Waste plastic pyrolysis method and system

Abstract

The invention relates to a waste plastic pyrolysis method and system, and the method comprises the following steps: enabling chlorine-containing waste plastics to enter a first screw type heating conveying device for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassed and volume-reduced plastics; enabling the dehydrated, degassed and volume-reduced plastic to enter a second screw type heating and conveying device to be in contact with a dechlorination adsorbent, and carrying out liquefaction treatment and dechlorination treatment to obtain dechlorinated plastic; the dechlorinated plastic enters a visbreaking unit for visbreaking treatment, and visbreaking plastic oil is obtained; the visbreaking plastic oil enters a heating unit to be heated, and heated plastic oil is obtained; the heated plastic oil enters a pyrolytic reaction unit to be subjected to pyrolytic reaction treatment, and a pyrolytic product and coke are obtained; the pyrolysis product enters a separation unit for separation treatment, and dry gas, liquefied gas and pyrolysis oil are obtained. Large-scale and continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics can be effectively realized, and the efficiency of a waste plastic pyrolysis process is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of waste plastic resource recycling, and in particular, to a method and system for pyrolyzing waste plastic. Background Art

[0002] Chemical recycling is generally considered to be a sustainable technology that can achieve high-value resource utilization of waste plastics, but globally, the development of this technology is still in its early stages, accounting for only 1% of the waste plastics processing volume. With the changes in global environmental policies, especially the proposal and implementation of commitments such as carbon emission reduction, carbon peak, and carbon neutrality, refining companies in various countries have gradually turned their attention to the chemical recycling of waste plastics, with the EU countries being the most prominent. For example, BUSF, BP, and Shell have all developed chemical recycling technologies for waste plastics. It is expected that by 2030, the chemical recycling technology for waste plastics will increase to 13%. At this stage, the mainstream treatment technology is still pyrolysis technology. Due to its advantages such as simple process, low cost, and wide adaptability of raw materials, the pyrolysis technology of waste plastics has certain economic advantages and technical feasibility. Waste plastics that can be treated by pyrolysis technology mainly include stale plastics dug out of landfills and waste plastics in dynamic daily garbage. However, due to the presence of these mixed plastics PVC and chlorine-containing additives, the chlorine content in the pyrolysis oil is relatively high, up to 4000 mg / kg, and most of them are organic chlorides, which greatly affects the quality of the oil. Therefore, it is urgent to develop a technology for deep dechlorination of chlorine-containing waste plastics to produce low-chlorine pyrolysis oil, which is of great significance for achieving closed-loop recycling of waste plastics.

[0003] 202010457518.3 discloses a method and system for treating chlorine-containing waste plastics. In this method, the chlorine-containing waste plastics are dechlorinated in a dechlorination device in the form of a shaftless stirring screw, isolated from the air and at 180-320°C to obtain a molten material and chlorine-containing gas; the molten material is then pyrolyzed in a pyrolysis device under vacuum conditions at 500-700°C to produce pyrolytic charcoal and pyrolytic steam. Due to the low heat transfer efficiency, uneven heating and low dechlorination temperature of the dechlorination device, the chlorine removal rate of the dechlorinated molten plastic is low, only 70%.

[0004] ZL201610606090.8 discloses a device and method for harmless treatment of waste plastics. In this method, a large screw feeding device heats the waste plastics to 100-250°C and enters a dechlorination diverter for dechlorination reaction. Since the dechlorination reaction of PVC and the addition reaction of olefins are carried out at the same time, the dechlorination rate is not high under the condition of separating HCl without external force; and the waste plastics are only softened into a plastic polymer material at 250°C, and its physical phase is a non-self-flowing non-liquid plastic solid, which is difficult to output from the dechlorination diverter.

[0005] 201810272820.4 discloses a method for preparing low-chlorine plastic cracking oil, which gradually heats mixed plastics containing PVC in sections, and after completely removing the released hydrogen chloride by nitrogen purging or vacuum extraction within the temperature range of PVC decomposition, a composite catalyst is added to perform deep dechlorination and catalytic thermal cracking of the remaining materials to obtain low-chlorine plastic cracking oil. This method is an intermittent reaction, and it is impossible to achieve large-scale and continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics. Because its dechlorination device also has problems such as low heat transfer efficiency, uneven heating and local overheating, the dechlorination is not thorough and it is difficult to avoid the production of more organic chlorides. The chlorine content in the pyrolysis light oil is still high (>1900mg / kg). Summary of the invention

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

[0007] In order to achieve the above-mentioned object, the present disclosure provides a method for pyrolyzing waste plastics in a first aspect, comprising the following steps:

[0008] S1, allowing the chlorine-containing waste plastic to enter a first screw-type heating and conveying device for dehydration, degassing and volume reduction treatment to obtain a dehydrated, degassed and volume-reduced plastic;

[0009] S2, allowing the dehydrated, degassed and volume-reduced plastic to enter a second screw-type heating and conveying device, contact with a dechlorination adsorbent, and perform liquefaction and dechlorination treatment to obtain a dechlorinated plastic;

[0010] S3, allowing the dechlorinated plastic to enter a visbreaking unit for visbreaking treatment to obtain visbreaking plastic oil;

[0011] S4, allowing the viscous and cracked plastic oil to enter a heating unit for heating treatment to obtain heated plastic oil;

[0012] S5, allowing the heated plastic oil to enter a pyrolysis reaction unit for pyrolysis reaction treatment to obtain pyrolysis products and coke;

[0013] S6. The pyrolysis product enters a separation unit for separation treatment to obtain dry gas, liquefied gas and pyrolysis oil.

[0014] Optionally, the second screw-type heating and 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;

[0015] The method further comprises: during the conveying process of the dehydrated, degassed and volume-reduced plastic in the second screw-type heating and conveying device, introducing a 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 to perform a dechlorination treatment;

[0016] Optionally, the interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet is 60 to 180 cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet is 60 to 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 0.5-20min, the conveying line speed is 0.002-0.08m / s, and the pressure inside the screw is 0.1-8MPa; 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 1-10min, the conveying line speed is 0.004-0.04m / s, and the pressure inside the screw is 0.1-5MPa;

[0018] Optionally, the feed rate of the chlorine-containing plastic is 10 to 130 g / s, preferably 20 to 100 g / s;

[0019] Optionally, the chlorine-containing 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 0.8-27min, the conveying line speed is 0.0015-0.05m / s, and the pressure inside the screw is 0.0001-5MPa; 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 1.6-20min, the conveying line speed is 0.002-0.025m / s, and the pressure inside the screw is 0.1-3MPa; optionally, the feed rate of the dehydrated, degassed and volume-reduced plastic is 10-130g / s, preferably 20-100g / s; the continuous feed rate of the dechlorination adsorbent is 1-80g / s, preferably 4-60g / 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 element in the chlorine-containing waste plastic is 1:0.1-20, preferably 1:0.5-10.

[0026] Optionally, in step S3, the conditions of the visbreaking treatment include: reaction temperature of 350-460°C, residence time of 2-150 min, reaction pressure of 0.0001-5 MPa; preferably, reaction temperature of 370-430°C, residence time of 5-120 min, reaction pressure of 0.0001-3 MPa;

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

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

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

[0030] Optionally, in step S5, the conditions for the pyrolysis reaction treatment include: the top pressure of the pyrolysis tower is 0.01-1 MPa, the pyrolysis reaction temperature is 430-560°C, and the pyrolysis reaction time is 10-120 s; preferably, the top pressure of the pyrolysis tower 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 comprises: under the action of a vacuum system, allowing the remaining chlorine-containing gas phase in the second screw-type heating and conveying device that is not adsorbed by the dechlorination adsorbent to enter a hydrogen chloride absorption unit to contact the hydrogen chloride absorbent, and perform hydrogen chloride absorption treatment to obtain a dechlorinated gas phase;

[0032] Optionally, the hydrogen chloride absorbent is water or an alkali solution with a pH greater than 7; optionally, the alkali 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] A second aspect of the present disclosure provides a system for pyrolyzing waste plastics, the system comprising a first screw-type heating and conveying device, a second screw-type heating and conveying device, a visbreaking unit, a heating unit, a pyrolysis reaction unit, and a separation unit;

[0034] The first screw-type heating and conveying device comprises a waste plastic inlet and a dehydrated, degassed and reduced-volume plastic outlet; the first screw-type heating and conveying device is configured to perform dehydration, degassing and volume reduction treatment on the chlorine-containing waste plastic to obtain dehydrated, degassed and reduced-volume plastic;

[0035] The second screw-type heating and conveying device comprises a dehydrated, degassed and volume-reduced plastic inlet, a dechlorination adsorbent inlet and a dechlorination plastic outlet; the dehydrated, degassed and volume-reduced plastic inlet is connected to the dehydrated, degassed and volume-reduced plastic outlet of the first screw-type heating and conveying device; the second screw-type heating and conveying device is configured to perform liquefaction and dechlorination treatment on the dehydrated, degassed and volume-reduced plastic to obtain the dechlorination plastic;

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

[0037] The heating unit comprises a visbreaking plastic oil inlet and a heated plastic oil outlet, wherein the visbreaking plastic oil inlet is connected to the visbreaking plastic oil outlet of the visbreaking unit; the heating unit is configured to heat the visbreaking plastic oil to obtain heated plastic oil;

[0038] The pyrolysis reaction unit comprises a heated plastic oil inlet and a pyrolysis product outlet; the heated plastic oil inlet is connected to the heated plastic oil outlet of the heating unit; the pyrolysis reaction unit is configured to perform pyrolysis reaction on the heated 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 product to obtain dry gas, liquefied gas and pyrolysis oil.

[0040] Optionally, the system further comprises a hydrogen chloride absorption unit, the hydrogen chloride absorption unit comprises a chlorine-containing gas inlet and a dechlorinated gas phase outlet, and a hydrogen chloride absorbent is further provided in the hydrogen chloride absorption unit; the second screw-type heating and conveying device further comprises 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 perform hydrogen chloride absorption treatment on the remaining chlorine-containing gas phase in the second screw-type heating and conveying device that is not adsorbed by the dechlorinated adsorbent to obtain a dechlorinated gas phase;

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

[0042] Preferably, the second screw-type heating and 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 transmission 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 scheme, the present disclosure provides a method and system for pyrolysis of waste plastics. The present disclosure reduces the viscosity and chlorine content of the liquefied waste plastics without coking and excessive cracking by dehydrating, degassing and reducing the volume, liquefying and dechlorinating the chlorine-containing waste plastics, and forming a uniform, fluid and low-chlorine fluidized waste plastic that can be transported by a pump; then the waste plastics are treated by a heating furnace and the like to quickly reach the pyrolysis reaction temperature, and the high-temperature liquefied waste plastics are transported to a pyrolysis tower for pyrolysis reaction. The dechlorination adsorbent added in the pyrolysis dechlorination process of the present disclosure can in situ adsorb HCl released by the decomposition of chlorine-containing compounds at high temperature in the whole process, reduce the generation of organic chlorides, and obtain low-chlorine pyrolysis oil. Through the method for pyrolysis of waste plastics disclosed in the present disclosure, waste plastics in landfills can be dehydrated, degassed, dechlorinated and reduced in volume in situ, and subsequent pyrolysis recovery can be processed in a centralized manner, which is easy to expand the production scale and reduce processing costs; the method has a simple process and relatively less equipment investment, and can effectively realize large-scale and continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics, thereby improving the pyrolysis efficiency of waste plastics.

[0044] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0046] Figure 1 It is a process flow chart of the method for pyrolysis of waste plastics provided by the present invention.

[0047] Description of Reference Numerals

[0048] 1-waste plastic silo, 2-first screw heating and conveying device, 3-second screw heating and conveying device, 4-dechlorination adsorbent silo, 5-dechlorination adsorbent silo, 6-dechlorination adsorbent silo, 7-hydrogen chloride absorption unit, 8-visbreaking unit, 9-heating unit, 10-pyrolysis reaction unit, 11-separation unit. DETAILED DESCRIPTION

[0049] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

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

[0051] S1, allowing the chlorine-containing waste plastic to enter the first screw-type heating and conveying device 2 for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassed and volume-reduced plastic;

[0052] S2, allowing the dehydrated, degassed and volume-reduced plastic to enter the second screw-type heating and conveying device 3, contact with the dechlorination adsorbent, and perform liquefaction and dechlorination treatment to obtain a dechlorinated plastic;

[0053] S3, allowing the dechlorinated plastic to enter the visbreaking unit 8 for visbreaking treatment to obtain visbreaking plastic oil;

[0054] S4, allowing the viscous and cracked plastic oil to enter the heating unit 9 for heating treatment to obtain heated plastic oil;

[0055] S5, allowing the heated plastic oil to enter the pyrolysis reaction unit 10 for pyrolysis reaction treatment to obtain pyrolysis products and coke;

[0056] S6. The pyrolysis product enters the separation unit 11 for separation treatment to obtain dry gas, liquefied gas and pyrolysis oil.

[0057] The present invention provides a method for pyrolysis of waste plastics, by dehydrating, degassing and reducing the volume of chlorine-containing waste plastics, liquefying, dechlorinating and viscous cracking treatment, reducing the viscosity and chlorine content of the liquefied waste plastics without coking and excessive cracking, forming a uniform, fluid low-chlorine fluidized waste plastic that can be transported by a pump; then the waste plastics are treated by a heating furnace or the like to quickly reach the pyrolysis reaction temperature, and the high-temperature liquefied waste plastics are transported to a pyrolysis tower for pyrolysis reaction. The dechlorination adsorbent added in the pyrolysis dechlorination process of the present invention can in situ adsorb HCl released by the decomposition of chlorine-containing compounds at high temperature in the whole process, reduce the generation of organic chlorides to obtain low-chlorine pyrolysis oil. Through the method for pyrolysis of waste plastics disclosed in the present invention, waste plastics in landfills can be dehydrated, degassed, dechlorinated and reduced in volume on site, and subsequent pyrolysis recovery can be processed in a centralized manner, which is easy to expand the production scale and reduce processing costs; the method has a simple process and relatively less equipment investment, and can effectively realize large-scale and continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics, thereby improving the pyrolysis efficiency of waste plastics.

[0058] In a 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 the present disclosure can be directly waste plastics in 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 0.5-20min, the conveying line speed is 0.002-0.08m / s, and the pressure inside the screw is 0.1-8MPa; the feed rate of the chlorine-containing plastic is 10-130g / s.

[0060] In a preferred embodiment, in step S1, the inlet temperature of the first screw-type heating and conveying device 2 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 pressure inside the screw is 0.1-5 MPa; the feed rate of the chlorine-containing plastic is 10-130 g / s, preferably 20-100 g / s. According to the conditions of this embodiment, dehydration, degassing and volume reduction treatment can be carried out to obtain a better waste plastic treatment effect.

[0061] In a preferred embodiment, Figure 1As shown, the second screw-type heating and conveying device 3 is sequentially provided with a first dechlorination adsorbent inlet, a second dechlorination adsorbent inlet and a third dechlorination adsorbent inlet along the material transmission 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 a 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, and contacting the dehydrated, degassed and volume-reduced plastic to perform dechlorination treatment. In the present disclosure, by setting three inlets for introducing the dechlorination adsorbent in different conveying processes, the dechlorination adsorbent can be fully contacted with the chlorine-containing plastic, and the inlet position of the dechlorination agent can be flexibly selected according to different chlorine-containing plastic raw materials and process conditions.

[0063] In a specific implementation manner, Figure 1 As shown, the first dechlorination adsorbent inlet is arranged at the inlet end of the second screw heating and conveying device 3, and the distance between it and the plastic inlet of the second screw heating and conveying device 3 can be 60 to 180 cm; the third dechlorination adsorbent inlet is arranged at the outlet end of the second screw heating and conveying device 3, and the distance between it and the outlet of the dechlorinated plastic of the second screw heating and conveying device 3 can be 0 to 60 cm; the interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet can be 60 to 180 cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet can be 60 to 180 cm.

[0064] In one embodiment, in step S2, the inlet temperature of the second screw heating and conveying device 3 is 150-350°C, the outlet temperature is 250-450°C, the residence time is 0.8-27min, the conveying line speed is 0.0015-0.05m / s, and the pressure inside the screw is 0.1-5MPa; optionally, the feed rate of the dehydrated, degassed and volume-reduced plastic is 10-130g / s; the continuous feed rate of the dechlorination adsorbent is 1-80g / 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 1.6-20min, the conveying line speed is 0.002-0.025m / s, and the pressure in the screw is 0.1-3MPa; optionally, the feed rate of the dehydrated, degassed and volume-reduced plastic is 20-100g / s; the continuous feed rate of the dechlorination adsorbent is 4-60g / s. The waste plastic treatment according to the optimized liquefaction and dechlorination treatment conditions in this embodiment can further improve the 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 element in the chlorine-containing waste plastic is 1:0.5-20, preferably 1:0.5-10.

[0071] In one embodiment, in step S3, the conditions of the visbreaking treatment include: a reaction temperature of 350 to 460°C, a residence time of 2 to 150 min, and a reaction pressure of 0.1 to 5 MPa; preferably, the reaction temperature is 370 to 430°C, the residence time is 5 to 120 min, and the reaction pressure is 0.1 to 3 MPa. The visbreaking plastic oil obtained by adopting the optimized visbreaking conditions provided in this embodiment can obtain a better pyrolysis effect in the subsequent pyrolysis process.

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

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

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

[0075] In one embodiment, in step S5, the conditions for the pyrolysis reaction treatment include: the top pressure of the pyrolysis tower is 0.01-1 MPa, the pyrolysis reaction temperature is 430-560°C, and the pyrolysis reaction time is 10-120 s; preferably, the top pressure of the pyrolysis tower 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 a specific embodiment, the method further comprises: under the action of a vacuum system, allowing the remaining chlorine-containing gas phase in the second screw-type heating and conveying device 3 that is not adsorbed by the dechlorination adsorbent to enter the hydrogen chloride absorption unit 7 to contact with the hydrogen chloride absorbent, and perform hydrogen chloride absorption treatment to obtain a dechlorinated gas phase;

[0077] Optionally, the hydrogen chloride absorbent is water or an alkali solution with a pH greater than 7; optionally, the alkali solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water. The present disclosure uses a hydrogen chloride absorption unit to further absorb the unabsorbed chlorine in the second screw-type heating and conveying device 3, and uses a vacuum system to quickly separate hydrogen chloride, avoid secondary reaction of hydrogen chloride, improve the dechlorination efficiency of waste plastics, and reduce the subsequent equipment anti-corrosion pressure.

[0078] A second aspect of the present disclosure provides a system for pyrolysis of waste plastics, such as Figure 1 As shown, the system includes a first screw heating and conveying device 2, a second screw heating and conveying device 3, a visbreaking 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, degassed and reduced-volume plastic outlet; the first screw-type heating and conveying device 2 is configured to perform dehydration, degassing and volume reduction treatment on the chlorine-containing waste plastic to obtain dehydrated, degassed and reduced-volume plastic;

[0080] The second screw-type heating and conveying device 3 includes a dehydrated, degassed and volume-reduced plastic inlet, a dechlorination adsorbent inlet and a dechlorination plastic outlet; the dehydrated, degassed and volume-reduced plastic inlet is connected to the dehydrated, degassed and volume-reduced 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 dehydrated, degassed and volume-reduced plastic to obtain the dechlorinated plastic;

[0081] The visbreaking unit 8 includes a dechlorinated plastic inlet and a visbreaking plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw heating and conveying device 3; the visbreaking unit 8 is configured to perform visbreaking treatment on the dechlorinated plastic to obtain visbreaking plastic oil;

[0082] The heating unit 9 includes a visbreaking plastic oil inlet and a heated plastic oil outlet, and the visbreaking plastic oil inlet is connected to the visbreaking plastic oil outlet of the visbreaking unit 8; the heating unit 9 is configured to heat the visbreaking plastic oil to obtain heated plastic oil;

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

[0085] In a specific implementation manner, Figure 1 As shown, the system further includes a hydrogen chloride absorption unit 7, the hydrogen chloride absorption unit 7 includes a chlorine-containing gas inlet and a dechlorinated gas phase outlet, and a hydrogen chloride absorbent is further provided in the hydrogen chloride absorption unit 7; 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 perform hydrogen chloride absorption treatment on the remaining chlorine-containing gas phase in the second screw-type heating and conveying device 3 that is not adsorbed by the dechlorinated adsorbent to obtain a dechlorinated gas phase;

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

[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 transmission 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 a specific embodiment, the pyrolysis reaction unit 10 may include one or more pyrolysis reaction tanks; for example, two pyrolysis reaction tanks 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 is a tank structure. All devices used in the present disclosure are conventional structures in the art.

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

[0090] The chlorine-containing waste plastic is passed from the waste plastic silo 1 into the first screw-type heating and conveying device 2, and is dehydrated, degassed and reduced in volume by the first screw-type heating and conveying device 2 to obtain a dehydrated, degassed and reduced-volume plastic; the dehydrated, degassed and reduced-volume plastic is then passed into the second screw-type heating and conveying device 3 and is contacted with the dechlorination adsorbent in the dechlorination adsorbent silo, so as to be liquefied and dechlorinated in the second screw-type heating and conveying device 3. During the dechlorination process, the remaining chlorine-containing gas phase that is not adsorbed by the dechlorination adsorbent in the second screw-type heating and conveying device 3 is passed into the hydrogen chloride absorption silo under the action of the vacuum system. Unit 7 is in contact with a hydrogen chloride absorbent to carry out hydrogen chloride absorption treatment to obtain a dechlorinated gas phase; the dechlorinated plastic obtained at the output end of the second screw-type heating and conveying device 3 enters a visbreaking unit 8 for visbreaking treatment to obtain visbreaking plastic oil and a first dry gas; the visbreaking plastic oil is first heated by a heating unit 9 to obtain heated plastic oil, and then the heated plastic oil is sent to a pyrolysis reaction unit 10 for pyrolysis reaction treatment to obtain pyrolysis products and coke; the obtained pyrolysis products enter a separation unit 11 for separation treatment to obtain a second dry gas, liquefied gas and pyrolysis oil.

[0091] The present disclosure is further described in detail by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0092] Example 1

[0093] according to Figure 1In the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurized to obtain chlorine-containing waste plastic particles; then, a dehydration, degassing and volume reduction treatment is performed through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 pressure inside 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: the inner diameter is 50cm, and the screw length is 240cm; wherein the first dechlorination adsorbent inlet is arranged at the inlet end of the second screw-type heating and conveying device 3, and the distance from the plastic inlet of the second screw-type heating and conveying device 3 is 30cm, and the third dechlorination adsorbent inlet is arranged at the outlet end of the second screw-type heating and conveying device 3, and the distance from the outlet of the dechlorinated plastic 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 plastics are mixed with calcium carbonate in the first dechlorination adsorbent silo at the input end inlet of the second screw-type heating and conveying device 3, the molar ratio of calcium carbonate to chlorine in the waste plastics is 1:1, the continuous feeding rate of the dechlorination adsorbent is 4g / s, the feeding rate of the dehydrated, degassed and volume-reduced plastics is 50g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200°C, the outlet temperature is 400°C, the pressure in the screw is 0.3MPa, the conveying line speed is 0.004m / s, the residence time is 10min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150mmHg.

[0095] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0096] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the residence time is 60 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0098] Example 2

[0099] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein the feed rate of the chlorine-containing plastic is 60g / s, the inlet temperature of the first screw-type heating and conveying equipment is 150°C, the outlet temperature is 200°C, the pressure in the screw is 0.5MPa, the conveying line speed is 0.005m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heating and conveying equipment is 8min; the specifications of the first screw-type heating and conveying device are the same as those in Example 1.

[0100] Then, the dehydrated, degassed and reduced-volume waste plastics are 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 plastics is 1:1, the continuous feeding rate of the dechlorination adsorbent is 4.8 g / s, the feeding rate of the dehydrated, degassed and reduced-volume plastics is 50 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200°C, the outlet temperature of the second screw-type heating and conveying equipment is 400°C, the pressure in the screw is 0.3 MPa, the conveying line speed is 0.004 m / s, the residence time is 10 min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0101] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent (NaOH solution, concentration of 30 wt%) for hydrogen chloride absorption treatment.

[0102] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the pressure is 0.1 MPa, and the residence time is 40 minutes to obtain liquefied dechlorinated waste plastic oil.

[0103] The liquefied dechlorinated waste plastic oil is first heated by a heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic, the outlet temperature of the heating furnace is 500°C, and the steam injection amount is 1% by weight; then the high-temperature liquefied waste plastic is sent to a pyrolysis reaction device, and pyrolyzed for 60 seconds at 480°C and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated and treated by a separation unit to obtain pyrolysis oil DDT-2, coke and pyrolysis gas, etc., wherein the chlorine content analysis results of the pyrolysis oil DDT-2 are listed in Table 1.

[0104] Example 3

[0105] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 pressure in 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 the same as those in Example 1.

[0106] Then, the dehydrated, degassed and volume-reduced waste plastics are 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 plastics is 1:1, the continuous feeding rate of the dechlorination adsorbent is 4g / s, the feeding rate of the dehydrated, degassed and volume-reduced plastics is 40g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200°C, the outlet temperature is 400°C, the pressure in the screw is 0.3MPa, the conveying line speed is 0.004m / s, the residence time is 10min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150mmHg.

[0107] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0108] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the residence time is 20 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0110] Example 4

[0111] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 160°C, the outlet temperature is 210°C, the pressure in 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 the same as those in Example 1.

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

[0113] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0114] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the residence time is 60 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0116] Example 5

[0117] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 140°C, the outlet temperature is 200°C, the pressure in 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 the same as those in Example 1.

[0118] Then, the dehydrated, degassed and volume-reduced waste plastics are 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 plastics is 1:3, the continuous feeding rate of the dechlorination adsorbent is 1.3 g / s, the feeding rate of the dehydrated, degassed and volume-reduced plastics is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 220°C, the outlet temperature is 390°C, the pressure in the screw is 0.3 MPa, the conveying line speed is 0.004 m / s, the residence time is 10 min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0119] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0120] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the residence time is 40 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0122] Example 6

[0123] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 pressure in the screw is 0.5 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 10 min; the specifications of the first screw-type heating and conveying device are the same as those in Example 1.

[0124] Then, the dehydrated, degassed and volume-reduced waste plastics are 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 plastics is 1:3, the continuous feeding rate of the dechlorination adsorbent is 1.3 g / s, the feeding rate of the dehydrated, degassed and volume-reduced plastics is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 210°C, the outlet temperature is 390°C, the pressure in the screw is 0.3 MPa, the conveying line speed is 0.004 m / s, the residence time is 10 min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0125] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0126] The liquefied dechlorinated waste plastic is sent to a visbreaking tank for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390°C, the residence time is 20 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0128] Example 7

[0129] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is carried out through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 pressure in 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 the same as those in Example 1.

[0130] Then, the dehydrated, degassed and reduced-volume waste plastics are mixed with calcium carbonate in the first dechlorination adsorbent silo at the input end inlet of the second screw-type heating and conveying device, the molar ratio of calcium carbonate to chlorine in the waste plastics is 1:1, the continuous feeding rate of the dechlorination adsorbent is 4g / s, the feeding rate of the dehydrated, degassed and reduced-volume plastics is 40g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200°C, the outlet temperature is 410°C, the pressure in the screw is 0.3MPa, the conveying line speed is 0.004m / s, the residence time is 10min, and liquefied dechlorinated waste plastics are obtained; the screw-type heating and conveying equipment is not vacuumed.

[0131] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 400° C., the residence time is 20 minutes, and the pressure is 0.15 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0133] Example 8

[0134] This embodiment treats waste plastics by referring to the treatment method in Example 1, and the difference from Example 1 is 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. The process conditions are changed: the feed rate of chlorine-containing plastics is 130g / s, the inlet temperature of the first screw-type heating and conveying device is 200°C, the outlet temperature is 300°C, the pressure in the screw is 6MPa, the conveying line speed is 0.08m / s, and the residence time of the material from the inlet to the outlet in the first screw-type heating and conveying device is 0.5min; the rest of the process is the same as implementation 1. Finally, pyrolysis oil DDT-8, coke and pyrolysis gas are obtained, and the chlorine content analysis results of pyrolysis oil DDT-8 are listed in Table 1.

[0136] Example 9

[0137] This embodiment treats waste plastics by referring to the treatment method in Example 1, and the difference from Example 1 is that:

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

[0139] Example 10

[0140] This embodiment treats waste plastics by referring to the treatment method in Example 1, and the difference from Example 1 is that:

[0141] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment: the temperature of the visbreaking treatment is 460°C, the residence time is 150min, and the pressure is 5MPa to obtain liquefied dechlorinated waste plastic oil. The rest of the process is the same as that of implementation 1. Finally, pyrolysis oil DDT-10, coke and pyrolysis gas are obtained, wherein the chlorine content analysis results of pyrolysis oil DDT-10 are listed in Table 1.

[0142] Embodiment 11

[0143] This embodiment treats waste plastics by referring to the treatment method in Example 1, and the difference from Example 1 is that:

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

[0145] Example 12

[0146] according to Figure 1 The process flow shown in the figure is to crush and remove impurities from a mixed plastic containing LDPE, HDPE, PP, PS and PVC (the mass fraction of PVC is 5% by weight) to obtain chlorine-containing waste plastic particles; then, the mixed plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and reduced-volume waste plastic, wherein the feed rate of the chlorine-containing plastic is 150 g / s, the inlet temperature of the first screw-type heating and conveying device is 80° C., the outlet temperature is 110° C., the pressure in the screw 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 heating and conveying device is 4 min; the specifications of the first screw-type heating and conveying device are the same as those in Example 1;

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

[0148] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0149] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 440° C., the residence time is 130 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0151] Comparative Example 1

[0152] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (the mass fraction of PVC is 5% by weight) is crushed and impurized to obtain chlorine-containing waste plastic particles; then, the mixed plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device to obtain dehydrated, degassed and reduced-volume waste plastic, wherein 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 pressure in 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;

[0153] Then, the dehydrated, degassed and volume-reduced waste plastics are 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 plastics is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200° C., the outlet temperature is 400° C., the pressure inside the screw is 0.3 MPa, the conveying line speed is 0.004 m / s, the residence time is 10 min, and liquefied dechlorinated waste plastics are obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0154] In the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit, where it is contacted with a hydrogen chloride absorbent (NaOH solution, with a concentration of 30 wt%) for hydrogen chloride absorption treatment to obtain a dechlorinated gas phase leading out of the hydrogen chloride absorption unit.

[0155] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 390° C., the residence time is 60 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

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

[0157] Comparative Example 2

[0158] according to Figure 1 In the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (PVC mass fraction is 5 weight%) is crushed and impurities are removed to obtain chlorine-containing waste plastic particles; then, dehydration, degassing and volume reduction treatment is performed through a first screw-type heating and conveying device 2 to obtain dehydrated, degassed and volume-reduced waste plastics, wherein 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 pressure inside 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 plastics are 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 plastics is 40 g / s, the inlet temperature of the second screw-type heating and conveying device 3 is 200° C., the outlet temperature is 390° C., and the residence time is 10 min to obtain liquefied dechlorinated waste plastics; the screw-type heating and conveying equipment is not vacuumed.

[0160] The liquefied dechlorinated waste plastic is sent to the visbreaking unit 8 (visbreaking tank) for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C., the residence time is 60 minutes, and the pressure is 0.1 MPa to obtain liquefied dechlorinated waste plastic oil.

[0161] The liquefied dechlorinated waste plastic oil is first heated by a heating unit 9 (heating furnace) to obtain high-temperature liquefied waste plastic, the outlet temperature of the heating furnace is 500°C, and the steam injection amount is 1% by weight; then the high-temperature liquefied waste plastic is sent to a pyrolysis reaction device, and pyrolyzed for 2 hours at 480°C and a tower top pressure of 0.2MPa. The obtained pyrolysis products are separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein 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, and the difference from Example 1 is:

[0164] The first screw heating and conveying device 2 is not provided, and the chlorine-containing waste plastic is not subjected to dehydration, degassing and volume reduction treatment. Instead, the chlorine-containing waste plastic is directly introduced into the second screw heating and conveying device 3. The remaining process is the same as that in Example 1, and pyrolysis oil DDT-15 is finally obtained.

[0165] Comparative Example 4

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

[0167] The visbreaking unit 8 is not provided, and the visbreaking treatment is not performed. The remaining process is the same as that of 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, and the difference from Example 1 is:

[0170] The heating unit 9 is not provided, and the visbreaking plastic oil from the visbreaking unit is directly introduced into the pyrolysis reaction unit 10 without heating treatment. The rest of the process is the same as that of Example 1, and finally the pyrolysis oil DDT-17 is obtained.

[0171] The viscosity of the liquefied dechlorinated waste plastic oil obtained after the above examples and comparative examples were treated in the visbreaking unit is listed in the following Table 1; the chlorine content analysis results of the pyrolysis oil obtained by the pyrolysis reaction device are listed in the following Table 1.

[0172] Table 1

[0173]

[0174] Note: The “—” in the table means that the measurement limit of the instrument is exceeded.

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

[0176] From the data in Table 1 above, we can see that:

[0177] Compared with Comparative Example 1 (no dechlorination adsorbent is added to the second screw conveying device) and Comparative Example 2 (no dechlorination adsorbent is added to the second screw conveying device, and no vacuum is drawn), the methods and systems provided by the present disclosure are used to treat waste plastics in Examples 1 to 12, and the dechlorination rate is higher.

[0178] Comparing Example 1 with Comparative Example 3 (without the first screw-type heating and conveying device 2), Example 1 treats waste plastics according to the process provided in the present application, and the dechlorination rate obtained is higher, and the liquefied dechlorinated waste plastic oil obtained during the treatment process has a lower viscosity at 200°C.

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

[0180] Comparing Example 12 with Examples 1 to 11, it can be seen that Examples 1 to 11 treat waste plastics according to the conditions provided in the present disclosure. Compared with Example 12, the liquefied dechlorinated waste plastic oil obtained in Examples 1 to 11 has a lower viscosity at 200°C and a higher dechlorination rate.

[0181] The mass compositions of the pyrolysis products obtained in the above examples and comparative examples are 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] Table 2

[0185] Product distribution / weight % Example 8 Example 9 Example 10 Embodiment 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] 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, we can see that:

[0189] Comparative Examples 1 to 5 did not treat waste plastics according to the method provided by the present disclosure, and the liquid content (including gasoline, diesel and wax oil) in the product distribution was 85.04 to 86.77% by weight, and the total content of charcoal and ash was 2.49 to 3.58% by weight; Examples 1 to 12 treated waste plastics according to the method and system provided by the present disclosure, and the liquid content in the product distribution could reach 88.52% by weight, and the total content of charcoal and ash could reach 2.11% by weight, indicating that the method and system for treating waste plastics provided by the present disclosure can obtain a higher liquid yield and a lower charcoal and ash yield;

[0190] Comparing Examples 1 to 11 of the present application with Example 12, it can be seen that in Examples 1 to 11, waste plastics are pyrolyzed according to the process conditions provided in the present disclosure. Compared with Example 12, Examples 1 to 11 can obtain a higher liquid yield and a lower coke and ash yield;

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

[0192] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

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

[0194] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for pyrolysis of waste plastics, characterized in that: The following steps are involved: S1, allowing the chlorine-containing waste plastic to enter the first screw-type heating and conveying device (2) for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassed and volume-reduced plastic; S2, allowing the dehydrated, degassed and volume-reduced plastic to enter a second screw-type heating and conveying device (3), to contact with a dechlorination adsorbent, to undergo liquefaction and dechlorination treatment, and to obtain a dechlorinated plastic; S3, allowing the dechlorinated plastic to enter a visbreaking unit (8) for visbreaking treatment to obtain visbreaking plastic oil and a first dry gas; S4, allowing the viscous and cracked plastic oil to enter a heating unit (9) for heating treatment to obtain heated plastic oil; S5, allowing the heated plastic oil to enter a pyrolysis reaction unit (10) for pyrolysis reaction treatment to obtain pyrolysis products and coke; S6. The pyrolysis product enters a separation unit (11) for separation treatment to obtain a 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 comprises: during the conveying process of the dehydrated, degassed and volume-reduced plastic in the second screw-type heating and conveying device (3), introducing a 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 to carry out a dechlorination treatment; Optionally, the interval between the first dechlorination adsorbent inlet and the second dechlorination adsorbent inlet is 60 to 180 cm, and the interval between the second dechlorination adsorbent inlet and the third dechlorination adsorbent inlet is 60 to 180 cm.

3. 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°C, the outlet temperature is 120-300°C, the residence time is 0.5-20min, the conveying line speed is 0.002-0.08m / s, and the pressure inside the screw is 0.1-8MPa; preferably, the inlet temperature of the first screw-type heating and conveying device (2) is 120-180°C, the outlet temperature is 150-250°C, the residence time is 1-10min, the conveying line speed is 0.004-0.04m / s, and the pressure inside the screw is 0.1-5MPa; Optionally, the feed rate of the chlorine-containing waste plastic is 10 to 130 g / s, preferably 20 to 100 g / s; Optionally, the chlorine-containing waste plastics include PVC and one or more selected from LDPE, HDPE, PP and PS.

4. 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°C, the outlet temperature is 250-450°C, the residence time is 0.8-27min, the conveying line speed is 0.0015-0.05m / s, and the pressure inside the screw is 0.0001-5MPa; preferably, 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 1.6-20min, the conveying line speed is 0.002-0.025m / s, and the pressure inside the screw is 0.1-3MPa; optionally, the feed rate of the dehydrated, degassed and volume-reduced plastic is 10-130g / s, preferably 20-100g / s; the continuous feed rate of the dechlorination adsorbent is 1-80g / s, preferably 4-60g / s.

5. 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; 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; 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, magnesium carbonate, copper carbonate and ammonium carbonate; Preferably, the molar ratio of the dechlorination adsorbent to the chlorine element in the chlorine-containing waste plastic is 1:0.1-20, preferably 1:0.5-10.

6. The method according to claim 1, characterized in that In step S3, the conditions of the visbreaking treatment include: reaction temperature of 350-460°C, residence time of 2-150 min, reaction pressure of 0.0001-5 MPa; preferably, reaction temperature of 370-430°C, residence time of 5-120 min, reaction pressure of 0.0001-3 MPa; Optionally, the visbreaking unit (8) uses a visbreaking reactor to perform the visbreaking treatment. Preferably, the visbreaking reactor is an adiabatic visbreaking reactor.

7. The method according to claim 1, characterized in that In step S4, the heating unit (9) is a heating furnace; Optionally, the conditions for the heating treatment include: the outlet temperature of the heating furnace is 430-580°C, and optionally, the steam injection amount is 0.1-6 weight %; preferably, the outlet temperature of the heating furnace is 450-550°C, and optionally, the steam injection amount is 0.5-5 weight %.

8. The method according to claim 1, characterized in that In step S5, the conditions for the pyrolysis reaction treatment include: the top pressure of the pyrolysis tower is 0.01-1 MPa, the pyrolysis reaction temperature is 430-560°C, and the pyrolysis reaction time is 10-120s; preferably, the top pressure of the pyrolysis tower is 0.05-0.6 MPa, the pyrolysis reaction temperature is 450-550°C, and the pyrolysis reaction time is 20-80s.

9. The method according to claim 1, characterized in that: The method further comprises: under the action of a vacuum system, allowing 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 to enter a hydrogen chloride absorption unit (7) to contact the hydrogen chloride absorbent, and perform hydrogen chloride absorption treatment to obtain a dechlorinated gas phase; Optionally, the hydrogen chloride absorbent is water or an alkali solution with a pH greater than 7; optionally, the alkali solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water.

10. A system for pyrolysis of waste plastics, characterized in that: The system comprises a first screw-type heating and conveying device (2), a second screw-type heating and conveying device (3), a visbreaking unit (8), a heating unit (9), a pyrolysis reaction unit (10) and a separation unit (11); The first screw-type heating and conveying device (2) comprises a waste plastic inlet and a dehydrated, degassed and volume-reduced plastic outlet; the first screw-type heating and conveying device (2) is configured to perform dehydration, degassing and volume-reducing treatment on the chlorine-containing waste plastic to obtain dehydrated, degassed and volume-reduced plastic; The second screw-type heating and conveying device (3) comprises a dehydrated, degassed and volume-reduced plastic inlet, a dechlorination adsorbent inlet and a dechlorination plastic outlet; the dehydrated, degassed and volume-reduced plastic inlet is connected to the dehydrated, degassed and volume-reduced plastic outlet of the first screw-type heating and conveying device (2); the second screw-type heating and conveying device (3) is configured to perform liquefaction treatment and dechlorination treatment on the dehydrated, degassed and volume-reduced plastic to obtain a dechlorination plastic; The visbreaking unit (8) comprises a dechlorinated plastic inlet and a visbreaking 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 visbreaking unit (8) is configured to perform visbreaking treatment on the dechlorinated plastic to obtain visbreaking plastic oil; The heating unit (9) comprises a visbreaking plastic oil inlet and a heated plastic oil outlet, wherein the visbreaking plastic oil inlet is connected to the visbreaking plastic oil outlet of the visbreaking unit (8); the heating unit (9) is configured to heat the visbreaking plastic oil to obtain heated plastic oil; The pyrolysis reaction unit (10) comprises a heated plastic oil inlet and a pyrolysis product outlet; the heated plastic oil inlet is connected to the heated plastic oil outlet of the heating unit (9); the pyrolysis reaction unit (10) is configured to perform a pyrolysis reaction on the heated plastic oil to obtain pyrolysis products and coke; The separation unit (11) comprises 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 product to obtain dry gas, liquefied gas and pyrolysis oil.

11. The system according to claim 10, characterized in that The system further comprises a hydrogen chloride absorption unit (7), the hydrogen chloride absorption unit (7) comprising a chlorine-containing gas inlet and a dechlorinated gas phase outlet, and a hydrogen chloride absorbent is further arranged in the hydrogen chloride absorption unit (7); the second screw-type heating and conveying device (3) further comprises 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 perform hydrogen chloride absorption treatment on the remaining chlorine-containing gas phase in the second screw-type heating and conveying device (3) that has not been adsorbed by the dechlorinated adsorbent, so as to obtain a dechlorinated gas phase; Optionally, the second screw heating and conveying device (3) comprises a screw heating and conveying device and a vacuum device connected to the screw heating and conveying device; preferably, the screw heating and conveying device is selected from a twin-screw or single-screw conveying device; Preferably, 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 transmission 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.

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