Biogas, produced in anaerobic digesters at Municipal Wastewater Treatment 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 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 to high range, 800scfm to 2000scfm. Many wastewater treatment facilities can see H2S concentrations generally around 800 to 1500ppmv. Siloxanes are often present.