Before the CO2 can be removed, it is necessary to dry the biogas and remove hydrogen sulphide (H2S) and other contaminants which can damage the membranes or that need to be removed to meet the specification of the gas grid or other specific application. Hydrogen sulphide and other contaminants are removed from the biogas using a double active carbon filter. Water is removed by cooling the biogas to approximately 5°C with a chiller.
For the separation of carbon dioxide Bright Biomethane uses membranes with the highest selectivity available in the market. They pass CO2 easier and quicker than methane. The membrane modules in the system are arranged in 3 stages. In this patented design the permeate gas from the different stages is recirculated to obtain the highest efficiency (>99.5%) and lowest methane loss (<0.5%). This is a significantly lower methane slip value than many other biogas purification technologies.