Integration of a liquefied natural gas liquefier with the production of liquefied natural gas

Abstract

A method for integrating a liquefied natural gas liquefier system with production of liquefied natural gas from a methane-containing gas stream. The liquefied natural gas is produced by feeding a methane-containing gas stream through a heat exchanger to a distillation column and liquefying the natural gas while capturing the gaseous nitrogen. The liquefied natural gas is captured and the nitrogen gas is recovered, fed through the heat exchanger to recover cold.

Having thus described the invention, what we claim is: 
     
         1 . A method for producing liquefied natural gas comprising the steps of:
 a) feeding a methane-containing gas stream to a heat exchanger, wherein the methane-containing gas stream will be cooled by the heat exchanger;   b) feeding the methane-containing gas to a reboiler of a distillation column, wherein the distillation column can be packed or contain sieve trays;   c) feeding the methane containing gas to a valve where part of the methane containing gas is vaporized and its temperature is decreased due to Joule Thompson effect;   d) feeding the methane containing gas to the top of a packed distillation column;   e) removing methane from the bottom of the packed distillation column as liquefied natural gas;   f) recovering nitrogen; and   g) feeding the recovered nitrogen through the heat exchanger.   
     
     
         2 . The method as claimed in  claim 1  wherein nitrogen is collected from the top of the packed distillation column and fed through a heat exchanger to recover cold. 
     
     
         3 . The method as claimed in  claim 1  wherein said methane-containing gas stream is selected from the group consisting of biogas and landfill gas. 
     
     
         4 . The method as claimed in  claim 1  wherein nitrogen from a mixed refrigerant source is fed through the heat exchanger to a first separator. 
     
     
         5 . The method as claimed in  claim 1  wherein the first separator feeds the nitrogen back through the heat exchanger. 
     
     
         6 . The method as claimed in  claim 1  wherein the nitrogen is purified by passing through a second separator. 
     
     
         7 . The method as claimed in  claim 6  wherein the purifying further comprises a step of compressing and coalescing the nitrogen. 
     
     
         8 . The method as claimed in  claim 1  wherein purifying the nitrogen comprises the steps of feeding nitrogen through the heat exchanger to the first separator; feeding the nitrogen to an inlet separator; feeding the nitrogen to a refrigerant compressor, wherein a mixed refrigerant is formed; feeding the mixed refrigerant to a coalescing filter; feeding the mixed refrigerant to a cooler; feeding the mixed refrigerant to the second separator wherein nitrogen is separated and fed through the heat exchanger to the first separator. 
     
     
         9 . The method as claimed in  claim 1  wherein the purified nitrogen provides cold to the heat exchanger. 
     
     
         10 . The method as claimed in  claim 1  wherein the methane-containing gas is at a pressure of 6 to 15 bar. 
     
     
         11 . The method as claimed in  claim 1  wherein the cooled methane-containing gas of step a) is at a temperature of about −145° C.