# US 5,706,645 A · Removal of oxides of nitrogen from gases in multi-stage coal combustion

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- Number: US 5,706,645 A
- Document ID: US5706645A
- Status: Granted
- Kind: A
- Application number: 08/635,422
- Filed: 1996-04-10
- Granted: 1998-01-13
- Earliest claimed: 1996-04-10
- Assignees: The United States of America as represented by the United States Department of Energy
- Inventors: Darren J. Mollot; Donald L. Bonk; Thomas E. Dowdy
- Web page: https://patentgrep.com/patent/US5706645A

## CPC

- F23R 3/346: {for staged combustion}
- F02C 3/205: {in a fluidised-bed combustor (in combination with a steam cycle see F01K23/061; fluidised-bed apparatus in general B01J8/18; fluidised-bed combustors in general F23C10/00)}
- F02C 3/28: using a separate gas producer for gasifying the fuel before combustion
- Y02E 50/10: Biofuels, e.g. bio-diesel
- F23R: GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS (fluidised bed combustion apparatus specially adapted for operation at superatmospheric pressures F23C10/16)
- F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

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.

## Claims

### Claim 1

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.

### Claim 2

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.

### Claim 3 (depends on 2)

The improvement as defined in claim 2 wherein said NO.sub.x -free, oxygen containing gas is preheated with energy from said fluidized bed reactor.