Gradient dehydration and resource pretreatment system and method for zero discharge of waste salt in high-salinity wastewater

Abstract

The invention discloses a gradient dehydration and resource pretreatment system and method for zero discharge of waste salt in high-salinity wastewater, the system comprises at least two parallel draining units, each draining unit comprises a combined pool body, the pool body is divided into an upper independent cavity and a lower independent cavity by a middle partition plate, and the upper independent cavity and the lower independent cavity are communicated with each other; the upper cavity is a waste salt storing and draining cavity, the lower cavity is a leachate collecting cavity, a plurality of round draining holes are evenly distributed in the middle partition plate, and draining caps are installed on the draining holes; the leachate collecting and treating unit is used for collecting leachate in each leachate collecting cavity; the multifunctional grab bucket is used for turning and pressurizing the waste salt; and the material transfer device is arranged above the draining unit and used for controlling the multifunctional grab bucket to move in the XYZ space. The industrial problem of dehydration bottleneck of static draining of middle and lower layer materials is ingeniously solved, and the water content of the waste salt is stably reduced through the idea of circulating refining in a mode of mainly physical draining and supplemented by flexible mechanical extrusion.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and solid waste resource utilization technology, specifically to a gradient dewatering and resource utilization pretreatment system and method for zero-discharge waste salt from high-salinity wastewater. Background Technology

[0002] "Zero discharge" has become an essential requirement for wastewater treatment in water-intensive industries such as coal chemical, power, pharmaceutical, and dyeing industries. At the end of the zero discharge process, multi-effect evaporation and MVR (Multi-Vacuum Reduction) evaporation crystallization technologies ultimately convert total dissolved solids into solid waste salt. However, this type of waste salt has a complex composition (often containing NaCl, Na2SO4, and small amounts of heavy metals, organic matter, and other impurities), and is mostly identified as hazardous waste. Traditional disposal methods include landfilling, which not only occupies land resources and poses environmental risks but also contradicts the policy orientation of "zero-waste cities" and the circular economy. Promoting the harmless and resource-based utilization of waste salt has become an industry consensus and development trend.

[0003] Existing high-salinity wastewater treatment processes involve continuous concentration and volume reduction, resulting in a high concentration of organic matter in the final wastewater before it enters the evaporation and crystallization system. This causes the waste salt produced by the evaporation and crystallization system to be discharged in the form of salt slurry or wet salt cake, with a high water content, generally between 10% and 30%. This has become a key technical bottleneck before the waste salt can be sent to resource recovery processes (such as high-temperature melting, high-temperature oxidation, and industrial product preparation). Direct drying of high-moisture-content waste salt is energy-intensive, as water evaporation requires a large amount of heat energy, significantly increasing equipment investment and operational burden. The large amount of water also increases the volume of ineffective hazardous waste transportation and disposal, causing unnecessary costs. Traditional mechanical dewatering equipment (such as plate and frame filter presses) suffers from high investment, easy clogging, difficult maintenance, and poor adaptability when used for this type of high-COD, highly corrosive, and unevenly crystalline waste salt.

[0004] Therefore, there is an urgent need to develop a dedicated dehydration pretreatment technology and device that is low-cost, highly efficient, stable in operation, and easy to maintain, specifically for the characteristics of waste salt. The aim is to reduce the moisture content of waste salt to below 10% through a method that primarily uses physical dehydration and secondarily uses flexible mechanical extrusion, based on the concept of cyclic refining. This will create favorable conditions for subsequent deep drying and resource utilization processes, thereby breaking through the economic and technical bottlenecks in the entire waste salt resource utilization chain. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a waste salt dehydration pretreatment system and method with simple system structure, low investment and operating costs, stable dehydration effect, adaptability to complex waste salt properties, and the ability to realize internal circulation of leachate, so as to effectively reduce the water content of waste salt to below 10%, thereby saving a lot of energy and cost for subsequent treatment.

[0006] The technical solution adopted in this application is as follows: A gradient dewatering and resource recovery pretreatment system for zero-discharge waste salt from high-salinity wastewater includes: At least two parallel drainage units, each drainage unit includes a combined pool body, which is divided into two independent chambers by a middle partition. The upper chamber is a waste salt storage and drainage chamber, and the lower chamber is a leachate collection chamber. Multiple circular drainage holes are evenly distributed on the middle partition, and drainage caps are installed on the drainage holes. The leachate collection and treatment unit is used to collect the leachate from each leachate collection chamber. A multi-functional grab bucket used to turn over and pressurize waste salt; The material transfer device is located above the draining unit and is used to control the movement of the multi-functional grab bucket in the XYZ space.

[0007] Furthermore, the waste salt storage and dredging chamber is an open-top tank used to receive and store wet waste salt. It can mix waste salt from different evaporation and crystallization systems in the waste salt storage and dredging chamber, so that the subsequent equipment feeds evenly and completes the main dewatering process.

[0008] Furthermore, the leachate collection chamber is used to collect the liquid seeping down from the upper waste salt storage chamber. The leachate collection chamber can be a semi-underground or above-ground structure, with an inspection hole located near the middle partition to facilitate the disassembly and maintenance of internal equipment. The bottom inner wall of the leachate collection chamber has a sloping gradient, and a water pit is located below the lowest side of the slope. A slurry pump is installed in the water pit to collect the crystallized impurities in the leachate.

[0009] The intermediate partition of the modular tank serves as a drainage layer, with multiple evenly distributed circular drainage holes ranging from DN32 to 100 mm in diameter. Drainage caps are installed on these holes; the caps are made of corrosion-resistant engineering plastics (such as ABS or PVDF) or ceramic, and their filtration accuracy is 50-200 μm, preferably 100 μm. A reinforced concrete crossbeam is provided at the bottom of the intermediate partition to provide sufficient load-bearing strength to support the waste salt layer and mechanical loads.

[0010] Furthermore, the inner wall of the combined pool and the surface of the intermediate partition are lined with fiberglass (FRP) or coated with polyethylene (PE) anti-corrosion layer. The two drainage units can be connected in parallel and switched to achieve continuous or semi-continuous operation with "one in standby" or "one drainage and one delivery".

[0011] The leachate collection and treatment unit includes a brine return pump and a slurry pump. The brine return pump is located at the upper outside of the leachate collection chamber and is used to return the saturated brine in the upper part of the leachate collection chamber to the evaporation and crystallization system. The slurry pump is located at the bottom of the leachate collection chamber and is used to return the fine salt slurry in the lower part of the leachate collection chamber to the corresponding waste salt storage chamber.

[0012] The lower leachate collection chamber of the combined tank collects the leachate dewatered from the upper waste salt storage chamber. Relying on gravity sedimentation, the entrained waste salt slowly settles into the water pit at the bottom of the leachate collection chamber.

[0013] The upper part of the leachate collection chamber is equipped with a brine return pump to return the collected leachate (which is basically saturated brine) to the front-end evaporation and crystallization system for re-evaporation and crystallization treatment.

[0014] The water pit at the bottom of the leachate collection chamber is equipped with a slurry pump, which can return the settled fine salt crystallization slurry to any of the upper waste salt storage chambers for further drainage, thereby achieving "secondary enrichment and recovery" of salt.

[0015] Each upper waste salt storage chamber is equipped with a high-pressure flushing device on its upper side wall. The high-pressure flushing device includes a high-pressure flushing water pipe and nozzles, used to periodically flush the intermediate partition and drain cap. The flushing wastewater is directly discharged into the lower leachate collection chamber and enters the system circulation.

[0016] The material transfer device includes a rail-mounted electric trolley and a lifting mechanism. The lifting mechanism is mounted on the rail-mounted electric trolley and can control the lifting mechanism to move in the XY plane. The multi-functional grab bucket is mounted at the lower end of the lifting mechanism and can control the multi-functional grab bucket to move up and down in the Z-axis direction.

[0017] The material transfer device is equipped with a multi-functional grab bucket to realize the transfer of waste salt materials and assist in the dewatering operation, including: Turning and crushing function: This multi-functional grab can grab, lift and re-spread waste salt in the waste salt storage chamber. This process can mix different batches of waste salt, crush salt blocks, change the pore structure of the salt layer, break the capillary effect, and significantly improve the gravity leaching efficiency.

[0018] Flexible pressurization function: The inner side of the multi-functional grab bucket's flaps can be lined with an elastic pad (such as a thick rubber sheet). After the flaps open to grab waste salt, they close again, applying a uniformly distributed flexible static pressure to the waste salt within the flaps. This pressure effectively squeezes out the interstitial water between the waste salt particles, unlike rigid pressure plates which can cause filter layer caking or damage to the drain caps, thus achieving deep drainage. Furthermore, after the flaps close, the multi-functional grab bucket can apply static pressure to the lower waste salt layer through its own weight or controlled downward pressure, maintaining this pressure for a period of time to squeeze out residual capillary water and weakly bound water.

[0019] Unloading function: After the dewatering is completed, the multi-functional grab bucket will grab the qualified waste salt and transfer it to the receiving port of the subsequent processing system.

[0020] This invention discloses a gradient dewatering and resource recovery pretreatment system for zero-discharge waste salt from high-salinity wastewater. By constructing a three-stage gradient dewatering process involving gravity leaching, mechanical agitation and reconstruction, and static pressure, it achieves progressively deeper removal of free water, capillary water, and some bound water from the waste salt, from the easiest to the most difficult stages. Specifically: First, the wet waste salt undergoes preliminary free water separation in the waste salt storage and dredging chamber by gravity. The waste salt storage and dredging chamber has a capacity to accommodate a retention time of more than 24 hours for gravity drainage. Secondly, by flipping the multi-functional grab bucket, the capillary structure formed by gravity compaction in the lower part of the salt layer is broken, the seepage channel is re-optimized, and the dehydration capacity of the salt layer is regenerated. Finally, the static pressure applied by the multi-functional grab bucket squeezes out the residual, difficult-to-remove moisture between the particles.

[0021] The three-stage action described above works in a gradient coordination in time and space to jointly ensure dehydration efficiency and depth.

[0022] The beneficial effects of this invention lie in its unique three-stage gradient dewatering mechanism, which simulates and enhances the natural draining process, achieving a similar dewatering effect with far lower energy consumption than mechanical pressure filtration. In particular, the 'turning and reconstructing' step cleverly solves the industry problem of dewatering the lower layer of material during static draining, and is the key innovation of this invention for achieving efficient dewatering.

[0023] Compared with the prior art, the present invention has the following outstanding advantages: 1. High drainage efficiency and good effect: It combines the triple effects of energy-free gravity seepage, mechanical turning to optimize the seepage channel, and static pressure drainage, which can stably reduce the moisture content of waste salt from 20-30% to below 10%, which is close to the effect of some centrifuges, but with extremely low energy consumption.

[0024] 2. High adaptability and non-clogging: The periodic turning of the multi-functional grab bucket can effectively prevent the clogging caused by the formation of a dense filter cake layer on the filter cap by the sticky substances in the waste salt, and the system can operate continuously for a long period of time.

[0025] 3. Low operating costs and investment: The main power consumption is only for the crane and pump, which is far lower than that of centrifuges or filter presses. The main body is a civil engineering structure with few corrosion-resistant parts, which greatly reduces investment and maintenance costs.

[0026] 4. Thorough resource recovery: It realizes a closed-loop circulation of leachate (saturated brine) and fine salt crystals, with no secondary waste liquid generated, thus improving the overall salt recovery rate.

[0027] 5. Flexible operation and intermittent operation: The dual-pool design can flexibly cope with the output fluctuations of the front-end evaporation and crystallization system, making it suitable for industrial applications. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall system layout; Figure 2 This is a cross-sectional structural diagram of a single drainage unit; Figure 3 This is a flowchart of a gradient dewatering and resource recovery pretreatment system for zero-discharge waste salt from high-salinity wastewater. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] Example: A gradient dewatering and resource recovery pretreatment system for zero-discharge waste salt from high-salinity wastewater, compared with a control system. Figures 1-2 It includes: at least two parallel drainage units, each drainage unit including a combined pool body, which is divided into two independent chambers by a middle partition 3. The upper chamber is the waste salt storage and drainage chamber 1, and the lower chamber is the leachate collection chamber 2. Multiple circular drainage holes are evenly distributed on the middle partition 3, and drainage caps 4 are installed on the drainage holes. The leachate collection and treatment unit is used to collect the leachate from each leachate collection chamber. The multi-functional grab bucket 8 is used to turn over and pressurize waste salt; The material transfer device is located above the draining unit and is used to control the movement of the multi-functional grab bucket in the XYZ space.

[0031] Comparison Figure 1 The waste salt storage chamber 1 is divided into two chambers, namely the first storage chamber 1A and the second storage chamber 1B.

[0032] The leachate collection and treatment unit includes a brine return pump 5 and a slurry pump 6. The brine return pump 5 is located at the upper exterior of the leachate collection chamber 1 and is used to return the saturated brine in the upper part of the leachate collection chamber 1 to the evaporation and crystallization system. The slurry pump 6 is located at the bottom of the leachate collection chamber 2 and is used to return the fine salt-containing slurry in the lower part of the leachate collection chamber 2 to the corresponding waste salt storage chamber 1.

[0033] The material transfer device includes a track-mounted electric trolley 7 and a lifting mechanism. The lifting mechanism is mounted on the track-mounted electric trolley 7 and can control the movement of the lifting mechanism in the XY plane. The multi-functional grab bucket is located at the lower end of the lifting mechanism, and the lifting mechanism can control the up-and-down movement of the multi-functional grab bucket in the Z-axis direction. The track-mounted electric trolley 7 is prior art; for example, Chinese patent CN121577383A discloses a similar electric trolley structure. The lifting mechanism is prior art and can use a telescopic cylinder to lift the multi-functional grab bucket 8.

[0034] The side wall of the waste salt storage chamber is equipped with a high-pressure flushing device 10.

[0035] Example 1 (Basic Example) A coal chemical plant's zero-discharge project for high-salt wastewater produces 30 tons / day of evaporated and crystallized mixed salts (wet basis, moisture content approximately 25%). The system of this invention is used, comprising two concrete drainage tanks, A and B, each measuring 6m × 5m × 4.5m (depth), with 5mm thick fiberglass reinforced plastic (FRP) inner walls for corrosion protection. Filter plates are positioned 2m from the tank bottom, covered with ABS drainage caps (100-micron precision) spaced 200mm apart.

[0036] Operation Process: On Day 1, wet salt is poured into Concrete A's drainage tank and piled up to a height of 2m. After standing for 4 hours, it is completely turned over once using a multi-functional grab bucket (the inside of the grab bucket is lined with a 20mm thick rubber plate). The multi-functional grab bucket is then closed to apply gentle pressure to the waste salt inside, squeezing out residual capillary water and weakly bound water. While the multi-functional grab bucket is closed, it is lightly pressed against the salt surface for 2 hours. The process of turning, gentle pressure, and light pressing is repeated once more. The tank is left to stand overnight. On the morning of Day 2, the surface salt moisture content is measured to be 9.2%, and the bottom salt content is 10.1%. All the waste salt from Concrete A's drainage tank is grabbed using the grab bucket and transported to the drying section. On the morning of Day 2, the process can be repeated to feed into Concrete B's drainage tank. After the leachate settles, the saturated brine is returned to the evaporation and crystallization raw water via the upper brine return pump, and the settled fine salt slurry is pumped back to the tank currently being fed through the bottom slurry pump once daily.

[0037] Results: The average moisture content of waste salt was reduced from 25% to below 10%, and the subsequent steam consumption for drying was reduced by about 60%. The system consumes only a small amount of electricity, has no easily damaged mechanical parts, and the annual operating cost is only 1 / 5 of that of the centrifuge solution.

[0038] Example 2 (Optimized and Innovative Extended Example) Based on Example 1, the following optimizations were made to further enhance automation and drainage performance: Intelligent Sensing and Control System: Online microwave or capacitive moisture meters are installed at different heights on the walls of concrete dewatering tanks A and B to monitor the salt layer moisture content gradient in real time. Pressure sensors and position encoders are integrated into the track-mounted electric trolley and the multi-functional grab bucket. The pressure sensor on the multi-functional grab bucket controls the pressure applied by the grab bucket to the waste salt; the position encoder controls the dwell or grabbing position of the multi-functional grab bucket in the waste salt hopper.

[0039] Adaptive Flexible Pressurization: Based on feedback from the moisture meter, the control system automatically plans the turning depth, path, pressure, and duration of the multi-functional grab bucket. For example, when high moisture content is detected in the bottom layer, the control system controls the multi-functional grab bucket to perform deep grabbing and focused turning; during pressurization, based on feedback from the pressure sensor, the pressure is maintained at a critical value that is both effective and does not cause filter bed caking.

[0040] Example 2 upgrades the present invention from an "experience-based operation" device to a "perception-decision-execution" intelligent drainage system by introducing online detection and feedback control.

[0041] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A gradient dewatering and resource recovery pretreatment system for zero-discharge waste salt from high-salinity wastewater, characterized in that, include: At least two parallel drainage units, each drainage unit includes a combined pool body, which is divided into two independent chambers by a middle partition. The upper chamber is a waste salt storage and drainage chamber, and the lower chamber is a leachate collection chamber. Multiple circular drainage holes are evenly distributed on the middle partition, and drainage caps are installed on the drainage holes. The leachate collection and treatment unit is used to collect the leachate from each leachate collection chamber. A multi-functional grab bucket used to turn over and pressurize waste salt; The material transfer device is located above the draining unit and is used to control the movement of the multi-functional grab bucket in the XYZ space.

2. The system as described in claim 1, characterized in that, The filtration accuracy of the drain cap is 50-200 microns, and the material is ABS, PVDF or ceramic.

3. The system as described in claim 1, characterized in that, The inner wall and the surface of the middle partition of the combined pool are provided with an anti-corrosion layer, which is made of fiberglass or polyethylene.

4. The system as described in claim 1, characterized in that, The leachate collection and treatment unit includes a brine return pump and a slurry pump. The brine return pump is located at the upper outside of the leachate collection chamber and is used to return the saturated brine in the upper part of the leachate collection chamber to the evaporation and crystallization system. The slurry pump is located at the bottom of the leachate collection chamber and is used to return the fine salt slurry in the lower part of the leachate collection chamber to the corresponding waste salt storage chamber.

5. The system as described in claim 4, characterized in that, The bottom inner wall of the leachate collection chamber is provided with an inclined slope, and a water pit is provided below the lowest side of the slope, in which the slurry pump is installed.

6. The system as described in claim 1, characterized in that, The inner side of the multi-functional grab bucket is lined with an elastic pad, which facilitates the opening of the grab bucket to grab waste salt. When the grab bucket is closed, it can apply a uniformly distributed flexible static pressure to the waste salt inside.

7. The system as described in claim 1, characterized in that, The material transfer device includes a rail-mounted electric trolley and a lifting mechanism. The lifting mechanism is mounted on the rail-mounted electric trolley and can control the lifting mechanism to move in the XY plane. The multi-functional grab bucket is mounted at the lower end of the lifting mechanism and can control the multi-functional grab bucket to move up and down in the Z-axis direction.

8. The system as described in claim 1, characterized in that, The sidewalls of the waste salt storage chamber are equipped with a high-pressure flushing device.

9. The method for pretreating waste salt drain water using the system as described in claim 1, characterized in that, Waste salt should be treated in the following gradient order: S1: The wet waste salt produced by the evaporation and crystallization system is transported to the upper waste salt storage chamber of one of the draining units; S2 First Gradient: Wet waste salt is left to stand in the waste salt storage and leaching chamber and undergoes gravity free leaching to remove most of the free water. The leachate flows into the lower leachate collection chamber through the leaching cap on the middle partition. S3 Second gradient: During or after the leachate process, the multi-functional grab bucket is used to grab, lift and scatter the waste salt in the waste salt storage chamber at least once, and the salt layer is reconstructed by mechanical turning, the capillary structure is destroyed, and the deep water is converted into free water and leachate again. S4 Third gradient: After step S3 is flipped, the multi-functional grab bucket is operated to grab the waste salt and then closed to apply flexible static pressure to the waste salt inside. By applying uniform flexible static pressure, the residual capillary water and weakly bound water are squeezed out. In the closed state of the multi-functional grab bucket, static pressure is applied to the waste salt layer by its own weight or controllable downward pressure and maintained for a period of time to squeeze out the residual capillary water and weakly bound water. S5: Steps S3 and S4 are performed alternately once or multiple times until the moisture content of the waste salt reaches the predetermined target. S6: Control the movement of the multi-functional grab bucket through the material transfer device to transfer the drained waste salt out and send it into the hopper of the subsequent drying unit; at the same time, the supernatant in the leachate collection chamber is reused to the evaporation crystallization system, and the fine salt slurry at the bottom of the leachate collection chamber is sent back to the corresponding waste salt storage chamber for treatment.

Images