Processes and Systems for Separating Liquified Natural Gas

Abstract

Disclosed are simplified and energy-efficient distillation processes and systems for separating a liquefied natural gas stream to obtain a natural gas stream and a national gas liquid stream. Substantial savings in construction costs and operation energy consumption can be achieved by using the processes and systems of this disclosure. Preferably the separation processes are integrated with other industrial processes such as petroleum refining, petrochemical production, chemical production, and the like.

1 . A process for separating an LNG stream, the process comprising:
 (I) providing an LNG stream comprising methane, ethane, and optionally C3+ hydrocarbons having a temperature ≤−80° C., and an absolute pressure of ≥500 kPa-a;   (II) feeding the LNG stream into a distillation column at the top-most ideal stage of the distillation column;   (III) supplying heat to the distillation column;   (IV) obtaining an overhead stream from the distillation column comprising methane at a concentration ≥70 wt %, based on the total weight of the hydrocarbons in the overhead stream, without using an overhead compressor, an overhead condenser, and an overhead reflux stream; and   (V) obtaining a bottoms stream from the distillation column comprising C2+ hydrocarbons and from 0.01 to 10 wt %/o methane, based on the total weight of the bottoms stream.   
     
     
         2 . The process of  claim 1 , wherein the distillation column has from 2 to 20 ideal stages. 
     
     
         3 . The process of  claim 1 , wherein the LNG stream has an absolute pressure of ≥2,000 kPa-a, preferably ≥4,000 kPa-a. 
     
     
         4 . The process of  claim 1 , further comprising:
 (VI) heating the overhead stream by a first heat source, preferably via a first heat exchanger, to obtain a superheated natural gas stream; and   (VII) supplying the superheated natural gas stream to a natural gas delivery network without further compression or a fuel system.   
     
     
         5 . The process of  claim 1 , further comprising:
 (VI′) heating the overhead stream by a second heat source, preferably via a second heat exchanger, to obtain an un-superheated heated natural gas stream having an absolute pressure ≥200 kPa-a;   (VII′) compressing without after-cooling the un-superheated heated natural gas stream to obtain a compressed superheated natural gas stream having an absolute pressure ≥400 kPa-a; and   (VII″) supplying without further compression the compressed superheated natural gas stream to a natural gas delivery network and/or an industrial fuel system.   
     
     
         6 . The process of  claim 1 , wherein step (III) comprises:
 (IIIa) drawing a recycle stream from the distillation column;   (IIIb) heating the recycle stream by using a third heat source, preferably via a third heat exchanger;   (IIIc) feeding at least a portion of the heated recycle stream obtained from step (IIIb) into the distillation column.   
     
     
         7 . The process of  claim 6 , wherein the recycle stream is a side stream or a split stream from the bottoms stream. 
     
     
         8 . The process of  claim 1 , further comprising:
 (VIII) heating at least a portion of the bottoms stream using a fourth heat source, preferably via a fourth heat exchanger, to obtain a heated bottoms stream, preferably via a third heat exchanger; and   (IX) conducting away the heated bottoms stream.   
     
     
         9 . The process of  claim 4 , wherein at least one of the first heat source, the second heat source, the third heat source, and the fourth heat source has a temperature ≤150° C. 
     
     
         10 . The process of  claim 1 , wherein at least one of the first heat source, the second heat source, the third heat source, and the fourth heat source has a temperature ≥30° C. 
     
     
         11 . The process of  claim 4 , wherein the first heat source and/or the second heat source and/or the third heat source and/or the fourth heat source is one or more of the following streams:
 a warm cooling water stream;   a steam condensate;   an excess low pressure steam stream;   a warm hydrocarbon stream;   a heat medium that comprises as at least a portion thereof a heat medium used in a heat exchanger other than the heat exchanger used the relevant step (VI), (IIIb) or (VIII); and   a mixture or a combination thereof.   
     
     
         12 . The process of  claim 1 , further comprising:
 (X) supplying at least a portion of the bottoms stream to one or more of the following:   a pyrolysis reactor, preferably a steam cracker;   a dehydrogenation reactor;   a separation column; and   an LPG blending stage for blending with another hydrocarbon stream.   
     
     
         13 . The process of  claim 1 , wherein the bottoms stream comprises from 0.1 to 5 mol % of methane, and at least a portion of the bottoms stream is supplied as a hydrocarbon feed to a hydrocarbon pyrolysis reactor. 
     
     
         14 . A process for separating an LNG stream, the process comprising:
 (i) providing an LNG stream comprising methane, ethane, and optionally C3+ hydrocarbons having a temperature 5-80° C. and an absolute pressure of ≥500 kPa-a;   (ii) heating the LNG stream to obtain a vapor-liquid mixture feed stream;   (iii) feeding the vapor-liquid mixture feed stream into a distillation column comprising 2 to 20 ideal stages;   (iv) obtaining a first overhead vapor stream from the distillation column comprising methane at a concentration ≥70 wt %, based on the total weight of the hydrocarbons in the overhead stream;   (v) condensing at least a portion of the first overhead vapor stream, without compressing the first overhead vapor stream, to obtain a vapor-liquid mixture overhead stream;   (vi) separating the vapor-liquid mixture overhead stream to obtain a liquid reflux stream and a second vapor overhead stream;   (vii) feeding at least a portion of the liquid reflux stream into the distillation column as a reflux stream;   (viii) providing heat to the distillation column; and   (ix) obtaining a bottoms stream from the distillation column comprising C2+ hydrocarbons and from 0.1 wt % to 10 wt % methane.   
     
     
         15 . The process of  claim 14 , wherein step (ii) comprises:
 (iia) heating the LNG stream or a portion thereof by indirectly exchanging heat with at least a portion of the first overhead vapor stream;   and step (v) comprises:   (va) cooling the first overhead vapor stream or a portion thereof by indirectly exchanging heat with at least a portion of the LNG stream.   
     
     
         16 . The process of  claim 14 , further comprising:
 heating the second vapor overhead stream by a first heat source, preferably via a first heat exchanger, to obtain a superheated natural gas stream; and   supplying the superheated natural gas stream to a natural gas delivery network without further compression and/or an industrial fuel system.   
     
     
         17 . The process of  claim 14 , further comprising:
 (x) heating the second vapor overhead stream by a second heat source, preferably via a second heat exchanger, to obtain an un-superheated heated natural gas stream having an absolute pressure ≥200 kPa-a;   (xi) compressing without after cooling the un-superheated heated natural gas stream to obtain a compressed superheated natural gas stream having an absolute pressure ≥400 kPa-a; and   (xii) supplying without further compression the compressed superheated natural gas stream to a natural gas delivery network and/or an industrial fuel system.   
     
     
         18 . The process of  claim 14 , wherein step (viii) comprises:
 (viiia) drawing a recycle stream from the distillation column;   (viiib) heating the recycle stream by using a third heat source, preferably via a third heat exchanger;   (viiic) feeding at least a portion of the heated side stream obtained from step (IIIb) into the distillation column.   
     
     
         19 . The process of  claim 14 , further comprising:
 heating at least a portion of the bottoms stream using a fourth heat source, preferably via a fourth heat exchanger, to obtain a heated bottoms stream; and   conducting away the heated bottoms stream.   
     
     
         20 . The process of  claim 16 , wherein at least one of the first heat source, the second heat source, the third heat source, and the fourth heat source has a temperature ≤150° C. 
     
     
         21 . The process of  claim 16 , wherein at least one of the first heat source, the second heat source, the third heat source, and the fourth heat source is one or more of the following streams:
 a warm cooling water stream;   a steam condensate;   an excess low pressure steam stream;   a warm hydrocarbon stream;   a heat medium that comprises as at least a portion thereof a heat medium used in a heat exchanger other than the heat exchanger used the relevant step (VI), (IIIb) or (VIII); and   a mixture or a combination thereof.   
     
     
         22 . A process for separating an LNG stream, the process comprising:
 (1) providing an vapor-liquid mixture LNG stream comprising methane, ethane, and optionally C3+ hydrocarbons having a temperature ≤−80° C. and an absolute pressure of ≥500 kPa-a;   (2) feeding the vapor-liquid mixture LNG stream into a flashing drum,   (3) obtaining an flashing drum overhead vapor effluent rich in methane and a flashing drum bottoms liquid effluent rich in ethane, wherein the flashing drum bottoms liquid effluent constitutes ≤50 wt % of the vapor-liquid mixture LNG stream; and   (4) separating the flashing drum bottoms liquid effluent in a distillation column.   
     
     
         23 . The process of  claim 22 , wherein step (1) comprises:
 (1a) providing a precursor LNG stream having a temperature ≤−80° C.; and   (1b) heating the precursor LNG stream to obtain the vapor-liquid mixture LNG stream by indirectly exchanging heat between the precursor LNG stream with a heat source having a temperature in a range from −50 to 150° C.   
     
     
         24 . The process of  claim 23 , wherein the heat source is one or more of the following streams:
 a warm cooling water stream;   a steam condensate;   an excess low pressure steam stream;   a warm hydrocarbon stream;   a heat medium that comprises as at least a portion thereof a heat medium used in a heat exchanger other than the heat exchanger used the relevant step (VI), (IIIb) or (VIII); and   a mixture or a combination thereof.   
     
     
         25 . The process of  claim 1 , wherein the process is integrated with a process in a petrochemical plant and a petroleum refining plant.