Biogas energy

WHAT IS BIOGAS ?

The term “biogas” is used for a gas produced by anaerobic fermentation of different forms of organic matter. This anaerobic process is driven by different varieties of bacteria, in anaerobic digester tanks this is usually at a temperature of 30 – 40° C.

FEEDSTOCK FOR PRODUCTION OF BIOGAS

Typical feedstock’s for biogas production are manure and sewage, residues of crop production (i.e., straw), the organic fraction of the waste from cities and municipalities, be it sewage sludge, waste from the food industry or collected from household organic waste bins, as well as energy crops including maize and grass silage. The process itself occurs in airtight biogas digesters without oxygen.  The rate of the process depends on the feedstock and several other parameters. The digestion time varies from several hours (for sugars, and alcohol) to several weeks (in case of hemicelluloses, fat, and protein).  

TYPE	Nm3  biogas
1 milking cow 20m³ liquid manure/a	500
1 pig 1.5 – 6 m³ liquid manure/a	42-168
1 cattle (beef) 3 -11t solid manure/a	240 – 880
100 chicken -1,8m³ dry litter	242
Maize silage 40 -60 green weight/ha	7040 - 10560
Grass 24 – 43 t fresh matter/ha	4118 - 6811

 

COMPOSITION OF BIOGAS

During this biological process a major portion of the carbon compounds are converted to CH4, CO2 and water. Biogas consists mainly of methane, carbon dioxide, and some other minor components.

Composition of bio gas

MATTER	%
CH4	50-75
CO2	25-45
H20	2-7
N2	<2
O2	<2
NH3,H2,H2S,trace gases

 

WORKING OF BIO GAS PLANT

Manure and sewage, residue of crop, the organic waste from cities and municipalities are collected together in preliminary tank & from there they are disposed into fermenter.

Fermenter or digester is a large cylindrical container with a conical or dome shape at top in which temperature is maintained at 30-40 degree in which anaerobic fermentation occurs which produce biogas.

This biogas is heated & supplied to CHP plant which contain a gas operated engine or motor coupled with a generator which produces electrical power which is delivered to grid.

Biogas is directly used as a fuel in gas operated auto mobs or for cooking at home.

REASON FOR SLOW DEVELOPMENT

Reasons for the slow deployment of biogas include: a lack of information about the possibilities of biogas, a lack of a trained labor force, high capital cost for the setting up of commercial plants, generally inadequate and unreliable government support policies and the competition of natural gas as a cheaper alternative in many parts of the world.

ADVANTAGE OF BIOGAS ENERGY

A specific advantage of biogas technology is in the utilization of organic wastes and other organic byproducts for energy production, as opposed to disposal via landfills, which inevitably leads to further emissions of greenhouse gases by the process of slow decomposition.

Reference : "WBA factsheet-Biogas- an important Renewable energy source"