Integrated NGL recovery in the production of liquefied natural gas

Abstract

Process for the liquefaction of natural gas and the recovery of components heavier than methane wherein natural gas is cooled and separated in a first distillation column into an overhead vapor enriched in methane and a bottoms stream enriched in components heavier than methane, wherein the first distillation column utilizes a liquefied methane-containing reflux stream. This reflux stream may be provided by a condensed portion of the overhead vapor or a portion of totally condensed overhead vapor that is subsequently warmed. The bottoms stream may be separated in one or more additional distillation columns to provide one or more product streams, any of which are partially or totally withdrawn as recovered hydrocarbons. A stream of unrecovered liquid hydrocarbons may be combined with either the condensed portion of the overhead vapor or a portion of totally condensed overhead vapor that is subsequently warmed.

1 . A process for the liquefaction of natural gas and the recovery of components heavier than methane from the natural gas, wherein the process comprises
 (a) cooling a natural gas feed to provide a cooled natural gas feed and introducing the cooled natural gas feed into a first distillation column;   (b) withdrawing from the first distillation column an overhead vapor stream enriched in methane and a bottoms stream enriched in components heavier than methane;   (c) cooling and condensing at least a portion of the overhead vapor stream to provide a condensed methane-enriched stream;   (d) separating the bottoms stream in one or more additional distillation columns to provide one or more product streams selected from the group consisting of a residual vapor stream comprising methane, a liquid stream enriched in ethane, a liquid stream enriched in propane, a liquid stream enriched in butane, and a liquid stream enriched in pentane;   (e) withdrawing as recovered hydrocarbons all or a portion of any of the one or more product streams; and   (f) introducing one or more reflux streams into the first distillation column, wherein the one or more reflux streams comprise either
 (f1) a liquefied methane-containing reflux stream and a stream of unrecovered liquid hydrocarbons that is pumped to a pressure in the first distillation column or 
 (f2) a combined stream comprising the liquefied methane-containing reflux stream and the stream of unrecovered liquid hydrocarbons that is pumped to the pressure in the first distillation column, 
   and wherein the liquefied methane-containing reflux stream is provided by a method selected from the group consisting of
 (1) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream and withdrawing a portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream, 
 (2) cooling and totally condensing a portion of the first overhead vapor stream to provide the liquefied methane-containing reflux stream, and 
 (3) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream and warming a portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream. 
   
   
   
       2 . The method of  claim 1  wherein the stream of unrecovered liquid hydrocarbons comprises any of
 (i) a portion of the liquid stream enriched in ethane,   (ii) a portion of the liquid stream enriched in propane,   (iii) a portion of the liquid stream enriched in butane,   (iv) a portion of the liquid stream enriched in pentane, and   (v) all or a portion of the residual vapor stream dissolved in a portion of the liquid stream enriched in propane and/or a portion of the liquid stream enriched in butane and/or a portion of the liquid stream enriched in pentane.   
   
   
       3 . The method of  claim 1  wherein the liquefied methane-containing reflux stream is introduced into the top of the first distillation column. 
   
   
       4 . The method of  claim 1  wherein the stream of unrecovered liquid hydrocarbons is introduced into the top of the first distillation column. 
   
   
       5 . The method of  claim 1  wherein the combined stream comprising the liquefied methane-containing reflux stream and the stream of unrecovered liquid hydrocarbons is introduced into the top of the first distillation column. 
   
   
       6 . The method of  claim 1  wherein the stream of unrecovered liquid hydrocarbons is introduced into the first distillation column at a location below the top of the column and above a location at which the cooled natural gas feed is introduced into the column. 
   
   
       7 . The method of  claim 1  wherein the cooling and condensing of at least a portion of the overhead vapor stream is effected in a main heat exchanger by indirect heat exchange with a first vaporizing refrigerant provided by reducing the pressure of a first cooled multicomponent liquid refrigerant. 
   
   
       8 . The method of  claim 7  wherein a portion of the overhead vapor stream is condensed in a heat exchanger separate from the main heat exchanger by indirect heat exchange with a stream of vaporizing refrigerant provided by withdrawing and reducing the pressure of a portion of the first cooled multicomponent liquid refrigerant. 
   
   
       9 . The method of  claim 7  wherein the first cooled multicomponent liquid refrigerant is provided by cooling a saturated multicomponent liquid refrigerant in the main heat exchanger and wherein the warming of the portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream is effected in a heat exchanger separate from the main heat exchanger by indirect heat exchange with a portion of the saturated multicomponent liquid refrigerant. 
   
   
       10 . The process of  claim 7  comprising subcooling at least a portion of the condensed methane-enriched stream to provide a pressurized liquefied natural gas product, wherein the subcooling is effected in the main heat exchanger by indirect heat exchange with a second vaporizing refrigerant provided by reducing the pressure of a second cooled multicomponent liquid refrigerant. 
   
   
       11 . The process of  claim 1  wherein the cooling of the natural gas feed to provide the cooled natural gas feed is effected by indirect heat exchange with the overhead vapor stream enriched in methane. 
   
   
       12 . The process of  claim 1  wherein the stream of unrecovered liquid hydrocarbons contains greater than about 50 mole % of hydrocarbons having three or more carbon atoms. 
   
   
       13 . The process of  claim 1  wherein the stream of unrecovered liquid hydrocarbons contains greater than about 50 mole % of pentane. 
   
   
       14 . The method of  claim 1  wherein the stream of unrecovered liquid hydrocarbons comprises a portion of the liquid stream enriched in propane and a portion of the liquid stream enriched in butane. 
   
   
       15 . The method of  claim 14  wherein the stream of unrecovered liquid hydrocarbons comprises a portion of the liquid stream enriched in ethane. 
   
   
       16 . The method of  claim 14  wherein the stream of unrecovered liquid hydrocarbons comprises a portion of the residual vapor stream comprising methane dissolved in a liquid comprising hydrocarbons heavier than methane. 
   
   
       17 . The method of  claim 1  wherein the molar flow rate of the unrecovered liquid hydrocarbons is less than about 25% of the molar flow rate of the liquefied methane reflux stream of (f1). 
   
   
       18 . An apparatus for the liquefaction of natural gas and the recovery of components heavier than methane from the natural gas, wherein the apparatus comprises
 (a) a cooling system adapted to cool a natural gas feed to provide a cooled natural gas feed;   (b) a first distillation column adapted to separate the cooled natural gas feed into an overhead vapor stream enriched in methane and a bottoms stream enriched in components heavier than methane;   (c) a main heat exchanger adapted to cool and condense at least a portion of the overhead vapor stream to provide a condensed methane-enriched stream;   (d) one or more additional distillation columns adapted to separate the bottoms stream into one or more product streams selected from the group consisting of a residual vapor stream comprising methane, a liquid stream enriched in ethane, a liquid stream enriched in propane, a liquid stream enriched in butane, and a liquid stream enriched in pentane;   (e) piping adapted to withdraw all or a portion of any of the one or more product streams as recovered hydrocarbons;   (f) piping adapted to introduce one or more reflux streams into the first distillation column, wherein the one or more reflux streams comprise either
 (f1) a liquefied methane-containing reflux stream and a stream of unrecovered liquid hydrocarbons that is pumped to a pressure in the first distillation column, wherein the liquefied methane-containing reflux stream is provided by a method selected from the group consisting of 
 (1) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream and withdrawing a portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream, 
 (2) cooling and totally condensing a portion of the first overhead vapor stream to provide the liquefied methane-containing reflux stream, and 
 (3) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream and warming a portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream; or 
 (f2) a combined stream comprising the liquefied methane-containing reflux stream and the stream of unrecovered liquid hydrocarbons that is pumped to the pressure in the first distillation column; and 
   (g) piping and pump or pumps adapted to transfer unrecovered liquid hydrocarbons from the one or more additional distillation columns to the piping adapted to introduce one or more reflux streams into the first distillation column.   
   
   
       19 . The apparatus of  claim 18  comprising a heat exchanger separate from the main heat exchanger that is adapted to condense a portion of the overhead vapor stream from the first distillation column by indirect heat exchange with a stream of vaporizing refrigerant. 
   
   
       20 . The apparatus of  claim 18  wherein the main heat exchanger is a wound coil heat exchanger. 
   
   
       21 . The apparatus of  claim 20  wherein the main heat exchanger comprises a first bundle adapted to cool and condense at least a portion of the overhead vapor stream to provide a condensed methane-enriched stream and a second bundle adapted to further cool the condensed methane-enriched stream to provide a subcooled liquid product. 
   
   
       22 . A process for the liquefaction of natural gas comprising
 (a) cooling a natural gas feed to provide a cooled natural gas feed and introducing the cooled natural gas feed into a first distillation column;   (b) withdrawing from the first distillation column an overhead vapor stream enriched in methane and a bottoms stream enriched in components heavier than methane;   (c) cooling and condensing at least a portion of the overhead vapor stream in a main heat exchanger to provide a condensed methane-enriched stream; and   (d) introducing a liquefied methane-containing reflux stream into the first distillation column, wherein the liquefied methane-containing reflux stream is provided by a method selected from the group consisting of
 (1) dividing the overhead vapor stream into a first vapor portion and a second vapor portion, and cooling and totally condensing the first vapor portion to provide the liquefied methane-containing reflux stream, and 
 (2) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream, dividing the condensed methane-enriched stream into a first portion and a second portion, warming the first portion to provide a warmed first portion, and utilizing the warmed first portion to provide the liquefied methane-containing reflux stream. 
   
   
   
       23 . The method of  claim 22  wherein the first vapor portion of the overhead vapor stream is condensed in a heat exchanger separate from the main heat exchanger by indirect heat exchange with a stream of vaporizing refrigerant. 
   
   
       24 . The method of  claim 22  wherein the warming of the first portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream is effected in a heat exchanger separate from the main heat exchanger. 
   
   
       25 . The process of  claim 22  comprising subcooling at least a portion of the condensed methane-enriched stream to provide a pressurized liquefied natural gas product, wherein the subcooling is effected in the main heat exchanger by indirect heat exchange with a stream of vaporizing refrigerant. 
   
   
       26 . An apparatus for the liquefaction of natural gas comprising
 (a) a cooling system adapted to cool a natural gas feed to provide a cooled natural gas feed;   (b) a first distillation column adapted to separate the cooled natural gas feed into an overhead vapor stream enriched in methane and a bottoms stream enriched in components heavier than methane;   (c) a main heat exchanger adapted to cool and condense at least a portion of the overhead vapor stream to provide a condensed methane-enriched stream; and   (d) piping adapted to introduce a liquefied methane-containing reflux stream into the first distillation column, wherein the liquefied methane-containing reflux stream provided by a method selected from the group consisting of
 (1) cooling and totally condensing a portion of the overhead vapor stream to provide the liquefied methane-containing reflux stream, and 
 (2) cooling and totally condensing the overhead vapor stream to form the condensed methane-enriched stream and warming a portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream. 
   
   
   
       27 . The apparatus of  claim 26  comprising a heat exchanger separate from the main heat exchanger that is adapted to condense the portion of the overhead vapor stream from the first distillation column by indirect heat exchange with a stream of vaporizing refrigerant. 
   
   
       28 . The apparatus of  claim 26  comprising a heat exchanger separate from the main heat exchanger that is adapted to warm the portion of the condensed methane-enriched stream to provide the liquefied methane-containing reflux stream. 
   
   
       29 . The apparatus of  claim 26  wherein the main heat exchanger is a wound coil heat exchanger. 
   
   
       30 . The apparatus of  claim 29  wherein the main heat exchanger comprises a first bundle adapted to cool and condense at least a portion of the overhead vapor stream to provide the condensed methane-enriched stream and a second bundle adapted to further cool at least a portion of the condensed methane-enriched stream to provide a subcooled liquid product.