H2S removal from biogas
H2S is the most notorious contaminate in biogas, and most biogas consumer equipment (boiler, engine) has strict requirement on the H2S concentration. In the combustion process, H2S is oxidised into SO2. Often the regulatory requirement on SO2 discharge in the exhaust is converted into the need to remove H2S beforehand.
There are five different technologies widely used for H2S removal:
Thiopaq process (caustic srubber followed by biological recovering),
Iron sponge absorption,
Activated carbon adsorption
Pure caustic scrubber is hardly used nowadays due to the high chemical consumption. Thiopaq process, which employs biological caustic recovery after chemical scrubber, is proven to be a cost-effective option. Biological trickling filter is another proven low-cost option as there is no chemical involved. Iron sponge and activated carbon are only used for small scale application or for polishing purpose, due to the high operation cost.