Split flow integrated lng production (sfi-lng)

Abstract

Processes for purifying and liquefying natural gas in conjunction and integration with cryogenic processing natural gas to recover natural gas liquids (NGL) is disclosed. In the process, the natural gas stream to be purified and liquefied is taken from top outlet stream of demethanizer in the cryogenic NGL recovery plant, first purified and then cooled under moderate pressure to condense it as a liquefied natural gas (LNG) product stream. Some of the cooling required for the demethanizer reflux stream is provided by natural gas liquefaction section before supplied to top of the column to serve as reflux. The top outlet stream from the demethanizer preferentially contains up to 3 mole percent of CO 2 and the majority of methane and small portion of any hydrocarbon heavier than methane, a split portion of this stream is taken and routed to cryogenic CO 2 removal section, in which a molecular sieve that forms a physical adsorption column is used to extract pure CO 2 as a product stream, then purified stream is routed to the liquefaction section where only two stages of coil-wound exchangers with a Semi-C3-MR cycle are used to liquefy natural gas. This present invention process is suited for LNG production in small-scale. This zeolite-based small-scale LNG process can be integrated with the design of any new natural gas facility and the technology can also be retrofitted to existing natural gas liquid (NGL) recovery plants, allowing for co-production of LNG and CO 2 with high purity.

1 . A process for removing CO 2  from a cryogenic gas stream (213° K and cooler) comprising dry sweet methane having a CO 2  concentration of up to 3 mole percent, the process comprising adsorptive carbon dioxide removal on a molecular sieve at a pressure of 1000-2000 kPag, wherein the molecular sieve is a zeolite, to obtain a carbon dioxide product stream and scrubbed natural gas stream, wherein the scrubbed natural gas stream has a carbon dioxide content of less than or equal to 50 part per million. 
     
     
         2 . The process of  claim 1 , wherein the cryogenic gas stream is at 173-213° K. 
     
     
         3 . The process of  claim 1 , wherein the cryogenic gas stream has a water content below 1 part per million. 
     
     
         4 . The process of  claim 1 , wherein the cryogenic gas stream has a maximum H 2 S concentration of 4 part per million. 
     
     
         5 . The process of  claim 1 , wherein the cryogenic gas stream has a CO 2  concentration of up to 3 mole percent. 
     
     
         6 . The process of  claim 1 , wherein adsorptive carbon dioxide removal on the molecular sieve is carried out at a pressure of 1000-2000 kPag. 
     
     
         7 . The process of  claim 1 , wherein the molecular sieve is a basic zeolite. 
     
     
         8 . The process of  claim 1 , wherein the molecular sieve is a LTA, FAU or GIS zeolite. 
     
     
         9 . A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
 introducing a dry sweet methane gas stream, having a CO 2  concentration of up to 3 mole percent, into an upper region of a demethanizer column;   removing a natural gas liquids (NGL) product stream from the bottom of said demethanizer column and flow rate and composition are same after SFI-LNG integration;   removing an overhead gaseous stream from the top of said demethanizer column at a cryogenic temperature and flow rate and composition are same after SFI-LNG integration;   subjecting a half portion of the overhead gaseous stream from said demethanizer column to cryogenic adsorptive carbon dioxide removal (cryogenic CO 2  removal) with a molecular sieve, to obtain a carbon dioxide product stream and scrubbed natural gas stream, wherein the scrubbed natural gas stream has a carbon dioxide content of less than or equal to 50 part per million;   liquefying said scrubbed natural gas stream by two stages of coil-wound heat exchangers to obtain a liquefied natural gas product stream in the absence of a propane pre-chilling process.   
     
     
         10 . The process of  claim 9 , wherein liquefying said scrubbed natural gas stream is by two stages in coil-wound heat exchangers. 
     
     
         11 . The process of  claim 9 , wherein liquefying said scrubbed natural gas stream comprises a propane precooled/mixed refrigerant (Semi-C3-MR) cycle, and no propane pre-chilling process is required. 
     
     
         12 . A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
 cooling a dry sweet methane gas feed stream containing light hydrocarbons in one or more primary heat exchangers, wherein said feed stream is cooled and partially condensed by heat exchange;   introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream;   segregating the overhead gaseous stream from the gas/liquid cold separator into first and second portions;   expanding said first portion of the overhead gaseous stream from the gas/liquid cold separator and introducing said expanded overhead gaseous stream into an upper region of a demethanizer column;   introducing at least a portion of the bottoms liquid stream from gas/liquid cold separator into said demethanizer column at an intermediate point thereof;   removing a natural gas liquids (NGL) product stream from the bottom of said demethanizer column;   removing an overhead gaseous stream from the top of said demethanizer column at a cryogenic temperature;   subjecting a first portion of the overhead gaseous stream from said demethanizer column to indirect heat exchange in one of said primary heat exchangers, wherein heat is exchanged between said first portion of the overhead gaseous stream from said demethanizer column and said second portion of the overhead gaseous stream from the gas/liquid cold separator, to obtain a natural gas product stream;   subjecting a second portion of the overhead gaseous stream from said demethanizer column to cryogenic adsorptive carbon dioxide removal in a molecular sieve, to obtain a carbon dioxide product stream and scrubbed natural gas stream, wherein the scrubbed natural gas stream has a carbon dioxide content of less than or equal to 50 part per million;   liquefying said scrubbed natural gas stream by heat exchange to obtain a liquefied natural gas product stream.   
     
     
         13 . The process of  claim 9 , wherein the dry sweet methane gas stream has a water content below 1 part per million. 
     
     
         14 . The process of  claim 9 , wherein the dry sweet methane gas stream has a maximum H 2 S concentration of 4 part per million. 
     
     
         15 . The process of  claim 9 , wherein the dry sweet methane gas stream has a CO 2  concentration up to 3 mole percent. 
     
     
         16 . The process of  claim 11 , wherein adsorptive carbon dioxide removal on the molecular sieve is carried out at a pressure of 1000-2000 kPag. 
     
     
         17 . The process of  claim 9 , wherein the molecular sieve is a basic zeolite. 
     
     
         18 . The process of  claim 9 , wherein the molecular sieve is a LTA, FAU or GIS zeolite.