# US 5,344,629 A · Reducing Z.sub.20 emissions > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,344,629 A - Document ID: US5344629A - Status: Granted - Kind: A - Application number: 07/921,210 - Filed: 1992-07-29 - Granted: 1994-09-06 - Earliest claimed: 1992-01-03 - Assignees: A. Ahlstrom Corporation - Inventors: Folke Engstrom - Web page: https://patentgrep.com/patent/US5344629A ## CPC - B01D 53/8625: {Nitrogen oxides} - B01D 53/508: {by treating the gases with solids} - B01D 53/8628: {Processes characterised by a specific catalyst} - F23C 10/10: the separation apparatus being located outside the combustion chamber - F23C 10/16: specially adapted for operation at superatmospheric pressures, e.g. by the arrangement of the combustion chamber and its auxiliary systems inside a pressure vessel - F23J 15/02: of purifiers, e.g. for removing noxious material (traps for solid residues F23J3/04) - F23C 2206/101: Entrained or fast fluidised bed - F23J 2215/101: Nitrous oxide (N2O) - F23J 2215/20: Sulfur; Compounds thereof - F23J 2215/60: Heavy metals; Compounds thereof - F23J 2219/10: Catalytic reduction devices - F23J 2219/60: Sorption with dry devices, e.g. beds - 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) - F23C: METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN {A CARRIER GAS OR} AIR (burners F23D) - F23J: REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES (combustion apparatus for consuming smoke or fumes, e.g. exhaust gases, F23G7/06) - Y02C: CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG] ## Abstract The amount of N.sub.2 O in flue gases discharged from a fluidized bed combustion system is minimized by effecting vigorous and intimate mixing of the flue gases (with entrained particles) from a fluidized bed by increasing the velocity of the flue gases and then decreasing the velocity from the increased level, introducing a N.sub.2 O decomposing catalyst into the flue gases and particles immediately after increasing and decreasing of the velocity, and mixing the N.sub.2 O catalyst with the flue gases and particles, to effect decomposition of the N.sub.2 O. The catalyst is a calcium based sorbent, such as CaO or limestone, although and other catalysts also may be utilized. Normally the decomposition takes place without increasing the temperature of the flue gases. The increase in velocity is achieved by providing a constriction in the combustor vessel. The interior of the combustor vessel is lined with erosion resistant and thermal insulating material. Where the catalyst is calcium based sorbent, it is calcined, and the calcined particles are removed from the flue gases and recirculated to the fluidized bed, providing at least about 10 to 30% of the calcium based sulfur absorbing sorbent necessary to remove sulfur from the flue gases. ## Claims ### Claim 1 A method for reducing the emissions of N.sub.2 O in flue gases from the combustion of nitrogen containing fuel in a fluidized bed combustor, which has a combustion stage with a fluidized bed of particles, comprising the steps of continuously: (a) supplying nitrogen containing fuel and an oxygen containing gas for combustion of the fuel into the fluidized bed of the combustor to produce flue gases which contain particles; (b) maintaining a temperature of about 700.degree.-1000.degree. C. in the combustion stage; (c) supplying a Ca-based sulfur absorbing sorbent to the fluidized bed for reducing sulfur emissions in the flue gases; (d) without separate removal of the particles from the flue gases effecting vigorous and intimate mixing of the particles and flue gases by increasing the velocity of the flue gases before leaving the combustion stage, and then decreasing the velocity from the increased level; (e) introducing an N.sub.2 O decomposing catalyst into the flue gases and particles immediately after increasing and decreasing of the velocity thereof; (f) mixing the N.sub.2 O decomposing catalyst with the flue gases and particles to effect decomposition of the N.sub.2 O; and (g) discharging the flue gases with particles and decomposed N.sub.2 O therein from the combustor. ### Claim 2 (depends on 1) A method as recited in claim 1 comprising the further step (h), immediately after step (g), of removing particles from the flue gases, and recirculating the particles to the fluidized bed of the combustion stage. ### Claim 3 (depends on 2) A method as recited in claim 2 comprising the further step of introducing fly ash into the flue gases immediately after increasing and decreasing of the velocity thereof. ### Claim 4 (depends on 2) A method as recited in claim 2 wherein steps (d) and (f) are practiced by passing the flue gases with particles through a constriction in the cross-section of the combustor. ### Claim 5 (depends on 4) A method as recited in claim 4 wherein the combustor has side walls, and wherein the constriction in the cross-section of the combustor is formed by only one of the side walls. ### Claim 6 (depends on 4) A method as recited in claim 4 wherein steps constriction in the cross-section of the combustor is axial. ### Claim 7 (depends on 4) A method as recited in claim 4 wherein steps (d)-(g) are practiced without significantly raising the temperature of the flue gases. ### Claim 8 (depends on 4) A method as recited in claim 4 wherein steps (d) and (f) are practiced by passing the gases through a constriction having a cross-sectional area of about 40-60% of the combustion stage. ### Claim 9 (depends on 1) A method as recited in claim 1 wherein the N.sub.2 O decomposing catalyst is a Ca-based sorbent which is calcined during the practice of steps (d)-(g); and wherein step (c) is practiced at least in part by recirculating Ca-based sorbent introduced in step (e) and calcined in step (d)-(g) into the fluidized bed combustor. ### Claim 10 (depends on 9) A method as recited in claim 9 wherein at least about 10-30% of the Ca-based sorbent introduced in step (c) and necessary for sulfur capture is introduced in step (e) and recirculated to the fluidized bed. ### Claim 11 (depends on 9) A method as recited in claim 9 comprising the further step of lining the combustor interior at the constriction with erosion resistant and heat insulating material so as to facilitate maintenance of the temperature of the flue gases after the constriction at about the same level as before the constriction, to facilitate calcination of Ca-based sorbent catalyst. ### Claim 12 (depends on 1) A method as recited in claim 1 wherein step (e) is practiced by adding a catalyst selected from the group consisting essentially of calcium based sorbents, siderite, ankerite, NiO, CuO, and Mgo. ### Claim 13 (depends on 1) A method as recited in claim 1 wherein step (e) is practiced by adding a catalyst selected from the group consisting of limestone, Ca(OH).sub.2, and CaO, having a particle size of about 1-1000 microns. ### Claim 14 (depends on 1) A method as recited in claim 1 wherein steps (d) through (g) are practiced so as to provide a velocity, decreased from the increased level, of about 3-10 m/s. ### Claim 15 (depends on 1) A method as recited in claim 1 wherein steps (d)-(g) are practiced without significantly raising the temperature of the flue gases. ### Claim 16 (depends on 1) A method as recited in claim 1 wherein step (e) is practiced by introducing the catalyst entrained in air. ### Claim 17 A method for reducing the emissions of N.sub.2 O in flue gases from the combustion of nitrogen containing fuel in a fluidized bed combustor, which has a combustion stage with a fluidized bed of particles, comprising the steps of continuously: (a) supplying nitrogen containing fuel and an oxygen containing gas for combustion of the fuel into the fluidized bed of the combustor to produce flue gases which contain particles; (b) maintaining a temperature of about 700.degree.-1000.degree. C. in the combustion stage; (c) supplying a Ca-based sulfur absorbing sorbent to the fluidized bed for reducing sulfur emissions in the flue gases; (d) introducing a Ca-based N.sub.2 O decomposing catalyst to effect decomposition of the N.sub.2 O into the flue gases and particles after the fluidized bed and intimately mixing it with the flue gases, while maintaining temperature high enough to produce calcined sorbent; (e) discharging the flue gases with particles, decomposed N.sub.2 O, and calcined sorbent therein, from the combustor; and (f) removing the calcined sorbent from the discharged flue gases and recirculating it to provide part of the sorbent introduced in step (c). ### Claim 18 (depends on 17) A method as recited in claim 17 wherein steps (c)-(f) are practiced to introduce in step (d) about 10-30% of the sorbent needed to effect sulfur removal from the flue gases. ### Claim 19 A method for reducing the emissions of N.sub.2 O in flue gases from the combustion of nitrogen containing fuel in a fluidized bed combustor, which has a combustion stage with a fluidized bed of particles, comprising the steps of continuously: (a) supplying nitrogen containing fuel and an oxygen containing gas for combustion of the fuel into the fluidized bed of the combustor to produce flue gases which contain particles; (b) maintaining a temperature of about 700.degree.-1000.degree. in the combustion stage; (c) supplying a Ca-based sulfur absorbing sorbent entrained in air to the fluidized bed for reducing sulfur emissions in the flue gases; (d) passing the flue gases through a constriction in the combustor; (e) introducing an N.sub.2 O decomposing catalyst into the flue gases immediately after they pass through the constriction, to effect mixing of the catalyst with the flue gases and decomposition of the N.sub.2 O; and (f) discharging the flue gases with decomposed N.sub.2 O therein from the combustor. ### Claim 20 (depends on 19) A method as recited in claim 19 wherein the N.sub.2 O decomposing catalyst is a Ca-based sorbent which is calcined during the practice of steps (d)-(f); and wherein step (c) is practiced at least in part by recirculating Ca-based sorbent introduced in step (e) and calcined in step (d)-(f) into the fluidized bed combustor. ### Claim 21 (depends on 19) A method as recited in claim 19 wherein step (d) is practiced by passing the gases through a constriction having a cross-sectional area of about 40-60% of the combustion stage.