Systems and methods for water gas shift with reduced steam consumption

Abstract

A water gas shift reaction is carried out on a feed gas comprising carbon monoxide to produce carbon dioxide and hydrogen gas. The feed gas is split into multiple input streams flowed into respective reactors coupled in series. Steam is supplied to the input stream fed to the first reactor. The shift reaction is carried out in each reactor, with an overall reduced consumption of steam relative to the amount of gas shifted. The water gas shift reaction may be performed in conjunction with removing acid gas compounds from a process gas such as, for example, syngas or natural gas, by flowing a feed gas into a desulfurization unit to remove a substantial fraction of sulfur compounds from the feed gas and flowing the resulting desulfurized gas into a CO 2 removal unit to remove a substantial fraction of CO 2 from the desulfurized gas.

What is claimed is: 
     
         1 . A method for removing acid gases from a gas stream, the method comprising:
 flowing a feed gas into a desulfurization unit to remove a substantial fraction of a sulfur compound from the feed gas, wherein the desulfurization unit produces a desulfurized feed gas;   flowing the desulfurized feed gas into a CO 2  removal unit to remove a substantial fraction of CO 2  from the desulfurized feed gas; and   before or after desulfurizing the feed gas, subjecting the feed gas to a water-gas shift reaction by:   splitting a flow of feed gas comprising carbon monoxide (CO) into a plurality of feed gas streams comprising at least a first feed gas stream, a second feed gas stream, and a third feed gas stream;   combining the first feed gas stream with a steam stream to produce a first input gas stream;   flowing the first input gas stream into a first shift reactor containing a first shift catalyst;   reacting the CO with the steam in the presence of the first shift catalyst to produce a first product gas stream comprising carbon dioxide (CO 2 ) and hydrogen (H 2 );   combining the first product gas stream with the second feed gas stream to produce a second input gas stream heated by the first product gas stream;   flowing the second input gas stream into a second shift reactor containing a second shift catalyst;   reacting the CO of the second input gas stream with the steam in the presence of the second shift catalyst to produce a second product gas stream comprising CO 2  and H 2 ;   combining the second product gas stream with the third feed gas stream to produce a third input gas stream heated by the second product gas stream;   flowing the third input gas stream into a third shift reactor containing a third shift catalyst; and   reacting the CO of the third input gas stream with the steam in the presence of the third shift catalyst to produce a third product gas stream comprising CO 2  and H 2 .   
     
     
         2 . The method of  claim 1 , comprising a step selected from the group consisting of:
 before combining the first product gas stream with the second feed gas stream, adding water as a spray to the first product gas stream to vaporize the water into steam, wherein the first product gas stream is cooled before being combined with the second feed gas stream;   before combining the second product gas stream with the third feed gas stream, adding water as a spray to the second product gas stream to vaporize the water into steam, wherein the second product gas stream is cooled before being combined with the third feed gas stream; and   both of the foregoing.   
     
     
         3 . The method of  claim 1 , comprising adding water as a spray into the first feed gas stream or the first input gas stream. 
     
     
         4 . The method of  claim 1 , wherein flowing the feed gas into the desulfurization unit is done in a temperature range selected from the group consisting of: about 400° F. or greater; and about 400° F. to about 1200° F. 
     
     
         5 . The method of  claim 1 , wherein flowing the desulfurized gas into the CO 2  removal unit is done in range selected from the group consisting of: about −80° F. to about 30° F.; about 30° F. to about 130° F.; and about 200° F. to about 900° F. 
     
     
         6 . The method of  claim 1 , wherein flowing the feed gas into the desulfurization unit comprises flowing the feed gas into contact with a sorbent. 
     
     
         7 . The method of  claim 6 , wherein sorbent is selected from the group consisting of: a metal oxide, zinc oxide, copper oxide, iron oxide, vanadium oxide, manganese oxide, stannous oxide, nickel oxide, a metal titanate, zinc titanate, a metal ferrite, zinc ferrite, copper ferrite, a sorbent comprising an alumina (Al 2 O 3 ) support, a sorbent comprising a silicon dioxide (SiO 2 ) support, a sorbent comprising a titanium dioxide (TiO 2 ) support, a sorbent comprising a zeolite support, a sorbent having an average particle size in a range from about 35 μm to about 175 μm, and a combination of two or more of the foregoing. 
     
     
         8 . The method of  claim 6 , wherein flowing the feed gas into contact with a sorbent comprises flowing the feed gas into contact with a sorbent stream comprising the sorbent and a carrier gas. 
     
     
         9 . The method of  claim 8 , wherein flowing the feed gas into contact with the sorbent stream is done in an adsorber unit, and further comprising outputting the desulfurized gas and sulfided sorbent from the adsorber unit. 
     
     
         10 . The method of  claim 9 , comprising flowing the sulfided sorbent into a regenerating unit to produce a regenerated sorbent and a sulfur compound, and flowing the regenerated sorbent into the adsorber unit. 
     
     
         11 . The method of  claim 1 , wherein flowing the desulfurized gas into the CO 2  removal unit comprises flowing the desulfurized gas into contact with a CO 2  removing agent. 
     
     
         12 . The method of  claim 11 , wherein flowing the desulfurized gas into contact with the CO 2  removing agent is done in an absorber or adsorber unit, and further comprising outputting from the absorber or adsorber unit a treated gas comprising the substantially reduced fractions of sulfur and CO 2 . 
     
     
         13 . The method of  claim 12 , wherein flowing the desulfurized gas into contact with the CO 2  removing agent produces in the absorber or adsorber unit a CO 2 -rich stream comprising the CO 2  removing agent and CO 2 , and further comprising:
 flowing the CO 2 -rich stream from the absorber or adsorber unit to a regenerator unit;   removing CO 2  from the CO 2 -rich stream in the regenerator unit to produce a CO 2 -lean fluid stream; and   flowing the CO 2 -lean stream into the absorber or adsorber unit.   
     
     
         14 . The method of  claim 1 , wherein the feed gas comprises syngas. 
     
     
         15 . The method of  claim 1 , wherein the first shift catalyst, the second shift catalyst, and the third shift catalyst are sulfur-tolerant. 
     
     
         16 . The method of  claim 1 , wherein the plurality of feed gas streams comprises one or more additional feed gas streams, and further comprising reacting the CO of the one or more additional feed gas streams with steam in one or more additional shift reactors, respectively, downstream from the third shift reactor. 
     
     
         17 . The method of  claim 1 , comprising producing a local steam supply by flowing liquid water into thermal contact with a heated gas stream selected from the group consisting of: the first feed gas stream; the second feed gas stream; the third feed gas stream; the first input gas stream; the second input gas stream; the third input gas stream; and a combination of two or more of the foregoing. 
     
     
         18 . The method of  claim 17 , wherein combining the first feed gas stream with the steam stream comprises flowing steam from the local steam supply into the first feed gas stream. 
     
     
         19 . The method of  claim 1 , comprising heating the first feed gas stream or the first input gas stream by flowing the first feed gas stream or the first input gas stream into thermal contact with a heated gas stream selected from the group consisting of: the first product gas stream; the second product gas stream; the third product gas stream; and a combination of two or more of the foregoing. 
     
     
         20 . The method of  claim 1 , wherein the plurality of feed gas streams comprises a bypass gas stream, and further comprising combining the bypass gas stream with the third product gas stream to produce an output gas stream having a desired H 2 /CO ratio. 
     
     
         21 . The method of  claim 1 , comprising controlling a steam/dry gas ratio in the first input gas stream by a step selected from the group consisting of: controlling a flow rate of the steam stream added to the first feed gas stream; controlling a flow rate of a liquid water stream added to the first feed gas stream; and both of the foregoing. 
     
     
         22 . The method of  claim 1 , comprising controlling a steam/dry gas ratio in at least one of the second input gas stream or the third input gas stream by controlling a flow rate of a liquid water stream added to at least one of the second feed gas stream, the second input gas stream, the third feed gas stream, or the third input gas stream. 
     
     
         23 . A gas processing system, comprising:
 a desulfurization unit configured for removing a substantial fraction of one or more sulfur compounds from a process gas to produce a desulfurized gas;   a CO 2  removal unit positioned downstream from the desulfurization unit, and configured for removing a substantial fraction of CO 2  from the desulfurized gas; and   a water-gas shift unit positioned upstream or downstream from the desulfurization unit, the water-gas shift unit comprising:   a flow splitter configured for splitting a flow of feed gas comprising carbon monoxide (CO) into at least a first feed gas stream, a second feed gas stream, and a third feed gas stream;   a first input gas line configured for conducting a first input gas stream, the first input gas stream comprising a combination of the first feed gas stream and steam;   a first shift reactor comprising a first vessel, a first shift catalyst disposed in the first vessel, a first inlet configured for conducting the first input gas stream into the first vessel, and a first outlet, wherein the first shift reactor is configured for reacting the CO and the steam in the first input gas stream in the presence of the first shift catalyst to produce a first product gas stream comprising carbon dioxide (CO 2 ) and hydrogen (H 2 );   a first product gas line configured for receiving the first product gas stream from the first outlet;   a second input gas line configured for conducting a second input gas stream, the second input gas stream comprising a combination of the second feed gas stream and the first product gas stream;   a second shift reactor comprising a second vessel, a second shift catalyst disposed in the second vessel, a second inlet configured for conducting the second input gas stream into the second vessel, and a second outlet, wherein the second shift reactor is configured for reacting the CO and the steam in the second input gas stream in the presence of the second shift catalyst to produce a second product gas stream comprising CO 2  and H 2 ;   a second product gas line configured for receiving the second product gas stream from the second outlet;   a third input gas line configured for conducting a third input gas stream, the third input gas stream comprising a combination of the third feed gas stream and the second product gas stream; and   a third shift reactor comprising a third vessel, a third shift catalyst disposed in the third vessel, a third inlet configured for conducting the third input gas stream into the third vessel, and a third outlet, wherein the third shift reactor is configured for reacting the CO and the steam in the third input gas stream in the presence of the third shift catalyst to produce a third product gas stream comprising CO 2  and H 2 .   
     
     
         24 . The gas processing system of  claim 23 , comprising a component selected from the group consisting of:
 a sprayer configured for adding water as a spray into the first product gas stream;   a sprayer configured for adding water as a spray into the second product gas stream; and   both of the foregoing.   
     
     
         25 . The gas processing system of  claim 23 , comprising a sprayer configured for adding water as a spray into the first input gas stream.