Muhammad Mufti Azis
Masters student in Innovative and Sustainable Chemical Engineering,
Chalmers University of Technology, Sweden
Member of Chalmers Students for Sustainability (CSS)
ABSTRACT:
The paper focuses on utilization of biomass energy from lignin. Extraction of lignin (pulp mill residue) from kraft black liquor through LignoBoost process has been well-developed. High purity lignin produced from LignoBoost process is a potential alternative to reduce fossil fuel consumption in pulp mill, local electricity generation and district heating system. Furthermore, utilization of biomass is environmentally friendly and inline with public demand to rely on renewable energy. Finally, lignin extraction is a promising breakthrough to bring off pulp mill industry as a biorefinery industry in the future.
Keywords: lignin; LignoBoost; biomass energy; kraft black liquor
Introduction
Recently, demand of bioenergy becomes a pinnacle issue as an effect of climate protection policy. For this reason, development of bioenergy in terms of either biofuel or biomass becomes more demanding. Biomass energy currently contributes 11 percent of total world energy consumption (IEA 2004 cited Miller 2007). At this share, biomass is the single largest of renewable energy. Second generation of biofuel which is dominated by forestry products becomes of importance in future. As a result, it puts wood-based materials as the most potential source for future bioenergy (ölz et al 2007).
Woody plants are divided into softwood and hardwood which contain 25-31 percent and 16-24 percent lignin respectively (Smook 2002). Softwood and hardwood are main raw materials in pulp and paper industries. For this reason, it is conceivable that the availability of industrial lignin material is mainly from pulp and paper industries (Lebo et al 2001). Total world production of black liquor recently is 175 million tDS or equal to 600 TWh of energy. Apparently demand for pulp and paper will steady increase on average 3.5 percent/year. It results the black liquor supply will show more increase in the future (Ekbom et al 2001).
Lignoboost process
Since 1996, Chalmers University of Technology and STFI-Packforsk initiated to investigate lignin extraction process under “Ecocyclic Pulp Mill” (KAM) and FRAM-programs. One of common methods to extract lignin is by acidifying kraft black liquor followed by precipitation of lignin. Afterwards, lignin should be separated from black liquor by filtration. On the first part of the project, it was found that traditional single stage washing caused complete or partial plugging of washing water. As a result, it led to high impurity of lignin product (Axegård 2007).
Later on, it was found that the main cause of plugging was the change of lignin solubility. Further study shows this phenomenon occurs due to high gradient of pH and ion strength (in terms of sodium content) during washing steps as depicted in figure 1. From this figure, it can be seen that just after the washing, the pH is level out on high pH while in the same time ion strength start decreasing dramatically. Thus, high pH combined with low ion strength was believed as influential factor of lignin dissolution. This finding opens up opportunity to invent new washing method. The new method of lignin washing consists of two washing steps accomplished with re-slurry tank in between (öhman et al 2007). Figure 2 shows the improved washing method. On the first dewatering stage, washing is carried out in high pH condition which is approximately pH 10. The cake formed from first filtration is then re-dispersed onto re-slurry tank. The aim of re-slurrying step is to provide ample space to control lignin solution to reach low pH (approximately 2-4). Final pH should be low in order to obtain low sodium content which is favored if lignin would be used as biofuel. From this explanation, plugging problem has been resolved by new improved washing method. Later on, this new washing method is named LignoBoost process (Axegård 2007).
Masters student in Innovative and Sustainable Chemical Engineering,
Chalmers University of Technology, Sweden
Member of Chalmers Students for Sustainability (CSS)
ABSTRACT:
The paper focuses on utilization of biomass energy from lignin. Extraction of lignin (pulp mill residue) from kraft black liquor through LignoBoost process has been well-developed. High purity lignin produced from LignoBoost process is a potential alternative to reduce fossil fuel consumption in pulp mill, local electricity generation and district heating system. Furthermore, utilization of biomass is environmentally friendly and inline with public demand to rely on renewable energy. Finally, lignin extraction is a promising breakthrough to bring off pulp mill industry as a biorefinery industry in the future.
Keywords: lignin; LignoBoost; biomass energy; kraft black liquor
Introduction
Recently, demand of bioenergy becomes a pinnacle issue as an effect of climate protection policy. For this reason, development of bioenergy in terms of either biofuel or biomass becomes more demanding. Biomass energy currently contributes 11 percent of total world energy consumption (IEA 2004 cited Miller 2007). At this share, biomass is the single largest of renewable energy. Second generation of biofuel which is dominated by forestry products becomes of importance in future. As a result, it puts wood-based materials as the most potential source for future bioenergy (ölz et al 2007).
Woody plants are divided into softwood and hardwood which contain 25-31 percent and 16-24 percent lignin respectively (Smook 2002). Softwood and hardwood are main raw materials in pulp and paper industries. For this reason, it is conceivable that the availability of industrial lignin material is mainly from pulp and paper industries (Lebo et al 2001). Total world production of black liquor recently is 175 million tDS or equal to 600 TWh of energy. Apparently demand for pulp and paper will steady increase on average 3.5 percent/year. It results the black liquor supply will show more increase in the future (Ekbom et al 2001).
Lignoboost process
Since 1996, Chalmers University of Technology and STFI-Packforsk initiated to investigate lignin extraction process under “Ecocyclic Pulp Mill” (KAM) and FRAM-programs. One of common methods to extract lignin is by acidifying kraft black liquor followed by precipitation of lignin. Afterwards, lignin should be separated from black liquor by filtration. On the first part of the project, it was found that traditional single stage washing caused complete or partial plugging of washing water. As a result, it led to high impurity of lignin product (Axegård 2007).
Later on, it was found that the main cause of plugging was the change of lignin solubility. Further study shows this phenomenon occurs due to high gradient of pH and ion strength (in terms of sodium content) during washing steps as depicted in figure 1. From this figure, it can be seen that just after the washing, the pH is level out on high pH while in the same time ion strength start decreasing dramatically. Thus, high pH combined with low ion strength was believed as influential factor of lignin dissolution. This finding opens up opportunity to invent new washing method. The new method of lignin washing consists of two washing steps accomplished with re-slurry tank in between (öhman et al 2007). Figure 2 shows the improved washing method. On the first dewatering stage, washing is carried out in high pH condition which is approximately pH 10. The cake formed from first filtration is then re-dispersed onto re-slurry tank. The aim of re-slurrying step is to provide ample space to control lignin solution to reach low pH (approximately 2-4). Final pH should be low in order to obtain low sodium content which is favored if lignin would be used as biofuel. From this explanation, plugging problem has been resolved by new improved washing method. Later on, this new washing method is named LignoBoost process (Axegård 2007).
Fig.1 The pH profile during washing stage. Sodium and lignin concentration are also shown on the right. (experimental conditions: wash water pH 1.05, wash water temperature 20oC and precipitation pH 10). From: öhman et.al. (2007)
Lignin produced from LignoBoost has high purity and energy content. Effective heat value (dry) of lignin is 25.4 MJ/Kg Dry Solid with sodium content 0.03 percent on dry weight. Low sodium content means cleaner combustion when lignin is used as biofuel or co-firing fuel (Axegård 2007).
Pilot plant with capacity 4000 tones annually was built in Bäckhammar. Lignin produced is used in lime kiln, bark boiler and Fortum’s heat and power plant in Stockholm. The possibility to use either CO2 from lime kiln or ethanol plant to precipitate lignin is also considered in future. Long research and development of LignoBoost has filled two patent applications and established new company, LignoBoost AB, on 2006 to investigate further development of this technology (Axegård 2007).
Fig.2 LignoBoost process. The area within dash-box is the modified part on lignin washing. From: öhman et.al. (2006)
Environmental gain
Forest and pulp industry has important role to fulfill Swedish target for CO2 reduction. According to life cycle study, average CO2 emission from Kraft Pulp in year 2000 is 220 Kg CO2/ADt. This value is dominated by emission from production and transportation of chemicals. As comparison, reference mill emits -260 Kg CO2/ADt which means that society’s net emission of CO2 is reduced as a result of pulp production. This figure is obtained due to potential to generate power from bark and surplus black liquor. Its utilization replaces power from natural gas combined cycle. Hence it is obvious if lignin utilization as bioenergy could also decrease CO2 emission (Backlund 2007).
Co-firing combustion between coal and biomass is an interesting alternative. Incineration test lignin-liquid coal in 410 MW PFBC (Pressurized Fluided Bed Combined-cycle) shows promising result. Furthermore, laboratory result shows that 10-15 percent of lignin could be readily mixed with coal paste without any handling problem (Axegård 2007). In short term, IEA noticed that co-firing biomass is still a most cost-effective way to utilize biomass (IEA, 2007).
Socio-economic aspect
Lignin extraction was initially purposed to debottleneck pulp mill capacity. Roughly, LignoBoost investment is only one-half of investment to up-grade recovery boiler. Recent study investigated several scenarios by increasing 25 percent capacity in model pulp-mill. Combined with heat integration, there is possibility whether exporting lignin 346 GWh/year or increasing electricity by 109 GWh/year with upgraded boiler. With lignin price 15€/MWh, lignin separation becomes more profitable than upgrading boiler capacity. In addition, it also concludes that electricity prices to lignin ratio should be below 1.9-2.3 to make lignin extraction becomes viable (Axelsson et al 2006).
Sweden is well known as leading country in bioenergy utilization. Biofuel contributes 116 TWh out of 624 TWh of total energy supply in Sweden year 2006. Two eminent sources of energy suppliers are still nuclear power and crude oil which altogether contributes 400 TWh. Recently, Swedish government introduces green electricity certificate in order to boost renewable electricity utilization by 17 TWh in 2016. In addition, impose tax on fossil fuel also has made biofuel becomes more competitive. Consequently, market is prepared to pay a high price (Swedish Energy Agency 2007).
Kraft pulp mill has prime potential to be biorefinery plant in future. In his article, Ben Thorp (2005) showed that new model pulp industry should develop wide range value added products through market driven innovation. Several strategies should be taken into account such as increase sustainable forestry, extract hemi cellulose, convert tall oil to biodiesel, replace recovery boiler with gasifier and usage of solid fuel gasifiers. Lignin extraction is only one small step to enter modern forest biorefinery. It is hoped that pulp mill will produce diverse chemical products and eventually could replace petro-based chemicals in future.
Conclusion
LignoBoost has introduced alternative biofuel from lignin. State of the art from this new process is laid on two washing stages. First dewatering stage is carried out in high pH (approximately 10) and second dewatering is performed on low pH (approximately 2-4). Sodium content of produced lignin is below 1 percent which is favorable if later used as fuel. Moreover, incineration test shows promising result in which lignin could replace 10-15 percent of coal.
In the case of increasing pulp mill capacity (debottleneck), it is more viable to extract lignin than invest on up-grading recovery boiler capacity. Further comparison should take into account potential of exporting lignin or exporting electricity from improved recovery boiler. It is concluded when electricity prices to lignin ratio is lower than 1.9-2.3, lignin investment becomes more interesting. According to Sweden’s experience, government plays important role to develop bioenergy by issuing pro-renewable energy policies.
Kraft pulp mill in future has prime potential to adopt biorefinery concept. The big picture is to have modern forest biorefinery plant which is able to produce wide range chemical products in future. From environmental aspect, lignin utilization will lead to reduction of CO2 emission or even further could reach negative emission. All by all, reliance on bio-based product will make us one step closer to reach sustainable society.
References
1. AXEGÅRD, P., 2007. The Kraft Pulp Mill as a Biorefinery [online]. Available from:
http://www.celuloseonline.com.br/imagembank/Docs/DocBank/Eventos/430/3AxegardOral.pdf [Accessed 15 March 2008].
2. AXELSSON, E., OLSSON, M.R. AND BERNTSSON, T., 2006. Increased capacity in kraft pulp mills: Lignin separaton and reduced steam demand compared with recovery boiler upgrade. Nordic Pulp and Paper Research Journal [online], 21(4). Available from: http://www.spci.se/html/storage/xfl_bsvamhtrqc.pdf [Accessed 15 March 2008].
3. BACKLUND, B., 2007. Towards Increased Closure and Efficiency. In: EK, M., GELLERSTEDT, G. AND HENRIKSSON, G., Ljungberg Textbook: Book 2 Pulping Chemistry and Technology. Stockholm: KTH.
4. EKBOM, T., LINDBOLM, M., BERGLIN, N. AND AHLVIK, P., 2003. Technical and Commercial Feasibility Study of Black Liquor Gasification with Methanol/DME Production as Motor Fuels for Automotive Uses-BLGMF. Stockholm: Nykom Synergetics AB.
5. IEA, 2007. Biomass for Power Generation and CHP [online]. IEA Energy Technology Essentials. Available from : http://www.iea.org/textbase/techno/essentials3.pdf [Accessed 15 March 2008].
6. LEBO Jr., S.E., GARGULAK, J.D. AND MCNALLY, T.J., 2001. Lignin. In: Kirk-Othmer Encyclopedia of Chemical Technology [online]. Wiley Interscience. Available from: http://www.mrw.interscience.wiley.com.proxy.lib.chalmers.se/emrw/9780471238966/kirk/article/lignlin.a01/current/html?hd=All,lignin [Accessed 15 March 2008].
7. MILLER Jr., G.T., 2007. Living in the Environment 15th ed. Belmont CA: Thomson Brooks/Cole.
8. SMOOK, G.A., 2002. Handbook for Pulp and Paper Technologies 3rd ed. Vancouver: Angus Wilde Publications Inc.
9. SWEDISH ENERGY AGENCY, 2007. Energy in Sweden 2007. Stockholm: SWEDISH ENERGY AGENCY.
10. THORP, B., 2005. Biorefinery offers Industry Leaders Business Model for Major Change. Pulp and Paper, Nov.
11. ÖHMAN, F., WALLMO, H. AND THELIANDER, H., 2006. An Improved Method for Washing Lignin Precipitated from Kraft Black Liquor-The key to new bio-fuel [online]. Available from:
http://www.lignoboost.com/upload/3878/Paper_Theliander_et_al_2006b.pdf
[Accessed 15 March 2008].
12. ÖLZ, S., SIMS, R. AND KIRCHNER, N., 2007. Contribution of Renewables to Energy Security [online]. IEA Information Paper. Available from: http://www.iea.org/textbase/papers/2007/so_contribution.pdf [Accessed 15 March 2008].
Lignin produced from LignoBoost has high purity and energy content. Effective heat value (dry) of lignin is 25.4 MJ/Kg Dry Solid with sodium content 0.03 percent on dry weight. Low sodium content means cleaner combustion when lignin is used as biofuel or co-firing fuel (Axegård 2007).
Pilot plant with capacity 4000 tones annually was built in Bäckhammar. Lignin produced is used in lime kiln, bark boiler and Fortum’s heat and power plant in Stockholm. The possibility to use either CO2 from lime kiln or ethanol plant to precipitate lignin is also considered in future. Long research and development of LignoBoost has filled two patent applications and established new company, LignoBoost AB, on 2006 to investigate further development of this technology (Axegård 2007).
Fig.2 LignoBoost process. The area within dash-box is the modified part on lignin washing. From: öhman et.al. (2006)
Environmental gain
Forest and pulp industry has important role to fulfill Swedish target for CO2 reduction. According to life cycle study, average CO2 emission from Kraft Pulp in year 2000 is 220 Kg CO2/ADt. This value is dominated by emission from production and transportation of chemicals. As comparison, reference mill emits -260 Kg CO2/ADt which means that society’s net emission of CO2 is reduced as a result of pulp production. This figure is obtained due to potential to generate power from bark and surplus black liquor. Its utilization replaces power from natural gas combined cycle. Hence it is obvious if lignin utilization as bioenergy could also decrease CO2 emission (Backlund 2007).
Co-firing combustion between coal and biomass is an interesting alternative. Incineration test lignin-liquid coal in 410 MW PFBC (Pressurized Fluided Bed Combined-cycle) shows promising result. Furthermore, laboratory result shows that 10-15 percent of lignin could be readily mixed with coal paste without any handling problem (Axegård 2007). In short term, IEA noticed that co-firing biomass is still a most cost-effective way to utilize biomass (IEA, 2007).
Socio-economic aspect
Lignin extraction was initially purposed to debottleneck pulp mill capacity. Roughly, LignoBoost investment is only one-half of investment to up-grade recovery boiler. Recent study investigated several scenarios by increasing 25 percent capacity in model pulp-mill. Combined with heat integration, there is possibility whether exporting lignin 346 GWh/year or increasing electricity by 109 GWh/year with upgraded boiler. With lignin price 15€/MWh, lignin separation becomes more profitable than upgrading boiler capacity. In addition, it also concludes that electricity prices to lignin ratio should be below 1.9-2.3 to make lignin extraction becomes viable (Axelsson et al 2006).
Sweden is well known as leading country in bioenergy utilization. Biofuel contributes 116 TWh out of 624 TWh of total energy supply in Sweden year 2006. Two eminent sources of energy suppliers are still nuclear power and crude oil which altogether contributes 400 TWh. Recently, Swedish government introduces green electricity certificate in order to boost renewable electricity utilization by 17 TWh in 2016. In addition, impose tax on fossil fuel also has made biofuel becomes more competitive. Consequently, market is prepared to pay a high price (Swedish Energy Agency 2007).
Kraft pulp mill has prime potential to be biorefinery plant in future. In his article, Ben Thorp (2005) showed that new model pulp industry should develop wide range value added products through market driven innovation. Several strategies should be taken into account such as increase sustainable forestry, extract hemi cellulose, convert tall oil to biodiesel, replace recovery boiler with gasifier and usage of solid fuel gasifiers. Lignin extraction is only one small step to enter modern forest biorefinery. It is hoped that pulp mill will produce diverse chemical products and eventually could replace petro-based chemicals in future.
Conclusion
LignoBoost has introduced alternative biofuel from lignin. State of the art from this new process is laid on two washing stages. First dewatering stage is carried out in high pH (approximately 10) and second dewatering is performed on low pH (approximately 2-4). Sodium content of produced lignin is below 1 percent which is favorable if later used as fuel. Moreover, incineration test shows promising result in which lignin could replace 10-15 percent of coal.
In the case of increasing pulp mill capacity (debottleneck), it is more viable to extract lignin than invest on up-grading recovery boiler capacity. Further comparison should take into account potential of exporting lignin or exporting electricity from improved recovery boiler. It is concluded when electricity prices to lignin ratio is lower than 1.9-2.3, lignin investment becomes more interesting. According to Sweden’s experience, government plays important role to develop bioenergy by issuing pro-renewable energy policies.
Kraft pulp mill in future has prime potential to adopt biorefinery concept. The big picture is to have modern forest biorefinery plant which is able to produce wide range chemical products in future. From environmental aspect, lignin utilization will lead to reduction of CO2 emission or even further could reach negative emission. All by all, reliance on bio-based product will make us one step closer to reach sustainable society.
References
1. AXEGÅRD, P., 2007. The Kraft Pulp Mill as a Biorefinery [online]. Available from:
http://www.celuloseonline.com.br/imagembank/Docs/DocBank/Eventos/430/3AxegardOral.pdf [Accessed 15 March 2008].
2. AXELSSON, E., OLSSON, M.R. AND BERNTSSON, T., 2006. Increased capacity in kraft pulp mills: Lignin separaton and reduced steam demand compared with recovery boiler upgrade. Nordic Pulp and Paper Research Journal [online], 21(4). Available from: http://www.spci.se/html/storage/xfl_bsvamhtrqc.pdf [Accessed 15 March 2008].
3. BACKLUND, B., 2007. Towards Increased Closure and Efficiency. In: EK, M., GELLERSTEDT, G. AND HENRIKSSON, G., Ljungberg Textbook: Book 2 Pulping Chemistry and Technology. Stockholm: KTH.
4. EKBOM, T., LINDBOLM, M., BERGLIN, N. AND AHLVIK, P., 2003. Technical and Commercial Feasibility Study of Black Liquor Gasification with Methanol/DME Production as Motor Fuels for Automotive Uses-BLGMF. Stockholm: Nykom Synergetics AB.
5. IEA, 2007. Biomass for Power Generation and CHP [online]. IEA Energy Technology Essentials. Available from : http://www.iea.org/textbase/techno/essentials3.pdf [Accessed 15 March 2008].
6. LEBO Jr., S.E., GARGULAK, J.D. AND MCNALLY, T.J., 2001. Lignin. In: Kirk-Othmer Encyclopedia of Chemical Technology [online]. Wiley Interscience. Available from: http://www.mrw.interscience.wiley.com.proxy.lib.chalmers.se/emrw/9780471238966/kirk/article/lignlin.a01/current/html?hd=All,lignin [Accessed 15 March 2008].
7. MILLER Jr., G.T., 2007. Living in the Environment 15th ed. Belmont CA: Thomson Brooks/Cole.
8. SMOOK, G.A., 2002. Handbook for Pulp and Paper Technologies 3rd ed. Vancouver: Angus Wilde Publications Inc.
9. SWEDISH ENERGY AGENCY, 2007. Energy in Sweden 2007. Stockholm: SWEDISH ENERGY AGENCY.
10. THORP, B., 2005. Biorefinery offers Industry Leaders Business Model for Major Change. Pulp and Paper, Nov.
11. ÖHMAN, F., WALLMO, H. AND THELIANDER, H., 2006. An Improved Method for Washing Lignin Precipitated from Kraft Black Liquor-The key to new bio-fuel [online]. Available from:
http://www.lignoboost.com/upload/3878/Paper_Theliander_et_al_2006b.pdf
[Accessed 15 March 2008].
12. ÖLZ, S., SIMS, R. AND KIRCHNER, N., 2007. Contribution of Renewables to Energy Security [online]. IEA Information Paper. Available from: http://www.iea.org/textbase/papers/2007/so_contribution.pdf [Accessed 15 March 2008].
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