Biogas Purification System

Purification of biogas by vacuum pressure swing adsorption was evaluated to produce fuel grade methane (FGM). Two different adsorbents were employed to evaluate the process performance with equilibrium- and kinetic-based adsorbents. A five-step cycle configuration (feed, intermediate depressurization, blow down, purge, and pressurization) was employed to compare with results obtained with a four-step cycle without intermediate depressurization. The effect of different operating variables like step times and pressure conditions of the cycle was analyzed.
VPSA (Vacuum Pressure swing Adsorption) Technology Based Biogas purification Unit :-

PROCESS DESCRIPTION

The Bio-gas which was collected in gas-holder from bio-gas digester will be feed to a blower and this blower boost bio-gas up to 0.7 bar (7000 mmwc) pressure. This gas is passed through Desulphurization unit, where most of H2S removed. Now this gas pass through cooling water/child water cooler to cool down and remove water content then feed to a composite bad of molecular sieve towers unit bottom to top which has twin tower arrangement filled with different grade of molecular sieve (composite bad) where H2O, H2S and CO2 will absorbed and outlet gas from tope of the tower will be free of H2O, H2S and CO2 4-5%.In this process one tower is in adsorption and other tower is taken for regeneration. In this VPSA process regeneration is in two stapes as bellow:-

• - Depressurization of the tower.

• - Create Vacuum in the tower by vacuum pump.

• - The change over from one tower to another tower is fully automatic. There is a surge vessel which helps to give outlet purified gas flow continuously.