- Biogas enters. The membrane separates the methane by retaining it (“retentate”). Undesirable molecules like carbon dioxide (CO2), water (H2O), sulfides (H2S), and ammonia (NH3) pass through the membrane (“permeate”). High quality biogas (renewable natural gas) exits.
- Membranes are made of polymers and, for gas separation, are typically formed into very thin, hollow fibers. These fibers are clustered into modules consisting of thousands of fibers. A high pressure pump forces the gas through the fiber into a lumen hole that runs down the center of the fiber where it is collected with permeate from other fibers.
- To improve separation, multiple stages may be used. Two-stage systems are common (shown below) which increase the longevity of the membrane modules. Most installations include a desulfurization and drying step before raw biogas is sent through the membrane.