The Varec 234/235 Series Gas Purifier is designed as a cost effective method for hydrogen sulfide removal. The process removes hydrogen sulfide (H2S) from small volumes of gas. The design uses iron sponge technology which is still the preferred method for biogas applications. Biogas is generated by the anaerobic digestion of organic solids that contain small amounts of H2S. It is produced in anaerobic digesters, lagoons, and municipal landfills. Although the total composition of H2S in biogas is relatively small, it is often sufficient enough to corrode metals and damage equipment. This can create maintenance and operational problems especially in plants where the biogas is recovered to fuel engine-generators or boilers. In addition to corrosion problems, H2S is also a toxic air pollutant that can create a severe odor nuisance even in minute concentrations. The treatment of biogas for removal of sulfur compounds has become increasingly important as regulations restricting sulfur emissions have become tighter.
Biogas contains H2S in concentrations from 150 to 3000 ppm or more, depending on the influent wastewater composition. The odor of hydrogen sulfide becomes offensive at 3 to 5 ppms. An atmospheric concentration of 300 ppm can be lethal. Even small amounts of hydrogen sulfide can cause piping corrosion, gas engine pitting, and clogged piston rings. Many engine manufacturers require the H2S content to be as low as 90 ppm. Other gas utilization equipment can be affected by H2S corrosion.
When biogas is burned or flared, the H2S can generate sulfur dioxide (SO2) emissions. H2S removal is a must when your local Regulatory Commission limits SO2 emissions.
The 234/235 Series Purifier is designed to remove most of the H2S from the gas stream. It is usually installed immediately downstream of the digester, after the condensate and sediment trap or condensate accumulator. This vessel is also recommended upstream of a gas engine generator or a boiler.
The following parameters should be measured for proper operation: Inlet biogas flow rate, inlet and outlet biogas pressures, inlet and outlet H2S concentrations, condensation (drip water), and pH of drip water. Isolation valves (supplied by others) are recommended for field installation in the inlet and outlet piping of each compartment. Drip traps are recommended for installation the drain connection to provide for safe condensate removal.
