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Life-Cycle Analysis of Biofuels:
Issues and Results
Michael Wang
Center for Transportation Research
Argonne National Laboratory
Presentation to the Special Committee on Domestic Biofuels
State of Wisconsin Joint Legislative Council
Madison, WI, October 14, 2008
Life-Cycle Analysis for Vehicle/Fuel Systems
Has Been Evolved in the Past 30 Years
Historically, evaluation of vehicle/fuel systems from wells to
wheels (WTW) was called fuel-cycle analysis
Pioneer transportation WTW analyses began in 1980s
Early studies were motivated primarily by battery-powered
EVs
Recent studies were motivated primarily by introduction of new
fuels such as hydrogen and biofuels
Pursuing reductions in transportation GHG emissions now
demands for intensive and extensive WTW analyses
Early WTW studies were for evaluation of individual technologies
or processes; the current focus has been expanded to general
policy evaluation
Many studies conclude with the quantity of energy and emissions;
some studies carry all the way to impact assessment
2
The GREET (Greenhouse gases, Regulated
Emissions, and Energy use in Transportation) Model
Vehicle Cycle GREET 2.7
The GREET model and its documents are
available at Argonne’s website at
http://www.transportation.anl.gov/software/GREET/
The most recent GREET version (GREET
1.8b) was released in May 2008
As of July 2008, there are 9,000 registered
GREET users worldwide
Well to Wheels
Fuel Cycle GREET 1.8
3
As of July 2008, the Number of GREET Users Has Grown to 9,000
10,000
9,000
Cumulative Number of GREET Users
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
2001 2002 2003 2004 2005 2006 2007 2008
University Industry Other
North America Europe Asia Other
Government Consulting NGO
GREET Includes More Than 100 Fuel Production
Pathways from Various Energy Feedstocks
5
GREET Includes Some of the Potential
Biofuel Production Pathways
Sugar Crops for EtOH Oils for Biodiesel/Renewable
Sugar cane Diesel
Sugar beet Soybeans
Sweet sorghum Algaes Rapeseed
Oils Palm oil
Starch Crops for EtOH
Hydrogen Jatropha
Corn Waste cooking oil
Wheat Butanol Production
Animal fat
Cassava Corn
Sugar beet Cellulosic Biomass for EtOH
Sweet potato
Corn stover, rice straw,
Cellulosic Biomass via wheat straw
Gasification Forest wood residue
Fitscher-Tropsch diesel Municipal solid waste
Hydrogen Energy crops
Methanol Black liquor
The feedstocks that are underlined are already included in the GREET model.
6
The 2007 Energy Independence and Security Act Established
Aggressive Biofuel Production Targets
21000
Corn EtOH Adv. Biofuels
18000
Million Gallons of EtOH/Yr
15000
12000
9000
6000
3000
0
1980
1982
1986
1990
1994
2000
2004
2008
2012
2018
2022
1984
1988
1992
1996
1998
2002
2006
2010
2014
2016
2020
The 2007 EISA Requires US EPA To Conduct
Life-Cycle Analysis for Fuels
LCA is conducted to determine if given fuel types meet
mandated minimum GHG reductions compared to 2005
baseline petroleum fuels
Ethanol produced from corn: 20% (only applies to fuel produced in
new facilities)
Cellulosic biofuels: 60%
Biomass-based diesel (e.g., biodiesel): 50%
Other advanced biofuels (e.g., imported sugarcane ethanol,
renewable diesel, CNG/LNG made from biogas): 50%
Life cycle analysis includes
All major GHGs (CO2, CH4, and N2O)
Both production and use of biofuels
Direct and indirect land use change impacts
8
GREET Ethanol Life-Cycle Analysis Includes
Activities from Fertilizer to Ethanol at Stations
Agricultural chemical production
Agricultural chemical transportation
Corn Crop residue Switchgrass Fast growing Forest residue Sugar cane
farming collection farming tree farming collection farming
Corn ethanol Cellulosic ethanol Sugar cane
production production ethanol production
Animal feed Ethanol transportation Co-produced electricity
Ethanol blending at bulk
terminal
Ethanol blends at Ethanol blend use in
refueling station vehicles
9
Key Issues Affecting Biofuel WTW Results
Continued technology advancements
Agricultural farming: continued crop yield increase and resultant reduction
of energy and chemical inputs per unit of yield
Energy use in ethanol plants: reduction in process fuel use and switch of
process fuel types
Methods of estimating emission credits of co-products of
ethanol
Distillers grains and solubles (DGS) for corn ethanol: 0-50%
Electricity for cellulosic and sugarcane ethanol
Animal feed and specialty chemicals for biodiesel
Direct and indirect land use changes and resulted GHG
emissions
Life-cycle analysis methodologies
Attributional LCA
Consequential LCA
10
Accurate Ethanol Energy Analysis Must Account
for Increased Productivity in Farming Over Time
Corn Yield Normalized by Nitrogen Fertilizer Applied
1.00 U.S. Corn Output Per Pound of Fertilizer
Has Risen by 55% in The Past 35 Years
(bushel/lb N fertilizer)
0.80
0.60
1970 1974 1978 1982 1986 1990 1994 1998 2002
Based on harvested acreage. Source: USDA
11
Energy Use for Corn Farming Varies
Considerably Among Corn-Producing States
2001 U.S. Corn Farming Energy Use: Btu/Bushel
9-State
IL IN IA MN NE OH MI SD WI Average
Diesel 3,259 4,180 3,910 4,883 12,032 4,474 8,142 5,388 7,285 6,366
Gasoline 1,194 1,725 922 1,389 1,842 1,504 2,555 1,660 1,246 2,856
LPG 1,631 1,923 4,047 5,083 2,631 3,853 2,692 405 1,237 2,102
Electricity 225 683 379 644 3,931 276 766 891 173 829
Natural gas 518 1,003 0 317 7,158 1,306 1,931 66 934 1,749
Custom work 2,001 1,197 1,417 1,294 1,291 1,434 1,859 1,913 2,526 1,581
Input hauling 143 167 178 176 242 209 254 121 251 202
Total 8,971 10,878 10,853 13,785 29,127 13,056 18,200 10,444 13,652 15,685
• Corn farming energy use varies by three times among nine corn-producing states.
• From 1996 to 2001, U.S. corn farming energy use in Btu/bushel was reduced by 34%.
12
In General, Infrastructure-Related Activities Are Not A
Major Contributor to WTW Results –
GRRET Simulation of Farming Equipment for Ethanol WTW Analysis
Size of farm Equipment Weight Lifetime
(tons) (yr)
Life time of equipment Large tractor 10 15
Energy for producing Small tractor 5.7 15
equipment materials (the Field cultivator 2.6 10
majority of equipment Chisel plow/ripper 4.0 10
materials is steel and Planter 3.7 10
Combine 13.7 15
rubber)
Corn combine head 4.0 10
Argonne has found that Gravity box (4) 7.3 15
farming equipment may Auger 0.9 10
contribute to <2% of energy Grain bin (3) 10.5 15
and ~1% GHG emissions for Irrigation 5.3 12
corn ethanol Sprayer 0.6 10
13
Improved Technology and Plant Design Has Reduced
Energy Use and Operating Costs in Corn Ethanol Plants
70,000 Average in 1980s
Average in 2005
60,000
New NG EtOH Plant
New Coal EtOH Plant
50,000 ~1/3 of Energy is
Spent on DDGS Drying
Btu/Gallon
40,000
30%
30,000 reduction
20,000 50%
reduction
10,000
0
Wet Mill Dry Mill
There are indications that the ethanol industry continues
to reduce plant energy use.
14
Co-Products with Biofuels
Types of co-products
Corn ethanol: animal feeds (distillers grains and solubles, DGS)
Sugarcane ethanol: electricity
Cellulosic ethanol: electricity
Biodiesel and renewable diesel from soybean and rapeseed:
animal feeds, glycerin, and other chemicals
Ways of dealing with co-products
Displacement method (or the system boundary expansion
approach)
Allocation methods
• Mass based
• Energy content based
• Economic revenue based
Production plant process purpose based
Scale of biofuel production (and resultant scale of co-product
production) can affect the choice of methods
Proper Accounting for Animal Feed Is Key to
Corn Ethanol’s Lifecycle Analysis
Source: RFA, 2008
Allocation Method Wet milling Dry milling
Weight 52% 51%
Energy content 43% 39%
Process energy 36% 41%
Market value 30% 24%
Displacement ~16% ~20%
Argonne uses the displacement method.
17
Key Issues Affecting Cellulosic Ethanol Results
Cellulosic biomass feedstock types
Fast growing trees
• Soil carbon could increase
• Fertilizer may be applied
• Irrigation to be needed?
Switchgrass and other native grass
• Soil carbon could increase
• Fertilizer will be applied
• Irrigation to be needed?
Crop residues
• soil carbon could decrease
• Additional fertilizer will be needed to supplement nutrient removal
Forest wood residues: collection effort could be extensive
Co-production of ethanol and electricity
The amount of electricity produced
The types of conventional electric generation to be displaced
Land use changes could have less effects on cellulosic ethanol’s GHG
results
GHG Emissions of Corn Ethanol Vary
Considerably Among Process Fuels in Plants
GHG Emission Reductions By Ethanol Relative to Gasoline
GHG effects of potential land use changes are not fully included in these results.
19
Approach to Address GHG Emissions of Potential Land Use
Change by Large-Scale Biofuel Production
Potential land use changes
Direct land use change: regional or national scale
Indirect land use change: global scale
Both can be simulated with global general equilibrium models
The resolution level of global GE models could be a key factor
Carbon profiles of major land types
Models in the U.S. and Europe are available
Carbon profiles of land types in other parts of the world (South America, Asia,
Africa) may be less understood
Time horizon of biofuel programs; “for-ever biofuels” can mathematically
result in zero GHG emission changes from land use changes
At present, GREET includes the following soil CO2 sources/sinks for ethanol
Corn ethanol: CO2 source of 73 grams/gal. EtOH from soil C reduction
Cellulosic ethanol
• Fast growing trees: CO2 sink of 1,250 g/gal. EtOH from soil C increase
• Switchgrass: CO2 sink of 540 g/gal. EtOH from soil C increase
Modeling of Land Use Changes by Biofuel Production
Baseline definition
Global trend of demand for food and thus agricultural commodities
Global trend of supply of agricultural commodities
Current and future global land use patterns (including agricultural
sector and other sectors)
Various worldwide biofuel programs: are they parts of a
biofuel system or competing programs?
Growth of crop yields
Trend yield growth
Yield growth response to price increase
How to value animal feeds in modeling? – nutrition value vs.
market price approach
Land use changes vs. land use intensification
21
Change in Soil Carbon Content Differ Among Land
Use Changes and Over Time
(The Three Profiles Here Are for Illustrative Purpose Only)
Soil Carbon Content
Farming with Initial C Increase
Baseline
Farming with C Decrease
Farming with Initial C Decrease
Beginning of Year End of Biofuel
Biofuel Program Program?
22
GHG Benefits and Burdens for Fuel Ethanol Cycle Occur
at Different Stages (and With Different Players)
CO2 in the
CO2 via atmosphere
Photosynthesis
Energy inputs
for farming Fossil energy
inputs to
ethanol plant CO2 emissions
during fermentation CO2 emissions
from ethanol
combustion
Carbon in Carbon in
Fertilizer kernels ethanol
Change in
soil carbon DGS
N2O emissions
from soil and
water streams
In direct land use changes
for other crops and in
other regions
Conventional animal
feed production cycle
Facility-Level Certification for LCFS?
Corn Ethanol GHG Reductions
Leaders
Industry baseline (default?)
Laggards (leakage to non-LCFS states?)
Individual Facility
24
Four FT Diesel Production Options Were Evaluated
on the Well-to-Wheels Basis by Argonne
Natural gas to liquids (GTL)
Coal to liquids (CTL)
Biomass to liquids (BTL)
Co-firing of coal and biomass to liquids (C/BTL)
85/15 C/B co-feeding
38/62 C/B co-feeding: GHG breakeven with petroleum diesel
All options were evaluated with and without
carbon capture and storage (CCS) in FTD
plants
Key Issues and Assumptions for FT Diesel Plants
FT diesel plant designs
Standalone to produce diesel, naphtha, and other products
Co-generation of steam and/or electricity for export
This study evaluated standalone plants
GTL plant assumptions in this study
Energy conversion efficiency of 63%
Carbon conversion efficiency of 80%
CTL plant assumptions in this study
Based on studies by National Energy Technology Laboratory (2003 and 2007)
Energy conversion efficiency of 50%
A carbon capture and storage (CCS) case with a carbon capture rate of 90% at
FT plants
BTL plant assumptions in this study
Based on studies completed in Europe
Energy conversion efficiency of 50%
A CCS case with a carbon capture rate of 90%
C/B TL plant assumptions
This is a case for diluting carbon from coal
Assumptions are based on CTL and BTL plants
Engineering details need to be examined
Logistic and costs of two separate feedstocks are a key issue
Trade-Offs Between Petroleum Reductions and GHG
Reductions by FT Diesel from Different Feedstocks
Biodiesel Is An Renewable Alternative to Petroleum Diesel
Produced from various biological
sources (soybeans, rapeseeds, animal
fats, sunflower seeds, palm oil…) via
the transesterification process
In US, a majority of biodiesel is
produced from soybeans
High cetane value of 50-65 (vs. 40 for
petroleum diesel)
Can be blended with conventional
diesel fuel in any proportion
Production & sales volume for Increased by
biodiesel in U.S. has increased 1000 times
dramatically during 8 years
Hydrogenation process can also be
used to produce renewable diesel
Source: National Biodiesel Board
28
Pathways of Biodiesel and Renewable Diesel
Soy Oil Diesel Vehicle
BD T&D
Transesterification Operation
Soybean Soybean Soybean Oil
Farming Transportation Extraction
Fertilizer Diesel Vehicle
RD Production RD T&D
Production Operation
Well-to-Pump Pump-to-Wheels
Well-to-Wheels
Existing in GREET Existing and updated in this work Newly Expanded
29
Four Allocation Approaches Were Employed to
Address Various Co-Products
Fertilizer
Manufacturing
Soybean Soybean Soy Oil Soy Oil BD BD
Farming Transportation Extraction Transesterification Transportation Combustion
Soy Meal Glycerin
Soy Oil RD-I RD-I
Hydrogenation Transportation Combustion
1. Displacement Fuel gas
Heavy Oils
2. Energy value-based allocation
Soy Oil RD-II RD-II
Hydrogenation Transportation Combustion
3. Market value-based allocation
4. Hybrid approach: combination of Propane fuel mix
displacement and allocation
30
Co-Product Methodologies Significantly Influence Results
for Soybean-Based Biodiesel or Renewable Diesel
100,000 100%
1 2 3 4 1 2 3 4 1 2 3 4
60,000 60%
WTW GHG Emissions (g/mmBtu) .
20,000 20%
Relative GHG Emission Chnages
-20,000 -20%
-60,000 -60%
-100,000 -100%
PTW emissions
WTP emissions
-140,000 -140%
WTW emissions
Emission changes
-180,000 -180%
Petroleum BD RD-I RD-II
Diesel
1, Displacement; 2, Energy-value–based allocation; 3, Market-value–based allocation; 4, Hybrid
31
Outstanding LCA Issues
Purpose of LCAs and their models has been evolving over the past 30 years
Scope of LCAs:
Representation of LCA scoping is a key factor; misrepresentation can cause
confusion to the least
Average vs. marginal analysis
Industry vs. facilities: significant implications on LCFS and carbon trading
National vs. regional analysis: national or regional LCFS; need to avoid double-
counting and/or leakage
Transparency of methodologies and input data
Technology advancement over time need to be considered
System boundary of LCAs: has been a moving target
Consistency vs. intuition (an issue of resource availability)
Research vs. policy development
Aggregate effects vs. attribution (and responsibility): consequential vs.
attributional LCAs
32
If We Are Going to Consider Different Farming
Practices for GHG Regulations for Fuels, We Will
Need to Address:
Chemical and energy inputs to individual
farms, a given county, or a given state?
Different tillage practices?
Practicality, traceability, and verifiability of
input data for the feedstock (e.g., corn0 into
a specific biofuel facility
A balance between operationability of a
regulation and incentivizing of advanced
farming practices
33
Some Thoughts
While the current discussion/debate/research efforts
are on land use changes by large-scale biofuel
production and the uncertainties caused by them, can
we separate
Technology effects and certainties – should the
society continue to promote technology
advancement?
Social, behavioral, and/or economic effects and
uncertainties – are some of them mitigatable?
We need to design a biofuel policy with flexibility to
address uncertainties, to help advance technologies,
and to avoid potential risks
34
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