Fuel compositions comprising natural gas and synthetic hydrocarbons and methods for preparation of same

Abstract

The invention is directed to compositions comprising mixtures of natural gas and synthetic light hydrocarbons, such as C 2 to C 5 paraffins, olefins and mixtures thereof, obtained via a hydrocarbon synthesis reactions, which are suitable for use as fuel compositions, and particularly to blends of such synthetic light hydrocarbons and a natural gas derived from LNG produced in an LNG process. Alternatively, such blends may also be obtained by liquefaction of the synthetic light hydrocarbons with natural gas in an LNG process. The synthetic light hydrocarbons are added, for example, to a lean natural gas to improve the heat value thereof. In embodiments, the synthetic light hydrocarbons are conveniently derived, at least in part, from low value CO 2 contaminant that may be present in a raw natural gas stream used to prepare LNG. Also disclosed are methods to prepare the mixtures.

1 . A composition comprising a virgin natural gas component and a synthetic hydrocarbon component comprised of light hydrocarbons.  
     
     
         2 . The composition of  claim 1  wherein the virgin natural gas component is a lean natural gas.  
     
     
         3 . The composition of  claim 2  wherein the lean natural gas employed comprises less than about 3 mol % of C 2  to C 5  virgin light hydrocarbons, with the balance of the lean natural gas being essentially methane, based on the composition of the lean natural gas.  
     
     
         4 . The composition of  claim 1  wherein the synthetic hydrocarbon component is present in an amount of less than 25 mol % based on the total composition.  
     
     
         5 . The composition of  claim 1  wherein the natural gas component is derived from a regasified LNG product produced in an LNG process.  
     
     
         6 . The composition of  claim 1  having a heating value of from about 1000 BTU/scf to about 1200 BTU/scf.  
     
     
         7 . The composition of  claim 1  wherein the synthetic hydrocarbon component comprises C 2  to C 5  hydrocarbons selected from paraffins, olefins, and mixtures thereof.  
     
     
         8 . The composition of  claim 7  wherein the synthetic hydrocarbon component is derived from a Fischer-Tropsch process.  
     
     
         9 . The composition of  claim 7  wherein the synthetic hydrocarbon component is derived from an MTO process.  
     
     
         10 . A method for preparing a fuel blend comprising mixing a virgin natural gas component and a synthetic hydrocarbon component comprised of light synthetic hydrocarbons.  
     
     
         11 . The method of  claim 10  wherein the virgin natural gas component is derived from a regasified LNG product prepared in a LNG process.  
     
     
         12 . The method of  claim 11  further comprising: 
 pre-treating a natural gas stream comprising acid gases, water and other contaminants therein to remove at least a portion of the contaminants therefrom and provide a natural gas feed;    cooling the natural gas feed in the LNG process to liquefy at least a portion of the natural gas component and thereby produce a LNG product; and    re-gasifying the LNG product to obtain the natural gas component.    
     
     
         13 . The method of  claim 12  further comprising: 
 providing the synthetic hydrocarbon component; and    mixing the synthetic hydrocarbon component with the virgin natural gas component to obtain the fuel blend.    
     
     
         14 . The method of  claim 13  wherein mixing of the virgin natural gas component and the synthetic hydrocarbon component occurs at a site remote from the location where the virgin natural gas component originates.  
     
     
         15 . The method of  claim 11  wherein the synthetic hydrocarbon component is blended in an amount such that the concentration of the synthetic hydrocarbon component in the fuel blend is less than 25 mol % based on the total fuel blend.  
     
     
         16 . The method of  claim 11  wherein the fuel blend has a heating value of from about 1000 BTU/scf to about 1200 BTU/scf.  
     
     
         17 . The method of  claim 10  further comprising: 
 pre-treating a natural gas stream comprising acid gases, water and other contaminants therein to remove at least a portion of the contaminants therefrom and provide a natural gas feed for a LNG process;    mixing the synthetic hydrocarbon component into the natural gas feed within a LNG process at a temperature and in an amount such that the synthetic hydrocarbon does not solidify and form a separate solid phase during liquefaction of the natural gas feed in the LNG process; and    cooling the resulting natural gas and synthetic hydrocarbon mixture within the LNG process to a temperature of from about −240° F. (−151° C.) to about −260° F. (−162° C.) or less so as to liquefy at least a portion of the mixture and thereby produce a blended liquid product at substantially atmospheric pressure; and    re-gasifying the blended liquid product to produce the fuel blend.    
     
     
         18 . The method of  claim 17  wherein the fuel blend comprises the synthetic hydrocarbon component in an amount of 25 mole % or less based on the total fuel blend.  
     
     
         19 . A method for preparing a fuel blend comprising virgin natural gas and synthetic hydrocarbons, the method comprising: 
 pre-treating a natural gas stream comprising acid gases, water and other contaminants therein to remove at least a portion of the contaminants therefrom and provide a natural gas feed;    cooling the natural gas feed in a LNG process to liquefy at least a portion of the natural gas feed and thereby produce a LNG product;    providing a synthetic hydrocarbon component;    re-gasifying the LNG product to obtain a virgin natural gas component; and    mixing the synthetic hydrocarbon component with the virgin natural gas component to obtain the fuel blend.