Salt-containing wastewater carbon sequestration alkali production system and alkali production method thereof

Abstract

The invention relates to the technical field of wastewater treatment, and provides a salt-containing wastewater carbon sequestration alkali production system and an alkali production method thereof. The output end of the pretreatment unit is connected with an evaporation and concentration unit, and the pretreatment unit is used for removing silicon, fluorine, COD (Chemical Oxygen Demand) and impurities in the salt-containing wastewater; the evaporation and concentration unit is used for carrying out evaporation and concentration on the pretreated salt-containing wastewater and outputting a saturated salt solution; the carbonization unit is used for carrying out carbonization reaction treatment on the saturated salt solution and outputting sodium bicarbonate precipitate; the roasting unit is used for filtering and roasting the sodium bicarbonate precipitate to obtain filtered mother liquor and an alkali product; and the crystallization unit is used for carrying out evaporation and concentration treatment on the filtered mother liquor output by the roasting unit so as to separate ammonium chloride and ammonium sulfate through fractional crystallization. Carbon sequestration is carried out through the salt-containing wastewater to prepare sodium carbonate with high added value, zero emission, carbon sequestration environmental protection and resource utilization of the salt-containing wastewater are organically combined together, and great environmental protection benefits and economic benefits are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a salt-containing wastewater carbon fixation and alkali production system and an alkali production method thereof. BACKGROUND

[0002] With the global emphasis on environmental protection and sustainable development, countries have introduced strict environmental protection policies and strictly limited the discharge of industrial wastewater. Salt-containing wastewater, as a common industrial wastewater, will cause serious pollution to water environment, soil, etc. and destroy the ecological balance if it is directly discharged without effective treatment. At present, zero discharge of coal chemical salt-containing wastewater has been proposed. At the same time, the traditional alkali production process is often accompanied by high carbon emissions, while the carbon fixation and alkali production technology can effectively utilize the carbon resources in salt-containing wastewater, realizing carbon fixation and emission reduction.

[0003] Salt-containing wastewater usually contains sodium, chlorine and other valuable resources. Through the green low-carbon salt-containing wastewater carbon fixation and alkali production technology, these resources can be recycled and utilized to produce important chemical products such as soda ash, which not only realizes carbon fixation and reduction, reduces the dependence on natural resources, but also reduces the production cost of enterprises, improves the utilization efficiency of resources and realizes the recycling of resources.

[0004] The traditional soda ash manufacturing process such as ammonia soda method and combined soda method still has some deficiencies. For example, the ammonia soda method produces a large amount of calcium chloride waste residue, which is difficult to handle and can easily cause environmental pollution; the combined soda method still has problems such as large carbon emissions and serious equipment corrosion, although it improves the utilization rate of raw materials to some extent. SUMMARY

[0005] Therefore, the embodiments of the present application provide a salt-containing wastewater carbon fixation and alkali production system and an alkali production method thereof to solve the problems of the ammonia soda method producing a large amount of calcium chloride waste residue, which is difficult to handle and can easily cause environmental pollution, and the combined soda method having large carbon emissions and serious equipment corrosion.

[0006] A first aspect of the embodiments of the present application provides a salt-containing wastewater carbon fixation and alkali production system, comprising: A pretreatment unit, an input end for receiving salt-containing wastewater, an output end connected to an evaporation and concentration unit, for removing silicon, fluorine, COD and impurities in the salt-containing wastewater; An evaporation and concentration unit, an input end connected to the output end of the pretreatment unit and the crystallization unit, an output end connected to a carbonization unit, for evaporating and concentrating the pretreated salt-containing wastewater, and outputting a saturated salt solution; A carbonization unit, an output end connected to a calcination unit, for carbonization reaction treatment of the saturated salt solution, and outputting sodium bicarbonate precipitate; a calcination unit connected to an output end of the crystallization unit, configured to filter and calcine the sodium bicarbonate precipitate to obtain a filtered mother liquor and an alkali product, wherein CO2 generated by the calcination unit is output to the carbonation unit; a crystallization unit configured to evaporate and concentrate the filtered mother liquor output by the calcination unit to separate ammonium chloride and ammonium sulfate by fractional crystallization, and output the mother liquor after separation of the ammonium chloride and ammonium sulfate to the evaporation and concentration unit.

[0007] In an embodiment, the pretreatment unit comprises a desiliconization device, a defluorination device, and a COD removal device; The desiliconization device is an electric flocculation device or a chemical precipitation device; The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device; The COD removal device is at least one of a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electro-catalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

[0008] In an embodiment, the pretreatment unit further comprises a sludge removal device, which is an ultrahigh-pressure elastic squeezer or a plate-and-frame filter press.

[0009] In an embodiment, the evaporation and concentration unit is a mechanical vapor recompression evaporator and / or a multiple-effect evaporator.

[0010] In an embodiment, the carbonation unit comprises a high-efficiency carbonation tower.

[0011] In an embodiment, the calcination unit comprises a filtration device, a drying device, and a calcination device connected in sequence, the filtration device is configured to filter the sodium bicarbonate precipitate output by the carbonation unit to separate sodium bicarbonate and a filtered mother liquor, the drying device is configured to dry the sodium bicarbonate, and the calcination device is configured to calcine the dried sodium bicarbonate to obtain sodium carbonate, CO2, and H2O, the sodium carbonate being output as an alkali product.

[0012] In an embodiment, the crystallization unit comprises a mechanical vapor recompression evaporator and / or a multiple-effect evaporator for evaporation and concentration, and a filtration separation device and / or a centrifugal separation device for solid-liquid separation.

[0013] A second aspect of the embodiments of the present application provides a method for producing alkali by a salt-containing wastewater carbon fixation and alkali production system, comprising: Silicon, fluorine, COD, and impurities in the salt-containing wastewater are removed by a pretreatment unit; The pretreated salt-containing wastewater is mixed with the mother liquor after separation of the ammonium chloride and ammonium sulfate, and evaporation and concentration are performed by an evaporation and concentration unit to obtain a saturated salt solution. carrying out carbonation reaction on the saturated salt solution and carbon dioxide in a carbonation unit to generate sodium bicarbonate precipitate; filtering the sodium bicarbonate precipitate to obtain filtrate and sodium bicarbonate; carrying out drying and calcination on the separated sodium bicarbonate by using a calcination unit to obtain alkali product; carrying out evaporation concentration on the filtrate to separate ammonium chloride and ammonium sulfate by fractional crystallization; The filtrate after separation of ammonium chloride and ammonium sulfate is output to the evaporation concentration unit to be mixed with the pretreated salt-containing wastewater.

[0014] In an embodiment, the generated carbon dioxide by the calcination is output to the carbonation unit for the carbonation reaction.

[0015] In an embodiment, the evaporation concentration on the filtrate to separate ammonium chloride and ammonium sulfate by fractional crystallization comprises: carrying out ammonia absorption treatment on the filtrate to adjust the pH of the solution to alkaline to obtain ammonia mother liquor; carrying out evaporation on the ammonia mother liquor until the ammonium chloride solution is saturated, and separating ammonium chloride precipitate after freeze crystallization; carrying out evaporation on the mother liquor after separation of the ammonium chloride precipitate until the ammonium sulfate solution is saturated; carrying out freeze crystallization treatment on the ammonium sulfate solution to separate ammonium sulfate crystals; The end point temperature is controlled between -5℃ and 60℃, and the evaporation crystallization time is 30-180 min when carrying out evaporation on the ammonia mother liquor and carrying out evaporation on the mother liquor after separation of the ammonium chloride precipitate.

[0016] The first aspect of the embodiment provides a salt-containing wastewater carbon fixation and alkali production system. The system mixes and concentrates the pretreated wastewater and the crystallization mother liquor, which not only improves the utilization rate of raw materials, but also fixes sodium ions in the wastewater into sodium bicarbonate through carbonation reaction, and then converts them into high-purity alkali product. At the same time, the system recycles the carbon dioxide generated by calcination into the carbonation unit, and recycles the crystallization mother liquor into the evaporation unit, which fundamentally reduces the input of external materials and the discharge of waste, and realizes the dual goals of zero discharge and resource utilization of salt-containing wastewater. The system uses salt-containing wastewater to fix carbon and produce high-value soda ash, which combines zero discharge of salt-containing wastewater, carbon fixation, environmental protection, and resource utilization, and achieves significant environmental and economic benefits.

[0017] It can be understood that the beneficial effects of the second aspect described above can be referred to the related description in the first aspect described above, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative effort.

[0019] Figure 1 is a kind of salt-containing wastewater carbon fixation system provided by an embodiment of the present application. DETAILED DESCRIPTION

[0020] In the following description, specific details are set forth in order to provide a thorough understanding of embodiments of the present application. However, persons skilled in the art will understand that embodiments of the present application can be practiced without these specific details. In other instances, well-known systems, structures, circuits, and methods have not been described in detail in order to avoid obscuring the present application.

[0021] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0022] It should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0023] It should be understood that when used in the specification and the appended claims of the present application, the term "comprising" indicates the presence of the described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or sets thereof.

[0024] It should also be understood that the term "and / or" used in the specification and the appended claims of the present application means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0025] Reference to“one embodiment” or“some embodiments” etc. in the present application description means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrases“in one embodiment”,“in some embodiments”,“in other embodiments”,“in additional embodiments” etc. in various places in the specification are not necessarily all referring to the same embodiment, although the phrases can be so referred to. The terms“comprising”,“having”,“including”, and their variants mean“including but not limited to”, unless otherwise expressly specified.

[0026] As Figure 1 shown, the salt-containing wastewater carbon fixation and alkali production system provided by the embodiments of the present application comprises: a pretreatment unit 1, an input end of which is configured to receive salt-containing wastewater, and an output end of which is connected to an evaporation and concentration unit 2, configured to remove silicon, fluorine, COD and impurities in the salt-containing wastewater; the evaporation and concentration unit 2, an input end of which is connected to the pretreatment unit 1 and an output end of the crystallization unit 5, and an output end of which is connected to a carbonization unit 3, configured to evaporate and concentrate the pretreated salt-containing wastewater, and output saturated salt solution; the carbonization unit 3, an output end of which is connected to a calcination unit 4, configured to perform carbonization reaction on the saturated salt solution, and output sodium bicarbonate precipitate; the calcination unit 4, an output end of which is connected to the crystallization unit 5, configured to filter and calcine the sodium bicarbonate precipitate, and obtain filtered mother liquor and alkali product, wherein the CO2 generated by the calcination unit 4 is output to the carbonization unit 3; the crystallization unit 5, configured to evaporate and concentrate the filtered mother liquor output by the calcination unit 4, to separate out ammonium chloride and ammonium sulfate by step crystallization, and output the mother liquor after separation of the ammonium chloride and the ammonium sulfate to the evaporation and concentration unit 2.

[0027] In application, the carbon fixation principle of the salt-containing wastewater is: mNa2SO4 + nNaCl + (2m+n)NH3 + (2m+n)CO2 + (2m+n)H2O → (2m+n)NaHCO3↓ +m(NH4)2SO4 + nNH4Cl, wherein m, n≥0, and m, n are not 0 at the same time; 2NaHCO3 → Na2CO3 + CO2↑ + H2O↑ The salt-containing wastewater carbon fixation and alkali production system provided by the embodiments of the present application mixes and concentrates the pretreated wastewater and the crystallization mother liquor, thereby improving the utilization rate of raw materials, and fixing sodium ions in the wastewater into sodium bicarbonate through a carbonation reaction, and then converting the sodium bicarbonate into a high-purity alkali product. At the same time, the system recycles the carbon dioxide generated by calcination to the carbonation unit 3, and recycles the crystallization mother liquor to the evaporation unit, thereby fundamentally reducing the input of external materials and the discharge of waste, and achieving the dual goals of zero discharge and resource utilization of salt-containing wastewater.

[0028] The embodiments of the present application use salt-containing wastewater as raw material to produce soda ash. Compared with the traditional combined soda process and the ammonia soda process, the salt-containing wastewater generated in the production process of the enterprise can be reasonably recycled, which not only reduces the raw material cost of soda ash, but also solves the problem of waste salt disposal, and realizes the recycling of water resources.

[0029] The embodiments of the present application use a mother liquor circulation process, and the theoretical recovery rate of each element is greater than 99.5%, which is much higher than the recovery rate of the existing quality and step-by-step crystallization process.

[0030] The embodiments of the present application realize the utilization rate of CO2 and NH3 greater than 99% through the CO2 circulation in the calcination process and the ammonia absorption circulation of tail gas, which is much higher than that of the traditional ammonium bicarbonate alkali production process.

[0031] In one embodiment, the pretreatment unit 1 includes a desiliconization device, a defluorination device, and a COD removal device. The desiliconization device is an electric flocculation device or a chemical precipitation device. The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device. The COD removal device is at least one of a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electrocatalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

[0032] The embodiments of the present application provide a modular and combined solution for different impurity components. The electric flocculation and chemical precipitation are directed to silicon elements, various physical and chemical methods are directed to fluorine elements, and the advanced oxidation technology group is directed to refractory COD. The integrated design of such multi-technical paths ensures that the system can efficiently and flexibly process industrial salt-containing wastewater with complex and variable components, and provides essential raw material support for the stable operation of subsequent units.

[0033] In one embodiment, the pretreatment unit 1 further includes a sludge removal device, and the sludge removal device is an ultrahigh-pressure elastic press or a plate-and-frame filter press.

[0034] The embodiment of the present application adds a sludge treatment device, and completes the final disposal link of the solid waste of the pretreatment unit 1. The ultrahigh pressure elastic squeezer or plate frame filter press can efficiently dewater and dry the sludge generated by impurity removal, greatly reducing the volume and amount, thereby reducing the sludge transportation and disposal cost, avoiding secondary pollution, and forming a complete and environment-friendly treatment chain for the entire pretreatment process.

[0035] In one embodiment, the evaporation concentration unit 2 is a mechanical steam recompression evaporator and / or a multi-effect evaporator.

[0036] The embodiment of the present application adopts mechanical steam recompression or multi-effect evaporation equipment. By ingeniously utilizing the latent heat of secondary steam, the large amount of heat energy required for concentrating the solution to the saturated state is significantly reduced, thereby fundamentally reducing the cost of the entire system operation, and embodying the technical concept of green and low carbon.

[0037] In one embodiment, the carbonation unit 3 includes a high-efficiency carbonation tower.

[0038] The high-efficiency carbonation tower of the embodiment of the present application provides a basis for gas-liquid-solid three-phase reaction. The carbonation tower realizes sufficient contact and efficient mass transfer between carbon dioxide gas and saturated salt solution, ensures that the carbonation reaction proceeds quickly and sufficiently, maximizes the precipitation efficiency of sodium ions converted into sodium bicarbonate, and guarantees the yield and quality of the soda ash product.

[0039] In one embodiment, the calcination unit 4 includes a filter device, a drying device and a calcination device connected in sequence, the filter device is used for filtering the sodium bicarbonate precipitate output by the carbonation unit 3 to separate sodium bicarbonate and filter mother liquor, the drying device is used for drying the sodium bicarbonate, and the calcination device is used for calcining the dried sodium bicarbonate to obtain sodium carbonate, CO2 and H2O, and the sodium carbonate is used as an alkali product output.

[0040] The embodiment of the present application decomposes the treatment of sodium bicarbonate into three steps of filtering, drying and calcining. Not only the purity of the sodium carbonate product is guaranteed, but also the separate collection and high-purity reuse of the byproduct carbon dioxide are realized, so that the carbon element forms a closed loop in the system, greatly improves the raw material utilization rate, reduces carbon emissions, and improves environmental protection.

[0041] In one embodiment, the crystallization unit 5 includes a mechanical steam recompression evaporator and / or a multi-effect evaporator for evaporation concentration, and a filter separation device and / or a centrifugal separation device for solid-liquid separation.

[0042] The crystallization unit 5 of the embodiment of the application combines an efficient evaporator with a variety of solid-liquid separation devices. The combination can accurately control the temperature and concentration of the crystallization process, thereby successfully achieving step-by-step and sequential crystallization and separation of ammonium chloride and ammonium sulfate, and finally obtaining two high-purity by-product fertilizers, greatly improving the resource utilization output and value of the entire process.

[0043] The second aspect of the embodiment of the application provides a method for producing alkali by a salt-containing wastewater carbon fixation alkali system, comprising: Silicon, fluorine, COD and impurities in the salt-containing wastewater are removed by the pretreatment unit 1. The pretreated salt-containing wastewater is mixed with the mother liquor after separation of ammonium chloride and ammonium sulfate, and evaporation and concentration are performed by the evaporation and concentration unit 2 to obtain a saturated salt solution. The saturated salt solution is subjected to carbonation reaction with carbon dioxide in the carbonation unit 3 to generate sodium bicarbonate precipitate. The sodium bicarbonate precipitate is filtered to obtain a filtered mother liquor and sodium bicarbonate. The separated sodium bicarbonate is dried and calcined by the calcination unit 4 to obtain an alkali product. The filtered mother liquor is subjected to evaporation and concentration, and ammonium chloride and ammonium sulfate are separated by step-by-step crystallization. The mother liquor after separation of ammonium chloride and ammonium sulfate is output to the evaporation and concentration unit 2 to be mixed with the pretreated salt-containing wastewater.

[0044] In application, the pretreatment unit 1 uses electrocoagulation or chemical precipitation technology to remove silicon elements in the salt-containing wastewater; uses one of chemical precipitation method, ion exchange, membrane separation or adsorption fluorine removal technology to remove fluorine elements in the wastewater; uses one or more of fenton oxidation, LDO wet hydrogen peroxide oxidation, WAO wet catalytic oxidation, electrochemical catalytic oxidation, and multi-element synergistic high-efficiency catalytic oxidation to remove COD in the wastewater; and the sludge formed by silicon removal, fluorine removal and COD removal in the pretreatment unit 1 is removed by using an ultrahigh-pressure elastic press or a plate-and-frame filter press.

[0045] In application, the evaporation and concentration unit 2 uses one or several of MVR, multi-effect evaporation or MVR coupled with multi-effect evaporation.

[0046] In application, the carbonation unit 3 fully absorbs and fixes CO2 to the salt-containing wastewater to be acidic (pH<7), so that sodium ions are converted into NaHCO3↓.

[0047] In one embodiment, the calcination unit 4 outputs the generated carbon dioxide to the carbonation unit 3 for the carbonation reaction.

[0048] In one embodiment, the evaporation and concentration of the filtered mother liquor and the step-by-step crystallization and separation of ammonium chloride and ammonium sulfate comprise: The filtrate mother liquor was subjected to ammonia absorption treatment to adjust the pH of the solution to alkaline, thereby obtaining an ammonia mother liquor; The ammonia mother liquor was evaporated until it was saturated with ammonium chloride, and then the ammonium chloride precipitate was separated by freezing crystallization. The mother liquor after separating the ammonium chloride precipitate is evaporated until the ammonium sulfate solution is saturated; Ammonium sulfate solution was subjected to freeze crystallization to separate ammonium sulfate crystals; When evaporating the ammonia mother liquor and the mother liquor after separating the ammonium chloride precipitate, the endpoint temperature is controlled between -5℃ and 60℃, and the evaporation and crystallization time is 30 to 180 minutes.

[0049] In applications, the solid-liquid separation process of ammonium sulfate and ammonium chloride is any one or a combination of several of the following: hydrocyclone separation, centrifugal separation, sedimentation separation, or filtration separation.

[0050] This application's embodiments achieve efficient separation of ammonium salts through precise pH adjustment and staged temperature control. Ammonia absorption creates optimal conditions for crystallization, while the evaporation and cooling crystallization steps, tailored to the solubility characteristics of different ammonium salts, ensure that ammonium chloride and ammonium sulfate can be crystallized separately with high recovery rates and purity, contributing to high-quality products and resource utilization.

[0051] Example 1 The following is a specific embodiment to illustrate this system and its alkali production method: Pretreatment Unit 1: Pretreatment Unit 1 uses sodium aluminate desilication + high-efficiency aluminum salt coupled defluorination + advanced oxidation to remove COD + sludge thickening and drying to purify and remove impurities from saline wastewater.

[0052] Flow rate 100m 3 At a temperature of 40℃ and a flow rate of [h], saline wastewater was treated using sodium metachlorite as a chemical agent. Sodium aluminate underwent a hydrolysis reaction in the water, forming a uniformly dispersed system and dissociating positively charged Al atoms. 3+ It can adsorb negatively charged SiO3 in wastewater 2- And it destroys colloidal silicon {[SiO2]mSiO3} 2- ·2(nx)H +}·2xH + The stability of the active and inactive silicon causes them to gradually aggregate and flocculate into larger particles, thus removing SiO2 from the saline wastewater.

[0053] A novel high-efficiency composite aluminum salt is used to remove fluoride from saline wastewater. After the novel high-efficiency composite aluminum salt is added to the water, Al... 3+ With F - The complexation of aluminum salts and the intermediate products of aluminum salt hydrolysis and the final product Al(OH)3(am), Al 13O4(OH) 24 7+ The polymeric hydroxyl cation and the amorphous Al(OH)3(am) formed after hydrolysis of the polymeric hydroxyl cation form positively charged colloidal particles in water, exchange ligands with fluoride ions in the wastewater, physically adsorb and sweep the fluoride ions to form a strong chemical bond of a polydentate ligand, and are aggregated into larger flocculent precipitates through mutual complexation between colloidal particles.

[0054] The multi-element synergistic high-efficiency catalytic oxidation technology is adopted, and through the dual catalytic action of homogeneous and heterogeneous salt-tolerant catalysts, the oxidant is efficiently converted into high-density hydroxyl radicals, and rapid oxidation reactions occur between the hydroxyl radicals and the functional groups of pollutants, so that the COD in the salt-containing wastewater is removed.

[0055] The sludge concentration and drying is divided into four steps: (1) sludge concentration, which preliminarily reduces the volume of the sludge; (2) sludge digestion, which decomposes the organic matter in the sludge and stabilizes the properties of the sludge; (3) sludge dewatering and drying by using a plate and frame filter press; and (4) the pretreated wastewater is sent to the evaporation concentration unit 2.

[0056] The evaporation concentration unit 2: after the removal of impurities such as fluorine, silicon and heavy metals in the wastewater by pretreatment, the wastewater is mixed with mother liquor IV and then concentrated to 40% by using MVR coupling double-effect, and the salt-containing wastewater with a concentration of 40% is secondarily absorbed with ammonia to form ammonia mother liquor II which enters the carbonization unit 3.

[0057] The carbonization unit 3: mother liquor II reacts with NH3 and CO2 in the carbonization tower to generate sodium bicarbonate slurry through countercurrent contact reaction, and the heat released in the reaction is removed by circulating water. The reaction product, which contains heavy alkali, is sent to a plate and frame filter to separate sodium bicarbonate, and the mother liquor is sent to the crystallization unit 5. The carbonization tail gas is vented after washing.

[0058] The crystallization unit 5: after the carbonization, the mother liquor from which sodium bicarbonate is separated is supplemented with NH3 to adjust the pH of the solution to be alkaline, and then evaporated to ammonium chloride saturation. After freezing and crystallization, ammonium chloride precipitate is separated by centrifugation. Subsequently, the solution is evaporated to ammonium sulfate saturation, and then cooled and crystallized to separate ammonium sulfate crystals. Finally, mother liquor IV enters the evaporation concentration unit 2.

[0059] The calcination unit 4: after drying, sodium bicarbonate is sent to the calcination unit 4 to generate sodium carbonate, CO2 and H2O through calcination. CO2 is recycled to the carbonization unit 3, and H2O is recycled to the production device.

[0060] In this embodiment, the device runs for 8400 hours per year, and the produced products, soda ash, ammonium sulfate and ammonium chloride, meet the requirements of (GB / T 210-2022) type II qualified products, (GB 535-2020) type I product, and (GB / T 2946-2018) agricultural ammonium chloride, respectively.

[0061] 6 million tons of carbon sequestration per year, 145,000 tons of ammonium sulfate per year, 118,000 tons of soda per year, 42,000 tons of ammonium chloride per year. The annual sales of products is about 300 million yuan. While solving the environmental problem of zero discharge of salt-containing wastewater coupled with carbon sequestration, significant economic and social benefits are achieved. The composition table of salt-containing wastewater before treatment is shown in Table 1, and the product water quality table is shown in Table 2. Among them, the product water of the system is used for circulating water device water replenishment and other production water.

[0062] Table 1 Table 2 The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A system for carbon sequestration and alkali production from saline wastewater, characterized in that, include: The pretreatment unit has an input end for receiving saline wastewater and an output end connected to an evaporation and concentration unit for removing silicon, fluorine, COD and impurities from the saline wastewater. The evaporation and concentration unit has its input end connected to the output end of the pretreatment unit and the crystallization unit, and its output end connected to the carbonization unit. It is used to evaporate and concentrate the pretreated saline wastewater and output a saturated salt solution. The carbonization unit, with its output end connected to the calcination unit, is used to perform a carbonization reaction on the saturated salt solution and output sodium bicarbonate precipitate. The calcination unit, with its output end connected to the crystallization unit, is used to filter and calcine the sodium bicarbonate precipitate to obtain the mother liquor and alkali product. The CO2 generated by the calcination unit is output to the carbonation unit. The crystallization unit evaporates and concentrates the mother liquor output from the roasting unit to separate ammonium chloride and ammonium sulfate in steps, and outputs the mother liquor after separating ammonium chloride and ammonium sulfate to the evaporation and concentration unit.

2. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The pretreatment unit includes a desiliconization device, a defluorination device, and a COD removal device; The desilication device is an electrocoagulation device or a chemical precipitation device; The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device; The COD removal device is at least one of the following: a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electrocatalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

3. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The pretreatment unit also includes a sludge removal device, which is an ultra-high pressure elastic press or a plate and frame filter press.

4. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The evaporation and concentration unit is a mechanical vapor recompression evaporator and / or a multi-effect evaporator.

5. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The carbonization unit includes a high-efficiency carbonization tower.

6. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The calcination unit includes a filtration device, a drying device, and a calcination device connected in sequence. The filtration device is used to filter the sodium bicarbonate precipitate output from the carbonation unit to separate sodium bicarbonate and the mother liquor. The drying device is used to dry the sodium bicarbonate. The calcination device is used to calcine the dried sodium bicarbonate to obtain sodium carbonate, CO2, and H2O. The sodium carbonate is used as an alkali product for output.

7. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The crystallization unit includes a mechanical vapor recompression evaporator and / or a multi-effect evaporator for evaporation and concentration, and a filtration separation device and / or a centrifugal separation device for solid-liquid separation.

8. A method for producing alkali using a saline wastewater carbon fixation and alkali production system as described in any one of claims 1 to 7, characterized in that, include: The pretreatment unit removes silicon, fluorine, COD and impurities from saline wastewater. The pretreated saline wastewater is mixed with the mother liquor from which ammonium chloride and ammonium sulfate have been separated, and then concentrated by evaporation and concentration unit to obtain a saturated salt solution. A saturated salt solution is reacted with carbon dioxide in a carbonization unit to produce sodium bicarbonate precipitate. The sodium bicarbonate precipitate was filtered to obtain the mother liquor and sodium bicarbonate. The separated sodium bicarbonate was dried and roasted using a roasting unit to obtain an alkali product; The mother liquor was evaporated and concentrated, and ammonium chloride and ammonium sulfate were separated by stepwise crystallization. The mother liquor after separating ammonium chloride and ammonium sulfate is output to the evaporation and concentration unit and mixed with the pretreated saline wastewater.

9. The alkali production method as described in claim 8, characterized in that, The carbon dioxide generated by the roasting unit is output to the carbonization unit for the carbonization reaction.

10. The alkali production method according to claim 8, characterized in that, The step of evaporating and concentrating the filtrate mother liquor, and then separating ammonium chloride and ammonium sulfate by step crystallization, includes: The filtrate mother liquor was subjected to ammonia absorption treatment to adjust the pH of the solution to alkaline, thereby obtaining an ammonia mother liquor; The ammonia mother liquor was evaporated until it was saturated with ammonium chloride, and then the ammonium chloride precipitate was separated by freezing crystallization. The mother liquor after separating the ammonium chloride precipitate is evaporated until the ammonium sulfate solution is saturated; Ammonium sulfate solution was subjected to freeze crystallization to separate ammonium sulfate crystals; When evaporating the ammonia mother liquor and the mother liquor after separating the ammonium chloride precipitate, the endpoint temperature is controlled between -5℃ and 60℃, and the evaporation and crystallization time is 30 to 180 minutes.

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