Process and apparatus for steam-methane reforming

Abstract

Methane is reacted with steam, to generate carbon monoxide and hydrogen in a first catalytic reactor ( 14 ); the resulting gas mixture can then be used to perform Fisher-Tropsch synthesis in a second catalytic reactor ( 26 ). In performing the steam/methane reforming, the gas mixture is passed through a narrow channel in which the mean temperature and exit temperature are both in the range 750° C. to 900° C., the residence time being less than 0.5 second, and the channel containing a catalyst, so that only those reactions that have comparatively rapid kinetics will occur. The heat is provided by combustion of methane in adjacent channels ( 17 ). The ratio of steam to methane should preferably be 1.4 to 1.6, for example about 1.5. Almost all the methane will undergo the reforming reaction, almost entirely forming carbon monoxide. After performing Fischer-Tropsch synthesis, the remaining hydrogen is preferably fed back ( 34 ) to the combustion channels ( 17 ). The steam for the reforming step is preferably generated from water generated by the chemical reactions, by condensing ( 30, 32 ) the products from the Fischer-Tropsch synthesis and by condensing ( 19 ) water vapour generated in the combustion.

1 . A process for performing steam/methane reforming to generate carbon monoxide and hydrogen, wherein the gas mixture is caused to flow through a narrow flow channel between metal sheets separating the flow channel from a source of heat, the flow channel containing a fluid-permeable catalyst structure, the residence time in the channel being less than 0.5 second, and both the average temperature along the channel and the exit temperature of the channel being in the range 750° C. to 900° C., wherein the steam is supplied at least in part by condensing water vapour from combustion of a combustible gas.  
     
     
         2 . A process as claimed in  claim 1  wherein the combustible gas from which at least part of the steam is derived comprises methane.  
     
     
         3 . A process as claimed in  claim 1  wherein the reforming reaction is carried out at atmospheric pressure.  
     
     
         4 . A process as claimed in  claim 1  wherein the ratio of steam to methane is in the range 1.3 to 1.6.  
     
     
         5 . A process as claimed in  claim 1  performed using a catalytic reactor defining adjacent channels for the steam/methane reforming reaction and for an exothermic reaction, arranged alternately, the exothermic reaction being the combustion of the combustible gas from which at least a part of the steam is derived.  
     
     
         6 . A process as claimed in  claim 1  wherein the combustible gases comprise both methane and hydrogen.  
     
     
         7 . A process as claimed in  claim 6  wherein at least some of the hydrogen is that generated by the steam/methane reforming process.  
     
     
         8 . A process as claimed in  claim 7  wherein the hydrogen that undergoes combustion is hydrogen that remains after subjecting the carbon monoxide and hydrogen from the steam/methane reforming process to a subsequent Fischer-Tropsch synthesis.  
     
     
         9 . A process as claimed in  claim 1  wherein the steam is supplied in part by condensing water vapour emerging from the steam/reforming process.  
     
     
         10 . A process as claimed in  claim 1  wherein the steam is supplied in part by water generated by subjecting the carbon monoxide and hydrogen from the steam/methane reforming process to a subsequent Fischer-Tropsch synthesis.  
     
     
         11 . A process as claimed in  claim 10  wherein the stream supplied from the Fischer-Tropsch synthesis to the steam/methane reforming includes not only steam but vapour of water-soluble organic compounds generated in the said synthesis.  
     
     
         12 . Plant for processing methane by a process as claimed in  claim 1 .  
     
     
         13 . A process for converting methane to higher molecular weight hydrocarbons comprising the steps of: 
 (a) mixing a feed gas comprising methane with steam to form a gas mixture;    (b) subjecting the gas mixture to reforming to generate carbon monoxide and hydrogen by causing the gas mixture to flow through a narrow channel between metal sheets separating the flow channel from a source of heat, the flow channel containing a fluid-permeable catalyst structure, the residence time in the channel being less than 0.5 second, and both the average temperature along the channel and the exit temperature of the channel being in the range 750° C. to 900° C.;    (c) subjecting the carbon monoxide and hydrogen from the reforming step to a subsequent Fischer-Tropsch synthesis;    (d) separating water and higher molecular weight hydrocarbons from the gases emerging from the Fischer-Tropsch synthesis, so as to leave a gas stream including hydrogen;    (e) providing the source of heat for the reforming step by combustion of a gas stream containing hydrogen; and    (f) condensing water vapour produced by the combustion so as to provide water, and using this water to supply at least some of the steam for the reforming step.