11. What kind of gas cleaning is necessary?

Desulphurization

Cleaning with filters: With using ferrous-filters after the gas production. The filter must be changed after saturation of the filling substrate.
The cleaning directly in the gas storage with adding oxygen. The hydrogen sulphide will be turned into sulphur. The sulphur will stay in the gas storage and the biogas will be conducted. That is the current method, but because of saving sulphur in the gas storage the concentration of hydrogen sulphide should not be too much.
When the input substrate has a high concentration of proteins- like in industry food waste- the biogas will have a high hydrogen sulphide concentration. Any filter will remove the hydrogen sulphide and the changing to sulphur is not recommended. It is better to put ferrous-II-ions in the digester. This will bind the sulphur and become insolvable solid in the manure.

But all remove systems should keep in mind that the hydrogen sulphur concentration of the manure should not be too high. The bacteria will only tolerate smaller amounts.

Compression

Often the supply of biogas into the natural gas system needs a compression. For example, using biogas for vehicles requires a compression to 22 bars.

Drying

The biogas output from the digester is warm and humid. In order to prevent corrosions, it should be dehumidified and cooled. One method is to fill the gas into a cool subterranean storage or dry it with compression cooling.

Removing CO₂

Removing CO2 is a current method for the reduction of ammoniac. It is executed through gas washing, pressure-washing or adsorption washing. Further methods include cryogen gas separations with low temperatures or separation with membranes.