2.4 Evaluation of Energy Consumption of Anaerobic Fermentation Process
57
used as the local average temperature and anaerobic fermentation process at the constant moderate temperature of 35 °C was adopted. A continuous stirred tank reactor
(CSTR) was used as the fermentation tank and the volume of a single-phase reaction
tank was 500 m
3 . In the CHMP-AF process, the volume of the tank for hydrogen
production was 50 m
3 , while the volume of the tank for methane production was
450 m
3 . Moreover, height-diameter ratio of all tanks was 5:4. The tanks were manufactured by using splicing technology of steel plates and rock wool was used in
interlayer of the tanks for heat preservation. Heating coils were added on internal
walls for keeping the constant temperature of anaerobic fermentation liquids. Owing
to thermal resistance (R = 3.45 × 10
–4 m
2 °C/W) of steel plates was very small
and far smaller than that of rock wool (R = 4.2 m
2 °C/W), it can be neglected. The
thermal energy for heat preservation of tanks is calculated according to the following
formula.
E J = S J × Tem × Time/R
(2.1)
E L = S L × Tem × Time/R
( 2 . 2 )
S L = S H + S C
(2.3)
where, E J represents the total energy consumption of heat preservation of tanks in the
single-phase methane-production process, E L indicates the total energy consumption
of heat preservation of tanks in the combined production process. S J and S L stand
for the surface areas of tanks for single-phase methane production and combined
production separately. S H and S C denote the surface areas of tanks for hydrogen and
methane production, respectively. Tem = 15
◦ C shows the differences between
ambient temperature and constant temperature of anaerobic fermentation. Time =
1 d demonstrates the unit time of anaerobic fermentation process and it is 1 d. R
represents the thermal resistance of rock wool and R = 4.2 m
2 °C/W.
Through the calculation, the surface area of tank for single-phase process of
methane production is S J = 351.68 m
2 , while that of the two-phase reactor for
combined production process is S L = 402.53 m
2 . In addition, E J = 30.144 KW h
and E L = 34.503 KW h.
2.4.2 Energy Consumption in Feeding and Heating
Assuming that one ton of kitchen wastes are treated by the treatment plant of anaerobic fermentation every day and ambient temperature is 20 °C, hydrothermal pretreatment is performed at 90 °C and residual heat of kitchen wastes after hydrothermal
pre-treatment is recovered. A plate heat exchanger with the heat transfer efficiency
of η = 80% is used (Li et al. 2014). Therefore, the calculation formula for energy
consumption in feeding and heating is shown as follows.
57
used as the local average temperature and anaerobic fermentation process at the constant moderate temperature of 35 °C was adopted. A continuous stirred tank reactor
(CSTR) was used as the fermentation tank and the volume of a single-phase reaction
tank was 500 m
3 . In the CHMP-AF process, the volume of the tank for hydrogen
production was 50 m
3 , while the volume of the tank for methane production was
450 m
3 . Moreover, height-diameter ratio of all tanks was 5:4. The tanks were manufactured by using splicing technology of steel plates and rock wool was used in
interlayer of the tanks for heat preservation. Heating coils were added on internal
walls for keeping the constant temperature of anaerobic fermentation liquids. Owing
to thermal resistance (R = 3.45 × 10
–4 m
2 °C/W) of steel plates was very small
and far smaller than that of rock wool (R = 4.2 m
2 °C/W), it can be neglected. The
thermal energy for heat preservation of tanks is calculated according to the following
formula.
E J = S J × Tem × Time/R
(2.1)
E L = S L × Tem × Time/R
( 2 . 2 )
S L = S H + S C
(2.3)
where, E J represents the total energy consumption of heat preservation of tanks in the
single-phase methane-production process, E L indicates the total energy consumption
of heat preservation of tanks in the combined production process. S J and S L stand
for the surface areas of tanks for single-phase methane production and combined
production separately. S H and S C denote the surface areas of tanks for hydrogen and
methane production, respectively. Tem = 15
◦ C shows the differences between
ambient temperature and constant temperature of anaerobic fermentation. Time =
1 d demonstrates the unit time of anaerobic fermentation process and it is 1 d. R
represents the thermal resistance of rock wool and R = 4.2 m
2 °C/W.
Through the calculation, the surface area of tank for single-phase process of
methane production is S J = 351.68 m
2 , while that of the two-phase reactor for
combined production process is S L = 402.53 m
2 . In addition, E J = 30.144 KW h
and E L = 34.503 KW h.
2.4.2 Energy Consumption in Feeding and Heating
Assuming that one ton of kitchen wastes are treated by the treatment plant of anaerobic fermentation every day and ambient temperature is 20 °C, hydrothermal pretreatment is performed at 90 °C and residual heat of kitchen wastes after hydrothermal
pre-treatment is recovered. A plate heat exchanger with the heat transfer efficiency
of η = 80% is used (Li et al. 2014). Therefore, the calculation formula for energy
consumption in feeding and heating is shown as follows.