Improved waste water zero-discharge crystallization byproduct salt elutriation and classification device

Abstract

The utility model provides an improved wastewater zero-discharge crystallization byproduct salt elutriation and classification device. The improved wastewater zero-discharge crystallization byproduct salt elutriation and classification device comprises a cylindrical barrel structure, namely a salt leg, which extends downwards from the bottom of an evaporation crystallizer; a transition straight pipe section is arranged between the bottom of the crystallizer and the salt leg and connected through a flange; an emptying pipe is arranged at the bottom of the salt leg, and a flushing water pipe is arranged above the emptying pipe; a plurality of elutriation liquid feeding pipes are symmetrically arranged at the same height of the lower part of the salt leg, and elutriation liquid is uniformly distributed to each pipe for feeding; a crystal mush discharging pipe is arranged at the middle lower part of the salt leg and above the elutriation liquid feeding pipe; and sight glasses are arranged on the salt legs. The device is simple in structure, remarkable in effect and low in cost, and the purity, granularity and organic impurity content of the byproduct salt can be greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater zero discharge and salt separation and resource utilization, and particularly relates to a modified wastewater zero discharge and salt separation and resource utilization device. BACKGROUND

[0002] In recent years, in the treatment project of industrial wastewater zero discharge, the end often uses evaporation crystallization technology to realize salt separation and resource utilization. Because the front-end wastewater quality mostly contains complex organic impurities, the enrichment effect of the concentration process, combined with the volatility of the water quality and the instability of the device operation, the residual organic impurities content of the obtained by-product salt is generally high. At the same time, the existence of high-concentration organic impurities in the crystallization system hinders the growth of the crystalline particles, and the obtained particle size is generally small, which seriously causes the difficulty of centrifugal separation. For the above reasons, the by-product salt obtained by the enterprise at high cost encounters great obstacles in sales and use, which seriously affects the enthusiasm of environmental protection management, and also hinders the resource utilization process of the by-product salt. For example, the by-product sodium chloride salt of wastewater zero discharge is used in the scene of ion-exchange membrane caustic soda, which is subject to strict quality restrictions. If the by-product sodium chloride salt has low purity and high organic impurity content, it will affect the efficiency and safety of the ion-exchange membrane and the electrolytic cell. If the particle size of the by-product sodium chloride salt is too small, it will cause the difficulty of settlement in the salt melting tank due to light weight, and a large amount of floating salt particles will be retained in the upper part of the salt melting tank and be solidified, so that the salt water concentration is difficult to control. Even the undissolved fine salt enters the overflow tank of the salt melting tank, causing pipeline blockage, salt melting tank overflow, and affecting normal production.

[0003] The salt washing device is commonly used in salt making plants to improve the quality of crystalline salt, that is, the salt slurry discharged from the evaporation tank is thickened by a hydrocyclone and then enters the salt washing device. The washing brine enters the salt washing device from the lower part of the salt washing device, and is usually introduced into the salt washing device through several small pipes in the form of a ring-shaped brine pipe. The washing brine and the salt slurry are countercurrently washed, and the washed salt slurry is discharged from the lower conical part of the salt washing device. This device is provided with a salt washing device outside the evaporation tank and connected by a pipeline. For crystalline salt whose solubility decreases significantly with temperature, the temperature drop after the pipeline will cause a large amount of crystalline salt to be cooled and precipitated, which will easily cause pipe blockage and affect the continuous salt discharge operation. The structure of the ring-shaped brine pipe easily causes the difference between the pressure drops at the near end and the far end of the water inlet side, resulting in uneven water discharge speed of each small pipe of the washing brine, uneven washing flow field, and even disordered channeling, which causes poor washing and grading effect.

[0004] Currently, some manufacturers improve the quality of wastewater zero discharge crystallization by-product salt by setting salt legs and washing pipelines in the lower part of the crystallizer. A circular cylinder is set inside the salt leg as a flow guide cylinder, and the washing brine enters the salt leg in multiple stages along the height direction. The top washing brine flows into the lower part of the flow guide cylinder and flows upward through the annular gap between the flow guide cylinder and the salt leg wall. The flow velocity affects the purity and particle size distribution of the crystalline salt. The internal structure of the device salt leg is complex, difficult to process, and high in manufacturing cost. The multi-stage feeding of washing liquid can easily cause the internal washing flow field of the salt leg to interfere and become disordered, which is not conducive to the washing and grading of the crystalline salt.

[0005] Based on this, some research attempts to improve this situation, for example, patent CN 106977032 A discloses a washing salt leg structure, but the special structure makes the washing leg difficult to process, high in manufacturing cost, and time-consuming and laborious to clear the salt accumulation in the salt leg.

[0006] Patent CN 108191130 A discloses a washing leg structure with an internal circulation washing pipe to solve the problems of small particle size and low crystalline purity of high-salt and high-organic wastewater evaporation crystallization. However, in actual application, the internal flow field of the washing leg still interferes and becomes disordered after the superposition of the internal circulation washing system, which is not conducive to the formation of a uniform upward washing liquid flow field, and the washing and grading effect cannot be expected.

[0007] Patent CN 113634005 A discloses a salt foot washing device. Although the multi-stage washing device is beneficial to the improvement of the washing effect, the complex and mutually influencing washing flow field is not conducive to the particle size grading of the crystalline salt, and also increases the processing and manufacturing difficulty and cost of the salt leg, and makes it difficult to repair and clear the blockage. The inclined outlet arrangement on the horizontal plane of the secondary washing branch pipe has no flow state flushing effect on the salt accumulation in the salt foot cone bottom.

[0008] Patent CN 222118918 U discloses a salt leg device. The washing pipeline is sequentially provided with a first branch, a second branch, and a third branch from top to bottom, and the discharge pipeline is arranged at the bottom of the salt leg body. By setting multiple branch washing and adopting different washing liquid entering angles and control modes for each branch, the salt leg washing effect is improved. However, in the limited salt leg space, multiple feedings in the axial direction can easily form a complex, disordered, and mutually influencing washing liquid flow field in the salt leg, which is not conducive to the particle size grading of the crystalline salt. In addition, the use of different control modes and feeding modes for each washing branch increases the operation control difficulty and processing cost.

[0009] In addition, the above does not consider the consequences of flow field disorder and unevenness caused by unilateral feeding of the washing liquid, and the washing and grading effect of the crystalline salt will be greatly reduced. Practical new type content

[0010] The application provides an improved wastewater zero-discharge crystallization by-product salt elutriation grading device, which can be used to solve the technical problem of flow field disorder and unevenness caused by one-side feeding of elution liquid.

[0011] The improved wastewater zero-discharge crystallization by-product salt elutriation grading device, which comprises a cylindrical barrel structure extending downward from the bottom of an evaporation crystallizer, i.e., a salt leg; a transition straight pipe section is arranged between the bottom of the crystallizer and the salt leg, and is connected by a flange; a discharge pipe is arranged at the bottom of the salt leg, and a flushing water pipe is arranged on the discharge pipe; a plurality of elution liquid feeding pipes are arranged at the same height on the lower part of the salt leg in a symmetrical manner, and the elution liquid is evenly divided into each pipe; a crystal slurry discharge pipe is arranged above the elution liquid feeding pipes on the middle and lower parts of the salt leg; and a sight glass is arranged on the salt leg, so that the internal slurry flow state of the salt leg can be observed.

[0012] Preferably, the evaporation crystallizer is an external heating forced circulation crystallizer, and the flow rate and temperature of the feed liquid are easy to control, so that the heat transfer efficiency and crystallization rate are accelerated. When the salt concentration in the main cavity of the evaporation crystallizer reaches supersaturation, crystals are precipitated, part of which is returned to the main cavity through the circulation pipe to continue to grow, and part of which enters the salt leg due to gravity settling. The solid content of the crystals in the salt leg increases continuously, which plays a role of thickening and concentration. Compared with the scheme of arranging a salt washing device outside the crystallizer and connecting it by a pipeline, the salt leg is directly arranged below the main body of the evaporation crystallizer in the application, so that the overall structure of the device is more compact, the connection path is shortened, and the risk of heat loss and pipeline blockage is reduced.

[0013] Preferably, a plurality of elution liquid feeding pipes are arranged, and are arranged in a symmetrical manner at the same height.

[0014] Preferably, two elution liquid feeding pipes are arranged, and are arranged in a symmetrical manner at 180° on the lower part of the salt leg, and should not be arranged too high.

[0015] More preferably, the arrangement height of the elution liquid feeding pipe is less than 1 / 3 of the total height of the salt leg. If the elution liquid feeding pipe is arranged too high, the effect of dispersing the salt accumulated at the bottom of the salt leg is weakened, the crystalline salt cannot be fluidized and solidified, and it is not conducive to the continuous discharge of the crystal slurry at the salt leg.

[0016] Preferably, the elution liquid feeding pipe extends into the interior of the salt leg and is folded towards the bottom of the salt leg.

[0017] More preferably, the extension length of the elution liquid feeding pipe in the pipe is 1 / 4 to 1 / 3 of the diameter of the salt leg, and the folding length downwards is 1 / 6 to 1 / 4 of the diameter of the salt leg.

[0018] Preferably, the salt leg is provided with a conical bottom, which is beneficial for discharging the material liquid and the crystalline salt particles in the salt leg. Meanwhile, the elutriation liquid feeding pipe is arranged to extend inwardly and fold downward, which scatters the salt accumulated in the conical bottom and keeps the crystalline salt in a fluidized state.

[0019] The elutriation liquid is evenly distributed into the elutriation liquid feeding pipe, and the outlet of the elutriation liquid feeding pipe flows at a certain speed to the side of the conical bottom, scatters the salt accumulated in the conical bottom, rebounds upward after colliding with the side, and forms an upward elutriation liquid flow field. Since the elutriation liquid feeding pipes are symmetrically arranged and the flow of the elutriation liquid is evenly distributed, the horizontal component of the rebounding upward of the elutriation liquid after colliding with the side is counteracted. The upward elutriation liquid flow field is no longer in an unstable and irregular curve flow, but in a stable and uniform central circular upward flow, and the elutriation and classification effect is significantly improved. The crystalline salt particles of different particle sizes settle at different speeds, and the flow of the elutriation liquid is controlled to achieve different upward elutriation speeds. The crystalline salt particles with small particle size and small settling speed are easily taken back to the main space of the evaporative crystallizer by the elutriation liquid with large upward speed to continue to grow, so that the classification of the crystalline salt particles is realized, that is, the crystal slurry with large particle size is obtained in the salt leg, which is beneficial for separation by the centrifugal device at the rear end. Since the elutriation liquid has a lower content of organic matter and does not reach the saturated concentration compared with the crystal slurry in the salt leg, the upward elutriation liquid and the downward settling crystalline salt particles are in reverse contact, the elutriation liquid dissolves the impurity ions and organic matter on the surface of the salt particles, and thus the elutriation and purification of the crystalline salt particles are realized.

[0020] Preferably, the crystal slurry discharge pipe is an inclined upwardly extending pipe, and the end of the pipe is located at the central axis of the salt leg and is spaced apart from the discharging bottom of the salt leg by less than 1 / 2 of the total height of the salt leg.

[0021] More preferably, the end of the pipe is obliquely cut to form a pipe opening. This is beneficial for continuously discharging the crystal slurry to maintain a high solid content and a large particle size, and ensures the normal operation of the centrifugal separation device at the rear end, and also avoids the accumulation of salt in the crystal slurry discharge pipe to block the pipe.

[0022] Preferably, the flushing water pipe is connected to the discharging pipe to assist in the rapid dissolution and unblocking of the accumulated salt in the pipe, so as to ensure that the accumulated salt in the salt leg is quickly discharged in the event of an accident or during maintenance of the evaporative crystallizer. More preferably, the flushing water can be the hot distillation liquid generated by the evaporative crystallization system, which can more quickly and effectively dissolve the salt and unblock the pipe.

[0023] The present application only provides one elutriation liquid feeding pipe in the height direction, and no internal member such as a flow guide cylinder is arranged inside, which effectively simplifies the structure of the salt leg and reduces the processing and manufacturing difficulty. The elutriation liquid feeding pipes of the present application are symmetrically arranged along the circumference of the salt leg, which effectively overcomes the interference and disorder of the elutriation flow field in the salt leg caused by unilateral elutriation liquid feeding, and significantly reduces the elutriation and classification effect of the crystalline salt. The downwardly folded structure of the elutriation liquid feeding pipe and the appropriate arrangement height, in combination with the conical bottom structure of the salt leg, not only provide the upward elutriation flow field in the salt leg, but also effectively scatter and fluidize the salt accumulated in the bottom of the salt leg.

[0024] The device has simple structure, remarkable effect and low cost, can greatly improve the purity, particle size and organic impurity content of by-product salt, meet the limitation requirements of different industries on the quality of by-product salt recycling, and truly realize the purpose of high-value resource utilization of wastewater salt. After being treated by the improved by-product salt elutriation grading device, the purity of the obtained crystalline salt can reach more than 98.5%, the content of organic impurities is less than 15 ppm, and the particle size is greater than 350 um, so that the direct and efficient resource utilization of wastewater zero-emission crystalline by-product salt can be truly realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a structure diagram of an improved wastewater zero-emission crystalline by-product salt elutriation grading device.

[0026] Figure 2 It is a schematic diagram of the arrangement of the elution liquid feeding pipe and the crystal slurry discharging pipe.

[0027] Figure 3 It is a process flow diagram of the wastewater zero-emission disposal process of polysilicon production described in the embodiment.

[0028] In the figure: 1 - evaporation crystallizer, 2 - salt leg, 3 - sight glass, 4 - elution liquid feeding pipe, 5 - blow-off pipe, 6 - flushing water pipe, 7 - crystal slurry discharging pipe, 8 - flange, 9 - polysilicon production wastewater, 10 - MVR evaporator, 11 - three-effect evaporation crystallizer, 12 - centrifugal dehydrator, 13 - dryer, 14 - by-product sodium chloride salt, 15 - impure salt crystallization system device. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application more clear, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0030] Firstly, the embodiments of the present application will be introduced below with reference to the drawings.

[0031] Embodiment 1

[0032] The wastewater discharged by a certain polysilicon enterprise is disposed by using a wastewater zero-emission process, and the salt content of the wastewater is mainly composed of sodium chloride and calcium chloride. The sodium chloride salt in the wastewater is evaporated and recovered by using an MVR evaporation + three-effect evaporation crystallization process. The salt-containing wastewater is evaporated and concentrated by the first two effects of the MVR evaporation and three-effect evaporation crystallization system, and when the concentration of sodium chloride reaches the supersaturation precipitation concentration, sodium chloride is continuously precipitated. When the solid content reaches a certain value, the crystal slurry is discharged to a centrifugal dehydrator for solid-liquid separation, and the wet sodium chloride salt is dried to obtain by-product salt. The centrifugal mother liquor is discharged to an impure salt crystallization system for further disposal.

[0033] The last-effect crystallizer of the triple-effect evaporative crystallization system adopts the elutriation grading device described in the present application. The last-effect crystallizer adopts an external heating forced circulation crystallizer. The circulating feed liquid is led out from the side of the conical bottom of the crystallizer, and is returned to the crystallizer from the upper part of the crystallizer after passing through a circulating pump and a crystallization heater. An excess section is arranged at the conical bottom of the crystallizer, and is connected to the salt leg 2 through a flange 8. The salt leg 2 is arranged in a conical bottom, and is connected to the discharge pipe 5. The flushing water pipe 6 is arranged on the salt leg 2. The flushing water is high-temperature distillation liquid generated by the MVR evaporation system. The elutriation liquid feed pipe 4 is arranged at a position 1 / 4 of the height of the salt leg 2 from the bottom of the discharge pipe. Two elutriation liquid feed pipes are arranged at the same height and are symmetrically arranged at an angle of 180°. The elutriation liquid feed pipe 4 extends into the inside of the salt leg 2, and the length of the extension is 1 / 3 of the diameter of the salt leg 2. The extension is folded towards the bottom of the salt leg 2, and the length of the downward folding is 1 / 6 of the diameter of the salt leg 2. The elutriation liquid is mixed from the last-effect feed and the centrifugal mother liquor, and the flow rate of each is 50%. The elutriation liquid flows at a certain speed from the outlet of the elutriation liquid feed pipe 4 to the side of the conical bottom, and scatters the salt accumulated at the conical bottom. The crystalline salt is always kept in a fluidized state, which is beneficial to the continuous discharge of the crystalline slurry. The elutriation liquid rebounds upwards after colliding with the side, thereby forming an upward elutriation liquid flow field. Since the two elutriation liquid feed pipes 4 are symmetrically arranged at an angle of 180° in the horizontal direction, and the flow rates of the elutriation liquid distributed by the two elutriation liquid feed pipes are the same, the horizontal component forces of the elutriation liquid rebounding upwards after colliding with the side cancel each other out. The elutriation liquid flows stably and uniformly in a central circular shape and vertically upwards, and the elutriation grading effect is better and more reliable. The crystalline particles with small particle sizes from the main body of the crystallizer will be brought back to the main space of the evaporative crystallizer 1 by the elutriation liquid when the settling speed of the crystalline particles is less than the upward flow speed of the elutriation liquid, and continue to grow. The crystalline particles with large particle sizes meeting the requirements will sink into the space of the salt leg when the settling speed of the crystalline particles is greater than the upward flow speed of the elutriation liquid, and continuously increase in concentration.

[0034] The crystalline slurry discharge pipe 7 is arranged at a position 3 / 8 of the height of the salt leg 2 from the bottom of the discharge pipe. The crystalline slurry discharge pipe 7 is an inclined upwardly extending pipe, and the end of the pipe is located at the central axis of the salt leg 2. The end of the pipe is obliquely cut to avoid the accumulation of salt in the crystalline slurry discharge pipe. When the solid content in the space of the salt leg is greater than 30%, the crystalline slurry is discharged from the crystalline slurry discharge pipe 7 to the inlet pipeline of the centrifugal dewatering machine 12 through a pump. If the crystalline slurry in the salt leg is not discharged in time through the crystalline slurry discharge pipe 7 due to improper operation or other reasons, the solid content of the crystalline particles in the salt leg is too high, the crystalline salt accumulates in the middle and lower parts of the salt leg, and the crystalline slurry discharge pipe 7 is blocked. At this time, high-temperature distillation liquid is injected from the flushing water pipe to quickly dissolve the hardened salt block, and the salt block is discharged from the discharge pipe to gradually dredge the salt leg.

[0035] After the crystalline slurry subjected to the elutriation grading effect of the salt leg is treated by the centrifugal dewatering machine and the drying machine, high-quality by-product sodium chloride salt is obtained. The purity of the sodium chloride salt is 99%, the content of organic impurities is 8-10 ppm, the particle size is 450-650 um, and the sodium chloride salt can be directly used as ion membrane caustic soda salt to realize resource recycling.

[0036] The above-described embodiments of the application are not intended to limit the scope of the application.

Claims

1. An improved wastewater zero-discharge crystallization by-product salt washing and grading device, characterized in that, The improved wastewater zero-discharge crystallization by-product salt washing and grading device includes: The bottom of the evaporator crystallizer (1) has a cylindrical structure that extends downwards, which is the salt leg (2); A transition straight pipe section is provided between the bottom of the crystallizer and the salt leg, and is connected by a flange (8); a drain pipe (5) is provided at the bottom of the salt leg (2), and a flushing water pipe (6) is provided above the drain pipe (5); multiple washing liquid feed pipes (4) are symmetrically arranged at the same height at the bottom of the salt leg (2), and the washing liquid is evenly distributed to each pipe for feeding; a crystal slurry discharge pipe (7) is provided in the middle and lower part of the salt leg (2) and above the washing liquid feed pipe (4); A viewing mirror (3) is provided on the salt leg (2).

2. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, Multiple washing liquid inlet pipes (4) are set up and arranged symmetrically at the same height.

3. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 2, characterized in that... Two feed pipes (4) for washing liquid are provided, and the two pipes are arranged symmetrically at 180° at the bottom of the salt leg (2).

4. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, The distance between the height of the washing liquid inlet pipe (4) and the bottom of the salt leg (2) after it has been drained is less than 1 / 3 of the total height of the salt leg.

5. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, The washing liquid feed pipe (4) extends into the inside of the salt leg (2) and folds towards the bottom of the salt leg (2).

6. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 5, characterized in that, The length of the inner extension of the washing liquid feed pipe (4) is 1 / 4 to 1 / 3 of the diameter of the salt leg (2), and the length of the downward folding is 1 / 6 to 1 / 4 of the diameter of the salt leg (2).

7. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, Salt leg (2) is set with a conical bottom.

8. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, The crystal slurry discharge pipe (7) is an inclined upward inward extension pipe, with its end located at the central axis of the salt leg (2), and the distance between it and the bottom of the salt leg (2) is less than 1 / 2 of the total height of the salt leg.

9. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, The end of the crystal slurry discharge pipe (7) is beveled.

10. The improved wastewater zero-discharge crystallization by-product salt washing and grading device according to claim 1, characterized in that, The evaporator crystallizer (1) adopts an externally heated forced circulation crystallizer.

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