Methods for operating hydrocarbon removal systems from natural gas streams

Abstract

Methods for increasing ethane and non-freezing heavier hydrocarbons recovery in natural gas streams for the liquefaction of natural gas to form liquefied natural gas (LNG), and in particular, utilizing scrub columns to treat the natural gas feedstreams, are provided. Other independent variations of the methods are disclosed herein.

1 . A method for operating a hydrocarbon removal system, the method comprising the steps of:
 (a) separating at least a portion of a natural gas stream to produce a split stream and a separated natural gas stream;   (b) cooling at least a portion of the separated natural gas feed stream in one or more heat exchangers to form a pre-cooled feed stream;   (c) feeding the pre-cooled feed stream into a column, the column comprising an upper section, a mid-section, and a lower section;   (d) separating a methane-rich overhead stream and a bottom stream from a C5+ hydrocarbon-rich mixture in the upper section of the column;   (e) cooling the methane-rich overhead stream in a first heat exchanger to produce a first cooled methane-rich stream; and   (f) subsequently,
 (i) feeding the first cooled methane-rich stream to a reflux drum to produce a reflux stream; and/or 
 (ii) feeding the first cooled methane-rich stream to a Main Cryogenic Heat Exchanger (MCHX) to produce a second cooled methane-rich stream, and feeding the second cooled methane-rich stream to the reflux drum to produce a second overhead stream that is essentially free of heavy hydrocarbons. 
   
     
     
         2 . The method of  claim 1 , wherein the split stream is depressurized to a lower pressure to produce a stripping gas and the stripping gas is fed directly into the column. 
     
     
         3 . The method of  claim 2 , wherein the split stream is depressurized utilizing at least one Joule-Thomson (JT) valve. 
     
     
         4 . The method of  claim 1 , wherein the split stream is depressurized to a lower pressure using a reboiler to produce a stripping gas and the stripping gas is fed directly into the column. 
     
     
         5 . The method of  claim 2 , wherein the stripping gas is fed into the lower section of the column. 
     
     
         6 . The method of  claim 1 , wherein the stripping gas regulates methane slippage to the bottom of the column. 
     
     
         7 . The method of  claim 1 , further comprising feeding the reflux stream into the column. 
     
     
         8 . The method of  claim 1 , wherein the heat exchangers utilize an external refrigerant comprising propane. 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . The method of  claim 1 , further comprising feeding the second overhead stream to the MCHX to be liquefied under cryogenic conditions to produce a liquefied stream. 
     
     
         12 . The method of  claim 1 , wherein the cooling of at least a portion of the separated natural gas feed stream and a generation of a reflux by the split stream is integrated in one heat exchanger. 
     
     
         13 . (canceled) 
     
     
         14 . The method of  claim 1 , wherein the method further comprises a CO2 removal step and/or a H2S removal step. 
     
     
         15 . A method for operating a hydrocarbon removal system, the method comprising the steps of:
 (a) separating at least a portion of a natural gas stream to produce a split stream and a separated natural gas stream;   (b) cooling at least a portion of the separated natural gas feed stream in a single heat exchanger to form a pre-cooled feed stream;   (c) feeding the pre-cooled feed stream into a column, the column comprising an upper section, a mid-section, and a lower section;   (d) separating a methane-rich overhead stream and a bottom stream from a C5+ hydrocarbon-rich mixture in the upper section of the column;   (e) cooling the methane-rich overhead stream in the single heat exchanger to produce a two-phase stream;   (f) feeding the two-phase stream into a reflux drum to produce a second overhead stream and a reflux stream; and   (g) feeding the second overhead stream into a Main Cryogenic Heat Exchanger (MCHX) of a liquefaction system comprising at least two cooling cycles to produce Liquefied Natural Gas (LNG).   
     
     
         16 . The method of  claim 15 , wherein the separated natural gas feed stream is depressurized to a lower pressure prior to the cooling. 
     
     
         17 . The method of  claim 16 , wherein the separated natural gas feed stream is depressurized utilizing at least one Joule-Thomson (JT) valve. 
     
     
         18 . The method of  claim 15 , wherein the separated natural gas feed stream is depressurized to a lower pressure using a reboiler. 
     
     
         19 . The method of  claim 15 , wherein the method further comprises feeding the reflux stream into the column. 
     
     
         20 . The method of  claim 15 , wherein the cooling cycles comprise a warm mixed refrigerant cycle and a cold mixed refrigerant cycle. 
     
     
         21 . The method of  claim 20 , wherein the method comprises cooling the second overhead stream in the warm mixed refrigerant cycle to about −100° F. (about −73° C.). 
     
     
         22 . The method of  claim 21 , wherein the method comprises cooling the second overhead stream in the cold mixed refrigerant cycle after the warm mixed refrigerant cycle to produce a cryogenic fluid. 
     
     
         23 . (canceled) 
     
     
         24 . The method of  claim 15 , wherein the warm mixed refrigerant cycle comprises a warm mixed refrigerant and the warm mixed refrigerant comprises propane, iso-butane and ethane. 
     
     
         25 . (canceled) 
     
     
         26 . The method of  claim 15 , wherein the cold mixed refrigerant cycle comprises a cold mixed refrigerant and the cold mixed refrigerant comprises methane, ethane, propane, and nitrogen. 
     
     
         27 .- 29 . (canceled)