Method and system for removing H₂S from a natural gas stream

摘要

A method for removing hydrogen sulphide (H2S) from a natural gas stream comprising methane (CH4) and H2S comprises: —cooling the natural gas stream in a heat exchanger assembly (13,16,18); —feeding at least part of the cooled natural gas stream through a feed conduit (19,21) into a cyclonic expansion and separation device (1) in which the cooled natural gas stream is expanded in a nozzle (4) and thereby further cooled to a temperature and pressure below the dew point of H2S and is separated by inducing the cooled natural gas stream to swirl in a tubular separation chamber (9) thereby inducing centrifugal forces to separate the cooled natural gas stream into a cooled low density fluid fraction, which is H2S depleted and methane enriched, and a cooled high density fluid fraction, which is H2S enriched and methane depleted; —feeding the cooled low density fluid fraction to a product gas conduit (33) which is connected to the heat exchanger assembly (14) for cooling the natural gas stream fed to the cyclonic expansion and separation device (1); and —feeding the cooled high density fluid fraction to a fractionating column (8) for further separation.

主权项

1. A method for removing hydrogen sulphide from a natural gas stream comprising methane and hydrogen sulphide, the method comprising:
cooling the natural gas stream in a heat exchanger assembly; feeding at least part of the cooled natural gas stream through a feed conduit into a cyclonic expansion and separation device in which the cooled natural gas stream is expanded in a nozzle and thereby further cooled to a temperature and pressure below the dew point of hydrogen sulphide and is separated by inducing the cooled natural gas stream to swirl in a tubular separation chamber thereby inducing centrifugal forces to separate the cooled natural gas stream into a cooled low density fluid fraction, which is hydrogen sulphide depleted and methane enriched, and a cooled high density fluid fraction which is hydrogen sulphide enriched and methane depleted; feeding the cooled low density fluid fraction to a product gas conduit which is connected to the heat exchanger assembly for cooling the natural gas stream fed to the cyclonic expansion and separation device; and feeding the cooled high density fluid fraction to a fractionating column for further separation, and wherein the fractionating column is configured to separate the high density fluid fraction discharged by the cyclonic expansion and separation device into a hydrogen sulphide enriched and methane depleted bottom fraction and a hydrogen sulphide depleted and methane enriched upper fraction, which upper fraction is discharged from the upper part of the fractionating column into a reflux conduit in which a reflux refrigerator is arranged and which discharges the cooled upper fraction into a reflux separation vessel in which the cooled upper fraction is separated into:
a) a cooled substantially gaseous hydrogen sulphide depleted and methane enriched fraction, which is mixed with the cooled low density fluid fraction fed to the product gas conduit after being discharged by the cyclonic expansion and separation device, wherein the mixing occurs downstream from the heat exchanger assembly, andb) a cooled hydrogen sulphide enriched and methane depleted substantially liquid fluid fraction, which is re-circulated into the feed conduit; wherein the feed conduit includes a water separation vessel; and wherein the heat exchanger assembly includes:
a first heat exchanger in which the natural gas stream is cooled by the cooled low density fluid fraction flowing through the product gas conduit to a temperature below the dew point of said natural gas stream, from which first heat exchanger the cooled natural gas enters the water separation vessel,a second heat exchanger in which the natural gas stream discharged by the water separation vessel is cooled by the cooled substantially gaseous hydrogen sulphide depleted and methane enriched fraction discharged by the reflux separation vessel, andan inlet refrigerator cooling the natural gas stream from the second heat exchanger; wherein the feed conduit further includes a gas liquid separation vessel separating natural gas from the inlet refrigerator into a gas separated stream and a liquid separated stream; wherein the gas separated stream is fed to the cyclonic expansion and separation device as the at least part of the cooled natural gas stream, and the liquid separated stream is fed into the fractionating column; wherein the cooled hydrogen sulphide enriched and methane depleted substantially liquid fluid fraction is injected into the feed conduit upstream of the second heat exchanger and downstream of the water separation vessel.