250 (250 bar)

250 bar (approximately 3,625 psi or 25 MPa) is the high-pressure storage and dispensing specification for compressed biogas and compressed natural gas cylinder systems in India. It represents an upward shift from the older 200 bar standard and is now the preferred pressure rating for new SATAT-scheme CBG plants, mother stations, and transport cascades.

The transition from 200 to 250 bar reflects two engineering drivers. First, storage density: increasing pressure from 200 to 250 bar adds approximately 25% more gas mass per cylinder volume, reducing the number of cylinders needed for a given energy stored and lowering the total footprint of cascade storage. Second, filling speed: vehicle filling stations need high-pressure buffer storage above the target tank pressure of 200 bar in order to achieve fast fills. With a 250-bar buffer cascade, vehicles can be filled to nominal 200-bar tank pressure in 3–5 minutes against 8–12 minutes with a 220-bar cascade. The Bureau of Indian Standards specification IS 15663 now explicitly accommodates 250-bar dispensing as the standard for new infrastructure.

Operating at 250 bar imposes specific engineering and regulatory requirements. Cylinders and pressure vessels must be designed to ASME Section VIII Division 1 or IS 7285 (Type 1 steel) / IS 15490 (Type 2/3/4 composite) for 1.25× working pressure, with hydrostatic test pressure of 312.5 bar. PESO certification under the Gas Cylinder Rules, 2016 is mandatory for every cylinder, with periodic re-testing every 3–5 years. Compressors require an additional fifth stage versus 200-bar duty, raising specific energy consumption by 10–15% to 0.30–0.40 kWh per kg. Pressure relief devices must be set at 1.1× working pressure, and all valves, fittings, and pipework must be rated to ANSI Class 2500 or higher. Safety distances to occupied buildings and ignition sources increase under PESO siting rules — typically a minimum of 6 m for cascade storage above 1,000 kg capacity. The trade-off is significant: 250-bar systems cost 15–25% more in capex than 200-bar equivalents but pay back through smaller cylinder count, faster turnaround, and higher operational throughput at the dispensing point.