Plastic pyrolysis plant with a screw conveyor arranged in a reactor tube

Abstract

To improve a plastic pyrolysis plant with at least one reactor tube for heating a conveyed material, wherein a screw conveyor is arranged in the reactor tube for conveying the conveyed material, which has a screw shaft extending in the longitudinal direction of the reactor tube and a screw wing extending circumferentially around the screw shaft, in such a way that a better temperature distribution and mixing is achieved when heating the conveyed material inside the reactor tube, it is proposed that the screw wing be shaped in such a way that it causes the conveyed material to be conveyed in the axial direction and additionally in the radial direction towards the screw shaft.

Description

Technical field

[0001] The invention relates to a plastic pyrolysis plant with at least one reactor tube for heating a conveyed material, wherein a conveying screw is arranged in the reactor tube for conveying the conveyed material, which has a screw shaft extending in the longitudinal direction of the reactor tube and screw wings extending circumferentially around the screw shaft. State of the art

[0002] EP 029 7424 B1 describes a process for cooling hot pyrolysis gas produced during the pyrolysis of waste material containing plastic, rubber or other hydrocarbons, wherein the pyrolysis oil obtained is cooled by direct heat exchange in at least two cooling stages through which the pyrolysis gas flows successively. Description of the invention: Problem, solution, advantages

[0003] The object of the present invention is to improve a plastic pyrolysis plant with at least one reactor tube for heating a conveyed material, wherein a conveying screw is arranged in the reactor tube for conveying the conveyed material, which has a screw shaft extending in the longitudinal direction of the reactor tube and a screw wing extending circumferentially around the screw shaft, in such a way that better mixing of the conveyed material is achieved when passing through the reactor tube.

[0004] According to the invention, it is proposed that the screw wing is shaped in such a way as to convey the conveyed material in the axial direction and additionally in the radial direction towards the screw shaft.

[0005] In the reactor tube of the plastic pyrolysis plant, a thermochemical cracking of organic compounds is achieved through targeted heat application with complete exclusion of oxygen.

[0006] The plastic pyrolysis plant is used for the thermochemical decomposition of organic compounds through targeted heat application at temperatures exceeding 350°C. This leads to the breaking of bonds within large molecules in the complete absence of oxygen. Its primary function is to process PE- and PP-containing plastic waste, primarily to obtain pyrolysis oil and gas.

[0007] A plastics pyrolysis plant is therefore a process engineering facility for processing plastic waste (polyolefins) to recover valuable materials such as high-quality oils, gases, diesel, and carbon. Possible substances and mixtures include LDPE, HDPE, LLDPE, PP, PP+C, and / or PE.

[0008] The plastics pyrolysis plant operates on the basis of the thermochemical decomposition of organic compounds at temperatures exceeding 350°C. For example, the substance or mixture of substances, or the material being processed, is heated inside the reactor tube to a temperature range between 400°C and 600°C. This process differs from gasification and combustion because it occurs solely through heat and in the absence of oxygen. Gases, liquids, and solids are produced, with the proportions and composition of each depending not only on the specific material but also on the process temperature, the added additives, the pressure conditions, and the treatment duration.

[0009] The reactor tube has an inlet and an outlet on opposite ends. The screw conveyor is arranged longitudinally inside the reactor tube and conveys the material from the inlet to the outlet, i.e., along the length of the reactor tube, meaning axially. For this purpose, the screw shaft is positioned centrally within the reactor tube.

[0010] Heating elements, such as heating sleeves, are arranged on the outer wall of the reactor tube to heat the tube wall. Several individually controllable heating elements can be arranged in series along the length of the reactor tube. This allows for a continuous increase in temperature from the inlet to the outlet. The heating elements can be individually controlled.

[0011] The screw conveyor guides the material through the reactor tube in an axial direction, i.e., the main conveying direction. The material is guided primarily along the inner wall of the reactor tube, where it is heated by the heat input from the heating elements located on the outer wall of the reactor tube.

[0012] A disadvantage of this is that only a small amount of heat exchange takes place within the conveyed material towards the screw shaft, as the conveyed material is not mixed well enough when it is pulled along the inner wall of the reactor tube.

[0013] According to the invention, the screw flight is shaped to also convey material radially towards the screw shaft. This guides the conveyed material from the inner wall of the reactor tube towards the screw shaft, resulting in better and more continuous mixing of the material radially along the entire conveying path. Consequently, the material exhibits more uniform temperatures in the radial direction. With thorough mixing, the temperature of the material near the screw shaft can be almost identical to the temperature of the material near the inner wall of the reactor. This transforms the material, or the polymer melt, into a free-flowing liquid, thereby reducing its viscosity.

[0014] Preferably, the screw flight is angled inwards towards the screw shaft, at least in sections. Particularly preferably, the screw flight is angled not only in sections, but completely, i.e., along the entire length of the screw shaft. For the purposes of the invention, an angled screw flight means that it is bent in such a way as to create a geometric break. This further promotes radial conveyance towards the screw shaft.

[0015] It is also preferably provided that the screw flight has cutouts. By providing cutouts in the screw flight, a screw flight with a multitude of wings is created, or a conveying screw with a multitude of screw flights arranged around the screw shaft.

[0016] The cutouts preferably extend radially from an outer flank of the screw blade. Thus, the cutouts are directed from the outer flank or outer edge of the screw blade towards the screw shaft. For the purposes of the invention, the outer flank of the screw blade is the end face circumferential edge of the screw blade, or the section of the blade that faces the inner wall of the reactor tube. For example, the cutout can extend over at least 50% of the width of the screw blade. However, it is particularly preferred that the cutout extends over at least 25% of the width of the screw blade.

[0017] Furthermore, it is preferably provided that the cutouts are V-shaped. The process gas generated during heating can then flow axially through the V-shaped cutouts towards the gas outlet without back pressure. This prevents the build-up of overpressure inside the reactor tube, which further increases overall process safety.

[0018] Preferably, the snail wing, or the wing blades formed by the cutouts, are angled at an angle between 5° and 45°, more preferably between 10° and 30°, and most preferably between 12° and 20°. In particular, the snail wing, or the wing blades, can be angled at 15°.

[0019] The combination of the angled screw wing and the cutouts or the wing blades of the screw wing created by the cutouts results in a kind of interlocking of these wing blades, which further promotes conveyance in the radial direction.

[0020] Preferably, the screw conveyor has at least two sections in the axial direction with different screw flight geometries. This allows the changes in the conveyed material to be taken into account along the conveying path. For example, the geometry in the solid phase area can be designed differently than in the liquid phase area.

[0021] Furthermore, it is preferably provided that the at least two sections extend over different lengths. That is, the at least two sections with different screw flight geometries are of different lengths. For example, the first section could be shorter than the second section, since the conveyed material is still in the solid phase in the area of ​​the first section, but relatively quickly begins to become viscous and thus transitions into the liquid phase.

[0022] It is also preferably provided that the screw flight has V-shaped cutouts, with the cutouts in a first section being smaller than in a second section. The first section is positioned upstream of the second section in the conveying direction. The conveyed material thus passes through the first section first and then the second section.

[0023] The size of the V-shaped cutouts can be defined by the depth of the cutout and / or the cutout angle. According to the invention, in the first section, the V-shaped cutouts are thus formed over a smaller width of the worm gear and / or have a smaller cutout angle. In the second section, by contrast, the V-shaped cutouts are arranged over a larger width of the worm gear and / or have a larger cutout angle.

[0024] The larger V-shaped cutouts in the second section increase the mixing and thus the Reynolds number of the conveyed material in the liquid phase. Furthermore, this intensifies the crossflow along the screw shaft, causing the impeller blades along the shaft to draw the liquid or conveyed material radially. This forced flow guides the liquid or conveyed material precisely along the inner pipe wall and thus the heat transfer surface.

[0025] The aim is to reduce the time required for liquid evaporation through the geometry described in the second section, thereby increasing the overall efficiency of the pyrolysis reactor. By improving the effective heat transfer surface, the temperature difference between the electrical heating elements on the outer wall of the reactor tube and the process medium or material inside the reactor tube can be reduced. This saves electrical energy for heating the heating elements. Furthermore, the V-shaped geometry reduces the deposition of solids, as these can now be sheared off more effectively.

[0026] Preferably, heating elements in the form of heating sleeves are arranged circumferentially around the reactor tube, with several individually controllable heating elements arranged one behind the other in the longitudinal direction of the reactor tube, such that an outer wall of the reactor tube is encased at least 80%, preferably completely.

[0027] The plastic pyrolysis plant preferably has a second reactor tube with a second screw conveyor. Both reactor tubes are arranged one behind the other with respect to the conveying direction. This means that the material is first passed through the first reactor tube and then conveyed through the second reactor tube.

[0028] Both reactor tubes can be identical or different in design. This means that the two reactor tubes can have the same or different lengths and diameters. Furthermore, the heating elements on the outer wall of the reactor tubes can be controlled differently; that is, different target temperature ranges can be provided for the first and second reactor tubes.

[0029] Furthermore, the two screw conveyors can be identical or different in design. In particular, the second screw conveyor, i.e., the screw conveyor in the second reactor tube, has a similar geometry to the second section of the first screw conveyor. However, the second screw conveyor can also have sections with different blade geometries. Brief description of the drawings

[0030] The invention is explained below by way of example using preferred embodiments. The schematic representations show: Fig. 1: An exploded view of a screw conveyor that can be inserted into a reactor tube, Fig. 2: a perspective view of a section of a screw conveyor, and Fig. 3: A schematic diagram of the components of a plastics pyrolysis plant. Preferred embodiments of the invention

[0031] Fig. Figure 1 shows an exploded view of a screw conveyor 11 that can be inserted into a reactor tube 10. The reactor tube 10 is part of a plastic pyrolysis plant 100, which is shown in the following diagram for clarity: Fig. 1 itself is not shown.

[0032] The material being conveyed is transported longitudinally or axially 14 through the reactor tube 10 by means of the screw conveyor 11. During this process, the material is continuously heated. Heating elements 20 are arranged on the outer wall of the reactor tube for this purpose.

[0033] The screw conveyor 11 has a screw shaft 12 extending longitudinally along the reactor tube 10 and a screw flight 13 extending circumferentially around the screw shaft 12. By continuously rotating the screw conveyor 11 within the reactor tube 10, the material is continuously conveyed in an axial direction 14 over the entire length of the reactor tube 10, i.e., from the inlet to the outlet.

[0034] The material being conveyed is heated by contact with the inner wall of the reactor tube 10. To ensure more uniform heating, the screw flights 13 are shaped to also convey the material radially 15 towards the screw shaft 12. This results in better mixing of the material and a more uniform temperature distribution within it.

[0035] In Fig. Figure 2 is a perspective view of a section of the screw conveyor 11. Fig. 1 shown.

[0036] The screw conveyor 11 has two adjacent sections in the axial direction 14, namely a first section 18 and a second section 19 with different screw flight geometries 13. In both sections 18 and 19, the screw flight 13 is cut and has V-shaped notches. These V-shaped notches form individual flight blades, which are additionally angled or cranked inwards towards the screw shaft 12.

[0037] The V-shaped cutouts 16 and the angled blades of the screw wing 13 facilitate the conveying of the material in a radial direction 15.

[0038] By providing two sections 18 and 19 with different screw vane geometries 13, the change in the conveyed material due to heating within the reactor tube 10 is taken into account. In the first section 18, the V-shaped cutouts 16 are smaller than in the second section 19. In the transition area from the first section 18 to the second section 19, the conveyed material assumes a more viscous or more liquid state, whereby the mixing of the conveyed material in this area is promoted by the larger V-shaped cutouts.

[0039] Fig. Figure 3 shows a plastic pyrolysis plant 100 with its essential components. In this example, there are two reactor tubes 10, 21, each with a screw conveyor 11, 22 (the screw conveyors 11, 22 are shown in the diagram for clarity). Fig.(3 not shown) is provided. The material passes through both reactor tubes 10, 21 sequentially. Subsequently, the resulting pyrolysis gas is condensed in two condensation stages 5, 6 and the remaining solids are collected via the solids discharge 31. Reference symbol list 100 plastic pyrolysis plants 10 reactor tube 11 auger 12 worm shaft 13 snail wings 14 axial direction 15 radial direction 16 Excerpt 17 Outer flank of the snail's wing 18 first section 19 second section 20 heating elements 21 second reactor tube 22 second screw conveyor 30 valve 31 Solids discharge 32 Capacitor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 029 7424 B1

[0002]

Claims

[1] Plastic pyrolysis plant (100) with at least one reactor tube (10) for heating a conveyed material, wherein a conveying screw (11) is arranged in the reactor tube (10) for conveying the conveyed material, which has a screw shaft (12) extending in the longitudinal direction of the reactor tube (10) and a screw vane (13) extending circumferentially around the screw shaft (12), characterized by , that the screw vane (13) is shaped in such a way as to convey the conveyed material in the axial direction (14) and additionally in the radial direction (15) towards the screw shaft (12). [2] Plastic pyrolysis plant (100) according to claim 1, characterized by , that the worm blade (13) is angled inwards towards the worm shaft (12) at least in sections. [3] Plastic pyrolysis plant (100) according to claim 1 or 2, characterized by , that the snail wing (13) has cutouts (16). [4] Plastic pyrolysis plant (100) according to claim 3, characterized by , that the cutouts (16) extend from an outer flank (17) of the snail wing (13) in a radial direction (15). [5] Plastic pyrolysis plant (100) according to one of claims 3 or 4, characterized by , that the cutouts (16) are v-shaped. [6] Plastic pyrolysis plant (100) according to any one of claims 2 to 5, characterized by that the snail vanes (13) are angled at an angle between 5° and 45°, preferably between 10° and 30°, particularly preferably between 12° and 20°. [7] Plastic pyrolysis plant (100) according to one of the preceding claims, characterized by , that the screw conveyor (11) has at least two sections (18, 19) with different geometries of the screw wings (13) in the axial direction (14). [8] Plastic pyrolysis plant (100) according to claim 7, characterized by , that the at least two sections (18, 19) extend over different lengths. [9] Plastic pyrolysis plant (100) according to one of claims 7 or 8, characterized by , that the snail wings (13) have v-shaped cutouts (16), the cutouts (16) being smaller in a first section (18) than in a second section (19). [10] Plastic pyrolysis plant (100) according to one of the preceding claims, characterized by , that heating elements (20) in the form of heating sleeves are arranged circumferentially around the reactor tube (10), wherein several individually controllable heating elements (20) are arranged one behind the other in the longitudinal direction of the reactor tube (10), such that an outer wall of the reactor tube (10) is encased at least 80%, preferably completely. [11] Plastic pyrolysis plant (100) according to one of the preceding claims, characterized by , that the plastic pyrolysis plant (100) has a second reactor tube (21) with a second screw conveyor (22).

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