SCHEMATIC DIAGRAM OF VPSA BASED BIOGAS PURIFICATION PLANT
VPSA system has different stages to perform for purification of the Bio gas. Firstly, Bio gas stored in the gas holder goes through Suction process by Blower and pressurized. The pressurized Biogas passes through water Scrubber. In this process, water is used as an absorbent to remove partially H2S and ammonia. The water is supplied from the top of the column while the raw biogas is allowed to pass from the bottom to top. Ammonia and H2S trapped in the water and CH4 with CO2 and some traces of other gases along with moisture leave at the top of the water scrubber. After water scrubbing the gas passes through Chemical Scrubber where further H2S is trapped in iron flakes. After Chemical Scrubber process, the gas is made to pass through customized Biogas Dehumidifier where gas is cooled down to 8-10 Deg C and moisture is condensed and removed in cyclonic moisture separator which is automatically discharged through auto drain valve. Now the outgoing low temperature gas is passed through economizer / reheater to reduce the inlet Biogas temperature to reduce load on chiller and also outgoing gas is heated up to 30 Deg C for enhancing the RH of the Dehumidified gas so that no further condensation takes place due to expansion in Adsorber Towers. Next, we are using Activated Carbon Filter to remove impurities like H2S, VOC & Siloxane etc., For further purification of Bio Gas, we use VPSA technology. This method is particularly used to remove CO2 present in cleaned and dehumidified biogas. The dry biogas (after moisture removal) enters at the bottom of the adsorption column filled with different grades of molecular Sieves, Activated Alumina/Silica Gel where CO2 is adsorbed and pure dry methane leaves from the top of the towers which is sent to a surge vessel for analysis. When one tower is in Adsorption process the other adsorber tower undergoes in Regeneration by depressurization process and vacuum with the help of a vacuum pump. The exhaust gas mainly containing CO2 is released into the atmosphere at elevated height. After a preset timing the process is changed from one tower to another to keep producing the pure gas continuously. It is done through automatic changeover valves signaled through a PLC. Stored pure gas in surge vessel is analyzed for purity and sent to the final storage if minimum methane percentage is achieved.