Hydromethanation of a carbonaceous feedstock

Abstract

The present invention relates to processes for hydromethanating a carbonaceous feedstock to a methane product stream and electrical power, in which heat energy from the hot methane-enriched synthesis gas is used to generate a dry saturated steam stream, the dry saturated steam stream is converted into a superheated steam stream via pressure drop for feeding into the hydromethanation reactor to satisfy the steam demand of the hydromethanation reaction, and heat generated from a downstream gas methanation processing is recovered to produce a superheated process steam stream which is used to generate the electric power.

1 . A process for generating a cooled methane product stream and electrical power from a non-gaseous carbonaceous material, the process comprising the steps of:
 (a) preparing a carbonaceous feedstock from the non-gaseous carbonaceous material;   (b) introducing the carbonaceous feedstock, a hydromethanation catalyst, a steam stream and an amount of oxygen into a hydromethanation reactor, wherein the hydromethanation reactor is operating at a first pressure condition;   (c) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor with oxygen to generate carbon monoxide, hydrogen and heat energy;   (d) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor in the presence of carbon monoxide, hydrogen, steam and hydromethanation catalyst to produce a methane-enriched raw product gas;   (e) withdrawing a methane-enriched raw product gas stream of the methane-enriched raw product gas from the hydromethanation reactor, wherein the methane-enriched raw product gas stream comprises methane, carbon monoxide, hydrogen, carbon dioxide, hydrogen sulfide, steam and heat energy;   (f) introducing the methane-enriched raw product stream into a first heat exchanger unit to recover heat energy and generate a cooled methane-enriched raw product stream and a dry saturated steam stream, wherein the dry saturated steam stream is at a second pressure condition that is higher than the first pressure condition;   (g) providing at least a portion of the dry saturated steam stream to the hydromethanation reactor under a reduced pressure condition such that the portion of dry saturated steam stream provided to the hydromethanation reactor is converted to a first superheated steam stream at or prior to introduction into the hydromethanation reactor, wherein the reduced pressure condition is higher than the first pressure condition but lower than the second pressure condition;   (h) steam shifting a portion of the carbon monoxide in the cooled methane-enriched raw product stream to generate a hydrogen-enriched raw product stream;   (i) removing a substantial portion of the carbon dioxide and a substantial portion of the hydrogen sulfide from the hydrogen-enriched raw product stream to produce a sweetened gas stream, wherein the sweetened gas stream comprises a substantial portion of the hydrogen, carbon monoxide and methane from the hydrogen-enriched raw product stream;   (j) methanating a substantial portion of the carbon monoxide in the sweetened gas stream with hydrogen in the sweetened gas stream to generate a methane-enriched treated product stream and heat energy;   (k) recovering a portion of the heat energy from step (j) to generate the cooled methane product stream;   (l) generating a second superheated steam stream from at least a portion of the heat energy recovered in step (k); and   (m) generating electrical power from at least a portion of the second superheated steam stream generated in step (l),   wherein
 (1) the reaction of step (d) has a steam demand and a heat demand, 
 (2) the steam demand is substantially satisfied by the steam stream, 
 (3) the steam stream substantially comprises steam from the dry saturated steam stream, and 
 (4) the amount of oxygen introduced into the hydromethanation reactor is sufficient so that the heat demand of the reaction of step (d) is substantially satisfied by the reaction of step (c). 
   
     
     
         2 . The process of  claim 1 , wherein the steam demand is at least satisfied by the steam stream. 
     
     
         3 . The process of  claim 1 , wherein the steam stream comprises only steam from the dry saturated steam stream. 
     
     
         4 . The process of  claim 2 , wherein the steam stream comprises only steam from the dry saturated steam stream. 
     
     
         5 . The process of  claim 1 , wherein the second pressure condition is at least about 25 psi (about 172 kPa) greater than the first pressure condition. 
     
     
         6 . The process of  claim 5 , wherein the second pressure condition is at least about 50 psi (about 345 kPa) greater than the first pressure condition. 
     
     
         7 . The process of  claim 6 , wherein the second pressure condition is at least about 100 psi (about 690 kPa) greater than the first pressure condition. 
     
     
         8 . The process of  claim 7 , wherein the second pressure condition is about 200 psi (about 1379 kPa) or less greater than the first pressure condition. 
     
     
         9 . The process of  claim 1 , wherein the second pressure condition is at least about 5% greater than the first pressure condition. 
     
     
         10 . The process of  claim 9 , wherein the second pressure condition is at least about 10% greater than the first pressure condition. 
     
     
         11 . The process of  claim 10 , wherein the second pressure condition is about 20% or less greater than the first pressure condition. 
     
     
         12 . The process of  claim 1 , wherein the first pressure condition is about 400 psig (about 2860 kPa) or greater. 
     
     
         13 . The process of  claim 12 , wherein the first pressure condition is about 450 psig (about 3204 kPa) or greater. 
     
     
         14 . The process of  claim 1 , wherein the first pressure condition is about 1000 psig or less (about 6996 kPa). 
     
     
         15 . The process of  claim 14 , wherein the first pressure condition is about 900 psig (about 6307 kPa) or less. 
     
     
         16 . The process of  claim 15 , wherein the first pressure condition is about 600 psig (about 4238 kPa) or less. 
     
     
         17 . The process of  claim 12 , wherein the first pressure condition is about 1000 psig or less (about 6996 kPa). 
     
     
         18 . The process of  claim 17  wherein the second pressure condition is at least about 25 psi (about 172 kPa) greater than the first pressure condition. 
     
     
         19 . The process of  claim 17 , wherein the second pressure condition is at least about 5% greater than the first pressure condition.