# US 8,147,785 B2 · Combustion flue gas NOx treatment

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- Number: US 8,147,785 B2
- Document ID: US8147785B2
- Status: Granted
- Kind: B2
- Application number: 12/778,675
- Filed: 2010-05-12
- Published: 2010-11-18
- Granted: 2012-04-03
- Earliest claimed: 2009-05-15
- Assignees: FMC Corporation
- Inventors: Henry A. Pfeffer; David E. Smith
- Web page: https://patentgrep.com/patent/US8147785B2

## CPC

- B01D 53/60: Simultaneously removing sulfur oxides and nitrogen oxides
- B01D 53/56: Nitrogen oxides (B01D53/60 takes precedence)
- B01D 53/75: Multi-step processes
- B01D 53/8625: {Nitrogen oxides}
- B01D 53/869: {Multiple step processes}
- B01D 53/58: Ammonia
- B01D 2251/106: Peroxides
- B01D 2251/206: Ammonium compounds
- B01D 2251/2062: Ammonia
- B01D 2251/2067: Urea
- B01D 2251/304: of sodium
- B01D 2251/404: of calcium
- B01D 2251/606: Carbonates
- Y02A 50/20: Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
- Y02C 20/10: of nitrous oxide (N2O)
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- Y02A: TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02C: CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]

## Abstract

Combustion flue gas containing NOX and SOX is treated to remove NOX in a multistep system in which NOX is reduced in the flue gas stream via selective catalytic reduction or selective non-catalytic reduction with ammonia or an ammonia-forming compound, followed treatment with hydrogen peroxide to remove residual ammonia and, optionally, treatment with an alkali reagent to reduce residual NOX in the flue gas stream. The NOX-depleted flue gas stream may also be subjected to a desulfurization treatment for removal of SOX.

## Claims

### Claim 1

A method for removing NOX from a flue gas stream comprising
injecting ammonia or an ammonia-forming compound into a combustion flue gas stream containing NOX, wherein an excess of ammonia is introduced into the flue gas stream as an agent for reducing the NOX, to yield a flue gas stream containing unreacted residual ammonia and a reduced concentration of NOX;
thereafter injecting hydrogen peroxide into the flue gas stream containing unreacted residual ammonia, the flue gas having a temperature of about 250° F. to about 800° F.,in an amount sufficient to react with residual ammonia present in the flue gas stream, to yield an ammonia-depleted flue gas stream; and
contacting the ammonia-depleted flue gas stream with an alkali reagent in an amount sufficient to remove NOX present in the gas stream, yielding a flue gas stream with reduced concentrations of ammonia and NOX.

### Claim 2 (depends on 1)

The method of claim 1 wherein the ammonia is introduced into flue gas stream in an amount sufficient to provide at least about 50% stoichiometric molar excess, based on the amount of NOX present in the flue gas stream.

### Claim 3 (depends on 1)

The method of claim 1 wherein the combustion flue gas stream temperature during the ammonia injection operation is between about 300° F. to about 1200° F.

### Claim 4 (depends on 1)

The method of claim 1 wherein the hydrogen peroxide is employed as an aqueous hydrogen peroxide solution in combination with an activator.

### Claim 5 (depends on 1)

The method of claim 1 wherein the hydrogen peroxide is injected into the ammonia-containing flue gas stream in an amount sufficient to provide at least about ¼ mole H2O2 per mole NH3 up to about 15 moles of H2O2 per mole NH3 present in the flue gas stream.

### Claim 6 (depends on 1)

The method of claim 1 wherein sufficient hydrogen peroxide is contacted with the ammonia-containing flue gas stream to reduce the ammonia concentration in the H2O2-treated flue gas stream to less than about 10 ppm NH3.

### Claim 7 (depends on 1)

The method of claim 1 which further comprises injecting the ammonia into the flue gas stream in conjunction with a selective catalyst reduction operation used to treat the combustion flue gas stream.

### Claim 8 (depends on 7)

The method of claim 7 wherein the combustion flue gas stream temperature during the selective catalyst reduction operation is between about 300° F. to about 800° F.

### Claim 9 (depends on 7)

The method of claim 7 wherein sufficient hydrogen peroxide is contacted with the ammonia-containing flue gas stream to reduce the ammonia concentration in the H2O2-treated flue gas stream to less than about 5 ppm NH3.

### Claim 10 (depends on 1)

The method of claim 1 wherein the alkali reagent is selected from the group consisting of soda ash, trona, sodium sesquicarbonate, nahcolite, sodium bicarbonate, wegscheiderite, lime, slaked lime, limestone and mixtures of these.

### Claim 11 (depends on 1)

The method of claim 1 wherein the alkali reagent is contacted with the flue gas stream as a dry sorbent, by injection of dry particulate sorbent having a mean particle size of less than about 100 μm into the flue gas stream.

### Claim 12 (depends on 1)

The method of claim 1 wherein the alkali reagent is contacted with the flue gas stream as a slurry of particulate sorbent in admixture with water, by injecting or spraying the reagent-containing slurry into the flue gas stream.

### Claim 13 (depends on 1)

The method of claim 1 wherein the alkali reagent is contacted with the flue gas stream as a solution of the reagent at least partially dissolved in an aqueous medium, by injecting or spraying reagent-containing solution into the flue gas stream.

### Claim 14 (depends on 1)

The method of claim 1 wherein the alkali reagent is contacted with the flue gas stream as a solution or slurry of the reagent in an aqueous medium in a wet scrubber or absorber.

### Claim 15 (depends on 1)

The method of claim 1 wherein sufficient alkali reagent is contacted with the ammonia-depleted flue gas stream to reduce the NOX concentration in the alkali reagent-treated flue gas stream to less than about 50% of the NOX concentration in the ammonia-depleted flue gas stream.

### Claim 16 (depends on 1)

The method of claim 1 wherein the alkali reagent is introduced into the ammonia-depleted flue gas stream and which further comprises subjecting the flue gas stream to a solids recovery operation following the introduction of the reagent.

### Claim 17 (depends on 16)

The method of claim 16 wherein the solids recovery operation is selected from the group consisting of baghouse filtration and electrostatic precipitation.

### Claim 18 (depends on 1)

The method of claim 1 wherein the NOX-containing flue gas stream further comprises SOX as a contaminant and which further comprises subjecting the NOX-depleted flue gas stream to a desulfurization operation.