How biogenic CO₂ capture works at a biogas plant

Upgrading raw biogas leaves a CO₂ stream that most plants vent. Here is what it takes to turn that stream into a certified product.

A biogas upgrading plant separates methane from raw biogas. What remains is a CO₂-rich off-gas — typically 96–99% pure — that is usually vented. Capturing it costs far less than capturing CO₂ from flue gas, because the concentration is already high.

Step 1: pre-treatment

Trace hydrogen sulphide, siloxanes and volatile organics have to go first. Activated carbon beds handle most of it; the sizing depends on your feedstock, so a gas analysis is the starting point of any project.

Step 2: drying and liquefaction

The gas is dried to a dew point below −60 °C, then compressed and cooled until it condenses at roughly −25 °C and 18 bar. Boil-off from the storage tank is routed back to the compressor rather than lost.

Step 3: quality control

Before the product goes to a food customer, an online analyser checks oxygen, moisture and total hydrocarbons against ISBT limits. Any batch outside spec is recirculated instead of shipped.