Proceedings

Digestion of organic sewage creates digester biogas. Biogas is always wet and generally a mixture of methane & CO2.  It is conventionally combusted in CHP plants or flared. Combustion is generally poor as the biogas is wet and contains a high percentage of carbon dioxide.

This paper describes a process that improves biogas quality, to that of the quality of natural gas, producing a high quality digester biogas that can be used on site as a replacement for natural gas. This results in significant cost savings where an alternative feed gas such as high quality biogas can be used on site instead of natural gas or as a supplement.

The paper also shows that, as most sewage works are located close to the coast, the process can be enhanced by using seawater. Any contaminants such as siloxanes, sulphides and toluene are removed from the biogas stream by the seawater, leaving a biogas that is rich in methane and suitable for combustion.  The final stage provides water removal so that there is no excess water to damage the CHP.