Hybrid triple-effect mvr evaporation crystallization system

Abstract

The application discloses a mixed three-effect MVR evaporation crystallization system, which comprises a feed unit, a preheating unit, a first-effect evaporation unit, a second-effect evaporation unit and a third-effect crystallization unit connected in sequence, and a steam compressor; the feed unit comprises a raw material tank and a feed pump connected in sequence; the preheating unit comprises a plate preheater and a non-condensing steam preheater connected in sequence; the first-effect evaporation unit comprises a first-effect plate evaporator, a first-effect separator and a first-effect circulating pump; the second-effect evaporation unit comprises a second-effect plate evaporator, a second-effect separator and a second-effect circulating pump; and the third-effect crystallization unit comprises a third-effect tube heater, a crystallization separator and a third-effect circulating pump. The application adopts a three-effect evaporation and mechanical steam re-compression coupling structure, and the energy consumption of system operation is significantly reduced compared with a traditional single-effect tube device.

Description

Technical Field

[0001] This invention relates to the field of high-salt wastewater evaporation and crystallization treatment technology, and in particular to a hybrid triple-effect MVR evaporation and crystallization system. Background Technology

[0002] In the field of high-salinity wastewater treatment, evaporation crystallization is the core process for achieving brine fractionation and zero discharge, and it is widely used in the treatment of high-salinity wastewater generated by industries such as coal chemical, power, and printing and dyeing. Existing evaporation crystallization devices mainly adopt two technical routes: multi-effect evaporation and single-effect mechanical steam recompression. Multi-effect evaporation relies on live steam to heat the material effect by effect, with an operating cost of about 120 yuan per ton of water evaporated. It also requires a large-flow circulating cooling water system to condense the secondary steam in the last effect, resulting in high energy and water consumption. Although the single-effect shell-and-tube forced circulation mechanical steam recompression device uses a steam compressor to pressurize and heat the secondary steam for reuse as a heat source, reducing the operating cost to about 60 yuan per ton of water, the heat transfer coefficient of the shell-and-tube heat exchanger is relatively low, requiring a large heat exchange area. The equipment cost can easily reach millions or even tens of millions of yuan. Furthermore, the steam compressor in the single-effect configuration has a large processing load and requires high specifications, further increasing equipment investment and operating costs. Meanwhile, existing shell-and-tube forced circulation devices have significantly lower heat exchange efficiency than plate evaporators in the concentration stage of low-concentration saline wastewater. The forced circulation pumps consume a large amount of power, and the systems have a large footprint and lengthy processes. While plate evaporators offer high heat exchange efficiency, they are prone to scaling and clogging during the crystallization stage of high-concentration crystalline slurry, making them unsuitable for direct application in the crystallization process. The crystallization stage typically uses ordinary crystallizers, lacking a grain-grading and separating structure, resulting in fine crystal particles and a low solid-liquid ratio. After centrifugation, the filter cake has a high moisture content, often requiring additional drying equipment for secondary drying of the finished salt, further increasing system investment and operating costs. These shortcomings make it difficult for existing evaporation crystallization devices to simultaneously optimize both equipment investment and operating energy consumption, hindering the widespread application of high-salinity wastewater evaporation crystallization technology. Summary of the Invention

[0003] The purpose of this invention is to provide a hybrid triple-effect MVR evaporation crystallization system to solve the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention provides the following solution: The present invention provides a hybrid triple-effect MVR evaporation and crystallization system, comprising a feeding unit, a preheating unit, a first-effect evaporation unit, a second-effect evaporation unit, and a third-effect crystallization unit connected in series, as well as a steam compressor;

[0005] The feeding unit includes a raw material tank and a feeding pump connected in series;

[0006] The preheating unit includes a plate preheater and a non-condensable steam preheater connected in series.

[0007] The first-effect evaporation unit includes a first-effect plate evaporator, a first-effect separator, and a first-effect circulation pump. The first-effect plate evaporator and the first-effect separator are connected in series. The bottom outlet of the first-effect separator is divided into two paths. One path returns to the first-effect plate evaporator via the first-effect circulation pump to form a circulation branch. The other path is connected in series to the second-effect evaporation unit.

[0008] The double-effect evaporation unit includes a double-effect plate evaporator, a double-effect separator, and a double-effect circulation pump. The double-effect plate evaporator and the double-effect separator are connected in series. The bottom outlet of the double-effect separator is divided into two paths. One path returns to the double-effect plate evaporator via the double-effect circulation pump to form a circulation branch. The other path is connected in series to the triple-effect crystallization unit.

[0009] The triple-effect crystallization unit includes a triple-effect tube heater, a crystallizer separator, and a triple-effect circulation pump. The triple-effect tube heater is connected in series with the crystallizer separator, and the bottom outlet of the crystallizer returns to the triple-effect tube heater via the triple-effect circulation pump to form a circulation branch.

[0010] The inlet of the steam compressor is connected to the top of the crystallizer, and the outlet is connected to the heating side inlet of the single-effect plate evaporator and the triple-effect tube heater, respectively.

[0011] According to the hybrid triple-effect MVR evaporation and crystallization system provided by the present invention, the bottom outlet of the raw material tank is connected to the inlet of the feed pump, the outlet of the feed pump is connected to the material inlet of the plate preheater, the material outlet of the plate preheater is connected to the material inlet of the non-condensable steam preheater, the material outlet of the non-condensable steam preheater is connected to the material inlet of the first-effect plate evaporator, and the raw material tank, the feed pump, the plate preheater, the non-condensable steam preheater and the first-effect plate evaporator are connected in series.

[0012] According to the hybrid triple-effect MVR evaporation and crystallization system provided by the present invention, the first-effect plate evaporator is a rising film plate evaporator, the first-effect separator is a cyclone separator, the material outlet of the first-effect plate evaporator is connected to the middle inlet of the first-effect separator, the top of the first-effect separator is provided with a steam outlet, the bottom of the first-effect separator is provided with a conical bottom, the lower end outlet of the conical bottom is divided into two paths, one path is connected to the inlet of the first-effect circulation pump, the outlet of the first-effect circulation pump is connected to the material inlet of the first-effect plate evaporator to form a circulation loop, and the other path is connected to a transfer pipeline, the transfer pipeline is connected to the material inlet of the second-effect plate evaporator.

[0013] According to the hybrid triple-effect MVR evaporation and crystallization system provided by the present invention, the second-effect plate evaporator is a rising film plate evaporator, the second-effect separator is a cyclone separator, the material outlet of the second-effect plate evaporator is connected to the middle inlet of the second-effect separator, the top of the second-effect separator is provided with a steam outlet, the bottom of the second-effect separator is provided with a conical bottom, the lower end outlet of the conical bottom is divided into two paths, one path is connected to the inlet of the second-effect circulation pump, the outlet of the second-effect circulation pump is connected to the material inlet of the second-effect plate evaporator to form a circulation loop, and the other path is connected to the transfer pipeline, the transfer pipeline is connected to the material inlet of the triple-effect tube heater.

[0014] According to the hybrid triple-effect MVR evaporation crystallization system provided by the present invention, the triple-effect tube heater includes a first tube heater and a second tube heater, the first tube heater and the second tube heater are arranged in parallel, the outlet of the triple-effect circulation pump is connected to a material distribution pipeline, the material distribution pipeline is respectively connected to the material inlet of the first tube heater and the material inlet of the second tube heater, the material outlet of the first tube heater and the material outlet of the second tube heater are connected to a material confluence pipeline, the material confluence pipeline is connected to the middle inlet of the crystallization separator, the crystallization separator is an FC type crystallization separator, the bottom of the crystallization separator is provided with a sludge leg, the lower end outlet of the sludge leg is connected to the inlet of the triple-effect circulation pump to form a circulation loop.

[0015] According to the hybrid triple-effect MVR evaporation and crystallization system provided by the present invention, a first steam outlet is provided at the top of the first-effect separator, a second steam outlet is provided at the top of the second-effect separator, and a third steam outlet is provided at the top of the crystallization separator. The first steam outlet, the second steam outlet, and the third steam outlet are respectively connected to steam branch pipes. The three steam branch pipes are connected to a steam main pipe after converging. The steam main pipe is connected to the inlet of the steam compressor. The outlet of the steam compressor is connected to a steam distribution pipe. The steam distribution pipe is divided into two paths: one path is connected to the heating steam inlet of the first-effect plate evaporator, and the other path is connected to the heating steam inlet of the triple-effect tube heater.

[0016] The hybrid triple-effect MVR evaporation crystallization system provided by the present invention further includes a discharge pump, a centrifuge, a mother liquor tank, and a mother liquor pump. The bottom outlet of the crystallizer is also connected to a discharge pipeline. The discharge pipeline is connected to the inlet of the centrifuge via the discharge pump. The centrifuge has a solid phase outlet at its bottom and a liquid phase outlet on its side. The liquid phase outlet is connected to the inlet of the mother liquor tank. The bottom outlet of the mother liquor tank is connected to the inlet of the mother liquor pump. The outlet of the mother liquor pump is connected to the inlet of the triple-effect circulating pump.

[0017] The hybrid triple-effect MVR evaporation crystallization system provided by the present invention further includes a mechanical seal water tank, a vertical pump, and a mechanical seal water cooler. The top of the mechanical seal water tank is provided with a softened water inlet, the bottom outlet of the mechanical seal water tank is connected to the inlet of the vertical pump, the outlet of the vertical pump is connected to the mechanical seal water inlet of the mechanical seal water cooler, the mechanical seal water outlet of the mechanical seal water cooler is connected to the mechanical seal water main pipe, the mechanical seal water main pipe is respectively connected to the mechanical seal cooling water inlets of the feed pump, the first-effect circulation pump, the second-effect circulation pump, the third-effect circulation pump, and the discharge pump, and the mechanical seal water cooler is respectively provided with a cooling water inlet and a cooling water outlet.

[0018] The present invention discloses the following technical effects:

[0019] This invention employs a hybrid configuration of the first two effects plate evaporators and the last effect tube heater. In the low-concentration section, the high heat transfer coefficient and small heat transfer area of ​​the plate evaporator are utilized to reduce the cost and footprint of the first two effects. In the last effect crystallization section, the tube heater is used to adapt to the heating conditions of crystalline slurry, avoiding the problem of easy blockage in the crystallization section of the plate evaporator, thus significantly reducing the overall equipment investment.

[0020] This invention adopts a triple-effect evaporation and mechanical steam recompression coupling structure. The secondary steam flashed by the triple-effect separator is pressurized and heated by the compressor and then reused as a heat source for heating the first and third effects. The secondary steam is fully recycled. Under the triple-effect configuration, the compressor's processing load and selection specifications are reduced accordingly, and the system's operating energy consumption is significantly reduced compared to the traditional single-effect tube unit.

[0021] The triple-effect crystallizer of this invention adopts an FC-type structure and has a washing leg at the bottom. The crystal-containing slurry is classified by gravity in the washing leg. Large crystal particles are discharged from the bottom and enter the centrifuge, while fine crystals are returned with the mother liquor to continue growing. The produced crystal particles are uniform, the solid-liquid ratio is improved, and the moisture content of the centrifuge filter cake is reduced, which can eliminate the need for subsequent drying equipment. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a process flow diagram of the hybrid triple-effect MVR evaporation crystallization system of the present invention.

[0024] The components include: 1. Feeding unit; 2. Preheating unit; 3. First-effect evaporation unit; 4. Second-effect evaporation unit; 5. Third-effect crystallization unit; and 6. Steam compressor. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Reference Figure 1 The present invention provides a hybrid triple-effect MVR evaporation and crystallization system, comprising a feeding unit 1, a preheating unit 2, a first-effect evaporation unit 3, a second-effect evaporation unit 4 and a triple-effect crystallization unit 5 connected in series, and a steam compressor 6;

[0028] Feeding unit 1 includes a raw material tank and a feed pump connected in series;

[0029] Preheating unit 2 includes a plate preheater and a non-condensable steam preheater connected in series;

[0030] The first-effect evaporation unit 3 includes a first-effect plate evaporator, a first-effect separator, and a first-effect circulation pump. The first-effect plate evaporator and the first-effect separator are connected in series. The bottom outlet of the first-effect separator is divided into two paths. One path returns to the first-effect plate evaporator through the first-effect circulation pump to form a circulation branch. The other path is connected in series to the second-effect evaporation unit 4.

[0031] The double-effect evaporation unit 4 includes a double-effect plate evaporator, a double-effect separator, and a double-effect circulation pump. The double-effect plate evaporator and the double-effect separator are connected in series. The bottom outlet of the double-effect separator is divided into two paths. One path returns to the double-effect plate evaporator via the double-effect circulation pump to form a circulation branch. The other path is connected in series to the triple-effect crystallization unit 5.

[0032] The triple-effect crystallization unit 5 includes a triple-effect tube heater, a crystallizer separator, and a triple-effect circulation pump. The triple-effect tube heater is connected in series with the crystallizer separator. The bottom outlet of the crystallizer returns to the triple-effect tube heater via the triple-effect circulation pump to form a circulation branch.

[0033] The inlet of the steam compressor 6 is connected to the top of the crystallizer separator, and the outlet is connected to the heating side inlet of the single-effect plate evaporator and the triple-effect tube heater, respectively.

[0034] Low-concentration saline wastewater is first temporarily stored in a raw material tank. After being pressurized by a feed pump, it is sequentially fed into a plate preheater and a non-condensable steam preheater for two-stage preheating. In the plate preheater, the material exchanges heat with the system condensate to recover waste heat. Subsequently, it is further heated to its boiling point in the non-condensable steam preheater. The material that has reached the boiling point enters a first-effect plate rising film evaporator, where it is evenly distributed in a film shape along the plate surface and rises rapidly. It is heated and boiled by the heating steam between the plates. The resulting gas-liquid mixture is tangentially fed from the outlet of the first-effect plate evaporator into the middle of the first-effect cyclone separator. The gas-liquid mixture rotates in the separator cylinder, generating centrifugal force, and the liquid is thrown against the separator wall and flows along... The wall-mounted flow achieves gas-liquid separation. The separated secondary steam exits from the top of the first-effect separator and flows into the main steam pipe. The concentrated liquid at the bottom flows out in two streams: one stream is pressurized by the first-effect circulating pump and returned to the material inlet of the first-effect plate evaporator for continued circulation and evaporation; the other stream is sent to the material inlet of the second-effect plate evaporator via a transfer pipe. The material entering the second-effect plate evaporator is also heated and evaporated. The resulting gas-liquid mixture is tangentially sent to the second-effect cyclone separator for gas-liquid separation. The secondary steam exits from the top and flows into the main steam pipe. The concentrated liquid at the bottom is either returned to the second-effect plate evaporator via the second-effect circulating pump for continued circulation and evaporation, or transferred to the third-effect tube separator. Heater; The triple-effect tube heater consists of two tube heaters arranged in parallel. The material is pressurized by a triple-effect circulating pump and then fed into the two tube heaters through material distribution pipelines. Inside the tubes, it is heated by external steam. The heated material is then sent to the middle of the FC-type crystallizer for flash evaporation through a material collection pipeline. The secondary steam generated by flash evaporation is discharged from the top of the crystallizer and merged into the steam main pipe. The bottom slurry containing crystals enters the settling leg, where gravity achieves crystal classification. Large crystals settle to the bottom of the settling leg; one path returns to the triple-effect tube heater via a triple-effect circulating pump for further circulation and concentration, while the other path reaches the discharge concentration. The product is fed into a centrifuge via a discharge pump for solid-liquid separation. The solid salt product separated by the centrifuge is discharged from the system, while the liquid mother liquor is temporarily stored in a mother liquor tank and then returned to the inlet of the triple-effect circulating pump via a mother liquor pump for further concentration. The secondary steam discharged from the top of the first-effect separator, the second-effect separator, and the crystallizer is combined through steam branch pipes and then sent to the steam compressor 6. The steam compressor 6 pressurizes and heats the low-pressure, low-temperature secondary steam into high-quality heating steam, which is then sent to the heating side of the first-effect plate evaporator and the triple-effect tube heater via steam distribution pipes as a heat source. The heating steam releases heat and condenses to form condensate, which is then discharged from the system, thus realizing the closed-loop recycling of steam.

[0035] The scheme is further optimized so that the bottom outlet of the raw material tank is connected to the inlet of the feed pump, the outlet of the feed pump is connected to the material inlet of the plate preheater, the material outlet of the plate preheater is connected to the material inlet of the non-condensable steam preheater, and the material outlet of the non-condensable steam preheater is connected to the material inlet of the first-effect plate evaporator. The raw material tank, feed pump, plate preheater, non-condensable steam preheater and first-effect plate evaporator are connected in series.

[0036] The raw material tank acts as a buffer and homogenizer for the incoming material, stabilizing the flow rate and concentration of the material entering the system and preventing fluctuations in the feed from impacting subsequent evaporation operations. The feed pump provides the power to transport the material, overcoming the resistance of the preheater and pipelines, and steadily pressurizing the material before sending it into the preheating section. The plate preheater utilizes the waste heat from the system's discharged condensate to preheat the material, recovering the sensible heat of the condensate and reducing the consumption of external heat sources. The non-condensable steam preheater utilizes the waste heat carried by the system's non-condensable steam to further heat the material to its boiling point temperature, ensuring that the material reaches its bubble point before entering the first-effect evaporator. This avoids the presence of a sensible heat heating section within the evaporator, allowing the entire heat exchange area of ​​the evaporator to be used for boiling evaporation, thus improving the utilization rate of the effective evaporation area. The two-stage preheating is arranged in series, with the temperature of the heat transfer medium and the material temperature matched step by step. This avoids thermal stress and heat loss caused by excessive temperature differences in single-stage preheating, making the feed preheating process thermodynamically closer to reversible heat exchange and reducing system heat loss.

[0037] Further optimization of the scheme: the first-effect plate evaporator is a rising film plate evaporator, the first-effect separator is a cyclone separator, the material outlet of the first-effect plate evaporator is connected to the middle inlet of the first-effect separator, the top of the first-effect separator is equipped with a steam outlet, the bottom of the first-effect separator is equipped with a conical bottom, the lower end of the conical bottom outlet is divided into two paths, one path is connected to the inlet of the first-effect circulating pump, the outlet of the first-effect circulating pump is connected to the material inlet of the first-effect plate evaporator to form a circulation loop, and the other path is connected to the transfer pipe, which is connected to the material inlet of the second-effect plate evaporator.

[0038] In a rising film plate evaporator, the material enters from the bottom of the plate channel, is heated to its boiling point by the steam between the plates, and generates steam bubbles. These steam bubbles rapidly expand and rise between the narrow plates, dragging the surrounding material upwards in a film-like flow along the plate surface. The liquid film is extremely thin and constantly renewed, resulting in a much higher lateral convective heat transfer coefficient than in a full-tube evaporator. Simultaneously, the short residence time of the material in the heating zone reduces high-temperature scaling and decomposition of heat-sensitive components. The gas-liquid mixture enters tangentially from the center of the separator, forming a forced rotating flow field within the cylinder. Higher density droplets are thrown against the wall by centrifugal force, spiraling down the wall to collect at the conical bottom, while lower density secondary steam exits from the top center. The acceleration of centrifugal separation is much greater than that of gravity, resulting in a significantly higher separation efficiency than gravity settling. Furthermore, the cyclone separator has no internal components, low pressure drop, and is less prone to material blockage. The conical bottom cross-sectional area gradually decreases from top to bottom, eliminating the dead zone of a flat-bottom structure and ensuring stable collection and discharge of the concentrated liquid. The circulation loop returns the concentrated liquid from the bottom of the separator to the evaporator inlet via a circulation pump. After mixing with the fresh feed, it is evaporated again, resulting in a material flow rate in the evaporator that is much greater than the net feed rate. This increases the flow velocity between the plates, stabilizes the film flow, and further enhances the heat transfer coefficient. Simultaneously, the circulation dilution effect reduces the concentration gradient within the evaporator, delaying concentration polarization and scaling. The transfer pipeline, after the concentrated liquid reaches the target concentration, branches off from the circulation branch and sends the material to the second effect, achieving continuous inter-effect transfer.

[0039] Further optimization of the scheme: the double-effect plate evaporator is a rising film plate evaporator, the double-effect separator is a cyclone separator, the material outlet of the double-effect plate evaporator is connected to the middle inlet of the double-effect separator, the top of the double-effect separator is equipped with a steam outlet, and the bottom of the double-effect separator is equipped with a conical bottom. The lower end outlet of the conical bottom is divided into two paths: one path is connected to the inlet of the double-effect circulating pump, and the outlet of the double-effect circulating pump is connected to the material inlet of the double-effect plate evaporator to form a circulation loop; the other path is connected to the transfer pipeline, and the transfer pipeline is connected to the material inlet of the triple-effect tube heater.

[0040] The second-effect evaporator receives the feed from the first-effect evaporator. At this point, the material concentration is significantly higher than the initial feed. A rising film plate evaporator is then used, leveraging the plate heat exchanger's ability to maintain a high heat transfer coefficient in the medium-to-high concentration range for a second stage of concentration. This further increases the material concentration before it enters the third-effect crystallization section, reducing the evaporation load on the third-effect shell-and-tube heater. The second-effect cyclone separator also relies on centrifugal force for efficient gas-liquid separation. The conical bottom collects the concentrated liquid, and the circulation loop maintains a high flow rate within the second-effect evaporator, ensuring a stable liquid film between the plates and preventing scaling caused by low-speed flow of high-concentration material between the plates. The second-effect feed transfer line then delivers the material to the third-effect shell-and-tube heater, completing the process switch from low-concentration plate concentration to high-concentration shell-and-tube crystallization. This ensures that both the plate evaporator and the shell-and-tube heater operate within their optimal concentration ranges, fully utilizing the structural advantages of both types of heat exchangers.

[0041] Further optimization of the scheme: The triple-effect tube heater includes a first tube heater and a second tube heater, which are arranged in parallel. The outlet of the triple-effect circulating pump is connected to a material distribution pipeline, which is connected to the material inlet of the first tube heater and the material inlet of the second tube heater respectively. The material outlets of the first tube heater and the second tube heater are connected to a material merging pipeline, which is connected to the middle inlet of the crystallizer. The crystallizer is an FC type crystallizer, and a washing leg is set at the bottom of the crystallizer. The lower outlet of the washing leg is connected to the inlet of the triple-effect circulating pump to form a circulation loop.

[0042] In the triple-effect stage, the material concentration is high and crystals have already precipitated. The tube heater has a large flow cross-sectional area and smooth tube walls, making it less prone to blockage by crystals when the crystalline slurry flows inside. Furthermore, the tube structure is wear-resistant and easy to clean, making it suitable for forced circulation heating of crystalline slurry. The two heaters are arranged in parallel, distributing the total heat exchange area between them. This reduces the flow rate per tube and the flow velocity within the tube, minimizing erosion and wear on the tube walls caused by the high-speed crystalline slurry and extending the heater's service life. The parallel configuration also provides redundancy; when one heater is under maintenance or cleaning, the other can maintain low-load operation of the system. The material distribution pipeline evenly distributes the slurry from the circulating pump outlet to the inlets of the two heaters. The material collection pipeline collects the heated slurry and sends it to the crystallizer, ensuring balanced flow and heat load between the two heaters and preventing overheating and scaling in one heater due to uneven flow. In the FC-type crystallizer, the heated slurry enters tangentially from the center. Within the separator, it undergoes flash evaporation and cooling to create supersaturation, allowing crystals to grow in a suspended bed. The upper part is the clarification zone, and the lower part is the crystal slurry suspension zone. The slurry-containing strip is a vertically extended section at the bottom of the separator. After entering the strip, the liquid flows upward while the crystals settle downward under gravity, creating a counter-current slurry field. Large crystal particles have a free settling velocity greater than the upward liquid velocity and are discharged from the bottom of the strip into the centrifuge; small crystal particles have a settling velocity less than the upward liquid velocity and are carried back to the separator by the rising liquid flow to continue growing. The strip achieves crystal size classification, ensuring that the discharged crystals reach the target particle size, improving product particle size uniformity, and allowing fine crystals to return to the system for continued growth, thus increasing the crystallization yield and the solid-liquid ratio within the separator.

[0043] The scheme is further optimized by setting a first steam outlet at the top of the single-effect separator, a second steam outlet at the top of the double-effect separator, and a third steam outlet at the top of the crystallization separator. The first, second, and third steam outlets are respectively connected to steam branch pipes. The three steam branch pipes are connected to the steam main pipe after they merge. The steam main pipe is connected to the inlet of the steam compressor 6. The outlet of the steam compressor 6 is connected to the steam distribution pipe. The steam distribution pipe is divided into two paths: one path is connected to the heating steam inlet of the single-effect plate evaporator, and the other path is connected to the heating steam inlet of the triple-effect shell and tube heater.

[0044] The secondary steam discharged from the tops of the first-effect, second-effect cyclone separators, and third-effect crystallizer is collected into the main steam pipe via its respective steam branch pipes. This ensures that all secondary steam generated by the multi-effect system is recovered, eliminating steam venting losses. Furthermore, the combined steam flow and pressure at the compressor inlet are stable, preventing the impact of single-effect steam fluctuations on compressor operation. The steam compressor 6 utilizes a high-speed rotating impeller to perform work on the low-pressure, low-temperature secondary steam, adiabatically compressing it to a higher pressure. The steam saturation temperature rises accordingly, regaining its potential as a heating source. The shaft work input during compression is converted into steam enthalpy increase, upgrading the secondary steam from low-grade waste heat to high-grade heating steam. The high-quality heating steam at the compressor outlet is split into two paths via a steam distribution pipe: one path supplies the heating side of the first-effect plate evaporator, and the other path supplies the heating side of the third-effect shell-and-tube heater. This parallel heating ensures that the pressure and temperature of the heating steam in both effects are consistent, facilitating unified control. The steam flow can be distributed according to the heat load of each effect via pipe diameter or regulating valves. The heating steam releases heat and condenses into condensate in the heater and is discharged. The secondary steam is compressed and recycled. The entire steam system operates in a closed loop and does not require continuous replenishment of live steam. Only the compressor shaft power needs to be input to compensate for system heat loss and temperature rise, which fundamentally changes the energy consumption mode of multi-effect evaporation that relies on a large amount of live steam.

[0045] Further optimization of the scheme also includes a discharge pump, a centrifuge, a mother liquor tank, and a mother liquor pump. The bottom outlet of the crystallizer is also connected to a discharge pipeline, which is connected to the inlet of the centrifuge via the discharge pump. A solid phase outlet is set at the bottom of the centrifuge, and a liquid phase outlet is set on the side of the centrifuge. The liquid phase outlet is connected to the inlet of the mother liquor tank, the bottom outlet of the mother liquor tank is connected to the inlet of the mother liquor pump, and the outlet of the mother liquor pump is connected to the inlet of the triple-effect circulating pump.

[0046] The slurry containing large crystal particles discharged from the bottom of the crystallizer's washing leg is pressurized and sent to the centrifuge via a discharge pump after reaching the discharge concentration. The discharge pump provides the power for slurry transport and overcomes the pressure required at the centrifuge inlet. The centrifuge utilizes the strong centrifugal force generated by the high-speed rotation of the drum to throw the denser crystal particles against the drum wall, forming a filter cake, which is continuously discharged as finished salt from the bottom solid phase outlet. The less dense mother liquor passes through the gap between the filter cake and the filter screen and is discharged from the side liquid phase outlet. The separation factor of centrifugal separation is much higher than that of gravity filtration, and the filter cake has a low moisture content, achieving efficient and continuous solid-liquid separation. The mother liquor discharged from the centrifuge is sent to a mother liquor tank for temporary storage and buffering. The mother liquor tank homogenizes and stabilizes the mother liquor flow, preventing flow fluctuations caused by direct return of mother liquor from impacting the triple-effect evaporation process. At the same time, the mother liquor tank can settle fine crystals carried in the mother liquor, reducing wear on the impeller of the circulating pump. The mother liquor at the bottom of the mother liquor tank is pressurized by the mother liquor pump and sent to the inlet of the triple-effect circulating pump. After mixing with the circulating slurry at the bottom of the crystallizer, it enters the triple-effect tube heater for further evaporation and concentration. This allows the dissolved salts and fine crystals in the mother liquor that have not yet crystallized to re-enter the crystallization system, thereby improving the total salt recovery rate. The entire material system is a closed-loop circulation system with no mother liquor discharge, which meets the process requirements for zero discharge of high-salt wastewater.

[0047] Further optimization of the scheme also includes a mechanical seal water tank, a vertical pump, and a mechanical seal water cooler. The top of the mechanical seal water tank is equipped with a softened water inlet, the bottom outlet of the mechanical seal water tank is connected to the inlet of the vertical pump, the outlet of the vertical pump is connected to the mechanical seal water inlet of the mechanical seal water cooler, the mechanical seal water outlet of the mechanical seal water cooler is connected to the mechanical seal water main pipe, the mechanical seal water main pipe is connected to the mechanical seal cooling water inlets of the feed pump, the first-effect circulating pump, the second-effect circulating pump, the third-effect circulating pump, and the discharge pump, respectively, and the mechanical seal water cooler is equipped with a cooling water inlet and a cooling water outlet.

[0048] Softened water enters from the top of the mechanical seal water tank. Having removed calcium and magnesium ions, the softened water serves as cooling water for the mechanical seals, preventing scale buildup on the sealing surfaces and avoiding cooling failure and increased wear caused by scale. The mechanical seal water tank also acts as a pressure stabilizer and buffer, ensuring stable water supply pressure. At the bottom of the tank, the softened water is pressurized by a vertical pump, overcoming the resistance of the cooler and pipelines before being delivered to the mechanical seals of each pump. The vertical pump is compact and space-saving, suitable for conveying mechanical seal water at low flow rates and high head. The mechanical seal water at the vertical pump outlet first enters the mechanical seal water cooler, where it is indirectly cooled by the circulating cooling water, maintaining a low temperature and ensuring effective cooling of the sealing surfaces. Inside the cooler, the mechanical seal water exchanges heat counter-currently with the circulating cooling water. The cooler has separate inlets and outlets for the cooling water, and the continuous flow of circulating cooling water carries away the heat carried by the mechanical seal water from the sealing surfaces. After cooling, the mechanical seal water is supplied in parallel through the main mechanical seal water pipe to the mechanical seal cooling water inlets of the feed pump, first-effect circulating pump, second-effect circulating pump, third-effect circulating pump, and discharge pump. This parallel water supply ensures consistent mechanical seal water pressure across all pumps, facilitating unified adjustment. Once inside the mechanical seal, the mechanical seal water forms a stable liquid film between the rotating and stationary ring end faces. This film removes heat generated by friction at the seal end faces, preventing overheating and burnout due to dry friction. It also acts as a lubricant, reducing the coefficient of friction. Simultaneously, the liquid film itself forms a sealing barrier, preventing leakage of high-pressure materials from the pump. All five pumps are critical rotating equipment operating continuously within the system. Unified mechanical seal water supply ensures long-term reliable operation of each pump's seals, preventing unplanned downtime due to mechanical seal cooling failure.

[0049] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0050] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A hybrid triple-effect MVR evaporation crystallization system, characterized in that, It includes a feeding unit (1), a preheating unit (2), a first-effect evaporation unit (3), a second-effect evaporation unit (4), and a third-effect crystallization unit (5) connected in series, as well as a steam compressor (6). The feeding unit (1) includes a raw material tank and a feeding pump connected in series; The preheating unit (2) includes a plate preheater and a non-condensable steam preheater connected in series; The first-effect evaporation unit (3) includes a first-effect plate evaporator, a first-effect separator and a first-effect circulation pump. The first-effect plate evaporator is connected in series with the first-effect separator. The bottom outlet of the first-effect separator is divided into two paths. One path returns to the first-effect plate evaporator through the first-effect circulation pump to form a circulation branch. The other path is connected in series to the second-effect evaporation unit (4). The double-effect evaporation unit (4) includes a double-effect plate evaporator, a double-effect separator and a double-effect circulation pump. The double-effect plate evaporator is connected in series with the double-effect separator. The bottom outlet of the double-effect separator is divided into two paths. One path returns to the double-effect plate evaporator through the double-effect circulation pump to form a circulation branch. The other path is connected in series to the triple-effect crystallization unit (5). The triple-effect crystallization unit (5) includes a triple-effect tube heater, a crystallizer, and a triple-effect circulation pump. The triple-effect tube heater is connected in series with the crystallizer. The bottom outlet of the crystallizer returns to the triple-effect tube heater via the triple-effect circulation pump to form a circulation branch. The inlet of the steam compressor (6) is connected to the top of the crystallizer, and the outlet is connected to the heating side inlet of the single-effect plate evaporator and the triple-effect tube heater, respectively.

2. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, The bottom outlet of the raw material tank is connected to the inlet of the feed pump, the outlet of the feed pump is connected to the material inlet of the plate preheater, the material outlet of the plate preheater is connected to the material inlet of the non-condensable steam preheater, and the material outlet of the non-condensable steam preheater is connected to the material inlet of the first-effect plate evaporator. The raw material tank, the feed pump, the plate preheater, the non-condensable steam preheater, and the first-effect plate evaporator are connected in series.

3. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, The first-effect plate evaporator is a rising film plate evaporator, and the first-effect separator is a cyclone separator. The material outlet of the first-effect plate evaporator is connected to the middle inlet of the first-effect separator. The top of the first-effect separator is provided with a steam outlet, and the bottom of the first-effect separator is provided with a conical bottom. The lower end outlet of the conical bottom is divided into two paths. One path is connected to the inlet of the first-effect circulating pump, and the outlet of the first-effect circulating pump is connected to the material inlet of the first-effect plate evaporator to form a circulation loop. The other path is connected to the transfer pipe, and the transfer pipe is connected to the material inlet of the second-effect plate evaporator.

4. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, The double-effect plate evaporator is a rising film plate evaporator, and the double-effect separator is a cyclone separator. The material outlet of the double-effect plate evaporator is connected to the middle inlet of the double-effect separator. The top of the double-effect separator is provided with a steam outlet, and the bottom of the double-effect separator is provided with a conical bottom. The lower end outlet of the conical bottom is divided into two paths. One path is connected to the inlet of the double-effect circulating pump, and the outlet of the double-effect circulating pump is connected to the material inlet of the double-effect plate evaporator to form a circulation loop. The other path is connected to the transfer pipe, and the transfer pipe is connected to the material inlet of the triple-effect tube heater.

5. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, The triple-effect tube heater includes a first tube heater and a second tube heater, which are arranged in parallel. The outlet of the triple-effect circulating pump is connected to a material distribution pipeline, which is connected to the material inlet of the first tube heater and the material inlet of the second tube heater, respectively. The material outlets of the first tube heater and the second tube heater are connected to a material collection pipeline, which is connected to the middle inlet of the crystallizer. The crystallizer is an FC-type crystallizer, and a washing leg is provided at the bottom of the crystallizer. The lower outlet of the washing leg is connected to the inlet of the triple-effect circulating pump to form a circulation loop.

6. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, The top of the first-effect separator is provided with a first steam outlet, the top of the second-effect separator is provided with a second steam outlet, and the top of the crystallization separator is provided with a third steam outlet. The first steam outlet, the second steam outlet, and the third steam outlet are respectively connected to steam branch pipes. The three steam branch pipes are connected to the steam main pipe after they merge. The steam main pipe is connected to the inlet of the steam compressor (6). The outlet of the steam compressor (6) is connected to the steam distribution pipe. The steam distribution pipe is divided into two paths. One path is connected to the heating steam inlet of the first-effect plate evaporator, and the other path is connected to the heating steam inlet of the third-effect tube heater.

7. The hybrid triple-effect MVR evaporation crystallization system according to claim 1, characterized in that, It also includes a discharge pump, a centrifuge, a mother liquor tank, and a mother liquor pump. The bottom outlet of the crystallizer is also connected to a discharge pipeline. The discharge pipeline is connected to the inlet of the centrifuge via the discharge pump. The centrifuge has a solid phase outlet at its bottom and a liquid phase outlet on its side. The liquid phase outlet is connected to the inlet of the mother liquor tank. The bottom outlet of the mother liquor tank is connected to the inlet of the mother liquor pump. The outlet of the mother liquor pump is connected to the inlet of the triple-effect circulating pump.

8. The hybrid triple-effect MVR evaporation crystallization system according to claim 7, characterized in that, It also includes a mechanical seal water tank, a vertical pump, and a mechanical seal water cooler. The top of the mechanical seal water tank is provided with a softened water inlet, the bottom outlet of the mechanical seal water tank is connected to the inlet of the vertical pump, the outlet of the vertical pump is connected to the mechanical seal water inlet of the mechanical seal water cooler, the mechanical seal water outlet of the mechanical seal water cooler is connected to the mechanical seal water main pipe, the mechanical seal water main pipe is respectively connected to the mechanical seal cooling water inlets of the feed pump, the first-effect circulating pump, the second-effect circulating pump, the third-effect circulating pump, and the discharge pump, and the mechanical seal water cooler is provided with a cooling water inlet and a cooling water outlet.

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