Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
2003-06-02
2004-03-09
Rinehart, Kenneth B. (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S230000, C110S210000, C110S242000
Reexamination Certificate
active
06701855
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a process for the pyrolysis of waste materials particularly medical waste. More particularly, the invention relates to a pyrolysis process, wherein the waste material is placed in a sealed container. The sealed container is inserted in a load chamber and the waste material is subjected to the process of pyrolysis.
In recent years, government agencies, industries, and other organizations have had to address various problems relating to the handling and processing of organic waste materials including chemical and biological products. The disposal of medical waste is a particularly difficult problem, because of the presence of infectious bacteria, viruses, and other pathogens in the waste. It has been found that heating such organic waste materials to extremely high temperatures causes the components to thermally decompose. The heat energy converts the chemical components of the waste material (primarily carbon, hydrogen, and trace elements) to gases. A pyrolysis process is commonly used to thermally decompose and chemically transform the waste materials.
The term, “pyrolysis”, can have different meanings depending on its context. For example, “pyrolysis” is defined as the “transformation of a compound into one or more substances by heat alone, i.e., without oxidation.” (
Hawley's Condensed Chemical Dictionary
, 13
th
Ed. (1997).) In the Code of Federal Regulations (CFR) setting forth standards for the performance of hospital/medical/infectious waste incinerators, “pyrolysis” means “the endothermic gasification of waste materials using external energy.” (40 C.F.R. §60.51c) Typically, in commercial pyrolysis operations, waste material is loaded into a pyrolysis furnace or chamber, and there is generally some small amount of air (oxygen) present in the furnace. There can be several reasons for the presence of the air in the furnace. Some air may enter the furnace during the loading of the waste in the furnace chamber as the door to the chamber is opened and closed. Also, some air may be entrained within the waste. Further, the pyrolysis furnace may be operated at a slight negative pressure resulting in a small amount of air being drawn into the furnace through deficient seals. Thus, the term, “pyrolysis”, is commonly used in the industry and used herein to encompass processes, wherein the atmosphere in the pyrolysis furnace may at times contain a very small amount of air (oxygen) during the pyrolysis reaction, but the amount is so small as to preclude the presence of visible combustion.
For industrial applications, the pyrolysis of the waste materials is typically a first step in the overall destruction of the materials. The pyrolysis process volatilizes or gasifies the organic compounds found in the waste and produces exhaust gases containing volatile organic compounds. In a second step, a burner unit combusts or oxidizes the volatile organic compounds.
Pyrolysis furnaces should not be confused with incinerators that operate in a starved-air mode. Such incinerators typically include primary and secondary combustion chambers. In the incineration process, a burner or other ignition source produces an open flame in the primary chamber. Combustion air is supplied to the primary chamber at a rate which is less than the stoichiometric amount of oxygen required to achieve complete combustion of the volatile organic compounds evolved from the thermal decomposition of the organic waste materials. Then, in the secondary combustion chamber, excess combustion air is supplied to completely decompose and oxidize the waste exhaust gases. Lewis, U.S. Pat. Nos. 4,474,121 and 4,517,906 disclose methods and apparatus for controlling the addition of an auxiliary fuel to a two-stage combustion furnace system which is operated in a starved-air mode in the first stage and in an excess air mode in the second stage. One problem with such starved-air incinerators is that the open flame in the primary combustion chamber produces turbulence and causes the suspension of particles in the exhaust gas stream. The particulate passes through the secondary combustion chamber and is emitted as pollutants, unless additional pollution control systems (e.g., scrubbers) are employed. It is expensive to install such air pollution control systems on incinerators, but such systems are often necessary to meet emission standards.
As discussed above, pyrolysis processes for destroying waste materials are generally known in the industry. For example, Hansen et al., U.S. Pat. No. 5,868,085 discloses a waste treatment unit having: a main frame; an input stage through which the waste material to be treated is introduced through an arrangement of valves that can be controlled to prevent unwanted incorporation of air or oxygen into the pyrolytic process; and a pyrolytic assembly comprising a thermally-insulated outer housing coaxially surrounding an ellipsoidally-shaped pyrolytic chamber. A rotatable screw conveys waste through the retort as the pyrolysis reaction takes place. A heating chamber is defined as the space between the outer housing and the retort. Fuel gases are combusted within the heating chamber to provide a source of heat energy for the pyrolysis. According to the '085 Patent, the gases liberated from the feed material during pyrolysis are processed to draw off pollutants contained therein by a combination of condensation and thermal oxidation. The gases are then either vented to the atmosphere or routed to supply energy, such as to a steam generator.
Keough, U.S. Pat. No. 4,648,328 discloses an apparatus and process for the pyrolysis of used vehicular tires. The apparatus includes a reaction chamber. According to the '328 Patent, tire fragments are introduced into and removed from the reaction chamber through airlock mechanisms to prevent the ingress of ambient air as the fragments are conveyed through the chamber by a chain and flight conveyor. The process includes shredding the used tires, preheating the tire fragments, passing the fragments through the reaction chamber, separating solid and gaseous products, and recycling a portion of the gaseous product to the heating means.
Also, incinerator processes, which introduce a flame into the incinerator chamber to burn the waste, are known. Brookes, U.S. Pat. No. 4,603,644 discloses an incinerator having a receiving chamber with an opening (vent) in a rear wall. An ignition chamber is supplied with fuel and air and fires a flame down onto the biomass placed in the chamber. The opening in the receiving chamber leads to an afterburner chamber having a burner member which bums the volatile constituents in the gases from the receiving chamber. The afterburner chamber transfers the heat to ducts which occupy the space under the receiving chamber, a heat transfer chamber.
One problem with the foregoing processes is that firing the burner in the chamber can cause instability and turbulence leading to the emission of particulate and ash material. These materials may be emitted from the system as pollutants. Accordingly, there is a need for a pyrolysis process, wherein a flame is not introduced in the pyrolysis chamber to thermally decompose the waste. One object of the present invention is to provide such a pyrolysis process.
In addition, Brookes, U.S. Pat. No. 5,611,289 discloses a gasifier for gasifying biomass waste. The gasifier comprises a primary chamber for receiving the waste, a fume transfer vent, and a mixing chamber to accept the pyrolysis gases from the primary chamber. The fumes then flow to an afterburner chamber, where a burning flame oxidizes the constituents of the fumes. According to the '289 Patent, a partitioning wall is disposed between the flame chamber and the primary chamber so as to preclude the heating flame from entering the chamber. A heat transfer chamber accepts the fully oxidized fumes, and heat from the fumes causes the heat transfer chamber to be heated. The primary chamber has a heat conductive floor and is superimposed on the heat transfer chamber.
Barlow Josephs & Holmes, Ltd.
Global Environmental Technologies, LLC
Rinehart Kenneth B.
LandOfFree
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