Question 29: What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.
Answer:
Biomass is organic matter which is made from the living organisms like plants and animals which is used to fuel the electric generators. The energy from the living organisms is obtained from the direct or indirect means. When biomass is burned to create heat is a direct method and conversion into biofuel is an indirect method. Cow-dung cakes (used as heating source), plants and animal products or we planted trees and obtained wood (fire- wood) these all are used as a fuel for a very long time.
Residue of the plant materials like vegetable waste, sewage or cow- dung cakes are first decomposed in the absence of oxygen to make bio- gas or from cow- dung is known as ‘gobar- gas’.
Working of the biogas plant:
Biogas plants are dome-like structures made with bricks. A semi- liquid mixture (slurry) of cow- dung and water is made in the mixing tank from where it is fed into the digester. Digester is a sealed chamber where no oxygen can enter. The complex compounds of cow- dung slurry break down with the help of anaerobic microorganisms. It takes a few days to complete the decomposition process and to generate the gases- methane, carbon dioxide, hydrogen and hydrogen sulphide. Then the biogas is stored in the gas tank above the digester from which they are drawn through the pipes.
Biogas is an excellent fuel which contains 75% of methane. It burns without smoke and does not leave any residual ash; heating capacity is very high. The slurry that is left behind can be used as excellent manure which is rich in nitrogen and phosphorus.
Maximum utilisation of bio- waste and sewage material provides a safe method for the waste- disposal.
Diagram:
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