A water recovery system and method for high concentration crystalline salt extraction from coking wastewater

Abstract

The present application relates to a kind of high-concentration crystallized salt extraction of coking wastewater water recovery system and method.The system at least includes filter assembly.Filter assembly filter box is divided into slow-flow section, filter section and output section by being provided with different filter structures in the inside and dividing its cavity.The slow-flow section is provided with filter flow board staggered on two opposite side walls of its inner cavity.Filter flow board can be selectively pulled out from the chamber, so that the filter flow board with impurities intercepted is taken out from the chamber to remove precipitated impurities.The present application aims at the defects of prior art, and wants to separate the mixed industrial salt solution of sodium chloride and sodium sulfate after removing tar, sludge and other solid substances from coking wastewater, so that sodium chloride and sodium sulfate in the mixed state of industrial salt solution can be quickly and sufficiently separated, and after different evaporation crystallization processes are used to evaporate and crystallize the salt solution with different components, crystallized salt product reaching the purity standard of industrial salt is directly output.

Description

[0001] The original basis for this divisional application is patent application number CN202210436368.7, filed on April 22, 2022, entitled "A Coking Wastewater Crystallization Separation Device and Process". Technical Field

[0002] This invention relates to the technical field of coking wastewater treatment equipment, and in particular to a water recovery system and method for extracting high-concentration crystalline salts from coking wastewater. Background Technology

[0003] A large amount of coking wastewater is generated during the coke production process. Coking wastewater generally contains ammonia, cyanide, thiocyanate, phenols and other organic matter. Due to the multiple processes involved in the coke production process and the differences in the coking production processes of various coking plants, the concentration of the main pollutants in coking wastewater varies within a certain range. However, the characteristics of coking wastewater are roughly the same, which can be summarized as follows: (1) Coking wastewater exhibits a complex toxicity effect; (2) High pollutant concentration, high internal energy and poor degradability; (3) Complex composition of coking wastewater, with multiple phases and multiple element species coexisting; (4) High C / N ratio, rich in nitrogen and deficient in phosphorus; (5) High salinity and high color. At present, enterprises generally use a coupled process of pretreatment, biological treatment and deep treatment to treat coking wastewater. In order to meet the "zero discharge" requirements of the coal chemical industry, desalination process has also become an indispensable link in the treatment of coking wastewater.

[0004] As a product of end-of-pipe resource utilization in coking wastewater treatment, the production process of crystalline salt and the purity of the generated industrial salt have become stumbling blocks to the "zero discharge" requirement of coking wastewater treatment, and are problems that related industries urgently need to solve.

[0005] The patent document with publication number CN109809592A discloses a method for the resource utilization of salts in nanofiltration concentrate of coking wastewater. The crystallization method of this patent is still a traditional classification crystallization method, which requires separate crystallization of different components. The crystallization time is long and the energy consumption is large. It is impossible to reuse the heat dissipated during the operation of the evaporation crystallization device.

[0006] In view of the shortcomings of existing technologies that cannot simultaneously achieve the evaporation and crystallization treatment of multiple coking wastewater components, especially the problem of excessive heat energy consumption and low actual utilization rate in existing evaporation and crystallization steps, this application provides a separation device that can improve the efficiency of heat energy utilization in the evaporation and crystallization process while reducing the time required for the evaporation and crystallization process by preheating.

[0007] Chinese patent CN107902822A discloses a method for recovering and treating high-salinity wastewater containing sodium chloride and sodium sulfate, belonging to the field of industrial wastewater treatment. The method involves nanofiltration, where the filtrate that permeates the nanofiltration membrane is evaporated and crystallized to obtain sodium chloride, while the retained liquid that does not permeate the nanofiltration membrane is evaporated and crystallized to obtain sodium sulfate. The primary mother liquor is returned to the system and mixed with the raw materials for continued recycling. This patented method effectively recovers and utilizes sodium sulfate and sodium chloride from high-salinity wastewater, not only achieving the goal of treating high-salinity wastewater and meeting current environmental protection requirements, but also turning waste into treasure, realizing the resource utilization of salts, and increasing factory profits.

[0008] However, the separation component used in this patent is a conventional nanofiltration membrane. This type of separation component is a functional semi-permeable membrane that allows solvent molecules or certain low-molecular-weight solutes or low-valence ions to pass through. Its working principle is that, driven by a pressure difference, salts and small molecules pass through the nanofiltration membrane, while large molecules are retained—a liquid separation method. The separation component of this invention can change the distribution of sodium chloride in the liquid flow, allowing the sodium chloride in the liquid flow to redistribute during the splitting / merging process, increasing the probability of sodium chloride contacting the flow channel wall, and enabling sodium chloride to be separated from the liquid flow more effectively.

[0009] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention provides a coking wastewater crystallization separation device, which includes at least a crystallization component capable of crystallizing at least two separated coking wastewater components. The filtrate and retentate separated from the coking wastewater in the separation component selectively enter different evaporation and crystallization channels of the crystallization component, thereby completing the salt evaporation and crystallization treatment of the filtrate and retentate through different evaporation processes. The crystallization component is further provided with a preheating unit capable of sequentially preheating the separated filtrate and retentate. The preheating unit covers the liquid flow branch of the crystallization component, enabling the preheating unit to simultaneously and orderly complete the preheating treatment of the filtrate and retentate. Its advantages lie in the fact that the preheating unit can simultaneously preheat both the filtrate and the retentate after separation by the separation component. In particular, it differs from the double-effect evaporation crystallization process used for the filtrate and the triple-effect evaporation crystallization process used for the retentate. The preheating unit first preheats the filtrate with high-temperature steam, and then uses the exhaust steam generated in the exothermic reaction to preheat the retentate. This sequential preheating operation ensures the effectiveness and applicability of the preheating. The triple-effect evaporation crystallization process provides more heat energy to the retentate. Therefore, compared to the filtrate requiring double-effect evaporation crystallization, the retentate can achieve the required preheating effect simply by heating with exhaust steam. Furthermore, the preheating process reduces the heat consumed by the material during the evaporation crystallization process. In addition, the crystallization component can use its own heat dissipation to reheat the condensed liquid in the preheating unit while evaporating and crystallizing the filtrate and retentate, allowing the evaporation unit to quickly convert the heated liquid into high-temperature steam.

[0011] According to a preferred embodiment, the preheating unit includes at least a preheating coil that can be coiled around the outside of the pipe wall of the first liquid flow branch for conveying the filtrate and a deheating coil that can be coiled around the outside of the pipe wall of the second liquid flow branch for conveying the retentate.

[0012] According to a preferred embodiment, the preheating coil and the waste heating coil are connected in such a way that they form interconnected upstream and downstream pipelines, so that the high-temperature steam flowing through the preheating coil heats the first liquid flow branch and then flows into the waste heating coil along the pipeline, thereby heating the second liquid flow branch.

[0013] According to a preferred embodiment, the first liquid flow branch connects its downstream pipe outlet to the first crystallization component in such a way that the preheated filtrate in its pipe is transported to the crystallization treatment structure, so that the preheated filtrate can evaporate and crystallize in the first crystallization component.

[0014] According to a preferred embodiment, the retentate in the second liquid flow branch can be directionally transported to the second crystallization component after being preheated by exhaust steam, and the second crystallization component performs evaporation and crystallization treatment on the retentate after preheating.

[0015] According to a preferred embodiment, the exhaust steam generated by the exothermic reaction of the heating steam flowing directionally in the preheating coil can flow into the exhaust heating coil; the gas-liquid mixture generated after the exhaust steam flowing directionally in the exhaust heating coil releases heat to heat the entrapped liquid in the second liquid flow branch can be transported to the condensation unit. According to a preferred embodiment, the liquid produced by the condensation unit can flow back to the evaporation unit; the high-temperature steam generated by the evaporation unit can flow directionally into the preheating coil; the evaporation unit includes at least a first heating unit disposed outside the first crystallization component and the second crystallization component in a covering manner, the first heating unit being able to absorb the heat emitted by the first crystallization component and the second crystallization component during the evaporation crystallization process to heat the liquid.

[0016] According to a preferred embodiment, the evaporation unit further includes a second vaporization unit capable of vaporizing the heated liquid, the second vaporization unit being connected to the preheating coil.

[0017] According to a preferred embodiment, the output ends of the first crystallization component and the second crystallization component are further connected to a separation component capable of separating the crystallized salt and the residual mother liquor, and a salt leg for storing the crystallized salt.

[0018] This application also provides a process for separating crystallized salts from coking wastewater, which includes at least the following steps: Impurities in coking wastewater are filtered out through pretreatment filtration. The coking wastewater that has undergone impurity filtration is subjected to water reduction treatment. To separate concentrated sodium sulfate and concentrated sodium chloride from coking wastewater; The separated sodium sulfate concentrate and sodium chloride concentrate were evaporated and crystallized using a salt extraction evaporation crystallization device to obtain crystalline salt.

[0019] This invention provides a water recovery system for high-concentration crystalline salt extraction from coking wastewater, comprising at least a filtration assembly for receiving coking wastewater generated during industrial production, and after hardening and filtration treatment, conveying the treated coking wastewater to a concentration unit for dewatering and concentration treatment. The filtration assembly's filter housing divides its chamber into at least three interconnected filtration zones by setting different filtration structures internally. These three interconnected and orderly arranged filtration zones are a slow-flow section, a filtration section, and an output section. Preferably, the slow-flow section has filter plates staggered on two opposite side walls of its inner cavity, arranged at intervals along its chamber axis. The filter plates are inclinedly connected to the cavity wall, and can be selectively pulled out of the chamber, thereby removing the filter plates containing intercepted impurities from the chamber for sediment removal.

[0020] According to a preferred embodiment, after the concentration unit performs dehydration and concentration treatment on the coking wastewater, the concentrated coking wastewater is then separated into sodium chloride and sodium sulfate components in the separation component. Preferably, the separation component includes an outer tube and a separation filter structure, wherein the outer tube is suspended along its axial direction within the tube cavity by a support structure, and the separation filter structure capable of separating the coking wastewater is mounted thereon.

[0021] According to a preferred embodiment, the flow channel of the separation and filtration structure is streamlined, and at least one mixing structure capable of diverting and secondary mixing the liquid flow within the flow channel is arranged inside the flow channel. Preferably, the mixing structure can divide the flow channel of the separation and filtration structure into two sub-flow channels, so that the liquid flow can be divided into two sub-liquid flows flowing into different sub-flow channels by the front end of the mixing structure. The sub-liquid flows flowing into the sub-flow channels can merge at the end of the mixing structure after flowing out of the sub-flow channels, so that the two merging sub-liquid flows can generate a relative impact force, causing the components in the sub-liquid flows to undergo secondary mixing.

[0022] According to a preferred embodiment, the slow-flow section can perform coarse filtration and buffer diversion treatment on the coking wastewater flowing in from the top of the filter box, so that the coking wastewater can flow into the filter section evenly and dispersedly. Preferably, the sum of the plate areas of two adjacent filter plates is greater than the cross-sectional area of ​​the filter box.

[0023] According to a preferred embodiment, the filter plate has multi-stage progressive sedimentation stepped tanks on its surface to separate settleable impurities. Preferably, the multiple sedimentation stepped tanks, spaced apart along the water flow direction, for intercepting and containing settleable impurities, can progressively filter impurities of different volumes and masses in a graded filtration manner.

[0024] According to a preferred embodiment, the sedimentation stepped tanks are selectively opened such that their arc axis is located inside or outside the tank. Multiple sedimentation stepped tanks are arranged laterally by gradually increasing the curvature of their surfaces along the water flow direction, so that the sedimentation stepped tanks located on the same filtration module and in the downstream area of ​​the water flow can resist the power of the water flow with a larger curvature of the tank walls.

[0025] According to a preferred embodiment, the filter plate is further provided with interception modules at intervals on the multiple strip surfaces separated by the sedimentation stepped grooves, which are capable of intercepting flocculent impurities. Preferably, the multiple interception modules are arranged alternately with the sedimentation stepped grooves, thereby forming a stepped, multi-layered impurity interception structure on the filter plate, which improves the efficiency of intercepting unprecipitated impurities and also increases the total amount of impurities that can be intercepted by a single filter plate.

[0026] According to a preferred embodiment, the interception module disposed on the filter plate surface can cooperate with the sedimentation stepped tank to separate impurities in the coking wastewater flow. Preferably, the interception module is disposed in combination with multiple sedimentation stepped tanks.

[0027] According to a preferred embodiment, the interception module's interception mesh is capable of intercepting floating debris in the sedimentation stepped tank upstream that has not settled. Preferably, the interception modules on the same filter plate progressively reduce the mesh size of their interception meshes according to their different positions, thereby achieving filtration of impurities of different sizes through a step-by-step filtration method.

[0028] The present invention also provides a coking wastewater crystallization separation device, which includes at least a crystallization component capable of crystallizing at least two separated coking wastewater components. The filtrate and retentate separated from the coking wastewater in the separation component selectively enter different evaporation crystallization channels of the crystallization component, thereby completing the salt evaporation crystallization treatment of the filtrate and retentate through different evaporation processes. The crystallization component is further provided with a preheating unit capable of preheating the separated filtrate and retentate sequentially. The preheating unit covers the liquid flow branch of the crystallization component, so that the preheating unit can complete the preheating treatment of the filtrate and retentate simultaneously and in an orderly manner. Its advantages lie in the fact that the preheating unit can simultaneously preheat both the filtrate and the retentate after separation by the separation component. In particular, it differs from the double-effect evaporation crystallization process used for the filtrate and the triple-effect evaporation crystallization process used for the retentate. The preheating unit first preheats the filtrate with high-temperature steam, and then uses the exhaust steam generated in the exothermic reaction to preheat the retentate. This sequential preheating operation ensures the effectiveness and applicability of the preheating. The triple-effect evaporation crystallization process provides more heat energy to the retentate. Therefore, compared to the filtrate requiring double-effect evaporation crystallization, the retentate can achieve the required preheating effect simply by heating with exhaust steam. Furthermore, the preheating process reduces the heat consumed by the material during the evaporation crystallization process. In addition, the crystallization component can use its own heat dissipation to reheat the condensed liquid in the preheating unit while evaporating and crystallizing the filtrate and retentate, allowing the evaporation unit to quickly convert the heated liquid into high-temperature steam.

[0029] According to a preferred embodiment, the preheating unit includes at least a preheating coil that can be coiled around the outside of the pipe wall of the first liquid flow branch for conveying the filtrate and a deheating coil that can be coiled around the outside of the pipe wall of the second liquid flow branch for conveying the retentate.

[0030] According to a preferred embodiment, the preheating coil and the waste heating coil are connected in such a way that they form interconnected upstream and downstream pipelines, so that the high-temperature steam flowing through the preheating coil heats the first liquid flow branch and then flows into the waste heating coil along the pipeline, thereby heating the second liquid flow branch.

[0031] According to a preferred embodiment, the first liquid flow branch connects its downstream pipe outlet to the first crystallization component in such a way that the preheated filtrate in its pipe is transported to the crystallization treatment structure, so that the preheated filtrate can evaporate and crystallize in the first crystallization component.

[0032] According to a preferred embodiment, the retentate in the second liquid flow branch can be directionally transported to the second crystallization component after being preheated by exhaust steam, and the second crystallization component performs evaporation and crystallization treatment on the retentate after preheating.

[0033] According to a preferred embodiment, the exhaust steam generated by the exothermic reaction of the heating steam flowing directionally in the preheating coil can flow into the exhaust heating coil; the gas-liquid mixture generated after the exhaust steam flowing directionally in the exhaust heating coil releases heat to heat the entrapped liquid in the second liquid flow branch can be transported to the condensation unit. According to a preferred embodiment, the liquid produced by the condensation unit can flow back to the evaporation unit; the high-temperature steam generated by the evaporation unit can flow directionally into the preheating coil; the evaporation unit includes at least a first heating unit disposed outside the first crystallization component and the second crystallization component in a covering manner, the first heating unit being able to absorb the heat emitted by the first crystallization component and the second crystallization component during the evaporation crystallization process to heat the liquid.

[0034] According to a preferred embodiment, the evaporation unit further includes a second vaporization unit capable of vaporizing the heated liquid, the second vaporization unit being connected to the preheating coil.

[0035] According to a preferred embodiment, the output ends of the first crystallization component and the second crystallization component are further connected to a separation component capable of separating the crystallized salt and the residual mother liquor, and a salt leg for storing the crystallized salt.

[0036] This application also provides a process for separating crystallized salts from coking wastewater, which includes at least the following steps: Impurities in coking wastewater are filtered out through pretreatment filtration. The coking wastewater that has undergone impurity filtration is subjected to water reduction treatment. To separate concentrated sodium sulfate and concentrated sodium chloride from coking wastewater; Crystallized salt was obtained by evaporating and crystallizing the separated sodium sulfate concentrate and sodium chloride concentrate using a salt extraction evaporation crystallization device. The remaining mother liquor after evaporation and crystallization is put into a mixed salt crystallization device to produce mixed salt. The obtained mixed salt is then re-dissolved and transported back to a circulating nanofiltration device for further salt separation. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a preferred coking wastewater crystallization separation device proposed in this invention; Figure 2 This is a schematic diagram of a preferred coking wastewater crystallization separation device proposed in this invention; Figure 3 This is a schematic diagram of the structure of the separation component of a preferred coking wastewater crystallization separation device proposed in this invention; Figure 4 This is a side view of the filter plate of a preferred coking wastewater crystallization separation device proposed in this invention; Figure 5 This is a plan view of the filter plate of a preferred coking wastewater crystallization separation device proposed in this invention.

[0038] List of reference numerals 1: Filter assembly; 2: Concentration unit; 3: Separation assembly; 4: Crystallization assembly; 5: Preheating unit; 6: Separation assembly; 7: Salt leg; 11: Filter housing; 12: Inlet pipe; 13: Outlet pipe; 111: Filter plate; 112: Sedimentation stepped tank; 113: Interception module; 114: Opening; 115: Adsorption unit; 116: Isolation layer; 21: Medium-pressure membrane concentration unit; 22: High-pressure membrane concentration unit; 31: Outer casing; 32: Separation and filtration structure; 33: Support structure; 321: Mixed flow structure; 322: Sub-channel; 323: Microchannel; 41: First crystallization component; 42: Second crystallization component; 43: Liquid flow branch; 431: First liquid flow branch; 432: Second liquid flow branch; 51: Preheating coil; 52: Exhaust heating coil; 53: Condensation unit; 54: Evaporation unit; 541: First heating unit; 542: Second vaporization unit. Detailed Implementation

[0039] The following is a detailed explanation with reference to the accompanying drawings.

[0040] Example 1 This application provides a coking wastewater crystallization separation device, which may include a filtration component 1, a concentration unit 2, a separation component 3, a crystallization component 4, and a preheating unit 5.

[0041] According to one specific embodiment, the filter assembly 1 receives coking wastewater generated during industrial production. After hardening and filtration treatment, the treated coking wastewater is transported to the concentration unit 2 for dehydration and concentration to increase the proportion of salt-containing substances (sodium chloride and sodium sulfate) in the coking wastewater. After concentration, the coking wastewater undergoes separation treatment in the separation assembly 3 to separate sodium chloride and sodium sulfate components. The output end of the separation assembly 3 is also connected to a crystallization assembly 4, which can evaporate and crystallize the separated filtrate and retentate, which have single components. A preheating unit 5 is installed on the liquid delivery pipeline of the crystallization assembly 4 to preheat the filtrate and retentate separated by the separation assembly 3, respectively. The preheating unit 5 can also absorb the heat dissipated by the crystallization assembly 4 during the evaporation and crystallization process. The preheating unit 5 can increase the temperature of the filtrate and retentate flowing into the evaporation and crystallization device of the crystallization assembly 4 by heating different liquid flow branches 43 of the crystallization assembly 4. The preheating unit 5 can selectively preheat the liquid with steam at different temperatures depending on the different evaporation and crystallization processes performed on the filtrate and retentate separated from the coking wastewater in the crystallization component 4. The preheating unit 5 can perform secondary liquefaction and vaporization treatment on the steam-water mixture generated after heat release, thereby realizing the cyclic heat absorption and release operation of the preheating unit 5.

[0042] like Figure 1 As shown, the crystallization assembly 4 includes a first crystallization assembly 41 and a second crystallization assembly 42 capable of performing different evaporation and crystallization operations on the filtrate and retentate after separation of coking wastewater, respectively. The crystallization assembly 4 also includes liquid flow branches 43 that connect different output ends of the separation assembly 3 to the first crystallization assembly 41 and the second crystallization assembly 42, respectively. Specifically, the first liquid flow branch 431 connects the filtrate output end of the separation assembly 3 to the first crystallization assembly 41; the second liquid flow branch 432 connects the retentate output end of the separation assembly 3 to the second crystallization assembly 42. Preferably, the preheating unit 5 preheats the filtrate flowing through the first liquid flow branch 431 and the retentate flowing through the second liquid flow branch 432 by heating the first liquid flow branch 431 and the second liquid flow branch 432 with flowing high-temperature steam.

[0043] like Figure 1As shown, the preheating unit 5 includes a preheating coil 51 coiled around the outer wall of a portion of the first liquid flow branch 431 and a waste heating coil 52 coiled around the outer wall of a portion of the second liquid flow branch 432. Preferably, the high-temperature steam flowing directionally in the preheating coil 51 can transfer heat exothermically into a portion of the cavity of the first liquid flow branch 431 it encloses, thereby increasing the temperature of the filtered liquid flowing through the first liquid flow branch 431. Preferably, a waste heating coil 52 is also connected downstream of the preheating coil 51. After the high-temperature steam completes one heat release, its heat content decreases and waste steam generated by the exothermic reaction is transported downstream to the pipeline. The waste steam further releases heat in the waste heating coil 52 to generate a gas-liquid mixture with liquid as the main component. Preferably, the waste steam releases heat in a manner that transfers heat to the cavity of the second liquid flow branch 432 in the waste heating coil 52. Preferably, the exposed outer walls of the preheating coil 51 and the exhaust heating coil 52 are wrapped with heat-insulating material, and the parts of the preheating coil 51 and the exhaust heating coil 52 near the first liquid flow branch 431 and the second liquid flow branch 432 are made of a material that facilitates heat transfer, so that the heat released by the steam and exhaust steam in the exothermic reaction can be directionally conducted.

[0044] Preferably, the gas-liquid mixture generated after the directional flow of exhaust steam in the exhaust heating coil 52 releases heat to heat the entrapped liquid in the second liquid flow branch 432 can be transported to the condensing unit 53. By condensing and liquefying the gas-liquid mixture generated after the exhaust steam releases heat, the preheated steam can finally release heat and liquefy before flowing back to the evaporating unit 54. Thus, the evaporating unit 54 can evaporate the liquid again. The condensing unit 53 prevents the evaporating unit 54 from directly heating and evaporating the gas-liquid mixture generated after the exhaust steam releases heat. This avoids the gas-liquid mixture failing to effectively absorb the heat generated by the heating structure of the evaporating unit 54, which could cause the heating structure to dry-burn or other abnormal operating conditions, thus reducing its service life. In the process of generating high-temperature steam through cyclic heating, steam generation is a process of vaporizing liquid. If the substance to be heated itself is vaporized, the heat generated or transferred by the heating structure may not be fully transferred. This phenomenon can easily lead to the heating structure being exposed to excessively high temperatures for a long time, causing damage. Therefore, filling the heating space of the heating structure with the liquid to be heated can achieve better heat transfer and avoid damage to the heating structure caused by overheating. Preferably, the liquid produced by the condensation unit 53 can be returned to the evaporation unit 54. The high-temperature steam generated by the evaporation unit 54 can flow directionally into the preheating coil 51. The evaporation unit 54 includes a first heating unit 541 that surrounds the first crystallization component 41 and the second crystallization component 42, and a second vaporization unit 542 that vaporizes the heated liquid. The second vaporization unit 542 is connected to the preheating coil 51. The first heating unit 541 can heat the liquid by absorbing the heat emitted by the first crystallization component 41 and the second crystallization component 42 during the salt evaporation and crystallization process. This reduces the energy consumption of the evaporation unit 54 when generating steam, and also allows for the secondary recovery and reuse of the heat that is not fully utilized and emitted during the evaporation and crystallization process, reducing the overall energy consumption of the equipment and improving the salt production efficiency of the device.

[0045] The downstream outlet of the first liquid flow branch 431 is connected to the first crystallization component 41, allowing the preheated filtrate to crystallize rapidly in the first crystallization component 41. By directly introducing the preheated filtrate into the first crystallization component 41 for double-effect crystallization, the amount of steam required for heating the filtrate in the first crystallization component 41 is significantly reduced, accelerating the production speed of crystallized salt. Simultaneously, the preheating process ensures the overall temperature of the filtrate, improving the quality and particle size uniformity of the crystallized salt and reducing the number of fine crystals generated due to uneven heating of the filtrate. The retentate in the second liquid flow branch 432, after preheating with exhaust steam, can be directionally transported to the second crystallization component 42, where the preheated retentate undergoes evaporation crystallization. Preferably, the first crystallization component 41 can process the separated concentrated water containing sodium chloride as follows: after MVR concentration, it enters the salt double-effect evaporator crystallizer; salt exits from the low-temperature section of the evaporator crystallizer, thickens through a thickener, is then dehydrated by a centrifuge, and enters a dryer; the dried sodium chloride is then sent to the product packaging line. Preferably, the second crystallization component 42 can treat the separated concentrated water containing sodium sulfate as follows: after MVR concentration, it enters a countercurrent triple-effect evaporator crystallizer; the high-temperature section of the evaporator crystallizer outputs nitrate; after thickening by a thickener, it is dehydrated by a centrifuge and then enters a dryer; the dried sodium sulfate product is sent to the product packaging line. Preferably, the output ends of the first crystallization component 41 and the second crystallization component 42 are also connected to a separation component 6 capable of separating the crystallized salt and residual mother liquor, and a salt leg 7 for storing the crystallized salt. Preferably, the residual mother liquor separated by the separation component 6 can enter a double-effect mixed salt crystallizer for mixed salt crystallization treatment; the produced mixed salt crystals are re-dissolved and then enter a primary nanofiltration device for further salt separation treatment. Preferably, the separation component 6 can be a separation sieve capable of separating the crystallized salt and mother liquor. Preferably, the salt leg 7 is also connected to a backwash pump capable of backwashing its internal chamber. The backwash pump pumps diluted stock solution or gas into the salt leg through the backwash port, causing the fine crystals inside the salt leg to float again and enter the crystal growth zone, while qualified large particles settle at the bottom of the salt leg 7, thereby ensuring the crystallization quality and particle size uniformity of the product. At the same time, the stock solution or gas introduced into the salt leg 7 can also wash the product, flushing away crystals adhering to the inner wall of the salt leg to reduce internal blockage.

[0046] Example 2 The industrial production of coke often generates a large amount of coking wastewater. Coking wastewater generally contains large amounts of ammonia, cyanide, thiocyanate, phenols and other organic matter. It is characterized by complex toxic effects, high pollutant concentration, high internal energy, poor degradability and complex composition. In order to meet the "zero discharge" requirements of the chemical industry, a coupled process of pretreatment, biological treatment and deep treatment is generally required to treat coking wastewater. Among them, desalination treatment of coking wastewater is an essential link in the coking wastewater treatment process. Although existing coking wastewater treatment processes can effectively control the output of pollutants at each stage of the entire coking wastewater treatment process, the formation mechanism of the final crystallized salt is still unclear. The composition of crystallized salt in existing technologies is relatively mixed, and it is impossible to directly produce crystallized salt with the purity required for industrial salt. Therefore, this application addresses the shortcomings of existing technologies by performing component separation treatment on the industrial salt solution of sodium chloride and sodium sulfate mixture after removing solid substances such as tar and sludge from coking wastewater. This will enable rapid and thorough separation of sodium chloride and sodium sulfate in the mixed industrial salt solution, and after evaporating and crystallizing salt solutions of different components using different evaporation crystallization processes, crystallized salt products that meet the purity standards for industrial salt can be directly output.

[0047] like Figure 2 As shown, the upper axial end face of the filter housing 11 of the filter assembly 1 is connected to an inlet pipe 12, which allows the coking wastewater to be treated to be injected into the filter housing 11. The lower axial end of the filter housing 11 is connected to an outlet pipe 13. The outlet pipe 13 is connected to a concentration unit 2, which concentrates the pretreated coking wastewater. The filter housing 11 is divided into at least three interconnected filtration zones by different filtration structures within it. More preferably, the three interconnected and orderly arranged filtration zones are a slow-flow section, a filtration section, and an output section. The slow-flow section can perform coarse filtration and buffer diversion treatment on the coking wastewater flowing in from the top of the filter housing 11, so that the coking wastewater can flow into the filtration section evenly and dispersedly. Preferably, the slow-flow section has filter plates 111 staggered on two opposite side walls of its inner cavity, arranged at intervals along the axis of its chamber. The filter plate 111 is inclinedly connected to the cavity wall, and the filter plate 111 can be selectively pulled out of the cavity, thereby removing the filter plate 111 that has intercepted a certain amount of impurities from the cavity for the removal of precipitated impurities. Preferably, the sum of the plate areas of two adjacent filter plates 111 is greater than the cross-sectional area of ​​the filter box 11.

[0048] like Figure 4 and 5As shown, the filter plate 111 has multi-stage progressive sedimentation stepped grooves 112 on its surface to separate settleable impurities. Preferably, multiple strip surfaces of the filter plate 111 separated by the sedimentation stepped grooves 112 are also provided with interception modules 113 for intercepting flocculent impurities. More preferably, the interception module 113 includes an interception net vertically supported on the surface of the filter plate 111 and an interception column disposed on the side of the interception net away from the filter plate 111. Preferably, multiple interception modules 113 are alternately arranged with the sedimentation stepped grooves 112, thereby forming a stepped multi-layer impurity interception structure on the filter plate 111. This improves the efficiency of intercepting unprecipitated impurities and also increases the total amount of impurities that can be intercepted by a single filter plate 111, thus improving the coarse filtration performance of the filter plate 111 to a certain extent, thereby meeting the requirements of large-scale industrial coking wastewater treatment for long-term sustainable use of the equipment. The sedimentation stepped tank 112 prevents the coking wastewater from flowing smoothly and directly over the filter plate 111 as it passes through the plate. As the water flows through the sedimentation stepped tank 112, settleable impurities in the coking wastewater gradually settle on the surface of the filter plate 111 and fall into the sedimentation stepped tank 112. Therefore, as the water continues downstream, the settleable impurities are intercepted and accumulated in the sedimentation stepped tank 112, thus separating the settleable impurities from the coking wastewater. Preferably, multiple sedimentation stepped tanks 112 spaced apart along the water flow direction for intercepting and containing settleable impurities can progressively filter impurities of different volumes and masses in a staged filtration manner. In particular, the interception module 113, which is set up in conjunction with the sedimentation stepped tank 112, can achieve solid-liquid separation of impurities in coking wastewater through multiple filtrations by gradually reducing the mesh size of its interception net.

[0049] Preferably, the cross-sectional area of ​​the sedimentation stepped tank 112 on a single filter plate 111 gradually decreases along the water flow direction, so that the sedimentation stepped tank 112 located upstream can filter out more settleable impurities from the water flow with more impurities and achieve effective impurity containment. Preferably, the sedimentation stepped tank 112 in the downstream region of the same filter plate 111 is set with a smaller cross-sectional area, so that when the water flows through this position, the influence of the tank on the water flow is reduced, the flow velocity of the water is reduced, and the water flow can flow through this region at a relatively slow speed. This allows impurities that are carried forward by the water flow but are not settled and / or intercepted upstream to be separated and settled in the relatively gentle water flow, and thus settle in the sedimentation stepped tank 112 downstream.

[0050] Preferably, the cross-sectional area of ​​the sedimentation stepped tank 112 can be set to an arc shape, and the curvature of the arc can be adjusted according to the different positions of the sedimentation stepped tank 112 on the filter plate 111, so that the curvature of the cross-section of the sedimentation stepped tank 112 located in the upstream area of ​​the water flow is greater than that of the cross-section of the tank in the downstream area, so that the upstream tank can accommodate more large-volume settleable impurities. Preferably, the sedimentation stepped tank 112 is selectively set up such that its arc axis is located inside or outside the tank. For example, the sedimentation stepped tank 112 located in the upstream area of ​​the water flow is opened with its arc axis A located above the tank cavity, and the curvature of the surface formed by its tank cavity is small. This means that the sedimentation stepped tank 112 at this location does not have a significant impact on the flow velocity of the water. Under the action of gravity, the water flows through the upstream area at a relatively fast speed, so the sedimentation stepped tank 112 in the upstream area does not generate significant resistance to the water flow. The sedimentation stepped tank 112 in this area mainly provides a space to accommodate larger sedimentable impurities. The sedimentation stepped tank 112 located in the downstream area of ​​the water flow is opened with its arc axis B located inside the tank cavity. The sedimentation stepped tank 112 in the downstream area is opened with its groove cross-section arc forming a certain angle with the plate body of the filter plate 111. This allows the impurities carried into the sedimentation stepped tank 112 by the water flow to be effectively intercepted by the arc-shaped groove, and the kinetic energy carried by the impurities is offset, so that the impurities are captured by the arc-shaped groove.

[0051] Preferably, the multiple sedimentation stepped tanks 112 are arranged laterally by gradually increasing the curvature of their surfaces along the direction of water flow. This allows the sedimentation stepped tanks 112 located on the same filtration module and in the downstream area of ​​the water flow to resist the force of the water flow with their large curved tank walls, effectively slowing down the flow rate. As a result, the fine and low-weight impurities carried by the water flow can be settled in the sedimentation stepped tanks 112 in the downstream area, thereby obtaining coking wastewater with higher purity.

[0052] Preferably, the interception module 113 provided on the surface of the filter plate 111 can cooperate with the sedimentation stepped tank 112 to separate impurities in the coking wastewater flow. Specifically, the interception module 113 can intercept floating impurities such as unsedimented flocculent matter, thereby further improving the purity of the coking wastewater. Preferably, the interception module 113 is arranged in combination with multiple sedimentation stepped tanks 112, that is, an interception module 113 is provided downstream of each sedimentation stepped tank 112, that is, an interception module 113 is supported on the surface of the filter plate 111 between two adjacent sedimentation stepped tanks 112. Preferably, the interception net of the interception module 113 can intercept floating debris in the sedimentation stepped tank 112 upstream that has not settled. As debris gradually accumulates, the water permeability of the interception module 113 gradually decreases, causing the upstream water level to gradually rise. The interception module 113 is also connected to an interception column on the interception net to intercept large-volume flocculent impurities floating in the water flow. Preferably, the intercepting columns are spaced apart at the upper edge of the intercepting net, so that when the water level reaches a certain height, the intercepting module 113 improves the flow efficiency of the water by intercepting only a portion of the large-volume flocculent matter. Preferably, the unfiltered water impurities in the upstream intercepting module 113 are filtered secondary or multiple times by the downstream intercepting module 113, thereby gradually improving the purity of the coking wastewater. Preferably, the intercepting modules 113 on the same filter plate 111 gradually reduce the mesh size of their intercepting nets according to their different positions, thereby achieving filtration of impurities of different sizes through a step-by-step filtration method. Preferably, in addition to intercepting floating impurities that cannot settle in the sedimentation stepped tank 112, the intercepting net of the intercepting module 113 can also intercept settleable impurities carried forward by the water flow according to the size of the impurities, thereby further achieving the interception of impurities missed by the sedimentation stepped tank 112.

[0053] Preferably, the filter plates 111, which are staggered along the axis of the chamber in the slow-flow section of the filter housing 11, are fixed to the chamber wall of the slow-flow section by means of inclined flow guidance. After being filtered by the previous filter plate 111, the coking wastewater detaches from the plate and falls precisely onto the next filter plate 111, thus completing secondary filtration on the next filter plate 111. Preferably, the multiple filter plates 111 are manually disassembled according to their usage cycle, filtration capacity, etc., to clean the impurities they have intercepted. Preferably, the chamber wall of the filter housing 11 has multiple openings 114 for inserting and fixing the filter plates 111.

[0054] Preferably, a filtration section is further provided downstream of the slow-flow section of the filter housing 11. Preferably, the filtration section of the filter housing 11 is provided with an adsorption unit 115 capable of further adsorbing and removing fine impurities in the coking wastewater. Preferably, the adsorption unit 115 can be made of fine coke powder produced after coking, so that the coking wastewater after pretreatment and filtration is discharged from the lower axial end of the filtration section by slowly wetting the adsorption unit 115. Preferably, the fine coke powder produced after coking has had its moisture and volatile organic compounds discharged through high-temperature pyrolysis, resulting in a large-area porous structure inside the fine coke powder, thus possessing extremely strong adsorption capacity. If these fine coke powders can be used to adsorb and purify coking wastewater, the coking wastewater treatment efficiency will be greatly improved. Preferably, an isolation layer 116 is provided at the lower axial end of the filtration section to support the adsorption unit 115. The isolation layer 116 can limit the position of the adsorption unit 115 and ensure that the coking wastewater after impurity adsorption can pass through the isolation layer 116 to flow to the output section. Preferably, the isolation layer 116 can be a filter screen made of multiple layers of fine mesh, which allows coking wastewater to flow through the isolation layer 116, but the adsorption unit 115 composed of fine coke powder will not fall into the output section of the filter box 11.

[0055] Preferably, the adsorption unit 115 can be divided into two adsorption sub-modules by a partition, thereby changing the adsorption sub-module located axially below the filter plate 111 by rotating the adsorption unit 115. This facilitates the replacement of the adsorption unit 115 by the operator, ensuring the continuous adsorption capacity of the adsorption unit 115 during uninterrupted operation. The output section of the filter box 11 can collect the filtered coking wastewater and flow it from the outlet pipe 13 into the concentration unit 2, which can concentrate the coking wastewater. Preferably, the concentration unit 2 can include a medium-pressure membrane concentration unit 21 and a high-pressure membrane concentration unit 22. The filtered coking wastewater can pass through the medium-pressure membrane concentration unit 21 and the high-pressure membrane concentration unit 22 in sequence, thereby completing the concentration and volume reduction treatment of the coking wastewater.

[0056] Existing technologies typically introduce a pre-treated industrial salt solution of coking wastewater into a negative pressure chamber, allowing sodium chloride in the wastewater to precipitate through a nanofiltration membrane under negative pressure, thus separating the sodium chloride and sodium sulfate solutions in the mixed salt solution. However, existing technologies cannot guarantee the separation effect of sodium chloride and sodium sulfate solutions; the separated sodium sulfate solution still contains a large amount of sodium chloride, resulting in the purity of the crystalline salt formed from the sodium sulfate solution failing to meet the purity requirements of the finished industrial salt. This application addresses the shortcomings of existing sodium chloride and sodium sulfate solution separation devices by improving the separation component 3. Sodium chloride separation is achieved by controlling the flow state of the coking wastewater in the flow channel, specifically by changing the flow velocity, hydraulic pressure, and flow rate of the coking wastewater in different regions of the liquid flow channel. This allows the coking wastewater to fully contact the nanofiltration membrane that constitutes the flow channel wall of the separation filtration structure 32, promoting the effective permeation of sodium chloride in the coking wastewater through the nanofiltration membrane and its separation from the sodium sulfate solution.

[0057] Preferably, a separation component 3 is connected downstream of the concentration unit 2, capable of separating the components of the coking wastewater after filtration and concentration. For example... Figure 3 As shown, the separation component 3 includes an outer tube 31 and a separation filtration structure 32. The outer tube 31 is suspended along its axial direction within its cavity by a support structure 33, and the separation filtration structure 32, capable of separating coking wastewater, is located therein. Specifically, certain components of the coking wastewater that are permeable to the nanofiltration membrane enter the cavity channel between the outer tube 31 and the separation filtration structure 32 by passing through the flow channel wall. The remaining coking wastewater that cannot be filtered out by the separation filtration structure 32 flows directionally along the liquid flow channel formed by the separation filtration structure 32. Thus, the separation of coking wastewater components is achieved by connecting different crystallization components 4 to the output end of the outer tube 31 and the output end of the separation filtration structure 32. Preferably, the specific component permeable to the nanofiltration membrane in the liquid flow of the coking wastewater is a sodium chloride solution, while the liquid retained in the flow channel is a sodium sulfate solution.

[0058] Preferably, the flow channel of the separation and filtration structure 32 is streamlined. At least one mixing structure 321 capable of diverting and secondary mixing the liquid flow within the flow channel is disposed within the flow channel of the separation and filtration structure 32. Specifically, the mixing structure 321 is a diversion island disposed within the flow channel of the separation and filtration structure 32. The mixing structure 321 can divide the flow channel of the separation and filtration structure 32 into two sub-flow channels 322, allowing the liquid flow to be divided by the front end of the mixing structure 321 into two sub-liquid flows flowing into different sub-flow channels 322. More preferably, the sub-liquid flows flowing into the sub-flow channel 322 can merge at the end of the mixing structure 321 after flowing out of the sub-flow channel 322, thereby generating a relative impact force between the two merging sub-liquid flows, causing secondary mixing of the components in the sub-liquid flows. Preferably, the flow channel of the separation and filtration structure 32 is arranged in a wave-like undulating manner according to the longitudinal cross-section of its internal chamber, that is, the transverse cross-sectional area of ​​the internal chamber of the flow channel changes in a manner that first gradually increases and then gradually decreases. A mixing structure 321 is provided in the region of the internal chamber with a larger transverse cross-sectional area, which can construct two sub-flow channels 322 in a manner that cooperates with the flow channel wall. The mixing structure 321 can be configured as a spindle-shaped structure that can cooperate with the internal flow channel chamber, so that the section of the flow channel with a larger cross-sectional area can be divided into two parallel sub-flow channels 322 by the mixing structure 321. Preferably, the first ends of the two sub-flow channels 322 are interconnected; the tail ends of the two sub-flow channels 322 are also interconnected. When the liquid flow in the concentration unit 2 enters the flow channel, the liquid flow is a mixed liquid. When passing through the section of the mixing structure 321, the liquid flow is divided into two mixed sub-liquid flows, and the sub-liquid flows directionally along the sub-flow channels 322. When the sub-liquid flows out of the sub-channel 322, the two sub-liquid flows merge at the interconnected ends of the two sub-channels 322. Preferably, the sub-channel 322 can alter the distribution of sodium chloride in the liquid flow, allowing the sodium chloride to redistribute during the flow splitting / merging process, increasing the probability of sodium chloride contact with the channel wall, and enabling more effective separation of sodium chloride from the liquid flow. Preferably, the total flow rate of the two sub-channels 322 is greater than the flow rate of the mixing section of the channel, causing the liquid flow in the sub-channel 322 to accelerate the movement of liquid component molecules during the splitting process while reducing the overall flow velocity of the sub-liquid flow. This allows the sodium chloride in the sub-liquid flow to maintain continuous movement and make sufficient contact with the channel wall, thereby accelerating the permeation of sodium chloride through the channel wall and ultimately achieving component separation of the liquid flow. Preferably, the mixing section refers to the section of the channel that is not divided into two sub-channels 322 by the mixing structure 321.For the sodium chloride component with low activity that is still present in the sub-flow and located inside the flow, the residual sodium chloride component gains kinetic energy during the secondary merging of the two sub-flows through a secondary merging process. This increases the activity of the residual sodium chloride component in the flow, allowing it to pass through the channel wall more quickly, thereby achieving component separation of the flow.

[0059] Preferably, the mixing structure 321 is streamlined, which can split the liquid flow in the flow channel at the beginning of the streamline of the mixing structure 321, so that the two parts of the liquid flow can flow along the two sub-flow channels 322, thereby forming a split liquid flow. At the end of the streamline, the split flow channels are connected in a streamlined manner, so that the split liquid flows in the two sub-flow channels 322 converge and mix to form the first mixed liquid flow. During the liquid flow mixing process, the overall flow channel narrows and the hydraulic pressure of the liquid flow increases, which is beneficial to increase the micro-positive pressure of the liquid flow. In addition, during the liquid flow mixing process, due to the changes in the pressure and velocity of the liquid flow, the coking wastewater components that can pass through the flow channel wall can be accelerated to separate from the coking wastewater under the conditions of mixing, impact and pressure of the coking wastewater liquid flow, and enter the cavity channel between the outer sleeve 31 and the separation and filtration structure 32 through the flow channel wall of the separation and filtration structure 32. Preferably, when the coking wastewater stream is diverted into the sub-channel 322, the contact area between the stream and the channel wall of the separation and filtration structure 32 increases, and the mixing state of specific components in the coking wastewater is re-stirred, allowing these specific components to better permeate through the channel wall of the sub-channel 322 region for seepage-type component separation. Preferably, when the two diverted streams mix at the end of the sub-channel 322, the merging of the streams can be accelerated, eliminating the defects of uneven composition within the stream caused by filtration, thereby facilitating component separation in subsequent structures. Preferably, the merging of the streams in the sub-channel 322 may also generate eddies, which can better transfer higher concentrations of filterable components from within the stream to the surface, thereby accelerating their passage through the channel wall in contact with the stream surface.

[0060] Preferably, the separation and filtration structure 32 is constructed by arranging a nanofiltration membrane capable of separating sodium chloride and sodium sulfate components on a flow channel forming structure mesh. More preferably, the specific flow channel shape of the separation and filtration structure 32 can be adjusted according to requirements, and the structure mesh can be made of a flexible material with high corrosion resistance. Preferably, the flow channel wall of the separation and filtration structure 32 is the nanofiltration membrane capable of separating sodium chloride and sodium sulfate components, wherein the nanofiltration membrane can be attached to the inner wall side of the flow channel forming structure mesh, so that the structure mesh does not affect the flow of liquid within the flow channel. Preferably, the filtrate that can pass through the nanofiltration membrane is sodium chloride liquid, while the liquid retained by the nanofiltration membrane is sodium sulfate liquid.

[0061] Preferably, when multiple mixing structures 321 are spaced apart in the streamlined separation and filtration structure 32, the contour of the mixing channel is adapted to the mixing structure 321, and the mixing section between two mixing structures 321 is arranged with a narrowing channel width. Preferably, when the mixed liquid flow after the first split encounters the second splitting module again, the first mixed liquid flow splits and converges again, thereby generating a second mixed liquid flow. Preferably, the liquid outlet of the channel is set as a streamlined aggregation channel that facilitates liquid convergence, that is, the liquid outlet is located at the end of the mixing structure 321. At this time, the liquid flow in the sub-channel 322 converges, the hydraulic pressure increases, and the resulting micro-hydraulic pressure is relatively large, which is more conducive to sodium chloride liquid passing through the channel wall of the mixing section. Preferably, the multiple streamlined channels can be interconnected, allowing the airflow to be arbitrarily split and converged.

[0062] Preferably, the mixing structure 321 further includes at least one microchannel 323 that communicates with the sub-channel 322. Preferably, the groove direction of the microchannel 323 is consistent with the flow of the liquid in the sub-channel 322, and the inlet of the microchannel 323 is configured to penetrate the surface of the mixing structure 321 and communicate with the sub-channel 322, enabling the microchannel 323 to perform secondary diversion of the sub-liquid flow in the sub-channel 322. Preferably, the microchannel 323 within the mixing structure 321 can also selectively converge and diverge flows. Preferably, the microchannel 323 connects the starting and ending regions of the sub-channel 322. Because the microchannel 323 can partially divert the sub-liquid flow into the sub-channel 322, the hydraulic pressure of the sub-liquid flow before and after the inlet of the microchannel 323 changes, thereby further increasing the activity of sodium chloride in the sub-liquid flow. This promotes the accelerated movement of sodium chloride, allowing it to contact the channel wall better and faster, thus improving the efficiency of sodium chloride passing through the channel wall. Preferably, the aperture of the microchannel 323 is smaller than that of the sub-channel 322. Under the same hydraulic pressure conditions, the gas velocity in the microchannel 323 is faster, thereby achieving more efficient component separation in the coking wastewater flow. Furthermore, the microchannel 323 compensates for the slower flow rate of the coking wastewater within the subchannel 322, mitigating the drawback of reduced flow velocity due to decreased hydraulic pressure in the subchannel 322. This avoids the disadvantage of reduced flow velocity caused by diversion in the overall flow channel, which hinders component separation. Through the microchannel 323, this invention ensures that the coking wastewater maintains a consistently high flow rate, efficiently achieving component separation.

[0063] Example 3 This application also provides a process for separating crystallized salts from coking wastewater, which includes at least the following steps: (1) Pretreatment: mainly removes hardness, silica, F-, CODcr and residual impurities from coking wastewater, eliminates the impact of impurities on membrane concentration and evaporation crystallization, ensures the quality of crystallized salt, and minimizes the amount of waste crystallized salt. Most of the hardness is removed by lime-soda softening, and the remaining hardness is completely removed by ion exchange.

[0064] (2) Membrane concentration: mainly using two-stage membrane concentration to reduce the volume of water and increase the salt content of the concentrated water; on this basis, using two-stage nanofiltration membranes to separate sodium sulfate and sodium chloride.

[0065] The effluent from the weak acid cation exchange bed first enters the GTR3 medium-pressure membrane thickener for concentration and volume reduction. The concentrate produced by the GTR3 medium-pressure membrane thickener then enters the GTR4 high-pressure membrane thickener for further concentration and volume reduction. The concentrate produced by the GTR4 high-pressure membrane thickener has undergone significant concentration in terms of hardness, F-, silica, COD, and other indicators, so it needs further treatment before entering the subsequent systems.

[0066] (3) Salt separation: After hardness removal using chelating resin, the water enters the first-stage nanofiltration membrane unit for salt separation. In order to improve the purity of sodium chloride crystals and the recovery rate of sodium sulfate crystals, the permeate from the first-stage nanofiltration membrane unit enters the second-stage sodium filtration membrane unit. The concentrate from the second-stage sodium filtration membrane unit is returned to the first-stage nanofiltration membrane unit for further treatment. The permeate from the second-stage sodium filtration membrane unit enters the sodium chloride RO unit for concentration. The concentrated brine from the sodium chloride RO unit enters the sodium chloride evaporation crystallization module. The concentrate from the first-stage nanofiltration membrane unit is oxidized by ozone to reduce COD and then enters the sodium sulfate evaporation crystallization module for evaporation crystallization treatment. The permeate from the GTR3 and GTR4 membrane concentration units and the sodium chloride RO unit enters the recycled water tank.

[0067] (4) Salt extraction and evaporation crystallization: mainly to separate sodium sulfate, sodium chloride crystallized salt and other products. In this application, sodium sulfate crystallized salt is obtained by nitro MVR + countercurrent triple-effect evaporation crystallization; sodium chloride crystallized salt is obtained by salt MVR + co-current double-effect evaporation crystallization; the mother liquor of nitro triple-effect evaporation crystallization and the mother liquor of salt double-effect evaporation crystallization are jointly fed into mixed salt double-effect evaporation crystallization, and the remaining mother liquor is fed into an integrated evaporation crystallization and drying machine.

[0068] Nitrate-containing concentrated water is concentrated by MVR and then enters a countercurrent triple-effect evaporator crystallizer. Nitrate is discharged from the high-temperature section of the evaporator crystallizer, thickened by a thickener, and then dehydrated by a centrifuge before entering a dryer. The dried sodium sulfate product is then sent to the product packaging line.

[0069] After being concentrated by MVR, the salt-containing concentrated water enters the salt double-effect evaporator crystallizer. The salt exits from the low-temperature section of the evaporator crystallizer, is thickened by a thickener, and then dehydrated by a centrifuge before entering the dryer. The dried sodium chloride product is then sent to the product packaging line.

[0070] The remaining mother liquor from the nitrate crystallizer and the salt crystallizer enters the double-effect mixed salt crystallizer to produce mixed salt, which is then re-dissolved and enters the first-stage nanofiltration unit for further salt separation.

[0071] The remaining mother liquor from the mixed salt crystallizer is dried by an integrated evaporation-crystallization-drying machine to produce mixed salt.

[0072] It should be noted that the specific embodiments described above are exemplary. Those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents. Throughout the text, features introduced by "preferred" are merely optional and should not be construed as mandatory. Therefore, the applicant reserves the right to abandon or delete relevant preferred features at any time.

Claims

1. A water recovery system for high-concentration crystalline salt extraction from coking wastewater, comprising at least a filter assembly (1) for receiving coking wastewater generated during industrial production, and for conveying the treated coking wastewater to a concentration unit (2) for dewatering and concentration after hardening and filtration treatment. Its features are, The filter housing (11) of the filter assembly (1) divides its chamber into at least three interconnected filter zones by setting different filter structures inside. The three interconnected and orderly arranged filter zones are a slow-flow section, a filter section, and an output section, wherein... The slow-flow section has filter plates (111) arranged alternately on two opposite side walls of its inner cavity in a manner that is spaced along the axis of its cavity. The filter plates (111) are inclinedly connected to the cavity wall, and the filter plates (111) can be selectively pulled out from the cavity, thereby removing the filter plates (111) that have intercepted impurities from the cavity for the removal of precipitated impurities. After the concentration unit (2) performs dehydration and concentration treatment on the coking wastewater, the concentrated coking wastewater undergoes separation treatment of sodium chloride and sodium sulfate components in the separation component (3). The separation component (3) includes an outer tube (31) and a separation filter structure (32). The outer tube (31) has a separation filter structure (32) suspended in the tube cavity along its axial direction by a support structure (33) to separate coking wastewater. The flow channel of the separation and filtration structure (32) is streamlined, and at least one mixing structure (321) capable of diverting and secondary mixing the liquid flow within the flow channel is provided inside the flow channel. The mixing structure (321) can divide the flow channel of the separation and filtration structure (32) into two sub-flow channels (322), so that the liquid flow can be divided into two sub-liquid flows flowing to different sub-flow channels (322) by the front end of the mixing structure (321). The sub-liquid flows flowing into the sub-flow channel (322) can merge at the end of the mixing structure (321) after flowing out of the sub-flow channel (322). Thus, the two sub-liquid flows that merge can generate relative impact force, causing the components in the sub-liquid flows to undergo secondary mixing.

2. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 1, characterized in that, The slow-flow section can perform coarse filtration and buffer diversion treatment on the coking wastewater flowing in from the top of the filter box (11), so that the coking wastewater can flow into the filter section evenly and dispersedly.

3. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 2, characterized in that, The filter plate (111) has multi-stage progressive sedimentation stepped grooves (112) on its surface to separate settleable impurities. Multiple sedimentation stepped tanks (112) arranged at intervals along the water flow direction for intercepting and containing sedimentable impurities can gradually filter impurities of different volumes and masses in a graded filtration manner.

4. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 3, characterized in that, The sedimentation stepped tanks (112) are selectively opened in such a way that their arc axis is located inside or outside the tank. Multiple sedimentation stepped tanks (112) are arranged laterally by gradually increasing the curvature of their surfaces along the direction of water flow, so that the sedimentation stepped tanks (112) located on the same filter plate (111) and belonging to the downstream area of ​​the water flow can resist the power of the water flow with a larger curvature of the tank walls.

5. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 4, characterized in that, The filter plate (111) is further provided with multiple strip plates separated by the sedimentation stepped groove (112), and interception modules (113) capable of intercepting flocculent impurities are also arranged at intervals. The multiple interception modules (113) are arranged alternately with the sedimentation stepped groove (112), thereby forming a stepped multi-impact interception structure on the filter plate (111).

6. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 5, characterized in that, The interception module (113) provided on the filter plate (111) can cooperate with the sedimentation stepped tank (112) to separate impurities in the coking wastewater flow.

7. The water recovery system for high-concentration crystalline salt extraction from coking wastewater according to claim 6, characterized in that, The interception module (113) has an interception net that can intercept floating debris in the sedimentation stepped tank (112) upstream that has not settled, wherein, The interception module (113) on the same filter plate (111) gradually reduces the mesh size of its interception net according to its different positions, thereby achieving the filtration of impurities of different sizes in a step-by-step filtration manner.

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