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AssigneeThe United States of America as represented by the United States Department of Energy
InventorsDarren J. Mollot, Donald L. Bonk, Thomas E. Dowdy
Estimating the term…
Polluting NO.sub.x gas values are removed from off-gas of a multi-stage coal combustion process which includes an initial carbonizing reaction, firing of char from this reaction in a fluidized bed reactor, and burning of gases from the carbonizing and fluidized bed reactions in a topping combustor having a first, fuel-rich zone and a second, fuel-lean zone. The improvement by means of which NO.sub.x gases are removed is directed to introducing NO.sub.x -free oxidizing gas such as compressor air into the second, fuel-lean zone and completing combustion with this source of oxidizing gas. Excess air fed to the fluidized bed reactor is also controlled to obtain desired stoichiometry in the first, fuel-rich zone of the topping combustor.
In a multi-stage process which comprises partially gasifying coal in a first, pressurized carbonizer reactor whereby combustible syngas and a particulate char are produced, firing the resulting char in a second, pressurized fluidized bed reactor with NO.sub.x -free compressor air, producing a hot, oxygen-rich, NO.sub.x -containing off-gas, mixing the syngas and the off-gas from the fluidized bed reactor, and burning the resulting mixture in a topping combustor having a first, fuel-rich zone and a second, fuel-lean zone downstream from said first zone, the improvement which comprises introducing said oxygen-rich, NO.sub.x -containing off-gas into said first zone and introducing directly into said second zone as the only source of oxidizer being so introduced a NO.sub.x -free, oxygen containing gas whereby combustion of gases entering the second zone in from said first zone is completed and NO.sub.x gases therein are removed, the amount of oxygen in the off-gas from the fluidized bed reactor being controlled by regulating the amount of NO.sub.x -free air fed into said fluidized bed reactor to provide a combustible gas-to-oxygen equivalence ratio of 1.5 to 3.0 in the first zone of said topping combustor.
In a multi-stage process which comprises partially gasifying coal in a first, pressurized carbonizer reactor whereby combustible syngas and a particulate char are produced, firing the resulting char in a second, pressurized fluidized bed reactor with a NO.sub.x -free oxygen-containing gas, producing a hot, oxygen-rich, NO.sub.x -containing off-gas, mixing the syngas and the off-gas from the fluidized bed reactor, and burning the resulting mixture in a topping combustor having a first, fuel-rich zone and a second, fuel-lean zone downstream from said first zone, the improvement which comprises preheating said NO.sub.x -free oxygen-containing gas with energy from at least one of said reactors, introducing the resulting preheated oxygen-rich, NO.sub.x -containing off-gas into said first zone and introducing directly into said second zone as the only source of oxidizer being so introduced a NO.sub.x -free, oxygen containing gas whereby combustion of gases entering the second zone in from said first zone is completed and NO.sub.x gases therein are removed.
Dependencies are inferred from the claim text.