CN116903191A - Seed crystal evaporation process device for recycling treatment of polycrystalline silicon production wastewater - Google Patents

Abstract

A seed crystal evaporation process unit for polycrystalline silicon production waste water resourceful treatment, characterized by: the device comprises a seed crystal tank, wherein seed crystal slurry is prepared in the seed crystal tank in advance, and the seed crystal slurry is pumped into an evaporation circulation pipeline through a seed crystal feeding pump; the polysilicon production wastewater is stored in an evaporation feed tank and pumped into an evaporation circulation pipeline through an evaporation feed pump; after the feed liquid is evaporated and concentrated to reach the specified concentration, the evaporation concentrated liquid is led out from an evaporation circulating pipeline and pumped into a first-stage solid-liquid separator through a seed crystal circulating pump, supernatant enters a settling tank, salt crystal particles with smaller particle sizes gradually grow into larger particle sizes under the action of hydraulic conditions in the settling tank are precipitated and gathered at the bottom, slurry at the bottom of the settling tank is pumped into a second-stage solid-liquid separator through a slurry pump, and the supernatant after the salt crystal particles are removed enters a crystallization feeding tank. The application has simple flow, easy implementation, less investment, reliable operation and lower cost.

Description

Seed crystal evaporation process device for recycling treatment of polycrystalline silicon production wastewater

Technical Field

The application relates to a seed crystal evaporation process device for recycling treatment of polycrystalline silicon production wastewater, which is particularly suitable for salt-containing wastewater and an approximate material system in the production of polycrystalline silicon with high calcium and magnesium and high silicon content.

Background

The zero discharge and the recycling treatment of the waste water become the recommended treatment process for the main stream in the field of environmental protection treatment of the waste water in the production of the polysilicon, and the aim of maximizing and optimizing the recycling of the water and the salt while the pollution of the waste water in the production of the polysilicon is treated can be realized. At present, the key technical stuck point of the process route is that the evaporation and crystallization section process and the device are difficult to realize long-period stable operation and the salt recycling utilization level in the wastewater is generally not high. The former needs to be applied to solve the scaling problem of the evaporation crystallization section process and the device in the specific implementation operation, which not only can influence the process operation energy consumption, the device on-line rate and the maintenance cleaning frequency, but also can lead the device to be incapable of operating and stopping when serious, and the system process can not normally operate. The latter needs to solve the problem of high-efficiency mass separation of impurity salt from a feed liquid system, thereby improving the purity of byproduct salt.

Aiming at the industrial wastewater zero-emission treatment thought, the method is more prone to energy conservation, low carbonization and full realization of recycling of salt and moisture as much as possible in the operation process. The evaporation and concentration device runs stably under low scale, can maintain high heat transfer coefficient and high heat transfer efficiency of the heat exchange equipment of the system, and ensures low energy consumption and low running cost in the evaporation process. The zero discharge treatment of the salt-containing wastewater in the initial stage is mainly performed to recycle most of the water, and the water recovery rate is more than 95%. For salt, only the impurity salt is produced after evaporation and crystallization, and the salt has no use value basically. The mixed salt also needs to be used as dangerous waste for carrying out outward transportation treatment, and a high-energy-consumption incineration process is generally adopted, so that the treatment cost is high, about 3000-5000 yuan per ton is spent, and a heavy economic burden is brought to pollution control enterprises. The method can be further coupled with a mixed salt recovery process aiming at zero emission treatment of the salt-containing wastewater, so that main salt can be recovered, and the total recovery rate can reach more than 80%. However, due to the complex components of the salt-containing wastewater feed liquid, the byproduct salt obtained by the salt separation process is low in purity, and a resource utilization way with higher value of the byproduct salt is cut off.

At present, the application market adopts a non-seed crystal method for the process of the evaporation and concentration section of the salt-containing wastewater, namely, a severe feed liquid pretreatment means, such as two-alkali dosing and hardness removal, dosing and silicon removal, a system adding scale inhibitor and other means, is utilized, so that the concentration of scale forming ions in feed liquid entering an evaporation system is reduced as much as possible. The cost of the process medicament is generally higher, and the process medicament is more inapplicable to the waste water of the polysilicon production with high calcium, magnesium and high silicon content. Meanwhile, due to the addition of various medicaments, the water quality composition of the system is more complex, and the implementation difficulty and adverse effect of the later-stage salt separation crystallization process are increased.

Disclosure of Invention

The application aims to overcome the defects and shortcomings that the traditional seed crystal evaporation process and device are not suitable for the recycling treatment process of the waste water in the production of the polycrystalline silicon, and provides the evaporation process device which can not only realize efficient scale prevention and long-period low-consumption stable operation in the evaporation concentration process of the waste water in the production of the polycrystalline silicon, but also improve the purity of byproduct salt and facilitate the recycling treatment of the salt content of the waste water in the production of the polycrystalline silicon.

The technical scheme of the application is as follows:

a seed crystal evaporation process device for recycling treatment of polycrystalline silicon production wastewater, which is characterized by comprising:

the evaporation system comprises a separation chamber 5 and a heating chamber 8, the separation chamber 5 and the heating chamber 8 are connected through an evaporation circulation pipeline, and the polycrystalline silicon production wastewater is circularly heated and evaporated in the heating chamber 8 and the separation chamber 5;

a feeding system, which comprises a seed crystal tank 1 and an evaporation feeding tank 3, wherein seed crystal suspension liquid is prepared in the seed crystal tank 1 in advance, when the seed crystal concentration in the evaporation system is lower than a first concentration, the seed crystal suspension liquid is introduced into an evaporation circulation pipeline through a first pipeline, the evaporation feeding tank 3 is used for storing the pretreated polysilicon production wastewater from the upstream, and the evaporation feeding tank 3 is connected with the evaporation circulation pipeline, wherein the first concentration can be one concentration set according to the process and the seed crystal type;

the solid-liquid separation system comprises a first-stage solid-liquid separator 10, a settling tank 11 and a second-stage solid-liquid separator 13, wherein after the concentration of feed liquid in the evaporation system reaches a preset concentration, the feed liquid is led out to the first-stage solid-liquid separator 10 through an evaporation circulation pipeline, supernatant liquid in the first-stage solid-liquid separator 10 enters the settling tank 11, concentrated slurry at the lower layer returns to the evaporation circulation pipeline again, slurry at the bottom of the settling tank 11 is led into the second-stage solid-liquid separator 13, and the second-stage solid-liquid separator 13 discharges solid salt mud 18 into a crystallization feeding tank 14.

Based on the technical scheme, the scale formation ion concentration is increased to supersaturation in the evaporation and concentration process of the polysilicon production wastewater by utilizing the seed crystal scale prevention principle, and the precipitated tiny crystal grains are preferentially adsorbed on the surface of the calcium sulfate seed crystal which is added in advance in the system instead of the metal wall surface of the heat exchanger, so that the scale formation problem in the long-period operation of the evaporator is effectively solved; through setting two-stage solid-liquid separation, the first-stage solid-liquid separation device recovers seed crystals by utilizing a centrifugal separation principle, and the settling tank unit is used for better capturing and removing fine grain-size suspended matters in a system, so that grains with excessively small upstream grain sizes grow secondarily, and waste water impurity removal and purification are realized through second-stage solid-liquid separation after the grains grow up, thereby being beneficial to improving the impurity removal and purification effects of the waste water and improving the quality of byproduct salt obtained by salt separation recycling at the rear end; in addition, the scheme has simple flow and easy implementation, can realize continuous on-line solid-liquid separation and recovery of the seed crystal, and is beneficial to reducing the operation cost of the seed crystal method.

The sedimentation tank 11 comprises a guide cylinder 20 and a stirrer 21, wherein the incoming material of the evaporation circulation pipeline enters the guide cylinder 20 from an inlet 23, the incoming material of the upper layer of the first-stage solid-liquid separator 10 enters the guide cylinder 20 from an inlet 24, and the stirrer 21 is used for stirring at a controlled speed, so that the feed liquid with smaller salt particles flows upwards along the guide cylinder 20, flows to the top of the sedimentation tank 11 and then flows downwards along the tank wall.

Based on the technical scheme, the sedimentation tank is provided with the guide cylinder and the stirrer, a specific flow field of wastewater fluid in the sedimentation tank is created, continuous growth and growth of tiny particles and aggregation and subsidence among particles are facilitated, and finally, the second-stage solid-liquid separation device system is facilitated to discharge and recycle crystal salt beyond the requirement for seed crystal recovery, and meanwhile, impurity removal and purification of water entering the rear-end salt separation crystallization system are facilitated, and the quality of recycling recovered byproduct salt is higher.

The first-stage solid-liquid separator 10 is connected to the second-stage solid-liquid separator 13 so as to directly discharge the lower concentrated slurry of the first-stage solid-liquid separator 10 into the second-stage solid-liquid separator 13.

Based on the technical scheme, the concentration of the crystal seeds of the evaporation system can be further adjusted, and the concentration of the crystal seeds of the evaporation system can be rapidly reduced.

The secondary steam 15 generated by circularly heating and evaporating the polysilicon production wastewater in the heating chamber 8 and the separating chamber 5 is discharged after the action of the demister 7, and the secondary steam 15 is reused as distilled water after condensation treatment.

Based on the technical scheme, the secondary steam after condensation treatment can be used as distilled water for recycling, so that the recycling of wastewater is realized, and the production cost is reduced.

The heating chamber 8 is provided with a heating source which enters the heating chamber 8 from the inlet 16, and is discharged from the outlet 17 after releasing heat, and the polycrystalline silicon production wastewater is preheated by the heating source which is discharged from the outlet 17 and releases heat before entering the evaporation circulation pipeline. Based on the technical scheme, the waste heat of the high-temperature steam condensate is fully utilized, so that the heat efficiency of the evaporation system is improved, and the energy conservation and carbon reduction are realized.

The evaporation circulation line is connected to the seed tank 1 through a second line to introduce the circulation feed liquid as seed formulation liquid into the seed tank 1. Based on the technical scheme, the concentration of the seed crystal of the evaporation system can be better regulated, and fresh seed crystal is only required to be added when the device system is started, and lost seed crystal can be continuously supplemented by the new seed crystal generated in the process so as to achieve the balance in the system.

The seed crystal suspension liquid is prepared from one or more of anhydrous calcium sulfate, calcium sulfate dihydrate and power plant desulfurization gypsum with qualified heavy metal content. Based on the technical scheme, the treatment of waste by waste can be realized, and meanwhile, the salt mud can be recycled to serve as gypsum, magnesium sulfate and other salts, so that the recycling is realized.

The vaporization system uses mechanical vapor recompression MVR techniques in combination, including: the secondary steam 15 generated in the separation chamber 5 is introduced into a vapor compressor, and the vapor compressor heats, boosts and increases enthalpy of the secondary steam 15 and then serves as a heating source of the heating chamber 8. Based on the technical scheme, the method is beneficial to further saving the process energy consumption.

Mist entrainment in the secondary steam 15 is removed using a mist eliminator 7 before the secondary steam 15 is introduced into the steam compressor. Based on the technical scheme, the method is beneficial to improving the quality of secondary steam, can ensure safe and stable operation of the steam compressor in the process, and is beneficial to reducing impact and corrosion damage of salt water liquid drops to a steam pipeline and a steam compressor impeller.

The separation chamber 5 and the heating chamber 8 are coupled into an integrated evaporator, wherein the upper part of the integrated evaporator is the heating chamber 8, the lower part is the separation chamber 5, and the integrated evaporator adopts a falling film evaporation type.

Based on the technical scheme, the device system is more compact in structure and smaller in occupied area, and meanwhile, the manufacturing cost is reduced; meanwhile, the liquid flow is shorter, so that the energy consumption of the pump in the operation process is reduced, in addition, further, the liquid distribution form of plug-in components or multi-layer spraying can be adopted, the liquid distribution effect is more uniform, the liquid film is thinner, and the high vaporization rate and no dry point are realized.

The solid content of the seed crystal suspension liquid is 5-8%; or the calcium and magnesium content of the salt-containing wastewater is greater than or equal to a first index, and the silicon content is greater than or equal to a second index; or the solid content of the circulating feed liquid is 3-5%.

Based on the scheme, the inlet water has certain calcium, magnesium and silicon content, which is beneficial to the continuous operation of the seed crystal evaporation process with better and lower cost.

The heating chamber 8 adopts a non-direct contact heat exchange mode, the circulating feed liquid passes through a tube side, the heating source passes through a shell side, and the flow velocity of the feed liquid in the tube side of the heating chamber 8 is 1-3 m/s; alternatively, the first stage solid-liquid separator 10 may take the form of a cyclone to achieve continuous on-line solid-liquid separation operations.

Drawings

Fig. 1 is a schematic diagram of an evaporation process device for a seed crystal according to an embodiment of the present application.

Fig. 2 is a schematic structural diagram of an integrated evaporator device according to an embodiment of the present application.

Fig. 3 is a schematic structural diagram of a settling tank according to an embodiment of the present application.

Fig. 4 is a schematic diagram of an evaporation process device for a seed crystal according to an embodiment of the application.

In the figure: 1-seed tank, 2-seed feed pump, 3-evaporation feed tank, 4-evaporation feed pump, 5-separation chamber, 6-evaporation circulating pump, 7-demister, 8-heating chamber, 9-seed circulating pump, 10-first stage solid-liquid separator, 11-settling tank, 12-slurry pump, 13-second stage solid-liquid separator, 14-crystallization feed tank, 15-secondary steam, 16-heating source inlet, 17-heating source outlet, 18-solid salt mud, 19-slurry outlet, 20-guide cylinder, 21-stirring paddle, 22-rotary sealing device, 23-evaporation circulating pipeline inlet, 24-first stage solid-liquid separator upper layer inlet, 25-plate type preheater, 26-vapor compressor, 27-startup steam, 28-product distilled water.

Detailed Description

The technical scheme and the device of the application are further described below with reference to the attached drawings and specific embodiments.

When the salt-containing wastewater is treated by adopting a conventional seed crystal evaporation process, seed crystal particles with smaller particle size and larger quantity are easy to generate and enter a downstream salt separation recycling section, so that the purity of the subsequent byproduct salt is low. Therefore, the application provides a seed crystal evaporation process and a seed crystal evaporation device for recycling treatment of salt-containing wastewater, especially high-calcium-magnesium and high-silicon-content polycrystalline silicon production wastewater, which have important significance.

As shown in fig. 1-3.

A seed crystal evaporation process device for polycrystalline silicon production wastewater resourceful treatment wholly can divide into three parts namely:

the evaporation system comprises a separation chamber 5 and a heating chamber 8, wherein the separation chamber 5 and the heating chamber 8 are connected through an evaporation circulation pipeline, and the polycrystalline silicon production wastewater is circularly heated and evaporated in the heating chamber 8 and the separation chamber 5;

the feeding system comprises a seed crystal tank 1 and an evaporation feeding tank 3, wherein seed crystal suspension liquid is prepared in the seed crystal tank 1 in advance, when the seed crystal concentration in the evaporation system is lower than a first concentration, the seed crystal suspension liquid is introduced into an evaporation circulation pipeline through a first pipeline, the evaporation feeding tank 3 is used for storing pretreated polysilicon production salt wastewater from upstream, and the evaporation feeding tank 3 is connected with the evaporation circulation pipeline, wherein the first concentration can be a concentration set according to a process and a seed crystal type;

the solid-liquid separation system comprises a first-stage solid-liquid separator 10, a settling tank 11 and a second-stage solid-liquid separator 13, wherein after the concentration of feed liquid in the evaporation system reaches a preset concentration, the feed liquid is led out from an evaporation circulation pipeline to the first-stage solid-liquid separator 10, supernatant liquid in the first-stage solid-liquid separator 10 enters the settling tank 11, lower-layer concentrated slurry returns to the evaporation circulation pipeline again, slurry at the bottom of the settling tank 11 is led into the second-stage solid-liquid separator 13, the second-stage solid-liquid separator 13 discharges solid salt slurry 18 from a device, and clear liquid is discharged into a crystallization feeding tank 14. Through setting up two-stage solid-liquid separation for the seed crystal evaporation can effectively solve the scale deposit problem in the long-term operation of evaporimeter. Meanwhile, continuous on-line solid-liquid separation and seed crystal recovery can be realized, and the operation cost of a seed crystal method is reduced; the wastewater impurity removal and purification can be realized through the second-stage solid-liquid separation, and the quality of byproduct salt obtained by the recycling of the rear-end salt separation is obviously improved. By utilizing the seed crystal scale prevention principle, in the evaporation and concentration process of the salt-containing wastewater, the concentration of scale-forming ions is increased to supersaturation, and precipitated tiny crystal grains are preferentially adsorbed on the surface of a calcium sulfate seed crystal which is added in advance in the system instead of the metal wall surface of the heat exchanger, so that the scaling problem in the long-period operation of the evaporator is effectively solved. The first-stage solid-liquid separation device realizes continuous on-line solid-liquid separation and seed crystal recovery by utilizing the centrifugal separation principle, and the system does not need to continuously add fresh seed crystal, thereby reducing the operation cost. And the sedimentation tank is used for operation, so that the grains with the excessively small upstream grain diameter grow secondarily, after the grains grow up, the waste water impurity removal and purification are realized through the second-stage solid-liquid separation, the quality of byproduct salt obtained by the rear-end salt separation recycling is improved, and meanwhile, the solid salt mud can be recycled as salt such as gypsum, magnesium sulfate and the like, so that the recycling is realized. The scale prevention and the wastewater impurity removal and purification of the whole process are realized by cooperative cooperation. The two-stage solid-liquid separation seed crystal evaporating and concentrating technology has technological system capable of bearing polysilicon production effluent with high calcium, magnesium and silicon content. The settling tank is used for better capturing and removing suspended matters with small particle size in the system, and improves the impurity removal and purification effects of the wastewater.

The details are as follows:

a seed crystal suspension liquid with a certain concentration is prepared in the seed crystal tank 1 in advance, and when the concentration of the seed crystal of the evaporation system is lower than the optimal concentration range in the starting and running process of the device, the seed crystal is pumped into an evaporation circulation pipeline through the seed crystal feeding pump 2. The waste water from the polysilicon production, which has been pretreated upstream, is stored in an evaporation feed tank 3 and pumped into an evaporation circulation line by an evaporation feed pump 4. The separation chamber 5 and the heating chamber 8 of the evaporation system are connected with an evaporation circulating pump 6 and an evaporation circulating pipeline to realize the circulation heating and evaporation of the feed wastewater in the heating chamber 8 and the separation chamber 5, and the generated secondary steam 15 is discharged from the upper part of the separation chamber 5 after the action of a demister 7, and can be used as distilled water for recycling after condensation treatment. The heating chamber 8 is provided with a heating source inlet 16 and an outlet 17 for supplying heat required for heating up the circulating feed liquid entering the heating chamber 8. After the feed liquid is evaporated and concentrated to reach the designated concentration, the evaporation concentrated liquid is led out from the evaporation circulating pipeline and pumped into the first-stage solid-liquid separator 10 through the seed crystal circulating pump 9, the supernatant enters the settling tank 11 (shown in fig. 3), and the lower concentrated slurry returns to the evaporation circulating pipeline again. Meanwhile, a pipeline of the evaporation circulation pipeline in-line sedimentation tank 11 is arranged, and the concentration of the appropriate seed crystal of the evaporation system is regulated and maintained together. The supernatant is entrained with fine crystal particles with smaller particle size, the fine crystal particles gradually grow into salt crystal particles with larger particle size under the action of hydraulic force in a sedimentation tank 11, the salt crystal particles are precipitated at the bottom, slurry at the bottom of the sedimentation tank 11 is pumped into a second-stage solid-liquid separator 13 by a slurry pump 12, and the supernatant after removing the salt crystal particles enters a crystallization feeding tank 14 to be subjected to the next process treatment, as shown in fig. 1. The separated solid salt slurry 18 is used as a salt resource such as gypsum (calcium sulfate) and magnesium sulfate or is disposed of as solid waste. To rapidly reduce the seed concentration of the evaporation system, a line leading from the lower layer of the first-stage solid-liquid separator 10 to the front of the slurry pump 12 is provided for adjustment. The separation chamber 5 and the heating chamber 8 of the evaporation system can adopt a split structure in fig. 1, or an integrated structure in fig. 2, the separation chamber 5 and the heating chamber 8 are coupled into an integrated evaporator, the upper part is the heating chamber 8, the lower part is the separation chamber 5, a falling film evaporation type is adopted, and the secondary steam 15 is treated by the demister 7 before being discharged out of the separation chamber 5.

In the concrete implementation, the added seed crystal is anhydrous calcium sulfate and calcium sulfate dihydrate, and the power plant desulfurization gypsum with qualified heavy metal content can also be used for treating waste by waste. The waste water from polysilicon production can be preheated by using the exothermic heating source before being pumped into the evaporation circulation line by the evaporation feed pump 4. More preferably, if the heating source adopts steam, the high-temperature steam condensate after heat release is used for preheating the feed wastewater from normal temperature to about 95 ℃. The waste heat of the high-temperature steam condensate is fully utilized, the heat efficiency of the evaporation system is improved, and the energy is saved and the carbon is reduced.

In the running process of the device, the circulating feed liquid can be used as seed crystal preparation liquid, seed crystal suspension liquid with the solid content of 5-8% is prepared in a seed crystal tank 1, and is pumped back to an evaporation circulating pipeline through a seed crystal feeding pump 2 after being fully and uniformly stirred by an internal stirrer. In some embodiments, the recycle feed may be introduced directly into the seed tank 1 via the first line; it is also possible to draw a line, the second line, from the evaporation recycle line again to introduce the recycle feed to the seed tank 1.

When the device is started and debugged, the production water or the feed saline wastewater can be used as seed crystal preparation liquid. The introduction of the system seed crystal and the control of reasonable concentration are beneficial to the increase of the concentration of scale forming ions to supersaturation in the evaporation and concentration process of the salt-containing wastewater, and the precipitated tiny crystal grains are preferentially adsorbed on the surface of the calcium sulfate seed crystal which is added in advance in the system instead of the metal wall surface of the heat exchanger, so that the scaling problem in the long-period operation of the evaporator is effectively solved. The application can treat the polysilicon production wastewater with high calcium and magnesium and high silicon content, the polysilicon production wastewater does not need to reach severe residual calcium and magnesium and silicon content indexes (hardness is less than 50mg/L and silicon is less than 20 mg/L) after pretreatment, and the inflow water is left with a certain calcium and magnesium and silicon content, for example, the calcium and magnesium content can be greater than or equal to a first index, and the silicon content can be greater than or equal to a second index, thereby being beneficial to the continuous operation of a better and lower-cost seed crystal evaporation process. Only when the device system is started, fresh seed crystal is needed to be added, and the lost seed crystal can be continuously replenished by the new seed crystal generated in the process so as to reach the balance in the system. The first index and the second index can be set according to specific processes and wastewater.

In particular, the evaporation system combines mechanical vapor recompression (mechanical vapor recompression, MVR) technology, which saves more process energy. That is, the secondary steam 15 generated in the separation chamber 5 enters the steam compressor, and is heated, boosted and enthalpy-increased to serve as a heating source of the heating chamber 8, enters from the heating source inlet 16, condenses into distillate after heat release, is discharged from the heating source outlet 17, and is recycled as product water.

During implementation, the demister 7 is arranged before the secondary steam enters the steam compressor, entrainment of the secondary steam is removed, water quality of product water is improved, safe and stable operation of the steam compressor can be ensured in the process, and impact and corrosion damage of entrainment of saline water drops to a steam pipeline and a steam compressor impeller can not occur. Further preferably, the high temperature distillate at the outlet of the heating source can be used for preheating the feed wastewater, and the wastewater is cooled to normal temperature as reuse water. The feed wastewater preheated to 90-95 ℃ can be pumped into an evaporation circulation pipeline after passing through a deoxidizing and deaerating device. Dissolved oxygen, noncondensable gas and the like in the wastewater are removed by adopting a thermal method, so that the corrosion phenomenon of system equipment is slowed down, and the heat exchange performance of the system equipment is enhanced.

Furthermore, the liquid distribution mode of plug-in components or multilayer spraying is adopted, so that the liquid distribution effect is more uniform, the liquid film is thinner, the Gao Qihua rate is higher, and no dry point exists. The integral evaporator organically combines the heating chamber 8 and the separation chamber 5 together, so that the device has more compact structure and smaller occupied area. The integrated evaporator couples the heating chamber and the separation chamber in one device, so that the device system structure is more compact, the occupied area is smaller, and the manufacturing cost is reduced. The liquid flow is shorter, and the energy consumption of the pump in the running process is saved. The heating source can be waste heat resources such as byproduct low-pressure steam or low-temperature flue gas, and the like, and can also be secondary steam from a certain working section. The heating chamber 8 adopts a non-direct contact type heat exchange mode, such as a shell-and-tube heat exchanger. And (3) the waste water and feed liquid passes through a tube pass, and the heating source passes through a shell pass. The feed liquid with seed crystal passes through the tube side of the heating chamber at a high flow rate of 1-3 m/s, and the high flow rate scouring effect also plays a role in inhibiting and inhibiting the scale of the heat exchange tube to a certain extent. The solid content of the seed crystal of the evaporation circulation pipeline is controlled to be 3-5%, and when the concentration of the seed crystal is too low, the surface of the seed crystal in the feed liquid is not enough for adsorbing newly generated salt scale small crystals, so that the scale prevention effect of the seed crystal method is affected. When the concentration of the seed crystal is too high, the viscosity of the feed liquid is increased, the fluidity is deteriorated, and the thermal efficiency of the process of producing secondary steam by heating and evaporating the feed liquid is affected. At the same time, the risk of clogging of salt discharge lines, secondary steam lines and demisters is increased. The first-stage solid-liquid separator adopts a cyclone mode, can realize continuous on-line solid-liquid separation operation, the dilute phase clear liquid is discharged from the upper layer, the concentrated phase slurry is discharged from the lower layer and returned to the evaporation circulation pipeline, and the proper seed crystal concentration of the evaporation system is maintained. More preferably, when the concentration of the seed crystal in the evaporation system is higher (5-7%), a direct discharge downstream pipeline is arranged on the circulating pipeline for reducing the concentration of the seed crystal. When the concentration of the seed crystal of the evaporation system is high (7-10%), a direct discharging downstream pipeline is arranged on the lower concentrated phase slurry pipeline of the cyclone and is used for reducing the concentration of the seed crystal. The dilute phase clear liquid discharged from the first-stage solid-liquid separator 10 enters a settling tank 11 for crystal growing. According to the centrifugal separation principle of the cyclone, seed crystal particles with smaller particle size (less than 50 mu m) are entrained in the upper dilute phase clear liquid, and the salt crystal particles enter a downstream crystallization section, so that the purity of byproduct salt produced by a salt separation crystallization process can be influenced. Too small a particle size also results in conventional solid-liquid separation means being unable to efficiently remove it from the system. Setting a sedimentation tank 11, providing hydraulic conditions for the growth of seed crystal grain size, controlling the residence time of salt crystal grains in the sedimentation tank 11 to be 1-2 h, slowly growing the grain size (> 100 μm) and coagulating at the bottom, and pumping out by a slurry pump 12. The dense phase slurry at the lower layer of the first-stage solid-liquid separator 10 flows back to the evaporation circulation pipeline to maintain the concentration balance of the seed crystals of the evaporation system. If the seed crystal concentration of the system rises too fast and exceeds the proper concentration range, a pipeline on the lower dense-phase thick slurry discharge pipeline, which is communicated with the front of the downstream slurry pump 12, is arranged, and the seed crystal concentration of the system is regulated to be fast and stable in the optimal concentration range. The sedimentation tank 11 adopts a mode with a guide cylinder 20 and a stirring paddle 21, the incoming material of an evaporation circulation pipeline enters from an inlet 23, the incoming material of the upper layer of the first-stage solid-liquid separator enters from an inlet 24, the incoming material liquid at the upstream enters into the guide cylinder 20, and the feed liquid with smaller salt particles entrained by the feed liquid flows upwards along the guide cylinder 20 under the speed-control stirring action of the stirring paddle 21, flows downwards along the tank wall after reaching the top of the sedimentation tank 11. During the flowing process, fine crystals grow gradually, the particle size is increased from less than 50 mu m to more than 100 mu m, salt particles with larger particle size fall to the conical bottom of the settling tank 11 under the action of gravity, and are discharged from the bottom slurry outlet 19. The sedimentation tank is provided with the guide cylinder and the stirrer, and a specific flow field of wastewater fluid in the sedimentation tank is created, so that continuous growth and growth of tiny particles and aggregation and subsidence among particles are facilitated, and finally, the second-stage solid-liquid separation device system is facilitated to discharge and recycle crystal salt except for the seed crystal recovery of the seed crystal method, and meanwhile, impurity removal and purification of water quality entering a rear-end salt separation crystallization system are facilitated, and the quality of recycled byproduct salt is higher. The second-stage solid-liquid separator 13 adopts a plate-frame filter press, a rotary disc filter or a ceramic membrane filter, and the like, and adopts a high-temperature resistant filter plate material when the plate-frame filter press is adopted. The feed liquid from the upstream slurry pump 12 enters a second-stage solid-liquid separator 13, the solid-removed liquid enters a crystallization feed tank 14, and the suspended matter content of the crystallization feed liquid is not more than 5mg/L. The obtained solid slag mainly contains calcium sulfate, magnesium sulfate and a small amount of calcium carbonate, magnesium hydroxide, colloidal silicon, silicate and the like, and can be used as the salt of gypsum, magnesium sulfate and the like for recycling or as the solid waste for transportation and disposal. The second-stage solid-liquid separator is mainly used for realizing the continuous on-line solid-liquid separation of high-temperature feed liquid.

Example 1.

The salt-containing wastewater discharged by a certain polysilicon enterprise is subjected to wastewater zero discharge and recycling treatment process, wherein the salt-containing wastewater evaporation and concentration section adopts a seed crystal evaporation process which is suitable for recycling treatment as shown in fig. 4. The upstream pretreated salt-containing wastewater has the total dissolved solids (Total Dissolved Solids, TDS) content of 30000-45000 mg/L, the calcium ion content of 3000-5000 mg/L, the magnesium ion content of 100-200 mg/L, the soluble silicon dioxide content of 50-150 mg/L, the sulfate radical content of 1000-2000 mg/L and the chloride ion content of 15000-30000 mg/L.

When the device system is started, a heating source is started, reduced pressure steam in a factory is used as starting steam 27, production water is used for preparing suspension liquid with the solid content of seed crystal of 8% in a seed crystal tank 1, the seed crystal is industrial anhydrous calcium sulfate, and the industrial anhydrous calcium sulfate is pumped into an evaporation circulation pipeline through a seed crystal feeding pump 2, so that the solid content of the seed crystal is controlled to be about 3%.

In normal operation, the heating source is secondary steam heated by the vapor compressor 26 to increase the temperature, pressure and enthalpy. The liquid for preparing the seed crystal is prepared by an evaporation circulation pipeline. The feed salt-containing wastewater is stored in an evaporation feed tank 3, pumped into a plate type preheater 25 by an evaporation feed pump 4, preheated to 90-95 ℃, enters an evaporation circulation pipeline, and is mixed with circulating feed liquid to be jointly used as feed liquid for circulation operation under the action of an evaporation circulation pump 6. After being heated by the falling film type heating chamber 8, the circulating feed liquid falls into the separation chamber 5 below under the action of gravity, the secondary steam is flashed out, the secondary steam 15 with the liquid drops removed by the ring Zhou Dingbu demister 7 enters the steam compressor 26, and the electricity consumption is used for heating the secondary steam, boosting the pressure and increasing the enthalpy, and the secondary steam enters the heating chamber 8 from the inlet 16 as a heating source. Heat exchange is carried out with the feed liquid in the tube side, self-heat-releasing condensed liquid is discharged from the heating source outlet 17 at the temperature of 95-100 ℃, then the feed liquid enters the plate type preheater 25 to preheat the feed liquid, and after the self-temperature is reduced to about 25-30 ℃, the feed liquid is conveyed to the outside of the system for recycling by the distilled water 28.

When the concentration of the evaporated circulating feed liquid reaches the designed concentration ratio, a pipeline is led out from the feed liquid circulating pipeline, and the circulating feed liquid is pumped into the first-stage solid-liquid separator 10-cyclone through the seed crystal circulating pump 9. Under the centrifugal action, the supernatant with low solid content is discharged into a settling tank 11; the lower layer is slurry with multiple solid contents, and the slurry returns to the evaporation circulation pipeline. Through the seed crystal recycling operation, only fresh seed crystal is needed to be added when the device is started, and the solid content of the seed crystal in the evaporation system can be kept to be about 3% without adding during normal operation. When the upstream incoming water quality fluctuates greatly, seed crystals can be synchronously added in the operation process, the solid content of the seed crystals of the evaporation system is maintained at 3-5%, and the normal operation of the seed crystal evaporation process is ensured.

For the high calcium magnesium, high silicon content polysilicon production wastewater in this example, more tiny grains are generated in the seed crystal evaporation process, and these tiny grains (< 50 μm) are difficult to separate thoroughly in the first stage solid-liquid separator 10, and are discharged from the supernatant liquid into the settling tank 11 together with the feed liquid (see fig. 3). The feed liquid flows into the guide cylinder 20 from the inlet 24 at the bottom of the settling tank 11, the fine crystals are upwards along the guide cylinder under the stirring and driving action of the stirring paddle 21, then downwards along the wall surface of the settling tank after reaching the top of the settling tank, continuously gather and grow up in the running process along with the fluid, the particle size is gradually increased to be more than 100 mu m, and finally the fine crystals are settled at the bottom of the cone. The slurry is discharged from the conical bottom outlet 19 and pumped into the second stage solid-liquid separator 13, a plate and frame filter press, via the slurry pump 12. The slurry liquid is fed into a plate-and-frame filter press, solid crystal particles are trapped by filter cloth, filtrate is discharged along a pipeline and enters a crystallization feed tank 14, the content of suspended matters in the filtrate is less than 5mg/L, the content of TDS is 180000 ～ 200000mg/L, and the temperature is 80-90 ℃. The filter plate of the plate-and-frame filter press is made of high-temperature resistant materials, and does not deform during long-period running.

When the calcium and magnesium content and the silicon content of the feed salt-containing wastewater are too high, and the solid content of the generated new seed crystal is far greater than the optimal concentration range, a pipeline can be led out from a feed liquid circulating pipeline to directly discharge the circulating feed liquid to the bottom inlet 23 of the settling tank 11, or a pipeline can be led out from a lower layer discharge pipeline of the cyclone to directly lead out a pipeline to the inlet pipeline of the slurry pump 12, so that the adjustment of reducing the concentration of the seed crystal of the system is quickened.

Finally, the optimal concentration range of the seed crystal concentration in the system is 3-5%, the scaling phenomenon of the evaporation system comprising the heating chamber 8, the separation chamber 5 and the matched pipelines is reduced, the evaporation system integrally keeps high-heat-efficiency operation, and the device inspection and maintenance period is prolonged to 10-12 months. Meanwhile, the salt separation crystallization process is adopted at the downstream of the process, and the purity of the obtained sodium chloride byproduct salt is high (more than 98.5 percent), so that the sodium chloride byproduct salt reaches the first-grade standard of industrial salt, and can be recycled for the chlor-alkali industry. The solid salt slurry 18 obtained after being treated by the second-stage solid-liquid separator 13 can be used as gypsum salt with higher quality for recycling.

Example 2.

The seed crystal evaporation process and the device are adopted for the salt-containing wastewater discharged in the production of certain polysilicon, the TDS content of the feed wastewater is 25000-30000 mg/L, the calcium ion content is 400-800 mg/L, the magnesium ion content is 50-100 mg/L, the soluble silicon dioxide content is 50-100 mg/L, and the chloride ion content is 13000-16000 mg/L.

The device system is that the evaporation feed tank is connected with the inlet of the evaporation feed pump through a pipeline, the outlet of the feed pump is connected to the cold material inlet of the plate-type preheater through a pipeline, and the cold material outlet is connected to the circulating pipeline at the inlet of the circulating pump through a pipeline. The seed crystal tank is connected with the inlet of the seed crystal feeding pump through a pipeline, and the outlet of the seed crystal feeding pump is connected to the circulating pipeline at the inlet of the circulating pump through a pipeline. The circulating pump outlet circulating pipeline is connected to the top of the falling film heating chamber, and the feed liquid falls into the separation chamber below after passing through the falling film pipe and then is collected at the bottom and is connected to the circulating pump inlet through the pipeline. The top of the separation chamber is connected to the inlet of the vapor compressor through a pipeline, the outlet of the vapor compressor is connected to the inlet of the heating heat source of the heater through a pipeline, the outlet of the heating heat source of the heating chamber is connected to the hot material inlet of the plate type preheater through a pipeline, and the hot material outlet discharges distilled liquid cooled to room temperature. Meanwhile, a startup steam pipeline is arranged and connected into a heating heat source inlet pipeline of the heating chamber.

The outlet of the seed crystal circulating pump is connected to the inlet of the first-stage solid-liquid separator (cyclone) through a pipeline, the upper outlet is connected to the inlet of the settling tank through a pipeline, and the bottom outlet is connected to the circulating pipeline of the inlet of the circulating pump through a pipeline. The outlet of the circulating pump is connected with the inlet of the settling tank directly by a pipeline. The outlet at the bottom of the sedimentation tank is connected to the inlet of the slurry pump through a pipeline, and meanwhile, the outlet discharge pipe at the bottom of the first-stage solid-liquid separator is led out of a pipeline which is directly connected with the inlet pipeline of the slurry pump. The outlet of the slurry pump is connected to the inlet of the second-stage solid-liquid separator (ceramic membrane filter) through a pipeline, and the outlet is connected to the inlet of the crystallization feed tank through a pipeline.

After the treatment by the device, the whole evaporation and concentration process of the salt-containing wastewater keeps high-heat efficiency operation, and the energy consumption for ton water treatment is about 25-35 kWh. The device inspection and maintenance period is prolonged to more than half a year. During maintenance, no serious scaling corrosion phenomena including heat exchange equipment are found in the evaporation system. After the downstream salt separation crystallization process treatment, the obtained sodium chloride byproduct salt has high purity (more than 99 percent), reaches the first-grade standard of industrial grade salt, and can be recycled to industries such as chlor-alkali and the like.

The application is not related in part to the same as or can be practiced with the prior art.

Claims (12)

1. A seed crystal evaporation process device for recycling treatment of polycrystalline silicon production wastewater, characterized in that the process device comprises:

the evaporation system comprises a separation chamber (5) and a heating chamber (8), wherein the separation chamber (5) and the heating chamber (8) are connected through an evaporation circulation pipeline, and the polycrystalline silicon production wastewater is circularly heated and evaporated in the heating chamber (8) and the separation chamber (5);

the feeding system comprises a seed crystal tank (1) and an evaporation feeding tank (3), wherein seed crystal suspension liquid is prepared in the seed crystal tank (1) in advance, when the concentration of seed crystals in the evaporation system is lower than a first concentration, the seed crystal suspension liquid is introduced into an evaporation circulation pipeline through a first pipeline, the evaporation feeding tank (3) is used for storing the pretreated polycrystalline silicon production wastewater from the upstream, and the evaporation feeding tank (3) is connected with the evaporation circulation pipeline;

the solid-liquid separation system comprises a first-stage solid-liquid separator (10), a settling tank (11) and a second-stage solid-liquid separator (13), wherein after the concentration of feed liquid in the evaporation system reaches a preset concentration, the feed liquid is led out to the first-stage solid-liquid separator (10) through an evaporation circulation pipeline, supernatant liquid in the first-stage solid-liquid separator (10) enters the settling tank (11), concentrated slurry at the bottom of the settling tank (11) returns to the evaporation circulation pipeline again, slurry at the bottom of the settling tank (11) is led into the second-stage solid-liquid separator (13), and solid salt mud (18) is discharged out of a device through the second-stage solid-liquid separator (13) and is discharged into a crystallization feeding tank (14).

2. The process device according to claim 1, wherein the settling tank (11) comprises a guide cylinder (20) and a stirrer (21), the incoming material of the evaporation circulation pipeline enters the guide cylinder (20) from an inlet (23), the incoming material of the upper layer of the first-stage solid-liquid separator (10) enters the guide cylinder (20) from an inlet (24), and the stirrer (21) is used for stirring at a controlled speed, so that the feed liquid with smaller salt particles entrained by the feed liquid flows upwards along the guide cylinder (20) and flows downwards along the tank wall after flowing to the top of the settling tank (11).

3. Process plant according to claim 1 or 2, characterized in that the first stage solid-liquid separator (10) is connected to the second stage solid-liquid separator (13) to discharge the lower concentrated slurry of the first stage solid-liquid separator (10) directly into the second stage solid-liquid separator (13).

4. Process unit according to claim 1 or 2, characterized in that the waste water from the production of polysilicon is recycled in the heating chamber (8) and the separation chamber (5) and the secondary steam (15) produced by evaporation is discharged after the action of the demister (7), and the discharged secondary steam (15) is recycled as distilled water product after condensation treatment.

5. Process unit according to claim 1 or 2, characterized in that the heating chamber (8) is provided with a heating source which enters the heating chamber (8) from an inlet (16) and which discharges from an outlet (17) after heat release, the waste water from the production of polysilicon being preheated by the heating source discharged from the outlet (17) before entering the evaporation circulation line.

6. Process plant according to claim 1 or 2, characterized in that the evaporation circulation line is connected to the seed tank (1) via a second line for introducing the circulation feed liquid as seed formulation liquid into the seed tank (1).

7. The process device according to claim 1 or 2, characterized in that the seed crystal suspension slurry is prepared in the seed crystal tank (1) by adopting one or more of anhydrous calcium sulfate, calcium sulfate dihydrate and power plant desulfurization gypsum with qualified heavy metal content.

8. The process unit according to claim 1 or 2, characterized in that the evaporation system uses a mechanical vapor recompression MVR technique in combination, comprising: introducing the secondary steam (15) generated by the separation chamber (5) into a steam compressor, wherein the steam compressor heats, boosts and increases enthalpy of the secondary steam (15) and then serves as a heating source of the heating chamber (8).

9. A process arrangement according to claim 8, characterized in that mist entrainment in the secondary steam (15) is removed using a mist eliminator (7) before the secondary steam (15) is introduced into the steam compressor.

10. Process unit according to claim 1 or 2, characterized in that the separation chamber (5) and the heating chamber (8) are coupled as an integrated evaporator, wherein the upper part of the integrated evaporator is the heating chamber (8), the lower part is the separation chamber (5), and the integrated evaporator is of the falling film evaporation type.

11. The process unit according to claim 1 or 2, wherein the seed crystal slurry has a solids content of 5-8%; or the calcium and magnesium content of the polycrystalline silicon production wastewater is greater than or equal to a first index, and the silicon content is greater than or equal to a second index; or the solid content of the circulating feed liquid is 3-5%.

12. The process device according to claim 1 or 2, wherein the heating chamber (8) adopts a non-direct contact heat exchange mode, the circulating feed liquid passes through a tube side, the heating source passes through a shell side, and the flow rate of the feed liquid in the tube side of the heating chamber (8) is 1-3 m/s; or the first-stage solid-liquid separator (10) adopts a cyclone mode so as to realize continuous on-line solid-liquid separation operation.