Off-service photovoltaic module pyrolysis tail gas treatment method based on photocatalysis technology

Abstract

The invention belongs to the technical field of tail gas treatment, and relates to a tail gas treatment method for decommissioned photovoltaic module pyrolysis based on a photocatalysis technology, which comprises the following steps: heat treatment, photocatalysis treatment and alkaline solution treatment. The photovoltaic module main body is firstly placed in the vacuum pyrolyzing furnace for heat treatment, fluorine-containing gas is generated in the pyrolyzing process, then the fluorine-containing gas is pumped into the photocatalytic furnace for photocatalytic treatment, fluorohydrocarbon in the fluorine-containing gas is subjected to an oxidation-reduction reaction through photocatalytic treatment, CO2 gas, HF gas and water are generated, and the CO2 gas, the HF gas and the water are recycled. Finally, the CO2 gas and the HF gas subjected to photocatalysis treatment are filled into an alkaline solution, the CO2 gas and the HF gas are absorbed through the alkaline solution, treatment of the fluorine-containing gas is completed, the fluorine-containing gas generated in the high-temperature heat treatment process can be effectively treated through photocatalysis treatment, the fluorine-containing gas is prevented from being directly discharged into the atmosphere, and the fluorine-containing gas is prevented from being directly discharged into the atmosphere. Therefore, harm to human health and damage to the ecological environment are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of tail gas treatment, and relates to a tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology. Background Art

[0002] The photovoltaic industry is booming in my country. However, as the design life of photovoltaic modules approaches, my country will face the problem of decommissioning or abandoning a large number of photovoltaic modules. Photovoltaic modules contain a variety of recyclable materials, such as frames, glass, silicon wafers, silver aluminum, etc., and also contain EVA (ethylene-vinyl acetate copolymer). The polymer adhesive layer material of the photovoltaic module is encapsulated by EVA to achieve the bonding of glass, battery cells, welding strips and TPT / KPK backboards. When recycling, the valuable materials such as frames, glass, silicon wafers, silver aluminum, etc. need to be separated from EVA and TPT / KPK backboards to achieve resource reuse.

[0003] At present, heat treatment is often used to separate photovoltaic modules. The EVA and TPT / KPK backplane in the photovoltaic modules are decomposed at a high temperature above 480°C to recover the glass, solder ribbon and silicon cells. The silicon cells are then etched to obtain pure silicon.

[0004] However, since the TPT / KPK backplane is a fluorine-containing material, toxic and harmful fluorine-containing gases will be generated during the high-temperature heat treatment process. The treatment of fluorine-containing gases is relatively difficult. If the fluorine-containing gases are directly discharged into the atmosphere, it will not only harm human health, but also damage the ecological environment. Summary of the invention

[0005] The purpose of the present invention is to provide a method for treating tail gas from pyrolysis of retired photovoltaic modules based on photocatalytic technology, which can effectively treat fluorine-containing gases generated during high-temperature heat treatment and avoid direct discharge of fluorine-containing gases into the atmosphere.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] A method for treating tail gas from pyrolysis of retired photovoltaic modules based on photocatalytic technology comprises the following steps:

[0008] The photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, and fluorine-containing gas is generated during the pyrolysis process;

[0009] The fluorine-containing gas is pumped into a photocatalytic furnace for photocatalytic treatment, and the photocatalytic treatment causes the fluorinated hydrocarbons in the fluorine-containing gas to undergo oxidation-reduction reactions to generate CO2 gas, HF gas and water;

[0010] The CO2 gas and HF gas after the photocatalytic treatment are filled into an alkaline solution, and the CO2 gas and HF gas are absorbed by the alkaline solution to complete the treatment of the fluorine-containing gas.

[0011] The present invention is also characterized in that:

[0012] When the photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, the vacuum degree of the vacuum pyrolysis furnace is 0.1Pa to 10Pa.

[0013] The heat treatment temperature is 480°C to 550°C, and the heat treatment time is 20min to 40min.

[0014] When the fluorine-containing gas is pumped into the photocatalytic furnace for photocatalytic treatment, ultraviolet light is emitted by an ultraviolet lamp to irradiate TiO2 for photocatalytic reaction.

[0015] The photocatalytic treatment time is 60 minutes to 90 minutes.

[0016] The TiO2 is arranged on the inner wall of the photocatalytic furnace, and the thickness of the TiO2 is 2 mm to 4 mm.

[0017] The power of the ultraviolet lamp is greater than 100W~150W, and the wavelength of the ultraviolet light is 280nm~315nm.

[0018] The chemical formula of the redox reaction of fluorinated hydrocarbons in the fluorine-containing gas caused by photocatalytic treatment is:

[0019] [-CF2-CF2-]n+O2 - +OH - →nCO2+nHF+nH2O.

[0020] The tail gas treatment method of the retired photovoltaic module pyrolysis based on photocatalytic technology of the present invention has the following advantages:

[0021] The photovoltaic module body is first placed in a vacuum pyrolysis furnace for heat treatment, and fluorine-containing gas is generated during the pyrolysis process. The fluorine-containing gas is then pumped into a photocatalytic furnace for photocatalytic treatment. The photocatalytic treatment causes the fluorinated hydrocarbons in the fluorine-containing gas to undergo oxidation-reduction reactions to generate CO2 gas, HF gas and water. Finally, the CO2 gas and HF gas after the photocatalytic treatment are filled into an alkaline solution, and the CO2 gas and HF gas are absorbed by the alkaline solution to complete the treatment of the fluorine-containing gas. The photocatalytic treatment can effectively treat the fluorine-containing gas generated during the high-temperature heat treatment process, thereby preventing the fluorine-containing gas from being directly discharged into the atmosphere, thereby avoiding harm to human health and damage to the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall process structure of the present invention;

[0023] Figure 2It is a schematic diagram of the connection structure between the photocatalytic furnace and the alkaline solution tank of the present invention.

[0024] Reference numerals:

[0025] 1. Photocatalytic furnace; 2. Alkaline solution tank. DETAILED DESCRIPTION

[0026] The technical solution in the present application will be described clearly and in detail below in conjunction with the accompanying drawings. Among them, in the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, such as A and / or B, which can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" refers to two or more than two. The following terms "first" and "second" are used for descriptive purposes only and cannot be understood as implying or suggesting relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0027] like Figure 1 As shown, the present invention provides a method for treating tail gas from pyrolysis of retired photovoltaic modules based on photocatalytic technology.

[0028] A method for treating tail gas from pyrolysis of retired photovoltaic modules based on photocatalytic technology comprises the following steps:

[0029] The photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, and fluorine-containing gas is generated during the pyrolysis process;

[0030] The fluorine-containing gas is pumped into the photocatalytic furnace 1 for photocatalytic treatment, and the fluorinated hydrocarbons in the fluorine-containing gas undergo oxidation-reduction reactions through the photocatalytic treatment to generate CO2 gas, HF gas and water;

[0031] The CO2 gas and HF gas after the photocatalytic treatment are filled into an alkaline solution, and the CO2 gas and HF gas are absorbed by the alkaline solution to complete the treatment of the fluorine-containing gas.

[0032] In summary, when the photovoltaic module is heat-treated, the main body of the photovoltaic module is first placed in a vacuum pyrolysis furnace for heat treatment. Fluorine-containing gas is generated during the pyrolysis process, and the fluorine-containing gas is then pumped into the photocatalytic furnace 1 for photocatalytic treatment. The photocatalytic treatment causes the fluorinated hydrocarbons in the fluorine-containing gas to undergo oxidation-reduction reactions to generate CO2 gas, HF gas and water. Finally, the CO2 gas and HF gas after the photocatalytic treatment are filled into an alkaline solution, and the CO2 gas and HF gas are absorbed by the alkaline solution to complete the treatment of the fluorine-containing gas. The photocatalytic treatment can effectively treat the fluorine-containing gas generated during the high-temperature heat treatment process to avoid direct discharge of the fluorine-containing gas into the atmosphere, thereby avoiding harm to human health and damage to the ecological environment.

[0033] like Figure 1 As shown, when the photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, the vacuum degree of the vacuum pyrolysis furnace is 0.1Pa~10Pa, the heat treatment temperature is 480℃~550℃, and the heat treatment time is 20min~40min.

[0034] like Figure 2 As shown, when the fluorine-containing gas is pumped into the photocatalytic furnace for photocatalytic treatment, an ultraviolet lamp is used to emit ultraviolet rays to irradiate TiO2 for photocatalytic reaction. The photocatalytic treatment time is 60min to 90min. TiO2 is arranged on the inner wall of the photocatalytic furnace. The thickness of TiO2 is 2mm to 4mm. The power of the ultraviolet lamp is greater than 100W to 150W, and the wavelength of the ultraviolet rays is 280nm to 315nm.

[0035] Specifically, the fluorine-containing gas generated by the heat treatment is pumped to the photocatalytic furnace 1. The wavelength of the ultraviolet light in the photocatalytic furnace 1 is 280nm~315nm (medium frequency ultraviolet / medium wave ultraviolet), and the photon energy is 3.94eV~4.43eV, which can fully excite the electron transition of TiO2 (TiO2 band gap width 3.0eV~3.2eV), and can generate electron-holes. The power of the ultraviolet lamp is set to more than 100W, and a layer of TiO2 with a thickness of 2mm~4mm is coated on the inner wall of the catalytic furnace. The air H2O and O2 in the photocatalytic furnace 1 will generate a large number of active oxygen groups (O2 - OH - These highly active groups oxidize and decompose the fluorine-containing gas (HF gas and fluorinated hydrocarbon gas). The redox reaction time in the photocatalytic furnace is 60min to 90min to ensure complete reaction.

[0036] The wavelength of ultraviolet light in the photocatalytic furnace 1 is 280nm to 315nm. The principle of photocatalysis is to use ultraviolet light to irradiate semiconductor materials, such as TiO2, to generate electron and hole pairs, and then initiate redox reactions. When ultraviolet light irradiates the photocatalyst, if the energy of the photon is greater than or equal to the energy gap of the catalyst, the electrons in the valence band will be excited to the conduction band, leaving holes. These electrons and holes can participate in the redox reaction to generate active oxygen groups with strong oxidizing ability. These groups can react with fluorocarbons (-CF2-CF2-) substances to oxidize and reduce them into CO2, HF and H2O. The chemical formula of the redox reaction is:

[0037] [-CF2-CF2-]n+O2 - +OH - →nCO2+nHF+nH2O.

[0038] like Figure 2 As shown, the alkaline solution is stored in the alkaline solution tank 2, the photocatalytic furnace 1 is connected to the alkaline solution tank 2, and the CO2 gas and HF gas after photocatalytic treatment are absorbed by the alkaline solution in the alkaline solution tank 2.

[0039] Example 1

[0040] When performing thermal treatment on retired PV panels, the details are as follows:

[0041] 1) Remove the aluminum frame and junction box from the retired PV modules (size 991mm×1.650mm).

[0042] 2) The main body of the photovoltaic module is placed in a vacuum pyrolysis furnace with a vacuum degree of 0.1 Pa. The pyrolysis furnace is heated to 450°C for 40 minutes and then cooled to room temperature.

[0043] 3) The air pump draws the fluorine-containing gas inside the pyrolysis furnace into the photocatalytic furnace 1 for treatment. An ultraviolet lamp that can emit 280nm to 315nm ultraviolet light is selected, with a power of 150W and a tail gas treatment time of 70min.

[0044] 4) The CO2 gas and HF gas generated after the photocatalytic treatment are filled into the alkaline solution tank 2 to absorb and treat the CO2 gas and HF gas.

[0045] 5) The solder strips and battery fragments are then separated by chemical-metallurgical processes to obtain silicon and metals with higher purity.

[0046] Example 2

[0047] The difference from Example 1 is that the photovoltaic module body is placed in a vacuum pyrolysis furnace, the pyrolysis furnace is heated to 500° C., the pyrolysis time is 30 minutes, and then the temperature is cooled to room temperature.

[0048] Example 3

[0049] The difference from Example 1 is that the photovoltaic module body is placed in a vacuum pyrolysis furnace, the pyrolysis furnace is heated to 580° C., the pyrolysis time is 30 minutes, and then the temperature is cooled to room temperature.

[0050] Example 4

[0051] The difference from Example 2 is that the air pump draws the tail gas inside the pyrolysis furnace into the photocatalytic furnace 1 for treatment, and an ultraviolet lamp that can emit 280nm to 315nm ultraviolet light is selected, with a power of 80W and a tail gas treatment time of 70min.

[0052] Example 5

[0053] The difference from Example 4 is that the air pump draws the tail gas inside the pyrolysis furnace into the photocatalytic furnace 1 for treatment, and an ultraviolet lamp that can emit 280nm to 315nm ultraviolet light is selected, with a power of 180W and a tail gas treatment time of 40min.

[0054] Example 6

[0055] The difference from Example 1 is that the fluorine-containing gas is treated by using the existing technology, and the fluorine-containing gas is directly introduced into the alkaline solution for treatment.

[0056] The content of fluoride in the pyrolysis gas after treatment in Examples 1 to 6 was detected using a high-resolution mass spectrometer and a gas chromatograph, as shown in Table 1 below.

[0057] Table 1 Parameters and treatment effects of various embodiments

[0058]

[0059] During the vacuum pyrolysis of waste photovoltaic modules, EVA film and TPT / KPK backboard decompose at temperatures above 450°C and decompose into fluorinated hydrocarbon gas and other olefinic substances. The weight of EVA and TPT / KPK backboard in retired photovoltaic modules accounts for about 9.6% of the total weight of the modules. Therefore, the greater the weight loss ratio of the modules after pyrolysis, the more complete the pyrolysis of EVA and backboard is, and the more conducive to the clean recovery of glass and solar cells. The tail gas after pyrolysis is mainly hydrogen fluoride and carbon dioxide gas after photocatalytic decomposition, and then the fluorine-containing tail gas can be treated by passing through an alkaline solution tank. This patent can treat fluorine-containing gas to 10mg / m 3 the following.

[0060] As can be seen from Table 1, the pyrolysis temperature of Example 1 is 450°C, which is lower than the 480°C of this patent. Even after 40 minutes of treatment, a large amount of oily substances are found to be attached to the surfaces of the glass and the battery cells, and the thermal weight loss ratio of the components is low, indicating that the EVA and the backplane are poorly decomposed and not completely decomposed into gaseous substances. The process parameters of Example 2 are within the scope of this patent, and the treatment results are the best. The pyrolysis temperature of Example 3 is 580°C, which exceeds the upper limit of 550°C in the scope of this patent, causing the entire piece of glass to deform and shatter severely, resulting in a decrease in the value of the glass and a decrease in the recycling value. Example 4 is based on the optimal process parameters of Example 2, but changes the power of the UV lamp to 80W, which is also lower than the 100W power setting of the UV lamp in this patent, resulting in a fluorine content of 15.76 mg / m 3 , more than 10mg / m 3 Example 5 is based on Example 4, but the power of the UV lamp is changed to 180W, and the time is shortened to 40min, and the fluoride content reaches 10.55mg / m 3 , there is a risk of not meeting the exhaust gas standards, and the 180W ultraviolet lamp has a large radiation, which causes losses to the operator and surrounding personnel. Example 6 uses the existing technology to treat fluorine-containing gas, and the treatment effect is the worst.

[0061] In summary, the present invention uses low-cost photocatalytic treatment of fluorine-containing gas, which can treat more than 90% of fluorine-containing gas and reduce the fluorine-containing gas content to 10 mg / m 3 Below, the use of photocatalytic treatment technology can solve the "bottleneck" problem of the current pyrolysis technology of waste photovoltaic modules that is difficult to treat exhaust gas, and further promote the application of pyrolysis technology of waste photovoltaic modules; the photocatalytic technology used is easy to operate and low cost.

[0062] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A method for treating tail gas from pyrolysis of retired photovoltaic modules based on photocatalytic technology, characterized in that: The following steps are involved: The photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, and fluorine-containing gas is generated during the pyrolysis process; The fluorine-containing gas is pumped into a photocatalytic furnace for photocatalytic treatment, and the photocatalytic treatment causes the fluorinated hydrocarbons in the fluorine-containing gas to undergo oxidation-reduction reactions to generate CO2 gas, HF gas and water; The CO2 gas and HF gas after the photocatalytic treatment are filled into an alkaline solution, and the CO2 gas and HF gas are absorbed by the alkaline solution to complete the treatment of the fluorine-containing gas.

2. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 1 is characterized in that: When the photovoltaic module body is placed in a vacuum pyrolysis furnace for heat treatment, the vacuum degree of the vacuum pyrolysis furnace is 0.1Pa to 10Pa.

3. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 2 is characterized in that: The temperature of the heat treatment is 480° C. to 550° C., and the time of the heat treatment is 20 min to 40 min.

4. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 1 is characterized in that: When the fluorine-containing gas is pumped into the photocatalytic furnace for photocatalytic treatment, ultraviolet light is emitted by an ultraviolet lamp to irradiate TiO2 for photocatalytic reaction.

5. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 4 is characterized in that: The photocatalytic treatment time is 60 minutes to 90 minutes.

6. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 4 is characterized in that: The TiO2 is arranged on the inner wall of the photocatalytic furnace, and the thickness of the TiO2 is 2 mm to 4 mm.

7. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 4 is characterized in that: The power of the ultraviolet lamp is greater than 100W-150W, and the wavelength of the ultraviolet rays is 280nm-315nm.

8. The tail gas treatment method of pyrolysis of retired photovoltaic modules based on photocatalytic technology according to claim 1 is characterized in that: The photocatalytic treatment causes the fluorinated hydrocarbons in the fluorine-containing gas to undergo an oxidation-reduction reaction with the chemical formula: [-CF2-CF2-] n +O2 - +OH - →nCO2+nHF+nH2O.

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