Environmental Engineering Reference
In-Depth Information
100,000
50,000
Pump-to-wheel
Well-to-pump, hybrid
Well-to-pump, market
0
Well-to-pump, energy
Well-to-pump, displacement
-50,000
Well-to-pump
-100,000
Renewable
gasoline
Biodiesel
Supercetane
Green diesel
-150,000
FIGure 11.19
GHG emissions for six fuel production pathways. (From Huo, H., et al.,
Life-Cycle Assessment
of Energy and Greenhouse Gas Effects of Soybean-Derived Biodiesel and Renewable Fuels.
ANL/ESD 08-2,
Argonne National Laboratory, Argonne, IL, 2008.)
displacement method, supercetane reduces GHG emissions by 130% compared with petroleum die-
sel, and renewable gasoline reduces GHG emissions by 174% compared with gasoline. The reason
for these savings is that not only do the primary products (i.e., supercetane and renewable gasoline)
displace liquid petroleum fuels, but their co-products also displace substantial amounts of fossil
fuels. Using the energy, market, and hybrid allocation methods, life-cycle GHG emissions were
calculated as declining by 57-94% across the four modeled biofuel pathways.
11.2.4 o
thEr
B
iofuEl
S
ourcES
U.S. corn and Brazilian sugarcane dominate the global ethanol production market, but other bio-
fuel crops have received attention around the world on the basis of their suitability to regional cli-
mates and resources. A wide range of biofuel feedstocks, although not all, have been evaluated with
LCA—a few alternative feedstock sources are discussed in Sections 11.2.4.1 and 11.2.4.2.
11.2.4.1 ethanol
One proposed source (Kalogo et al. 2007) of ethanol is municipal solid waste (MSW). It has
been estimated that approximately 2-3.6 billion gallons of ethanol could be produced from MSW
annually (compare this with the 9 billion gallons of ethanol produced in the United States in 2008;
see Figure 11.2), and that conversion of MSW to ethanol for vehicle use would reduce fossil fuel
use by displacing gasoline and corn ethanol. It could also reduce GHG emissions by 65 and 58%,
compared with gasoline and corn ethanol, respectively. As of July 2009, the EPA intends to disal-
low MSW as an ethanol fuel source under the Energy Policy Act of 2007, but it is seeking further
comment on this issue because exclusion would narrow available options for meeting legislative
transportation fuel GHG reduction targets (EPA 2009a).
11.2.4.2 Biodiesel
One study (Reijnders and Huijbregts 2008) of the production of palm oil, which can be converted to
biodiesel, assessed agriculture and palm oil production processes in South Asia. The authors point
out that large amounts of organic residue are generated during palm oil production. These residues
could be combusted to produce steam and electricity, although this is rarely done in practice; they
assumed 75% of palm oil production energy was provided by fossil fuels, in accordance with actual
practice. Wang et al. (2007) found that sugarcane bagasse displacement of grid electricity was the
largest contributor to life-cycle GHG emissions reductions. However, the dominant GHG emissions
source in Reijnders and Huijbregts (2008) was the direct conversion of natural lands to palm oil
plantations. Total life-cycle GHG emissions were estimated to be in the broad range of 2.6-18.2 t
CO
2
e/t of palm oil. Conversion of forests and peat lands contributed between 1.5 and 17 t CO
2
e/t
