Biomedical Engineering Reference
In-Depth Information
The feeding of wet solid biomass, which is fibrous and widely varying in
composition, is another major challenge. A slurry pump has been used to
feed solid slurry into high-pressure reactors, but it has not been tested for
feeding biomass slurry into a supercritical reactor with ultrahigh pressure.
The drop in gasification efficiency and gas yield with an increase in dry
solids in the feed may be a major obstacle to commercial SCWG. Efforts
are being made to improve this ratio using different catalysts, but a cost-
effective method has yet to be discovered.
Separation of carbon dioxide from other gases may require the addition of
large amounts of water at high pressure (see
Section 9.7.6
). This can
greatly increase the system's cost and reduce its overall energy
efficiency.
The heating of biomass slurry in the heat exchanger and reactor is likely
to cause fouling or plugging because of the tar and char produced during
the preheating stage. Further research is required to address this important
challenge. A final problem that might
inhibit commercialization of
SCWG is the corrosion of the reactor wall.
SYMBOLS AND NOMENCLATURE
A
cross-sectional area (m
2
)
C
i
mole fraction of the component i in the gas product
F
c
carbon fraction in feed
k
g
reaction rate (s
2
1
)
H
enthalpy of products for product-out, product-in, and feed-in (kJ)
L
length of gasifier reactor (m)
Q
0
volume flow-rate through reactor (m
3
/s)
V
volume of reactor (m
3
)
W
p
product gas flow-rate (kmol/s)
W
f
feed rate (kg/s)
X
c
carbon conversion fraction
Y
gasification yield
viscosity (N s/m
2
)
~
~
number of carbon atoms of component i in the gas product
i
η
heat-exchange efficiency
τ
residence time (s)
density in bulk, kg/m
3
ρ
b
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