A method and device for preventing calcium scale formation on the surface of a waste sulfuric acid neutralization system device

Abstract

The present invention provides a method and device for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system. In the present invention, sodium sulfate and other soluble sulfates, lime emulsion to adjust the pH of the waste acid, and polyaluminum chloride solution are sequentially added to the effluent (waste acid) of the original first limestone neutralization process in the original waste acid treatment system. After the addition of the reagent, the effluent is still subjected to the second lime neutralization process according to the original process. 2+ 、SO4 2‑ The characteristic of easy formation of calcium sulfate is that it is regulated by chemical agents. The present invention only adds soluble sulfates such as sodium sulfate, regulates the pH of waste acid and uses polyaluminium chloride to directly reduce the Ca content in waste acid. 2+ concentration, while increasing SO4 in waste acid 2‑ The invention reduces the concentration of scale-forming components in the liquid phase of the waste acid by directly producing ettringite in the reaction tank. With only minor adjustments, this invention can prevent the formation of calcium scale on the surface of the waste sulfuric acid neutralization system and improve the operational stability of the waste acid treatment device.

Description

Technical Field

[0001] The present invention relates to the technical field of descaling, and in particular to a method and equipment for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device. Background Art

[0002] In the waste sulfuric acid neutralization system, the alkaline reagent limestone suspension and lime emulsion (or only lime emulsion) are required to neutralize the waste sulfuric acid. Calcium scale easily forms on the surface of the equipment, and the most serious areas are the surfaces of the second-stage lime neutralization reaction tank and subsequent equipment and pipelines. Due to the excessive calcium ions in the neutralization solution, calcium sulfate and complex salts of calcium sulfate and calcium oxide are easily precipitated, resulting in the formation of very thick calcium scale on the surface of the equipment. Generally, after three months of operation, the calcium scale on the surface of the neutralization reaction tank can reach 10cm. Within six months, the cross-sectional area of ​​the steel-lined PO pipeline that transports the neutralization solution is blocked by calcium scale by nearly half.

[0003] Because the formed calcium scale has a dense structure, even with the use of chemicals such as hydrochloric acid or ammonia water for cleaning, the treatment effect is not ideal. The commonly used method at present is to regularly use a mechanical scraper to remove the calcium scale on the surface of the neutralization reaction tank and the agitator; dismantle the pipeline and flush and flush the pipeline with high-pressure water in sections. The consequences of this method are: it is easy to damage the corrosion-resistant rubber lining of the tank body, the workload of dismantling and installing the pipeline is large, and the pipeline still scales quickly after flushing. Usually, all steel-lined PO composite pipes need to be replaced within two years.

[0004] To this end, it is urgent to develop a method to prevent the formation of calcium scale on the surface of the waste sulfuric acid neutralization system device, prevent the precipitation of calcium scale on the surface of the device, avoid the pipeline being blocked by calcium scale, and ensure the reliability of equipment operation. Summary of the Invention

[0005] In response to the above problems, the present invention provides a method and apparatus for preventing the formation of calcium scale on the surface of a waste sulfuric acid neutralization system device. The purpose is to solve the problem of calcium scale formation and difficulty in removal on the surface of the waste sulfuric acid neutralization system device. Based on the existing device and process flow, only minor adjustments are made to achieve the effect of preventing the formation of calcium scale on the surface of the waste sulfuric acid neutralization system device, thereby improving the operational stability of the waste acid treatment device.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is:

[0007] A method and device for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device, comprising the following steps: S1, discharging the waste acid that has undergone a first-stage neutralization reaction and solid-liquid sedimentation separation into a sulfate reaction tank, and subsequently adding lime emulsion and sodium sulfate solution into the sulfate reaction tank; S2, fully mixing the waste acid in step S1 through a pipeline and then flowing it into an aluminum salt reaction tank, and adding a polyaluminum chloride solution into the aluminum salt reaction tank; S3, controlling the waste acid in step S2 to flow into a second-stage neutralization reaction tank, adding lime emulsion again to adjust the pH, and subsequently controlling the waste acid to flow into a flocculation reaction tank; S4, adding sedimentation material into the flocculation reaction tank and fully mixing the waste acid to complete solid-liquid sedimentation separation.

[0008] Preferably, the concentration of lime emulsion added in step S1 is 10%, the concentration of sodium sulfate solution is 10% to 15%, and the amount of sodium sulfate added is 12 to 20 kg / m 3 .

[0009] Preferably, the concentration of the polyaluminium chloride solution in step S2 is 13%.

[0010] Preferably, the concentration of the lime emulsion added in step S3 is 10%, and the pH range of the waste acid is controlled to be 8-11.

[0011] Preferably, the sedimentation material in step S4 is a non-ionic polyacrylamide solution with a concentration of 1% to 5% and a dosage of 50 to 80 g / m 3 .

[0012] Preferably, the sedimentation material is added and mixed, and then reacted for 5 to 20 minutes before entering the second-stage thickener for sludge sedimentation.

[0013] A device for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device, comprising a suction device installed at the bottom of a reaction tank, and a spray device installed on the surface of a stirring shaft of a stirring device, wherein the suction device and the spray device are respectively connected to a circulation device via a conveying pipeline, a high-pressure nozzle extending toward the inner wall of the reaction tank is installed at the end of the spray device, and a lifting control device for controlling the vertical height of the spray device is also included.

[0014] Preferably, the suction device is arranged tangentially at the edge of the bottom of the reaction tank.

[0015] Preferably, the spraying device includes a mounting base fixed to the surface of the stirring shaft of the stirring equipment, and a support frame is fixed to the side wall of the mounting base for fixing the high-pressure nozzle.

[0016] The beneficial effects of the present invention are:

[0017] 1. Based on the original waste acid treatment process and equipment, only the treatment process and operating parameters were appropriately adjusted, which directly reduced the possibility of calcium sulfate scale formation on the surface of the treatment equipment (especially the second neutralization device and subsequent devices). More than two years of practice have shown that there has been no blockage of calcium sulfate scale in the pipelines and filter cloths, which has directly improved the operation cycle of the pipelines and filter cloths; the thickness of the accumulated mud layer on the weir and tank surface of the neutralization reaction tank, thickener has been reduced from the original 5cm to within 1cm, ensuring the waste liquid flux of the device operation.

[0018] 2. By adding sodium sulfate solution and polyaluminium chloride solution, very little calcium sulfate scale is formed on the surface of the neutralization reaction tank, neutralization liquid pipeline, thickener, supernatant pipeline and other devices. In recent years, there has been no pipeline blockage. The equipment can efficiently circulate the corresponding solutions, accelerate the efficiency of mixing different liquids in the waste acid, and improve the waste acid treatment efficiency. At the same time, it can also efficiently flush the inner wall of the reaction tank, discharge and collect the calcium scale in time, further reducing the amount of calcium scale on the surface of the waste acid neutralization system device and ensuring the stable operation of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the waste sulfuric acid neutralization system device of the present invention.

[0020] Figure 2 This is a schematic diagram of the device for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device according to the present invention.

[0021] In the figure: 1. First-stage neutralization reaction tank; 101. Waste liquid flow meter; 102. First pH meter; 103. Second pH meter; 104. Third pH meter; 2. First-stage thickener; 3. First underflow pump; 4. First-stage dehydrator; 5. Sulfate reaction tank; 6. Aluminum salt reaction tank; 7. Second-stage neutralization reaction tank; 8. Flocculation reaction tank; 9. Second-stage thickener; 10. Second underflow pump; 11. Second-stage dehydrator.

[0022] 100. Reaction tank; 200. Stirring device; 300. Suction device; 400. Spray device; 410. Mounting base; 420. Support frame; 430. High-pressure nozzle; 500. Lifting control device. DETAILED DESCRIPTION

[0023] Waste sulfuric acid is the dilute sulfuric acid discharged from the sulfuric acid production system, with a concentration of 0.5% to 15%. The waste acid is obtained after the first stage neutralization reaction and solid-liquid sedimentation separation.

[0024] The sulfate may be soluble sulfates such as sodium sulfate, ferric sulfate, ferrous sulfate, etc. The present invention uses sodium sulfate as an expression, but does not mean that other soluble sulfates are not contained.

[0025] The present invention will be further described below with reference to the accompanying drawings and examples.

[0026] Please refer to the attached Figure 1 A method for preventing calcium scale formation on the surface of a waste sulfuric acid neutralization system device, comprising the following steps:

[0027] 1) The waste acid after the first-stage neutralization reaction and solid-liquid sedimentation separation (specifically, the waste acid after the first-stage neutralization reaction in the first-stage neutralization reaction tank 1 and the sedimentation separation in the first-stage thickener 2, and containing the filtrate of the first-stage dehydrator 4) enters the sulfate reaction tank 5. At the inlet of the sulfate reaction tank 5, lime milk with a concentration of about 10% is added. At the outlet of the sulfate reaction tank 5, sodium sulfate solution (with a concentration of 10% to 15%) is added to the waste acid. A first pH meter 102 is used to control the amount of lime milk added to the sulfate reaction tank 5, and the pH of the waste acid on the outlet pipe of the sulfate reaction tank 5 is controlled to be 5 to 7 (preferably pH = 5.5 to 6.5). The amount of sodium sulfate added is determined by counting the waste liquid flowmeter 101. The amount of sodium sulfate added is 12 to 20 kg / m 3 , (preferably 16 kg / m 3 ), the spent acid is mixed through the pipeline and flows into the aluminum salt reaction tank 6;

[0028] 2) Add polyaluminium chloride solution (concentration of about 13%) into the aluminium salt reaction tank 6. The amount of addition is determined by the count of the waste liquid flow meter 101, which is equivalent to 0.15-0.30 kg / m of Al2O3. 3 , the preferred Al2O3 dosage is 0.21kg / m 3 ), control the pH value of the liquid outflow of the reaction tank to 4.5-6.0 (preferably 5.0-5.5), and use a second pH meter 103 to react for 30-60 minutes. The waste acid flows into the second-stage neutralization reaction tank 7. The purpose of this step is to combine the hydrolyzates of sulfate, calcium ions and aluminum ions in the liquid phase of the neutralized solution to form ettringite complex salt, as shown in chemical formula (1), and to migrate the scaling substances in the liquid phase to the gypsum solid phase, thereby directly reducing the concentration of scaling components in the liquid phase;

[0029]

[0030] 3) Lime emulsion (concentration of approximately 10%) is added to the second-stage neutralization reaction tank 7. A third pH meter 104 is used to control the pH of the waste acid to 8-11 (preferably 9.5-10). The reaction is continued for 30-60 minutes. The waste acid then enters the flocculation reaction tank 8. This step aims to neutralize small amounts of metal contaminants in the solution to form hydroxide precipitates, while also promoting the formation of precipitates from fluoride and calcium ions.

[0031] 4) Add nonionic polyacrylamide (PAM) solution (with a concentration of 1% to 5%) into the flocculation reaction tank 8, with a PAM dosage of 50 to 80 g / m 3 (Preferably 60g / m 3 ), react for 5 to 20 minutes, and then enter the second-stage thickener 9 for sludge sedimentation. The purpose of this step is to form dense particles of colloids and fine suspended matter in the waste liquid to facilitate sedimentation;

[0032] 5) In the second-stage thickener 9, the waste acid completes solid-liquid sedimentation separation. The waste liquid stays in the second-stage thickener 9 for 4 to 7 hours (preferably 5.5 to 6.0 hours). The clear liquid from the second-stage thickener 9 is discharged or processed, and the bottom flow is processed in the second-stage dehydrator 11 to obtain dihydrate gypsum.

[0033] This application study revealed that, previously, without the addition of sodium sulfate solution or polyaluminium chloride solution, calcium sulfate scale formed on the surfaces of the neutralisation reaction tank, neutralisation liquid pipeline, thickener, and supernatant liquid pipeline. This scale, particularly on the neutralisation liquid delivery pipeline, was frequently clogged. However, subsequent research and the addition of reagents have significantly reduced scale formation on these surfaces, and no pipeline blockages have occurred in recent years.

[0034] Please refer to the attached Figure 2 ; A device for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device, comprising a suction device 300 installed at the bottom of a reaction tank 100, and a spray device 400 installed on the surface of a stirring shaft of a stirring device 200. The suction device 300 and the spray device 400 are respectively connected to a circulation device through a conveying pipeline. The circulation device can control the circulation of the waste acid and the added solution in the reaction tank 100, accelerate the mixing efficiency of the waste acid and the added solvent, and shorten the time of the waste acid treatment process; and a high-pressure nozzle 430 extending toward the inner wall of the reaction tank 100 is installed at the end of the spray device 400, and also includes a lifting control device for controlling the vertical height of the spray device 400. 500; During the rotation of the stirring shaft of the stirring device 200, the injection device 400 can be driven to rotate synchronously, so that the high-pressure nozzle 430 at the end is in different positions, and high-pressure injection can be performed on different surfaces of the inner wall of the reaction tank 100 to remove the calcium scale formed on the inner wall surface of the reaction tank 100. The calcium scale falls to the bottom and is circulated and sucked into the circulation device by the suction device 300. The filtering device installed in the circulation device can collect this part of the calcium scale, which can further reduce the amount of calcium scale on the surface of the reaction tank 100. The calcium scale can be efficiently removed from the moment it is formed, which greatly reduces the amount of calcium scale on the surface of the waste acid neutralization system device and ensures the stable operation of the entire system.

[0035] In addition, the lifting control device 500 can control the linear movement of the injection device 400 in the vertical height direction, and the inner wall of the reaction tank 100 can be cleaned efficiently in all directions in combination with the rotation of the lifting control device 500; the lifting control device 500 here can be selected as a winch device driven by a traction rope, and for the continuously rotating lifting control device 500, a rotating seal can be installed at its rotating connection to ensure the normal circulation and transportation of waste acid and added solvent.

[0036] Specifically, the suction device 300 is arranged tangentially at the edge of the bottom of the reaction tank 100. The suction device 300 continuously sucks the liquid at the bottom, and can continuously extract the calcium scaling materials, thereby reducing the frequency and difficulty of cleaning the reaction tank 100 in the later stage. At the same time, the tangentially arranged suction device 300 can more efficiently and centrally absorb and collect the detached calcium scaling.

[0037] The injection device 400 here includes a mounting base 410 fixed to the surface of the stirring shaft of the stirring equipment 200. A support frame 420 is fixed to the side wall of the mounting base 410 for fixing the high-pressure nozzle 430. The high-pressure nozzle 430 can be supported by the support frame 420. The high-pressure nozzle 430 here is set tangentially at a certain angle, which can efficiently clean the inner wall of the reaction tank 100.

[0038] The device is suitable for installation in each reaction tank of the waste sulfuric acid neutralization system, can accelerate the efficiency of mixing different solutions with waste sulfuric acid, greatly shortens the time of waste sulfuric acid treatment, and is particularly suitable for installation in reaction tanks where more calcium scale is generated, such as when installed in the aluminum salt reaction tank 6, greatly reducing the accumulation of calcium scale, ensuring the stability of the overall waste sulfuric acid treatment system while reducing the burden of subsequent cleaning on operators.

[0039] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0040] Example 1

[0041] 1) After the first-stage limestone neutralization reaction, solid-liquid separation in the first-stage thickener 2, and underflow dehydration treatment, the waste acid enters the sulfate reaction tank 5. Lime milk is added to the waste acid inlet of the sulfate reaction tank 5. The first pH meter 102 is used to detect the waste acid pH on the waste acid pipeline and control the waste acid pH to 6.0±0.2. Sodium sulfate solution (concentration of 15%) is added to the outlet of the sulfate reaction tank 5. The waste acid flow rate is measured by the waste liquid flow meter 101 to determine the amount of sodium sulfate to be added. The amount of sodium sulfate used is 15 kg / m 3 , after mixing through the pipeline, the waste acid flows into the aluminum salt reaction tank 6;

[0042] 2) Add polyaluminium chloride solution (concentration of 13%) to the aluminium salt reaction tank 6. The dosage is determined by the count of the waste liquid flow meter 101, which is equivalent to 0.25kg / m3 of Al2O3. 3 , control the pH value of the effluent of the aluminum salt reaction tank 6 to 5.2±0.2, the residence time of the spent acid aluminum salt reaction tank 6 is 60min, and then flows into the second-stage neutralization reaction tank 7;

[0043] 3) Lime emulsion is added at the inlet of the second-stage neutralization reaction tank 7 to raise the pH of the waste acid to 9.5±0.2. The waste acid stays in the second-stage neutralization reaction tank 7 for 45 minutes, and then enters the flocculation reaction tank 8;

[0044] 4) At the inlet of the flocculation reaction tank 8, add nonionic polyacrylamide (PAM) solution (with a concentration of 5%) to the waste acid, and calculate the waste acid flow rate according to the waste liquid flow meter 101. The PAM dosage is 70g / m 3 The flocculation reaction lasts for 12 minutes, and the sludge enters the second-stage thickener 9 for sedimentation. The bottom flow is pumped into the second-stage dehydrator 11 for dehydration treatment, and the supernatant of the second-stage dehydrator 11 is directly discharged.

[0045] 5) The waste acid stays in the second-stage thickener 9 for 6 hours. The clear liquid from the thickener is discharged or processed. The bottom flow is processed by the second-stage dehydrator 11. The filter cake is dihydrate gypsum. The filtrate is returned to the second-stage neutralization reaction tank 7.

[0046] 6) Application effect

[0047] After operating for 6 months according to the above process parameters, the mesh of the filter cloth of the second-stage dehydrator 11 was checked to be still clearly visible, with no mud residue blocking the surface; no blockage or obstruction occurred in the pipelines and valves; and no scaling occurred in the pipelines through which the waste acid flowed.

[0048] Example 2

[0049] 1) After the first-stage limestone neutralization reaction, solid-liquid separation in the first-stage thickener 2, and underflow dehydration treatment, the waste acid enters the sulfate reaction tank 5. Lime milk is added to the waste acid inlet of the sulfate reaction tank 5. The first pH meter 102 is used to detect the waste acid pH on the waste acid pipeline and control the waste acid pH to 5.2±0.2. Sodium sulfate solution (concentration of 15%) is added to the outlet of the sulfate reaction tank 5. The waste acid flow rate is measured by the waste liquid flow meter 101 to determine the amount of sodium sulfate to be added. The amount of sodium sulfate used is 13 kg / m 3 , after mixing through the pipeline, the waste acid flows into the aluminum salt reaction tank 6;

[0050] 2) Add polyaluminium chloride solution (concentration of 13%) to the aluminium salt reaction tank 6. The amount of addition is determined by the count of the waste liquid flow meter 101, which is equivalent to 0.16 kg / m Al2O3 addition. 3, control the pH value of the effluent of the aluminum salt reaction tank 6 to 4.7±0.2, the residence time of the spent acid aluminum salt reaction tank 6 is 45min, and then flows into the second-stage neutralization reaction tank 7;

[0051] 3) Lime emulsion is added at the inlet of the second-stage neutralization reaction tank 7 to raise the pH of the waste acid to 8.2±0.2. The waste acid stays in the second-stage neutralization reaction tank 7 for 30 minutes, and then enters the flocculation reaction tank 8;

[0052] 4) At the inlet of the flocculation reaction tank 8, add nonionic polyacrylamide (PAM) solution (with a concentration of 5%) to the waste acid, and calculate the waste acid flow rate according to the waste liquid flow meter 101. The PAM dosage is 50g / m 3 The flocculation reaction lasts for 10 minutes, and the sludge enters the second-stage thickener 9 for sedimentation. The bottom flow is pumped into the second-stage dehydrator 11 for dehydration treatment, and the supernatant of the second-stage dehydrator 11 is directly discharged.

[0053] 5) The waste acid stays in the second-stage thickener 9 for 5 hours. The clear liquid from the thickener is discharged or processed. The bottom flow is processed by the second-stage dehydrator 11. The filter cake is dihydrate gypsum. The filtrate is returned to the second-stage neutralization reaction tank 7.

[0054] 6) Application effect

[0055] After six months of operation according to the above process parameters, it was found that some meshes of the filter cloth of the second-stage dehydrator 11 were slightly blocked by scaling, but there was no obvious mud blockage on the surface of the filter cloth. After cleaning with high-pressure water, the filter cloth could still be put into use; there was no blockage or obstruction in the pipelines and valves; and there was no scaling in the pipelines through which the waste acid flowed.

[0056] Example 3

[0057] 1) After the first-stage limestone neutralization reaction, solid-liquid separation in the first-stage thickener 2, and underflow dehydration treatment, the waste acid enters the sulfate reaction tank 5. Lime milk is added to the waste acid inlet of the sulfate reaction tank 5. The first pH meter 102 is used to detect the waste acid pH on the waste acid pipeline and control the waste acid pH to 6.7±0.2. Sodium sulfate solution (concentration of 15%) is added to the outlet of the sulfate reaction tank 5. The waste acid flow rate is measured by the waste liquid flow meter 101 to determine the amount of sodium sulfate to be added. The amount of sodium sulfate used is 18 kg / m 3 , after mixing through the pipeline, the waste acid flows into the aluminum salt reaction tank 6;

[0058] 2) Add polyaluminium chloride solution (concentration of 13%) to the aluminium salt reaction tank 6. The amount of addition is determined by the count of the waste liquid flow meter 101, which is equivalent to 0.20 kg / m Al2O3 addition. 3 , control the pH value of the effluent of the aluminum salt reaction tank 6 to 5.6±0.2, the residence time of the spent acid aluminum salt reaction tank 6 is 35min, and then flows into the second-stage neutralization reaction tank 7;

[0059] 3) Lime emulsion is added at the inlet of the second-stage neutralization reaction tank 7 to raise the pH of the waste acid to 10.6±0.2. The waste acid stays in the second-stage neutralization reaction tank 7 for 55 minutes, and then enters the flocculation reaction tank 8;

[0060] 4) At the inlet of the flocculation reaction tank 8, add non-ionic polyacrylamide (PAM) solution (with a concentration of 5%) to the waste acid, and calculate the waste acid flow rate according to the waste liquid flow meter 101. The PAM dosage is 80g / m 3 The flocculation reaction lasts for 10 minutes, and the sludge enters the second-stage thickener 9 for sedimentation. The bottom flow is pumped into the second-stage dehydrator 11 for dehydration treatment, and the supernatant of the second-stage dehydrator 11 is directly discharged.

[0061] 5) The waste acid stays in the second-stage thickener 9 for 6.5 hours. The clear liquid from the thickener is discharged or processed. The bottom flow is processed by the second-stage dehydrator 11. The filter cake is dihydrate gypsum. The filtrate is returned to the second-stage neutralization reaction tank 7.

[0062] 6) Application effect

[0063] After operating for 6 months according to the above process parameters, check that the filter cloth of the second-stage dehydrator 11 is not blocked by scaling; there is no blockage or obstruction in the pipelines and valves; and there is no scaling in the pipelines through which the waste acid flows.

[0064] Comparative Example

[0065] Compared with the embodiment, the comparative example was not treated with the addition of sodium sulfate and polyaluminium chloride.

[0066] 1) After the first-stage limestone neutralization reaction, solid-liquid separation in the first-stage thickener 2, and underflow dehydration treatment, the waste acid enters the sulfate reaction tank 5. Lime milk is added to the waste acid inlet of the sulfate reaction tank 5. The waste acid pH is tested on the waste acid pipeline using a first pH meter 102 to control the waste acid pH to 6.0±0.2. Then, the waste acid flows into the second-stage neutralization reaction tank 7.

[0067] 2) Lime emulsion is added at the inlet of the second-stage neutralization reaction tank 7 to raise the pH of the waste acid to 8.8±0.2. The waste acid stays in the second-stage neutralization reaction tank 7 for 45 minutes, and then flows into the flocculation reaction tank 8;

[0068] 3) At the inlet of the flocculation reaction tank 8, add non-ionic polyacrylamide (PAM) solution (with a concentration of 5%) to the waste acid, and calculate the waste acid flow rate according to the waste liquid flow meter 101. The PAM dosage is 60-80 g / m 3 The flocculation reaction lasts for 10 minutes. Then, the waste acid enters the second-stage thickener 9 for sludge sedimentation. The bottom flow is sent to the second-stage dehydrator 11 for dehydration treatment through a delivery pump, and the supernatant of the second-stage dehydrator 11 is directly discharged.

[0069] 4) The waste acid stays in the second-stage thickener 9 for 6 hours. The clear liquid from the thickener is discharged or processed. The bottom flow is processed by the second-stage dehydrator 11. The filter cake is dihydrate gypsum. The filtrate is returned to the second-stage neutralization reaction tank 7.

[0070] 5) Operation results

[0071] After three months of operation using the process and parameters of the comparative example, the filter cloth of the second-stage dehydrator 11 showed obvious dense calcium sulfate scaling in many areas, and the filter cloth mesh was significantly clogged by scaling. High-pressure water jets were used monthly to flush the pipe elbows and valves to prevent pipe blockage and valve obstruction. Severe salt scaling appeared at the pipe interfaces through which the waste acid flowed. The above is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preventing calcium scale formation on the surface of a waste sulfuric acid neutralization system device, characterized in that: The steps include: S1, the waste acid after the first stage neutralization reaction and solid-liquid sedimentation separation is discharged into the sulfate reaction tank (5), and then lime emulsion and sodium sulfate solution are added to the sulfate reaction tank (5); S2, the waste acid in step S1 is fully mixed through the pipeline and then flows into the aluminum salt reaction tank (6), and the polyaluminum chloride solution is added into the aluminum salt reaction tank (6); S3, controlling the waste acid in step S2 to flow into the second-stage neutralization reaction tank (7), adding lime emulsion again to adjust the pH, and then controlling the waste acid to flow into the flocculation reaction tank (8); S4, adding sedimentation materials into the flocculation reaction tank (8) and fully mixing them to complete solid-liquid sedimentation separation of the waste acid; In step S1, the concentration of the lime emulsion added is 10%, the concentration of the sodium sulfate solution is 10% to 15%, and the amount of sodium sulfate added is 12 to 20 kg / m³; The concentration of the polyaluminium chloride solution in step S2 is 13%; The concentration of the lime emulsion added in step S3 is 10%, and the pH range of the waste acid is controlled to be 8-11.

2. The method for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device according to claim 1, characterized in that: The precipitated material in step S4 is a non-ionic polyacrylamide solution with a concentration of 1% to 5% and a dosage of 50 to 80 g / m³.

3. The method for preventing calcium scale from forming on the surface of a waste sulfuric acid neutralization system device according to claim 2, characterized in that: After the sedimentation material is added and mixed, it reacts for 5 to 20 minutes and then enters the second-stage thickener (9) for sludge sedimentation.

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