Process for liquefaction of natural gas

Abstract

A process and system for production of liquefied natural gas (LNG) from natural gas. The natural gas is first partially purified by removal of water and other contaminants, followed by partial chilling to freeze some contaminants and to allow for production of a purge stream to remove other contaminants. These contaminants may be removed from the stream. The process has advantages of low cost and improved removal of contaminants.

1 . A process for liquefaction of a hydrocarbon stream, said process comprising:
 a) sending a cooled hydrocarbon stream to a quench unit; and   b) sending a quantity of a liquefied hydrocarbon stream to said quench unit to be combined with said cooled hydrocarbon steam to produce a bottoms stream comprising a liquid stream comprising solid impurities and a top stream comprising methane and incondensable impurities.   
     
     
         2 . The process of  claim 1  wherein said liquefied hydrocarbon stream is at least 15 degrees C. cooler than a freeze point of solid impurities in the cooled hydrocarbon stream. 
     
     
         3 . The process of  claim 1  wherein the liquefied hydrocarbon is relatively evenly distributed across the quench unit. 
     
     
         4 . The process of  claim 1  wherein a portion of said bottom stream is used to produce liquefied natural gas. 
     
     
         5 . The process of  claim 1  further comprising sending said bottoms stream to a unit to remove said solid impurities to a produce a purified bottoms stream. 
     
     
         6 . The process of  claim 1  wherein a portion of said bottom stream is returned to said quench unit. 
     
     
         7 . The process of  claim 1  wherein before said natural gas stream is cooled, at least a portion of water within said natural gas stream is removed. 
     
     
         8 . The process of  claim 1  wherein said natural gas stream is cooled to a temperature of about −25° to −75° C. 
     
     
         9 . The process of  claim 1  wherein said natural gas stream is cooled to a temperature of about −55° to −60° C. 
     
     
         10 . The process of  claim 1  wherein said solid impurities are selected from the group consisting of carbon dioxide, C 5  and C 6  hydrocarbons and water. 
     
     
         11 . The process of  claim 1  wherein said incondensable impurities are selected from the group consisting of nitrogen, oxygen and hydrogen. 
     
     
         12 . The process of  claim 1  wherein said bottoms stream is at a temperature from about −75° to −120° C. 
     
     
         13 . The process of  claim 1  wherein said bottoms stream is at a temperature from about 
     
     
         14 . A system for producing liquefied natural gas from a supply of natural gas, comprising:
 a) a device for supplying a stream of natural gas;   b) a separation device to remove water from said stream of natural gas to produce a partially dried stream of natural gas;   c) a means for feeding said partially dried stream of natural gas to a chilling device and then to a column;   d) a means for feeding a quantity of a chilled liquid to said column where said chilled liquid and said partially dried stream of natural gas are present in said column and a means to vent a purge stream from said quench tower;   e) a means to transport a combination of said chilled liquid and said partially dried stream of natural gas to a particle removal unit;   f) a means to transport a purified stream from said filter unit to a chiller to produce liquefied natural gas; and   g) a means to send said liquefied natural gas to a storage device.   
     
     
         15 . The system of  claim 14  wherein said separation device removes additional contaminants from said stream of natural gas. 
     
     
         16 . The system of  claim 14  wherein said column is a quench tower. 
     
     
         17 . The system of  claim 14  wherein said chilled liquid is a quantity of liquefied natural gas.