Biomedical Engineering Reference
In-Depth Information
9.5.1 Energy Conversion
All three of the following important feedstock for the energy industry can be
produced by biomass conversion in SCW:
Bio-oil: Potential use in the transport sector
Methanol: Though a chemical feedstock, may be used for combustion
Hydrogen: Potential use in fuel cells
The overall efficiency of an energy conversion system depends on the
technology route, on the wetness of the biomass, and on many other factors.
Yoshida et al. (2003) compared the effect of moisture content on the net effi-
ciency of seven options for electricity generation, including an SCWG com-
bined cycle. Interestingly, the SCWG-based system shows a total efficiency
independent of moisture content, while for all other systems, total efficiency
decreases with increasing moisture. Total electricity generation efficiency is
even higher than that for conventional combustion-based systems. Integrated
gasification combined cycle (IGCC) efficiency is higher than that of SCWG
for biomass containing less than 40% moisture. Above 40%, its efficiency
drops below that of SCWG (
Figure 9.9
).
Yoshida et al. (2003) also compared the total heat utilization efficiency
of seven energy conversion processes:
1. Direct combustion of biomass
2. Combustion of biomass-oil produced by liquefaction or pyrolysis
3. Combustion of methanol produced by thermal gasification
4. Combustion of methanol produced by SCWG
5. Combustion of biogas produced by thermal gasification
40
Direct combustion
Thermal gasification combined
cycle
Methanol combustion (from
supercritical water gasification)
Methanol combustion (from
thermal gasification)
Supercritical water gasification
combined cycle
Biomass reforming fuel cell
Anaerobic digestion gas
combustion
35
30
25
20
15
10
5
0
0 1020304050607080
Moisture content (%)
FIGURE 9.9
Dependence of the net electricity generation efficiency of different biomass-based
processes on the biomass moisture content (Yoshida et al., 2003).
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