Patent GB-1427231-A (GB)
Title: Diminishing gaseous pollutants in combustion flue gas
IPC: F23L9/00
Filed: 1973-01-02
Abstract: 1427231 Steam generators; combustion apparatus AQUA-CHEM Inc 2 Jan 1973 [6 Jan 1972 5 Oct 1972] 206/73 Headings F4A F4B and F4T Fuel burning apparatus, e.g. for a steam generator or furnace, adapted for diminishing nitrogen oxides in its exhaust gas has means defining a primary combustion zone 38, Fig. 1, and means for introducing into said zone fuel and less than the amount of oxygen and nitrogen containing gas required for complete combustion to produce a stream of gaseous combustion products including some NOX and residual combustible products including some CO and a substantial proportion of unburned carbonaceous materials and unburned hydrocarbons, means defining a secondary combustion zone coupled to said primary zone 38 for receiving said combustion products stream, said secondary zone including at least one tube 31 extending into the path of said stream within said secondary zone, said tube or tubes 21 being arranged to supply combustion supporting gas to plural regions of said combustion products stream within said secondary zone for oxidizing said residual combustion products before discharge from said secondary zone. The temperature in the secondary zone is maintained below about 2700‹ F. to reduce oxidation of nitrogen. The apparatus may burn gas or liquid fuel and may be applied to a residential or commercial furnace, a space heater, an incinerator, hot water heater or a heating or power generating boiler. A steam generating boiler, Fig. 1, comprises a combustion space defined between upper and lower water drums 11, 12 and interconnected water tubes 13 extending between the drums. A primary combustion chamber 38 has a burner installed in a refractory lined chamber 14, the primary combustion products 42 passing via apertures in refractory holders 18 into a gas dispersion bed 19. The bed 19 is formed of refractory materials such as silicon carbide or alumina in aggregate form, or may be an open celled metallic sponge or a monolithic porous refractory member. The bed may include a catalyst such as compounds or alloys of iron, nickel, chromium, copper and platinum. CO and NOX react in the bed to yield N 3  and CO 2  which pass together with the other combustion products from the primary zone into a secondary combustion zone defined around porous or perforated ceramic or metallic secondary air supplying tubes 31. In a second boiler, Figs. 5, 6, fuel is injected into a primary combustion zone from a nozzle 225 and air enters via openings 230, the primary combustion products passing to a secondary combustion zone 261 housing a device comprising two or more rows of tubes 253, 254. Each tube 253 or 254 has two rows of secondary air outlet apertures directed downstream and at 120 degrees to each other. A fan 233 driven by a motor 231 supplies air to a main duct 235 and thence via a damper 246, ducts 241, 243 and openings 230 to the primary combustion zone, a minor part of the air passing via a damper 245 and duct 240 to the secondary combustion zone. The rows of tubes 253, 254 may have a common air supply, or may have separate air supplies effectively dividing the secondary zone into a secondary and a tertiary combustion zone. A bidirectional motor 239 controls damper 246 and, via a cam 246, a fuel control valve to maintain the desired air/fuel ratio in the primary combustion zone under varying states of heat demand. The secondary combustion products leave the boiler via a stack 215 having a sensor 251 sensing, for example, CO level and controlling a motor 249 to open and close damper 245 in response to increase and decrease respectively in the detected CO level. In a modification a main damper is located in the main duct 235 and is driven together with damper 246 and the fuel valve by motor 239 in response to boiler demands. Alternatively motor 239 may control the main damper and the fuel valve and dampers 245, 246 are controlled by motor 249. Each tube 253, 254 may be surrounded by a respective coaxial tube so that cooling water may flow through the space between the tubes, radial air supplying flutes passing from holes in the inner tube 253, or 254 through said space, Figs. 9-11 (not shown).