A blowcase is a pressure vessel that collects fluid at low pressure, then upon fillage is pressurized with high pressure gas, causing the collected fluid to dispel into a medium pressure system. The blowcase performs the same function as a pump, only it utilizes high pressure gas to displace fluid. They have been used many years for transferring fluid, and were typically installed where there was an ample supply of high pressure gas, such as waterfloods and large oil fields where gas lift was employed. In this latter case, satellite separation and testing facilities were often needed to perform well tests and separate fluid for transfer into separate collection systems.
To reduce the backpressure on producing wells, and allow use of low pressure separation equipment, blowcases transferred fluid from low pressure separators into the higher pressure collection lines – without pumps or tanks. Another typical installation is compression of “wet” gathering lines, where fluid must be removed prior to compressing the gas, and re-introduced downstream of the compressor. Perhaps the most common applications at present are the use of five gallon vessels to collect compressor skid drain liquids, and glycol reconcentrator condensation for transfer to larger storage tanks.
The prevention of atmospheric storage tank vapor losses, and prevention of oxygen entry has resulted in additional blowcase applications in “wet” gathering/compression facilities. Instead of directing all separator liquids to atmospheric tanks, installing gas blankets and vapor recovery compressors, and finally pumps to remove the fluid, some operators elect to install blowcases. Tanks are sometimes installed as emergency backup. Economics favor the blowcase, since it usually costs far less than gas blankets, vapor recovery, pumps, and chemicals.