Biomass for Power Generation

Biomass refers to all the materials that constitute and originate from plants and animals.

Examples: Wood, Cereals, Grass, Crop Residues, Sugar Cane, Aquatic Plants, Corn, Cassava, Municipal Solid Waste, Industrial Waste, Animal Manure etc.

Biomass combustion provides energy. That is, by burning biomass, energy is produced. This energy meets the requirement for cooking, heating, lighting and electrification of rural household. Biomass energy is also useful in processing industries in rural and urban areas.

Bio - Gas Digestor :

Bio - gas may be defined as the mixture of methane (CH4) and carbon dioxide (CO2) with traces of hydrogen sulphide (H2S). It is produced by anaerobic digestion from animal dung, human excreta and green plants.

Figure shows the cross sectional view of a biogas digestor. It contains a pit (1.5 to 1.6 m dia., and 4.0 to 6.0 m deep) excavated below the ground level. It is lined with bricks. The partition wall divides the space in pit into two compartments. The bottom of the pit is finished with cement concrete basement. Two slanting cement pipes reach the bottom of the pit on either side of the partition. One pipe conveys slurry of biomass from inlet into the pit and the other pipe discharges the slurry (after digestion) to the sludge outlet. The outlet pipe dips lower into the pit than inlet pipe. The slurry may be prepared from the cattle dung and water in 4 : 5 ratio.

Depending on the variation of atmospheric temperature, decomposition of biomass slurry takes place. It is called digestion which liberates methane. The optimum temperature for methanogenic bacteria is 35°C. Maintaining constant temperature is essential for effective digestion. The retention period varies from 30 to 50 days depending on the temperature variations. The biogas is collected by the dome shaped gas holder located at the top of digestor. The gas is tapped as and when required from the gas holder.

Uses : The biogas (CH4 + CO2) is used as a fuel for domestic purpose and rural electrification. It improves rural sanitation as all the waste and sewage, animal and human residues are made use of. It helps elimination of smoke and discomfort. It provides readily available manure for the agricultural fields.

Demerits :

• land area required is relatively large

• cost of energy produced is higher in urban areas

• cannot be bottled like LPG into cylinders because biogas cannot be liquified.