Increasing boiler output with oxygen

Abstract

A fuel-fired steam generation apparatus such as a boiler can produce steam at a rate higher than the maximum rate at which it can produce steam using air as the only source of oxygen for combustion, by combusting the fuel with oxidant having a higher oxygen content than air but feeding the oxidant at a volumetric flow rate lower than the rate at which maximum steam production is obtained with air as the only source of oxygen for combustion.

1 . A method of modifying a steam generation apparatus, comprising
 (A) providing a steam generation apparatus comprising   (1) a combustion chamber into which gaseous oxidant and fuel are fed, and in which said fuel and said gaseous oxidant are combusted thereby producing heat and hot flue gas,   (2) a preheater into which and through which said hot flue gas passes for transferring heat to said gaseous oxidant before said gaseous oxidant is fed to said combustion chamber, and   (3) a pathway into which water is fed, from which heated steam is obtained at an outlet, and within which the water is evaporated and converted to said heated steam by heat transferred thereto in one or more heat exchangers in said pathway and within said steam generation apparatus to which heat of said combustion is radiated and in one or more convective heat exchangers in said pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred by convective heat exchange,   the pathway further comprising one or more devices that can pass coolant into steam in the pathway to reduce the temperature of said steam,   wherein the highest mass flow rate at which said apparatus can provide steam at said outlet at a temperature within a given temperature range, when said gaseous oxidant is air and said air is the only source of oxygen for said combustion, is limited by the maximum flue gas temperature to which said heat exchangers can be exposed, by maximum rates at which said fuel can be fed into said combustion chamber and at which said flue gas can be withdrawn therefrom, and by the maximum rate at which said coolant can be passed into said steam, and   (B) increasing the rate at which steam is provided at said outlet at a temperature within said given temperature range to a mass flow rate higher than said highest mass flow rate, by   (1) increasing the mass flow rate into said pathway of water by an amount equal to the desired increased flow rate of steam and increasing the mass flow rate of fuel into said combustion chamber by an amount corresponding to the increased amount of heat needed to produce said steam at said increased rate, while   (2) increasing the oxygen content of said gaseous oxidant with which said fuel is combusted but decreasing the volumetric flow rate at which said gaseous oxidant having increased oxygen content with which said fuel is combusted is fed into said combustion chamber to values effective to provide said increased mass flow rate of steam without exceeding any of said maxima, and   (3) combusting said fuel in said combustion chamber with said gaseous oxidant having said increased oxygen content fed at said decreased volumetric flow rate,   without decreasing or increasing the heat transfer area of any of said heat exchangers,   wherein flue gas produced in said combustion chamber that exits from said apparatus is not fed back into said apparatus, and the temperature of said flue gas entering said preheater is lower than when said flue gas is produced by combustion in said apparatus when air is the only source of oxygen for combustion.   
   
   
       2 . A method according to  claim 1  wherein said gaseous oxidant fed into said combustion chamber in step (A)(1) is air. 
   
   
       3 . A method according to  claim 1  wherein said fuel is coal. 
   
   
       4 . A method according to  claim 1  wherein steam is provided at said outlet at a temperature within said given temperature range at said increased oxygen content and decreased volumetric flow rate of said oxidant without passing any coolant into said steam. 
   
   
       5 . A method according to  claim 1  wherein said gaseous oxidant and fuel are combusted in said combustion chamber at a plurality of burners, and at least one of said burners is at a higher elevation than at least one other burner, the method further comprising
 feeding more than half of the total amount of fuel that is fed to all of said plurality of burners to a group of burners which contains at least half but fewer than all of said burners, in which group all burners are at a lower elevation than all burners not in said group.   
   
   
       6 . A method according to  claim 1  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, and all oxidant necessary for complete combustion of said fuel is fed through said burners. 
   
   
       7 . A method according to  claim 1  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, wherein a portion of the oxidant necessary for complete combustion of said fuel is fed through said burners and the balance of the oxidant necessary for complete combustion of said fuel is fed into said combustion chamber through one or more overfire ports separate from and vertically above said one or more burners, provided that the oxygen content of the oxidant fed through said one or more overfire ports is less than the oxygen content of the oxidant fed through said one or more burners. 
   
   
       8 . A method of operating a steam generation apparatus, comprising
 (A) providing a steam generation apparatus comprising   (1) a combustion chamber into which gaseous oxidant and fuel are fed, and in which said fuel and said gaseous oxidant are combusted thereby producing heat and hot flue gas,   (2) a preheater into which and through which said hot flue gas passes for transferring heat to said gaseous oxidant before said gaseous oxidant is fed to said combustion chamber, and   (3) a pathway into which water is fed, from which heated steam is obtained at an outlet, and within which the water is evaporated and converted to said heated steam by heat transferred thereto in one or more heat exchangers in said pathway and within said steam generation apparatus to which heat of said combustion is radiated and in one or more convective heat exchangers in said pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred by convective heat exchange,   the pathway further comprising one or more devices that can pass coolant into steam in the pathway to reduce the temperature of said steam,   wherein the highest mass flow rate at which said apparatus can provide steam at said outlet at a temperature within a given temperature range, when said gaseous oxidant is air and said air is the only source of oxygen for said combustion, is limited by the maximum flue gas temperature to which said heat exchangers can be exposed, by maximum rates at which said fuel and gaseous oxidant can be fed into said combustion chamber and at which said flue gas can be withdrawn therefrom, and by the maximum rate at which said coolant can be passed into said steam, and   (B) providing steam at said outlet at a temperature within said given temperature range at a desired mass flow rate which is higher than said highest mass flow rate, by   (1) feeding water into said pathway at a mass flow rate equal to the desired mass flow rate of steam and feeding fuel into said combustion chamber at a mass flow rate corresponding to the amount of heat needed to produce said steam at said desired mass flow rate, while   (2) feeding into said combustion chamber gaseous oxidant with which said fuel is combusted having a higher oxygen content than air, at a volumetric flow rate lower than the volumetric flow rate of air at which said highest mass flow rate of steam is provided when air is the only source of oxygen for said combustion, at values of said oxygen content and said volumetric flow rate which are effective to provide said desired mass flow rate of steam without exceeding any of said maxima, and   (3) combusting said fuel in said combustion chamber with said air and said gaseous oxidant having said increased oxygen content fed at said lower volumetric flow rate,   wherein the heat transfer area of said heat exchangers is the same as when air is the only source of oxygen for said combustion, and wherein flue gas produced in said combustion chamber that exits from said apparatus is not fed back into said apparatus, and the temperature of said flue gas entering said preheater is lower than when said flue gas is produced by combustion in said apparatus when air is the only source of oxygen for combustion.   
   
   
       9 . A method according to  claim 8  wherein said fuel is coal. 
   
   
       10 . A method according to  claim 8  wherein steam is provided at said outlet at a temperature within said given temperature range at said increased oxygen content and decreased volumetric flow rate of said oxidant without passing any coolant into said steam. 
   
   
       11 . A method according to  claim 8  wherein said gaseous oxidant and fuel are combusted in said combustion chamber at a plurality of burners, and at least one of said burners is at a higher elevation than at least one other burner, the method further comprising
 feeding more than half of the total amount of fuel that is fed to all of said plurality of burners to a group of burners which contains at least half but fewer than all of said burners, in which group all burners are at a lower elevation than all burners not in said group.   
   
   
       12 . A method according to  claim 8  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, and all oxidant necessary for complete combustion of said fuel is fed through said burners. 
   
   
       13 . A method according to  claim 8  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, wherein a portion of the oxidant necessary for complete combustion of said fuel is fed through said burners and the balance of the oxidant necessary for complete combustion of said fuel is fed into said combustion chamber through one or more overfire ports separate from and vertically above said one or more burners, provided that the oxygen content of the oxidant fed through said one or more overfire ports is less than the oxygen content of the oxidant fed through said one or more burners. 
   
   
       14 . A method of modifying a steam generation apparatus, comprising
 (A) providing a steam generation apparatus comprising   (1) a combustion chamber into which gaseous oxidant and fuel are fed, and in which said fuel and said gaseous oxidant are combusted thereby producing heat and hot flue gas,   (2) a preheater into which and through which said hot flue gas passes for transferring heat to said gaseous oxidant before said gaseous oxidant is fed to said combustion chamber,   (3) a pathway into which water is fed, from which heated steam is obtained at an outlet, and within which the water is evaporated and converted to said heated steam by heat transferred thereto in one or more heat exchangers in said pathway and within said steam generation apparatus to which heat of said combustion is radiated and in one or more convective heat exchangers in said pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred by convective heat exchange,   the pathway further comprising one or more devices that can pass coolant into steam in the pathway to reduce the temperature of said steam, and   (4) a second pathway into which steam is fed, from which said steam is obtained at an outlet, and within which said steam is heated by heat transferred thereto in one or more additional heat exchangers in said second pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred, the second pathway further comprising one or more devices that can pass coolant into steam in said second pathway to reduce the temperature of said steam therein,   wherein the highest mass flow rate at which said apparatus can provide steam at said outlet at a temperature within a given temperature range, when said gaseous oxidant is air and said air is the only source of oxygen for said combustion, is limited by the maximum flue gas temperature to which said heat exchangers can be exposed, by maximum rates at which said fuel can be fed into said combustion chamber and at which said flue gas can be withdrawn therefrom, and by the maximum rate at which said coolant can be passed into said steam, and   (B) increasing the rate at which steam is provided at said outlet at a temperature within said given temperature range to a mass flow rate higher than said highest mass flow rate, by   (1) increasing the mass flow rate into said pathway of water by an amount equal to the desired increased flow rate of steam and increasing the mass flow rate of fuel into said combustion chamber by an amount corresponding to the increased amount of heat needed to produce said steam at said increased rate, while   (2) increasing the oxygen content of said gaseous oxidant with which said fuel is combusted but decreasing the volumetric flow rate at which said gaseous oxidant having increased oxygen content with which said fuel is combusted is fed into said combustion chamber to values effective to provide said increased mass flow rate of steam without exceeding any of said maxima, and   (3) combusting said fuel in said combustion chamber with said gaseous oxidant having said increased oxygen content fed at said decreased volumetric flow rate,   without decreasing or increasing the heat transfer area of any of said heat exchangers,   wherein flue gas produced in said combustion chamber that exits from said apparatus is not fed back into said apparatus, and the temperature of said flue gas entering said preheater is lower than when said flue gas is produced by combustion in said apparatus when air is the only source of oxygen for combustion.   
   
   
       15 . A method according to  claim 14  wherein said gaseous oxidant fed into said combustion chamber in step (A)(1) is air. 
   
   
       16 . A method according to  claim 14  wherein said fuel is coal. 
   
   
       17 . A method according to  claim 14  wherein steam is provided at said outlet at a temperature within said given temperature range at said increased oxygen content and decreased volumetric flow rate of said oxidant without passing any coolant into said steam. 
   
   
       18 . A method according to  claim 14  wherein said gaseous oxidant and fuel are combusted in said combustion chamber at a plurality of burners, and at least one of said burners is at a higher elevation than at least one other burner, the method further comprising
 feeding more than half of the total amount of fuel that is fed to all of said plurality of burners to a group of burners which contains at least half but fewer than all of said burners, in which group all burners are at a lower elevation than all burners not in said group.   
   
   
       19 . A method according to  claim 14  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, and all oxidant necessary for complete combustion of said fuel is fed through said burners. 
   
   
       20 . A method according to  claim 14  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, wherein a portion of the oxidant necessary for complete combustion of said fuel is fed through said burners and the balance of the oxidant necessary for complete combustion of said fuel is fed into said combustion chamber through one or more overfire ports separate from and vertically above said one or more burners, provided that the oxygen content of the oxidant fed through said one or more overfire ports is less than the oxygen content of the oxidant fed through said one or more burners. 
   
   
       21 . A method of operating a steam generation apparatus, comprising
 (A) providing a steam generation apparatus comprising   (1) a combustion chamber into which gaseous oxidant and fuel are fed, and in which said fuel and said gaseous oxidant are combusted thereby producing heat and hot flue gas,   (2) a preheater into which and through which said hot flue gas passes for transferring heat to said gaseous oxidant before said gaseous oxidant is fed to said combustion chamber,   (3) a pathway into which water is fed, from which heated steam is obtained at an outlet, and within which the water is evaporated and converted to said heated steam by heat transferred thereto in one or more heat exchangers in said pathway and within said steam generation apparatus to which heat of said combustion is radiated and in one or more convective heat exchangers in said pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred by convective heat exchange,   the pathway further comprising one or more devices that can pass coolant into steam in the pathway to reduce the temperature of said steam, and   (4) a second pathway into which steam is fed, from which said steam is obtained at an outlet, and within which said steam is heated by heat transferred thereto in one or more additional heat exchangers in said second pathway and within said steam generation apparatus to which heat in said hot flue gas is transferred, the second pathway further comprising one or more devices that can pass coolant into steam in said second pathway to reduce the temperature of said steam therein,   wherein the highest mass flow rate at which said apparatus can provide steam at said outlet at a temperature within a given temperature range, when said gaseous oxidant is air and said air is the only source of oxygen for said combustion, is limited by the maximum flue gas temperature to which said heat exchangers can be exposed, by maximum rates at which said fuel and gaseous oxidant can be fed into said combustion chamber and at which said flue gas can be withdrawn therefrom, and by the maximum rate at which said coolant can be passed into said steam, and   (B) providing steam at said outlet at a temperature within said given temperature range at a desired mass flow rate which is higher than said highest mass flow rate, by   (1) feeding water into said pathway at a mass flow rate equal to the desired mass flow rate of steam and feeding fuel into said combustion chamber at a mass flow rate corresponding to the amount of heat needed to produce said steam at said desired mass flow rate, while   (2) feeding into said combustion chamber gaseous oxidant with which said fuel is combusted having a higher oxygen content than air, at a volumetric flow rate lower than the volumetric flow rate of air at which said highest mass flow rate of steam is provided when air is the only source of oxygen for said combustion, at values of said oxygen content and said volumetric flow rate which are effective to provide said desired mass flow rate of steam without exceeding any of said maxima, and   (3) combusting said fuel in said combustion chamber with said air and said gaseous oxidant having said increased oxygen content fed at said lower volumetric flow rate,   wherein the heat transfer area of said heat exchangers is the same as when air is the only source of oxygen for said combustion, and wherein flue gas produced in said combustion chamber that exits from said apparatus is not fed back into said apparatus, and the temperature of said flue gas entering said preheater is lower than when said flue gas is produced by combustion in said apparatus when air is the only source of oxygen for combustion.   
   
   
       22 . A method according to  claim 21  wherein said fuel is coal. 
   
   
       23 . A method according to  claim 21  wherein steam is provided at said outlet at a temperature within said given temperature range at said increased oxygen content and decreased volumetric flow rate of said oxidant without passing any coolant into said steam. 
   
   
       24 . A method according to  claim 21  wherein said gaseous oxidant and fuel are combusted in said combustion chamber at a plurality of burners, and at least one of said burners is at a higher elevation than at least one other burner, the method further comprising
 feeding more than half of the total amount of fuel that is fed to all of said plurality of burners to a group of burners which contains at least half but fewer than all of said burners, in which group all burners are at a lower elevation than all burners not in said group.   
   
   
       25 . A method according to  claim 21  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, and all oxidant necessary for complete combustion of said fuel is fed through said burners. 
   
   
       26 . A method according to  claim 21  wherein said gaseous oxidant and fuel are combusted in said combustion chamber in one or more burners, wherein a portion of the oxidant necessary for complete combustion of said fuel is fed through said burners and the balance of the oxidant necessary for complete combustion of said fuel is fed into said combustion chamber through one or more overfire ports separate from and vertically above said one or more burners, provided that the oxygen content of the oxidant fed through said one or more overfire ports is less than the oxygen content of the oxidant fed through said one or more burners.