Photovoltaic waste acid solution treatment system

Abstract

The utility model provides a photovoltaic waste acid liquid treatment system which comprises a reaction kettle, a filter, an evaporator, a fractionating tower and a condenser which are connected in sequence, the reaction kettle comprises a feeding opening and a liquid discharging opening; the filter is connected with the liquid outlet; the evaporator is connected with the filter and is used for evaporating the filtered solution to obtain mixed steam and evaporated residual liquid; the fractionating tower is connected with the upper part of the evaporator and is used for fractionating the mixed steam to obtain concentrated hydrofluoric acid and wastewater; and the wastewater is condensed by the condenser and then is sent to sewage treatment equipment. According to the system, photovoltaic waste acid is recycled into mixed acid containing hydrofluoric acid, the recycling process is simple, the recycled acid can be reused for an original photovoltaic etching production line and can also be used for etching treatment of ultrathin display screens, and the market capacity is large.

Description

Technical Field

[0001] This utility model relates to the field of waste liquid treatment technology, and in particular to a photovoltaic waste acid liquid treatment system. Background Technology

[0002] In the production process of silicon-based photovoltaic cells, high-purity cleaning is required multiple times using HF or mixed acids (HF+HCl or HF+HNO3). This includes cleaning after alkaline texturing, cleaning after boron or phosphorus diffusion, and cleaning of tools such as quartz boats. The waste acid after cleaning is sent to a wastewater treatment plant for harmless treatment. The concentration of HF in the pickling solution used by each production company varies depending on its needs, generally ranging from 5% to 22%. After cleaning, the waste acid components will increase with fluorosilicic acid and soluble metal salts, with the fluorosilicic acid content generally ranging from 0.82% to 5.96% and the metal salt content ≤0.01%.

[0003] Hydrogen fluoride (HF) has a molecular weight of 20.01 and is readily soluble in water and ethanol. Anhydrous hydrogen fluoride (AHF) is a colorless, transparent liquid under low temperature or pressure, with a boiling point of 19.4℃, a melting point of -83.37℃, and a density of 1.008 g / cm³. 3 (Water = 1). It readily volatilizes into a white fumes at room temperature and ambient temperature. It is chemically extremely reactive, reacting with alkalis, metals, oxides, and silicates. Hydrogen fluoride is the foundation of modern fluorine chemical industry and the most basic raw material for producing elemental fluorine, various fluorinated refrigerants, fluorine-containing new materials, inorganic fluoride salts, and various organic fluorides. Hydrogen fluoride and water can be mixed in any mass ratio to form hydrofluoric acid (HF).

[0004] Potassium fluorosilicate is an inorganic compound with the chemical formula K2SiF6. It is a white crystalline powder that is almost insoluble in cold water, insoluble in liquid ammonia and alcohol, but soluble in hydrochloric acid. It is mainly used for wood preservation, pesticides, ceramic enamel manufacturing, aluminum and magnesium smelting, and the manufacture of optical glasses such as potassium fluorochlorate and potassium glass. It is also used as a raw material for synthetic mica and welding electrodes.

[0005] CN116692874A discloses a method for recycling semiconductor waste acid. This method uses soluble potassium salts to precipitate fluorosilicic acid, followed by solid-liquid separation to remove the fluorosilicic acid. Urea is reacted with nitric acid to generate urea nitrate precipitate, and nitric acid is extracted through solid-liquid separation. The solution after nitric acid removal is then distilled to obtain a hydrofluoric acid solution. However, due to the high solubility of urea nitrate under acidic conditions, especially in hydrofluoric acid, the purity of the final hydrofluoric acid solution is limited.

[0006] Therefore, it is necessary to propose a photovoltaic waste acid treatment system to better recycle and utilize the effective resources of photovoltaic waste acid. Utility Model Content

[0007] This utility model proposes a photovoltaic waste acid treatment system.

[0008] The technical solution of this utility model is implemented as follows:

[0009] A method for treating photovoltaic waste acid includes the following steps:

[0010] S1 potassium fluorosilicate reaction

[0011] Potassium hydroxide is added to photovoltaic waste acid solution and reacted under stirring to obtain a reaction solution; then the reaction solution is introduced into a settling tank, and then filtered and washed to obtain potassium fluorosilicate filter cake and mixed acid mother liquor; the photovoltaic waste acid solution is waste acid solution containing hydrofluoric acid and nitric acid from photovoltaic production line.

[0012] S2 mother liquor evaporation

[0013] The mixed acid mother liquor is evaporated by vacuum evaporation to obtain mixed steam and evaporation residue; the KNO3 or KCl content in the evaporation residue is controlled to be higher than 10% and the potassium fluorosilicate content is not higher than 5%; the evaporation residue is cooled to room temperature and then returned to the potassium fluorosilicate reaction step.

[0014] S3 fractionation and concentration

[0015] The mixed steam is fractionated to control the HF content of the overhead condensate to ≤1%, while the bottom of the column is a concentrated mixed acid with an HF content ≥15%.

[0016] In some embodiments, the molar amount of potassium hydroxide added is twice the molar amount of fluorosilicic acid in the original waste acid; the reaction is carried out at room temperature and pressure.

[0017] In some embodiments, the amount of evaporation residue added is determined based on the concentration of fluorosilicic acid and the quantity of waste acid in the photovoltaic waste acid solution.

[0018] The mixed steam consists of HF and HNO3 or HCl and water evaporated from the mixed acid solution. The evaporated mixed steam is then sent to a fractionation and concentration process. The evaporation pressure is ≤-0.085MPa, and the evaporation temperature is 58℃~70℃.

[0019] In some embodiments, the fractionation tower operates at a pressure ≤ -0.09 MPa and a temperature of 55℃~65℃ during the fractionation process.

[0020] A system for treating photovoltaic waste acid includes: a reaction vessel, a filter, an evaporator, a fractionation tower, and a condenser connected in sequence.

[0021] The reactor includes a feeding port and a drain port. Photovoltaic waste liquid and potassium hydroxide are successively fed into the feeding port. After thorough stirring and reaction, the resulting reaction liquid is discharged from the drain port.

[0022] The filter is connected to the drain port to filter the reaction solution and separate potassium fluorosilicate precipitate and filtrate solution.

[0023] The evaporator is connected to the filter to evaporate the filtered solution, obtaining mixed vapor and evaporation residue;

[0024] The fractionation tower is connected to the upper part of the evaporator to fractionate the mixed steam to obtain concentrated hydrofluoric acid and wastewater;

[0025] The wastewater is condensed by the condenser and then sent to the sewage treatment equipment.

[0026] In some embodiments, a filter press is also included downstream of the filter for drying and pressing the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake.

[0027] In some embodiments, the evaporator and the reaction vessel are connected by a pipeline, and the residual evaporation liquid is refluxed into the reaction vessel.

[0028] Compared with the prior art, this utility model has the following advantages:

[0029] (1) The system has a reasonable layout and compact structure, which facilitates industrial promotion and application.

[0030] (2) This system recovers photovoltaic waste acid into mixed acid containing hydrofluoric acid. The recovery process is simple. The recovered acid can not only be reused in the original photovoltaic etching production line, but also used for etching treatment of ultra-thin display screens. The market capacity is large.

[0031] (3) Electronic grade potassium hydroxide is used as the potassium source, and the recovered mixed acid solution can be reused in the photovoltaic cell production line. The ultra-thin glass of the display panel is a major trend at present. The main formula of the etching treatment acid solution for ultra-thin display screens is a mixed acid solution of hydrofluoric acid and nitric acid (or hydrochloric acid). Ordinary reagent grade potassium hydroxide is used to recover the photovoltaic fluorine waste acid into a mixed acid containing hydrofluoric acid, which can be used for the etching treatment of ultra-thin display screens. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Fig. 1 This is a diagram illustrating the process of treating photovoltaic waste acid liquid according to this utility model.

[0034] Fig. 2 This is a schematic diagram of the photovoltaic waste acid treatment system in Example 1;

[0035] in:

[0036] 10 reactor, 20 filter, 30 evaporator, 40 distillation tower, 50 condenser, 60 filter press. Detailed Implementation

[0037] The technical solutions in the embodiments of this utility model will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0038] Example 1

[0039] Reference Figs. 1-2 As shown, a system for treating photovoltaic waste acid includes: a reaction vessel 10, a filter 20, an evaporator 30, a fractionation tower 40, and a condenser 50 connected in sequence. The reaction vessel 10 includes a feed port and a drain port. Photovoltaic waste liquid and potassium hydroxide are successively added through the feed port. After thorough stirring and reaction, the resulting reaction solution is discharged through the drain port. The filter 20 is connected to the drain port to filter the reaction solution and separate potassium fluorosilicate precipitate and the filtered solution. The evaporator 30 is connected to the filter 20 to evaporate the filtered solution, obtaining mixed steam and evaporation residue.

[0040] Fractionating tower 40 is connected to the upper part of evaporator 30 to fractionate the mixed steam to obtain concentrated hydrofluoric acid and wastewater. The wastewater is then condensed by condenser 50 and sent to wastewater treatment equipment.

[0041] This utility model also includes a filter press 60, located after the filter 20, for drying and pressing the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake.

[0042] In this invention, the evaporator 30 and the reaction vessel 10 are connected by a pipeline, and the residual liquid from evaporation is refluxed back into the reaction vessel 10.

[0043] The specific process is as follows:

[0044] Photovoltaic waste liquid and potassium hydroxide are added sequentially through the inlet of reactor 10 and reacted under stirring. The reaction liquid is introduced into filter 20, and then filtered and washed to separate potassium fluorosilicate precipitate and filtrate solution. The potassium fluorosilicate precipitate is then filtered through filter press 60 to obtain potassium fluorosilicate filter cake.

[0045] The filtered solution enters the evaporator 30 for evaporation, yielding mixed steam and evaporation residue. The fractionation tower 40 is connected to the upper part of the evaporator 30, which can fractionate the mixed steam to obtain concentrated hydrofluoric acid and wastewater. The wastewater is condensed by the condenser 50 and then sent to the sewage treatment equipment, while the concentrated hydrofluoric acid is recovered and stored in a storage tank for later use.

[0046] Evaporator 30 is connected to reactor 10 via a pipeline, so that the residual liquid from evaporation can be refluxed back into reactor 10 for further processing.

[0047] Application Example 2

[0048] The waste acid solution used in this embodiment is a waste acid solution containing hydrofluoric acid and nitric acid from a photovoltaic production line. All other reagents used are commercially available. The composition of the photovoltaic waste acid solution is shown in Table 1. The system used is the system from Example 1.

[0049] Table 1 Composition of Raw Material Photovoltaic Waste Acid

[0050] .

[0051] A method for treating photovoltaic waste acid includes the following steps:

[0052] 1. At room temperature, add photovoltaic waste acid liquid to the potassium fluorosilicate reactor at a rate of 1000 kg / hr, start the stirrer, and when the reactor level reaches 50%, add 40% potassium hydroxide solution to the reactor continuously at a certain rate according to the concentration and flow rate of fluorosilicic acid in the photovoltaic waste acid liquid. After the reaction liquid reaches the overflow port, the reaction liquid overflows into the settling tank and settles naturally.

[0053] When the residual liquid tank of the evaporation system reaches the level that allows for continuous operation, the residual liquid feed into the potassium fluorosilicate reactor is increased, and the residual liquid transfer pump is started. After cooling, the residual liquid is pumped into the potassium fluorosilicate reactor at a certain flow rate. The transfer of potassium hydroxide is not affected by the residual liquid feed.

[0054] 2. Overflow the supernatant from the settling tank into the mother liquor tank. When the settling tank begins to overflow, turn on the centrifuge. Once the centrifuge is running normally, open the discharge valve at the bottom of the settling tank and introduce the potassium fluorosilicate slurry into the fully automatic centrifuge. The filter cake is washed with ultrapure water during the washing process (the washing time needs to be controlled to control the amount of washing water). The washing liquid is discharged into the mother liquor tank. The filter cake is packaged and sold.

[0055] 3. When the mother liquor tank reaches the level required for continuous operation of the evaporation system (after the potassium fluorosilicate centrifuge has been running for 8-10 hours), start the vacuum pump and open the condenser at the top of the distillation column; adjust the vacuum valve to control the pressure at the top of the column to ≤-0.09MPa;

[0056] 4. Pump the filtered mother liquor into the mother liquor evaporator at a certain flow rate. When the mother liquor level reaches 60% of the evaporator level, start the jacket heating steam to begin evaporating the mother liquor.

[0057] 5. When liquid appears in the top of the fractionation tower (introduced into the acidic wastewater collection tank and sent to the sewage treatment plant for treatment), slightly open the reflux valve. As the output flow rate increases, slowly open the reflux valve wider. Regularly analyze the HF content in the output acidic wastewater and control the HF content in the output acidic wastewater to ≤1%. When the HF content in the output wastewater stabilizes at a certain value below 1%, the reflux ratio is considered to have been adjusted properly.

[0058] 6. When the liquid level in the bottom of the fractionation tower rises to a certain height (controlled at around 60%), start to collect the recovered acid from the bottom of the tower. After cooling, it is introduced into the recovered acid collection tank. The opening degree of the regulating valve is controlled to keep the liquid level in the bottom of the tower at a certain stable position. The recovered mixed acid is sold or sent to the etching production line for acid preparation.

[0059] 7. When the liquid level in the evaporator reaches 80%, take a sample to analyze the composition of the residual liquid. Control the potassium fluorosilicate content in the residual liquid to be no higher than 5% and the potassium nitrate content to be no lower than 10%. Start adjusting the residual liquid discharge valve and introduce the residual liquid into the residual liquid tank after cooling. When the residual liquid tank reaches the point where it can operate stably, use a pump to pump the residual liquid into the potassium fluorosilicate reaction vessel.

[0060] 8. When the acquired waste acid is used up, stop the waste acid transfer pump, stop the potassium hydroxide feed pump, and stop the residual liquid transfer pump. Pump the used reaction liquid into a centrifuge for separation. When the mother liquor tank is empty, stop the mother liquor transfer pump, stop the evaporator heating steam, stop the vacuum pump, break the vacuum in the evaporation and fractionation system, and stop the condenser cooling water. Transfer the evaporator residual liquid to the residual liquid collection tank, and pump the bottom liquid of the fractionation tower into the recovery acid collection tank. Shutdown complete.

[0061] The logistics data and component analysis results after the experimental device ran continuously for 3 days are shown in Tables 2-6.

[0062] Table 2 Material Flow Data Table

[0063] .

[0064] Table 3 Composition of Potassium Fluorosilicate Filter Cake

[0065] .

[0066] Table 4 Composition of Evaporation Residue

[0067] .

[0068] Table 5. Composition and Recovery Rate of Recovered Acid

[0069] .

[0070] Table 6 Composition of Acidic Wastewater

[0071] .

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. A photovoltaic waste acid treatment system, characterized in that, include: The reactor, filter, evaporator, distillation column, and condenser are connected in sequence. The reactor includes a feed port and a drain port. Photovoltaic waste acid and potassium hydroxide are successively fed into the feed port. After thorough stirring and reaction, the resulting reaction solution is discharged from the drain port. The filter is connected to the drain port to filter the reaction solution and separate potassium fluorosilicate precipitate and filtrate solution. The evaporator is connected to the filter to evaporate the filtered solution, obtaining mixed vapor and evaporation residue; The fractionation tower is connected to the upper part of the evaporator to fractionate the mixed steam to obtain concentrated hydrofluoric acid and wastewater; The wastewater is condensed by the condenser and then sent to the sewage treatment equipment. It also includes a filter press, located downstream of the filter, for drying and pressing the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake; The evaporator and the reaction vessel are connected by a pipeline, and the residual liquid from the evaporation is refluxed back into the reaction vessel.

Images