A seed evaporation process device for polycrystalline silicon production wastewater resource disposal

Abstract

A kind of seed evaporation process device for polysilicon production wastewater resource disposal, it is characterized by: it includes seed tank, seed slurry is prepared in advance in seed tank, and seed slurry is pumped into evaporation circulating pipeline by seed feed pump;Polysilicon production wastewater is stored in evaporation feed tank, and is pumped into evaporation circulating pipeline by evaporation feed pump;After concentration of feed liquid evaporation reaches specified concentration, evaporation concentrated liquid is led out from evaporation circulating pipeline and is pumped into first stage solid-liquid separator by seed circulating pump, upper clear liquid enters settling tank, and small salt particles are gradually grown into larger salt crystal particles under the action of hydraulic condition in settling tank and are settled in bottom, slurry in the bottom of settling tank is pumped into second stage solid-liquid separator by slurry pump, and after removing salt crystal particles, clear liquid enters crystallization feed tank.The process of the present application is simple, easy to implement, has less investment, reliable operation and lower cost.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of seed evaporation process device for polycrystalline silicon production wastewater resource disposal, especially for high calcium magnesium, high silicon content polycrystalline silicon production salt-containing wastewater and approximate material system. BACKGROUND

[0002] Wastewater zero discharge and resource disposal has become the mainstream recommended implementation process in the field of polycrystalline silicon production wastewater environmental protection treatment, which can realize the pollution control of polycrystalline silicon production wastewater, and the water and salt are maximized and optimized for resource recycling. At present, the key technical points of this process route are that the evaporation crystallization section process and device are difficult to realize long-period stable operation, and the salt resource utilization level in wastewater is generally not high. The former needs to solve the scaling problem of evaporation crystallization section process and device in the specific implementation operation, which not only affects the process energy consumption, device online rate and maintenance cleaning frequency, but also causes the device to be unable to run and stop, and the system process cannot run normally. The latter needs to solve the efficient separation of impurity salt from the feed liquid system, so as to improve the purity of by-product salt.

[0003] For industrial wastewater zero discharge disposal, more energy-saving and low-carbonization in the running process, and the salt and water contained are as much as possible to realize resource recycling. Low-scale stable operation of evaporation concentration device can maintain high heat transfer coefficient and high heat transfer efficiency of system heat exchange equipment, to ensure low energy consumption and low operation cost of evaporation process. At the initial stage, the water recovery rate of salt-containing wastewater zero discharge disposal is more than 95%. For salt, only the impurity salt is obtained after evaporation crystallization, which has basically no utilization value. The impurity salt also needs to be transported and disposed as hazardous waste, usually using high-energy consumption incineration process, with high treatment cost of about 3000-5000 yuan per ton, which brings heavy economic burden to pollution control enterprises. Now, for salt-containing wastewater zero discharge disposal, the impurity salt separation and recovery process can be further coupled to recover the main salt, with a total recovery rate of more than 80%. However, due to the complex composition of salt-containing wastewater feed liquid, the purity of by-product salt obtained by salt separation process is not high, which cuts off the higher value resource utilization way of by-product salt.

[0004] At present, the non-seed method is mostly used in the evaporation concentration section process of salt-containing wastewater in the application market, that is, the concentration of scaling ions in the feed liquid entering the evaporation system is as low as possible by using strict feed liquid pretreatment methods, such as two-alkali dosing to remove hardness, dosing to remove silicon, and adding scale inhibitor in the system. This process has generally high cost of reagent, and is more unsuitable for high calcium magnesium and high silicon content polycrystalline silicon production wastewater. At the same time, the addition of various reagents makes the water quality composition of the system more complex, which increases the difficulty and adverse effects of the implementation of the salt separation and crystallization process in the later stage. SUMMARY

[0005] The purpose of this invention is to address the shortcomings and deficiencies of traditional seed evaporation processes and devices that are not suitable for the resource-based treatment of polysilicon production wastewater. This invention provides an evaporation process and device that can achieve efficient scale prevention and long-term stable operation with low consumption during the evaporation and concentration process of polysilicon production wastewater, while also improving the purity of by-product salts, thus facilitating the resource-based utilization and treatment of salts in polysilicon production wastewater.

[0006] The technical solution of this invention is:

[0007] A seed evaporation process apparatus for the resource-based treatment of polysilicon production wastewater, characterized in that the apparatus comprises:

[0008] An evaporation system is provided, comprising a separation chamber 5 and a heating chamber 8, wherein the separation chamber 5 and the heating chamber 8 are connected by an evaporation circulation pipeline, wherein polysilicon production wastewater is circulated and heated and evaporated in the heating chamber 8 and the separation chamber 5;

[0009] A feeding system includes a seed tank 1 and an evaporation feeding tank 3. The seed tank 1 contains a pre-prepared seed suspension. When the seed concentration in the evaporation system is lower than a first concentration, the seed suspension is introduced into the evaporation circulation pipeline through a first pipeline. The evaporation feeding tank 3 is used to store pre-treated polysilicon production wastewater from upstream. The evaporation feeding tank 3 is connected to the evaporation circulation pipeline. The first concentration can be a concentration set according to the process and seed type.

[0010] A solid-liquid separation system includes a first-stage solid-liquid separator 10, a settling tank 11, and a second-stage solid-liquid separator 13. After the concentration of the feed liquid in the evaporation system reaches a predetermined concentration, the feed liquid is led out from the evaporation circulation pipeline to the first-stage solid-liquid separator 10. The upper clear liquid in the first-stage solid-liquid separator 10 enters the settling tank 11, and the lower concentrated slurry returns to the evaporation circulation pipeline. The slurry at the bottom of the settling tank 11 is introduced into the second-stage solid-liquid separator 13. The second-stage solid-liquid separator 13 discharges solid salt mud 18 and discharges the clear liquid into the crystallization feed tank 14.

[0011] Based on the above technical scheme, by using the crystal seed anti-fouling principle, in the evaporation and concentration process of the polysilicon production wastewater, the concentration of the scale-forming ions increases to supersaturation, and the small crystal grains are precipitated and preferentially adsorbed on the surface of the pre-added calcium sulfate crystal seeds in the system instead of the metal wall of the heat exchanger, thereby effectively solving the scaling problem in the long-period operation of the evaporator; by setting two-stage solid-liquid separation, the first-stage solid-liquid separation device recovers the crystal seeds by using the centrifugal separation principle, and the settling tank unit is used for better capturing and removing the fine-particle-size suspended solids in the system, so that the small crystal grains in the upstream grow again, and after growing up, the wastewater is purified by the second-stage solid-liquid separation, which is beneficial to improving the wastewater purification effect and improving the quality of the by-product salt obtained by resource utilization of the downstream salt separation; in addition, the scheme has a simple process and is easy to implement, can realize continuous online solid-liquid separation and recovery of crystal seeds, and is beneficial to reducing the operation cost of the crystal seed method.

[0012] The settling tank 11 includes a draft tube 20 and an agitator 21, the incoming material of the evaporation circulating pipeline enters the draft tube 20 from an inlet 23, the incoming material of the first-stage solid-liquid separator 10 enters the draft tube 20 from an inlet 24, and the agitator 21 is used for speed control stirring and makes the material liquid carrying small salt particles flow upward along the draft tube 20, and after flowing to the top of the settling tank 11, flows downward along the tank wall.

[0013] Based on the above technical scheme, the settling tank is provided with a draft tube and an agitator, a specific flow field of wastewater flow is created in the settling tank, which is beneficial to the growth and enlargement of small particles and the aggregation and sinking of particles, and finally is beneficial to the discharge and recovery of crystal salt other than the crystal seed recovery required by the system of the second-stage solid-liquid separation device, and is also beneficial to the impurity removal and purification of the water quality entering the downstream salt separation crystallization system, and the quality of the by-product salt recovered by resource utilization is higher.

[0014] The first-stage solid-liquid separator 10 is connected with 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.

[0015] Based on the above technical scheme, it is beneficial to further adjust the crystal seed concentration of the evaporation system, and the crystal seed concentration of the evaporation system can be quickly reduced.

[0016] The polysilicon production wastewater is circulated and heated in the heating chamber 8 and the separation chamber 5, and the secondary steam 15 generated by evaporation is discharged after the action of the demister 7, and after condensation treatment, the secondary steam 15 is reused as product distilled water.

[0017] Based on the above technical scheme, the secondary steam after condensation treatment can be reused as product distilled water, so as to realize the resource utilization of wastewater and reduce the production cost.

[0018] The heating chamber 8 is provided with a heating heat source entering the heating chamber 8 from the inlet 16, and the heating heat source is discharged from the outlet 17 after heat release, and the polysilicon production wastewater is preheated by the heating heat source discharged from the outlet 17 before entering the evaporation circulating pipeline. Based on the above technical scheme, it is beneficial to fully utilize the waste heat of the high-temperature steam condensate, thereby improving the heat efficiency of the evaporation system, saving energy and reducing carbon.

[0019] The evaporation circulating pipeline is connected with the seed tank 1 through a second pipeline to introduce the circulating liquid as a seed preparation liquid into the seed tank 1. Based on the above technical scheme, the seed concentration of the evaporation system can be better adjusted, and only fresh seeds need to be added when the device system is started, and the new seeds generated in the process will continuously supplement the lost seeds to achieve balance in the system.

[0020] The seed slurry in the seed tank 1 is prepared by using one or more of anhydrous calcium sulfate, calcium sulfate dihydrate, and power plant desulfurization gypsum with qualified and standard heavy metal content. Based on the above technical scheme, waste is treated with waste, and salt mud can be recycled as gypsum, magnesium sulfate and other salts, realizing resource utilization.

[0021] The evaporation system combines the use of mechanical vapor recompression MVR technology, including: introducing the secondary steam 15 generated by the separation chamber 5 into a steam compressor, and the steam compressor increases the temperature, pressure and enthalpy of the secondary steam 15 as the heating heat source of the heating chamber 8. Based on the above technical scheme, it is beneficial to further save process energy consumption.

[0022] Before the secondary steam 15 is introduced into the steam compressor, a demister 7 is used to remove the mist entrainment in the secondary steam 15. Based on the above technical scheme, it is beneficial to improve the water quality of the secondary steam, and the safe and stable operation of the steam compressor can also be ensured, which is beneficial to reduce the impact and corrosion damage of the entrained salt water droplets on the steam pipeline and the steam compressor impeller.

[0023] 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, and the lower part is the separation chamber 5, and the integrated evaporator adopts a falling film evaporation type.

[0024] Based on the above technical scheme, the device system structure is more compact, occupies less area, and is beneficial to reduce manufacturing cost; at the same time, the liquid flow is shorter, which is beneficial to save the energy consumption of the pump in the running process, in addition, further, plug-in or multi-layer spraying liquid distribution form can be used, so that the liquid distribution effect is more uniform, the liquid film is thinner, which is beneficial to realize high vaporization rate and no dry point.

[0025] The solid content of the seed crystal suspension 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 material liquid is 3-5%.

[0026] Based on the above scheme, the influent water remains a certain calcium and magnesium and silicon content, which is beneficial to the better and lower-cost continuous operation of the seed crystal evaporation process.

[0027] The heating chamber 8 adopts a non-direct contact heat exchange form, the circulating material liquid is in the tube pass, the heating heat source is in the shell pass, and the flow rate of the material liquid in the tube pass of the heating chamber 8 is 1-3 m / s; or, the first-stage solid-liquid separator 10 adopts a cyclone form to realize continuous online solid-liquid separation operation. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A seed crystal evaporation process device provided by the embodiment of the present application is shown in the figure.

[0029] Figure 2 A structure schematic diagram of an integrated evaporator device provided by the embodiment of the present application is shown in the figure.

[0030] Figure 3 A structure schematic diagram of a settling tank provided by the embodiment of the present application is shown in the figure.

[0031] Figure 4 A seed crystal evaporation process device provided by the embodiment of the present application is shown in the figure.

[0032] In the figure: 1-seed crystal tank, 2-seed crystal feed pump, 3-evaporation feed tank, 4-evaporation feed pump, 5-separation chamber, 6-evaporation circulating pump, 7-demister, 8-heating chamber, 9-seed crystal 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 heat source inlet, 17-heating heat source outlet, 18-solid salt mud, 19-slurry outlet, 20-flow guide cylinder, 21-stirring paddle, 22-rotary sealing device, 23-evaporation circulating pipeline feed inlet, 24-first-stage solid-liquid separator upper layer feed inlet, 25-plate preheater, 26-steam compressor, 27-start-up steam, and 28-product distilled water. DETAILED DESCRIPTION

[0033] The technical scheme and device of the present application will be further described below in combination with the drawings and specific embodiments.

[0034] The conventional seed evaporation process is used to treat the polysilicon production wastewater with high calcium magnesium and high silicon content, and small size and large number of seed particles are easily produced and enter the downstream salt separation and resource utilization section, resulting in low purity of the subsequent by-product salt. Therefore, the seed evaporation process and device for resource utilization of salt-containing wastewater, especially polysilicon production wastewater with high calcium magnesium and high silicon content, are of great significance.

[0035] As Figures 1-3 shown.

[0036] A seed evaporation process device for resource utilization of polysilicon production wastewater, which can be divided into three parts, namely:

[0037] An evaporation system, the evaporation system includes 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, wherein the polysilicon production wastewater is heated and evaporated in the heating chamber 8 and the separation chamber 5;

[0038] A feeding system, the feeding system includes a seed tank 1 and an evaporation feeding tank 3, wherein the seed tank 1 is pre-prepared with seed slurry, when the seed concentration in the evaporation system is lower than the first concentration, the seed slurry is introduced into the evaporation circulation pipeline through the first pipeline, the evaporation feeding tank 3 is used to store the pretreated polysilicon production salt wastewater from the upstream, the evaporation feeding tank 3 is connected with the evaporation circulation pipeline, wherein the first concentration can be a concentration set according to the process and the type of seed;

[0039] 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 when the concentration of the feed liquid in the evaporation system reaches a predetermined concentration, the feed liquid is led out from the evaporation circulation pipeline to the first stage solid-liquid separator 10, the supernatant in the first stage solid-liquid separator 10 enters the settling tank 11, and the lower layer of thick slurry is returned to the evaporation circulation pipeline, the slurry at the bottom of the settling tank 11 is introduced into the second stage solid-liquid separator 13, the second stage solid-liquid separator 13 discharges the solid salt mud 18 from the device, and the supernatant is discharged into the crystallization feed tank 14. By setting two stages of solid-liquid separation, the scaling problem in the long-period operation of the evaporator can be effectively solved by the seed evaporation. At the same time, continuous online solid-liquid separation and recovery of the seed can be realized, and the operation cost of the seed method is reduced; the second stage solid-liquid separation can also realize the impurity removal and purification of the wastewater, and the quality of the by-product salt obtained by the resource utilization of the downstream salt separation is significantly improved. By using the seed anti-scaling principle, in the evaporation and concentration process of the salt-containing wastewater, the concentration of the scaling ions increases to supersaturation, and the small crystal grains are preferentially adsorbed on the surface of the calcium sulfate seed previously added in the system instead of the metal wall surface of the heat exchanger, thereby effectively solving the scaling problem in the long-period operation of the evaporator. The first stage solid-liquid separation device realizes continuous online solid-liquid separation and recovery of the seed by using the centrifugal separation principle, and the system does not need to continuously add fresh seed, thereby reducing the operation cost. By using the settling tank operation, the small crystal grains from the upstream are grown, and after growing, the impurities in the wastewater are removed and purified by the second stage solid-liquid separation, which is beneficial to improving the quality of the by-product salt obtained by the resource utilization of the downstream salt separation, and the solid salt mud can be recycled as gypsum, magnesium sulfate and other salts, thereby realizing resource utilization. The anti-scaling and wastewater impurity removal and purification in the overall process are realized in cooperation.

[0040] The details are as follows:

[0041] A certain concentration of seed crystal suspension is prepared in the seed tank 1, and when the concentration of seed crystals in the evaporation system is lower than the optimal concentration range during the start-up and operation of the device, it is pumped into the evaporation circulating pipeline through the seed feeding pump 2. The upstream pretreated polysilicon production wastewater is stored in the evaporation feed tank 3 and pumped into the evaporation circulating pipeline through the evaporation feed pump 4. The separation chamber 5 and the heating chamber 8 of the evaporation system are connected by the evaporation circulating pump 6 and the evaporation circulating pipeline, realizing the circulation heating of the feed wastewater in the heating chamber 8 and the separation chamber 5 and evaporation, and the generated secondary steam 15 is discharged from the upper part of the separation chamber 5 after the action of the demister 7, and after condensation treatment, it can be reused as product distilled water. The heating chamber 8 is provided with a heating heat source inlet 16 and an outlet 17 to provide the heat required for the temperature rise of the circulating feed liquid entering the heating chamber 8. After the feed liquid is evaporated and concentrated to the specified 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 circulating pump 9, and the upper clear liquid enters the settling tank 11 (as shown in Figure 3 ), and the lower thick slurry is returned to the evaporation circulating pipeline. At the same time, a pipeline directly discharging the settling tank 11 is provided in the evaporation circulating pipeline to jointly adjust and maintain the appropriate seed crystal concentration of the evaporation system. There are fine crystal particles with small particle size in the upper clear liquid, which gradually grow into salt crystal particles with large particle size under the action of the hydraulic conditions in the settling tank 11 and settle at the bottom. After the slurry pump 12 pumps the slurry at the bottom of the settling tank 11 into the second stage solid-liquid separator 13, the clear liquid after removing the salt crystal particles enters the crystallization feed tank 14 and is treated in the next process, as shown in Figure 1 . The separated solid salt mud 18 is used as a salt resource such as gypsum (calcium sulfate), magnesium sulfate, etc. or as a solid waste for external disposal. In order to quickly reduce the seed crystal concentration of the evaporation system, a pipeline from the lower thick slurry discharge pipeline of the first stage solid-liquid separator 10 before 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, or an integrated structure, which couples the separation chamber 5 and the heating chamber 8 into an integrated evaporator, the upper part is the heating chamber 8, and the lower part is the separation chamber 5, which adopts a falling film evaporation type, and the secondary steam 15 is treated by the demister 7 before being discharged from the separation chamber 5. Figure 1 Figure 2

[0042] In specific implementation, the added seed crystal is anhydrous calcium sulfate, calcium sulfate dihydrate, or desulfurization gypsum from power plants with qualified and standard heavy metal content, which is waste treatment with waste. The polysilicon production wastewater can be preheated by the heat released after the heating heat source before being pumped into the evaporation circulating pipeline by the evaporation feed pump 4. More preferably, if the heating heat source is steam, the high-temperature steam condensate after heat release is used to preheat the feed wastewater from room temperature to about 95°C. The waste heat of the high-temperature steam condensate is fully utilized to improve the thermal efficiency of the evaporation system and save energy and reduce carbon.

[0043] ​​During the operation of the device, the circulating liquid can also be used as a crystal seed preparation liquid to prepare a crystal seed suspension liquid with a solid content of 5-8% in the crystal seed tank 1. After being fully stirred and uniformly distributed by the built-in stirrer, the crystal seed suspension liquid is pumped back to the evaporation circulation pipeline through the crystal seed feed pump 2. In some embodiments, the circulating liquid can be directly introduced into the crystal seed tank 1 through the first pipeline; or a pipeline, i.e., the second pipeline, can be introduced from the evaporation circulation pipeline to introduce the circulating liquid into the crystal seed tank 1.

[0044] During the start-up and commissioning of the device, the production water or the feed salt-containing wastewater can also be used as a crystal seed preparation liquid. The introduction of the system crystal seed and the control of the reasonable concentration are beneficial to the increase of the concentration of the scale-forming ions to supersaturation during the evaporation and concentration of the salt-containing wastewater, and the preferential adsorption of the tiny crystal grains on the surface of the pre-added calcium sulfate crystal seed in the system rather than the metal wall surface of the heat exchanger, thereby effectively solving the scaling problem in the long-term operation of the evaporator. The present application can process polysilicon production wastewater with high calcium and magnesium content and high silicon content. After pretreatment, the polysilicon production wastewater does not need to reach the stringent residual calcium and magnesium and silicon content indicators (hardness < 50 mg / L, silicon < 20 mg / L), and the inlet water is left with a certain amount of calcium and magnesium and silicon content, for example, the calcium and magnesium content can be greater than or equal to a first indicator, and the silicon content can be greater than or equal to a second indicator, which is beneficial to the better and lower-cost continuous operation of the crystal seed evaporation process. Only during the start-up of the device system, fresh crystal seeds need to be added, and the new crystal seeds generated during the process will continuously supplement the lost crystal seeds to achieve balance in the system. The first indicator and the second indicator can be set according to the specific process and wastewater.

[0045] In specific implementation, the evaporation system combines the use of mechanical vapor recompression (MVR) technology, which further saves process energy consumption. That is, the secondary steam 15 generated in the separation chamber 5 enters the steam compressor, which increases the temperature, pressure and enthalpy of the secondary steam 15 to serve as a heating heat source of the heating chamber 8, and the secondary steam 15 enters from the heating heat source inlet 16, is condensed into distillate after heat release, and is discharged from the heating heat source outlet 17 to be reused as product water.

[0046] In specific implementation, a demister 7 is arranged before the secondary steam enters the steam compressor to remove the mist entrainment of the secondary steam, improve the product water quality, and ensure the safe and stable operation of the steam compressor during the process, so that the impact and corrosion damage of the salt water droplets on the steam pipeline and the impeller of the steam compressor will not occur. Further preferably, the high-temperature distillate at the heating heat source outlet can be used to preheat the feed wastewater, and itself is reduced to normal temperature to be reused as water. The feed wastewater preheated to 90-95°C can be pumped into the evaporation circulation pipeline after being subjected to an oxygen removal and degassing device. The dissolved oxygen and non-condensable gas in the wastewater are removed by using the thermal method to slow down the corrosion phenomenon of the system equipment and enhance the heat exchange performance of the system equipment.

[0047] Further, the liquid distribution form of plug-in or multi-layer spraying is adopted, so that the liquid distribution effect is more uniform, the liquid film is thinner, the vaporization rate is high, and there is no dry point. The integrated evaporator organically combines the heating chamber 8 and the separation chamber 5, so that the device structure is more compact and the floor area is smaller. The integrated evaporator couples the heating chamber and the separation chamber in one device, so that the device system structure is more compact, the floor area is smaller, and the manufacturing cost is reduced. The liquid flow is shorter, and the energy consumption of the pump during operation is saved. The heating heat source can be selected from waste heat resources such as by-product low-pressure steam or low-temperature flue gas, or can be secondary steam from a certain section. The heating chamber 8 adopts a non-direct contact heat exchange form, such as a tube-shell heat exchanger. The waste water and liquid pass through the tube, and the heating heat source passes through the shell. The liquid with entrained seed crystals passes through the heating chamber tube at a high flow rate, and the flow rate is 1-3 m / s. The high flow rate scouring effect also plays a certain degree of scale inhibition effect on the heat exchange tube. The seed crystal solid content in the evaporation circulating pipeline is controlled at 3-5%. When the seed crystal concentration is too low, there are not enough seed crystal surfaces in the liquid to adsorb newly generated small salt scale crystals, which affects the scale prevention effect of the seed crystal method. When the seed crystal concentration is too high, the viscosity of the liquid increases, the flowability becomes poor, and the process heat efficiency of the liquid heating and evaporation to generate secondary steam is affected. At the same time, it also increases the risk of blockage of the salt discharge pipeline, the secondary steam pipeline and the demister. The first-stage solid-liquid separator adopts a cyclone form, which can realize continuous online solid-liquid separation operation. The dilute phase clear liquid is discharged from the upper layer, and the concentrated phase slurry is discharged from the lower layer and returned to the evaporation circulating pipeline to maintain the appropriate seed crystal concentration of the evaporation system. More preferably, when the seed crystal concentration of the evaporation system is high (5-7%), a direct downstream pipeline is provided on the circulating pipeline for reducing the seed crystal concentration. When the seed crystal concentration of the evaporation system is very high (7-10%), a direct downstream pipeline is provided on the concentrated phase slurry pipeline of the lower layer of the cyclone for reducing the seed crystal concentration. The dilute phase clear liquid discharged from the first-stage solid-liquid separator 10 enters the settling tank 11 for seed crystal growth. According to the centrifugal separation principle of the cyclone, the upper layer dilute phase clear liquid entrains small-sized (<50 μm) seed crystal particles. These salt crystal particles enter the downstream crystallization section, which affects the purity of the by-product salt produced by the salt separation and crystallization process. And the particle size is too small to be removed from the system by conventional solid-liquid separation methods. The settling tank 11 is provided to provide the hydraulic conditions for the growth of the seed crystal particle size. The salt crystal particles stay in the settling tank 11 for 1-2 h, the particle size slowly grows (>100 μm) and is deposited at the bottom, and is pumped out by the slurry pump 12. The concentrated phase slurry of the lower layer of the first-stage solid-liquid separator 10 is returned to the evaporation circulating pipeline to maintain the seed crystal concentration balance of the evaporation system. If the system seed crystal concentration rises too fast and exceeds the appropriate concentration range, a concentrated phase slurry discharge pipeline is provided on the lower layer of the cyclone, which is connected to the pipeline before the downstream slurry pump 12, to adjust the system seed crystal concentration to be quickly and stably within the optimal concentration range.The settling tank 11 adopts a type with a draft tube 20 and a stirring paddle 21. The evaporation circulating pipeline is connected to the inlet 23. The first-stage solid-liquid separator is connected to the inlet 24. The upstream liquid enters the draft tube 20. Under the control of the stirring paddle 21, the liquid with small salt particles flows upwards along the draft tube 20, and then flows downwards along the wall of the settling tank 11 after reaching the top of the settling tank 11. During the flowing process, the fine crystals gradually grow, and the particle size increases from less than 50 μm to more than 100 μm. The salt particles with large particle size fall to the conical bottom of the settling tank 11 under the action of gravity and are discharged from the bottom paddle outlet 19. The settling tank is provided with a draft tube and a stirrer to create a specific flow field of the wastewater in the settling tank, which is beneficial to the growth and agglomeration of the small particles and the sinking of the particles, and finally beneficial to the second-stage solid-liquid separation device system to discharge and recycle the crystals other than the seed crystals. At the same time, it is beneficial to the purification of the water quality entering the downstream salt separation and crystallization system and the recycling of the by-product salt with higher quality. The second-stage solid-liquid separator 13 adopts a plate-and-frame filter, a rotary disc filter or a ceramic membrane filter. When the plate-and-frame filter is used, a high-temperature-resistant filter plate material is selected. The upstream slurry pump 12 is connected to the inlet of the second-stage solid-liquid separator 13. The clear liquid is discharged to the crystallization feed tank 14. The content of the suspended solids in the crystallization feed liquid is not more than 5 mg / L. The solid residue mainly contains calcium sulfate, magnesium sulfate and a small amount of calcium carbonate, magnesium carbonate, magnesium hydroxide, colloidal silicon and silicate, which can be used as a salt resource such as gypsum and magnesium sulfate or as a solid waste for external disposal. The second-stage solid-liquid separator is mainly used to realize the continuous online solid-liquid separation of the high-temperature liquid.

[0048] Example 1.

[0049] A certain polysilicon enterprise adopts a wastewater zero discharge and resource disposal process for the salt-containing wastewater discharged from the whole plant. The salt-containing wastewater evaporation and concentration section adopts a seed evaporation process suitable for resource disposal as shown in Figure 4 The upstream salt-containing wastewater after pretreatment has a total dissolved solids (TDS) content of 30,000-45,000 mg / L, a calcium ion content of 3,000-5,000 mg / L, a magnesium ion content of 100-200 mg / L, a soluble silicon dioxide content of 50-150 mg / L, a sulfate radical content of 1,000-2,000 mg / L and a chloride ion content of 15,000-30,000 mg / L.

[0050] When the device system is started, the heating heat source is started by using the in-plant reduced-pressure steam as the starting steam 27. The seed crystal is prepared in the seed tank 1 by using the production water to prepare a slurry with a solid content of 8%. The seed crystal is selected from industrial-grade anhydrous calcium sulfate. The seed crystal is pumped into the evaporation circulating pipeline through the seed crystal feed pump 2, so that the solid content of the seed crystal is controlled at about 3%.

[0051] During normal operation, the heating heat source uses secondary steam after being heated, pressurized and increased in enthalpy by the steam compressor 26. The prepared liquid required for seed addition uses the incoming liquid of the evaporation circulating pipeline. The feed containing salt wastewater is stored in the evaporation feed tank 3, pumped into the plate preheater 25 by the evaporation feed pump 4, preheated to 90-95°C, and then enters the evaporation circulating pipeline. After being mixed with the circulating liquid, under the action of the evaporation circulating pump 6, the two operate together as liquid circulating operation. The circulating liquid is heated and warmed by the falling-film heating chamber 8, and then falls into the lower separation chamber 5 under the action of gravity. The secondary steam 15 after being removed from the entrained liquid droplets by the circumferential top mist eliminator 7 enters the steam compressor 26. The consumption of electric power makes the secondary steam heated, pressurized and increased in enthalpy, and enters the heating chamber 8 from the inlet 16 as a heating heat source. After heat exchange with the liquid in the pipe, the heating heat source is condensed into liquid 95-100°C from the heating heat source outlet 17, and then enters the plate preheater 25 to preheat the feed liquid. After the temperature of the heating heat source is reduced to about 25-30°C, the product distilled water 28 is transported to the outside of the system for reuse.

[0052] When the concentration of the evaporation circulating liquid reaches the design concentration factor, a pipeline is drawn from the liquid circulating pipeline, and the circulating liquid is pumped into the first-stage solid-liquid separator 10, cyclone, by the seed circulating pump 9. Under the action of centrifugal force, the upper layer is clear liquid with low solid content, which is discharged into the settling tank 11; the lower layer is slurry with high solid content, which is returned to the evaporation circulating pipeline. Through the seed circulating recovery operation, only fresh seed needs to be added when the device is started. During normal operation, no seed needs to be added to maintain the solid content of the seed in the evaporation system at about 3%. When the water quality of the upstream incoming water fluctuates greatly, the seed can also be added synchronously during operation to maintain the solid content of the seed in the evaporation system at 3-5% to ensure the normal operation of the seed evaporation process.

[0053] For the high-calcium-magnesium and high-silicon content polysilicon production wastewater in this embodiment, more small crystals will be produced during the seed evaporation process. These small crystals (<50 μm) are difficult to completely separate in the first-stage solid-liquid separator 10 and are discharged from the upper clear liquid into the settling tank 11 together with the liquid (see Figure 3 ). The liquid flows into the flow guide cylinder 20 from the bottom inlet 24 of the settling tank 11, and the fine crystals are driven upward along the flow guide cylinder by the stirring paddle 21, and then downward along the wall of the settling tank after reaching the top of the settling tank. During the operation of the fluid, the fine crystals continuously coalesce and grow, and the particle size gradually increases to more than 100 μm. Finally, the fine crystals are settled in the conical bottom. The slurry is discharged from the conical bottom outlet 19, pumped into the second-stage solid-liquid separator 13, plate-and-frame filter press, by the slurry pump 12. The slurry liquid enters the plate-and-frame filter press, and the solid crystal particles are intercepted by the filter cloth. The filtrate is discharged from the pipeline, enters the crystallization feed tank 14, and the suspended solids content of the filtrate is less than 5 mg / L, the TDS content is 180000-200000 mg / L, and the temperature is 80-90°C. The filter plate of the plate-and-frame filter press is made of high-temperature resistant material and does not deform during long-period operation.

[0054] 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 introduced from the circulating pipeline to directly discharge the circulating feed liquid to the bottom inlet 23 of the sedimentation tank 11, or a pipeline can be introduced from the lower layer of the cyclone to the inlet pipeline of the slurry pump 12, to accelerate the adjustment of the seed crystal concentration in the system.

[0055] Finally, the seed crystal concentration in the system is within the optimal concentration range of 3-5%, the scaling phenomenon of the evaporation system including the heating chamber 8, the separation chamber 5 and the supporting pipeline is reduced, the evaporation system as a whole maintains high thermal efficiency operation, and the device inspection and maintenance cycle is extended to 10-12 months. At the same time, a salt separation crystallization process is used downstream of the process, and the obtained sodium chloride by-product salt has high purity (>98.5%), reaching the first-class standard of industrial-grade salt, and can be recycled for use in the chlor-alkali industry. The solid salt mud 18 obtained after being treated by the second-stage solid-liquid separator 13 can be used as high-quality gypsum salt for resource utilization.

[0056] Example 2.

[0057] The salt-containing wastewater discharged by a polysilicon production plant is treated by the seed crystal evaporation process and device of the present application, the TDS content of the feed wastewater is 25,000-30,000 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 13,000-16,000 mg / L.

[0058] The device system is that the evaporation feed tank is connected to the inlet of the evaporation feed pump by a pipeline, the outlet of the feed pump is connected to the cold feed inlet of the plate preheater by a pipeline, the cold feed outlet is connected to the inlet circulating pipeline of the circulating pump by a pipeline. The seed crystal tank is connected to the inlet of the seed crystal feed pump by a pipeline, the outlet of the seed crystal feed pump is connected to the inlet circulating pipeline of the circulating pump by a pipeline. The outlet circulating pipeline of the circulating pump is connected to the top of the falling film heating chamber, the feed liquid falls into the lower separation chamber after passing through the falling film tube, and is then collected at the bottom and connected to the inlet of the circulating pump by a pipeline. The top of the separation chamber is connected to the inlet of the steam compressor by a pipeline, the outlet of the steam compressor is connected to the heating heat source inlet of the heater by a pipeline, the heating heat source outlet of the heating chamber is connected to the hot feed inlet of the plate preheater by a pipeline, and the hot feed outlet discharges the distilled liquid that has been reduced to room temperature. At the same time, a start-up steam pipeline is connected to the heating heat source inlet pipeline of the heating chamber.

[0059] The outlet circulation pipeline of the circulating pump is connected with a pipeline connected with the inlet of the seed circulating pump, the outlet of the seed circulating pump is connected with the inlet of the first stage solid-liquid separator (cyclone) through a pipeline, the upper outlet is connected with the inlet of the settling tank through a pipeline, and the bottom outlet is connected with the inlet of the circulating pump circulation pipeline through a pipeline. The outlet circulation pipeline of the circulating pump is connected with a pipeline directly connected with the inlet of the settling tank. The bottom outlet of the settling tank is connected with the inlet of the slurry pump through a pipeline, and the bottom outlet discharge pipeline of the first stage solid-liquid separator is connected with the inlet pipeline of the slurry pump. The outlet of the slurry pump is connected with the inlet of the second stage solid-liquid separator (ceramic membrane filter) through a pipeline, and the outlet is connected with the inlet of the crystallization feed tank through a pipeline.

[0060] After the above device is processed, the whole evaporation and concentration process of the salt-containing wastewater is kept in high thermal efficiency operation, and the energy consumption per ton of water treatment is about 25-35 kWh. The inspection and maintenance period of the device is extended to more than half a year. During the inspection and maintenance period, no serious scaling and corrosion phenomenon is found in the evaporation system including the heat exchange equipment. After being treated by the downstream salt separation and crystallization process, the by-product salt of sodium chloride has high purity (more than 99%), which reaches the first level standard of industrial salt and can be recycled for use in the chlor-alkali industry.

[0061] The part of the present application not involved is the same as the prior art or can be realized by using the prior art.

Claims

1. A seed evaporation process device for polycrystalline silicon production wastewater resource disposal, characterized in that, The process device comprises: an evaporation system, which comprises a separation chamber (5) and a heating chamber (8), and the separation chamber (5) and the heating chamber (8) are connected through an evaporation circulating pipeline, wherein the polysilicon production wastewater is heated and evaporated in the heating chamber (8) and the separation chamber (5); a feeding system, which comprises a seed tank (1) and an evaporation feeding tank (3), wherein the seed tank (1) is previously prepared with a seed slurry, and when the seed concentration in the evaporation system is lower than a first concentration, the seed slurry is introduced into the evaporation circulating pipeline through a first pipeline, and the evaporation feeding tank (3) is used for storing the pretreated polysilicon production wastewater from upstream, and the evaporation feeding tank (3) is connected with the evaporation circulating pipeline; a solid-liquid separation system, which comprises a first-stage solid-liquid separator (10), a settling tank (11), and a second-stage solid-liquid separator (13), wherein when the concentration of the feed liquid in the evaporation system reaches a predetermined concentration, the feed liquid is introduced from the evaporation circulating pipeline into the first-stage solid-liquid separator (10), the supernatant in the first-stage solid-liquid separator (10) enters the settling tank (11), and the lower thick slurry is returned to the evaporation circulating pipeline, the slurry at the bottom of the settling tank (11) is introduced into the second-stage solid-liquid separator (13), the second-stage solid-liquid separator (13) discharges solid salt mud (18) and discharges the supernatant into a crystallization feeding tank (14); the heating chamber (8) is provided with a heating heat source inlet (16) for entering the heating chamber (8), and the heating heat source is discharged from an outlet (17) after heat release; the polysilicon production wastewater is preheated by the heating heat source discharged from the outlet (17) before entering the evaporation circulating pipeline; the evaporation circulating pipeline is connected with the seed tank (1) through a second pipeline, so as to introduce the circulating feed liquid as a seed preparation liquid into the seed tank (1); the solid content of the seed slurry is 5-8%, or the solid content of the circulating feed liquid is 3-5%.

2. The process apparatus of claim 1, wherein, The settling tank (11) comprises a draft tube (20) and an agitator (21), the feed liquid from the evaporation circulating pipeline enters the draft tube (20) from an evaporation circulating pipeline feed liquid inlet (23), the supernatant from the first-stage solid-liquid separator enters the draft tube (20) from a first-stage solid-liquid separator supernatant inlet (24), and the agitator (21) is used for speed-controlled stirring and makes the feed liquid carrying small salt particles flow upwards along the draft tube (20) and then flow downwards along the tank wall after flowing to the top of the settling tank (11).

3. Process arrangement according to claim 1 or 2, characterized in that The first-stage solid-liquid separator (10) is connected with the second-stage solid-liquid separator (13), so as to directly discharge the lower thick slurry in the first-stage solid-liquid separator (10) into the second-stage solid-liquid separator (13).

4. The process apparatus according to claim 1 or 2, characterized in that The polysilicon production wastewater is heated in the heating chamber (8) and the separation chamber (5), and the generated secondary steam (15) is discharged after being treated by the demister (7), and the discharged secondary steam (15) is reused as product distilled water after condensation treatment.

5. The process apparatus according to claim 1 or 2, characterized in that The seed tank (1) uses one or more of anhydrous calcium sulfate, calcium sulfate dihydrate, and desulfurization gypsum from a power plant with qualified heavy metal content to prepare the seed slurry.

6. The process apparatus of claim 4, wherein, The evaporation system combines the use of mechanical vapor recompression (MVR) technology, which includes introducing the secondary steam (15) generated by the separation chamber (5) into a steam compressor, and the steam compressor increases the temperature, pressure, and enthalpy of the secondary steam (15) to serve as the heating source for the heating chamber (8).

7. The process apparatus of claim 6, wherein, Before the secondary steam (15) is introduced into the steam compressor, a demister (7) is used to remove mist entrainment in the secondary steam (15).

8. The process apparatus according to claim 1 or 2, characterized in that 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.

9. The process apparatus according to claim 1 or 2, characterized in that The heating chamber (8) adopts a non-direct contact heat exchange form, the circulating feed liquid flows in the tube, the heating source flows in the shell, and the flow rate of the feed liquid in the tube of the heating chamber (8) is 1-3 m / s; alternatively, the first stage solid-liquid separator (10) adopts a cyclone form to realize continuous online solid-liquid separation operation. The heating chamber (8) adopts a non-direct contact heat exchange form, the circulating feed liquid flows in the tube, the heating source flows in the shell, and the flow rate of the feed liquid in the tube of the heating chamber (8) is 1-3 m / s; alternatively, the first stage solid-liquid separator (10) adopts a cyclone form to realize continuous online solid-liquid separation operation.

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