Environmental Engineering Reference
In-Depth Information
Combustion without soot emission is still a challenge and should be addressed in large
continuous combustion test facilities. Though the physical and chemical properties
are similar to conventional hydrocarbon fuels, engine modi
cations might be nec-
essary. Further, properties of HED fuels can vary from batch to batch.
Pioneering research in the synthesis and combustion of this type of fuels has
been done over two decades ago in the United States and currently pursued in India.
However, due to the limited demand of such fuels, major oil manufactures have not
played an active role in the development and production HED fuels.
3.2 Biofuels
The most plausible candidate now for alternate fuels is biofuels with the potential of
sustainability and has drawn international attention in the past couple of decades.
Government mandates and
financial support, consumer advocates and green energy
supporters together with the keen interest from academia, government, and industry
—
in particular small business
gave a boost to biofuel development. In the United
States, organizations such as Commercial Alternate Aviation Fuels Initiative
(CAAFI) with participation of government, industry, and academia leaders aid in
promoting biojet fuel research and development. Biodiesel fuel development also gets
equal attention, and gas stations selling biodiesel fuel are common sight in Asian
countries. While biofuel development based on current technologies is an evolu-
tionary approach, there are several limitations to those.
Transesteri
—
cation of vegetable oils to produce biodiesel has the disadvantage of
using food sources and only limited parts of the plant source. Further, it has higher
viscosity and freeze point, poor cold
flow properties, and limited shelf life.
Conventional hydro-processing is low in ef
fl
ciency, higher in hydrogen consump-
tion and operating costs and results in undesirable byproducts. The entire plant
material is not fully utilized. In conventional biochemical conversion, and ethanol
produced from starch and grains divert valuable food sources. Cellulosic biomass to
fuel is still under development with challenges in hemicellulose and lignin
conversion to sugar. The process produces only gasoline additive and not a biojet or
biodiesel fuel. Biomass/coal gasi
cation produces pollutants (NO
x
and SO
x
) and
requires expensive upstream air separation. Fischer
Tropsch process,
though
-
extensively used, involves expensive liquifaction.
3.2.1 Feedstock Challenges
Biofuel production is getting serious attention from the fundamental aspects to
production plants. Some of the biofuel feedstocks with their oil content are shown
in Fig.
5
.
Innovative technologies will need novel catalysts and reactors. Suf
cient
knowledge of the chemistry, process
fl
flexibility, and pretreatment requirements must
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