Membrane Biogas Upgrading System
Membrane-based biogas upgrading to >98% biomethane for CBG, RNG, and grid injection
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Compact, dry-process upgrading to >98% biomethane
CRA's Membrane Biogas Upgrading System separates CO₂ from raw biogas to produce high-purity biomethane (RNG) at over 98% methane, using a multi-stage membrane process with no water or solvents. Because membrane life and methane recovery depend on clean, stable inlet gas, we engineer the upstream gas train in-house (H₂S scrubbing, dehumidification, and compression) and integrate it with the membrane skid as one package. The result is a compact, modular, low-OPEX system delivered containerised or skid-mounted for grid injection, Compressed Biogas (CBG / Bio-CNG), Bio-LNG, and industrial use.
Methane Recovery
>99.5%
CO₂ in Product
<0.5%
Biomethane Purity
>98% CH₄
Process
Dry membrane
What is a Membrane Biogas Upgrading System?
A membrane biogas upgrading system separates CO₂ from methane using hollow-fibre membrane modules, producing high-purity biomethane suitable for grid injection, compressed biogas (CBG/Bio-CNG), Bio-LNG, or industrial fuel, without water, solvents, or chemicals.
How it works
Compressed, dried, and desulphurised biogas enters the membrane module under pressure, where CO₂ and methane separate based on how fast each permeates through the hollow-fibre walls.
Biogas is compressed, dried, and desulphurised before it enters the membrane module, since membrane performance depends on clean, stable inlet gas.
CO₂ permeates through the hollow-fibre walls faster than methane and exits as a permeate stream, while methane-rich gas exits as the retentate.
Multi-stage configurations recirculate methane from intermediate permeate streams, pushing recovery above 99.5%.
Key Benefits
Achieves >98% methane, enabling direct grid injection or vehicle fuel use
Dry membrane process minimises energy, water, and chemical consumption
Upgrading, H₂S scrubbing, and compression engineered under CRA’s roof
Containerised or skid-mounted for easy deployment and scalability
Supports RNG, Bio-CNG, and Bio-LNG pathways for decarbonization goals.
The CRA Edge
Decades of gas processing experience with reliable project delivery
End-to-end design, R&D, and manufacturing under one roof for speed and quality
ISO 9001 certified; designs aligned with ASME, API and CE
Customised designs engineered for your process needs and the applicable regulations
Applications
Built to help you specify.
Sizing tools, decision guides, and technical references. Use them before, during, and after your evaluation.
Frequently Asked Questions
How does membrane biogas upgrading work?
Membrane biogas upgrading separates CO₂ from methane using selective polymer membranes. Compressed, cleaned biogas passes through multi-stage membrane modules, CO₂ permeates through the membrane wall and methane is retained as the product gas. The process is dry, with no water or solvents, which keeps utilities and operating cost low and the footprint compact. CRA's membrane upgrading systems are designed for greater than 98% methane and are supplied with the upstream gas train, H₂S scrubbing, dehumidification and compression, engineered in-house so that the membranes receive clean, stable inlet gas.
How does membrane upgrading compare with other biogas upgrading technologies?
Membrane separation is a dry process with a compact footprint, low operating cost and a modular, scalable layout, which is why CRA uses membranes for its upgrading systems. Other technologies exist in the market: water scrubbing is a wet process that consumes water and needs wastewater handling, chemical (amine) scrubbing uses reagents and carries a higher operating cost, and pressure swing adsorption is a dry adsorption process with its own capital and operating profile. CRA does not offer pressure swing adsorption. The right choice depends on gas flow, product specification and site utilities, and CRA integrates membranes from established suppliers.
When is a biogas upgrading system needed and what purity does it reach?
A biogas upgrading system is needed when the gas is to be injected into a natural gas grid, compressed as vehicle fuel (CBG or Bio-CNG) or liquefied as Bio-LNG, since all of these require pipeline-quality biomethane with the CO₂ removed. CRA's membrane upgrading systems are designed for greater than 98% methane with H₂S below 5 ppm in the product gas. Grid injection specifications and vehicle fuel standards vary by country, so CRA designs the membrane configuration and the upstream train to the product specification that applies at the site.
What does the gas train from raw biogas to biomethane look like?
The gas train starts with H₂S removal, followed by polishing, drying, upgrading and compression. For CBG duty CRA uses a chemical scrubber with biological regeneration as the wet scrubbing stage, which is designed for an outlet of about 100 ppm H₂S, followed by activated carbon polishing to bring H₂S down to the level the membranes need and to remove siloxanes. A refrigeration dehumidifier then dries the gas to a controlled dew point before compression and the multi-stage membrane unit. The product gas is compressed to grid pressure or to CBG cylinder filling pressure. CRA supplies this train from the raw biogas inlet to final compression as one package.
What determines the reliability of a membrane biogas upgrading system?
Membrane life and product purity depend on the condition of the gas entering the modules more than on the membrane itself. H₂S, water and siloxanes in the feed gas shorten membrane life and reduce methane recovery, so the upstream scrubbing, polishing and drying stages decide how the plant performs over time. CRA engineers the full upstream train in-house around the membrane skid. Systems are designed for greater than 98% methane, H₂S below 5 ppm and methane recovery above 99.5% through multi-stage membrane configurations.