Conversion of carbonaceous materials to synthetic natural gas by pyrolysis, reforming, and methanation

Abstract

The production of synthetic natural gas from a carbonaceous material, preferably a biomass material, such as wood. The carbonaceous material is first pyrolyzed, then subjected to steam reforming to produce a syngas, which is then passed to several clean-up steps then to a methanation zone to produce synthetic natural gas.

1 . A process for converting carbonaceous material to synthetic natural gas, which process comprising:
 a) feeding said carbonaceous material and an effective amount of superheated steam through a plurality of vertically oriented tubes in a pyrolysis furnace, which tubes are at a temperature of about 400° C. to about 650° C. for an effective amount of time to produce a reaction product stream;   b) quenching the reaction product stream thereby resulting in a gaseous fraction, a liquid fraction and a solids fraction;   c) collecting at least a portion of the solids fraction;   d) passing the gaseous and liquid fractions of the reaction product stream to a separation zone wherein the gaseous fraction is separated from the liquid fraction;   e) collecting the gaseous fraction for further use;   f) passing at least a portion of the liquid fraction and an effective amount of superheated steam to a reforming zone operated at a temperature of about 850° C. to about 1000° C. and a pressure form about 3 psig to about 500 psig wherein said liquid fraction is reformed to produce a synthetic gaseous product comprised of hydrogen, carbon monoxide, carbon dioxide, and methane, which synthetic gaseous product stream is at an elevated temperature;   g) passing said synthetic gaseous product stream at an elevated temperature to a heat recovery zone wherein its temperature is substantially lowered;   h) passing said lowered temperature synthetic gaseous product stream to a solids recovery zone wherein substantially all remaining solids are removed;   i) passing said synthetic gaseous product stream having a reduced amount of solids to an organics removal zone wherein substantially any remaining organic material is removed by contact with an organic liquid in which the organic material is at least partially soluble;   j) passing said synthetic gaseous product stream from said organics removal zone to an acid gas removal zone wherein substantially all acid gases are removed;   k) passing said synthetic gaseous product stream from said acid gas removal zone to a methanation process unit containing at least one methanation catalyst and operated at methanation process conditions thereby resulting in a product stream comprised predominantly of methane.   
     
     
         2 . The process of  claim 1  wherein the carbonaceous material is a source of fossil fuels selected from the group consisting of coal, peat, lignite, tar sands, and bitumen from oil shale. 
     
     
         3 . The process of  claim 1  wherein the carbonaceous material is a biomass material. 
     
     
         4 . The process of  claim 3  wherein the biomass material is a cellulosic material. 
     
     
         5 . The process of  claim 4  wherein the cellulosic material is selected from the group consisting of wood, bagasse, rice hulls, rice straw, kennaf, old railroad ties, dried distiller grains, corn stalks and cobs and straw. 
     
     
         6 . The process of  claim 5  wherein the cellulosic material is selected from wood and dried distiller grains. 
     
     
         7 . The process of  claim 1  wherein the carbonaceous material is dried to a moisture content of less than or equal to about 15% by weight before pyrolysis. 
     
     
         8 . The process of  claim 1  wherein the carbonaceous material is with the size range of about 1/16 inch to about ½ inch. 
     
     
         9 . The process of  claim 1  wherein the gaseous product collected from the separation zone is a fuel gas a portion of which is used to fuel the pyrolysis unit, the reforming zone, or both. 
     
     
         10 . The process of  claim 1  wherein the heat recovery zone uses water to recover heat and wherein at least a portion of the heated water is used as preheated steam to the pyrolysis unit, the reforming zone, or both. 
     
     
         11 . The process of  claim 1  wherein the scrubbing agent used in the acid gas removal zone is selected from the group consisting of alcohols and amines. 
     
     
         12 . The process of  claim 11  wherein the scrubbing agent is an alcohol. 
     
     
         13 . The process of  claim 12  wherein the alcohol is methanol. 
     
     
         14 . The process of  claim 11  wherein the amine is selected from the group consisting of diethanol amine and mono-ethanol amine. 
     
     
         15 . The process of  claim 14  wherein the amine is diethanol amine. 
     
     
         16 . The process of  claim 1  wherein the methanation zone contains three reactors in series and wherein heat is removed from the stream passing from the first reactor and the second reactor. 
     
     
         17 . The process of  claim 1  wherein at least a portion of the methane produced in the methanation unit is introduced into a natural gas pipeline. 
     
     
         18 . The process of  claim 17  wherein methane is removed from a pipeline and converted to a syngas. 
     
     
         19 . The process of  claim 1  wherein prior to organic removal step (j) the synthetic gaseous product stream is subjected to a water wash wherein is flowed countercurrent to a stream of water to remove any remaining solids material.