Process for producing a contaminant-depleted hydrocarbon gas stream with improved hydrocarbon recovery

Abstract

A process for producing a contaminant-depleted gas stream from a contaminated hydrocarbon feed gas stream comprises: (a) expanding the contaminated to obtain an expanded stream; (b) allowing at least part of the contaminants in the expanded stream to liquefy to form a dispersion of a contaminants enriched liquid comprising hydrocarbons and a gaseous phase with lowered contaminant content; (c) separating at least part of the contaminants enriched liquid from the gaseous phase in a first separator, thereby obtaining the contaminant-depleted gas stream and a liquid stream comprising contaminants and hydrocarbons; (d) separating hydrocarbons from the liquid stream in a second separator, thereby obtaining an overhead stream comprising hydrocarbons and a bottom stream depleted in hydrocarbons; and (e) leading the overhead stream to a point prior to step (c); further comprising the step of increasing the pressure of the liquid stream prior to step (d).

1 . A process for producing a contaminant-depleted gas stream from a contaminated hydrocarbon feed gas stream containing at least 10 vol. % of acidic contaminants, in particular H 2 S and CO 2 , the method comprising the steps of:
 (a) expanding the contaminated hydrocarbon feed gas stream in an expander to obtain an expanded contaminated hydrocarbon feed gas stream;   (b) allowing at least part of the contaminants in the expanded contaminated hydrocarbon feed gas stream to liquefy to form a dispersion of a contaminants enriched liquid phase still comprising a small amount of hydrocarbons and a gaseous phase with lowered contaminant content;   (c) separating at least part of the contaminants enriched liquid phase comprising hydrocarbons from the gaseous phase with lowered contaminant content in a first separator, thereby obtaining the contaminant-depleted gas stream and a liquid stream mainly comprising contaminants and further comprising remaining hydrocarbons;   (d) separating remaining hydrocarbons from the liquid stream in a second separator, thereby obtaining an overhead stream comprising remaining hydrocarbons and a bottom stream depleted in hydrocarbons;   (e) leading the overhead stream comprising remaining hydrocarbons to a point prior to step (c);   wherein step (d) prior to separating remaining hydrocarbons, further comprises the step of:   (d1) increasing the pressure of the liquid stream mainly comprising contaminants and further comprising remaining hydrocarbons to obtain a pressurised liquid stream mainly comprising contaminants and further comprising remaining hydrocarbons.   
     
     
         2 . A process according to  claim 1 , wherein step (d) prior to separating remaining hydrocarbons, further comprises one or more of the steps of:
 (d2) heating the liquid stream to obtain a heated liquid stream mainly comprising contaminants and further comprising remaining hydrocarbons;   (d3) fractionating the to obtain a fractionated liquid stream mainly comprising contaminants and further comprising remaining hydrocarbons;   (d4) lowering the pressure of the liquid stream or optionally overhead cooled dispersed phase from the fractionation column mainly comprising contaminants and further comprising part of remaining hydrocarbons, thereby evaporating at least part of the remaining hydrocarbons.   
     
     
         3 . A process according to  claim 1 , wherein in step (e) the overhead stream is cooled, optionally compressed and combined with the contaminated hydrocarbon feed gas stream and wherein the resulting combined stream is led to step (a). 
     
     
         4 . A process according to  claim 1 , wherein the overhead stream in step (e) is led to a compressor before leading to a point prior to step (c). 
     
     
         5 . A process according to  claim 1 , wherein the overhead stream from the second separator is combined with the contaminants enriched liquid phase obtained after step (a) and the combined stream is led to the first separator. 
     
     
         6 . A process according to  claim 1  wherein the first and/or the second separator is a centrifugal separator comprising a bundle of parallel channels that are arranged within a spinning tube parallel to an axis of rotation of the spinning tube. 
     
     
         7 . A process according to  claim 6 , wherein a swirling gas stream is introduced into the spinning tube. 
     
     
         8 . A process according to  claim 1 wherein the first and/or the second separator is a separation device comprising:
 1) a housing comprising a first, second and third separation section for separating liquid from the mixture, wherein the second separation section is arranged below the first separation section and above the third separation section, the respective separation sections are in communication with each other, and the second separation section comprises a rotating coalescer element;   2) tangentially arranged inlet means to introduce the mixture into the first separation section;   3) means to remove liquid from the first separation section;   4) means to remove liquid from the third separation section; and   5) means to remove a gaseous stream, lean in liquid, from the third separation section.   
     
     
         9 . A process according to  claim 8 , in which liquid is separated from the gaseous phase by migrating droplets under application of a centrifugal force to an inner wall of the first separation section, via which inner wall liquid is removed from the separation device or passed to a liquid collecting section which is arranged below the third separation section. 
     
     
         10 . A process according to  claim 9 , in which in liquid is separated from the gas by migrating the droplets under application of a centrifugal force to an inner wall of the first separation section, via which inner wall liquid is passed to a liquid collecting section which is arranged below the third separation section. 
     
     
         11 . A process according to  claim 1  in which liquid is separated from the gas by migrating droplets under application of a centrifugal force to an inner wall of the third separation section, via which inner wall liquid is removed from the separation device or passed to a liquid collecting section which is arranged below the third separation section. 
     
     
         12 . A process according to  claim 1  wherein the first and/or the second separator is a gas/liquid separator vessel, comprising a gas/liquid inlet at an intermediate level, a liquid outlet arranged below the gas/liquid inlet and a gas outlet arranged above the gas/liquid inlet. 
     
     
         13 . A process according to  claim 12 , wherein in the gas/liquid separator vessel a normally horizontal coalescer is present above the gas/liquid inlet and over the whole cross-section of the vessel and in which vessel a centrifugal liquid separator is arranged above the coalescer and over the whole cross-section of the vessel, the liquid separator comprising one or more swirl tubes. 
     
     
         14 . A process according to  claim 12 , which the gas inlet comprises an admittance with a supply and distribution assembly extending horizontally in the separator vessel, the assembly consisting of a longitudinal box-like structure connected to the gas inlet and having at least one open vertical side with a grid of guide vanes disposed one behind each other, seen in the direction of the flow. 
     
     
         15 . A process according to  claim 13 , in which the horizontal coalescer consists of one or more layers of gauze selected from metal gauze, non-metal gauze, and combinations thereof.