A closed heat-carrying desulfurization wastewater concentration crystallization treatment system and treatment method

Abstract

The present application belongs to the technical field of zero discharge treatment of desulfurization wastewater, and particularly relates to a closed heat-carrying desulfurization wastewater concentration crystallization treatment system and a treatment method. The system comprises a concentration reduction tower, which is sequentially provided with a gas phase outlet, a demisting device, a spraying atomization device, a gas inlet and a tower kettle from top to bottom. The tower kettle is connected with the spraying atomization device through a circulating pump and a first wide-flow channel heat exchanger. The tower kettle is also connected with a flash evaporation tower through a first conveying pump. A bottom material outlet of the flash evaporation tower is connected with a wastewater cyclone. A tower kettle of the flash evaporation tower is connected with an upper material inlet of the flash evaporation tower through a second circulating pump and a second wide-flow channel heat exchanger. An external heat source exchanges heat with a closed heat-carrying medium through a heat exchanger. The closed heat-carrying medium, as a heat source, is respectively introduced into the first wide-flow channel heat exchanger and the second wide-flow channel heat exchanger to heat circulating fluid. The system realizes efficient concentration of desulfurization wastewater, scale prevention, flash evaporation crystallization and solid-liquid separation integration.

Description

Technical Field

[0001] This invention belongs to the field of zero-discharge treatment technology for desulfurization wastewater, specifically relating to a closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system and method. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Currently, desulfurization wastewater concentration and crystallization treatment technologies generally employ open evaporation processes using air as the water carrier. These systems are directly connected to the outside atmosphere, making them susceptible to fluctuations in ambient temperature and humidity, seasonal variations, and weather conditions. This results in large fluctuations in evaporation load, unstable operating conditions, and difficulty in maintaining a stable concentration ratio. An unstable concentration ratio leads to fluctuations in the quality of the crystallized salt, increased water content, and reduced resource utilization value. Furthermore, maintaining a stable concentration ratio requires frequent adjustments to the heat source supply or makeup water flow, increasing energy consumption.

[0004] Furthermore, existing desulfurization wastewater concentration and crystallization treatment technologies rely on seed crystal methods for scale prevention, which have limited effectiveness in inhibiting heterogeneous scale such as calcium, magnesium, and silicon. At high concentration ratios, these technologies are prone to clogging towers and nozzles. Moreover, the system experiences large fluctuations in start-up and shutdown loads, making it difficult to achieve long-term, maintenance-free, stable operation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a closed-loop heat-transfer desulfurization wastewater concentration and crystallization treatment system and method. This system integrates closed-loop heat transfer, concentration and reduction tower, complexing agent for scale prevention, flash evaporation in a flash tank, and centrifugal separation into a single closed-loop process, achieving efficient concentration, scale prevention, flash crystallization, and solid-liquid separation of desulfurization wastewater.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system, comprising a concentration and reduction tower, which is provided with a gas phase outlet, a demisting device, a spray atomizing device, a gas inlet and a tower bottom from top to bottom, and the tower bottom is connected to the spray atomizing device through a circulating pump and a first wide flow channel heat exchanger. The bottom of the tower is also connected to the flash tower via a first transfer pump. The bottom material outlet of the flash tower is connected to the wastewater hydrocyclone. The bottom of the flash tower is connected to the upper feed inlet of the flash tower via a second circulation pump and a second wide-channel heat exchanger. An external heat source exchanges heat with a closed heat transfer medium through a heat exchanger. The closed heat transfer medium, as a heat source, is introduced into the first wide-channel heat exchanger and the second wide-channel heat exchanger to heat the circulating fluid.

[0007] Secondly, the present invention provides a closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method, comprising the following steps: Preheated air is introduced into the concentration and reduction tower, and desulfurization wastewater is circulated and sprayed in the concentration and reduction tower. Inside the concentration and reduction tower, the preheated air and the sprayed desulfurization wastewater flow counter-currently to transfer heat and mass, thereby concentrating the desulfurization wastewater. The desulfurization wastewater that has reached the set concentration ratio is recycled and flash-evaporated. The slurry after flash evaporation is then separated into solid and liquid components by a wastewater hydrocyclone. An external heat source heats the closed-loop heat transfer medium, and the heated closed-loop heat transfer medium is then used to heat the circulating slurry in the concentration and reduction tower as well as the circulating slurry in the flash evaporation process.

[0008] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention employs a closed-loop heat transfer medium as the heat transfer carrier to recover waste heat from flue gas, concentrate tower exhaust, or flash steam, forming an independent closed-loop circuit. External weather disturbances and temperature / humidity fluctuations have minimal impact on the system. The heat transfer medium heats wastewater, resulting in high waste heat utilization, strong system load adaptability, and smooth start-up and shutdown without shock.

[0009] This invention employs a large-diameter, wide-channel, stagnant-free, dead-zone-free anti-clogging heat exchanger. The channel width is 10mm-20mm, and the inner wall is smooth without protrusions or stagnation zones, allowing for the smooth passage of high-solids-content, high-hardness, and high-salt particles. It inhibits the adhesion and nucleation of calcium, magnesium, and silicates at the structural level, eliminating the need for ball cleaning and chemical acid washing, and increasing continuous operation cycles by more than three times.

[0010] The concentrated slurry is fed into a flash tower for circulating flash evaporation, where it undergoes phase change and rapid evaporation and crystallization in a low-pressure flash container. Attached Figure Description

[0011] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0012] Figure 1 This is a schematic diagram of the overall structure of the closed-loop heat-carrying scale prevention, concentration and volume reduction coupled flash evaporation centrifugal crystallization integrated system for desulfurization wastewater according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the demister housing according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the internal structure of the flash evaporator according to an embodiment of the present invention; Figure 4 This is a cross-sectional view of the flash evaporator according to an embodiment of the present invention.

[0013] Among them, 1-fan, 2-gas-gas heat exchanger, 3-concentration and reduction tower, 4-demist, 5-spray atomization device, 6-second heat exchanger, 7-hot water circulation pump, 8-first wide-channel heat exchanger, 9-circulation pump, 10-first transfer pump, 11-second circulation pump, 12-flash tower, 13-second wide-channel heat exchanger, 14-flash tower wastewater transfer pump, 15-wastewater hydrocyclone, 16-centrifugal crystallizer, 17-wastewater storage tank, 18-wastewater makeup pump, 19-gas-water heat exchanger, 20-vacuum pump set, 21-exhaust steam condensate tank, 22-exhaust steam condensate pump, 23-complex dosing tank, 24-dosing pump, 25-controller, 26-feed header, 27-tangential nozzle; 4-1. Coarse Detection Section; 4-2. Fan-shaped Nozzle; 4-3. Medium Detection Section; 4-4. Fine Detection Section; 4-5. High-Pressure Nozzle; 4-6. Inverted Triangular Liquid Blocking Plate; 4-7. Demister Housing. Detailed Implementation

[0014] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0015] In a first aspect, the present invention provides a closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system, comprising a concentration and reduction tower, which is provided with a gas phase outlet, a demisting device, a spray atomizing device, a gas inlet and a tower bottom from top to bottom, and the tower bottom is connected to the spray atomizing device through a circulating pump and a first wide flow channel heat exchanger. The bottom of the tower is also connected to the flash tower via a first transfer pump. The bottom material outlet of the flash tower is connected to the wastewater hydrocyclone. The bottom of the flash tower is connected to the upper feed inlet of the flash tower via a second circulation pump and a second wide-channel heat exchanger. An external heat source exchanges heat with a closed heat transfer medium through a heat exchanger. The closed heat transfer medium, as a heat source, is introduced into the first wide-channel heat exchanger and the second wide-channel heat exchanger to heat the circulating fluid.

[0016] As the core unit for concentrating desulfurization wastewater, the concentration and reduction tower achieves wastewater evaporation and concentration through countercurrent gas-liquid contact. The tower, arranged from top to bottom, includes a gas phase outlet, a demister, a spray atomizing device, a gas inlet, and a bottom vessel, forming a complete evaporation and concentration process.

[0017] Demisting devices are used to remove liquid droplets carried in the gas phase, preventing water droplets from flowing out with the gas phase and avoiding environmental pollution.

[0018] The spray atomization device atomizes desulfurization wastewater into fine droplets, increasing the contact area between the wastewater and the heat-carrying gas, and improving evaporation efficiency. The atomization effect directly affects the concentration efficiency and the heat and mass transfer effect within the tower.

[0019] The heat from the closed-loop heat transfer medium is used to heat the circulating desulfurization wastewater, providing the necessary thermal energy for wastewater evaporation. The wide-channel heat exchanger design helps reduce scaling and clogging, improving heat exchange efficiency and equipment operational stability.

[0020] The flash evaporator treats the concentrate from the concentration and reduction tower by flash evaporation, further separating moisture and contaminants. Inside the flash evaporator, the concentrate evaporates rapidly under reduced pressure, with moisture discharged as steam, while the slurry is further concentrated.

[0021] The wastewater hydrocyclone performs solid-liquid separation on the material discharged from the bottom of the flash tower, separating the concentrated calcium sulfate from the wastewater, thus realizing the recovery and utilization of calcium sulfate.

[0022] The closed-loop heat transfer medium acts as the heat transfer carrier, conveying heat from the external heat source to the first and second wide-channel heat exchangers, providing thermal energy for the evaporation, concentration, and flash evaporation of desulfurization wastewater. The closed-loop design reduces heat transfer medium loss, lowers operating costs, and improves system safety and stability.

[0023] In some embodiments, the spray atomizing device includes a first spray layer and a second spray layer, the first spray layer being located above the second spray layer, the nozzle orifice diameter of the first spray layer being 2-6 mm, and the nozzle orifice diameter of the second spray layer being 7-12 mm.

[0024] Preferably, the first spray layer and the second spray layer are connected to the same main pipe.

[0025] During the spray evaporation process of desulfurization wastewater inside the tower, as the liquid flows downwards along the tower wall, it gradually concentrates towards the tower wall, resulting in a much larger liquid flow rate near the tower wall than in the center area. This creates an uneven flow phenomenon, which leads to the following problems: uneven liquid distribution results in insufficient contact between the gas and liquid phases, reducing evaporation efficiency; the liquid stays on the tower wall for too long, making it easy for salts and suspended solids to deposit and form scale; uneven flow increases local resistance, increasing system energy consumption; and scale accumulation leads to uneven resistance distribution within the tower, affecting the long-term stable operation of the system.

[0026] In this invention, the large droplets generated by the large-aperture nozzles in the lower layer have greater momentum and gravitational settling velocity, forming a strong wall-scouring flow that actively disrupts the initial conditions for wall flow formation. The nozzles in the first spray layer have smaller apertures, and the droplets generated by these smaller-aperture nozzles have even smaller diameters and larger specific surface areas, allowing for more thorough contact with the heat-carrying gas and rapid water evaporation for concentration. The fine droplets, under the influence of the rising airflow, can be more evenly distributed within the tower space, preventing the natural accumulation of liquid on the wall.

[0027] The wall scouring effect of large droplets alters the radial velocity distribution within the tower, reducing the velocity difference between the central region and the wall region, and inhibiting fluid migration towards the wall. The complex flow field formed by the double-layer spray enhances the turbulence intensity within the tower, promotes uniform liquid distribution, and reduces the possibility of wall flow formation.

[0028] In some embodiments, the demister is sequentially configured with a coarse trapping section, a medium trapping section, a fine trapping section, and an anti-secondary entrainment section along the flue gas flow direction. The coarse extraction section is composed of a matrix of arc-shaped guide vanes, with the openings of the arc-shaped guide vanes facing the direction of the flue gas. The middle section is composed of a matrix of gradually narrowing guide channels, the inner diameter of which gradually narrows along the flue gas flow direction. The precision capture section is composed of several rows of staggered baffles; The anti-secondary entrainment section consists of several inverted triangular liquid blocking plates arranged side by side, with a gap between adjacent inverted triangular liquid blocking plates.

[0029] The coarse suction section consists of a matrix of arc-shaped guide vanes with their openings facing the flue gas. Utilizing the structural characteristics of these arc-shaped guide vanes, the flow direction of the flue gas is altered as it passes through. Larger droplets and dust particles impact the surface of the guide vanes due to inertia, achieving preliminary gas-liquid separation and dust collection. This effectively removes most of the larger droplets and particles from the flue gas, reducing the load on subsequent treatment units.

[0030] The middle section consists of a matrix of gradually narrowing guide channels. The inner diameter of these channels gradually decreases along the flue gas flow direction, and as the inner diameter decreases, the flue gas velocity gradually increases. During this process, smaller droplets are subjected to stronger inertial forces, colliding with the channel walls and coalescing into larger droplets. Simultaneously, the narrowing structure further enhances gas-liquid separation, capturing more small and medium-sized droplets and dust, thus improving overall demisting efficiency.

[0031] The fine dust collection section consists of several rows of staggered baffles. As the flue gas passes through these baffles, its flow direction continuously changes. Residual fine droplets and dust particles are impacted and captured by the baffle surfaces under the influence of inertia and centrifugal force. Through multiple collisions and separations, the remaining tiny droplets and dust particles in the flue gas are efficiently removed, ensuring the cleanliness of the flue gas.

[0032] The anti-secondary entrainment section consists of several inverted triangular liquid-blocking plates arranged side by side, with gaps between adjacent plates. After being processed by the previous three sections, the flue gas may still entrain some liquid droplets during its ascent. The special structure of the inverted triangular liquid-blocking plates effectively blocks and filters the flue gas, causing the entrained droplets to collide with the plate surface and accumulate. Under gravity, the droplets eventually fall back down, effectively preventing them from being carried back into subsequent equipment and ensuring the final demisting effect of the demister.

[0033] The four sections of the demister are arranged sequentially according to the flue gas flow direction, forming a graded treatment system. The coarse trap removes most of the larger droplets and particles, the intermediate trap further captures small and medium-sized droplets, the fine trap efficiently removes tiny droplets and dust, and the final anti-secondary entrainment section ensures the final demister effect. This graded treatment method can fully utilize the advantages of each section, gradually improving the cleanliness of the flue gas and achieving efficient gas-liquid separation.

[0034] Preferably, the radius of curvature of the arc-shaped guide vane is 50-80mm, the central angle of the arc-shaped guide vane is 35-45°, and the distance between two adjacent arc-shaped guide vanes is 20-25mm.

[0035] Preferably, the width of the small diameter end of the tapered flow guide channel is 10-20mm, the width of the large diameter end is 30-40mm, and the distance between two adjacent flow guide channels is 25-30mm.

[0036] Further preferably, the sidewalls of the tapered flow channel are coated with a hydrophobic anti-scaling coating. The hydrophobic anti-scaling coating is a fluorocarbon resin-based composite coating with a water contact angle ≥120°.

[0037] The water contact angle of the fluorocarbon resin-based composite coating is ≥120°, which makes it difficult for liquid to spread on the coating surface. Instead, it forms spherical droplets that easily roll off under gravity, reducing the time the liquid stays on the sidewalls of the channel.

[0038] Because of the extremely low surface energy of the coating, the main components of scale, such as calcium carbonate and magnesium hydroxide, are difficult to adhere to and deposit on its surface. Even if a small number of dirt particles come into contact with the coating surface, they will be carried away with the rolling of liquid droplets, effectively preventing the formation and accumulation of scale.

[0039] Fluorocarbon resins possess strong chemical inertness, enabling them to withstand the erosion of various chemicals such as acids, alkalis, and salts. In complex industrial environments, the coating is less prone to chemical reactions, maintaining the long-term stability of its hydrophobic and anti-scaling properties.

[0040] Preferably, in the fine capture section, the spacing between adjacent baffles in the same row is 25-35mm; the spacing between two adjacent rows of baffles is 40-50mm.

[0041] Preferably, the spacing between two adjacent triangular liquid-blocking plates is 20-30mm.

[0042] In some embodiments, differential pressure transmitters and flushing nozzle assemblies are provided at different sections of the demisting device. Both differential pressure transmitters and flushing nozzle assemblies are connected to the controller. When the ratio of the differential pressure signal of the corresponding section to the initial differential pressure value is greater than a set value, the corresponding flushing nozzle assembly is activated.

[0043] Preferably, when the ratio of the differential pressure signal of the corresponding segment to the initial differential pressure value is greater than 1.5, the corresponding flushing nozzle assembly is activated.

[0044] This invention abandons the traditional "timed and pressured" single flushing mode of demister flushing systems and constructs a feedback-adaptive variable-intensity flushing system based on differential pressure signals. The flushing system installs differential pressure transmitters on the upstream and downstream sides of the demister blade assembly to collect the pressure difference ΔP signal of gaseous substances flowing through the demister in real time, and dynamically compares this signal with a preset initial pressure difference ΔP0. When the ΔP / ΔP0 ratio reaches 1.5-2.0:1 (equivalent to the accumulated scale thickness on the blade surface reaching a critical value affecting the flow cross-section), the controller automatically starts the flushing program.

[0045] By using differential pressure change trends, the scaling and clogging status can be quantitatively characterized in real time, thereby accurately matching the flushing timing and flushing intensity, avoiding the problems of over-flushing (wasting flushing water) or under-flushing (incomplete flushing leading to increased scaling) in the traditional timed flushing mode.

[0046] Preferably, the orifice diameter of the flushing nozzle in the coarse catching section is 3-5 mm, the flushing water pressure is 0.3-0.5 MPa, the spray angle is 100°-120°, and the spray range covers the cross-section of the coarse catching section.

[0047] Preferably, a nozzle assembly is provided in the gap between the baffles in the fine capture section. The nozzle assembly is arranged around each baffle, the nozzle orifice diameter is 1-2mm, and the flushing water pressure is 0.6-1.0MPa.

[0048] In some embodiments, a complexing agent addition port is also provided at the lower end of the concentration and reduction tower.

[0049] A set of wide-channel anti-scaling heat exchangers is installed in both the concentration and reduction system and the flash crystallization system. The two systems are connected in series through a closed-loop heat transfer circulation pipeline to form a dual heat exchange station layout, sharing the same heat source loop. The inherent anti-scaling characteristics of the wide-channel heat exchanger structure, combined with the chemical anti-scaling effect of the complexing agent, enable the system to achieve long-term stable operation without relying on seed crystal methods, without the need for ball cleaning, or without chemical acid washing. The continuous operation cycle is significantly extended compared to traditional heat exchange systems.

[0050] In this dual-synergistic anti-scaling system, the wide-channel heat exchanger eliminates scale adhesion sites at the structural level, while the complexing agent enhances the supersaturation limit of the solution and stabilizes scale-causing ions at the chemical level. Both act at the ends of the tower and the heat exchanger, respectively, forming an anti-scaling barrier covering the entire process. This dual-protection system enables stable operation at concentration ratios of 5-10 times, overcoming the failure problem of single anti-scaling methods at high concentration ratios.

[0051] In some embodiments, the reboiler is connected to the lower feed port of the flash tower via a first delivery pump, and the reboiler of the flash tower is connected to the upper feed port of the flash tower via a second circulation pump and a second wide-channel heat exchanger. Both the lower feed port and the upper feed port are composed of tangential nozzle assemblies. The lower feed inlet is located at or below the design liquid level.

[0052] The upper feed inlet of the flash evaporator consists of tangential nozzles. This tangential feeding method ensures that the circulating heated fluid is evenly distributed along the tower wall, avoiding the central jet and short-circuit flow phenomena that can occur with traditional axial feeding. The fluid, under swirling action, can more fully utilize the space within the tower, accelerating water evaporation and improving flash evaporation efficiency. Furthermore, the swirling flow created by tangential feeding has a self-cleaning effect; the high-speed fluid flow effectively prevents solid particles from depositing on the tower wall and component surfaces, reducing scaling. Once the salts reach supersaturation, crystals precipitate in situ, forming a stable crystal slurry circulation, resulting in high crystallization efficiency and minimal scaling.

[0053] The lower-level feed nozzles are positioned close to the liquid surface of the flash tower. The high-speed injected liquid directly acts on the high-concentration zone at the bottom, creating a continuous rotating turbulent flow below the liquid surface. This prevents local oversaturation at the bottom from causing scaling ion precipitation and promotes uniform mixing between the high-concentration zone at the bottom and the low-concentration zone at the top.

[0054] Preferably, the tangential nozzle assembly of the lower feed inlet is disposed on the same feed header, and the tangential nozzle assembly of the upper feed inlet is disposed on the same feed header.

[0055] In some embodiments, the gas phase outlet of the concentration and reduction tower is preheated with air via a gas-to-gas heat exchanger.

[0056] The gas phase outlet of a concentration and reduction tower typically emits flue gas at a certain temperature, which contains a significant amount of waste heat. By recovering this waste heat through a gas-to-gas heat exchanger and using it to preheat air, the heat that would otherwise be directly released into the atmosphere can be reused, improving the overall energy efficiency of the system.

[0057] Preheated air enters the concentration and reduction tower, which can effectively improve the evaporation and concentration efficiency of desulfurization wastewater.

[0058] After flash evaporation, the crystal slurry is fed into the centrifugal crystallizer 16 via the underflow of the wastewater hydrocyclone, achieving rapid separation of the crystallized salt and the mother liquor. The crystallized salt has a low water content, making it easy to transport or utilize as a resource; the separated mother liquor is recycled back to the wastewater storage tank, eliminating secondary pollution and solid-liquid dead zones, replacing triplet tanks or sedimentation tanks, and offering high separation efficiency and simple operation and maintenance.

[0059] Secondly, the present invention provides a closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method, comprising the following steps: Preheated air is introduced into the concentration and reduction tower, and desulfurization wastewater is circulated and sprayed in the concentration and reduction tower. Inside the concentration and reduction tower, the preheated air and the sprayed desulfurization wastewater flow counter-currently to transfer heat and mass, thereby concentrating the desulfurization wastewater. The desulfurization wastewater that has reached the set concentration ratio is recycled and flash-evaporated. The slurry after flash evaporation is then separated into solid and liquid components by a wastewater hydrocyclone. An external heat source heats the closed-loop heat transfer medium, and the heated closed-loop heat transfer medium is then used to heat the circulating slurry in the concentration and reduction tower as well as the circulating slurry in the flash evaporation process.

[0060] In some embodiments, the external heat source is at least one of economizer / steam waste heat, thickener exhaust waste heat, or flash steam waste heat.

[0061] A closed-loop heat transfer medium circulation circuit is constructed, and three heat sources of different qualities are coupled and connected at the same time: economizer / steam waste heat, concentration tower exhaust waste heat, and flash steam waste heat, forming a multi-heat source cascade utilization network.

[0062] In some embodiments, the desulfurization wastewater circulating and sprayed inside the concentration and reduction tower is sprayed out in two layers. The lower layer sprays out large droplets with an average particle size of 2000-3000 μm to flush the tower wall; the upper layer sprays out small droplets with an average particle size of 1000-1500 μm for evaporation and concentration.

[0063] In some embodiments, when the airflow passes through the demister in the concentration and reduction tower, it first passes through the arc-shaped guide plate, where large-diameter mist droplets collide with the arc-shaped guide plate and are captured by it. As the airflow passes through the tapered guide channel, the flue gas velocity gradually increases, and the droplets in the fluid are adsorbed onto the side wall of the tapered guide channel by the shear force generated by the sudden change in flow velocity and are captured. When the airflow passes through the fine capture section, the flow direction changes continuously under the guidance of the misaligned baffle. Under the action of centrifugal force and inertia, the fine mist droplets remaining in the airflow are captured. After passing through the anti-secondary entrainment section, the airflow flows directly out of the concentration and reduction tower. The parallel inverted triangular liquid blocking plates form a protective wall to prevent the airflow from re-entraining the captured droplets.

[0064] Preferably, the method further includes a step of rinsing the demister. When the ratio of the pressure difference of each section of the demister to the initial pressure difference is greater than a set value, rinsing is initiated. The set value is 1.5 to 2.

[0065] In some embodiments, the method further includes the step of adding a complexing agent to the desulfurization wastewater in the concentration and reduction tower.

[0066] The complexing agent here can be ethylenediaminetetraacetic acid (EDTA), dithiocarbamates (DTC), 1,3,5-trithio-1,3,5-triazine-2,4,6-trithione (TMT-15), etc.

[0067] Complexing agents can form stable water-soluble complexes with ions such as calcium, magnesium, and sulfate, significantly increasing the saturation limit, inhibiting crystal nucleation, growth, and adhesion, and completely preventing structural blockage of tower walls, nozzles, or pipelines.

[0068] In some embodiments, when the desulfurization wastewater in the concentration and reduction tower reaches a set concentration ratio, its slurry is transported to the flash tower and enters the flash tower tangentially from the lower end of the flash tower below the liquid level.

[0069] Preferably, the slurry is subjected to circulating heating and flash evaporation, and the circulating heated slurry enters the flash evaporator tangentially from the top end of the flash evaporator.

[0070] The present invention will be further described below with reference to the embodiments.

[0071] Example like Figure 1 As shown, a closed-loop heat-carrying desulfurization wastewater concentration and crystallization treatment system includes a concentration and reduction tower 3, which is provided with a gas phase outlet, a demister 4, a spray atomizing device 5, a gas inlet, and a tower bottom from top to bottom. The tower bottom is connected to the spray atomizing device 5 through a circulating pump 9 and a first wide-channel heat exchanger 8. The gas phase outlet of the concentration and reduction tower 3 preheats the air through a gas-to-gas heat exchanger 2.

[0072] The reboiler is also connected to the lower feed inlet of the flash tower 12 via a first transfer pump 10. The bottom material outlet of the flash tower 12 is connected to the wastewater hydrocyclone 15. The reboiler of the flash tower 12 is connected to the upper feed inlet of the flash tower 12 via a second circulation pump 11 and a second wide-channel heat exchanger 13. Both the lower and upper feed inlets are composed of tangential nozzle 27 assemblies. The lower feed inlet is located at or below the design liquid level. Figure 3 and Figure 4 As shown.

[0073] The tangential nozzle assembly at the lower feed inlet is mounted on the same feed header 26, and the tangential nozzle assembly at the upper feed inlet is mounted on the same feed header. The lower supplementary feed nozzle is positioned close to the liquid surface of the flash tower 12. The high-speed injected liquid directly acts on the high-concentration zone at the bottom, creating a continuous rotating turbulent flow below the liquid surface. This prevents localized oversaturation at the bottom, which could lead to scaling and ion precipitation, while simultaneously promoting uniform mixing between the high-concentration zone at the bottom and the low-concentration zone at the top.

[0074] An external heat source exchanges heat with a closed heat transfer medium through a heat exchanger. The closed heat transfer medium, as a heat source, is introduced into the first wide-channel heat exchanger 8 and the second wide-channel heat exchanger 13 to heat the circulating fluid.

[0075] The spray atomizing device 5 includes a first spray layer and a second spray layer. The first spray layer is located above the second spray layer. The nozzle orifice diameter of the first spray layer is 2-6 mm, and the nozzle orifice diameter of the second spray layer is 7-12 mm. The first spray layer and the second spray layer are connected to the same main pipe.

[0076] like Figure 2 As shown, the demister device 4 includes a demister housing 4-7, which is sequentially arranged with a coarse trapping section 4-1, a medium trapping section 4-3, a fine trapping section 4-4, and an anti-secondary entrainment section along the flue gas flow direction. The coarse extraction section 4-1 is composed of a matrix of arc-shaped guide vanes, with the openings of the arc-shaped guide vanes facing the direction of the flue gas. The radius of curvature of the arc-shaped guide vanes is 50-80mm, the central angle of the arc-shaped guide vanes is 35-45°, and the distance between two adjacent arc-shaped guide vanes is 20-25mm.

[0077] The intermediate capture section 4-3 consists of a matrix of gradually narrowing guide channels, the inner diameter of which gradually narrows along the flue gas flow direction. The width of the smaller diameter end of each guide channel is 10-20 mm, and the width of the larger diameter end is 30-40 mm. The spacing between adjacent guide channels is 25-30 mm. Its sidewalls are coated with a hydrophobic anti-scaling coating. This coating is a fluorocarbon resin-based composite coating with a water contact angle ≥120°.

[0078] The fine-capture section is composed of several rows of staggered baffles; in the same row, the distance between adjacent baffles is 25-35mm; the distance between two adjacent rows of baffles is 40-50mm.

[0079] The anti-secondary entrainment section is composed of several inverted triangular liquid blocking plates 4-6 arranged side by side, with a gap of 20-30mm between adjacent inverted triangular liquid blocking plates 4-6.

[0080] The flushing system employs a zoned, independently controlled high-pressure water jet network: (1) Coarse Filter Section Flushing Zone: Equipped with high-flow-rate, low-pressure flushing nozzles (nozzle orifice diameter 3~5mm, flushing water pressure 0.3~0.5MPa), intermittent high-flow-rate impact flushing, mainly flushing the initial scale crystals adhering to the inlet guide plate of the coarse filter section. The nozzles are fan-shaped nozzles 4-2, with a spray angle of 100°~120°, and the coverage width covers the entire cross-section of the coarse filter section blade assembly. The flushing cycle is independently set through a differential signal, and the coarse filter section is sensitive to pressure differential and starts first.

[0081] (2) Fine-tuning section flushing zone: Multiple rows of staggered high-pressure nozzles 4-5 (nozzle orifice diameter 1~2mm, flushing water pressure 0.6~1.0MPa) are installed. The high-pressure nozzles 4-5 are installed in the gaps of the labyrinth-type baffles, evenly distributed in a 360° ring. Multiple independent flushing layers are set vertically from top to bottom, each layer is controlled by an independent solenoid valve, so as to achieve thorough cleaning of all corners of the labyrinth-type staggered baffles. The design of the flushing nozzles in the fine-tuning section refines the nozzle layout. In view of the staggered arrangement of the labyrinth-type baffles, the nozzle outlet direction fully covers the gaps of the baffles to ensure no flushing dead corners. The differential pressure feedback threshold setting of the fine-tuning section is more sensitive than that of the coarse-tuning section to maintain efficient demisting capability.

[0082] By coordinating the design of the demister structure itself (blade configuration, number of blade stages, surface coating, flow channel design) and the cleaning strategy (dynamic feedback adjustment based on differential pressure parameters, independent control of three zones with varying intensity), the common technical problems of easy scaling, difficult cleaning, and rapid resistance growth of demisters in closed heat transfer systems for high concentration ratio desulfurization wastewater have been solved, enabling long-term maintenance-free and stable operation of the demister under complex working conditions.

[0083] Differential pressure transmitters and flushing nozzle assemblies are installed at different sections of the demisting device. Both differential pressure transmitters and flushing nozzle assemblies are connected to controller 25. When the ratio of the differential pressure signal of the corresponding section to the initial differential pressure value is greater than 1.5, the corresponding flushing nozzle assembly is activated.

[0084] The operating process of the closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system is as follows: Gaseous substances are transported to the concentration and reduction tower 3 by the blower 1; the desulfurization wastewater is first stored in the desulfurization wastewater storage tank 17, and then sent to the bottom slurry pool of the concentration and reduction tower 3 by the wastewater makeup pump 18. The wastewater circulation pump 9 of the reduction tower draws wastewater from the bottom of the concentration and reduction tower 3 for forced circulation, and sprays it in the spray atomizing device 5 in the concentration and reduction tower 3. The spray atomizing device 5 has a main pipe divided into upper and lower spray layers. The upper and lower spray layers use hollow cone nozzles with variable aperture, arranged in layers according to the particle size gradient, so that the atomized particle size is uniform and the coverage is complete without dead corners; the lower spray 5-1 hollow cone nozzle has a larger aperture, with a diameter of 6-12mm and an average droplet size of about 2000-3000μm, which can take into account both coverage and penetration, and flush the tower wall to prevent scaling. The upper spray 5-2 hollow cone nozzle has a small orifice diameter of 2-6mm, and the average droplet size is about 1000-1500μm. It has a good atomization effect, effectively increases the gas-liquid contact area per unit volume, and allows wastewater to evaporate and transfer mass quickly when in contact with air. The forced-circulation wastewater is heated to 75℃-85℃ by a closed-loop heat transfer medium in the first wide-channel heat exchanger 8 via a hot water circulation pump 7 before entering the concentration and reduction tower 3. The wide-channel heat exchanger has a channel width ≥10mm, smooth inner wall, and wide channels without stagnant dead zones, making it less prone to scaling and clogging. The heat of the closed-loop heat transfer medium comes from economizer return water or steam, which is transferred through the second heat exchanger 6. The heated wastewater undergoes mass transfer and evaporation in the concentration and reduction tower 3 by counter-current contact with gaseous substances. The gaseous substances are in a saturated state with a temperature of 70-75℃. The gaseous substances then pass through a demister 4 to remove mist droplets, preventing the entrainment of mist droplets in the wastewater and causing condensation and corrosion in downstream equipment. The demister is equipped with zoned online flushing, has strong self-cleaning ability, stable resistance, and is free from scaling and clogging. Saturated gaseous substances exchange heat with the gaseous substances before entering the concentration and reduction tower 3 outside the tower via gas-to-gas heat exchanger 2, raising the temperature of the gaseous substances before entering the concentration and reduction tower 3. This allows the gaseous substances to circulate and recover waste heat, achieving cascade utilization of waste heat. During the wastewater concentration and reduction process, the complexing agent in the complexing agent dosing tank 23 is automatically added by the dosing pump 24 according to the hardness and flow rate of the wastewater, stabilizing calcium, magnesium, and silicon ions, inhibiting crystal nucleation, growth, and adhesion, and controlling the concentration ratio to 5-10 times.

[0085] After the concentrate reaches the set concentration, it is sent to flash tower 12 for low-pressure flash evaporation and rapid evaporation and crystallization. The concentrate is delivered to the bottom of the flash tower by the first transfer pump 10. The concentrate forms a forced circulation in the flash evaporation system by the second circulation pump 11. The concentrated concentrate in this forced circulation is heated to 75℃-85℃ by the hot water circulation pump 7 in the second wide-channel heat exchanger 13. The concentrate enters the flash tower 12 tangentially. The high-shear channel generates a strong shear effect, realizing the self-cleaning of the channel. The vacuum pump group 20 maintains the absolute pressure in the flash tower 12 at about 20 kPa. The exhaust steam from the flash evaporation of the concentrate is then passed through... The steam-water heat exchanger 19 heats the raw water or other process water, enabling the cascade utilization of waste heat. The condensate formed by the exhaust steam enters the exhaust steam condensate tank 21 and is discharged into the desulfurization process system via the exhaust steam condensate pump 22, achieving comprehensive utilization of water resources. Supersaturated concentrated salts precipitate fine crystals, forming a solid-liquid mixture in the concentrated circulating liquid. The crystal slurry circulates within the system until the crystals reach the enrichment standard. The mixture is then pumped into the wastewater hydrocyclone 15 via the flash tower wastewater transfer pump 14, and the overflow returns to the wastewater storage tank 17. The underflow crystal slurry is sent to a centrifuge for dehydration, achieving a water content of ≤10% for the crystallized salt. The collected crystallized salt is transported for disposal / resource utilization, while the mother liquor is returned to the wastewater storage tank 17. The entire system operates in a closed loop, preventing scaling and clogging, and ensuring continuous and stable operation.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A closed-loop heat-transfer desulfurization wastewater concentration and crystallization treatment system, characterized in that: It includes a concentration and reduction tower, which is provided from top to bottom with a gas outlet, a demister, a spray atomizing device, a gas inlet and a tower bottom. The tower bottom is connected to the spray atomizing device through a circulating pump and a first wide-channel heat exchanger. The bottom of the tower is also connected to the flash tower via a first transfer pump. The bottom material outlet of the flash tower is connected to the wastewater hydrocyclone. The bottom of the flash tower is connected to the upper feed inlet of the flash tower via a second circulation pump and a second wide-channel heat exchanger. An external heat source exchanges heat with a closed heat transfer medium through a heat exchanger. The closed heat transfer medium, as a heat source, is introduced into the first wide-channel heat exchanger and the second wide-channel heat exchanger to heat the circulating fluid. The spray atomizing device includes a first spray layer and a second spray layer. The first spray layer is located above the second spray layer. The nozzle orifice diameter of the first spray layer is 2-6 mm, and the nozzle orifice diameter of the second spray layer is 7-12 mm. The demisting device is sequentially configured with a coarse trapping section, a medium trapping section, a fine trapping section, and a section for preventing secondary entrainment along the flue gas flow direction. The coarse extraction section is composed of a matrix of arc-shaped guide vanes, with the openings of the arc-shaped guide vanes facing the direction of the flue gas; the radius of curvature of the arc-shaped guide vanes is 50-80mm, the central angle of the arc-shaped guide vanes is 35-45°, and the spacing between two adjacent arc-shaped guide vanes is 20-25mm. The middle section is composed of a matrix of gradually narrowing guide channels, the inner diameter of which gradually narrows along the flue gas flow direction. The precision capture section is composed of several rows of staggered baffles; The anti-secondary entrainment section is composed of several inverted triangular liquid blocking plates arranged side by side, with a gap between adjacent inverted triangular liquid blocking plates; Differential pressure transmitters and flushing nozzle assemblies are installed at different sections of the demisting device. Both differential pressure transmitters and flushing nozzle assemblies are connected to the controller. When the ratio of the differential pressure signal of the corresponding section to the initial differential pressure value is greater than the set value, the corresponding flushing nozzle assembly is activated. The narrowing guide channel has a small diameter end width of 10-20mm and a large diameter end width of 30-40mm, with a spacing of 20-25mm between adjacent guide channels. The sidewall of the narrowing guide channel is coated with a hydrophobic and anti-scaling coating, which is a fluorocarbon resin-based composite coating with a water contact angle ≥120°. In the fine capture section, the spacing between adjacent baffles in the same row is 25-35mm; the spacing between two adjacent rows of baffles is 40-50mm; and the spacing between two adjacent triangular liquid blocking plates is 20-30mm.

2. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system according to claim 1, characterized in that: The first and second spray layers are connected to the same main pipe.

3. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system according to claim 1, characterized in that: When the ratio of the differential pressure signal of the corresponding section to the initial differential pressure value is greater than 1.5, the corresponding flushing nozzle assembly is activated; The orifice diameter of the flushing nozzles in the coarse catching section is 3-5mm, the flushing water pressure is 0.3-0.5MPa, the spray angle is 100°-120°, and the spray range covers the cross-section of the coarse catching section. A nozzle assembly is installed in the gap between the baffles in the fine capture section. The nozzle assembly is arranged around each baffle, the nozzle orifice diameter is 1-2mm, and the flushing water pressure is 0.6-1.0MPa.

4. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system according to claim 1, characterized in that: The lower end of the concentration and reduction tower is also equipped with a complexing agent addition port.

5. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system according to claim 1, characterized in that: The bottom of the concentration and reduction tower is connected to the lower feed port of the flash tower via a first transfer pump. The bottom of the flash tower is connected to the upper feed port of the flash tower via a second circulation pump and a second wide flow channel heat exchanger. Both the lower and upper feed ports are composed of tangential nozzle assemblies. The lower feed inlet is located at or below the design liquid level; The tangential nozzle assembly of the lower feed inlet is set on the same feed header, and the tangential nozzle assembly of the upper feed inlet is set on the same feed header. The gas phase outlet of the concentration and reduction tower is preheated with air via a gas-to-gas heat exchanger.

6. A closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method, characterized in that: The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment system according to any one of claims 1-5 includes the following steps: Preheated air is introduced into the concentration and reduction tower, and desulfurization wastewater is circulated and sprayed in the concentration and reduction tower. Inside the concentration and reduction tower, the preheated air and the sprayed desulfurization wastewater flow counter-currently to transfer heat and mass, thereby concentrating the desulfurization wastewater. The desulfurization wastewater that has reached the set concentration ratio is recycled and flash-evaporated. The slurry after flash evaporation is then separated into solid and liquid components by a wastewater hydrocyclone. An external heat source heats the closed-loop heat transfer medium, and the heated closed-loop heat transfer medium is then used to heat the circulating slurry in the concentration and reduction tower as well as the circulating slurry in the flash evaporation process.

7. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method according to claim 6, characterized in that: The desulfurization wastewater circulating in the concentration and reduction tower is sprayed out in two layers. The lower layer sprays out large droplets with an average particle size of 2000-3000μm to flush the tower wall; the upper layer sprays out small droplets with an average particle size of 1000-1500μm for evaporation and concentration.

8. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method according to claim 6, characterized in that: Inside the concentration and reduction tower, when the airflow passes through the demister, it first passes through the arc-shaped guide plate, where large-diameter mist droplets collide with the arc-shaped guide plate and are captured by it. As the airflow passes through the tapered guide channel, the flue gas velocity gradually increases, and the droplets in the fluid are adsorbed onto the side wall of the tapered guide channel by the shear force generated by the sudden change in flow velocity and are captured. When the airflow passes through the fine capture section, the flow direction changes continuously under the guidance of the misaligned baffle. Under the action of centrifugal force and inertia, the fine mist droplets remaining in the airflow are captured. After passing through the anti-secondary entrainment section, the airflow flows directly out of the concentration and reduction tower. The parallel inverted triangular liquid blocking plates form a protective wall to prevent the airflow from re-entraining the captured droplets. It also includes a step of rinsing the demister. When the ratio of the pressure difference of each section of the demister to the initial pressure difference is greater than a set value, rinsing is started. The set value is 1.5-2:

1.

9. The closed-loop heat transfer desulfurization wastewater concentration and crystallization treatment method according to claim 6, characterized in that: It also includes the step of adding a complexing agent to the desulfurization wastewater in the concentration and reduction tower; When the desulfurization wastewater in the concentration and reduction tower reaches the set concentration ratio, its slurry is transported to the flash tower and enters the flash tower tangentially from the bottom of the flash tower below the liquid level. The slurry is heated and flash-evaporated through circulation. The heated slurry enters the flash tower tangentially from the top of the flash tower.

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