A nitrogen-protected pyrolysis paint wire paint removal tunnel furnace system and paint removal method

Abstract

This invention discloses a nitrogen-protected pyrolysis tunnel furnace system and method for stripping enameled wire. The system includes a feeding and conveying system, a mesh belt tunnel stripping furnace, an incinerator, a three-stage waste heat recovery system, a nitrogen supply system, and an electrical control system. The mesh belt tunnel stripping furnace in this invention adopts a three-section structure consisting of a preheating section, a pyrolysis section, and a cooling section. It is combined with a three-stage waste heat recovery system consisting of a first-stage high-temperature heat exchanger, a second-stage air preheater, and a third-stage waste heat boiler, achieving high recovery rate, low emissions, low energy consumption, and continuous large-scale operation in the enameled wire stripping process.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and waste gas treatment technology, specifically to a nitrogen-protected pyrolysis tunnel furnace system and method for devarnishing enameled wire. This system and method are suitable for the large-scale recycling and processing of waste enameled wire, waste motor winding wire, and other copper wires containing insulating varnish. Background Technology

[0002] Waste enameled wire is a major copper-containing waste product from scrapped electrical equipment such as motors and transformers. The insulating varnish adhering to its surface is mainly composed of organic polymer materials such as polyesterimide, polyurethane, and epoxy resin, and must be removed before copper recycling. Currently, the main methods for removing enameled wire from domestic and international markets include: (1) Burning method: The enameled wire is directly put into an incinerator and burned at high temperature to remove the enamel film. This method has simple equipment and low investment, but it has obvious drawbacks. The drawbacks are that copper is severely oxidized under high temperature and oxygen conditions, and the copper recovery rate is usually only 90%-95%; the volatile organic compounds (VOCs) generated by the burning of the enamel film are directly emitted, causing air pollution; at the same time, the organic components in the enamel film are completely burned, wasting their potential calorific value.

[0003] (2) Chemical stripping method: The paint film is dissolved by soaking in organic solvents (such as dichloromethane, N-methylpyrrolidone, etc.) or acid / alkali solutions. This method has a high copper recovery rate and the copper is basically not oxidized, but the solvent consumption is large, the waste liquid treatment cost is high, the operating environment is harsh, and it is difficult to carry out large-scale continuous production.

[0004] (3) Mechanical stripping method: The enamel film is removed by mechanical friction, sandblasting, etc. This method has no chemical pollution, but the processing efficiency is low, it has poor adaptability to fine-diameter enameled wires, and the mechanical force may damage the surface of the copper wire.

[0005] (4) Low-temperature pyrolysis method: Enamelled wire is heated in an oxygen-deficient or low-oxygen atmosphere, causing thermal decomposition of the enamel film instead of combustion. The pyrolysis gas is then incinerated. This method can avoid copper oxidation to some extent, but the existing technology has the following shortcomings: (a) It usually adopts intermittent operation, resulting in low processing efficiency; (b) The heat of the high-temperature flue gas generated by pyrolysis is not effectively utilized, resulting in low overall thermal efficiency of the system (usually below 40%); (c) The pyrolysis gas is directly discharged or simply incinerated, resulting in VOCs removal rate not meeting the standards; (d) There is a lack of cascade recovery design for the waste heat of pyrolysis gas and incineration flue gas, leading to high operating costs.

[0006] In summary, existing enameled wire stripping technologies suffer from problems such as low copper recovery rates, environmental pollution, high energy consumption, and difficulty in continuous large-scale operation. Therefore, there is an urgent need to propose an enameled wire stripping system and method that combines high copper recovery rates, environmental compliance, low energy consumption, and continuous operation to solve the aforementioned technical problems. Summary of the Invention

[0007] The purpose of this invention is to provide a nitrogen-protected pyrolysis tunnel furnace system and method for stripping enameled wire, which solves the problems of low copper recovery rate, environmental pollution, high energy consumption, and difficulty in continuous large-scale operation of existing enameled wire stripping technologies.

[0008] To solve the above-mentioned technical problems, the present invention provides a first solution: a nitrogen-protected pyrolysis tunnel furnace system for stripping enameled wire, specifically comprising the following structure: The feeding and conveying system (1) includes a vibrating feeder, a metering device and a material distributor, used to evenly distribute the enameled wire onto the mesh belt; The mesh belt tunnel paint stripping furnace (2) is divided into a preheating section, a pyrolysis section and a cooling section along the material travel direction. High-purity nitrogen is introduced into the furnace to maintain an inert atmosphere, and the furnace wall is equipped with a combustion flue gas heating jacket to receive the enameled wire conveyed by the feeding conveying system (1) and perform paint stripping. The incinerator (3) is connected to the mesh belt tunnel paint stripper (2) and is used to completely oxidize the pyrolysis gas generated by the mesh belt tunnel paint stripper (2) at 800-900°C to obtain incineration flue gas. The three-stage waste heat recovery system (4) includes a first-stage high-temperature heat exchanger, a second-stage air preheater and a third-stage waste heat boiler connected sequentially along the direction of the incineration flue gas flow. The first-stage high-temperature heat exchanger is used to heat the circulating heat medium in the furnace wall jacket of the mesh belt tunnel paint stripping furnace (2). The second-stage air preheater is used to preheat the combustion air from the first-stage high-temperature heat exchanger. The third-stage waste heat boiler is used to receive the air preheated by the second-stage air preheater and produce hot water. A nitrogen supply system (5) is connected to a mesh belt tunnel paint stripping furnace (2) and is used to supply inert gas to the furnace chamber of the mesh belt tunnel paint stripping furnace (2); The electrical control system (6) is electrically connected to the feeding and conveying system (1), the mesh belt tunnel devarnishing furnace (2), the incinerator (3), the three-stage waste heat recovery system (4), and the nitrogen supply system (5), respectively, and is used to control the automatic operation and safety interlock of the nitrogen-protected pyrolysis enameled wire devarnishing tunnel furnace system.

[0009] In one embodiment, the mesh belt tunnel paint stripping furnace (2) is a horizontal continuous conveying structure with a furnace length of 10-15 m, a furnace width of 1.5-2.0 m, a material layer thickness of 60-100 mm, a mesh belt running speed of 0.10-0.20 m / min, and a material residence time in the furnace of 80-90 min. The oxygen content in the mesh belt tunnel paint stripping furnace (2) is controlled below 100 ppm, and the furnace is maintained at a slight positive pressure of 50-150 Pa. The furnace wall of the mesh belt tunnel paint stripping furnace (2) is provided with a combustion flue gas heating jacket and a circulating heat medium filled inside it. The circulating heat medium is preferably high-temperature heat transfer oil or molten salt, which supplies heat to the furnace through the heat exchange between the walls.

[0010] In one embodiment, the incinerator (3) is a two-chamber regenerative thermal oxidizer (RTO) or a direct-fired oxidizer (TO), with an incineration temperature of 800-900°C and a VOCs removal rate of ≥99%. The gas volume of the incinerator (3) is accurately calculated based on the element balance method. The total gas volume entering the incinerator includes the volume of pyrolysis gas and the volume of carrier nitrogen. The gas volume designed for the incinerator is preferably 1.5-2.5 times the total gas volume.

[0011] In one embodiment, in the three-stage waste heat recovery system (4): the first-stage high-temperature heat exchanger reduces the temperature of the combustion flue gas from 800-900°C to 400-500°C, and raises the temperature of the circulating heat medium to 300-380°C; the second-stage air preheater reduces the temperature of the flue gas from 400-500°C to 180-250°C, and preheats the combustion air to 200-350°C; the third-stage waste heat boiler reduces the temperature of the flue gas from 180-250°C to 100-150°C, and produces hot water at 60-80°C.

[0012] In one embodiment, the nitrogen supply system (5) adopts a PSA pressure swing adsorption nitrogen generator to produce nitrogen with a purity of ≥99.99%, and at the same time provides protective gas and cooling section sealing gas to the furnace of the mesh belt tunnel paint stripping furnace (2); the preheating section and cooling section of the mesh belt tunnel paint stripping furnace (2) are respectively equipped with nitrogen sealing gas curtains to prevent outside air from entering the furnace.

[0013] In one embodiment, the electrical control system (6) uses a PLC programmable controller to realize the automatic operation of the entire system, online monitoring of oxygen content, alarm of combustible gas concentration and emergency shutdown interlock.

[0014] In one embodiment, the nitrogen-protected pyrolysis enameled wire stripping tunnel furnace system also includes an online oxygen analyzer and a combustible gas detector, which are used to monitor the oxygen content and combustible gas concentration inside the mesh belt tunnel stripping furnace (2), respectively. When the oxygen content inside the mesh belt tunnel stripping furnace (2) exceeds a preset threshold, the nitrogen supply system (5) is controlled to increase the nitrogen supply or to shut down the furnace in an emergency. When the combustible gas concentration inside the mesh belt tunnel stripping furnace (2) exceeds a preset threshold, the heat source is cut off and the nitrogen supply system (5) is controlled to increase the nitrogen purging volume.

[0015] To solve the above-mentioned technical problems, the present invention provides a second solution: a method for stripping enameled wire using nitrogen-protected pyrolysis, which includes the following steps: S1. Feeding: Configure any of the nitrogen-protected pyrolysis enameled wire devarnishing tunnel furnace systems in the first solution mentioned above. The waste enameled wire is fed and metered by a feeding and conveying system, and then evenly laid on the mesh belt at the feed end of the mesh belt tunnel devarnishing furnace by a material distributor. S2. Nitrogen replacement: Nitrogen gas with a purity of 99.99% or higher is introduced into the mesh belt tunnel paint stripping furnace using a nitrogen supply system to reduce the oxygen content in the furnace to below 100 ppm. S3. Segmented heating and pyrolysis: The mesh belt carries the waste enameled wire through the preheating section and pyrolysis section of the mesh belt tunnel devarnishing furnace in sequence. The temperature of the pyrolysis section is 400-600°C until the organic matter in the varnish film is thermally decomposed into pyrolysis gas containing hydrocarbons, H2, and CO and copper wire in an inert atmosphere. S4. Cooling and Discharging: The pyrolyzed copper wire is conveyed to the cooling section of the mesh belt tunnel paint stripping furnace, and discharged after cooling under nitrogen protection. S5. Pyrolysis gas incineration: The pyrolysis gas after pyrolysis is introduced into the incinerator and oxidized into incineration flue gas containing CO2 and H2O at 800-900°C. S6. Three-stage waste heat recovery: The first-stage high-temperature heat exchanger, the second-stage air preheater, and the third-stage waste heat boiler in the three-stage waste heat recovery system are used to recover the heat of the incineration flue gas in sequence. S7. Purified Emissions: The flue gas after the three-stage waste heat recovery is discharged in compliance with standards.

[0016] In one embodiment, in step S1, the thickness of the waste enameled wire layer is 60-100 mm, the mesh belt running speed is 0.10-0.20 m / min, and the processing capacity is 800-1200 kg / h; In one embodiment, in step S2, the nitrogen consumption is 30-40 Nm³. 3 / h, the furnace is maintained at a slight positive pressure of 50-150Pa; In one embodiment, in step S3, the residence time of the material in the pyrolysis section is 60-80 min, the temperature of the pyrolysis section is controlled at 400-600°C, and the oxygen content in the furnace is <100ppm.

[0017] In one embodiment, in step S4, the pyrolyzed copper wire enters the cooling section, is cooled to below 200°C under nitrogen protection by water cooling, and is then discharged to obtain clean, uncoated copper wire.

[0018] In one embodiment, in step S5, the pyrolysis gas generated in step S3 is introduced into an incinerator and preferably completely oxidized at 850°C, with a VOCs removal rate of ≥99%.

[0019] In one embodiment, the three-stage waste heat recovery in step S6 specifically includes: (a) First stage: The heat from the incineration flue gas is transferred to the circulating heat medium in the furnace wall jacket of the mesh belt tunnel paint stripping furnace through the first stage high-temperature heat exchanger, and heats the pyrolysis section of the mesh belt tunnel paint stripping furnace. After the waste heat is recovered by the first stage high-temperature heat exchanger, the temperature of the incineration flue gas drops to 400-500°C.

[0020] (b) Second stage: The heat of the incineration flue gas after heat exchange in the first stage high-temperature heat exchanger is transferred to the combustion air for use in the incinerator through the second stage air preheater. After the waste heat is recovered by the second stage air preheater, the temperature of the incineration flue gas drops to 180-250°C, and the combustion air is preheated from room temperature to 200-350°C.

[0021] (c) Third stage: The flue gas from the second stage air preheater is passed through the third stage waste heat boiler to produce hot water at 60-80°C. The flue gas temperature is reduced to 100-150°C after the waste heat is recovered by the third stage waste heat boiler.

[0022] In one embodiment, in step S7, the flue gas (<150°C) after three-stage waste heat recovery is discharged through a chimney in compliance with emission standards, with a VOCs emission concentration of <20mg / m³. 3 .

[0023] In one embodiment, the nitrogen-protected pyrolysis method for stripping enameled wire further includes: online monitoring of the oxygen content and combustible gas concentration inside the mesh belt tunnel stripping furnace; issuing an alarm signal when the oxygen content > 500 ppm and triggering an emergency shutdown interlock when the oxygen content > 1000 ppm; issuing an alarm signal when the combustible gas concentration > 25% LEL and triggering an emergency shutdown interlock when the combustible gas concentration > 50% LEL.

[0024] The advantages of this invention, which differ from the prior art, are as follows: 1) High copper recovery rate and excellent product quality. This invention adopts a nitrogen-protected pyrolysis process. By controlling the oxygen content in the furnace to below 100 ppm, the copper basically does not undergo oxidation reaction during the entire pyrolysis process, effectively avoiding the oxidation loss of copper under high temperature conditions. The copper recovery rate can reach more than 99%, which is significantly higher than the 90% to 95% of the traditional fire method. Moreover, the recovered copper has higher purity and requires less refining load in the subsequent process.

[0025] 2) Excellent exhaust gas emission standards and outstanding environmental friendliness. This invention introduces the pyrolysis gas generated from pyrolysis into an RTO / TO incinerator, achieving complete oxidation and decomposition at a high temperature of 850℃. The removal rate of volatile organic compounds (VOCs) is not less than 99%, and the exhaust gas emission concentration is less than 20 mg / m³. 3 All indicators are better than the limits specified in the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996) and the "Pollution Control Standard for Hazardous Waste Incineration" (GB 18484-2020), fundamentally solving the secondary pollution problem of traditional incineration and chemical stripping methods.

[0026] 3) Scalable energy utilization and significantly improved system thermal efficiency. This invention achieves efficient utilization of thermal energy through a three-stage waste heat recovery design—the first stage recovers sensible heat from flue gas using the furnace wall jacket for heating, the second stage preheats combustion air, and the third stage produces hot water—resulting in a progressively efficient utilization of thermal energy. The overall system thermal efficiency can reach over 58%, far exceeding the typically lower than 40% level of traditional pyrolysis systems. Specifically, the calorific value of the pyrolysis gas is approximately 18 MJ / kg. After waste heat recovery, the released heat can completely cover the 115.6 kW process heat demand of the pyrolysis furnace, achieving a self-heating balance rate of 173%. The auxiliary natural gas consumption is as low as 15 Nm³ / h, realizing near-self-sufficiency in system operation.

[0027] 4) Excellent operational economy and short investment payback period. Based on a processing scale of 1000 kg / h, the cost per ton of processing of this invention is about RMB 213, which is only 1 / 3 to 1 / 5 of that of the traditional chemical stripping method; the total investment of the equipment is about RMB 2.24 million, and the investment payback period is only about 4.7 months, which has outstanding economic benefits and market promotion value.

[0028] 5) Continuous process, suitable for large-scale industrial applications. This invention adopts a mesh belt tunnel furnace with continuous conveying structure, allowing for continuous material input and output and stable and controllable process parameters. It can achieve 24-hour uninterrupted continuous production with an annual processing capacity of up to 7,200 tons (based on 300 days of operation per year). This completely overcomes the shortcomings of traditional intermittent processing processes, such as low capacity and high labor intensity, and fully meets the needs of industrial-scale processing.

[0029] 6) Byproducts are available, and overall energy consumption is further reduced. The three-stage waste heat recovery system of this invention can produce approximately 2.57 t / h of 80°C hot water as a byproduct. The hot water produced can be used for district heating, domestic hot water supply, or other process heat applications, realizing the external transmission of energy from the treatment process and further reducing the overall energy consumption of the system.

[0030] 7) Significant energy conservation and emission reduction effects, with both environmental and social benefits. Relying on a substantial improvement in the overall energy efficiency of the system, this invention has significant carbon dioxide emission reduction benefits. Based on a processing scale of 1000 kg / h, it can reduce CO2 emissions by approximately 350 tons annually, achieving good economic, environmental, and social benefits. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of one embodiment of the nitrogen-protected pyrolysis method for stripping enameled wire tunnel furnace system in this invention; Figure 2 This is a process flow diagram of one embodiment of the nitrogen-protected pyrolysis method for removing enameled wire in this invention; In the diagram: 1-Feeding and conveying system, 2-Mesh belt tunnel paint stripping furnace, 201-Preheating section, 202-Pyrolysis section, 203-Cooling section, 3-Incinerator, 4-Three-stage waste heat recovery system, 401-First-stage high-temperature heat exchanger, 402-Second-stage air preheater, 403-Third-stage waste heat boiler, 5-Nitrogen supply system, 6-Electrical control system. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0034] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] Example 1 I. System Configuration Please see Figure 1 The specific structure of the nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system in this embodiment includes: Material feeding and conveying system 1 consists of a vibrating feeder, an electronic belt scale, and a vibrating material spreader. Waste enameled wire is unbundled and dispersed by the vibrating feeder, weighed in real-time by the electronic belt scale, and then evenly spread onto the mesh belt by the vibrating material spreader. In this embodiment, the thickness of the waste enameled wire spreader is 80 mm, and the width is 1.6 m.

[0036] Mesh Belt Tunnel Paint Stripping Furnace 2: The furnace body is a horizontal rectangular structure, 12 m in length and 1.8 m in width within the furnace chamber. The furnace body is divided along the material travel direction into a preheating section 201 (0-3 m, 20→400°C), a pyrolysis section 202 (3-10 m, 400-600°C), and a cooling section 203 (10-12 m, 600→200°C). The furnace wall has a double-layer jacket structure, with high-temperature heat transfer oil heated by the first-stage high-temperature heat exchanger flowing through the jacket to supply heat to the furnace chamber via heat exchange between the jackets. The furnace body insulation layer is 200 mm thick, and the outer wall temperature is ≤60°C. The mesh belt is a heat-resistant stainless steel wire woven mesh belt with an effective width of 1.6 m and a running speed of 0.145 m / min. The total residence time of the material in the furnace is approximately 83 min. Nitrogen sealing curtains are installed at the front and rear ends of the furnace chamber to maintain a slight positive pressure inside the furnace.

[0037] Incinerator 3: Employs a two-chamber regenerative thermal oxidizer (RTO), designed to process 200 Nm³ / h of gas (49.5 Nm³ of pyrolysis gas). 3 / h+Carrier gas nitrogen 35 Nm 3 / h, approximately 2.4 times the margin). The combustion temperature is 850°C, with ceramic packing for the heat storage medium and a heat recovery efficiency of 90%. The auxiliary natural gas burner has a power of approximately 150kW (corresponding to a natural gas consumption of 15Nm³ / h) and is used for start-up heating and stabilizing the combustion temperature.

[0038] The three-stage waste heat recovery system 4 includes, in sequence according to the flow direction of the incineration flue gas: the first-stage high-temperature heat exchanger 401 (flue gas side: 850→450°C, heat transfer oil side: 250→350°C), used to heat the circulating heat transfer oil in the furnace wall jacket; the second-stage air preheater 402 (flue gas side: 450→200°C, air side: 20→300°C), used to preheat the combustion air; and the third-stage waste heat boiler 403 (flue gas side: 200→120°C, water side: 60→80°C), which produces 80°C hot water.

[0039] Nitrogen supply system 5: PSA pressure swing adsorption nitrogen generator, nitrogen production 40 Nm³ 3 / h, purity 99.99%, outlet pressure 0.6MPa. Nitrogen gas is supplied to the furnace protective gas (30 Nm³ / h) via a distributor. 3 / h) and cooling section sealing gas (5 Nm 3 / h).

[0040] Electrical Control System 6: Employs a Siemens S7-1200 series PLC, equipped with an online oxygen analyzer (measurement range 0-1000 ppm), combustible gas detector, temperature sensor (K-type thermocouple), and pressure transmitter. This electrical control system 6 can realize closed-loop regulation of conveyor belt speed, PID control of furnace temperature, oxygen content alarm interlock (>500 ppm alarm, >1000 ppm emergency shutdown), and combustible gas concentration alarm interlock (>25% LEL alarm, >50% LEL emergency shutdown).

[0041] II. Process Operation Based on the above system structure configuration, the specific process operation steps are described in detail, and the process flow is as follows: Figure 2 As shown.

[0042] Taking waste enameled wire with a processing capacity of 1000 kg / h and an organic content of 5% as an example, the specific process parameters and operating steps are as follows: Step S1 (Feeding): Waste enameled wire is fed into the vibrating feeder hopper via a forklift. The vibrating feeder frequency is 30 Hz and the feed rate is 1000±20 kg / h. The electronic belt scale measures and provides feedback to adjust the feeding frequency in real time. The vibrating spreader has an amplitude of 5mm to spread the material evenly into an 80mm thick layer.

[0043] Step S2 (Nitrogen Replacement): Start the PSA nitrogen generator, initially at 60 Nm 3 The furnace was purged with nitrogen at a high flow rate of 35 Nm³ / h. After about 15 minutes, the oxygen content in the furnace dropped to <100 ppm, and then the flow rate was switched back to normal operation. 3 / h. The furnace pressure is maintained at a slightly positive pressure of 50-100Pa.

[0044] Step S3 (Segmented Heating and Pyrolysis): The conveyor belt runs at a speed of 0.145 m / min, and the material passes through the following stages sequentially: Preheating Section 201: Using hot nitrogen gas flowing counter-currently from the pyrolysis section, the material is gradually heated from 20°C to approximately 400°C. This stage mainly removes adsorbed moisture from the material surface; Pyrolysis Section 202: The material remains in the 400-600°C range for approximately 70 minutes, during which the organic matter in the paint film (polyesterimide / epoxy resin) undergoes a thermal decomposition reaction, generating pyrolysis gas mainly composed of CH4 (22.6%), H2 (45.3%), C2-C3 hydrocarbons (11.3%), CO (6.5%), and CO2 (3.1%), as well as a small amount of tar and carbon residue. The total volume of the pyrolysis gas is approximately 49.5 Nm³. 3 / h (standard state, including water vapor). The temperature of the heat transfer oil in the furnace wall jacket is controlled at 350±10°C, and approximately 115.6 kW of heat is transferred to the furnace through the partition wall.

[0045] Step S4 (Cooling and Discharge): The pyrolyzed copper wire (approximately 550°C) enters the cooling section 203, which is equipped with a water-cooling jacket. Under nitrogen protection, the temperature of the copper wire is reduced to approximately 200°C. The copper wire is discharged through the discharge sealing roller, resulting in a stripped copper wire with a purplish-red metallic luster and a copper recovery rate of ≥99%.

[0046] Step S5 (pyrolysis gas incineration): Pyrolysis gas (49.5 Nm³) 3 / h) and carrier nitrogen (approximately 35 Nm 3 The mixture ( / h) is then fed into the RTO incinerator. During the incinerator start-up phase, an auxiliary natural gas burner (15 Nm³) is used. 3 The temperature is raised to 850°C per hour. After normal operation, the calorific value of the pyrolysis gas itself (approximately 200 kW) can maintain the combustion temperature, and the auxiliary natural gas is only used for temperature fluctuation compensation. The alternating switching cycle of the two chambers of the incinerator is 60-120 s, the heat recovery efficiency of the regenerator is 90%, and the flue gas temperature is approximately 200°C. The residence time of VOCs at 850°C is >1.0 s, and the removal rate is ≥99%.

[0047] Step S6 (Three-stage waste heat recovery): (a) First stage: High-temperature flue gas at 850°C discharged from the incinerator (approximately 250 Nm³) 3(a) The flue gas (including auxiliary combustion products) enters the first-stage high-temperature heat exchanger and undergoes indirect heat exchange with the circulating heat transfer oil. The flue gas temperature drops to about 450°C, the heat transfer oil temperature rises to about 350°C, and about 115.6 kW of heat is recovered for heating the pyrolysis furnace; (b) The second stage: The 450°C medium-temperature flue gas enters the shell-and-tube second-stage air preheater, which preheats the combustion air from 20°C to about 300°C. The flue gas temperature drops to about 200°C, and about 35 kW of heat is recovered. It can also reduce the consumption of auxiliary natural gas by about 10%; (c) The third stage: The 200°C low-temperature flue gas enters the flue gas-water heat exchanger (i.e., the third-stage waste heat boiler), which produces about 2.5 t / h of 80°C hot water, recovers about 60 kW of heat, and the flue gas temperature drops to about 120°C.

[0048] Step S7 (Purification and Emission): The flue gas temperature, after three stages of waste heat recovery, is approximately 120°C and is discharged into the chimney via an induced draft fan. The VOCs concentration in the emitted flue gas is <20 mg / m³. 3 Particulate matter <30 mg / m³ 3 SO2 < 50 mg / m³ 3 NO x <200 mg / m 3 It meets the emission limits required by GB 16297-1996 and GB 18484-2020.

[0049] III. Operational Performance Test Based on the aforementioned system configuration and process operation steps, the main technical indicators of this embodiment were tested under continuous operation conditions. Environmental performance requirements were based on the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996) and the "Standard for Pollution Control of Hazardous Waste Incineration" (GB 18484-2020). Specific test results are shown in Table 1. Utilizing a three-stage cascade recovery system—the first stage heats the furnace wall jacket for the pyrolysis section (115.6kW), the second stage preheats the combustion air to 300°C (35kW), and the third stage produces 80°C hot water (60kW)—this embodiment achieves a comprehensive thermal efficiency of 58.1% and a self-heating balance rate of 173%, significantly higher than the typically lower than 40% level of traditional pyrolysis systems. Simultaneously, this invention employs a nitrogen-protected pyrolysis process, controlling the oxygen content in the furnace to below 100 ppm, ensuring that copper undergoes virtually no oxidation reaction throughout the pyrolysis process, achieving a copper recovery rate of over 99%, significantly higher than the 90%–95% of traditional combustion methods. With a processing capacity of 1000 kg / h, the annual processing capacity is 7200 tons, and the cost per ton is only 213 yuan, which is only 1 / 3 to 1 / 5 of that of the traditional chemical stripping method, with an investment payback period of 4.7 months. This proves that the system and method provided by this invention achieve high recovery rate, low emissions, low energy consumption, and continuous large-scale operation in the stripping treatment of enameled wire.

[0050] Table 1 The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A nitrogen-protected pyrolysis tunnel furnace system for stripping enameled wire, characterized in that, Includes the following structure: The feeding and conveying system (1) is used to evenly distribute the enameled wire onto the mesh belt; The mesh belt tunnel devarnishing furnace (2) is divided into a preheating section, a pyrolysis section and a cooling section along the material travel direction. High-purity nitrogen is introduced into the furnace to maintain an inert atmosphere, and the furnace wall is equipped with a combustion flue gas heating jacket for receiving the enameled wire conveyed by the feeding and conveying system (1) and performing devarnishing. An incinerator (3) is connected to the mesh belt tunnel paint stripping furnace (2) and is used to completely oxidize the pyrolysis gas generated by the mesh belt tunnel paint stripping furnace (2) at 800-900°C to obtain incineration flue gas. The three-stage waste heat recovery system (4) includes a first-stage high-temperature heat exchanger, a second-stage air preheater, and a third-stage waste heat boiler connected sequentially along the direction of the incineration flue gas flow. The first-stage high-temperature heat exchanger is used to heat the circulating heat medium in the furnace wall jacket of the mesh belt tunnel paint stripping furnace (2). The second-stage air preheater is used to preheat the combustion air from the first-stage high-temperature heat exchanger. The third-stage waste heat boiler is used to receive the air preheated by the second-stage air preheater and produce hot water. A nitrogen supply system (5) is connected to the mesh belt tunnel paint stripping furnace (2) and is used to supply inert gas to the furnace chamber of the mesh belt tunnel paint stripping furnace (2); The electrical control system (6) is electrically connected to the feeding and conveying system (1), the mesh belt tunnel devarnishing furnace (2), the incinerator (3), the three-stage waste heat recovery system (4), and the nitrogen supply system (5), respectively, and is used to control the automatic operation and safety interlock of the nitrogen-protected pyrolysis enameled wire devarnishing tunnel furnace system.

2. The nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system according to claim 1, characterized in that, The mesh belt tunnel paint stripping furnace (2) is a horizontal continuous conveying structure with a furnace length of 10-15 m, a furnace chamber width of 1.5-2.0 m, a material layer thickness of 60-100 mm, a mesh belt running speed of 0.10-0.20 m / min, and a material residence time in the furnace of 80-90 min. The oxygen content inside the mesh belt tunnel paint stripping furnace (2) is controlled below 100 ppm, and the furnace chamber is maintained at a slight positive pressure of 50-150 Pa. The furnace wall of the mesh belt tunnel paint stripping furnace (2) is provided with a combustion flue gas heating jacket and a circulating heat medium filled inside it. The circulating heat medium is high-temperature heat transfer oil or molten salt.

3. The nitrogen-protected pyrolysis tunnel furnace system for stripping enameled wire according to claim 1, characterized in that, The incinerator (3) is a two-chamber regenerative oxidizer or a direct-fired oxidizer with an incineration temperature of 800-900°C and a VOCs removal rate of ≥99%. The gas volume processed by the incinerator (3) is 1.5-2.5 times the total gas volume entering the incinerator (3).

4. The nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system according to claim 1, characterized in that, In the three-stage waste heat recovery system (4): The first-stage high-temperature heat exchanger reduces the temperature of the combustion flue gas from 800-900°C to 400-500°C, while raising the temperature of the circulating heat medium to 300-380°C. The second-stage air preheater reduces the flue gas temperature from 400-500°C to 180-250°C and preheats the combustion air to 200-350°C. The third-stage waste heat boiler reduces the flue gas temperature from 180-250°C to 100-150°C, producing hot water at 60-80°C.

5. The nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system according to claim 1, characterized in that, The nitrogen supply system (5) adopts a PSA pressure swing adsorption nitrogen generator unit, and simultaneously provides protective gas and sealing gas for the cooling section to the furnace of the mesh belt tunnel paint stripping furnace (2); The preheating section and cooling section of the mesh belt tunnel paint stripping furnace (2) are respectively equipped with nitrogen sealing curtains to prevent outside air from entering the furnace.

6. The nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system according to claim 1, characterized in that, The nitrogen-protected pyrolysis method enameled wire stripping tunnel furnace system also includes an online oxygen analyzer and a combustible gas detector, which are used to monitor the oxygen content and combustible gas concentration inside the mesh belt tunnel stripping furnace (2), respectively. When the oxygen content inside the mesh belt tunnel paint stripping furnace (2) exceeds the preset threshold, the nitrogen supply system (5) is controlled to increase the nitrogen supply or shut down the furnace in an emergency. When the concentration of combustible gas inside the mesh belt tunnel paint stripping furnace (2) exceeds a preset threshold, the heat source is cut off and the nitrogen supply system (5) is controlled to increase the nitrogen purging volume.

7. A method for stripping enameled wire using nitrogen-protected pyrolysis, characterized in that, Includes the following steps: S1. Feeding: Configure the nitrogen-protected pyrolysis enameled wire devarnishing tunnel furnace system as described in any of claims 1 to 6. The waste enameled wire is fed and metered by the feeding and conveying system and then evenly laid on the mesh belt at the feed end of the mesh belt tunnel devarnishing furnace. S2. Nitrogen replacement: Nitrogen gas with a purity of 99.99% or higher is introduced into the mesh belt tunnel paint stripping furnace using the nitrogen supply system to reduce the oxygen content in the furnace to below 100 ppm. S3. Segmented heating and pyrolysis: The mesh belt carries the waste enameled wire through the preheating section and the pyrolysis section of the mesh belt tunnel deenamelting furnace in sequence. The temperature of the pyrolysis section is 400-600°C until the organic matter in the enamel film is thermally decomposed into pyrolysis gas and copper wire in an inert atmosphere. S4. Cooling and Discharging: The pyrolyzed copper wire is conveyed to the cooling section of the mesh belt tunnel paint stripping furnace and discharged after cooling under nitrogen protection. S5. Pyrolysis gas incineration: The pyrolysis gas after pyrolysis is introduced into the incinerator and oxidized into incineration flue gas containing CO2 and H2O at 800-900°C. S6. Three-stage waste heat recovery: The heat of the incineration flue gas is recovered in sequence by the first-stage high-temperature heat exchanger, the second-stage air preheater, and the third-stage waste heat boiler in the three-stage waste heat recovery system. S7. Purified Emissions: The flue gas after the three-stage waste heat recovery is discharged in compliance with standards.

8. The method for stripping enameled wire using nitrogen-protected pyrolysis according to claim 7, characterized in that, In step S1, the thickness of the waste enameled wire layer is 60-100 mm, the mesh belt running speed is 0.10-0.20 m / min, and the processing capacity is 800-1200 kg / h. In step S2, the nitrogen consumption is 30-40 Nm. 3 / h, the furnace is maintained at a slight positive pressure of 50-150Pa; In step S3, the residence time of the material in the pyrolysis section is 60-80 minutes, the temperature of the pyrolysis section is controlled at 400-600°C, and the oxygen content in the furnace is <100ppm.

9. The method for stripping enameled wire using nitrogen-protected pyrolysis according to claim 7, characterized in that, In step S6, the heat from the incineration flue gas is transferred to the circulating heat medium in the furnace wall jacket of the mesh belt tunnel paint stripping furnace through the first-stage high-temperature heat exchanger, and heats the pyrolysis section of the mesh belt tunnel paint stripping furnace. The temperature of the incineration flue gas after the first-stage high-temperature heat exchanger recovers waste heat is reduced to 400-500°C. The heat of the incineration flue gas after heat exchange in the first-stage high-temperature heat exchanger is transferred to the combustion air used by the incinerator through the second-stage air preheater. After the waste heat is recovered by the second-stage air preheater, the temperature of the incineration flue gas is reduced to 180-250°C, and the combustion air is preheated from room temperature to 200-350°C. The flue gas from the second-stage air preheater is used to produce 60-80°C hot water through the third-stage waste heat boiler. After waste heat recovery by the third-stage waste heat boiler, the temperature of the flue gas from the incineration gas is reduced to 100-150°C.

10. The method for stripping enameled wire using nitrogen-protected pyrolysis according to claim 7, characterized in that, The nitrogen-protected pyrolysis method for stripping enameled wires also includes: The oxygen content and combustible gas concentration inside the mesh belt tunnel paint stripping furnace are monitored online. When the oxygen content is >500 ppm, an alarm signal is issued, and when the oxygen content is >1000 ppm, an emergency shutdown interlock is triggered. An alarm signal is issued when the concentration of combustible gas is >25% LEL, and an emergency shutdown interlock is triggered when the concentration of combustible gas is >50% LEL.

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