CNG Storage Cascades or CNG Ground Storage Vessels, CNG Spheres
One of the key components in a fast-fill CNG Fueling Station is the CNG Storage. In fact, the inclusion of ASME ground storage vessels really defines a fast-fill refueling application.
Fast-Fill stations allow vehicles to pull up and refuel in a short period of time. In order to fuel vehicles quickly, gas must be drawn from pre-pressurized storage vessels. Unlike gasoline stations, natural gas must be stored above ground. And because it is stored at high pressures it must be contained in ASME (American Society of Mechanical Engineers) coded vessels. Vessels are 20” in diameter and approximately 23 foot long. Each vessel will hold 10,000 cubic feet at 5,000 psi. They are arranged in a three bank cascade meaning that there is a low bank vessel, a medium bank vessel and a high bank vessel.
As a general rule of thumb, only 40% of the stored gas in a three bank cascade arrangement is available for refueling. This means that a 30,000 cubic foot storage cascade will deliver about 12,000 cubic feet of natural gas quickly. This equates to about 96 equivalent gallons of gasoline.
A priority sequential panel is used to direct compressor discharge to the high, then medium, then low bank. When filling, a vehicle will draw first from the low bank, then the medium bank and top off from the high bank. The Compressor will replenish the cascade by filling the high bank first, then the medium bank and finally the low bank.
Compressed Natural Gas Storage Vessels
The 20-inch outside diameter, cylindrical CNG storage vessels are for the commercial dispensing of compressed natural gas to motor vehicles at CNG fuel stations. The vessels can supply CNG at up to 5,500 psi to a fill-up nozzle. Typical commercial systems supply CNG to the customer vehicles’ fuel tanks at ~3,500 psi.
More information on Stack Cylinder Design CNG Storage vessels
The 48-inch inside diameter, 33.5-cf spherical CNG storage vessel is for the commercial dispensing of compressed natural gas to motor vehicles at CNG fuel stations. The vessel can supply CNG at up to 5,500 psi to a fill-up nozzle. The capacity of each spherical vessel is 12,360 – SCF at 5,500 psi, or 11,130 -SCF at 4,500 psi.
More information on 48 inch spherical design CNG storage vessels.
Another form of storage that has lost popularity are DOT bottles. They resemble welding bottles and have burst disks instead of ASME relief valve. We do not like these for a number of reasons. First they need to be re-certified every five years, and second they do not have any drain valves.