Method for reducing hardness of fly ash washing liquid

Abstract

The invention discloses a method for reducing hardness of fly ash washing liquid. According to the method, the hardness of the washing liquid is gradually reduced through a plurality of steps including precipitation, decalcification, heavy metal removal, neutralization and the like. Particularly, in the decalcification step, sodium sulfate and a sodium carbonate solution are added, so that calcium ions and magnesium ions can be effectively promoted to react with corresponding anions to generate precipitates, and the hardness is remarkably reduced. According to the method, in the treatment process, the pollution to the environment is reduced through the steps of solid-liquid separation, recycling and the like. Meanwhile, for removing heavy metals, a heavy metal chelating agent is adopted, so that the emission of the heavy metals can be effectively avoided, and the ecological environment is protected. And at the end of the process, resources are recycled through the evaporative crystallization system, so that the utilization rate of water resources is increased, and the treatment cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fly ash water washing liquid treatment, and in particular to a method for reducing the hardness of fly ash water washing liquid. Background Art

[0002] High-hardness washing liquid contains a large amount of calcium and magnesium ions, which are easy to form precipitates such as calcium carbonate and magnesium carbonate during heating or evaporation. These precipitates may clog pipes, valves and equipment, causing equipment failure and damage, and increasing maintenance costs. High-hardness washing liquid may have adverse effects on the environment when discharged. The calcium and magnesium ions in hard water react with other substances in the water body and may form sediments, affecting the ecological balance of the water body. Summary of the invention

[0003] The purpose of the present invention is to solve the above-mentioned background technical problems and to provide a method for reducing the hardness of fly ash water washing liquid.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A method for reducing hardness of fly ash water washing liquid comprises the following steps:

[0006] S1. Preliminary treatment: The water washing system transports the washing liquid into the sedimentation tank to precipitate the suspended solids, and the clean washing liquid enters the primary decalcification reaction tank;

[0007] S2, primary decalcification treatment: adding sodium sulfate solution and flocculant, reacting to generate calcium sulfate, and solid-liquid separation to obtain calcium sulfate dihydrate;

[0008] S3, secondary decalcification treatment: adding sodium carbonate solution and flocculant, reacting to generate calcium carbonate and magnesium carbonate, and solid-liquid separation to obtain calcium carbonate and magnesium carbonate;

[0009] S4. Heavy metal removal: Add fly ash-specific heavy metal chelating agent and flocculant to react to generate heavy metal precipitate, and separate the solid and liquid to obtain heavy metal sludge;

[0010] S5, ion exchange treatment: the water washing liquid treated in the above steps is passed through an ion exchange resin, and the ions on the resin are exchanged with the calcium and magnesium ions in the water washing liquid to further reduce the hardness of the water washing liquid;

[0011] S6. pH adjustment: Add hydrochloric acid into the neutralization tank to adjust the pH to 7.0-7.5, and then transport it to the water stabilization tank for temporary storage.

[0012] As a further solution of the present invention: in the preliminary treatment, the washing liquid transported by the washing system first enters the sedimentation tank to allow the suspended solids in the washing liquid to stand and precipitate;

[0013] The sediment is transported to the water washing unit through the sludge lifting pump;

[0014] The clean water washing liquid is transported to the primary decalcification reaction tank through the pipeline of the sedimentation tank for primary decalcification.

[0015] As a further solution of the present invention: sodium sulfate solution and flocculant are added to the primary decalcification reaction tank to promote the reaction and precipitation of sulfate ions and calcium ions, and calcium sulfate is obtained through the action of the high-efficiency sedimentation tank, and then transported to the primary decalcification solid-liquid separation device through a sludge lifting pump to obtain calcium sulfate dihydrate.

[0016] As a further solution of the present invention: the liquid phase returns to the primary decalcification reaction tank for further reaction, and the clear liquid passing through the high-efficiency sedimentation tank enters the secondary decalcification sedimentation tank for further softening treatment.

[0017] As a further scheme of the present invention: in the secondary decalcification treatment, it is necessary to add sodium carbonate solution and flocculant in the secondary decalcification reactor to promote the reaction and precipitation of carbonate ions with calcium ions and magnesium ions, and obtain calcium carbonate and magnesium carbonate precipitates through the action of the high-efficiency sedimentation tank, and then transport the calcium carbonate and magnesium carbonate obtained by the sludge lifting pump to the secondary decalcification solid-liquid separation device, and the liquid phase returns to the secondary decalcification reaction tank for further reaction, and the clear liquid passing through the secondary decalcification reactor enters the heavy metal removal sedimentation tank for heavy metal removal reaction.

[0018] As a further solution of the present invention: in the heavy metal removal step, it is necessary to add a fly ash-specific heavy metal chelating agent and a flocculant in the heavy metal removal sedimentation tank to promote the reaction and precipitation of heavy metal ions with the chelating agent, and obtain heavy metal precipitates through the action of the high-efficiency sedimentation tank, and then transport them to the heavy metal solid-liquid separation device through the sludge lifting pump to obtain a solid phase of heavy metal sludge, and the liquid phase returns to the heavy metal removal sedimentation tank to continue the reaction;

[0019] The clear liquid from the heavy metal removal sedimentation tank enters the neutralization tank to adjust the water pH.

[0020] As a further solution of the present invention: the dissolved water in the sodium sulfate dosing system and the sodium carbonate dosing system is taken from a water quality regulating tank.

[0021] Beneficial effects of the present invention: This method gradually reduces the hardness in the water washing liquid through multiple steps, including precipitation, decalcification, heavy metal removal and neutralization. In particular, in the decalcification step, by adding sodium sulfate and sodium carbonate solutions, it can effectively promote the reaction of calcium ions, magnesium ions and corresponding anions to generate precipitates, thereby achieving a significant reduction in hardness. During the treatment process, this method reduces environmental pollution through steps such as solid-liquid separation and recycling. At the same time, for the removal of heavy metals, the use of heavy metal chelating agents can effectively avoid the discharge of heavy metals and protect the ecological environment. At the end of the process, resources are recycled through an evaporation crystallization system, which improves the utilization rate of water resources and reduces processing costs. The introduction of ion exchange technology further improves the degree of water purification and ensures that the treated water washing liquid meets environmental protection requirements. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Embodiment 1, the present invention is a method for reducing the hardness of fly ash washing liquid, (1) the washing liquid transported by the washing system first enters a sedimentation tank to allow the solid suspended matter in the washing liquid to stand and settle;

[0024] The sediment is transported to the water washing unit through the sludge lifting pump; the clean water washing liquid is transported to the primary decalcification reaction tank through the pipeline of the sedimentation tank for primary decalcification;

[0025] (2) In the primary decalcification reaction tank, sodium sulfate solution and flocculant are added to promote the reaction and precipitation of sulfate ions and calcium ions, and calcium sulfate is obtained through the action of the high-efficiency sedimentation tank, and then transported to the primary decalcification solid-liquid separation device through the sludge lifting pump to obtain calcium sulfate dihydrate, and the liquid phase returns to the primary decalcification reaction tank for further reaction, and the clear liquid passing through the high-efficiency sedimentation tank enters the secondary decalcification sedimentation tank for further softening treatment;

[0026] (3) In the secondary decalcification reactor, sodium carbonate solution and flocculant are added to promote the reaction and precipitation of carbonate ions with calcium ions, magnesium ions, etc., and calcium carbonate and magnesium carbonate precipitates are obtained through the action of the high-efficiency sedimentation tank, and then transported to the secondary decalcification solid-liquid separation device through the sludge lifting pump. The obtained calcium carbonate and magnesium carbonate, the liquid phase, are returned to the secondary decalcification reaction tank for further reaction, and the clear liquid passing through the secondary decalcification reactor enters the heavy metal removal sedimentation tank for heavy metal removal reaction;

[0027] (4) In the heavy metal removal sedimentation tank, a fly ash-specific heavy metal chelating agent and flocculant are added to promote the reaction and precipitation of heavy metal ions with the chelating agent, and heavy metal precipitates are obtained through the action of the high-efficiency sedimentation tank. The sludge is then transported to the heavy metal solid-liquid separation device through a sludge lifting pump to obtain a solid phase of heavy metal sludge, and the liquid phase returns to the heavy metal removal sedimentation tank for further reaction; the clear liquid from the heavy metal removal sedimentation tank enters the neutralization tank for water quality pH adjustment;

[0028] (5) In the neutralization tank, hydrochloric acid is added to adjust the pH of the water wash to 7.0-7.5; then the water wash is transported to the water stabilization tank for temporary storage;

[0029] (6) The dissolved water in the sodium sulfate dosing system and the sodium carbonate dosing system is taken from the water quality regulating tank.

[0030] Embodiment 2:

[0031] (1) The washing liquid transported by the washing system first enters the sedimentation tank to let the suspended solids in the washing liquid stand for 24-72 hours until the suspended solids content of the supernatant is less than 400 mg / L and precipitates; the precipitate is transported to the washing unit through the sludge lifting pump for solid-liquid separation; the supernatant is transported to the primary decalcification reaction tank through the pipeline of the sedimentation tank for primary decalcification;

[0032] (2) An online hardness tester is installed on the primary decalcification tank to measure the hardness of the water washing liquid. The amount of sodium sulfate solution that needs to be added is calculated based on the online hardness data (CA2++SO42-=CASO4). In the primary decalcification reaction tank, sodium sulfate solution is added to promote the reaction (0.5-6h) and precipitation of sulfate ions and calcium ions, and calcium sulfate is obtained through the action of the primary decalcification sedimentation tank. After that, it is transported to the primary decalcification solid-liquid separation device through the sludge lifting pump to obtain calcium sulfate dihydrate. The liquid phase returns to the primary decalcification reaction tank for further reaction. The clear liquid passing through the high-efficiency sedimentation tank enters the secondary decalcification sedimentation tank for further softening treatment;

[0033] (3) An online hardness tester is installed on the secondary decalcification tank to measure the hardness of the water washing liquid. The amount of sodium carbonate solution to be added is calculated based on the online hardness data. In the secondary decalcification reactor, sodium carbonate solution and flocculant are added to promote the reaction and precipitation of carbonate ions with calcium ions, magnesium ions, etc. (0.5-6h), and calcium carbonate and magnesium carbonate precipitates are obtained through the action of the high-efficiency sedimentation tank. After that, they are transported to the secondary decalcification solid-liquid separation device through the sludge lifting pump. The obtained calcium carbonate and magnesium carbonate, the liquid phase, are returned to the secondary decalcification reaction tank for further reaction (0.5-6h), and the clear liquid passing through the secondary decalcification reactor enters the heavy metal removal sedimentation tank for heavy metal removal reaction;

[0034] CA2++SO42-=CASO4

[0035] CA2++CO32-=CACO3

[0036] Mg2++CO32-=MgCO3

[0037] (4) The washing liquid in the secondary decalcification reactor is sampled to determine the heavy metal content, and the amount of heavy metal remover and the ratio of the heavy metal remover (organic chelating agent: inorganic chelating agent) to be added are calculated according to the heavy metal component data. In the heavy metal removal sedimentation tank, a fly ash-specific heavy metal chelating agent (0.01%-0.1%; organic chelating agent: inorganic chelating agent = 1-3: 3-7) and a flocculant (0.1-0.5%) are added to promote the reaction and precipitation of heavy metal ions with the chelating agent (2-12h), and heavy metal precipitation is obtained through the action of the high-efficiency sedimentation tank. After that, it is transported to the heavy metal solid-liquid separation device through the sludge lifting pump to obtain a solid phase of heavy metal sludge, and the liquid phase returns to the heavy metal removal sedimentation tank for further reaction (4-12h); the clear liquid from the heavy metal removal sedimentation tank enters the neutralization tank for water quality pH adjustment;

[0038] (5) In the neutralization tank, hydrochloric acid is added to adjust the pH of the water wash to 7.0-7.5; then the evaporation crystallization system is used for resource recycling;

[0039] (6) Clean water, tap water or system recycled water should be used as the dissolving water in the sodium sulfate dosing system and the sodium carbonate dosing system.

[0040] Embodiment three:

[0041] (1) The washing liquid delivered by the washing system first enters the sedimentation tank to let the suspended solids in the washing liquid stand for 42 hours until the suspended solids content of the supernatant is less than 400 mg / L and precipitates; the precipitate is transported to the washing unit through the sludge lifting pump for solid-liquid separation; the supernatant is transported to the primary decalcification reaction tank through the pipeline of the sedimentation tank for primary decalcification;

[0042] (2) An online hardness tester is installed on the primary decalcification tank to measure the hardness of the water washing liquid. The amount of sodium sulfate solution that needs to be added is calculated based on the online hardness data (CA2++SO42-=CASO4). In the primary decalcification reaction tank, sodium sulfate solution is added to promote the reaction (4h) and precipitation of sulfate ions and calcium ions, and calcium sulfate is obtained through the action of the primary decalcification sedimentation tank. After that, it is transported to the primary decalcification solid-liquid separation device through the sludge lifting pump to obtain calcium sulfate dihydrate. The liquid phase returns to the primary decalcification reaction tank for further reaction. The clear liquid passing through the high-efficiency sedimentation tank enters the secondary decalcification sedimentation tank for further softening treatment;

[0043] (3) An online hardness tester is installed on the secondary decalcification tank to measure the hardness of the water washing liquid. The amount of sodium carbonate solution to be added is calculated based on the online hardness data. In the secondary decalcification reactor, sodium carbonate solution and flocculant are added to promote the reaction and precipitation of carbonate ions with calcium ions, magnesium ions, etc. (3h), and calcium carbonate and magnesium carbonate precipitates are obtained through the action of the high-efficiency sedimentation tank. After that, they are transported to the secondary decalcification solid-liquid separation device through the sludge lifting pump. The obtained calcium carbonate and magnesium carbonate, the liquid phase, are returned to the secondary decalcification reaction tank for further reaction (6h), and the clear liquid passing through the secondary decalcification reactor enters the heavy metal removal sedimentation tank for heavy metal removal reaction;

[0044] CA2++SO42-=CASO4

[0045] CA2++CO32-=CACO3

[0046] Mg2++CO32-=MgCO3

[0047] (4) The water washing liquid in the secondary decalcification reactor is sampled to determine the heavy metal content. The amount of heavy metal remover and the ratio of the heavy metal remover (organic chelating agent: inorganic chelating agent) to be added are calculated based on the heavy metal component data. In the heavy metal removal sedimentation tank, a fly ash-specific heavy metal chelating agent (0.06%; organic chelating agent: inorganic chelating agent = 3:5) and a flocculant (0.5%) are added to promote the reaction and precipitation of heavy metal ions with the chelating agent (7h), and heavy metal precipitation is obtained through the action of the high-efficiency sedimentation tank. After that, it is transported to the heavy metal solid-liquid separation device through the sludge lifting pump to obtain a solid phase of heavy metal sludge, and the liquid phase returns to the heavy metal removal sedimentation tank for further reaction (10h); the clear liquid from the heavy metal removal sedimentation tank enters the neutralization tank for water quality pH adjustment;

[0048] (5) Ion exchange treatment: The water washing liquid treated in the above steps is passed through an ion exchange resin, and the ions on the resin are exchanged with the calcium and magnesium ions in the water washing liquid to further reduce the hardness of the water washing liquid;

[0049] (6) In the neutralization tank, hydrochloric acid is added to adjust the pH of the water wash to 7.0; then the evaporation crystallization system is used for resource recovery;

[0050] (7) Clean water, tap water or system recycled water should be used as the dissolving water in the sodium sulfate dosing system and the sodium carbonate dosing system.

[0051] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the claims of the present invention.

Claims

1. A method for reducing hardness of fly ash water washing liquid, characterized in that: The following steps are involved: S1. Preliminary treatment: The water washing system transports the washing liquid into the sedimentation tank to precipitate the suspended solids, and the clean washing liquid enters the primary decalcification reaction tank; S2, primary decalcification treatment: adding sodium sulfate solution and flocculant, reacting to generate calcium sulfate, and solid-liquid separation to obtain calcium sulfate dihydrate; S3, secondary decalcification treatment: adding sodium carbonate solution and flocculant, reacting to generate calcium carbonate and magnesium carbonate, and solid-liquid separation to obtain calcium carbonate and magnesium carbonate; S4. Heavy metal removal: Add fly ash-specific heavy metal chelating agent and flocculant to react to generate heavy metal precipitate, and separate the solid and liquid to obtain heavy metal sludge; S5, ion exchange treatment: the water washing liquid treated in the above steps is passed through an ion exchange resin, and the ions on the resin are exchanged with the calcium and magnesium ions in the water washing liquid to further reduce the hardness of the water washing liquid; S6. pH adjustment: Add hydrochloric acid into the neutralization tank to adjust the pH to 7.0-7.5, and then transport it to the water stabilization tank for temporary storage.

2. The method for reducing hardness of fly ash water washing liquid according to claim 1, characterized in that: In the early stage of treatment, the washing liquid delivered by the washing system first enters the sedimentation tank to settle and precipitate the suspended solids in the washing liquid; The sediment is transported to the water washing unit through the sludge lifting pump; The clean water washing liquid is transported to the primary decalcification reaction tank through the pipeline of the sedimentation tank for primary decalcification.

3. The method for reducing hardness of fly ash water washing liquid according to claim 2, characterized in that: In the primary decalcification reaction tank, sodium sulfate solution and flocculant are added to promote the reaction and precipitation of sulfate ions and calcium ions, and calcium sulfate is obtained through the action of the high-efficiency sedimentation tank, and then transported to the primary decalcification solid-liquid separation device through the sludge lifting pump to obtain calcium sulfate dihydrate.

4. The method for reducing hardness of fly ash water washing liquid according to claim 3, characterized in that: The liquid phase returns to the primary decalcification reaction tank for further reaction, and the clear liquid passing through the high-efficiency sedimentation tank enters the secondary decalcification sedimentation tank for further softening treatment.

5. The method for reducing hardness of fly ash water washing liquid according to claim 2, characterized in that: In the secondary decalcification treatment, it is necessary to add sodium carbonate solution and flocculant into the secondary decalcification reactor to promote the reaction and precipitation of carbonate ions with calcium ions and magnesium ions, and obtain calcium carbonate and magnesium carbonate precipitates through the action of the high-efficiency sedimentation tank. The calcium carbonate and magnesium carbonate are then transported to the secondary decalcification solid-liquid separation device through the sludge lifting pump, and the liquid phase returns to the secondary decalcification reaction tank for further reaction. The clear liquid from the secondary decalcification reactor enters the heavy metal removal sedimentation tank for heavy metal removal reaction.

6. The method for reducing hardness of fly ash water washing liquid according to claim 2, characterized in that: In the heavy metal removal step, it is necessary to add fly ash-specific heavy metal chelating agents and flocculants into the heavy metal removal sedimentation tank to promote the reaction and precipitation of heavy metal ions with the chelating agents, and obtain heavy metal precipitates through the action of the high-efficiency sedimentation tank, and then transport them to the heavy metal solid-liquid separation device through the sludge lifting pump to obtain solid phase heavy metal sludge, and the liquid phase returns to the heavy metal removal sedimentation tank for further reaction; The clear liquid from the heavy metal removal sedimentation tank enters the neutralization tank to adjust the water pH.

7. The method for reducing hardness of fly ash water washing liquid according to claim 2, characterized in that: The dissolved water in the sodium sulfate dosing system and the sodium carbonate dosing system is taken from the water quality regulating tank.