Bioenergy Solutions for Today and the Future

7/27/2019 Bioenergy Solutions for Today and the Future

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Bioenergy solutions for today and the future

Jean-Bernard MICHEL

ABSTRACT

This paper provides an analysis of the biomass energy conversion systems with a short reviewof existing market solutions and some current technological development which may result in

a better overall efficiency and economy. Three different process categories are distinguished,namely the thermo-chemical, physico-chemical and biological conversion processes.

The first category is still, by far, the most developed and used at all scales from the domesticheating stove to the large power plants.

Developments are presented in the area of small scale CHP systems, microalgae production,torrefaction, gasification and anaerobic digestion.

Keywords: biomass energy, CHP, anaerobic digestion, torrefaction, gasification.

1 INTRODUCTIONIn most countries of the modern world, energy from biomass is not completely exploited.According to several sources, biomass energy amounts today to about 10% of the world total

primary energy consumption whereas in India it represents 32% of all the primary energy usein the country (see Figure 1). For power production, India reports a total capacity of around 1GW today and is planning to increase it by 10 times by 2020, so there is still an enormous

potential to be exploited by different routes and at different scales, from the small combinedheating and power (CHP) systems to the large cogeneration plants.

There exist many routes to biomass conversion and utilization as illustrated in Figure 2. Thetechno-economic aspects will depend very much on the feedstock availability and cost as wellas on the government policies and financial incentives.

The three main families of conversion processes, thermo-chemical, physicochemical andbiological, are discussed in the following sections.


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Figure 1: Evolution of Total Primary Energy Supply in India (after IEA) [1]

Figure 2: various pathways for biomass conversion into energy (simplified)

v

Press/

extraction

Esterification

Solidfuel

liquid

fuel

gaseous

fuel

pyrolysis

gasification

torrefaction

combustion

Fermentation/

hydrolysis

Methanisation

Power

Hot air

turbine

transport

biofuel

boiler

Motor/

Gas turbine

Fuel cell

Heat

steamThermochemical

Physico

chemical

Biological

F-.T


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2 Thermo-chemical processesThis process family comprises combustion, torrefaction, pyrolysis and gasification which alsoincludes charcoal production.

2.1 Biomass combustion and closed thermal cyclesAmongst all biomass conversion processes biomass combustion is certainly the simplest andmost mature technology. In its traditional utilization for heating and cooking, it had been themajor source of energy of mankind until the 19th century. It is now also becoming a verysignificant source of energy in the modern world, who strives for the replacement of thedepleting fossil fuel reserves and for the reduction of carbon dioxide emissions.

Larger biomass thermal power generation plants (> 30 MWth) are now a mature and reliabletechnology. A thorough review is available in [2] and we will not provide further details. Seealso Table 1.

Table 1 Closed thermal cycles for CHP with biomass, adapted from [2]

Working medium Engine type Typical size Status

Liquid and vapour(with phase change)

Steam turbine

Steam piston engine

Steam piston engine

Steam screw engine

500 kWe500MWe

25 kWe-1.5MWe

1.5 kWe, 15 kWth

Not established

Estimated range from

500 kWe-2 MWe

Proven technology

Proven technology

From Button Energy(see further)

One demonstrationplant with 730 kWeand turbine from

commercial screwcompressor

Steam turbine withorganic medium(ORC)

200 kWe1.5 MWe Some commercialplants with biomass

Scroll turbine withORC

10100 kWe Development andnew commercialsolutions

Gas (without phasechange)

Externally fired hotair turbine

> 100 kWe Development andpilot

Stirling engine 1 kWe100 kWe Development andpilot

The emphasis today lies in the development of combined heat and power production (CHP) atsmall and medium scales, for single family houses with a few kW overall capacity, and alsofor medium size district plants (2 10 MWth, 200 -1000 kWe). Conventional steam cyclesare not really adapted for small scale operation mainly due to cost considerations.

Currently three main types of small scale CHP from biomass are promising:

Small power with steam cycle and piston engine: for example a recent development madeby Button Energy in Austria includes a pellet fired boiler, a double floating piston engine


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and a linear motor. Nominal steam conditions are about 350C at 25-30 bars. Thermalpower varies from 3 to 15 kW and electric power from 0.3 to 1.5 kW. Such units are beingsold in Switzerland by the company Rieben Heizanlagen AG.

Thermal oil boilers coupled to an Organic Rankine Cycle, for example:

o The company Turboden in Italy for units greater than 400 kWo GMK and Adoratec in Germany for units above 500 kW

o Eneftech in Switzerland for units of 30 kWe [3]

Until recent years ORC power plant had not demonstrated their economic feasibility forunits smaller than 200 kWe. The Eneftechs ORC module is designed to produceelectricity from relatively low-temperature heat sources (below 200C). The miniaturizedunit provides 30kWe, and the modular design makes it perfect for a biomass fired boiler

Brayton cycle with an externally fired hot air turbine.

Closed-cycle externally fired gas turbines have been known since the 50s but they do not

seem to have met commercial success. For example a 1 MW peat fired boiler from theJohn Brown Company is given as an example by H.U. Frustschi in [4]

On the opposite, open cycle systems have been recently reported as a possible route toCHP from biomass and several developments are ongoing on this process [5, 6]

Such CHP systems seem to be a very appropriate solution for small power applications due totheir potential flexibility in accepting various biomass qualities, as opposed to gasification

processes that are very sensitive to the type and quality of biomass.

However, small scale combustion system will be faced with more stringent regulation in thefuture, especially with regard to particulate emissions. Fly ash from wood combustion is

extremely fine (mean diameter around 0.3 mm) and contains poly-aromatic hydrocarbonswhich can be effectively reduced by appropriate filters and catalysers, similar to those used ondiesel exhaust gases. This is being demonstrated by an on-going project in the IndustrialBioenergy Systems laboratory [7]

With the instability of fossil fuel prices and electricity and their ineluctable increase, it is quitecertain that biomass fired small scale CHP systems will spread in the near future.

2.2 Biomass pyrolysis and gasification

Significant progress has been achieved recently to increase the reliability of pyrolysis andgasification plants. Unfortunately, medium to large scale commercial wood gasification plants

have not yet significantly penetrated the market in Europe mainly because of the high cost andcomplexity of wood gas treatment and purification to the level required for CHP. There arevery few known commercial plants and extensive developments are still on-going at the pilotscale, as demonstrated by the great number of articles published in recent years.

Once cleaned from tar components and pollutants (sulphur and chlorine components), woodgas is mainly composed of carbon monoxide, hydrogen, methane and carbon dioxide.

A very comprehensive effort is carried out on wood gasification as part as the IEA task 33Thermal Gasification of Biomass [8] and a lot of useful reports and presentations can befound on their web site.

The case of the Gussing (AU) demonstration plant has been cited by many authors as areference plant. More recently in Austria, two plants were put into operation; their maincharacteristics are provided in Table 2.


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Table 2 Main characteristics of Austrian pilot and demonstration gasification plants

Plant Startedcontinuous

operation

Woodconsumption

(tons/year)

Fuel inputcapacity

(MW)

Electricalcapacity

(MWe)

Thermalcapacity

(MWth)

Gussing 2002 Not stated 8 2 4

Oberwart 2009 20000 8.5 2.8 4.1

Villach 2011 33000 15 3.9 6.7

In 2008 Gssing has been extended to upgrading wood gas to synthetic natural gas (BioSNG),via a water shift process (CO H2) and a methanisation process (H2, CO, CO2 CH4)

The plant produces about 300 m3/h of wood gas, resulting in a BioSNG flow of about 120m3/h.

Another BioSNG pilot plant is planned in Villach as part as an Austrian funded program.

Figure 3 Gussing process flow diagram

However, it has been reported that IGCC is more suitable at large scale (> 50 MWe) due tothe complexity of the plant and the high investment costs [9]. At the scale of the abovementioned projects, the economic viability can only be achieved with government support inthe form of subsidies for the investment costs and/or feed-in tariff policies.

On the contrary, small scale biomass gasification plants have been much more widespread in

India. As a matter of fact, it is an Indian company who supplied a pilot plant in Wila(Switzerland) which served as a basis for two other plants in Switzerland. In 2003, a report


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states that there were 1817 biogas gasification plants in India for a total of 55 MWe, i.e. anaverage of 30 kWe by plant [10]. This is in contrast to the findings of the IEA task 33, with 68CHP plants in 2011 in their data base of which 23 in the USA.

2.3 Biomass torrefaction

Biomass torrefaction on the other hand, consisting of a mild pyrolysis under reducing orneutral conditions and operating in the range of 230-300 C, has found a great interest inmany countries, and large industrial plants are being built or have been recentlycommissioned. Torrefaction provides a number of technical and economical benefits due tothe densification of energy content and the hydrophobic behaviour of the torrefied biomass.

Known reported projects and commercial plants are mainly located in Europe and USA withabout 12 plants in Europe from 5-50 tons/year and 8 plants in North America from 35000 to110000 tons/year. [11]

Several types of technologies are reported (when known):

- Rotating drum, 7 projects- Screw conveyor, 4 projects

- Vertical plug flow reactor (counter-flow), 3 projects

- Oscillating moving bed, 2 projects

- Multiple earth, 2 projects

- Fluidised bed swirling flow, 1 project

- Microwave reactor, 1 project

2.3.1

Biomass torrefaction project at the University of Applied Science inYverdon-les-Bains (CH)

The Industrial Bioenergy Systems group led by the author has been pioneering R&D in the

field of torrefaction at the small scale since 2008 with a first study on the combustion and lifecycle evaluation of torrefied wood pellets. The work has been reported elsewhere [12] and themain conclusions of this theoretical and experimental study where that:

- There was no need to adjust the operating conditions of a boiler designed for normalpellets. The combustion behavior of the torrefied pellets was found very similar to thatof the normal pellets with an improvement in the combustion characteristics (warm-up

period, thermal efficiency)

- The overall life-cycle-impact from wood harvesting to useful energy can be reducedby 50% as compared to normal pellets.

In 2012, a new project was started aiming at the design and construction of a 600 kg/hdemonstration plant using biomass residues which are otherwise incinerated or used forcompost.

At first, laboratory experiments have been carried out on a small scale batch reactor(Figure 4,left) with 500 g samples of various biomass types and varying operating conditions (flowtemperature, heating time and biomass residence time).


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Figure 4 Photographs of the batch laboratory torrefactor (left) and the 20 kg/htorrefaction pilot

First results are given in Table 3below showing a great variation in the potential increase ofhigh heating value (HHV) depending on biomass type and torrefaction temperature.

The maximum increase of HHV up to 28% for wood chips at 245C temperature during 13minutes. The effect of chip size was not found significant.

One can also see that anaerobic digestion wastes, which are of no value, can be upgradedsignificantly by torrefaction.

Table 3 Results of torrefaction of various biomass sources

Biomass typeTorrefaction

temperature (C)

Torrefactionduration

(minutes)

HHV

raw material

(MJ/kg dry)

HHV

torrefied material

(MJ/kg dry)

Mass loss

(% dry matter)

Forest wood chips

(coniferous/deciduous)245 13 19.7 25.2 56

Tree trimmings 250 30 21.5 21.2 21.7

Tree trimmings 260 10 21.5 22.9 19.9

Anaerobic digestion ligno-cellulosic wastes

210 15 16,3 15.8 3.9

Anaerobic digestion ligno-

cellulosic wastes244 20 20.4 18.7 33.4

Anaerobic digestion ligno-cellulosic wastes

230 7 12.3 13.2 burnt

Conifer wood chips 260 25 20.2 20.1 14.6

Conifer wood chips 250 20 20.2 20.4 7.6

Conifer wood chips length< 6 mm

250 20 19.9 21 9.13


250 20 19.9 20.6 10.8


250 20 19.9 20.4 9.2


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Then a 20 kg/h continuous reactor was built (Figure 4, right) as an intermediate step to the600 kg/h demonstration plant, foreseen to be built in 2013.

A preliminary economic evaluation was also carried out with various feedstock input andmarket prices. Depending on the type of biomass and energy prices, it was found that plantcapacities between 5000 and 20000 tons/year could be viable, with a break-even return on

investment of 3-5 years.

3 Physico-chemical processesThe second family concerns mainly the transport biofuels such as biodiesel or bio-ethanol.This family requires a so-called energy crop which can be rich in oil content such as Jatrophacurcas, rapeseed or microalgae for biodiesel or in lingo-cellulose and sugar content forethanol production.

However, the limitation resigns first in the very low efficiency of solar conversion to biomass.Zhu and co-authors calculated the theoretical maximal photosynthetic energy conversionefficiency for C3 plants of 4.6% and for C4 plants of 6% C4 based on the total initial solarenergy and the final energy stored in biomass. The conditions were a leaf temperature of 30Cand an atmospheric [CO2] of 380 ppm. In most crops, real efficiencies are about ten timeslower i.e. about 0.5%. [13].

For example, with a yearly cereal production of 10 tons/hectare and a calorific value of 5kWh/kg and a yearly solar radiation of 18000 MWh/hectare, the gross efficiency is 0.27%.The further conversion into biodiesel by transesterification (10% loss) and into power (70%loss), would thus result in a net efficiency of 0.07%. This figure should be compared with theefficiency of solar power systems (concentrated photovoltaics or concentrated thermal), onthe order of 25 % and we immediately can conclude that the use of arable land should be usedfor food production rather than for biofuel production. However, until the times where solar

power and wind power systems will be widely implemented, biodiesel seem to be a goodalternative to fossil fuels for transport in specific cases provided that the sustainability of the

production has been thoroughly examined.

One of the most productive plants, Jatropha curcas is reported with yields about 3 tons/hectareof oil in India, whereas soybeans yields only 375 kg per hectare in the United States andrapeseed yields about 1 ton per hectare in Europe.

On the other hand, microalgae seem a very promising feedstock for future bio-dieselproduction. Contrarily to agricultural crops, they can be produced in non arable areas, eitherin open pond or closed systems. In the case of microalgae cultivation with a rich CO 2 feed,efficiencies of up to 5 % have been reported. This opens the way for a complete new concept

of bio-refineries which will be able to produce nutrients and materials for the chemical andpharmaceutical industry and energy.

A study was carried out the University of Applied Science Western Switzerland in 2008 onthe potential production of biodiesel and power from microalgae at [14]. This included areview of existing processes reported in the literature for the main three categories:

Open-pond systems (Raceway) with a production of about 36 to 72 tons per hectareper year and oil content of 40-50%

Tubular systems with a production of about 126 to 144 tons per hectare per year

Photobioreactors (PBR) of high productivity reported with yields of 288 to 360 tonsper hectare and per year.


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The interesting aspect of PBR is their ability to be fed with the exhaust from thermal powerplants, rich in CO2 and their very rapid growth (doubling volume every day). The study wasmade with a yearly production of 80 tons of oil per hectare under Swiss climatic conditionsand with the assumption of indigenous microalgae. For a plant of 800 t/y (10 ha) theinvestment cost was estimated at about 9166000 , the operation cost at 250000, resulting

into a biodiesel cost of 1.46 /kg. Theoretically, the productivity can be much higher,depending on climatic conditions and microalgae strain.

In February 2010, the Defense Advanced Research Projects Agency (DARPA) announced thelarge-scale production oil from algal ponds into jet fuel with a cost of biodiesel less than $3 agallon (0.79 $/litre). A larger-scale refining operation, producing 50 million gallons a year, isexpected to start in 2013, with the possibility of lower per gallon costs so that algae-based fuelwould be competitive with fossil fuels. [15]

In India, there is a national program for Jatropha cultivation to reduce its dependency on fossilfuel by 20% by 2017 but the production is far below expectation due to economicconsiderations and the reluctance of the investors due to the inherent uncertainties of this

market.

4 Biological processesThe third family concerns mainly biogas production from organic wastes, biogas purificationto methane and injection in the natural gas network or biogas combustion in CHP plants. Theauthor presents below a new concept of automated small scale anaerobic digester beingdeveloped within the framework of a project financed by the European Union.

4.1 Waste processing with anaerobic digestion

The most common process for organic waste processing is known as anaerobic digestion.

Extensive literature exists on the subject and several reviews are available [ 16, 17, 18] so wewill only summarize some of the key features here.

There exist three main regimes of anaerobic digestion, characterized by their range oftemperature:

psychrophilic conditions as in ponds, from 10-25C,

mesophilic conditions as in the stomach of mammalians from 30-37C and

thermophilic conditions from 48-55C

In practice, however, only the two latter are commercially developed and widely used because

the yield of the psychrophilic is too low to be exploitable and the so-called hydraulic retentiontime (defined by the ratio volume of digester to input flow rate) would be too high.

A second classification can be made between:

Dry and wet processes

Horizontal (plug-flow) and vertical (stirred) reactors

Anaerobic digestion (AD) is suitable for the treatment of all kinds of organic wastes; exceptfor ligneous wastes, most agricultural and agro-food industrial wastes can be digested. InSwitzerland and many other countries, the wastes from water treatment plants are also

processed to produce biogas and electricity.

Most farm biogas installations operate in mesophylic conditions whereas industrial systemsoften use thermophylic operation (for example Kompogas and BRV/Linde)


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In simple terms, AD equipment consists of a waste conditioning system, a thermo-regulateddigester tank, a gas holder to store the biogas, and a gas-burning engine/generator set, ifelectricity is to be produced. The organic waste is broken down in the tank and 40-90% of thiswaste is converted into biogas; the rate of breakdown depends mainly on the nature of thewaste. The biogas has a calorific value typically between 50% and 70% of that of natural gas

and can be combusted directly in modified natural gas boilers or used to run internalcombustion engines. Apart from biogas, the process also produces a digestate, i.e. theresidue from the digester which may also be separated into liquid and solid components. Theliquid element can be used as a fertilizer and the solid element may be used as a soilconditioner or further processed to produce higher value organic compost. Alternatively it canalso be torrefied for pellet production.

The biogas production occurs in a series of biological transformations which are, of course,strongly coupled with the local conditions of the environment i.e. temperature, pH, localcomposition and concentration gradients, particle size, bacterial population, enzymaticactivity etc.

One parameter has been found to be extremely important for a good digestion: theCarbon/Nitrogen (C/N) ratio of the feedstock with an optimum in the range of 2030 based on

biodegradable organic carbon.

If the C/N ratio is very low this leads to the accumulation of ammonia and pH increase. A pHvalue above 8.5 will start to show a toxic effect on the methanogenic bacterial communities.

To maintain the C/N ratio at acceptable levels, materials with high C/N ratio such as meatwastes can be co-digested with those with a low C/N ratio which are higher in nitrogen suchas municipal sewage or animal manure.

Anaerobic digestion can be described in four main process steps, schematically shown inFigure 6:

1. Hydrolysis

2. Acidogenenis

3. Acetogenesis

4. Methanogenesis, which is coupled with acetogenesis and acidogenesis by syntrophy.

Anaerobic digestion modelling started in the early 1970s when the need for design andefficient operation of anaerobic systems became obvious, this led to the so-called ADM1model, widely used in the scientific world [17]


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Figure 5 : Methanogenesis synthrophy processes (after Aragno [19])

In the first phase of hydrolysis, aerobic bacteria transform the heavier organic substances(such as proteins, carbohydrates, fats, cellulose) into simpler molecules such as sugar, amino-acids, fatty acids and water. This is a slow process that depends on pH and retention time. Inthe second phase of acidification, acidifying bacteria decompose the intermediate products

into short-chain fatty acids such as acetic, propionic and butyric acids as well as carbondioxide and hydrogen. Small quantities of lactic acid and alcohols are also produced.


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During the third step of acetogenesis, other anaerobic bacteria such as acetobacterium produceacetic acid, carbon dioxide and hydrogen, which are necessary for methane production in thefourth step of methanogenesis. About 70% of the methane is produced from acetic acid andtherefore this is a rate limiting step. The other 30% are produced from hydrogen and carbondioxide. This reduces the hydrogen concentration which would otherwise inhibit the

acetogenesis.In modern installations there are two separate zones, allowing to separate the first two stepsfrom the last two and to adapt the local conditions to the needs of the bacteria and to obtain

better conversion efficiencies.

4.2 Economics and limitations of existing products

4.2.1 The case of rural areas in AsiaThe case of Asian countries and that of western countries has been very different until now: inrural India and China for example, the digesters are relatively small (6-10 m3 vessels) for use

in farms, communities, and in some cases hotels, processing some 10 to 100 kg/day of wastessuch as manure, food wastes, crop wastes etc. they are quite labour intensive but theiroperation is rather simple.

Figure 6 : Biogas promotion poster produced by the Khadi and Village Industry

Commission after [20]


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Such systems have been used in developing countries for over a century [21]. Small scalevertical digesters with volumes of up to 100 m3 are widespread In India and China. Accordingto Plchl [18], three major types of digesters have emerged in developing countries: theChinese fixed dome digester and the Indian floating drum digester (see Figure 6) and veryrecently, tube digesters.

The floating dome digester is fed semi continuously and has a relative high depth to widthratio. Therefore a wall is placed in the middle of the digester to prevent short-circuiting (directsubstrate flow from the inlet to the outlet) [22].

According to Lawbuary in 2000 [23], there were thought to be about 2.5 million biogas plantsinstalled around the country but this represented only a minor fraction of the energy use forcooking.

Two independent studies indicated that between 12 and 30 million household-size plantscould be installed over the subcontinent, and nearly one community-size plant for each villageunderlining the enormous potential for anaerobic digestion systems.

Subsidies have been granted on plants up to 10 m3 (a large family-sized system) though theremay be regional differences.

Several constraints were found to limit the expansion of these systems:- Provision of space and of water (to be added to cow dung)- Availability of subsidies to reduce the high investment cost- Difficulty for the workers, mainly women, to handle large volume of dung (often more

than 1000 kg/day)The author recently visited a biogas plant next to a hotel in Thiruvrananthapuram, processingthe hotel wastes and other local agro-wastes. The hotel owner was very satisfied with the

plant as it allowed him to reduce his energy consumption and he reported no problems ofoperation.

In this state, half of the total expense for installing biogas plants in homes will be given assubsidy by the Government [24] with a maximum of 35 Lakhs (49000 Euros). These biogas

projects are installed as part of the Garbage Free Kerala initiative. Under this, only 25% of thetotal cost needs to be paid by the investors. In total a 75% grant will be given to the Garbagetreatment plants run by Panchayaths, 50% by the Government and 25% by Panchayaths.

4.2.2 The case of industrialized areasIn highly industrialized areas of western countries, higher labour costs do not make it possible

to have an economically viable solution below 4000 tons/year of waste, corresponding to afarm with 60 cow equivalent and with a digester tank volume of about 400 m 3. This is morethan 10 times the critical threshold of Asia. Even in that case, it will be necessary to useadditional sources of organic waste such as restaurant wastes.

A techno-economic review was made by the ORIF association in France of existing plantsfrom various technologies [25]:

Dranco and Vallorga: vertical, dry

Kompogas and BR/Linde: horizontal, dry

BTA, vertical, wet

The investment costs of these systems are plotted as a function of plant size on Figure 7.


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Another study Beck reports similar values [26] as shown in Table 4.

One can see that the specific cost in /ton decreases with plant size which is to be expected inindustrial plants. Also the cost spread between various plants appears to be very large and todepend on the plants characteristics.

Figure 7 : Investment costs (Million ) in 2003 as a function of the processing capacity

(103t/year) of biogas plants after [25]

Table 4 Investment costs as a function of the processing capacity of biogas plants in 2004

after [26] (in 2004, 1 $ corresponds to approximately 1.2-1.3 )


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Large facilities for biomechanical treatment, biogas production and/or compost production,require large occupied areas, and, in the case of biogas production, require also ensuringmaximum profitability of all generated energy. This is possible where district heating systemsare already built, but require large investments where a new system must be built. Anothersolution is to refine the biogas in order to produce methane and inject it into the natural gasgrid but again, this is currently only profitable for large plants, processing more than 20000

tons/y of waste (e.g. Kompogas plants). In fact the profitability threshold for such plants

depends very much on the local conditions.In most cases, the only alternative for processingsmaller quantities of wastes, where a large digestion plant is not available in the area, is to

incinerate them. In such cases water can be first extracted by mechanical methods but thewastes still contain high moisture content and are of no energetic value to the incinerator.

The anaerobic digestion of organic fraction of municipal solid wastes (OFMSW) has beenintensively studied and both dry [total solids (TS) content 3040%] and wet (TS around 10%)anaerobic process modifications have been developed and demonstrated to be technicallyfeasible. Those reactor technologies are applied commercially for medium to large scaleapplications e.g. BRV (horizontal, rectangular plug flow reactor; dry, Linde licence), BTA(vertical, stirred reactor, wet), Kompogas (one-stage, horizontal plug flow design, dry),Dranco (vertical plug flow reactor, dry), ROM (mixed sequential batch reactors), WELtec

BioPower (Vertical, stirred reactor, wet). Most of these systems are applied to centralisedwaste processing plants with capacities of more than 5000 t/year and are often linked to a co-generation plant with electric power capacities greater than 100 kWe. An economic analysis ofcentralized biogas plants (22 Danish manure based plants) has shown that economic balancein large facilities can be achieved when the average biogas yield is higher than 30 m 3 of

biogas/m3 of biomass (approx 20 m3 of CH4/m3 of biomass) [27]. Coincidently, several

studies have shown that for capacities


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Figure 8: Input-output diagram of a conventional digestion facility

The on-going GreenGasGrids European project has reported the number of biogas plants inEurope including those with biogas upgrading and injection into the grid [30] See Table 5.

This is 3-year European project funded by the Intelligent Energy for Europe (IEE) programmewith the aim to boost the European biomethane market. The project will run until mid 2014and its goal is to contribute to the European Renewable Energy Directive (RED) targets of20% renewable energy and 10% renewable energy in transport in 2020.

Table 5 Number of biogas and biomethane plants in several European countries [30]

As for many new renewable energy power generation plants, the economic viability of powerfrom biogas is very dependent upon the government support for investment and feed-intariffs. For instance, in the case of Austria, the basic tariffs subsidies vary from 18.5 and 13

cent per kWh depending on the size (18.5 cent/kWh if less than 250 kW, 16.5 cent/kWh

from 250-500 kW and 13 cent/kWh above 500 kW)

4.3 The ORION European funded project

ORION stands for ORganic waste management by a small-scale Innovative automatedsystem of anaerobic digestion. It is a European funded project (seventh framework

programme) just started in 2012 under the scheme Research for the benefit of SMEassociations


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SME agro-food industries have to manage large quantities of organic waste, the industryproduced nearly 240 Million tons of organic waste in 2006 [31].

The project goal is to develop a small automatic user-friendly digestion machine that enablesthe domestic on-site treatment of a wide range of organic waste from about 100 up to 5000tons per year at low cost (50 per ton) and with low maintenance. We have seen in the

previous section that such a system does not exist at this small scale and at low cost forinvestment and maintenance.

The project groups together 22 partners: 7 SME associations, 9 R&D partners and 6 SMEs.The SME associations are based in 6 different countries (Belgium, UK, Spain, France Turkeyand Switzerland) and representing 7 different sectors of SMEs, in particular: biomass, agro-food industries (fisheries, vegetable oil producers, dairy, and cattle) markets and hotels.

The SMEs involved in this project have to manage from 100 tons to 3000 tons a year.However, the only solutions currently available for these SMEs organic waste treatment are

landfill and incineration which imply a grouping of the waste before treatment and so requireintermediate storage and/or waste transport (as most fish processing plants are located inremote areas); as such, SMEs must face high costs of waste treatment: storage costs in cool areas, specific transportation costs and finally costs for incineration or recovery. The cost ofdisposing of this waste varies per country but the price in Europe varies from 50 to 200 perton. The possible routes for waste elimination are summarized in Figure 9,together with theassociated problems.

On average, restaurants produce about 250 g/meal of food waste with a large variation inquantities depending on the type of restaurant. Hospital restaurants and school canteens tendto generate greater quantities. For a large canteen serving 1200 meals/day, the amount of foodwastes is about 110 tons/year. This represents a cost of:

- 25 /ton for handling, grinding and storage on-site

- 100150 /ton for transport management, biological treatment, landfills or incineration fees(depending on the region)

Until recent years it was possible to feed pigs with restaurant wastes but this is no longerallowed in Europe because of sanitary risks and animal disease outbreaks.

The trends indicate that organic waste disposal costs will continue to increase because ofmore stringent legislative regulations so there is a great incentive to find alternative solutions.


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Not allowed anymore in the EUand several countries. Causesmany environmental problems

Figure 9: The different routes for agro-food waste treatment Past and future

The innovations of the project will reside in two main categories:

Diagnostic and control tools and sensors:

Monitoring and control are important strategies for achieving a better process stability andhigher conversion efficiencies in anaerobic digesters. In addition to the common indicatorsfor the monitoring of the biogas process, novel types of sensors will be used for on linedetection volatile fatty acids), ammonia, and hydrogen. The objective will be to optimizedigester operation and to prevent failures on-line. The development of local and remotemaintenance strategies and of process improvement strategies is therefore an important part ofthe project.

The overall control architecture proposed comprises three levels as outlined in Figure 10

1. Low level controls and diagnostics. Safety is ensured here by the use of fail-safeprocesses.

2. Maintenance (local and remote) and complete diagnostics (full or detailed).3. Supervision and process improvements.

Agro-food

waste treatment

Landfills

Composting units

Incineration plants

Anaerobicdigestion plants

> 5000 t/y

Not applicable for putrescible

wastes such as meat, fish orstarch wastes

Expensive solution Highenergy consumption, emissionof NOx and of SO2

Only applicable where largewaste quantities are generatedin the area.

Need to be commerciallydevelopedThe main objectiveof the ORION project

Automated smallscale digesters


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Figure 10 Proposed control architecture of the ORION systemIn this way, the operation of the system will be made very easy and transparent for the end-user, who will see what can be called an Intelligent Waste Bin.

Such a scheme should make it possible to prevent biological breakdown by early remediation

Prevention of biological breakdowns is a complex issue that is not yet solved satisfactorily inexisting systems. As a matter of fact there are several cases of severe biological breakdown tothe point where it was not possible to recover (complete system inhibition), and where thedigester content had to be removed (sometimes with heavy mechanical means). Biological

breakdowns may be provoked by four main causes:

accidental temperature change inappropriate composition of the substrate

accidental addition of poisoning or oxidative compounds

breakdown internal to the biomass (e.g. occurrence of bacteriophages)

What is required for an automatic AD system and proposed in the current project is:

a. An early prevention of biological breakdowns.b. A remote maintenance scheme with a specialised company

Optimization of the anaerobic digestion system design and operation.

The system to be designed will be based on the retention of solids (solids substrate and

biomass) in the reactor by an internal settlement device using the Digesto concept [32] asshown in Figure 11. It will be improved by using a fixed bed system (biofilm) in the internal

Automatic digestionSystem

Client A

Maintenancelocal or remote

Full or detailed

diagnostics

Supervision andprocess improvements

Low level controlsand diagnostics

Upload

data

Parameters

reconfiguration

TCP/UDP-IP

interactions

Automatic digestion

SystemClient B

Automatic digestion

SystemClient C


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area occupied by the liquid fraction. A specific innovation of this project will be thedevelopment and testing of different types of microstructured surfaces to improve theimmobilization and structuring of the syntrophic microbial community.

Figure 11: Digesto concept with internal solid/liquid separation after [32]

5 ConclusionsThere are many different pathways to the generation of heat (and cold) and power from

biomass sources.

Biomass energy in its traditional utilization for heating and cooking had been for many yearsthe major source of energy of mankind. It is now becoming a very significant source ofenergy in the modern world, which strives for the replacement of the depleting fossil fuelreserves and for the reduction of carbon dioxide emissions.

In the area of heat and power production, pre-processing and combustion of biomass will stillbe the dominant energy conversion process in the following decades with the furtherdevelopment of small scale CHP systems with indirectly turbines (ORC or hot air).

Torrefaction of biomass, which is a mild pyrolysis at temperatures below 300C allows toincrease the technical and economical value of the feedstock without additional energy otherthan the biomass itself. The hydrophobic character and higher heating value of torrefied

products make them a very promising alternative to raw biomass. We thus can foresee thatbiomass torrefaction systems will enable to process and store biomass and biomass residueslocally, and open the way to trade and transport these new biomass fuels at much larger scaleas today, in a similar way to coal trade.

Gasification of biomass appears to be a very complex process to operate and has not reallyfound its way to large implementation in Europe. However, a lot of small biomass gasification

projects are reported in India and it would be worthwhile to evaluate and compare thetechnological differences, which was not the purpose of this paper.

A tank (1) for an apparatus for receiving andconditioning organic waste by anaerobicbioconversion, in particular, waste produced byrestaurant kitchens and other facilities, includes amain enclosure wherein bioconversion takes place,and a secondary enclosure (18) for receiving andstoring ground organic waste before it istransferred to the main enclosure for completionof its bioconversion. A hopper (4) or other devicefor receiving the organic waste is associated with agrinder (2) and is connected to the secondary

enclosure (18) of the tank for feeding the groundorganic waste. A recirculation system (12, 15) forrecycling the contents of the tank includes a pump(13), means for distributing (17a, 17b) thecontents of the main enclosure between thedifferent levels thereof, and separate means (9, 22)for removing solid residues and liquid waste.


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Regarding the production of biofuels from energy crops, the common solar to biomassconversion efficiency is very low and requires 20-60 times more land as compared to thin film

photovoltaic. This is the reason why, in the authors opinion, only the third generationbiofuels (such as microalgae) can provide sustainable solutions that do not compete withagricultural crops. Such solutions can also be combined effectively with other energy

conversion processes such as concentrated thermal power generation.Biofuels for transport have nevertheless a cost advantage, especially when using nonagricultural land or residues from various sources (forest, agricultural, food industry).

Improvements are foreseen in the raw biomass conversion efficiency which today is on theorder of 0.5-2% whereas the maximum theoretical conversion efficiency is 4.6% for C3, and6% for C4 photosynthesis under average climatic conditions. In this respect, the high yield

biomass production processes such as Jatropha Curcas or algae are a better alternative to thecereal cultivation.

In the case of microalgae cultivation with a rich CO2 feed, efficiencies which are close to 5%have been reported.

Finally, biogas production from various organic biomass sources, such as animal manure,waste water sludge, food wastes etc. is seen to increase in most countries. Developments arestill required to improve plant reliability, efficiency and automation as well as cost reductionon smaller scales through production in series. This is the purpose of a three years European

project which is starting in 2012.

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15914.Affolter, J.-F.et al. Evaluation des cots cibles de production dlectricit partir

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