Process for removing gaseous contaminants from a feed gas stream comprising methane and gaseous contaminants

Abstract

The invention provides a process for removing gaseous contaminants from a feed gas stream which comprises methane and gaseous contaminants, the process comprising: 1) providing the feed gas stream ( 1 ); 2) cooling the feed gas stream to a temperature at which liquid phase contaminant is formed as well as a methane enriched gaseous phase,—3) separating the two phases obtained in step 2) by means of a gas/liquid separator ( 4 ); and 4) subjecting the methane enriched gaseous phase obtained in step 3) to a distillation treatment in a distillation section ( 10 ) thereby obtaining a bottom stream ( 12 ) rich in liquid phase contaminant and lean in methane, and a top stream ( 11 ) rich in methane and lean in gaseous contaminant. The invention further concerns a device for carrying out the present process, the purified gas stream, and a process for liquefying a feed gas stream.

1 . A process for removing gaseous contaminants from a feed gas stream which comprises methane and gaseous contaminants, the process comprising:
 1) providing the feed gas stream;   2) cooling the feed gas stream to a temperature at which liquid phase contaminant is formed as well as a methane enriched gaseous phase;   3) separating the two phases obtained in step 2) with a gas/liquid separator; and   4) subjecting the methane enriched gaseous phase obtained in step 3) to a distillation treatment in a distillation device thereby obtaining a bottom stream rich in liquid phase contaminant and lean in methane, and a top stream rich in methane and lean in gaseous contaminant.   
     
     
         2 . A process according to  claim 1 , in which the feed gas stream is a natural gas stream in which the gaseous contaminants are carbon dioxide and/or hydrogen sulphide, preferably in which the natural gas stream comprises between 1 and 90 vol % of carbon dioxide, preferably between 5 and 80 vol % of carbon dioxide and/or wherein the natural gas stream comprises between 0.1 and 60 vol % of hydrogen sulphide. 
     
     
         3 . A process according to  claim 1 , in which the feed gas stream comprises between 20 and 80 vol % of methane. 
     
     
         4 . A process according to  claim 1 , in which the feed gas stream in step 1) has a temperature between −20 and 150° C. 
     
     
         5 . A process according to  claim 1 , in which the cooling in step 2) is done by isenthalpic expansion. 
     
     
         6 . A process according to  claim 5 , wherein the expansion is done using at least two expansion devices and the operating parameters of the expansion devices are chosen such that the liquefied acidic contaminants have a certain droplet size distribution. 
     
     
         7 . A process according to  claim 1 , in which the feed gas stream is cooled in step 2) to a temperature between −30 and −80° C. 
     
     
         8 . A process according to  claim 1 , in which the methane enriched gaseous phase obtained in step 3) is recompressed in one more compression steps before it is subjected to the distillation treatment in step 4. 
     
     
         9 . A process according to  claim 1 , in which the methane enriched gaseous phase obtained in step 3) or the recompressed methane enriched gaseous phase obtained in the one or more compression steps is cooled in a cooling step to a temperature at which liquid phase contaminant is formed as well as a methane enriched gaseous phase, and the methane enriched gaseous phase so obtained is subjected to the distillation treatment in step 4). 
     
     
         10 . A process according to  claim 1 , in which the bottom temperature of the distillation section is between 0 and 30° C. 
     
     
         11 . A process according to  claim 1 , in which the gas/liquid separator in step 3) comprises 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, in which 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. 
     
     
         12 . A process according to  claim 1 , in which the gas/liquid separator in step 3) comprises a centrifugal separator which comprises a bundle of parallel channels that are arranged within a spinning tube parallel to an axis of rotation of the spinning tube. 
     
     
         13 . A process according to  claim 1 , in which the gas/liquid separator in step 3) comprises a housing with a gas inlet for contaminated gas at one end of the vessel, a separating body, a gas outlet for purified gas at the opposite end of the housing and a contaminants outlet downstream of the separating body or upstream and downstream of the separating body, wherein the separating body comprises a plurality of ducts over a part of the length of the axis of the housing, which ducts have been arranged around a central axis of rotation, in which apparatus the separating body has been composed of a plurality of perforated discs wherein the perforations of the discs form the ducts. 
     
     
         14 . A gas/liquid separator comprising:
 a) a housing comprising a first, second and third separation section for separating liquid from a gas 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;   b) tangentially arranged inlet means to introduce the mixture into the first separation section;   c) means to remove liquid from the first separation section;   d) means to remove liquid from the third separation section; and   e) means to remove a gaseous stream, lean in liquid, from the third separation section   
     
     
         15 . (canceled)