Processing method and processing system for pyrolytic cracking of waste plastics

Abstract

A processing method and system for waste plastic pyrolysis cracking, comprising: S1, the waste plastic to be treated enters a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastic; S2, the liquefied waste plastic enters a plastic reduction and viscosity reduction unit for treatment to obtain liquefied waste plastic oil; S3, low-ash material is extracted from the upper part of the reactor of the plastic reduction and viscosity reduction unit to be heated to obtain high-temperature low-ash material; high-ash material is extracted from the lower part of the reactor; S4, the high-temperature low-ash material or the mixture of the high-temperature low-ash material and the high-ash material enters a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S5, further separation is performed to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction. The method and system provided by the application effectively realize the resource utilization, large-scale and continuous utilization of waste plastic, prolong the operation cycle of the device, and reduce coke generation.

Description

Technical Field

[0001] This invention relates to the field of waste plastic resource recycling, specifically to a processing method and system for the viscosity reduction, grading, pyrolysis, and cracking of waste plastics. Background Technology

[0002] With technological advancements and industrial development, plastics are now widely used as packaging materials in daily life. Used waste plastics cannot decompose naturally. While only a few types can be recycled through specific channels, a large amount ends up in landfills as household waste, occupying significant space due to their slow decomposition. Especially in recent years, the generation of waste plastics has increased, making the rapid and environmentally friendly recycling of waste plastics an urgent task.

[0003] The simplest chemical method for treating waste plastics is direct incineration, but this produces toxic gases harmful to humans and causes secondary environmental pollution. Waste plastic oiling technology involves pyrolyzing waste plastics under anaerobic or oxygen-deficient conditions through heating or with a catalyst, breaking down polymers into low-molecular-weight substances to obtain gasoline, kerosene, diesel fractions, and some pyrolysis gases. This technology alleviates the pollution caused by waste plastics while simultaneously enabling their recycling, representing an important direction for the resource-based treatment of waste plastics.

[0004] Currently, waste plastic oil recycling technologies mainly include waste plastic pyrolysis, catalytic pyrolysis, and pyrolysis-catalytic reforming technologies. Pyrolysis has advantages such as simple process, relatively low equipment investment, no need for catalysts, and short reaction flow, making it the lowest in unit oil recycling cost compared to the other two technologies. General-purpose waste plastics in municipal solid waste undergo high-temperature pyrolysis reactions between 380 and 500℃, with a relatively fast pyrolysis rate and relatively simple product composition, which can be used as oil or chemical raw materials.

[0005] CN109401774A discloses a continuous pyrolysis system and method for waste plastics. The system includes a feeding device, a pyrolysis reactor, and a slag discharge device connected in sequence. Since plastics are macromolecular polymers, they form non-Newtonian fluids during heating, and a screw propeller is used. This process suffers from uneven heating during plastic liquefaction, easily leading to coking and scale buildup. CN10461030A discloses a coking method for producing fuel oil from waste plastics. This method involves preheating high-aromatic components and waste plastics or plastic oil in a raw material buffer tank before introducing them into a tubular heater for heating, and then injecting them into a delayed coking tower for coking. The waste plastics mentioned in this method are one or more of polyethylene, polypropylene, and polystyrene, but do not contain polyvinyl chloride (PVC), therefore it cannot process waste plastic raw materials mixed with PVC. CN112538363A discloses a method for co-converting waste plastics in a delayed coking unit. This method converts waste plastics together with petroleum residue feedstock. The waste plastics are selected from polyethylene, polypropylene, polystyrene, PET, and multilayer plastics with added metals, but do not include waste plastics made from polyvinyl chloride. The waste plastics, formed during the melting process, constitute a high-viscosity polymer melt, which has a density difference with the hydrocarbon feedstock. Therefore, the mixture of hydrocarbons and polymer melt can cause problems such as blockage and coking in the delayed coking furnace tubes. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a processing method and system for reducing viscosity, grading, pyrolysis and cracking of waste plastics, which can effectively realize the resource utilization, large-scale and continuous utilization of waste plastics, extend the operating cycle and reduce coke generation.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a processing method for the pyrolysis and cracking of waste plastics, the method comprising the following steps: S1, the waste plastics to be processed are fed into a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics; S2, the liquefied waste plastics are fed into a plastic reduction and viscosity reduction unit for plastic reduction and viscosity reduction cracking treatment to obtain liquefied waste plastic oil with plastic reduction and viscosity reduction cracking; S3, low-ash material is extracted from the upper part of the reactor of the plastic reduction and viscosity reduction unit and heated to obtain high-temperature low-ash material; high-ash material is extracted from the lower part of the reactor; S4, the high-temperature low-ash material is fed into a pyrolysis reaction unit for pyrolysis reaction, or the high-temperature low-ash material is mixed with the high-ash material and then fed into the pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S5, the pyrolysis products are fed into a separation unit to separate dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.

[0008] Optionally, in step S1, the waste plastic liquefaction unit uses a rapid heating liquefaction conveying device to perform the liquefaction process; optionally, the rapid heating liquefaction conveying device includes a first screw-type heating conveying device; preferably, the first screw-type heating conveying device is selected from a twin-screw or single-screw heating conveying device with heating.

[0009] Preferably, the liquefaction process conditions include: an outlet temperature of 370–500°C, more preferably 380–450°C; and a residence time of 5–20 min, more preferably 5–15 min.

[0010] Optionally, in step S2, the plastic reduction and viscosity reduction unit uses a plastic reduction and viscosity reduction reactor to carry out the plastic reduction and viscosity reduction cracking treatment. Preferably, the plastic reduction and viscosity reduction reactor is an adiabatic plastic reduction and viscosity reduction reactor.

[0011] Preferably, the process conditions for the plasticity reduction and viscosity reduction cracking treatment include: a reaction temperature of 370–450°C, more preferably 380–420°C, and even more preferably 390–420°C; and a residence time of 2–120 min, more preferably 30–70 min.

[0012] Optionally, in step S3, the weight ratio of low-ash material to high-ash material extracted is 1-20:1, preferably 3-10:1; preferably, the plasticity reduction and viscosity reduction reactor is provided with a vertical baffle, the top of the baffle is closed and the bottom is open, wherein the material is fed into the middle of one side of the baffle, the low-ash material is extracted from the upper part of the other side and the high-ash material is extracted from the lower part.

[0013] The process conditions of the heating furnace include: the outlet temperature of the heating furnace is 480℃~600℃, preferably 500℃~580℃; optionally, water vapor is injected into the heating furnace, and the steam injection rate is 0.5~5% by weight, preferably 0.5~3% by weight.

[0014] Optionally, in step S4, the high-temperature, low-ash material and the high-ash material are mixed in a mixer at a weight ratio of 1-20:1; preferably, the mixing weight ratio is 3-10:1. The mixer is a currently known type of mixer.

[0015] Optionally, in step S5, the process conditions for the pyrolysis reaction include: a pyrolysis tower top pressure of 0.05–0.6 MPa, preferably 0.1–0.3 MPa; a pyrolysis reaction temperature of 450–580°C, preferably 480–550°C; and an operation cycle of 1 h–500 h, preferably 10 h–240 h. The operation cycle refers to the pyrolysis tower switching operation time or the single-tower operation time.

[0016] Optionally, before step S1, the method further includes: S0, feeding the chlorine-containing waste plastic raw material into the waste plastic melting and dechlorination unit for hot melting dechlorination treatment to obtain hydrogen chloride-containing gas and dechlorinated waste plastic material; feeding the dechlorinated waste plastic material into the waste plastic liquefaction unit; or feeding the dechlorinated waste plastic material into the waste plastic liquefaction unit by sequentially cooling and crushing treatment to obtain dechlorinated waste plastic particles; and feeding the dechlorinated waste plastic particles into the waste plastic liquefaction unit.

[0017] Optionally, the method further includes: introducing the hydrogen chloride-containing gas into a hydrogen chloride absorption unit, contacting it with a hydrogen chloride absorbent for hydrogen chloride absorption treatment, and obtaining a chlorine-containing absorbent and dechlorinated dry gas;

[0018] Optionally, the hydrogen chloride-containing gas is introduced into the hydrogen chloride absorption unit under the action of a vacuum system;

[0019] The hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7; optionally, the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0020] Optionally, the waste plastic preliminary melting, liquefaction and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices;

[0021] The process conditions for the hot-melt dechlorination treatment include: a feed rate of 5–5000 kg / h, preferably 100–4000 kg / h; an outlet temperature of 150–370℃, preferably 300–330℃; a reaction time of 0.1–0.5 h, preferably 0.1–0.3 h; a vacuum degree of 50–300 mmHg, preferably 50–150 mmHg; and preferably, the particle size of the dechlorinated waste plastic particles obtained by the pulverization treatment is 100–2000 μm.

[0022] Optionally, the method further includes: returning at least a portion of the wax oil fraction from the separation unit to the plastic reduction and viscosity reduction unit for recycling; preferably, the weight ratio of the recycled wax oil fraction to the waste plastic to be treated is 0.2 to 5.0:1, more preferably 0.2 to 2:1;

[0023] Preferably, the fraction with a distillation range greater than 350°C obtained by the separation unit is used as the wax oil fraction.

[0024] Optionally, the waste plastic to be treated includes one or more of LDPE, HDPE, PS, PP, PET and PVC; optionally, the PVC content in the waste plastic to be treated is less than 10% by weight; the ash content in the waste plastic to be treated is 1-40% by weight, preferably 2-30% by weight.

[0025] Secondly, the present invention provides a processing system for the pyrolysis and cracking of waste plastics. The processing system includes: a waste plastic liquefaction unit, a plastic reduction and viscosity reduction unit, a material heating unit, a pyrolysis reaction unit, and a separation unit. The waste plastic liquefaction unit includes a waste plastic inlet and a liquefied waste plastic outlet, and is configured to liquefy the waste plastic. The plastic reduction and viscosity reduction unit includes a liquefied waste plastic inlet, an upper outlet, and a lower outlet, and is configured to perform plastic reduction and viscosity reduction cracking treatment on the liquefied waste plastic. The material heating unit includes a heating inlet and a heating outlet, the heating inlet being connected to the upper part of the plastic reduction and viscosity reduction unit. The heating unit is configured to heat the low-ash material after plasticizing and viscosity-reducing cracking. The pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet. The pyrolysis reactant inlet is connected to the heating outlet of the material heating unit and the lower outlet of the plasticizing and viscosity-reducing unit. The pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on high-temperature liquefied waste plastics. The separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet, and a wax oil fraction outlet. The separation inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit. The separation unit is configured to separate the pyrolysis products.

[0026] Preferably, the waste plastic liquefaction unit includes a heated liquefaction conveying device; optionally, the heated liquefaction conveying device includes a first screw-type heated conveying device; preferably, the first screw-type heated conveying device is selected from a twin-screw or single-screw heated conveying device with heating.

[0027] Preferably, the plasticity reduction and viscosity reduction unit further includes a circulating oil inlet; the circulating oil inlet is connected to the wax oil fraction outlet of the separation unit.

[0028] Optionally, the system further includes a waste plastic melting and dechlorination unit and a hydrogen chloride absorption unit; the waste plastic melting and dechlorination unit includes a chlorine-containing waste plastic raw material inlet, a hydrogen chloride-containing gaseous material outlet, and a dechlorinated waste plastic liquid material outlet, and the waste plastic melting and dechlorination unit is configured to perform thermal melting dechlorination treatment on the chlorine-containing waste plastic raw material; the dechlorinated waste plastic liquid material outlet is connected to the waste plastic inlet to be treated of the waste plastic liquefaction unit; the hydrogen chloride absorption unit includes a hydrogen chloride-containing gaseous material inlet, a hydrogen chloride absorbent, and a dechlorinated dry gas outlet; the hydrogen chloride-containing gaseous material inlet is connected to the hydrogen chloride-containing gaseous material outlet of the waste plastic melting and dechlorination unit.

[0029] Preferably, the waste plastic melting and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices.

[0030] Optionally, the waste plastic melting and dechlorination unit may also include a non-condensable steam outlet.

[0031] Through the above technical solution, this invention provides a processing method and system for the pyrolysis and cracking of waste plastics. By rapidly liquefying and reducing the viscosity of the waste plastics, the viscosity is reduced without coking or excessive cracking, forming a uniform, highly fluidized waste plastic that can be pumped. Then, through grading of the reduced-viscosity material, the low-ash portion is fed into a heating furnace to rapidly reach the reaction temperature above pyrolysis, while the portion with high mechanical impurities is excluded from the furnace. This reduces the sedimentation of mechanical impurities in the furnace tubes, preventing blockage and extending the operating cycle. In this process, high-temperature, low-ash materials are mixed with low-temperature, high-mechanical-impurity materials to obtain the pyrolysis reaction temperature of waste plastics. The high-temperature liquefied waste plastics are then transported to a pyrolysis tower for pyrolysis, or high-temperature, low-ash materials are directly fed into the pyrolysis tower with lower-temperature, high-ash materials for reaction. This achieves the resource utilization of waste plastics and reduces coke generation. Through the processing method disclosed herein, waste plastics from landfills can be dehydrated, dechlorinated, and reduced in volume on-site. Subsequent cracking and recycling can be centrally processed, facilitating the expansion of production scale and reducing processing costs. The process is simple, requires relatively little equipment investment, and enables large-scale, continuous, and green resource recycling of waste plastics.

[0032] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0033] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof.

[0034] Figure 1 This is an exemplary flowchart of a processing method and system for reducing viscosity, grading, pyrolysis, and cracking of waste plastics provided in this disclosure.

[0035] Figure 2 This is another exemplary flowchart of the processing method and system for reducing viscosity, grading, pyrolysis and cracking of waste plastics provided in this disclosure.

[0036] Figure 3 This is an exemplary structural schematic diagram of the plastic reduction and viscosity reduction reactor provided in this disclosure.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1-Waste plastic storage tank, 2-Waste plastic melting and dechlorination unit, 3-Rapid heating liquefaction and conveying equipment, 4-Insulated plastic reduction and viscosity reduction reactor, 5-Heating furnace, 6-Pyrolysis reaction unit, 7-Separation unit, 8-Hydrogen chloride absorption unit, 10-Upper outlet, 12-Lower outlet, 13-Material mixer, 17-Diesel fraction outlet, 18-Liquefied gas and gasoline fraction outlet, 19-Dry gas outlet, 20-Wax oil fraction outlet, 9, 11, 14-16, 21-Pipelines, 23-Liquefied waste plastic inlet, 24-Baffle. Detailed Implementation

[0039] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0040] In this application, the terms "upper part," "lower part," and "bottom" are all based on the relative positional relationship of the container or component. Specifically, "bottom" refers to the position of the container from bottom to top of 0-10%, and "top" refers to the position of the container from bottom to top of 90-100%.

[0041] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] In a first aspect, the present invention provides a processing method for the pyrolysis and cracking of waste plastics, the method comprising the following steps: S1, the waste plastics to be processed are fed into a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics; S2, the liquefied waste plastics are fed into a plastic reduction and viscosity reduction unit for plastic reduction and viscosity reduction cracking treatment to obtain liquefied waste plastic oil with plastic reduction and viscosity reduction cracking; S3, low-ash material is extracted from the upper part of the reactor of the waste plastic plastic reduction and viscosity reduction unit and heated to obtain high-temperature low-ash material; high-ash material is extracted from the lower part of the reactor; S4, the high-temperature low-ash material is fed into a pyrolysis reaction unit for pyrolysis reaction, or the high-temperature low-ash material is mixed with the high-ash material and then fed into the pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S5, the pyrolysis products are fed into a separation unit to separate dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.

[0043] In one specific embodiment, the waste plastic to be treated includes one or more of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC).

[0044] Optionally, the PVC content in the waste plastic to be treated is less than 10% by weight; the ash content in the waste plastic to be treated is 1-40% by weight, preferably 2-30% by weight. The waste plastic raw materials in this disclosure can be directly sourced from landfills.

[0045] In a preferred embodiment, before step S1, the method further includes:

[0046] S0. The chlorine-containing waste plastic raw material is fed into the waste plastic melting and dechlorination unit for hot melting and dechlorination treatment to obtain gaseous material containing hydrogen chloride and dechlorinated waste plastic material.

[0047] The dechlorinated waste plastic material is fed into the waste plastic liquefaction unit; or

[0048] The dechlorinated waste plastic material is sequentially cooled and crushed to obtain dechlorinated waste plastic particles; the dechlorinated waste plastic particles are then fed into the waste plastic liquefaction unit.

[0049] In this disclosure, the hot melt dechlorination step and the waste plastic liquefaction step can use the same rapid heating liquefaction conveying equipment, or each can use a separate rapid heating liquefaction conveying equipment; for example, the rapid heating liquefaction conveying equipment is a screw-type heating conveying equipment with heating, etc.

[0050] In one embodiment, the method further includes:

[0051] The hydrogen chloride-containing gas is introduced into the hydrogen chloride absorption unit and comes into contact with the hydrogen chloride absorbent for hydrogen chloride absorption treatment, resulting in a chlorine-containing absorbent and dechlorinated dry gas.

[0052] Optionally, the hydrogen chloride-containing gas is introduced into the hydrogen chloride absorption unit under the action of a vacuum system.

[0053] This invention uses a preliminary melting and liquefaction dechlorination unit for waste plastics to decompose the chlorine in chlorine-containing PVC waste plastics into the gas phase. A vacuum system can be used to quickly separate hydrogen chloride, avoiding secondary reactions of hydrogen chloride, improving the dechlorination efficiency of waste plastics, and reducing the corrosion pressure on subsequent equipment.

[0054] In one specific embodiment, the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7; optionally, the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0055] In a preferred embodiment, the method further includes:

[0056] At least a portion of the wax oil fraction from the separation unit is returned to the plasticizing and viscosity-reducing unit for reprocessing;

[0057] Preferably, the fraction with a distillation range greater than 350°C obtained from the separation unit is used as the wax oil fraction. Processing according to this embodiment can further improve the utilization efficiency of waste plastic resources; and introducing the wax oil fraction into the plastic reduction and viscosity reduction unit is also beneficial to the viscosity reduction and cracking treatment of waste plastics.

[0058] In one specific embodiment, the weight ratio of the recycled wax oil fraction to the waste plastic to be treated is 0.2 to 5.0:1, optimized to 0.2 to 2:1.

[0059] In one embodiment, in step S1, the waste plastic liquefaction unit uses a rapid heating liquefaction conveying device for liquefaction treatment; optionally, the rapid heating liquefaction conveying device includes a first screw-type heating conveying device; preferably, the first screw-type heating conveying device is selected from a twin-screw or single-screw heating conveying device with heating. The rapid heating liquefaction conveying device used in this disclosure is beneficial for the rapid liquefaction treatment of solid waste plastics.

[0060] In a preferred embodiment, the liquefaction process conditions include: an outlet temperature of 370–500°C, preferably 380–450°C; and a residence time of 5–20 min, preferably 5–15 min.

[0061] In one embodiment, in step S2, the plastic reduction and viscosity reduction unit uses a plastic reduction and viscosity reduction reactor to perform the plastic reduction and viscosity reduction cracking treatment, preferably an adiabatic plastic reduction and viscosity reduction reactor. The plastic reduction and viscosity reduction reactor in this disclosure can be any reactor known in the art, such as an upflow plastic reduction and viscosity reduction reactor or a downflow plastic reduction and viscosity reduction reactor. Preferably, in step S2, the plastic reduction and viscosity reduction reactor is equipped with a vertical baffle, with a closed top and an open bottom. A central feed inlet is provided on one side of the reactor wall of the baffle, and an upper outlet and a lower outlet are provided on the other side of the reactor wall. Low-ash material is extracted from the upper outlet, and high-ash material is extracted from the lower outlet. The discharge ratio of the upper outlet to the lower outlet of the plastic reduction and viscosity reduction reactor is 20:1 to 1:1, preferably 10:1 to 3:1.

[0062] In a preferred embodiment, the process conditions for the plasticity reduction and viscosity reduction cracking treatment include: a reaction temperature of 370–450°C, preferably 380–420°C, more preferably 390–420°C; and a residence time of 2–120 min, preferably 30–70 min, and even more preferably 50–70 min.

[0063] In one embodiment, in step S3, the material heating unit includes a heating furnace;

[0064] Preferably, the process conditions for the heat treatment include: a furnace outlet temperature of 480℃~600℃, more preferably 500℃~580℃; and a steam injection rate of 0.5~5% by weight, optimized to 0.5~3% by weight.

[0065] In one embodiment, in step S4, the high-ash material and the low-ash high-temperature material are mixed in a mixer; preferably, the mixer is a known mixer, and the mixing process conditions include: the low-ash high-temperature material flows out from the hot furnace outlet at a temperature of 480℃~600℃, preferably 500℃~580℃; the high-ash material flows out from the lower outlet of the plasticizing and viscosity-reducing reactor at a temperature of 370~450℃, preferably 380~420℃; and the mixing ratio of the high-temperature material to the low-temperature material is 20:1~1:1, preferably 10:1~3:1.

[0066] In one embodiment, in step S5, the process conditions for the pyrolysis reaction include: the pressure at the top of the pyrolysis tower is 0.05-0.6 MPa, preferably 0.1-0.3 MPa; and the pyrolysis reaction temperature is 450-580°C, preferably 480-550°C.

[0067] In this invention, the pyrolysis reaction unit may include multiple pyrolysis towers arranged in parallel.

[0068] In one embodiment, the waste plastic preliminary melting, liquefaction and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices.

[0069] In a preferred embodiment, the process conditions for the hot melt dechlorination treatment include: a feed rate of 5–5000 kg / h, preferably 100–4000 kg / h; an outlet temperature of 150–370°C, preferably 300–330°C; a reaction time of 0.1–0.5 h, preferably 0.1–0.3 h; and a vacuum degree of 50–300 mmHg, preferably 50–150 mmHg, in the waste plastic preliminary melting and liquefaction dechlorination unit.

[0070] Preferably, the particle size of the dechlorinated waste plastic particles obtained by crushing is 100-2000 μm.

[0071] In this invention, the apparatus and method for cooling and pulverizing can be conventional apparatus and methods in the art.

[0072] The beneficial effects of the waste plastic viscosity reduction, grading, pyrolysis and cracking processing method provided by this invention are as follows:

[0073] Overcoming the technical problems existing in the field of waste plastic pyrolysis treatment, the inventors discovered during their research that one of the technical problems in the existing technology is that polyvinyl chloride (PVC) in waste plastics, when heated and decomposed into HCl, can rapidly undergo an addition reaction with the double bonds in the raw materials to generate chlorinated hydrocarbons, making it difficult for traditional reaction devices to efficiently remove chlorine from waste plastics. To address this technical problem, this invention uses specialized equipment to rapidly heat PVC-containing materials for decomposition and uses a vacuum method to quickly separate the decomposed HCl from the reactor, thereby improving dechlorination efficiency. The second technical problem overcome in existing technologies is that waste plastics are high-molecular polymers. Due to their large molecular weight and solid nature, heat transfer within the plastic is very slow. Traditional heating methods cause excessive cracking of the outer layer of the plastic while the interior remains solid, resulting in a high coking rate and high gas yield during pyrolysis. To address this second problem, specialized equipment is used to rapidly heat the waste plastics into a flowable liquid state through strong extrusion and agitation, reducing viscosity so that it can be pumped. As the waste plastics rapidly liquefy, the increased thermal conductivity of the liquid state allows for pyrolysis using heating furnaces or other heating equipment, achieving a higher liquid yield and a lower coking rate. The third technical problem overcome is that waste plastics have a low density, resulting in a slow rate of entry into the reaction device. Existing technologies have small processing scales and cannot meet the demands of modern large-scale recycling. To address this third problem, the method provided in this invention significantly increases the transport density of the raw material after liquefaction compared to solid waste plastics. Therefore, it not only enables large-scale waste plastic processing but also allows for continuous pyrolysis and recycling of waste plastics. The fourth technical problem overcome is the high ash content in waste plastics, which severely affects the service life of the heating furnace. To address this problem, the method provided by this invention liquefies the waste plastics and then separates them into two parts in a plastic reduction and viscosity reduction reactor: one part is high-ash waste plastic oil, and the other part is low-ash waste plastic oil. The low-ash waste plastic oil is heated in the heating furnace, while the high-ash waste plastic oil is not heated. They can be mixed in a mixer and then enter the pyrolysis tower or enter the pyrolysis tower separately for pyrolysis. This effectively solves the problem of furnace tube blockage caused by high ash content, which affects the operating cycle.

[0074] Secondly, the present invention provides a processing system for the viscosity reduction, grading, pyrolysis, and cracking of waste plastics, such as... Figure 1 and Figure 2 As shown, the processing system includes: a waste plastic liquefaction unit, a plastic reduction and viscosity reduction unit, a material heating unit, a pyrolysis reaction unit, and a separation unit;

[0075] The waste plastic liquefaction unit includes a waste plastic inlet and a liquefied waste plastic outlet, and the waste plastic liquefaction unit is configured to liquefy the waste plastic to be treated.

[0076] The plastic reduction and viscosity reduction unit includes a liquefied waste plastic inlet, an upper outlet, and a lower outlet. The plastic reduction and viscosity reduction unit is configured to perform plastic reduction and viscosity reduction cracking treatment on the liquefied waste plastic.

[0077] The material heating unit includes a heating inlet and a heating outlet. The heating inlet is connected to the upper outlet of the plastic reduction and viscosity reduction unit. The heating unit is configured to heat the low-ash material after plastic reduction and viscosity reduction cracking.

[0078] The pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet. The pyrolysis reactant inlet is connected to the heating outlet of the material heating unit and the lower outlet of the plastic reduction and viscosity reduction unit. The pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on high-temperature liquefied waste plastics.

[0079] The separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet, and a wax oil fraction outlet; the separation inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit, and the separation unit is configured to separate the pyrolysis products.

[0080] In a preferred embodiment, the plastic reduction and viscosity reduction unit further includes a circulating oil inlet; the circulating oil inlet is connected to the wax oil fraction outlet of the separation unit.

[0081] In one implementation, such as Figure 1 As shown, the system also includes a waste plastic melting and dechlorination unit and a hydrogen chloride absorption unit;

[0082] The waste plastic melting and dechlorination unit includes a chlorine-containing waste plastic raw material inlet, a hydrogen chloride-containing gaseous material outlet, and a dechlorinated waste plastic liquid material outlet. The waste plastic preliminary melting and liquefaction dechlorination unit is configured to perform thermal melting and dechlorination treatment on the chlorine-containing waste plastic raw material. The dechlorinated waste plastic liquid material outlet is connected to the waste plastic inlet to be treated in the waste plastic liquefaction unit.

[0083] The hydrogen chloride absorption unit includes a hydrogen chloride-containing gaseous material inlet, a hydrogen chloride absorbent, and a dechlorinated dry gas outlet; the hydrogen chloride-containing gaseous material inlet is connected to the hydrogen chloride-containing gaseous material outlet of the waste plastic preliminary melting and liquefaction dechlorination unit.

[0084] In one specific embodiment, the waste plastic liquefaction unit includes a heated liquefaction conveying device; optionally, the heated liquefaction conveying device includes a first screw-type heated conveying device; preferably, the first screw-type heated conveying device is selected from a twin-screw or single-screw heated conveying device with heating.

[0085] The waste plastic preliminary melting, liquefaction and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices.

[0086] In a preferred embodiment, the waste plastic preliminary melting, liquefaction and dechlorination unit and the waste plastic liquefaction unit adopt a heating liquefaction conveying device, including a first screw-type heating conveying device, and a gas outlet connected to a vacuum device is provided in the middle of the screw-type heating conveying device.

[0087] In one specific embodiment, the waste plastic preliminary melting, liquefaction and dechlorination unit also includes a non-condensable steam outlet for drawing out non-condensable steam.

[0088] In one specific implementation, as shown in the appendix Figure 3 As shown, the plastic reduction and viscosity reduction reactor is equipped with a vertical baffle. The top of the baffle is closed and the bottom is open. A middle feed inlet is provided on one side of the reactor wall of the baffle, and an upper outlet and a lower outlet are provided on the other side of the reactor wall. Low ash material is extracted from the upper outlet and high ash material is extracted from the lower outlet. The discharge ratio of the upper outlet to the lower outlet of the plastic reduction and viscosity reduction reactor is 20:1 to 1:1, preferably 10:1 to 3:1.

[0089] The process flow of the specific embodiments described above in this disclosure specifically includes, as shown in the appendix. Figure 1 Or attached Figure 2 As shown:

[0090] Waste plastics stored in waste plastic storage tank 1 or dehydrated and dechlorinated waste plastic particles enter waste plastic melting and dechlorination unit 2. After dehydration, deairing and dechlorination, hydrogen chloride-containing gaseous material and dechlorinated waste plastic material are obtained. The hydrogen chloride-containing gaseous material is drawn into hydrogen chloride absorption unit 8 through a vacuum system to contact with hydrogen chloride absorbent for hydrogen chloride absorption treatment, resulting in chlorine-containing absorbent and dechlorinated dry gas. A small amount of non-condensable gas is discharged through pipeline 9, and most of the dechlorinated dry gas is connected to the dry gas pipeline 19 obtained from the separation unit through pipeline 22. The waste plastic liquefaction unit uses a rapid heating liquefaction conveying device 3. The dechlorinated waste plastic liquid material from the waste plastic melting and dechlorination unit 2 can be discharged from the device for cooling and crushing to obtain dechlorinated waste plastic particles, or it can be directly fed into the rapid heating liquefaction conveying device 3 (waste plastic liquefaction unit) to obtain molten dechlorinated waste plastic liquid material. The molten dechlorinated waste plastic liquid material enters the adiabatic plastic reduction and viscosity reduction reactor 4 (waste plastic plastic reduction and viscosity reduction unit) for plastic reduction and viscosity reduction cracking treatment to obtain plastic reduction and viscosity reduction cracked liquefied waste plastic. Oil can also be used to simultaneously allow the wax oil fraction from separation unit 7 to enter the adiabatic plasticizing and viscosity-reducing reactor 4 for reprocessing; the low-ash material extracted from the upper outlet 10 of the plasticizing and viscosity-reducing cracking reactor is sent to the heating furnace 5 (heating unit). After being heated by the heating furnace 5, the high-temperature low-ash material enters the material mixer 13 through pipeline 11 and is mixed with the high-ash material extracted from the lower outlet of the plasticizing and viscosity-reducing cracking reactor. The mixed high-temperature material enters the pyrolysis reaction unit 6 through pipeline 14 for pyrolysis reaction to obtain pyrolysis products and coke.

[0091] Alternatively, see attached Figure 2 As shown, without material mixer 13, high-temperature low-ash material enters pyrolysis reaction unit 6 via pipeline 11 and low-temperature high-ash material enters via pipeline 12 for pyrolysis reaction.

[0092] The pyrolysis products of the pyrolysis reaction unit enter the subsequent separation unit 7 through pipeline 16 for separation processing: dry gas exits the unit through pipeline 19, liquefied gas and gasoline fractions exit the unit through pipeline 18, and diesel fraction exits the unit through pipeline 17; the wax oil fraction at the bottom of the tower is led out of the separation unit through pipeline 20, and some of the wax oil fraction can also be returned to the adiabatic plastic reduction and viscosity reduction reactor 4 (waste plastic viscosity reduction unit) through pipeline 15 for recycling, or it can be led out as a product through pipeline 21.

[0093] Appendix Figure 3 This is an exemplary structural schematic diagram of the plastic reduction and viscosity reduction reactor provided in this disclosure. (See attached diagram.) Figure 3As shown, a vertical baffle 24 is installed in the plastic reduction and viscosity reduction reactor. The top of the baffle 24 is sealed to the top of the reactor, and the bottom of the baffle is open to the bottom of the reactor. A feed inlet 23 is provided in the middle of one side of the baffle, and an upper outlet 10 is provided at the upper part of the other side to extract low-ash materials, and a lower outlet 12 is provided at the lower part to extract high-ash materials. The upper outlet is located at a height of 60%-90% from bottom to top, and the lower outlet is located at a height of 0-40% from bottom to top.

[0094] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0095] The analytical method for determining the chlorine content in liquefied waste plastics is: Q / SH 3360 270-2018.

[0096] The analytical methods for other elements in liquefied waste plastics are as follows: carbon and hydrogen (SH / T 0656-2017), oxygen (SH / T0986), nitrogen (SH / T 0704-2010), and sulfur (SH / T 0842-2010).

[0097] The distribution of pyrolysis products was obtained by simulated distillation according to the NB / SH / T 0829-2010 method.

[0098] The density analysis method for diesel and wax oil is SH / T0604-2000; the composition of pyrolysis gases is determined by RIPP 78-90 method; the hydrocarbon composition of naphtha, diesel, etc. is determined by chromatographic analysis.

[0099] In the following examples, the particle size range of the particles obtained after pulverization is 100–2000 μm.

[0100] Example 1

[0101] Waste agricultural film (mainly PE, with a chlorine content of 0.0162% by weight) is fed into the waste plastic hot melt dechlorination unit for hot melt dechlorination treatment. During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it to the hydrogen chloride absorption unit, where it contacts the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment. The waste plastic melting dechlorination unit includes a second twin-screw heating conveyor and a vacuum device connected to the second screw heating conveyor. The feed rate is approximately 100 kg / h, the outlet temperature is 220℃, the reaction time is 6 min, and the vacuum degree of the screw heating conveyor is 150 mmHg. The resulting waste plastic material is cooled and pulverized to obtain dechlorinated waste plastic particles WP-1, the properties of which are shown in Table 1.

[0102] The dechlorinated waste plastic granules WP-1 were fed into the waste plastic liquefaction unit for liquefaction. Further heating and liquefaction were achieved using a first twin-screw heated conveyor, with an outlet temperature of 400℃ and a residence time of 6 minutes. The resulting liquefied waste plastic was then fed into an adiabatic deplasticizing and viscosity-reducing reactor for deplasticizing, viscosity-reducing, and cracking treatment to obtain deplasticized and viscosity-reduced liquefied waste plastic oil. The reaction temperature was 400℃, and samples were taken at residence times of 30 minutes, 50 minutes, and 70 minutes, respectively, and labeled WP-1-30, WP-1-50, and WP-1-70. The rotational viscosity of the samples is shown in Table 2. At the aforementioned residence times, low-ash material was extracted from the upper outlet of the adiabatic deplasticizing and viscosity-reducing reactor, and high-ash material was extracted from the lower outlet, with a mass ratio of 4:1. The ash content of both is shown in Table 2.

[0103] Low-ash material with a residence time of 50 min for plastic reduction and viscosity reduction was heated to 520℃ in a furnace to obtain a high-temperature, low-ash material. Steam was injected into the furnace at a rate of 0.5% by weight. The high-temperature, low-ash material was then mixed with high-ash material (400℃, residence time of 50 min for plastic reduction and viscosity reduction) at a ratio of 4:1 and fed into a pyrolysis tower for reaction. The top pressure of the pyrolysis tower was 0.15 MPa, the reaction temperature was 480℃, and the operation cycle was 10 hours (including the pyrolysis tower switching operation time). Pyrolysis products and coke were obtained. The pyrolysis products were separated by a distillation tower to obtain dry gas, liquefied petroleum gas, gasoline fraction, diesel fraction, and wax oil fraction. Product distribution tests were conducted, and the distribution of the pyrolysis reaction products is shown in Table 4.

[0104] As shown in Table 2, when the plasticity reduction and viscosity lowering treatment meets the requirements of a reaction temperature of 390–420℃ and a residence time of 30–70 min, different viscosity lowering temperatures result in different optimal viscosity lowering times. With decreasing viscosity, the ash distribution in the plastic undergoes changes.

[0105] As can be seen from Example 1, waste agricultural film, after thermal dechlorination treatment, yields plastic WP-1. Since most of the chlorine in the waste agricultural film is inorganic chlorine, it does not decompose into hydrogen chloride during the dechlorination process but enters into WP-1, thus the chlorine content of WP-1 remains unchanged. After further plasticizing and viscosity-reducing treatment, the viscosity at 200℃ is reduced to 267.6 cp, and the sample flow state is stable. After staged heating and mixing, the sample undergoes a pyrolysis reaction in a pyrolysis tower, and is then fractionated in a fractionation tower to obtain dry gas, liquefied petroleum gas, gasoline, diesel, wax oil, and coke with yields of 1.61%, 2.54%, 15.15%, 40.06%, 32.22%, and 8.26%, respectively.

[0106] Comparative Example 1

[0107] Using the raw materials and waste plastic melting and dechlorination unit and method of Example 1, the difference was that the outlet temperature was set to 250℃. The morphology of the waste plastic after conveying under different outlet temperature conditions was tested, resulting in liquefied waste plastic WP-1-1. WP-1-1 was heated to 250℃ using a screw-type heating and conveying device and directly extruded into an atmospheric pressure container with a gas outlet and an internal temperature of 250℃. The container was held at this temperature for 60 minutes, and a sample of WP-1-1-60 was taken for viscosity testing. The viscosity was found to be excessively high, exceeding the measurement range, and the morphology was a plastic solid that did not flow on its own. This demonstrates that the steps for reducing plasticity and viscosity are crucial.

[0108] Example 2

[0109] Real waste plastic (plastic from a landfill, a mixed chlorine-containing plastic with a chlorine content of approximately 3% by weight) was fed into a waste plastic melting and dechlorination unit for hot-melt dechlorination treatment, the same as in Example 1. The feed rate was approximately 100 kg / h, the outlet temperature was 300°C, the reaction time was 6 min, and the vacuum degree of the second twin-screw heated conveyor was 70 mmHg, yielding dechlorinated waste plastic particles WP-2, the properties of which are shown in Table 3.

[0110] The dechlorinated waste plastic granules WP-2 were fed into the waste plastic liquefaction unit for liquefaction. Further heating and liquefaction were achieved using a first twin-screw heated conveyor, with an outlet temperature of 420℃ and a residence time of 12 minutes. The resulting liquefied waste plastic was then fed into an adiabatic deplasticizing and viscosity-reducing reactor for deplasticizing, viscosity-reducing, and cracking treatment to obtain deplasticized and viscosity-reduced liquefied waste plastic oil. The reaction temperature was 420℃, and the residence time was 30 minutes. A sample of WP-2-30 was taken to measure its rotational viscosity; the results are shown in Table 2. Low-ash material was extracted from the upper part of the adiabatic deplasticizing and viscosity-reducing reactor, and high-ash material was extracted from the lower part, with a mass ratio of 5:1. The ash content of both materials is shown in Table 2.

[0111] Low-ash material is heated to 500℃ in a furnace to obtain high-temperature, low-ash material. This high-temperature, low-ash material is then mixed with high-ash material (420℃) at a 5:1 ratio and fed into a pyrolysis tower for reaction. The top pressure of the pyrolysis tower is 0.15 MPa, the reaction temperature is 480℃, and the operation cycle is 10 hours (pyrolysis tower switching time). Pyrolysis products and coke are obtained. The pyrolysis products are separated in a distillation tower to obtain dry gas, liquefied petroleum gas, gasoline fraction, diesel fraction, and wax oil fraction. The distribution of pyrolysis reaction products is shown in Table 4.

[0112] As can be seen from Example 2, after hot-melt dechlorination treatment, most of the chlorine in the real waste plastic with high chlorine content was removed. After dechlorination, the plastic WP-2 was de-plasticized and reduced in viscosity at 420℃ for 30 minutes, and the viscosity at 200℃ dropped to 282.8 cp. The sample flow state was stable. After staged heating and mixing, it was sent to a coke tower for pyrolysis reaction. After fractionation in a distillation tower, the yields of dry gas, liquefied petroleum gas, gasoline, diesel, wax oil, and coke were 5.39%, 4.89%, 24.32%, 23.21%, 10.91%, and 20.96%, respectively. Since the waste plastic contains a certain amount of polyester and has undergone long-term oxidation, the raw materials contain a certain amount of oxygen. Therefore, the pyrolysis products contain a certain amount of CO and CO2.

[0113] Comparative Example 2

[0114] Referring to the process flow of Example 2, the same waste plastic raw materials were used. The difference from Example 2 is that the waste plastic oil after plastic reduction and viscosity reduction was not discharged in layers, but was directly introduced into the heating furnace for heating and then carried out a pyrolysis reaction. The specific process conditions were the same as those in Example 2. The furnace tube operation cycle of Example 2 was 10% longer than that of Comparative Example 2. The product distribution is shown in Table 4.

[0115] Compared with Comparative Example 2, Example 2 shows that the heating furnace has a longer service life, and the yield of dry gas and coke obtained from the pyrolysis products is lower.

[0116] Example 3

[0117] The dechlorinated waste plastic granules WP-1 obtained in Example 1 were fed into a waste plastic liquefaction unit for liquefaction. Further heating and liquefaction were performed using a first twin-screw heating conveyor, with an outlet temperature of 400°C and a residence time of 0.2 hours. The resulting liquefied waste plastic was then fed into an adiabatic deplasticizing and viscosity-reducing reactor for deplasticizing, viscosity-reducing, and cracking treatment to obtain deplasticized and viscosity-reduced liquefied waste plastic oil. The temperature of the adiabatic deplasticizing and viscosity-reducing reactor was 380°C, and the residence time was 1 hour. Low-ash material was extracted from the upper part of the reactor, and high-ash material was extracted from the lower part, with a mass ratio of 3:1. The ash content of both materials is shown in Table 2. The low-ash material was then heated in a furnace to an outlet temperature of 520°C to obtain high-temperature, low-ash material. The high-temperature, low-ash material was then mixed with the 380℃, high-ash material at a ratio of 3:1 and fed into a pyrolysis tower for reaction. The top pressure of the pyrolysis tower was 0.15 MPa, the pyrolysis reaction temperature was 520℃, and the operation cycle was 16 hours (pyrolysis tower switching operation time). Pyrolysis products and coke were obtained. The pyrolysis products were separated by a distillation tower to obtain dry gas, liquefied petroleum gas, gasoline fraction, diesel fraction, and wax oil fraction. The distribution of pyrolysis products is shown in Table 5, the distribution of gaseous products is shown in Table 6, and the liquid products were further processed to obtain naphtha, diesel, and wax oil components, the properties of which are shown in Table 7. The properties of the coke product are shown in Table 8.

[0118] As can be seen from Example 3, after processing waste agricultural film using the process provided in this disclosure, the liquid yield (including liquefied gas) from pyrolysis can reach 87.43%, while the coke yield is relatively low. The properties of the obtained naphtha, diesel, and wax oil show that each distillate has a high hydrogen content, a high olefin content, a low aromatic content, and low chlorine and silicon heteroatom content, allowing it to be directly fed into refineries for further processing. The sum of the triene mass fractions in the pyrolysis gases is high (>45% by weight), and the ash content of the coke is as high as 50.5% by weight, making it unsuitable for sale as a product but suitable for blending as boiler fuel.

[0119] Table 1 Properties of Waste Agricultural Film Particles

[0120] Instance number Example 1 Sample Name WP-1 Average particle size 1500μm Ash content / % 2.86 w(C) / % 83.28 w(H) / % 13.25 w(S) / % <0.1 w(N) / % 0.028 w(Cl) / % 0.0162 w(Si) / % 0.131 w(O) / % 1.45 w(Ca) / % 0.709

[0121] Table 2 Viscosity of Plastics with Reduced Plasticity and Tack

[0122]

[0123] Table 3 Material Properties

[0124]

[0125]

[0126] Table 4 Distribution of Pyrolysis Products from Waste Plastics

[0127]

[0128]

[0129] Table 5. Distribution of solution products in Example 3

[0130] Item, Quality Score / % Example 3 CO 0.05 <![CDATA[CO2]]> 0.23 dry air 2.81 Liquefied gas 5.91 Naphtha fraction (<180℃) 28.62 Diesel fraction (180℃~350℃) 30.12 Wax oil fraction (>350℃) 22.79 coke 9.53 total 100 Liquid recovery (including liquefied petroleum gas) 87.43

[0131] Table 6. Pyrolysis gas composition in Example 3

[0132]

[0133]

[0134] Table 7 Properties of Pyrolysis Liquid Products from Example 3

[0135]

[0136]

[0137] Table 8 Properties of coke in Example 3

[0138]

[0139]

[0140] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

Claims

1. A processing method for the pyrolysis and cracking of waste plastics, characterized in that, The method includes the following steps: S1. The waste plastic to be processed enters the waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastic. The process conditions for the liquefaction treatment include: outlet temperature of 370~500℃; residence time of 5~20min. S2. The liquefied waste plastic enters the plastic reduction and viscosity reduction unit for plastic reduction and viscosity reduction cracking treatment to obtain plastic reduction and viscosity reduction cracked liquefied waste plastic oil. The process conditions for plastic reduction and viscosity reduction cracking treatment include: reaction temperature of 370~450℃; residence time of 2~120min. S3. Low-ash material is extracted from the upper part of the reactor in the plastic reduction and viscosity reduction unit and fed into the heating furnace for heating treatment to obtain high-temperature low-ash material; high-ash material is extracted from the lower part of the reactor. S4. High-temperature, low-ash materials and high-ash materials enter the pyrolysis reaction unit to undergo pyrolysis reaction to obtain pyrolysis products and coke; S5. The pyrolysis products enter the separation unit and are separated to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.

2. The processing method for pyrolysis and cracking of waste plastics according to claim 1, characterized in that, In step S1, the waste plastic liquefaction unit uses a first screw-type heating and conveying device to perform the liquefaction process. The first screw-type heating and conveying device is selected from a twin-screw or single-screw heating and conveying device with heating.

3. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S1, the liquefaction process conditions include: an outlet temperature of 380~450℃ and a residence time of 5~15min.

4. The processing method for pyrolysis and cracking of waste plastics according to claim 1 or 2, characterized in that, In step S2, the plastic reduction and viscosity reduction unit uses an adiabatic plastic reduction and viscosity reduction reactor to carry out the plastic reduction and viscosity reduction cracking treatment.

5. The processing method for pyrolysis and cracking of waste plastics according to claim 4, characterized in that, In step S2, the process conditions for the plasticity reduction and viscosity reduction cracking treatment include: a reaction temperature of 380~420℃ and a residence time of 30~70min.

6. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S3, the weight ratio of low-ash material to high-ash material extracted is 1-20:

1.

7. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S3, a vertical baffle is installed in the reactor of the plastic reduction and viscosity reduction unit. The top of the baffle is closed and the bottom is open. Material is fed into the middle of one side of the baffle, and low ash material is extracted from the upper part and high ash material is extracted from the lower part of the other side.

8. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S3, the process conditions of the heating furnace include: the outlet temperature of the heating furnace is 480℃~600℃, and steam is injected into the heating furnace at a rate of 0.5~5% by weight.

9. The processing method for pyrolytic cracking of waste plastics according to claim 8, characterized in that, In step S3, the outlet temperature of the heating furnace is 500℃~580℃; the steam injection rate of the heating furnace is 0.5~3 by weight.

10. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S4, the high-temperature, low-ash material is mixed with the high-ash material and then enters the pyrolysis reaction unit to carry out the pyrolysis reaction to obtain pyrolysis products and coke.

11. The processing method for pyrolytic cracking of waste plastics according to claim 10, characterized in that, In step S4, the high-temperature low-ash material and the high-ash material are mixed in a mixer at a weight ratio of 1-20:

1.

12. The processing method for pyrolytic cracking of waste plastics according to claim 1 or 2, characterized in that, In step S4, the process conditions for the pyrolysis reaction include: the pressure at the top of the pyrolysis tower is 0.05~0.6MPa; the pyrolysis reaction temperature is 450~580℃; and the operation cycle is 1h~500h.

13. The processing method for pyrolysis and cracking of waste plastics according to claim 12, characterized in that, In step S4, the pressure at the top of the pyrolysis tower is 0.1~0.3 MPa; the pyrolysis temperature is 480~550℃; and the operation cycle is 10h~240h.

14. The processing method for pyrolytic cracking of waste plastics according to any one of claims 1, 2, 5, 9, 11, and 13, characterized in that, Before step S1, the method further includes: S0. Chlorine-containing waste plastic raw materials are fed into the waste plastic melting and dechlorination unit for hot melting and dechlorination treatment to obtain hydrogen chloride gas and dechlorinated waste plastic materials. The dechlorinated waste plastic material is fed into the waste plastic liquefaction unit; or The dechlorinated waste plastic material is sequentially cooled and crushed to obtain dechlorinated waste plastic particles; the dechlorinated waste plastic particles are then fed into the waste plastic liquefaction unit.

15. The processing method for pyrolytic cracking of waste plastics according to claim 14, characterized in that, The method also includes: The hydrogen chloride-containing gas is introduced into the hydrogen chloride absorption unit and comes into contact with the hydrogen chloride absorbent for hydrogen chloride absorption treatment, resulting in a chlorine-containing absorbent and dechlorinated dry gas; the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7.

16. The processing method for pyrolytic cracking of waste plastics according to claim 14, characterized in that, The waste plastic melting and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices; The process conditions for the hot melt dechlorination treatment include: feed rate of 5~5000 kg / h; outlet temperature of 150~370℃; reaction time of 0.1~0.5h; and vacuum degree of 50~300 mmHg. The particle size of the dechlorinated waste plastic particles obtained by crushing is 100~2000μm.

17. The processing method for pyrolytic cracking of waste plastics according to claim 16, characterized in that... The process conditions for the hot melt dechlorination treatment include: a feed rate of 100~4000 kg / h; an outlet temperature of 300~330℃; a reaction time of 0.1~0.3h; and a vacuum degree of 50~150 mmHg.

18. The processing method for pyrolytic cracking of waste plastics according to any one of claims 1, 2, 5, 9, 11, and 13, characterized in that, The method further includes returning at least a portion of the wax oil fraction from the separation unit to the plasticizing and viscosity-reducing unit for reprocessing.

19. The processing method for pyrolytic cracking of waste plastics according to claim 18, characterized in that, The weight ratio of recycled wax oil fraction to waste plastic to be treated is 0.2~5.0:1; the fraction with a distillation range greater than 350℃ obtained by the separation unit is used as the wax oil fraction.

20. The processing method for pyrolytic cracking of waste plastics according to any one of claims 1, 2, 5, 9, 11, and 13, characterized in that, The waste plastics to be treated include one or more of LDPE, HDPE, PS, PP, PET and PVC; the PVC content in the waste plastics to be treated is less than 10% by weight; and the ash content in the waste plastics to be treated is 1 to 40% by weight.

21. A waste plastic pyrolysis cracking processing system, used in the waste plastic pyrolysis cracking processing method according to any one of claims 1-20, characterized in that, The processing system includes: a waste plastic liquefaction unit, a plastic reduction and viscosity reduction unit, a heating furnace, a pyrolysis reaction unit, and a separation unit; The waste plastic liquefaction unit includes a waste plastic inlet and a liquefied waste plastic outlet, and the waste plastic liquefaction unit is configured to liquefy the waste plastic to be treated. The plastic reduction and viscosity reduction unit includes a liquefied waste plastic inlet, an upper outlet, and a lower outlet. The plastic reduction and viscosity reduction unit is configured to perform plastic reduction and viscosity reduction cracking treatment on the liquefied waste plastic. The heating furnace includes a heating inlet and a heating outlet. The heating inlet is connected to the upper outlet of the plastic reduction and viscosity reduction unit. The heating furnace is configured to heat the low-ash material in the waste plastic oil of plastic reduction and viscosity reduction cracking. The pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet. The pyrolysis reactant inlet is connected to the heating outlet of the heating furnace and the lower outlet of the plastic reduction and viscosity reduction unit. The pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on high-temperature waste plastic oil. The separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet, and a wax oil fraction outlet; the separation inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit, and the separation unit is configured to separate the pyrolysis products.

22. The waste plastic pyrolysis cracking processing system according to claim 21, characterized in that, The waste plastic liquefaction unit includes a first screw-type heating conveyor; the first screw-type heating conveyor is selected from a twin-screw or single-screw heating conveyor with heating.

23. The waste plastic pyrolysis cracking processing system according to claim 21, characterized in that, The plastic reduction and viscosity reduction unit also includes a circulating oil inlet; the circulating oil inlet is connected to the wax oil fraction outlet of the separation unit.

24. The waste plastic pyrolysis cracking processing system according to claim 21, 22 or 23, characterized in that, The system also includes a waste plastic melting and dechlorination unit and a hydrogen chloride absorption unit; The waste plastic melting and dechlorination unit includes a chlorine-containing waste plastic raw material inlet, a hydrogen chloride gas outlet, and a dechlorinated waste plastic liquid material outlet. The waste plastic melting and dechlorination unit is configured to perform thermal melting and dechlorination treatment on the chlorine-containing waste plastic raw material. The dechlorinated waste plastic liquid material outlet is connected to the waste plastic inlet to be treated in the waste plastic liquefaction unit. The hydrogen chloride absorption unit includes a hydrogen chloride gas inlet, a hydrogen chloride absorbent, and a dechlorinated dry gas outlet; the hydrogen chloride gas inlet is connected to the hydrogen chloride gas outlet of the waste plastic melting and dechlorination unit; The waste plastic melting and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; the second screw-type heating and conveying device is selected from twin-screw or single-screw conveying devices.

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