Method Of And A System For Combusting Fuel In An Oxyfuel Combustion Boiler

Abstract

A method of and a system for combusting fuel in an oxyfuel combustion boiler. Fuel is fed to a furnace of the boiler. Oxidant gas that includes a mixture of substantially pure oxygen and recycled flue gas is fed to the furnace, prior to the feeding of the oxidant gas. At least a portion of the oxidant gas is preheated to generate preheated oxidant gas. The fuel is combusted with the oxidant gas in the furnace so as to generate steam and to produce the flue gas, and at least a portion of the steam is superheated to generate superheated steam. The preheating of the at least a portion of the oxidant gas is performed by using a heat exchanger that transfers heat from a portion of the superheated steam to the oxidant gas.

1 . A method of combusting fuel in an oxyfuel combustion boiler, the method comprising the steps of:
 (a) feeding fuel to a furnace of the boiler;   (b) feeding oxidant gas consisting of a mixture of substantially pure oxygen and recycled flue gas to the furnace;   (c) prior to the feeding of the oxidant gas, preheating at least a portion of the oxidant gas to generate preheated oxidant gas;   (d) combusting the fuel with the preheated oxidant gas in the furnace so as to generate steam and to produce the flue gas; and   (e) superheating at least a portion of the steam to produce superheated steam, wherein the preheating of the at least a portion of the oxidant gas is performed by using a heat exchanger that transfers heat from a portion of the superheated steam to the oxidant gas.   
     
     
         2 . The method of  claim 1 , wherein the preheating of the oxidant gas is performed by preheating at least a portion of the recycled flue gas to produce preheated recycled flue gas, prior to mixing the preheated recycled flue gas with substantially pure oxygen, to generate the mixture of substantially pure oxygen and recycled flue gas. 
     
     
         3 . The method of  claim 2 , wherein the step of feeding the preheated oxidant gas to the furnace comprises introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as a secondary oxidant to the furnace. 
     
     
         4 . The method of  claim 2 , wherein the step of feeding the preheated oxidant gas to the furnace comprises introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as an overfire oxidant to the furnace. 
     
     
         5 . The method of  claim 1 , wherein the preheating of the oxidant gas is performed by preheating at least a portion of the mixture of substantially pure oxygen and recycled flue gas. 
     
     
         6 . The method of  claim 5 , wherein the step of feeding the oxidant gas to the furnace comprises introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as a secondary oxidant to the furnace. 
     
     
         7 . The method of  claim 5 , wherein the step of feeding the oxidant gas to the furnace comprises introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as an overfire oxidant to the furnace. 
     
     
         8 . The method of  claim 1 , wherein the oxidant gas is preheated in the heat exchanger to a temperature of at least 300° C. 
     
     
         9 . The method of  claim 1 , wherein the oxidant gas is preheated in the heat exchanger to a temperature of at least 350° C. 
     
     
         10 . A system for combusting fuel in an oxyfuel combustion boiler, the system comprising:
 a feed for feeding fuel to a furnace of the boiler;   a feed for feeding oxidant gas consisting of a mixture of substantially pure oxygen and recycled flue gas to the furnace;   a preheater for preheating at least a portion of the oxidant gas, arranged upstream of the feed for feeding the oxidant gas to the furnace, to generate preheated oxidant gas;   a combustor for combusting the fuel with the oxidant gas in the furnace so as to generate steam and to produce the flue gas; and   a superheater for superheating at least a portion of the steam to generate superheated steam,   wherein the preheater for preheating the at least a portion of the oxidant gas comprises a heat exchanger for preheating the portion of the oxidant gas by transferring heat from a portion of the superheated steam to the oxidant gas.   
     
     
         11 . The system of  claim 10 , wherein the preheater for preheating the oxidant gas comprises a preheater for preheating at least a portion of the recycled flue gas to generate preheated recycled flue gas, prior to mixing the preheated recycled flue gas with substantially pure oxygen, so as to generate the mixture of substantially pure oxygen and recycled flue gas. 
     
     
         12 . The system of  claim 11 , wherein the feed for feeding preheated oxidant gas to the furnace comprises a supply for introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as a secondary oxidant to the furnace. 
     
     
         13 . The system of  claim 11 , wherein the feed for feeding preheated oxidant gas to the furnace comprises a supply for introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as an overfire oxidant to the furnace. 
     
     
         14 . The system of any  claim 10 , wherein the preheater for preheating the oxidant gas comprises a preheater for preheating at least a portion of the mixture of substantially pure oxygen and the recycled flue gas. 
     
     
         15 . The system of  claim 14 , wherein the feed for feeding the preheated oxidant gas to the furnace comprises a supply for introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as a secondary oxidant to the furnace. 
     
     
         16 . The system of  claim 14 , wherein the feed for feeding the preheated oxidant gas to the furnace comprises a supply for introducing a portion of the mixture of substantially pure oxygen and recycled flue gas as an overfire oxidant to the furnace. 
     
     
         17 . The system of  claim 10 , wherein the heat exchanger preheats the oxidant gas to a temperature of at least 300° C. 
     
     
         18 . The system of  claim 10 , wherein the heat exchanger preheats the oxidant gas to a temperature of at least 350° C.