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Evaluation of assessment methods for bioethanol production

Dissertation
Author: Noorie Rajvanshi
Abstract:
Biofuels are emerging as a potential replacement for fossil fuel derived liquid fuels and with increasing production rates is has become essential to understand the environmental and energetic impacts of their production. This study focuses on ethanol production from four feedstocks: corn, sweet sorghum, sugarcane and pine. The main objective of this study is to evaluate the assessment methods used for calculating the impacts of biofuel production and this has been carried out with the help of five methods: net energy analysis, life cycle assessment, cumulative exergy analysis, consumptive water analysis, and emergy synthesis. Detailed data acquisition was carried out to obtain primary input data required for the four feedstocks. This data with some secondary data from literature was used to calculate the impacts using five assessment methods. A sensitivity analysis was also performed to evaluate the stability of the five assessment methods. Three scenarios were considered viz., change in biomass yield, change in transportation distance and change in ethanol yield. It was found that emergy synthesis and life cycle assessment are relatively less sensitive to changes in input than cumulative exergy and net energy analysis methods. Finally the five methods were compared and the advantages and limitations of each have been discussed. Two case studies to demonstrate combining two or more methods have also been presented.

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS

...............................................................................................................4 LIST OF TABLES

...........................................................................................................................9 LIST OF FIGURES

.......................................................................................................................13 LIST OF ABBREVIATIONS

........................................................................................................18 ABSTRACT ...................................................................................................................................19 CHAPTER 1 INTRODUCTION ..................................................................................................................21

1.1 Need for Assessment Studies

............................................................................................21 1.2 Choice of Feedstocks

........................................................................................................23 1.3 Research Objectives

..........................................................................................................25 2 LITERATURE REVIEW AND METHODS .........................................................................28

2.1 Ethanol Production

...........................................................................................................28 2.1.1 Sugar to Ethanol

.....................................................................................................28 2.1.2 Starch to Ethanol

....................................................................................................30 2.1.3 Cellulose to Ethanol

...............................................................................................30 2.2 Feedstocks and Agricultural Practices

..............................................................................34 2.2.1 Sweet Sorghum

.......................................................................................................34 2.2.2 Sugarcane

...............................................................................................................36 2.2.3 Corn

........................................................................................................................37 2.2.4 Woody Biomass

......................................................................................................37 2.3 Assessment Studies of Ethanol Production System

..........................................................38 2.3.1 Net Energy Analysis

...............................................................................................38 2.3.2 Life Cycle Assessment

...........................................................................................40 2.3.3 Thermodynamic/Exergy Analysis

..........................................................................45 2.3.4 Water Analysis

.......................................................................................................48 2.3.5 Emergy Synthesis

...................................................................................................50 3 DATA ACQUISITION ..........................................................................................................66

3.1 Corn

..................................................................................................................................66 3.2 Sweet Sorghum

.................................................................................................................67 3.3 Sugarcane

..........................................................................................................................69 3.4 Woody biomass

................................................................................................................71

6

4 NET ENERGY ANALYSIS ...................................................................................................77

4.1 Corn

..................................................................................................................................78 4.2 Sweet Sorghum

.................................................................................................................78 4.3 Sugarcane

..........................................................................................................................79 4.4 Woody biomass

................................................................................................................80 4.5 Conclusion

........................................................................................................................81 5 LIFE CYCLE ASSESSMENT ...............................................................................................90

5.1 Corn

..................................................................................................................................90 5.2 Sweet Sorghum

.................................................................................................................92 5.3 Sugarcane

..........................................................................................................................92 5.4 Woody Biomass

................................................................................................................93 5.5 Conclusion

........................................................................................................................94 6 CUMULATIVE EXERGY ANALYSIS ..............................................................................105

6.1 Corn

................................................................................................................................105 6.2 Sweet Sorghum

...............................................................................................................107 6.3 Sugarcane

........................................................................................................................107 6.4 Woody biomass

..............................................................................................................108 6.5 Conclusion

......................................................................................................................109 7 CONSUMPTIVE WATER ANALYSIS ..............................................................................123

7.1 Corn

................................................................................................................................123 7.2 Sweet Sorghum

...............................................................................................................123 7.3 Sugarcane

........................................................................................................................124 7.4 Woody biomass

..............................................................................................................125 7.5 Conclusion

......................................................................................................................125 8 EMERGY SYNTHESIS .......................................................................................................131

8.1 Corn

................................................................................................................................131 8.2 Sweet Sorghum

...............................................................................................................131 3.3 Sugarcane

........................................................................................................................132 8.4 Woody biomass

..............................................................................................................132 8.5 Conclusion

......................................................................................................................133 9 SENSITIVITY ANALYSIS .................................................................................................152

9.1 Scenario Selection

..........................................................................................................152 9.1.1 Scenario 1: Biomass Yield

...................................................................................153 9.1.2 Scenario 2: Change in transportation distance

.....................................................153 9.1.3 Scenario 3: Technological advances with increased ethanol yield

......................154 9.2 Results

.............................................................................................................................155 9.2.1 Scenario 1: Biomass Yield

...................................................................................155

7

9.2.2 Scenario 2: Change in transportation distance

.....................................................156 9.2.3 Scenario 3: Technological advances with increased ethanol yield

......................157 9.3 Conclusion

......................................................................................................................158 10 CONCLUSIONS AND DISCUSSION ................................................................................163

10.1 Comparison of Methods

...............................................................................................163 10.1.1 Net Energy Analysis (NEA)

...............................................................................163 10.1.2 Life Cycle Assessment (LCA)

............................................................................164 10.1.3 Cumulative Exergy Analysis (CExA)

................................................................165 10.1.4 Consumptive Water Analysis (CWA)

................................................................166 10.1.5 Emergy Synthesis (EmS)

....................................................................................166 10.2 Energy and Water-Land Index

......................................................................................167 10.3 Emergy Value of Water used in Ethanol Production

....................................................169 10.3.1 Resource Value (RV)

.........................................................................................169 10.3.2 Financial Value (FV)

..........................................................................................170 10.3.3 Environmental Value (EV)

.................................................................................170 10.3.4 Converting Emergy to Money

............................................................................171 10.3.5 Results and Conclusion

......................................................................................171 10.4 Thesis Limitations and Future Work ............................................................................172

APPENDIX A CORN ...................................................................................................................................178

A-1 Data Collection Visit to Glacial Lakes Energy LLC, Watertown, South Dakota

.........178 A-2 Cumulative Exergy Analysis for Corn Ethanol Production

..........................................184 A-3 Emergy Synthesis for Corn Ethanol Production

...........................................................188 B SWEET SORGHUM ............................................................................................................190

B-1 Cumulative Exergy Analysis for Ethanol from Sweet Sorghum

...................................190 B-2 Emergy Synthesis for Sweet Sorghum Ethanol Production

..........................................191 C SUGARCANE ......................................................................................................................194

C-1 Data Collection Visit to Jubilant Organosys, Nira, India

..............................................194 C-2 Calculation of Allocation Ratio for Molasses Production

.............................................197 C-3 Cumulative Exergy Analysis for Ethanol from Sugarcane

............................................198 C-4 Emergy Synthesis for Sugarcane Ethanol Production

...................................................199 D PINE .....................................................................................................................................201

D-1 Data Collection for Pine Plantations in Florida from the Visit to Andrew’s Nursery, Chiefland, Florida

.............................................................................................................201 D-2 Data Collection for Cellulosic Ethanol Production from Bluefire Ethanol, Irvine, California

..........................................................................................................................203 D-3 Cumulative Exergy analysis for cellulosic ethanol production

.....................................207

8

D-3 Emergy Synthesis for Pine Ethanol Production

............................................................209 E MISCELLANEOUS TABLES .............................................................................................211

E-1 Embodied Energy in Materials

......................................................................................211 E-2. Heating Values and Densities of Fuels

.........................................................................213 F INPUT TABLES FOR SENSITIVITY ANALYSIS ...........................................................214

F-1 Input Tables for Scenario 1

............................................................................................214 F-2 Input Tables for Scenario 2

............................................................................................215 F-3 Input Tables for Scenario 3

............................................................................................215 LIST OF REFERENCES

.............................................................................................................217 BIOGRAPHICAL SKETCH

.......................................................................................................228

9

LIST OF TABLES Table

page

1-1 Comparison of sweet sorghum and sugarcane for ethanol production (Reddy et al., 2007)

..................................................................................................................................26 2-1 Composition of various cellulosic biomasses

....................................................................53 2-2 Pretreatment technologies for lignocellulosic biomass

......................................................54 2-3 Summary of important net energy analysis literature

........................................................55 2-4 Bioenergy yield to fossil energy input ratios for bio-ethanol systems

...............................56 2-5 Typical emergy accounting table

.......................................................................................56 3-1 Chemical composition of softwoods

..................................................................................72 4-1 Output energy of corn ethanol production and co-product credit

......................................81 4-2 Input energy for ethanol production from corn (per1000 liters of ethanol)

.......................82 4-3 Output energy of sweet sorghum ethanol production and co-product credit

.....................83 4-4 Input energy for ethanol production from sweet sorghum (per 1000 liters of ethanol)

.....83 4-5 Input energy for ethanol production from sugarcane (per 1000 liters of ethanol)

.............84 4-6 Output energy of sugarcane ethanol production and co-product credit

.............................85 4-7 Output energy of pine ethanol production and co-product credit

......................................85 4-8 Input energy for pine production and transportation

.........................................................86 4-9 Input energy for ethanol production from pine

..................................................................87 4-10 Input energy for ethanol production (1000 liters of ethanol)

.............................................87 4-11 Net energy ratios with and without co-product credit

.......................................................88 5-1 Comparison of environmental impacts with those of Kim and Dale (2008)

.....................95 5-2 Environmental impacts from all four feedstocks

...............................................................95 6-1 Renewable and non-renewable exergy inputs in MJ per 1000 liters of ethanol

..............110 6-2 Output exergy of products and co-products in MJ per 1000 liters of ethanol

.................110

10

7-1 Recommended water application rates for corn in eastern South Dakota

.......................127 7-2 Water balance for Glacial Lakes Energy ethanol plant

...................................................127 7-3 Amount of water applied in Liters/ha

..............................................................................127 7-4 Water use per stage of growing pine (all values per functional units)

.............................128 7-5 Comparison of water use per functional unit (liters)

.......................................................128 7-6 Comparison of water use (liters of water per 1000 liters of ethanol) for sugarcane and sweet sorghum for Southeastern U.S. (Evans and Cohen, 2009) and India (this study)

.128 8-1 Emergy accounting table for corn ethanol production (based on 1000 liters of ethanol)

............................................................................................................................134 8-2 Summary of emergy flows, ratios and indices for corn ethanol production

....................136 8-3 Emergy accounting table for sweet sorghum ethanol (based on 1000 liters of ethanol)

.137 8-4 Summary of emergy flows, indices and ratios for sweet sorghum ethanol production

...139 8-5 Emergy accounting table for sugarcane ethanol (based on 1000 liters of ethanol)

.........140 8-6 Summary of emergy flows, indices and ratios for sugarcane ethanol production

...........142 8-7 Emergy accounting table for pine ethanol (based on 1000 liters of ethanol)

..................143 8-8 Summary of emergy flows, indices and ratios for pine ethanol production

....................146 8-9 Summary of various emergy indices for ethanol production from four feedstocks

........146 9-1 Sensitivity analysis for NEA for Scenario 1

....................................................................159 9-2 Sensitivity analysis for LCA for Scenario 1

....................................................................159 9-3 Sensitivity analysis for CExA for Scenario 1

..................................................................159 9-4 Sensitivity analysis for EmS for Scenario 1

....................................................................160 9-5 Sensitivity analysis for NEA for Scenario 2

....................................................................160 9-6 Sensitivity analysis for LCA for Scenario 2

....................................................................160 9-7 Sensitivity analysis for CExA for Scenario 2

..................................................................161 9-8 Sensitivity analysis for EmS for Scenario 2

....................................................................161 9-9 Sensitivity analysis for NEA for Scenario 3

....................................................................161

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9-10 Sensitivity analysis for LCA for Scenario 3

....................................................................162 9-11 Sensitivity analysis for CExA for Scenario 3

..................................................................162 9-12 Sensitivity analysis for EmS for Scenario 3

....................................................................162 10-1 Net energy value and energy-water-land index for ethanol production (all values per liter of ethanol)

.................................................................................................................175 10-2 Resource value of chemical potential of rain, groundwater and surface water for three feedstocks

................................................................................................................175 10-3 Environmental value of water for United States and India

..............................................176 10-4 Emergy to money ratio for United States and India

........................................................176 10-5 Total cost of water ($/m3) for producing ethanol from corn, sweet sorghum, sugarcane and pine

...........................................................................................................176 10-6 Comparison between total cost of water to produce 1000 liters of ethanol and cost of ethanol produced

..............................................................................................................176 A-1 Raw input data from GLE ethanol production facility

....................................................183 A-2 Group contribution for standard chemical exergy of Atrazine

........................................185 A-3 Cumulative exergy for production of Atrazine

................................................................186 A-4 Chemical exergy and cumulative exergy consumption of pesticides

..............................186 A-5 Chemical exergy and cumulative exergy consumption of chemicals used in industrial process

..............................................................................................................................187 A-6 Exergy calculations of yeast

............................................................................................187 A-7 Cumulative exergy of fuels and chemicals used in agricultural and industrial process of corn ethanol production

...............................................................................................188 A-8 Raw data for corn production obtained from USDA (Foreman, 2006)

...........................189 B-1 Chemical exergy and cumulative exergy consumption of pesticides

..............................190 B-2 Cumulative exergy of fuels and chemicals used in agricultural and industrial Process of sweet sorghum Ethanol Production

.............................................................................190 B-3 Exergy calculation of sweet sorghum juice

.....................................................................191 B-4 Exergy calculation of sweet sorghum grain

.....................................................................191

12

C-1 Input and output inventory for ethanol production from molasses

..................................195 C-2 Calculation of allocation ratio for calculating the energy and material requirements for molasses production (http://sugarcane-breeding.tn.nic.in/productivityfigures.htm) 197 .

C-3 Cumulative exergy of fuels and chemicals used in agricultural and industrial process of sugarcane ethanol production

......................................................................................198 C-4 Exergy calculations of sugarcane juice

............................................................................198 C-5 Exergy calculations of molasses

......................................................................................198 D-1 Chemical exergy and cumulative exergy consumption of pesticides

..............................207 D-2 Chemical exergy and cumulative exergy consumption of chemicals used in industrial process

..............................................................................................................................207 D-3 Cumulative exergy of fuels and chemicals used in agricultural and industrial process of pine ethanol production

...............................................................................................208 D-4 Exergy calculations for pine wood

..................................................................................208 E-1 Typical power, working capacity, weight and life time of selected agricultural machinery (Nemecek and Kagi, December 2007)

...........................................................211 E-2 Percentage compositions of some agricultural machinery (Nemecek and Kagi, December 2007)

...............................................................................................................212 E-3 Embodied energy in various materials

.............................................................................212 E-4 Heating values and densities of various fuels used in this study (Speight, 2008)

...........213 F-1 Scenario 1: input for corn ethanol

....................................................................................214 F-2 Scenario 1: input for sweet sorghum ethanol

...................................................................214 F-3 Scenario 1: input for sugarcane ethanol

...........................................................................214 F-4 Scenario 2: input for all four feestocks

............................................................................215 F-5 Scenario 3: input for agricultural stage of pine ethanol

...................................................215 F-6 Scenario 3: input for industrial stage of pine ethanol

......................................................216 F-7 Scenario 3: Outputs for industrial stage of pine ethanol

..................................................216

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LIST OF FIGURES Figure

page

1-1 Increasing trend of production of ethanol (Earth Policy Institute, 2006; RFA, 2008)

......27 1-2 The trend of increase in biofuel production mandated by EISA 2007

..............................27 2-1 Ethanol production from molasses

.....................................................................................56 2-2 Process for ethanol production from corn by dry milling technique

.................................57 2-3 Cellulose, hemicelluloses and hypothesized lignin chemical structure

.............................57 2-4 Generalized process diagram for cellulosic ethanol production

........................................58 2-5 Bluefire ethanol’s concentrated acid hydrolysis

................................................................58 2-6 Yield trend of corn in United States (USDA, 2009)

..........................................................59 2-7 Various uses of corn crop in 2008 in United States (Baker et al., 2008)

...........................59 2-8 Level 1 and 2 diagram for ethanol production from pine

..................................................60 2-9 Generic level diagram for life cycle assessment of ethanol production facility

................60 2-10 Agricultural water cycle (adopted from (National Research Council, 2008) )

..................61 2-11 System diagramming symbols (adopted from Sciubba and Ulgiati, 2005)

.......................62 2-12 General diagram for ethanol production from any crop

....................................................63 2-13 General systems diagram illustrating emergy performance indicators (Brown and Ulgiati, 1997)

.....................................................................................................................64 2-14 Scale and scope of various methods used in this dissertation. Each dashed line with different color encloses the system boundary for that method.

.........................................65 3-1 Map representing the corn production area around Watertown, South Dakota

.................72 3-2 Schematic of dry mill corn ethanol production process

.....................................................72 3-3 Map of western Maharashtra State in India where NARI is located

.................................73 3-4 Level 1 and 2 Diagram for ethanol production from sweet sorghum

................................73 3-5 Schematic of ethanol distillation plant for sweet sorghum (Rajvanshi, 1988)

..................74 3-6 Sugarcane production in the state of Maharashtra

.............................................................75

14

3-7 Material balance for ethanol production from sugarcane (all numbers for 1000 liters of ethanol produced)

..........................................................................................................75 3-8 Process flow diagram of the Arkenol process employed by Bluefire Ethanol

..................76 4-1 Total input energy per 1000 liter ethanol production from all four feedstocks

.................88 4-2 Total input energy by source per 1000 liters of ethanol production

..................................88 4-3 Total input energy by source per 1000 liters of ethanol production

..................................89 5-1 Level 1 and 2 diagram for ethanol production from corn

..................................................96 5-2 Level 2 and 3 diagram for ethanol production from corn

..................................................96 5-3 Environmental impacts by source of emissions for corn ethanol production

....................97 5-4 Environmental impacts by life cycle stage for corn ethanol

..............................................97 5-5 Level 1 and 2 diagram for ethanol production from sweet sorghum

.................................98 5-6 Level 3 and 4 diagram for ethanol production from sweet sorghum

.................................98 5-7 Environmental impacts by source of emissions for sweet sorghum ethanol production

...99 5-8 Environmental impacts by life cycle stage for sweet sorghum ethanol

.............................99 5-9 Level 1 and 2 diagram for ethanol production from sugarcane

.......................................100 5-10 Level 3 and 4 diagram for ethanol production from sugarcane

.......................................100 5-11 Environmental impacts by source of emissions for the sugarcane ethanol production

...101 5-12 Environmental impacts by life cycle stage for sugarcane ethanol

...................................101 5-13 Level 1 and 2 diagrams for ethanol production from pine

...............................................102 5-14 Level 3 and 4 diagram for ethanol production from pine

................................................102 5-15 Environmental impacts by source of emissions for pine ethanol production

..................103 5-16 Environmental impacts by life cycle stage for pine ethanol

............................................103 5-17 Environmental impacts by feedstock for producing 1000 liters of ethanol

.....................104 6-1 Input and output exergy flows for agricultural process of corn production. All values are MJ per 1000 liters of ethanol produced

.....................................................................111

15

6-2 Percentage contribution of non-renewable inputs in agricultural process for corn production

........................................................................................................................111 6-3 Input and output exergy flows for the industrial process of ethanol production from corn. All values are in MJ per 1000 liters of ethanol produced

.......................................112 6-4 Percentage contribution of non-renewable inputs in the industrial process for ethanol production from corn

.......................................................................................................112 6-5 Input and output exergy flows for the overall process for corn ethanol production. All values are in MJ per 1000 liters of ethanol produced

................................................113 6-6 Input and output exergy flows for agricultural process of sweet sorghum production. All values are MJ per 1000 liters of ethanol produced

....................................................113 6-7 Percentage contribution of non-renewable inputs in agricultural process for sweet sorghum production

.........................................................................................................114 6-8 Input and output exergy flows for the industrial process of sweet sorghum ethanol production. All values are in MJ per 1000 liters of ethanol produced

.............................114 6-9 Percentage contribution of non-renewable inputs in industrial process for sweet sorghum ethanol production

............................................................................................115 6-10 Input and output exergy flows for the sweet sorghum ethanol production process. All values are in MJ per 1000 liters of ethanol produced

......................................................115 6-11 Input and output exergy flows for agricultural process of sugarcane production. All values are MJ per 1000 liters of ethanol produced

..........................................................116 6-12 Input and output exergy flows for molasses production. All values are MJ per 1000 liters of ethanol produced

.................................................................................................116 6-13 Input and output exergy flows for ethanol production from sugarcane. All values are MJ per 1000 liters of ethanol produced

...........................................................................117 6-14 Percentage contribution of non-renewable inputs in agricultural and industrial process for sugarcane ethanol production

........................................................................117 6-15 Input and output exergy flows for the complete sugarcane ethanol production process. All values are in MJ per 1000 liters of ethanol produced

..................................118 6-16 Input and output exergy flows for the agricultural process of pine ethanol production. All values are in MJ per 1000 liters of ethanol produced

................................................119 6-17 Input and output exergy flows for the industrial process of pine ethanol production. All values are in MJ per 1000 liters of ethanol produced

................................................119

16

6-18 Percentage contribution of non-renewable inputs in agricultural process for pine production

........................................................................................................................120 6-19 Input and output exergy flows for the pine ethanol production process. All values are in MJ per 1000 liters of ethanol produced

.......................................................................120 6-20 Percentage contribution of non-renewable inputs in industrial process for pine production

........................................................................................................................121 6-21 Percentage contribution of non-renewable exergy inputs to ethanol production process

..............................................................................................................................121 6-22 Percentage contribution of exergy outputs

......................................................................122 7-1 Monthly water use in Glacial Lakes Energy ethanol plant from January to July 2008

...128 7-2 Irrigation requirements for sugarcane in Maharashtra

.....................................................129 7-3 Water use in million liters for agricultural phase (values based on 1000 liters of ethanol production)

..........................................................................................................129 7-4 Water use in thousand liters for industrial phase (values based on 1000 liters of ethanol production)

..........................................................................................................130 7-5 Comparison of water use for ethanol production between India (this study) and Southeastern U.S. (Evans and Cohen, 2009) (values based on 1000 liters of ethanol production)

.......................................................................................................................130 8-1 Systems diagram for emergy synthesis of ethanol production from corn

.......................147 8-2 Emergy signature of corn ethanol production process

.....................................................147 8-3 Systems diagram for emergy synthesis of sweet sorghum ethanol

..................................148 8-4 Emergy signature of sweet sorghum ethanol production process

....................................148 8-5 Systems diagram for emergy synthesis of sugarcane ethanol

..........................................149 8-6 Emergy signature of sugarcane ethanol production process

............................................149 8-7 Systems diagram for emergy synthesis of pine ethanol

...................................................150 8-8 Emergy signature of pine ethanol production process

.....................................................151 9-1 Projected corn yields for 2070

.........................................................................................162 10-1 Total cost of water ($/m3) for producing 1000 liters of ethanol from corn, sweet sorghum, sugarcane and pine

...........................................................................................177

17

10-2 Comparison of cost of water for producing ethanol and cost of 1000 liters of ethanol

...177 A-1 Process diagram for GLE’s corn ethanol production plant, Watertown, SD

...................180 A-2 Beer Column

....................................................................................................................181 A-3 Centrifuge and drum dryer

...............................................................................................182 A-4 Evaporators

......................................................................................................................183 A-5 Molecular structure of Atrazine

.......................................................................................184 C-1 Distillery system flow diagram

........................................................................................196 D-1 Simplified flow diagram of Arkenol’s concentrated acid hydrolysis technology

...........205

18

LIST OF ABBREVIATIONS AP Acidification Potential CDP Cumulative Degree of Perfection CExA Cumulative Exergy Analysis CExC Cumulative Exergy Consumption DDGS Distillers Dried Grains with Solubles EIS Emergy Index of Sustainability ELR Environmental Loading Ratio EmS Emergy Synthesis EP Eutrophication Potential Ex Exergy EYR Emergy Yield Ratio FU Functional Unit GWP Global Warming Potential LCA Life Cycle Assessment LHV Low Heating Value NER Net Energy Ratio NEV Net Energy Value UEV Unit Emergy Values

19

Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

EVALUATION OF ASSESSMENT METHODS FOR BIOETHANOL PRODUCTION By Noorie Rajvanshi

August 2010

Chair: H. A. Ingley Major: Mechanical Engineering

Biofuels are emerging as a potential replacement for fossil fuel derived liquid fuels and with increasing production rates is has become essential to understand the environmental and energetic impacts of their production. This study focuses on ethanol production from four feedstocks: corn, sweet sorghum, sugarcane and pine. The main objective of this study is to evaluate the assessment methods used for calculating the impacts of biofuel production and this has been carried out with the help of five methods: net energy analysis, life cycle assessment, cumulative exergy analysis, consumptive water analysis, and emergy synthesis. Detailed data acquisition was carried out to obtain primary input data required for the four feedstocks. This data with some secondary data from literature was used to calculate the impacts using five assessment methods. A sensitivity analysis was also performed to evaluate the stability of the five assessment methods. Three scenarios were considered viz., change in biomass yield, change in transportation distance and change in ethanol yield. It was found that emergy synthesis and life cycle assessment are relatively less sensitive to changes in input than cumulative exergy and net energy analysis methods.

20

Finally the five methods were compared and the advantages and limitations of each have been discussed. Two case studies to demonstrate combining two or more methods have also been presented.

21

CHAPTER 1 INTRODUCTION The energy crisis is one of the most important challenges faced by humankind in the 21st century. Liquid fuels derived from fossil fuels constitute one of the largest parts of energy consumption in the United States and worldwide. Biofuels like ethanol and biodiesel are seen as potential replacements for these fossil fuel-derived liquid fuels. Ethanol as a fuel for transportation began to attract attention during the 1970s energy crisis. According to some experts (Duffield and Collins, 2006), most of the current success of corn ethanol can be attributed to the government incentive programs started during this “energy crisis”. The subsequent laws (Energy Security Act 1980, Energy Policy Act 1992) helped the producers and consumers steer towards ethanol as an alternative transportation fuel. The production rate of ethanol has seen an overwhelming increase over last few years (USDOE, 2008). The ethanol production in the United States increased by more than 200% from 6.7 billion liters in 2001 to 24 billion liters in 2007. According to the Renewable Fuel Standards (RFS) of the Energy Independence and Security Act (EISA) of 2007, the volume of total renewable fuel produced by 2022 should be 136 billion liters. Figure 1-1 illustrates the increasing trend of ethanol production in United States and the world. 1.1 Need for Assessment Studies As mandated by EISA 2007, of the 136 million liters renewable fuels, conventional ethanol (produced from corn) will be only 57 billion liters and the rest will be advanced biofuel (cellulosic and biodiesel). Figure 1-2 illustrates the trend of biofuel production expected by EISA. With increasing production rates it has become important to understand the environmental and energetic impacts of production of ethanol. This need in turn has forced science to look for

22

ways to evaluate these impacts. Various studies have been conducted in past several years to analyze the feasibility of large-scale biofuel production, both environmentally and economically. These studies can be classified into various categories, such as net energy balance, life cycle assessment, second law of thermodynamics studies, etc. The details of these methods and some examples of each are explained in Chapter 2. Although abundant assessment studies for ethanol production are available in the science literature right now, there is now a need more than ever for providing a very thorough comparison of these impact assessment methods in as many ways as possible. This thesis attempts to achieve this task using five different assessment methods applied to four different feedstocks. Out of these four feedstocks, one uses a starch-to-ethanol conversion method (corn), two use a sugar-to-ethanol conversion method (sugarcane and sweet sorghum) and the last one uses a cellulosic conversion technology (woody biomass). The five different assessment methods are the following: 1) net energy analysis (NEA) (using first law of thermodynamics); 2) life cycle assessment (LCA); 3) cumulative exergy analysis (CExA) (using second law of thermodynamics); 4) consumptive water analysis (CWA) and 5) emergy synthesis (EmS). The assessment methods mentioned here all serve the purpose of determining the renewability and sustainability of the ethanol production process. These methods also determine the energetic, exergetic and environmental impacts of biofuel production The intent of the present research is not to provide a recommendation for one feedstock or one technology that is currently best suited for ethanol production, but the main objective is to make a contribution to the current field by performing a thorough comparative study of the five assessment methods mentioned above and provide advantages and disadvantages of each along with recommendations for improvements. The advantages and disadvantages discussed here will

23

be based on what each method is lacking in terms of assessing the impacts of ethanol production. also the unique features of each method will be highlighted. One more purpose will be to study the best combinations of these methods that can be used by policy makers. 1.2 Choice of Feedstocks Four different feedstocks were chosen for this study namely, corn, sweet sorghum, sugarcane and woody biomass (specifically southern pine). The rationale behind choosing these particular feedstocks is explained in this section. Currently 90% of the total fuel ethanol produced in United States comes from corn (De Oliveira et al., 2005). Corn ethanol has been under a lot of scrutiny because of the recent surge in the production. Some of the studies (Shapouri et al., 2003; Hill et al., 2006) have shown favorable results and have suggested that the net energy balance of ethanol production from corn is positive; whereas a study by Pimentel et al. (2005) states that approximately 29% more energy is required to produce a gallon of corn ethanol than the energy that is actually in the gallon of ethanol produced. Another study by Energy Resources group (Farrell et al., 2006) evaluated six previous analyses of corn ethanol to study the positive or negative contribution of ethanol to the energy and environment and concluded that the studies that reported negative net energy of ethanol production did so incorrectly due to old data and exclusion of co-product credit. Considering the controversy surrounding the corn ethanol debate, there is a need to define an alternative assessment method which is a combination of both the life cycle assessment and the net energy analysis in addition to three more impact assessment methods mentioned above to study the impacts of corn ethanol. The second feedstock, sweet sorghum, is a very unique crop that provides grain and stem that can be used for sugar, alcohol, syrup, fodder and fue,l etc. Sweet sorghum can compete economically with sugarcane due to its high-value grain production, short growing period and

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low water requirements (Nimbkar and Rajvanshi, 2003). Sweet sorghum is currently being used in India, South America, China and Philippines to produce ethanol. Interest has also been generated in United States (Donovan, 2008). Sweet sorghum can compare economically with sugarcane due to its high-value grain production. Other advantages of sweet sorghum are the following: 1. growth in temperate climates, 2. rapid growth rate, 3. less fertilization required and 4. contains 14-21% directly fermentable sugars. Some other comparative advantages of sweet sorghum over sugarcane are summarized in Table 1-1. It can be seen from Table 1-1, that approximately two sweet sorghum crops can be harvested in the same duration as one sugarcane crop. Even though the ethanol produced from two sweet sorghum crops is less than that from one sugarcane crop, the byproducts such as grain and fodder for livestock make sweet sorghum more desirable than sugarcane. The third feedstock considered in this study was sugarcane. The sugar industry is spread over more than 80 countries worldwide and produces more than 1.5 billion MT of sugar per year (Botha and von Blottnitz, 2006). Currently, 61% of world’s ethanol is produced from sugar crops like sugarcane, sugar beets and sweet sorghum (Shapouri et al., 2006). The largest producer of sugarcane ethanol is Brazil. The ethanol production in Brazil increased from 600 million liters in 1975 to 24 billion liters in 2007 which is equivalent to approximately half of total world production of ethanol (RFA, 2008; Smeets et al., 2008). There is extensive literature available for assessment studies of Brazilian ethanol industry (Khan and Fox, 1982; De Oliveira et al., 2005;

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Macedo et al., 2008; Smeets et al., 2008). This study hopes to cover the sugarcane ethanol industry in India. The fourth and final feedstock used in this study was woody biomass, specifically, slash pine (Pinus elliottii).. It has been stated by many experts that the large scale use of ethanol for fuel will certainly require cellulosic technology (Farrell et al., 2006). According to a technical feasibility study by U.S. Department of Energy and U.S. Department of Agriculture (Perlack et al., 2005), currently the total available biomass from forest resources is 334 million dry MT and from agricultural residues is 176 million dry MT annually. Southern pine species, mainly loblolly and slash are the most abundantly grown wood species in the southeastern United States and have a very good potential to be used as ligncellulosic biomass for production of ethanol. Thus it is important to study the impacts of this emerging feedstock on the resources of southeastern United States. 1.3 Research Objectives The main objective of this work is to provide a unique comparison of five different assessment methods. Considerable attention has been focused on various assessment methods of ethanol production over the last decade. Especially since the rate of production of ethanol has been increasing much faster than previously anticipated, concerns have been raised about ecological, economic and social impacts of ethanol production and their effects on sustainable development. The major goals and organization of chapters in this thesis are as follows: 1. Conduct a thorough literature review of ethanol assessment studies performed using the five assessment methods: NEA, LCA, CExA, CWA and EmS. The procedure to perform analysis using each of these methods is also explained in detail. (Chapter 2)

Full document contains 229 pages
Abstract: Biofuels are emerging as a potential replacement for fossil fuel derived liquid fuels and with increasing production rates is has become essential to understand the environmental and energetic impacts of their production. This study focuses on ethanol production from four feedstocks: corn, sweet sorghum, sugarcane and pine. The main objective of this study is to evaluate the assessment methods used for calculating the impacts of biofuel production and this has been carried out with the help of five methods: net energy analysis, life cycle assessment, cumulative exergy analysis, consumptive water analysis, and emergy synthesis. Detailed data acquisition was carried out to obtain primary input data required for the four feedstocks. This data with some secondary data from literature was used to calculate the impacts using five assessment methods. A sensitivity analysis was also performed to evaluate the stability of the five assessment methods. Three scenarios were considered viz., change in biomass yield, change in transportation distance and change in ethanol yield. It was found that emergy synthesis and life cycle assessment are relatively less sensitive to changes in input than cumulative exergy and net energy analysis methods. Finally the five methods were compared and the advantages and limitations of each have been discussed. Two case studies to demonstrate combining two or more methods have also been presented.