Biogas is arenewable energy resource produced by natural digestion of biological materialsby bacteria. It consists of methane, CO2, H2S, hydrogen, nitrogen, and watervapor, out of which CO2 and methane are in greater percentages. Pure biogas isexpected to contain a maximum percentage of pure methane, with zero or nearlyzero CO2 and H2S presence. The biogas purification is important mainly toreduce its impact on the emission of greenhouse gases. It also helps to improveenergy efficiency and reduce corrosive effects. Now the question arises as tohow we can remove the impure gases from biogas to get complete methaneconcentration.
How to use Molecular sieves to removeharmful gases from biogas?
The processof removing other gases from biogas is known as biogas upgradation. Thoughmolecular sieves of any pore size can be used for this process, it is preferredto use sieves of pore diameter 5A and 13X. These sieves show the most efficientadsorption of gases like CO2 and H2S.
Molecularsieves are activated porous substance which act as a filter by trappingmolecules of diameter less than the pore diameter. These pores are of fixeddiameter and possess high affinity towards select molecules. With uniform poresize, the sieves are available in different forms like pellet, beads andpowder. A polar molecule that is trapped by the sieve pore is known asadsorbate and the sieve is referred to as adsorbent in a general PSA system.
So, as wediscussed, molecular sieves can be used to filter out undesired gases from thebiogas to get a highly methane concentrated biogas. The physical setup is tohave a gas inlet, a sieve bed, and a gas outlet. Note to specifically usecarbon molecular sieve for best output. It is advised to hold a pair of sievebeds, so that a continuous carbon dioxide and hydrogen sulphide removal ispossible. Because, after certain amount of target molecules are trapped in thepores, the sieves will turn saturated and need to be activated by desorption.This process of desorption is purely harmless as it just needs a pressurerelease from the sieve bed.
Forefficient biogas upgrading, up to four molecular sieve beds are used. The mixeddry biogas enters the first sieve bed from bottom and the resultant gas leavesfrom top of the sieve bed. The sieve beds adsorbs the CO2, H2S, H2, H2O and N2molecules from the biogas to their pores as the gas pass over the bed. Theseadsorbed gases are extracted out when molecular sieve bed saturates, by removingthe pressure or passing raw biogas.
The finalgas output is to receive biogas of 97% or greater methane concentration. Theconcentration is improved from around 50% to above 97%. Clearly, this shows theefficiency of the PSA system by molecular sieves for removal of H2S and CO2gases from methane gas.
Advantages of using molecular sievefor methane purification
Uniform beadand pore size enhances the molecular sieves to possess maximum utilisablesurface area. This feature definitely improves the efficiency of adsorption.Also, the pressure swing adsorption is a physical adsorption at the surfacelevel and thus there is no fear of heat emission or by-product production. Highaffinity towards the polar molecules, high mechanical and chemical strength, andease of maintenance are some features of attraction with molecular sieves. Thecost of entire system is also considerable reduced by easily reusable CO2molecular sieves.
SorbeadIndia has been serving trusted customers for past years with high-qualitymolecular sieves. Sieves of all pore diameters and all forms are available inany desired quantity. We allow customized quantities and test sample packs alsoto be ordered to any place in India.