Compressor Station Blowdowns
Summary
Compressor stations along a transmission pipeline, gathering/boosting stations, and compressors at processing plants are periodically taken offline (depressurized) for operational or maintenance needs, for emergencies, or emergency shut down (ESD) system testing. To take a compressor station or an individual compressor offline, station or unit isolation valves are closed and the gas within the compressors and associated piping is manually or automatically vented to the atmosphere (i.e., blowdown) or sent to a flare.
Description
Gathering, processing, and transmission compression stations normally have spare compressors to allow for operational flexibility and maintenance without shutting down the entire movement of gas. In addition, on transmission pipelines, an entire compressor station may be bypassed during low gas movement. Compressors can be maintained under pressure (i.e., not requiring a blowdown) for short-term operational shutdowns. For longer term compressor or station shutdowns, combustible gas is evacuated from the compressor case and adjoining piping and vessels for safety, and also because most compressor seals are dynamic and leak more gas when the compressor is idle under pressure. The evacuated gas, or blowdown gas, is released to the atmosphere or sent to a flare.
Annual testing of a station’s ESD system involves opening and closing all atmospheric vent valves to ensure that they are all working properly. ESD systems are designed to automatically and quickly evacuate combustible gas from the station, and result in a large quantity of gas being released for a brief period. .
References
Energy Information Agency, Office of Oil and Gas. (2007, November). Natural gas compressor stations on the interstate pipeline network: Developments since 1996.https://www.eia.gov/naturalgas/archive/analysis_publications/ngcompressor/ngcompressor.pdf
Interstate Natural Gas Association of America. (2018, August). Improving methane emissions from natural gas transmission and storage.https://www.ingaa.org/File.aspx?id=34990&v=56603504
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