SUSTAINABILITY OF THE GREEN INTEGRATED … Vol 1-No 1/Sustainability of...EMERGING AREA CONTRIBUTIONS J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.1,

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55J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.1, NO.1, 2011

The development of a green integrated forest biorefinery (GIFBR) requires highly energy efficient chemical processes, as well as analysis of interactions within the site and the identification of energy impacts of the biorefining units. A unified methodology for energy integration has been proposed to improve the energy efficiency and to identify the energy implications and synergies within the site. Three biorefining units have been evaluated: lignin extraction, hemicellulose extraction and biomass gasification. The preliminary results show the GIFBR is energetically feasible and fossil fuel free.

ENRIQUE MATEOS-ESPEJEL*1, MARYAM MOSHKELANI, MOHAMMAD KESHTKAR AND JEAN PARIS

SUSTAINABILITY OF THE GREEN INTEGRATED FOREST BIOREFINERY: A QUESTION OF ENERGY

Biorefining is defined as the sustainable processing of biomass into a spectrum of marketable products and fuel [1]. The feedstock of the biorefineries can be ob-tained from several sectors: agricultural (dedicated crops and residues), forestry, industry and household (process resi-dues, leftovers, municipal solid waste and wastewater), and aquaculture (algae and seaweeds) [2]. The main product of agri-culture biorefineries is bioethanol, which is used to substitute non-renewable liquid fuels. Agricultural biorefineries have draw-backs such as competition for raw material with the food market and a negative net energy balance if all energy requirements (irrigation, transportation, fermentation and separation) exceed the energy deliv-ered by the biofuel [3]. Therefore, govern-ment incentives are necessary to assure their profitability [3]. On the contrary for-estry biorefineries have proven to be prof-itable when integrated into pulp and pa-per mills. Pulp and paper processes such as Kraft can be considered biorefineries because pulp (cellulose), and energy (com-bustion of hemicellulose and lignin), are produced from biomass. In recent years, the pulp and paper industry has traversed

a precarious situation in industrialized countries due to demand reduction, high energy prices and competition from devel-oping countries. To remain competitive the industry must develop a new spectrum of value-added products based on the valori-zation of lignin, hemicellulose and bark.

The integrated forest biorefinery consists of the addition of biorefining units to existing pulp and paper mills while maintaining the manufacturing of their

core product. The concept has significant economic advantages over autonomous greenfield biorefineries. Kraft pulping mills are particularly well suited for this type of enhancement. They offer the in-frastructure (utilities, laboratories, etc), support networks (suppliers, markets), di-rect access to raw materials, attractive util-ity costs (steam and water) and qualified manpower. However, the energy efficiency should be improved to respond to an in-crease in energy demand and reduction of

INTRODUCTION

JEAN PARIS École Polytechnique de MontréalDepartment of Chemical engineeringC.P. 6079, succ. Centre-villeMontreal QC,Canada, H3C 3A7

MARYAM MOSHKELANI École Polytechnique de MontréalDepartment of Chemical engineeringC.P. 6079, succ. Centre-villeMontreal QC,Canada, H3C 3A7

ENRIQUE MATEOS-ESPEJEL École Polytechniquede MontréalDepartment ofChemical engineeringC.P. 6079, succ.Centre-villeMontreal QC,Canada, H3C 3A7

MOHAMMAD KESHTKAR École Polytechnique de MontréalDepartment of Chemical engineeringC.P. 6079, succ. Centre-villeMontreal QC,Canada, H3C 3A7

*Contact: [email protected] E. Mateos-Espejel is now post-doctoral fellow at FPInnovations

56 J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.1, NO.1, 2011

black liquor calorific value. Additionally, water consumption and effluent produc-tion will also increase. It has been shown through intensive energy integration and optimization, the installed equipment of a typical Canadian mill could supply the steam and water requirements of the over-all facility [4-5]. This has led to the exten-sion of the concept to the green integrat-ed forest biofinery (GIFBR)which has for objective zero fossil fuel consumption and a significant reduction of greenhouse gas emissions. The integrated biorefinery will be a site with strong interactions at the lev-el of the process and utilities. Therefore, optimal energy efficiency is essential to in-crease the economic attractiveness of this kind of project [6]. In this study the ener-gy and material integration of two biore-finery units with a receptor Kraft process has been evaluated: hemicellulose extrac-tion and biomass gasification. The mate-rial integration aspects of lignin extraction are also part of the study. A unified energy integration methodology is presented to increase the energy efficiency of the com-plete site. This methodology encompasses several energy enhancing techniques. A detailed interactions analysis is performed to identify synergies and counter-actions between the different enhancing tech-niques and between the different process sections. The final objective is to develop an integrated eco-friendly site with maxi-mum energy efficiency and where energy costs will not hinder economic feasibility.

GREEN INTEGRATED FOREST BIOREFINERY (GIFBR)The GIFBR consists of a receptor Kraft mill and the integration of a biomass based biorefinery (Fig. 1). The final products are hemicellulose or lignin based compounds, power and energy. The implementation of the GIFBR will increase the overall steam demand while decreasing steam produc-tion capacity, as lignin or hemicellulose will not be burnt in the recovery boilers.

Fossil fuel is used in Kraft mills to fire the lime kiln and in some cases, for steam production. These issues in addition to the

effects on the demand and the produc-tion of steam could create a tendency to use of fossil fuels, but the use biomass for energy production could be an alternative. However, this means that part of the raw material should be burnt. In order to be a fossil fuel free facility, energy efficiency of the integrated site must be improved. The interactions between the receptor Kraft process and biomass-based biorefinery units should be identified and used to the benefit of the overall energy efficiency. In conclusion, the success of a GIFBR in terms of energy depends on three factors:- Energy optimization of the integrated site;- Identification of the energy implications of the biorefining units; - Identification and utilization of the interactions within the GIFBR.

In “Integration of biorefinery units” section, the energy implications and inter-actions of a hemicellulose-based biorefin-ery site are described. The feasibility of replacing the biomass boiler by a gasifier and the existing options for material inte-gration in the lignin extraction process are also analyzed.

UNIFIED METHODOLOGY FOR EN-ERGY INTEGRATIONThe methodology consists of six stages (Fig. 2) [7]. The first stage is the develop-ment of computer simulation, which will be used as a source of information for all further analysis. The steps required for the simulation development can befound in [8]. The models should represent the energy and water behaviour of the recep-tor Kraft process and the biorefinery units. The second stage consists of analyzing the

Fig. 1 - Green integrated forest biorefinery.

Fig. 2 - Unified methodology.

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utilities systems (steam and water) of the receptor Kraft process to identify inef-ficiencies in the operation of the boilers, utilization of steam (direct or indirect heat exchange), recovery of condensate, utili-zation of water at different temperature levels, reutilization of effluents and equip-ment insulation. At this stage several proj-ects regarding the previous issues can be identified. A pre-benchmarking analysis is performed to determine the energy effi-ciency of the overall process and each of its sections. Several tools are used to ac-complish this task. A diagnostic of equip-ment performance is used to identify poor operation, inefficient control strategies or lack of maintenance. It is recommended these issues be addressed or acknowledged before further analysis is performed. The utilization of water and steam is compared with a survey of average industrial prac-tice. Performance indicators that quantify the energy and exergy content of the efflu-ents and flue gases are used to measure the quantity and quality of the energy rejected by the process. The thermal and water composite curves are built to determine the minimum energy and water requirements and the maximum internal heat recovery and water reutilization within the process.

The core of the methodology is the interactions analysis (Fig. 3). Several energy-enhancing techniques are con-sidered, including internal heat recovery, water reutilization, elimination of inef-ficient direct mixing, water reutilization, condensate recovery and energy enhanc-ing and conversion. New process inte-gration tools are used to identify thermal inefficiencies (non-isothermal screening graph [9]) in combination with the stan-dard techniques (energy and water com-posite curves). The strong interactions be-tween water and energy systems are taken into account by a new procedure called the matrix method [10]. In this method all paths for water reutilization and their corresponding energy implications are analyzed. The synergies and counter-actions between the different enhanc-ing techniques and between the different

process sections are identified. The objec-tive is to maximize water and energy savings and opportunities for power production. The last two stages of the methodology consist of defining the steps required for the implementation of the enhancement

measures and of analyzing the perfor-mance of the process after optimization.

The methodology has been applied to a Canadian hardwood Kraft pulp mill producing 700 adt/d. The savings ob-tained are 5.6 GJ/adt of steam (27% of the current consumption), and 37 m3/adt of water (33.6% of the current consump-tion). As a result, the existing fossil fuel boiler can be shut down. In addition there is a power cogeneration potential of 35 MW. The payback time for the complete implementation is 1.3 years. The applica-tion of the unified methodology has re-sulted in steam savings of 30% in com-parison with 15% that could be achieved by pinch analysis as usually practiced.

In the case of the GIFBR, the analy-sis will also include the biorefinery units and the process used for the manufacture of value added-products. It is expected the interactions between the Kraft pro-cess and the biorefinery will not only be at the level of energy and water, but

also the material integration as will be shown in the case of lignin extraction. This analysis will also serve to identify the existing trade-offs and constraints for optimization of the processes.

INTEGRATION OF BIOREFINERY UNITSHemicellulose extractionHemicellulose is a heterogeneous polymer composed of five-carbon and six-carbon monomeric sugars. Hemicellulose extrac-tion from wood chips prior to Kraft pulp-ing and its transformation into high-value chemicals have been studied in two refer-ence cases: an operating Kraft mill and a dissolving pulp mill.

Integration to a Kraft millThe retrofit implementation has been per-formed in the same Canadian hardwood Kraft pulp mill where the unified meth-odology has been applied. It is considered that 10% of the initial content of hemi-cellulose in wood has been extracted prior to pulping and converted into furfural or ethanol while using the extracted wood chips to produce market Kraft pulp. Furfural (C-5 carbohydrates) is the only organic compound derived from biomass that can replace crude oil based organics

Fig. 3 - Interactions analysis.


used in the industry. Bio-ethanol can be used to complement liquid fuels such as gasoline. The production paths are shown in Fig. 4. More details on the paths for each product can be found in [4, 5, 11, 12].

For the purpose of analysis, it is con-sidered that the recovery boilers are at the Canadian average efficiency (65%), which would permit an increase of 27% over the current steam production of the mill. The steam production capacity of the mill is reduced by 19% after hemicellulose is ex-tracted and the fossil fuel boiler is shut-down (Table 1). The implementation of the biorefinery increases the steam demand of the process by 2.8 GJ/adt and 2.5 GJ/adt for furfural and ethanol production re-spectively (Table 2). The steam production capacity of the optimized mill can supply the steam required by the biorefinery and use the excess steam for power generation. These results show that improvements of energy efficiency at the level of process operation (efficiency of recovery boil-ers) and energy integration make feasible the implementation of biorefineries and increase their economic attractiveness.

Integration to a dissolved pulp mill and creation of clustersDissolving pulp is a high purity specialty

grade pulp made for processing into cellu-lose derivatives including rayon and acetate. While demand for this type of pulp has recently increased, current world produc-tion capacity cannot meet market require-ments (high revenues available) [13]. The transformation of a Kraft pulp mill into a dissolving pulp mill requires the extrac-tion of the hemicellulose prior to pulping. However, hemicellulose is typically sent to the recovery boilers for steam production.

A study to investigate the integra-tion of a hemicellulose-based biorefinery into a Canadian dissolving pulp mill with a production of 500 t/d, has previously been performed [11]. The amount of hemicellulose extracted in the prehydro-lysis step of a dissolving pulp mill varies according to the hydrolysis method used (steam, hot water, etc) and the type of wood. A typical value of 30% of hemi-celluloses extracted from wood chips was used in this study. The mill produces 700 t/d of hemicellulose hydrolysate. In or-der to increase economic attractiveness, a cluster involving several mills can be developed [14]. A pulp mill or a chemi-

cal plant will be used as the centre of the cluster where hemicellulose pre-hy-drolysate will be collected from several mills and converted to other products (furfural, ethanol, etc). In the case under study, the dissolving pulp mill is con-sidered as the centre of a cluster, where 7000 t/d of hemicellulose pre-hydrolysate are collected and converted to ethanol.

The steam consumption of the dis-solving pulp mill and the ethanol plant before energy optimization are 30.24 GJ/adt and 5.184 GJ/adt respectively (energy values based on the production of the dissolving pulp mill). The application of pinch analysis results in maximum steam savings of 30% of the current consump-tion for the dissolving pulp mill and 43% for the ethanol plant. An analysis of the thermal profiles (grand composite curve) of the integrated site (Fig. 5) confirms it is possible to recover 2.11 GJ/adt of waste heat from the ethanol plant (condens-ers of the distillation towers) that can be transported to the dissolving pulp mill. This is possible because the pinch point

TABLE 1 Steam Production Scenarios

Steam production (GJ/adt)

Kraft process 28

26.3Hemicellulose extraction

Shutdown fossil fuel boiler 23.2

TABLE 2 Steam Demand of the Hemicellulose Biorefinery

Steam demand (GJ/adt)

Optimized process 15.5

Biorefinery

Total

2.8

Excess of steam

Furfural Ethanol

15.5

2.5

18.3 18

4.9 5.2

Fig. 4 - Production paths for furfural and ethanol after hemicel-lulose extraction [5].



temperature (the lowest temperature dif-ference between the curves representing the heat demands and sources of the pro-cess) of the ethanol plant (89ºC) is higher than in the dissolving pulp mill (53.7ºC).

The minimum energy demand of the integrated site is 22 GJ/adt. As the steam production capacity of the mill has been reduced from 30.24 GJ/adt to 27.57 GJ/adt, there is still 5.57 GJ/adt of excess steam. However, the ap-plication of the complete unified meth-odology is required to ensure that the maximum steam savings are achieved.

Biomass gasificationGasification is the incomplete combus-tion of biomass resulting in the produc-tion of combustible gases such as CO, H2, and CH4. The objective of implementing a gasifier into the integrated biorefinery site is to replace the biomass boiler to produce steam (or release heat to the re-ceptor Kraft mill) and syngas. The syngas can be used in the lime kiln to eliminate the use of natural gas, to produce power or to generate other value-added prod-ucts (methanol, hydrogen, etc). There are three principal reactions in gasification: pyrolysis, oxidation (exothermic) and re-duction (endothermic) [15]. To reach the desired operating temperatures, endother-mic and exothermic reactions should be controlled by modifying the amount of steam or oxygen supplied. Another meth-od is to remove indirectly the heat (which could be recovered by the Kraft mill).

Mateos-Espejel et al [16] studied the implementation of a gasifier into an exist-ing Kraft mill with a production of 1780 adt/d. The study considered the same amount of biomass used by the boiler

would be used for gasification. The results show the syngas produced could meet the lime kiln’s needs and produce power in a gas turbine. Moshkelani et al [17] per-formed a pinch analysis on the process and determined that 3.3 GJ/adt of steam could be saved. Two scenarios were also analyzed for the utilization of syngas in the process (Table 3): syngas utilization

to drive a gas turbine, and syngas usage in the lime kiln and in the gas turbine. An analysis of the heat available from syngas cooling, flue gases of the gas turbine and the flue gases of the recovery boilers show

that all these energy sources could replace the energy supplied by the biomass boiler. The utilization of syngas in the lime kiln reduces the amount of power produced and increases the steam consumption of the process as less heat is available in syn-gas cooling and flue gases of the gas tur-bine. The best choice for syngas usage will depend on prices of power and fuel. How-

Fig. 5 - Heat exchange within the integrat-ed forest biorefinery.

Fig. 6 - Material integration of lignin extraction and the receptor Kraft process [18].

TABLE 3 Biomass Gasification Power and Energy Results

Steam Consumption (GJ/adt)

Gas turbine + optimization

18.35

Gas turbine + optimization + lime kiln

59.5

Base case

Power (MW)

42

13.88

53.2 14.08


ever, more research is being undertaken to determine the appropriate operating conditions for the biomass gasification as part of an integrated biorefinery site.

Lignin extractionLignin is a polymeric compound found in the wood, which is separated from the cellulose in the pulping operation and is subsequently concentrated and burnt for steam production. Lignin can also be used as a raw material to produce several value-added products such as adhesives, binders, phenols, etc. The steam production capac-ity of the Kraft process is reduced by lignin extraction. In this paper, the focus of this technology will only be the material inte-gration with the receptor Kraft process.

Lignin can be extracted from the re-sidual black liquor from pulping by pre-cipitation in acidic medium or by electrol-ysis. The ultrafiltration is a pre-treatment that can be used to separate the lignin by its molecular weight before precipita-tion. More details of these procedures can be found in [18 ]. In the case of the acidic precipitation CO2 is required for the acidification of the black liquor and H2SO4 for the washing and filtration. The profitability of this technique depends on the cost of CO2, H2SO4 and energy. The Kraft process has effluent streams where these two compounds can be re-covered. Figure 6 shows that CO2 could be captured from the flue gas of the re-covery boilers and of the lime kiln. The H2SO4 might also be available from the ClO2 making plant, although this alterna-tive depends on the operation of the mill as H2SO4 is often sent to the evaporators.

CONCLUSIONSThe energy efficiency optimization and the identification of interactions are pre-requisites for the implementation of a GIFBR. Even though the steam capacity decreases and the overall steam demand increases, a highly energy optimized site can fulfill its energy requirements without the need for any additional external fuel. Therefore, the application of the unified

methodology must be performed.

The development of clusters is essential to economic advantage. The amount of hemicellulose that can be ex-tracted from each mill will depend on the efficiency of the process. Only dis-solving pulp mills will be able to ex-tract more than 10% of hemicellulose.

The replacement of the biomass boilers by gasifiers is technically feasible. The syngas can be used to eliminate the natural gas in the limekiln, generate power and produce value-added chemicals. Al-though significant investment may be re-quired [17], available government incen-tives for green technologies can increase the economic feasibility of these ventures. The extraction of lignin from black liquor is more complicated than in the case of hemicellulose. Several unit operations are involved in addition to the need of high value chemicals (CO2 and H2SO4). Mate-rial integration with the Kraft process will have a positive effect on profitability.

It can be concluded that a GIFBR is feasible and this aspect can increase its profitability.

ACKNOWLEDGEMENTSThis work was supported by a grant from the R&D Cooperative program of the National Science and Engineering Re-search Council of Canada. The indus-trial partners to this project and, more particularly, the mills, which supplied the data, are gratefully acknowledged.

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Project. 2010; Available from: http://specialtycellulose.comMarinova, M., Eilers, H., Barreto Do Carmo, C., and Paris, J., “Opportunity for furfural production from hard-wood chips pre-hydrolysate” In 3rd International IUPAC conference on green chemistry, Ottawa (2010).Higman, C., and van der Burgt, M., Gasification. Burlington, USA, Elservier Science (2003).

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Mateos-Espejel, E., Moshkelani, M., and Paris, J., Development of a “green” Kraft mill Based on energy efficiency optimization. In 3rd Inter-national IUPAC conference on green chemistry, Ottawa (2010).Moshkelani, M., Mateos-Espejel, E., Kamal, W., and Paris, J., “Integration of a gasification unit into a Kraft pro-cess: energy and economic” In 97th Paperweek Conference, Montreal (2011).

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Perin-Levasseur, Z., Benali, M., and Paris, J., “Lignin extraction tech-nology integrated in Kraft pulp mill: implementation strategy” In 23rd ECOS, Lausanne (2010).

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SUSTAINABILITY OF THE GREEN INTEGRATED … Vol 1-No 1/Sustainability of...EMERGING AREA CONTRIBUTIONS J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.1,