A method for recycling and utilizing waste photovoltaic panels through pyrolysis

Abstract

This invention discloses a method for the pyrolysis and recycling of waste photovoltaic panels. The method includes: physically disassembling and removing the aluminum frame and junction box; heating in an inert atmosphere at 205°C for 7-8 minutes to first peel off the fluorine-containing backsheet, then peel off the silicon wafers and glass, suppressing hydrogen fluoride generation at the source; subjecting the remaining mixed materials to four-stage graded pyrolysis and implementing five-stage waste heat recovery; performing multi-stage sorting of the pyrolysis products to obtain silicon powder, silicon wafers, glass, and metals; after dry ice spraying and acid washing, the silicon material is recovered by wet displacement to obtain high-purity silicon. This invention achieves efficient and clean recycling of high-value components such as glass, silicon, and silver from waste photovoltaic panels through a synergistic process of low-temperature stripping, graded pyrolysis, and staged waste heat recovery.

Description

Technical Field

[0001] In the field of waste resource recycling technology, specifically, it relates to a method for recycling waste photovoltaic panels through pyrolysis. Background Technology

[0002] The recycling of waste photovoltaic modules is a crucial link in achieving the green and circular development of the photovoltaic industry. A typical crystalline silicon photovoltaic module mainly consists of an aluminum frame, junction box, tempered glass, ethylene-vinyl acetate copolymer (EVA) film, crystalline silicon solar cells, and a fluorinated backsheet (such as KPK or TPT). Glass accounts for approximately 75% of the total module weight, aluminum for approximately 9%, and silicon for approximately 4%. It also contains high-value metal materials such as silver and copper.

[0003] Currently, recycling technologies for waste photovoltaic modules mainly fall into three categories: physical-mechanical methods, chemical solvent methods, and pyrolysis methods. Physical-mechanical methods achieve material separation through crushing, screening, and sorting processes. While the process is simple, it suffers from severe cross-contamination, high silicon wafer breakage rates, and incomplete removal of the EVA film, making it difficult to achieve precise recovery of high-value components. Chemical solvent methods utilize organic solvents to dissolve the EVA film to separate the laminated components. Although this can yield relatively intact glass and silicon wafers, it consumes large amounts of solvent, incurs high processing costs, and leaves difficult-to-remove residues on the swollen EVA surface, generating large amounts of organic waste requiring secondary treatment, thus posing significant environmental challenges.

[0004] Pyrolysis, which involves heating and decomposing organic encapsulation materials such as EVA in an inert or oxygen-free atmosphere to achieve effective separation of components such as glass, silicon wafers, and metals, is one of the most promising technologies for industrial application. However, existing pyrolysis technologies still face the following key challenges: First, fluorinated backsheets (such as KPK and TPT) decompose during high-temperature pyrolysis, producing toxic and harmful gases such as hydrogen fluoride (HF), posing risks of equipment corrosion and secondary pollution. Second, conventional pyrolysis processes have high energy consumption and lack a systematic energy cascade utilization design, hindering economic efficiency. Third, improper control of pyrolysis parameters can easily lead to thermal stress damage to silicon wafers or glass breakage, affecting the recycling quality of high-value materials. Fourth, the organic gases generated during pyrolysis are not effectively utilized, resulting in energy waste.

[0005] To address the aforementioned issues, existing research has attempted to improve recycling efficiency by optimizing pyrolysis conditions. Studies have shown that pyrolysis temperature, heating rate, and atmosphere significantly affect EVA decomposition behavior and material recycling quality; a heating rate of 5℃ / min and a pyrolysis temperature of 500℃ are beneficial for obtaining intact solar cells. Other studies have proposed that heating at 150℃ for 5 minutes can completely recycle TPT backsheet material, but at this temperature, EVA is not sufficiently softened, requiring significant mechanical force for peeling, and the subsequent non-destructive separation of silicon wafers has not been systematically addressed. At the industrialization level, domestic companies have developed recycling technologies and complete sets of equipment based on "pyrolysis + AI visual recognition for precise separation," as well as technologies for efficient dismantling and clean recycling of retired crystalline silicon photovoltaic modules. However, existing technical solutions mostly focus on optimizing single stages and have not yet formed a comprehensive, collaborative process encompassing low-temperature harmless peeling, cascade pyrolysis, waste heat recovery, and multi-dimensional sorting. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention discloses a method for the pyrolysis treatment and recycling of waste photovoltaic panels, the technical solution of which includes the following steps:

[0007] Step 1: Physically disassemble the waste photovoltaic panels, removing the aluminum frames and junction boxes;

[0008] Step 2: Low-temperature softening first peels off the fluorine-containing backplane, and then peels off the silicon wafer and glass to suppress the generation of hydrogen fluoride;

[0009] Step 3: The remaining mixed material after stripping is subjected to staged pyrolysis in an inert atmosphere to recover waste heat in stages.

[0010] Step four: sort and recycle the pyrolyzed materials.

[0011] Preferably, the peeling in step two is carried out in an inert atmosphere at a temperature of 205°C for 7-8 minutes, with a peeling time of less than 5 minutes.

[0012] Preferably, the fluorinated backsheet in step two includes a KPK backsheet or a TPT backsheet.

[0013] Preferably, the inert atmosphere is at least one of nitrogen or carbon dioxide, and the oxygen content in the atmosphere is ≤0.5%, preferably ≤0.1%.

[0014] Preferably, the glass and silicon wafers obtained in step two are cooled to 80-100°C and subjected to dry ice spray washing in a dry environment to obtain clean glass and silicon wafers.

[0015] Preferably, the dry ice spraying pressure is 0.4-1.0 MPa, the spraying distance is 15-50 mm, the spraying angle is 45°-60°, and the spraying time is 20-50 seconds.

[0016] Preferably, in step three, the mixed material undergoes graded pyrolysis in a multi-stage temperature-controlled rotary kiln or fluidized bed pyrolysis furnace. The temperature stages are connected by a material conveying device and equipped with temperature sensors and an automatic temperature control system. The graded pyrolysis is divided into four temperature stages: first, a preheating stage, 100-195℃, for 15 minutes; second, a low-temperature stage, 195-300℃, for 22 minutes; third, a medium-temperature stage, 300-480℃, for 20 minutes; and fourth, a high-temperature stage, 480-800℃, for 15 minutes. During the graded pyrolysis process, the heating rate between adjacent temperature stages is 5-15℃ / min, and the temperature fluctuation within each stage is ≤±5℃.

[0017] Preferably, the waste heat in the cascade is divided into five levels according to temperature, including: waste heat from pyrolysis gas combustion, waste heat from the high-temperature section, waste heat from the medium-temperature section, waste heat from the low-temperature section, and residual waste heat; the waste heat generated by the combustion of pyrolysis gas enters the main combustion equipment to provide the main heat source; the waste heat from the high-temperature section is reused in the medium-temperature and low-temperature sections; the waste heat from the medium-temperature section is reused in the low-temperature section; the waste heat from the low-temperature section is reused in the preheating section, which is assisted by an external heat source during the start-up phase and maintained by the waste heat from the low-temperature section after normal operation; the residual waste heat enters the heat exchanger to provide hot water and heating.

[0018] Preferably, step four is divided into three steps: step a) vibrating sieve to separate silicon powder and fine glass powder; step b) sieve to separate conductors in the mixed material based on differences in conductivity; and step c) density sieve to separate silicon wafer fragments and coarse glass particles.

[0019] Preferably, the silicon wafer and the silicon wafer fragments in step c are acid-washed after dry ice spraying. After acid washing, the silicon powder in step a is used to remove metallic silver by wet displacement, leaving high-purity silicon, either separately or in combination. The acid used for acid washing is at least one of hydrochloric acid and nitric acid, and the acid washing temperature is 25-60°C for 10-30 minutes. If the silicon wafer fragments have been cooled to room temperature, they can be preheated to 80-100°C or cooled to 80-100°C before dry ice spraying.

[0020] The beneficial effects of this invention are as follows: By synergistically controlling the process of 205℃ low temperature + inert atmosphere + short-time stripping, the decomposition of fluorinated backsheets and the generation of hydrogen fluoride are suppressed at the source. Dry ice spraying is used to remove residual EVA from the glass and silicon wafers; the surface is cooled to 80-100℃ before spraying to avoid thermal shock and surface frosting. Precise control through four-stage segmented pyrolysis enables the energy utilization of organic components. A five-stage waste heat recovery system significantly reduces energy consumption and processing costs compared to solutions without waste heat recovery. This invention is applicable to crystalline silicon photovoltaic modules with KPK and TPT fluorinated backsheets, and can process retired modules that have reached their service life or defective products from the production process, showing promising prospects for widespread application. Detailed Implementation

[0021] Example 1

[0022] This invention discloses a method for the pyrolysis treatment and recycling of waste photovoltaic panels, aiming to solve the following problems: First, fluorine-containing backsheets decompose during conventional high-temperature pyrolysis, generating highly toxic hydrogen fluoride gas and causing environmental pollution; Second, under the current pyrolysis process, silicon wafers are damaged by thermal stress, affecting the recycling quality; Third, existing pyrolysis processes lack systematic energy cascade utilization, resulting in high energy consumption; Fourth, the removal of residual EVA on glass and silicon wafers is incomplete, affecting subsequent processing.

[0023] Therefore, before pyrolyzing waste photovoltaic panels, this invention first uses physical methods to remove the aluminum frame and junction box from the panels, and pre-recovers materials such as aluminum, copper, and plastic.

[0024] Because fluorinated backsheets contain PVF (TPT backsheet) and PVDF (KPK backsheet), toxic fluorinated gases are generated during pyrolysis, which not only corrode equipment but also harm human health. Therefore, separating the fluorinated backsheet from the glass, silicon wafer, and remaining mixed materials before pyrolysis significantly reduces the generation of fluorinated gases during the process. Due to the characteristics of EVA material, it begins to soften at 65°C, and its adhesion begins to decrease, with softening intensifying as the temperature rises, thus facilitating its peeling from the fluorinated backsheet. However, when the temperature exceeds 220°C or the time at high temperatures is prolonged, PVF, taking TPT backsheets as an example, will release hydrogen fluoride gas. Therefore, the two key factors for low-temperature glass are temperature and time. This invention uses 205°C, mainly because, on the one hand, at this temperature, EVA transforms from a solid to a fluid state, significantly reducing adhesion and facilitating the peeling of the fluorinated backsheet; similarly, the silicon wafer and glass are also easier to separate. On the other hand, at this temperature, PVF has not yet reacted, thus avoiding the release of hydrogen fluoride caused by high temperatures. Regarding the timing, although no harmful gases were released at 205℃, prolonged exposure still caused a slow release of hydrogen fluoride. A balance needed to be found between temperature and time. Therefore, a low-temperature stripping experiment was conducted. An inert atmosphere furnace with a nitrogen atmosphere and an oxygen content <0.1% was used to strip the same batch of waste photovoltaic panels. The temperatures were set at 190℃, 200℃, 205℃, 210℃, and 220℃, with a heating time of 8 minutes. After heating, a mechanical stripping device was used to peel off the fluorinated backsheet along the edge of the photovoltaic panel. After removing the laminate from the furnace, the entire mechanical stripping operation was completed within 3-4 minutes, meeting the requirement of a stripping time <5 minutes. The results are shown in Table 1.

[0025]

[0026] As shown in Table 1, the required peeling force decreases significantly at 205℃, and the HF in the exhaust gas meets emission standards. Although the wafer integrity rate is lower than at 190℃ and 200℃, auxiliary peeling is still required if the EVA is not fully melted. From 210℃ onwards, trace amounts of HF are detected, indicating that the PVF has begun to decompose slowly.

[0027] With the above conditions remaining essentially unchanged, the constant temperature was 205℃, and the heating times were 5 minutes, 7 minutes, 8 minutes, 10 minutes, and 15 minutes. The results are shown in Table 2.

[0028]

[0029] As can be seen from Table 2, the center temperature reached 203 degrees Celsius after heating for 7 minutes, at which point the peeling force decreased significantly. After reaching the preset temperature at 8 minutes, the peeling force still decreased. However, after heating for 10 and 12 minutes, the peeling force remained almost unchanged, but cracks began to appear on the silicon wafer, resulting in a decrease in the integrity rate.

[0030] The staged pyrolysis is carried out in a four-stage rotary kiln, which is divided into a preheating section, a low-temperature section, a medium-temperature section, and a high-temperature section. Each section is separated by insulating partitions and equipped with pneumatic gates. The material moves slowly from the feed end to the discharge end through the continuous rotation of the kiln, passing through the four temperature zones sequentially. The residence time is controlled by the kiln's rotational speed and inclination angle. The rotary kiln is divided into four temperature zones: Preheating zone: 100-195℃, residence time 15 minutes; Low-temperature zone: 195-300℃, residence time 22 minutes; Medium-temperature zone: 300-480℃, residence time 20 minutes; High-temperature zone: 480-800℃, residence time 15 minutes. The heating rate between adjacent temperature zones is controlled at 5-15℃ / min, and the temperature fluctuation within each zone is ≤±5℃. The entire pyrolysis process is carried out in an inert atmosphere (nitrogen, oxygen content ≤0.1%).

[0031] During the system startup phase, the main heat source is provided by external gas or electric heating; after the pyrolysis gas is generated and stabilized, the system switches to pyrolysis gas combustion for energy supply, and the external auxiliary heat source is gradually shut off. During the staged pyrolysis process, a five-stage waste heat recovery system is implemented: Stage 1 (pyrolysis gas waste heat): The organic gases generated by pyrolysis are collected and sent to the combustion chamber for combustion, and the high-temperature heat energy generated serves as the main heat source for the rotary kiln; Stage 2 (high-temperature section waste heat, 480-800℃): The hot flue gas discharged from the high-temperature section heats the heat transfer oil through a heat pipe heat exchanger, and the heat transfer oil circulates to the jackets of the medium-temperature and low-temperature sections to provide supplementary heat; Stage 3 (medium-temperature section waste heat, 300-480℃): The heat transfer oil (approximately 250-300℃) at the outlet of the medium-temperature section jacket enters the low-temperature section heat exchanger; Stage 4 (low-temperature section waste heat, 195-300℃): The waste heat discharged from the low-temperature section heats the feed air of the preheating section through a gas-water heat exchanger (preheating the air to 80-120℃); Stage 5 (residual waste heat, <100℃): The low-temperature flue gas (<100℃) at the end of the system is recovered through a plate heat exchanger for use in plant heating or heating cleaning water. The preheating section is heated by electric heating during the system startup phase, and the temperature is maintained by the fourth stage of waste heat after normal operation, without the need for an additional heat source.

[0032] After pyrolysis, the solid products are cooled and then sent to a multi-stage sorting system: First, the mixture is sieved through a vibrating screen. The undersize material is a mixture of silicon powder and fine glass powder, while the oversize material is coarse particles, including silicon wafer fragments, coarse glass particles, and metal solder strips. Second, the oversize material is sent to a conductivity separator, which uses the difference in conductivity of different materials to separate metallic conductors such as copper and silver. Third, the remaining non-conductive materials from step b (mainly silicon wafer fragments and coarse glass particles) are sent to a density sorting tank, where the density difference is used to separate the silicon wafer fragments from the coarse glass particles.

[0033] The silicon powder obtained from screening in step a and the silicon wafer fragments obtained from sorting in step c are collected separately. After cooling the silicon wafer fragments to room temperature, they are reheated to 80-100℃ in a preheating furnace, or kept in the residual heat state after peeling, and then subjected to dry ice blasting at the above temperature. Dry ice blasting conditions: relative humidity ≤45%, blasting pressure 0.4-1.0 MPa (preferably 0.7 MPa), blasting distance 15-50 mm (preferably 30 mm), blasting angle 45°-60°, blasting time 20-50 seconds, preferably 30 seconds. After dry ice blasting, the removal rate of residual EVA on the silicon wafer surface can reach over 95%. The EVA residue on the glass surface after dry ice blasting is removed and can be directly recycled as glass raw material. The silicon wafer fragments and silicon powder after dry ice blasting are then acid-washed separately. Acid washing conditions: using nitric acid solution, concentration 10%-15%, acid washing temperature 25-60℃, preferably 40℃, acid washing time 10-30 minutes, preferably 20 minutes. Pickling removes metallic impurities such as silver and aluminum from the silicon surface. The pickled silicon powder and wafer fragments can be combined or separately subjected to wet displacement silver extraction: a reducing agent is added to the pickling solution to reduce the dissolved silver ions to metallic silver precipitate, which is then filtered to obtain high-purity silver powder. The remaining solid is high-purity silicon with a purity ≥99%.

[0034] The technologies not described in detail in this article are existing technologies.

[0035] While the specific embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and modifications or variations without creative effort are still within the protection scope of the present invention.

Claims

1. A method for the pyrolysis treatment and recycling of waste photovoltaic panels, characterized in that, Includes the following steps: Step 1: Physically disassemble the waste photovoltaic panels, removing the aluminum frames and junction boxes; Step 2: Low-temperature softening first peels off the fluorine-containing backplane, and then peels off the silicon wafer and glass to suppress the generation of hydrogen fluoride; Step 3: The remaining mixed material after stripping is subjected to staged pyrolysis in an inert atmosphere to recover waste heat in stages. Step four: sort and recycle the pyrolyzed materials.

2. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 1, characterized in that, The peeling in step two is carried out in an inert atmosphere at a temperature of 205°C for 7-8 minutes, with a peeling time of less than 5 minutes.

3. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 2, characterized in that, The fluorinated backsheet in step two includes a KPK backsheet or a TPT backsheet.

4. A method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 1 or 2, characterized in that, The inert atmosphere is at least one of nitrogen or carbon dioxide, and the oxygen content in the atmosphere is ≤0.5%.

5. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 1, characterized in that, In step two, the glass and silicon wafers obtained by peeling are cooled to 80-100°C and subjected to dry ice spray washing to obtain clean glass and silicon wafers.

6. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 5, characterized in that, The dry ice spraying is carried out in an environment with a relative humidity of ≤45%, with a spraying pressure of 0.4-1.0MPa, a spraying distance of 15-50 mm, a spraying angle of 45°-60°, and a spraying time of 20-50 seconds.

7. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 1, characterized in that, In step three, the mixed materials undergo staged pyrolysis in a multi-stage temperature-controlled rotary kiln or fluidized bed pyrolysis furnace. The temperature stages are connected by a material conveying device and equipped with temperature sensors and an automatic temperature control system. The staged pyrolysis is divided into four temperature stages: first, preheating stage, 100-195℃, time 15 minutes; second, low temperature stage, 195-300℃, time 22 minutes; third, medium temperature stage, 300-480℃, time 20 minutes. Fourth, the high-temperature section, 480-800℃, for 15 minutes; during the staged pyrolysis process, the heating rate between adjacent temperature sections is 5-15℃ / min, and the temperature fluctuation within each temperature section is ≤±5℃.

8. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 7, characterized in that, The waste heat in the cascade is divided into five levels according to temperature, including: waste heat from pyrolysis gas combustion, waste heat from the high-temperature section, waste heat from the medium-temperature section, waste heat from the low-temperature section, and residual waste heat. The waste heat generated by the combustion of pyrolysis gas enters the main combustion equipment to provide the main heat source; the waste heat from the high-temperature section is reused in the medium-temperature and low-temperature sections; the waste heat from the medium-temperature section is reused in the low-temperature section; the waste heat from the low-temperature section is reused in the preheating section. The preheating section is assisted by an external heat source during the start-up phase, and is maintained by the waste heat from the low-temperature section after normal operation; the residual waste heat enters the heat exchanger to provide hot water and heating.

9. The method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 1, characterized in that, Step four is divided into three steps: step a) vibrating sieve to separate silicon powder and fine glass powder; step b) sieve the conductors in the mixed material according to the difference in conductivity; and step c) density method to separate silicon wafer fragments and coarse glass particles.

10. A method for pyrolysis treatment and recycling of waste photovoltaic panels according to claim 5 or 9, characterized in that, The silicon wafers obtained by dry ice spraying in step two and the silicon wafer fragments in step c are respectively acid-washed. After acid washing, the silicon powder in step a is respectively or combined to replace the metallic silver by wet process and leave high-purity silicon. The acid used for acid washing is at least one of hydrochloric acid and nitric acid, the acid washing temperature is 25-60℃, and the time is 10-30 minutes.

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