A method and system for pyrolysis of waste plastics

Abstract

This disclosure relates to a method and system for the pyrolysis of waste plastics, comprising the following steps: feeding chlorine-containing waste plastics into a first screw-type heating and conveying device for dehydration, degassing, and volume reduction treatment to obtain dehydrated, degassed, and volume-reduced plastics; feeding the dehydrated, degassed, and volume-reduced plastics into a second screw-type heating and conveying device, where they are contacted with a dechlorination adsorbent for liquefaction and dechlorination treatment to obtain dechlorinated plastics; feeding the dechlorinated plastics into a viscosity-reducing cracking unit for viscosity-reducing cracking treatment to obtain viscosity-reducing cracked plastic oil; feeding the viscosity-reducing cracked plastic oil into a heating unit for heating treatment to obtain heated plastic oil; feeding the heated plastic oil into a pyrolysis reaction unit for pyrolysis reaction treatment to obtain pyrolysis products and coke; and feeding the pyrolysis products into a separation unit for separation treatment to obtain dry gas, liquefied petroleum gas, and pyrolysis oil. This method can effectively achieve large-scale, continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics, improving the efficiency of the waste plastic pyrolysis process.

Description

Technical Field

[0001] This disclosure relates to the field of waste plastic resource recycling, and specifically to a method and system for pyrolysis of waste plastics. Background Technology

[0002] Chemical recycling is widely considered a sustainable technology capable of high-value utilization of waste plastics. However, globally, its development is still in its early stages, accounting for only 1% of waste plastic processing. With changes in global environmental policies, particularly the commitments to carbon reduction, carbon peaking, and carbon neutrality, refining companies worldwide are increasingly focusing on chemical recycling of waste plastics, especially in EU countries. Companies like BUSF, BP, and Shell have developed chemical recycling technologies for waste plastics, and it is projected that by 2030, chemical recycling technology will account for 13% of waste plastic recycling. Currently, pyrolysis remains the mainstream processing technology. Its simplicity, low cost, and wide adaptability to raw materials give it economic advantages and technical feasibility. Waste plastics that can be processed by pyrolysis mainly include aged plastics excavated from landfills and waste plastics from dynamic household waste. However, the presence of mixed plastics like PVC and chlorine-containing additives results in high chlorine content in the pyrolysis oil, reaching up to 4000 mg / kg, with the majority being organochlorides, significantly impacting oil quality. Therefore, it is urgent to develop a technology for deep dechlorination of chlorine-containing waste plastics to prepare low-chlorine pyrolysis oil. This technology is of great significance for realizing the closed-loop recycling of waste plastics.

[0003] 202010457518.3 discloses a method and system for treating chlorinated waste plastics. The method involves dechlorinating the chlorinated waste plastics in a dechlorination device using a shaftless stirring screw, isolating air and at 180-320℃, to obtain molten material and chlorine-containing gas. The molten material is then pyrolyzed in a pyrolysis device under vacuum conditions at 500-700℃ to produce pyrolytic carbon and pyrolysis steam. However, due to problems such as low heat transfer efficiency, uneven heating, and low dechlorination temperature in the dechlorination device, the chlorine removal rate of the dechlorinated molten plastics is low, only 70%.

[0004] ZL201610606090.8 discloses a device and method for the harmless treatment of waste plastics. In this method, a large screw feeder heats the waste plastics to 100-250°C and feeds them into a dechlorination separator for dechlorination reaction. Since the dechlorination reaction of PVC and the addition reaction of olefins occur simultaneously, the dechlorination rate is not high under the condition of separating HCl without external force. Moreover, at 250°C, the waste plastics only soften into plastic polymer materials, and their phase is a non-flowing, non-liquid, plastic solid, which is difficult to output from the dechlorination separator.

[0005] Patent No. 201810272820.4 discloses a method for preparing low-chlorinated plastic pyrolysis oil. This method involves staged, stepwise heating of a mixed plastic containing PVC. Within the temperature range where PVC decomposes and releases hydrogen chloride, the released hydrogen chloride is completely removed by nitrogen purging or vacuum extraction. A composite catalyst is then added to deeply dechlorinate and catalytically pyrolyze the remaining material, yielding low-chlorinated plastic pyrolysis oil. However, this method is a batch reaction and cannot achieve large-scale, continuous production of low-chlorinated pyrolysis oil from chlorinated waste plastics. Furthermore, its dechlorination unit suffers from low heat transfer efficiency, uneven heating, and localized overheating, resulting in incomplete dechlorination and the unavoidable production of significant amounts of organochlorides. Consequently, the chlorine content in the pyrolysis light oil remains high (>1900 mg / kg). Summary of the Invention

[0006] The purpose of this disclosure is to provide a method and system for the pyrolysis of waste plastics, which can effectively realize the large-scale, continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics and improve the efficiency of the waste plastic pyrolysis process.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a method for pyrolyzing waste plastics, comprising the following steps:

[0008] S1. Chlorine-containing waste plastic is fed into the first screw-type heating and conveying device for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastic.

[0009] S2. The dehydrated, degassed, and volume-reduced plastic is fed into the second screw-type heating and conveying device, where it comes into contact with the dechlorination adsorbent and undergoes liquefaction and dechlorination treatment to obtain dechlorinated plastic.

[0010] S3. The dechlorinated plastic is fed into a viscosity-reducing cracking unit for viscosity-reducing cracking treatment to obtain viscosity-reduced cracked plastic oil;

[0011] S4. The viscosity-reducing cracked plastic oil is fed into a heating unit for heating treatment to obtain heated plastic oil;

[0012] S5. The heated plastic oil is introduced into the pyrolysis reaction unit for pyrolysis reaction treatment to obtain pyrolysis products and coke.

[0013] S6. The pyrolysis products are fed into a separation unit for separation processing to obtain dry gas, liquefied gas and pyrolysis oil.

[0014] Optionally, the second screw-type heating conveyor is provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet in sequence along the material conveying direction;

[0015] The method further includes: during the conveying of the dehydrated, degassed, and volume-reduced plastic in the second screw-type heating and conveying device, introducing dechlorination adsorbent into the second screw-type heating and conveying device through any one or more of the first dechlorination adsorbent inlet, the second dechlorination adsorbent inlet, and the third dechlorination adsorbent inlet, so as to contact the dehydrated, degassed, and volume-reduced plastic for dechlorination treatment;

[0016] Optionally, the interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet is 60-180 cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet is 60-180 cm.

[0017] Optionally, in step S1, the inlet temperature of the first screw-type heating and conveying device is 100–200°C, the outlet temperature is 120–300°C, the residence time is 0.5–20 min, the conveying line speed is 0.002–0.08 m / s, and the screw internal pressure is 0.1–8 MPa; preferably, the inlet temperature of the first screw-type heating and conveying device is 120–180°C, the outlet temperature is 150–250°C, the residence time is 1–10 min, the conveying line speed is 0.004–0.04 m / s, and the screw internal pressure is 0.1–5 MPa.

[0018] Optionally, the feeding rate of the chlorinated plastic is 10-130 g / s, preferably 20-100 g / s;

[0019] Optionally, the chlorinated plastic includes PVC and one or more selected from LDPE, HDPE, PP and PS.

[0020] Optionally, in step S2, the inlet temperature of the second screw-type heating and conveying device is 150–350°C, the outlet temperature is 250–450°C, the residence time is 0.8–27 min, the conveying line speed is 0.0015–0.05 m / s, and the screw internal pressure is 0.0001–5 MPa; preferably, the inlet temperature of the second screw-type heating and conveying device is 200–300°C, the outlet temperature is 300–430°C, the residence time is 1.6–20 min, the conveying line speed is 0.002–0.025 m / s, and the screw internal pressure is 0.1–3 MPa; optionally, the feeding rate of the dehydrated, degassed, and volume-reducing plastic is 10–130 g / s, preferably 20–100 g / s; the continuous feeding rate of the dechlorination adsorbent is 1–80 g / s, preferably 4–60 g / s.

[0021] Optionally, in step S2, the dechlorination adsorbent is selected from one or more of metal oxides, metal hydroxides, and carbonates;

[0022] Optionally, the metal oxide is selected from one or more of calcium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, nickel oxide, and copper oxide;

[0023] The metal hydroxide is selected from one or more of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, iron hydroxide, and aluminum hydroxide;

[0024] The carbonate is selected from one or more of calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, magnesium carbonate, copper carbonate, and ammonium carbonate.

[0025] Preferably, the molar ratio of the dechlorination adsorbent to the chlorine in the chlorine-containing waste plastic is 1:0.1 to 20, and more preferably 1:0.5 to 10.

[0026] Optionally, in step S3, the conditions for the viscosity-reducing cracking treatment include: a reaction temperature of 350–460°C, a residence time of 2–150 min, and a reaction pressure of 0.0001–5 MPa; preferably, the reaction temperature is 370–430°C, the residence time is 5–120 min, and the reaction pressure is 0.0001–3 MPa.

[0027] Optionally, the viscosity reduction cracking unit uses a viscosity reduction reactor to perform the viscosity reduction cracking treatment. Preferably, the viscosity reduction reactor is an adiabatic viscosity reduction reactor.

[0028] Optionally, in step S4, the heating unit is a heating furnace;

[0029] Optionally, the heating treatment conditions include: the outlet temperature of the heating furnace is 430–580°C, and the steam injection rate is 0.1–6% by weight; preferably, the outlet temperature of the heating furnace is 450–550°C, and the steam injection rate is 0.5–5% by weight.

[0030] Optionally, in step S5, the conditions for the pyrolysis reaction treatment include: a pyrolysis tower top pressure of 0.01–1 MPa, a pyrolysis reaction temperature of 430–560 °C, and a pyrolysis reaction time of 10–120 s; preferably, the pyrolysis tower top pressure is 0.05–0.6 MPa, the pyrolysis reaction temperature is 450–550 °C, and the pyrolysis reaction time is 20–80 s.

[0031] Optionally, the method further includes: under the action of a vacuum system, the remaining chlorine-containing gas phase that has not been adsorbed by the dechlorination adsorbent in the second screw heating and conveying device enters the hydrogen chloride absorption unit and contacts the hydrogen chloride adsorbent to perform hydrogen chloride absorption treatment, thereby obtaining a dechlorinated gas phase;

[0032] Optionally, the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7; optionally, the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0033] The second aspect of this disclosure provides a system for the pyrolysis of waste plastics, the system comprising a first screw-type heating and conveying device, a second screw-type heating and conveying device, a viscosity-reducing cracking unit, a heating unit, a pyrolysis reaction unit, and a separation unit;

[0034] The first screw-type heating and conveying device includes a waste plastic inlet and a dehydrated, degassed, and volume-reduced plastic outlet; the first screw-type heating and conveying device is configured to dehydrate, degassed, and reduce the volume of chlorine-containing waste plastic to obtain dehydrated, degassed, and volume-reduced plastic.

[0035] The second screw-type heating and conveying device includes a dehydration, degassing, and volume-reducing plastic inlet, a dechlorination adsorbent inlet, and a dechlorinated plastic outlet; the dehydration, degassing, and volume-reducing plastic inlet is connected to the dehydration, degassing, and volume-reducing plastic outlet of the first screw-type heating and conveying device; the second screw-type heating and conveying device is configured to liquefy and dechlorinate the dehydration, degassing, and volume-reducing plastic to obtain dechlorinated plastic;

[0036] The viscosity-reducing cracking unit includes a dechlorinated plastic inlet and a viscosity-reducing cracked plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw-type heating and conveying device; the viscosity-reducing cracking unit is configured to perform viscosity-reducing cracking treatment on the dechlorinated plastic to obtain viscosity-reducing cracked plastic oil;

[0037] The heating unit includes a viscosity-reducing cracked plastic oil inlet and a heated plastic oil outlet, wherein the viscosity-reducing cracked plastic oil inlet is connected to the viscosity-reducing cracked plastic oil outlet of the viscosity-reducing cracking unit; the heating unit is configured to heat the viscosity-reducing cracked plastic oil to obtain heated plastic oil.

[0038] The pyrolysis reaction unit includes a heating plastic oil inlet and a pyrolysis product outlet; the heating plastic oil inlet is connected to the heating plastic oil outlet of the heating unit; the pyrolysis reaction unit is configured to perform a pyrolysis reaction on the heating plastic oil to obtain pyrolysis products and coke.

[0039] The separation unit includes a pyrolysis product inlet, a dry gas outlet, a liquefied gas outlet, and a pyrolysis oil outlet; the pyrolysis product inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit; the separation unit is configured to separate the pyrolysis products to obtain dry gas, liquefied gas, and pyrolysis oil.

[0040] Optionally, the system further includes a hydrogen chloride absorption unit, which includes a chlorine-containing gas inlet and a dechlorinated gas phase outlet, and is also equipped with a hydrogen chloride absorbent; the second screw-type heating and conveying device further includes a chlorine-containing gas phase outlet; the chlorine-containing gas inlet of the hydrogen chloride absorption unit is connected to the chlorine-containing gas phase outlet of the second screw-type heating and conveying device; the hydrogen chloride absorption unit is configured to absorb the remaining chlorine-containing gas phase in the second screw-type heating and conveying device that has not been adsorbed by the dechlorination absorbent to obtain a dechlorinated gas phase;

[0041] Optionally, the second screw-type heating conveying device includes a screw-type heating conveying equipment and a vacuum device connected to the screw-type heating conveying equipment; preferably, the screw-type heating conveying equipment is selected from twin-screw or single-screw conveying equipment;

[0042] Preferably, the second screw-type heating conveying device is provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet in sequence along the material conveying direction. The first dechlorination adsorbent inlet is connected to the first dechlorination adsorbent silo, the second dechlorination adsorbent inlet is connected to the second dechlorination adsorbent silo, and the third dechlorination adsorbent inlet is connected to the third dechlorination adsorbent silo.

[0043] Through the above technical solution, this disclosure provides a method and system for the pyrolysis of waste plastics. This disclosure reduces the viscosity and chlorine content of liquefied waste plastics by dehydrating, degassing, and reducing volume, liquefying and dechlorinating, and then performing viscosity reduction and cracking treatments, without coking or excessive cracking. This results in a homogeneous, highly fluid, low-chlorine liquefied waste plastic that can be pumped. The plastic is then rapidly heated to the pyrolysis reaction temperature using a furnace or similar method, and transported to a pyrolysis tower for further pyrolysis. The dechlorination adsorbent added during the pyrolysis dechlorination process can adsorb HCl released from the high-temperature decomposition of chlorinated compounds in situ, reducing the formation of organochlorides and yielding low-chlorine pyrolysis oil. Using this waste plastic pyrolysis method, landfill waste plastics can be dehydrated, degassed, dechlorinated, and reduced in volume on-site. Subsequent pyrolysis and recycling can be centrally processed, facilitating large-scale production and reducing processing costs. The method is simple, requires relatively little equipment investment, and can effectively achieve large-scale, continuous production of low-chlorine pyrolysis oil from chlorinated waste plastics, improving the efficiency of waste plastic pyrolysis.

[0044] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0045] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0046] Figure 1 This is a process flow diagram of the waste plastic pyrolysis method disclosed in this publication.

[0047] Explanation of reference numerals in the attached figures

[0048] 1-Waste plastic silo, 2-First screw-type heating and conveying device, 3-Second screw-type heating and conveying device, 4-Dechlorination adsorbent silo, 5-Dechlorination adsorbent silo, 6-Dechlorination adsorbent silo, 7-Hydrogen chloride absorption unit, 8-Viscosity reduction cracking unit, 9-Heating unit, 10-Pyrolysis reaction unit, 11-Separation unit. Detailed Implementation

[0049] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0050] The first aspect of this disclosure provides a method for pyrolyzing waste plastics, comprising the following steps:

[0051] S1. Chlorine-containing waste plastic is fed into the first screw-type heating and conveying device 2 for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastic.

[0052] S2. The dehydrated, degassed, and volume-reduced plastic is fed into the second screw-type heating and conveying device 3, where it comes into contact with the dechlorination adsorbent and undergoes liquefaction and dechlorination treatment to obtain dechlorinated plastic.

[0053] S3. The dechlorinated plastic is fed into the viscosity reduction cracking unit 8 for viscosity reduction cracking treatment to obtain viscosity reduction cracked plastic oil.

[0054] S4. The viscosity-reducing cracked plastic oil is introduced into the heating unit 9 for heating treatment to obtain heated plastic oil;

[0055] S5. The heated plastic oil is introduced into the pyrolysis reaction unit 10 for pyrolysis reaction treatment to obtain pyrolysis products and coke.

[0056] S6. The pyrolysis products are fed into the separation unit 11 for separation processing to obtain dry gas, liquefied gas and pyrolysis oil.

[0057] This disclosure provides a method for the pyrolysis of waste plastics. By subjecting chlorine-containing waste plastics to dehydration, degassing, and volume reduction treatments, liquefaction and dechlorination treatments, and viscosity reduction and cracking treatments, the viscosity and chlorine content of the liquefied waste plastics are reduced without coking or excessive cracking, forming a homogeneous, highly fluid, low-chlorine pyrolysis waste plastic that can be pumped. This fluidized waste plastic is then rapidly heated to the pyrolysis reaction temperature using a furnace or similar method, and transported to a pyrolysis tower for further pyrolysis. The dechlorination adsorbent added during the pyrolysis dechlorination process in this disclosure can adsorb HCl released from the high-temperature decomposition of chlorine-containing compounds in situ, reducing the formation of organochlorides and yielding low-chlorine pyrolysis oil. Through this waste plastic pyrolysis method, landfill waste plastics can be dehydrated, degassed, dechlorinated, and reduced in volume on-site. Subsequent pyrolysis and recycling can be centrally processed, facilitating large-scale production and reducing processing costs. This method is simple, requires relatively little equipment investment, and can effectively achieve large-scale, continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics, improving the efficiency of waste plastic pyrolysis.

[0058] In one specific embodiment, the chlorine-containing plastic includes polyvinyl chloride (PVC) and one or more selected from low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP). The waste plastics in this disclosure can be directly sourced from landfills.

[0059] In one embodiment, in step S1, the inlet temperature of the first screw-type heating and conveying device 2 is 100-200°C, the outlet temperature is 120-300°C, the residence time is 0.5-20 min, the conveying line speed is 0.002-0.08 m / s, and the screw internal pressure is 0.1-8 MPa; the feeding rate of the chlorinated plastic is 10-130 g / s.

[0060] In a preferred embodiment, in step S1, the inlet temperature of the first screw-type heating conveyor 2 is 120–180°C, the outlet temperature is 150–250°C, the residence time is 1–10 min, the conveying linear speed is 0.004–0.04 m / s, and the screw internal pressure is 0.1–5 MPa; the feeding rate of the chlorinated plastic is 10–130 g / s, preferably 20–100 g / s. Performing dehydration, degassing, and volume reduction treatment according to the conditions of this embodiment can achieve better waste plastic treatment results.

[0061] In a preferred embodiment, such as Figure 1As shown, the second screw-type heating conveying device 3 is provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet in sequence along the material conveying direction; wherein the first dechlorination adsorbent inlet is connected to the first dechlorination adsorbent silo, the second dechlorination adsorbent inlet is connected to the second dechlorination adsorbent silo, and the third dechlorination adsorbent inlet is connected to the third dechlorination adsorbent silo.

[0062] The method further includes: during the conveying process of the dehydrated, degassed, and volume-reduced plastic in the second screw-type heating and conveying device 3, introducing dechlorination adsorbent into the second screw-type heating and conveying device 3 through any one or more of the first, second, and third dechlorination adsorbent inlets, so as to contact the dehydrated, degassed, and volume-reduced plastic for dechlorination treatment. In this disclosure, by setting three inlets for introducing dechlorination adsorbent in different conveying processes, the dechlorination adsorbent can be made to fully contact the chlorinated plastic, and the inlet position of the dechlorination adsorbent can be flexibly selected according to different chlorinated plastic raw materials and process conditions.

[0063] In one specific implementation, such as Figure 1 As shown, the first dechlorination adsorbent inlet is located at the inlet end of the second screw-type heating and conveying device 3, and its distance from the plastic inlet of the second screw-type heating and conveying device 3 can be 60-180cm. The third dechlorination adsorbent inlet is located at the outlet end of the second screw-type heating and conveying device 3, and its distance from the dechlorinated plastic outlet of the second screw-type heating and conveying device 3 can be 0-60cm. The interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet can be 60-180cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet can be 60-180cm.

[0064] In one embodiment, in step S2, the inlet temperature of the second screw-type heating and conveying device 3 is 150–350°C, the outlet temperature is 250–450°C, the residence time is 0.8–27 min, the conveying line speed is 0.0015–0.05 m / s, and the screw internal pressure is 0.1–5 MPa; optionally, the feeding rate of the dehydrated, degassed, and volume-reducing plastic is 10–130 g / s; and the continuous feeding rate of the dechlorination adsorbent is 1–80 g / s.

[0065] In a preferred embodiment, in step S2, the inlet temperature of the second screw-type heating and conveying device 3 is 200–300°C, the outlet temperature is 300–430°C, the residence time is 1.6–20 min, the conveying linear speed is 0.002–0.025 m / s, and the screw internal pressure is 0.1–3 MPa. Optionally, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 20–100 g / s; the continuous feed rate of the dechlorination adsorbent is 4–60 g / s. Treating waste plastics according to the optimized liquefaction and dechlorination conditions in this embodiment can further improve liquefaction and dechlorination efficiency.

[0066] In one embodiment, in step S2, the dechlorination adsorbent is selected from one or more of metal oxides, metal hydroxides, and carbonates;

[0067] Optionally, the metal oxide is selected from one or more of calcium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, nickel oxide, and copper oxide;

[0068] The metal hydroxide is selected from one or more of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, iron hydroxide, and aluminum hydroxide;

[0069] The carbonate is selected from one or more of calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, magnesium carbonate, copper carbonate, and ammonium carbonate.

[0070] In a preferred embodiment, the molar ratio of the dechlorination adsorbent to the chlorine in the chlorine-containing waste plastic is 1:0.5 to 20, preferably 1:0.5 to 10.

[0071] In one embodiment, in step S3, the conditions for the viscosity-reducing cracking treatment include: a reaction temperature of 350–460°C, a residence time of 2–150 min, and a reaction pressure of 0.1–5 MPa; preferably, the reaction temperature is 370–430°C, the residence time is 5–120 min, and the reaction pressure is 0.1–3 MPa. The viscosity-reducing cracked plastic oil obtained using the optimized viscosity-reducing cracking conditions provided in this embodiment can achieve better pyrolysis results in subsequent pyrolysis processes.

[0072] In one specific embodiment, the viscosity reduction cracking unit 8 uses a viscosity reduction reactor to perform the viscosity reduction cracking treatment. Preferably, the viscosity reduction reactor is an adiabatic viscosity reduction reactor.

[0073] In one embodiment, in step S4, the heating unit 9 is a heating furnace;

[0074] Optionally, the heating treatment conditions include: the outlet temperature of the heating furnace is 430–580°C, and the steam injection rate is 0.1–6% by weight; preferably, the outlet temperature of the heating furnace is 450–550°C, and the steam injection rate is 0.5–5% by weight.

[0075] In one embodiment, in step S5, the conditions for the pyrolysis reaction treatment include: a pyrolysis tower top pressure of 0.01–1 MPa, a pyrolysis reaction temperature of 430–560°C, and a pyrolysis reaction time of 10–120 s; preferably, the pyrolysis tower top pressure is 0.05–0.6 MPa, the pyrolysis reaction temperature is 450–550°C, and the pyrolysis reaction time is 20–80 s.

[0076] In one specific embodiment, the method further includes: under the action of a vacuum system, the remaining chlorine-containing gas phase in the second screw-type heating and conveying device 3 that has not been adsorbed by the dechlorination adsorbent enters the hydrogen chloride absorption unit 7 to contact the hydrogen chloride adsorbent and perform hydrogen chloride absorption treatment to obtain a dechlorinated gas phase;

[0077] Optionally, the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7; optionally, the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water. This disclosure employs a hydrogen chloride absorption unit to further absorb the unadsorbed chlorine in the second screw-type heating and conveying device 3, and uses a vacuum system to quickly separate the hydrogen chloride, avoiding secondary reactions of hydrogen chloride, improving the dechlorination efficiency of waste plastics, and reducing the corrosion pressure on subsequent equipment.

[0078] The second aspect of this disclosure is a system for the pyrolysis of waste plastics, such as Figure 1 As shown, the system includes a first screw-type heating and conveying device 2, a second screw-type heating and conveying device 3, a viscosity-reducing cracking unit 8, a heating unit 9, a pyrolysis reaction unit 10, and a separation unit 11;

[0079] The first screw-type heating and conveying device 2 includes a waste plastic inlet and a dehydrated, deaerated, and volume-reduced plastic outlet; the first screw-type heating and conveying device 2 is configured to dehydrate, deaerated, and reduce the volume of chlorine-containing waste plastic to obtain dehydrated, deaerated, and volume-reduced plastic.

[0080] The second screw-type heating and conveying device 3 includes a dehydration, degassing, and volume-reducing plastic inlet, a dechlorination adsorbent inlet, and a dechlorinated plastic outlet; the dehydration, degassing, and volume-reducing plastic inlet is connected to the dehydration, degassing, and volume-reducing plastic outlet of the first screw-type heating and conveying device 2; the second screw-type heating and conveying device 3 is configured to liquefy and dechlorinate the dehydration, degassing, and volume-reducing plastic to obtain dechlorinated plastic.

[0081] The viscosity reduction cracking unit 8 includes a dechlorinated plastic inlet and a viscosity reduction cracked plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw-type heating and conveying device 3; the viscosity reduction cracking unit 8 is configured to perform viscosity reduction cracking treatment on the dechlorinated plastic to obtain viscosity reduction cracked plastic oil.

[0082] Heating unit 9 includes a viscosity-reducing cracked plastic oil inlet and a heated plastic oil outlet. The viscosity-reducing cracked plastic oil inlet is connected to the viscosity-reducing cracked plastic oil outlet of viscosity-reducing cracking unit 8. Heating unit 9 is configured to heat-treat the viscosity-reducing cracked plastic oil to obtain heated plastic oil.

[0083] The pyrolysis reaction unit 10 includes a heating plastic oil inlet and a pyrolysis product outlet; the heating plastic oil inlet is connected to the heating plastic oil outlet of the heating unit 9; the pyrolysis reaction unit 10 is configured to perform a pyrolysis reaction on the heating plastic oil to obtain pyrolysis products and coke.

[0084] The separation unit 11 includes a pyrolysis product inlet, a dry gas outlet, a liquefied gas outlet, and a pyrolysis oil outlet; the pyrolysis product inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit 10; the separation unit 11 is configured to separate the pyrolysis products to obtain dry gas, liquefied gas, and pyrolysis oil.

[0085] In one specific implementation, such as Figure 1 As shown, the system also includes a hydrogen chloride absorption unit 7, which includes a chlorine-containing gas inlet and a dechlorinated gas phase outlet. The hydrogen chloride absorption unit 7 is also equipped with a hydrogen chloride absorbent. The second screw-type heating and conveying device 3 also includes a chlorine-containing gas phase outlet. The chlorine-containing gas inlet of the hydrogen chloride absorption unit 7 is connected to the chlorine-containing gas phase outlet of the second screw-type heating and conveying device 3. The hydrogen chloride absorption unit 7 is configured to absorb the remaining chlorine-containing gas phase in the second screw-type heating and conveying device 3 that has not been adsorbed by the dechlorination absorbent, thereby obtaining a dechlorinated gas phase.

[0086] Optionally, the second screw-type heating conveying device 3 includes a screw-type heating conveying equipment and a vacuum device connected to the screw-type heating conveying equipment; preferably, the screw-type heating conveying equipment is selected from twin-screw or single-screw conveying equipment.

[0087] In a preferred embodiment, the second screw-type heating and conveying device 3 is provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet in sequence along the material conveying direction. The first dechlorination adsorbent inlet is connected to the first dechlorination adsorbent silo, the second dechlorination adsorbent inlet is connected to the second dechlorination adsorbent silo, and the third dechlorination adsorbent inlet is connected to the third dechlorination adsorbent silo.

[0088] In one specific embodiment, the pyrolysis reaction unit 10 may include one or more pyrolysis reaction vessels; for example, it may include two pyrolysis reaction vessels arranged in parallel. The heating unit 9 may be a heating furnace; the separation unit 11 may be a product separation tower; and the hydrogen chloride absorption unit 7 may be a tank structure. All the devices used in this disclosure are conventional structures in the art.

[0089] use Figure 1 The waste plastic pyrolysis system shown includes the following processes for pyrolyzing waste plastics:

[0090] The chlorine-containing waste plastic is fed from the waste plastic silo 1 into the first screw-type heated conveyor 2, where it undergoes dehydration, degassing, and volume reduction treatment to obtain dehydrated, degassed, and volume-reduced plastic. This dehydrated, degassed, and volume-reduced plastic then enters the second screw-type heated conveyor 3 and comes into contact with the dechlorination adsorbent in the dechlorination adsorbent silo. In the second screw-type heated conveyor 3, it undergoes liquefaction and dechlorination treatment. During the dechlorination process, under the action of a vacuum system, the remaining chlorine-containing gas phase in the second screw-type heated conveyor 3 that has not been adsorbed by the dechlorination adsorbent is drawn into a hydrogen chloride absorption chamber. Unit 7 contacts the hydrogen chloride absorbent for hydrogen chloride absorption treatment, resulting in a dechlorinated gas phase. The dechlorinated plastic obtained from the output of the second screw-type heating and conveying device 3 enters the viscosity-reducing cracking unit 8 for viscosity-reducing cracking treatment, resulting in viscosity-reduced cracked plastic oil and first dry gas. The viscosity-reduced cracked plastic oil is first heated by the heating unit 9 to obtain heated plastic oil, and then sent to the pyrolysis reaction unit 10 for pyrolysis reaction treatment, resulting in pyrolysis products and coke. The obtained pyrolysis products enter the separation unit 11 for separation treatment, resulting in second dry gas, liquefied gas, and pyrolysis oil.

[0091] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0092] Example 1

[0093] according to Figure 1The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heating and conveying device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heating and conveying device is 150°C, the outlet temperature is 200°C, the internal pressure of the screw is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heating and conveying device is 8 min. The specifications of the first screw-type heating and conveying device are as follows: inner diameter of 50cm and screw length of 240cm; wherein the first dechlorination adsorbent inlet is located at the inlet end of the second screw-type heating and conveying device 3, and its distance from the plastic inlet of the second screw-type heating and conveying device 3 is 30cm; the third dechlorination adsorbent inlet is located at the outlet end of the second screw-type heating and conveying device 3, and its distance from the dechlorinated plastic outlet of the second screw-type heating and conveying device 3 is 30cm; the interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet is 90cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet is 90cm;

[0094] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the first dechlorination adsorbent silo at the inlet of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:1. The continuous feed rate of the dechlorination adsorbent is 4 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 50 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature is 400℃, the internal pressure of the screw is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0095] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0096] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 60min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0097] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 50s at 480℃ and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-1, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-1 are listed in Table 1.

[0098] Example 2

[0099] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5% by weight) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 60 g / s, the inlet temperature of the first screw-type heated conveyor is 150°C, the outlet temperature is 200°C, the screw internal pressure is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor is 8 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0100] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the second dechlorination adsorbent silo in the middle section of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:1. The continuous feed rate of the dechlorination adsorbent is 4.8 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 50 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature of the second screw-type heating and conveying device is 400℃, the internal pressure of the screw is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying device is 150 mmHg.

[0101] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) for hydrogen chloride absorption treatment.

[0102] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, the pressure is 0.1MPa, and the residence time is 40min to obtain liquefied dechlorinated waste plastic oil.

[0103] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 60s at 480℃ and 0.2MPa at the top of the tower. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-2, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-2 are listed in Table 1.

[0104] Example 3

[0105] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor device is 150°C, the outlet temperature is 200°C, the screw internal pressure is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 8 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0106] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the third dechlorination adsorbent silo at the end of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:1. The continuous feed rate of the dechlorination adsorbent is 4 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature is 400℃, the screw internal pressure is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0107] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0108] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosified cracked liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 20min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0109] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 40s at 480℃ and a tower top pressure of 0.25MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-3, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-3 are listed in Table 1.

[0110] Example 4

[0111] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5% by weight) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor device is 160°C, the outlet temperature is 210°C, the screw internal pressure is 0.5 MPa, the conveying linear speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 8 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0112] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the first dechlorination adsorbent silo at the inlet of the second screw-type heating and conveying device. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:3. The continuous feed rate of the dechlorination adsorbent is 1.3 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 220℃, the outlet temperature is 390℃, the screw internal pressure is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0113] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0114] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 60min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0115] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 50s at 480℃ and a tower top pressure of 0.2MPa. The pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-4, coke and pyrolysis gas. The chlorine content analysis results of pyrolysis oil DDT-4 are listed in Table 1.

[0116] Example 5

[0117] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor device is 140°C, the outlet temperature is 200°C, the screw internal pressure is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 8 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0118] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the second dechlorination adsorbent silo in the middle section of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:3. The continuous feed rate of the dechlorination adsorbent is 1.3 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 220℃, the outlet temperature is 390℃, the internal pressure of the screw is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0119] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0120] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 40min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0121] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 50s at 480℃ and a tower top pressure of 0.15MPa. The pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-5, coke and pyrolysis gas. The chlorine content analysis results of pyrolysis oil DDT-5 are listed in Table 1.

[0122] Example 6

[0123] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor device is 150°C, the outlet temperature is 200°C, the screw internal pressure is 0.5 MPa, the conveying linear speed is 0.004 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 10 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0124] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the third dechlorination adsorbent silo at the end of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:3. The continuous feed rate of the dechlorination adsorbent is 1.3 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 210℃, the outlet temperature is 390℃, the screw internal pressure is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0125] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0126] The liquefied dechlorinated waste plastic is fed into a viscosity reduction tank for viscosity reduction cracking treatment to obtain liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 20min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0127] The dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 50s at 480℃ and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-6, coke and pyrolysis gas. The chlorine content analysis results of pyrolysis oil DDT-6 are listed in Table 1.

[0128] Example 7

[0129] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor device is 150°C, the outlet temperature is 200°C, the screw internal pressure is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 8 min. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0130] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the first dechlorination adsorbent silo at the inlet of the second screw-type heating and conveying device. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:1. The continuous feed rate of the dechlorination adsorbent is 4 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature is 410℃, the screw internal pressure is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied dechlorinated waste plastic. The screw-type heating and conveying equipment is not vacuumed.

[0131] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 400℃, residence time is 20min, and pressure is 0.15MPa to obtain liquefied dechlorinated waste plastic oil.

[0132] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 50s at 480℃ and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-7, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-7 are listed in Table 1.

[0133] Example 8

[0134] This embodiment treats waste plastics using the same method as in Embodiment 1, but differs from Embodiment 1 in that:

[0135] The first screw-type heating and conveying device 2 performs dehydration, degassing, and volume reduction treatment to obtain dehydrated, degassed, and volume-reduced waste plastics. During this process, the process conditions are changed: the feed rate of the chlorine-containing plastics is 130 g / s, the inlet temperature of the first screw-type heating and conveying device is 200℃, the outlet temperature is 300℃, the screw internal pressure is 6 MPa, the conveying linear speed is 0.08 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heating and conveying device is 0.5 min; the remaining processes are the same as in implementation 1. Finally, pyrolysis oil DDT-8, coke, and pyrolysis gas are obtained. The chlorine content analysis results of the pyrolysis oil DDT-8 are listed in Table 1.

[0136] Example 9

[0137] This embodiment treats waste plastics using the same method as in Embodiment 1, but differs from Embodiment 1 in that:

[0138] In the process of treating dehydrated, degassed, and volume-reduced waste plastics in the second screw-type heating and conveying device 3: the dehydrated, degassed, and volume-reduced waste plastics are mixed with calcium carbonate in the first dechlorination adsorbent silo at the inlet of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastics is 1:20. The continuous feed rate of the dechlorination adsorbent is 0.2 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastics is 130 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 350℃, the outlet temperature is 450℃, the screw internal pressure is 5 MPa, the conveying linear speed is 0.04 m / s, and the residence time is 1 min, resulting in liquefied dechlorinated waste plastics. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg. The remaining processes are the same as in Implementation 1. Finally, pyrolysis oil DDT-9, coke, and pyrolysis gas are obtained. The chlorine content analysis results of the pyrolysis oil DDT-9 are listed in Table 1.

[0139] Example 10

[0140] This embodiment treats waste plastics using the same method as in Embodiment 1, but differs from Embodiment 1 in that:

[0141] During the process of feeding the liquefied dechlorinated waste plastic into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment: the viscosity reduction cracking treatment temperature is 460℃, the residence time is 150min, and the pressure is 5MPa, to obtain liquefied dechlorinated waste plastic oil. The remaining process is the same as in embodiment 1. Finally, pyrolysis oil DDT-10, coke, and pyrolysis gas are obtained, among which the chlorine content analysis results of pyrolysis oil DDT-10 are listed in Table 1.

[0142] Example 11

[0143] This embodiment treats waste plastics using the same method as in Embodiment 1, but differs from Embodiment 1 in that:

[0144] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 580℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 120s at 560℃ and 1MPa at the top of the tower. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-11, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-11 are listed in Table 1.

[0145] Example 12

[0146] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5% by weight) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 150 g / s, the inlet temperature of the first screw-type heated conveyor device is 80°C, the outlet temperature is 110°C, the screw internal pressure is 8.5 MPa, the conveying line speed is 0.1 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor device is 4 minutes. The specifications of the first screw-type heated conveyor device are the same as in Example 1.

[0147] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with calcium carbonate in the first dechlorination adsorbent silo at the inlet of the second screw-type heating and conveying device 3. The molar ratio of calcium carbonate to chlorine in the waste plastic is 1:25. The continuous feed rate of the dechlorination adsorbent is 0.16 g / s, the feed rate of the dehydrated, degassed, and volume-reduced plastic is 140 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 140℃, the outlet temperature is 240℃, the screw internal pressure is 5.5 MPa, the conveying linear speed is 0.026 m / s, and the residence time is 1.5 min, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 100 mmHg.

[0148] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0149] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 440℃, residence time is 130min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0150] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 420℃ and the steam injection rate is 7% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 100s at 440℃ and 1MPa at the top of the tower. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-12, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-12 are listed in Table 1.

[0151] Comparative Example 1

[0152] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heated conveyor is 150℃, the outlet temperature is 200℃, the internal pressure of the screw is 0.5 MPa, the conveying line speed is 0.005 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heated conveyor is 8 min.

[0153] Then, the dehydrated, degassed, and volume-reduced waste plastic is directly liquefied and dechlorinated in the second screw-type heating and conveying device 3 without adding a dechlorination adsorbent. The feed rate of the dehydrated, degassed, and volume-reduced waste plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature is 400℃, the screw internal pressure is 0.3 MPa, the conveying linear speed is 0.004 m / s, and the residence time is 10 min, resulting in liquefied and dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0154] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit. The gaseous material is then contacted with the hydrogen chloride absorbent (NaOH solution, concentration 30% by weight) to absorb the hydrogen chloride, resulting in a dechlorinated gas phase that exits the hydrogen chloride absorption unit.

[0155] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 390℃, residence time is 60min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0156] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 2 hours at 480℃ and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil DDT-8, coke and pyrolysis gas, etc. The chlorine content analysis results of pyrolysis oil DDT-13 are listed in Table 1.

[0157] Comparative Example 2

[0158] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (PVC mass fraction of 5 wt%) to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heating and conveying device 2 to obtain dehydrated, degassed, and reduced-volume waste plastic. The feed rate of the chlorine-containing plastic is 50 g / s, the inlet temperature of the first screw-type heating and conveying device is 150°C, the outlet temperature is 200°C, the internal pressure of the screw is 0.4 MPa, the conveying line speed is 0.004 m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heating and conveying device is 8 min.

[0159] Then, the dehydrated, degassed, and volume-reduced waste plastic is directly liquefied and dechlorinated in the second screw-type heating and conveying device 3 without adding dechlorination adsorbent. The feeding rate of the dehydrated, degassed, and volume-reduced waste plastic is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200℃, the outlet temperature is 390℃, and the residence time is 10 min, resulting in liquefied and dechlorinated waste plastic. The screw-type heating and conveying equipment is not vacuumed.

[0160] The liquefied dechlorinated waste plastic is fed into the viscosity reduction cracking unit 8 (viscosity reduction tank) for viscosity reduction cracking treatment to obtain viscosity-reduced liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 380℃, residence time is 60min, and pressure is 0.1MPa to obtain liquefied dechlorinated waste plastic oil.

[0161] The liquefied dechlorinated waste plastic oil is first heated in heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500℃ and the steam injection rate is 1% by weight. Then, the obtained high-temperature liquefied waste plastic is sent to the pyrolysis reactor and pyrolyzed for 2 hours at 480℃ and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated by the separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc. The chlorine content analysis results of the pyrolysis oil DDT-14 are listed in Table 1.

[0162] Comparative Example 3

[0163] This comparative example refers to the process flow and treatment method in Example 1, but differs from Example 1 in that:

[0164] Instead of setting up the first screw-type heating and conveying device 2 and performing dehydration, degassing and volume reduction treatment on the chlorine-containing waste plastic, the chlorine-containing waste plastic is directly introduced into the second screw-type heating and conveying device 3. The rest of the process is the same as in Example 1, and finally pyrolysis oil DDT-15 is obtained.

[0165] Comparative Example 4

[0166] This comparative example refers to the process flow and treatment method in Example 1, but differs from Example 1 in that:

[0167] Without setting up the viscosity reduction cracking unit 8, without performing viscosity reduction cracking treatment, the rest of the process is the same as in Example 1, and finally pyrolysis oil DDT-16 is obtained.

[0168] Comparative Example 5

[0169] This comparative example refers to the process flow and treatment method in Example 1, but differs from Example 1 in that:

[0170] Without setting up heating unit 9, the viscosity-reducing cracked plastic oil from the viscosity-reducing cracking unit is directly introduced into the pyrolysis reaction unit 10 without heating treatment. The rest of the process is the same as in Example 1, and finally the pyrolysis oil DDT-17 is obtained.

[0171] The viscosities of the liquefied dechlorinated waste plastic oils obtained after treatment in the viscosity-reducing cracking unit of the above examples and comparative examples are listed in Table 1 below; the chlorine content analysis results of the pyrolysis oil obtained from the pyrolysis reactor are listed in Table 1 below.

[0172] Table 1

[0173]

[0174] Note: "—" in the table refers to measurements exceeding the instrument's upper limit.

[0175] The dechlorination rate (%) is calculated as follows: (mass fraction of chlorine in the original plastic - mass fraction of chlorine in the intermediate product after dechlorination and viscosity reduction) / mass fraction of chlorine in the original plastic × 100%.

[0176] As can be seen from the data in Table 1 above:

[0177] Compared with Comparative Example 1 (no dechlorination adsorbent was added to the second screw conveyor) and Comparative Example 2 (no dechlorination adsorbent was added to the second screw conveyor and no vacuum was applied), the dechlorination rate of waste plastics treated by the method and system provided in this disclosure in Examples 1 to 12 is higher.

[0178] Compared with Comparative Example 3 (without the first screw-type heating conveying device 2), Example 1, which processes waste plastics according to the process provided in this application, achieves a higher dechlorination rate and a lower viscosity of the liquefied dechlorinated waste plastic oil obtained during the process at 200°C.

[0179] Comparing Example 1 with Examples 8-9, it can be seen that the process conditions for dehydration, degassing, and volume reduction treatment in the first screw-type heating and conveying device 2 and liquefaction treatment in the second screw-type heating and conveying device 3 in Example 1 are within the optimized range provided in this disclosure. Therefore, compared with Examples 8-9, the viscosity of the viscosity-reducing cracked plastic oil obtained in Example 1 is lower, and the final dechlorination rate is higher.

[0180] Comparing Example 12 with Examples 1-11, it can be seen that Example 1-11, which treats waste plastics according to the conditions provided in this disclosure, has a lower viscosity at 200°C and a higher dechlorination rate than Example 12.

[0181] The mass composition of the pyrolysis products obtained from the above embodiments and comparative examples is listed in Table 2 below.

[0182] Table 2

[0183] Product distribution / weight % Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 CO 0.15 0.11 0.10 0.25 0.23 0.20 0.27 <![CDATA[CO2]]> 0.04 0.05 0.07 0.13 0.10 0.17 0.18 gas 9.18 9.49 9.65 9.95 10.13 10.05 9.66 liquid 88.52 87.82 87.91 87.21 87.13 87.23 87.68 Coke + Ash 2.11 2.53 2.27 2.46 2.41 2.35 2.21 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00

[0184] Continued from Table 2

[0185] Product distribution / weight % Example 8 Example 9 Example 10 Example 11 Example 12 CO 0.13 0.18 0.19 0.31 0.18 <![CDATA[CO2]]> 0.03 0.09 0.13 0.17 0.11 gas 9.13 9.56 9.72 10.15 10.17 liquid 88.06 88.02 87.95 87.09 86.78 Coke + Ash 2.65 2.15 2.01 2.28 2.76 total 100.00 100.00 100.00 100.00 100.00

[0186] Continued from Table 2

[0187] Product distribution / weight % Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 CO 0.36 0.39 0.51 0.31 0.56 <![CDATA[CO2]]> 0.21 0.25 0.32 0.17 0.35 gas 9.65 10.15 9.89 9.96 10.47 liquid 86.70 86.72 86.75 86.77 85.04 Coke + Ash 3.08 2.49 2.53 2.79 3.58 total 100.00 100.00 100.00 100.00 100.00

[0188] According to the data in Table 2 above:

[0189] Comparative Examples 1-5, which did not treat waste plastics according to the method provided in this disclosure, had a liquid content (including gasoline, diesel, and wax oil) of 85.04-86.77% by weight and a total carbon and ash content of 2.49-3.58% by weight in the product distribution. Examples 1-12, which treated waste plastics according to the method and system provided in this disclosure, had a liquid content of 88.52% by weight and a total carbon and ash content of 2.11% by weight in the product distribution. This demonstrates that the waste plastic treatment method and system provided in this disclosure can achieve a higher liquid yield and a lower carbon and ash yield.

[0190] Comparing Examples 1-11 with Example 12 of this application, it can be seen that the waste plastic pyrolysis in Examples 1-11, carried out according to the process conditions provided in this disclosure, can achieve higher liquid yield and lower coke and ash yield compared to Example 12.

[0191] Comparing Example 1 with Examples 8-11, it can be seen that Example 1 uses the optimized process conditions provided by this disclosure to pyrolyze waste plastics. Compared with Examples 8-11, the pyrolysis products obtained in Example 1 have a higher liquid yield and lower coke and ash yields.

[0192] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0193] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0194] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for pyrolyzing waste plastics, characterized in that, Includes the following steps: S1. Chlorine-containing waste plastics are fed into the first screw-type heating and conveying device (2) for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastics; S2. The dehydrated, degassed, and volume-reduced plastic is fed into the second screw-type heating and conveying device (3) to come into contact with the dechlorination adsorbent for liquefaction and dechlorination treatment to obtain liquefied dechlorinated plastic; the molar ratio of the dechlorination adsorbent to the chlorine in the chlorine-containing waste plastic is 1:0.1~20. S3. The liquefied dechlorinated plastic is fed into the viscosity reduction cracking unit (8) for viscosity reduction cracking treatment to obtain viscosity reduction cracked plastic oil and first dry gas; The conditions for the viscosity-reducing cracking treatment include: a reaction temperature of 350~460℃, a residence time of 20~150min, and a reaction pressure of 0.1~5MPa; S4. The viscosity-reducing cracked plastic oil is introduced into the heating unit (9) for heating treatment to obtain heated plastic oil; S5. The heated plastic oil is introduced into the pyrolysis reaction unit (10) for pyrolysis reaction treatment to obtain pyrolysis products and coke; the conditions of the pyrolysis reaction treatment include: the pressure at the top of the pyrolysis tower is 0.01~1MPa, the pyrolysis reaction temperature is 430~560℃, and the pyrolysis reaction time is 10~120s. S6. The pyrolysis products are fed into the separation unit (11) for separation processing to obtain the second dry gas, liquefied gas and pyrolysis oil.

2. The method according to claim 1, characterized in that, The second screw-type heating and conveying device (3) is provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet in sequence along the material conveying direction; The method further includes: during the conveying process of the dehydrated, degassed, and volume-reduced plastic in the second screw-type heating and conveying device (3), introducing dechlorination adsorbent into the second screw-type heating and conveying device (3) through any one or more of the first dechlorination adsorbent inlet, the second dechlorination adsorbent inlet, and the third dechlorination adsorbent inlet, so as to contact the dehydrated, degassed, and volume-reduced plastic for dechlorination treatment.

3. The method according to claim 2, characterized in that, The interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet is 60~180cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet is 60~180cm.

4. The method according to claim 1, characterized in that, In step S1, the inlet temperature of the first screw-type heating and conveying device (2) is 100~200℃, the outlet temperature is 120~300℃, the residence time is 0.5~20min, the conveying line speed is 0.002~0.08m / s, and the screw internal pressure is 0.1~8MPa.

5. The method according to claim 4, characterized in that, The inlet temperature of the first screw-type heating and conveying device (2) is 120~180℃, the outlet temperature is 150~250℃, the residence time is 1~10min, the conveying line speed is 0.004~0.04m / s, and the screw internal pressure is 0.1~5MPa.

6. The method according to claim 4, characterized in that, The feeding rate of the chlorine-containing waste plastic is 10~130g / s.

7. The method according to claim 6, characterized in that, The feeding rate of the chlorine-containing waste plastic is 20~100g / s.

8. The method according to claim 1, characterized in that, The chlorine-containing waste plastics include PVC and one or more selected from LDPE, HDPE, PP and PS.

9. The method according to claim 1, characterized in that, In step S2, the inlet temperature of the second screw-type heating and conveying device (3) is 150~350℃, the outlet temperature is 250~450℃, the residence time is 0.8~27min, the conveying line speed is 0.0015~0.05m / s, and the screw internal pressure is 0.0001~5MPa.

10. The method according to claim 9, characterized in that, The inlet temperature of the second screw-type heating and conveying device (3) is 200~300℃, the outlet temperature is 300~430℃, the residence time is 1.6~20min, the conveying line speed is 0.002~0.025m / s, and the screw internal pressure is 0.1~3MPa.

11. The method according to claim 1, characterized in that, The feeding rate of the dehydrated, degassed, and volume-reducing plastic is 10~130 g / s; the continuous feeding rate of the dechlorination adsorbent is 1~80 g / s.

12. The method according to claim 11, characterized in that, The feeding rate of the dehydrated, degassed, and volume-reducing plastic is 20~100 g / s; the continuous feeding rate of the dechlorination adsorbent is 4~60 g / s.

13. The method according to claim 1, characterized in that, In step S2, the dechlorination adsorbent is selected from one or more of metal oxides, metal hydroxides and carbonates.

14. The method according to claim 13, characterized in that, The metal oxide is selected from one or more of calcium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, nickel oxide and copper oxide; The metal hydroxide is selected from one or more of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, iron hydroxide, and aluminum hydroxide; The carbonate is selected from one or more of calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, copper carbonate, and ammonium carbonate.

15. The method according to claim 1, characterized in that, In step S2, the molar ratio of the dechlorination adsorbent to the chlorine in the chlorine-containing waste plastic is 1:0.5~10.

16. The method according to claim 1, characterized in that, In step S3, the conditions for the viscosity reduction cracking treatment include: a reaction temperature of 370~430℃, a residence time of 20~120min, and a reaction pressure of 0.1~3MPa.

17. The method according to claim 1, characterized in that, In step S3, the viscosity reduction cracking unit (8) uses a viscosity reduction reactor to perform the viscosity reduction cracking treatment.

18. The method according to claim 17, characterized in that, The viscosity-reducing reactor is an adiabatic viscosity-reducing reactor.

19. The method according to claim 1, characterized in that, In step S4, the heating unit (9) is a heating furnace.

20. The method according to claim 19, characterized in that, The conditions for the heat treatment include: the outlet temperature of the heating furnace is 430~580℃.

21. The method according to claim 19, characterized in that, The conditions for the heat treatment include: the steam injection rate of the heating furnace is 0.1~6 by weight.

22. The method according to claim 20, characterized in that, The conditions for the heat treatment include: the outlet temperature of the heating furnace is 450~550℃.

23. The method according to claim 21, characterized in that, The conditions for the heat treatment include: the steam injection rate of the heating furnace is 0.5 to 5% by weight.

24. The method according to claim 1, characterized in that, In step S5, the conditions for the pyrolysis reaction treatment include: the pressure at the top of the pyrolysis tower is 0.05~0.6MPa, the pyrolysis reaction temperature is 450~550℃, and the pyrolysis reaction time is 20~80s.

25. The method according to claim 1, characterized in that, The method further includes: under the action of a vacuum system, the remaining chlorine-containing gas phase in the second screw heating and conveying device (3) that has not been adsorbed by the dechlorination adsorbent enters the hydrogen chloride absorption unit (7) and comes into contact with the hydrogen chloride adsorbent to perform hydrogen chloride absorption treatment and obtain a dechlorinated gas phase.

26. The method according to claim 25, characterized in that, The hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7.

27. The method according to claim 26, characterized in that, The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

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