Waste plastic pyrolysis oil-gas separation and purification system

Abstract

The invention relates to a waste plastic pyrolysis oil-gas separation and purification system which is characterized in that a condensation separation unit adopts a multi-stage condensation and gas-liquid separation mode to condense water vapor in pyrolysis oil gas into liquid water, and the liquid water and the pyrolysis oil are separated from gas; the pyrolysis gas subjected to circulation treatment enters an adsorption purification unit through a pipeline, and separated pyrolysis oil and liquid water are recycled; the adsorption purification unit adopts two specific adsorbents for adsorption water and oil removal, and the two specific adsorbents desorb adsorbed impurities through regenerated gas; a gas inlet of the membrane separation refining unit is connected with a gas outlet of the adsorption purification unit, and a polyimide composite membrane is adopted to screen gas components, so that residual water vapor and pyrolytic oil are finally removed, and the purity of non-condensable gas is ensured. The problems that the pyrolytic oil and the water vapor cannot be efficiently removed at the same time and the high-quality purification requirement is difficult to meet in a traditional condensation and adsorption method are solved, and pure non-condensable gas containing no water vapor and pyrolytic oil is obtained.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic treatment technology and relates to a waste plastic pyrolysis oil-gas separation and purification system. Background Technology

[0002] With the widespread use of plastic products, the amount of plastic waste is increasing daily, putting enormous pressure on the environment. Plastic pyrolysis, as an effective waste treatment and resource recycling method, has received increasing attention. During plastic pyrolysis, pyrolysis gas is one of the important byproducts. Its composition is complex, containing pyrolysis oil, water vapor, and non-condensable gases. The non-condensable gases mainly contain hydrogen, methane, propane, carbon monoxide, and nitrogen.

[0003] The density of pyrolysis oil is approximately 850 kg / m³. 3 The distillation range of pyrolysis oil is 105-550℃. If not removed, it can cause blockages and corrosion in subsequent equipment, affecting stable operation and service life. For example, heavy components in pyrolysis oil may deposit on pipe and equipment surfaces, forming difficult-to-remove scale and reducing heat and mass transfer efficiency. The presence of water vapor not only dilutes the flammable components in non-condensable gases, lowering their calorific value, but may also condense into water at low temperatures, causing pipe corrosion and freezing. In cold winters, if the water vapor content in non-condensable gases is high, pipes are prone to freezing and cracking during transportation, leading to gas leaks and safety hazards.

[0004] Currently, traditional purification methods such as simple condensation and adsorption often cannot simultaneously and efficiently remove pyrolysis oil and water vapor, failing to meet the demand for high-quality purification of non-condensable gases. While condensation can remove some pyrolysis oil and water vapor, it is ineffective at removing tiny droplets and low-boiling-point components; adsorption methods suffer from limited adsorption capacity, easy saturation of adsorbents, and difficulties in regeneration. Therefore, developing an innovative and efficient high-temperature pyrolysis gas purification system and method after plastic pyrolysis to obtain pure non-condensable gas free of water vapor and pyrolysis oil has significant practical implications and application value, playing a crucial role in promoting the resource utilization and environmental protection of plastic waste. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a waste plastic pyrolysis oil and gas separation and purification system. This system solves the problem that traditional methods such as condensation and adsorption in the prior art cannot simultaneously and efficiently remove pyrolysis oil and water vapor, and are difficult to meet the requirements of high-quality purification. The system achieves the goal of obtaining pure non-condensable gas that does not contain water vapor and pyrolysis oil.

[0006] The solution to the technical problem of this invention is: a waste plastic pyrolysis oil and gas separation and purification system, comprising a reactor, a condensation separation unit, an adsorption purification unit, a membrane separation and refining unit and a non-condensable gas storage tank connected in sequence by pipelines, and the whole system is automatically controlled by a central PLC control system. The reactor serves as the source of pyrolysis oil and gas, and its gas outlet is connected to the gas inlet of the condensation and separation unit via a pipeline. The condensation separation unit adopts a multi-stage condensation and gas-liquid separation method to condense water vapor in pyrolysis oil and gas into liquid water, and then separate the liquid water and pyrolysis oil from the gas; the pyrolysis gas after circulation treatment enters the adsorption purification unit through pipeline, and the separated pyrolysis oil and liquid water are recycled. The adsorption purification unit uses two specific adsorbents to adsorb and remove water and oil. Through selective adsorption, it achieves deep removal of residual water vapor and pyrolysis oil in the pyrolysis gas. The two specific adsorbents desorb the adsorbed impurities through regeneration gas, so that the adsorbents can be recycled. The gas inlet of the membrane separation and purification unit is connected to the gas outlet of the adsorption and purification unit. A polyimide composite membrane is used to screen the gas components to achieve the final removal of residual water vapor and pyrolysis oil, ensuring the purity of non-condensable gas. The gas passing through the membrane separation and purification unit enters the non-condensable gas storage tank.

[0007] Furthermore, the condensation separation unit includes a primary condenser, a primary gas-liquid separator, a secondary condenser, a secondary gas-liquid separator, an oil-water separator, a pyrolysis oil collection device, and a condensate collection device; The gas outlet of the first-stage condenser is connected to the gas inlet of the first-stage gas-liquid separator, the gas outlet of the first-stage gas-liquid separator is connected to the gas inlet of the second-stage condenser, the gas outlet of the second-stage condenser is connected to the gas inlet of the second-stage gas-liquid separator, and the gas outlet of the second-stage gas-liquid separator is connected to the gas inlet of the adsorption purification unit. The liquid outlets of the primary condenser, primary gas-liquid separator, secondary condenser, and secondary gas-liquid separator are each connected to a liquid inlet of the oil-water separator. The oil phase outlet of the oil-water separator is connected to the oil phase inlet of the pyrolysis oil collection device, and the water phase outlet of the oil-water separator is connected to the water phase inlet of the condensate collection device.

[0008] Furthermore, the primary and secondary condensers are shell-and-tube condensers; The cooling medium for the primary condenser includes circulating water or heat transfer oil; The cooling medium for the secondary condenser includes aqueous ethylene glycol solution, chilled water, or liquid nitrogen.

[0009] Furthermore, the inlet temperature of the cooling medium in the first-stage condenser is controlled at 80-90℃, and the outlet temperature is controlled at 100-110℃; the inlet temperature of the cooling medium in the second-stage condenser is controlled at 30-40℃, and the outlet temperature is controlled at 50-60℃.

[0010] Furthermore, the primary gas-liquid separator and the secondary gas-liquid separator adopt a gravity-centrifugal composite gas-liquid separator, with spiral guide plates and baffles installed inside.

[0011] Furthermore, the adsorption purification unit includes a composite adsorption tower A, a composite adsorption tower B, and an adsorbent regeneration device; the two composite adsorption towers are designed in parallel, with one composite adsorption tower performing adsorption while the other composite adsorption tower is performing purging and regeneration, alternating between working states. When the composite adsorption tower is purged and regenerated, the temperature and pressure of the regeneration gas are controlled within a set range by the adsorbent regeneration device. Then, the regeneration gas is introduced into the composite adsorption tower. After a predetermined desorption time, the adsorbent is regenerated and ready for use. The regeneration gas includes nitrogen or medium-pressure superheated steam.

[0012] Furthermore, the adsorbents in composite adsorption towers A and B are modified molecular sieves and activated carbon fibers, mixed at a mass ratio of 7:3. The modified molecular sieve is a 13X type molecular sieve modified with silane coupling agent KH-550, with a pore size controlled to 0.5-0.8 nm. The activated carbon fibers have a specific surface area ≥1500 m². 2 / g, mesopore volume ≥0.6cm³ 3 / g; Composite adsorption towers A and B are fixed-bed adsorption towers with three layers of adsorbent beds and porous distribution plates between the beds. The pyrolysis gas enters from the bottom of the composite adsorption tower, with the inlet temperature controlled at 30-40℃, the operating pressure at 0.3-0.5 MPa, and the gas hourly space velocity (GHSV) controlled at 500-800 h⁻¹. -1 The gas flows from bottom to top through the adsorbent bed, and the purified gas is discharged from the top of the tower.

[0013] Furthermore, the regeneration process is divided into two steps: heating and desorption, and cooling. In the first step, regeneration gas at 200-250°C is introduced into the composite adsorption tower. The flow rate of the regeneration gas is 50% of the working gas volume in the adsorption stage, and the desorption time is 2 hours, so that the adsorbed water vapor and pyrolysis oil are desorbed. In the second step, the temperature of the regeneration gas is reduced to 40-50°C, and the adsorbent is cooled for 1 hour. After the adsorbent is regenerated, it is ready for use.

[0014] Furthermore, the separation and purification system is also equipped with a steam buffer tank, the outlet of which is divided into two paths: one path is connected to the steam purging port of the primary condenser and the primary gas-liquid separator for periodic purging to prevent ice blockage; the other path is connected to the regeneration steam inlet of the adsorbent regeneration device for adsorbent regeneration.

[0015] Furthermore, the polyimide composite membrane has a support layer of porous alumina and a separation layer of polyimide film with a thickness of 50-100 nm; the gas permeability of the membrane is as follows: hydrogen permeability coefficient ≥80 Barrer, methane permeability coefficient ≥20 Barrer, water vapor permeability coefficient ≤0.5 Barrer, and pyrolysis oil component permeability coefficient ≤0.1 Barrer. The operating pressure on the feed side of the membrane module is controlled at 0.5-1.0 MPa, the pressure on the permeate side is controlled at 0.1-0.2 MPa, and the operating temperature is controlled at 30-50℃.

[0016] The advantages of this invention compared to the prior art are: (1) Efficient removal of pyrolysis oil and water vapor: Through the synergistic effect of multi-stage condensation separation, adsorption for water and oil removal and membrane separation enhancement technology, this invention can significantly reduce the content of pyrolysis oil and water vapor in pyrolysis gas, obtain pure non-condensable gas, avoid problems such as pipeline blockage and corrosion, and improve the stability of equipment operation.

[0017] (2) Improve the calorific value and utilization value of non-condensable gas: After effectively removing water vapor, the concentration of combustible components (such as hydrogen, methane and propane) in non-condensable gas is significantly increased, and the calorific value is greatly improved, providing high-quality raw materials for subsequent energy conversion or chemical applications and enhancing the economic efficiency of resource recovery.

[0018] (3) Adapting to complex environments and low-temperature conditions: In response to the problem that water vapor is easy to condense in winter in cold regions, which leads to pipeline freezing and cracking, the deep purification technology of this invention can significantly reduce water vapor residue, ensure gas transportation safety, reduce leakage risk, and expand the adaptability of application scenarios.

[0019] (4) Energy saving and adsorbent recycling: The present invention uses modified molecular sieve and activated carbon fiber composite material, combined with heating and depressurization regeneration process, so that the adsorbent can be recycled and the operating cost is reduced; the optimized design of multi-stage condensation and membrane separation further reduces energy consumption and improves overall energy efficiency.

[0020] (5) Promoting the resource utilization and environmental protection of plastic waste: This invention provides an efficient and stable pyrolysis gas purification scheme, which promotes the transformation of plastic waste into high-value energy or chemical raw materials, reduces environmental pollution, and helps the development of the circular economy, with significant social and ecological benefits. Attached Figure Description

[0021] Figure 1This is a schematic diagram of a waste plastic pyrolysis oil-gas separation and purification system according to the present invention. Detailed Implementation

[0022] The core objective of this invention is to solve the key technical problems caused by pyrolysis oil and water vapor carried in pyrolysis gas, such as pipeline blockage, equipment corrosion, and low subsequent utilization efficiency. It provides a waste plastic pyrolysis oil and gas separation and purification system, which creatively adopts a multi-stage synergistic process of "cascade condensation + adsorption + membrane separation" to deeply purify pyrolysis gas and obtain high-quality non-condensable gas products.

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1 like Figure 1 As shown in the figure, the waste plastic pyrolysis oil and gas separation and purification system proposed in this embodiment includes a reactor, a condensation separation unit, an adsorption purification unit, a membrane separation and refining unit and a non-condensable gas storage tank connected in sequence by pipelines. The whole system is automatically controlled by a central PLC control system. The reactor serves as the source of pyrolysis oil and gas, and its gas outlet is connected to the gas inlet of the condensation and separation unit via a pipeline. The condensation separation unit adopts a multi-stage condensation and gas-liquid separation method to condense water vapor in pyrolysis oil and gas into liquid water, and then separate the liquid water and pyrolysis oil from the gas; the pyrolysis gas after circulation treatment enters the adsorption purification unit through pipeline, and the separated pyrolysis oil and liquid water are recycled. The adsorption purification unit uses two specific adsorbents to adsorb and remove water and oil. Through selective adsorption, it achieves deep removal of residual water vapor and pyrolysis oil in the pyrolysis gas. The two specific adsorbents desorb the adsorbed impurities through regeneration gas, so that the adsorbents can be recycled. The gas inlet of the membrane separation and purification unit is connected to the gas outlet of the adsorption and purification unit. A polyimide composite membrane is used to screen the gas components to achieve the final removal of residual water vapor and pyrolysis oil, ensuring the purity of non-condensable gas. The gas passing through the membrane separation and purification unit enters the non-condensable gas storage tank.

[0025] The following provides a detailed description of each component of the separation and purification system: (1) System preheating and inerting: Before introducing pyrolysis gas, the system preheating procedure is initiated. The high-temperature medium pipeline in the entire separation and purification system is slowly heated by an electric heater or by introducing external hot flue gas, so that the inner wall temperature is stabilized above 300℃, ensuring that no moisture or heavy components condense during the initial flow of the pyrolysis gas. At the same time, the separation and purification system is purged and replaced with high-purity nitrogen until the oxygen content in the system is below 1%, forming an inert atmosphere to ensure operational safety.

[0026] Pyrolysis gas generation and introduction: The pyrolysis feedstock undergoes high-temperature pyrolysis in the reactor to generate high-temperature pyrolysis gas (temperature range typically 450-600℃). This high-temperature gas is transported to the condensation and separation unit via insulated pipes.

[0027] (2) The core principle of the condensation separation unit is to utilize the different condensation temperature characteristics of pyrolysis oil and water vapor to achieve preliminary separation of the two through gradient cooling. It is divided into two-stage condensation and two-stage gas-liquid separation units. The equipment parameters and operating conditions of each unit are strictly controlled.

[0028] Specifically, the condensation separation unit consists of a primary condenser, a primary gas-liquid separator, a secondary condenser, a secondary gas-liquid separator, an oil-water separator, a pyrolysis oil collection device, and a condensate collection device.

[0029] The gas outlet of the first-stage condenser is connected to the gas inlet of the first-stage gas-liquid separator, the gas outlet of the first-stage gas-liquid separator is connected to the gas inlet of the second-stage condenser, the gas outlet of the second-stage condenser is connected to the gas inlet of the second-stage gas-liquid separator, and the gas outlet of the second-stage gas-liquid separator is connected to the gas inlet of the adsorption purification unit. The liquid outlets of the primary condenser, primary gas-liquid separator, secondary condenser, and secondary gas-liquid separator are each connected to a liquid inlet of the oil-water separator. The oil phase outlet of the oil-water separator is connected to the oil phase inlet of the pyrolysis oil collection device, and the water phase outlet of the oil-water separator is connected to the water phase inlet of the condensate collection device.

[0030] The pyrolysis oil and gas first enter the primary condenser, where circulating cooling water acts as the refrigerant, engaging in efficient counter-current heat exchange with the pyrolysis oil and gas. Most of the water vapor and high-boiling-point pyrolysis oil components are condensed into liquid at this stage and flow into the oil-water separator. The gaseous mixture then enters the primary gas-liquid separator, where gas-liquid separation is achieved through gravity settling. The separated condensate (mainly water and heavy oil) is periodically discharged to the oil-water separator, while the preliminarily dried and purified gas flows out from the top of the primary gas-liquid separator and enters the secondary deep condensation separator.

[0031] Selection of primary condenser equipment: The primary condenser adopts a shell-and-tube condenser. The shell side is purged with pyrolysis gas, and the tube side is purged with a cooling medium. Circulating water, low-temperature heat transfer oil, or other fluids that can be used as cooling media can be selected.

[0032] Operating parameters: The inlet temperature of the cooling medium is controlled at 80-90℃, and the outlet temperature is controlled at 100-110℃. Through precise adjustment by the temperature control system, the cooling temperature of the pyrolysis gas in the first-stage condenser is stabilized in the range of 100-120℃.

[0033] Separation effect: Within this temperature range, 70% (volume fraction) of water vapor in the pyrolysis gas condenses into liquid water, while heavy components in the pyrolysis oil with boiling points above 110℃ (such as long-chain hydrocarbons with C20 or higher) condense simultaneously, forming a gas-liquid mixture that is discharged.

[0034] The primary gas-liquid separator adopts a gravity-centrifugal composite gas-liquid separator, with internal spiral guide plates and baffles. The separator diameter is determined according to the gas flow rate (diameter ≥ 1.2m when the flow rate is 1000 Nm³ / h), and the effective separation height is ≥ 2.5m.

[0035] Operating principle of gas-liquid separator: The gas-liquid mixture discharged from the first-stage condenser enters the first-stage gas-liquid separator at a speed of 10-15 m / s. Guided by the spiral guide plate, it generates centrifugal rotation. Under the action of centrifugal force, liquid water and heavy pyrolysis oil are thrown towards the wall of the separator and settle down to the bottom of the separator. At the same time, the baffle further blocks the tiny droplets, and secondary separation is achieved by gravity settling.

[0036] Material discharge: The separated liquid water and pyrolysis oil mixture is discharged from the valve at the bottom of the primary gas-liquid separator (the discharge frequency is based on the level gauge display, and discharge is carried out when the liquid level reaches 1 / 3 of the total volume of the primary gas-liquid separator). The gas with the heavy components initially removed is discharged from the top outlet of the primary gas-liquid separator and enters the secondary deep condensation separation.

[0037] The two-stage deep condensation separation is achieved through a two-stage condenser and a two-stage gas-liquid separator.

[0038] The gas discharged from the primary gas-liquid separator enters the secondary condenser, where the cooling medium temperature is further reduced to ensure that remaining water vapor and more types of pyrolysis oil are deeply condensed and precipitated. The separated gaseous products enter the secondary gas-liquid separator for further removal of residual fine droplets. The resulting condensate enters the oil-water separator, and the separated gas enters the adsorption purification unit.

[0039] Operating parameters of the secondary condenser: The inlet temperature of the cooling medium is controlled at 30-40℃ and the outlet temperature is controlled at 50-60℃. The pyrolysis gas cooling temperature is stabilized in the range of 50-70℃ by adjusting the refrigeration unit.

[0040] The secondary condenser is a shell-and-tube condenser. In this embodiment, the cooling medium of the secondary condenser can be an aqueous solution of ethylene glycol (40% by mass, freezing point ≤ -25℃).

[0041] Separation effect: At this temperature, water vapor in the gas further condenses, and at the same time, medium-boiling-point components (such as C12-C19 hydrocarbons) in the pyrolysis oil with boiling points of 70-110℃ condense. After separation by a two-stage gas-liquid separator, the water vapor content in the pyrolysis gas can be reduced to 1-3%, and the pyrolysis oil content can be reduced to 1-2%, completing the initial purification.

[0042] In practice, to enhance the separation effect, the cooling medium of the secondary condenser can also be low-temperature chilled water, liquid nitrogen, or other available cooling media for deeper cooling to strengthen liquid condensation.

[0043] (3) The adsorption purification unit consists of a composite adsorption tower A, a composite adsorption tower B, and an adsorbent regeneration device. The design of the two adsorption towers in parallel is adopted. The two composite adsorption towers alternately enter the working state. That is, when composite adsorption tower A is working, composite adsorption tower B is purging and regenerating. When the regeneration is finished, composite adsorption tower B turns to the working state, and composite adsorption tower A is purging and regenerating. This alternation is to maintain the continuity of operation.

[0044] Composite adsorption tower A and composite adsorption tower B use modified molecular sieves and activated carbon fiber composite adsorbents to achieve deep removal of residual water vapor and pyrolysis oil in pyrolysis gas through selective adsorption.

[0045] Gas enters from the bottom of a composite adsorption tower (e.g., composite adsorption tower A) that is in operation. Two specific adsorbents packed inside the tower play a key role: modified molecular sieves preferentially adsorb trace amounts of water molecules in the gas; and activated carbon fibers efficiently capture residual light pyrolysis oil components.

[0046] After passing through the adsorption layer, the gas is deeply purified. This process is monitored by a PLC system. When the humidity of the outlet gas is detected to be close to the set threshold, the system automatically switches to the backup adsorption tower (composite adsorption tower B) and starts the regeneration program for composite adsorption tower A.

[0047] When the composite adsorption tower is purged and regenerated, the temperature and pressure of the regeneration gas are controlled within a set range by the adsorbent regeneration device. Then, the regeneration gas is introduced into the composite adsorption tower. After a predetermined desorption time, the adsorbent is regenerated and ready for use.

[0048] In this embodiment, the composite adsorbent can be selected as: modified molecular sieve (using 13X type molecular sieve, modified with silane coupling agent KH-550, with pore size controlled to 0.5-0.8 nm) and activated carbon fiber (specific surface area ≥1500 m²). 2 / g, mesopore volume ≥0.6cm³ 3 Mix (g) at a mass ratio of 7:3.

[0049] Adsorption performance: Under normal pressure and at 25℃, the static adsorption capacity for water vapor is ≥25% (mass fraction), the static adsorption capacity for light components (C5-C11 hydrocarbons) in pyrolysis oil is ≥18% (mass fraction), and the adsorption breakthrough time is ≥8h (for a gas flow rate of 1000Nm³). 3 / h time).

[0050] Composite Adsorption Tower Equipment Design: A fixed-bed adsorption tower is adopted, with a single tower diameter of 1.0m and a height of 4.5m. It contains three layers of adsorbent beds, each 1.2m high, with porous distribution plates (5mm pore size, 30% open area) between the beds to ensure uniform gas distribution. Two adsorption towers are installed, one in operation and the other in regeneration, enabling continuous operation. Operating conditions: Pyrolysis gas enters from the bottom of the composite adsorption tower, with an inlet temperature controlled at 30-40℃, an operating pressure of 0.3-0.5MPa, and a gas hourly space velocity (GHSV) controlled at 500-800 h⁻¹. -1 The gas flows from bottom to top through the adsorbent bed. Water vapor molecules and pyrolysis oil molecules are captured by the active sites on the surface of the adsorbent, and the purified gas is discharged from the top of the tower. Regeneration Process: When the adsorbent reaches saturation (judged by a water vapor content ≥0.8% in the top gas), switch to regeneration mode. The regeneration process consists of two steps: heating desorption and cooling. First, introduce regeneration gas (200-250℃, using nitrogen as an example, with a purity ≥99.99%) into the composite adsorption tower. The nitrogen flow rate is 50% of the working gas volume during the adsorption stage, and the desorption time is 2 hours, allowing the adsorbed water vapor and pyrolysis oil to desorb. Second, lower the nitrogen temperature to 40-50℃ and cool the adsorbent for 1 hour, completing the adsorbent regeneration and reserving it for later use. In practice, medium-pressure superheated steam can also be used as the regeneration gas.

[0051] Purification effect: After treatment by the composite adsorption tower, the water vapor content in the pyrolysis gas decreased from 3% (volume fraction) to 0.5% (volume fraction), and the pyrolysis oil content decreased from 2% (volume fraction) to 0.3% (volume fraction), meeting the feed requirements of the subsequent membrane separation and purification unit.

[0052] In this embodiment, a steam buffer tank is also provided to provide purging and regeneration steam for the separation and purification system. The outlet of the steam buffer tank is divided into two paths: one path is connected to the steam purging port of the primary condenser and the primary gas-liquid separator for periodic purging to prevent ice blockage; the other path is connected to the regeneration steam inlet of the adsorbent regeneration device for adsorbent regeneration.

[0053] (4) The adsorbed gas enters the membrane separation and purification unit. This unit uses a polyimide composite membrane with a precise pore size (0.1-1 nm) that is selective for gas components. Polar macromolecules such as water vapor and a small amount of oil and gas are efficiently retained, while target non-condensable gases such as hydrogen, methane, and carbon monoxide can quickly permeate through the membrane wall. Through this final purification step, the residual water vapor and pyrolysis oil are ultimately removed, ensuring the purity of non-condensable gases. The water vapor content of the produced gas can be stably kept below 10 ppm, and the pyrolysis oil content is below 5 ppm, meeting the requirements for high-quality utilization.

[0054] The specific process design is as follows: Membrane material selection: Polyimide composite membrane is selected, with porous alumina (pore size 0.1μm) as the support layer and polyimide film (thickness 50-100nm) as the separation layer. Gas permeation performance of the membrane: hydrogen permeability coefficient ≥80 Barrer, methane permeability coefficient ≥20 Barrer, water vapor permeability coefficient ≤0.5 Barrer, and pyrolysis oil component (C5-C11) permeability coefficient ≤0.1 Barrer. Membrane module structure: Hollow fiber membrane modules are used, with a single module membrane area ≥ 50m². 2 The component housing is made of 316L stainless steel and is equipped with a feed inlet, a permeate gas outlet (non-condensable gas), and a retentate outlet (a mixture of water vapor and pyrolysis oil). The number of components is determined based on the gas volume to be processed (1000 Nm³). 3 When the speed is / h, 8-10 sets of components need to be connected in parallel.

[0055] Key parameters: The operating pressure on the feed side of the membrane module is controlled at 0.5-1.0 MPa, the pressure on the permeate side is controlled at 0.1-0.2 MPa, and the operating temperature is controlled at 30-50℃; the feed gas flow rate is stabilized at the design value through the flow regulating valve to ensure uniform flow velocity on the membrane surface and avoid concentration polarization.

[0056] (5) System optimization and intelligent control: The entire separation and purification system is controlled by a PLC, which can not only achieve sequential control, but also perform dynamic optimization and adjustment. For example, in a cold environment, the set temperature of the first-stage condenser is automatically increased to prevent internal freezing. The system can also optimize the regeneration cycle and regeneration gas consumption according to the saturation level of the adsorption tower, thereby minimizing energy and material consumption while ensuring the purification effect.

[0057] This invention is applicable not only to the pyrolysis gas separation and purification process in the pyrolysis oil production process of waste plastics, but also to the pyrolysis treatment process of organic matter such as municipal solid waste, biomass, waste tires, and medical hazardous waste.

[0058] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0059] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A waste plastic pyrolysis oil-gas separation and purification system, characterized in that, The system includes a reactor, a condensation separation unit, an adsorption purification unit, a membrane separation and purification unit, and a non-condensable gas storage tank, which are connected in sequence by pipelines. The entire system is automatically controlled by a central PLC control system. The reactor serves as the source of pyrolysis oil and gas, and its gas outlet is connected to the gas inlet of the condensation and separation unit via a pipeline. The condensation separation unit adopts a multi-stage condensation and gas-liquid separation method to condense water vapor in pyrolysis oil and gas into liquid water, and then separate the liquid water and pyrolysis oil from the gas; the pyrolysis gas after circulation treatment enters the adsorption purification unit through pipeline, and the separated pyrolysis oil and liquid water are recycled. The adsorption purification unit uses two specific adsorbents to adsorb and remove water and oil. Through selective adsorption, it achieves deep removal of residual water vapor and pyrolysis oil in the pyrolysis gas. The two specific adsorbents desorb the adsorbed impurities through regeneration gas, so that the adsorbents can be recycled. The gas inlet of the membrane separation and purification unit is connected to the gas outlet of the adsorption and purification unit. A polyimide composite membrane is used to screen the gas components to achieve the final removal of residual water vapor and pyrolysis oil, ensuring the purity of non-condensable gas. The gas passing through the membrane separation and purification unit enters the non-condensable gas storage tank.

2. The waste plastic pyrolysis oil-gas separation and purification system according to claim 1, characterized in that, The condensation separation unit includes a primary condenser, a primary gas-liquid separator, a secondary condenser, a secondary gas-liquid separator, an oil-water separator, a pyrolysis oil collection device, and a condensate collection device. The gas outlet of the first-stage condenser is connected to the gas inlet of the first-stage gas-liquid separator, the gas outlet of the first-stage gas-liquid separator is connected to the gas inlet of the second-stage condenser, the gas outlet of the second-stage condenser is connected to the gas inlet of the second-stage gas-liquid separator, and the gas outlet of the second-stage gas-liquid separator is connected to the gas inlet of the adsorption purification unit. The liquid outlets of the primary condenser, primary gas-liquid separator, secondary condenser, and secondary gas-liquid separator are each connected to a liquid inlet of the oil-water separator. The oil phase outlet of the oil-water separator is connected to the oil phase inlet of the pyrolysis oil collection device, and the water phase outlet of the oil-water separator is connected to the water phase inlet of the condensate collection device.

3. The waste plastic pyrolysis oil-gas separation and purification system according to claim 2, characterized in that, The primary and secondary condensers are shell-and-tube condensers. The cooling medium for the primary condenser includes circulating water or heat transfer oil; The cooling medium for the secondary condenser includes aqueous ethylene glycol solution, chilled water, or liquid nitrogen.

4. The waste plastic pyrolysis oil-gas separation and purification system according to claim 2, characterized in that, The inlet temperature of the cooling medium in the first-stage condenser is controlled at 80-90℃, and the outlet temperature is controlled at 100-110℃; the inlet temperature of the cooling medium in the second-stage condenser is controlled at 30-40℃, and the outlet temperature is controlled at 50-60℃.

5. The waste plastic pyrolysis oil-gas separation and purification system according to claim 2, characterized in that, The primary gas-liquid separator and the secondary gas-liquid separator adopt a gravity-centrifugal composite gas-liquid separator, with spiral guide plates and baffles installed inside.

6. The waste plastic pyrolysis oil-gas separation and purification system according to claim 1, characterized in that, The adsorption purification unit includes a composite adsorption tower A, a composite adsorption tower B, and an adsorbent regeneration device; the two composite adsorption towers are designed in parallel, with one composite adsorption tower performing adsorption while the other composite adsorption tower is performing purging and regeneration, alternating between working states. When the composite adsorption tower is purged and regenerated, the temperature and pressure of the regeneration gas are controlled within a set range by the adsorbent regeneration device. Then, the regeneration gas is introduced into the composite adsorption tower. After a predetermined desorption time, the adsorbent is regenerated and ready for use. The regeneration gas includes nitrogen or medium-pressure superheated steam.

7. The waste plastic pyrolysis oil-gas separation and purification system according to claim 6, characterized in that, The adsorbents in composite adsorption towers A and B are modified molecular sieves and activated carbon fibers, mixed at a mass ratio of 7:

3. The modified molecular sieve is a 13X type, modified with silane coupling agent KH-550, with a pore size controlled to 0.5-0.8 nm. The activated carbon fibers have a specific surface area ≥1500 m². 2 / g, mesopore volume ≥0.6cm³ 3 / g; Composite adsorption towers A and B are fixed-bed adsorption towers with three layers of adsorbent beds and porous distribution plates between the beds. The pyrolysis gas enters from the bottom of the composite adsorption tower, with the inlet temperature controlled at 30-40℃, the operating pressure at 0.3-0.5 MPa, and the gas hourly space velocity (GHSV) controlled at 500-800 h⁻¹. -1 The gas flows from bottom to top through the adsorbent bed, and the purified gas is discharged from the top of the tower.

8. The waste plastic pyrolysis oil-gas separation and purification system according to claim 6, characterized in that, The regeneration process consists of two steps: heating and desorption, and cooling. In the first step, regeneration gas at 200-250°C is introduced into the composite adsorption tower. The flow rate of the regeneration gas is 50% of the working gas volume in the adsorption stage, and the desorption time is 2 hours, so that the adsorbed water vapor and pyrolysis oil are desorbed. In the second step, the temperature of the regeneration gas is reduced to 40-50°C, and the adsorbent is cooled for 1 hour. After the adsorbent is regenerated, it is ready for use.

9. The waste plastic pyrolysis oil-gas separation and purification system according to claim 6, characterized in that, The separation and purification system is also equipped with a steam buffer tank. The outlet of the steam buffer tank is divided into two paths: one path is connected to the steam purging port of the primary condenser and the primary gas-liquid separator for periodic purging to prevent ice blockage; the other path is connected to the regeneration steam inlet of the adsorbent regeneration device for adsorbent regeneration.

10. The waste plastic pyrolysis oil-gas separation and purification system according to claim 1, characterized in that, The polyimide composite membrane has a support layer of porous alumina and a separation layer of polyimide film with a thickness of 50-100 nm; the gas permeability of the membrane is as follows: hydrogen permeability coefficient ≥80 Barrer, methane permeability coefficient ≥20 Barrer, water vapor permeability coefficient ≤0.5 Barrer, and pyrolysis oil component permeability coefficient ≤0.1 Barrer. The operating pressure on the feed side of the membrane module is controlled at 0.5-1.0 MPa, the pressure on the permeate side is controlled at 0.1-0.2 MPa, and the operating temperature is controlled at 30-50℃.

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