What is Bio Gas/ Bio-CNG/ Purification System(PSA) ?

Biogas is a combustible gaseous fuel that is collected from the microbial degradation of organic matter in anaerobic conditions. Biogas is principally a mixture of methane (CH4 ) and carbon dioxide (CO2) along with other trace gases. Biogas can be collected from landfills, covered lagoons, or enclosed tanks called anaerobic digesters. The biogas typically has 60% methane and 35% carbon dioxide. There is also some percentage of hydrogen, nitrogen, oxygen, ammonia, moisture etc.

Waste / Bio-mass sources like agricultural residue, cattle dung, sugarcane press mud, municipal solid waste and sewage treatment plant waste, etc. produce bio-gas through the process of anaerobic decomposition. The bio-gas is purified to remove hydrogen sulfide (H2S), carbon dioxide (CO2), water vapor and compressed as Compressed Bio Gas (CBG), which has methane (CH4) content of more than 90%.

Pressure Swing Adsorption (PSA): This technology is most prevalent for large bio-gas systems in India. With this technique, carbon dioxide is separated from the biogas by adsorption on a surface under elevated pressure. The adsorbing material, usually activated carbon or zeolites, is regenerated by a sequential decrease in pressure before the column is reloaded again, hence the name of the technique. Hydrogen sulphide and water needs to be removed before the PSA-column. There is significant loss of methane (20-30%) in this process.