LNG system with enhanced turboexpander configuration

Abstract

Natural gas liquefaction system employing a turboexpander to convert excess pressure within a predominantly methane stream into work useable in another location within the liquefaction system. Primarily, the turboexpander is used to compress a refrigerant used in at least one of the refrigeration cycles within the liquefaction system.

1 . A method of liquefying a natural gas stream, said method comprising the steps of: 
 (a) cooling a pressurized, predominantly methane stream in a first refrigerant chiller;    (b) separating at least a portion of the cooled predominantly methane stream into a primarily liquid stream and a primarily gaseous stream;    (c) passing at least a portion of the primarily gaseous stream through a turboexpander to thereby generate work and provide a reduced-pressure predominantly methane stream; and    (d) directing at least a portion of the reduced-pressure predominantly methane stream to a heavies removal column for removal of heavy hydrocarbon components.    
   
   
       2 . The method according to  claim 1;  and 
 (e) passing at least a portion of the primarily liquid stream to the heavies removal column.    
   
   
       3 . The method according to  claim 1 , 
 said heavies removal column being a stripping column having internal packing.    
   
   
       4 . The method according to  claim 3;  and 
 (f) using a portion of the cooled predominantly methane stream as a stripping gas in the heavies removal column.    
   
   
       5 . The method according to  claim 4 , said at least a portion of the reduced-pressure predominantly methane stream entering the heavies removal column at a location above the internal packing, 
 said stripping gas entering the heavies removal column at a location below the internal packing.    
   
   
       6 . The method according to  claim 5;  and 
 (g) introducing at least a portion of the primarily liquid stream into the heavies removal column at a location below the internal packing.    
   
   
       7 . The method according to  claim 6;  and 
 (h) separating in the heavies removal column the at least a portion of the primarily liquid stream, the stripping gas, and the at least a portion of the reduced-pressure predominantly methane stream into a heavies depleted stream and a heavies rich stream.    
   
   
       8 . The method according to  claim 7;  and 
 (i) cooling said heavies depleted stream in an ethylene refrigerant chiller.    
   
   
       9 . The method according to  claim 7;  and 
 (j) directing said heavies depleted stream to an open-methane refrigeration cycle.    
   
   
       10 . The method according to  claim 9 , 
 said open-methane refrigeration cycle comprising a plurality of expansion-cooling steps.    
   
   
       11 . The method according to  claim 1;  and 
 (k) measuring the pressure of the primarily gaseous stream prior to step (c), and based on the pressure measurement, selectively opening or closing a by-pass valve capable of diverting at least part of the primarily gaseous stream around the turboexpander.    
   
   
       12 . The method according to  claim 1 , 
 said first refrigerant chiller comprising a propane refrigerant chiller.    
   
   
       13 . The method according to  claim 1 , 
 said first refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       14 . The method according to  claim 1;  and 
 (l) using at least a portion of the work generated by the turboexpander to power a compressor.    
   
   
       15 . The method according to  claim 14;  and 
 (m) directing the reduced-pressure predominantly methane stream to a second refrigerant chiller prior to step (d).    
   
   
       16 . The method according to  claim 15 , 
 said compressor being used to compress a refrigerant employed in the operation of at least one of said first or second refrigerant chillers.    
   
   
       17 . The method according to  claim 15 , 
 said second refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       18 . The method according to  claim 1 , 
 said predominantly methane stream having a pressure of at least about 638 psia immediately prior to step (b).    
   
   
       19 . The method according to  claim 18 , 
 said reduced-pressure predominantly methane stream having a pressure that is less than about 95% of the pressure of the predominantly methane stream immediately prior to step (b).    
   
   
       20 . The method according to  claim 1 , 
 steps (a), (b), (c), and (d) being carried out in a cascade-type LNG facility having at least three sequential cooling cycles, each employing a different refrigerant.    
   
   
       21 . The method according to  claim 20 , 
 said cascade-type LNG facility employing an open-methane refrigeration cycle.    
   
   
       22 . The method according to  claim 1;  and 
 (n) vaporizing liquefied natural gas produced via steps (a)-(d).    
   
   
       23 . A computer simulation process comprising the step of using a computer to simulate the method of  claim 1 .  
   
   
       24 . A liquefied natural gas product produced by the method of  claim 1 .  
   
   
       25 . A method of liquefying a natural gas stream, said method comprising the steps of: 
 (a) cooling a pressurized, predominantly methane stream in a first refrigerant chiller;    (b) separating at least a portion of the cooled predominantly methane stream into a primarily liquid stream and a primarily gaseous stream;    (c) passing at least a portion of the primarily gaseous stream through a turboexpander to thereby generate work and provide a reduced-pressure predominantly methane stream;    (d) directing at least a portion of the reduced-pressure predominantly methane stream to a second refrigerant chiller to provide a cooled, reduced-pressure predominantly methane stream;    (e) passing at least a portion of the cooled, reduced-pressure predominantly methane stream to a heavies removal column for removal of heavy hydrocarbon components;    (e) passing at least a portion of the primarily liquid stream to the heavies removal column; and    (f) using a portion of the cooled predominantly methane stream as a stripping gas in the heavies removal column.    
   
   
       26 . The method according to  claim 25 , 
 said heavies removal column being a stripping column having internal packing.    
   
   
       27 . The method according to  claim 26;  and 
 (g) introducing at least a portion of the primarily liquid stream into the heavies removal column at a location below the internal packing.    
   
   
       28 . The method according to  claim 25;  and 
 (h) measuring the pressure of the primarily gaseous stream prior to step (c), and based on the pressure measurement, selectively opening or closing a by-pass valve capable of diverting at least part of the primarily gaseous stream around the turboexpander.    
   
   
       29 . The method according to  claim 25 , 
 said first refrigerant chiller comprising a propane refrigerant chiller.    
   
   
       30 . The method of according to  claim 25 , 
 said first refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       31 . The method according to  claim 25 , 
 said second refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       32 . The method according to  claim 25 , 
 (i) using at least a portion of the work generated by the turboexpander to power a compressor.    
   
   
       33 . The method according to  claim 32 , 
 said compressor being used to compress a refrigerant employed in the operation of at least one of the first or second refrigerant chillers.    
   
   
       34 . The method according to  claim 25 , 
 said predominantly methane stream having a pressure of at least about 638 psia immediately prior to step (b).    
   
   
       35 . The method according to  claim 34 , 
 said reduced-pressure predominantly methane stream having a pressure that is less than about 95% of the pressure of the predominantly methane stream immediately prior to step (b).    
   
   
       36 . The method according to  claim 25;  and 
 (j) separating in the heavies removal column the at least a portion of the primarily liquid stream, the stripping gas, and the at least a portion of the reduced-pressure predominantly methane stream into a heavies depleted stream and a heavies rich stream.    
   
   
       37 . The method according to  claim 36;  and 
 (k) cooling said heavies depleted stream in an ethylene refrigerant chiller.    
   
   
       38 . The method according to  claim 36;  and 
 (l) directing said heavies depleted stream to an open-methane refrigeration cycle.    
   
   
       39 . The method according to  claim 38 , 
 said open-methane refrigeration cycle comprising a plurality of expansion-cooling steps.    
   
   
       40 . The method according to  claim 25 , 
 steps (a)-(f) being carried out in a cascade-type LNG facility having at least three sequential cooling cycles, each employing a different refrigerant.    
   
   
       41 . The method according to  claim 40 , 
 said cascade-type LNG facility employing an open-methane refrigeration cycle.    
   
   
       42 . The method according to  claim 25;  and 
 (m) vaporizing liquefied natural gas produced via steps (a)-(f).    
   
   
       43 . A computer simulation process comprising the step of using a computer to simulate the method of  claim 25 .  
   
   
       44 . A liquefied natural gas product produced by the method of  claim 25 .  
   
   
       45 . An apparatus for liquefying a predominantly methane stream, said apparatus comprising: 
 (a) a first refrigerant chiller operable to cool at least a portion of the predominantly methane stream;    (b) a separation vessel located downstream of said first refrigerant chiller for separating at least a portion of the cooled predominantly methane stream into a primarily gaseous stream and a primarily liquid stream;    (c) a turboexpander located downstream of said separation vessel and capable of generating work as the primarily gaseous stream passes therethrough thereby forming a reduced-pressure predominantly methane stream; and    (d) a heavies removal column located downstream of said separation vessel for receiving at least a portion of the primarily liquid stream.    
   
   
       46 . The apparatus according to  claim 45;  and 
 (e) a second refrigerant chiller located downstream of said turboexpander operable to cool at least a portion of the reduced-pressure predominantly methane stream.    
   
   
       47 . The apparatus according to  claim 46 , 
 said second refrigerant chiller comprising an ethylene refrigerant chiller    
   
   
       48 . The apparatus according to  claim 46;  and 
 (f) a compressor operable to compress the refrigerant used in at least one of said first or second refrigerant chillers, said compressor being powered at least in part by the work produced from said turboexpander.    
   
   
       49 . The apparatus according to  claim 45 , 
 said heavies removal column comprising a stripping column having internal packing.    
   
   
       50 . The apparatus according to  claim 45;  and 
 (g) a bypass line including a bypass valve capable of diverting at least a portion of the primarily gaseous stream around said turboexpander.    
   
   
       51 . The apparatus according to  claim 45 , 
 said first refrigerant chiller comprising a propane refrigerant chiller.    
   
   
       52 . The apparatus according to  claim 45 , 
 said first refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       53 . The apparatus according to  claim 45;  and 
 (h) an open-methane refrigeration cycle located downstream from said heavies removal column.    
   
   
       54 . An apparatus for liquefying a predominantly methane stream, said apparatus comprising: 
 (a) a first refrigerant chiller operable to cool at least a portion of the predominantly methane stream;    (b) a separation vessel located downstream of said first refrigerant chiller for separating at least a portion of the cooled predominantly methane stream into a primarily gaseous stream and a primarily liquid stream;    (c) a turboexpander located downstream of said separation vessel and capable of generating work as the primarily gaseous stream passes therethrough thereby forming a reduced-pressure predominantly methane stream;    (d) a heavies removal column located downstream of said separation vessel for receiving at least a portion of the primarily liquid stream;    (e) a second refrigerant chiller located downstream of said turboexpander operable to cool at least a portion of the reduced-pressure predominantly methane stream; and    (f) a compressor operable to compress the refrigerant used in at least one of said first or second refrigerant chillers, said compressor being powered at least in part by the work produced from said turboexpander.    
   
   
       55 . The apparatus according to  claim 54 , 
 said heavies removal column comprising a stripping column having internal packing.    
   
   
       56 . The apparatus according to  claim 54;  and 
 (g) a by-pass line including a by-pass valve capable of diverting at least a portion of the primarily gaseous stream around said turboexpander.    
   
   
       57 . The apparatus according to  claim 54 , 
 said first refrigerant chiller comprising a propane refrigerant chiller.    
   
   
       58 . The apparatus according to  claim 54 , 
 said first refrigerant chiller comprising an ethylene refrigerant chiller.    
   
   
       59 . The apparatus according to  claim 54;  and 
 (h) an ethylene refrigerant chiller located downstream from said heavies removal column.    
   
   
       60 . The apparatus according to  claim 54;  and 
 (i) an open-methane refrigeration cycle located downstream from said heavies removal column.