Biogas is an energy-rich gas produced by anaerobic decomposition of biomass. It is produced from waste / bio-mass sources like agriculture residue, cattle dung, sugarcane press mud, municipal solid waste, sewage treatment plant waste, etc.
Biogas, a renewable fuel, constitutes mainly of methane (~60%), carbon dioxide (~40%), and traces of hydrogen sulfide. It can be burned directly as a fuel or purified & upgraded by removing carbon dioxide (CO2), hydrogen sulfide (H2S) and compressed to make Compressed Bio-Gas (CBG). The CBG has methane content of more than 90%, which is similar to the commercially available natural gas in composition and energy potential.
Production of biogas could be a continuous process. The utilization of biogas as an efficient energy source depends strongly on its methane concentration. Therefore, biogas purification is essential in order to have more energy per unit volume of compressed biogas and to get rid of the corrosive effect of H2S. Biogas purification process increases the methane concentration and decreases the carbon dioxide concentration in biogas, which in turn would result in higher calorific value. The purified biogas is compressed as CBG with methane content of more than 90%, and the CBG shall be complied to IS 16087:2016 specifications of BIS.
Some of the technologies which are prevalent in removal of carbon dioxide are Pressure Swing Adsorption (PSA), Vacuum Swing Adsorption (VSA), Water scrubbing, Membrane Separation and Chemical scrubbing - Monoethylammine (MEA) system.
The purified biogas with more than 90% of methane can be compressed at 250 bar, and transported in gas cylinders (cascades) for the end use.
Cascade storage & transportation:
The compressed biogas will be filled and transported through cascades which is a group of high pressure cylindrical vessel. For delivery of CBG, 3000 litres metal cascades or cascades of higher capacity shall be used. Steel cylinder cascades and composite cascades may be used for transportation of CBG. For steel cylinder cascades, IS 7285 shall be applicable. If type-3 or type-4 composite cascades are used, respective BIS specifications like IS 15935 or relevant specifications shall be applicable.
CBG has calorific value and other properties similar to CNG and hence can be utilized as green renewable automotive fuel. Thus it can replace CNG in automotive, industrial and commercial areas. Ministry of Road Transport and Highways, Government of India had permitted usage of bio-compressed natural gas (bio- CNG) for motor vehicles as an alternate composition of the compressed natural gas (CNG).
Compressed Bio Gas (CBG) produced from the CBG plant will be retailed through the CBG dispensing unit set-up by the Oil Marketing Companies within the radius of 25 kms. CBG supplied under SATAT scheme shall meet IS 16087:2016 specifications of BIS as follows:
|IS 16087 : 2016 Standard|
|1||Methane (CH4), minimum %||90.0%|
|2||Only Carbon Dioxide (CO2), maximum %||4%|
|3||Carbon Dioxide (CO2) + Nitrogen (N2) + Oxygen (O2), maximum %||10%|
|4||Oxygen (O2), maximum %||0.5%|
|5||Total sulphur (including H2S) mg/m3, maximum %||20 mg/m3|
|6||Moisture mg/m3, maximum %||5 mg/m3|