Photovoltaic concentrated acid wastewater multi-stage crystallization process and used multi-stage crystallization bed system

Abstract

The invention discloses a photovoltaic concentrated acid wastewater multi-stage crystallization process and a used multi-stage crystallization bed system, a plurality of groups of water outlet partition plates and water inlet partition plates which are arranged at intervals are mounted in a total tank body to form multi-stage crystallization bed reactors, concentrated acid wastewater is continuously pumped into a first-stage crystallization bed reactor, a lime solution is added into each stage of crystallization bed reactor, and the first-stage crystallization bed reactor and the second-stage crystallization bed reactor are continuously pumped into a second-stage crystallization bed reactor; the load of each stage of crystallization bed reactor is kept not higher than 200kg Ca (OH) 2 / m < 3 >. D, the concentrated acid wastewater sequentially enters each stage of crystallization bed reactor for neutralization crystallization reaction, crystals of each stage of crystallization bed reactor are regularly discharged into a crystal collection pool, and the crystals are packaged after being dehydrated, so that the concentrated acid wastewater is obtained. The effluent of the last stage of crystallization bed reactor enters a comprehensive adjusting tank for comprehensive treatment, so that the wastewater reaches the discharge standard and is discharged, according to the process, large-particle calcium fluoride crystal products with high purity and low water content can be obtained and can be directly subjected to resource sale, the sludge treatment cost is avoided, and the economic benefit is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a multi-stage crystallization process for photovoltaic concentrated acid wastewater and a multi-stage crystallization bed system used therein. Background Art

[0002] High-concentration hydrofluoric acid solution is used in the cleaning process of photovoltaic cell production technology. Therefore, some concentrated acid wastewater containing high concentration of hydrofluoric acid (fluorine concentration is 1%-5%) will be produced. This concentrated acid wastewater is a dangerous substance with strong acidity and corrosiveness. At the same time, the composition of this part of concentrated acid wastewater is relatively simple, and the main pollutant is high-concentration fluorine. The fluorine in the concentrated acid wastewater accounts for 60%-80% of the total fluorine in the photovoltaic wastewater. If the fluorine in the concentrated acid wastewater can be recovered separately to form a high-purity product, it can not only solve the fluorine pollution problem, but also create higher economic value.

[0003] At present, the treatment method of concentrated acid wastewater by photovoltaic enterprises is to collect concentrated acid wastewater and other wastewater (dilute acid wastewater, dilute alkali wastewater, concentrated alkali wastewater) separately and discharge them into a comprehensive regulating pool, and then remove fluorine by adjusting the pH of the comprehensive wastewater, adding calcium salts, defluorinating agents, etc. This treatment method can achieve fluorine standards, but it will form a large amount of low-purity fluorine-containing sludge (calcium fluoride content 40%-65%), which is difficult to recycle and is generally outsourced as solid waste, resulting in high sludge treatment costs.

[0004] Patent number CN221344327U provides a photovoltaic wastewater treatment system, which treats wastewater with a concentration of 300-1500 mg / L. It mentions that after adding liquid alkali to adjust the pH of high-concentration hydrofluoric acid waste liquid, calcium chloride is added to generate calcium fluoride precipitate. Although this method can achieve the purpose of fluorine removal and the output calcium fluoride has a high purity, it also has certain shortcomings: on the one hand, the process requires the addition of a large amount of liquid alkali, resulting in high operating costs; on the other hand, the generated precipitate calcium fluoride exists in the form of sludge, with small particle size and high water content, and cannot be directly sold as a resource; in addition, the addition of calcium chloride will produce a large amount of chloride ions, affecting the discharge of wastewater;

[0005] In order to reduce the impact of chloride ions on wastewater discharge, there is a process that uses lime to directly add concentrated acid wastewater for neutralization and fluorine removal. However, since fluorine mainly exists in the form of fluoride ions under neutral conditions, it will cause excessive supersaturation when combined with calcium ions and produce a large number of primary nuclei, making the calcium fluoride particles generated by the reaction very fine and existing in the form of turbidity or SS. Calcium fluoride needs to be recovered through flocculation and precipitation in the form of sludge with a higher water content. Summary of the invention

[0006] In order to overcome the above-mentioned defects, the present invention provides a photovoltaic concentrated acid wastewater multi-stage crystallization process and a multi-stage crystallization bed system used therein. The photovoltaic concentrated acid wastewater multi-stage crystallization process can improve the purity of calcium fluoride crystals and obtain large-particle calcium fluoride crystal products that can be directly recycled.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows: a multi-stage crystallization bed system, including a multi-stage series crystallization bed, a crystal collection pool, a crystal dehydration device and a comprehensive regulating pool, wherein the multi-stage series crystallization bed includes a total pool body, a water outlet baffle and a water inlet baffle, wherein the lower side of the side wall at one end of the total pool body is provided with a total water inlet, and the upper side of the side wall at the other end of the total pool body is provided with a total water outlet, a plurality of water outlet baffles and a plurality of water inlet baffles are alternately fixedly installed in the total pool body, and at least one group of water outlet baffles and water inlet baffles are fixedly installed in the total pool body. The total tank body is divided into a plurality of crystallization bed reactors, the bottom surface and two opposite side walls of the water outlet baffle are sealedly connected to the bottom surface and the opposite side walls of the total tank body, the two opposite side walls of the water inlet baffle are sealedly connected to the two opposite side walls of the total tank body, the bottom surface of the water inlet baffle and the bottom surface of the total tank body form the water inlet of the next stage crystallization bed reactor, the upper end height of the water outlet baffle is lower than the height of the total tank body and the upper end height of the water inlet baffle, so that the upper end of the water outlet baffle forms the water outlet of the overflow structure of the previous stage crystallization bed reactor, and the upper The height of the water outlet of the first-stage crystallization bed reactor is higher than the height of the water inlet of the next-stage crystallization bed reactor. A baffled water channel is formed between adjacent water outlet baffles and water inlet baffles to connect the water outlet of the upper-stage crystallization bed reactor and the water inlet of the next-stage crystallization bed reactor. The water outlet of the upper-stage crystallization bed reactor enters the next-stage crystallization bed reactor along the baffled water channel under the action of its own weight. The crystallization bed reactors at each stage are also provided with a reagent adding port for adding reagents, a crystal discharge port for discharging crystals and an agitator. The agitator can stir the concentrated acid wastewater and the reagent in the crystallization bed reactors at each stage. The crystal discharge ports of the crystallization bed reactors at each stage are connected to the crystal collection pool through pipelines, so that the crystals discharged from the crystal discharge ports of the crystallization bed reactors at each stage enter the crystal collection pool. The water-containing crystals collected in the crystal collection pool can be sent to a crystal dehydration device, and the crystal dehydration device can dehydrate the water-containing crystals. The total water outlet of the multi-stage series crystallization bed is connected to a comprehensive regulating pool, and the comprehensive regulating pool can treat the wastewater therein to meet the standards.

[0008] As a further improvement of the present invention, a concentrated acid collection tank and a concentrated acid water inlet pump are also provided. The concentrated acid collection tank is used to collect concentrated acid wastewater generated in the production process of photovoltaic panels. The concentrated acid collection tank is connected to the water inlet of the first-stage crystallization bed reactor of the multi-stage series crystallization bed through a water supply pipe. The concentrated acid water inlet pump can pump the concentrated acid wastewater in the concentrated acid collection tank into the first-stage crystallization bed reactor.

[0009] A multi-stage crystallization process for concentrated acid wastewater from photovoltaic power generation, wherein calcium fluoride crystals are loaded into the reaction chambers of each stage of crystallization bed reactor as an inducing agent, concentrated acid wastewater is pumped into the first stage crystallization bed reactor, lime solution is added to each stage of crystallization bed reactor through a reagent adding port, and the load of each stage of crystallization bed reactor is maintained at no more than 200 kg Ca(OH)2 / m 3 .d. The concentrated acid wastewater enters the crystal bed reactors of each level in sequence for neutralization and crystallization reaction. The crystal discharge ports of the crystal bed reactors of each level are opened regularly to discharge the crystals, and the crystals collected in the crystal collection pool are transported to the crystal dehydration equipment for dehydration treatment. The dehydrated crystals are packaged to form products that are directly sold externally. The effluent from the last stage of the crystal bed reactor enters the comprehensive regulating tank for comprehensive treatment so that the wastewater meets the discharge standards for discharge.

[0010] The method of multi-stage batch addition of lime solution is adopted. When adding lime solution in batches, the pH value of the wastewater is appropriately increased, and the free fluoride ions in the wastewater are gradually released to react with the calcium ions in the lime solution, thereby controlling the supersaturation of the reaction system within an appropriate range. At the same time, combined with induced crystallization, the number of new crystal nuclei is controlled to promote the growth of newly generated calcium fluoride on the surface of the seed crystal, thereby obtaining large-particle crystal products that can be directly recycled.

[0011] This process can increase or decrease the number of crystallization bed reactors according to the fluoride ion concentration in the treated wastewater. When the fluoride removal rate in the wastewater reaches more than 90%, the treated wastewater flows out of the multi-stage series crystallization bed into the comprehensive regulating tank for subsequent comprehensive treatment to achieve final compliance with emission standards.

[0012] The purity of crystals produced by each level of crystal bed reactor can reach more than 90%. The crystals are regularly discharged into the crystal collection pool. The crystal particle size is controlled within a designed range by controlling the crystal discharge time. The crystals are dehydrated (centrifuged or dried to make the water content of the crystals less than 10%) by the crystal dehydration equipment in the dehydration workshop before they can be formed into products for external sale.

[0013] As a further improvement of the present invention, the particle size of the calcium fluoride crystals used as the inducing agent is controlled at 0.05-0.2 mm, and calcium fluoride crystals are provided as seeds in the crystallization reactor, and the particle size is controlled by particle size screening before addition. After the system is running, the large crystals at the bottom of the reactor are regularly discharged to control the particle size of the crystals in the reaction within a certain range.

[0014] As a further improvement of the present invention, the concentration of the lime solution is 2.5-10%, and the lime solution is used to adjust the pH of the concentrated acid wastewater and provide a calcium source at the same time.

[0015] As a further improvement of the present invention, the time for the concentrated acid wastewater to enter the crystallization bed reactors at each level for neutralization reaction is not less than 10 minutes to ensure sufficient reaction.

[0016] As a further improvement of the present invention, the amount of lime solution added to each crystallization bed reactor is controlled to be no more than 200 kg Ca(OH)2 / m 3 .d shall prevail.

[0017] The invention has the beneficial effects that: the invention adopts a multi-stage batch adding method of lime solution, appropriately increases the pH value of wastewater when adding lime solution in batches, gradually releases free fluorine ions in wastewater to react with calcium ions in lime, and then controls the supersaturation of the reaction system to be within an appropriate range, and at the same time combines with the induced crystallization process to control the number of newly added crystal nuclei to promote the growth of newly generated calcium fluoride on the surface of the seed crystal, thereby obtaining a large-particle calcium fluoride crystal product that can be directly recycled. The invention adopts a baffled connection structure as a whole, so that the concentrated acid wastewater generated in photovoltaic production forms a multi-stage baffle, and is stirred by a stirrer, so that the wastewater and the reagent in each stage of the crystal bed reactor are completely in a uniformly mixed state, which can ensure that the concentrated acid wastewater and the lime solution fully react, and can prevent short-circuiting to the maximum extent, thereby ensuring full utilization of the reagent and improving the purity of the calcium fluoride crystal. The process of the invention can obtain a high-purity, low-water-content, large-particle calcium fluoride crystal product, which can be directly sold as a resource, eliminating the cost of sludge disposal, and achieving improved economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of the present invention;

[0019] Figure 2 It is the principle diagram of the multi-stage crystallization bed system of the present invention. DETAILED DESCRIPTION

[0020] In order to make the advantages, technical solutions and innovations of the present invention clearer, the present invention will be further described in detail below in conjunction with the above drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0021] Embodiment: A multi-stage crystallization bed system comprises a multi-stage series crystallization bed, a crystal collection pool 5, a crystal dehydration device 6 and a comprehensive regulating pool 7, wherein the multi-stage series crystallization bed comprises a total pool body 10, a water outlet baffle 11 and a water inlet baffle 12, wherein a total water inlet 1 is provided on the lower side of a side wall at one end of the total pool body 10, and a total water outlet 2 is provided on the upper side of a side wall at the other end of the total pool body 10, a plurality of water outlet baffles 11 and a plurality of water inlet baffles 12 are alternately fixedly installed in the total pool body 10, and at least one group of water outlet baffles 11 and water inlet baffles 12 connect the total pool body 10 to the total pool body 10. 0 is divided into a plurality of crystallization bed reactors, the bottom surface and two opposite side walls of the water outlet baffle 11 are sealedly connected to the bottom surface and the opposite side walls of the total tank body 10, the two opposite side walls of the water inlet baffle 12 are sealedly connected to the two opposite side walls of the total tank body 10, and the bottom surface of the water inlet baffle 12 and the bottom surface of the total tank body 10 form the water inlet of the next stage crystallization bed reactor, the upper end height of the water outlet baffle 11 is lower than the total tank body 10 and the upper end height of the water inlet baffle 12, so that the upper end of the water outlet baffle 11 forms the outlet of the overflow structure of the previous stage crystallization bed reactor The water outlet of the upper crystal bed reactor is higher than the water inlet of the lower crystal bed reactor. A baffle 11 and a baffle 12 are formed between the adjacent water outlet baffles 11 and the water inlet baffles 12 to connect the water outlet of the upper crystal bed reactor with the water inlet of the lower crystal bed reactor. The water outlet of the upper crystal bed reactor enters the lower crystal bed reactor along the baffle water channel under the action of its own weight. The crystal bed reactors at each level are also provided with a reagent adding port 4 for adding reagents, a crystal discharge port 3 for discharging crystals and a stirrer 13. The stirrer 13 The concentrated acid wastewater and the reagent in the crystal bed reactors at each level can be stirred. The crystal discharge ports 3 of the crystal bed reactors at each level are connected with the crystal collection pool 5 through pipelines, so that the crystals discharged from the crystal discharge ports 3 of the crystal bed reactors at each level enter the crystal collection pool 5. The water-containing crystals collected in the crystal collection pool 5 can be sent to the crystal dehydration equipment 6. The crystal dehydration equipment 6 can dehydrate the water-containing crystals. The total water outlet 2 of the multi-stage series crystallization bed is connected with the comprehensive regulating pool 7. The comprehensive regulating pool 7 can treat the wastewater therein to meet the standards.

[0022] A plurality of crystallization bed reactors are connected in sequence to form a multi-stage series crystallization bed. During treatment, concentrated acid wastewater only needs to be pumped into the first-stage crystallization bed reactor through the total water inlet 1 by the concentrated acid inlet pump 9. The concentrated acid inlet pump 9 continuously feeds concentrated acid wastewater into the first-stage crystallization bed reactor. The wastewater that has completed the reaction in the first-stage crystallization bed reactor overflows from the water outlet and enters the second-stage crystallization bed reactor for the next stage of neutralization and crystallization reaction. In this way, the concentrated acid wastewater can be continuously and quantitatively pumped into the first-stage crystallization bed reactor to realize that the concentrated acid wastewater sequentially enters the crystallization bed reactors of each stage, and is finally discharged from the total water outlet 2 at the other end of the total pool body 10. The concentrated acid wastewater sequentially enters the crystallization bed reactors of each stage, and the pH value of the wastewater in the crystallization bed reactors of each stage is appropriately increased by adding lime solution in batches at multiple stages, thereby gradually releasing the free fluoride ions in the wastewater, so that the free fluoride ions react with the lime. The calcium ions are fully reacted, and then the supersaturation of the reaction system is controlled to be within an appropriate range. At the same time, combined with induced crystallization, the number of newly added crystal nuclei is controlled to promote the growth of newly generated calcium fluoride on the surface of the seed crystal, so as to obtain a large-particle crystal product that can be directly recycled. The system adopts a baffle connection as a whole, and is accompanied by stirring by a stirrer 13, so that the wastewater and the reagent in each stage of the crystal bed reactor are completely in a uniformly mixed state, which can ensure that the concentrated acid wastewater and the lime solution fully react, which is conducive to the rapid crystallization of calcium fluoride, and can prevent short-circuiting to the maximum extent, thereby ensuring the full utilization of the lime reagent, improving the purity of the calcium fluoride crystals, and the consistency of the crystal particle size after crystallization. The system can obtain a large-particle crystal product with high purity and low water content, which can be directly sold as a resource, eliminating the cost of sludge disposal and achieving improved economic benefits.

[0023] A concentrated acid collection tank 8 and a concentrated acid water inlet pump 9 are also provided. The concentrated acid collection tank 8 is used to collect concentrated acid wastewater generated in the production process of photovoltaic panels. The hydrofluoric acid concentrated acid wastewater generated in the production process of solar photovoltaic panels is collected separately through the concentrated acid collection tank 8, so that it is homogenized in the concentrated acid collection tank 8, which is beneficial to ensure the purity of crystals produced by subsequent crystallization reactions. The concentrated acid collection tank 8 is connected to the water inlet 1 of the first-stage crystallization bed reactor of the multi-stage series crystallization bed through a water supply pipeline, and the concentrated acid water inlet pump 9 can pump the concentrated acid wastewater in the concentrated acid collection tank 8 into the first-stage crystallization bed reactor.

[0024] A multi-stage crystallization process for photovoltaic concentrated acid wastewater, the specific steps are as follows:

[0025] 1) Collect and homogenize the concentrated hydrofluoric acid wastewater generated in the production process of solar photovoltaic panels through a concentrated acid collection pool. At this time, the fluorine content in the concentrated acid wastewater is between 10,000 and 20,000 ppm; prepare a lime solution with a concentration of 6% to 10%, and the lime solution is a milky white liquid;

[0026] 2) Connecting 10 stages of crystallization bed reactors in series to form a multi-stage series crystallization bed, each stage of the crystallization bed reactor is provided with a water inlet, a reagent dosing port, a water outlet and a crystal discharge port, the water outlet of each stage of the crystallization bed reactor is connected to the water inlet of the next stage of the crystallization bed reactor, and the two adjacent stages of the crystallization bed reactors are connected in a baffled form;

[0027] 3) simultaneously filling calcium fluoride crystals as an inducing agent into each level of crystallization bed reactor, and the particle size of the calcium fluoride crystals is controlled to be 0.1-0.2 mm;

[0028] 4) The concentrated acid wastewater in the concentrated acid collection tank is pumped into the first stage crystallization bed reactor, and lime solution is added to the reaction chambers of each stage crystallization bed reactor through each reagent addition port. The lime load of the 1st to 5th stage crystallization bed reactors is controlled to be 50kgCa(OH)2 / m 3 .d, the lime load of the 6th-8th stage crystallization bed reactor is controlled to be 30kg Ca(OH)2 / m 3 .d, the lime load of the 9th-10th stage crystallization bed reactor is controlled to be 30kg Ca(OH)2 / m 3 .d. The effective residence time of concentrated acid wastewater in each stage of crystallization bed reactor is set to 15min. The concentrated acid wastewater passes through each stage of crystallization bed reactor in sequence for step-by-step crystallization reaction. The fluorine concentration of the effluent from the last stage of crystallization bed reactor is lower than 1000ppm. It enters the comprehensive regulating tank for comprehensive treatment. Finally, the wastewater meets the discharge standard for discharge.

[0029] 5) The crystals produced by each stage of the crystal bed reactor are discharged from their respective crystal discharge ports into the seed crystal collection pool, and then transferred to the dehydration equipment for dehydration. The water content of the dehydrated calcium fluoride crystals is controlled below 5%, and the purity of the calcium fluoride crystals can reach 90%-92%. They are directly sold after packaging.

Claims

1. A multi-stage crystallization bed system, characterized in that: The invention comprises a multi-stage series crystallization bed, a crystal collecting pool (5), a crystal dehydration device (6) and a comprehensive regulating pool (7), wherein the multi-stage series crystallization bed comprises a total pool body (10), a water outlet baffle (11) and a water inlet baffle (12), wherein a total water inlet (1) is provided on the lower side of a side wall at one end of the total pool body (10), and a total water outlet (2) is provided on the upper side of a side wall at the other end of the total pool body (10), and a plurality of water outlet baffles (11) and a plurality of water inlet baffles (12) are fixedly installed in the total pool body (10) at intervals and in alternating manners, and at least one group of water outlet baffles (11) and water inlet baffles (12) connect the total pool body (10) to the total pool body (10). ) is divided into a plurality of crystallization bed reactors, the bottom surface and two opposite side walls of the water outlet baffle (11) are sealedly connected to the bottom surface and the opposite side walls of the total tank body (10), the two opposite side walls of the water inlet baffle (12) are sealedly connected to the two opposite side walls of the total tank body (10), the bottom surface of the water inlet baffle (12) and the bottom surface of the total tank body (10) form a water inlet of the next stage crystallization bed reactor, the upper end height of the water outlet baffle (11) is lower than the height of the total tank body (10) and the upper end height of the water inlet baffle (12), so that the upper end of the water outlet baffle (11) forms an overflow structure of the previous stage crystallization bed reactor. The crystal bed reactor of the first stage has a water outlet, and the height of the water outlet of the first stage crystal bed reactor is higher than the height of the water inlet of the second stage crystal bed reactor. A baffled water channel is formed between the adjacent water outlet baffles (11) and the water inlet baffles (12) to connect the water outlet of the first stage crystal bed reactor and the water inlet of the second stage crystal bed reactor. The water outlet of the first stage crystal bed reactor enters the second stage crystal bed reactor along the baffled water channel under the action of its own weight. The crystal bed reactors of each stage are also provided with a reagent adding port (4) for adding reagents, a crystal discharge port (3) for discharging crystals, and a stirrer (13). The stirrer (13) can The concentrated acid wastewater and the reagent are stirred in the crystal bed reactors at each level. The crystal discharge ports (3) of the crystal bed reactors at each level are connected to the crystal collection pool (5) through pipelines, so that the crystals discharged from the crystal discharge ports (3) of the crystal bed reactors at each level enter the crystal collection pool (5). The water-containing crystals collected in the crystal collection pool (5) can be sent to the crystal dehydration device (6). The crystal dehydration device (6) can dehydrate the water-containing crystals. The total water outlet (2) of the multi-stage series crystal beds is connected to the comprehensive regulating pool (7). The comprehensive regulating pool (7) can treat the wastewater therein to meet the standards.

2. The multi-stage crystallization bed system according to claim 1, characterized in that: A concentrated acid collection tank (8) and a concentrated acid water inlet pump (9) are also provided. The concentrated acid collection tank (8) is used to collect concentrated acid wastewater generated in the production process of photovoltaic panels. The concentrated acid collection tank (8) is connected to the total water inlet (1) of the multi-stage series crystallization bed through a water supply pipeline. The concentrated acid water inlet pump (9) can pump the concentrated acid wastewater in the concentrated acid collection tank (8) into the first-stage crystallization bed reactor through the total water inlet.

3. A multi-stage crystallization process for photovoltaic concentrated acid wastewater using the multi-stage crystallization bed system described in claims 1-2, characterized in that: Calcium fluoride crystals are filled into the reaction chambers of the crystallization bed reactors at each stage as an inducing agent, concentrated acid wastewater is pumped into the first stage crystallization bed reactor, lime solution is added into the crystallization bed reactors at each stage through the reagent addition port (4), and the load of the crystallization bed reactors at each stage is maintained at no more than 200 kg Ca(OH)2 / m 3 .d, the concentrated acid wastewater enters the crystallization bed reactors of each level in sequence for neutralization and crystallization reaction, the crystal discharge ports (3) of the crystallization bed reactors of each level are opened at a fixed time to discharge the crystals, and the crystals collected in the crystal collection pool (5) are transported to the crystal dehydration equipment (6) for dehydration treatment, and the dehydrated crystals are packaged to form products that are directly sold to the outside, and the effluent from the last crystallization bed reactor enters the comprehensive regulating tank (7) for comprehensive treatment so that the wastewater meets the discharge standard for discharge.

4. The photovoltaic concentrated acid wastewater multi-stage crystallization process according to claim 3, characterized in that: The particle size of the calcium fluoride crystal used as an inducer is controlled at 0.05-0.2 mm.

5. The photovoltaic concentrated acid wastewater multi-stage crystallization process according to claim 3, characterized in that: The concentration of the lime solution is 2.5-10%.

6. The photovoltaic concentrated acid wastewater multi-stage crystallization process according to claim 3, characterized in that: The time for concentrated acid wastewater to enter the crystallization bed reactors at each level for neutralization reaction is not less than 10 minutes.

7. The photovoltaic concentrated acid wastewater multi-stage crystallization process according to claim 3, characterized in that: The dosage of lime solution in each crystallization bed reactor is controlled to be no more than 200kg Ca(OH)2 / m 3 .d shall prevail.

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