A plastic pyrolysis forced dechlorination system and method

Abstract

This invention relates to the field of plastic pyrolysis dechlorination technology, and particularly to a forced dechlorination system and method for plastic pyrolysis. The system includes a dechlorination tower, a pyrolysis unit, a dechlorinating agent silo, and a demineralized water unit, all connected to the dechlorination tower via pipelines. The outlet of the dechlorination tower is connected to a No. 1 high-temperature membrane dust collector. The outlet of the No. 1 high-temperature membrane dust collector is connected to both the dechlorination tower and the dechlorinating agent waste silo. The outlet of the dechlorinating agent waste silo is connected to a No. 2 high-temperature membrane dust collector, and the discharge port of the No. 2 high-temperature membrane dust collector is connected to the dechlorinating agent waste silo. This invention increases the rate of hydrogen chloride conversion during the pyrolysis of chlorine-containing waste plastics by forcibly extracting the pyrolysis gas. The converted hydrogen chloride is then rapidly absorbed by the dechlorination tower, and unreacted dechlorinating agent is recycled, improving the absorption efficiency of hydrogen chloride. This effectively inhibits the formation of large amounts of chlorinated hydrocarbons during the pyrolysis of chlorine-containing waste plastics, avoiding excessively high total chlorine content in the pyrolysis products, and also improving the utilization rate of the dechlorinating agent.

Description

Technical Field

[0001] This invention relates to the field of plastic pyrolysis dechlorination technology, and in particular to a plastic pyrolysis forced dechlorination system and method. Background Technology

[0002] Plastics, due to their stable properties, low cost, and portability, have rapidly become an indispensable material in people's lives since their invention. While bringing convenience, plastics have also caused serious environmental damage. Current methods for handling plastic waste mainly include landfill, incineration, and recycling. Landfill and incineration cause severe environmental pollution and waste large amounts of land and energy, making high-value recycling a focus of attention in recent years. High-value recycling can be divided into energy recovery, mechanical recovery, and chemical recovery. Energy recovery, or incineration, not only pollutes the environment but also increases carbon emissions. Mechanical recovery, also known as physical recycling, reshapes waste plastics, but the resulting recycled plastics not only have deteriorated performance and can only be used at a lower grade, but also struggle to compensate for the costs of recycling and processing. Chemical recycling refers to the decomposition of waste plastics into small molecules or monomers, and then using these small molecules to prepare fuel oil, chemicals, etc. This method can transform waste plastics into higher-value products and can handle mixed and polluted low-end waste plastics, becoming a focus of research in various fields in recent years. Among these methods, the pyrolysis of plastics is the core technology of chemical recycling.

[0003] Chlorine is very common in waste plastics, mainly from PVC products and various chlorine-containing additives. The chlorine content in PVC alone exceeds 50%. During pyrolysis, this chlorine forms organic chlorine (such as chloroform, dichloroethane, and trichloroethane) and inorganic chlorine (existing in the form of hydrogen chloride). When hydrogen chloride and organic chlorine enter the pyrolysis products, they can cause catalyst poisoning and severe equipment corrosion during product utilization, resulting in a huge increase in investment and operating costs for product utilization.

[0004] The control of chlorine mainly involves the following three aspects:

[0005] Firstly, control the source of waste plastic raw materials by restricting the recycling of chlorinated plastics to reduce the introduction of chlorine. However, this method greatly increases the cost of chemical recycling materials due to the limited availability of raw materials, and at the same time, it makes it impossible to recycle many chlorinated plastics.

[0006] Secondly, under the premise of source control, chlorine is removed during the pyrolysis process to reduce the amount of chlorine entering the pyrolysis products.

[0007] Finally, after implementing the first two measures, chlorine is removed during subsequent product processing to reduce catalyst poisoning and equipment corrosion.

[0008] As can be seen from the above, improving the dechlorination efficiency during pyrolysis is crucial. If the dechlorination efficiency during pyrolysis can be improved, raw materials with high chlorine content can be used, increasing the sources of waste plastics, reducing the cost of chemical recycling, and expanding the application scope of chemical recycling. If the chlorine in the pyrolysis products can be removed to the level of <10ppm in existing fuel oil and chemical chlorine, the investment and operating costs of pyrolysis product processing can be greatly reduced.

[0009] The basic laws governing chlorine conversion during the pyrolysis of chlorine-containing waste plastics are as follows, using PVC as an example:

[0010] The pyrolysis of PVC resin begins at 200-220℃ and can be divided into three stages: the first weight loss stage (200-320℃), the stabilization stage (320-420℃), and the second weight loss stage (420-600℃). This pyrolysis reaction is a first-order reaction. HCl is produced in the first weight loss stage. Because the binding energy of the C-Cl bond in the PVC structure is lower than that of the C-C and C-H bonds, the C-Cl bond breaks first, generating chlorine free radicals, which then further generate HCl. The second weight loss stage involves the reorganization of some structures. In this stage, HCl may undergo secondary reactions with other alkenes, aromatics, etc., ultimately generating various chlorinated hydrocarbons.

[0011] The chemical formula for the reaction in the first weightlessness stage is as follows:

[0012] CnHmCLx——CnH(mx)+xHCL

[0013] From the above process and reaction, we can see that: 1. During the pyrolysis of plastics, chlorine is preferentially released and forms HCl in the gas phase. 2. The HCl release process is a chemical reaction that increases volume. 3. The HCl formed in the gas phase, as the temperature and residence time increase, will recombine with the organic matter generated during the pyrolysis process to regenerate chlorinated hydrocarbons.

[0014] Based on the above characteristics, in order to reduce the amount of chlorine entering the pyrolysis product, a well-known common method is to react the generated HCl with one or more alkaline solid substances to form alkaline chloride, thereby fixing the chlorine in the gaseous HCl in the alkaline dechlorination agent.

[0015] Existing plastic dechlorination technologies have the following drawbacks: 1. Chlorine cannot be rapidly converted into HCl during the pyrolysis of chlorine-containing waste plastics. 2. The converted HCl cannot be rapidly absorbed by the dechlorinating agent, inhibiting its repolymerization into chlorinated hydrocarbons, and the total chlorine content in the pyrolysis products exceeds 10 ppm. Summary of the Invention

[0016] To address at least one of the aforementioned technical problems, this invention proposes a forced dechlorination system for plastic pyrolysis. The aim is to increase the rate at which chlorine-containing waste plastics are converted into hydrogen chloride during pyrolysis, and then rapidly absorb the converted hydrogen chloride through a dechlorination tower. Unreacted dechlorinating agents are recycled, thus solving the problems of excessive chlorinated hydrocarbon generation, high total chlorine content in the pyrolysis products, and low utilization rate of the dechlorinating agent during the pyrolysis of chlorine-containing waste plastics.

[0017] To achieve the above objectives, the present invention adopts the following technical solution:

[0018] The first aspect of the present invention provides a plastic pyrolysis forced dechlorination system, comprising a pyrolysis unit for pyrolysis reaction of plastic, a dechlorination agent silo for storing dechlorination agent, a desalination water unit, a dechlorination tower, a No. 1 high-temperature membrane dust collector, a dechlorination agent waste silo, and a No. 2 high-temperature membrane dust collector;

[0019] The pyrolysis unit is connected to the inlet of the dechlorination tower via a first pyrolysis gas pipeline equipped with a first high-temperature fan, which is used to draw high-chlorine pyrolysis gas from the pyrolysis unit into the dechlorination tower and maintain the pressure in the pyrolysis unit at a preset pressure value; and draws low-chlorine pyrolysis gas to the subsequent process via a second pyrolysis gas pipeline equipped with a second high-temperature fan.

[0020] The dechlorination agent chamber is connected to the dechlorination tower via a pipeline, and is used to transport the dechlorination agent into the dechlorination tower to dechlorinate the high-chlorine pyrolysis gas to form dechlorinated pyrolysis gas. The dechlorination agent is a metal oxide and / or a metal hydroxide and / or a metal carbonate.

[0021] The demineralized water unit is connected to the dechlorination tower via a demineralized water pipeline and is used to spray demineralized water onto the surface of the dechlorinating agent in the dechlorination tower. The spray inlet of the demineralized water and the delivery port of the dechlorinating agent are located at the same horizontal plane.

[0022] The outlet of the dechlorination tower is connected to the inlet of the No. 1 high-temperature membrane dust collector via a pipeline. The No. 1 high-temperature membrane dust collector is used to perform gas-solid separation on the dechlorination pyrolysis gas to form primary dust removal pyrolysis gas and primary dechlorination agent ash. The outlet of the No. 1 high-temperature membrane dust collector is connected to the third high-temperature fan and the subsequent process via pipelines. The primary dust removal pyrolysis gas is pressurized by the third high-temperature fan to form a transport gas source.

[0023] The lower part of the No. 1 high-temperature membrane dust collector is equipped with a funnel-shaped ash storage bin for storing primary dechlorination agent ash. The discharge port of the ash storage bin is connected to the inlet of the dechlorination tower through a first dust removal discharge pipe, which is used to transport the primary dechlorination agent ash with a dechlorination agent content higher than a preset content into the dechlorination tower under the action of the conveying air source; and it is connected to the inlet of the dechlorination agent waste bin through a second dust removal discharge pipe, which is used to transport the primary dechlorination agent ash with a dechlorination agent content lower than the preset content into the dechlorination agent waste bin under the action of the conveying air source;

[0024] The outlet of the dechlorinating agent waste silo is connected to the No. 2 high-temperature membrane dust collector. The No. 2 high-temperature membrane dust collector is used to perform gas-solid separation on the primary dust removal pyrolysis gas, which serves as the conveying gas source, to form secondary dust removal pyrolysis gas and secondary dechlorinating agent ash. The secondary dust removal pyrolysis gas is conveyed to the subsequent process by the fourth high-temperature fan, and the secondary dechlorinating agent ash is discharged to the dechlorinating agent waste silo through the discharge port of the No. 2 high-temperature membrane dust collector. The discharge port of the dechlorinating agent waste silo is connected to the solid waste silo through a pipeline.

[0025] Preferably, the pyrolysis unit includes a pyrolyzer, which is provided with a plurality of No. 1 exhaust pipes connected to the first pyrolysis gas pipeline and a plurality of No. 2 exhaust pipes connected to the second pyrolysis gas pipeline; each of the No. 1 and No. 2 exhaust pipes is provided with a pyrolysis gas pressure gauge and a pyrolysis gas temperature gauge for measuring the pyrolysis gas pressure and temperature inside the pipe, and a No. 1 gas analyzer is provided on the first pyrolysis gas pipeline.

[0026] Preferably, the system further includes a dechlorination agent preparation unit for preparing the dechlorination agent. The discharge port of the dechlorination agent preparation unit is sequentially connected to a #3 rotary feed valve, a #1 dechlorination agent bin, a #2 rotary feed valve, a #2 dechlorination agent bin, and a #1 rotary feed valve via a pipeline along the dechlorination agent flow direction. The discharge port of the #1 rotary feed valve is connected to the inlet of the #1 pneumatic conveying valve. The air inlet of the #1 pneumatic conveying valve is connected to the outlet of the third high-temperature fan via a pipeline equipped with a #1 conveying air control valve. The discharge port of the #1 pneumatic conveying valve is connected to the dechlorination tower.

[0027] Preferably, it also includes a nitrogen storage tank, the outlet of which is connected to the outlet of the rotary feeder valve No. 3 via a pipeline equipped with a nitrogen control valve No. 1, and the inlet of the rotary feeder valve No. 2 via a pipeline equipped with a nitrogen control valve No. 2; the dechlorinating agent No. 1 silo is equipped with a level gauge No. 1 and a gas analyzer No. 2, and the dechlorinating agent No. 2 silo is equipped with a level gauge No. 2.

[0028] Preferably, the first dust removal and discharge pipeline is equipped with a No. 4 rotary feed valve, the outlet of the No. 4 rotary feed valve is connected to the inlet of the No. 2 pneumatic conveying valve, the outlet of the No. 2 pneumatic conveying valve is connected to the inlet of the dechlorination tower, and the No. 2 pneumatic conveying valve is connected to the outlet of the third high-temperature fan through the No. 2 conveying gas control valve.

[0029] Preferably, the second dust removal pipeline is equipped with a No. 5 rotary feeder valve, the outlet of which is connected to the inlet of a No. 3 pneumatic conveying valve, the outlet of which is connected to the dechlorinating agent waste bin, and the inlet of which is connected to the outlet of the third high-temperature fan through a No. 3 conveying gas control valve; the outlet of the nitrogen storage tank is connected to the inlet of the No. 3 pneumatic conveying valve through a No. 3 nitrogen control valve.

[0030] Preferably, the demineralized water pipeline is equipped with a temperature control valve, and the No. 1 exhaust pipe and the No. 2 exhaust pipe are respectively equipped with a high chlorine control valve and a low chlorine control valve; the dechlorination tower is equipped with a dechlorination tower thermometer; the dechlorination agent waste silo is equipped with a No. 4 level gauge, a No. 4 gas analyzer and a waste silo pressure gauge.

[0031] Preferably, the ash storage silo is equipped with a No. 3 level gauge and a sampling analyzer; a No. 3 gas analyzer and a No. 1 shut-off valve are sequentially installed between the outlet of the No. 2 high-temperature membrane dust collector and the inlet of the fourth high-temperature fan.

[0032] Preferably, the preset pressure range is 0-1 kPa, and the preset content range is 5%-10%.

[0033] A second aspect of the present invention provides a method for forced dechlorination of plastics by pyrolysis as described in the first aspect, comprising the following steps:

[0034] S1, under the action of the gas source, an excess of dechlorinating agent is delivered into the dechlorination tower. At the same time, dechlorinating water is sprayed into the dechlorination tower through the dechlorination water spray port which is on the same plane as the dechlorinating agent delivery port, forming a liquid film on the surface of the dechlorinating agent.

[0035] S2, in the pyrolysis unit, waste plastics are pyrolyzed to generate pyrolysis gas. According to the critical temperature of the pyrolysis gas, the high-chlorine pyrolysis gas is pumped to the dechlorination tower to react with the dechlorination agent in the dechlorination tower, and the low-chlorine pyrolysis gas is transported to the next process through pipeline.

[0036] S3: The mixed gas after dechlorination reaction in the dechlorination tower is transported to the No. 1 high-temperature dust collector for gas-solid separation; the content of unreacted dechlorinating agent in the separated primary dechlorinating agent ash is monitored; under the action of the gas source, the primary dechlorinating agent ash with the content of unreacted dechlorinating agent below the preset content is transported to the dechlorinating agent waste bin, and the primary dechlorinating agent ash with the content of unreacted dechlorinating agent above the preset content is transported to the dechlorination tower for recycling; part of the separated primary dust removal pyrolysis gas is pressurized by the third high-temperature fan and used as a gas source, and the other part is transported to the subsequent process;

[0037] S4, the primary dust removal gas entering the dechlorinating agent waste silo is transported to the No. 2 high-temperature membrane dust collector for gas-solid separation. The separated secondary dechlorinating agent ash is transported to the dechlorinating agent waste silo, and the separated secondary dust removal pyrolysis gas is transported to the next process.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. This invention utilizes the characteristic that low pressure favors hydrogen chloride generation. By rapidly extracting the pyrolysis gas with a high hydrogen chloride content generated during pyrolysis, the concentration of hydrogen chloride in the gas phase is reduced, and the pressure inside the pyrolyzer is controlled at 0-1 kPa, thus reducing the contact time between the high-chlorine pyrolysis gas and the molten waste plastic. Simultaneously, by using 320°C as the critical temperature to extract the high-chlorine and low-chlorine pyrolysis gases separately, backmixing of the two is effectively reduced, minimizing the chance of repolymerization to form chlorinated hydrocarbons.

[0040] 2. This invention uses nitrogen as the protective gas source for the dechlorinating agent chamber and clean primary dust removal pyrolysis gas pressurized by a third high-temperature fan as the conveying power to transport the dechlorinating agent to the dechlorination tower. This reduces the amount of other impurity gases that are easily reacted with the dechlorinating agent in the dechlorination tower carried during the transportation process. This operation is simple, safe and easy to control.

[0041] 3. This invention sprays dechlorinated water into the dechlorination tower, forming a transient liquid film on the surface of the alkaline dechlorinating agent. This facilitates the rapid reaction of hydrogen chloride with the agent, improving dechlorination efficiency. By adding excess dechlorinating agent, sufficient absorption of hydrogen chloride is ensured, resulting in a total chlorine content of less than 10 ppm after dechlorination. This reduces the investment and operating costs associated with dechlorination in the refining process to avoid catalyst poisoning, and mitigates the severe corrosion of oil refining equipment by high chlorine levels, thereby lowering the investment and operating costs for subsequent refining of pyrolysis products. Simultaneously, the efficient dechlorination allows for the high-value recovery of high-chlorinated plastics through chemical recycling, broadening the range of raw materials for chemically recycled plastics.

[0042] 4. This invention uses a sampling analyzer to determine the dechlorinating agent content in the primary dechlorinating agent ash, and then recycles the primary dechlorinating agent ash with a dechlorinating agent content higher than the predetermined content back to the dechlorinating agent tower via a conveying gas source, thereby improving the utilization rate of the dechlorinating agent. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a plastic pyrolysis forced dechlorination system;

[0044] In the diagram: 1. Pyrolysis unit; 1-1. High chlorine control valve; 1-2. Low chlorine control valve; 1-3. Pyrolysis gas pressure gauge; 1-4. Pyrolysis gas thermometer; 1-5. First high-temperature fan; 1-6. Second high-temperature fan; 1-7. Exhaust pipe #1; 1-8. Exhaust pipe #2; 1-9. First pyrolysis gas pipeline; 1-9-1. Gas analyzer #1; 1-10. Second pyrolysis gas pipeline;

[0045] 2. Dechlorinating agent preparation unit; 2-1, 3# rotary feed valves; 2-2, dechlorinating agent 1# bin; 2-2-1, 1# level gauges; 2-2-2, 2# gas analyzers; 2-2-3, 1# nitrogen control valve; 2-2-4, 2# nitrogen control valve; 2-3, 2# rotary feed valve; 2-4, dechlorinating agent 2# bin; 2-4-1, 2# level gauges; 2-5, 1# rotary feed valve; 2-6, 1# pneumatic conveying valve; 2-6-1, 1# conveying gas control valve;

[0046] 3. Dechlorination tower; 3-1. Dechlorination tower thermometer; 3-2. Temperature regulating water control valve; 3-3. No. 1 high-temperature membrane dust collector; 3-3-1. No. 3 level gauge; 3-3-2. Sampling analyzer; 3-3-3. No. 4 rotary feeder valve; 3-3-4. No. 2 pneumatic conveying valve; 3-3-4-1. No. 2 conveying gas control valve; 3-4. Third high-temperature fan;

[0047] 4. Dechlorinating agent waste bin; 4-1, 4# level gauges; 4-2, 6# rotary feeder valves; 4-3, 5# rotary feeder valves; 4-4, 3# pneumatic conveying valves; 4-4-1, 3# conveying gas control valves; 4-5, 3# nitrogen control valves; 4-6, 1# shut-off valve; 4-7, 2# high-temperature membrane dust collector; 4-7-1, 3# gas analyzers; 4-7-2, fourth high-temperature fan; 4-8, 4# gas analyzer; 4-9, waste bin pressure gauge. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments of the present invention.

[0049] Please refer to Figure 1As shown, a plastic pyrolysis forced dechlorination system includes a pyrolysis unit 1 for pyrolysis reaction of plastic, a dechlorinating agent silo for storing dechlorinating agent, a desalination water unit, a dechlorination tower 3, a No. 1 high-temperature membrane dust collector 3-3, a dechlorinating agent waste silo 4, and a No. 2 high-temperature membrane dust collector 4-7.

[0050] The dechlorination method of the above system includes the following steps:

[0051] S1, under the action of the gas source, an excess of dechlorinating agent is delivered into the dechlorination tower 3. At the same time, dechlorinating water is sprayed into the dechlorination tower 3 through the dechlorination water spray port which is on the same plane as the dechlorinating agent delivery port, forming a liquid film on the surface of the dechlorinating agent.

[0052] S2, in pyrolysis unit 1, waste plastic is pyrolyzed to generate pyrolysis gas. According to the critical temperature of the pyrolysis gas, the high-chlorine pyrolysis gas is pumped into dechlorination tower 3 to react with the dechlorination agent in dechlorination tower 3, and the low-chlorine pyrolysis gas is transported to the next process through pipeline.

[0053] S3: The mixed gas after dechlorination reaction in dechlorination tower 3 is transported to high-temperature dust collector #1 for gas-solid separation; the content of unreacted dechlorinating agent in the separated primary dechlorinating agent ash is monitored; under the action of the gas source, the primary dechlorinating agent ash with the content of unreacted dechlorinating agent lower than the preset content is transported to the dechlorinating agent waste bin 4, and the primary dechlorinating agent ash with the content of unreacted dechlorinating agent higher than the preset content is transported to dechlorination tower 3 for recycling; part of the separated primary dust removal pyrolysis gas is pressurized by the third high-temperature fan 3-4 and used as a gas source, and the other part is transported to the next process;

[0054] S4, the primary dust removal gas entering the dechlorinating agent waste silo 4 is transported to the No. 2 high-temperature membrane dust collector 4-7 for gas-solid separation. The separated secondary dechlorinating agent ash is transported to the dechlorinating agent waste silo 4, and the separated secondary dust removal pyrolysis gas is transported to the next process.

[0055] Therefore, the main components of the dechlorination process in this system are roughly as follows: dechlorination agent preparation and feeding into the dechlorination agent silo, plastic pyrolysis, dechlorination of pyrolysis gas, gas-solid separation of pyrolysis gas, and recovery of dechlorination agent waste. The following section will combine... Figure 1 Provide a detailed description of the system's connection relationships and dechlorination steps.

[0056] (1) Pyrolysis of plastics

[0057] The pyrolysis unit 1 is connected to the air inlet of the dechlorination tower 3 through the first pyrolysis gas pipeline 1-9 equipped with the first high-temperature fan 1-5, which is used to draw the high-chlorine pyrolysis gas in the pyrolysis unit 1 into the dechlorination tower 3; and the low-chlorine pyrolysis gas is drawn to the subsequent process through the second pyrolysis gas pipeline 1-10 equipped with the second high-temperature fan 1-6.

[0058] The aforementioned pyrolysis unit 1 includes a pyrolyzer, which is provided with several #1 exhaust pipes 1-7 connected to the first pyrolysis gas pipeline 1-9 and several #2 exhaust pipes 1-8 connected to the second pyrolysis gas pipeline 1-10. The number of #1 exhaust pipes 1-7 and #2 exhaust pipes 1-8 can be determined according to the size of the pyrolyzer itself. In this application, the distance between #1 exhaust pipes 1-7 and #2 exhaust pipes 1-8 is 300mm-500mm, and the pipe diameter is 150mm-200mm.

[0059] Both exhaust pipe #1 (1-7) and exhaust pipe #2 (1-8) are equipped with a pyrolysis gas pressure gauge 1-3 and a pyrolysis gas thermometer 1-4 for measuring the pressure and temperature of the pyrolysis gas inside the pipe. A gas analyzer 1-9-1 is installed on the first pyrolysis gas pipeline 1-9. Furthermore, a high-chlorine control valve 1-1 and a low-chlorine control valve 1-2 are respectively installed on exhaust pipe #1 (1-7) and exhaust pipe #2 (1-8). For ease of control, the aforementioned pyrolysis gas thermometer 1-4, pyrolysis gas pressure gauge 1-3, high-chlorine control valve 1-1, and low-chlorine control valve 1-2 are all connected to the control system. All the pipeline valves and measuring devices described below are also connected to the control system.

[0060] As described above, after the plastic enters the pyrolysis unit, pyrolysis begins at 200-220℃ and can be divided into three stages: the first weight loss stage (200-320℃), the stabilization stage (320-420℃), and the second weight loss stage (420-600℃). This pyrolysis reaction is a first-order reaction. From the pyrolysis reaction formula, it can be seen that the gas volume increases during the pyrolysis reaction. Therefore, reducing the pressure is beneficial to the pyrolysis reaction. Thus, the pressure inside the pyrolysis unit can be reduced by forcibly pumping out the pyrolysis gas produced during pyrolysis.

[0061] Based on the reaction temperatures and products of the three stages of pyrolysis, this embodiment uses 320℃ as the critical temperature to extract high-chlorine pyrolysis gas and low-chlorine pyrolysis gas from the pyrolyzer. It should be noted that high-chlorine pyrolysis gas here refers to pyrolysis gas with a high hydrogen chloride content, and similarly, low-chlorine pyrolysis gas refers to pyrolysis gas with a low hydrogen chloride content.

[0062] Specifically, the temperature inside the pyrolyzer is measured using thermometers 1-4 on exhaust pipes 1-7 and 2-8. When the temperature is between 200-320℃, the hydrogen chloride content in the pyrolyze gas is high. At this point, the low-chlorine control valve 1-2 is closed via the control system, and the high-chlorine pyrolyze gas is pumped into the dechlorination tower 3. Similarly, when the temperature is above 320℃, the high-chlorine control valve 1-1 is closed via the control system, and the low-chlorine pyrolyze gas is pumped into the dechlorination tower 3.

[0063] Meanwhile, based on the pressure inside the pyrolysis gas measured by the pyrolysis gas pressure gauge 1-3, when the pressure value is close to 0 kPa, the pressure inside the pyrolyzer is increased by reducing the flow rate of the high chlorine control valve 1-1 or the low chlorine control valve 1-2; when the pressure value is 1 kPa, the pressure inside the pyrolyzer is decreased by increasing the flow rate of the high chlorine control valve 1-1 or the low chlorine control valve 1-2 through the control system.

[0064] The above operations can significantly reduce the contact time between high-chlorine pyrolysis gas and molten waste plastic. Simultaneously, by using 320℃ as the critical temperature to extract high-chlorine and low-chlorine pyrolysis gas separately, the backmixing of the two is effectively reduced, decreasing the chance of repolymerization to form chlorinated hydrocarbons.

[0065] (2) Preparation of dechlorination agent and feeding of dechlorination agent silo

[0066] In this embodiment, the dechlorinating agent is provided through the dechlorinating agent preparation unit 2. The discharge port of the dechlorinating agent preparation unit 2 is sequentially connected via pipelines to rotary feed valve 2-1 (3#), dechlorinating agent bin 2-2 (1#), rotary feed valve 2-3 (2#), dechlorinating agent bin 2-4 (2#), and rotary feed valve 2-5 (1#). The discharge port of rotary feed valve 2-5 (1#) is connected to the inlet of pneumatic conveying valve 2-6 (1#). The inlet of pneumatic conveying valve 2-6 (1#) is connected to a conveying gas source via a pipeline equipped with a conveying gas control valve 2-6-1 (1#). The discharge port of pneumatic conveying valve 2-6 (1#) is connected to the dechlorination tower 3. Specifically, bin 2-2 (1#) is equipped with a level gauge 2-2-1 (1#) and a gas analyzer 2-2-2 (2#), and bin 2-4 (2#) is equipped with a level gauge 2-4-1 (2#).

[0067] It should be noted that the dechlorinating agent in this application can be one or more of the following: metal oxides, such as oxides of potassium, sodium, calcium, magnesium, and iron; metal hydroxides, such as sodium hydroxide; and metal carbonates, mixed in a certain proportion and then processed into particles with a particle size of 1-100 μm through the dechlorinating agent preparation unit 2. The preparation of the dechlorinating agent is prior art and is not the focus of protection in this application, and will not be elaborated here.

[0068] In this embodiment, nitrogen is used as the protective gas source for feeding the dechlorinating agent. The outlet of the nitrogen storage tank is connected to the outlet of the rotary feeder 2-1 through a pipeline equipped with nitrogen control valve 2-2-3, and is connected to the inlet of the rotary feeder 2-3 through a pipeline equipped with nitrogen control valve 2-2-4.

[0069] The feeding process for the above-mentioned dechlorinating agent silo 1# 2-2 and dechlorinating agent silo 2# 2-4 is as follows:

[0070] When the level gauge 2-2-1 of dechlorinating agent silo 1# (2-2) shows a level between 1 / 4 and 1 / 3, feed is required. The control system closes rotary feed valve 2-1 (3-1) and nitrogen control valve 2-2-4 (2-2-4), and opens nitrogen control valve 2-2-3 (1-2-3) and rotary feed valve 2-3. Nitrogen gas is then used to force the pyrolysis gas from dechlorinating agent silo 1# (2-2) into dechlorinating agent silo 2# (2-4) from the top. When the nitrogen content measured by gas analyzer 2-2-2 is above 95%, rotary feed valve 2-3 (2-3) and nitrogen control valve 2-2-3 (1-2-3) are closed, and rotary feed valve 2-1 (3-1) is opened. The dechlorinating agent processed in dechlorinating agent preparation unit 2 then enters dechlorinating agent silo 1# (2-2).

[0071] When the level gauge 2-2-1 of the dechlorinating agent silo 1# shows that the level is in the range of 2 / 4-3 / 4, open the nitrogen control valve 2-2-4. Use nitrogen to force the air in the dechlorinating agent silo 1# into the dechlorinating agent preparation unit 2 from the bottom of the silo 1#. When the nitrogen content measured by the gas analyzer 2-2-2 is above 95%, close the rotary feed valve 3# and the nitrogen control valve 2-2-4, and open the rotary feed valve 2-3. The dechlorinating agent in the dechlorinating agent silo 1# enters the dechlorinating agent silo 2#.

[0072] When the level gauge 2-4-1 of dechlorinant bin 2-4 shows the level in the range of 2 / 4-3 / 4, close the rotary feed valve 2-3. Dechlorinant bin 1-2 repeats the above operation to replenish dechlorinant according to the level.

[0073] In this embodiment, nitrogen is used as the protective gas source for the dechlorinating agent chamber, and clean primary dust removal pyrolysis gas pressurized by the third high-temperature fan 3-4 is used as the conveying power to transport the dechlorinating agent to the dechlorination tower 3. This reduces the amount of other impurity gases that are easily reacted with the dechlorinating agent in the dechlorination tower 3 during the transportation process. This operation is simple, safe and easy to control.

[0074] (3) Dechlorination of pyrolysis gas

[0075] The prepared dechlorinating agent and the high-chlorine pyrolysis gas in the pyrolysis gas are transported to dechlorination tower 3 to undergo a dechlorination reaction, as detailed below:

[0076] Open the high-chlorine control valve 1-1, and under the action of the first high-temperature fan 1-5, the pyrolysis gas with a high hydrogen chloride content is transported to the dechlorination tower 3. The hydrogen chloride content in the first pyrolysis gas pipeline 1-9 is measured by the gas analyzer 1-9-1.

[0077] In order to remove hydrogen chloride from the high-chlorine pyrolysis gas to the maximum extent, an excess of dechlorinating agent is used to react with hydrogen chloride. In this embodiment, the molar ratio of dechlorinating agent to hydrogen chloride is 3.5-7.

[0078] The control system opens the No. 1 rotary feed valve 2-5 and controls the opening degree of the No. 1 rotary feed valve 2-5 according to the above ratio. Under the action of the conveying air source and the No. 1 pneumatic conveying valve 2-6, the dechlorinating agent is conveyed to the dechlorination tower 3.

[0079] The gas velocity of the hyperchlorinated pyrolysis gas can be specifically determined based on the density and particle size of the dechlorinating agent particles, as well as the temperature and density of the gas. In this embodiment, the gas velocity of the hyperchlorinated pyrolysis gas is 40-50 m / s.

[0080] It is understandable that the high-velocity pyrolysis gas from the high-chlorine pyrolysis process undergoes violent collisions, allowing the dechlorinating agent to fully contact and react with the pyrolysis gas. Taking a calcium-based alkaline dechlorinating agent as an example, the reaction is as follows: Ca(OH)2 + HCl → CaCl2 + H2O.

[0081] As is well known, the two-film theory of gas-liquid mass transfer reactions states that gas absorption is the process by which the absorbate in the gas phase is transferred to the liquid phase through the interphase interface. When gas and liquid come into contact, even if the bulk of the fluid is turbulent, stable gas stagnant layers (gas films) and liquid stagnant layers (liquid films) still exist on both sides of the gas-liquid interface. The absorption process involves absorbate molecules moving from the bulk gas phase to the gas film surface, then diffusing through the gas film to reach the gas-liquid interface. At the interface, the absorbate dissolves into the liquid phase and then diffuses through the liquid film back into the bulk liquid phase. Without the presence of a liquid, the reaction of hydrogen chloride with an alkaline dechlorinating agent, which is a gas-solid phase reaction, can only be facilitated by the micropores on the surface of the dechlorinating agent, which provide sufficient specific surface area to create a favorable environment for hydrogen chloride absorption. When the dechlorinated water is sprayed in, although the dechlorinated water evaporates rapidly during the spraying process, it can still come into brief contact with the dechlorinating agent, forming a liquid film on the surface of the dechlorinating agent. This creates conditions for the formation of a double film, which is conducive to the absorption of hydrogen chloride, thereby promoting the chemical absorption reaction between hydrogen chloride and the alkaline solid dechlorinating agent.

[0082] Based on the above principles, to further improve the reaction efficiency between the high-chlorine pyrolysis gas and the dechlorinating agent, in this embodiment, demineralized water from the demineralized water unit is injected into the dechlorination tower 3 through a demineralized water pipeline. Simultaneously, to ensure sufficient contact between the demineralized water and the dechlorinating agent, the injection port of the demineralized water and the delivery port of the dechlorinating agent are at the same horizontal level in this embodiment. When the demineralized water is injected into the dechlorination tower 3, the gas temperature inside the dechlorination tower 3 decreases by approximately 5-10°C. The specific temperature drop can be calculated by the difference between the temperature value measured by the thermometer installed in the dechlorination tower 3 and the temperature value of the high-chlorine pyrolysis gas.

[0083] To facilitate control of the amount of demineralized water injected, a temperature control valve 3-2 is installed on the aforementioned demineralized water pipeline.

[0084] This implementation ensures sufficient absorption of hydrogen chloride by spraying temperature-controlled dechlorination water into dechlorination tower 3 and adding an excess of dechlorinating agent. This results in a total chlorine content of less than 10 ppm after dechlorination, reducing the investment and operating costs associated with dechlorination in the refining process to avoid catalyst poisoning. It also mitigates the severe corrosion of oil refining equipment by high chlorine levels, thereby lowering the investment and operating costs for subsequent refining of pyrolysis products. Simultaneously, the efficient dechlorination allows for the high-value recovery of high-chlorinated plastics through chemical recycling, broadening the range of raw materials for chemically recycled plastics.

[0085] (4) Gas-solid separation of pyrolysis gas

[0086] The mixed gas discharged from the outlet of dechlorination tower 3 will carry a certain amount of reacted and unreacted dechlorination agent into the No. 1 high-temperature membrane dust collector 3-3, where gas-solid separation will take place.

[0087] The primary dust removal pyrolysis gas separated by the No. 1 high-temperature membrane dust collector 3-3 has a dust concentration of less than 10 mg / Nm3 and a hydrogen chloride concentration of less than 10 ppm / Nm3. A portion of this primary dust removal pyrolysis gas enters the outlet of the No. 1 high-temperature membrane dust collector 3-3 and is pressurized to 30 kPa by the third high-temperature fan 3-4 as a transport gas source. The remaining clean primary dust removal pyrolysis gas is mixed with the low-chlorine pyrolysis gas from the second high-temperature fan 1-6 and sent to subsequent processes.

[0088] The separated solid reactants and unreacted dechlorinating agents fall into the funnel-shaped ash storage silo at the bottom of the No. 1 high-temperature membrane dust collector 3-3. To facilitate timely adjustment of the material level in the ash storage silo, the above-mentioned ash storage silo is equipped with a No. 3 level gauge 3-3-1.

[0089] Specifically, in this embodiment, the material level of the material level gauge 3-3-1 in the ash storage bin of the high-temperature membrane dust collector 3-3 is controlled between 1 / 2 and 2 / 3. When the material level is below 1 / 2, the opening of the rotary feed valve 3-3-3 of the 4th generation is reduced; when the material level is above 2 / 3, the opening of the rotary feed valve 3-3-3 of the 4th generation is increased.

[0090] Meanwhile, in order to improve the utilization rate of the dechlorinating agent, a sampling analyzer 3-3-2 is installed in the above-mentioned ash storage silo. The discharge port of the No. 1 high-temperature membrane dust collector 3-3 is connected to the inlet of the dechlorination tower 3 through the first dust removal discharge pipeline. The first dust removal discharge pipeline is equipped with a No. 4 rotary feed valve 3-3-3. The discharge port of the No. 4 rotary feed valve 3-3-3 is connected to the inlet of the No. 2 pneumatic conveying valve 3-3-4. The discharge port of the No. 2 pneumatic conveying valve 3-3-4 is connected to the inlet of the dechlorination tower 3. The No. 2 pneumatic conveying valve 3-3-4 is connected to the outlet of the third high-temperature fan 3-4 through the No. 2 conveying gas control valve 3-3-4-1.

[0091] The discharge port of the #1 high-temperature membrane dust collector 3-3 is connected to the inlet of the dechlorinating agent waste bin 4 through the second dust removal discharge pipeline. The second dust removal pipeline is equipped with a #5 rotary feeder valve 4-3. The outlet of the #5 rotary feeder valve 4-3 is connected to the inlet of the #3 pneumatic conveying valve 4-4. The outlet of the #3 pneumatic conveying valve 4-4 is connected to the dechlorinating agent waste bin 4. The air inlet of the #3 pneumatic conveying valve 4-4 is connected to the air outlet of the third high-temperature fan 3-4 through the #3 conveying air control valve 4-4-1.

[0092] Specifically, in this embodiment, the preset content of dechlorinating agent in the primary dechlorination agent ash is 5%-10%. However, the specific value of the preset content needs to be determined in conjunction with the pressure difference of dechlorination tower 3 and the hydrogen chloride content of the pyrolysis gas exiting dechlorination tower 3. The following uses a preset content of 8% to specifically explain the ash discharge path of the primary dechlorination agent ash.

[0093] When the sampling analyzer 3-3-2 measures that the effective dechlorinating agent content in the primary dechlorinating agent ash is less than 8%, the 5# rotary feed valve 4-3 and the 3# conveying gas control valve 4-4-1 are opened. The unreacted alkaline dechlorinating agent and the primary dechlorinating agent ash in the ash storage bin at the bottom of the 1# high-temperature membrane dust collector 3-3 are taken out through the 3# pneumatic conveying valve 4-4 under the action of the conveying gas source.

[0094] During the discharge of primary dechlorinating agent ash containing less than 8% effective dechlorinating agent, the effective dechlorinating agent content in the primary dechlorinating agent ash inside dechlorination tower 3 will gradually increase.

[0095] When the sampling analyzer 3-3-2 detects that the effective dechlorinating agent content in the primary dechlorinating agent ash is greater than 10%, close the No. 5 rotary feed valve 4-3 to stop the removal of the primary dechlorinating agent ash. After the No. 5 rotary feed valve 4-3 is closed, delay for 30 seconds and then close the No. 3 conveying gas control valve 4-4-1. The purpose is to blow away the residual unreacted alkaline dechlorinating agent and the reacted dechlorinating agent mixture ash.

[0096] Open the #4 rotary feed valve 3-3-3 and the #2 conveying gas control valve 3-3-4-1. The unreacted alkaline dechlorinating agent and the primary dechlorinating agent ash in the ash storage bin at the bottom of the #1 high-temperature membrane dust collector 3-3 are circulated into the dechlorination tower 3 through the #2 pneumatic conveying valve 3-3-4 under the action of the conveying gas source.

[0097] This implementation uses a sampling analyzer 3-3-2 to determine the dechlorinating agent content in the primary dechlorinating agent ash. The primary dechlorinating agent ash with a dechlorinating agent content higher than the predetermined content is transported back to the dechlorinating agent tower for recycling through a gas supply, thereby improving the utilization rate of the dechlorinating agent.

[0098] (5) Dechlorination agent waste recycling

[0099] Primary dechlorinating agent ash with a dechlorinating agent content lower than the preset content enters the dechlorinating agent waste bin 4 through the No. 3 pneumatic conveying valve 4-4 under the action of the conveying air source. The air outlet of the dechlorinating agent waste bin 4 is connected to the upper part of the No. 2 high-temperature membrane dust collector 4-7. The No. 2 high-temperature membrane dust collector 4-7 is used to perform gas-solid separation on the primary dust removal pyrolysis gas, which serves as the conveying air source, to form secondary dust removal pyrolysis gas and secondary dechlorinating agent ash.

[0100] A gas analyzer (4-7-1) and a shut-off valve (4-6) are installed sequentially between the outlet of the No. 2 high-temperature membrane dust collector (4-7-1) and the inlet of the fourth high-temperature fan (4-7-2). The secondary dust removal pyrolysis gas is transported to the next process through the fourth high-temperature fan (4-7-2).

[0101] The secondary dechlorination agent ash separated by the No. 2 high-temperature membrane dust collector 4-7 is discharged into the dechlorination agent waste silo 4 through the funnel-shaped ash storage bin at the bottom of the No. 2 high-temperature membrane dust collector 4-7. The discharge port of the dechlorination agent waste silo 4 is connected to the solid waste silo through a pipeline equipped with a No. 6 rotary feed valve 4-2.

[0102] Specifically, when the dechlorinating agent waste silo 4 is fed, the #1 shut-off valve 4-6 opens and the fourth high-temperature fan 4-7-2 starts. The primary dust removal pyrolysis gas, which serves as the conveying gas, carries primary dechlorinating agent ash with a low effective content of dechlorinating agent into the #2 high-temperature membrane dust collector 4-7.

[0103] After dust removal, the secondary dust removal pyrolysis gas enters the fourth high-temperature fan 4-7-2 through the outlet of the No. 2 high-temperature membrane dust collector 4-7 and the No. 1 shut-off valve 4-6. Under the suction action of the fourth high-temperature fan 4-7-2, the secondary dust removal pyrolysis gas and the low-chlorine pyrolysis gas are mixed and enter the next process.

[0104] The unreacted alkaline dechlorinating agent and the reacted dechlorinating agent mixture separated from the gas-solid separation of the No. 2 high-temperature membrane dust collector 4-7 enter the dechlorinating agent waste silo 4 through the outlet of the funnel-shaped ash storage silo at the bottom of the No. 2 high-temperature membrane dust collector 4-7.

[0105] When the chlorine waste silo 4 stops feeding, the fourth high-temperature fan 4-7-2 is shut down through the control system.

[0106] In order to facilitate the control of the material level in the dechlorinating agent waste silo 4, in this embodiment the dechlorinating agent waste silo 4 is equipped with a 4# material level gauge 4-1, a 4# gas analyzer 4-8 and a waste silo pressure gauge 4-9, and the outlet of the nitrogen storage tank is connected to the inlet of the 3# pneumatic conveying valve 4-4 through the 3# nitrogen control valve 4-5.

[0107] Specifically, when the level gauge 4-1 detects that the level of the dechlorinating agent waste silo 4 is between 1 / 2 and 2 / 3, the control system opens the nitrogen control valve 4-5 to purge the ash removal system. The purging exhaust gas and the secondary dust removal pyrolysis gas are mixed with the low-chlorine pyrolysis gas along the same path and then enter the next process.

[0108] When the nitrogen content displayed by gas analyzers #3 (4-7-1) and #4 (4-8) is greater than 95%, the nitrogen control valve #3 (4-5) is partially closed. The pressure inside the dechlorinating agent waste bin 4 is maintained at a slightly positive pressure using the waste bin pressure gauge 4-9. In this embodiment, the slightly positive pressure range is 0.1-1 kPa. At this time, the shut-off valve #1 (4-6) is closed, and the rotary feed valve #6 (4-2) is opened, allowing the secondary dechlorinating agent ash in the waste bin 4 to be discharged to the solid waste warehouse. It is important to note that during the discharge of the secondary dechlorinating agent ash, the waste bin is maintained at a slightly positive pressure, and the nitrogen content analyzed by gas analyzers #3 (4-7-1) and #4 (4-8) is both above 95%. When the level gauge #4 (4-1) detects that the level in the dechlorinating agent waste bin 4 is less than 1 / 3, the control system closes the rotary feed valve #6 (4-2) and the nitrogen control valve #3 (4-5).

[0109] This invention utilizes the characteristic that low pressure favors hydrogen chloride generation. By rapidly extracting the pyrolysis gas with a high hydrogen chloride content generated during pyrolysis, the concentration of hydrogen chloride in the gas phase is reduced, and the pressure inside the pyrolyzer is controlled at 0-1 kPa, minimizing the contact time between the high-chlorine pyrolysis gas and the molten waste plastic. Simultaneously, by using 320°C as the critical temperature to extract the high-chlorine and low-chlorine pyrolysis gases separately, backmixing of the two is effectively reduced, decreasing the chance of repolymerization to form chlorinated hydrocarbons.

[0110] By using nitrogen as the protective gas source for the dechlorinating agent chamber and clean primary dust removal pyrolysis gas pressurized by the third high-temperature fan 3-4 as the conveying power, the dechlorinating agent is conveyed to the dechlorination tower 3. This reduces the amount of other impurity gases that are easily reacted with the dechlorinating agent in the dechlorination tower 3 carried during the conveying process. This operation is simple, safe and easy to control.

[0111] By spraying temperature-controlled dechlorinated water into the dechlorinating agent in dechlorination tower 3, a transient liquid film is formed on the surface of the alkaline dechlorinating agent, which facilitates the rapid reaction of hydrogen chloride with it, thus improving dechlorination efficiency. Increasing the amount of excess dechlorinating agent ensures sufficient absorption of hydrogen chloride, resulting in a total chlorine content of less than 10 ppm after dechlorination. This reduces the investment and operating costs associated with dechlorination in the refining process to avoid catalyst poisoning, and mitigates the severe corrosion of oil refining equipment by high chlorine levels, thereby lowering the investment and operating costs for subsequent refining of pyrolysis products. Simultaneously, the efficient dechlorination allows for the high-value recovery of high-chlorinated plastics through chemical recycling, broadening the range of raw materials for chemically recycled plastics.

[0112] The dechlorinating agent content in the primary dechlorinating agent ash was determined by a sampling analyzer 3-3-2. The primary dechlorinating agent ash with a dechlorinating agent content higher than the predetermined content was transported back to the dechlorinating agent tower for recycling through a conveying gas source, thereby improving the utilization rate of the dechlorinating agent.

[0113] The above description is a specific implementation of the embodiments of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A plastic pyrolysis forced dechlorination system, characterized in that, It includes a pyrolysis unit (1) for pyrolysis reaction of plastics, a dechlorinating agent silo for storing dechlorinating agent, a demineralized water unit, a dechlorination tower (3), a No. 1 high-temperature membrane dust collector (3-3), a dechlorinating agent waste silo (4), and a No. 2 high-temperature membrane dust collector (4-7); The pyrolysis unit (1) is connected to the inlet of the dechlorination tower (3) through a first pyrolysis gas pipeline (1-9) equipped with a first high-temperature fan (1-5), which is used to draw high-chlorine pyrolysis gas from the pyrolysis unit (1) into the dechlorination tower (3) and maintain the pressure in the pyrolysis unit (1) at a preset pressure value; low-chlorine pyrolysis gas is drawn to the subsequent process through a second pyrolysis gas pipeline (1-10) equipped with a second high-temperature fan (1-6); The dechlorination agent chamber is connected to the dechlorination tower (3) through a pipeline, and is used to transport the dechlorination agent to the dechlorination tower (3) to dechlorinate the high-chlorine pyrolysis gas to form dechlorinated pyrolysis gas. The dechlorination agent is a metal oxide and / or a metal hydroxide and / or a metal carbonate. The demineralized water unit is connected to the dechlorination tower (3) through a demineralized water pipeline and is used to spray demineralized water onto the surface of the dechlorinating agent in the dechlorination tower (3). The spray inlet of the demineralized water and the delivery port of the dechlorinating agent are located at the same horizontal plane. The outlet of the dechlorination tower (3) is connected to the inlet of the No. 1 high-temperature membrane dust collector (3-3) through a pipeline. The No. 1 high-temperature membrane dust collector (3-3) is used to perform gas-solid separation on the dechlorination pyrolysis gas to form primary dust removal pyrolysis gas and primary dechlorination agent ash. The outlet of the No. 1 high-temperature membrane dust collector (3-3) is connected to the third high-temperature fan (3-4) and the subsequent process through pipelines. The primary dust removal pyrolysis gas is pressurized by the third high-temperature fan (3-4) to form a transport gas source. The lower part of the No. 1 high-temperature membrane dust collector (3-3) is provided with a funnel-shaped ash storage bin for storing primary dechlorination agent ash. The discharge port of the ash storage bin is connected to the inlet of the dechlorination tower (3) through a first dust removal discharge pipe, which is used to transport the primary dechlorination agent ash with a dechlorination agent content higher than the preset content to the dechlorination tower (3) under the action of the conveying air source; and is connected to the inlet of the dechlorination agent waste bin (4) through a second dust removal discharge pipe, which is used to transport the primary dechlorination agent ash with a dechlorination agent content lower than the preset content to the dechlorination agent waste bin (4) under the action of the conveying air source; The outlet of the dechlorinating agent waste bin (4) is connected to the No. 2 high-temperature membrane dust collector (4-7). The No. 2 high-temperature membrane dust collector (4-7) is used to perform gas-solid separation on the primary dust removal pyrolysis gas, which serves as the conveying gas source, to form secondary dust removal pyrolysis gas and secondary dechlorinating agent ash. The secondary dust removal pyrolysis gas is conveyed to the subsequent process through the fourth high-temperature fan (4-7-2). The secondary dechlorinating agent ash is discharged to the dechlorinating agent waste bin (4) through the discharge port of the No. 2 high-temperature membrane dust collector (4-7). The discharge port of the dechlorinating agent waste bin (4) is connected to the solid waste bin through a pipeline. The system also includes a dechlorination agent preparation unit (2) for preparing dechlorination agent. The discharge port of the dechlorination agent preparation unit (2) is connected in sequence to a 3# rotary feeder valve (2-1), a dechlorination agent 1# bin (2-2), a 2# rotary feeder valve (2-3), a dechlorination agent 2# bin (2-4), and a 1# rotary feeder valve (2-5) through a pipeline along the dechlorination agent flow direction. The discharge port of the 1# rotary feeder valve (2-5) is connected to the inlet of the 1# pneumatic conveying valve (2-6). The air inlet of the 1# pneumatic conveying valve (2-6) is connected to the outlet of the third high-temperature fan (3-4) through a pipeline equipped with a 1# conveying air control valve (2-6-1). The discharge port of the 1# pneumatic conveying valve (2-6) is connected to the dechlorination tower (3).

2. The plastic pyrolysis forced dechlorination system according to claim 1, characterized in that, The pyrolysis unit (1) includes a pyrolyzer, which is provided with several No. 1 exhaust pipes (1-7) connected to the first pyrolysis gas pipeline (1-9) and several No. 2 exhaust pipes (1-8) connected to the second pyrolysis gas pipeline (1-10); both No. 1 exhaust pipes (1-7) and No. 2 exhaust pipes (1-8) are provided with pyrolysis gas pressure gauges (1-3) and pyrolysis gas thermometers (1-4) for measuring the pyrolysis gas pressure and gas temperature inside the pipe, and No. 1 gas analyzer (1-9-1) is provided on the first pyrolysis gas pipeline (1-9).

3. The plastic pyrolysis forced dechlorination system according to claim 2, characterized in that, It also includes a nitrogen storage tank, the outlet of which is connected to the outlet of the rotary feeder valve (2-1) via a pipeline equipped with a nitrogen control valve (2-2-3) and the inlet of the rotary feeder valve (2-3) via a pipeline equipped with a nitrogen control valve (2-2-4); the dechlorinating agent silo 1 (2-2) is equipped with a level gauge (2-2-1) and a gas analyzer (2-2-2), and the dechlorinating agent silo 2 (2-4) is equipped with a level gauge (2-4-1).

4. The plastic pyrolysis forced dechlorination system according to claim 2, characterized in that, The first dust removal discharge pipeline is equipped with a 4# rotary feed valve (3-3-3). The outlet of the 4# rotary feed valve (3-3-3) is connected to the inlet of the 2# pneumatic conveying valve (3-3-4). The outlet of the 2# pneumatic conveying valve (3-3-4) is connected to the inlet of the dechlorination tower (3). The 2# pneumatic conveying valve (3-3-4) is connected to the outlet of the third high-temperature fan (3-4) through the 2# conveying gas control valve (3-3-4-1).

5. The plastic pyrolysis forced dechlorination system according to claim 3, characterized in that, The second dust removal and discharge pipeline is equipped with a No. 5 rotary feeder valve (4-3). The outlet of the No. 5 rotary feeder valve (4-3) is connected to the inlet of the No. 3 pneumatic conveying valve (4-4). The outlet of the No. 3 pneumatic conveying valve (4-4) is connected to the dechlorinating agent waste bin (4). The air inlet of the No. 3 pneumatic conveying valve (4-4) is connected to the outlet of the third high-temperature fan (3-4) through the No. 3 conveying gas control valve (4-4-1). The outlet of the nitrogen storage tank is connected to the inlet of the No. 3 pneumatic conveying valve (4-4) through the No. 3 nitrogen control valve (4-5).

6. The plastic pyrolysis forced dechlorination system according to claim 2, characterized in that, The desalination water pipeline is equipped with a temperature control valve (3-2), and the No. 1 exhaust pipe (1-7) and No. 2 exhaust pipe (1-8) are respectively equipped with a high chlorine control valve (1-1) and a low chlorine control valve (1-2); the dechlorination tower (3) is equipped with a dechlorination tower (3) thermometer; the dechlorination agent waste silo (4) is equipped with a No. 4 level gauge (4-1), a No. 4 gas analyzer (4-8) and a waste silo pressure gauge (4-9).

7. The plastic pyrolysis forced dechlorination system according to claim 1, characterized in that, The ash storage silo is equipped with a No. 3 level gauge (3-3-1) and a sampling analyzer (3-3-2); between the outlet of the No. 2 high-temperature membrane dust collector (4-7) and the inlet of the fourth high-temperature fan (4-7-2), a No. 3 gas analyzer (4-7-1) and a No. 1 shut-off valve (4-6) are installed in sequence.

8. The plastic pyrolysis forced dechlorination system according to claim 1, characterized in that, The preset pressure value range is 0-1 kPa, and the preset content range is 5%-10%.

9. A method for a plastic pyrolysis forced dechlorination system as described in claim 1, characterized in that, Includes the following steps: S1, under the action of the gas source, an excess of dechlorinating agent is delivered into the dechlorination tower (3). At the same time, dechlorinating water is sprayed into the dechlorination tower (3) through the dechlorination water spray port which is on the same plane as the dechlorinating agent delivery port, forming a liquid film on the surface of the dechlorinating agent. S2, in the pyrolysis unit (1), waste plastic is pyrolyzed to generate pyrolysis gas. According to the critical temperature of the pyrolysis gas, the high-chlorine pyrolysis gas is pumped into the dechlorination tower (3) to react with the dechlorination agent in the dechlorination tower (3) and the low-chlorine pyrolysis gas is transported to the next process through the pipeline. S3, the mixed gas after dechlorination reaction in the dechlorination tower (3) is transported to the No. 1 high temperature dust collector for gas-solid separation; the content of unreacted dechlorinating agent in the separated primary dechlorinating agent ash is monitored, and under the action of the gas source, the primary dechlorinating agent ash with the content of unreacted dechlorinating agent lower than the preset content is transported to the dechlorinating agent waste bin (4), and the primary dechlorinating agent ash with the content of unreacted dechlorinating agent higher than the preset content is transported to the dechlorination tower (3) for recycling; part of the separated primary dust removal pyrolysis gas is pressurized by the third high temperature fan (3-4) and used as a gas source, and the other part is transported to the subsequent process; S4, the primary dust removal gas entering the dechlorinating agent waste silo (4) is transported to the No. 2 high temperature membrane dust collector (4-7) for gas-solid separation. The separated secondary dechlorinating agent ash is transported to the dechlorinating agent waste silo (4), and the separated secondary dust removal pyrolysis gas is transported to the next process.

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