Environmental Engineering Reference
In-Depth Information
taBle 11.3
nonrenewable energy requirements
nonrenewable energy (tJ/ha)
cs
cc
cc50
cwc70
Agricultural process
0.46
0.72
0.8
0.91
Wet milling
0.81
1.63
1.61
1.7
Avoided co-product systems
a
-0.07
-1.89
-1.87
-1.98
Soybean milling
0.22
-
-
-
Biodiesel production
0.12
-
-
-
B20 driving
b
1.83
-
-
-
Avoided B20 driving system
-2.27
-
-
-
Corn stover conversion
-
-
0.13
0.2
Avoided electricity
-
-
-0.41
-0.6
E10 driving
b
26.6
53.7
75.1
88.4
Avoided E10 driving system
-28.5
-57.5
-80.5
-94.8
Total
-0.77
-3.38
-5.14
-6.17
Source:
Kim, S. and Dale, B.E.,
Biomass Bioenergy,
29, 426-439, 2005.
a
Co-products: corn oil, corn gluten meal, corn gluten feed, and soybean meal and
glycerine (CS system).
b
Transportation and distribution included.
The energy values in the avoided rows are negative because they were credited to the system using
displacement allocation by system expansion. Clearly, the volume of biofuel production (E10 driv-
ing) and consequent offset of nonbiofuel driving (avoided E10 driving system) had the greatest effect
on life-cycle nonrenewable energy consumption. The CC50 and CwC70 systems outperformed the
others primarily because the collected corn stover provided more feedstock for conversion to etha-
nol at a relatively low increase in agricultural input energy (see Table 11.3).
Stover electricity conversion efficiency and co-product allocation were the most sensitive parame-
ters affecting nonrenewable energy results. When the efficiency of converting stover to electricity was
increased from 15% to 32%, as suggested by one study (Stahl 1998), nonrenewable energy consump-
tion was reduced by 16% in the CC50 system and 20% in the CwC70 cropping system. Kim and Dale
(2005) also considered allocation by mass and found that it improved (decreased) the nonrenewable
energy consumption of the CS system but reduced the benefits of the CC, CC50, and CwC70 cropping
systems by 55%, 36%, and 31%, respectively, compared with the baseline (displacement allocation).
Switchgrass is a promising alternative ethanol feedstock because it is not a food crop, can be
grown on agriculturally marginal land, and has relatively low fertilizer and pesticide requirements
(Hill et al. 2006). A large body of data exists on annual corn yields, but not for switchgrass yields.
A 5-year USDA study (Schmer et al. 2008) was carried out to evaluate switchgrass yield poten-
tial in several midwestern U.S. locations through larger-scale field trials on marginal cropland,
rather than on small research plots. Reported agricultural data from the study were entered into the
EBAMM model to calculate well-to-wheel energy. Only 1 MJ of petroleum was required to produce
13.2 MJ of ethanol over the fuel's life-cycle. This result, although presented differently in Schmer
et al. (2008), approximately agrees with Farrell et al.'s (2006) EBAMM determined result for cel-
lulosic ethanol in Figure 11.3; recalculating Schmer et al.'s (2008) result yields 1 MJ petroleum/13.2
MJ ethanol ≈ 0.08 MJ petroleum/MJ ethanol.
The United States produces more than half of the world's fuel ethanol, followed by Brazil. In
Brazil, most ethanol is derived from sugarcane, and laws mandate that internally sold gasoline
contain at least 25% ethanol. Wang et al. (2007) examined the well-to-wheel life-cycle of sugarcane
ethanol and compared the results to those of corn ethanol using the GREET model. The baseline
