Method for co-disposing wet desulfurization wastewater with reduced sulfate enrichment and sinter dust

Abstract

The application discloses a method for cooperatively disposing wet desulfurization wastewater with reduced sulfate enrichment and sinter dust, which comprises the following steps: S1, mixing and stirring the sinter dust and the desulfurization wastewater to perform water washing, performing solid-liquid separation on the eluate, and then sequentially performing first-stage purification magnesium hardness removal and ammonia nitrogen removal treatment on the separated supernatant after entering a water quantity regulating tank for regulation, and then performing first-stage flocculation and first-stage sedimentation treatment; S2, after the first-stage sedimentation treatment, performing solid-liquid separation, and then performing second-stage purification calcium hardness removal, second-stage flocculation and second-stage sedimentation to perform solid-liquid separation, adjusting the pH value of the filtrate to neutral, and then performing heavy metal removal treatment and third-stage sedimentation to perform solid-liquid separation, and then filtering the filtrate to remove suspended matters and then entering a concentrated brine regulating tank for treatment, sending the water out of the concentrated brine regulating tank to an evaporation crystallization system to obtain high-purity potassium chloride and sodium chloride, and then returning part of the evaporation mother liquor to the water quantity regulating tank in step S1; the method can realize effective resource utilization and solve the problem of sulfate enrichment.

Description

Technical Field

[0001] This invention relates to the fields of industrial wastewater treatment and sintering dust resource utilization, specifically to a method for the co-treatment of wet desulfurization wastewater and sintering dust that can reduce sulfate enrichment. Background Technology

[0002] A leading technology for sintering dust disposal is the potassium chloride recovery process, which involves water washing for potassium removal, solid-liquid separation, impurity removal and purification, solid-liquid separation, and evaporation crystallization. This process can utilize sintering dust to produce high-quality potassium chloride and sodium chloride. However, the water washing for potassium removal primarily uses fresh industrial water. This introduces a large amount of fresh industrial water, and the resulting eluent has a low TDS (Total Dissolved Solids), which is detrimental to evaporation crystallization. Furthermore, since sintering wet desulfurization wastewater and sintering dust are both located in the same sintering unit, there is a possibility of waste-to-waste treatment. The sintering wet desulfurization wastewater uses the limestone-gypsum method for desulfurization, resulting in high total hardness, high chloride ion concentration, and high TDS. Using this wastewater to wash away alkali metal potassium and sodium from the sintering dust further increases the TDS of the eluent, allowing for evaporation crystallization without membrane concentration to obtain potassium chloride and sodium chloride crystals. However, the wet desulfurization wastewater contains sulfate ions, which accumulate during the evaporation crystallization process. If the problem of sulfate ion enrichment in the evaporation mother liquor is not resolved, it will seriously affect the quality of potassium chloride and sodium chloride crystal salts and increase the amount of miscellaneous salts to be disposed of, resulting in a decline in economic benefits.

[0003] Therefore, in order to solve the above problems, there is an urgent need for a treatment method that can effectively utilize resources while reducing sulfate accumulation. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for the co-treatment of wet desulfurization wastewater and sintering dust that can reduce sulfate accumulation, thereby achieving effective resource utilization and solving the problem of sulfate accumulation.

[0005] The present invention provides a method for the co-treatment of wet desulfurization wastewater and sintering dust that reduces sulfate accumulation, comprising the following steps:

[0006] S1, the sintering dust and desulfurization wastewater are mixed and stirred for water washing, the eluent is separated into solid and liquid, the separated supernatant is entered into the water volume adjustment tank for adjustment, and then undergoes primary purification to remove magnesium hardness and ammonia nitrogen, followed by primary flocculation and primary sedimentation.

[0007] S2, after primary sedimentation treatment, solid-liquid separation is performed, followed by secondary purification to remove calcium and hardness, secondary flocculation, and secondary sedimentation for solid-liquid separation. The pH of the filtrate is adjusted to neutral, followed by heavy metal removal treatment and tertiary sedimentation for solid-liquid separation. After filtering to remove suspended solids, the filtrate is sent to a concentrated brine equalization tank for treatment. The effluent from the concentrated brine equalization tank is sent to an evaporation crystallization system to obtain high-purity potassium chloride and sodium chloride. Then, part of the mother liquor from the evaporation is returned to the water volume equalization tank in step S1.

[0008] Furthermore, the reflux ratio of the evaporated mother liquor is between 0% and 30%.

[0009] Furthermore, after the refluxed mother liquor enters the water flow equalization tank, the molar ratio of calcium ions to sulfate ions is 1:1-10:1.

[0010] Furthermore, calcium hydroxide is used for primary purification to remove magnesium hardness, and an ammonia stripping tank is used to remove ammonia nitrogen and promote the further reaction of sulfate ions with calcium hydroxide to generate calcium sulfate precipitate. The magnesium hydroxide precipitate and calcium sulfate precipitate generated during magnesium hardness removal are flocculated through primary flocculation treatment.

[0011] Furthermore, sodium carbonate is used for secondary purification to remove calcium and hardness. The secondary flocculation flocculates the calcium carbonate produced by sodium carbonate and calcium ions.

[0012] Furthermore, in addition to the treatment of heavy metals, heavy metal trapping agents and flocculants are added simultaneously.

[0013] The beneficial effects of this invention are as follows: The method for co-treating wet desulfurization wastewater and sintering dust that reduces sulfate accumulation disclosed in this invention obtains high-quality potassium chloride and sodium chloride crystalline salts through process units such as water washing, hardening removal, ammonia removal, flocculation, sedimentation, weight removal, filtration, and evaporation crystallization. By refluxing the evaporation mother liquor with calcium hardening, calcium hardening is reduced while removing sulfate ions, thereby reducing the amount of sodium carbonate added subsequently and lowering reagent costs. Simultaneously, it solves the problem of sulfate accumulation leading to a decline in the quality of crystalline salts, achieving zero discharge of wet desulfurization wastewater while extracting high-value-added alkali metals potassium and sodium from sintering dust, generating significant economic benefits. Furthermore, by stripping away ammonia nitrogen, the method further promotes the reaction of sulfate and calcium ions to form calcium sulfate precipitate, achieving a further effect of sulfate removal. This invention significantly reduces the degree of sulfate ion accumulation and improves the quality of potassium chloride and sodium chloride crystalline salts obtained from the co-treatment of wet desulfurization wastewater and sintering dust. In addition, the reflux and sedimentation process removes some calcium carbonate and sulfate ions through flocculation and sedimentation, preventing them from reacting with sodium carbonate in the secondary purification unit to form sodium sulfate. Since some calcium carbonate is already removed through flocculation and sedimentation, the amount of sodium carbonate added is also reduced. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0015] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0016] The method for co-treating wet desulfurization wastewater and sintering dust that can reduce sulfate accumulation in this embodiment includes the following steps:

[0017] S1. Sintering dust and desulfurization wastewater are mixed and washed with water. The eluent is then subjected to solid-liquid separation. The supernatant is adjusted in a water flow regulating tank and then subjected to primary purification for magnesium hardening and ammonia nitrogen removal, followed by primary flocculation and primary precipitation. In the first purification step for magnesium hardening removal, calcium hydroxide is added to remove magnesium hardening. A stripping device is also provided. After adding calcium hydroxide, the pH of the solution increases, and stripping can reduce the ammonia nitrogen in the solution. Then, a stripping tank is used to further remove ammonia nitrogen and promote the further reaction of sulfate ions with calcium hydroxide to generate calcium sulfate precipitate, thereby reducing calcium hardness while reducing sulfate ion concentration. Then, the solution enters the primary flocculation unit, where magnesium hydroxide generated from magnesium hardening removal is flocculated, and calcium sulfate generated from sulfate ions and calcium hydroxide is flocculated. Finally, primary precipitation is performed.

[0018] S2, after primary sedimentation treatment, solid-liquid separation is performed, followed by secondary purification to remove calcium and hardness, secondary flocculation, and secondary sedimentation for solid-liquid separation. The pH of the filtrate is adjusted to neutral, followed by heavy metal removal treatment and tertiary sedimentation for solid-liquid separation. After filtering to remove suspended solids, the filtrate is sent to a concentrated brine equalization tank for treatment. The effluent from the concentrated brine equalization tank is sent to an evaporation crystallization system to obtain high-purity potassium chloride and sodium chloride. Then, part of the mother liquor from evaporation is returned to the water volume equalization tank in step S1.

[0019] In this embodiment, wet desulfurization wastewater enters the water washing and mixing tank through a self-priming pump, and sintering dust enters the water washing and mixing tank from the ash storage silo through a pneumatic diaphragm pump. The mixture generated by water washing and mixing is called the eluent. An electric gate valve is installed at the bottom of the washing and mixing tank to discharge the eluent and send it to a plate and frame filter press for solid-liquid separation. The sludge cake is sent to the sintering unit for reuse, and the filtrate enters the water flow regulating tank. It is then thoroughly mixed with a portion of the returned evaporation mother liquor by a circulating pump and enters the primary purification unit to remove magnesium hardening. The primary purification unit is equipped with a rotary blower for stripping. Due to the high temperature of the returned evaporation mother liquor, it is conducive to the stripping of ammonia. The ammonia nitrogen is further removed in the stripping tank, which is also equipped with a rotary blower. The sludge enters the flocculation unit, where 0.5% polyacrylamide is added to flocculate calcium sulfate and magnesium hydroxide. The sludge enters the vertical flow sedimentation tank to precipitate calcium sulfate and magnesium hydroxide, preventing calcium sulfate from reacting with sodium carbonate in the secondary purification unit to form sodium sulfate. The sludge at the bottom of the sedimentation tank is discharged through an electric gate valve and sent to the plate and frame filter press for filtration. The filtrate is pumped into the secondary purification unit, and the sludge cake is transported to the sintering unit for reuse. The supernatant from the vertical flow sedimentation tank flows by gravity into the secondary purification unit. Since some calcium carbonate has already reacted with the enriched sulfate ions to form calcium sulfate precipitate, which is removed in the primary sedimentation tank, the amount of sodium carbonate added for calcium carbonate removal will be further reduced. The secondary flocculation unit also adds 0.5% polyacrylamide, which then enters the vertical flow sedimentation tank to precipitate calcium carbonate. The settled sludge is discharged to the plate and frame filter press via an electric gate valve. The sludge cake is sent to the sintering unit for reuse. The filtrate enters the pH adjustment tank, where hydrochloric acid is added to maintain the pH between 6.5 and 7. It then enters the heavy metal removal unit, where an organic sulfur precipitant is added to remove heavy metals. 0.5% polyacrylamide is added to flocculate the heavy metal organic sulfur compounds. The filtrate then enters the vertical flow sedimentation tank. The settled sludge is discharged to the plate and frame filter press via an electric gate valve. The sludge cake can be mixed with sludge cake from the washing mixing tank, primary sedimentation tank, and secondary sedimentation tank and then sent to the sintering unit for reuse. The filtrate enters the filtration unit to further remove suspended solids, then enters the concentrated brine conditioning tank, and finally enters the evaporation and crystallization unit. Through thermal separation, sodium chloride and potassium chloride crystalline salts are obtained, both of which meet the quality standards of secondary industrial salt.

[0020] In this embodiment, the reflux ratio of the evaporated mother liquor is between 0% and 30%; "between 0% and 30%" means that the reflux ratio is greater than 0 and less than 30%.

[0021] In this embodiment, after the refluxed evaporation mother liquor enters the water flow regulating tank, the molar ratio of calcium ions to sulfate ions is 1:1-10:1; during the heavy metal removal treatment, heavy metal scavengers and flocculants are added simultaneously.

[0022] Example 1

[0023] 1) Sintering dust and sintering dust are mixed at a certain water-ash ratio of 3:1 and stirred for 5 hours to produce an eluent. Then, solid and liquid are separated. The filtrate enters the primary purification unit and calcium hydroxide is added to remove magnesium hardness. The primary purification unit is equipped with a stripping device (after adding calcium hydroxide, the solution pH increases, and stripping can reduce the ammonia nitrogen in the solution). Then, it enters the stripping tank to further remove ammonia nitrogen and promote the further reaction of sulfate ions with calcium hydroxide to form calcium sulfate precipitate. This reduces the calcium hardness while reducing the sulfate ion concentration.

[0024] 2) Entering the primary flocculation unit: magnesium hydroxide flocculates from the removal of magnesium hardness, and calcium sulfate flocculates from the reaction of sulfate ions and calcium hydroxide; then it enters the primary sedimentation tank for solid-liquid separation; then it enters the secondary purification unit: sodium carbonate is added to further remove calcium hardness; then it enters the secondary flocculation unit: calcium carbonate flocculates from the reaction of sodium carbonate and calcium ions.

[0025] 3) It enters the secondary sedimentation tank for solid-liquid separation; then it enters the pH adjustment tank to adjust the pH to 6.5 to 7; then it enters the heavy removal unit, where heavy removal agent and flocculant are added at the same time; it enters the tertiary sedimentation tank for solid-liquid separation; it enters the filtration unit to further remove suspended solids; and it enters the evaporation crystallization system to obtain high-purity potassium chloride and sodium chloride (part of the evaporation mother liquor is returned to the water flow adjustment tank).

[0026] In this embodiment, the reflux ratio of the evaporation mother liquor is 10%; after the refluxed evaporation mother liquor enters the water flow regulating tank, the molar ratio of calcium ions to sulfate ions is 2:1. The sulfate removal rate can reach 84%, and the sodium carbonate reagent saving rate can reach 27%. Both potassium chloride crystal salt and sodium chloride crystal salt reach the level of superior industrial salt.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the co-treatment of wet desulfurization wastewater and sintering dust that can reduce sulfate accumulation, characterized in that: Includes the following steps: S1, sintering dust and desulfurization wastewater are mixed and washed with water. The eluent is then subjected to solid-liquid separation. The separated supernatant is fed into a water flow regulating tank for adjustment and then undergoes primary purification to remove magnesium hardness and ammonia nitrogen, followed by primary flocculation and primary precipitation. Calcium hydroxide is used for primary purification to remove magnesium hardness. Ammonia nitrogen is removed using an ammonia stripping tank, and sulfate ions are further reacted with calcium hydroxide to form calcium sulfate precipitate. The magnesium hydroxide precipitate and calcium sulfate precipitate generated during magnesium hardness removal are flocculated through primary flocculation. S2, after primary precipitation treatment, solid-liquid separation is performed, followed by secondary purification to remove calcium and hardness, secondary flocculation, and secondary precipitation for solid-liquid separation. The pH of the filtrate is adjusted to neutral, followed by heavy metal removal treatment and tertiary precipitation for solid-liquid separation. The filtrate is filtered to remove suspended solids and then sent to a concentrated brine conditioning tank for treatment. The effluent from the concentrated brine conditioning tank is sent to an evaporation crystallization system to obtain high-purity potassium chloride and sodium chloride. Then, part of the mother liquor from evaporation is returned to the water volume conditioning tank in step S1. Sodium carbonate is used for secondary purification to remove calcium and hardness. The secondary flocculation flocculates the calcium carbonate produced by sodium carbonate and calcium ions. During heavy metal removal treatment, heavy metal trapping agents and flocculants are added simultaneously.

2. The method for co-treating wet desulfurization wastewater and sintering dust as described in claim 1, which can reduce sulfate accumulation, is characterized in that: The reflux ratio of the evaporated mother liquor is between 0% and 30%.

3. The method for co-treating wet desulfurization wastewater and sintering dust as described in claim 2, which can reduce sulfate accumulation, is characterized in that: After the refluxed mother liquor enters the water flow equalization tank, the molar ratio of calcium ions to sulfate ions is 1:1-10:1.

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