Oxy-fuel combustion process

Abstract

Production of oxygen-enriched gas streams is disclosed herein. Air streams contact an oxygen-selective mixed conductor particularly a perovskite material whereby oxygen is retained or adsorbed on the perovskite and can be employed in a variety of processes such as in combusting a fuel gas, heat recovery and boiler related operations.

Having thus described the invention, what we claim is:  
     
         1 . A method of combusting a fuel gas in a combustion zone comprising the steps of: 
 (a) feeding into said combustion zone said fuel gas;    (b) feeding into said combustion zone an oxygen-enriched gas from an oxygen retention system;    (c) combusting said fuel gas; and    (d) recovering and recycling the combustion exhaust gas from said combustion zone to said oxygen retention system.    
     
     
         2 . The method as claimed in  claim 1  wherein said oxygen retention system contains a ceramic adsorbent.  
     
     
         3 . The method as claimed in  claim 2  wherein said ceramic adsorbent is an oxygen-selective mixed conductor.  
     
     
         4 . The method as claimed in  claim 3  wherein said oxygen-selective mixed conductor is a perovskite type ceramic having the structural formula A 1−x M x BO 3−δ .  
     
     
         5 . The method as claimed in  claim 4  wherein A is a rare earth ion, M is Sr, Ca, Ba, V or mixtures of these; B is Co, Mn, Cr, Fe or mixtures of these; x varies from greater than 0 to about 1; and δ is the deviation from stoichiometric composition resulting from the substitution of Sr, Ca and Ba for rare earth ions.  
     
     
         6 . The process as claimed in  claim 5  wherein x varies from about 0.1 to about 1.  
     
     
         7 . The process as claimed in  claim 4  wherein A is La, Y or mixtures of these; M is Sr, Ca or mixtures of these; and B is Co, Fe or mixtures of these.  
     
     
         8 . The process as claimed in  claim 4  wherein x is about 0.2 to 1.  
     
     
         9 . The method as claimed in  claim 1  wherein said oxygen-enriched gas is delivered at temperatures greater than 150° C.  
     
     
         10 . The method as claimed in  claim 1  wherein said oxygen-enriched gas is produced at pressures of about 1 to about 20 bar.  
     
     
         11 . The method as claimed in  claim 1  wherein said oxygen retention system produces oxygen-enriched gas through a two-step process of retention and purge.  
     
     
         12 . The method as claimed in  claim 11  wherein oxygen is adsorbed from an oxygen-containing feed gas stream.  
     
     
         13 . The method as claimed in  claim 12  wherein nitrogen is removed from said retention system  
     
     
         14 . The method as claimed in  claim 1  wherein high purity nitrogen is produced as a by-product during the oxygen retention step.  
     
     
         15 . The method as claimed in  claim 1  wherein said oxygen retention system comprises two or more adsorbent beds.  
     
     
         16 . A method for producing oxygen-enriched gas for use in a combustion zone comprising the steps: 
 (a) feeding air to a retention system;    (b) retaining oxygen from said air onto an oxygen-selective mixed conductor;    (c) removing nitrogen from said retention system;    (d) feeding oxygen-enriched gas to said combustion zone;    (e) combusting a fuel gas in the presence of said oxygen-enriched gas; and    (f) feeding the exhaust gas from said combustion zone to said retention system.    
     
     
         17 . The method as claimed in  claim 16  wherein said method is cyclical.  
     
     
         18 . The method as claimed in  claim 16  wherein a portion of said exhaust gas from step (f) is withdrawn.  
     
     
         19 . The method as claimed in  claim 18  wherein CO 2  is recovered from said exhaust gas.  
     
     
         20 . The method as claimed in  claim 16  wherein said oxygen retention system contains a ceramic adsorbent.  
     
     
         21 . The method as claimed in  claim 20  wherein said ceramic adsorbent is an oxygen-selective mixed conductor.  
     
     
         22 . The method as claimed in  claim 21  wherein said oxygen-selective mixed conductor is a perovskite type ceramic having the structural formula A 1−x M x BO 3−δ .  
     
     
         23 . The method as claimed in  claim 22  wherein A is a rare earth ion, M is Sr, Ca, Ba, V or mixtures of these; B is Co, Mn, Cr, Fe or mixtures of these; x varies from greater than 0 to about 1; and δ is the deviation from stoichiometric composition resulting from the substitution of Sr, Ca and Ba for rare earth ions.  
     
     
         24 . The process as claimed in  claim 23  wherein x varies from about 0.1 to about 1.  
     
     
         25 . The process as claimed in  claim 24  wherein A is La, Y or mixtures of these; M is Sr, Ca or mixtures of these; and B is Co, Fe or mixtures of these.  
     
     
         26 . The process as claimed in  claim 25  wherein x is about 0.2 to 1.  
     
     
         27 . The method as claimed in  claim 16  wherein said oxygen-enriched gas is produced at temperatures greater than 300° C.  
     
     
         28 . The method as claimed in  claim 16  wherein said oxygen-enriched gas is produced at pressures of about 1 to about 20 bar.  
     
     
         29 . The method as claimed in  claim 16  wherein said oxygen retention system produces oxygen-enriched gas through a two-step process of retention and purge.  
     
     
         30 . The method as claimed in  claim 29  wherein oxygen is adsorbed from an oxygen-containing feed gas stream.  
     
     
         31 . The method as claimed in  claim 30  wherein nitrogen is purged from said retention system.  
     
     
         32 . The method as claimed in  claim 31  wherein said oxygen retention system comprises two or more adsorbent beds.  
     
     
         33 . A method for combusting a gas stream and recovering heat from said combustion comprising the steps: 
 (a) passing an air gas stream into a retention system containing an oxygen-conducting ceramic;    (b) retaining oxygen from said air gas stream onto said oxygen-conducting ceramic;    (c) passing a combustible gas over said oxygen-conducting ceramic whereby said combustible gas combusts in the presence of the retained oxygen producing carbon dioxide, H 2 O and heat; and    (d) recovering said carbon dioxide, H 2 O and heat in the form of super-heated steam.    
     
     
         34 . The method as claimed in  claim 33  wherein said retention system is a circulating fluidized bed reactor.  
     
     
         35 . The method as claimed in  claim 33  wherein a fuel stream is passed over said oxygen-conductive ceramic in step (c).  
     
     
         36 . The method as claimed in  claim 33  wherein said fuel stream comprises CH 4 , H 2 , CO, C 2 H 4 , C 2 H 6  and mixtures thereof.  
     
     
         37 . The method as claimed in  claim 33  wherein said ceramic adsorbent is an oxygen-selective mixed conductor.  
     
     
         38 . The method as claimed in  claim 34  wherein said oxygen-selective mixed conductor is a perovskite type ceramic having the structural formula A 1−x M x BO 3−δ .  
     
     
         39 . The method as claimed in  claim 38  wherein A is a rare earth ion, M is Sr, Ca, Ba, V or mixtures of these; B is Co, Mn, Cr, Fe or mixtures of these; x varies from greater than 0 to about 1; and δ is the deviation from stoichiometric composition resulting from the substitution of Sr, Ca and Ba for rare earth ions.  
     
     
         40 . The process as claimed in  claim 39  wherein x varies from about 0.1 to about 1.  
     
     
         41 . The process as claimed in  claim 40  wherein A is La, Y or mixtures of these; M is Sr, Ca or mixtures of these; and B is Co, Fe or mixtures of these.  
     
     
         42 . The process as claimed in  claim 40  wherein x is about 0.2 to 1.  
     
     
         43 . A method of operating a boiler to generate heat comprising the steps: 
 (a) passing air over an oxygen-conducting perovskite in a reactor system and retaining oxygen on said oxygen-conducting perovskite;    (b) passing the effluent gas from said boiler to said oxygen-conducting perovskite; and    (c) feeding a gas stream containing oxygen to said boiler with a fuel gas wherein said gas stream combusts in said boiler to fuel said boiler.    
     
     
         44 . The process as claimed in  claim 43  wherein said process is cyclic.  
     
     
         45 . The method as claimed in  claim 43  wherein said ceramic adsorbent is an oxygen-selective mixed conductor.  
     
     
         46 . The method as claimed in  claim 44  wherein said oxygen-selective mixed conductor is a perovskite type ceramic having the structural formula A 1−x M x BO 3−δ .  
     
     
         47 . The method as claimed in  claim 46  wherein A is a rare earth ion, M is Sr, Ca, Ba, V or mixtures of these; B is Co, Mn, Cr, Fe or mixtures of these; x varies from greater than 0 to about 1; and δ is the deviation from stoichiometric composition resulting from the substitution of Sr, Ca and Ba for rare earth ions.  
     
     
         48 . The process as claimed in  claim 47  wherein x varies from about 0.1 to about 1.  
     
     
         49 . The process as claimed in  claim 48  wherein A is La, Y or mixtures of these; M is Sr, Ca or mixtures of these; and B is Co, Fe or mixtures of these.  
     
     
         50 . The process as claimed in  claim 48  wherein x is about 0.2 to 1.51. A method of converting a feed gas to a product gas in a cyclical process comprising the steps: 
 (a) introducing said feed gas containing an oxidant into a first reactor, wherein said first reactor contains a catalyst contained between inert materials having heat transfer properties disposed at each end of said first reactor, and said first reactor having an opening at both ends wherein at least one heat exchanger with channels is connected to said openings of said first reactor; wherein said first feed gas is preheated by heat transfer with said product gas in said heat exchanger prior to introducing said first feed gas into said first reactor;  
 (b) withdrawing a first product gas from said first reactor;  
 (c) introducing a second flow of said feed gas into a second reactor, wherein said second reactor contains a catalyst contained between inert materials disposed at each end of said second reactor and said second reactor having an opening at both ends wherein at least one heat exchanger with channels is connected to said openings of said second reactor; wherein said second feed gas is preheated by heat transfer with said product gas in said heat exchanger prior to introducing said second feed gas into said second reactor;  
 (d) withdrawing a second product gas from said second reactor;  
 (e) diverting said first feed gas flow into said second reactor thereby forming said first product gas and diverting said second feed gas flow into said first reactor thereby forming said second product gas.  
 
     
     
         52 . The method as claimed in claim  51  wherein said feed gas is a reducing gas.  
     
     
         53 . The method as claimed in clam  52  wherein said reducing gas is natural gas.  
     
     
         54 . The method as claimed in claim  51  wherein said first product gas and said second product gas are the same gas.  
     
     
         55 . The method as claimed in claim  51  wherein said product gas is a mixture of carbon monoxide and hydrogen.  
     
     
         56 . The method as claimed in claim  51  wherein said catalyst is a perovskite type mixed conductor.