A method and system for the co-treatment of desulfurization gypsum and desulfurization wastewater

Abstract

This invention discloses a method and system for the synergistic treatment of desulfurization gypsum and desulfurization wastewater. The method includes: 1) pretreating the desulfurization wastewater to remove heavy metals and magnesium ions, obtaining a mixture; 2) separating the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase; 3) mixing the first liquid phase from step 2) with desulfurization gypsum and then introducing it into desulfurization flue gas for a metathesis reaction to obtain reaction products; 4) separating the reaction products from step 3) into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase; 5) crystallizing the second liquid phase from step 4) to obtain a mixture of ammonium sulfate and ammonium chloride and sodium sulfate product; 6) heat-treating the mixture of ammonium sulfate and ammonium chloride from step 5) to obtain ammonium sulfate and ammonium chloride products. This invention achieves the synergistic treatment of desulfurization gypsum and desulfurization wastewater, solving the problem of the disposal of desulfurization gypsum and the problem of zero discharge of desulfurization wastewater.

Description

Technical Field

[0001] This invention relates to the field of waste resource utilization technology, specifically to a method and system for the co-treatment of desulfurized gypsum and desulfurized wastewater. Background Technology

[0002] By the end of 2020, my country's total installed power generation capacity reached 2.2 billion kW, with thermal power accounting for 56.58% of the total. Thermal power units will continue to dominate the power generation industry for a considerable period. To meet SO2 emission standards, domestic coal-fired power units generally use lime-limestone slurry to desulfurize boiler flue gas. During SO2 absorption, the slurry generates a mixture primarily composed of calcium sulfate dihydrate; the dehydrated solid product is desulfurization gypsum. Simultaneously, this process uses limestone as the absorbent, and for every ton of sulfur dioxide removed, approximately 0.7 tons of carbon dioxide are emitted, increasing carbon emissions from power plants. According to data jointly compiled by the Ministry of Ecology and Environment and the Huajing Industry Research Institute, my country's desulfurization gypsum production in 2019 was 110-130 million tons. As a solid industrial waste, desulfurization gypsum is difficult to utilize directly within thermal power plants and requires suitable storage sites. This not only occupies large areas of land but also easily causes secondary pollution to the environment during the stockpiling process. Especially in economically underdeveloped areas, where gypsum consumption is low and desulfurization gypsum cannot be sold, the problem of stockpiling and waste is prominent. Large-scale, high-value disposal and utilization of desulfurization gypsum generated by thermal power units is one of the urgent problems to be solved in the environmental protection field of the power industry.

[0003] For some power companies that cannot effectively utilize desulfurization gypsum, the large amount of gypsum produced as a byproduct has become a heavy economic and environmental burden, with greater pressure to reduce carbon emissions, directly impacting the sustainable, high-quality, and healthy development of these companies. Therefore, developing new technologies and methods to offset the generation of desulfurization gypsum has become an urgent problem for some companies.

[0004] CN102583443B discloses a method for producing ammonium sulfate using ammonium bicarbonate as the main raw material. The method includes taking solid ammonium bicarbonate, process water, liquid ammonia, or gaseous ammonia, and adding them to a dissolving tank according to a metering ratio to prepare an ammonium carbonate solution. The ammonium carbonate solution is then pumped into a conversion reactor, and phosphogypsum is added in proportion to carry out the conversion reaction, controlling the density of the reaction slurry to be 1.35–1.40 g / cm³. The reaction slurry is pumped to a filter and filtered under vacuum to separate ammonium sulfate filtrate and calcium carbonate residue filter cake. The ammonium sulfate filtrate is then pumped into an evaporator for crystallization, and after crystallization, an ammonium sulfate slurry is obtained. Finally, the ammonium sulfate product is obtained through centrifugation and drying.

[0005] CN101284676B discloses a low-cost ammonium sulfate manufacturing process, characterized by: adding gypsum powder with a particle size of 150-200 mesh to ammonia water containing CO2 at a concentration of 180-200 droplets and a temperature of 40℃-50℃; heating to react the carbonated ammonia water with the gypsum; the pH of the mixed liquid during the reaction is 7.2-7.5; the reaction temperature is controlled at 50-55℃; and the reaction time is 1-2 hours; the mixed liquid after the reaction is filtered; the ammonium sulfate liquid from which CaCO3 is separated is cooled and crystallized; and the water is separated from the crystallized ammonium sulfate liquid to obtain the ammonium sulfate product, with calcium carbonate as a byproduct.

[0006] CN110697731A discloses a method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum. The method uses solid ammonium bicarbonate and high-concentration desulfurized gypsum slurry as reactants. After two-step reaction, a solid product with high calcium carbonate content and ammonium sulfate crystals can be obtained.

[0007] In the aforementioned domestic patents, calcium carbonate and ammonium sulfate are prepared using gypsum, phosphogypsum, or desulfurized gypsum as raw materials. Although these methods can solve the problem of desulfurized gypsum treatment to a certain extent, they offer limited utilization of desulfurized gypsum. Furthermore, the high energy consumption of ammonium sulfate evaporation and crystallization makes it difficult to achieve targeted resource utilization of desulfurized gypsum. Summary of the Invention

[0008] In view of this, the main objective of the present invention is to provide a method and system for the synergistic treatment of desulfurized gypsum and desulfurized wastewater, thereby achieving the synergistic treatment of desulfurized gypsum and desulfurized wastewater and solving the problem of the disposal of desulfurized gypsum and the problem of zero discharge of desulfurized wastewater.

[0009] To achieve the above-mentioned objectives, the first aspect of this invention provides a method for the co-treatment of desulfurization gypsum and desulfurization wastewater, comprising the following steps:

[0010] 1) The desulfurization wastewater is pretreated to remove heavy metals and magnesium ions, resulting in a mixture;

[0011] 2) Separate the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase;

[0012] 3) After mixing the first liquid phase in step 2) with desulfurized gypsum, the mixture is introduced into the desulfurized flue gas to carry out a metathesis reaction to obtain the reaction products;

[0013] 4) Separate the reaction product from step 3) into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase;

[0014] 5) The second liquid phase in step 4) is subjected to crystallization treatment to obtain a mixture of ammonium sulfate, ammonium chloride and sodium sulfate product;

[0015] 6) Heat-treat the mixture of ammonium sulfate and ammonium chloride obtained in step 5) to obtain ammonium sulfate product and ammonium chloride product.

[0016] Furthermore, the pretreatment of desulfurization wastewater in step 1) includes: adding an excess of ammonia water to the desulfurization wastewater and allowing it to react fully to remove magnesium ions and heavy metals from the desulfurization wastewater.

[0017] Furthermore, the ammonia water and the Mg in the desulfurization wastewater 2+ The ratio of the sum of the amounts of CaSO4 in desulfurized gypsum is n(NH3): [n(Mg2+)] 2+ )+n(CaSO4)]=2-3:1.

[0018] Furthermore, the conditions for the metathesis reaction in step 3) include: the reaction temperature is controlled at 20-60℃, the reaction time is 40-120 min, and the stirring rate is 60-400 r / min.

[0019] Furthermore, the molar ratio of CO2 in the desulfurized flue gas to CaSO4 in the desulfurized gypsum is 1-2:1, and / or the mass ratio of desulfurized gypsum to the first liquid phase is 1:5-10.

[0020] Furthermore, the calcium carbonate obtained in step 4) is recycled to the limestone-gypsum flue gas desulfurization system for flue gas desulfurization.

[0021] Further, the crystallization process in step 5) includes: evaporating and crystallizing the second liquid phase to obtain a mixture of ammonium sulfate and ammonium chloride, preferably, the evaporation and crystallization temperature is 70-90℃.

[0022] Further, the heat treatment in step 6) includes: heating and separating the mixture of ammonium sulfate and ammonium chloride to obtain ammonium sulfate and ammonium chloride products; preferably, the heating temperature is 200-350℃.

[0023] Furthermore, the condensate obtained from the evaporation and crystallization is recovered and used as makeup water for the desulfurization system.

[0024] Furthermore, the mother liquor generated from evaporation and crystallization is subjected to freeze crystallization to recover sodium sulfate product, and the freeze crystallization mother liquor is returned to the evaporation and crystallization unit; preferably, the freeze crystallization temperature is -5 to 15°C.

[0025] Furthermore, the desulfurized gypsum, desulfurized wastewater, and desulfurized flue gas originate from a limestone-gypsum flue gas desulfurization system.

[0026] A second aspect of the present invention also provides a co-treatment system for desulfurized gypsum and desulfurized wastewater, comprising:

[0027] The pretreatment unit is used to remove heavy metals and magnesium ions from the desulfurization wastewater to obtain a mixture;

[0028] The first solid-liquid separation unit is used to separate the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase;

[0029] The reactor is used to carry out a metathesis reaction of the first liquid phase, desulfurized gypsum, in the presence of desulfurized flue gas to obtain reaction products.

[0030] The second solid-liquid separation unit is used to separate the reaction products into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase.

[0031] A crystallization unit is used to crystallize the second liquid phase to obtain ammonium sulfate, ammonium chloride and sodium sulfate products;

[0032] A heat treatment unit is used to heat treat the mixture of ammonium sulfate and ammonium chloride to obtain ammonium sulfate product and ammonium chloride product.

[0033] Furthermore, the crystallization unit includes an evaporation crystallization unit and a freeze crystallization unit.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] This invention pretreats desulfurization wastewater to remove heavy metals and magnesium ions. The solid product after solid-liquid separation is high-purity magnesium hydroxide. The liquid product is thoroughly mixed with desulfurization gypsum and undergoes a metathesis reaction in the presence of desulfurization flue gas. After solid-liquid separation, the main component of the solid product is calcium carbonate. The main components of the liquid product are ammonium sulfate, ammonium chloride, and sodium sulfate. After crystallization and appropriate heat treatment, ammonium sulfate, ammonium chloride, and sodium sulfate products are obtained respectively. Therefore, this invention can simultaneously treat desulfurization gypsum, desulfurization wastewater, and part of the carbon dioxide in desulfurization flue gas, solving the problem of desulfurization gypsum disposal, reducing carbon emissions, achieving zero discharge of desulfurization wastewater, saving desulfurization wastewater treatment costs, and achieving low overall treatment costs.

[0036] Other features and advantages of the present invention will be described in detail through the following specific embodiments. Attached Figure Description

[0037] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0038] Figure 1 This is a schematic diagram of the process flow for a method of co-treating desulfurized gypsum and desulfurized wastewater, as exemplified by the present invention. Detailed Implementation

[0039] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0040] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0041] Unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and connections within two components or interactions between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0042] The first aspect of this invention provides a method for the synergistic treatment of desulfurization gypsum and desulfurization wastewater, comprising:

[0043] 1) The desulfurization wastewater is pretreated to remove heavy metals and magnesium ions, resulting in a mixture;

[0044] 2) Separate the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase;

[0045] 3) After mixing the first liquid phase in step 2) with desulfurized gypsum, the mixture is introduced into the desulfurized flue gas to carry out a metathesis reaction to obtain the reaction products;

[0046] 4) Separate the reaction product from step 3) into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase;

[0047] 5) The second liquid phase in step 4) is subjected to crystallization treatment to obtain a mixture of sodium sulfate, ammonium sulfate and ammonium chloride;

[0048] 6) Heat-treat the mixture of ammonium sulfate and ammonium chloride obtained in step 5) to obtain ammonium sulfate product and ammonium chloride product.

[0049] In a specific example, step 1) of pretreating the desulfurization wastewater includes: adding excess ammonia water to the desulfurization wastewater and allowing it to react fully to remove magnesium ions and heavy metals from the wastewater. The reaction principle is as follows:

[0050] Mg 2+ +2NH3·H2O=Mg(OH)2+2NH4 +

[0051] Preferably, the ammonia water and the Mg in the desulfurization wastewater 2+ The ratio of the sum of the amounts of CaSO4 in desulfurized gypsum is n(NH3): [n(Mg2+)] 2+ [n(CaSO4)] = 2-3:1, so that the reaction is complete.

[0052] In a specific example, in step 2), the first liquid phase is thoroughly mixed with the desulfurized gypsum, and a certain amount of desulfurized flue gas is introduced, allowing the desulfurized gypsum, residual ammonia, and carbon dioxide in the flue gas to undergo a complete metathesis reaction under certain reaction conditions. The reaction principle is as follows:

[0053] CaSO4·2H2O+CO2+2NH3·H2O=CaCO3+(NH4)2SO4+3H2O

[0054] Preferably, the conditions for the metathesis reaction in step 3) include: the reaction temperature is controlled at 20-60℃, the reaction time is 40-120 min, and the stirring rate during the reaction is 60-400 r / min. Under the above reaction conditions, a higher gypsum conversion rate can be obtained.

[0055] Preferably, the molar ratio of CO2 in the flue gas to CaSO4 in the desulfurized gypsum is 1-2:1 to ensure complete reaction.

[0056] Preferably, the mass ratio of desulfurized gypsum to the first liquid phase is 1:5-10 to ensure complete reaction.

[0057] Preferably, the calcium carbonate obtained in step 4) is recycled to the limestone-gypsum flue gas desulfurization system for flue gas desulfurization.

[0058] In a specific example, the crystallization process in step 5) includes: the second liquid phase mainly consists of ammonium sulfate, ammonium chloride, and sodium sulfate, which is evaporated and crystallized to obtain a mixture of ammonium sulfate and ammonium chloride. Preferably, the evaporation and crystallization temperature is 70-90°C; crystallization is difficult at lower temperatures.

[0059] In a specific example, the heat treatment in step 6) includes: heating and separating the obtained ammonium sulfate and ammonium chloride mixture to obtain high-purity ammonium sulfate and ammonium chloride products; preferably, the heating and separation temperature is 200-350℃, and it is difficult to heat separate at a lower temperature.

[0060] In a specific example, the condensate obtained from the evaporation and crystallization is recovered and used as makeup water for the desulfurization system.

[0061] In a specific example, the mother liquor generated from evaporation and crystallization is subjected to freeze crystallization to recover sodium sulfate product, and the freeze crystallization mother liquor is returned to the evaporation and crystallization unit; preferably, the freeze crystallization temperature is -5 to 15°C.

[0062] Preferably, the desulfurization gypsum, desulfurization wastewater, desulfurization flue gas, and ammonia water come from a limestone-gypsum flue gas desulfurization system.

[0063] A second aspect of the present invention also provides a co-treatment system for desulfurized gypsum and desulfurized wastewater, comprising:

[0064] The pretreatment unit is used to remove heavy metals and magnesium ions from the desulfurization wastewater to obtain a mixture;

[0065] The first solid-liquid separation unit is used to separate the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase;

[0066] The reactor is used to carry out a metathesis reaction of the first liquid phase, desulfurized gypsum, in the presence of desulfurized flue gas to obtain reaction products.

[0067] The second solid-liquid separation unit is used to separate the reaction products into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase.

[0068] A crystallization unit is used to crystallize the second liquid phase to obtain ammonium sulfate, ammonium chloride and sodium sulfate products;

[0069] A heat treatment unit is used to heat treat the mixture of ammonium sulfate and ammonium chloride to obtain ammonium sulfate product and ammonium chloride product.

[0070] In a specific example, the pretreatment unit is a reactor with stirring.

[0071] In a specific example, the first solid-liquid separation unit includes one or more of the following processes: sedimentation tank, clarifier, filter, hydrocyclone separator, filter press, and drying.

[0072] In a specific example, the second solid-liquid separation unit includes one or more of the following processes: sedimentation tank, clarifier, filter, hydrocyclone separator, and filter press.

[0073] In a specific example, the crystallization unit includes an evaporation crystallization unit and a freeze crystallization unit.

[0074] In a specific example, the heat treatment unit includes a heater and a condenser recovery unit.

[0075] The invention is further described below with detailed exemplary embodiments, but these embodiments do not constitute any limitation on the invention.

[0076] Example 1

[0077] A limestone-gypsum flue gas desulfurization system in a certain factory: the CaSO4·2H2O content in the desulfurization gypsum is 94.8%, the carbon dioxide volume fraction in the desulfurization flue gas is 14.5%, and the salt content, chloride ion content, calcium ion content, magnesium ion content, and heavy metal content in the desulfurization wastewater are 10 mg / L, 36000 mg / L, 15000 mg / L, 760 mg / L, 1300 mg / L, and 10 mg / L, respectively.

[0078] like Figure 1 The process flow shown describes a limestone-gypsum flue gas desulfurization system at a certain factory. The desulfurization wastewater is sent to a pretreatment unit, where excess ammonia (purchased externally) is added and reacted thoroughly to remove magnesium ions and heavy metals, yielding a solid-liquid reaction product. The addition of NH3 reacts with the magnesium ions in the wastewater. 2+ The ratio of the sum of the amounts of CaSO4 in the desulfurized gypsum to that in the NH3 is n(NH3): [n(Mg2+)]. 2+ The reaction ratio is 2.4:1:n(CaSO4) + n(CaSO4)] = 2.4:1. The reaction principle is as follows:

[0079] Mg 2+ +2NH3·H2O=Mg(OH)2+2NH4 +

[0080] The solid and liquid products from the above reaction enter the first solid-liquid separation unit for precipitation, pressure filtration, and drying. The resulting solid product is high-purity magnesium hydroxide. The first liquid product is thoroughly mixed with desulfurized gypsum and then introduced into a metathesis reactor. A certain amount of flue gas is introduced, and the desulfurized gypsum, residual ammonia, and carbon dioxide in the flue gas react fully under certain reaction conditions. The molar ratio of CO2 in the flue gas to CaSO4 in the gypsum is 1.5:1. The reaction temperature is controlled at 40℃, the reaction time is 90 min, and the reaction stirring rate is 300 r / min. The reaction principle is as follows:

[0081] CaSO4·2H2O+CO2+2NH3·H2O=CaCO3+(NH4)2SO4+3H2O

[0082] The solid-liquid products generated after the reaction enter the second solid-liquid unit for precipitation and pressure filtration. The resulting solid product is calcium carbonate, which is recycled to the desulfurization system for flue gas desulfurization. The resulting second liquid product mainly consists of ammonium sulfate, ammonium chloride, and sodium sulfate. After evaporation and crystallization, a mixture of ammonium sulfate and ammonium chloride is obtained. The recovered condensate is reused as makeup water for the desulfurization system. The evaporation and crystallization temperature is 80°C. The mother liquor generated from evaporation and crystallization is subjected to freeze crystallization to recover sodium sulfate product, and the freeze crystallization mother liquor is refluxed to the evaporation and crystallization unit. The freeze crystallization temperature is 3°C. The resulting mixture of ammonium sulfate and ammonium chloride is heated and separated to obtain high-purity ammonium sulfate and ammonium chloride products. The heating and separation temperature is 260°C.

[0083] In this embodiment, the magnesium hydroxide obtained has a purity of 98%, which meets the Class I standard of industrial magnesium hydroxide specification (HG / T3607-2007); the ammonium sulfate product has an ammonia nitrogen content of 20.8%, which meets the Class I standard of fertilizer grade ammonium sulfate (GB535-2020); and the ammonium sulfate product has an ammonia nitrogen content of 24.8%, which meets the first-class standard of fertilizer grade ammonium sulfate (GB535-2020).

[0084] Example 2

[0085] The desulfurization gypsum contains 95.6% CaSO4·2H2O, the desulfurization flue gas contains 13% carbon dioxide by volume, and the desulfurization wastewater contains 28,000 mg / L salt, 9,000 mg / L chloride, 650 mg / L calcium, 2,500 mg / L magnesium, and 5 mg / L heavy metals.

[0086] like Figure 1 The process flow shown involves sending desulfurization wastewater discharged from the desulfurization system to a pretreatment unit. After adding excess ammonia and allowing it to react fully, magnesium ions and heavy metals in the wastewater are removed, yielding a solid-liquid reaction product. The addition of NH3 reacts with the magnesium ions in the wastewater... 2+ The ratio of the sum of the amounts of CaSO4 in the desulfurized gypsum to that in the NH3 is n(NH3): [n(Mg2+)]. 2+ The reaction ratio is 2.6:1:n(CaSO4) + n(CaSO4)] = 2.6:1. The reaction principle is as follows:

[0087] Mg 2+ +2NH3·H2O=Mg(OH)2+2NH4 +

[0088] The solid and liquid products generated after the reaction enter the first solid-liquid separation unit for clarification, pressure filtration, and drying. The resulting solid product is high-purity magnesium hydroxide. The resulting first liquid product is thoroughly mixed with desulfurized gypsum and then introduced into a metathesis reactor. A certain amount of flue gas is introduced, and the desulfurized gypsum, residual ammonia, and carbon dioxide in the flue gas react fully under certain reaction conditions. The molar ratio of CO2 in the flue gas to CaSO4 in the gypsum is 1.7:1. The reaction temperature is controlled at 50℃, the reaction time is 120 min, and the reaction stirring rate is 200 r / min. The reaction principle is as follows:

[0089] CaSO4·2H2O+CO2+2NH3·H2O=CaCO3+(NH4)2SO4+3H2O

[0090] The solid and liquid products generated after the reaction are sent to the second solid-liquid separation unit, which specifically involves precipitation and filtration. The resulting solid product, calcium carbonate, is recycled to the desulfurization system for flue gas desulfurization. The resulting second liquid product mainly consists of ammonium sulfate, ammonium chloride, and sodium sulfate. After evaporation and crystallization, a mixture of ammonium sulfate and ammonium chloride is obtained. The recovered condensate is reused as makeup water for the desulfurization system. The evaporation and crystallization temperature is 90°C. The mother liquor generated from evaporation and crystallization is subjected to freeze crystallization to recover sodium sulfate, and the freeze crystallization mother liquor is returned to the evaporation and crystallization unit. The freeze crystallization temperature is 10°C. The resulting mixture of ammonium sulfate and ammonium chloride is then heated and separated to obtain high-purity ammonium sulfate and ammonium chloride products. The heating and separation temperature is 310°C.

[0091] The results show that the magnesium hydroxide obtained in this embodiment has a purity of 98.5%, which meets the Class I standard of industrial magnesium hydroxide specification (HG / T3607-2007); the ammonia nitrogen content in the ammonium sulfate product is 20.9%, which meets the Class I standard of fertilizer grade ammonium sulfate (GB535-2020); and the ammonia nitrogen content in the ammonium sulfate product is 25.1%, which meets the first-class standard of fertilizer grade ammonium sulfate (GB535-2020).

[0092] The results demonstrate that the process of the embodiments of the present invention has the following advantages:

[0093] The method of this invention can simultaneously treat desulfurized gypsum, desulfurized wastewater, and part of the flue gas carbon dioxide, solving the problem of the disposal of desulfurized gypsum, reducing carbon emissions, and achieving zero discharge of desulfurized wastewater.

[0094] This invention can convert waste gypsum from desulfurization, desulfurization wastewater, and flue gas carbon dioxide into high-value-added magnesium hydroxide, calcium carbonate, ammonium sulfate, and ammonium chloride. Calcium carbonate is recycled and used in the desulfurization system for flue gas desulfurization, reducing the need for ore mining. The high-purity magnesium hydroxide, ammonium sulfate, and ammonium chloride can be sold as products.

[0095] This invention uses desulfurization wastewater that removes magnesium and heavy metals as the reaction medium, ensuring the purity of ammonium sulfate and ammonium chloride. The evaporation and crystallization recovery of ammonium sulfate is carried out simultaneously with the evaporation and crystallization of desulfurization wastewater, achieving zero discharge of desulfurization wastewater, saving the cost of desulfurization wastewater evaporation, and resulting in low overall treatment cost.

[0096] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A method for the co-treatment of desulfurization gypsum and desulfurization wastewater, characterized in that, Includes the following steps: 1) Pre-treat the desulfurization wastewater to remove heavy metals and magnesium ions, resulting in a mixture; the pre-treatment includes adding excess ammonia to the desulfurization wastewater to remove magnesium ions and heavy metals. 2) The mixture is separated into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase; 3) After mixing the first liquid phase in step 2) with desulfurized gypsum, the mixture is introduced into the desulfurized flue gas to carry out a metathesis reaction to obtain the reaction products; 4) Separate the reaction product from step 3) into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase; 5) The second liquid phase in step 4) is subjected to crystallization treatment to obtain a mixture of ammonium sulfate and ammonium chloride and sodium sulfate product; 6) Heat-treat the mixture of ammonium sulfate and ammonium chloride obtained in step 5) to obtain ammonium sulfate product and ammonium chloride product; The desulfurized gypsum, desulfurized wastewater, and desulfurized flue gas come from the limestone-gypsum flue gas desulfurization system.

2. The collaborative processing method according to claim 1, characterized in that, The ratio of the sum of the amount of substance of Mg 2+ and CaSO4 in the desulfurization wastewater to the amount of substance of NH3 in the ammonia water in the step 1) is n(NH3):[n(Mg 2+ )+n(CaSO4)]=2-3:

1.

3. The collaborative processing method according to claim 1, characterized in that, The conditions for the metathesis reaction in step 3) include: the reaction temperature is controlled at 20-60℃, the reaction time is 40-120 min, and the stirring rate is 60-400 r / min.

4. The collaborative processing method according to claim 1 or 3, characterized in that, The molar ratio of CO2 in the desulfurized flue gas to CaSO4 in the desulfurized gypsum is 1-2:1, and / or the mass ratio of desulfurized gypsum to the first liquid phase is 1:5-10.

5. The collaborative processing method according to claim 1, characterized in that, The crystallization process in step 5) includes: evaporating and crystallizing the second liquid phase to obtain a mixture of ammonium sulfate and ammonium chloride.

6. The collaborative processing method according to claim 5, characterized in that, In step 5), the evaporation and crystallization temperature is 70-90℃.

7. The collaborative processing method according to claim 1 or 5, characterized in that, The heat treatment in step 6) includes: heating the mixture of ammonium sulfate and ammonium chloride to separate the ammonium sulfate product and the ammonium chloride product.

8. The collaborative processing method according to claim 7, characterized in that, In step 6), the heating temperature is 200-350℃.

9. The collaborative processing method according to claim 5, characterized in that, The mother liquor produced by evaporation and crystallization is frozen and crystallized to recover sodium sulfate product. The frozen crystallization mother liquor is then returned to the evaporation and crystallization unit.

10. The collaborative processing method according to claim 9, characterized in that, The freezing crystallization temperature is -5 to 15℃.

11. A system for the co-treatment of desulfurized gypsum and desulfurized wastewater, characterized in that, include: The pretreatment unit is used to remove heavy metals and magnesium ions from the desulfurization wastewater to obtain a mixture; The first solid-liquid separation unit is used to separate the mixture into solid and liquid phases to obtain magnesium hydroxide solid and a first liquid phase; The reactor is used to carry out a metathesis reaction of the first liquid phase, desulfurized gypsum, in the presence of desulfurized flue gas to obtain reaction products. The second solid-liquid separation unit is used to separate the reaction products into solid and liquid phases to obtain calcium carbonate solid and a second liquid phase. A crystallization unit is used to crystallize the second liquid phase to obtain a mixture of ammonium sulfate, ammonium chloride, and sodium sulfate product; A heat treatment unit is used to heat treat the mixture of ammonium sulfate and ammonium chloride to obtain ammonium sulfate product and ammonium chloride product.

12. The collaborative processing system according to claim 11, characterized in that, The crystallization unit includes an evaporation crystallization unit and a freeze crystallization unit.

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