Biofuels production 199= 570-423.5
= 146.5 L/dayThe design and operation of a biogas digester can follow those outlined in the
above example. In practice, the process of digester size selection may be as
follows. First, gas plant size is determined. This requires an estimate of the daily
requirements of biogas (see Table 4.22), coupled with the availability of the
organic materials which is given in Chapter 2. In calculating the required
volume for digester, the amount of dilution water needed and additional space
for gas storage should be considered.
4.6 End uses of biogas and digested slurry
4.6.1 Biogas
Based on the heat value of the biogas (4,500-6,300 k-cal/m
3
), Hesse (1982)
estimated that on complete combustion one m^3 of biogas is sufficient to:
- run a 1 horsepower (hp) engine for 2 hours
- provide 1.25 kWatt-hour of electricity
- provide heat for cooking three meals a day for five people
- provide 6 hours of light equivalent to a 60-Watt bulb
- run a refrigerator of 1-m^3 capacity for 1 hour
- run an incubator of 1-m^3 capacity for 0.5 hour.
Therefore 1 m^3 of biogas is equivalent to 0.4 kg of diesel oil, 0.6 kg petrol or
0.8 kg of coal. Quantities of biogas required for specific application are
presented in Table 4.22. Figure 4.17 shows examples of stoves and lamps that
use biogas as fuel for their operation.
In China and India a large number of rural households are being served by
biogas (Barnett et al. 1978). About 95% of all the biogas plants in Asia are of
family-size type and therefore the principal uses of their output are cooking and
lighting. The remaining 5% of biogas plants are being used for other purposes
like refrigeration, electricity generation, and running irrigation pumps. For these
purposes it becomes necessary to compress and store the gas in containers made
of a variety of materials such as PVC, rubber and polyethylene which are
commercially available as shown in Figure 4.18.