Enhanced Membrane Fuel Gas Conditioning Solutions for Compressor Stations with Ultra High BTU Gases in Oil-rich Shale Plays
Compressor stations use raw unprocessed natural gas as fuel for compressor drives and power generation turbines due to the unavailability of pipeline gas in many new production areas. In the condensate rich shale gas plays such as Utica, Bakken, Niobrara, Marcellus, Eagle Ford, etc. the raw natural gas is very rich in heavy hydrocarbons content and has a very high BTU content. The presence of high amounts of ethane, propane and C4+ hydrocarbons results in a very low methane number for gas engines, or too high of a Wobbe Index for turbines. Moreover, high levels of C5+ components result in pre-detonation issues and require derating of the engines for consistent operation. In addition, burning high BTU fuel gas also damages or fouls engine components, causing mechanical reliability issues & reduced compressor efficiencies, thereby leading to frequent shutdowns. The immediate impact of this is loss of gas and oil production until the components are replaced or fixed. This paper describes the use of unique reverse selective membranes to preferentially remove heavy hydrocarbons from raw shale gas and produce clean fuel gas at these compressor stations. For Ultra-rich fuel gases, MTR has developed and demonstrated a unique hybrid design combining the proven membrane process with a Joule Thompson (JT) process for fuel gas conditioning. In this design, the JT process comprising of a heat exchanger and a pressure reducing valve is installed upstream of membranes. The JT process reduces the heavy hydrocarbons load on the membranes and also provides superheated feed gas to membranes. This design is the cost optimized solution that provides flexibility to handle wide swings in the raw feed gas quality, pressures and temperatures and still generate spec-quality fuel gas with a lower BTU value. Finally, instead of burning the valuable heavy hydrocarbons in the raw fuel gas in the engines, the membranes recover and route them back to the pipeline to be recovered in the downstream
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