Patent Application
20090084292
The field of the invention is furnaces, and especially furnaces involved with liberating gas from solid fuel. (Class 110/229).
Pyrolysis employs high temperatures in a relatively oxygen free environment to remove volatiles from solid fuels, as well as gases that can be released at high temperature from breaking down a feedstock. Depending on the feedstock, the volatiles can then be burned to produce usable energy.
It is known to pyrolyze innumerable different types of fuels, including trash, old tires, and other municipal wastes. As discussed in commonly-assigned U.S. patent application Ser. No. 10/517,023 to Walker, which is a national phase entry of PCT/US02/20362, filed Jun. 26, 2002, and U.S. Pat. No. 6,619,214 to Walker (September 2003), a typical waste treatment system utilizing pyrolysis includes: (a) an input structure for introducing waste; (b) a pyrolytic converter for breaking down a feedstock and generating waste gases; and (c) a thermal oxidizer that burns the waste gases (also referred to herein as “syngas” or “syn gases”). In preferred embodiments a portion of the heated gases can be transported back into an outer chamber of the pyrolyzer to help sustain continued pyrolysis of the feedstock.
Conventional thermal oxidizers burn syn gases in the hot flame and exhaust of a natural gas burner. Sometimes baffles are included in the thermal oxidizer to produce turbulence, which is believed to facilitate combustion of the syn gases. Nevertheless, the process is relatively slow and inefficient, requiring 4 seconds or more of residence time within the oxidizer. Longer residence times require larger oxidizers, and are therefore more costly in terms of materials and space.
In other fields, furnaces sometimes include burner cones with perforations (also referred to herein as “openings”). Such burner cones establish a turbulent fuel/air mixing zone, which in turn increases the fuel/air mixing efficiency, and thus the combustion efficiency of the furnace. (see e.g., U.S. Pat. No. 4,171,199 to Henriques (October 1979). Other examples include U.S. Pat. No. 5,259,755 to Irwin et al. (November 1993), U.S. Pat. No. 5,540,213 to Shell et al. (July 1996), U.S. Pat. No. to Sheley (March 1995), U.S. Pat. No. 4,431,403 to Nowak et al. (February 1984).
Conventional burner cones are adequate for small operations such as those described in Henriques and others, but can still provide insufficient turbulence for proper combustion in a thermal oxidizer, where the large size of the chamber and the use of syngas having relatively low combustibility militate against efficient burning. Both situations exist in municipal waste pyrolyzers. The syngas produced in pyrolysis of municipal waste, for example, typically includes hydrogen, carbon monoxide, methane, and lower molecular weight hydrocarbons, as well as nitrogen and carbon dioxide.
U.S. Pat. App. No. 2006/0090748 to White (May 2004) teaches perforations with protrusions (although not in a burner cone) for generating turbulent air flow. In that case the protrusions increase the surface area of the heat shield, and generate turbulence around the heat shield to improve the conduction of heat away from the heat shield. White fails to teach protrusions in the context of burner cones to improve combustion efficiency.
Walker, Henriques, Irwin, Shell, Sheley, Nowak, and White, and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for systems, methods and apparatus that increase combustion efficiency of pyrolysis waste gases in a thermal oxidizer.
The present invention provides apparatus, systems and methods in which a burner cone has protrusions that facilitate turbulence of combustion gases. Such cones can advantageously be utilized in thermal oxidizers that receive syn gases from pyrolyzing municipal or other wastes.
Preferred burner cones have a frustoconical shape with a narrow end diameter of at least 0.3 meters, a wide end diameter of at least 1 meter, and a length of at least 1 meter. Those skilled in the art will appreciate, however, that the actual dimensions will depend entirely on the installation. The wall is preferably about 0.5 to 1 cm thick, although here again the actually thicknesses will depend upon the installation. The wall can be made of any suitable material, including suitable alloys and especially stainless plate. Unless a contrary meaning is apparent from the context, all ranges described herein are inclusive of their endpoints.
Preferred openings can have any suitable number, including anywhere from a few openings to several dozen or more. Openings can have any suitable sizes, but are currently contemplated to be optimal between about 50 cm2 and 200 cm2. Such openings preferably have curved edges (e.g., a round or oblong punch out), but in alternative embodiments can have edges that are straight (e.g., rectangle punch out) or star shaped (e.g., star punch out). Further, it is contemplated that the openings can be disposed at any suitable positions around the wall of the cone.
The protrusions can be produced in any suitable manner, but are preferably derived from the wall portions being punched out to form the openings. However, in alternative embodiments, the protrusions can be attached to, extend from, or otherwise be disposed at any other suitable locations on the burner cone. There can be multiple protrusions adjacent or formed from a single opening, as for example where the openings are produced by bending out the four sections created with an “X” cut into the wall.
Burner cones are contemplated with any suitable number of openings and protrusions, including up to 10, 20, 30, 40, 50 or more protrusions. Protrusions should be large enough to have a meaningful effect on turbulence, which increases combustion efficiency sufficient to reduce residence time in the thermal oxidizer by at least 1 and more preferably at least 2 seconds. Currently preferred protrusions have an area of between 50 cm2 and 200 cm2, and a curved shape. Protrusions can extend inwardly or outwardly (or possibly even both) relative to the wall of the cone by at least 5 cm to 10 cm, and at an suitable angle from the wall, including for example at least 10°, 20°, 30°, 40°, 50°, 60°, 70° and 80°.
Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawings in which like numerals represent like components.
Burner cone 100 has a wall 120A disposed between a first and a second end 121A, 121B, respectively. Burner cone 100 can have any suitable dimension, including especially a frustoconical shape. Preferred burner cones have an upstream end diameter of at least 0.3 meters, a downstream end diameter of at least 1 meter, and a length of at least 1 meter. Those skilled in the art will appreciate, however, that the actual dimensions will depend entirely on the installation. The wall is preferably about 0.5 to 1 cm thick, although here again the actually thicknesses will depend upon the installation. The wall can be made of any suitable material, including suitable alloys and especially stainless plate.
Openings 122A are disposed within wall 120A of burner cone 100. Preferred openings 122A can have any suitable number, including anywhere from a few openings to several dozen or more. Openings 122A can have any suitable sizes, but are currently contemplated to be optimal between about 50 cm2 and 200 cm2. It is contemplated that openings 122A can be disposed at either: (a) equal distances from the narrow end 121A forming concentric rows of openings 122A, or (b) at different distances from the narrow end 121A forming staggered rows of openings 122A. Openings 122A can be separated by any suitable distance. As shown in
As shown in
Currently preferred protrusions 123A have an area of between 50 cm2 and 200 cm2, and a curved shape. Protrusions 123A should be large enough to have a meaningful effect on turbulence, which increases combustion efficiency sufficient to reduce residence time in the thermal oxidizer by at least 1 and more preferably at least 2 seconds. As shown in
Preferred pyrolyzer 220 is depicted generally as having an outer housing 221, an inner housing 225, a heated outer chamber 221A between the inner and outer housings, and an inner reaction chamber 225A in which pyrolysis occurs. Both inner and outer housings are preferably constructed from stainless steel or other alloy capable of withstanding temperatures of 2200 degrees Fahrenheit (about 1200 degree Celsius). Conveyor 226 is disposed within inner housing 225 and receives waste input 205 from hopper 210. Preferably conveyor 226 is a screw type conveyor that transports a stream of waste through inner reaction chamber 225A as pyrolysis occurs. Waste input 205 exits inner reaction chamber 225A as char 224, and syn gases 227 (pyrolysis waste gases) are transported out of inner reaction chamber 225A via conduit 230. Optionally, outer housing 221 can have a burner 222 supplied by a gas input 223. Burner 223 can be used to heat outer chamber 221A. Outer chamber 221A conducts heat to the waste in inner reaction chamber 225A to sustain pyrolysis.
Preferred thermal oxidizer 240 is depicted generally as having burner 242, gas supply 243, burner cone 244, baffles 247, and exhaust gas conduit 250. In preferred embodiments, burner cone 244 receives syngas 227, which is produced in the inner reaction chamber 225A of pyrolyzer 220. The syngas 227 produced by pyrolysis of municipal waste for example, typically includes hydrogen, carbon monoxide, methane, and lower molecular weight hydrocarbons, as well as nitrogen and carbon dioxide. Thermal oxidizer 240 is used to reduce pollutants from syngas 227 generated by pyrolysis.
Burner 242 disposed within the wall of thermal oxidizer 240 is supplied by gas input 243. Gas input 243 is preferably natural gas or any other suitable gas. Burner 242 is used to ignite syngas 227 as the gas flows into burner cone 244. As syngas 227 passes through and around openings/protrusions 245 in burner cone 244 turbulence is generated. The turbulent mixing effect of openings/protrusions 245 is shown generally by arrows 246, which significantly enhances the combustion efficiency of thermal oxidizer 240 relative to a similar burner without the protrusions. In addition, baffles 247 and optional baffle holes 248 are disposed within thermal oxidizer 240 to aid in the turbulent mixing of syngas 227 and thereby increasing the combustion efficiency of thermal oxidizer 240.
Syngas 227 exits thermal oxidizer 240 as combusted heated exhaust gas 252 via exhaust gas conduit 250. In preferred embodiments, a portion of the heated exhaust gas 252 can be transported back into the outer chamber 221A of the pyrolyzer 220, as generally depicted by arrows 254 via conduit 253, to sustain continued pyrolysis of the feedstock within the inner reaction chamber 225A. Additionally, heated exhaust gas 252 can be used to: (a) dry waste input materials, (b) be transported to a boiler (not shown) to generate steam, which operates a steam turbine (not shown) to produce electricity; and (c) be used in other downstream heat driven processes. Further, heated exhaust gas 252 contains known toxic substances, which are removed from exhaust gas 252 by a scrubber device (not shown) so that the gases can be safely discharged to atmosphere.
Optional features of the burner cone include: a burner cone having a frustoconical shape 151; an opening having an area of between 50 cm2 and 200 cm2 152; a protrusion extending outwardly from the wall by at least 5 cm 153; a protrusion extending outwardly from the wall by at least 10 cm 154; a protrusion extending outwardly from the wall at and angle of at least 50° 155; a protrusion being disposed at a location other than at an opening 156; a first and second protrusion being disposed at a single opening 157; a protrusion being derived from a portion of the wall forming an opening 158; an opening having an upstream edge and a downstream edge, and a protrusion being disposed at one of the upstream and downstream edges 159; an opening having an upstream edge and a downstream edge, and a protrusion being disposed intermediate the upstream and downstream edges 160; the wall of the burner cone having an inner surface and an outer surface, and a protrusion extending inwardly from the inner surface 161; and the wall of the burner cone having an inner surface and an outer surface, and a protrusion extending outwardly from the outer surface 162.
It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
