Abstract:
A gas conduit for venting high temperature reactor comprising a conduit portion in direct communication with the reactor for receiving gas therefrom where the conduit includes a Venturi for creating a high pressure zone in the area prior to exit of the reactor. The conduit, accordingly, has a portion having first and second diameters, where the second diameter less than the first diameter and is dimensioned in order to provide an area of high pressure in the region of the first diameter.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to a high temperature reactors and, more particularly, to gas conduits for such reactors. 
     2. Description of the Problem 
     High temperature reactors, such as plasma reactors used for pyrolitic conversion of waste to constituent metals and organic matter, can create gaseous matter that may be used in many other processes. However, those skilled in the relevant arts will recognize that the reactor environment is highly ionized, and, the gaseous matter extracted from the reactor is ionized. A concern arises that due to the high energy levels found in ionized gases, unreformed gases may be removed from the reactor into the extraction conduit where the control of temperatures is not that accurate. A possible undesired result is, therefore, reformations of gases into undesired chemicals in the extraction conduit beyond the reactor. 
     SUMMARY 
     The present invention seeks to remedy this problem by providing a gas conduit for venting a high temperature reactor that is configured to create a localized high pressure area that enhances the environment for desired chemical reformations prior gases being completely extracted from the reactor. The conduit includes first and second diameters, where the second diameter is less than the first diameter and both diameters are dimensioned in order to provide an area of high pressure in the region of said first diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
         FIG. 1A  is an exemplary plasma gasification system with a vent to a gas pipe adapted to include a Venturi throat; 
         FIG. 1B  is a more detail view of the gas pipe and Venturi throat of  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments of the present invention and their advantages are best understood by referring to  FIGS. 1A and 1B  of the drawings. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Throughout the drawings, like numerals are used for like and corresponding parts of the various drawings. 
     Furthermore, reference in the specification to “an embodiment,” “one embodiment,” “various embodiments,” or any variant thereof means that a particular feature or aspect of the invention described in conjunction with the particular embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment,” “in another embodiment,” or variations thereof in various places throughout the specification are not necessarily all referring to its respective embodiment. Moreover, features described with respect to a particular embodiment may also be employed in other disclosed embodiments as those skilled in the relevant arts will appreciate. This invention may be provided in other specific forms and embodiments without departing from the essential characteristics as described herein. The embodiments described below are to be considered in all aspects as illustrative only and not restrictive in any manner. 
     Referring now in detail to the drawings, there is illustrated in  FIG. 1A , a pictorial diagram of an apparatus  10  for plasma gasification of hazardous and non-hazardous waste materials contained in organic and inorganic products. The apparatus  10  includes a waste feeder system  12 , and a refractory-lined reactor vessel  14 . The waste feeder system  12  is provided for feeding the hazardous and non-hazardous waste materials consisting of organic and inorganic components into the refractory lined reactor vessel  14  at a controlled rate. The waste feeder system feeds a stream of shredded and compact waste materials into the reactor vessel in a continuous manner. The hazardous and non-hazardous waste materials may include, but are not limited to, municipal solid waste (MSW), medical type waste, radioactive contaminated waste, agricultural waste, pharmaceutical waste, and the like. 
     The waste materials are delivered into the reactor vessel at a controlled rate so as to expose a predetermined amount of compacted waste to the thermal decomposition (pyrolysis) process for regulating the formation of product synthesis gases (syngas). The feed rate is dependent upon the characteristics of the waste materials as well as the temperature and oxygen conditions within the reactor vessel. Inside of the reactor vessel  14 , a high temperature plasma arc generates temperatures in excess of 2,900 degrees F. so that, upon entry of the waste stream, it is immediately dissociated with the organic portion of the waste material being converted to carbon and hydrogen and the inorganic portion and metals of the waste material melted with the metal oxides being reduced to metal. A DC graphite electrode  28  and a conductive plate defining a cathode electrode  30  formed in the bottom of the reactor vessel are connected to a DC power supply (not shown) so as to create the high temperature plasma arc, as will be more fully described below. Alternatively, when two separate DC power supplies are used, each one is connected to one of the top electrodes and the bottom cathode electrode. 
     The bottom  16  of the reactor vessel  14  defines a hearth for receiving a molten metal bed or bath  26  which is heated by the DC graphite electrode  28  (anode) and a conductive plate defining a cathode electrode  30 . The anode electrode  28  extends downwardly with its lower end being submerged in the molten bath  26 . The cathode electrode  30  is mounted to and forms a portion of the bottom  16  of the reactor vessel, facing opposite to the anode electrodes. Alternatively, it should be understood by those skilled in the art that a single cathode electrode may be formed in the center of the bottom  16  of the reactor vessel or multiple cathodes may be spaced uniformly throughout the bottom  16  of the reactor vessel in lieu of using the conductive plate as illustrated. 
     During operation, the molten bath  26  filling the bottom  16  of the reactor vessel  14  will be separated into a bottom metal (iron) layer  34  and an inorganic “foamy” or “gassy” slag layer  36 . It will be noted that the lower end of the anode electrode  28  is preferably submerged into the slag layer  36 . The waste materials are fed into the vessel  14  via a feeder extrusion tube  38  and opening  40 . By injecting the waste materials directly into the slag layer  36  of the molten bath  26 , the waste materials are immediately subjected to very high temperatures, i.e., above 2900 degrees F., that completely disassociates the waste materials. 
     The organic portion of the waste material will disassociate into the synthetic gas (or “syngas”)  44  consisting of a carbon and hydrogen mixture. The inorganic portion of the waste material will be melted with the metal oxides and will be reduced to a metal, which is accumulated at the bottom of the molten bath. All of the inorganic compounds will form the vitreous slag layer  36  disposed above the metal layer  34 . 
     A gas vent or duct  48  is also provided in the upper end of the reactor vessel  14 , which is designed to convey the produced syngas  44  at a temperature of about 875 to 1,000 degrees C. via a gas pipe  52  for further processing. The gas pipe  52  has a diameter to control the gas exiting velocity in order to minimize particulate entrapment and to maximize the efficiency of the plasma gasification. 
     The process of the present invention for converting the mixture of organic and inorganic portions of the waste materials into the vitreous slag and the syngas will now be explained. Initially, it should be understood that the present process has particular applications for the destruction of a wide variety of waste materials as well as for use in such industrial processes as coal gasification or the gasification of other waste materials. As the waste materials are delivered into the processing chamber  22  of the reactor vessel  14  by the feeder system  12 , the waste materials will absorb energy by convection, conduction, and radiation from the long plasma arc discharges generated, the hot vitreous slag, the heated refractory lining, and the heated gases circulating within the processing chamber  22 . As the organic portion of the waste materials is heated, it becomes increasingly unstable until it eventually disassociates into its elemental components consisting mainly of carbon and hydrogen. 
     The syngas  44  expands rapidly and flows from the processing chamber  22  to the gas pipe  52  via the gas vent or outlet  48 , carrying with it a portion of any fine carbon particulate generated by the disassociation of the waste. The process is designed to deliver the syngas  44  at a temperature of about 875 to 1,100 degrees C. for further processing. The gas pipe  52  is designed to be airtight so as to prevent the syngas  44  from escaping or allowing atmospheric air to enter. The gas pipe  52  is also preferably refractory lined in order to maintain the effective temperature of the syngas  44  above 875 degrees C. to substantially prevent the formation of complex organic components and to recover as much of the latent gas enthalpy as possible. Gas pipe  52  includes exhaust fan  62  for creating a low pressure area downstream from the vent  48  to assist in drawing syngas  44  from the reaction chamber  22 . 
     Those skilled in the relevant arts will recognize that the reactor interior environment is ionized. Ionized gas molecules may be drawn out of the reactor and into the exhaust vent  48  of the plasma vessel. A concern arises that due to the high energy levels found in ionized gases, full reforming reactions desired may not have completed before entry into the gas pipe  52 . As such, unreformed gases will move into the gas pipe  52  where the control of temperatures is not that accurate. A possible undesired result is, therefore, reformations of gases into undesired chemicals. 
     To ameliorate this, the gas pipe  52  is adapted to include a Venturi  58 . This Venturi  58  will cause an area of high pressure  60  relative to the remainder of the conduit to be generated prior exacted upon the gas as it is drawn through the throat. The high pressure area  60  will accelerate reaction time and thus improve the chances that all reformation will occur in the reactor and not in the ductwork. Any head losses caused by the Venturi  58  should be small enough that they can be compensated by the exhaust fan  62 . Like the reaction chamber, the surface of the Venturi  58  should be refractory lined. A Venturi  58  comprises at least a first, or starting diameter  71  which is the portion of the conduit in direct communication with the reactor, and a second, narrower diameter  75 . It is known in the art that in the region of the second diameter an area of lower pressure exists. 
     The internal diameter of the Venturi  58  will depend upon the density of the syngas and its velocity. The density of the syngas depends upon the material processed in the reactor. The velocity depends in part upon the conduit internal diameter and the exhaust fan. Issues such as gas viscosity, Bernoulli&#39;s Principle, Reynold&#39;s Number and friction losses caused by the walls of the Venturi are also significant, as would be appreciated by those skilled in the relevant arts. It is possible to operate this and other systems using additional oxygen and have complete oxidation of the gases. As the purpose of the use of a Venturi is to increase the efficiency of the system, care must be taken to size the Venturi with an awareness of the efficiencies of the draft generating mechanism in the system. With this in mind, a Venturi suitable for application in this invention should have starting diameter and a narrow diameter dimensioned to provide up to about a 3 psi pressure differential between the high pressure area to the low pressure area. 
     As described above and shown in the associated drawings, the present invention comprises a gas conduit for plasma gasification reactors. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is, therefore, contemplated that any claims issuing in an ensuing patent will cover any and all such modifications that incorporate those features or those improvements that embody the spirit and scope of the present invention.