biomethane (biomethane)

Biomethane is upgraded biogas in which methane content has been raised from the raw 55-65% level to 90-99% by removing CO2, hydrogen sulfide, water vapour, and trace contaminants. The resulting product is chemically and energetically equivalent to natural gas and can be used interchangeably with fossil CNG as a vehicle fuel, injected into city gas distribution pipelines, compressed for bottled distribution, or liquefied as bio-LNG for long-distance transport. India's SATAT initiative (Sustainable Alternative Towards Affordable Transportation) brands compressed biomethane as Compressed Bio-Gas (CBG), with mandated specifications under IS 16087:2016 requiring minimum 90% methane and maximum 4% CO2, 16 mg/Nm3 H2S, and 5 mg/Nm3 oil.

Four upgrading technologies dominate Indian deployment:

• Water scrubbing (PWS): most common in India; high CO2 capture efficiency, methane purity 95-98%, methane slip 1-2%.
• Pressure Swing Adsorption (PSA): produces 96-98% methane with adsorbent regeneration; lower water consumption.
• Membrane separation: compact, modular, methane purity 90-97% depending on stages; rising adoption for sub-5 TPD plants.
• Chemical (amine) scrubbing: highest purity (99%+) but capital-intensive; rare in Indian SATAT plants.

Each technology trades capex against opex, methane slip, and water/energy demand. Water scrubbing has low chemical cost but consumes 3-5 cubic metres of process water per Nm3 of CBG and 0.25-0.35 kWh per Nm3 for compression. PSA uses 0.30-0.45 kWh per Nm3 and consumes adsorbent material every 5-10 years.

The economic logic of biomethane under SATAT is the floor price guarantee: oil marketing companies (IOCL, BPCL, HPCL) procure CBG at a base price of 54-72 INR per kg (2024 SATAT pricing, varies by zone) and provide 20-year offtake guarantees. A typical 10 TPD CBG plant produces 4-5 tonnes per day of biomethane, generating 8-12 crore INR in annual CBG revenue plus 2-4 crore INR from fermented organic manure (FOM) by-product. Beyond SATAT, biomethane increasingly attracts voluntary green-gas certificates and corporate Scope 1 offset purchases at premiums of 5-15% over base SATAT price, making upgrading economics central to plant viability.