Auger combustor with fluidized bed

Furnaces – Refuse incinerator

Reexamination Certificate

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C110S1010CD, C110S110000, C110S243000, C110S244000, C110S245000

Reexamination Certificate

active

06349658

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to incinerators, and more particularly to incinerators for the combustion of heterogenous waste materials such as household and commercial refuse. In the embodiments described, it teaches the provision of a removable noncombustible granular substrate beneath the material being consumed in the primary combustion chamber/gasifier of a rotating auger incinerator to aid in the more complete diffusion of combustion air through the materials being burned, to facilitate treatment of undesirable emissions from the materials being burned, and most importantly, to act as an “air bearing” for the material being consumed and to thereby facilitate its movement through said chamber. It also teaches the provision of an auger with expandable flights in such an incinerator, the suspension of treatment particles in the gas stream leaving said combustor/gasifier, and numerous other improvements.
2. Prior Art in the Field
a) General Background Information
Much of the world's energy needs have been, and continue to be, filled by hydrocarbon fuels. In the past, such fuels provided a convenient, plentiful, and inexpensive energy source. The current rising costs of such fuels and concerns over the adequacy of their supply in the future has made them a less desirable energy source and has led to an intense investigation of alternative sources of energy. The ideal alternative energy source is a fuel which is renewable, inexpensive, and plentiful, with examples of such fuels being the byproducts of wood, pulp, and paper mills, and household and commercial refuse.
The use of such alternative energy sources is not problem-free, however, since there is reason for concern over the contents of the emissions from the combustion of such fuels as well as the environmental ramifications of acquiring and transporting the fuel and disposing of the residue of combustion. Starved-air combustors, wherein the air supplied for combustion is controlled in order to control temperature conditions (and the rates of combustion) so as to consume the fuel entirely, have proved very useful in the utilization of such alternative energy sources while simultaneously maintaining a high degree of environmental quality in emissions. Such starved-air combustors are capable of burning various types of fuel and producing significant amounts of heat which can be employed for any number of purposes including the production of process steam for use in manufacturing and in the generation of electricity.
Unfortunately, most starved-air combustors, as originally developed and operated, were not entirely satisfactory in consuming the combustible elements of the fuel at high throughput while not producing noxious emissions. This problem resulted, in part, from the use of such combustors to burn a wide variety of fuels, including many which were nonhomogeneous, such as household or commercial refuse. While the pollution problem can be solved to a degree by the utilization of scrubbers and other antipollution devices, such mechanisms are very expensive and their cost may militate against the use of alternative energy sources previously described.
b) The Auger Combustor/Gasifier
Many of the drawbacks of such prior art devices were overcome by the development of the auger combustor/gasifier by the inventor and others. See, U.S. Pat. No. 4,009,667 (describing the original auger combustor/gasifier utilized in the system); U.S. Pat. No. 4,315,468 (describing an incinerator control means for the system); U.S. Pat. No. 4,331,084 (describing a refuse fuel feed mechanism for the system); U.S. Pat. No. 4,331,085 (describing a flame stabilization means for the system); U.S. Pat. No. 4,332,206 (describing an afterburner for the system); and U.S. Pat. No. 4,332,206 (describing a hot gas recycle mechanism for use with the system). The auger combustion technology taught and described in the foregoing patents offers a cost-effective approach to clean, efficient combustion of prepared solid waste and other solid fuels. It employs a starved-air combustion technique, partially combusting or gasifying solid fuel in a primary chamber (the “combustor/gasifier”), then passing the combustible gases to an afterburner where sufficient air is added to complete combustion.
One of the unique features of the auger combustor/gasifier system is the variable-pitch auger. The fuel enters the combustor/gasifier at a controlled rate and is shaped into a pile by the first auger flight. It is then pushed and tumbled through the combustor/gasifier chamber by the auger. As the auger moves the fuel through this horizontal cylinder, it stirs the material to maximize exposure to the oxidizing air injected into the chamber. The pitch of the auger decreases along the path of material flow to accommodate the decrease of fuel bulk as the material combusts. This ability to manage fuel-bed configuration permits control of forced-draft combustion air to gasify nearly all the fuel without complete combustion taking place, thereby allowing the combustor/gasifier to operate at what is, for an incinerator, a uniformly moderate temperature (e.g. 1,500-1800F).
c) The Use of Granular Substrates
The combination of fuel bed stirring and air injection with precise temperature control gives the auger combustor/gasifier system several advantages over prior technology: Reliability and clean operation; high throughput; low gasifier temperature, afterburner combustion of only gaseous fuels, precise flame structure and temperature control; longer material life (refractory and auger); fully automatic control; and the ability to combust a wide variety of heterogenous solid fuels. However, it has been discovered that several of these advantages may be further strengthened by the addition of a substrate of appropriate granular materials to act as an “air bearing” in the auger combustor/gasifier chamber, to aid in the diffusion of combustion air through the material being burned, and to facilitate treatment of harmful emissions from the materials being burned. Moreover, the advantages inherent in the use of such a substrate are even further magnified by its use in conjunction with a combustor/gasifier chamber wherein the pressure of the air forced through the substrate is at its maximum at the fuel input end of the chamber and at its minimum at the output end of the chamber.
Granular fuels being burned in incinerators have been, in the past, formed into fluidized beds via the insertion from underneath of combustion air at appropriate pressures. In such incinerators, the granular fuel forming the fluidized bed is moved by the fluidization means or by a movable grate under the bed. The fluidization of the granular fuel aids in its combustion and its movement through the combustion chamber. However, the inventor is aware of no incinerators in which a fluidized bed acts as a substrate for the material being burned and is formed from a noncombustible material which remains generally stationary with respect to such material, acts as an “air bearing” for such material, aids in the diffusion of combustion air into and through such material, and may be utilized to help treat and eliminate undesirable emissions from the material being burned.
In addition to those patents enumerated above with regard to the auger combustor/gasifier, representative patents illustrating the current state of the art in the area of starved air incinerators include the following:
1. “Apparatus for the Combustion of Poorly Combustible Fuels” issued to Cosar (U.S. Pat. No. 4,809,620) in 1989.
2. “Method and Apparatus for Regulating the Furnace Output of Incineration Plants” issued to Martin (U.S. Pat. No. 4,953,477 in 1990.
3. “Method and Apparatus for the Efficient Combustion of a Mass Fuel” issued to Barlow (U.S. Pat. No. 5,044,288) in 1991.
4. “Incinerating-Fusing System for City Refuse Disposal” issued to Tsunemi et al. (U.S. Pat. No. 5,078,065 in 1992.
5. “Process and Apparatus for Emissions Reduction from Waste Incineration” issued to Khinkis et al. (U

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