Environmental Engineering Reference
In-Depth Information
1.2
Published values
Commensurate values
Gasoline
EBAMM cases
Gasoline
1.0
0.8
0.6
0.4
CO
2
Intensive
Pimentel
To day
0.2
de Oliveira
Wang
Cellulosic
Patzek
Shapouri
Graboski
-
-8
-6
-4
-2
0
2
4
6 8
Net energy (MJ/L)
10
12
14
16
18
20
22
24
FIGure 11.3
EBAMM net energy and petroleum requirements of corn and cellulosic ethanol. (From
Farrell, A.E. et al.,
Science
, 311, 506-508, 2006.)
taBle 11.2
cropping system scenarios
cropping system scenarios
Winter cover
crop
residue
removal (%)
crop rotation
CS
Corn-soybean
No
0
CC
Continuous corn
No
0
CC50
Continuous corn
No
50
CwC70
Continuous corn
Wheat
70
Source:
Kim, S. and Dale, B.E.,
Biomass Bioenergy,
29, 426-439, 2005.
(cellulosic technology is still in development). According to the Farrell et al. (2006) analysis, the
most sensitive life-cycle parameters were biofuel refinery energy, farm yield, biofuel refinery yield,
co-product credits, nitrogen fertilizer energy, and nitrogen fertilizer application rate. Agriculture
was found to demand 45-80% of the petroleum inputs across the six analyzed studies. Policies tar-
geted at the agriculture sector could effectively reduce life-cycle petroleum consumption.
Kim and Dale (2005) examined four cropping scenarios, including two that utilized corn stover
(residue), as summarized in Table 11.2. Stover refers to the nongrain portion of the plant above the
ground. When stover was collected, it was used to produce ethanol and burned for electricity genera-
tion, which was assumed to offset grid electricity. It was also assumed that on a mass per acre basis,
equal amounts of corn grain and stover were available for collection (i.e., 50% residue collection in
the CC50 scenario means that for each unit of harvested grain, a half-unit of stover was also har-
vested). The corn-soybean rotation scenario is important to consider because it represents the most
common cropping system used in the United States. The study's functional unit was 1 hectare (ha)
of arable land considered over a 40-year period.
The nonrenewable energy impacts of each cropping system over the 40-year study period are
presented in Table 11.3. The CS system consumed the least nonrenewable energy in the agricul-
ture production phase. This is due to reduced field operations and nitrogen fertilizer requirements.
