9.4.6 Comparison of Fermentation Energy Conversion
Methods and Energy Conversion Efficiency
Ethanol and methane fermentation are well-known methods for the production of
fermentation energy. Their generation reactions from glucose and theoretic energy
conversion efficiencies are as follows (Tanisho 2011):
1. Ethanol fermentation
C 6 H 12 O 6 ! 2CH 3 CH 2 OH þ 2CO 2
Energy conversion ratio ¼ ð2 Â 1371:3Þ=2817 Â 100 ¼ 97:4%
2. Methane fermentation
C 6 H 12 O 6 ! 3CH 4 þ 3CO 2
Energy conversion ratio ¼ ð3 Â 882:4Þ=2817 Â 100 ¼ 94:0%
3. Hydrogen fermentation
C 6 H 12 O 6 ! 2CH 3 COOH þ 2CO 2 þ 4H 2
Energy conversion ratio ¼ ð4 Â 285:9Þ=2817 Â 100 ¼ 40:6%
As this shown, ethanol fermentation and methane fermentation have much higher
theoretical energy conversion rates than hydrogen fermentation. Since ethanol fermentation can produce concentrations as low as 8–10%, however, a treatment
process is required to enrich the concentrations to 99% or greater for usage as
energy. This process is more complex than the fermentation process, and the ratio is
greater. Any comparison of energy conversion ratios is therefore without practical
significance unless it uses the same final usage forms rather than theoretical values.
For this reason, comparison will focus on the usage of the final form for electricity.
The general process of energy production from biomass raw material follows the
following stages:
1. Ethanol
Raw material ! fermentation ! enrichment/separation ! thermal power
generation ! general efficiency
2. Methane
Raw material ! fermentation ! desulfurization ! diesel power generation ! general efficiency
3. Hydrogen
Raw material ! fermentation ! desulfurization ! fuel cell power generation ! general efficiency
General efficiency is assessed according to the following formula:
General efficiency = Theoretical fermentation efficiency  (1 − processing
energy) Â Effective power generation efficiency
As Table 9.7 shows, the results indicate no major difference among the three
approaches. At the same time, great differences exist in post-fermentation
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9 Marine Bioenergy Production
Methods and Energy Conversion Efficiency
Ethanol and methane fermentation are well-known methods for the production of
fermentation energy. Their generation reactions from glucose and theoretic energy
conversion efficiencies are as follows (Tanisho 2011):
1. Ethanol fermentation
C 6 H 12 O 6 ! 2CH 3 CH 2 OH þ 2CO 2
Energy conversion ratio ¼ ð2 Â 1371:3Þ=2817 Â 100 ¼ 97:4%
2. Methane fermentation
C 6 H 12 O 6 ! 3CH 4 þ 3CO 2
Energy conversion ratio ¼ ð3 Â 882:4Þ=2817 Â 100 ¼ 94:0%
3. Hydrogen fermentation
C 6 H 12 O 6 ! 2CH 3 COOH þ 2CO 2 þ 4H 2
Energy conversion ratio ¼ ð4 Â 285:9Þ=2817 Â 100 ¼ 40:6%
As this shown, ethanol fermentation and methane fermentation have much higher
theoretical energy conversion rates than hydrogen fermentation. Since ethanol fermentation can produce concentrations as low as 8–10%, however, a treatment
process is required to enrich the concentrations to 99% or greater for usage as
energy. This process is more complex than the fermentation process, and the ratio is
greater. Any comparison of energy conversion ratios is therefore without practical
significance unless it uses the same final usage forms rather than theoretical values.
For this reason, comparison will focus on the usage of the final form for electricity.
The general process of energy production from biomass raw material follows the
following stages:
1. Ethanol
Raw material ! fermentation ! enrichment/separation ! thermal power
generation ! general efficiency
2. Methane
Raw material ! fermentation ! desulfurization ! diesel power generation ! general efficiency
3. Hydrogen
Raw material ! fermentation ! desulfurization ! fuel cell power generation ! general efficiency
General efficiency is assessed according to the following formula:
General efficiency = Theoretical fermentation efficiency  (1 − processing
energy) Â Effective power generation efficiency
As Table 9.7 shows, the results indicate no major difference among the three
approaches. At the same time, great differences exist in post-fermentation
328
9 Marine Bioenergy Production