Combustion systems and processes for burning fossil fuel with reduced emissions

Abstract

A combustion system includes a combustion zone comprising a burner for converting a fuel, under fuel rich conditions, to a flue gas; an intermediate staged air zone downstream from the combustion zone for supplying intermediate staged air to the flue gas and producing fuel lean conditions; a reburn zone downstream from the intermediate staged air zone for receiving the flue gas; and an inlet downstream from the combustion zone for supplying a mixture of air and a reduction reagent to the flue gas, wherein the reduction reagent is configured to reduce an amount of a pollutant species in the flue gas.

1 . A combustion system, comprising:
 a combustion zone comprising a burner for converting a fuel, under fuel rich conditions, to a flue gas;   an intermediate staged air zone downstream from the combustion zone for supplying intermediate staged air to the flue gas and producing fuel lean conditions;   a reburn zone downstream from the intermediate staged air zone for receiving the flue gas; and   an inlet downstream from the combustion zone for supplying a mixture of air and a reduction reagent to the flue gas, wherein the reduction reagent is configured to reduce an amount of pollutant species in the flue gas.   
   
   
       2 . The combustion system of  claim 1 , wherein the inlet is disposed in the intermediate staged air zone and configured to supply a mixture of the intermediate staged air and the reduction reagent into the flue gas. 
   
   
       3 . The combustion system of  claim 1 , wherein the intermediate staged air comprises boosted air. 
   
   
       4 . The combustion system of  claim 1 , further comprising an overfire air inlet configured to supply overfire air to a burnout zone downstream from the reburn zone and a boosted overfire air inlet configured to supply boosted overfire air at a pressure higher than a pressure of the overfire air. 
   
   
       5 . The combustion system of  claim 4 , wherein the overfire air inlet is configured to supply a mixture of the overfire air and the reduction reagent into the flue gas. 
   
   
       6 . The combustion system of  claim 4 , wherein the boosted overfire air inlet is configured to supply a mixture of the boosted overfire air and the reduction reagent into the flue gas. 
   
   
       7 . The combustion system of  claim 4 , wherein the boosted overfire air inlet is disposed in the intermediate staged air zone. 
   
   
       8 . The combustion system of  claim 1 , further comprising a boiler nose downstream from the reburn zone, wherein the boiler nose comprises a plurality of ports disposed therein configured to supply a mixture of overfire air and the reduction reagent into the flue gas. 
   
   
       9 . The combustion system of  claim 1 , further comprising a burner disposed in the combustion zone, wherein the burner comprises a first duct configured to channel a fuel flow into the combustion zone; and a second duct substantially concentrically-aligned with and extending through the first duct, wherein the second duct is configured to channel a mixture of air and the reduction reagent into the combustion zone. 
   
   
       10 . The combustion system of  claim 9 , wherein the air comprises intermediate staged air. 
   
   
       11 . The combustion system of  claim 1 , wherein the reduction reagent comprises a sorbent composition, a nitrogen oxides reduction agent, an oxidizing composition, or a combination comprising at least one of the foregoing. 
   
   
       12 . The combustion system of  claim 1   1 , wherein the sorbent composition comprises calcium carbonate, limestone, calcium oxide, calcium hydroxide, calcium phosphate, cement, cement kiln dust, lime kiln dust, sugar beet lime, clay, talc, or a combination comprising at least one of the foregoing. 
   
   
       13 . A process for using a combustion system, said process comprising:
 supplying a fuel and air under fuel rich conditions to a combustion zone comprising a burner to form a flue gas;   supplying intermediate staged air to the flue gas through an intermediate staged air inlet downstream of the combustion zone in an amount effective to produce fuel lean conditions;   channeling the flue gas to pass to a reburn zone downstream from the intermediate staged air inlet; and   supplying a reduction reagent to the flue gas, wherein the reduction reagent is configured to reduce an amount of pollutant species in the flue gas.   
   
   
       14 . The process of  claim 13 , wherein supplying the reduction reagent further comprises mixing the reduction reagent with the intermediate staged air. 
   
   
       15 . The process of  claim 13 , wherein supplying intermediate staged air to the flue gas further comprises supplying intermediate staged air to the flue gas as boosted air. 
   
   
       16 . The process of  claim 13 , further comprising:
 supplying fuel to the reburn zone through a reburn inlet; and   supplying overfire air to a burnout zone downstream from the reburn zone through an overfire air inlet.   
   
   
       17 . The process of  claim 16 , wherein supplying the reduction reagent further comprises mixing the reduction reagent with the overfire air. 
   
   
       18 . The process of  claim 13 , further comprising supplying overfire air through a port in a boiler nose downstream from the reburn zone. 
   
   
       19 . The process of  claim 18 , wherein supplying the reduction reagent further comprises mixing the reduction reagent with the overfire air from the boiler nose. 
   
   
       20 . A process for reducing at least sulfur oxides and/or mercury in a flue gas of a combustion system, the method comprising:
 supplying a fuel and air under fuel rich conditions to a combustion zone comprising a burner to form a flue gas;   supplying intermediate staged air to the flue gas through an intermediate staged air inlet downstream of the combustion zone to produce fuel lean conditions;   channeling the flue gas to pass to a reburn zone downstream from the intermediate staged air inlet;   supplying overfire air to a burnout zone downstream from the reburn zone through an overfire air inlet; and   mixing a sorbent composition with the overfire air and/or the intermediate staged air before supplying the air to the flue gas.