Ethanol Life Cycle Analysis: Consideration of System Boundary ...

Ethanol Life Cycle Analysis:
Consideration of System Boundary
Expansion and Technology
Improvements
Michael Wang
Center for Transportation Research
Argonne National Laboratory
2011 Annual TRB Meeting, Washington, DC
January 26, 2011

Background
U.S. corn ethanol production in 2009
10.6 billion gallons
5.4% of US gasoline market (on the energy basis)
Has this caused international land use changes and
other unintended consequences? Maybe not
Will continuous growth of corn ethanol to 15 B
gallons cause unintended consequences? Nobody
knows with certainty
Have technologies in farming and corn ethanol
production improved?
2

GREET Includes Many Potential Biofuel Production Pathways
Sugar Crops for EtOH
Sugar cane
Sugar beet
Sweet sorghum
Starch Crops for EtOH
Corn
Wheat
Cassava
Sweet potato
Cellulosic Biomass for EtOH
Corn stover, rice straw, wheat straw
Forest residues
Municipal solid waste
Dedicated energy crops
Black liquor
Landfill Gas
CNG/LNG
Fischer-Tropsch diesel
Hydrogen
Methanol
DME
Fischer-Tropsch jet fuel
Algae
Biodiesel
Butanol
Corn
Sugar beet
Renewable diesel
Oils for Biodiesel/Renewable
Diesel/Renewable Jet Fuel
Soybeans
Rapeseed
Palm oil
Jatropha
Waste cooking oil
Animal fat
Cellulosic Biomass via Gasification
Fischer-Tropsch diesel
Hydrogen
Methanol
DME
Fischer-Tropsch jet fuel
The feedstocks and fuels that are underlined are already included in the GREET model.
3

Life-Cycle Analysis System Boundary:
Corn to Ethanol
Energy inputs
for farming
N 2O emissions
from soil and
water streams
Direct land
use change
Fertilizer
CO 2 via
photosynthesis
Indirect land use
changes for other crops
and in other regions
CO 2 in the
atmosphere
Carbon in kernels
CO 2 emissions
during fermentation
Conventional Animal
Feed Production
Carbon in
ethanol
DGS
CO 2 emissions
from ethanol
combustion
4

Life-Cycle Analysis System boundary:
Switchgrass to Cellulosic Ethanol
N 2O emissions
from soil and
water streams
Energy inputs
for farming
Fertilizer
CO 2 via
photosynthesis
Direct land
use change Indirect land use
changes for other
crops and in other
regions
CO 2 in the
atmosphere
Cellulosic
biomass
CO 2 emissions
during fermentation
Lignin
Conventional
electricity generation
Ethanol
CO 2 emissions
from ethanol combustion
On-site
power
generation
5

Life-Cycle Analysis System Boundary:
Petroleum to Gasoline
6

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
Direct and indirect land use changes and resulted GHG
emissions
Life-cycle analysis methodologies
Attributional LCA
Consequential LCA

U.S. Efforts on Modeling LUCs of Biofuel
Production
Searchinger et al. with FAPRI for corn ethanol
CARB/UCB/Purdue with GTAP for corn ethanol
EPA/Texas A&M/Iowa State U. with FASOM and
FAPRI for corn ethanol, biodiesel, sugarcane
ethanol, and cellulosic ethanol
DOE/ANL/Purdue with GTAP for corn ethanol and
cellulosic ethanol
Others have been applying models to examine LUCs
8

Direct and Indirect Land Use Change Modeling:
ANL and Purdue Collaboration on GTAP Upgrade
Land availability in key countries
Increases in yields in response to elevated commodity
price
Future grain supply and demand trends without
ethanol production
Substitution of conventional animal feed with byproducts
of ethanol manufacturing (DGS)
Updated GHG emissions from direct and indirect land
use change impacts
9

Acres/1000 Ethanol Gallons
Land Use Change Simulated for US Corn Ethanol
Production from Completed Studies
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
FAPRI
Searchinger et al.
2008
FAPRI
&FASOM
Effects of several critical factors in CGE models:
Available land types
Yield responses to price increase
Animal feed modeling
Growth in both demand and supply
GTAP - unrevised
GTAP - revised
EPA 2010b CARB 2009 Hertel et al. 2010 Tyner et al. 2010: Tyner et al. 2010: Tyner et al. 2010:
a
2001 Baseline
b
2006 Baseline – 2006 Baseline c –
partial update update through
2015
FAPRI – Food and Agricultural Policy Research Institute (Iowa State)
FASOM – Forest and Agricultural Sector Optimization Model (Texas A&M)

Greenhouse Gas Emissions of Land Use
Changes of Corn Ethanol from Completed Studies
FAPRI
FAPRI
&FASOM
Additional uncertainties introduced from LUCs
to LUC-induced GHGs:
Land types for meeting simulated LUCs:
historical observation vs. future change
Above- and below-ground biomass and
carbon: equilibrium vs. stock
Lifetime of a biofuel program vs. lifetime
of a policy?
GTAP - unrevised
FAPRI – Food and Agricultural Policy Research Institute (Iowa State)
FASOM – Forest and Agricultural Sector Optimization Model (Texas A&M)
GTAP - revised
2001 Baseline 2006 Baseline –
partial update
2006 Baseline –
update through
2015
11

Trend of 35 Studies in the Past 35 Years: Energy Use in
U.S. Corn Ethanol Plants Has Decreased Significantly
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
Historical Ethanol Plant Energy Use: Btu/Gallon
Dry Mill Wet Mill Average
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
12

Fertilizer Use in U.S. Corn Farming Has
Reduced Significantly in the Past 40 Years
Fertilizer Use Per Bushel of Corn (relative to 1970)
110%
100%
90%
80%
70%
60%
50%
40%
30%
Nitrogen
K2O
P2O5
13

Energy Use for Corn Farming Has Been Reduced
The unusual high farming energy use in 1996 may be caused by the wet weather
in that year in the Midwest.
14

Intensity of Fertilizer Use in U.S. Corn Farming and Energy Use and
GHG Emissions of Fertilizer Production and Use
Nitrogen Phosphate Potash Lime
Fertilizer Use Intensity: lb of
nutrient per bushel of corn
Energy Use for Fertilizer
0.96 0.34 0.40 2.44
Production: Btu/lb of nutrient
GHG Emissions of Fertilizer
20,741 5,939 3,719 3,398
Production: g CO2e/lb of nutrient
GHG Emissions from Fertilizer in
1,359 460 302 274
Field: g CO2e/lb of nutrient 2,965a 0 0 200b Total GHG Emissions: g CO2e/lb
of fertilizer
Total GHG Emissions: g
4,324 460 302 474
CO2e/bushel of corn 4,151 156 121 1,157
a This is CO2e emissions of N 2O from nitrification and denitrification of nitrogen fertilizer in cornfields.
b This is CO2 emissions of converting calcium carbonate (limestone) to calcium oxide (burnt lime) in cornfields.
15

GHG Emissions Benefits of Animal Feed By-
Products
Distillers’ Grains Solids (DGS) can offset animal feeds of corn,
soybeans, and urea
Conventional feed displacement yields GHG “credits” for
ethanol that are simulated in GREET
Reduction in LUCs also results from conventional feed
displacement
Displacement of corn
Displacement of soy meals
16

Displacement Ratios between DGS and
Conventional Animal Feeds
DDGS and WDGS
DDGS Dispalcement Ratio
WDGS Displacement Ratio
US Market Share
(kg/kg DDGS)
(kg/kg WDGS)
Market
Market Share Soybean
Share
Soybean
Feedlot Level
(%) Corn meal Urea (%) Corn meal Urea
Beef Cattle 40.6% 35.7% 1.203 0.000 0.068 50.0% 1.276 0.000 0.037
Dairy Cattle 40.6% 35.7% 0.445 0.545 0.000 50.0% 0.445 0.545 0.000
Swine 12.8% 19.5% 0.577 0.419 0.000
Poultry 6.0% 9.2% 0.552 0.483 0.000
Average 0.751 0.320 0.024 0.861 0.273 0.019
DDGS and WDGS Displacement Ratio
(kg/kg DDGS&WDGS)
Soybean
Corn meal Urea
U.S. Consumption Level a
U.S. and Export Market Combined b
0.788 0.304 0.022
0.781 0.307 0.023
17

Most Recent Studies Show Positive Net Energy
Balance for Corn Ethanol
Energy balance here is defined as Btu content a gallon of ethanol minus fossil energy used to produce a gallon of ethanol
18

Energy Use by Type Varies Considerably Among
Energy Products
Life-Cycle Energy Use (MJ/MJ)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
Renewable
Petroleum
NG
Coal
Corn Ethanol Cellulosic Ethanol Electricity Gasoline
19

GHG Emissions of Corn Ethanol Vary Considerably
Among Process Fuels in Plants; Cellulosic Ethanol
Consistently Achieve Large Reductions
20

GHG Emission Sources of Ethanol and Gasoline
21

gCO2e/MJ
Well-to-Pump GHG Emissions of Petroleum Gasoline
40
35
30
25
20
15
10
5
0
Charpentier et al. (2009)
GREET (2010)
Bruijn (2010)
Energy-Redefining, LLC (2010)
Conventional Crude
Without Gas
Flaring
Conventional Crude - Flaring
Breakdown
Gasoline combustion: about 75 g/MJ GHG emissions
With Significant Gas Flaring
Surface Mining
In-Situ Production
Surface Mining
Average
Average
Oil Sands
In-Situ Production
Surface Mining
Average
In-Situ Production: With Cyclic Steam Stimulation
In Situ Production: With Steam-Assisted Gravity Drainage
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Conclusions
Corn ethanol life cycle GHG emissions are approximately 24%
below those of gasoline
Cellulosic ethanol life cycle GHG emissions could achieve close to
100% below those of gasoline
It is critical to consider evolving technology and feedstock types in
biofuel LCAs
A philosophic issue in ethanol LCAs in the past several years:
If we are not certain about the magnitude of certain risks, should we assign
somewhat high negative values to manage them?
However, doing so may indeed generate other risks
Lost opportunities of achieving GHG reductions immediately (though moderate and
incremental)
High-carbon fuels may seize the opportunity
To use analysis results for policy making, should we pursue
underlined causes to address uncertainties, or should we aggregate
old and new results all together to address “perceived”
uncertainties/risks?
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