Apparatus and method for reduction of NOx emissions from a fluid bed combustion system through staged combustion
AssigneeFoster Wheeler Energy Corporation
InventorThomas E. Taylor
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Abstract
Apparatus and method for the reduction of nitrogen oxides (NOx) in the emissions of a fuel burning fluidized bed combustion system. Using a staged combustion technique, an overfire air inlet is provided in the freeboard zone above the bed. In the first stage, residual oxygen (O.sub.2) in the off-gas just above the bed is held in the 0.4 to 0.8% range by the actual coal and air rates. In the second stage, carbon monoxide (CO) and unburned hydrocarbons, both present in the first stage off-gas, are combined with additional air using the overfire air inlet. CO levels in the final effluent are reduced with little or no increase in NOx emissions.
Claims7
A non-catalytic two stage combustion process for reducing emissions of nitrogen oxides (NOx) produced during combustion of nitrogen-containing fuel while maintaining efficient capture of sulfur oxides (SOx), comprising the steps of:
- (a) providing a non-catalytic fluidized bed of particulate material including a nitrogen-containing fuel without catalyst and an adsorbent for the capture of sulfur oxides (SOx), wherein the temperature in said non-catalytic fluidized bed is within the range of 1500.degree. to 1650.degree. F.;
- (b) introducing air into said fuel to fluidize said bed and promote the combustion of said fuel to form a primary combustion stage;
- (c) introducing additional fuel to said bed to replenish the combusted fuel;
- (d) controlling the fuel feed rate or controlling the air feed rate to achieve combustion in said primary combustion stage under continuous substoichiometric conditions;
- and,
- (e) providing a second combustion zone which is not a fluidized bed by introducing air into the combustion off-gas above said fluidized bed to produce combustion under stoichiometric conditions, wherein the temperature in said second combustion zone is within the range of 1300.degree. to 1650.degree. F.;
- whereby said combustion process has a reduced NOx emissions level while maintaining efficient capture of sulfur oxides (SOx).
Dependencies are inferred from the claim text.