A method and system for liquefying solid waste plastics

Abstract

This disclosure relates to a method and system for liquefying solid waste plastics, comprising the following steps: S1, feeding the solid waste plastics into a deoxidation unit for deoxidation treatment to obtain deoxidized plastics; S2, feeding the deoxidized plastics into a softening unit for softening and dechlorination treatment to obtain chlorine-containing gas and softened dechlorinated plastics; S3, feeding the softened dechlorinated plastics into a liquefaction unit for liquefaction treatment to obtain pyrolysis gas and liquid plastics; S4, feeding the chlorine-containing gas from step S2 and the pyrolysis gas from step S3 into an alkaline washing unit for alkaline washing treatment; and returning at least a portion of the liquid plastics from step S3 as recycled material to the liquefaction unit for further processing after heating. This method can continuously provide liquid feed for the pyrolysis of waste plastics.

Description

Technical Field

[0001] This disclosure relates to the field of waste plastic utilization, and more specifically, to a method and system for liquefying solid waste plastics. Background Technology

[0002] Waste plastics are mainly disposed of through landfill and incineration. Landfilled waste plastics are difficult to degrade naturally, resulting in the long-term occupation of large amounts of land resources; during the landfill period, harmful substances from the waste plastics may leach into the soil, causing secondary pollution. Incineration is not economically viable and has negative impacts such as producing highly toxic substances like dioxins.

[0003] Plastics, with their high molecular structure, can have their carbon-carbon bonds broken through thermal cracking to produce petrochemical products such as cracked oil. Waste plastic pyrolysis technology enables the reuse of waste resources, offering significant economic value and representing an important measure for developing a circular economy in my country. However, current technology is not yet fully developed. Waste plastic pyrolysis requires high temperatures and pressures. Since waste plastic raw materials are mostly plastic films or granules, the high porosity of solid plastics makes continuous feeding difficult to achieve self-sealing of the material flow, easily leading to leakage of pyrolysis products upstream. Therefore, existing pyrolysis technologies mostly employ intermittent methods, resulting in low production efficiency. Furthermore, the high porosity of plastic films or granules leads to a significant amount of air content. The high temperatures during pyrolysis generate a certain amount of light hydrocarbons. Direct feeding of plastic films or granules increases the possibility of an explosion due to the mixing of oxygen and light hydrocarbons. Simultaneously, oxygen participates in the pyrolysis reaction, producing oxidation products that affect product quality and liquid phase yield. Moreover, solid waste plastics contain a certain amount of PVC, which decomposes upon heating to generate various chlorides. Improper handling can cause severe equipment corrosion and affect product quality.

[0004] CN114262621A discloses a waste plastic liquefaction pyrolysis system and method. This invention proposes liquefying waste plastics by introducing hot nitrogen gas into the bottom of a liquid phase tank. Two sealing plates are installed at the top of the liquid phase tank, and their alternating opening and closing achieves continuous sealed feeding. However, this method contains pyrolysis gas between the two sealing plates. When the first sealing plate is opened for feeding, pyrolysis gas is released. Furthermore, this method cannot effectively prevent contact between air and high-temperature pyrolysis gas. Summary of the Invention

[0005] The purpose of this disclosure is to provide a method and system for liquefying solid waste plastics, which can continuously provide liquid feed for the pyrolysis of waste plastics.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a method for liquefying solid waste plastics, comprising the following steps:

[0007] S1. Solid waste plastic is fed into a deoxidation unit for deoxidation treatment to obtain deoxidized plastic;

[0008] S2. The deoxidized plastic is fed into a softening device for softening and dechlorination treatment to obtain chlorine-containing gas and softened dechlorinated plastic;

[0009] S3. The softened dechlorinated plastic is fed into a liquefaction device for liquefaction treatment to obtain pyrolysis gas and liquid plastic.

[0010] S4. The chlorine-containing gas mentioned in step S2 and the pyrolysis gas mentioned in step S3 are introduced into the alkaline washing device for alkaline washing treatment; at least a portion of the liquid plastic mentioned in step S3 is heated as recycled material and then returned to the liquefaction device for further processing.

[0011] Optionally, the deoxidation device includes a solid waste plastic inlet and a deoxidized plastic outlet; a sealing unit is respectively provided on the inlet pipeline of the solid waste plastic inlet and the outlet pipeline of the deoxidized plastic outlet;

[0012] Optionally, the sealing unit includes an upstream pipe, a valve, and a downstream pipe connected in sequence; the inner diameter of the upstream pipe is smaller than the inner diameter of the valve, and the inner diameter of the downstream pipe is the same as the inner diameter of the valve; the outlet of the upstream pipe is connected to the valve, and a protective gas inlet pipe is provided on the side wall of the upstream pipe near the outlet.

[0013] Optionally, the upstream pipeline of the valve includes a constant diameter section and a variable diameter section arranged sequentially from top to bottom. The inner diameter of the constant diameter section is smaller than the inner diameter of the valve. The inner diameter of the top of the variable diameter section is the same as the inner diameter of the constant diameter section, and the inner diameter of the bottom of the variable diameter section is the same as the inner diameter of the valve. The protective gas inlet pipeline is disposed on the side wall of the variable diameter section.

[0014] Preferably, the inclination angle between the protective gas inlet pipe and the central axis of the upstream pipe of the valve is an acute angle, preferably 10 to 80°; optionally, the ratio of the inner diameter of the equal diameter section of the upstream pipe of the valve to the inner diameter of the valve is 0.5 to 0.9; the height of the variable diameter section of the upstream pipe of the valve is 10 to 500 mm.

[0015] Alternatively, the sealing unit includes an upstream pipe, a valve, and a downstream pipe connected in sequence; the inner diameters of the upstream pipe and the downstream pipe are the same as the inner diameter of the valve; the outlet of the upstream pipe is connected to the valve, and a protective gas inlet pipe is provided on the side wall of the upstream pipe near the outlet; and a protective baffle is provided circumferentially on the inner wall near the outlet of the upstream pipe; preferably, the inclination angle between the protective gas inlet pipe and the central axis of the upstream pipe is an acute angle, preferably 10 to 80°; optionally, the width of the protective baffle is 2 to 150 mm.

[0016] Optionally, step S1 includes:

[0017] The solid waste plastic is introduced into the deoxidation device through the solid waste plastic inlet at the top of the deoxidation device via the sealing unit; inert gas is continuously introduced into the deoxidation device through the inert gas inlet on the side wall of the deoxidation device for continuous purging to displace the air in the deoxidation device; optionally, the inert gas rate is 10 to 2000 L / min, preferably 50 to 500 L / min;

[0018] Alternatively, the solid waste plastic is introduced into the deoxidizer via a solid waste plastic inlet at the top of the deoxidizer through a sealing unit; inert gas is introduced into the deoxidizer through an inert inlet on the side wall of the deoxidizer to 0.1–1.0 MPa, preferably 0.3–0.5 MPa, and then the deoxidizer is depressurized to below 0.1 MPa; this process is repeated 1–10 times, preferably 2–5 times; preferably, during the process of the solid waste plastic flowing through the sealing unit into the deoxidizer, protective gas is introduced into the sealing unit through the protective gas inlet pipe to purge the solid waste plastic in the sealing unit; preferably, the protective gas is selected from one or more of air, inert gas, and liquid hydrocarbons, preferably nitrogen; optionally, the flow rate of the protective gas is 10–2000 L / min, preferably 50–500 L / min.

[0019] Optionally, in step S2, the softening device is a first screw compressor; the first screw compressor includes a screw inlet, a screw outlet, a first exhaust port, and a first heating element;

[0020] Preferably, the inlet temperature of the first screw compressor is 0-100℃, the material residence time is 30-1200s, and the outlet temperature of the first screw compressor is 80-300℃; preferably, the inlet temperature of the first screw compressor is 20-60℃, the material residence time is 120-300s, and the outlet temperature of the first screw compressor is 120-200℃.

[0021] Preferably, the chlorine content of the softened dechlorinated plastic is less than 0.1% by weight.

[0022] Optionally, in step S3, the liquefaction device is a stirring device, and a second heating element is provided on the outer side of the bottom of the stirring device to heat the material in the stirring device;

[0023] Optionally, the liquefaction treatment conditions include: a temperature of 150–500℃, a pressure of -0.09–1.0 MPa, and a time of 0.1–1.0 h; preferably, a temperature of 250–400℃, a pressure of 0.05–0.5 MPa, and a time of 0.1–0.2 h; optionally, a stirring rate of 10–500 r / min; preferably 50–200 r / min.

[0024] Optionally, in step S3, the liquefaction device is a second screw compressor, which includes a third heating element for heating the material inside the second screw compressor;

[0025] The liquefaction conditions include: the inlet temperature of the second screw compressor is 80-300°C, the material residence time is 30-1200s, and the outlet temperature of the second screw compressor is 250-500°C; preferably, the inlet temperature of the second screw compressor is 120-200°C, the material residence time is 100-300s, and the outlet temperature of the second screw compressor is 250-400°C.

[0026] Optionally, in step S4, the recycled material accounts for 10-90% by weight of all liquid material from the liquefaction unit, preferably 30-60% by weight; preferably, the temperature of the recycled material after heating is 300-500°C, preferably 350-450°C.

[0027] Optionally, the weight ratio of the recycled material to the softened dechlorinated plastic from the softening device is 0.1 to 9:1, preferably 0.5 to 3:1.

[0028] Optionally, the method further includes:

[0029] The pyrolysis gas from the liquefaction unit is fed into a gas-liquid separation unit for gas-liquid separation to obtain gaseous and liquid materials.

[0030] The gaseous material is introduced into the alkaline washing device for alkaline washing treatment; the liquid material is then introduced into the subsequent liquefied plastics processing device.

[0031] Optionally, the alkaline washing agent in the alkaline washing device is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0032] The second aspect of this disclosure provides a system for liquefying solid waste plastics, the system comprising: a deoxidation unit, a softening unit, a liquefaction unit, and an alkaline washing unit;

[0033] The deoxidation device includes a solid waste plastic inlet, an inert gas inlet, and a deoxidized plastic outlet;

[0034] The softening device includes a deoxidizing plastic inlet, a chlorine-containing gas outlet, and a softened dechlorinated plastic outlet, wherein the deoxidizing plastic inlet is connected to the deoxidizing plastic outlet of the deoxidizing device.

[0035] The liquefaction device includes a softening and dechlorinating plastic inlet, a pyrolysis gas outlet, and a liquid plastic outlet. The softening and dechlorinating plastic inlet is connected to the softening and dechlorinating plastic outlet of the softening device, and the liquid plastic outlet is connected to the softening and dechlorinating plastic inlet of the liquefaction device via a liquid plastic circulation pipeline.

[0036] The alkaline washing device includes an inlet for the material to be washed, an inlet for the alkaline washing agent, an outlet for the waste liquid, and an exhaust port; the inlet for the material to be washed is connected to the chlorine-containing gas outlet of the softening device and the pyrolysis gas outlet of the liquefaction device, respectively.

[0037] Optionally, the system further includes a sealing unit, which includes an upstream pipe, a valve, and a downstream pipe connected in sequence.

[0038] Optionally, the system includes multiple deoxidation devices; preferably, the system includes two deoxidation devices arranged in parallel; each deoxidation device has a sealing unit installed on the inlet pipeline of the waste plastic inlet and the outlet pipeline of the deoxidized plastic outlet; wherein the outlet of the downstream pipe of the valve of the sealing unit located on the inlet pipeline of the waste plastic inlet is connected to the solid waste plastic inlet of the deoxidation device; the inlet of the downstream pipe of the valve of the sealing unit located on the outlet pipeline of the deoxidized plastic outlet is connected to the deoxidized plastic outlet of the deoxidation device, and the outlet of the downstream pipe of the valve is connected to the deoxidized plastic inlet of the softening device;

[0039] Optionally, the deoxygenation device is a vertical tank; the softening device is a first screw compressor; the liquefaction device is a stirred tank or a second screw compressor; and the alkaline washing device is a washing tower.

[0040] Through the above technical solution, this disclosure provides a method and system for liquefying solid waste plastics, which includes at least the following beneficial effects:

[0041] (1) Solid waste plastics are deoxygenated in a deoxygenation device with good sealing performance. The device has a low failure rate and a long continuous operation cycle. After deoxygenation, the plastic has a low oxygen content, which can effectively reduce the possibility of oxygen and subsequent high-temperature pyrolysis gas mixing and explosion. At the same time, it reduces the participation of oxygen in the pyrolysis reaction, reduces the gas phase yield and increases the liquid yield, and reduces the content of oxygen-containing compounds in the liquid phase product.

[0042] (2) In the softening device, the plastic softens at a relatively low temperature, where the chlorine-containing plastic decomposes and releases chlorine-containing gas, which is extracted through multiple exhaust ports set in the softening device. The softened plastic has a low chlorine content, which can effectively reduce corrosion to subsequent equipment and reduce the chlorine content in the liquid phase product.

[0043] (3) The residence time inside the plastic liquefaction device is short and the asphalt content of the product is low; the pressure drop of the plastic liquefaction device itself is low and the internal gas-liquid flow is smooth, which can effectively avoid the coking and blockage of the equipment by liquid plastic and the backflow of internal materials upstream, and the operation of the device is highly safe.

[0044] (4) Convert solid plastics into liquid plastics to continuously supply liquid plastics to downstream pyrolysis units, thereby enabling continuous and safe production of the units.

[0045] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0046] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0047] Figure 1 This is a flowchart illustrating the method for liquefying solid waste plastics provided in this disclosure;

[0048] Figure 2 This is a schematic diagram of the structure of a sealing unit provided in one embodiment of the present disclosure;

[0049] Figure 3 This is a schematic diagram of the structure of a sealing unit provided for another embodiment of this disclosure.

[0050] Figure Labels

[0051] 1-Solid waste plastic; 2-Sealing unit; 3-Deoxidation device; 4-Deoxidized plastic; 5-Softening device; 6-Liquefaction device; 7-Liquid plastic; 8-Gas-liquid separation device; 9-Liquefied gas; 10-Alkali washing device; 11-Alkali solution; 12-Emission gas; 13-Waste alkali solution; 14-Softened plastic; 15-Circulating material; 16-Heating furnace; 17-Nitrogen; 18-Acidic gas; 19-Valve; 20-Protective gas inlet pipe; 21-Protective baffle; 23-Upstream pipe of valve; 24-Downstream pipe of valve. Detailed Implementation

[0052] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0053] The first aspect of this disclosure provides a method for liquefying solid waste plastics, such as... Figure 1 As shown, it includes the following steps:

[0054] S1. Solid waste plastic is fed into deoxidation device 3 for deoxidation treatment to obtain deoxidized plastic;

[0055] S2. The deoxidized plastic is fed into the softening device 5 for softening and dechlorination treatment to obtain chlorine-containing gas and softened dechlorinated plastic;

[0056] S3. The softened dechlorinated plastic is fed into the liquefaction device 6 for liquefaction treatment to obtain pyrolysis gas and liquid plastic.

[0057] S4. The chlorine-containing gas mentioned in step S2 and the pyrolysis gas mentioned in step S3 are introduced into the alkaline washing device 10 for alkaline washing treatment; at least a portion of the liquid plastic mentioned in step S3 is heated as recycled material and then returned to the liquefaction device 6 for further processing.

[0058] This disclosure provides a method for liquefying solid waste plastics. The solid waste plastics are deoxygenated in a well-sealed deoxygenation device. After deoxygenation, the plastics have a low oxygen content, effectively reducing the possibility of an explosion caused by the mixing of oxygen and subsequent high-temperature pyrolysis gases. In a softening device, the plastics soften at a relatively low temperature. Chlorine-containing plastics decompose and release chlorine-containing gases, which are extracted through multiple exhaust ports within the softening device. The low chlorine content of the softened plastics effectively reduces corrosion to downstream equipment. The plastic liquefaction device itself has a low pressure drop and smooth internal gas-liquid flow, effectively preventing the liquid plastic from coking and clogging the equipment, and avoiding upstream backflow of internal materials. The device has high operational safety. By converting solid plastics into liquid plastics, a continuous supply of liquid plastics can be provided to the downstream pyrolysis unit, enabling continuous and safe production.

[0059] In one specific embodiment, the solid waste plastic includes one or more of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET); the solid waste plastic has a chlorine content of 0.01-3% by weight, a water content of less than 30% by weight, and an organic impurity content of less than 20% by weight; the solid waste plastic can be a film sheet or granules.

[0060] In one embodiment, the deoxidizing device 3 includes a solid waste plastic inlet and a deoxidized plastic outlet; a sealing unit 2 is respectively installed on the inlet pipeline of the solid waste plastic inlet and the outlet pipeline of the deoxidized plastic outlet. The sealing unit 2 used in this disclosure is composed of a valve, an anti-blocking structure, and a protective fluid combination to achieve effective sealing of the deoxidizing device 3. The sealing unit 2 provided in this disclosure includes two forms:

[0061] In the first specific implementation, such as Figure 2 As shown, the sealing unit 2 includes an upstream valve pipe 23, a valve 19, and a downstream valve pipe 24 arranged sequentially. The inner diameter of the upstream valve pipe 23 is smaller than that of the valve 19, and the inner diameter of the downstream valve pipe 24 is the same as that of the valve 19. The outlet of the upstream valve pipe 23 is connected to the valve 19, and a protective gas inlet pipe 20 is provided on the side wall of the upstream valve pipe 23 near the outlet. Optionally, the upstream valve pipe 23 includes a constant diameter section and a variable diameter section arranged sequentially from top to bottom. The inner diameter of the constant diameter section is smaller than that of the valve 19, the inner diameter of the top of the variable diameter section is the same as that of the constant diameter section, and the inner diameter of the bottom of the variable diameter section is the same as that of the valve 19. The protective gas inlet pipe 20 is provided on the side wall of the variable diameter section. In this embodiment, the inclination angle between the protective gas inlet pipe 20 and the central axis of the valve upstream pipe 23 is an acute angle, preferably 10 to 80°; the ratio of the inner diameter of the equal diameter section of the valve upstream pipe 23 to the inner diameter of the valve 19 is 0.5 to 0.9; and the height of the variable diameter section of the valve upstream pipe 23 is 10 to 500 mm.

[0062] In the second implementation, such as Figure 3 As shown, the sealing unit 2 includes an upstream valve pipe 23, a valve 19, and a downstream valve pipe 24 arranged sequentially. The inner diameters of the upstream valve pipe 23 and the downstream valve pipe 24 are the same as the inner diameter of the valve 19. The outlet of the upstream valve pipe 23 is connected to the valve 19, and a protective gas inlet pipe 20 is provided on the side wall of the upstream valve pipe 23 near the outlet. A protective baffle 21 is circumferentially provided on the inner wall near the outlet of the upstream valve pipe 23. In this embodiment, the inclination angle between the protective gas inlet pipe 20 and the central axis of the upstream valve pipe 23 is an acute angle, preferably 10 to 80°. Optionally, the width of the protective baffle 21 is 2 to 150 mm.

[0063] In this disclosure, during the deoxidation treatment of solid waste plastics, deoxidation devices 3 are respectively equipped at the inlet and outlet. Figure 2 or Figure 3 The sealing unit shown has an upstream pipe diameter smaller than the valve's inner diameter. Figure 2 Alternatively, a protective baffle can be installed on the inner wall of the upstream pipeline near the valve. Figure 3Both of these methods can limit the flow area of ​​solid plastic, thus preventing it from falling into the valve slide and obstructing normal valve opening and closing to some extent. To further reduce the probability of solid plastic falling into the valve slide, when solid plastic passes through the valve, nitrogen gas is used to purge the valve slide at an appropriate angle. Nitrogen purging stops when no solid plastic flows through the valve. The sealing unit disclosed herein can prevent valve sealing failure caused by solid plastic falling into the valve slide during valve opening and closing, thereby achieving long-term sealing in solid conveying pipelines that require frequent opening and closing.

[0064] In one specific embodiment, during the process of the solid waste plastic flowing through the sealing unit 2 into the deoxygenation device 3, a protective gas is introduced into the sealing unit 2 through the protective gas inlet pipe 20 to purge the solid waste plastic in the sealing unit 2; preferably, the protective gas is selected from one or more of air, inert gas and liquid hydrocarbon, preferably nitrogen; optionally, the flow rate of the protective gas is 10 to 2000 L / min, preferably 50 to 500 L / min.

[0065] In one embodiment, step S1 includes the following two methods for deoxygenation treatment:

[0066] The solid waste plastic is introduced into the deoxygenation device 3 through the solid waste plastic inlet at the top of the deoxygenation device 3 via the sealing unit 2; inert gas is continuously introduced into the deoxygenation device 3 through the inert gas inlet on the side wall of the deoxygenation device 3 for continuous purging to displace the air in the deoxygenation device 3; optionally, the inert gas rate is 10 to 2000 L / min, preferably 50 to 500 L / min; preferably, in this method, a tank can be used as the deoxygenation device;

[0067] Alternatively, the solid waste plastic is introduced into the deoxidation device 3 through the solid waste plastic inlet at the top of the deoxidation device 3 via the sealing unit 2; inert gas is introduced into the deoxidation device 3 through the inert inlet on the side wall of the deoxidation device 3 to 0.1-1.0 MPa, preferably 0.3-0.5 MPa, and then the deoxidation device 3 is depressurized to below 0.1 MPa; this process is repeated 1-10 times, preferably 2-5 times; preferably, in this method, two tanks can be connected in parallel as the deoxidation device. In this disclosure, the oxygen content of the deoxidized solid plastic can be effectively reduced by continuously purging with inert gas, or by filling the deoxidation device with inert gas to a certain pressure, and then releasing the gas in the deoxidation device, repeating the above process to replace oxygen.

[0068] In one specific embodiment, when two tanks are arranged in parallel as deoxidation devices, one deoxidation device is controlled to be in the deoxidation process, while the other deoxidation device is in the process of completing the deoxidation process and conveying deoxidized plastic to the softening device 5. The processing of the two deoxidation devices is switched as the reaction progresses to ensure that the deoxidation device can continuously provide deoxidized plastic to the softening device, thereby continuously providing liquid feed for the pyrolysis of waste plastics.

[0069] In one embodiment, in step S2, the softening device 5 is a first screw compressor; the first screw compressor includes a screw inlet, a screw outlet, a first exhaust port, and a first heating element;

[0070] Preferably, the inlet temperature of the first screw compressor is 0-100℃, the material residence time is 30-1200s, and the outlet temperature is 80-300℃; preferably, the inlet temperature of the first screw compressor is 20-60℃, the material residence time is 120-300s, and the outlet temperature is 120-200℃.

[0071] Preferably, the chlorine content of the softened and dechlorinated plastic is less than 0.1% by weight. The softening device used in this disclosure is a screw compressor with a heating function (first heating element) and an exhaust port (first exhaust port). In the plastic softening section, the solid plastic moves under the push of the screw and softens at a relatively low temperature. Most of the chlorine in the plastic decomposes and is extracted from the exhaust port of the plastic softener. The softened plastic has a low chlorine content, which can significantly reduce the corrosion of subsequent equipment by chlorine impurities. In this disclosure, the softening device is provided with multiple first exhaust ports at different temperatures, preferably two first exhaust ports.

[0072] The liquefaction device used in this disclosure can be a stirred tank with heating function; or it can be a screw compressor with heating function and a structure that facilitates gas-liquid flow.

[0073] In one specific embodiment, in step S3, the liquefaction device 6 is a stirring device, and a second heating element is provided on the outer side of the bottom of the stirring device to heat the material in the stirring device;

[0074] Optionally, the liquefaction treatment conditions include: a temperature of 150–500°C, a pressure of -0.09–1.0 MPa, and a time of 0.1–1.0 h; preferably, a temperature of 250–400°C, a pressure of 0.05–0.5 MPa, and a time of 0.1–0.2 h.

[0075] Optionally, the stirring rate is 10–500 r / min; preferably 50–200 r / min.

[0076] In another specific embodiment, in step S3, the liquefaction device 6 is a second screw compressor, and the second screw includes a third heating element for heating the material inside the second screw compressor; optionally, when the liquefaction device 6 is a second screw compressor, the cross-sectional area of ​​the liquefaction device outlet pipe is 50% to 300% of the cross-sectional area of ​​the second screw compressor body; preferably, the cross-sectional area of ​​the liquefaction device outlet pipe is equal to the cross-sectional area of ​​the second screw compressor body.

[0077] The liquefaction conditions include: the inlet temperature of the second screw compressor is 80-300°C, the residence time is 30-1200s, and the outlet temperature of the second screw compressor is 250-500°C; preferably, the inlet temperature of the second screw compressor is 120-200°C, the residence time is 100-300s, and the outlet temperature of the second screw compressor is 250-400°C.

[0078] In this disclosure, the plastic liquefaction section operates at a relatively high temperature, and a small amount of plastic decomposes to produce a certain amount of gas. The mixing tank or screw compressor with a large outlet cross-sectional area has the characteristic of low pressure drop, allowing the liquefied material, characterized by high viscosity and a gas-liquid two-phase flow, to pass smoothly through the liquefaction equipment. This avoids the problem of localized overheating of high-temperature liquid plastic due to poor flow, leading to coking and equipment blockage.

[0079] In one specific embodiment, the stirring device or the second screw compressor can be configured as a single stage or a multi-stage system connected in series to improve processing efficiency.

[0080] In a preferred embodiment, in step S4, the circulating material accounts for 10-90% by weight of all liquid material from the liquefaction device 6, preferably 30-60% by weight; preferably, the temperature of the circulating material after heating is 300-500°C, preferably 350-450°C.

[0081] Optionally, the weight ratio of the recycled material to the softened dechlorinated plastic from the softening device 5 is 0.1 to 9:1, preferably 0.5 to 3:1.

[0082] In one specific embodiment, the liquefaction device 6 is a stirring device. Liquid plastic is obtained at the bottom of the stirring tank, and the gas phase outlet at the top is connected to the gas-liquid separation device 8. The top of the gas-liquid separation device 8 obtains pyrolysis gas, and the bottom of the gas-liquid separation device 8 obtains another part of liquid plastic, which can be used in subsequent liquefaction plastic processing devices.

[0083] The liquefaction unit 6 is the second screw compressor, and the outlet of the last screw compressor is connected to the gas-liquid separator 8. The top of the gas-liquid separator receives pyrolysis gas, which is used to enter the subsequent alkaline washing unit 10, and the bottom receives liquid plastic. The liquid plastic at the bottom of the gas-liquid separator 8 can be used in the subsequent liquefaction plastic processing unit.

[0084] In one implementation, such as Figure 1 As shown, the method also includes:

[0085] The pyrolysis gas from the liquefaction device 6 is introduced into the gas-liquid separation device 8 for gas-liquid separation to obtain gaseous and liquid materials.

[0086] The gaseous material is introduced into the alkaline washing device 10 for alkaline washing treatment; the liquid material is introduced into the subsequent liquefied plastics processing device.

[0087] In one specific embodiment, the alkaline washing agent in the alkaline washing device is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0088] A second aspect of this disclosure provides a system for liquefying solid waste plastics, such as... Figure 1 As shown, the system includes: a deoxidizing unit 3, a softening unit 5, a liquefaction unit 6, and an alkaline washing unit 10;

[0089] The deoxidation unit 3 includes a solid waste plastic inlet, an inert gas inlet, and a deoxidized plastic outlet;

[0090] The softening device 5 includes a deoxidized plastic inlet, a chlorine-containing gas outlet, and a softened dechlorinated plastic outlet. The deoxidized plastic inlet is connected to the deoxidized plastic outlet of the deoxidizing device 3.

[0091] The liquefaction unit 6 includes a softening and dechlorinating plastic inlet, a pyrolysis gas outlet, and a liquid plastic outlet. The softening and dechlorinating plastic inlet is connected to the softening and dechlorinating plastic outlet of the softening unit 5, and the liquid plastic outlet is connected to the softening and dechlorinating plastic inlet of the liquefaction unit 6 via a liquid plastic circulation pipeline.

[0092] The alkaline washing device 10 includes an inlet for the material to be washed, an inlet for the alkaline washing agent, an outlet for the waste liquid, and an exhaust port; the inlet for the material to be washed is connected to the chlorine-containing gas outlet of the softening device 5 and the pyrolysis gas outlet of the liquefaction device 6, respectively.

[0093] In one implementation, such as Figure 1 As shown, the system also includes a sealing unit 2, which comprises an upstream pipe 23, a valve 19, and a downstream pipe 24 connected in sequence. The sealing unit 2 is as follows... Figure 2 or Figure 3 As shown. The specific structure of sealing unit 2 has been described in detail above and will not be repeated here.

[0094] In a preferred embodiment, such as Figure 1As shown, the system includes multiple deoxidation devices 3; preferably, the system includes two deoxidation devices 3 arranged in parallel; each deoxidation device 3 has a sealing unit 2 installed on the inlet pipeline of the waste plastic inlet and the outlet pipeline of the deoxidized plastic outlet; wherein the outlet of the valve downstream pipe 24 of the sealing unit 2 located on the inlet pipeline of the waste plastic inlet is connected to the solid waste plastic inlet of the deoxidation device 3; the inlet of the valve downstream pipe 24 of the sealing unit 2 located on the outlet pipeline of the deoxidized plastic outlet is connected to the deoxidized plastic outlet of the deoxidation device 3, and the outlet of the valve downstream pipe 24 is connected to the deoxidized plastic inlet of the softening device 5.

[0095] In one specific embodiment, the deoxygenation device 3 is a vertical tank structure; the softening device 5 is a first screw compressor; the chemical treatment device 6 is a mixing tank or a second screw compressor; and the alkaline washing device 10 is a washing tower.

[0096] In one specific implementation, such as Figure 1 As shown, the system also includes a heating furnace 16, the inlet of which is connected to the liquid plastic outlet of the liquefaction device 6, and the outlet of which is connected to the softened and dechlorinated plastic inlet of the liquefaction device 6, for heating the liquid plastic returned to the liquefaction device 6 for further processing.

[0097] In one specific implementation, such as Figure 1 As shown, the system also includes a gas-liquid separator 8 for further separation of the pyrolysis gas from the liquefaction unit 6. The inlet of the gas-liquid separator 8 is connected to the pyrolysis gas outlet of the liquefaction unit 6, the gas phase outlet of the gas-liquid separator 8 is connected to the inlet of the material to be alkali-washed in the alkali washing unit 10, and the liquid phase outlet of the gas-liquid separator 8 can collect and flow out with the material stream (liquid plastic) 7. The gas-liquid separator 8 can be a gas-liquid separation tank.

[0098] use Figure 1 The system shown includes the following processes for liquefying solid waste plastics:

[0099] The system includes two deoxidizing units 3 connected in parallel. Crushed solid waste plastic 1 is introduced into the two deoxidizing units 3 via a sealing unit 2 on the solid waste plastic inlet pipeline. The two deoxidizing units 3 operate in parallel: the sealing unit 2 at the top of one deoxidizing unit 3 is closed, disconnecting it from the upstream, and nitrogen protective gas is not supplied. The sealing unit 2 at the bottom of this deoxidizing unit 3 is open, and nitrogen protective fluid is supplied, sending deoxidized plastic 4 to the softening unit 5. The sealing unit 2 at the bottom of the other deoxidizing unit 3 is closed, and nitrogen protective gas is not supplied, disconnecting it from the downstream softening unit 5. The sealing unit 2 at the top of this deoxidizing unit 3 is open, and nitrogen protective fluid is supplied, receiving solid waste plastic 1. After receiving sufficient raw material, the top sealing unit 2 is closed, and nitrogen protective gas is not supplied. Nitrogen gas 17 is introduced to fill the deoxidizing unit 3 until the pressure reaches 0.3 MPa, then depressurized to 0.05 MPa. This process is repeated three times to complete the plastic deoxidation. Deoxidized plastic 4 enters softening unit 5, where it is heated to a softened state. Chlorine-containing plastic decomposes, releasing acidic gas 18, which enters alkaline washing unit 10. Softened plastic 14 enters liquefaction unit 6. Gas from the top of liquefaction unit 6 is introduced into gas-liquid separation unit 8, and the liquefied gas from the top of gas-liquid separation unit 8 enters alkaline washing unit 10. The liquid plastic at the bottom of liquefaction unit 6 is divided into two parts: one part is circulating material 15, which is heated by heating furnace 16 and sent to the inlet of liquefaction unit 6 to provide some heat for plastic liquefaction; the other part is liquid plastic 7, which can be used for subsequent processing, such as entering a delayed coking unit.

[0100] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0101] Example 1

[0102] use Figure 1 The solid waste plastic liquefaction system shown includes the following structural parameters for each device:

[0103] The structure of sealing unit 2 is as follows: Figure 2 As shown, the inclination angle between the central axis of the protective gas inlet pipe 20 and the valve upstream pipe 23 is an acute angle of 45°; the ratio of the inner diameter of the equal diameter section of the valve upstream pipe 23 to the inner diameter of the valve 19 is 0.8; the height of the variable diameter section of the valve upstream pipe 23 is 100mm; the dimensions of the deoxygenation device 3 are 600mm (inner diameter) × 1500mm (height); the softening device 5 is a first screw compressor, the major diameter of the screw of the first screw compressor is 50mm, and the screw length is 3000mm; the liquefaction device 6 is a stirring device, the dimensions of the stirring device are 300mm (inner diameter) × 500mm (height).

[0104] The process of liquefying solid waste plastics using the above system includes:

[0105] Solid waste plastics include polypropylene, polyethylene, and polyvinyl chloride, with a chlorine content of 0.5% by weight.

[0106] The crushed solid waste plastic 1 is introduced into two deoxidation devices 3 through the sealing unit 2 on the solid waste plastic inlet inlet pipeline of the deoxidation device 3. Two deoxidation units 3 operate in parallel: the sealing unit 2 at the top of one deoxidation unit 3 is closed, disconnected from the upstream, and no nitrogen protective gas is supplied. This deoxidation unit has completed the deoxidation process. The sealing unit 2 at the bottom of this deoxidation unit 3 is open, and nitrogen protective gas is supplied at a flow rate of 150 L / min, feeding deoxidized plastic 4 to the softening unit 5. The sealing unit 2 at the bottom of the other deoxidation unit 3 is closed, and no nitrogen protective gas is supplied, disconnecting it from the downstream softening unit 5. The sealing unit 2 at the top of this deoxidation unit 3 is open, and nitrogen protective fluid is supplied. It receives solid waste plastic 1. After receiving sufficient raw materials, the top sealing unit 2 is closed, and no nitrogen protective gas is supplied. Nitrogen gas 17 is supplied to fill the deoxidation unit 3 until the pressure reaches 0.3 MPa, and then the pressure is released to 0.05 MPa. This process is repeated 3 times to complete the plastic deoxidation. During continuous processing, the two deoxidation units are switched between each other, and the deoxidation conditions are the same.

[0107] Deoxidized plastic 4 enters softening device 5, where it is heated to a softened state. Chlorine-containing plastic decomposes and releases acidic gas 18, which enters alkaline washing device 10. During the softening process, the inlet temperature of the first screw is 25°C, the feed rate of the deoxidized plastic is 41.7 g / s, the screw linear speed is 0.1 m / s, the material residence time is 300 s, and the outlet temperature is 150°C.

[0108] The softened plastic 14 enters the liquefaction device 6; the liquefaction conditions include: temperature of 300℃, pressure of 0.05Mpa, time of 0.2h; and stirring rate of 100r / min.

[0109] The gas at the top of the liquefaction unit 6 is introduced into the gas-liquid separation unit 8, and the liquefied gas at the top of the gas-liquid separation unit 8 enters the alkaline washing unit 10. The liquid plastic at the bottom of the liquefaction unit 6 is divided into two parts. One part is the circulating material 15 (the circulating material accounts for 33% by weight of all liquid material from the liquefaction unit 6; the weight ratio of the circulating material to the softened dechlorinated plastic from the softening unit 5 is 0.5:1). After being heated to 350°C by the heating furnace 16, it is sent to the inlet of the liquefaction unit 6 to provide some heat for the liquefaction of the plastic. The other part is the liquid plastic 7, which can be used for subsequent processing.

[0110] Example 2

[0111] This embodiment refers to the system and method of Embodiment 1, but differs from Embodiment 1 in that: the sealing unit 2 is not provided, while the rest of the devices and processes are the same as in Embodiment 1.

[0112] Example 3

[0113] This embodiment uses the same method and system as Embodiment 1, but differs from Embodiment 1 in that:

[0114] The softened plastic 14 enters the liquefaction device 6; the liquefaction conditions include: temperature of 300℃, pressure of 0.05Mpa, time of 0.3h; and stirring rate of 100r / min.

[0115] The gas at the top of the liquefaction unit 6 is introduced into the gas-liquid separation unit 8, and the liquefied gas at the top of the gas-liquid separation unit 8 enters the alkaline washing unit 10. The liquid plastic at the bottom of the liquefaction unit 6 is divided into two parts. One part is the circulating material 15 (the circulating material accounts for 20% by weight of all liquid material from the liquefaction unit 6; the weight ratio of the circulating material to the softened dechlorinated plastic from the softening unit 5 is 0.25:1). After being heated to 350°C by the heating furnace 16, it is sent to the inlet of the liquefaction unit 6 to provide some heat for the liquefaction of the plastic. The other part is the liquid plastic 7, which can be used for subsequent processing.

[0116] Example 4

[0117] This embodiment uses the same method and system as Embodiment 3, but differs from Embodiment 3 in that:

[0118] The softened plastic 14 enters the liquefaction device 6; the liquefaction conditions include: temperature of 300℃, pressure of 0.05Mpa, time of 0.5h; and stirring rate of 100r / min.

[0119] The gas at the top of the liquefaction unit 6 is introduced into the gas-liquid separation unit 8, and the liquefied gas at the top of the gas-liquid separation unit 8 enters the alkaline washing unit 10. The liquid plastic at the bottom of the liquefaction unit 6 is divided into two parts. One part is the circulating material 15 (the circulating material accounts for 5% by weight of all liquid material from the liquefaction unit 6; the weight ratio of the circulating material to the softened dechlorinated plastic from the softening unit 5 is 0.05:1). After being heated to 350°C by the heating furnace 16, it is sent to the inlet of the liquefaction unit 6 to provide some heat for plastic liquefaction. The other part is liquid plastic 7, which can be used for subsequent processing.

[0120] Example 5

[0121] This embodiment uses the same method and system as Embodiment 1, but differs from Embodiment 1 in that:

[0122] The second screw compressor is used as the liquefaction device. The screw of the second screw compressor has a major diameter of 50 mm and a screw length of 4000 mm.

[0123] The liquefaction conditions include: the inlet temperature of the second screw compressor is 150°C, the material residence time is 260s, the outlet temperature of the second screw compressor is 300°C, and the rest of the process is the same as in Example 1.

[0124] Example 6

[0125] This embodiment uses the same method and system as Embodiment 1, but differs from Embodiment 1 in that:

[0126] Solid waste plastic is introduced into the deoxidation device 3 through the solid waste plastic inlet at the top of the deoxidation device 3 via the sealing unit 2; inert gas is continuously introduced into the deoxidation device 3 through the inert gas inlet on the side wall of the deoxidation device 3 for continuous purging to replace the air in the deoxidation device 3; the inert gas rate is 200 L / min; the rest of the process is the same as in Example 1.

[0127] Example 7

[0128] This embodiment refers to the system and method in Embodiment 1, but differs from Embodiment 1 in that: it adopts... Figure 3 The sealing unit shown includes an upstream valve pipe 23, a valve 19, and a downstream valve pipe 24 connected in sequence. The inner diameters of the upstream valve pipe 23 and the downstream valve pipe 24 are the same as the inner diameter of the valve 19. The outlet of the upstream valve pipe 23 is connected to the valve 19, and a protective gas inlet pipe 20 is provided on the side wall of the upstream valve pipe 23 near the outlet. A protective baffle 21 is provided circumferentially on the inner wall near the outlet of the upstream valve pipe 23. The inclination angle between the protective gas inlet pipe 20 and the central axis of the upstream valve pipe 23 is 45°. The width of the protective baffle 21 is 20 mm. The rest of the process is the same as in Example 1.

[0129] Comparative Example 1

[0130] This embodiment refers to the system and method of Embodiment 1, but differs from Embodiment 1 in that: no deoxygenation device is set up, while the rest of the devices and processes are the same as in Embodiment 1.

[0131] Comparative Example 2

[0132] This embodiment refers to the system and method of Embodiment 1, but differs from Embodiment 1 in that the liquid plastic from the liquefaction device 6 is not recirculated, while the rest of the device and process are the same as in Embodiment 1.

[0133] The processing results of the above embodiments and comparative examples are listed in Table 1 below.

[0134] Table 1

[0135]

[0136] In Table 1, the symbol ">" means "more than", and the symbol "~" means "approximately".

[0137] Comparing Example 1 with Comparative Examples 1-2, it can be seen that Comparative Example 1 does not have a deoxygenation device, and Comparative Example 2 does not recycle the liquid plastic. In Example 1, the solid waste plastic liquefaction method provided by this disclosure can obtain a lower CO+CO2 yield and a lower asphaltene content in the liquid plastic.

[0138] Comparing Example 1 and Example 2, it can be seen that Example 2 does not have a sealing unit and the continuous operation cycle is only about 20 hours. This shows that the sealing unit provided by this disclosure can avoid the consequences of solid plastic falling into the valve slide during the valve opening and closing process, which would cause the valve to not seal properly. Thus, long-cycle sealing can be achieved on solid conveying pipelines that need to be opened and closed frequently.

[0139] Comparing Example 1 with Examples 3-4, it can be seen that the process conditions in the liquefaction device in Example 1, within the optimized conditions provided in this disclosure, result in a lower asphaltene content in the liquid plastic 7 prepared in Example 1 compared to Examples 3-4.

[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.

[0141] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0142] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for liquefying solid waste plastics, characterized in that, Includes the following steps: S1. Solid waste plastic is fed into the deoxidation device (3) for deoxidation treatment to obtain deoxidized plastic; S2. The deoxidized plastic is fed into the softening device (5) for softening and dechlorination treatment to obtain chlorine-containing gas and softened dechlorinated plastic; S3. The softened dechlorinated plastic is fed into the liquefaction device (6) for liquefaction treatment to obtain pyrolysis gas and liquid plastic; S4. The chlorine-containing gas mentioned in step S2 and the pyrolysis gas mentioned in step S3 are introduced into the alkaline washing device (10) for alkaline washing treatment; at least a portion of the liquid plastic mentioned in step S3 is heated as a circulating material and then returned to the liquefaction device (6) for further processing; The deoxidation device (3) includes a solid waste plastic inlet and a deoxidized plastic outlet; a sealing unit (2) is provided on the inlet pipeline of the solid waste plastic inlet and the outlet pipeline of the deoxidized plastic outlet respectively. The sealing unit (2) includes the following structure (1) or structure (2): Structure (1): The sealing unit (2) includes a valve upstream pipe (23), a valve (19) and a valve downstream pipe (24) connected in sequence; the inner diameter of the valve upstream pipe (23) is smaller than the inner diameter of the valve (19), and the inner diameter of the valve downstream pipe (24) is the same as the inner diameter of the valve (19); the outlet of the valve upstream pipe (23) is connected to the valve (19), and a protective gas inlet pipe (20) is provided on the side wall of the valve upstream pipe (23) near the outlet. Structure (2): The sealing unit (2) includes a valve upstream pipe (23), a valve (19) and a valve downstream pipe (24) arranged in sequence; the inner diameter of the valve upstream pipe (23) and the inner diameter of the valve downstream pipe (24) are the same as the inner diameter of the valve (19); the outlet of the valve upstream pipe (23) is connected to the valve (19), and a protective gas inlet pipe (20) is provided on the side wall of the valve upstream pipe (23) near the outlet; and a protective baffle (21) is provided circumferentially on the inner wall near the outlet of the valve upstream pipe (23). Step S1 includes either method (1) or method (2): Method (1): The solid waste plastic enters the deoxygenation device (3) through the solid waste plastic inlet at the top of the deoxygenation device (3) via the sealing unit (2); inert gas is continuously introduced into the deoxygenation device (3) through the inert gas inlet on the side wall of the deoxygenation device (3) to continuously purge the air in the deoxygenation device (3) out of the deoxygenation device (3); Method (2): The solid waste plastic enters the deoxidation device (3) through the solid waste plastic inlet at the top of the deoxidation device (3) via the sealing unit (2); inert gas is introduced into the deoxidation device (3) through the inert gas inlet on the side wall of the deoxidation device (3), and then the deoxidation device (3) is depressurized.

2. The method according to claim 1, characterized in that, In the structure (1): The valve upstream pipe (23) includes a constant diameter section and a variable diameter section arranged sequentially from top to bottom. The inner diameter of the constant diameter section is smaller than the inner diameter of the valve (19). The inner diameter of the top of the variable diameter section is the same as the inner diameter of the constant diameter section, and the inner diameter of the bottom of the variable diameter section is the same as the inner diameter of the valve (19). The protective gas inlet pipe (20) is arranged on the side wall of the variable diameter section.

3. The method according to claim 2, characterized in that, In the structure (1): the inclination angle between the central axis of the protective gas inlet pipe (20) and the valve upstream pipe (23) is an acute angle.

4. The method according to claim 3, characterized in that, In the structure (1): the inclination angle between the central axis of the protective gas inlet pipe (20) and the valve upstream pipe (23) is 10~80°.

5. The method according to claim 3, characterized in that, In the structure (1): the ratio of the inner diameter of the equal diameter section of the upstream pipe (23) of the valve to the inner diameter of the valve (19) is 0.5~0.9; the height of the variable diameter section of the upstream pipe (23) of the valve is 10~500mm.

6. The method according to claim 1, characterized in that, In the structure (2): The angle of inclination between the central axis of the protective gas inlet pipe (20) and the valve upstream pipe (23) is an acute angle.

7. The method according to claim 6, characterized in that, In the structure (2): the inclination angle between the central axis of the protective gas inlet pipe (20) and the valve upstream pipe (23) is 10~80°.

8. The method according to claim 1, characterized in that, In the structure (2): the width of the protective baffle (21) is 2~150mm.

9. The method according to claim 1, characterized in that, In the method (1), the rate of the inert gas is 10~2000 L / min.

10. The method according to claim 9, characterized in that, In the method (1), the rate of the inert gas is 50~500 L / min.

11. The method according to claim 1, characterized in that, In the manner (2), the method includes: Inert gas is introduced into the deoxygenation device (3) through the inert gas inlet on the side wall of the deoxygenation device (3) to 0.1~1.0 MPa, and then the deoxygenation device (3) is depressurized to below 0.1 MPa; this is repeated 1~10 times.

12. The method according to claim 11, characterized in that, In the method (2), the method includes: introducing inert gas into the deoxygenation device (3) to 0.3~0.5 MPa through an inert gas inlet on the side wall of the deoxygenation device (3).

13. The method according to claim 11, characterized in that, In the method (2), the number of repetitions is 2 to 5 times.

14. The method according to claim 11, characterized in that, In the method (2), the method further includes: During the process of the solid waste plastic flowing through the sealing unit (2) into the deoxygenation device (3), protective gas is introduced into the sealing unit (2) through the protective gas inlet pipe (20) to purge the solid waste plastic in the sealing unit (2).

15. The method according to claim 14, characterized in that, In the manner (2), the protective gas is selected from one or more of air, inert gas and liquid hydrocarbon.

16. The method according to claim 14, characterized in that, The protective gas is nitrogen.

17. The method according to claim 14, characterized in that, In the method (2), the flow rate of the protective gas is 10~2000L / min.

18. The method according to claim 17, characterized in that, In the method (2), the flow rate of the protective gas is 50~500L / min.

19. The method according to claim 1, characterized in that, In step S2, the softening device (5) is a first screw compressor; the first screw compressor includes a screw inlet, a screw outlet, a first exhaust port and a first heating element.

20. The method according to claim 19, characterized in that, The inlet temperature of the first screw compressor is 0~100℃, the material residence time is 30~1200s, and the outlet temperature of the first screw compressor is 80~300℃.

21. The method according to claim 20, characterized in that, The inlet temperature of the first screw compressor is 20~60℃, the material residence time is 120~300s, and the outlet temperature of the first screw compressor is 120~200℃.

22. The method according to claim 1, characterized in that, In step S2, the chlorine content of the softened dechlorinated plastic is less than 0.1% by weight.

23. The method according to claim 1, characterized in that, In step S3, the liquefaction device (6) is a stirring device, and a second heating element is provided on the outer side of the bottom of the stirring device to heat the material in the stirring device.

24. The method according to claim 23, characterized in that, In step S3, the liquefaction conditions include: a temperature of 150~500℃, a pressure of -0.09~1.0Mpa, and a time of 0.1~1.0h.

25. The method according to claim 24, characterized in that, The liquefaction conditions include: a temperature of 250~400℃, a pressure of 0.05~0.5Mpa, and a time of 0.1~0.2h.

26. The method according to claim 23, characterized in that, The conditions for the liquefaction process include a stirring rate of 10~500 r / min.

27. The method according to claim 26, characterized in that, The conditions for the liquefaction process include a stirring rate of 50~200 r / min.

28. The method according to claim 1, characterized in that, In step S3, the liquefaction device (6) is a second screw compressor, which includes a third heating element for heating the material inside the second screw compressor; The liquefaction conditions include: the inlet temperature of the second screw compressor is 80~300℃, the material residence time is 30~1200s, and the outlet temperature of the second screw compressor is 250~500℃.

29. The method according to claim 28, characterized in that, The inlet temperature of the second screw compressor is 120~200℃, the material residence time is 100~300s, and the outlet temperature of the second screw compressor is 250~400℃.

30. The method according to claim 1, characterized in that, In step S4, the recycled material accounts for 10 to 90% of the total weight of the liquid material from the liquefaction unit (6).

31. The method according to claim 30, characterized in that, The recycled material accounts for 30 to 60% of the total weight of the liquid material from the liquefaction unit (6).

32. The method according to claim 30, characterized in that, The temperature of the recycled material after heating is 300~500℃.

33. The method according to claim 32, characterized in that, The temperature of the recycled material after heating is 350~450℃.

34. The method according to claim 1, characterized in that, In step S4, the weight ratio of the recycled material to the softened dechlorinated plastic from the softening device (5) is 0.1 to 9:

1.

35. The method according to claim 34, characterized in that, In step S4, the weight ratio of the recycled material to the softened dechlorinated plastic from the softening device (5) is 0.5~3:

1.

36. The method according to claim 1, characterized in that, The method also includes: The pyrolysis gas from the liquefaction device (6) is introduced into the gas-liquid separation device (8) for gas-liquid separation to obtain gaseous material and liquid material; The gaseous material is introduced into the alkaline washing device (10) for alkaline washing treatment; the liquid material is introduced into the subsequent liquefied plastic processing device.

37. The method according to claim 36, characterized in that, The alkaline washing agent in the alkaline washing device is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

38. A system for the method of liquefying solid waste plastics as described in claim 1, characterized in that, The system includes: a deoxygenation unit (3), a softening unit (5), a liquefaction unit (6), and an alkaline washing unit (10). The deoxidation device (3) includes a solid waste plastic inlet, an inert gas inlet, and a deoxidized plastic outlet; The softening device (5) includes a deoxidized plastic inlet, a chlorine-containing gas outlet, and a softened dechlorinated plastic outlet. The deoxidized plastic inlet is connected to the deoxidized plastic outlet of the deoxidizing device (3). The liquefaction device (6) includes a softening and dechlorinating plastic inlet, a pyrolysis gas outlet and a liquid plastic outlet. The softening and dechlorinating plastic inlet is connected to the softening and dechlorinating plastic outlet of the softening device (5), and the liquid plastic outlet is connected to the softening and dechlorinating plastic inlet of the liquefaction device (6) via a liquid plastic circulation pipeline. The alkaline washing device (10) includes an inlet for the material to be washed, an inlet for the alkaline washing agent, an outlet for the waste liquid, and an exhaust port; the inlet for the material to be washed is connected to the chlorine gas outlet of the softening device (5) and the pyrolysis gas outlet of the liquefaction device (6), respectively.

39. The system according to claim 38, characterized in that, The system includes multiple of the aforementioned deoxygenation devices (3).

40. The system according to claim 39, characterized in that, The system includes two deoxygenation devices (3) arranged in parallel; each of the deoxygenation devices (3) has a sealing unit (2) installed on the inlet pipeline of the waste plastic inlet and the outlet pipeline of the deoxygenated plastic outlet; wherein the outlet of the valve downstream pipe (24) of the sealing unit (2) located on the inlet pipeline of the waste plastic inlet is connected to the solid waste plastic inlet of the deoxygenation device (3); the inlet of the valve downstream pipe (24) of the sealing unit (2) located on the outlet pipeline of the deoxygenated plastic outlet is connected to the deoxygenated plastic outlet of the deoxygenation device (3), and the outlet of the valve downstream pipe (24) is connected to the deoxygenated plastic inlet of the softening device (5).

41. The system according to claim 40, characterized in that, The deoxygenation device (3) is a vertical tank; the softening device (5) is a first screw compressor; the liquefaction device (6) is a stirred tank or a second screw compressor; and the alkaline washing device (10) is a washing tower.

Images