Biogas, produced in anaerobic digesters or covered lagoons at meat/poultry, food or beverage processing facilities is often used as fuel for boilers or other process equipment, to power generator sets, or is converted to CNG on-site or at third-party compressor stations through utility pipeline transmission.
When used as a fuel source, the presence of H2S in the biogas will have a damaging effect on reciprocating or turbine engine life, increase maintenance costs, and shorten time between rebuilds. Generator set manufacturers have begun setting limits on H2S concentrations as part of their conditions imposed on the user to maintain warranty coverage.
In order to meet sulfur dioxide emission limits on engine exhausts, H2S may need to be removed prior to combustion. In cases of extremely low general emission limits, where a catalytic converter is necessary, the H2S must be removed prior to combustion or the life of the expensive catalyst will be reduced substantially.
If the biogas is converted to CNG, those specifications include very low limits on H2S. When the gas is transported via a utility pipeline to a CNG compression station, even lower pipeline specifications will have priority.
Flow rates are typically mid-range, 300scfm to 1500scfm, but H2S concentrations are generally high, in some cases up to 10,000ppm. Importantly, concentrations can vary widely and seasonally according to water sources and the addition of other material to the digester.