Raw natural gas pretreatment prior to liquefaction - by removing acid gases, drying, expanding, scrubbing and fractionating to give methane, ethane and propane

摘要

Raw natural gas at 800 psig is pretreated prior to liquefaction by a process comprising (a) passing the stream to a sweetening zone for removal of acid gases (CO2 and H2S), (b) passing the stream to a first drying zone to form a dry gas stream having a dew point of -20 degrees F, (c) expanding the stream in an energy recovery means (developing shaft horsepower) to 300 psig, (d) scrubbing the stream with a lean hydrocarbon liq. to remove from it all 2C hydrocarbon and form a CH4-rich gas stream (I) and a rich liq. hydrocarbon stream (II), (e) passing (I) to a solid desiccant drying zone to form a dry gas stream having a dew point of -240 degrees F, (f) fractionating (II) to separate streams rich in methane, ethane and propane respectively and obtain a =4C liq. hydrocarbon stream (III), and (g) dividing (III) into two portions and passing one portion as the lean hydrocarbon liq. to the scrubbing zone in step (d). Liquefaction refrigeration power requirements are reduced by utilising the energy recovered in expanding the raw gas. The volume of gas which must be dried in expensive desiccant beds prior to liquefaction is reduced.