Environmental Engineering Reference
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If the oxygen content can be reduced by using torrefaction of biomass, catalytic
cracking, and hydrotreating (Jacobson et al.
2013
) of bio-oils, the energy density of
the biomass and bio-oils can be improved and in turn will also reduce the RQ factor
of the fuels. But such a process also reduces the yield of bio oil. Though renewable
fuels are argued to be carbon neutral, their potential to emit carbon is much higher
(higher RQ when compared to coal). Coupled with its lower energy density, var-
iability in production and process ef
ciencies and land usage pattern, studies should
be done to effectively use fossil fuels with reduced RQ factor.
3.3.2 RQ Factor for Fuel Processing
Even though biomass is a renewable fuel where CO
2
produced by direct com-
bustion is neutralized by CO
2
used in production of fuel, the processing of biomass
(electrical power for pumping water, heat required for drying, fertilizer used for
cultivation, fuels used for collection and transportation, etc.) releases CO
2
if fossil
fuels are used to grow and process biomass. Then, one can de
ne equivalent RQ
value (RQ
process,biomass
) for biomass processing by estimating tons of CO
2
released
per GJ of heat content of biomass delivered to power plants. RQ
process,biomass
can be
de
ned according to Eq. (
18
) (Thanapal
2014
).
8
<
:
9
=
;
GJ
kg biomass
GJ
kg biomass
RQ
1
p
elec
:
RQ
2
q
heat
RQ
biomass
C
%
12
RQ
process
;
biomass
¼
219
01
þ
þ
RQ
3
þ
RQ
4
g
g
burner
:
ð
18
Þ
where RQ
1
refers to fossil fuel used for electric power generation, RQ
2
refers to
another fossil fuel used for direct heat production,
ƞ
: power plant ef
ciency,
ƞ
burner
:
burner ef
ciency, RQ
3
refers to CO
2
released during collection and transportation,
RQ
4
for CO
2
produced while producing fertilizers and C%, carbon mass% in bio-
mass fuels. RQ (by direct oxidation) is relatively
fixed for most biomass fuels.
However, C% decreases when there is more oxygen, moisture, and ash in biomass
fuel. Thus, higher amount of biomass would be needed for the same heat input and
larger the CO
2
emitted during the processing of renewable biomass fuels. Hence,
RQ
process,biomass
increases and if it reaches same as coal, then such a biomass is not
useful as renewable fuel, i.e., criteria must be RQ
process,biomass
<RQ
coal
if biomass is
used to replace coal in order to reduce GWP. Lifecycle assessment of willow biomass
production was analyzed by Heller et al. (
2003
). Based on the analysis, it was
estimated that the total energy consumed for the production of willow based biomass
was 98.3 GJ/ha over seven harvest rotations. Around 13.6 oven dry tonnes per
hectare per year was estimated to be the average yield of the biomass. Assuming
mesquite and juniper will also consume similar amount of energy when cultivated on
a large scale solely for the utilization of these woody biomass for power production,
RQ
process,biomass
can be determined based on the data provided by Heller et al. (
2003
).
The RQ
process,biomass
for both mesquite and juniper was found to be 0.03 based on the
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