- Email: [email protected]
Ethanol from corn
21st European Symposium on Computer Aided Process Engineering – ESCAPE 21 E.N. Pistikopoulos, M.C. Georgiadis and A.C. Kokossis (Editors) © 2011 Elsevier B.V. All rights reserved.
Ethanol from corn: screening options and power supply improvement to ethanol plant in Italy Marco Soldà,a Franjo Cecelja,a Aidong Yang,a Piyalap Manakita a
PRISE Centre for Process and Information System Engineering University of Surrey, Guildford, UK
Abstract Bioethanol is currently the most important biofuel for automotive transportation and the European Community has set common objectives about the utilization of biofuels for all member states. The current Italian production of bioethanol is not sufficient to achieve these goals. In this work the existing processes for ethanol production from corn and for energy generation from corn stover are analyzed with an exhaustive simulation approach. They are supplemented by local (internal) energy generation used to supply heat and/or electrical power to minimize the energy consumption from fossil sources. Different scenarios are analyzed to determine better, if not the best, way of production bioethanol from corn while minimizing the energy consumption from fossil sources. An economic and profitability analysis for every scenario is also provided. Keywords: Ethanol from corn; corn stover; economic analysis.
1. Introduction In 2009 alone, about 19.5 billion gallons of ethanol (73.9 billion liters) was produced worldwide. It is evident that the United States are the biggest world producer, while Brazil is a close second. At the same time, the European Community produced only 1.04 billion gallons (3.9 billion liters) with likely increase in years to come (RFA – 2010). Given the importance of bioethanol as a renewable fuel, the European Community has recently set common objectives for all member states regarding the utilization of bioethanol in the automotive sector. The first directive 2003/30/EC, which has already been implemented in the Italian law, is followed by the 2009/28/EC for which the deadline for the transposition in the member state’s law is December 5th 2010. The first directive requires all the member states to reach the utilization of 2% of bioethanol in 2005 and 5.75% in 2010, while the second directive raises the percentage of bioethanol to 10% by the end of 2020 (data taken from http://europa.eu/). In Italy, the favorite feedstock is corn because of very high yields that can be obtained, especially in the northern Italy: 10÷14 tonnes/ha. However, the Italian production of ethanol as a biofuel has just started with modest 72 million liters in 2009. To reach imposed objectives, the need for new plants for ethanol production is obvious. The technology definitely matures and relative to the first generation of biofuels are already in use. In reflection, this work will focus on this type of processes with the main objectives to demonstrate that by using corn stover it is possible to significantly reduce the energy intake from fossil sources. It was also hopped that it will be possible to define the configuration that ensures the largest profitability. The processes for ethanol production taken into account in this work are traditional dry milling (TDM) (Drapcho et. al. – 2008; Bothast and Schlicher – 2004; Perkis et. al. – 2007), dry milling with recycle of distillers’ grains (DMR) (Kim et. al. – 2007; Perkis et. al. – 2007) and quick germ – quick fiber (QG-QF) (Luis F. Rodrigues et. al. – 2010) while those for energy
M. Soldà et. al.
1664
generation from corn stover are combustion for process heat generation (PH) (S. Sokhansanj et. al. – 2009; S. Mani et. al. - 2009), combined heat and electricity generation (CHP) (Sokhansanj et. al. – 2009; S. Mani et. al. - 2009) and gasification (GAS) (Ajay Kumar et. al. – 2010).
2. Methodology The exhaustive simulation approach was found the best suited to build two stage configurations with one simplified model built for every single process for ethanol production and for energy generation. Combining them together, all possible scenarios are easy to set for each configuration. In the considered models, a process is represented as a block with a few streams: main input material, main output material, energy and auxiliary material requirements, as well as energy, environmental emission and byproduct outputs, as shown in Figure 1. For example, every ethanol process has been represented with its main input (corn), the main output (ethanol), energy requirements in the form of electricity or steam together with useful by-products and environmental effects (emissions). Only DDGS for the TDM and the DMR and four for QG-QF (DDGS, protein, bran and oil) are considered as useful byproducts. The environmental effects (emissions) are represented as kilograms of carbon dioxide emitted per litre of ethanol produced. The last facet shown in the models is the energy required in the form of electricity and/or heat. The heat required is steam at about 0.4 MPa and 110°C for all the ethanol processes. For all the energy generation processes, the main input is corn stover, the outputs are electricity and/or heat generated, while the main by-product is ash. As for the ethanol processes, the environmental effects are shown as kilograms of carbon dioxide emitted, but this time it is per tonne of stover processed. The thermal and/or electrical energy requests expressed per tonne of stover processed are also reported.
Figure 1: Simplified model example
The 75 million liters per year production volume was set for all the configurations, with all other data scaled respectively: amount of corn and soil required, corn stover available, electrical and thermal energy required by the ethanol and the stover plant, amount of thermal and/or electrical energy generated from corn stover, amount of byproducts, as well as environmental emissions. The amount of corn needed to produce 75 million liters of ethanol has been determined on the base of the ethanol yield characteristic of each process. Required soil has been calculated considering a corn yield of 12 ton/ha and the corn stover production on the base of one tonne of stover above ground per tonne of corn harvested. However, the corn stover that can be sustainably collected is about 30÷35% of the global stover production (Kiran and McMillan – 2002). With the labour costs deliberately omitted, the costs taken into account include corn, corn stover, electricity, natural gas etc. and are summarized in Table 1 with the most recent prices.
Ethanol from cor: analysis of using corn stover to supplyr to ethanol plant
1665
Table 1: Prices reflecting the first four months of 2010
Item Corn [$/bu] Corn stover [$/ton] Electricity [$/kWh] Natural gas [$/m3] Ethanol [$/gal] DDGS [$/ton] Bran [$/ton] Protein [$/ton] Oil [$/ton] Selling electricity [$/ton] Ash disposal cost [$/ton]
Price 3.42 19.6 0.176 0.43 1.63 105.6 92.02 400 893 0.098 22
Reference USDA market news Sokhansanj et. al. – 2002 Autorità per l’energia elettrica e il gas Eurostat USDA market news USDA market news USDA market news Dickey et. al. – 2010 USDA – Oil crops outlook 2010 Autorità per l’energia elettrica e il gas Mani et. al. – 2009
The plant costs have been calculated by updating and rescaling the plant costs available from literature to the first quarter of 2010 using the Marshal and Swift cost index and then rescaled using as equipment cost attribute for the ethanol plant and the energy generation plant, respectively, ethanol production and amount of corn stover processed. The profitability analysis has been provided on the basis of 20 years plant life and a construction period of 2 years. A straight line depreciation method of 10 years with an interest rate of 5% was considered. The working capital and the savage value have been respectively calculated as the 15% and the 3% of the capital investment, respectively (Douglas – 2008). Then, three profitability parameters were calculated: discounted payback period (PBP), discounted cumulative cash position (NPV) and discounted cash flow rate of return (IRR) with limits: the PBP must be below 20 year, the NPV must be greater than zero and the IRR should be above 10% to consider the process profitable. Because of high variation of some prices over last few years, it has been decided to study the profitability trend over time. As a result, we consider process profitable only if it showed acceptable economic results for the whole of selected period.
3. Results and discussion As described above, each ethanol process/plant was supplied by energy generated from corn stover. In most cases required energy was higher; the difference was provided from natural gas to generate steam and/or from the electricity grid to balance electrical energy. In other cases, it has been necessary to reduce the amount of stover processed or sell the excess electricity in the market. As an illustration, in the gasification process, the product gas is fed to a CHP generation system which is optimized for electricity generation using both gas and steam turbine. Then the heat produced is considered as a sort of by-product. In fact, it is only hot water that cannot be used to supply heat to the ethanol plant. So, it has been chosen to produce the right amount of electricity reducing the amount of corn stover processed. In this way, it is also possible to hold down the plant costs that, for the gasification, are significantly higher than the others. In the same way, it has been reduced the amount of corn stover processed in the PH and CHP processes. The engineering analysis for all the configurations is given in Table 2. As evident from Table 2, the required soil, which depends on type of ethanol process, is the lovest for configuration 2, 5 and 8: DMR is the process with the highest yild while QGQF is with the lovest. For electrical energy requirements better configurations are those with a gasification process because they have a null value of this parameter, with
M. Soldà et. al.
1666
configuration 4 and 6 even providing suffice amount. Also, there are three configurations, 1, 3 and 6 which do not require any thermal energy input, as opposed to gasification process with very high thermal requirements. Finally, the CO2 emission is comparatevly similar for all configurations: here the CO2 emission only include amount directly generated by the process. Table 2: Simplified models analysis
Conf. No.
Configuration
1 2 3 4 5 6 7 8 9
TDM + PH DMR + PH QG-QF + PH TDM + CHP DMR + CHP QG-QF + CHP TDM + GAS DMR + GAS QG-QF + GAS
Req. soil [ha] 14951 12335 15593 14951 12335 15593 14951 12335 15593
Stover available [ton]* 62795 (91.3%) 51807 (100%) 65490 (69.7%) 62795 (100%) 51807 (100%) 65490 (79%) 62795 (14.9%) 51807 (22.2%) 65790 (15.8%)
Elec. required [kWh/l] 0.36 0.42 0.37 0.03 -
Heat required [kWh/l] 0.6 0.09 0.86 2.86 3.25 2.34
CO2 emission [kg/l] 0.87 0.82 0.85 0.90 0.82 0.86 0.84 0.82 0.85
*The number given in brackets is the percentage of available corn stover that has been used.
The results of profitability analysis are summarized in Table 3. As evident, there is a significant variability in the capital investment ranging from 70 to 92 M$ which is independent of the type of processes. By varying the amount of stover, it is possible to reduce the scale of the energy generation and hence to keep the plant costs low. Table 3: Economic and profitability results
Config. 1 2 3 4 5 6 7 8 9
Ethanol plant TDM DMR QG–QF TDM DMR QG–QF TDM DMR QG–QF
Stover plant PH PH PH CHP CHP CHP GAS GAS GAS
Investment [M$] 71.88 70.86 81.62 83.77 80.84 92.43 69.17 70.11 81.01
Profit [M$] 8.28 8.35 19.19 14.0 12.63 24.06 6.23 8.90 18.69
Payback period [years] 15.5 15.0 7.1 9.6 10.2 6.5 19.9 13.5 7.2
NPV [M$] 1.3 2.4 62.3 28.6 22.0 83.4 -9.6 6.4 59.6
IRR [%] 5.2 5.4 12.3 8.5 7.8 13.4 3.4 5.98 12.0
The configuration No. 7 is uneconomic because of negative NPV value. In addition, configuration No. 1 and 2, show a acceptable PBP but they have a very small NPV and IRR: with small increase in interest rate these configuration will become unprofitable. On the other the good economic performances are mainly due to the QG-QF fiber process that generates a large number of valuable by-products. The final analysis includes configuration feasibility with changing prices. The results include economic indexes trend over time, with payback period summarized in Figure 2. It is that the trend is the same for all the configurations but with some options below the imposed limits (horizontal lines). As a result, the configurations that show acceptable economic results for the whole period of time considered are number 3, 6 and 9.
Ethanol from cor: analysis of using corn stover to supplyr to ethanol plant
1667
Payback period [years]
21
14
7
III tri 2006
III tri 2007
III tri 2008
III tri 2009
Time [2006-2010]
Figure 2: Payback period trend over time
4. Conclusions Considering the most important processes for ethanol production from corn and for energy generation from corn stover, nine different options have been studied with an exhaustive simulation approach. Both engineering and economic/profitability analysis have shown that the best configuration, among those taken into account, is composed of QG-QF and CHP processes. In fact it can produce a large number of valuable byproducts, and this make the configuration more flexible, and it has also shown the better economic performances demonstrating a broad profitability. However, this configuration has also the biggest capital investment and the biggest soil request. Then, it is important to mark that also the third and ninth options, composed by QG-QF and respectively PH and GAS processes, have good engineering and economic performances and their capital investments are about 11 M$ less than the one for number six.
References Ajay Kumar, Yasaf Demirel, David D.Jones, Milford A.Hanna, 2010. Optimization and economic evaluation of industrial gas production and combined heat and power generation from gasification of corn stover and distillers grains. Bioresource Technology, 101, 3696-3701 Caye M Drapcho, Nghiem Phu Nhuan, Terry H.Walker, 2008. Biofuels Engineering Process Technology. McGraw-Hill David Perkis, Wallace Tyner, Rhys Dale, 2007. Economic analysis of a modified dry grind ethanol process with recycle of pretreated and end enzymaticcaly hydrolyzed distillers' grains. Bioresource Technology, 99, 5243-5249 James M.Douglas, 1988. Conceptual design of chemical processes, McGraw-Hill Kiran L.Kadam, James D.McMillan, 2002. Availability of corn stover as sustainable feedstock for bioethanol production. Bioresource Technology, 88, 17-25 Luis F.Rodrigruez, Changying Li, Madhu Khanna, Aslihan D.Spaulding, Tao Lin, Steven R.Eckhoff, 2010. An engineering and economic evaluation of quick germ-quick fiber process for dry-grind ethanol facilities: Analysis. Bioresource Technology, 101, 5282-5289 R.J.Bothast, M.A.Schlincher, 2004. Biotechnological processes for conversion of corn into ethanol. Applied Microbiology and Biotechnology, 67, 19-25. Shahab Sokhansanj, Anthony Turhollow, Janet Cushman, John Cundiff, 2002. Engineering aspects of collecting corn stover for bioenergy. Biomass & Bioenergy, 23, 347-355 Youngmi Kim, Nathan Moiser, Michael R.Ladisch, 2007. Process simulation of modified dry grind ethanol plant whit recycle of pretreated and enzymatcally hydrilyzed distillers' grains. Bioresource Technology, 99, 5177-5192
Ethanol from corn: screening options and power supply improvement to ethanol plant in Italy Marco Soldà,a Franjo Cecelja,a Aidong Yang,a Piyalap Manakita a
PRISE Centre for Process and Information System Engineering University of Surrey, Guildford, UK
Abstract Bioethanol is currently the most important biofuel for automotive transportation and the European Community has set common objectives about the utilization of biofuels for all member states. The current Italian production of bioethanol is not sufficient to achieve these goals. In this work the existing processes for ethanol production from corn and for energy generation from corn stover are analyzed with an exhaustive simulation approach. They are supplemented by local (internal) energy generation used to supply heat and/or electrical power to minimize the energy consumption from fossil sources. Different scenarios are analyzed to determine better, if not the best, way of production bioethanol from corn while minimizing the energy consumption from fossil sources. An economic and profitability analysis for every scenario is also provided. Keywords: Ethanol from corn; corn stover; economic analysis.
1. Introduction In 2009 alone, about 19.5 billion gallons of ethanol (73.9 billion liters) was produced worldwide. It is evident that the United States are the biggest world producer, while Brazil is a close second. At the same time, the European Community produced only 1.04 billion gallons (3.9 billion liters) with likely increase in years to come (RFA – 2010). Given the importance of bioethanol as a renewable fuel, the European Community has recently set common objectives for all member states regarding the utilization of bioethanol in the automotive sector. The first directive 2003/30/EC, which has already been implemented in the Italian law, is followed by the 2009/28/EC for which the deadline for the transposition in the member state’s law is December 5th 2010. The first directive requires all the member states to reach the utilization of 2% of bioethanol in 2005 and 5.75% in 2010, while the second directive raises the percentage of bioethanol to 10% by the end of 2020 (data taken from http://europa.eu/). In Italy, the favorite feedstock is corn because of very high yields that can be obtained, especially in the northern Italy: 10÷14 tonnes/ha. However, the Italian production of ethanol as a biofuel has just started with modest 72 million liters in 2009. To reach imposed objectives, the need for new plants for ethanol production is obvious. The technology definitely matures and relative to the first generation of biofuels are already in use. In reflection, this work will focus on this type of processes with the main objectives to demonstrate that by using corn stover it is possible to significantly reduce the energy intake from fossil sources. It was also hopped that it will be possible to define the configuration that ensures the largest profitability. The processes for ethanol production taken into account in this work are traditional dry milling (TDM) (Drapcho et. al. – 2008; Bothast and Schlicher – 2004; Perkis et. al. – 2007), dry milling with recycle of distillers’ grains (DMR) (Kim et. al. – 2007; Perkis et. al. – 2007) and quick germ – quick fiber (QG-QF) (Luis F. Rodrigues et. al. – 2010) while those for energy
M. Soldà et. al.
1664
generation from corn stover are combustion for process heat generation (PH) (S. Sokhansanj et. al. – 2009; S. Mani et. al. - 2009), combined heat and electricity generation (CHP) (Sokhansanj et. al. – 2009; S. Mani et. al. - 2009) and gasification (GAS) (Ajay Kumar et. al. – 2010).
2. Methodology The exhaustive simulation approach was found the best suited to build two stage configurations with one simplified model built for every single process for ethanol production and for energy generation. Combining them together, all possible scenarios are easy to set for each configuration. In the considered models, a process is represented as a block with a few streams: main input material, main output material, energy and auxiliary material requirements, as well as energy, environmental emission and byproduct outputs, as shown in Figure 1. For example, every ethanol process has been represented with its main input (corn), the main output (ethanol), energy requirements in the form of electricity or steam together with useful by-products and environmental effects (emissions). Only DDGS for the TDM and the DMR and four for QG-QF (DDGS, protein, bran and oil) are considered as useful byproducts. The environmental effects (emissions) are represented as kilograms of carbon dioxide emitted per litre of ethanol produced. The last facet shown in the models is the energy required in the form of electricity and/or heat. The heat required is steam at about 0.4 MPa and 110°C for all the ethanol processes. For all the energy generation processes, the main input is corn stover, the outputs are electricity and/or heat generated, while the main by-product is ash. As for the ethanol processes, the environmental effects are shown as kilograms of carbon dioxide emitted, but this time it is per tonne of stover processed. The thermal and/or electrical energy requests expressed per tonne of stover processed are also reported.
Figure 1: Simplified model example
The 75 million liters per year production volume was set for all the configurations, with all other data scaled respectively: amount of corn and soil required, corn stover available, electrical and thermal energy required by the ethanol and the stover plant, amount of thermal and/or electrical energy generated from corn stover, amount of byproducts, as well as environmental emissions. The amount of corn needed to produce 75 million liters of ethanol has been determined on the base of the ethanol yield characteristic of each process. Required soil has been calculated considering a corn yield of 12 ton/ha and the corn stover production on the base of one tonne of stover above ground per tonne of corn harvested. However, the corn stover that can be sustainably collected is about 30÷35% of the global stover production (Kiran and McMillan – 2002). With the labour costs deliberately omitted, the costs taken into account include corn, corn stover, electricity, natural gas etc. and are summarized in Table 1 with the most recent prices.
Ethanol from cor: analysis of using corn stover to supplyr to ethanol plant
1665
Table 1: Prices reflecting the first four months of 2010
Item Corn [$/bu] Corn stover [$/ton] Electricity [$/kWh] Natural gas [$/m3] Ethanol [$/gal] DDGS [$/ton] Bran [$/ton] Protein [$/ton] Oil [$/ton] Selling electricity [$/ton] Ash disposal cost [$/ton]
Price 3.42 19.6 0.176 0.43 1.63 105.6 92.02 400 893 0.098 22
Reference USDA market news Sokhansanj et. al. – 2002 Autorità per l’energia elettrica e il gas Eurostat USDA market news USDA market news USDA market news Dickey et. al. – 2010 USDA – Oil crops outlook 2010 Autorità per l’energia elettrica e il gas Mani et. al. – 2009
The plant costs have been calculated by updating and rescaling the plant costs available from literature to the first quarter of 2010 using the Marshal and Swift cost index and then rescaled using as equipment cost attribute for the ethanol plant and the energy generation plant, respectively, ethanol production and amount of corn stover processed. The profitability analysis has been provided on the basis of 20 years plant life and a construction period of 2 years. A straight line depreciation method of 10 years with an interest rate of 5% was considered. The working capital and the savage value have been respectively calculated as the 15% and the 3% of the capital investment, respectively (Douglas – 2008). Then, three profitability parameters were calculated: discounted payback period (PBP), discounted cumulative cash position (NPV) and discounted cash flow rate of return (IRR) with limits: the PBP must be below 20 year, the NPV must be greater than zero and the IRR should be above 10% to consider the process profitable. Because of high variation of some prices over last few years, it has been decided to study the profitability trend over time. As a result, we consider process profitable only if it showed acceptable economic results for the whole of selected period.
3. Results and discussion As described above, each ethanol process/plant was supplied by energy generated from corn stover. In most cases required energy was higher; the difference was provided from natural gas to generate steam and/or from the electricity grid to balance electrical energy. In other cases, it has been necessary to reduce the amount of stover processed or sell the excess electricity in the market. As an illustration, in the gasification process, the product gas is fed to a CHP generation system which is optimized for electricity generation using both gas and steam turbine. Then the heat produced is considered as a sort of by-product. In fact, it is only hot water that cannot be used to supply heat to the ethanol plant. So, it has been chosen to produce the right amount of electricity reducing the amount of corn stover processed. In this way, it is also possible to hold down the plant costs that, for the gasification, are significantly higher than the others. In the same way, it has been reduced the amount of corn stover processed in the PH and CHP processes. The engineering analysis for all the configurations is given in Table 2. As evident from Table 2, the required soil, which depends on type of ethanol process, is the lovest for configuration 2, 5 and 8: DMR is the process with the highest yild while QGQF is with the lovest. For electrical energy requirements better configurations are those with a gasification process because they have a null value of this parameter, with
M. Soldà et. al.
1666
configuration 4 and 6 even providing suffice amount. Also, there are three configurations, 1, 3 and 6 which do not require any thermal energy input, as opposed to gasification process with very high thermal requirements. Finally, the CO2 emission is comparatevly similar for all configurations: here the CO2 emission only include amount directly generated by the process. Table 2: Simplified models analysis
Conf. No.
Configuration
1 2 3 4 5 6 7 8 9
TDM + PH DMR + PH QG-QF + PH TDM + CHP DMR + CHP QG-QF + CHP TDM + GAS DMR + GAS QG-QF + GAS
Req. soil [ha] 14951 12335 15593 14951 12335 15593 14951 12335 15593
Stover available [ton]* 62795 (91.3%) 51807 (100%) 65490 (69.7%) 62795 (100%) 51807 (100%) 65490 (79%) 62795 (14.9%) 51807 (22.2%) 65790 (15.8%)
Elec. required [kWh/l] 0.36 0.42 0.37 0.03 -
Heat required [kWh/l] 0.6 0.09 0.86 2.86 3.25 2.34
CO2 emission [kg/l] 0.87 0.82 0.85 0.90 0.82 0.86 0.84 0.82 0.85
*The number given in brackets is the percentage of available corn stover that has been used.
The results of profitability analysis are summarized in Table 3. As evident, there is a significant variability in the capital investment ranging from 70 to 92 M$ which is independent of the type of processes. By varying the amount of stover, it is possible to reduce the scale of the energy generation and hence to keep the plant costs low. Table 3: Economic and profitability results
Config. 1 2 3 4 5 6 7 8 9
Ethanol plant TDM DMR QG–QF TDM DMR QG–QF TDM DMR QG–QF
Stover plant PH PH PH CHP CHP CHP GAS GAS GAS
Investment [M$] 71.88 70.86 81.62 83.77 80.84 92.43 69.17 70.11 81.01
Profit [M$] 8.28 8.35 19.19 14.0 12.63 24.06 6.23 8.90 18.69
Payback period [years] 15.5 15.0 7.1 9.6 10.2 6.5 19.9 13.5 7.2
NPV [M$] 1.3 2.4 62.3 28.6 22.0 83.4 -9.6 6.4 59.6
IRR [%] 5.2 5.4 12.3 8.5 7.8 13.4 3.4 5.98 12.0
The configuration No. 7 is uneconomic because of negative NPV value. In addition, configuration No. 1 and 2, show a acceptable PBP but they have a very small NPV and IRR: with small increase in interest rate these configuration will become unprofitable. On the other the good economic performances are mainly due to the QG-QF fiber process that generates a large number of valuable by-products. The final analysis includes configuration feasibility with changing prices. The results include economic indexes trend over time, with payback period summarized in Figure 2. It is that the trend is the same for all the configurations but with some options below the imposed limits (horizontal lines). As a result, the configurations that show acceptable economic results for the whole period of time considered are number 3, 6 and 9.
Ethanol from cor: analysis of using corn stover to supplyr to ethanol plant
1667
Payback period [years]
21
14
7
III tri 2006
III tri 2007
III tri 2008
III tri 2009
Time [2006-2010]
Figure 2: Payback period trend over time
4. Conclusions Considering the most important processes for ethanol production from corn and for energy generation from corn stover, nine different options have been studied with an exhaustive simulation approach. Both engineering and economic/profitability analysis have shown that the best configuration, among those taken into account, is composed of QG-QF and CHP processes. In fact it can produce a large number of valuable byproducts, and this make the configuration more flexible, and it has also shown the better economic performances demonstrating a broad profitability. However, this configuration has also the biggest capital investment and the biggest soil request. Then, it is important to mark that also the third and ninth options, composed by QG-QF and respectively PH and GAS processes, have good engineering and economic performances and their capital investments are about 11 M$ less than the one for number six.
References Ajay Kumar, Yasaf Demirel, David D.Jones, Milford A.Hanna, 2010. Optimization and economic evaluation of industrial gas production and combined heat and power generation from gasification of corn stover and distillers grains. Bioresource Technology, 101, 3696-3701 Caye M Drapcho, Nghiem Phu Nhuan, Terry H.Walker, 2008. Biofuels Engineering Process Technology. McGraw-Hill David Perkis, Wallace Tyner, Rhys Dale, 2007. Economic analysis of a modified dry grind ethanol process with recycle of pretreated and end enzymaticcaly hydrolyzed distillers' grains. Bioresource Technology, 99, 5243-5249 James M.Douglas, 1988. Conceptual design of chemical processes, McGraw-Hill Kiran L.Kadam, James D.McMillan, 2002. Availability of corn stover as sustainable feedstock for bioethanol production. Bioresource Technology, 88, 17-25 Luis F.Rodrigruez, Changying Li, Madhu Khanna, Aslihan D.Spaulding, Tao Lin, Steven R.Eckhoff, 2010. An engineering and economic evaluation of quick germ-quick fiber process for dry-grind ethanol facilities: Analysis. Bioresource Technology, 101, 5282-5289 R.J.Bothast, M.A.Schlincher, 2004. Biotechnological processes for conversion of corn into ethanol. Applied Microbiology and Biotechnology, 67, 19-25. Shahab Sokhansanj, Anthony Turhollow, Janet Cushman, John Cundiff, 2002. Engineering aspects of collecting corn stover for bioenergy. Biomass & Bioenergy, 23, 347-355 Youngmi Kim, Nathan Moiser, Michael R.Ladisch, 2007. Process simulation of modified dry grind ethanol plant whit recycle of pretreated and enzymatcally hydrilyzed distillers' grains. Bioresource Technology, 99, 5177-5192