Treatment method and device for resource utilization of desulfurization wastewater

Abstract

The invention relates to a treatment method and device for resource utilization of desulfurization wastewater in the technical field of desulfurization wastewater treatment, and the device comprises a pretreatment module, a magnesium removal module, a calcium removal module, a nanofiltration salt separation module, a concentration reduction module and a flue evaporation module, the method comprises the steps of pretreatment, magnesium removal treatment, calcium removal treatment, nanofiltration salt separation treatment, evaporative crystallization treatment and the like, heavy metals and suspended solids in the desulfurization wastewater are removed in the pretreatment module, a high-purity magnesium hydroxide product is extracted through the magnesium removal module, after calcium ions are removed in the calcium removal module, salt separation treatment is conducted through the nanofiltration salt separation module, and the high-purity magnesium hydroxide product is obtained. One part of the separated monovalent saline water is recycled, the other part of the separated monovalent saline water is concentrated and reduced by the concentration and reduction module and then enters the flue evaporation module to be evaporated, and the separated divalent saline water is recycled to a desulfurization system. The method has the advantages of simplicity and convenience in operation, economical operation, environment-friendly process and the like, high-purity magnesium hydroxide can be recycled, complete zero emission of the desulfurization high-chlorine wastewater is realized, and the method has a relatively high commercial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of desulfurization wastewater treatment, and relates to a treatment method and device for resource utilization of desulfurization wastewater. Background Art

[0002] The limestone wet desulfurization process in coal-fired power plants produces wastewater with high magnesium ion content. As a compound with high recovery value, the extraction and utilization of magnesium hydroxide has significant environmental and economic significance. However, due to the extremely high chloride and sulfate ion content in desulfurization wastewater and the unique physical and chemical properties of magnesium hydroxide itself, its purification and separation are difficult, the process is complex, and the equipment investment is high, which restricts its industrial application. At present, the typical technical solutions and existing problems for the method of extracting magnesium hydroxide from desulfurization wastewater are as follows: Ion exchange method: For example, the method disclosed in CN117383721A involves pretreatment, ion exchange, two-stage nanofiltration salt separation, electrodialysis + reverse osmosis concentration, and magnesium hydroxide synthesis. Calcium hydroxide is added to the ion exchange resin regeneration solution to precipitate magnesium hydroxide, which is then filtered and dried to obtain a solid. However, this method suffers from a short ion resin regeneration cycle (only 15 hours) and frequent regeneration. The magnesium hydroxide precipitation process is complex and its purity remains to be verified. Furthermore, the filter press has poor reliability, and the multi-effect evaporation unit is expensive and prone to scaling and clogging. Traditional double-alkali method: The method proposed in CN109095731B involves pretreatment with aeration, electrocoagulation, oil removal, ammonia nitrogen, and COD removal. During the dosing and salt separation stage, double alkali is added to separate most calcium ions and some magnesium ions. Nanofiltration is then used to separate monovalent and divalent ions, resulting in a solution with a high magnesium ion concentration. In the magnesium recovery stage, sodium hydroxide is added to produce a magnesium hydroxide precipitate. The precipitate is then filtered, dried, and dehydrated to produce a high-purity magnesium hydroxide product. However, this process requires a complex pretreatment system with high power consumption, high investment in ammonia nitrogen and COD removal, and the introduction of strong oxidants reduces the membrane life of the subsequent concentration system. The dosing stage requires a large amount of sodium carbonate to adjust the pH, which easily forms a mixed precipitate of magnesium hydroxide and calcium carbonate, leading to magnesium loss. Furthermore, the filter cake after filter pressing fails to meet industrial product standards. Other pretreatment processes: The hardness ion resource recovery pretreatment process disclosed in CN106007046A involves pre-coagulation and sedimentation, followed by three stages of softening and sedimentation. However, due to the addition of multiple reagents, such as sodium hydroxide, lime, and a polymer flocculation compound, during the first stage of softening and sedimentation, the magnesium component cannot be isolated independently. Subsequent phosphate treatment is required, and the process lacks wastewater reduction. The recovery system in CN212246246U includes a heavy metal and suspended solids removal unit, a calcium carbonate recovery unit, and a magnesium hydroxide recovery unit. The organic sulfur flocculant added to this system affects the operating cycle of the concentration membrane. Tubular membrane filtration consumes high power, while the circulating crystallization fluidized bed requires high investment and is difficult to monitor parameters. Magnesium hydroxide separation still relies on a filter press, and the drying process is not clearly defined. The treatment method in CN113955893B results in approximately 50% magnesium ion loss during the pretreatment stage, and the magnesium hydroxide separation process and drying steps are not fully developed. In summary, existing technologies generally suffer from complex operational processes, high operating costs, low magnesium resource recovery rates, insufficient product purity, and poor industrial adaptability. In particular, under the goal of zero discharge of high-chloride wastewater, how to achieve stable system operation while efficiently separating magnesium hydroxide has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0003] In view of the above problems, the purpose of the present invention is to develop a treatment method and device that is simple to operate, economical to run, can achieve complete zero discharge of desulfurized high-chloride wastewater and recover high-purity magnesium hydroxide.

[0004] Based on one of the purposes of the present invention, the present invention proposes the following technical solution: A method for resource utilization of desulfurization wastewater comprises the following steps: 1) Pretreatment: The desulfurization wastewater is pretreated to remove heavy metals and suspended solids to obtain pretreated effluent; Among them, the preprocessing includes the following steps: 11) treating the desulfurization wastewater by flocculation and sedimentation to obtain a second supernatant; 12) adding calcium hydroxide emulsion to the second supernatant to perform a weight removal reaction, adjusting the pH value of the mixed solution after the reaction to 8.5-9.0, to obtain a third supernatant; 13) The third supernatant is filtered through sand to obtain pretreated effluent, and the suspended solids in the pretreated effluent are less than 10 mg / L.

[0005] 2) Magnesium removal treatment: Sodium hydroxide solution is added to the pre-treated effluent to adjust the pH value to 10.8-11.5 for magnesium removal reaction. After the magnesium removal reaction, a mixed solution is obtained. The mixed solution is concentrated and separated by a tubular membrane to obtain a concentrated solution and produced water. The concentrated solution is diluted and then spray-dried under high pressure to obtain a magnesium hydroxide product with a purity of ≥90%; Among them, the filtration accuracy of tubular membrane concentration and separation is ≤0.1μm, and the turbidity of produced water is ≤5NTU. The appropriate filtration accuracy can be selected according to the operating power consumption and backwash frequency. The heat source of high-pressure spray drying can be clean dry flue gas or exhaust gas from the hot side of the heat exchanger or steam.

[0006] In this step, the pH value of the magnesium removal reaction is preferably 11.4. If it is too low, the magnesium ion reaction is insufficient, and if it is too high, it will cause waste of reagents. When the concentrated solution is diluted, a two-stage dilution and tubular membrane concentration process can be set to improve the purity of magnesium hydroxide.

[0007] 3) Calcium removal treatment: Sodium carbonate solution is added to the produced water in step 2) to carry out a calcium removal reaction. After the calcium removal reaction, precipitation separation is carried out to obtain a first supernatant and a calcium carbonate precipitate to remove calcium ions in the wastewater. The generated calcium carbonate can be reused as an absorbent in the desulfurization system.

[0008] 4) Nanofiltration salt separation treatment: The first supernatant in step 3) is subjected to nanofiltration salt separation treatment after adjusting the pH value to 6.0-8.0 to obtain monovalent brine and divalent brine. A portion of the monovalent brine is reused in steps 1), 2), and 3) for drug dispensing or pipeline flushing to save external process water, and a portion is subjected to concentration and reduction treatment. The divalent brine contains a large amount of sulfate ions and can be directly reused in the desulfurization system slurry pool to generate calcium sulfate.

[0009] Preferably, during the concentration and reduction treatment, multi-stage nanofiltration concentration can be used to increase the concentration of chloride ions in the wastewater during the subsequent flue evaporation treatment.

[0010] 5) Evaporation and crystallization treatment: The monovalent brine in step 4) is concentrated and reduced to obtain concentrated water and fresh water. The concentrated water is evaporated and crystallized to achieve zero wastewater discharge; the fresh water is reused in step 2) to dilute the concentrated solution.

[0011] Preferably, in step 11), a compounded inorganic super flocculant is added during the flocculation and sedimentation process to accelerate the settling of suspended solids in the wastewater. More preferably, the compounded inorganic super flocculant is HD-SS-03. The weight removal reaction in step 12) is carried out under stirring at a speed of 60 to 200 rpm, and the mass fraction of the calcium hydroxide emulsion is 10 to 15%.

[0012] Preferably, in step 2), the magnesium removal reaction is carried out under stirring, with a stirring speed of 200-500 rpm, a reaction time of 20-30 min, and a mass fraction of the sodium hydroxide solution of 32%.

[0013] Preferably, in step 2), the concentrated solution can be directly recycled into the mixed solution to form a precipitate, the precipitate is filtered and washed, and then diluted to a magnesium hydroxide emulsion with a solid content of 20-40%, and the magnesium hydroxide emulsion is high-pressure spray dried to obtain a magnesium hydroxide product with a purity of ≥90%.

[0014] Preferably, in step 3), the calcium removal reaction is carried out under stirring at a speed of 60-200 rpm for 20-30 minutes, and the mass fraction of the sodium carbonate solution is 10-15%. The amount of sodium carbonate added should be sufficient to completely remove the calcium ions. A low amount of sodium carbonate will reduce the calcium ion removal effect, while a high amount will result in waste of reagents.

[0015] Preferably, in step 4), nanofiltration salt separation is performed using a disc-tube, wide-channel, and contamination-resistant DTNF membrane system at an operating pressure between 2.0 and 3.8 MPa, preferably 2.5 MPa. A pressure too low can lead to poor salt separation and low monovalent brine yields; a pressure too high can easily cause divalent brine crystallization and blockage, compromising safe operation. The volume flow ratio of monovalent to divalent brine is preferably 9-3. Concentration and volume reduction is performed using a disc-tube, wide-channel, and contamination-resistant DTRO membrane system at an operating pressure of no less than 13 MPa, preferably 14-15 MPa, to minimize the proportion of brine, ensuring a ratio of freshwater to brine volume flow of no less than 2.

[0016] Preferably, in step 4), the pH of the first supernatant is adjusted by adding hydrochloric acid, and the adjusted pH is preferably 7.0. A pH too low will cause waste of reagents and significantly increase the amount of chloride ions introduced externally. The hydrochloric acid is an aqueous solution of hydrogen chloride, wherein the mass fraction of hydrogen chloride is 33%.

[0017] Preferably, in step 5), the evaporation crystallization treatment comprises the following steps: 51) Spraying concentrated water into the boiler bypass flue evaporator to completely evaporate and form a crystallized product, which is mixed with fly ash in the flue gas; 52) The mixture of crystallized products and fly ash in the flue gas is collected and stored through the fly ash collection and transportation system of the power plant, and then used as a raw material for building materials.

[0018] Based on one of the purposes of the present invention, the following technical solution is also proposed: A treatment device for resource utilization of desulfurization wastewater, used to implement the above-mentioned treatment method for resource utilization of desulfurization wastewater, comprising: A pretreatment module is used for pre-treating desulfurization wastewater; the pretreatment module includes a pre-sedimentation tank, a degravity tank, a sand filter, a cyclone, a sludge box, and a filter press; the desulfurization wastewater enters the pre-sedimentation tank and is mixed with a flocculant for natural sedimentation; the effluent from the pre-sedimentation tank is filtered through the sand filter and then connected to the water inlet of the degravity tank; the sludge from the pre-sedimentation tank and the degravity tank is respectively sorted by the corresponding cyclone and then returned to the pre-sedimentation tank or the degravity tank; the sludge is collected in the sludge box and filtered out using a filter press; In the pretreatment module, the cyclone is used to sort the effluent to increase its concentration, and the sludge is temporarily stored in the sludge box, which can greatly save the sludge discharge time of the filter press.

[0019] Magnesium removal module: used for magnesium removal of pre-treated effluent, including a magnesium removal tank, a tubular membrane filter, a magnesium hydroxide storage tank and a spray dryer. A magnesium removal agitator is provided in the magnesium removal tank; the water outlet of the magnesium removal tank is connected to the water inlet of the tubular membrane filter, and the concentrated water outlet of the tubular membrane filter is connected to the water inlets of the magnesium removal tank and the magnesium hydroxide storage tank respectively through pipes. The water outlet of the magnesium hydroxide storage tank is connected to the spray dryer. A silo pump is provided at the bottom of the spray dryer, and the silo pump is connected to the magnesium hydroxide dry powder storage bin through a pneumatic conveying pipe; Decalcification module: used for decalcification of produced water after magnesium removal treatment, including a decalcification tank and a pH adjustment tank. The water inlet of the decalcification tank is connected to the produced water outlet of the tubular membrane filter, and the water outlet of the decalcification tank is connected to the pH adjustment tank. A decalcification agitator is provided in the decalcification tank; Nanofiltration salt separation module: used for nanofiltration salt separation of water produced after decalcification treatment, including sand filter 2, high-pressure water pump 1 and a first disc-tube reverse osmosis membrane system. The effluent of the pH adjustment tank is filtered by the sand filter 2 and connected to the water inlet of the high-pressure water pump 1. The suspended solids in the effluent of the sand filter 2 are less than 10 mg / L. The outlet of the high-pressure water pump 1 is connected to the water inlet of the first disc-tube reverse osmosis membrane system, and the first disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTNF membrane system. Concentration and reduction module: used for concentrating and reducing the monovalent brine obtained by nanofiltration salt separation, including a security filter, a second high-pressure water pump and a second disc-tube reverse osmosis membrane system. The monovalent brine is connected to the water inlet of the second high-pressure water pump through the security filter, and the water inlet of the second high-pressure water pump is connected to the water inlet of the second disc-tube reverse osmosis membrane system. The second disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTRO membrane system. The flue evaporation module includes a boiler bypass flue evaporator, which is used to evaporate and crystallize the concentrated water obtained after the concentration reduction process. The boiler bypass flue evaporator uses a dual-fluid spray gun with a pressure ratio of atomizing air to concentrated water between 0.9 and 1.4, and a dual-fluid spray gun pressure of no less than 0.3 MPa to achieve good atomization and ensure rapid and complete evaporation of the concentrated water.

[0020] The working principle of the present invention is to remove heavy metals and suspended matter in the desulfurization wastewater in the pretreatment module, extract high-purity magnesium hydroxide product through the magnesium removal module, remove calcium ions in the calcium removal module, and then perform salt separation treatment through the nanofiltration salt separation module. Part of the separated monovalent brine is reused, and part is concentrated and reduced in the concentration and reduction module and then evaporated in the flue evaporation module. The separated divalent brine is reused in the desulfurization system.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention changes the traditional double-alkali method of adjusting the pH value in one stage to a staged pH adjustment method. In the first stage, calcium hydroxide is still used to adjust the pH value of the desulfurization wastewater from 5-6 to 8.5-9.0. While removing heavy metal impurities, it avoids the problem of large amounts of magnesium being lost with calcium sulfate precipitation. At the same time, due to the small pH adjustment range, the amount of calcium hydroxide used is greatly reduced compared to the traditional double-alkali method, and the additional calcium ions introduced are greatly reduced. In the second stage, sodium hydroxide solution is used to adjust the pH value to 10.8-11.5. The precipitate produced in this stage is high-purity magnesium hydroxide, which solves the problem of separating magnesium hydroxide from the source.

[0022] 2. The present invention is the first in the industry to use a tubular membrane filter to filter and separate a suspension containing magnesium hydroxide, solving the problem of difficult precipitation and separation of magnesium hydroxide and avoiding the impact of high molecular organic flocculants on the subsequent membrane concentration system.

[0023] 3. The present invention creatively uses a combination of a tubular membrane filter and a high-pressure spray dryer in the process of magnesium removal, which more simply and directly obtains industrial-grade magnesium hydroxide powder. Compared with the existing process flow of filter pressing, washing, evaporation drying, and crushing, the process is simple, the equipment reliability is high, and the investment is relatively small.

[0024] 4. The present invention takes into account the water balance and ion balance of the entire system, and reduces as much as possible the amount of water added by external process water and the amount of sodium carbonate additionally increased by the large amount of calcium hydroxide used, resulting in relatively low operating costs.

[0025] 5. The present invention helps to achieve zero discharge of desulfurized high-chloride wastewater by setting up a flue evaporation module, and the crystalline product obtained after evaporation can be used as a building material together with fly ash, which helps to reduce the cost of solid waste treatment and realize the recycling of solid waste resources.

[0026] In summary, the present invention has the advantages of simple operation, economical operation and environmentally friendly process, can recycle high-purity magnesium hydroxide, and can achieve complete zero discharge of desulfurized high-chloride wastewater, and has great commercial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is a simple process flow chart of a treatment method for resource utilization of desulfurization wastewater in an embodiment of the present invention; Figure 2 Detailed process flow chart of a treatment method for resource utilization of desulfurization wastewater according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the arrangement structure of a treatment device for resource utilization of desulfurization wastewater according to an embodiment of the present invention; Figure 4 This is a comparison table of water quality parameter detection before, during and after desulfurization wastewater treatment in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are 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 making creative efforts are within the scope of protection of the present invention.

[0029] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0030] There is no particular limitation on the purity of all raw materials in the present invention, and the present invention preferably adopts conventional purity used in the art.

[0031] The devices used in the present invention are not particularly limited and can be devices commonly used in the art.

[0032] Example like Figure 3 As shown, this embodiment proposes a treatment device for resource utilization of desulfurization wastewater, comprising: A pretreatment module is used for pre-treating desulfurization wastewater in a power plant desulfurization system 19; the pretreatment module includes a pre-sedimentation tank 1, a degravity removal tank 2, a sand filter 3, a cyclone 4, a sludge box 5, and a filter press 6; the desulfurization wastewater enters the pre-sedimentation tank and is mixed with a flocculant for natural sedimentation; the effluent from the pre-sedimentation tank is filtered through a sand filter and then connected to the water inlet of the degravity removal tank; the sludge from the pre-sedimentation tank and the degravity removal tank is respectively separated by the corresponding cyclones and the clear liquid is returned to the pre-sedimentation tank or the degravity removal tank; the sludge is collected in the sludge box and filtered out using a filter press; In the pretreatment module, the cyclone is used to sort the effluent to increase its concentration, and the sludge is temporarily stored in the sludge box, which can greatly save the time of the filter press to discharge the sludge.

[0033] Magnesium removal module: used for magnesium removal of pre-treated effluent, including a magnesium removal tank 7, a tubular membrane filter 8, a magnesium hydroxide storage tank 9 and a spray dryer 10, wherein a magnesium removal agitator (not shown in the figure) is provided in the magnesium removal tank; the water outlet of the magnesium removal tank is connected to the water inlet of the tubular membrane filter, and the concentrated water outlet of the tubular membrane filter is connected to the water inlets of the magnesium removal tank and the magnesium hydroxide storage tank respectively through pipes, and the water outlet of the magnesium hydroxide storage tank is connected to the spray dryer, and a silo pump (not shown in the figure) is provided at the bottom of the spray dryer, and the silo pump is connected to the magnesium hydroxide dry powder storage silo (not shown in the figure) through a pneumatic conveying pipe (not shown in the figure); In this embodiment, an intermediate storage tank 11 and a second filter press 12 are further provided between the concentrated water outlet pipe of the tubular membrane filter and the water inlet of the magnesium hydroxide storage tank. The intermediate storage tank is used to cache the concentrated water to improve the stability of the device operation, and the second filter press is used to filter and wash the magnesium hydroxide to improve the purity of the magnesium hydroxide.

[0034] Decalcification module: used for decalcifying the produced water after magnesium removal treatment, including a decalcification tank 13 and a pH adjustment tank 14. The water inlet of the decalcification tank is connected to the produced water outlet of the tubular membrane filter, and the water outlet of the decalcification tank is connected to the pH adjustment tank. A decalcification agitator (not shown in the figure) is provided in the decalcification tank. Nanofiltration salt separation module: used for nanofiltration salt separation of water produced after decalcification treatment, including sand filter 2 15, high-pressure water pump 1 (not shown in the figure) and a first disc-tube reverse osmosis membrane system 16. The effluent from the pH adjustment tank is filtered by sand filter 2 and connected to the water inlet of high-pressure water pump 1. The suspended solids in the effluent from sand filter 2 are less than 10 mg / L. The outlet of high-pressure water pump 1 is connected to the water inlet of the first disc-tube reverse osmosis membrane system, and the first disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTNF membrane system. Concentration and reduction module: used for concentrating and reducing the monovalent brine obtained by nanofiltration salt separation, including a security filter (not shown in the figure), a high-pressure water pump 2 (not shown in the figure) and a second disc-tube reverse osmosis membrane system 17. The monovalent brine is connected to the water inlet of the high-pressure water pump 2 through the security filter, and the water inlet of the high-pressure water pump 2 is connected to the water inlet of the second disc-tube reverse osmosis membrane system. The second disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTRO membrane system; The flue evaporation module includes a boiler bypass flue evaporator 18, which is used to evaporate and crystallize the concentrated water obtained after the concentration reduction process. The boiler bypass flue evaporator uses a dual-fluid spray gun (not shown). The pressure ratio of the atomizing air to the concentrated water is between 0.9 and 1.4, and the dual-fluid spray gun pressure is not less than 0.3 MPa to achieve good atomization and ensure rapid and complete evaporation of the concentrated water.

[0035] like Figure 1 、 Figure 2 As shown, based on the above-mentioned treatment device for resource utilization of desulfurization wastewater, this embodiment also proposes a treatment method for resource utilization of desulfurization wastewater, which is used to treat desulfurization wastewater discharged from a desulfurization system of a power plant. The raw water quality is as follows: Figure 4 As shown, the processing method includes the following steps: Desulfurization wastewater first enters the pretreatment module, and the HD-SS-03 compound inorganic super flocculant of Beijing Huade Chuangye Environmental Protection Equipment Co., Ltd. is added to the pre-sedimentation tank to accelerate sedimentation; a calcium hydroxide emulsion with a mass fraction of 10-15% is added to the degravity tank to remove heavy metals in the wastewater. The suspended matter in the water is removed by precipitation and filtration. After pretreatment, the heavy metal content in the water is detected as follows: Figure 4 shown.

[0036] The pretreated product water enters the magnesium removal module. A 30-33% sodium hydroxide solution is added to the magnesium removal tank, circulated and stirred for 50 minutes, and the pH is adjusted to 11.0. This produces a large amount of magnesium hydroxide, which is uniformly and stably suspended. The product water passes through a 50μm bag filter, with minimal turbidity change. The product water passes through a 0.1μm tubular membrane filter with a flux of ≤90L / h.㎡, resulting in virtually no suspended solids and a turbidity of ≤5NTU, demonstrating the effectiveness of the 0.1μm tubular membrane filter in separating magnesium hydroxide. The concentrated water from the tubular membrane returns to the magnesium removal tank, where it settles at the bottom and is regularly discharged into an intermediate storage tank. After filtration and rinsing in a second filter press, the filter cake is diluted to a magnesium hydroxide emulsion with a solids content of 20-40%. This emulsion is then stored in a magnesium hydroxide storage tank and pumped to a centrifugal spray dryer for high-pressure spray drying. Clean dry flue gas can be used as the heat source for high-pressure spray drying. The centrifugal disk rotates at a speed of about 10,000-20,000 rpm. The moisture content of the obtained magnesium hydroxide dry powder is less than 0.5%, the purity of the magnesium hydroxide reaches 93%, and the bulk density is 0.3 kg / m³, meeting the Class II standard of the Industrial Magnesium Hydroxide Specification (HG / T3607-2007).

[0037] The water produced by the magnesium removal module enters the calcium removal module. A 12% sodium carbonate solution is added to the decalcification tank. The amount of addition is determined by the calcium ion content of the influent water and stirred for about 30 minutes. A small amount of calcium carbonate precipitation is produced and the supernatant flows into the pH adjustment tank. Hydrochloric acid with a mass fraction of 33% hydrogen chloride is added and stirred in a cycle for about 10 minutes to adjust the pH value to 7.0. Figure 4 It can be seen that the main ions in the produced water are sulfate, chloride, sodium, etc.

[0038] After the water produced by the decalcification module is filtered by the sand filter for the second time, it enters the nanofiltration salt separation module for nanofiltration salt separation treatment to obtain monovalent brine and divalent brine. Part of the monovalent brine is reused in other steps for drug preparation or pipeline flushing to save external process water, and part is concentrated and reduced. The divalent brine contains a large amount of sulfate, which can be directly reused in the desulfurization system slurry pool to generate calcium sulfate. During the implementation process, two types of disc-tube wide-flow nanofiltration membranes and one medium-volume nanofiltration membrane were used successively. When the inlet pH was 7~8, the conductivity was 47~59ms / cm, and the Ca 2+ Under influent conditions of less than 40 mg / L and a membrane flux ≤22 L / h.m2, the first disc-tube nanofiltration membrane achieved optimal sulfate separation at an operating pressure of approximately 2.6 MPa, achieving a sulfate removal rate of approximately 99.5% in the product water. The volume flow ratio of monovalent to divalent brine was 6. When the pressure was further increased to approximately 5-6 MPa, the ratio reached 9, achieving a sulfate removal rate of approximately 99.9% in the product water. However, rapid crystallization on the concentrate side caused blockage. Considering economic efficiency and operational stability, the operating pressure was ultimately selected to be between 2.5 and 3.8.

[0039] The monovalent salt water produced by the nanofiltration salt separation module passes through the security filter and enters the concentration and reduction module to obtain concentrated water and fresh water. The concentrated water is evaporated and crystallized to achieve zero wastewater discharge; the fresh water is reused in the magnesium removal module to dilute the concentrated solution. The nanofiltration salt separation module uses a 16Mpa high-pressure pump and a disc-type wide-channel DTRO membrane system. Under the inlet water pH 7~8, conductivity: 45~51ms / cm, membrane flux ≤11L / h.㎡, when the operating pressure is 14.5Mpa, the ratio of the volume flow of fresh water to concentrated water is 2, and the recovery rate is about 67%. By the attached Figure 4 It can be seen that the concentration ratio of chloride ions in concentrated water is about 4 compared with that of influent water.

[0040] The concentrated water produced by the nanofiltration salt separation module enters the flue evaporation module for evaporation and crystallization. This evaporation and crystallization process involves spraying the concentrated water into the boiler bypass flue evaporator, where it completely evaporates to form a crystalline product. This crystalline product is then mixed with fly ash in the flue gas. The mixture of crystalline product and fly ash in the flue gas is collected and stored by the power plant's fly ash collection and transportation system, and then used as a building material.

[0041] The working principle of the present invention is to remove heavy metals and suspended matter in the desulfurization wastewater in the pretreatment module, extract high-purity magnesium hydroxide product through the magnesium removal module, remove calcium ions in the calcium removal module, and then perform salt separation treatment through the nanofiltration salt separation module. Part of the separated monovalent brine is reused, and part is concentrated and reduced in the concentration and reduction module and then evaporated in the flue evaporation module. The separated divalent brine is reused in the desulfurization system.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for resource utilization of desulfurization wastewater, characterized in that: The following steps are involved: 1) Pretreatment: The desulfurization wastewater is pretreated to remove heavy metals and suspended solids to obtain pretreated effluent; 2) Magnesium removal treatment: Sodium hydroxide solution is added to the pre-treated effluent to adjust the pH value to 10.8-11.5 for magnesium removal reaction. After the magnesium removal reaction, a mixed solution is obtained. The mixed solution is concentrated and separated by a tubular membrane to obtain a concentrated solution and produced water. The concentrated solution is diluted and then spray-dried under high pressure to obtain a magnesium hydroxide product with a purity of ≥90%; 3) Decalcification: Sodium carbonate solution is added to the produced water in step 2) to carry out a decalcification reaction. After the decalcification reaction, precipitation separation is performed to obtain a first supernatant and a calcium carbonate precipitate. The calcium carbonate precipitate is recycled to the desulfurization system for use as an absorbent. 4) Nanofiltration salt separation: The first supernatant in step 3) is subjected to nanofiltration salt separation after adjusting the pH value to 6.0-8.0 to obtain monovalent brine and divalent brine. A portion of the monovalent brine is reused in steps 1), 2), and 3) for drug dispensing or pipeline flushing, and a portion is subjected to concentration and reduction treatment. The divalent brine is reused to the desulfurization system slurry tank; 5) Evaporation and crystallization treatment: The monovalent brine in step 4) is concentrated and reduced to obtain concentrated water and fresh water. The concentrated water is evaporated and crystallized to achieve zero wastewater discharge; the fresh water is reused in step 2) to dilute the concentrated solution.

2. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: The preprocessing of step 1) includes the following steps: 11) treating the desulfurization wastewater by flocculation and sedimentation to obtain a second supernatant; 12) adding calcium hydroxide emulsion to the second supernatant to perform a weight removal reaction, adjusting the pH value of the mixed solution after the reaction to 8.5-9.0, to obtain a third supernatant; 13) The third supernatant is filtered through sand to obtain pretreated effluent, and the suspended solids in the pretreated effluent are less than 10 mg / L.

3. The method for resource utilization of desulfurization wastewater according to claim 2, characterized in that: In step 11), a compounded inorganic super flocculant is added during the flocculation and sedimentation treatment, and the model of the compounded inorganic super flocculant is HD-SS-03; in step 12), the weight removal reaction is carried out under stirring, the stirring speed is 60-200 rpm, and the mass fraction of the calcium hydroxide emulsion is 10-15%.

4. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 2), the magnesium removal reaction is carried out under stirring at a stirring speed of 200-500 rpm, a reaction time of 20-30 min, and a mass fraction of the sodium hydroxide solution of 32%.

5. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 2), the concentrated solution can be directly reused in the mixed solution to form a precipitate, the precipitate is filtered and washed, and then diluted to a magnesium hydroxide emulsion with a solid content of 20-40%, and the magnesium hydroxide emulsion is high-pressure spray dried to obtain a magnesium hydroxide product with a purity of ≥90%.

6. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 3), the decalcification reaction is carried out under stirring at a stirring speed of 60 to 200 rpm, a reaction time of 20 to 30 min, and a mass fraction of the sodium carbonate solution of 10 to 15%.

7. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 4), a disc-tube, wide-channel, anti-fouling DTNF membrane system is used for nanofiltration salt separation treatment, the operating pressure is between 2.0 and 3.8 MPa, and the ratio of the volume flow of monovalent brine to divalent brine is 9 to 3; a disc-tube, wide-channel, anti-fouling DTRO membrane system is used for concentration and reduction treatment, the operating pressure is not less than 13 MPa, and the ratio of the volume flow of fresh water to concentrated water is not less than 2.

8. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 4), the pH value of the first supernatant is adjusted by adding hydrochloric acid, wherein the hydrochloric acid is an aqueous solution of hydrogen chloride, wherein the mass fraction of hydrogen chloride is 33%.

9. The method for resource utilization of desulfurization wastewater according to claim 1, characterized in that: In step 5), the evaporation crystallization treatment comprises the following steps: 51) spraying concentrated water into the boiler bypass flue evaporator to completely evaporate and form a crystal product, and the crystal product is mixed with the fly ash in the flue gas; 52) The mixture of crystallized products and fly ash in the flue gas is collected and stored through the fly ash collection and transportation system of the power plant, and then used as a raw material for building materials.

10. A treatment device for resource utilization of desulfurization wastewater, used to implement the treatment method for resource utilization of desulfurization wastewater according to any one of claims 1 to 9, characterized in that: include: A pretreatment module is used for pre-treating desulfurization wastewater; the pretreatment module includes a pre-sedimentation tank, a degravity tank, a sand filter, a cyclone, a sludge box, and a filter press; the desulfurization wastewater enters the pre-sedimentation tank and is mixed with a flocculant for natural sedimentation; the effluent from the pre-sedimentation tank is filtered through the sand filter and then connected to the water inlet of the degravity tank; the sludge from the pre-sedimentation tank and the degravity tank is respectively sorted by the corresponding cyclone and then returned to the pre-sedimentation tank or the degravity tank; the sludge is collected in the sludge box and filtered out using a filter press; Magnesium removal module: used for magnesium removal of pre-treated effluent, including a magnesium removal tank, a tubular membrane filter, a magnesium hydroxide storage tank and a spray dryer. A magnesium removal agitator is provided in the magnesium removal tank; the water outlet of the magnesium removal tank is connected to the water inlet of the tubular membrane filter, and the concentrated water outlet of the tubular membrane filter is connected to the water inlets of the magnesium removal tank and the magnesium hydroxide storage tank respectively through pipes. The water outlet of the magnesium hydroxide storage tank is connected to the spray dryer. A silo pump is provided at the bottom of the spray dryer, and the silo pump is connected to the magnesium hydroxide dry powder storage bin through a pneumatic conveying pipe; Decalcification module: used for decalcification of produced water after magnesium removal treatment, including a decalcification tank and a pH adjustment tank. The water inlet of the decalcification tank is connected to the produced water outlet of the tubular membrane filter, and the water outlet of the decalcification tank is connected to the pH adjustment tank. A decalcification agitator is provided in the decalcification tank; Nanofiltration salt separation module: used for nanofiltration salt separation of water produced after decalcification treatment, including sand filter 2, high-pressure water pump 1 and a first disc-tube reverse osmosis membrane system. The effluent from the pH adjustment tank is filtered by the sand filter 2 and connected to the water inlet of the high-pressure water pump 1. The water outlet of the high-pressure water pump 1 is connected to the water inlet of the first disc-tube reverse osmosis membrane system, and the first disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTNF membrane system. Concentration and reduction module: used for concentrating and reducing the monovalent brine obtained by nanofiltration salt separation, including a security filter, a second high-pressure water pump and a second disc-tube reverse osmosis membrane system. The monovalent brine is connected to the water inlet of the second high-pressure water pump through the security filter, and the water inlet of the second high-pressure water pump is connected to the water inlet of the second disc-tube reverse osmosis membrane system. The second disc-tube reverse osmosis membrane system adopts a disc-tube wide-channel DTRO membrane system. Flue evaporation module: includes a boiler bypass flue evaporator, which is used to evaporate and crystallize the concentrated water obtained after the concentration and reduction treatment. The boiler bypass flue evaporator adopts a dual-fluid spray gun, and when the dual-fluid spray gun is in use, the pressure ratio of the atomizing air to the concentrated water is between 0.9 and 1.4, and the injection pressure of the dual-fluid spray gun is not less than 0.3Mpa.

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