Method of refining natural gas and natural gas refining system

Abstract

A method and system of refining natural gas that improves the quality of liquefied natural gas and enables separation and recovery of hydrocarbons other than methane. The method of refining natural gas containing methane; any other hydrocarbon selected from the group consisting of ethane, ethylene, propane, propylene, n-butane, isobutane, 1-butene, n-pentane, and isopentane; carbon dioxide; and hydrogen sulfide, includes adjusting a pressure and temperature of the natural gas so that the methane is in the gas phase, the other hydrocarbon in the liquid phase, and the carbon dioxide and the hydrogen sulfide in the solid phase, respectively; separating the natural gas, of which the pressure and temperature has been adjusted, into a gas containing the methane and a suspension liquid; and separating the separated suspension liquid into a liquid containing the other hydrocarbon and a solid containing the carbon dioxide and the hydrogen sulfide.

1 . A method of refining natural gas containing methane; any other hydrocarbon selected from the group consisting of ethane, ethylene, propane, propylene, n-butane, isobutane, 1-butene, n-pentane, and isopentane; carbon dioxide; and hydrogen sulfide, the method comprising the steps of:
 adjusting a pressure and temperature of the natural gas so that the methane is in the gas phase, the other hydrocarbon in the liquid phase, and the carbon dioxide and the hydrogen sulfide in the solid phase, respectively;   separating the natural gas, of which the pressure and temperature has been adjusted, into a gas containing the methane and a suspension liquid; and   separating the separated suspension liquid into a liquid containing the other hydrocarbon and a solid containing the carbon dioxide and the hydrogen sulfide.   
   
   
       2 . The method of refining natural gas according to  claim 1 , wherein the temperature of the natural gas is adjusted to a value less than a boiling point of ethylene but equal to or higher than a melting point of n-pentane. 
   
   
       3 . The method of refining natural gas according to  claim 1 , wherein the pressure of the natural gas is adjusted in a range from 1 to 10 atm. 
   
   
       4 . The method of refining natural gas according to  claim 1 , wherein the pressure and temperature of the natural gas is adjusted by adiabatic-expanding the natural gas with expanding means. 
   
   
       5 . The method of refining natural gas according to  claim 1 , wherein the pressure and temperature of the natural gas is adjusted by mixing liquefied natural gas in the natural gas with mixing means. 
   
   
       6 . The method of refining natural gas according to  claim 1 , wherein the suspension liquid is separated into the liquid containing the other hydrocarbon and the solid containing the carbon dioxide and the hydrogen sulfide with a cyclone. 
   
   
       7 . The method of refining natural gas according to  claim 1 , wherein in the range in which the pressure of the natural gas is 1 atm or more and the temperature of the natural gas is a value less than a melting point of the hydrogen sulfide but equal to or higher than a melting point of n-pentane, the pressure and temperature of the natural gas is adjusted so that a concentration of methane in the gas phase is 90% or more. 
   
   
       8 . The method of refining natural gas according to  claim 7 , wherein the temperature of the natural gas is adjusted to a value less than a boiling point of ethylene. 
   
   
       9 . The method of refining natural gas according to  claim 7 , wherein the pressure of the natural gas is adjusted to 10 atm or below. 
   
   
       10 . The method of refining natural gas according to  claim 7 , wherein the temperature of the natural gas is adjusted to a value less than a boiling point of ethylene and the pressure of the natural gas is adjusted to 10 atm or below. 
   
   
       11 . A natural gas refining system for refining gas containing methane; any other hydrocarbon selected from the group consisting of ethane, ethylene, propane, propylene, n-butane, isobutane, 1-butene, n-pentane, and isopentane; carbon dioxide; and a hydrogen sulfide, the refining system comprising:
 pressure/temperature adjusting means for adjusting a pressure and temperature of the natural gas so that the methane is in the gas phase, the other hydrocarbon in the liquid phase, and the carbon dioxide and the hydrogen sulfide in the solid phase, respectively;   gas separating means for separating the natural gas, of which the pressure and temperature adjusted by the pressure/temperature adjusting means, into a gas containing the methane and a suspension liquid; and   solid/liquid separating means for separating the suspension liquid separated by the gas separating means into a liquid containing the other hydrocarbon and a solid containing the carbon dioxide and the hydrogen sulfide.   
   
   
       12 . The natural gas refining system according to  claim 11 , wherein the pressure/temperature adjusting means adjusts the temperature of the natural gas to a value less than a boiling point of ethylene and equal to or higher than a melting point of n-pentane. 
   
   
       13 . The natural gas refining system according to  claim 11 , wherein the pressure/temperature adjusting means adjusts the pressure of the natural gas in a range from 1 to 10 atm. 
   
   
       14 . The natural gas refining system according to  claim 11 , wherein the pressure/temperature adjusting means has expanding means for adiabatic-expanding the natural gas. 
   
   
       15 . The natural gas refining system according to  claim 11 , wherein the pressure/temperature adjusting means has mixing means for mixing liquefied natural gas in the natural gas. 
   
   
       16 . The natural gas refining system according to  claim 11 , wherein the solid/liquid separating means is a cyclone. 
   
   
       17 . The natural gas refining system according to  claim 11 , wherein in the range in which the pressure of the natural gas is 1 atm or more and the temperature of the natural gas is a value less than a melting point of the hydrogen sulfide but equal to or higher than a melting point of n-pentane, the pressure/temperature adjusting means adjusts the pressure and temperature of the natural gas so that a concentration of methane in the gas phase is 90% or more. 
   
   
       18 . The natural gas refining system according to  claim 17 , wherein the pressure/temperature adjusting means adjusts the temperature of the natural gas to a value less than a boiling point of ethylene. 
   
   
       19 . The natural gas refining system according to  claim 17 , wherein the pressure/temperature adjusting means adjusts the pressure of the natural gas to 10 atm or below. 
   
   
       20 . The natural gas refining system according to  claim 17 , wherein the pressure/temperature adjusting means adjusts the temperature of the natural gas to a value less than a boiling point of ethylene and also adjusts the pressure of the natural gas to 10 atm or below.