Patent Publication Number: US-2015083572-A1

Title: Reactor for Gasifying and/or Cleaning, Especially for Depolymerizing, Plastic Material and Associated Method

Description:
The invention relates to a reactor for gasifying and/or cleaning, especially for the depolymerizing of plastic material, with (a) a reactor vessel for receiving a starting material, especially the plastic material, (b) a metal bath which is arranged in the reactor vessel and includes a liquid metallic material having a metal bath melting temperature, (c) a heating system for heating the plastic material in the reactor vessel and (d) a residual material-removal device for at least partially removing residual material which are produced during the gasification and/or cleaning of the starting material. 
     A reactor of this sort is described in WO 2010/130 404 and is used to gasify plastic materials, in particular polymers. To this end, the plastic material is introduced into the reactor vessel of the reactor, for example by extruder, where it comes into contact with a metal bath. The high temperatures and, where applicable, the present catalytic effect of the metal bath cause the depolymerization of the plastic material. 
     The starting material may comprise materials, which are either completely inert or not fully gasified, such that residual material is deposited. This residual material must be removed from the reactor vessel so that it remains in constant operation. It has been proven that the removal of the residual material is a restrictive factor with regards to enabling an economic operation of the reactor. 
     The invention aims to improve the removal of residual material from the reactor vessel. 
     DE 197 35 153 A1 describes a method and a device for gasifying of residual material. For this purpose, the starting material to be gasified is preferably introduced into a heated reactor, which has previously been filled with liquid slag, in such a way that an impulse causes the slag to rotate. The organic elements of the starting material are gasified and the mineral elements are fused and absorbed by the slag. This results in an increase in the volume of the slag. Should the slag volume exceed a particular limit, part of the slag runs through a side opening of a centrally located pipe in the reactor into a water bath, where it then solidifies. 
     DE 196 29 544 C2 describes a method for processing polyvinylchloride. In this method, the PVC is also added to a rotating slag bath, in which a gaseous part is separated off and the remaining material is absorbed by the slag. The resulting slag is also directed through a central outflow into a water bath. 
     The invention aims to improve the removal of the residual material from the reactor vessel. 
     The invention solves the problem by means of a reactor in accordance with the preamble, wherein the residual material-removal device comprises an overflow which is centrally arranged in the reactor vessel so that residual material that floating on the metal bath can be removed via the overflow. According to a second aspect, the invention solves the problem by means of an operation method for a reactor of this sort that includes the following steps: (i) raising a gauge of a metal bath so that the residual material enters the overflow, and (ii) removing the residual material through the overflow. 
     It has been proven that a centrally situated overflow is particularly well suited for the effective removal of residual material from the reactor vessel. It is thus advantageous if the overflow is always at the same temperature as the metal bath surrounding it. This eliminates the possibility of the residual material cooling down and clumping together upon removal. 
     A further advantage is that the gas development that occurs during the operation of the reactor enhances the removal of the residual material. It is a surprising revelation that the gas development on the radial outer edge of the inner space of the reactor vessel is particularly large. The rising gas bubbles slightly raise the gauge of the metal bath over a period of time, such that the residual material floating on the metal bath experience a force acting radially inwards. This results in a radially inward flow of residual material, which can be removed particularly effectively through the centrally located overflow. 
     The surprising realisation that the residual material has a preferred direction of flow, namely radially inwards, also contributes to a relatively rapid movement of the residual material into the overflow. If the overflow is arranged radially outwards, it may result in the formation of areas on the surface of the metal bath in which the residual material residence time is so high that the residual material clumps together. This results in the difficult removal of the residual material from the reactor vessel. 
     The central location of the overflow does have the disadvantage that it is more difficult to exert an external influence, for example to remove residual material that has stuck together. However, the above advantages more than compensate for this disadvantage. 
     The term reactor vessel should be understood in particular to mean a device which, during operation, accommodates the metal bath, the filling element and the starting material. 
     The term metal bath should be understood to mean a concentration of liquid metal, in particular molten metal, which takes the form of a liquid at an operating temperature of the reactor. 
     In particular, the metal bath comprises Wood&#39;s metal, the Lipowitz alloy, the Newton alloy, the Lichtenberg alloy and/or an alloy which contains gallium and indium. In principle, the metal bath has a density of more than 9 grams per cubic centimetre, so that the starting material experiences a strong buoyant force. The metallic material has a particular melting temperature of at least 300° C. 
     However, lower melting points are possible. The melting temperature preferably has a maximum value of 600° C. During operation of the reactor, the metal bath has a temperature of T from 300° C. to 600° C. 
     According to a preferred embodiment, the overflow consists of a removal pipe that is in thermal contact with the metal bath. This ensures that the removal pipe is of the same temperature as the metal bath, thereby avoiding the possibility of the materials clumping together when they cool down. The removal pipe is preferably a metal pipe, in particular a ferromagnetic metal pipe. 
     The term heater should be understood in particular to mean a device by means of which the plastic material can be directly or indirectly heated. In particular, the heater is an induction heater by means of which one component of the reactor can be heated. For example, the filling elements are ferromagnetic, so they can be heated by induction. However, it is conceivable that, in addition or alternatively to the filling elements, the overflow and/or the reactor vessel are ferromagnetic. 
     The starting material in particular is heated such that the filling elements are heated, which in turn heat the metal bath. The metal bath then transfers the heat to the starting material. 
     The residual material removal device is in particular a device by means of which the solid, fluid and/or paste-like matter that occurs during gasification and/or cleaning can be removed. 
     According to a preferred embodiment, a residual material support device is arranged inside the removal pipe, which is designed to use a mechanical impact to move residual material. For example, this may refer to a screw conveyor that can scrape along the inside of the removal pipe so as to prevent or remove blockages. 
     The removal pipe preferably has an inner pipe diameter that is at least a tenth of an inner reactor vessel diameter of the reactor vessel. This enables the efficient removal of the residual material. 
     It is beneficial if the residual material removal device comprises a storage vessel and a gas-tight lock, such that the storage vessel can be detached from the reactor vessel, while remaining gas-proof in the process. In other words, it is possible to detach the storage vessel from the reactor vessel without allowing the gas to infiltrate the reactor vessel and escaping out of the storage vessel. This reduces the risk of fire, as otherwise flammable gases can escape. 
    
    
     
       In the following, the invention will be explained in more detail with the aid of a drawing. It shows 
         FIG. 1  a reactor according to the invention for conducting a method according to the invention. 
     
    
    
       FIG. 1  shows a reactor  10  for gasifying a starting material in the form of plastic material  12 , in particular polyolefin polymers. The reactor comprises, for example, an essentially cylindrical reactor vessel  14  for heating the plastic material  12 , which is introduced into the reactor vessel  14  via an extruder  16 . 
     The reactor  10  comprises a heater, for example an induction heater  18 , which has a number of coils  20 . 1 ,  20 . 2 , . . . ,  20 . 4 , by means of which an alternating magnetic field is created in an inner space  22  of the reactor vessel  14 . The coils  20  (reference numbers without a numerical suffix refer to all respective object) are connected with a power supply unit, not depicted, which induces an alternating current on the coils. The frequency f of the alternating current is, for example, in the region of 4 to 50 kHz. Higher frequencies are possible, but they lead to an increase in the so-called skin effect, which is undesirable. 
     A deceleration device  24  is arranged in the inner space  22  of the reactor vessel  14 , by means of which the upward flow of liquefied plastic material  12  in the reactor vessel  14  can be slowed down. The deceleration device  24  comprises a number of movable filling elements  25 . 1 ,  25 . 2 , . . . arranged in the inner space  22 . These elements are made of ferromagnetic material and in the present invention take the form of spheres with a radius R. The sphere radius R may be between 0.5 and 50 millimetres, for example. 
     As a result of their ferromagnetic properties, the filling elements  25  are heated by the induction heater  18  and thereby heat a metal melt  26 , i.e. molten metal, present in the reactor vessel  14 . The specification that an object such as the filling elements  25  is made of ferromagnetic material means that the object is ferromagnetic at a room temperature of 23° C. 
     The filling elements  25  have a Curie temperature T C,25,  above which the magnetic susceptibility χ sinks abruptly. The connection to the electromagnetic field emitted by the induction heater suddenly becomes smaller and the filling element&#39;s  25  heat emission reduces dramatically. The heat input created by the induction heater is thus lower with hot filling elements than cold filling elements. 
     The metal melt  26  has a melting point of T Schmelz =300° C. and is introduced into the reactor vessel  14  to a filling level of H füll . Along with the plastic material, it fills the spaces of the filling elements  25 . For example, the metal melt  26  is made of Wood&#39;s metal, the Lipowitz alloy, the Newton alloy, the Lichtenberg alloy and/or an alloy that comprises gallium and indium. In principle, the metal melt  26  has a density of at least 9 grams per cubic centimetre, so that the plastic material  12  experiences a strong buoyant force. This buoyancy accelerates the plastic material  12 . The filling elements  25  counteract this acceleration. 
     A temperature T prevails in the reactor vessel  14 : this temperature is above a reaction temperature T R  at which the plastic material  12  gradually disintegrates. In this process, gas bubbles  28  are formed, which move upwards. The metal melt  26  can have a catalytic effect on the disintegration process, such that the reactor  10  may refer to a thermo catalytic depolymerisation reactor. The plastic material  12  introduced via the extruder  16  enters the inner space  22  through an entry opening  30 , which is preferably located on the base of the reactor vessel  14 . 
     The deceleration device  24  may comprise restraint devices, such as a grid stretched across a frame, whose mesh is so small that the filling elements  25  cannot move upwards through it. However, this is not necessary. For example, a filling of spheres is sufficient, as depicted here. The distribution of the filling elements  25 , in the present case the spheres, is schematically depicted in  FIG. 1 . 
     As a result of their buoyancy, one part of the filling elements  25  floats in the metal melt  26  and another part is pressed into the metal melt  26  by filling elements  25  that are positioned further up. The filling elements  25  are also depicted in  FIG. 1  in a constant radius R. It is possible that the filling elements have variable radii, wherein, for example, the radius R decreases in an upward direction. 
     In addition to this,  FIG. 1  depicts a removal pipe  36  arranged in the reactor vessel  14 , via which the residual material  38  floating on the metal bath can be removed. In the present case, the removal pipe  36  runs coaxially to a longitudinal axis L of the reactor vessel  14 . The residual material  38  is, for example, impurities of the plastic material  12  and/or the additional catalyst which can be introduced via the extruder  16  or a second available extruder. 
     The removal pipe  36  can be made of ferromagnetic pipe material with a pipe Curie temperature T C,36 . As a result, the removal pipe  36  heats up to T C,36  when the induction heater  18  is driven with a sufficiently high power. The pipe material Curie temperature T C,36  may, for example, correspond to the filling element Curie temperature T C,25, 1 : it may also be lower or higher. However, it is also possible that the removal pipe  36  is constructed using a non-ferromagnetic material, such as an austenitic steel or titan. 
     The reactor vessel  14  is constructed of a wall material on at least the side facing the inner space  22 . The wall material may be ferromagnetic, for example iron or magnetic steel. Alternatively, the wall material may also be non-magnetic. 
     If the wall material is ferromagnetic, it has a wall material Curie temperature T C,14 . This may be lower than the filling element Curie temperature T C,25 . In this case, the wall of the reactor vessel  14  is colder during operation than the filling elements  25 . 
     The removal pipe  36  is part of a pollutant removal system  40 . As typical residual material impurities  38 , such as sand, have a lower density than the metal bath  26 , they float and can be removed at the top. In addition, the pollutant removal system  40  comprises a storage vessel, which may also be referred to as a settling tank  48 , that collects residual material. The residual material  38  may contain not entirely depolymerized organic material, alongside inorganic material. The organic material floats on the inorganic material and can be lead back into the reactor vessel  14  through a recycling pipeline  50  on the bottom of the container. 
     The reactor  10  comprises a gas outlet  42  that flows into a condenser  44  and removes the resulting gas. The fluid material leaving the condenser  44  lands in a collector  46 . 
     The reactor described can be operated with, for example, waste oil as a starting material instead of plastic material, and then be used for recycling and processing. 
     A method according to the invention is conducted by initially raising the gauge H füll , for example, by introducing the metal bath  26  to the reactor vessel  14 . This may occur by introducing solid metal spheres made of the metallic material into the reactor vessel  14  so that they melt. It is also possible to increase the flow of plastic material  12 , in particular by operating the extruder at a higher power. This increases the volume of both gasified and non-gasified plastic material present in the reactor vessel  14 , so that the gauge H füll  rises, for example in the form of the removal pipe  36 . The residual material  38  are then removed: this means that they either automatically flow through the removal pipe or they are transported through the removal device by a corresponding device, in the present case the removal pipe  36 . 
     It can be advantageous to lower the supply of plastic material prior to raising the metal gauge so as to reduce the formation of gas bubbles. This has the advantage that less gas bubbles form, thereby decreasing losses in the metal bath caused by splattering. 
     The gauge will preferably be lowered again after raising the gauge in the metal bath and removing the residual material through the overflow, for example by draining the metal bath. 
     It is preferable if a gauge of the metal bath is set such that the residual material layer is set at a thickness H 38  of at least 10 cm, whereby the thickness H 38  may fall below this value when the metal bath gauge is raised for the removal of the residual material through the overflow. 
     In other words, the fact that the residual material layer has a thickness H 38  of at least 10 cm should be understood to mean that this thickness is achieved and exceeded at least 75% of the time. The thickness H 38  is the distance from the boundary layer between the metal bath and residual material layer to the upper edge of the residual material layer on the other. The thickness is preferably regulated by means of a feedback control system. This means that the reactor  10  has a thickness registration device, which is not depicted, by means of which the thickness Has can be recorded. Should a maximum thickness Has be exceeded, the above described method for the removal of residual material is conducted. 
     REFERENCE LIST 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 10 
                 Reactor 
               
               
                 12 
                 Plastic material 
               
               
                 14 
                 Reactor vessel 
               
               
                 16 
                 Extruder 
               
               
                 18 
                 Induction heater 
               
               
                 20 
                 Coil 
               
               
                 22 
                 Inner space 
               
               
                 24 
                 Deceleration device 
               
               
                 25 
                 Filling elements 
               
               
                 26 
                 Metal bath 
               
               
                 28 
                 Gas bubble 
               
               
                 30 
                 Entry opening 
               
               
                 32 
                 Catalyst 
               
               
                 34 
                 Outer wall 
               
               
                 36 
                 Removal pipe 
               
               
                 38 
                 Residual material 
               
               
                 40 
                 Pollutant removal system 
               
               
                 42 
                 Gas outlet 
               
               
                 44 
                 Condenser 
               
               
                 46 
                 Collector 
               
               
                 48 
                 Settling tank 
               
               
                 50 
                 Recycling pipeline 
               
               
                 χ 
                 Magnetic susceptibility 
               
               
                 f 
                 Frequency 
               
               
                 L 
                 Longitudinal axis 
               
               
                 R 
                 Sphere radius 
               
               
                 H full   
                 Filling height, gauge 
               
               
                 H 38   
                 Thickness 
               
               
                 d 14   
                 Reactor vessel inner diameter 
               
               
                 d 36   
                 Pipe inner diameter 
               
               
                 T Schmelz   
                 Metal bath melting 
               
               
                   
                 temperature 
               
               
                 T 
                 Temperature 
               
               
                 T R   
                 Reaction temperature 
               
               
                 T C,36   
                 Pipe material Curie temperature 
               
               
                 T C,25   
                 Filling element Curie temperature 
               
               
                 T C,14   
                 Wall material Curie temperature