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; 2) cooling the feed gas stream to a first 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 first gas/liquid separator; 4) cooling the methane enriched gaseous phase obtained in step 3) at least party by means of an external refrigerant to a second temperature at which liquid phase contaminant is formed as well as a methane enriched gaseous phase; and 5) separating the two phases obtained in step 4) by means of a second gas/liquid separator. 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 first 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 first gas/liquid separator;   4) cooling the methane enriched gaseous phase obtained in step 3) at least partly by means of an external refrigerant to a second temperature at which liquid phase contaminant is formed as well as a methane enriched gaseous phase; and   5) separating the two phases obtained in step 4) by means of a second gas/liquid separator.   
     
     
         2 . A process according to  claim 1 , in which at least one of the first and second gas/liquid separators comprises a centrifugal which comprises a bundle of parallel channels that are arranged within a spinning tube parallel to an axis of rotation of the spinning tube. 
     
     
         3 . A process according to  claim 1 , in which the first and/or second gas/liquid separator 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 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. 
     
     
         4 . A gas separation system, 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.   
     
     
         5 . A process according  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. 
     
     
         6 . A process according to  claim 5 , in which the natural gas stream comprises between 1 and 90 vol % of carbon dioxide, and between 0.1 and 60 vol % of hydrogen sulphide. 
     
     
         7 . A process  claim 1 , in which the feed gas stream comprises between 20 and 80 vol % of methane. 
     
     
         8 . A process according to  claim 1 , in which the feed gas stream in step 1) has a temperature between −20 and 150° C., preferably between −10 and 70° C., and a pressure between 10 and 150 bara, preferably between 80 and 120 bara. 
     
     
         9 . A process according to  claim 1 , in which the cooling in step 2) is done by isenthalpic expansion. 
     
     
         10 . A process according to  claim 9 , 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. 
     
     
         11 . A process  claim 1 , in which the feed gas stream is cooled in steps 2) and 4) to a temperature between −30 and −80° C., preferably between −40 and −65° C. 
     
     
         12 . A process  claim 1 , in which the pressure applied in step 4) is higher than the pressure applied in step 2), and in which the second temperature in step 4) is lower than the first temperature in step 2). 
     
     
         13 . A process according  claim 1 , in which the external refrigerant has a higher molecular weight than the methane enriched gaseous phase to be cooled. 
     
     
         14 . A process according to  claim 1 , in which the first and/or second gas/liquid separator 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. 
     
     
         15 . (canceled)