Method for pyrolyzing plastic material and system therefor

Abstract

The invention relates to a method and a system for pyrolyzing plastic material. The method comprises the following steps: heating and compacting the plastic material; transporting the plastic material to one or more reactors; pyrolyzing the plastic material in one or more reactors; and maintaining the plastic material in a heated state during the transport step wherein the plastic material is transported at a positive angle to the horizontal plane.

Description

[0001] This application is a divisional application. The international application number of the original application is PCT / GB2020 / 053304, the filing date is December 18, 2020, the application number in the Chinese national phase is 202080095415.5, and the invention title is "Method and System for Pyrolyzing Plastic Materials". Technical Field

[0002] The present disclosure relates to a method and a system for pyrolyzing plastic materials. Background Art

[0003] End-of-life plastic chemical recycling is an emerging technology designed to recycle mixed waste plastics into various liquid hydrocarbon products. Waste plastics used in such processes can include, for example, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and / or polypropylene (PP). These waste plastics are converted into liquid hydrocarbon products by heating the plastic feed in a molten form and then pumping it into a reactor vessel. The reactor vessel is heated to a temperature above 350 °C by a combustion system. This produces saturated hydrocarbon-rich vapors from the molten plastic. The hydrocarbon vapors flow out of the reactor vessel through a contactor vessel and condense the heavier vapor fractions to maintain a target outlet temperature set point determined by the final product specifications. Then, the hydrocarbon vapors are distilled in a downstream condenser tower at a pressure close to atmospheric pressure. Summary of the Invention

[0004] According to the present invention, there is provided a method for pyrolyzing plastic materials, the method comprising the steps of: heating and densifying the plastic materials; transporting the plastic materials to one or more reactors; and pyrolyzing the plastic materials in one or more reactors; characterized in that the plastic materials are maintained in a heated state during the transportation step.

[0005] Optionally, the plastic materials are transported to two or more reactors, and the heated plastic materials are fed into one reactor at a time.

[0006] Optionally, the step of heating and densifying the plastic materials is achieved by extruding the plastic materials.

[0007] Optionally, the plastic materials are maintained in a molten state during the transportation step.

[0008] Optionally, the temperature of the plastic materials is maintained at a temperature within a target temperature range.

[0009] Optionally, the target temperature range is lower than the decomposition temperature of the plastic materials.

[0010] Optionally, the temperature of the plastic materials is maintained at a temperature of at least 265 °C.

[0011] Optionally, the temperature of the plastic material is maintained at a temperature of at least 280 °C.

[0012] Optionally, the temperature of the plastic material is maintained at a temperature not exceeding 310 °C.

[0013] Optionally, the temperature of the plastic material is maintained at a temperature not exceeding 300 °C.

[0014] Optionally, the plastic material is heated to a temperature within a target temperature range during the heating and densification steps.

[0015] Optionally, the plastic material is at a temperature within a target temperature range at the end of the heating and densification steps.

[0016] Optionally, the plastic material is transported at a positive angle to the horizontal plane.

[0017] Optionally, the angle is selected from the range of 10° to 45°.

[0018] According to the present invention, there is also provided a system for pyrolyzing plastic materials, the system comprising: a pump for heating and densifying plastic materials; one or more reactors for pyrolyzing plastic materials; and a pipe for transporting plastic materials between the pump and the one or more reactors; wherein the pipe is configured to keep the plastic materials in a heated state.

[0019] Optionally, the system includes two or more reactors, and the system further includes a plurality of valves arranged such that the heated plastic materials can be fed to one reactor at a time.

[0020] Optionally, the pump includes an extruder.

[0021] Optionally, the pipe is configured to keep the plastic materials in a molten state.

[0022] Optionally, the pipe includes a heating device.

[0023] Optionally, the heating device includes electric tracing.

[0024] Optionally, the pipe is oriented at a positive angle to the horizontal plane.

[0025] Optionally, the angle is selected from the range of 10° to 45°.

[0026] Optionally, the system includes a plurality of interlocking valves for feeding the heated plastic materials to two or more reactors. Description of the Drawings

[0027] Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, wherein:

[0028] Figure 1shows a schematic diagram of a known chemical recycling apparatus as disclosed in WO-A-2011077419;

[0029] Figure 2 shows a perspective view of an initial stage of a chemical recycling apparatus forming part of the present disclosure;

[0030] Figure 3 shows Figure 2 an alternative tube arrangement as shown; and

[0031] Figure 4 shows a Figure 2 system for Figure 3 or an alternative tube arrangement for a Detailed Description

[0032] Scrap or contaminated plastic waste feedstock for plastic chemical recycling can be received from, for example, municipal recycling facilities, recycling plants, or other plastic collection sources. In a pretreatment process, the feedstock can be refined such that it contains only plastics suitable for the chemical recycling process, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and / or polypropylene (PP). Unsuitable materials, such as metals, paper and cardboard, glass, and moisture in the plastic waste, can be removed.

[0033] Figure 1 Shows a known chemical recycling apparatus 1 as disclosed in WO-A-2011077419, in which the tube 2 of the present disclosure can be employed. The pretreated plastic feedstock can be processed into pellet or flake form, which can enter the system at one or more infeed hoppers 3. A conveyor belt 4 can transport the plastic material via a weighing belt 6 to a pump 5. The plastic material can be melted in the pump 5 by a heating process, which can involve one or more heating and cooling stages, with a final maximum temperature in the range of 300 °C. The molten plastic can be transported via the tube 2 to one or more reactors 10.

[0034] In one or more reactors 10, the feedstock can be heated in the absence of oxygen to effect pyrolysis such that the polymer molecules can decompose to form a saturated hydrocarbon vapor-rich gas. The hydrocarbon vapor can flow through a contactor 11 having a row of condenser elements 12. Some of the long-chain hydrocarbon components can be condensed, and the condensed long-chain material can be returned to the reactor 10 for further pyrolysis, thereby effecting thermal degradation into shorter carbon-carbon chains; the components can leave the contactor 11 as a vapor.

[0035] The hydrocarbon vapor from the contactor can be received by a condensation tower 13, which can separate the hydrocarbon vapor into condensable components and non-condensable syngas components by molecular weight.

[0036] Condensable components with a relatively large molecular weight can accumulate in one or more regions near the middle and bottom of the condensation tower 13 and can be extracted therefrom. For example, light oil and raw diesel can be extracted from the condensation tower 13.

[0037] Non-condensable syngas components with a relatively small molecular weight can accumulate in the region near the top of the condensation tower 13. These can be extracted from the top of the condensation tower 13 and can be used, for example, for combustion in a furnace (not shown) of the recovery device 1.

[0038] As a result of this process, condensable gases can be converted into hydrocarbon products, while non-condensable syngas can be separately collected and burned for process energy. The hydrocarbon products can be sold to the petrochemical industry, for example, to be converted back into the original plastics, oils, or into transportation fuels. The syngas can be used within the chemical recovery device.

[0039] Figure 2 More details are shown of the initial stage of the chemical recovery device 1 as Figure 1 shown before the pyrolysis of the feedstock. The feed system 30 can include a feed hopper 3 (or silo), a conveyor belt (not shown), a weighing belt (or weighing scale referred to as a "load cell") (not shown), and a pump 5.

[0040] Advantageously, the feedstock can be transported to each reactor 10 at a controlled temperature within a target temperature range. Optimally, the temperature of the feedstock can be as close as possible to the operating temperature of the reactor 10 so that it does not have an adverse effect on the thermal performance of the reactor 10; the temperature drop in the reactor 10 can be slowed down, and even the depolymerization process can be stopped. During the feeding stage, the operating temperature of the reactor 10 can be in the range of 380 °C - 410 °C. Additionally, if the temperature of the feedstock is too low, the feedstock may be too viscous to be transported along the pipe 2. In this regard, the temperature of the feedstock can be at least 265 °C, optionally at least 280 °C. This can ensure that the feedstock is in an appropriate molten state. However, if the temperature of the feedstock is too high, the feedstock may start to decompose before reaching the reactor 10. If the feedstock starts to decompose, coke (a form of carbon residue) may start to form, which can be disadvantageous, as described below. Therefore, the target temperature range can be lower than the decomposition temperature of the feedstock. In this regard, the temperature of the feedstock can be no greater than 310 °C, optionally no greater than 300 °C. Therefore, a suitable target temperature range can be 265 °C to 310 °C, optionally 280 °C to 300 °C.

[0041] The pump 5 can perform three functions: it can heat the raw material to a temperature within a target temperature range; it can densify the raw material, thereby removing any air pockets in the raw material; and it can provide a driving force to transport the raw material through the tube 2 to the reactor 10. In one exemplary embodiment, the pump 5 can include an extruder, which generally can include an auger 40 (or screw) located in a closely fitting barrel 41. These three functions can be achieved by the action of the auger 40. The pump 5 can heat the raw material from ambient conditions to a temperature within the target temperature range by applying shear force to the raw material, which is the result of the relative movement between the auger 40 and the wall of the barrel 41. In this way, the temperature of the raw material in the pump 5 can gradually increase towards the outlet 42 of the pump 5. This can be beneficial for achieving the temperature within the target temperature range. In contrast, the normal operation of existing pumps may be such that the temperature of the raw material peaks at a certain point within the pump and decreases towards the outlet. The pump 5 can be equipped with a variable speed drive (not shown), which can allow a lower flow rate to be fed to the reactor 10, if needed, while maintaining the temperature at the outlet 42 of the pump 5 within the target temperature range.

[0042] The pump 5 can be equipped with one or more dual heating and cooling zones 43. When the raw material passes through the auger 40, the one or more dual heating and cooling zones 43 can help incrementally control the temperature of the raw material. The heating function can be mainly used to melt the raw material entrained in the auger 40 during system startup. The cooling function can be used during normal operation to prevent the zone temperature from exceeding its respective set point. The heating function may be rarely used during normal operation because the shear force generated by the action of the auger screw can provide sufficient heat to melt the raw material and reach the temperature within the target temperature range at the outlet 42.

[0043] The cooling of the barrel 41 can be achieved by a closed-loop oil cooling circuit or a fan (not shown). Temperature sensors can monitor the temperature of each barrel zone. Overheating observed by the temperature sensors can cause the inlet valve on the corresponding barrel zone to open, or start a separate cooling fan, to allow cooling to the temperature set point.

[0044] The tube 2 can connect the pump 5 to one or more reactors 10. Preferably, the tube 2 can connect the pump 5 to a plurality of reactors 10. In Figure 2 One exemplary arrangement shown, the tube 2 can connect the pump 5 to one or more reactors 10 via a single header pipe 50. The header pipe 50 can be connected to each of the one or more reactors via respective feed pipes 61. In Figure 3In an alternative exemplary embodiment shown, the tube 2 may connect the pump 5 to one or more reactors 10 via an auxiliary tube 60, with an auxiliary tube 60 provided for each reactor 10. Each auxiliary tube 60 may be connected to its reactor 10 via a feed tube 61. In both arrangements, the feed tube 61 may generally be vertical.

[0045] The dense and molten raw material exiting the outlet 42 of the pump 5 may enter the tube 2 at a sufficient pressure and be driven along the tube 2 such that the raw material is driven along the tube 2 at the desired flow rate and temperature, provided that the pressure of the raw material when it reaches the reactor 10 is not too high considering the pressure drop along the tube 2. When leaving the pump 5 (i.e., at the pump outlet 42), the suitable pressure of the raw material may be in the range of 3 MPaG to 15 MPaG (30 BarG to 150 BarG), optionally 5 MPaG to 8 MPaG (50 BarG to 80 BarG).

[0046] Figure 4 The tube 2 is shown in more detail in [reference]. The tube 2 may be made of any suitable material (e.g., stainless steel or carbon steel). The tube 2 may be equipped with a heating device 51. The heating device 51 may include electrical tracing (also known as "heat tape" or "surface heating"). The heating device 51 may be used to ensure that the temperature within the target temperature range is maintained along the tube 2. The heating device 51 may also be used to heat (and melt) the existing raw material entrained in the tube 2 during system startup.

[0047] One or more temperature sensors 52 and / or pressure sensors (not shown) may be provided to monitor the temperature and pressure along the tube 2, thereby ensuring a stable flow. The temperature sensors 52 may include thermocouples. The tube 2 may also be equipped with an insulation 53.

[0048] The diameter of the tube 2 may be selected to be small enough such that heat can be retained in the tube 2 via the heating device 51 (or the raw material can be heated during system startup). However, the diameter must be large enough to achieve the desired flow rate and pressure. The diameter of the tube 2 may be selected from the range of 150 mm - 200 mm, optionally 200 mm.

[0049] The length of the pipe 2 can be minimized while maintaining a sufficient length to allow mechanical flexibility in the pipe 2 (so that the pipe 2 can absorb thermal expansion stress). Minimizing the length of the pipe 2 may be beneficial in reducing the extent of the heating device 51 required for the pipe 2. Minimizing the length of the pipe 2 may be beneficial in reducing the likelihood of "coking" in the pipe 2, and for a longer pipe 2, the risk of coking may be greater due to the longer residence time of the raw material in the longer pipe 2. If a continuous flow of the raw material is not maintained in the pipe 2 such that the raw material may remain in the pipe 2 at a high temperature for a long time, coke (a form of carbon residue) may start to deposit in the pipe 2. Such coke deposits can reduce the diameter of the pipe 2, thereby reducing the flow rate in the pipe 2 and increasing the pressure in the pipe 2. The coke deposits can also act as a heat insulation layer, which can result in the need for more energy input from the heating device 51. The length of the pipe 2 can be selected from the range of 5 m to 11 m, optionally 8 m.

[0050] The pipe 2 can be oriented at a positive angle to the horizontal plane such that it can be inclined at a generally upward angle (i.e., not downward or horizontally) in the direction from the pump 5 to the main pipe 50 or the auxiliary pipe 60. A suitable angle can be in the range of 10° to 45°. The raw material at a temperature within the target temperature range may have the potential to flow under gravity. Orienting the pipe 2 at an upward angle can ensure that the pipe 2 can only be discharged under the action of the pump 5 and not under the action of gravity. This can serve to prevent the pipe from being emptied during operation. If the pipe 2 is emptied, resulting in an opening in the pipe between the pump 5 and the reactor 10, the hydrocarbon vapor from the reactor 10 may be released into the open pump section, and / or air may enter the reactor system, which may lead to ignition.

[0051] If the pipe 2 is divided into two (or more) auxiliary pipes, a portion of the molten raw material in the pipe 2 may be simultaneously directed into each auxiliary pipe. Due to undefined and variable preferential flow, the molten raw material may not be evenly distributed between the two (or more) auxiliary pipes. Instead, one auxiliary pipe may have an unpredictable preferred flow. Thus, if multiple reactors 10 are simultaneously fed by their respective auxiliary pipes 60 (e.g., as Figure 3 shown), or if multiple reactors 10 are simultaneously fed by a single main pipe 50 (e.g., as Figure 2 shown), it may be extremely difficult (or even impossible) to control the volume of the raw material fed to each reactor 10, resulting in an inability to control consistent and repeatable batch cycles.

[0052] Advantageously, the feedstock can be changed to be delivered to only one reactor 10 at a time. Two or more reactors 10 can be sequentially fed through the pipe 2 via the main pipe 50 or the auxiliary pipe 60. Each reactor 10 can be equipped with a valve 54 to initiate or prevent the supply of feedstock to the respective reactor 10. Depending on the arrangement, the valve 54 for a particular reactor 10 can be located, for example, on the main pipe 50, the auxiliary pipe 60, or the feed pipe 61. The respective valves 54 for two or more reactors 10 can be interlocked to ensure that feedstock can only be fed to a single reactor 10 at any given time. This arrangement can allow a single pump 5 and a single pipe 2 to feed multiple reactors 10 independently of each other.

[0053] The structure of the main pipe 50 can be similar to that of the pipe 2. The main pipe 50 can include one or more of the following features of the pipe 2: the heating device 51; one or more temperature and / or pressure sensors; and / or the heat insulation layer 53. The main pipe 50 can be horizontally oriented. The diameter of the main pipe 50 can be selected from the range of 100 mm to 200 mm, optionally 150 mm. The length of the main pipe 50 can be selected from the range of 7 m to 16 m, optionally 11 m. The pressure in the main pipe 50 can be selected from the range of 1 MPaG to 6 MPaG (10 BarG to 60 BarG), optionally 2 MpaG to 4 MPaG (20 BarG to 40 BarG).

[0054] The structure of the auxiliary pipe 60 can again be similar to that of the pipe 2. The auxiliary pipe 60 can include one or more of the following features of the pipe 2: the heating device 51; one or more temperature and / or pressure sensors; and / or the heat insulation layer 53. The auxiliary pipe 60 can be horizontally oriented. The diameter of each auxiliary pipe 60 can be selected from the range of 100 mm to 200 mm, optionally 150 mm. The pressure in each auxiliary pipe 60 can be selected from the range of 1 MPaG to 6 MPaG (10 BarG to 60 BarG), optionally 2 MpaG to 4 MPaG (20 BarG to 40 BarG).

[0055] In use, at the start of the system (e.g., after turnaround), the existing feedstock that may be in a solid state and already entrained in the system can be heated. The feedstock entrained in the pump 5 can be heated using the heating function of one or more of the dual heating and cooling zones 43. The feedstock entrained in the pipe 2 can be heated using the heating device 51.

[0056] When the existing feedstock entrained in the system reaches a temperature within the target temperature range, new feedstock can be added to the system. The new feedstock can arrive at the pump 5 in the form of granules or flakes and can be heated to a temperature within the target temperature range by the pump 5 by applying shear force to the feedstock. The action of the screw conveyor 40 can also drive the feedstock into and along the pipe 2.

[0057] When the raw material is transported along the pipe 2, its temperature can be maintained within a target temperature range by the heating device 51.

[0058] The raw material can be sequentially fed into the reactor 10. In an example system having three reactors 10, the first reactor can be de-isolated and fed a predetermined volume of raw material, after which it can be isolated. After the first reactor has been isolated, the second reactor can be de-isolated and fed a predetermined volume of raw material, and then the second reactor can be isolated. The same process can be repeated for the third reactor. During the isolation of each reactor 10, the reactor 10 can continue to pyrolyze the raw material to produce hydrocarbon vapor. After the full sequence, the pyrolysis of the existing raw material in the first reactor can be substantially completed so that the first reactor can be ready to be fed again.

[0059] Advantageously, the closed system can ensure that no air can enter the pipe 2. Additionally, pushing the raw material in a single direction (from the pump 5 towards the reactor 10) in the closed system can compress the molten raw material and force any air pockets in the opposite direction.

Claims

1. A method for pyrolyzing plastic materials, the method comprising the following steps: Heating and densifying the plastic materials; Transporting the plastic materials to one or more reactors; Pyrolyzing the plastic materials in the one or more reactors; And Maintaining the plastic materials in a heated state during the transporting step, wherein the plastic materials are transported at a positive angle to the horizontal plane.

2. The method according to claim 1, wherein, The angle is 10° or greater.

3. The method according to claim 1 or claim 2, wherein The angle is selected from the range of 10° to 45°.

4. The method according to any one of the preceding claims, wherein, The heated plastic materials are fed into one reactor at a time.

5. The method according to any one of the preceding claims, wherein, The step of heating and densifying the plastic materials is achieved by extruding the plastic materials.

6. The method according to any one of the preceding claims, wherein, The plastic materials are maintained in a molten state during the transporting step.

7. The method according to any one of the preceding claims, wherein, The temperature of the plastic materials is maintained at a temperature within a target temperature range.

8. The method according to claim 7, wherein The target temperature range is lower than the decomposition temperature of the plastic materials.

9. The method according to any one of the preceding claims, wherein, The temperature of the plastic materials is maintained at a temperature of at least 265 °C.

10. The method according to any one of the preceding claims, wherein, The temperature of the plastic materials is maintained at a temperature of at least 280 °C.

11. The method according to any one of the preceding claims, wherein, The temperature of the plastic materials is maintained at a temperature not exceeding 310 °C.

12. The method according to any one of the preceding claims, wherein, The temperature of the plastic materials is maintained at a temperature not exceeding 300 °C.

13. The method according to claim 7 or any one of claims 8 to 12 dependent on claim 6, wherein The plastic materials are heated to a temperature within a target temperature range during the heating and densifying step.

14. The method according to claim 13, wherein, The plastic materials are at a temperature within a target temperature range at the end of the heating and densifying step.

15. A system for pyrolyzing plastic materials, the system comprising: A pump for heating and densifying plastic materials; One or more reactors for pyrolyzing the plastic materials; And A pipe for transporting the plastic materials between the pump and the one or more reactors; wherein The pipe is configured to maintain the plastic materials in a heated state; and The pipe is oriented at a positive angle to the horizontal plane.

16. The system according to claim 15, wherein, The angle is 10° or greater.

17. The system according to claim 15 or 16, wherein The angle is selected from the range of 10° to 45°.

18. The system according to any one of claims 15 to 17, wherein The system includes two or more reactors for pyrolyzing the plastic materials, and wherein the system further includes a plurality of valves arranged such that the heated plastic materials can be fed into one reactor at a time.

19. The system according to any one of claims 15 to 18, wherein, The pump includes an extruder.

20. The system according to any one of claims 15 to 19, wherein The pipe is configured to maintain the plastic materials in a molten state.

21. The system according to any one of claims 15 to 20, wherein The pipe includes a heating device.

22. The system according to claim 21, wherein, The heating device includes electric tracing.

23. The system according to any one of claims 15 to 22, wherein, The system includes a plurality of interlocking valves for feeding the heated plastic materials to two or more reactors.

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