatron reactor. □, , ,X: H2, CO, CH4, CO2. trsf : reaction time of solid sample in furnace after loading. (a) 573,

(b) 773, (c) 873 K.

Effects of Temperature in the Accumulated Gaseous Products

The accumulated masses of gaseous products from three pyrolysis reaction temperatures of MRM about 10 g using a plasmatron reactor are shown in Table 1. The yields of accumulated mass of the effluent gaseous products relative to total mass of gaseous products (CO, H2, CH4, and CO2) (excluding the carrier gas N2) in wt. % are also shown in Table 1. In the same Table, the residues in the reactor for different conditions of pyrolysis after the cooling process are as well as pointed out. The maximum accumulated mass fractions and the corresponding occurring temperatures of CO, H2, CH4 and CO2 of pyrolysis of MRM are 82.65 wt.% at 873 K, 7.31 wt.% at 873, 7.63 wt.% at 773 K and 14.37 wt.% at 773 K, respectively. The production of CO and H2 (syngas) are the major components in the gaseous products with 89.96 wt.% at 873K; it can be proved from the highest input power of 4.56 kW. The temperature yielding the summary maximum accumulated gaseous mass ratio (= sum masses of gaseous products / dry basis of MRM) and lowest total residue ratio (= sum masses of residues / dry basis of MRM) are all at 773 K with 37.98 and 16.51 wt.%, respectively. The increase of the production mass of H2 is clear seen and this may be due to the decomposition of CH4 to supply the hydrogen source at 873 K. Regarding the production of greenhouse gasses, such as CO2, the accumulated yield and ratio of CO2 have the lowest values of 7.06 and 2.25 wt.% at 873 K, respectively. Similar tendencies also appear in the accumulated masses of CH4. This may be due to the increase of a steam methane reforming reaction (CH4 + 2 H2O → CO + 3H2) and the promotion reactions of Boudouard reaction (CO2 + C → 2 CO), and the inhibition of the methane production reaction (C + 2 H2 → CH4) [6-7].Therefore, the plasmatron pyrolysis at 873 K and higher loading of input power show a positive benefit regarding the inhibition of GHG production in the major reaction time.



Conclusions

In this study, a 10 kW plasmatron reactor was used for pyrolysis of the biomass waste of MRM. Almost 90% of gaseous products appear within 2 min reaction times with relatively high reaction rates. The production of CO and H2 (syngas) are the major components in the gas products. The inorganic components were converted into non-leachable vitrified lava which is non-hazardous. Regarding the production of greenhouse gasses, such as CO2 and CH4, the accumulated yield and ratio have the lowest values at the highest temperature because of the increase of a steam methane reforming reaction, and the promotion reactions of Boudouard reaction, and the inhibition of the methane production reaction. The obtained information is useful for pyrolysis design via plasmatron for treating MSW.

Table 1 Accumulated masses of gaseous products and effluent gasses from the gasification of MRMa using a plasmatron reactor (excluding of H2O, NOx, SOx, and N2)

aMRM: Municipal solid waste mixed with raw wood (MSW/RW) from Steam Mechanical Heat Treatment (SMHT)(MSW:RW=8:1). bdry basis. cYield = mass / sum mass of CO, H2, CH4 and CO2. dRatio = mass / dry sample mass x 100%.

Acknowledgements

We express our sincere thanks to the National Science Council of Taiwan for their generous financial support, under the contract No. NSC 100-3113-E-002-013.

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STUDY ON COMBINED SEWAGE SLUDGE PYROLYSIS AND GASIFICATION PROCESS: MASS AND ENERGY BALANCE

Z. Wang, D.Z. Chen *

Thermal & Environmental Engineering Institute, Tongji University, Shanghai, China * Corresponding author. Tel: +86 15800446445, E-mail: [email protected]

ABSTRACT A combined pyrolysis and gasification process of sewage sludge disposal was studied in this paper. Two samples of sewage sludge, SS1 and SS2, were dried and then undergone pyrolysis within temperature of 400°C ~ 550°C. The yields of bio-char are varied from 48.86% to 53.75% for SS1, which is corresponded to higher ash content and smaller lower heat value (LHV); while for SS2, the yields of bio-char are within 43.73%~46.34%. Two bio-char samples were gasified to produce fuel gas, and LHV of the fuel gas is around 5.31MJ/m3 ~ 5.65 MJ/m3, which was used as an auxiliary fuel for the whole drying and pyrolysis process. The energy consumption of each run was calculated and it has been found that for the sewage sludge with LHV less than 15MJ/kg, auxiliary fuel is needed to ensure the pyrolysis processes that take place in the tested temperature range. With the help of fuel gas from bio-char gasification, sewage sludge can be disposed through pyrolysis without extra energy supply and produce bio-char finally if LHV of dry mass is higher than 15MJ/kg and moisture content is lower than 80%wt.

Keywords: Sewage sludge, Pyrolysis, Gasification, Bio-char

Introduction

Disposal of sewage sludge now became a pressing problem due to its huge generation and shortage of land space for landfill. The most common moisture content of sewage sludge discharged from waste water treatment plant is about 78~80wt %, which makes its disposal highly energy consuming. Thermal treatments such as incineration and gasification has the superiority of reducing the sludge volume dramatically. However for incineration disposal, in addition to expensive investment, in most cases auxiliary fuel is needed due to the high moisture content. Pyrolysis of sewage sludge can be an alternative considering its lower cost in air pollution control and flexibility in product choice[1].

There are three products from pyrolysis of sewage sludge: tar, gas and bio-char, while tar and gas leaving the pyrolysis furnace as volatile. Sanchez[2] studied the pyrolysis oil with GC-MS and found that the pyrolysis oil is highly complicated in constituents. Gas was also found to have a high heat value, comparable to that of fossil fuel[3]. Bio-char, the third product from pyrolysis has been received more concern in recent years because of its porous structure, it can be utilized as supporting matrix of soil modifier[4].

Gasification of sewage sludge is another choice and fuel gas can be produced, but the gas heavily contaminated with tar meets trouble in its utilization. However, as bio-char is basified, much lower tar will appear in the produced gas.

In this paper sewage sludge was undergone pyrolysis process first and then the obtained bio-char is gasified to produce fuel gas as auxiliary fuel to balance the energy consumption for the whole process with bio-char as final product. Two samples with different LHVs were used to check the feasibility of the process and the requirements on sewage sludge quality.


Sewage Sludge Samples

Two samples of sewage sludge were taken from Quyang municipal wastewater treatment plant in Shanghai at different time and they were labelled as SS1 and SS2, respectively. The proximate analysis and ultimate analysis of two sewage sludge samples are shown in Table 1. The LHV was tested by XRY-1A Bomb-Calorimeter and ultimate analysis was carried out in Vario EL III Elemental Analyzer.

Sewage Sludge Pyrolysis



Sewage sludge samples are firstly dried in the ventilated drier, after the moisture content is reduced from 78% to 3%, the dried sewage sludge is put into a horizontal quartz reactor placed in an electrical oven under the pre-set temperature range of 400°C~550°C. About 50g of dried sewage sludge is used in each run. In order to ensure an inert atmosphere argon flow is passing through the reactor with a flow rate of 40ml/min. The bio-char is collected and measured after the oven is cooling down. The oil is condensed in a two stage ice-cooled condenser, and the non-condensable gas is collected for analysis in a gas chromatograph (model GC9160).

Table 1. Proximate analysis and ultimate analysis of sewage sludge samples

Sample Proximate analysis (dry basis) Ultimate analysis(%)

Moisture content(%)

Volatile content (%)

Ash content (%)

LHV (MJ/kg)

C H N O S

SS1 77.78 58.87 30.14 14.92 30.89 5.06 5.42 19.7 0.7

SS2 78.38 55.33 25.38 15.65 37.53 5.85 5.36 12.3 0.6

Bio-char gasification

The gasification of bio-char is carried out in a small tube furnace. About 10g of bio-char is used and the air supply is arranged to make the excess air ratio of 0.35~0.4, the temperature is maintained to be 800°C[5] with help of electricity heating occasionally. The fuel gas produced passes the ice-cooled condenser before goes to gas chromatograph.


Mass Distribution of Sewage Sludge Pyrolysis Products

Fig.1 shows the change of the bio-char yields and volatile fractions with the pyrolysis temperature. As reported by other researchers[3], an increase in the final pyrolysis temperature gives rise to volatile production and a decrease in the bio-char fraction. Bio-char production from SS1 pyrolysis is greater than that from SS2. This is due to the greater ash content associated with SS1. In general bio-char production is around or less than 50% of the dry mass.

Energy Consumption of Sewage Sludge Pyrolysis

Energy consumption is made up with three parts: the first and the most part is moistrure evaporation; the second part is to heat dry sewage sludge from its initial temperature to pyrolysis temperature; and the third part is reaction energy. They are given in Table 2.

Figure 1. Mass distribution of sewage sludge pyrolysis under different temperatures



Table 2. Energy consumption of SS1 and SS2 pyrolysis

Pyrolysis temperature (°C)

Moisture evaporation (MJ/kg-ss)*

Heating of dry sewage sludge (MJ/kg-ss)

Reaction energy consumption (MJ/kg-ss)

Total energy consumption (MJ/kg-ss)

400 1.94~1.96

(2.14~2.16)**

0.13~0.14 0.26~0.27 2.55 450 0.14~0.15 0.29~0.30 2.59 500 0.16~0.17 0.30~0.32 2.62~2.63 550 0.18~0.19 0.34~0.35 2.68

*The unit of kg-ss means kg of wet sewage sludge; **those amounts of heat should be supplied if heated by steam

Energy Balance and Product Choice

Table 3 shows the energy of bio-chars and volatiles produced under different pyrolysis temperatures. Since the volatile produced during pyrolysis is a mixture of tar and gas, it is difficult to separate the former from the latter, so the best choice is to burn the hot volatile on line to supply energy for pyrolysis process. From Table 3 it can be seen that volatile alone cannot provide enough energy for pyrolysis; and theoretically the sum of volatile energy and bio-char energy can meet with the energy requirement for pyrolysis process.

Table 3. Energy balance for pyrolysis processes under different temperatures

Sample Total energy in

bio-char by LHV (MJ/kg-ss)

Total energy in volatile by LHV

(MJ/kg-ss)

Sum of energy (MJ/kg-ss)

Energy demanded for pyrolysis

(MJ/kg-ss) SS1-400°C 1.42 1.90 3.30 2.55 SS1-450°C 1.06 2.25 3.31 2.59 SS1-500°C 0.97 2.34 3.31 2.63 SS1-550°C 0.87 2.44 3.31 2.68 SS2-400°C 1.45 1.93 3.38 2.55 SS2-550°C 0.96 2.43 3.39 2.68

It can be also noticed that energy demand increases as temperature rises up, but sum of volatile energy and bio-char energy remains the same with energy moving to volatile. The difference between the energy input and the outcome is attributed to the increase in apparent heat carried by volatile with pyrolysis temperature rising, which was not accounted in Table 3.

To supply enough energy for pyrolysis process, part or whole bio-char is gasified to generate fuel gas as a complementarily fuel to the volatile. Bio-char samples of SS1-400°C and SS2-400°C were used for this purpose and Table 4 shows gas production and LHV of the gas.

By comparing data in Table 3 and 4, it can be seen that when all of the bio-char was gasified to produce fuel gas, the sum of energy from pyrolysis volatile and gas may meet the energy demand for pyrolysis process, but the boiler firing the volatile and gas should have a heat recovery efficiency, 87.3% for SS1-400°C and 85.7% for SS2-400°C, respectively, while heat recovery efficiency of gas boiler firing with waste gases is seldom higher than 85%; thus for SS1-400°C, a small amount auxiliary energy is needed to run the whole process. If bio-char is expected to be kept as product, definitely auxiliary energy should be provided. When pyrolysis temperature increases the necessary auxiliary energy will be reduced since more energy can be provided by the volatile while only small increases appear for energy demand.



Table 4. Fuel gas yields from bio-char gasification and LHV of fuel gas

Sample LHV of char (MJ/kg-char)

Fuel gas yield

(m3/kg-char)

LHV of fuel gas

(MJ/m3-gas)

Sum of energy from volatile

and gas SS1-400°C 11.89 1.612 5.31 2.92(MJ/kg-ss) SS2-400°C 14.47 1.844 5.65 2.97(MJ/kg-ss)

Conclusions

Sewage sludge has been investigated to check an innovate disposal through combined pyrolysis and gasification process. Two samples, SS1 and SS2 were undergone pyrolysis firstly and then bio-char produced was gasified to produce fuel gas. The fuel gas is used as auxiliary fuel to volatile for heating the pyrolysis reactor. For the sewage sludge who’s LHV is lower than 15MJ/kg and the pyrolysis temperature is below 500°C, auxiliary fuel or energy is needed; while for sewage sludge with LHV higher than 15 MJ/kg the combined pyrolysis and gasification process energy can be supplied by the process itself.

Acknowledgements

The work is financed by Program of New Century Excellent Talents in Universities (NCET-10-0596).

References [1] D. Fytili, A.Zabaniotou. 2008.Utilization of sewage sludge in EU application of old and new

methods--A review. Renewable and Sustainable Energy Reviews.12:116-140. [2] M.E. Sanchez, J.A. Menindez, A. Dominguez. 2009.Effect of pyrolysis temperature on the

composition of the oils obtained from sewage sludge. Biomass and Bioenergy.33:933-940. [3] M. Inguanzo, A. Dominguez, J.A. Menindez. 2002.On the pyrolysis of sewage sludge: the influence

of pyrolysis conditions on solid, liquid and gas fractions. Journal of Analytical and Applied Pyrolysis.63:209-222.

[4] M.K. Hossain, V. Strezov, P.F. Nelson. 2009.Thermal characterisation of the products of wastewater sludge pyrolysis. Journal of Analytical and Applied Pyrolysis.85:442-446.

[5] I. Petersen. J.Werther. 2005.Experimental investigation and modeling of gasification of sewage sludge in the circulating fluidized bed. Chemical Engineering and Processing.44:717-736.



APPLICATION OF SEWAGE SLUDGE PYROLYSIS BIO-CHAR TO PLANT CULTIVATION

X.D. Song, D.Z. Chen *, Z.H. Wang

Thermal & Environmental Engineering Institute, Tongji University, Shanghai, China *Corresponding auther.Tel:+86 15800446445, E-mail:[email protected]

ABSTRACT Behaviors of sewage sludge pyrolysis under temperature of 550 were studied with the purpose to produce bio-char products suitable for being used as a soil modifier in land application, and the bio-char properties including nitrogen, phosphorus and potassium (NPK) contents as well as heavy metal leaching from them were investigated. The fertility of bio-char on plant cultivation is firstly proven by using the bio-char-amended soil for garlic planting, then the suitable bio-char/soil ratio (C/S ratio) was investigated. The results showed that the garlic planted in the bio-char-amended soil grows faster than those planted in normal soil but their heavy metals contents are little higher than the latter; and the garlic’s planted in bio-char-amended soil with C/S ratio of 1:5 are characterized with highest length and most heavy final dry matters. Those results are helpful for guiding sewage sludge utilization as bio-char resource.

Keywords: Sewage sludge, Pyrolysis, Bio-char, Land application

Introduction

The increasing of wastewater generation and its treatment capacity in big and small cities results in a rapidly raise in sewage sludge generation. Sewage sludge is an unwanted and inevitable by-product during the wastewater treatment process, and could cause secondary pollution if disposed improperly. Presently the common methods for disposing sewage sludge are landfill, incineration and land applications, but all of these have their own drawbacks [1].

At the mean time sewage sludge is a kind of bio-mass. When undergone pyrolysis process, sewage sludge would be decomposed into carbonaceous residue, tar (condensable volatiles), and non-condensable gas. The solid carbonaceous residue is rich in nutrients, and maybe, it could be used as a kind of bio-char to amend poor soil. Many researchers have studied land application of bio-char, and found that bio-char additions had nutrient retention capacities on the long term [2] and could improve N fertilizer use efficiency [3], and finally could increase crop production [4]. These bio-chars are mainly from other bio-mass resources such as wood, grass clippings, wheat straw and so on. In this paper the potential of producing bio-char from sewage sludge pyrolysis as a soil ameliorant is investigated.


The sewage sludge samples were obtained from Quyang domestic wastewater treatment plants in Shanghai, which has been subjected to aerobic digestion with moisture content about 78%. The pyrolysis of sewage sludge is carried out in a horizontal quartz reactor, which is placed in a laboratory electrical furnace [5]. After finish pyrolysis process under 550 , the solid carbonaceous residue is collected and then used for cultivating experiments. The experimental soil was collected from local garden and sieved through a 4 mm aperture sieve. The sieve material was heated in an oven at the temperature of 378K for 1 hour to kill pathogens inside. Garlic is chosen as the testing plant because it grows fast and has evident external properties such as height and single weight.

The experiment is divided into two steps, as shown in Table 1. The first step is to check the effectiveness of bio-char for cultivating. After finishing the experiments, the garlic stems are collected and then dried in the oven at 105 to check the heavy metal contents. The second step is to find the suitable C/S ratio.



Table 1. Experimental arrangement and planting pot list

Step 1 Pot No. No.1-1 No.1-2 No.1-3 No.1-4 No.2-1 No.2-2 No.2-3 No.2-4

C/S ratio 1:4 0

Step 2 Pot No. 1:2 1:3 1:4 1:5 1:6

C/S ratio 1:2 1:3 1:4 1:5 1:6

The bio-char-amended soils are put into small plastic cylindrical pots, where plants are growing. Three seeds of garlic are planted in each pot. After finishing cultivation, the dry matters of garlic are weighted.


Characteristics of Sewage Sludge and its Pyrolysis Bio-char

Table 2 shows the elemental analysis of bio-char from sewage sludge obtained at 550

Table 2. Elemental analysis of bio-char

Temperature( ) C (wt%) H (wt%) N (wt%) C/N(molar ratio) 550 19.59 1.80 2.13 10.72

It shows the bio-char has a high organic content. In Table 3 several important heavy metals in sewage sludge and its bio-char are listed. It can be seen that the heavy metal contents in both sewage sludge and bio-char are lower than the discharge limitations. The total nutrient NPK contents in bio-char is much higher than 3%, which is the lower limit for fertilizer, meaning that theoretically the bio-char could be used as a fertilizer. Compared with sludge, bio-char has higher level of heavy metal contents, but as its leaching test was performed according to standard HT/300, leaching data in Table 2 showed that the leaching ratios of heavy metals are extremely low, and for Ni, Cd and Cr their leaching can be even neglected. Those results suggest that pyrolysis alone can be a good solution for sewage sludge disposal even if bio-char utilization is not considered, for bio-char is safe to go to landfill.

Table 3. Heavy metals’ contents and leaching from sewage sludge and its bio-char /mg·g-1

a Under 550 b Not detected.

Influence of Bio-char on Cultivation

Figure 1 gives the heights of the garlic sprouts with growing time. Garlic in No.2-4 pot did not grow, which may be due to the bad quality of garlic. From Figure 1, it can be seen that in general the averaged heights in group No.1 were higher than those in group No.2, showing that the bio-char can enhance the growth of garlic.

Items As Zn Pb Ni Cd Cr Cu K P GB/T 23486-2009

pH<6.5 <0.075 <2 <0.3 <0.1 <0.005 <0.6 <0.8 total nutrients [TN+TP+TK]≥

3% pH≥6.5 <0.075 <4 <1 <0.2 <0.02 <1 <1.5

Sewage sludge 0.018 0.744 0.042 0.023 n.d. b 0.020 0.165 3.973 15.408 Bio-char a 0.013 1.773 0.100 0.054 0.002 0.050 0.382 11.980 38.017 Leaching from bio-char 0.001 0.007 0.0001 0.001 n.d. n.d. 0.001 1.625 0.99 Heavy metal leaching rate in bio-char/% 7.69 0.39 0.74 0.00 0.00 0.00 0.10 13.56 2.60



Table 4 shows that heavy metals such as As, Pb, Cd appearing in the garlic from group No.2 without bio-char are only around 50% of those in group No.1, which indicates that garlic planted in No.1 group pots absorbed more heavy metals from the bio-char. Thus it is suggested that bio-char from sewage sludge should not used for food plants growing.

Table 4. Heavy metals in garlic /%

Items As Pb Ni Cd Cr Cu K P

No.1 0.004 0.018 0.017 0.034 0.020 0.052 22.511 8.593 No.2 0.002 0.009 0.009 0.028 0.012 0.033 26.979 9.216

Effect of C/S Ratio

Testing pots for different C/S ratio is shown in Figure 2, and the averaged height of garlic sprouts in each pot is shown in Figure 3; their final dry matter weights are shown in Figure 4.

Figure 2. Growing process of garlic with different bio-char/soil ratio

The averaged height of garlic growing with bio-char spike soil is higher than those in comparison pot except for Pot No.1:2. The average height in Pot No.1:5 is highest. However, at the beginning, garlic in Pot No.1:2 grew fast, then their growth became slow and leaves became withered. In Pot No.1:2, the C/S ratio is the highest with C/N ratio of 10.72 (see Table 1), which may promote garlic to sprout, but it is not suitable for leaves growing. Finally, the seed may be hurt by the low C/N ratio in bio-char-amended soil. From Figure 3, it is easy to find that the dry matter weight of garlic in Pot No.1:5 is the heaviest one. So, the preliminary conclusion can be drawn that the C/S ratio 1:5 may be suitable for cultivating garlic. Whether this ratio is also suitable for other plants growing, it should be tested further.

Figure 1. Comparison of growing process of garlic

with and without bio-char



Conclusion

Applying bio-char from sewage sludge pyrolysis to soil as a modifier (or fertilizer) was investigated, and the suitable bio-char/soil ratio was found to be 1:5 for garlic growing. However, heavy metal contents in the garlic planted in bio-char-amended soil are higher, so bio-char is not suggested for food plants. Other factors such as pyrolysis temperature and plant species should be investigated to evaluate the application of sewage sludge bio-char.

Acknowledgements

The work is financed by Program for New Century Excellent Talents in University (NCET-10-0596).

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pyrolysis. J. Anal. Appl. Pyrolysis 85 (2009) 442–446. [2] B. Glaser, J. Lehmann, C. Steiner. Potential of pyrolyzed organic matter in soil amelioration. In:

L.X.Wang, D.Y.Wu, X.N.Tu, J. Nie (eds). Proceedings of the 12th International ISCO Conference. 26 - 31 May 2002, Beijing, China, p.421–427.

[3] K.Y. Chan, L.V. Zwieten , I. Meszaros. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45 (2007) 629–634.

[4] A.F. Zhang, L.Q. Cui, G.X. Pan. Effect of biochar amendment on yield and methane and nitrous oxide emissions from a rice paddy from Tai Lake plain, China. Agriculture, Ecosystems and Environment 139 (2010) 469–475.

[5] J. Brego, J. Arauzo, J.L. Sanchez. Structural changes of sewage sludge char during fixed-bed pyrolysis. Ind. Eng. Chem. Res. 48(2009) 3211–3221.



DRY MATTER LOSSES AND GASEOUS EMISSIONS DURING STORAGE AND BIODRYING OF WOODY BIOMASS

X. He 1*, A. Lau 1, S. Sokhansanj 1,2 1 Department of Chemical and Biological Engineering, University of British Columbia, Canada

2 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA * Corresponding author: E-mail: [email protected], Tel: +1-604 8273178

ABSTRACT Off-gas emissions and biomass losses during the storage of fresh woody biomass were rarely studied in the past researches. The objectives of this study are to measure and determine dry matter losses and gaseous emissions from stored feed stocks. The experimental study involves storage at room temperature and storage with external heating to mimic higher temperatures encountered in practice. Lab-scale vessels are set up to simulate different storage conditions to study the temperature effect on dry matter losses and off-gas emissions. Results showed that the maximum concentrations of CO2, CO and CH4 were 13.8%, 0.16% and 0.15%, respectively. During this period, the oxygen level kept decreasing and was close to 0% at times. Volatile organic compounds (VOCs) were detected by GC/MS. The major chemical compounds include alcohols, terpenes, aldehydes, acids, acetone, benzene, ethers and esters, and their maximum total concentration reached 85 ppm. We observed dry matter losses ranging from 0.78-2.0%.

Keywords: Woody biomass, Dry matter losses, VOCs, Storage, Biodrying

Introduction

Biomass materials used as solid biofuels or processed in biorefineries to produce liquid biofuels for electricity and heat generation becomes an important element of sustainability with their low heating price in today’s world. The immediate use of forest biomass residues after harvest is often infeasible for various reasons. A large proportion of these biomass residues are left in the field or stored for an extended period before they are used to make products. During the transition time, the properties of biomass residues can change due to physical, chemical and microbiological processes. Microbial activity in the stored biomass, especially fungal growth, is the major cause of the initial heat development, which in turn encourages further growth thus leading to high temperatures in the pile. In extreme cases, this would result in self-ignition and fire [1]. Besides, the loss of dry matter and fermentable carbohydrates has a negative economic impact [2]. Gases such as CO2, CO, CH4 and VOCs are the main air emission from storage. During storage, the depletion of oxygen along with emission of toxic gases can also endanger the life and health of people exposed to the storage environment. Incidents of injuries and even fatalities have occurred among workers in recent years [3]. It has been reported that VOCs are emitted from wood pellets during storage, exerting a negative impact on the indoor environment [4]. Odour is generated due to a synergistic effect of many VOCs [5]. It is possible to reduce the amount of VOCs during storage of woody biomass and also reduce any possible risk to the health of workers with optimal production parameters[6]. Since there are very few studies on storage of fresh woody biomass, the aim of this study was to investigate the composition and concentration of gaseous emissions from these fresh feed stocks in enclosed storage under different temperature conditions. The study also measured the dry matter changes during the storage period. These will help us to better understand the storage aspect of the supply chain of forest residues from harvest point to biorefinery, and gain more insight into the issues related to worker health in the industry.


Equipment and Experimental Materials

Branches obtained from the Pacific Spirit Park (Vancouver, Canada) were used as materials in this study. The major species are Douglas Fir, Western Hemlock and Western Red Cedar which are all softwoods. Branches were cut into uniform size 22-25 mm in diameter and 180-200 mm long. These materials were tested with the bark intact. Moisture content of the raw materials averaged 38% (wb).

Four plastic containers (two 10 L in volume and two 12.5 L in volume) were fitted with valves and sampling ports and assembled as reactors for the experiment. When fully loaded with the biomass materials, two reactors (12.5 L reactor 1 and 10 L reactor 3) were sealed and placed under room temperature around 15oC,



while the other two (12.5 L reactor 2 and 10 L reactor 4) were sealed and placed in an oven with temperature setting at 35oC.

Method and Apparatus

The composition of off-gas emissions from the reactors was analyzed by gas chromatography (Model GC-14A, Shimadzu Corporation, Japan) for CO2, CO, CH4 and O2, using a fused silica capillary column. The GC was calibrated regularly with the corresponding standard gases. Argon and compressed air were used as the reference and carrier gases. The total concentration of VOCs was measured by a portable VOC monitor (Model PGM-7240). GC/MS (Model Varian CP-3800) was used for qualitative analysis of the VOCs. Each day, two sets of gas sampling were made. Firstly, 10-mm volume gas samples were taken out from each reactor to measure CO2, CO, CH4 and O2. Then, another set of 10-mm gas samples was drawn from each reactor to analyze VOC composition. The moisture content of biomass was determined by drying it in the oven at 103oC for 24 hours.


Off-gas Emissions

The results of gaseous emissions from the reactors with fresh softwood branches are shown in Figures 1-3. It is clearly seen that the concentrations of CO and CH4 in the sealed reactors increased during the storage period, with a faster rate at the earlier stage and gradually leveling off in the remaining time. At a higher temperature of 35oC increased, the gas concentrations increased significantly. Among the off-gas emissions, CO2 concentration was the highest whereas CO and CH4 concentrations are approximately within the same range. The peak concentration of CO2, CO and CH4 were observed to be 138000 ppm, 1600 ppm and 1500 ppm, respectively after 10 days. As of Days 10-15, depending on temperature, the concentration of CO2 slowly declined. This may be attributed to the depletion of oxygen in the later period. The decrease in CO2 concentration may also be due to the adsorption by biomass materials. Figure 4 shows the oxygen concentration profile. It started out at 13.5-15.5% at the onset of the test and decreased to less than 1-2% within 10 days. Thereafter, the oxygen concentration had negligible changes. At times, oxygen level was close to 0% implying anaerobic conditions. In the sealed container, O2 was primarily consumed by the chemical oxidation of woody biomass, leading to its depletion and the generation of CO2 and CO. Another reason for the fast oxygen depletion in the initial stage could be the chemical and biological adsorption by the materials. We compared our findings to Svedberg et al.’s work [3] on emissions from stored wood pellets. Their measured values of CO, CO2 and CH4 concentrations were 1460–14650 ppm, 2960–21570 ppm, and 79.9–956 ppm, respectively, while oxygen levels were between 16.9 and 0.8%. It was suggested that fresh biomass with higher moisture content could experience more activated chemical and biological reactions.

Temperature is a significant factor affecting gas emissions from stored branches. Higher temperature will lead to higher gas concentrations and faster emission rates. In the study by Kuang et al [7], it was pointed out that storage temperature is one of the critical factors that affect the off-gassing from stored wood pellets. Biomass may be decomposed both chemically and biologically. It was suggested that chemical process was the dominant mechanism for emissions of CO2, CO and CH4 during the process, while biological process also contributed to the emissions. The threshold limit value–time weighted average (TLV–TWA) for 8 h exposure to CO2, CO and CH4 are set at 5000 ppm, 25ppm and 1000ppm, respectively. The peak concentrations of gas emissions from our experiment were much greater than TLV-TWA values. This observation was also made by Kuang et al and Svedberg et al [3, 7, 8] working on wood pellets storage. Pressure was tested in the four reactors both at the beginning and the end of the simulated storage period. Results show there were essentially very little changes in all of the reactors.

Characteristics of VOCs and Dry Matter Losses

The highest total VOC concentrations of 84.7ppm and 60pm were observed in the reactors under 35oC and room temperature, respectively. This was similar to the results presented by Rupar and Sanati for the release of a specific class of VOCs (terpenes) [9]. They showed that air emissions increased when the temperature directly above the wood chip pile increased. For the gas samples analyzed by GC/MS, a range of chemical



compounds were found; they include alcohols, terpenes, aldehydes, acids, acetone, benzene, ethers, esters, sulfur and nitrogen compounds. Some of these compounds were also detected from wood pellets storage system according to Svedberg et al. and Arshadi et al.[4, 5]. Dry matter losses in the four reactors amounted to 1.17%, 2.29%, 0.78% and 1.33%, respectively, during the 35-day storage of biomass with initial moisture content of 38% (wb). The reactor under 35oC had the largest dry matter losses. Based on literature review, factors such as temperature, moisture content, biomass particle size and storage methods all have influences on dry matter losses [10]. At higher temperature conditions, more dry matter losses can result from higher initial moisture content and smaller particle size of materials stored [10-12].

Conclusion

The results show that storage temperature is a crucial factor in biomass storage system. Higher temperature leads to higher gas concentrations and gas emission rates. The concentrations of CO2, CO and CH4 emitted from stored fresh woody biomass were close to or exceed the TLV-TWA standard values which may be dangerous in closed spaces. A wide range of VOC compounds were qualitatively detected in the process. Highest total VOC concentration was observed in the reactor under higher temperature. In general, there are more dry matter losses at higher temperature experienced during extended storage of fresh woody biomass.

References [1] R. Jirjis. 1995. Storage and drying of wood fuel. Biomass and Bioenergy. 9: 181-190. [2] A.E. Wiselogel, F.A. Agblevor and D.K. Johnson. 1996. Compositional changes during storage of

large round switchgrass bales. Bioresource technology. 56: 103-109.



[3] U. Svedberg, J. Samuelsson S. Melin. 2008. Hazardous off-gassing of carbon monoxide and oxygen depletion during ocean transportation of wood pellets. Annals of Occupational Hygiene. 52: 259-266.

[4] U. Svedberg, HE. Hogberg, J. Hogberg, B. Galle. 2004. Emission of hexanal and carbon monoxide from storage of wood pellets, a potential occupational and domestic health hazard. Ann. Occup. Hyg. 48: 339-349.

[5] M. Arshadi, R. Gref. 2005. Emission of volatile organic compounds from softwood pellets during storage. Forest products journal. 55: 132-135.

[6] M. Arshadi, P. Geladi, R. Gref, P. Fjallstrom. 2009. Emission of Volatile Aldehydes and Ketones from Wood Pellets under Controlled Conditions. Annals of Occupational Hygiene. 53: 797-805.

[7] X. Kuang, T.J. Shankar, X.T. Bi, S. Sokhansanj, C.J. Lim and S. Melin. 2008. Characterization and kinetics study of off-gas emissions from stored wood pellets. Annals of Occupational Hygiene. 52: 675-683.

[8] X. Kuang, T.J. Shankar, X.T. Bi, C.J. Lim, S. Sokhansanj, S. Melin. 2009. Rate and Peak Concentrations of Off-Gas Emissions in Stored Wood Pellets--Sensitivities to Temperature, Relative Humidity, and Headspace Volume. Annals of Occupational Hygiene. 53: 789-796.

[9] K. Rupar, M. Sanati. 2005. The release of terpenes during storage of biomass. Biomass and Bioenergy. 28: 29-34.

[10] M. Wihersaari. 2005. Evaluation of greenhouse gas emission risks from storage of wood residue. Biomass and Bioenergy. 28: 444-453.

[11] M. Pettersson, T. Nordfjell. 2007. Fuel quality changes during seasonal storage of compacted logging residues and young trees. Biomass and Bioenergy. 31: 782-792.

[12] M.T. Afzal, A.H. Bedane, S. Sokhansanj, W. Mahmood. 2010. Storage of comminuted and uncomminuted forest biomass and its effect on fuel quality. BioResources. 5: 55-69.

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