Abstract:
Apparatus and method for treating waste products containing plastic materials by pyrolysis is disclosed. The method includes pyrolytically decomposing the waste products containing plastic materials by thermolysis to obtain useful liquid and gaseous organic raw materials. The method is carried out continuously.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from German patent application 10 2007 027629.1 filed on 12 Jun. 2007, the contents of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an apparatus for and a method of a method of obtaining liquid and gaseous organic raw materials from waste containing plastic material by way of thermolysis. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are methods that can be used to process hydrocarbon-containing and/or halogenated waste products to produce useful raw materials by incinerating them at high temperature in an open flame and utilizing the energy obtained from this. 
         [0004]    Unfortunately, during the incineration of hydrocarbon-containing and/or halogenated waste products a large number of different reaction products are obtained which are questionable in varying degrees as regards their environmental compatibility. Moreover, these processes tend to be conducted at temperatures of between 800 to 1600° C. which can result complete degradation of the potentially useful waste products and the production of toxic by-products. 
         [0005]    EP-A-0 592 057 discloses a process for the pyrolysis of used vehicle tyres, and an apparatus for carrying out the process. The pyrolysis takes place with the exclusion of air and water and is operated under reduced pressure at an operating temperature of 450-550° C., preferably below 500° C. This process can have limited applicability with respect to the types of waste materials which maybe processed, for example, upon thermolysis or pyrolysis some plastic materials there is a tendency to give off large amounts of gas in a short time severely disrupting the efficacy of the overall process. 
         [0006]    Another common disadvantage of the known methods and apparatus for processing of hydrocarbon containing waste materials is that the resultant product mixture is of a low grade and only contains relatively small amounts of high-grade fractions such as gasoline and kerosene. Moreover, many of the known processes are batch processes which generally do not easily lend themselves to economical scaling. 
         [0007]    It is desirable that the present invention provide an apparatus and a method with which it is possible to process a wide variety of plastic wastes which, for example, contain polyethylene, polypropylene or polystyrene. 
         [0008]    In that respect the apparatus and the method are to be such that as far as possible no harmful substances such as for example dioxins are produced in the thermolysis of the plastic material-containing waste. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with aspects of the invention there is provided an apparatus having a container which is closed except for inlets and outlets and which in operation is to be filled with a liquid metal bath up to a liquid metal level and which has a gas space above the liquid metal level. In addition the container has a waste feed opening for feeding waste to be treated and a residual material outlet opening for solid waste residues. Arranged between the waste feed opening and the residual material outlet opening is a substantially horizontally extending waste conveyor device which is adapted to convey waste, at least in portion-wise manner, beneath the liquid metal level from the waste feed opening to the residual material outlet opening and in that operation to periodically dip the waste which floats up in the liquid metal bath deeper into the liquid metal bath. The apparatus also has a gas feed line for an inert gas, which opens into the gas space, and a gas outlet which is connected to the gas feed line to afford a gas circuit, by way of conduits. Arranged in the gas circuit is a condenser for condensing condensable gas constituents of the gas which is flushed out of the gas space and which is produced by thermolysis or pyrolysis. Opening into the condenser is a carrier liquid feed line by way of which a for example parafins-dissolving carrier liquid can be introduced into the condenser in such a way that for example condensed parafins which are deposited at the condenser walls can be dissolved by the carrier liquid and flushed away. Arranged at the base point of the condenser is a liquid discharge line in order to be able to discharge the carrier liquid together with the thermolysis products dissolved therein. In addition condensed, liquid thermolysis products such as for example oils can also be discharged by way of the liquid discharge line. 
         [0010]    In some embodiments, a sacrificial tub is provided for the liquid metal bath, which tub can be replaced without the complete container having to be renewed. That is advantageous because the liquid metal used is, in some embodiments, liquid tin which results in severe corrosion of other metals. 
         [0011]    The component parts of the apparatus including the container and the waste conveyor device comprise stainless steel of type 1.43.01 in some embodiments. 
         [0012]    The conveyor device is enclosed by its own casing within the container in some embodiments. The casing extends in a first portion of the conveyor device near the waste feed opening, in part above the liquid metal level, so that its own gas space is formed within the casing. In the further configuration of the conveyor device, to a position in the proximity of the residual material outlet opening, the casing of the conveyor device and thus the conveyor device itself extends beneath the level of the liquid metal. 
         [0013]    In some embodiments, the conveyor device has conveyor elements which are arranged around an at least approximately horizontally extending axis of rotation of the conveyor device. 
         [0014]    It is advantageous if the axis of rotation and thus the conveyor device are not oriented exactly horizontally but rise slightly in the conveyor direction. That promotes transportation of the waste which has a tendency to float up in the liquid metal bath. 
         [0015]    In some embodiments, the conveyor elements include rotating blade-like entrainment members which rotate about the axis of rotation and which extend at least approximately as far as the casing of the conveyor device and which go in the proximity of the axis of rotation into a chute plate extending inclinedly relative to the axis of rotation. In that case the chute plate is arranged in such a way that it moves away from an edge of the entrainment members, which is near the casing, to an increasing extent in the conveyor direction, and is also arranged on the flat side of the entrainment member, which leads in the direction of rotation, so that waste material engaged by the entrainment member is pushed in a downward movement of the entrainment member beyond the horizontal by buoyancy forces along the entrainment member in the direction of the axis of rotation of the conveyor device and there encounters the chute plate. As a consequence of the orientation of the chute plate the waste residues which tend to float up then slide along the chute plate in the conveyor direction into a next longitudinal portion of the conveyor device, which also has an entrainment member with a chute adjoining same. 
         [0016]    Besides those entrainment members the conveyor device, in some embodiments, has further entrainment plates which extend in the longitudinal direction of the conveyor device in parallel relationship with the axis of rotation and which extend in the radial direction to close to the casing wall. In comparison with the entrainment members however the entrainment plates are substantially shorter in the radial direction. 
         [0017]    In some embodiments, the conveyor device has a plurality of longitudinal portions with a respective entrainment member and a chute. One or two first longitudinal portions of the conveyor device, which are near the waste feed opening, are of a larger diameter than further longitudinal portions, adjoining same, of the conveyor device. The larger diameter of the conveyor device in its initial region also results in a casing of larger diameter which—as already mentioned—projects upwardly at least in part beyond the liquid metal level. That part of the casing of the conveyor device has its own gas space for receiving the pyrolysis gases which are almost abruptly produced when the waste to be treated dips into the liquid metal bath. 
         [0018]    In some embodiments, for feeding the waste there is provided a waste feed means which passes through an outer upper wall of the container and which opens from above into the casing of the conveyor device. 
         [0019]    At the end of the conveyor device in the proximity of the residual material outlet the casing of the conveyor device, on its top side, beneath the liquid metal level, also has an opening which opens into a discharge chamber whose flat bottom extends precisely at the level of the liquid metal surface. By virtue of the opening at the end of the conveyor device, solid residual materials of the waste can float up to the level of the liquid metal. Arranged in the discharge chamber is a rotating bladed wheel having blades which extend as far as the bottom of the discharge chamber and the edge of the discharge chamber. Those blades are of such a configuration that they pass uniformly over an entry opening of the discharge chamber, which opening is in communication with the outlet opening of the casing of the conveyor device at its end, and in so doing entrain solid residues which are floating on the surface of the liquid metal. Arranged in the bottom of the discharge chamber, on the side remote from the entry opening, is a fall opening through which residual materials transported by the blades of the bladed wheel can drop out of the discharge chamber. 
         [0020]    The individual longitudinal portions of the conveyor device are fixedly connected together so that they can rotate jointly at the same speed about a common axis of rotation. Alternatively individual longitudinal portions of the conveyor device can move at different speeds of rotation. 
         [0021]    Electrical heating elements are provided for heating the liquid metal bath. Tubular heating element receiving means which are accessible from an upper cover of the container and which extend to below the level of the liquid metal are provided for receiving the electrical heating elements. The arrangement has a plurality of those heating element receiving means so that the liquid metal can be heated with a plurality of electrical heating elements. The arrangement of the heating element receiving means, extending from an upper cover of the container, has the advantage that no liquid metal can escape to the exterior from the container through the heating element receiving means, in the event of damage to the heating element receiving means. 
         [0022]    The method according to the invention for the treatment of plastic material-containing waste comprises the following steps: 
         [0023]    introducing waste into a container containing a liquid metal bath and a gas atmosphere thereabove; 
         [0024]    immersing the waste into the liquid metal bath; 
         [0025]    conveying the waste within the liquid metal bath to produce thermolysis gas and solid residue materials; 
         [0026]    flushing the gas atmosphere with an inert gas; 
         [0027]    separating the thermolysis gas from the inert gas in a condenser; 
         [0028]    dissolving condensed pyrolysis gas in a carrier liquid; 
         [0029]    draining the carrier liquid and liquid condensed thermolysis products from the condenser, and 
         [0030]    removing remaining solid materials from the liquid metal bath. 
         [0031]    In some embodiments, the method is carried out continuously. 
         [0032]    An oil or tuluol is used as the carrier liquid in some embodiments. 
         [0033]    In some embodiments, lime is added to the liquid metal bath for binding chlorine which is produced in the course of the thermolysis operation. The method is carried out at temperatures of between 450° C. and 500° C. 
         [0034]    In some embodiments, tin is entirely or predominantly used as the metal for the liquid metal bath. 
         [0035]    In some embodiments, the method is carried out in such a way that the residence time of waste to be treated in the liquid metal bath is about two minutes. 
         [0036]    In some embodiments, the waste to be treated is conveyed in an at least approximately horizontal direction in the liquid metal bath. 
         [0037]    Further advantages of the invention and other variants will be apparent from the description hereinafter of a preferred embodiment by way of example and further appending claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    The invention will now be described in greater detail by means of an embodiment by way of example with reference to the Figures in which: 
           [0039]      FIG. 1   a  shows an external top view of the apparatus for the treatment of waste, 
           [0040]      FIG. 1   b  shows an external bottom view of the apparatus for the treatment of waste, 
           [0041]      FIG. 2  shows a section through the apparatus for the treatment of waste, 
           [0042]      FIG. 3  shows a view of the apparatus with the cover removed, 
           [0043]      FIGS. 4   a ,  4   b  and  4   c  show perspective views of the conveyor device from the outside, 
           [0044]      FIG. 5  shows a perspective view of rotating conveyor elements of the conveyor device, and 
           [0045]      FIG. 6  shows a perspective view of a bladed wheel for the discharge of solid waste residues from a discharge chamber of the apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    As can be seen from  FIGS. 1   a  and  1   b  the apparatus  10  for the treatment of waste materials has a container  12  with a tub-like lower portion  14  and a three-part cover  16 . The apparatus has a first electric drive  18  for driving rotating conveyor elements in the interior of the container. The apparatus has a second electric drive  20  for driving a bladed wheel for the discharge of solid waste residues. 
         [0047]    A central portion  22  of the three-part cover  16  has a total of ten heating element receiving means  24  which project from the cover  16  in the direction of the bottom of the tub-shaped lower portion  14  of the container  12 . A respective electrical heating element can be introduced into each of the heating element receiving means  24 . 
         [0048]      FIG. 2  shows a view in longitudinal section through the container  12  and discloses a conveyor device  30  which is arranged in the container, as an external view. The conveyor device  30  has a waste feed opening which is connected to a waste feed line  32 . Provided at the other longitudinal end of the conveyor device  30  is a residual material outlet opening which is connected by way of a short pipe connection  34  to a discharge chamber  36  of the apparatus  10 . The conveyor device  30  is enclosed by a casing  40  disposed in the container  12 . 
         [0049]      FIG. 3  shows the apparatus for the treatment of waste with the cover removed. That means that the conveyor device  30  in the interior of the tub-shaped lower portion  14  of the container  12  can be clearly seen, and it is also possible to clearly see the gas discharge lines  42  as well as the discharge chamber  38 , with a bladed wheel  46  arranged therein. 
         [0050]      FIGS. 4   a, b  and  c  illustrate the complete conveyor device  30  including the first electric drive  18  and the discharge chamber  38 . Connected to the casing  40  of the conveyor device are gas discharge lines  42  which serve for the discharge of vapours and gases produced as a consequence of the thermolysis operation.  FIG. 4   a  also clearly shows the waste feed opening  44  for the feed of waste to be treated, to the conveyor device  30 . 
         [0051]      FIG. 5  shows the rotating conveyor elements  50  disposed in the interior of the casing  40  of the conveyor device  30 . The conveyor elements  50  have a total of four longitudinal portions of which two longitudinal elements  52  which are near the waste feed opening are of a larger diameter than four other longitudinal portions  54 . Each longitudinal portion  52  or  54  of the rotating conveyor elements  50  has an entrainment member  56  which extends as far as the casing of the conveyor device  30  and which in the proximity of an axis of rotation of the rotating conveyor elements  50  goes into a chute  58 , the chute plate bottom  60  of which extends inclinedly with respect to the axis of rotation. 
         [0052]    In operation the rotating conveyor elements  50  rotate in a counter-clockwise direction in relation to  FIG. 5 . Waste material is engaged by a respective entrainment member  56  and when an entrainment member  56  moves downwardly in its downward movement beyond the horizontal, as a result of buoyancy forces, it slides in the direction of the chute  58 . As a consequence of the chute bottom  60  extending inclinedly with respect to the axis of rotation of the rotating conveyor elements  50  the upwardly floating waste substances are conveyed in the conveyor direction into the next longitudinal portion of the rotating conveyor elements  50  until the rotating waste materials reach the end of the rotating conveyor elements, which is shown at top left in relation to  FIG. 5 . 
         [0053]    Besides the entrainment members  56  the rotating conveyor elements  50  have a plurality of entrainment plates  62  which project from the inside as far as the casing  40  of the conveyor device  30 . 
         [0054]    In the fourth longitudinal portion of the conveyor device  30  the rotating conveyor elements  50 , instead of the entrainment plates, have a plurality of shafts with freely rotating toothed wheels  64  which are arranged thereon and which have an axis of rotation extending parallel to the axis of rotation of the rotating conveyor elements and which project to close to the casing  40  of the conveyor device  30 . The wheels  64  are suitable for comminuting solid waste constituents which pass between the casing  40  of the conveyor device  30  and the wheels  64 . 
         [0055]      FIG. 6  shows a portion  70  of the cover  16 , which covers the discharge chamber  38 . In addition  FIG. 6  shows the bladed wheel  46  and the second electric drive  20  for driving the bladed wheel  46 . The bladed wheel  46  is arranged in such a way that it passes over the bottom  72  of the discharge chamber  38 . The bottom  72  of the discharge chamber  38  is disposed exactly at the level of the surface of the liquid metal in the container  12 . Upwardly floating solid waste residue materials which issue from the conveyor device  30  by way of the connection  36  therefrom float in the entry opening of the discharge chamber  38  on the surface of the liquid metal bath and can thus be engaged by the blades  48  of the bladed wheel  46  when the bladed wheel  46  rotates. The waste residues are thereby conveyed by the blades of the bladed wheel  46  to the residual material outlet opening  76  in the bottom  74  of the discharge chamber  38 . The discharge chamber  38  is of a round configuration in plan, the diameter thereof corresponding to the width of the blades  48  of the bladed wheel  46 . 
         [0056]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.