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Net energy analysis of bioethanol production system from high-yield rice plant in Japan
Applied Energy 87 (2010) 2164–2168
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Applied Energy journal homepage: www.elsevier.com/locate/apenergy
Net energy analysis of bioethanol production system from high-yield rice plant in Japan Kiyotaka Saga a, Kenji Imou b, Shinya Yokoyama b, Tomoaki Minowa a,* a b
Biomass Technology Research Center, National Institute of Advanced Industrial Science and Technology, 2-2-2 Hiro-Suehiro, Kure, Hiroshima 737-0197, Japan Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-865, Japan
a r t i c l e
i n f o
Article history: Received 18 August 2009 Received in revised form 22 December 2009 Accepted 22 December 2009 Available online 13 January 2010 Keywords: Bioethanol High-yield rice Net energy balance Net energy ratio I/O table
a b s t r a c t This study analyzes the energy balance of a bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol: one in which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which they are converted to ethanol, and byproducts such as lignin and unreacted holocellulose are used for cogeneration (scenario 2). Energy input in the agricultural process including transportation is estimated to be 52.3 GJ/ha from an Input Output Table. The heating values of produced rice and cellulose feedstocks are 120.7 GJ/ha and 162.3 GJ/ha, respectively. The net energy balance (NEB) of scenario 1 is 129.2 GJ/ha, which produces 3.6 kL/ha of ethanol and 9420 kWh/ha of external electricity. On the other hand, NEB of scenario 1 is 11.7 GJ/ha, which produces 7.1 kL/ha of ethanol. Both NEBs are positive, but NEB of scenario 2 is much higher than that of scenario 1. An acid hydrolysis technology of cellulosic biomass applied to scenario 2 needs a large amount of heat energy for sulfuric acid recovery. If an enzyme hydrolysis of cellulosic biomass is developed, there is a possibility of improving NEB of scenario 2. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The Biomass Nippon Strategy, an initiative of the Ministry of Agriculture, Forestry and Fisheries (MAFF) in cooperation with other ministries, was the first national strategy for biomass utilization. It was approved by the cabinet in 2002 and revised in 2006. In the 2006 version, biofuel were emphasized as a major product. The Biomass Nippon Strategy Promotion Council developed a roadmap entitled the Large Scale Expansion of Domestic Biofuel Production in February 2007. In the short-term until 2010, it says that ethanol production from currently available starch and waste materials can reach 50,000 kL. In the middle and long term, it seeks to resolve technical and institutional problems for bioethanol production from cellulosic biomass such as rice straw, unused timbers and energy crop. Estimated ethanol production could reach six million kL if successful [1]. From the point of view of global warming prevention, it is important whether the net GHG emission reduction for biofuel production is positive or not [2–4]. Life cycle assessment (LCA) is one method for such an evaluation, many LCA studies about biofuel production have been carried out [5–7]. The net energy ratio (NER) is also important indicator for analyzing the energy efficiency of
* Corresponding author. Address: AIST Chugoku, 2-2-2 Hiro-Suehiro, Kure, Hiroshima 737-0197, Japan. Tel./fax: +81 823 72 1953. E-mail address: [email protected] (T. Minowa). 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.12.014
biofuel production. NER is the ratio of total energy outputs to total energy inputs, and NER should be positive so that the net GHG emission reduction is positive. In Brazil, NER of sugar cane ethanol is clearly positive because of the byproduct bagasse, which is used to produce heat and power that are needed for ethanol conversion plants. It is reported that NER of sugar cane is 8.3–10.2 [8]. In USA, NERs of corn ethanol also are evaluated, and it is reported that NERs of corn ethanol are 0.71 [9] and 1.67 [10]. In Japan, uncropped agricultural land has been increasing because of decreasing population and rice consumption and increasing rice yields. The area of uncropped agricultural land in 2005 was 380,000 ha, and it is feared that this area may increase. When the uncropped agricultural land is left, it gradually becomes difficult to use the land as a productive farmland. It is effective in the maintenance of the farmland to make the bioethanol by using the uncropped agricultural, and the use of such a farmland becomes one choices from the viewpoint of the food security. This paper analyzes the energy balance of a bioethanol production system from high yielding rice plant in Japan. Two energy conversion technologies of cellulosic biomass are also considered. 2. Bioethanol production system from rice cropping Fig. 1 shows the process flow of bioethanol production system from rice cropping. The system is divided into two processes: agricultural and conversion. The agricultural process includes not only
K. Saga et al. / Applied Energy 87 (2010) 2164–2168
Ethanol Biomass conversion Rice
Agricultural production
Ethanol Conversion
Cogeneration Straw and husk
Power and heat
Power
(1) Ethanol and power production scenario
2165
the expense by its price. Next, the direct energy is calculated by multiplying consumption by energy unit per quantity (MJ/L or MJ/kWh) [12]. The direct energy, shown in Table 1, is calculated to be 13.2 GJ/ha. This study considers the energy used for fertilizer or agricultural machine production defined as the indirect energy. This energy is calculated by multiplying expense for rice production by energy unit per expense (MJ/¥). This energy unit adopts data calculated from an input output table (I/O table) and an energy balance table for Japan [13]. The I/O table segment is adjusted to the appropriate segment of the MAFF statistics data. Expense of agricultural production is categorized as follows, together with an explanation of how the adopted energy units are calculated.
Ethanol
Agricultural production
Rice Straw Husk
Ethanol Conversion
Power and heat
Cogeneration
Lignin Biomass conversion
(2) Whole rice plant ethanol production scenario Fig. 1. Process flow of bioethanol production system from rice cropping.
cultivation but also transportation. Two technologies are considered in the conversion process of rice straw and husk. Rice is converted to ethanol in both systems: one in which cellulose feedstocks, straw and husk, are used for cogeneration and surplus power is exported (scenario 1: ethanol and power production scenario), and the other in which cellulose feedstocks are converted to ethanol, and byproduct lignin is used for cogeneration (scenario 2: whole rice plant ethanol production scenario). 3. Methodology 3.1. Agricultural process 3.1.1. Agricultural production process In order to calculate energy inputs of agricultural production process, this study uses the statistical data of the expense for rice production published by the Ministry of Agriculture, Forestry, and Fisheries of Japan (MAFF) [11]. We classify the energy inputs of the agricultural production process into direct and indirect energy. Direct input energy is defined as fossil fuel and power used by agricultural machinery. On the other hand, indirect input energy is defined as fertilizer, herbicides, agricultural machinery, and so on. The direct input energy includes petroleum products and power. At first, these consumptions are calculated by dividing
Table 1 Direct input energy of agricultural production.
Diesel oil Kerosene Gasoline Motor oil Mixing oil Power
Expense [11] (¥/ha)
Consumption
Energy unit [12]
10,680 4870 8850 1770
123 L 73 L 72 L 4L
43.1 MJ/L 39.9 MJ/L 43.3 MJ/L 41.3 MJ/L
5301 2913 3118 165
1590
10 L
43.3 MJ/L
433
6250 34,010
120 kWh –
10.9 MJ/kWh –
Input energy (MJ/ha)
1308 13,238
(1) Seedling: The ‘‘Seedling” segment of the I/O table (16.45 kJ/ ¥) is adopted. (2) Fertilizer: Using the ‘‘Organic fertilizer” (35.13 kJ/¥) and ‘‘Chemical fertilizer” (104.43 kJ/¥) segments, the weighted average (84.11 kJ/¥) by expense ratio is adopted. (3) Herbicides: The ‘‘Herbicides” segment of the I/O table (16.45 kJ/¥) is adopted. (4) Other materials: Many kinds of small items are included in this category, such as vinyl sheet, polyethylene, string, soil for seedlings, and timber. Using the ‘‘Thermoplastic resin” (142.02 kJ/¥), ‘‘Organic fertilizer” (35.13 kJ/¥), and ‘‘Lumbering” (21.05 kJ/¥) segments, a weighted average (84.11 kJ/¥) by expense ratio is adopted. (5) Land improvement and water supply: Using the ‘‘Agricultural service” (45.92 kJ/¥) and ‘‘Waterworks” (32.05 kJ/¥) segments, the weighted average (43.87 kJ/¥) by expense ratio is adopted. (6) Agricultural service: This category includes such activities as cooperative herbicide application, agricultural machinery lending, and cooperative rice drying. Therefore, the ‘‘Agricultural service” segment of the I/O table (45.92 kJ/¥) is adopted. (7) Facility: This category includes the depreciation and maintenance expense of drainage, concrete borders, soil dressing and so on. Therefore the ‘‘Agricultural public works” segment of the I/O table (38.36 kJ/¥) is adopted. (8) Vehicle: The ‘‘Automobile” segment of the I/O table (39.69 kJ/¥) is adopted. (9) Agricultural machinery: The ‘‘Agricultural machinery” segment of the I/O table (44.00 kJ/¥) is adopted. (10) Production management: This category includes various items such as business supplies, personal computer, copier, fax, and telephone. Therefore, the ‘‘Information service” segment of the I/O table (12.43 kJ/¥) is adopted. Table 2 shows that the indirect energy is 34.8 GJ/ha, and the input energy for agricultural production that includes direct and indirect energy is 48.0 GJ/ha. The indirect energy is larger than the direct energy, it becomes clear that the proportion of the agricultural machinery (28%), outsourcing (18%), fertilizers (19%), and herbicides (14%) in the indirect energy is large and these segments are very sensitive. 3.1.2. Biomass yield In Japan, the average rice yield without husk is 5.3 t/ha (15 wt.% moisture) in 2006 [11]. If rice plant is cultivated as an energy crop, a high biomass yield is required. This study assumes that the highyield rice developed for feed production is used for ethanol production. The yield of high-yield rice is set to be 8.3 t/ha (15 wt.% moisture) [14]. The amounts of straw and husk are calculated by the grain: byproduct ratio (dry basis). The ratios of straw and husk are 1.2
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Table 2 Indirect input energy of agricultural production. Energy unit (kJ/¥) Seeding Fertilizer Herbicide and insecticide Other materials Land improvement and water supply Agricultural service Facility Vehicle Agricultural machinery Production management Total
Expense [11] (¥/ha)
Input energy (MJ/ha)
16.45 84.11 69.93 41.81 43.87
37,040 78,020 70,160 20,500 58,210
609 6562 4906 857 2554
45.92 38.36 39.69 44.00 12.43 –
136,550 48,450 31,400 223,850 2920 707,100
6270 1859 1246 9849 36 34,750
and 0.22, respectively [15]. The moisture content and the low heat value (LHV) of rice are 15% and 14.63 MJ/kg (wet basis) [16], and those of straw and husk are 30% and 11.41 MJ/kg (wet basis) [17]. Therefore, the produced energy of rice is 120.7 GJ/ha and that of straw and husk is 162.3 GJ/ha. 3.1.3. Collection and transportation process Annual straw production is about nine million tonnes in Japan (2005), and straw is currently used and disposed of by plowing into fields 61.5%, animal feed 11.6%, compost 10.1%, cattle house bedding 6.5%, and handicrafts 1.3% [18]. After harvesting unhulled rice, most straw is left in the paddy field. In order to use the straw as an energy resource, it must be collected and compacted for transport. A baler is usually used to compress low bulk density straw, so we assumed that a self-propelled roll baler collects and compacts left straw in the field. The energy of harvesting unhulled rice is included in agricultural production energy, but the energy of collecting straw and transporting biomass are not. Straw collection energy (0.8 GJ/ha) is calculated by multiplying the energy unit of diesel oil (43.1 MJ/L) by diesel oil consumption (17.4 L/ha) [19]. Unhulled rice and straw are transported to a biomass conversion plant by a 4-tonne truck. Biomass transportation energy (4.3 GJ/ha) is calculated from fuel consumption (5.5 km/L), average return trip distance (100 km), biomass amount (22.0 t/ha), and diesel heat value (43.1 MJ/L). Therefore collection and transportation energy is calculated to be 4.8 GJ/ha. 3.2. Conversion process 3.2.1. Ethanol conversion Table 3 shows input energy of ethanol production from rice. Because both rice and corn are starch feedstock, we used the data for input energy of corn-based ethanol production [20]. Table 3 shows
Table 3 Input energy of ethanol conversion. Consumption [9]
Energy unit [12]
Input energy (MJ/L)
Rice Electricity Steam Water Sum
0.392 kWh 4.2 kg 40 kg
10.9 MJ/kWh 2.53619 MJ/kg 0.00225 MJ/kg
4.27 10.65 0.09 15
Straw, husk Electricity Steam Water Sulfuric acid Lime Sum
0.529 kWh 6.5 kg 125 kg 94 g 36 g
10.9 MJ/kWh 2.53619 MJ/kg 0.00225 MJ/kg 0.70200 MJ/kg 7.97600 MJ/kg
5.77 16.49 0.28 0.07 0.29 22.89
input energy of ethanol production from straw and husk. Straw and husk are categorized as cellulosic biomass. To produce ethanol from cellulosic biomass, cellulose and hemicellulose must be hydrolyzed to fermentable sugar before fermentation. Lignin cannot be broken down to sugar by hydrolysis. This study assumed that holocellulose is hydrolyzed by concentrated sulfuric acid technology. The compositions of straw and husk are similar to that of switchgrass, so we adopted the input energy data of ethanol production from switchgrass [20]. Power and steam consumption of cellulosic feedstock is greater than that of starch feedstock, because a large amount of steam is used for sulfuric acid recovery. Table 3 also shows the energy consumption of water, sulfuric acid, and lime for neutralization. In both starch and cellulosic feedstocks, the proportion of the steam energy necessary for the ethanol conversion is 70% or more. In ethanol conversion process, heat energy for steam production is very sensitive. 3.2.2. Ethanol production Ethanol production is calculated from theoretical yield and process efficiency. Rice grain contains 87 wt.% of starch (dry basis) [16]. If whole starch is converted to ethanol, the theoretical ethanol yield from rice is 629 L/dry-t. Process efficiencies of hydrolysis, fermentation, and distillation are assumed to be 95%, 90%, and 95% respectively. Therefore ethanol yield from rice is 511 L/dry-t. Rice straw contains 43 wt.% of cellulose, 25 wt.% of hemicellulose, 12% of lignin, and 20% of ash (dry basis) [20]. Rice husk contains 35 wt.% of cellulose, 25 wt.% of hemicellulose, 20% of lignin, and 20% of ash (dry basis) [20]. If whole holocellulose is converted to ethanol, theoretical ethanol yields from straw and husk are 495 L/dry-t and 437 L/dry-t. Process efficiencies of hydrolysis, fermentation, and distillation are assumed to be 85%, 90%, and 95% respectively. Therefore, ethanol yield from straw and husk are 373 L/t and 328 L/t respectively. After hydrolysis and fermentation, the byproducts, such as lignin and unreacted holocellulose, is separated and can be used for power and heat generation. The amounts of lignin produced from 1 dry-t of straw and husk are 120 dry-kg and 200 dry-kg respectively. The moisture content of the byproducts is assumed to be 70 wt.% and the available energy is calculated by subtracting water latent heat (9.6 MJ/kg) from lignin heat value (26.7 MJ/kg). 3.2.3. Cogeneration Many power generation technologies involve direct combustion, gasification, Integrated Gasification Combined Cycle (IGCC), and so on. We assumed power generation by gasification. Power generation by direct combustion has been used, but the efficiency of generation is very low if more than 1 MW of power is generated. Gasification power generation plants have been developed in Japan, and they can be highly efficient on a small scale, generating from 10 to 100 kW. The temperature of waste heat by gasification is high, so the technology is suitable for cogeneration. The efficiency of power generation by cogeneration is assumed to be 30%, but as 6% electricity is used for the process itself, the overall efficiency is 24% [21]. Furthermore it is assumed that efficiency of heat recovery is 50%. 4. Results and discussion 4.1. Energy flow Fig. 2 shows the energy flows of scenarios 1 and 2. These energy flows convert input and output energy into primary energy, so input and output energy do not balance. The agricultural process, including collection and transportation, is common to both
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Water :0.3
Agricultural Production:52.3 (Including Collection and Transportation process)
Rice
Agricultural production
120.7
Ethanol:79.2
Ethanol Conversion
Power:15.3 Steam:38.2
Cogeneration Straw and husk :162.3
Power:102.6
(1) Ethanol and power production scenario Agricultural Production:52.3 (Including Collection and Transportation process)
Power:5.2 Steam:76.6 Others:2.7
Agricultural production
Ethanol:159.7
Ethanol Conversion
Power: 31.1 Steam: 21.6
Rice, Straw, Husk :283.0
Cogeneration Byproducts :42.9
(2) Whole rice plant ethanol production scenario Fig. 2. Energy flow of bioethanol production system.
scenarios. Input energy of agricultural process is 52.3 GJ/ha. In scenario 1, ethanol production is 3.6 kL (79.2 GJ)/ha. Power and steam energy for ethanol conversion is 1400 kWh (15.3 MJ)/ha and 38.2 GJ/ha, respectively, and these energies are covered by cogeneration from straw and husk. Surplus power is 9420 kWh (102.6 GJ)/ha, which can be exported to the external grid. Therefore input energy of the ethanol conversion process is 0.3 GJ/ha that is used for industrial water. For scenario 2, ethanol production is 7.1 kL (156.3 GJ) per ha. Power, and steam energy for ethanol conversion, are 3250 kWh (35.4 GJ)/ha, and 38.2 MJ/ha, respectively. Power generation by byproduct lignin gasification produces 2240 kW (24.4 GJ)/ha of power and 16.9 GJ/ha of steam energy. Therefore net input energy for ethanol conversion is 92.4 GJ/ha which is added to 1020 kWh (11.1 GJ)/ha of power, 78.8 GJ/ha of steam energy, and 2.5 GJ/ha of others.
(GJ/ha)
Net energy value Agricultural process Ethanol
Conversion process Power
200
150
100
50
0
4.2. NEB and NER Fig. 3 shows NEB of the two scenarios. NEB is defined as the value of subtracting total input energy from total output energy. Total output energy is the sum of energy of produced ethanol and surplus power, and total input energy is the sum of agricultural and biomass conversion processes. NEBs of both scenarios are positive, so it is possible to produce ethanol from high-yield rice plant in Japan in terms of energy production. NEB of scenario 1 (129.2 GJ/ ha) is greater than that of scenario 2 (11.7 GJ/ha), because scenario 2 produced twice as much ethanol as scenario 1, but a large amounts of power and steam energy are needed for ethanol conversion. Table 4 shows NER of the two scenarios and other biofuels. NER is the ratio of total energy outputs to total energy inputs which are
Output
Input
Scenario(1)
Balance
Output
Input
Balance
Scenario(2)
Fig. 3. Energy balance of bioethanol production system from rice cropping.
composed by the biomass production, transportation, and conversion processes. Byproducts treatments are different at each research, so total energy outputs are also different. These results cannot be compared by a same standard, but there are some tendencies. NER of the high-yield rice ethanol is lower than that of the sugar cane ethanol and palm oil diesel. NER of the high-yield rice ethanol (scenario 1b: surplus power is not included) is located in the fluctuation band of the corn ethanol NER. NER of the highyield rice is the same level as NER of corn ethanol.
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Table 4 NER of biofuels. Ref. No. Sugar cane ethanol [8] Scenario 1a Scenario 2b Corn ethanol Shapouri (2004) Pimentel (2005) Palm oil diesel Biodiesel and byproducts Biodiesel only
NER
Byproducts treatment
8.3 10.2
Heat value of surplus bagasse is included
[10]
1.67
[9]
0.71
References [7]
3.58 2.42
High-yield rice plant ethanol Scenario 1 This 3.46 study Scenario 1 1.51 Scenario 2 1.17 a b
Dried distiller’s grains and solubles (DDGS) is allocated with value based DDGS is not included in results
2.7 million kL of ethanol could be produced. In Japan, it is regulated that the maximum blending ratio of ethanol should be less than 3% (E3) because of safety for existing vehicles. Present gasoline consumption is about 60 million kL, and the amount of ethanol necessary for E3 is about 1.8 million kL. Therefore, uncropped land could supply enough bioethanol to substitute 3% of gasoline at current levels of consumption. There is enough potential in the bioethanol production using the uncropped land from the viewpoint of the quantity supplied.
Heat values of glycerol, palm kernel, and shell are included Not included in results Surplus power is included Surplus power is not included Lignin and unreacted holocellulose is used for process energy
Based on the average values of energy and material consumption. Based on the minimum consumption with the use of the best technology.
In scenario 2, the energy inputs of the ethanol conversion is larger than that of agricultural production. This study assumed that straw and husk are hydrolyzed by concentrated sulfuric acid technology. Hydrolysis technology for cellulosic biomass is mainly categorized by using the acid and enzyme. Acid hydrolysis technology uses a large amount of energy for sulfuric acid recovery. It is reported that there is a possibility to reduce energy inputs for cellulosic ethanol conversion by enzyme hydrolysis [22]. It will be necessary to evaluate NEB and NER in consideration of the conversion pathway of the cellulosic ethanol production in the future. 5. Conclusion It is a precondition that NEB and NER of bioehtanol production is positive. This study analyzes NEB and NER of bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol; one which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which straw and husk are converted to ethanol, and byproduct lignin is used for cogeneration (scenario 2). NEB of scenario 1 is 129.0 GJ/ha, which produces 3.6 kL/ha of ethanol and 9420 kWh/ha of external electricity. NEB of scenario 2 is 11.7 GJ/ha, which produces 7.1 kL/ha of ethanol. Both energy balances are positive, but the energy balance of scenario 1 is much higher than that of scenario 2. NER of scenarios 1 and 2 are 3.46 and 1.17, respectively. NER of scenario 1 without surplus power is 1.51, this value indicates that NER of the high-yield rice is the same level as NER of corn ethanol in USA. Energy balance is a first step in evaluating biofuel production process, and the environmental and economic impacts should be further studied for an overall assessment. Scenario 2 can produce 7.1 kL/ha of bioethanol. In 2006, uncropped land in Japan totaled 380,000 ha, from which about
[1] Matsumoto N, Sano D, Elder M. Biofuel initiatives in Japan: strategies, policies, and future potential. Appl Energy 2009;86:S69–76. [2] Borjesson P. Good or bad bioethanol from a greenhouse gas perspective – What determines this? Appl Energy 2009;86:589–94. [3] Yan J. Biofuels in Asia. Appl Energy 2009;86:S1–10. [4] Prabhakar SVRK, Elder M. Biofuels and resource use efficiency in developing Asia: back to basics. Appl Energy 2009;86:S30–6. [5] Yee KF, Tan KT, Abdullah AZ, Lee KT. Life cycle assessment of palm biodiesel: revealing facts and benefits for sustainability. Appl Energy 2009;86:S189–96. [6] Ou XM, Zhang XL, Chang SY, Guo QF. Energy consumption and GHG emissions of six biofuel pathways by LCA in (the) People’s Republic of China. Appl Energy 2009;86:S197–208. [7] Pleanjai S, Gheewala SH. Full chain energy analysis of biodiesel production from palm oil in Thailand. Appl Energy 2009;86:S209–14. [8] Macedo I, Lima MR, Leal V, Azevedo Ramos da Silva JE. Assessment of greenhouse gas emissions in the production and use of fuel ethanol in Brazil. São Paulo (Brazil): Government of the State of São Paulo; 2004. [9] Pimentel D, Patzek T. Ethanol production using corn, switchgrass, and wood; biodiesel production using soybean and sunflower. Nat Resour Res 2005;141:65–76. [10] Shapouri H. The 2001 net energy balance of corn-ethanol. Washington (DC, United States): Department of Agriculture; 2004. [11] Ministry of Agricultural, Forestry, and Fisheries of Japan (MAFF), Rice production cost; 2006 [in Japanese]. [12] Japan Environmental Management for Industry. Environmental load data for 4000 social stock. Introduction of LCA practice; 1999 [in Japanese]. [13] National Institute for Environmental Studies. Center for global environmental research, embodied energy and emission intensity data for Japan using inputoutput tables (3EID); 2000. [14] Yoshida S, Nagata K, Fukuda A. Characteristics of seedling emergence and dry matter production of direct-seeded rice cultivars for whole-crop silage in Tohoku region. Bull Natl Agric Res Center Tohoku Region 2006;105:63–71 [in Japanese]. [15] Ogawa K, Takeuchi Y, Katayama M. Biomass production and amounts of absorbed inorganic elements by crops in arable lands in Hokkaido, and its evaluation. Res Bull Hokkaido Natl Agric Exp Station 1988;149:57–91 [in Japanese]. [16] Ministry of Education, Culture, Sports, Science and Technology (MEXT). Standard tables of food composition in Japan fifth revised and enlarged edition; 2005 [in Japanese]. [17] The Japan Institute of Energy. Biomass handbook. Ohmsha; 2005 [in Japanese]. [18] Ministry of Agricultural, Forestry, and Fisheries of Japan (MAFF). Documents related to feed crop; 2006 [in Japanese]. [19] Saga K, Imou K, Yokoyama S, Fujimoto S, Yanagida T, Minowa T. Study on rice straw collection system for bioethanol production. Energy Resour 2008;29(6):371 [in Japanese]. [20] National Agricultural Research Organization. Standard tables of feed composition in Japan (2001). Japan Livestock Industry Association; 2002 [in Japanese]. [21] Yakushidou K, Sakai M. A high efficiency co-generation system adopted new gasification technology of vegetable biomass. Res J Food Agr 2005;28-3:20–3 [in Japanese]. [22] Saga K, Fujimoto S, Yanagida T, Tada C, Bespyatko L, Elmer B, Minowa T. Comparative evaluation of ethanol production process from cellulosic biomass with different pretreatment and saccharification method. Energy Resour 2009;30(2):133 [in Japanese].
Contents lists available at ScienceDirect
Applied Energy journal homepage: www.elsevier.com/locate/apenergy
Net energy analysis of bioethanol production system from high-yield rice plant in Japan Kiyotaka Saga a, Kenji Imou b, Shinya Yokoyama b, Tomoaki Minowa a,* a b
Biomass Technology Research Center, National Institute of Advanced Industrial Science and Technology, 2-2-2 Hiro-Suehiro, Kure, Hiroshima 737-0197, Japan Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-865, Japan
a r t i c l e
i n f o
Article history: Received 18 August 2009 Received in revised form 22 December 2009 Accepted 22 December 2009 Available online 13 January 2010 Keywords: Bioethanol High-yield rice Net energy balance Net energy ratio I/O table
a b s t r a c t This study analyzes the energy balance of a bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol: one in which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which they are converted to ethanol, and byproducts such as lignin and unreacted holocellulose are used for cogeneration (scenario 2). Energy input in the agricultural process including transportation is estimated to be 52.3 GJ/ha from an Input Output Table. The heating values of produced rice and cellulose feedstocks are 120.7 GJ/ha and 162.3 GJ/ha, respectively. The net energy balance (NEB) of scenario 1 is 129.2 GJ/ha, which produces 3.6 kL/ha of ethanol and 9420 kWh/ha of external electricity. On the other hand, NEB of scenario 1 is 11.7 GJ/ha, which produces 7.1 kL/ha of ethanol. Both NEBs are positive, but NEB of scenario 2 is much higher than that of scenario 1. An acid hydrolysis technology of cellulosic biomass applied to scenario 2 needs a large amount of heat energy for sulfuric acid recovery. If an enzyme hydrolysis of cellulosic biomass is developed, there is a possibility of improving NEB of scenario 2. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The Biomass Nippon Strategy, an initiative of the Ministry of Agriculture, Forestry and Fisheries (MAFF) in cooperation with other ministries, was the first national strategy for biomass utilization. It was approved by the cabinet in 2002 and revised in 2006. In the 2006 version, biofuel were emphasized as a major product. The Biomass Nippon Strategy Promotion Council developed a roadmap entitled the Large Scale Expansion of Domestic Biofuel Production in February 2007. In the short-term until 2010, it says that ethanol production from currently available starch and waste materials can reach 50,000 kL. In the middle and long term, it seeks to resolve technical and institutional problems for bioethanol production from cellulosic biomass such as rice straw, unused timbers and energy crop. Estimated ethanol production could reach six million kL if successful [1]. From the point of view of global warming prevention, it is important whether the net GHG emission reduction for biofuel production is positive or not [2–4]. Life cycle assessment (LCA) is one method for such an evaluation, many LCA studies about biofuel production have been carried out [5–7]. The net energy ratio (NER) is also important indicator for analyzing the energy efficiency of
* Corresponding author. Address: AIST Chugoku, 2-2-2 Hiro-Suehiro, Kure, Hiroshima 737-0197, Japan. Tel./fax: +81 823 72 1953. E-mail address: [email protected] (T. Minowa). 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.12.014
biofuel production. NER is the ratio of total energy outputs to total energy inputs, and NER should be positive so that the net GHG emission reduction is positive. In Brazil, NER of sugar cane ethanol is clearly positive because of the byproduct bagasse, which is used to produce heat and power that are needed for ethanol conversion plants. It is reported that NER of sugar cane is 8.3–10.2 [8]. In USA, NERs of corn ethanol also are evaluated, and it is reported that NERs of corn ethanol are 0.71 [9] and 1.67 [10]. In Japan, uncropped agricultural land has been increasing because of decreasing population and rice consumption and increasing rice yields. The area of uncropped agricultural land in 2005 was 380,000 ha, and it is feared that this area may increase. When the uncropped agricultural land is left, it gradually becomes difficult to use the land as a productive farmland. It is effective in the maintenance of the farmland to make the bioethanol by using the uncropped agricultural, and the use of such a farmland becomes one choices from the viewpoint of the food security. This paper analyzes the energy balance of a bioethanol production system from high yielding rice plant in Japan. Two energy conversion technologies of cellulosic biomass are also considered. 2. Bioethanol production system from rice cropping Fig. 1 shows the process flow of bioethanol production system from rice cropping. The system is divided into two processes: agricultural and conversion. The agricultural process includes not only
K. Saga et al. / Applied Energy 87 (2010) 2164–2168
Ethanol Biomass conversion Rice
Agricultural production
Ethanol Conversion
Cogeneration Straw and husk
Power and heat
Power
(1) Ethanol and power production scenario
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the expense by its price. Next, the direct energy is calculated by multiplying consumption by energy unit per quantity (MJ/L or MJ/kWh) [12]. The direct energy, shown in Table 1, is calculated to be 13.2 GJ/ha. This study considers the energy used for fertilizer or agricultural machine production defined as the indirect energy. This energy is calculated by multiplying expense for rice production by energy unit per expense (MJ/¥). This energy unit adopts data calculated from an input output table (I/O table) and an energy balance table for Japan [13]. The I/O table segment is adjusted to the appropriate segment of the MAFF statistics data. Expense of agricultural production is categorized as follows, together with an explanation of how the adopted energy units are calculated.
Ethanol
Agricultural production
Rice Straw Husk
Ethanol Conversion
Power and heat
Cogeneration
Lignin Biomass conversion
(2) Whole rice plant ethanol production scenario Fig. 1. Process flow of bioethanol production system from rice cropping.
cultivation but also transportation. Two technologies are considered in the conversion process of rice straw and husk. Rice is converted to ethanol in both systems: one in which cellulose feedstocks, straw and husk, are used for cogeneration and surplus power is exported (scenario 1: ethanol and power production scenario), and the other in which cellulose feedstocks are converted to ethanol, and byproduct lignin is used for cogeneration (scenario 2: whole rice plant ethanol production scenario). 3. Methodology 3.1. Agricultural process 3.1.1. Agricultural production process In order to calculate energy inputs of agricultural production process, this study uses the statistical data of the expense for rice production published by the Ministry of Agriculture, Forestry, and Fisheries of Japan (MAFF) [11]. We classify the energy inputs of the agricultural production process into direct and indirect energy. Direct input energy is defined as fossil fuel and power used by agricultural machinery. On the other hand, indirect input energy is defined as fertilizer, herbicides, agricultural machinery, and so on. The direct input energy includes petroleum products and power. At first, these consumptions are calculated by dividing
Table 1 Direct input energy of agricultural production.
Diesel oil Kerosene Gasoline Motor oil Mixing oil Power
Expense [11] (¥/ha)
Consumption
Energy unit [12]
10,680 4870 8850 1770
123 L 73 L 72 L 4L
43.1 MJ/L 39.9 MJ/L 43.3 MJ/L 41.3 MJ/L
5301 2913 3118 165
1590
10 L
43.3 MJ/L
433
6250 34,010
120 kWh –
10.9 MJ/kWh –
Input energy (MJ/ha)
1308 13,238
(1) Seedling: The ‘‘Seedling” segment of the I/O table (16.45 kJ/ ¥) is adopted. (2) Fertilizer: Using the ‘‘Organic fertilizer” (35.13 kJ/¥) and ‘‘Chemical fertilizer” (104.43 kJ/¥) segments, the weighted average (84.11 kJ/¥) by expense ratio is adopted. (3) Herbicides: The ‘‘Herbicides” segment of the I/O table (16.45 kJ/¥) is adopted. (4) Other materials: Many kinds of small items are included in this category, such as vinyl sheet, polyethylene, string, soil for seedlings, and timber. Using the ‘‘Thermoplastic resin” (142.02 kJ/¥), ‘‘Organic fertilizer” (35.13 kJ/¥), and ‘‘Lumbering” (21.05 kJ/¥) segments, a weighted average (84.11 kJ/¥) by expense ratio is adopted. (5) Land improvement and water supply: Using the ‘‘Agricultural service” (45.92 kJ/¥) and ‘‘Waterworks” (32.05 kJ/¥) segments, the weighted average (43.87 kJ/¥) by expense ratio is adopted. (6) Agricultural service: This category includes such activities as cooperative herbicide application, agricultural machinery lending, and cooperative rice drying. Therefore, the ‘‘Agricultural service” segment of the I/O table (45.92 kJ/¥) is adopted. (7) Facility: This category includes the depreciation and maintenance expense of drainage, concrete borders, soil dressing and so on. Therefore the ‘‘Agricultural public works” segment of the I/O table (38.36 kJ/¥) is adopted. (8) Vehicle: The ‘‘Automobile” segment of the I/O table (39.69 kJ/¥) is adopted. (9) Agricultural machinery: The ‘‘Agricultural machinery” segment of the I/O table (44.00 kJ/¥) is adopted. (10) Production management: This category includes various items such as business supplies, personal computer, copier, fax, and telephone. Therefore, the ‘‘Information service” segment of the I/O table (12.43 kJ/¥) is adopted. Table 2 shows that the indirect energy is 34.8 GJ/ha, and the input energy for agricultural production that includes direct and indirect energy is 48.0 GJ/ha. The indirect energy is larger than the direct energy, it becomes clear that the proportion of the agricultural machinery (28%), outsourcing (18%), fertilizers (19%), and herbicides (14%) in the indirect energy is large and these segments are very sensitive. 3.1.2. Biomass yield In Japan, the average rice yield without husk is 5.3 t/ha (15 wt.% moisture) in 2006 [11]. If rice plant is cultivated as an energy crop, a high biomass yield is required. This study assumes that the highyield rice developed for feed production is used for ethanol production. The yield of high-yield rice is set to be 8.3 t/ha (15 wt.% moisture) [14]. The amounts of straw and husk are calculated by the grain: byproduct ratio (dry basis). The ratios of straw and husk are 1.2
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Table 2 Indirect input energy of agricultural production. Energy unit (kJ/¥) Seeding Fertilizer Herbicide and insecticide Other materials Land improvement and water supply Agricultural service Facility Vehicle Agricultural machinery Production management Total
Expense [11] (¥/ha)
Input energy (MJ/ha)
16.45 84.11 69.93 41.81 43.87
37,040 78,020 70,160 20,500 58,210
609 6562 4906 857 2554
45.92 38.36 39.69 44.00 12.43 –
136,550 48,450 31,400 223,850 2920 707,100
6270 1859 1246 9849 36 34,750
and 0.22, respectively [15]. The moisture content and the low heat value (LHV) of rice are 15% and 14.63 MJ/kg (wet basis) [16], and those of straw and husk are 30% and 11.41 MJ/kg (wet basis) [17]. Therefore, the produced energy of rice is 120.7 GJ/ha and that of straw and husk is 162.3 GJ/ha. 3.1.3. Collection and transportation process Annual straw production is about nine million tonnes in Japan (2005), and straw is currently used and disposed of by plowing into fields 61.5%, animal feed 11.6%, compost 10.1%, cattle house bedding 6.5%, and handicrafts 1.3% [18]. After harvesting unhulled rice, most straw is left in the paddy field. In order to use the straw as an energy resource, it must be collected and compacted for transport. A baler is usually used to compress low bulk density straw, so we assumed that a self-propelled roll baler collects and compacts left straw in the field. The energy of harvesting unhulled rice is included in agricultural production energy, but the energy of collecting straw and transporting biomass are not. Straw collection energy (0.8 GJ/ha) is calculated by multiplying the energy unit of diesel oil (43.1 MJ/L) by diesel oil consumption (17.4 L/ha) [19]. Unhulled rice and straw are transported to a biomass conversion plant by a 4-tonne truck. Biomass transportation energy (4.3 GJ/ha) is calculated from fuel consumption (5.5 km/L), average return trip distance (100 km), biomass amount (22.0 t/ha), and diesel heat value (43.1 MJ/L). Therefore collection and transportation energy is calculated to be 4.8 GJ/ha. 3.2. Conversion process 3.2.1. Ethanol conversion Table 3 shows input energy of ethanol production from rice. Because both rice and corn are starch feedstock, we used the data for input energy of corn-based ethanol production [20]. Table 3 shows
Table 3 Input energy of ethanol conversion. Consumption [9]
Energy unit [12]
Input energy (MJ/L)
Rice Electricity Steam Water Sum
0.392 kWh 4.2 kg 40 kg
10.9 MJ/kWh 2.53619 MJ/kg 0.00225 MJ/kg
4.27 10.65 0.09 15
Straw, husk Electricity Steam Water Sulfuric acid Lime Sum
0.529 kWh 6.5 kg 125 kg 94 g 36 g
10.9 MJ/kWh 2.53619 MJ/kg 0.00225 MJ/kg 0.70200 MJ/kg 7.97600 MJ/kg
5.77 16.49 0.28 0.07 0.29 22.89
input energy of ethanol production from straw and husk. Straw and husk are categorized as cellulosic biomass. To produce ethanol from cellulosic biomass, cellulose and hemicellulose must be hydrolyzed to fermentable sugar before fermentation. Lignin cannot be broken down to sugar by hydrolysis. This study assumed that holocellulose is hydrolyzed by concentrated sulfuric acid technology. The compositions of straw and husk are similar to that of switchgrass, so we adopted the input energy data of ethanol production from switchgrass [20]. Power and steam consumption of cellulosic feedstock is greater than that of starch feedstock, because a large amount of steam is used for sulfuric acid recovery. Table 3 also shows the energy consumption of water, sulfuric acid, and lime for neutralization. In both starch and cellulosic feedstocks, the proportion of the steam energy necessary for the ethanol conversion is 70% or more. In ethanol conversion process, heat energy for steam production is very sensitive. 3.2.2. Ethanol production Ethanol production is calculated from theoretical yield and process efficiency. Rice grain contains 87 wt.% of starch (dry basis) [16]. If whole starch is converted to ethanol, the theoretical ethanol yield from rice is 629 L/dry-t. Process efficiencies of hydrolysis, fermentation, and distillation are assumed to be 95%, 90%, and 95% respectively. Therefore ethanol yield from rice is 511 L/dry-t. Rice straw contains 43 wt.% of cellulose, 25 wt.% of hemicellulose, 12% of lignin, and 20% of ash (dry basis) [20]. Rice husk contains 35 wt.% of cellulose, 25 wt.% of hemicellulose, 20% of lignin, and 20% of ash (dry basis) [20]. If whole holocellulose is converted to ethanol, theoretical ethanol yields from straw and husk are 495 L/dry-t and 437 L/dry-t. Process efficiencies of hydrolysis, fermentation, and distillation are assumed to be 85%, 90%, and 95% respectively. Therefore, ethanol yield from straw and husk are 373 L/t and 328 L/t respectively. After hydrolysis and fermentation, the byproducts, such as lignin and unreacted holocellulose, is separated and can be used for power and heat generation. The amounts of lignin produced from 1 dry-t of straw and husk are 120 dry-kg and 200 dry-kg respectively. The moisture content of the byproducts is assumed to be 70 wt.% and the available energy is calculated by subtracting water latent heat (9.6 MJ/kg) from lignin heat value (26.7 MJ/kg). 3.2.3. Cogeneration Many power generation technologies involve direct combustion, gasification, Integrated Gasification Combined Cycle (IGCC), and so on. We assumed power generation by gasification. Power generation by direct combustion has been used, but the efficiency of generation is very low if more than 1 MW of power is generated. Gasification power generation plants have been developed in Japan, and they can be highly efficient on a small scale, generating from 10 to 100 kW. The temperature of waste heat by gasification is high, so the technology is suitable for cogeneration. The efficiency of power generation by cogeneration is assumed to be 30%, but as 6% electricity is used for the process itself, the overall efficiency is 24% [21]. Furthermore it is assumed that efficiency of heat recovery is 50%. 4. Results and discussion 4.1. Energy flow Fig. 2 shows the energy flows of scenarios 1 and 2. These energy flows convert input and output energy into primary energy, so input and output energy do not balance. The agricultural process, including collection and transportation, is common to both
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Water :0.3
Agricultural Production:52.3 (Including Collection and Transportation process)
Rice
Agricultural production
120.7
Ethanol:79.2
Ethanol Conversion
Power:15.3 Steam:38.2
Cogeneration Straw and husk :162.3
Power:102.6
(1) Ethanol and power production scenario Agricultural Production:52.3 (Including Collection and Transportation process)
Power:5.2 Steam:76.6 Others:2.7
Agricultural production
Ethanol:159.7
Ethanol Conversion
Power: 31.1 Steam: 21.6
Rice, Straw, Husk :283.0
Cogeneration Byproducts :42.9
(2) Whole rice plant ethanol production scenario Fig. 2. Energy flow of bioethanol production system.
scenarios. Input energy of agricultural process is 52.3 GJ/ha. In scenario 1, ethanol production is 3.6 kL (79.2 GJ)/ha. Power and steam energy for ethanol conversion is 1400 kWh (15.3 MJ)/ha and 38.2 GJ/ha, respectively, and these energies are covered by cogeneration from straw and husk. Surplus power is 9420 kWh (102.6 GJ)/ha, which can be exported to the external grid. Therefore input energy of the ethanol conversion process is 0.3 GJ/ha that is used for industrial water. For scenario 2, ethanol production is 7.1 kL (156.3 GJ) per ha. Power, and steam energy for ethanol conversion, are 3250 kWh (35.4 GJ)/ha, and 38.2 MJ/ha, respectively. Power generation by byproduct lignin gasification produces 2240 kW (24.4 GJ)/ha of power and 16.9 GJ/ha of steam energy. Therefore net input energy for ethanol conversion is 92.4 GJ/ha which is added to 1020 kWh (11.1 GJ)/ha of power, 78.8 GJ/ha of steam energy, and 2.5 GJ/ha of others.
(GJ/ha)
Net energy value Agricultural process Ethanol
Conversion process Power
200
150
100
50
0
4.2. NEB and NER Fig. 3 shows NEB of the two scenarios. NEB is defined as the value of subtracting total input energy from total output energy. Total output energy is the sum of energy of produced ethanol and surplus power, and total input energy is the sum of agricultural and biomass conversion processes. NEBs of both scenarios are positive, so it is possible to produce ethanol from high-yield rice plant in Japan in terms of energy production. NEB of scenario 1 (129.2 GJ/ ha) is greater than that of scenario 2 (11.7 GJ/ha), because scenario 2 produced twice as much ethanol as scenario 1, but a large amounts of power and steam energy are needed for ethanol conversion. Table 4 shows NER of the two scenarios and other biofuels. NER is the ratio of total energy outputs to total energy inputs which are
Output
Input
Scenario(1)
Balance
Output
Input
Balance
Scenario(2)
Fig. 3. Energy balance of bioethanol production system from rice cropping.
composed by the biomass production, transportation, and conversion processes. Byproducts treatments are different at each research, so total energy outputs are also different. These results cannot be compared by a same standard, but there are some tendencies. NER of the high-yield rice ethanol is lower than that of the sugar cane ethanol and palm oil diesel. NER of the high-yield rice ethanol (scenario 1b: surplus power is not included) is located in the fluctuation band of the corn ethanol NER. NER of the highyield rice is the same level as NER of corn ethanol.
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Table 4 NER of biofuels. Ref. No. Sugar cane ethanol [8] Scenario 1a Scenario 2b Corn ethanol Shapouri (2004) Pimentel (2005) Palm oil diesel Biodiesel and byproducts Biodiesel only
NER
Byproducts treatment
8.3 10.2
Heat value of surplus bagasse is included
[10]
1.67
[9]
0.71
References [7]
3.58 2.42
High-yield rice plant ethanol Scenario 1 This 3.46 study Scenario 1 1.51 Scenario 2 1.17 a b
Dried distiller’s grains and solubles (DDGS) is allocated with value based DDGS is not included in results
2.7 million kL of ethanol could be produced. In Japan, it is regulated that the maximum blending ratio of ethanol should be less than 3% (E3) because of safety for existing vehicles. Present gasoline consumption is about 60 million kL, and the amount of ethanol necessary for E3 is about 1.8 million kL. Therefore, uncropped land could supply enough bioethanol to substitute 3% of gasoline at current levels of consumption. There is enough potential in the bioethanol production using the uncropped land from the viewpoint of the quantity supplied.
Heat values of glycerol, palm kernel, and shell are included Not included in results Surplus power is included Surplus power is not included Lignin and unreacted holocellulose is used for process energy
Based on the average values of energy and material consumption. Based on the minimum consumption with the use of the best technology.
In scenario 2, the energy inputs of the ethanol conversion is larger than that of agricultural production. This study assumed that straw and husk are hydrolyzed by concentrated sulfuric acid technology. Hydrolysis technology for cellulosic biomass is mainly categorized by using the acid and enzyme. Acid hydrolysis technology uses a large amount of energy for sulfuric acid recovery. It is reported that there is a possibility to reduce energy inputs for cellulosic ethanol conversion by enzyme hydrolysis [22]. It will be necessary to evaluate NEB and NER in consideration of the conversion pathway of the cellulosic ethanol production in the future. 5. Conclusion It is a precondition that NEB and NER of bioehtanol production is positive. This study analyzes NEB and NER of bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol; one which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which straw and husk are converted to ethanol, and byproduct lignin is used for cogeneration (scenario 2). NEB of scenario 1 is 129.0 GJ/ha, which produces 3.6 kL/ha of ethanol and 9420 kWh/ha of external electricity. NEB of scenario 2 is 11.7 GJ/ha, which produces 7.1 kL/ha of ethanol. Both energy balances are positive, but the energy balance of scenario 1 is much higher than that of scenario 2. NER of scenarios 1 and 2 are 3.46 and 1.17, respectively. NER of scenario 1 without surplus power is 1.51, this value indicates that NER of the high-yield rice is the same level as NER of corn ethanol in USA. Energy balance is a first step in evaluating biofuel production process, and the environmental and economic impacts should be further studied for an overall assessment. Scenario 2 can produce 7.1 kL/ha of bioethanol. In 2006, uncropped land in Japan totaled 380,000 ha, from which about
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