Silicon removal process and silicon removal system for photovoltaic concentrated alkali water

Abstract

The application discloses a photovoltaic concentrated alkali water desilication process and a desilication system, wherein concentrated alkali water and concentrated acid water are collected through a concentrated acid wastewater adjusting tank and a concentrated alkali water adjusting tank respectively, the concentrated alkali water and the concentrated acid water are sent into a neutralization tank to control the pH value to be 4-9, the water from the acid-alkali mixing tank is discharged into a gelatinization desilication tank, a silicon-containing gelatin solution is generated through stirring, the silicon-containing gelatin solution is sent into a dehydration device to be dehydrated, the silicon gel after dehydration is treated as solid waste, and the desilication filtrate is subjected to subsequent fluorine removal treatment. The application does not need to additionally increase other medicaments, more than 90% of silicon in the concentrated alkali water is removed, the purity of calcium fluoride in a fluorine removal system is improved, and sludge treatment cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a photovoltaic concentrated alkali water silicon removal process and treatment equipment. BACKGROUND

[0002] With the proposal of the sustainable development strategy, the use of non-renewable resources such as coal and oil is being gradually replaced by new energy. Solar photovoltaic energy, as a clean energy and relatively mature technology, is developing rapidly. In 2023, the newly installed capacity of photovoltaic energy reached 216.3GW, with a year-on-year growth of 147.5%. The cumulative installed capacity has reached 608.92GW, surpassing the installed capacity of hydropower and becoming the second largest power source after thermal power in terms of installed capacity. (Data source: China Photovoltaic Industry Association CPIA, 2024.2)

[0003] The photovoltaic industry mainly uses solar cells (single crystal silicon, polycrystalline silicon, etc.) for energy conversion. During the production of solar cells, a large amount of hydrofluoric acid and sodium hydroxide are used for etching, texturing, cleaning, etc. Therefore, it will produce acidic wastewater containing high concentration of fluorine ions and alkaline wastewater containing high concentration of silicon. Since the photovoltaic industry emission standard has higher requirements for fluorine and no clear emission index requirements for silicon, the removal of high-concentration fluorine-containing acidic wastewater is the focus of photovoltaic cell wastewater treatment. The usual method is to homogenize all wastewater and use chemical precipitation and coagulation sedimentation to remove fluorine in wastewater by generating calcium fluoride sludge. The reagents used are generally lime, calcium chloride and other soluble calcium salts. The alkaline wastewater containing silicon is usually homogenized and diluted in acidic wastewater as a pH regulator. This method can reduce the fluorine in the water to below the emission standard, but due to the presence of a large amount of silicon in the alkaline water, the calcium fluoride sludge produced by fluorine removal contains a large amount of silicon dioxide, not only increasing the sludge output, but also significantly reducing the purity of the sludge (calcium fluoride content is only 40%-65%), which seriously affects the quality and resource value of the sludge. The silicon concentration in concentrated alkali water is as high as 3000mg / L or more, and the total amount of silicon accounts for more than 80% of the total silicon content in the wastewater. Therefore, removing silicon from concentrated alkali water is of great significance to improve the purity of calcium fluoride sludge.

[0004] Currently, there is no specific method for treating concentrated alkaline wastewater from the photovoltaic industry to remove silicon. Chinese invention patent CN112158983A provides a highly efficient silicon and fluoride removal system and method for photovoltaic wastewater. The system proposes a process involving homogenization, flotation, primary silicon and fluoride removal, secondary fluoride removal, and subsequent treatment. After homogenizing the wastewater, flotation is used with the addition of flocculants to remove elemental and colloidal silicon. Then, calcium oxide is added to adjust the pH to alkalinity, followed by the addition of calcium chloride to generate calcium silicate precipitate for silicon removal. While this method can remove silicon from the water, the addition of calcium salts results in the removal of a large amount of fluoride during the silicon removal process. This leads to the formation of calcium silicate sludge containing a high amount of calcium fluoride, meaning the resulting sludge is still mixed sludge, and it also causes insufficient fluoride recovery in the subsequent secondary fluoride removal unit. Summary of the Invention

[0005] To overcome the above-mentioned defects, the present invention provides a silicon removal process and system for photovoltaic concentrated alkaline water, which can effectively remove silicon from concentrated alkaline water without the addition of additional reagents.

[0006] The technical solution adopted by this invention to solve its technical problem is: a silicon removal process using concentrated alkaline water from photovoltaic systems, characterized by the following specific steps:

[0007] Step 1: The concentrated alkaline water (silicon concentration range 2000-20000mg / L) and concentrated acid water discharged from the photovoltaic cell production line are sent into the acid-base mixing tank in a certain proportion for neutralization reaction, so that the pH of the mixed wastewater is controlled within the range of 4-9. During mixing, the ratio of concentrated acid water to concentrated alkaline water is controlled according to the pH of the mixed wastewater.

[0008] Step 2: Discharge the effluent from the acid-base mixing tank into the gelation and desiliconization tank. Stirring the acid-base mixture causes it to react and generate a silica-containing gel solution, causing the silica in the wastewater to precipitate out in the form of gel.

[0009] Step 3: The silica gel solution is sent to a dehydration device for dehydration. The dehydrated silica gel is treated as solid waste. The desiliconized filtrate is pumped and piped into a comprehensive wastewater equalization tank for subsequent defluorination treatment.

[0010] After the above treatment, more than 90% of the silicon in the desiliconization filtrate is removed, which greatly reduces the concentration of silicon ions in the filtrate. The wastewater after silicon removal then enters the defluorination system, and the purity of the calcium fluoride sludge is significantly improved. This not only increases the value of the calcium fluoride sludge but also reduces the sludge treatment cost.

[0011] As a further improvement of the present application, in step one, the concentrated alkali water discharged from the photovoltaic cell production line is first collected in a concentrated alkali water adjusting tank, and the concentrated acid water is collected in a concentrated acid wastewater adjusting tank, and then the concentrated alkali water in the concentrated alkali water adjusting tank and the concentrated acid water in the concentrated acid wastewater adjusting tank are sent into the acid-alkali mixing tank in proportion through the lifting pump. The separate collection of concentrated acid water and concentrated alkali water in advance can make the concentrated acid water and concentrated alkali water in the concentrated acid wastewater adjusting tank and the concentrated alkali water adjusting tank homogenized, which is beneficial to the subsequent uniform mixing.

[0012] As a further improvement of the present application, in step three, 10% to 60% of the dewatered silicon gel is sent into the concentrated alkali water adjusting tank, and the concentrated alkali water is mixed and dissolved with the refluxed silicon gel through the stirring device. The part of the dewatered silicon gel is refluxed to the front-end concentrated alkali water adjusting tank and dissolved by the concentrated alkali water, which can increase the silicon content in the concentrated alkali water adjusting tank. After the silicon concentration is increased, on the one hand, it helps to shorten the silicon gelation reaction time, and on the other hand, it enhances the neutral silicon removal effect of the alkali water with low silicon concentration, and expands the silicon concentration application range of the concentrated alkali water.

[0013] As a further improvement of the present application, the dissolution and adjustment time of the concentrated alkali water and the refluxed silicon gel in the concentrated alkali water adjusting tank is not less than 12h, which ensures the sufficient dissolution of the refluxed silicon gel and guarantees the subsequent gelation effect.

[0014] As a further improvement of the present application, in step three, the dewatering device adopts a stacked screw machine and a filter press, wherein part of the silicon gel-containing solution is dewatered by the stacked screw machine to form a silicon gel filter cake and a filtrate, the silicon gel filter cake is returned and dissolved in the front-end concentrated alkali water adjusting tank, and the filtrate enters the comprehensive wastewater adjusting tank for subsequent treatment; the remaining silicon gel-containing solution is sent into the filter press for pressure filtration dewatering, the silicon gel sludge cake after pressure filtration is transported out as solid waste for disposal, and the filtrate enters the comprehensive wastewater adjusting tank through the pump and pipeline for subsequent treatment.

[0015] The stacked screw machine and the filter press are respectively used for dewatering the silicon gel-containing solution, which facilitates the quantitative control of the silicon gel refluxed into the concentrated alkali water adjusting tank, the stacked screw machine facilitates the real-time discharge and reflux of the silicon gel filter cake, and the filter press can fully dewater the silicon gel, so that the automatic quantitative reflux of the silicon gel can be realized while reducing the water content of the solid waste, which is beneficial to the solid waste treatment. Of course, the dewatering device can also use one of the above two dewatering devices, and a part of the dewatered silicon gel is refluxed as solid waste for treatment, which is an equivalent replacement scheme easily thought of by those skilled in the art according to the present application and also belongs to the protection scope of the present patent.

[0016] As a further improvement of the present application, in step one, the mixing time of the concentrated alkali water and the concentrated acid water in the acid-alkali mixing tank is 10-60min, and the pH control is used to control the water inlet proportion of the concentrated acid water and the concentrated alkali water.

[0017] As a further improvement of the present application, the gelation reaction time of the mixed acid and alkali effluent into the gelation desilication tank is 0.5-24h.

[0018] A photovoltaic concentrated alkali water desilication system comprises an acid and alkali mixing tank, a gelation desilication tank, a dehydration device and a comprehensive waste water conditioning tank. The acid and alkali mixing tank is provided with a concentrated alkali water inlet and a concentrated acid water inlet. Concentrated alkali water and concentrated acid water can enter the acid and alkali mixing tank through the concentrated alkali water inlet and the concentrated acid water inlet respectively. The acid and alkali mixing tank is further provided with a pH detection device which can detect the pH value of the mixed waste water in the acid and alkali mixing tank in real time. The acid and alkali mixing tank is connected with the gelation desilication tank through a pipeline. The mixed waste water in the acid and alkali mixing tank can be discharged into the gelation desilication tank along the pipeline. The gelation desilication tank is provided with a stirrer which can stir the mixed waste water in the gelation desilication tank to form a gel state through acid and alkali neutralization reaction. The gelation desilication tank is connected with the dehydration device through a pipeline. The silicon-containing gel solution in the gelation desilication tank can be sent into the dehydration device along the pipeline. The dehydration device can dehydrate the silicon-containing gel solution. The drain outlet of the dehydration device is connected with the comprehensive waste water conditioning tank through a pipeline. The waste water discharged from the dehydration device can enter the comprehensive waste water conditioning tank along the pipeline for subsequent treatment.

[0019] The mixed waste water in the acid and alkali mixing tank can be sent into the gelation desilication tank through a lifting pump or discharged by gravity. Similarly, the silicon-containing gel solution in the gelation desilication tank can be sent into the dehydration device through a lifting pump or discharged by gravity.

[0020] As a further improvement of the present application, a concentrated acid waste water conditioning tank, a concentrated alkali water conditioning tank, a lifting pump, a silicon gel backflow conveying device and a control system are further provided. The concentrated alkali water conditioning tank is used to collect the concentrated alkali water discharged from the photovoltaic cell production line. The concentrated acid waste water conditioning tank is used to collect the concentrated acid water discharged from the photovoltaic cell production line. The concentrated alkali water conditioning tank and the concentrated acid waste water conditioning tank are respectively connected with the concentrated alkali water inlet and the concentrated acid water inlet of the acid and alkali mixing tank through pipelines. The concentrated acid water in the concentrated acid waste water conditioning tank and the concentrated alkali water in the concentrated alkali water conditioning tank can be respectively sent into the acid and alkali mixing tank through the respective lifting pumps. One end of the silicon gel backflow conveying device is connected with the discharge of the dehydration device. The other end of the silicon gel backflow conveying device is connected with the concentrated alkali water conditioning tank. The silicon gel backflow conveying device can convey the dehydrated silicon gel discharged from the dehydration device into the concentrated alkali water conditioning tank. The pH detection device in the acid and alkali mixing tank communicates with the control system to transmit the pH data in the acid and alkali mixing tank to the control system in real time. The control system controls the lifting pumps in the concentrated acid waste water conditioning tank and the concentrated alkali water conditioning tank to adjust the flow rate and start and stop. The control system also controls the start and stop of the silicon gel backflow conveying device.

[0021] Through setting the control system, real-time detection and data feedback are carried out by the pH detection device, so that the intelligent automatic control is realized for the wastewater desilication treatment, manual operation is not needed, the processing time of each step can be set through software in the control system, such as the mixing time of the concentrated acid water and the concentrated alkali water in the acid-alkali mixing tank, the mixing ratio, the gelation reaction time of the mixed wastewater in the gelation desilication tank, the stirring speed of the stirrer, the amount of the silicon gel backflow to the concentrated alkali water adjusting tank, etc., and the silicon concentration detection device can also be set in the concentrated alkali water adjusting tank to detect the silicon concentration in the concentrated alkali water in real time, so as to accurately control the silicon gel backflow amount and ensure the silicon content in the concentrated alkali water in the concentrated alkali water adjusting tank to ensure the subsequent efficient gelation reaction.

[0022] As a further improvement of the application, the dewatering device comprises a screw press and a filter press, the gelation desilication tank is communicated with the liquid inlet of the screw press and the filter press through pipelines respectively, two lifting pumps are arranged in the gelation desilication tank, the two lifting pumps in the gelation desilication tank pump the silicon-containing gel solution in the gelation desilication tank into the screw press and the filter press through pipelines respectively, one end of the silicon gel backflow conveying device is communicated with the discharge port of the screw press, the drain outlets of the screw press and the filter press are communicated with the comprehensive wastewater adjusting tank, and the control system controls the flow and start-stop of the two lifting pumps in the gelation desilication tank.

[0023] Two dewatering devices are adopted to respectively carry out targeted dewatering on the silicon-containing gel solution, and the silicon gel backflow amount can be controlled by controlling the flow of the two lifting pumps in the gelation desilication tank, and the control is convenient.

[0024] The beneficial effects of the application are as follows: the concentrated alkali water and the concentrated acid water discharged from the photovoltaic cell production line are mixed and stirred according to a proportion, so that silicon ions form gel materials, which are removed after dewatering, the silicon concentration in the concentrated alkali water treated by the process in the application is removed by more than 90%, the wastewater after desilication enters a defluorination system, the purity of calcium fluoride sludge is significantly improved, the value of the calcium fluoride sludge is improved, and the sludge treatment cost is reduced, the concentrated acid water generated in a photovoltaic enterprise can be directly used to remove silicon from the concentrated alkali water, waste is treated by waste, no additional other reagents are needed, the operation cost is reduced, the silicon content in the concentrated alkali water adjusting tank is increased by setting the silicon gel backflow to dissolve in the front-end concentrated alkali water adjusting tank in the process of the application, which helps to shorten the desilication gelation reaction time, on the other hand, the neutral desilication effect of the alkali water with a low silicon concentration is enhanced, the silicon concentration application range of the concentrated alkali water is expanded, and efficient desilication is realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The process flowchart of the application is shown in the figure. DETAILED DESCRIPTION

[0026] Example 1: The water quality and quantity of the wastewater from a certain photovoltaic industry are as follows:

[0027] The water quantity of the concentrated acid water is 350 t / d, the fluorine ion concentration is 4590-9964 mg / L, and the silicon ion concentration is 12-18 mg / L;

[0028] The water quantity of the concentrated alkali water is 100 t / d, the fluorine ion concentration is 15-22 mg / L, and the silicon ion concentration is 5400-6250 mg / L.

[0029] The photovoltaic concentrated alkali water silicon removal process of the application is used to treat the above wastewater, and the specific steps are as follows:

[0030] Step one: the above concentrated alkali water is collected in the conditioning tank for homogenization, and the concentrated alkali water is mixed and dissolved with the subsequent silicon gel reflux from the screw machine through the stirring device, and the conditioning time is 10 h; the concentrated acid water is collected in the concentrated acid water conditioning tank for homogenization;

[0031] Step two: the homogenized concentrated alkali water and concentrated acid water are sent to the acid-alkali mixing tank at a certain flow rate for neutralization reaction, the mixing time is 10 min, and the mixing pH is controlled in the range of 5.5-6.0;

[0032] Step three: the effluent from the acid-alkali mixing tank enters the gelation silicon removal tank, the reaction time is 2 h, and the silicon in the water is precipitated in the form of gel through stirring to form a gel-containing solution;

[0033] Step four: 10%-20% of the gel-containing solution generated in the gelation silicon removal tank is sent to the screw machine for dehydration to form a gel filter cake and a filtrate, the gel filter cake is refluxed and dissolved in the concentrated alkali water conditioning tank, the silicon concentration in the filtrate is reduced to below 80 mg / L, and the filtrate enters the comprehensive wastewater conditioning tank;

[0034] Step five: the remaining gel-containing solution enters the plate and frame filter press for mud-water separation, and the obtained silicon-containing sludge cake (dry sludge yield is 1.09-1.27 t / d) can be treated as solid waste; the silicon concentration in the filter press filtrate is below 80 mg / L, and the fluorine concentration is consistent with that of the raw water, which will enter the comprehensive wastewater conditioning tank;

[0035] Step six: the purity of the calcium fluoride sludge generated in the subsequent fluorine removal device in the comprehensive wastewater conditioning tank reaches 92.2%-94.3%.

[0036] Example 2: The water quality and quantity of the wastewater from a certain photovoltaic industry are as follows:

[0037] The water quantity of the concentrated acid water is 150 t / d, the fluorine ion concentration is 10286-15433 mg / L, and the silicon ion concentration is 9.3-21.8 mg / L;

[0038] The water quantity of the concentrated alkali water is 80 t / d, the fluorine ion concentration is 12.3-21.1 mg / L, and the silicon ion concentration is 2266-2844 mg / L.

[0039] The concentrated alkali water is treated by the silicon removal process of the photovoltaic concentrated alkali water, and the specific steps are as follows:

[0040] Step one: the concentrated alkali water is collected in the adjusting pool for homogenization, the concentrated alkali water is mixed and dissolved with the silicon gel refluxed from the stacked screw machine through the stirring device, and the adjusting time is 16 h; the concentrated acid water is collected in the concentrated acid water adjusting pool for homogenization;

[0041] Step two: the homogenized concentrated alkali water and concentrated acid water are sent into the acid-alkali mixing pool at a certain flow rate for neutralization reaction, the mixing time is 50 min, and the mixing pH is controlled in the range of 7.5-8.5;

[0042] Step three: the effluent of the acid-alkali mixing pool enters the gelation silicon removal pool, the reaction time is 10 h, the silicon in the water is precipitated in the form of gel by stirring to generate a gel-containing solution;

[0043] Step four: 50%-60% of the gel-containing solution generated in the gelation silicon removal pool is sent into the stacked screw machine for dehydration to form a gel filter cake and a filtrate, the gel filter cake is refluxed and dissolved in the concentrated alkali water adjusting pool, the silicon concentration in the filtrate is reduced to below 60 mg / L, and the filtrate enters the comprehensive waste water adjusting pool;

[0044] Step five: the remaining gel-containing solution enters the plate and frame filter press for mud-water separation, the obtained silicon-containing sludge cake (dry sludge yield is 0.37-0.45 t / d) can be treated as solid waste outsourcing; the pressure filtrate has a silicon concentration of below 60 mg / L and a fluorine concentration consistent with the original water, and enters the comprehensive waste water adjusting pool;

[0045] Step six: the waste water in the comprehensive waste water adjusting pool is treated by the calcium fluoride sludge generated by the subsequent fluorine removal device, and the purity of the calcium fluoride sludge reaches 94.5%-96.6%.

Claims

1. A process for the removal of silicon from photovoltaic concentrated alkali water, characterized in that: The specific steps are as follows: Step one: first, the concentrated alkali water discharged from the photovoltaic cell production line is collected in the concentrated alkali water adjusting tank, and the concentrated acid water is collected in the concentrated acid wastewater adjusting tank, then the concentrated alkali water in the concentrated alkali water adjusting tank and the concentrated acid water in the concentrated acid wastewater adjusting tank are sent into the acid-alkali mixing tank for neutralization reaction through the lifting pump, so that the pH of the mixed wastewater is controlled in the range of 4-9; Step two: the effluent of the acid-alkali mixing tank is discharged into the gelatinization silicon removal tank, and the acid-alkali mixed solution is reacted to generate a silicon-containing gel solution through stirring, so that the silicon in the wastewater is precipitated in the form of gel; Step three: the silicon-containing gel solution is sent into the dewatering device for dewatering, and the dewatering device adopts a stacking screw machine and a filter press, wherein part of the silicon-containing gel solution is dewatered by extrusion through the stacking screw machine to form a silicon gel filter cake and a filtrate, the silicon gel filter cake is returned and dissolved in the front-end concentrated alkali water adjusting tank, and the filtrate enters the comprehensive wastewater adjusting tank for subsequent fluorine removal treatment through a pump and a pipeline; the remaining silicon-containing gel solution is sent into the filter press for pressure filtration dewatering, and the silicon gel sludge cake after pressure filtration is transported out as solid waste for disposal, and the filtrate enters the comprehensive wastewater adjusting tank for subsequent treatment through a pump and a pipeline.

2. The process for the removal of silicon from photovoltaic concentrated alkali water according to claim 1, characterized in that: In step three, 10%-60% of the dewatered silicon gel is sent into the concentrated alkali water adjusting tank, and the concentrated alkali water and the refluxed silicon gel are uniformly mixed and dissolved through a stirring device.

3. The process for the removal of silicon from photovoltaic concentrated alkali water according to claim 2, characterized in that: The dissolution and adjustment time of the concentrated alkali water and the refluxed silicon gel in the concentrated alkali water adjusting tank is not less than 12h.

4. The photovoltaic concentrated alkali water desilication process of claim 1, wherein: In step one, the concentrated alkali water and the concentrated acid water are mixed in the acid-alkali mixing tank for 10-60min, and the proportion of the concentrated acid water and the concentrated alkali water is controlled by pH.

5. The photovoltaic concentrated alkali water desilication process of claim 1, wherein: The gelatinization reaction time of the effluent of the acid-alkali mixing tank in the gelatinization silicon removal tank is 0.5-24h.

6. A photovoltaic concentrated alkali water desilication system for use in the photovoltaic concentrated alkali water desilication process of claim 1, characterized by: The acid-alkali mixing tank, the gelatinization silicon removal tank, the dewatering device and the comprehensive wastewater adjusting tank are provided with a concentrated alkali water inlet and a concentrated acid water inlet, and the concentrated alkali water and the concentrated acid water can enter the acid-alkali mixing tank through the concentrated alkali water inlet and the concentrated acid water inlet respectively, a pH detection device is further arranged in the acid-alkali mixing tank, which can detect the pH value of the mixed wastewater in the acid-alkali mixing tank in real time, the acid-alkali mixing tank is communicated with the gelatinization silicon removal tank through a pipeline, and the mixed wastewater in the acid-alkali mixing tank can be discharged into the gelatinization silicon removal tank along the pipeline, a stirrer is arranged in the gelatinization silicon removal tank, which stirs the mixed wastewater in the gelatinization silicon removal tank to form a gel state through acid-alkali neutralization reaction, the gelatinization silicon removal tank is communicated with the dewatering device through a pipeline, and the silicon-containing gel solution in the gelatinization silicon removal tank can be sent into the dewatering device along the pipeline, the dewatering device can dewater the silicon-containing gel solution, and the drain outlet of the dewatering device is communicated with the comprehensive wastewater adjusting tank through a pipeline, and the wastewater discharged from the dewatering device enters the comprehensive wastewater adjusting tank along the pipeline for subsequent treatment.

7. The photovoltaic concentrated alkali water desilication system of claim 6, wherein: The application also provides a photovoltaic cell production line, which comprises the above-mentioned acid-alkali mixing device, a gelation and desilication device, a dehydration device, a comprehensive waste water adjusting tank and a control system, wherein the gelation and desilication device is connected with the acid-alkali mixing device through a pipeline, the dehydration device is connected with the gelation and desilication device through a pipeline, and the comprehensive waste water adjusting tank is connected with the dehydration device through a pipeline.

8. The photovoltaic concentrated alkali water desilication system of claim 7, wherein: The dehydration device comprises a screw stacker and a filter press, the gelation and desilication device is connected with the screw stacker and the filter press through pipelines, two lifting pumps are arranged in the gelation and desilication device, the two lifting pumps in the gelation and desilication device respectively pump the silicon-containing gel solution in the gelation and desilication device into the screw stacker and the filter press through pipelines, one end of the silicon gel backflow conveying device is connected with a discharge port of the screw stacker, and the discharge ports of the screw stacker and the filter press are connected with the comprehensive waste water adjusting tank, the control system controls the flow and start-stop of the two lifting pumps in the gelation and desilication device.

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