SUSTAINABILITY OF THE GREEN INTEGRATED FOREST BIOREFINERY: A QUESTION OF ENERGY ENRIQUE MATEOS-ESPEJEL* 1, MARYAM MOSHKELANI, MOHAMMAD KESHTKAR AND JEAN PARIS ABSTRACT 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. INTRODUCTION 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 obtained from several sectors: agricultural (dedicated crops and residues), forestry, industry and household (process residues, leftovers, municipal solid waste and wastewater), and aquaculture (algae and seaweeds) [2]. The main product of agriculture biorefineries is bioethanol, which is used to substitute non-renewable liquid fuels. Agricultural biorefineries have drawbacks 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 delivered by the biofuel [3]. Therefore, government incentives are necessary to assure their profitability [3]. On the contrary forestry biorefineries have proven to be profitable when integrated into pulp and paper mills. Pulp and paper processes such as Kraft can be considered biorefineries because pulp (cellulose), and energy (combustion 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 developing countries. To remain competitive the industry must develop a new spectrum of value-added products based on the valorization 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 ENRIQUE MATEOS -ESPEJEL Department of Chemical engineering MARYAM MOSHKELANI Department of Chemical engineering *Contact: enrique.mateos-espejel@fpinnovations.ca 1 E. Mateos-Espejel is now post-doctoral fellow at FPInnovations 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 infrastructure (utilities, laboratories, etc), support networks (suppliers, markets), direct access to raw materials, attractive utility costs (steam and water) and qualified manpower. However, the energy efficiency should be improved to respond to an increase in energy demand and reduction of MOHAMMAD KESHTKAR Department of Chemical engineering JEAN PARIS Department of Chemical engineering 55
black liquor calorific value. Additionally, water consumption and effluent production 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 overall facility [4-5]. This has led to the extension of the concept to the green integrated 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 level of the process and utilities. Therefore, optimal energy efficiency is essential to increase the economic attractiveness of this kind of project [6]. In this study the energy and material integration of two biorefinery units with a receptor Kraft process has been evaluated: hemicellulose extraction and biomass gasification. The material 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 complete site. This methodology encompasses several energy enhancing techniques. A detailed interactions analysis is performed to identify synergies and counter-actions between the different enhancing techniques and between the different process sections. The final objective is to develop an integrated eco-friendly site with maximum 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 production 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 56 J-FOR Fig. 1 - Green integrated forest biorefinery. effects on the demand and the production 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 interactions of a hemicellulose-based biorefinery site are described. The feasibility of replacing the biomass boiler by a gasifier and the existing options for material integration in the lignin extraction process are also analyzed. UNIFIED METHODOLOGY FOR ENERGY INTEGRATION The methodology consists of six stages (Fig. 2) [7]. The first stage is the development of computer simulation, which will be used as a source of information for all further analysis. The steps required for the simulation development can be found in [8]. The models should represent the energy and water behaviour of the receptor Kraft process and the biorefinery units. The second stage consists of analyzing the Fig. 2 - Unified methodology. Journal of Science & Technology for Forest Products and Processes: VOL.1, NO.1, 2011
utilities systems (steam and water) of the receptor Kraft process to identify inefficiencies in the operation of the boilers, utilization of steam (direct or indirect heat exchange), recovery of condensate, utilization of water at different temperature levels, reutilization of effluents and equipment insulation. At this stage several projects regarding the previous issues can be identified. A pre-benchmarking analysis is performed to determine the energy efficiency of the overall process and each of its sections. Several tools are used to accomplish this task. A diagnostic of equipment 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 practice. Performance indicators that quantify the energy and exergy content of the effluents 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 considered, including internal heat recovery, water reutilization, elimination of inefficient direct mixing, water reutilization, condensate recovery and energy enhancing and conversion. New process integration tools are used to identify thermal inefficiencies (non-isothermal screening graph [9]) in combination with the standard techniques (energy and water composite curves). The strong interactions between 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 counteractions between the different enhancing techniques and between the different process sections are identified. The objective 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 Fig. 3 - Interactions analysis. measures and of analyzing the performance of the process after optimization. The methodology has been applied to a Canadian hardwood Kraft pulp mill producing 700 adt/d. The savings obtained are 5.6 GJ/adt of steam (27% of the current consumption), and 37 m 3 /adt of water (33.6% of the current consumption). 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 application of the unified methodology has resulted in steam savings of 30% in comparison with 15% that could be achieved by pinch analysis as usually practiced. In the case of the GIFBR, the analysis 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 process 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 UNITS Hemicellulose extraction Hemicellulose is a heterogeneous polymer composed of five-carbon and six-carbon monomeric sugars. Hemicellulose extraction from wood chips prior to Kraft pulping and its transformation into high-value chemicals have been studied in two reference cases: an operating Kraft mill and a dissolving pulp mill. Integration to a Kraft mill The retrofit implementation has been performed in the same Canadian hardwood Kraft pulp mill where the unified methodology has been applied. It is considered that 10% of the initial content of hemicellulose 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 57
TABLE 1 Steam Production Scenarios Steam production (GJ/adt) Kraft process 28 Hemicellulose extraction 26.3 Shutdown fossil fuel boiler 23.2 TABLE 2 Steam Demand of the Hemicellulose Biorefinery Steam demand (GJ/adt) Furfural Ethanol Optimized process 15.5 15.5 Fig. 4 - Production paths for furfural and ethanol after hemicellulose extraction [5]. Biorefinery 2.8 2.5 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 considered 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 extracted and the fossil fuel boiler is shutdown (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 respectively (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 boilers) and energy integration make feasible the implementation of biorefineries and increase their economic attractiveness. Integration to a dissolved pulp mill and creation of clusters Dissolving pulp is a high purity specialty Total Excess of steam grade pulp made for processing into cellulose derivatives including rayon and acetate. While demand for this type of pulp has recently increased, current world production capacity cannot meet market requirements (high revenues available) [13]. The transformation of a Kraft pulp mill into a dissolving pulp mill requires the extraction of the hemicellulose prior to pulping. However, hemicellulose is typically sent to the recovery boilers for steam production. 18.3 18 4.9 5.2 A study to investigate the integration 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 prehydrolysis 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 hemicelluloses extracted from wood chips was used in this study. The mill produces 700 t/d of hemicellulose hydrolysate. In order to increase economic attractiveness, a cluster involving several mills can be developed [14]. A pulp mill or a chemical plant will be used as the centre of the cluster where hemicellulose pre-hydrolysate will be collected from several mills and converted to other products (furfural, ethanol, etc). In the case under study, the dissolving pulp mill is considered 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 dissolving 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 consumption 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 (condensers of the distillation towers) that can be transported to the dissolving pulp mill. This is possible because the pinch point 23 58
temperature (the lowest temperature difference between the curves representing the heat demands and sources of the process) of the ethanol plant (89ºC) is higher than in the dissolving pulp mill (53.7ºC). Mateos-Espejel et al [16] studied the implementation of a gasifier into an existing Kraft mill with a production of 1780 adt/d. The study considered the same amount of biomass used by the boiler 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 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 application of the complete unified methodology is required to ensure that the maximum steam savings are achieved. Base case TABLE 3 Gas turbine + optimization Gas turbine + optimization + lime kiln Biomass Gasification Power and Energy Results Power (MW) 42 59.5 Steam Consumption (GJ/adt) 18.35 13.88 53.2 14.08 Fig. 5 - Heat exchange within the integrated forest biorefinery. 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] performed 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 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 syngas cooling and flue gases of the gas turbine. The best choice for syngas usage will depend on prices of power and fuel. How- Biomass gasification Gasification is the incomplete combustion of biomass resulting in the production of combustible gases such as CO, H 2, and CH 4. 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 receptor 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 products (methanol, hydrogen, etc). There are three principal reactions in gasification: pyrolysis, oxidation (exothermic) and reduction (endothermic) [15]. To reach the desired operating temperatures, endothermic and exothermic reactions should be controlled by modifying the amount of steam or oxygen supplied. Another method is to remove indirectly the heat (which could be recovered by the Kraft mill). Fig. 6 - Material integration of lignin extraction and the receptor Kraft process [18]. 59
ever, more research is being undertaken to determine the appropriate operating conditions for the biomass gasification as part of an integrated biorefinery site. Lignin extraction Lignin 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 valueadded products such as adhesives, binders, phenols, etc. The steam production capacity of the Kraft process is reduced by lignin extraction. In this paper, the focus of this technology will only be the material integration with the receptor Kraft process. Lignin can be extracted from the residual black liquor from pulping by precipitation in acidic medium or by electrolysis. The ultrafiltration is a pre-treatment that can be used to separate the lignin by its molecular weight before precipitation. More details of these procedures can be found in [18 ]. In the case of the acidic precipitation CO 2 is required for the acidification of the black liquor and H 2 for the washing and filtration. The profitability of this technique depends on the cost of CO 2, H 2 and energy. The Kraft process has effluent streams where these two compounds can be recovered. Figure 6 shows that CO 2 could be captured from the flue gas of the recovery boilers and of the lime kiln. The H 2 might also be available from the ClO 2 making plant, although this alternative depends on the operation of the mill as H 2 is often sent to the evaporators. CONCLUSIONS The energy efficiency optimization and the identification of interactions are prerequisites 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 extracted from each mill will depend on the efficiency of the process. Only dissolving pulp mills will be able to extract 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. Although significant investment may be required [17], available government incentives 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 (CO 2 and H 2 ). Material 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. ACKNOWLEDGEMENTS This work was supported by a grant from the R&D Cooperative program of the National Science and Engineering Research Council of Canada. The industrial partners to this project and, more particularly, the mills, which supplied the data, are gratefully acknowledged. REFERENCES 1. 2. IEA. IEA bioenergy task 42 on biorefineries: co-production of fuels, chemicals, power and materials from biomass. In minutes of the third. Minutes of the third Task meeting 2008 [cited 2010] www.biorefinery. nl/ieabioenergy-task42/>;2009. Cherubini, F., The biorefinery concept: using biomass instead of oil for producing energy and chemicals Energy Conversion and Management, 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 51(7):1412-1421(2010). Pimentel, D., Ethanol fuels: energy balance, economics, and environmental impacts are negative Natural Resources Research, 12(2):127-134 (2003). Marinova, M., Mateos-Espejel, E., Jemaa, N., and Paris, J., Addressing the increased energy demand of a Kraft mill biorefinery: the hemicellulose extraction case Chemical Engineering Research and Design, 87:1269-1275 (2009). Marinova, M., Mateos-Espejel, E., and Paris, J., Towards a sustainable forest biorefinery. In SEEP 2009, Dublin, 246-51 (2009). Lange, J.P., Lignocellulose conversion: an introduction to chemistry, process and economics Biofuels, Bioproducts and Biorefining, 1(1):39 48 (2007). Mateos-Espejel, E., Savulescu, L., Marechal, F., and Paris, J., Unified methodology for thermal energy efficiency improvement: application to Kraft process Chemical Engineering Science, 66:135-151 (2011). Mateos-Espejel, E., Marinova, M., Schneider, S., and Paris, J., Simulation of a Kraft pulp mill for the integration of biorefinery technologies and energy analysis Pulp & Paper Canada, 111(3):T37-T41 (2010). Savulescu, L.E., and Alva-Argaez, A., Direct heat transfer considerations for improving energy efficiency in pulp and paper Kraft mills Energy, 33:1562-1571 (2008). Alva-Argaez, A., and Savulescu, L., Water reuse project selection. A retrofit path to water and energy savings. In Pres09, Paper 100, Rome (2009). Marinova, M., Mateos-Espejel, E., and Paris, J., Successful conversion of a Kraft pulp mill into a forest biorefinery: energy analysis issues In 23rd ECOS, Paper 91, Lausanne, (2010). Marinova, M., Mateos-Espejel, E., and Paris, J., From kraft mills to forest biorefinery: an energy and water perspective part II: case study Cellulose Chemistry and Technology, 44(1-3):21-26 (2010). Forthress specialty cellulose. Thurso 23 60
14. 15. Project. 2010; Available from: http:// specialtycellulose.com Marinova, M., Eilers, H., Barreto Do Carmo, C., and Paris, J., Opportunity for furfural production from hardwood 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). 16. 17. Mateos-Espejel, E., Moshkelani, M., and Paris, J., Development of a green Kraft mill Based on energy efficiency optimization. In 3rd International 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 process: energy and economic In 97th Paperweek Conference, Montreal (2011). 18. Perin-Levasseur, Z., Benali, M., and Paris, J., Lignin extraction technology integrated in Kraft pulp mill: implementation strategy In 23rd ECOS, Lausanne (2010). www.paptac.ca Emerging Forestry Areas: J-FOR CALL FOR PAPERS Traditional Areas: (covering all pulping processes, both wood and non-wood) Pulping, bleaching and papermaking fundamentals, processes and technologies Energy and chemical recovery fundamentals, processes and technologies Recycled fibre and recycling technology Development of sensors, analytical methods and process control logics Mill water and energy usages and optimization Environmental concerns and their mitigation Emerging forest-based products and their chains of added value Fundamentals of converting forest-based biomass into biofuels and other bioproducts Nanotechnology and other high added-value processes Development of chemical, biochemical and thermochemical processes for the forestry industry Integrating emerging and sustainable processes into the pulp and paper industry Harvesting and procurement of forest and other biomass feedstocks J-FOR publishes peer-reviewed articles of the highest quality, dealing with the science and technology of traditional and emerging areas that are pertinent to the forest industry. PAPTAC s preeminent and flagship publication, it incorporates a broad scope of target areas and brings together a wide range of scientific, technological and technical papers. To submit a paper, please visit www.paptac.ca or contact PAPTAC (514-392-0265 / tech@paptac.ca). PAPTAC NEWS 61