Thermal decomposition recovery method of photovoltaic module

Abstract

The invention discloses a thermal decomposition recovery method of a photovoltaic module, and belongs to the technical field of photovoltaic module recovery. The method comprises the following steps of S1, dismantling an aluminum frame and a junction box of the retired photovoltaic module, and performing dust removal treatment on the dismantled composite module; s2, performing three-section gradient temperature control thermal decomposition treatment on the composite component subjected to dust removal treatment under an inert atmosphere condition, namely raising the temperature to 120-150 DEG C, and keeping the temperature for 30-40 minutes; the temperature is increased to 220-250 DEG C at the heating rate of 5-8 DEG C / min, and heat preservation is conducted for 60-80 min; the temperature is increased to 280-300 DEG C, and heat preservation is conducted for 20-30 min; tail gas generated by thermal decomposition treatment is recycled; and S3, separating and purifying the glass, the silicon wafer, the back plate and the metal of the composite assembly, and preparing the packaging material from the recovered tail gas. Through a three-section type gradient temperature control technology, efficient separation of a packaging material and a base material in a photovoltaic module is achieved, and high-valued recovery of glass, silicon wafers, metal and a regenerated packaging material is achieved in combination with a subsequent material purification process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photovoltaic module recycling, and particularly relates to a thermal decomposition recycling method of a photovoltaic module. BACKGROUND

[0002] The global photovoltaic industry is developing rapidly, and the installed capacity is increasing year by year. It is estimated that the total amount of retired photovoltaic modules worldwide will exceed 10 million tons in 2030. Retired modules contain recyclable resources such as glass (about 70%), silicon wafers (about 10%), EVA (ethylene-vinyl acetate copolymer) adhesive film (about 5%), and metals (aluminum, copper, silver, about 10%). If not properly handled, not only will it cause resource waste, but also will cause environmental pollution due to fluorine-containing backboard and heavy metals. The development of photovoltaic module recycling technology has become a key to the sustainable development of the industry. Current mainstream photovoltaic module recycling technologies are divided into three categories: physical disassembly separation, chemical treatment, and thermal decomposition treatment. Among them, physical disassembly technology generally separates each part of the module through mechanical cutting, crushing, and peeling. However, the silicon wafer is brittle, with a breakage rate of over 40% during cutting, and cannot separate the EVA adhesive film from the substrate, requiring subsequent processing, which has low recycling value. For example, patent number CN120243598A discloses a separation and recycling method for retired crystalline silicon photovoltaic modules. The method pre-treats the photovoltaic module, removes the frame, backboard, and encapsulation layer to obtain a mixed solid, then crushes and classifies the mixed solid, and then separates different components by magnetic fluid density separation to obtain different component fractions for recycling. The method fails to separate the EVA adhesive film from the substrate, and the EVA cannot be recycled.

[0003] Chemical treatment technology generally uses strong acid (hydrofluoric acid and nitric acid mixture) to dissolve EVA adhesive film and impurities. Although it can separate silicon wafers, it generates a large amount of harmful wastewater, has high processing cost, and the metal is easily corroded and lost. For example, patent number CN120268775A discloses a recycling device and method for silicon in waste photovoltaic modules. In the recycling method, an automatic ultrasonic acid pickling structure is provided, a chemical solvent is filled in an acid pickling tank, and an ultrasonic wave is used to form a cavitation effect on the surface of the silicon wafer in the acid pickling liquid to separate the silicon wafer and the EVA.

[0004] The thermal decomposition technology generally decomposes the EVA adhesive film by heating to separate the substrates. Compared with the first two types of technologies, the thermal decomposition technology has the potential of no wastewater discharge and less damage to silicon wafers in theory. However, the existing thermal decomposition technology has the following significant defects: the temperature control is not accurate, the tail gas treatment is difficult, the material separation efficiency is low, and the economy and adaptability are poor. The inaccurate temperature control leads to material damage or incomplete decomposition. The tail gas generated by pyrolysis has complex components, and improper recovery and treatment will cause environmental pollution. The physical properties of the materials after decomposition are similar, resulting in low separation efficiency. The overall economy is poor, and it is difficult to realize industrialized application. Patent No. CN109570195A discloses a double-glass structure assembly separation and recovery method, which removes the EVA of the double-glass assembly separating double-sided glass by using an EVA thermal decomposition device.

[0005] In summary, there is a need in the art for a new method of recycling photovoltaic modules that can overcome the above-mentioned shortcomings and achieve efficient, clean, and high-value recycling of photovoltaic modules. SUMMARY

[0006] To solve the above problems, the main purpose of the present application is to provide a thermal decomposition and recovery method for photovoltaic modules with gradient temperature control, tail gas recovery, and high recovery degree, which can effectively solve the problems of incomplete EVA decomposition, silicon wafer oxidation damage, environmental pollution and resource waste caused by direct discharge of tail gas generated during the thermal decomposition process, and low sorting efficiency in the existing thermal decomposition and recovery technology. The method realizes efficient separation of packaging materials and substrates, improves the recovery rate and purity of each separated material, and reduces the environmental impact of the recovery process, providing a feasible path for industrialization and large-scale promotion.

[0007] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: The present application provides a thermal decomposition and recovery method for photovoltaic modules, which comprises the following steps: Step S1, remove the aluminum frame and junction box of the retired photovoltaic module, and perform dust removal treatment on the removed composite assembly; Step S2, perform three-stage gradient temperature control thermal decomposition treatment on the dust-removed composite assembly under inert atmosphere, including: in the first stage, the temperature is raised to 120-150℃, and the temperature is maintained for 30-40min to preliminarily soften the EVA adhesive film; in the second stage, the temperature is raised to 220-250℃ at a heating rate of 5-8℃ / min, and the temperature is maintained for 60-80min to decompose the EVA adhesive film; in the third stage, the temperature is raised to 280-300℃, and the temperature is maintained for 20-30min to desorb residual organic matter; and the tail gas generated during the thermal decomposition treatment is recovered; Step S3, after the thermal decomposition is completed, separate and purify the glass, silicon wafer, back plate, and metal of the composite assembly, and prepare packaging materials from the recovered tail gas.

[0008] Further, the step S3, after the thermal decomposition is completed, the glass, the silicon wafer, the metal and the packaging material of the composite assembly are separated and purified, and the recovered tail gas is prepared into a packaging material, comprising: Substrate separation: the glass, the silicon wafer and the back plate are separated from each other by mechanical vibration, and the glass and the silicon wafer are collected by vacuum adsorption, and the back plate is collected after removing the residual impurities by manual sorting; Silicon wafer purification: the collected silicon wafer is sequentially subjected to ultrasonic cleaning and plasma polishing; Packaging material regeneration: the tail gas generated by the thermal decomposition treatment is condensed and recovered to obtain an EVA decomposition product, the EVA decomposition product is subjected to catalytic reforming reaction to generate ethylene-vinyl acetate copolymer monomers, and the regenerated EVA film raw material is obtained by polymerization reaction; Metal recovery: the collected back plate is subjected to metal electrode separation, and the separated metal electrode is subjected to magnetic impurity removal and induction smelting treatment.

[0009] Further, in step S1, the dust removal treatment adopts high-pressure air blowing, and the pressure is 0.2-0.3MPa.

[0010] Further, in step S1, the aluminum frame obtained after separation is collected after high-pressure spray cleaning and hot air drying, the water temperature of the high-pressure spray is 40-50℃, the pressure is 0.3-0.5MPa, and the temperature of the hot air drying is 60-80℃, and the air speed is 1-2m / s.

[0011] Further, in step S2, the flow rate of the inert atmosphere is 5-10L / min; the inert atmosphere is argon, and the argon purity is ≥99.99%.

[0012] Further, in the substrate separation process of step S3, the frequency of mechanical vibration is 40-60Hz, the amplitude is 1-3mm, and the adsorption force of vacuum adsorption is 0.06-0.08MPa.

[0013] Further, in the silicon wafer purification process of step S3, the frequency of ultrasonic cleaning is 40-60kHz, the cleaning temperature is 40-50℃, and the cleaning time is 15-20min.

[0014] Further, in the silicon wafer purification process of step S3, the cleaning liquid is a mixture of deionized water and neutral detergent, and the mass percentage of the neutral detergent is 0.2-1.0%.

[0015] Further, in the silicon wafer purification process of step S3, the power of plasma polishing is 120-160W, and the time is 8-12min.

[0016] Further, in the encapsulating material regeneration process of step S3, the condensation recovery condensation temperature is -10 to -5 DEG C.

[0017] Further, in the encapsulating material regeneration process of step S3, the catalyst of the catalytic reforming reaction is ZSM-5 molecular sieve, the reaction temperature is 350-400 DEG C, and the reaction pressure is 0.1-0.2 MPa.

[0018] Further, in the encapsulating material regeneration process of step S3, the temperature of the polymerization reaction is 80-100 DEG C.

[0019] Further, in the encapsulating material regeneration process of step S3, the initiator in the polymerization reaction is dibenzoyl peroxide, and the initiator addition amount accounts for 0.3-0.6% of the mass percentage of the reaction material.

[0020] Further, the initiator is selected from one or more of dibenzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile and tert-butyl peroxyl benzoate.

[0021] Further, in the metal recovery process of step S3, the magnetic field strength of the magnetic impurity removal is 0.8-1.2 T, and the smelting temperature of the induction smelting treatment is 1150-1250 DEG C, and the holding time is 20-30 min.

[0022] Further, in the recycling method, the thermal decomposition efficiency of the EVA adhesive film in the photovoltaic module is ≥92%, the complete recovery rate of the silicon wafer is ≥92%, the glass recovery rate is ≥95%, and the metal recovery rate is ≥97%.

[0023] Compared with the prior art, the present application has the following beneficial effects: (1) The thermal decomposition recycling method of the photovoltaic module realizes efficient separation of the encapsulating material and the base material in the photovoltaic module through a three-stage gradient temperature control technology, and realizes high-value recycling of glass, silicon wafer, metal and regenerated encapsulating material by combining subsequent material purification processes. Among them, the decomposition efficiency of the EVA adhesive film is ≥92%, the complete recovery rate of the silicon wafer is ≥92%, the glass recovery rate is ≥95%, and the metal recovery rate is ≥97%.

[0024] (2) The present application recovers the tail gas generated by the thermal decomposition treatment, and converts the valuable encapsulating material by using condensation recovery and catalytic reforming and polymerization process, realizes the closed-loop recycling of EVA adhesive film, and solves the problem of secondary pollution.

[0025] (3) In the silicon wafer purification process of the present application, the combination of ultrasonic cleaning and plasma polishing treatment makes the regenerated silicon wafer have high purity and small surface damage, and can be directly used in high-value fields.

[0026] (4) The application solves the problems of high breakage rate of traditional mechanical disassembly of silicon wafers and large pollution of chemical treatment, and can realize full recycling of aluminum profiles, junction boxes, glass, silicon wafers, back plates, metal electrodes and EVA raw materials in the recycled components, thereby providing an efficient and environmentally friendly new path for photovoltaic component recycling.

[0027] Other features and effects of the present application will be described in the subsequent description, and some will become apparent from the description, or be understood by implementing the present application. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0029] Figure 1 A flowchart of a thermal decomposition recycling method of a photovoltaic module of the present application is shown. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] In order to achieve the above-mentioned purpose, the embodiments of the present application provide a thermal decomposition recycling method of a photovoltaic module, the process flow of the method is shown in Figure 1 , comprising the following steps: Step S1, component pretreatment: removing the aluminum frame and junction box of the retired photovoltaic module, and performing dust removal treatment on the removed composite components (mainly glass-EVA film-silicon wafer-back plate); Step S2, gradient temperature control thermal decomposition: performing three-stage gradient temperature control thermal decomposition treatment on the dust-removed composite components under inert atmosphere, including: in the first stage, the temperature is raised to 120-150 DEG C, and the temperature is kept for 30-40 min, so that the EVA film is preliminarily softened; in the second stage, the temperature is raised to 220-250 DEG C at a temperature rising rate of 5-8 DEG C / min, and the temperature is kept for 60-80 min, so that the EVA film is thermally decomposed; in the third stage, the temperature is raised to 280-300 DEG C, and the temperature is kept for 20-30 min, so that the residual organic matter is desorbed; and the tail gas generated in the thermal decomposition treatment is recycled; Step S3, material separation and purification: after the thermal decomposition is completed, the glass, silicon wafer, metal and packaging material of the composite assembly are separated and purified, and the recovered tail gas is prepared into a packaging material, including: Substrate separation: after the composite assembly is cooled to 80-100 DEG C after the thermal decomposition is completed, the composite assembly is taken out, the glass, silicon wafer and back plate are separated from each other by mechanical vibration, and the glass and silicon wafer are collected by vacuum adsorption, and the back plate is collected after removing the residual impurities by manual sorting; Silicon wafer purification: the collected silicon wafer is sequentially subjected to ultrasonic cleaning and plasma polishing; Packaging material regeneration: the tail gas generated by the thermal decomposition treatment is condensed and recovered to obtain an EVA decomposition product, the EVA decomposition product is subjected to a catalytic reforming reaction to generate ethylene-vinyl acetate copolymer monomers, and the regenerated EVA film raw material is obtained by polymerization reaction.

[0032] In addition, in the packaging material regeneration process, an activated carbon adsorption process is also included, which is used to adsorb trace amounts of volatile organic compounds (VOCs) remaining in the tail gas after catalytic reforming, to ensure that the tail gas meets the emission standard (VOCs content <10 mg / m 3 ). The tail gas treatment process is as follows: thermal decomposition gas -> condenser (recovering EVA decomposition product) -> catalytic reforming reactor (converting decomposition product into copolymer monomer) -> activated carbon adsorption tower (adsorbing residual VOCs) -> meeting the emission standard.

[0033] Metal recovery: the collected back plate is subjected to metal electrode separation, and the separated metal electrode is subjected to magnetic impurity removal and induction smelting treatment.

[0034] The present application sets three-stage gradient temperature control thermal decomposition, and clearly defines the temperature stages of functional partition (softening, decomposition, desorption), which ensures efficient and complete decomposition of the EVA film, and at the same time maximizes the protection of the silicon wafer from oxidation damage, laying a foundation for subsequent high-value recovery. In the three-stage gradient temperature control thermal decomposition process, a PID temperature controller is used to control the temperature accuracy to be ±1 DEG C. The whole recycling process of the present application realizes the full-component recycling path from the retired photovoltaic module to various reusable materials (glass, silicon wafer, metal, packaging material, back plate, aluminum frame and junction box), fundamentally improves the economic efficiency and resource utilization rate of the process, solves the problems of high silicon wafer breakage rate in traditional mechanical disassembly and large pollution in chemical treatment, and provides an efficient and environmentally friendly new idea for photovoltaic module recycling.

[0035] In some preferred embodiments of the present application, in step S1, the dust removal treatment adopts high-pressure air blowing, with a pressure of 0.2-0.3 MPa; in step S1, the aluminum frame obtained after separation is collected after high-pressure spray cleaning and hot air drying, the water temperature of the high-pressure spray is 40-50℃, the pressure is 0.3-0.5 MPa, and the temperature of the hot air drying is 60-80℃, with a wind speed of 1-2 m / s. Through the above treatment, the cleaning recovery of the material is ensured, and the quality of the recovered material is effectively improved.

[0036] In some preferred embodiments of the present application, in step S2, the flow rate of the inert atmosphere is 5-10 L / min; the inert atmosphere is argon, with a purity of ≥99.99%. The high-purity argon and the specific flow rate provide a reliable inert protective atmosphere for the silicon wafer, effectively preventing its oxidation at high temperatures, which is a key guarantee measure to achieve a high complete recovery rate (≥93%) of the silicon wafer.

[0037] In some preferred embodiments of the present application, in the substrate separation process of step S3, the frequency of mechanical vibration is 40-60 Hz, the amplitude is 1-3 mm, and the adsorption force of vacuum adsorption is 0.06-0.08 MPa. Through the non-damaging combination of mechanical vibration and vacuum adsorption, efficient and gentle separation of brittle glass and silicon wafers is achieved. This method avoids the hard impact of traditional mechanical disassembly and minimizes the breakage rate of silicon wafers during the separation stage.

[0038] In some preferred embodiments of the present application, in the silicon wafer purification process of step S3, the frequency of ultrasonic cleaning is 40-60 kHz, the cleaning temperature is 40-50℃, and the cleaning time is 15-20 min; the power of plasma polishing is 120-160 W, and the time is 8-12 min. Further, the cleaning liquid is a mixture of deionized water and neutral detergent, and the mass percentage of the neutral detergent in the cleaning liquid is 0.2-1.0%. A neutral detergent within this mass range will not corrode the silicon wafer, a low concentration can adapt to silicon wafers with less surface carbide, and a high concentration can cope with scenarios where carbide is attached thick.

[0039] The present application effectively removes surface impurities and trace carbides remaining after thermal decomposition through ultrasonic cleaning, and repairs the slight damage to the silicon wafer surface during the thermal decomposition process through plasma polishing, obtaining regenerated silicon wafers with a resistivity of ≥1000 Ω cm, greatly improving the value of the recovered silicon wafers.

[0040] In some preferred embodiments of the present application, in the encapsulating material recycling process of step S3, the condensation recovery condensation temperature is -10℃ to -5℃, the catalyst for the catalytic reforming reaction is ZSM-5 molecular sieve, the reaction temperature is 350-400℃, and the reaction pressure is 0.1-0.2 MPa. The temperature of the polymerization reaction is 80-100℃, and an initiator is added in the polymerization reaction, and the initiator addition amount accounts for 0.3-0.6% of the mass percentage of the reaction material.

[0041] Further, the initiator can be specifically selected according to process requirements, and some free radical initiators can be selected, for example, can be selected from dibenzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, and tertiary butyl peroxide (such as tert-butyl peroxyl benzoate). Among them, dicumyl peroxide (DCP) and dibenzoyl peroxide are suitable for scenarios that require to improve the heat resistance of the product, the addition amount is 0.4-0.6%, the decomposition temperature matches the reaction system, and the product residue is low; azobisisobutyronitrile (AIBN) is suitable for scenarios with high requirements for reaction rate, the addition amount is 0.2-0.4%, the decomposition uniformity is good, and the color difference of the polymerization product can be reduced; tertiary butyl peroxide is suitable for continuous production, the addition amount is 0.3-0.5%, the storage stability is better than that of dibenzoyl peroxide, and the process safety risk is reduced.

[0042] In the present application, the EVA decomposition product in the tail gas is converted from gaseous state to liquid state for recycling, which realizes preliminary enrichment of resources, and through specific catalyst and catalytic reforming reaction conditions, the recycled EVA decomposition product is converted and regenerated into the original monomer of EVA, and the regenerated monomer is recombined into usable EVA film raw material. In some preferred embodiments of the present application, in the metal recovery process of step S3, the collected back plate is subjected to metal electrode separation, specifically including: blowing off the residual EVA decomposition debris on the surface of the back plate to expose the metal electrodes inlaid on the back plate, and heating and softening the back plate adhesive layer by rolling (pressure 0.05-0.1 MPa, temperature 50-60℃), and manually peeling off and taking out the metal electrodes to obtain separated metal electrodes. The separated metal electrodes are subjected to magnetic impurity removal and induction melting treatment, the magnetic field strength of the magnetic impurity removal is 0.8-1.2T, and the melting temperature of the induction melting treatment is 1150-1250℃, and the holding time is 20-30min. Through the above recovery process, efficient recovery and high-value utilization of metal resources are realized.

[0043] In some preferred embodiments of the present application, through the above photovoltaic module thermal decomposition recovery method, the thermal decomposition efficiency of the EVA film in the photovoltaic module is ≥92%, the complete recovery rate of the silicon wafer is ≥92%, the glass recovery rate is ≥95%, and the metal recovery rate is ≥97%.

[0044] The application will be further described in conjunction with specific embodiments which should not be construed as limiting the scope of the application as claimed.

[0045] Example 1 A thermal decomposition recycling method of a photovoltaic module, which is applicable to moderately aged monocrystalline silicon modules, comprises the following steps: Step S1: Module pretreatment: The retired photovoltaic module is preliminarily disassembled, and the aluminum frame and junction box are removed by a mechanical disassembly mechanism. The separated aluminum frame is collected after high-pressure spraying (pressure 0.4 MPa, water temperature 45°C) cleaning and hot air drying (temperature 70°C, air speed 1.5 m / s). The remaining "glass-EVA-silicon wafer-back plate" composite module is sent to the thermal decomposition furnace after dust removal treatment (high-pressure air blowing, pressure 0.25 MPa).

[0046] Step S2: Gradient temperature control thermal decomposition: Inert protective gas (argon purity 99.99%, flow rate 8 L / min) is introduced into the thermal decomposition furnace, and three-stage gradient temperature control is adopted. First stage (low-temperature preheating): the temperature is raised to 135°C, and the temperature is maintained for 35 min, so that the EVA film is preliminarily softened, and the adhesion between the film and the glass and the silicon wafer is destroyed; Second stage (medium-temperature decomposition): the temperature is slowly raised to 235°C at a rate of 6.5°C / min, and the temperature is maintained for 70 min. The EVA film undergoes thermal decomposition to generate small-molecule organic gas (mainly ethylene and vinyl acetate), while avoiding oxidation of the silicon wafer (silicon wafer oxidation temperature > 400°C); Third stage (high-temperature desorption): the temperature is raised to 290°C, and the temperature is maintained for 25 min to completely desorb the small-molecule organic matter remaining on the surface of the glass and the silicon wafer, ensuring complete separation of the materials. The tail gas generated during the thermal decomposition process is subjected to tail gas purification and recovery.

[0047] Step S3: Material separation and purification: Substrate separation: after the thermal decomposition is completed, the temperature in the furnace is lowered to 90°C, and the composite module is removed. The glass, silicon wafer, and back plate are naturally separated by mechanical vibration (frequency 50 Hz, amplitude 2 mm), and the glass and silicon wafer are collected using a vacuum suction device (suction force 0.07 MPa). The back plate is collected after removing the residual impurities by manual sorting; Silicon wafer purification: the separated silicon wafer is placed in an ultrasonic cleaning tank (frequency 50 kHz, cleaning liquid is deionized water and 0.5% mass fraction of neutral detergent, temperature 45°C) for 17.5 min to remove the trace amount of carbide on the surface; then plasma polishing (power 140 W, time 10 min) is performed to repair the slight damage to the surface of the silicon wafer during the thermal decomposition process, and a regenerated silicon wafer is obtained; Packaging material regeneration: The thermal decomposition tail gas is condensed to recover EVA decomposition products at a condensation temperature of -7.5°C, which are sent to a catalytic reforming reactor (catalyst: ZSM-5 molecular sieve, reaction temperature: 375°C, pressure: 0.15 MPa) to generate ethylene-vinyl acetate copolymer monomers, which are then subjected to a polymerization reaction (temperature: 90°C, initiator: dibenzoyl peroxide, addition amount: 0.4%) to obtain regenerated EVA film raw materials; active carbon is used to adsorb trace amounts of volatile organic compounds (VOCs) remaining in the tail gas after catalytic reforming to ensure that the tail gas meets the emission standard (VOCs content <10 mg / m 3 ); Metal recovery: The EVA decomposition debris remaining on the surface of the back plate are collected by purging, exposing the copper electrodes embedded in the back plate, and the back plate adhesive layer is heated and softened by rolling (pressure: 0.5 MPa, temperature: 50°C) to manually peel off and remove the metal electrodes, finally obtaining separated copper electrodes; The separated copper electrodes are subjected to magnetic separation (magnetic field strength: 1.0 T) to remove impurities, and then sent to a medium-frequency induction melting furnace (melting temperature: 1200°C, holding time: 25 min) to remove impurities and cast into high-purity copper ingots (purity: 99.7%).

[0048] In the thermal decomposition and recovery process of the photovoltaic module in this embodiment, the thermal decomposition efficiency of the EVA film in the photovoltaic module is 92.7%, the complete recovery rate of the silicon wafer is 94.6%, the glass recovery rate is 97.2%, and the metal recovery rate is 97.0%.

[0049] Example 2 A thermal decomposition and recovery method for a photovoltaic module, which is suitable for slightly aged single-crystal silicon modules, comprises the following steps: Step S1: Module pretreatment: The retired photovoltaic module is preliminarily disassembled, and the aluminum frame and junction box are removed by a mechanical frame disassembly mechanism. The separated aluminum frame is collected after high-pressure spraying (pressure: 0.5 MPa, water temperature: 50°C) cleaning and hot air drying (temperature: 80°C, air speed: 2 m / s). The remaining "glass-EVA-silicon wafer-back plate" composite module is sent to a thermal decomposition furnace after dust removal treatment (high-pressure air blowing, pressure: 0.3 MPa).

[0050] Step S2: Gradient temperature control thermal decomposition: Inert protective gas (argon, purity: 99.99%, flow rate: 10 L / min) is introduced into the thermal decomposition furnace, and three-stage gradient temperature control is adopted: First stage (low-temperature preheating): the temperature is raised to 150°C, and the temperature is maintained for 40 min to preliminarily soften the EVA film and destroy the adhesion between the EVA film and the glass and silicon wafer; The second stage (middle temperature decomposition): the temperature is slowly increased to 250°C at a rate of 8°C / min, and the temperature is kept for 80 min. The EVA adhesive film is decomposed to generate small molecule organic gas (mainly ethylene and vinyl acetate), and the silicon wafer is prevented from being oxidized (the oxidation temperature of the silicon wafer is greater than 400°C); The third stage (high temperature desorption): the temperature is increased to 300°C, and the temperature is kept for 30 min. Small molecule organic matter remaining on the surface of the glass and the silicon wafer is completely desorbed, and the material separation is ensured to be complete. The tail gas generated in the thermal decomposition process is subjected to tail gas purification and recovery.

[0051] Step S3: material separation and purification: Substrate separation: after the thermal decomposition is completed, the temperature in the furnace is reduced to 100°C, the composite assembly is taken out, the glass, the silicon wafer and the back plate are naturally separated through mechanical vibration (frequency 60 Hz, amplitude 3 mm), the glass and the silicon wafer are collected by using a vacuum suction device (suction force 0.08 MPa), and the back plate is collected after the residual impurities are removed by manual sorting; Silicon wafer purification: the separated silicon wafer is placed into an ultrasonic cleaning tank (frequency 60 kHz, cleaning liquid is deionized water and 1.0% mass fraction of neutral detergent, temperature 50°C) for cleaning for 17.5 min to remove the trace carbide on the surface, and then plasma polishing (power 160 W, time 12 min) is performed to repair the slight damage to the surface of the silicon wafer in the thermal decomposition process, so as to obtain a regenerated silicon wafer; Packaging material regeneration: the thermal decomposition tail gas is condensed and recovered (condensation temperature -5°C) to obtain EVA decomposition products, which are sent into a catalytic reforming reactor (catalyst is ZSM-5 molecular sieve, reaction temperature 400°C, pressure 0.2 MPa) to generate ethylene-vinyl acetate copolymer monomers, and then polymerization reaction (temperature 100°C, initiator is dibenzoyl peroxide, and the addition amount is 0.5%) is performed to obtain regenerated EVA adhesive film raw materials; active carbon is used to adsorb trace volatile organic compounds (VOCs) remaining in the tail gas after the catalytic reforming, so that the tail gas can be discharged in a standard manner (the content of VOCs is less than 10 mg / m 3 ); Metal recovery: the EVA decomposition debris remaining on the surface of the collected back plate is blown and collected, the copper electrode embedded in the back plate is exposed, the back plate adhesive layer is heated and softened through rolling (pressure 0.1 MPa, temperature 60°C), and the metal electrode is manually peeled off and taken out, so that a separated copper electrode is obtained; The separated copper electrode is subjected to magnetic separation (magnetic field strength 1.2 T) to remove impurities, and then is sent into a medium frequency induction melting furnace (melting temperature 1250°C, holding time 30 min) to remove impurities and cast into high-purity copper ingots (purity 99.8%).

[0052] In the thermal decomposition recycling process of the photovoltaic module in this embodiment, the thermal decomposition efficiency of the EVA adhesive film in the photovoltaic module is 92.5%, the complete recovery rate of the silicon wafer is 93.0%, the glass recovery rate is 97.7%, and the metal recovery rate is 97.1%.

[0053] Embodiment 3 A thermal decomposition recycling method of a photovoltaic module, which can be adapted to a heavily aged polycrystalline silicon module, comprises the following steps: Step S1: module pretreatment: The retired photovoltaic module is preliminarily disassembled, and the aluminum frame and the junction box are removed by a mechanical frame disassembly mechanism. The separated aluminum frame is collected after high-pressure spraying (pressure 0.3 MPa, water temperature 40℃) cleaning and hot air drying (temperature 60℃, air speed 1 m / s). The remaining "glass-EVA-silicon wafer-back plate" composite module is sent to a thermal decomposition furnace after dust removal treatment (high-pressure air blowing is used, and the pressure is 0.2 MPa).

[0054] Step S2: gradient temperature control thermal decomposition: Inert protective gas (argon purity 99.99%, flow rate 5 L / min) is introduced into the thermal decomposition furnace, and three-stage gradient temperature control is adopted. First stage (low-temperature preheating): the temperature is raised to 120℃, and the temperature is kept for 30 min, so that the EVA adhesive film is preliminarily softened, and the adhesion between the adhesive film and the glass and the silicon wafer is destroyed; Second stage (medium-temperature decomposition): the temperature is slowly raised to 220℃ at a rate of 5℃ / min, and the temperature is kept for 60 min. The EVA adhesive film is thermally decomposed to generate small-molecule organic gas (mainly ethylene and vinyl acetate), and at the same time, the silicon wafer is prevented from being oxidized (the oxidation temperature of the silicon wafer is >400℃); Third stage (high-temperature desorption): the temperature is raised to 280℃, and the temperature is kept for 20 min, so that the small-molecule organic matter remaining on the surface of the glass and the silicon wafer is completely desorbed, and the material separation is ensured to be complete. The tail gas generated in the thermal decomposition process is subjected to tail gas purification and recycling.

[0055] Step S3: material separation and purification: Substrate separation: after the thermal decomposition is completed, the composite module is taken out when the temperature in the furnace is reduced to 80℃. The glass, the silicon wafer, and the back plate are naturally separated by mechanical vibration (frequency 40 Hz, amplitude 1 mm). The glass and the silicon wafer are collected by using a vacuum suction device (suction force 0.06 MPa). The back plate is collected after the residual impurities are removed by manual sorting. Silicon wafer purification: the separated silicon wafer is placed in an ultrasonic cleaning tank (frequency 40 kHz, cleaning liquid is deionized water and neutral detergent with a mass ratio of 0.2%, and temperature 40℃) for cleaning for 15 min to remove the trace carbide on the surface. Then, plasma polishing (power 120 W, time 8 min) is performed to repair the slight damage to the surface of the silicon wafer in the thermal decomposition process, and a regenerated silicon wafer is obtained. Packaging material regeneration: The thermal decomposition tail gas is condensed to recover EVA decomposition products at a condensation temperature of -10°C, which are sent to a catalytic reforming reactor (catalyst: ZSM-5 molecular sieve, reaction temperature: 350°C, pressure: 0.1 MPa) to generate ethylene-vinyl acetate copolymer monomers, which are then subjected to a polymerization reaction (temperature: 80°C, initiator: dibenzoyl peroxide, addition amount: 0.3%) to obtain regenerated EVA film raw materials; activated carbon is used to adsorb trace amounts of volatile organic compounds (VOCs) remaining in the tail gas after catalytic reforming to ensure that the tail gas meets the emission standard (VOCs content <10 mg / m 3 ); Metal recovery: The copper electrode separated from the assembly is subjected to magnetic separation (magnetic field strength: 0.8 T) to remove impurities, and then sent to a medium-frequency induction melting furnace (melting temperature: 1150°C, holding time: 20 min) to remove impurities and cast into high-purity copper ingots (purity: 99.6%).

[0056] In the thermal decomposition recovery process of the photovoltaic assembly in this embodiment, the thermal decomposition efficiency of the EVA film in the photovoltaic assembly is 92.2%, the complete recovery rate of the silicon wafer is 92.9%, the glass recovery rate is 96.2%, and the metal recovery rate is 97.0%.

[0057] Comparative Example 1 A traditional one-stage thermal decomposition process is used for photovoltaic assembly recovery, and the process flow includes the following steps: Step S1: Assembly pretreatment stage: consistent with Step 1 of Example 1; Step S2: Thermal decomposition stage: the thermal decomposition furnace only uses a single temperature control, argon gas (purity: 99.99%, flow rate: 3 L / min) is introduced, and the temperature is directly raised to 250°C and held for 150 min without gradient preheating and high-temperature desorption process; the separated tail gas is only subjected to simple condensation treatment without catalytic reforming and activated carbon adsorption; Step S3: Material separation and purification stage: when the furnace temperature drops to 90°C, mechanical vibration separation finds that a large amount of carbonized EVA residue is attached to the surface of the glass and silicon wafer, which needs to be manually scraped off (time-consuming: 2 hours / 100 pieces); the silicon wafer is oxidized and yellowed due to local temperature exceeding 400°C, and some edges are damaged; the metal electrode and the back plate are tightly bonded and have a high breakage rate when peeled off. The final recovery data: EVA film thermal decomposition efficiency: 88.2%, glass recovery rate: 92.0%, surface residual carbonized material needs secondary acid washing, silicon wafer complete recovery rate: 85.0%, metal recovery rate: 96.0%, tail gas VOCs emission concentration: 85 mg / m 3 , which is much higher than the <10 mg / m 3 of the present application.

[0058] Due to the lack of gradient temperature control in the one-stage thermal decomposition in the comparative example, the EVA adhesive film is "partially carbonized and not completely decomposed", and the thermal decomposition efficiency is 4.5 percentage points lower than that of Example 1; the silicon wafer is damaged due to uncontrolled temperature oxidation, and the complete recovery rate is 9.6 percentage points lower than that of Example 1, and the exhaust gas pollution is serious and the labor cost increases sharply. The above data can fully prove the necessity and superiority of the three-stage gradient temperature control process of the present application.

[0059] Comparative Example 2 The traditional improved two-stage thermal decomposition process recovery method, which is often combined with inert atmosphere and auxiliary separation means, realizes material separation in two core temperature stages, and the specific steps are as follows: Step S1: Pretreatment disassembly: first mechanically remove the aluminum frame and junction box of the photovoltaic module, and use a vacuum chuck to adsorb and fix the glass surface to ensure the integrity of the module main structure. Clean the glass surface before adsorbing the vacuum chuck to reduce impurities.

[0060] Step S2: First stage low temperature softening separation: place the module on the heating platform, control the temperature to 200℃, and keep it for 2min to soften the EVA adhesive film, then slowly peel off the surface glass through the flexible roller mechanism. This stage avoids high temperature damage to the glass and silicon wafer; Second stage high temperature pyrolysis separation: move the remaining battery layer and back plate / back glass into an inert gas pyrolysis furnace, heat to 480℃ and keep it, let the residual EVA adhesive film fully decompose, and cooperate with ultrasonic vibration to assist the separation of silicon wafer and glass.

[0061] Step S3: Material sorting and recovery: after cooling, separate the silicon wafer and glass debris by air flow sorting, then extract the solder strip metal with a magnetic separation device, and the gas products produced by pyrolysis can be recycled after treatment. The final recovery data: EVA adhesive film thermal decomposition efficiency 90.2%, glass recovery rate 93.2%, silicon wafer complete recovery rate 88.6%, and metal recovery rate 96.5%.

[0062] Due to the large span of the two-stage thermal decomposition temperature control interval in the comparative example, the EVA adhesive film is prone to incomplete cracking or residual adhesion to the silicon wafer and glass, affecting purity, and the thermal decomposition efficiency is 2.5 percentage points lower than that of Example 1. The heating uniformity is difficult to control, which can easily lead to uneven heating of the silicon wafer and damage. The complete recovery rate of the silicon wafer is 6.1 percentage points lower than that of Example 1, and the exhaust gas is not discharged in time, which is difficult to adapt to large-scale industrial production.

[0063] Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions described in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for thermal decomposition and recycling of photovoltaic modules, characterized in that, The method includes the following steps: Step S1: Remove the aluminum frame and junction box of the retired photovoltaic module, and perform dust removal treatment on the removed composite module; Step S2 involves subjecting the dust-removed composite components to a three-stage gradient temperature-controlled thermal decomposition process under an inert atmosphere, including: the first stage, raising the temperature to 120-150℃ and holding for 30-40 minutes; the second stage, raising the temperature to 220-250℃ at a heating rate of 5-8℃ / min and holding for 60-80 minutes; and the third stage, raising the temperature to 280-300℃ and holding for 20-30 minutes; and recovering the exhaust gas generated during the thermal decomposition process. Step S3: After thermal decomposition, the glass, silicon wafer, backplane, and metal of the composite component are separated and purified, and the recovered exhaust gas is used to prepare encapsulation materials.

2. The method for thermal decomposition and recycling of photovoltaic modules according to claim 1, characterized in that, In step S3, after thermal decomposition, the glass, silicon wafer, metal, and encapsulation material of the composite component are separated and purified, and the recovered tail gas is used to prepare encapsulation material, including: Substrate separation: The glass, silicon wafer and backplane are separated by mechanical vibration, and the glass and silicon wafer are collected separately by vacuum adsorption. The backplane is collected after manual sorting to remove residual impurities. Silicon wafer purification: The collected silicon wafers are sequentially subjected to ultrasonic cleaning and plasma polishing; Regeneration of encapsulation materials: The exhaust gas generated by thermal decomposition is condensed and recovered to obtain EVA decomposition products. The EVA decomposition products are then subjected to catalytic reforming to generate ethylene-vinyl acetate copolymer monomers, which are then polymerized to obtain recycled EVA film raw materials. Metal recycling: The collected backplate is separated into metal electrodes, and the separated metal electrodes are subjected to magnetic separation to remove impurities and induction melting.

3. The method for thermal decomposition and recycling of photovoltaic modules according to claim 1, characterized in that, In step S1, the dust removal process uses high-pressure air purging at a pressure of 0.2-0.3 MPa. In step S1, the aluminum frame obtained after separation is collected after being cleaned by high-pressure spray and dried by hot air. The water temperature of the high-pressure spray is 40-50℃ and the pressure is 0.3-0.5 MPa. The temperature of the hot air drying is 60-80℃ and the wind speed is 1-2 m / s.

4. The method for thermal decomposition and recycling of photovoltaic modules according to claim 1, characterized in that, In step S2, the flow rate of the inert atmosphere is 5-10 L / min; the inert atmosphere is argon with a purity ≥99.99%.

5. The method for thermal decomposition and recycling of photovoltaic modules according to claim 2, characterized in that, During the substrate separation process in step S3, the frequency of mechanical vibration is 40-60Hz, the amplitude is 1-3mm, and the adsorption force of vacuum adsorption is 0.06-0.08MPa.

6. The method for thermal decomposition and recycling of photovoltaic modules according to claim 2, characterized in that, In the silicon wafer purification process in step S3, the ultrasonic cleaning frequency is 40-60kHz, the cleaning temperature is 40-50℃, and the cleaning time is 15-20min; the plasma polishing power is 120-160W, and the time is 8-12min; the cleaning solution is a mixture of deionized water and neutral detergent, wherein the mass percentage of neutral detergent is 0.2-1.0%.

7. The method for thermal decomposition and recycling of photovoltaic modules according to claim 2, characterized in that, In the encapsulation material regeneration process in step S3, the condensation temperature of the condensation recovery is -10℃ to -5℃, the catalyst of the catalytic reforming reaction is ZSM-5 molecular sieve, the reaction temperature is 350-400℃, and the reaction pressure is 0.1-0.2MPa.

8. The method for thermal decomposition and recycling of photovoltaic modules according to claim 2, characterized in that, In the encapsulation material regeneration process in step S3, the polymerization reaction temperature is 80-100℃; an initiator is added to the polymerization reaction, and the amount of initiator added accounts for 0.3-0.6% of the mass percentage of the reactants; the initiator is selected from one or more of benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, and tert-butyl peroxide.

9. The method for thermal decomposition and recycling of photovoltaic modules according to claim 2, characterized in that, In the metal recovery process of step S3, the magnetic field strength of the magnetic separation for impurity removal is 0.8-1.2T, the melting temperature of the induction melting treatment is 1150-1250℃, and the holding time is 20-30min.

10. The method for thermal decomposition and recycling of photovoltaic modules according to any one of claims 1 to 9, characterized in that, In the recycling method, the thermal decomposition efficiency of EVA film in photovoltaic modules is ≥92%, the integrity recovery rate of silicon wafers is ≥92%, the glass recovery rate is ≥95%, and the metal recovery rate is ≥97%.

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