Why it is necessary to reduce the H2S
Biogas contains 50-70% methane (CH4), 30-50% carbon dioxide (CO2) and 0.1 to 3.0% (1,000 to 30,000ppm) hydrogen sulfide (H2S). Under combustion the H2S will convert into sulphuric acid (H2SO4) which will lead to severe corrosion of gas engine and auxiliary equipment. The corrosion will literally reduce the gas engines lifetime by years! Furthermore, income will be lost during overhauls and break downs. On top of that there will be substantial expenditures for repairs and frequent oil shifts. This is why the leading gas engine manufacturers – as condition for providing full warranty on the engines – request that H2S in the clean gas must not exceed 250ppm. However, where required, BioGasclean® can reduce the H2S content to significantly lower values.
BioGasclean®’s desulphurization technology is biological. This gives very low operational costs as the gas cleaners do not consume caustic soda or similar chemicals. The only residual product from the process is a valuable fertilizer. Therefore, a gas cleaner from BioGasclean® is not only economical but also an environmentally good investment.
Why it is necessary to dry the gas
After H2S removal the gas is fully saturated with water; the
relative humidity (RH) is 100%. If water droplets should reach
the cylinder heads and combustion chambers the water will
destroy the oil film. This will lead to increased wear of moving
parts as well as substantial reduction of the lifetime of the
engine oil. Therefore, it is necessary to dry the gas to avoid
condensation in the pipe system and the engine’s gas train
The cleaned gas is cooled from typically 40°C or 55°C -
depending on whether the anaerobic digester is mesophilic or
thermophilic - down to 10-15°C. After cooling the RH is still
100% but the gas contains 10 g water/kg gas only at 15°C
compared to 50 g at 40°C and 115 g at 55°C. When the gas is
compressed in the gas booster the temperature is raised to 30-
35°C and the RH reduced to 30-40% before the gas train.