Biomethane upgrading

Raw biogas is typically around half methane, with carbon dioxide, water, and hydrogen sulfide. Upgrading raises the methane share. Several types are offered. They are not interchangeable.

• Cascade — a low-cost step. Anaerobic supernatant falls over a series of waterfalls, carbon dioxide escapes, and the methane share rises to 65 percent.
• Membrane — the biogas is compressed and passed through membranes. Compression makes it energy intensive.
• Amine scrubber — carbon dioxide is taken into a solvent. There is no compression. Capital cost is higher and operating cost is lower.
• Hydrogen biomethanisation — renewable hydrogen converts the carbon dioxide into more methane, instead of separating it. That route has its own page.

Hydrogen sulfide is removed before a membrane or an amine contactor. See hydrogen sulfide scrubbers. Liquefaction to bio-LNG follows a route that has already produced a rich gas. The cascade, at 65 percent methane, is not that feed. Upgrading does not create a carbon credit by itself.