Water resource recycling process for sewage treatment process in polycrystalline silicon industry

Abstract

The invention provides a sewage treatment process and a water resource recycling process in the polycrystalline silicon industry, aiming at effectively treating high-salinity wastewater. The process comprises the following steps: removing suspended solids and large-particle impurities in the wastewater through pretreatment equipment; preheating through a multi-stage preheater; concentrating the high-salinity wastewater through an MVR (mechanical vapor recompression) evaporation system; the wastewater reversely flows into a multi-effect evaporator; the high-salinity wastewater is concentrated and then enters a crystallization slicing machine, and calcium chloride crystals are obtained. A multi-stage preheater is used in the preheating stage, and preheating heat sources comprise dead steam condensate water and live steam condensate water. The dead steam condensate water is obtained by condensing secondary steam generated by the first-effect evaporator and dead steam generated by the third-effect evaporator; and the live steam condensate water comes from condensate water generated by the first-effect evaporator and the second-effect evaporator. According to the process, heat energy of dead steam and condensate water is fully utilized, energy consumption is remarkably reduced, the cyclic utilization rate of water resources is increased, and high economic and environment-friendly benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of polysilicon, in particular to the technical field of polysilicon high-salt wastewater treatment, and in particular to a water resource recycling process for wastewater treatment in the polysilicon industry. Background Art

[0002] With the rapid development of the polysilicon industry, the high-concentration wastewater generated during the production process contains a large amount of organic matter and inorganic salts, which is difficult to treat and consumes a lot of energy. Existing wastewater treatment technologies, such as mechanical vapor recompression (MVR) and multiple-effect evaporation processes, can solve the wastewater treatment problem to a certain extent, but they are still insufficient in terms of heat recovery and water resource reuse. Therefore, how to efficiently recover heat energy and realize the recycling of water resources has become an urgent problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to provide an efficient wastewater treatment process for the polysilicon industry, which can significantly improve the energy efficiency and water resource utilization rate of the system by improving the heat recovery of exhaust steam and the reuse of condensed water, and realize the efficient recovery and reuse of water resources. The following technical solutions are adopted:

[0004] A water resource recycling process for wastewater treatment in the polysilicon industry, wherein the wastewater is high-salt wastewater, comprises the following steps:

[0005] S1, pretreatment, high-salinity wastewater passes through a pretreatment device, which is used to remove suspended matter and large particle impurities;

[0006] S2, preheating, the pretreated high-salinity wastewater is preheated by a multi-stage preheater;

[0007] S3, MVR concentration, the preheated high-salt wastewater is concentrated through the MVR evaporation system;

[0008] S4, multi-effect evaporation concentration, the high-salt wastewater after MVR concentration countercurrently enters the multi-effect evaporator, the multi-effect evaporator is a three-effect evaporator, a two-effect evaporator, and a first-effect evaporator connected in sequence, the first-effect evaporator and the two-effect evaporator both use raw steam to provide heat, and the three-effect evaporator uses secondary steam generated by the two-effect evaporator to provide heat;

[0009] S5, cooling and slicing, when the concentration of the high-salt wastewater after countercurrent triple-effect evaporation reaches the required level, it enters the crystallization slicer, and the calcium chloride in the high-salt wastewater is cooled, crystallized and sliced ​​out by the crystallization slicer to obtain calcium chloride crystals;

[0010] Among them, the heat source of the multi-stage preheater in step S2 includes exhaust steam condensate and live steam condensate. The exhaust steam condensate is produced by condensing the secondary steam generated by the first-effect evaporator and the exhaust steam generated by the three-effect evaporator in step S4, and the live steam condensate is the condensate generated by the first-effect evaporator and the second-effect evaporator in step S4.

[0011] Furthermore, the present invention further comprises the following steps:

[0012] S6, the secondary steam generated by the first-effect evaporator and the exhaust steam generated by the three-effect evaporator in step S4 are condensed in exhaust steam condensers to obtain exhaust steam condensed water, the condensed water is collected in an exhaust steam condensed water tank and pumped into a multi-stage preheater for heat exchange with high-salt wastewater, and the exhaust steam condensed water after heat exchange is returned to the reclaimed water reuse pool.

[0013] Furthermore, the pretreatment equipment in step S1 is a multi-media filter.

[0014] Furthermore, the MVR evaporation system in step S3 includes an MVR evaporation concentrator and an MVR steam compressor. The MVR evaporation concentrator is used to evaporate and concentrate the high-salt wastewater, and the MVR steam compressor is used to compress and heat the exhaust steam generated by the MVR evaporation concentrator so that it can be reused in the MVR evaporation concentrator.

[0015] Furthermore, the exhaust steam condensate produced by the MVR evaporation concentrator is collected in an exhaust steam condensate tank.

[0016] Furthermore, the raw steam used in the first-effect evaporator in step S4 is saturated steam of 1.0 MPa.

[0017] Furthermore, the raw steam used in the second-effect evaporator in step S4 is saturated steam of 0.2 MPa.

[0018] Furthermore, the present invention further comprises the following steps:

[0019] S7, collecting the raw steam condensate produced by the first-effect evaporator and the second-effect evaporator in step S4 into a raw steam condensate tank and pumping it into a multi-stage preheater for heat exchange with high-salt wastewater, and transporting the raw steam condensate after heat exchange to an outside area for reuse.

[0020] The beneficial effects of the present invention include at least one of the following:

[0021] The present invention combines the triple-effect evaporator with the MVR system to fully utilize the waste heat of secondary steam and exhaust steam, greatly reducing the demand for external energy, improving the overall thermal efficiency of the system, and significantly reducing energy consumption and operating costs.

[0022] Through the multi-stage preheater system and the effective use of exhaust steam and live steam condensate, the present invention significantly improves the wastewater reuse efficiency. The condensate after condensation and preheating can be recycled in the process flow, reducing the use of fresh water and achieving efficient reuse of water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] Reference Figure 1 This embodiment proposes a water resource reuse process for a wastewater treatment process in the polysilicon industry, wherein the wastewater is high-salt wastewater, and includes the following steps:

[0027] S1, preprocessing

[0028] High-salinity wastewater first enters the pretreatment equipment for preliminary treatment. The pretreatment equipment is a multi-media filter that is used to remove suspended matter and large particle impurities in the wastewater to ensure the smooth progress of subsequent treatment processes.

[0029] S2, preheating

[0030] The high-salinity wastewater after pretreatment enters the multi-stage preheater for preheating. The heat source of the multi-stage preheater consists of the following two parts:

[0031] Exhaust steam condensate: comes from the exhaust steam condensate transfer tank, which collects the MVR exhaust steam condensate, the secondary steam condensate of the first-effect evaporator, the secondary steam condensate of the second-effect evaporator and the exhaust steam condensate of the third-effect evaporator.

[0032] Raw steam condensate: comes from the raw steam condensate transfer tank, which collects the raw steam condensate in the first-effect evaporator and the second-effect evaporator.

[0033] These condensates are pumped into the multi-stage preheater to exchange heat with the high-salinity wastewater. Through the waste heat preheating of the exhaust steam condensate and the live steam condensate, the temperature of the high-salinity wastewater is gradually increased, creating suitable temperature conditions for the subsequent MVR concentration and three-effect evaporation concentration processes.

[0034] S3, MVR Concentrate

[0035] The preheated high-salinity wastewater is transported to the MVR evaporation concentrator, which evaporates and concentrates the wastewater through a mechanical vapor recompression system.

[0036] The MVR evaporation system is equipped with an MVR steam compressor, which is used to compress and heat the exhaust steam generated by the MVR evaporation concentrator so that it can be reused in the MVR evaporation concentrator to further improve the evaporation efficiency and save energy.

[0037] After the exhaust steam generated from the MVR evaporation concentrator is condensed, the exhaust steam condensate is transported to the exhaust steam condensate transfer tank.

[0038] S4, multi-effect evaporation concentration:

[0039] The high-salt wastewater concentrated by MVR flows countercurrently into the multi-effect evaporator, which consists of a three-effect evaporator, a two-effect evaporator and a first-effect evaporator connected in sequence:

[0040] First-effect evaporator: uses 1.0MPa saturated steam to provide heat, the raw steam condensate generated is sent to the raw steam condensate transfer tank, and the secondary steam generated enters the first-effect exhaust steam condenser;

[0041] Second-effect evaporator: uses 0.2MPa saturated steam to provide heat, the raw steam condensate generated is sent to the raw steam condensate transfer tank, and the secondary steam generated enters the third-effect evaporator;

[0042] Three-effect evaporator: The secondary steam generated by the two-effect evaporator is used to provide heat. The exhaust steam generated enters the three-effect exhaust steam condenser, and the exhaust steam condensate generated is sent to the raw steam condensate transfer tank.

[0043] S5, cooling and tableting:

[0044] After triple-effect evaporation, the concentration of calcium chloride in the high-salinity wastewater reaches more than 60%. At this time, the concentrated wastewater is transported to a crystal slicer, where the wastewater is cooled, and the calcium chloride is crystallized and sliced ​​to form a solid calcium chloride crystal product.

[0045] S6, exhaust steam condensate treatment:

[0046] The exhaust steam generated by the first-effect evaporator and the third-effect evaporator is condensed by the exhaust steam condenser, and the exhaust steam condensed water formed is collected in the exhaust steam condensed water transfer tank.

[0047] The exhaust steam condensate is pumped to the multi-stage preheater to exchange heat with the high-salt wastewater in the preheating stage. After the heat exchange, the exhaust steam condensate is sent back to the reclaimed water pool and recycled as process water.

[0048] S7, Steam condensate treatment:

[0049] The raw steam used in the first-effect evaporator and the second-effect evaporator forms raw steam condensate during the condensation process, and the condensate is collected in a raw steam condensate transfer tank.

[0050] The collected raw steam condensate is pumped to a multi-stage preheater for heat exchange with the high-salt wastewater in the preheating stage. The raw steam condensate after heat exchange is transported to the outside through a pipeline for reuse.

[0051] Through the above process, calcium chloride in high-salt wastewater in the polysilicon industry can be effectively concentrated and crystallized, and wastewater can be recycled by reusing exhaust steam and live steam condensate. The entire process has high thermal efficiency and low energy consumption, which reduces the demand for fresh water resources and reduces environmental pollution load, with significant economic and environmental benefits.

Claims

1. A water resource reuse process for wastewater treatment in the polysilicon industry, wherein the wastewater is high-salt wastewater, characterized in that: The following steps are involved: S1, pretreatment, high-salinity wastewater passes through a pretreatment device, which is used to remove suspended matter and large particle impurities; S2, preheating, the pretreated high-salinity wastewater is preheated by a multi-stage preheater; S3, MVR concentration, the preheated high-salt wastewater is concentrated through the MVR evaporation system; S4, multi-effect evaporation concentration, the high-salt wastewater after MVR concentration countercurrently enters the multi-effect evaporator, the multi-effect evaporator is a three-effect evaporator, a two-effect evaporator, and a first-effect evaporator connected in sequence, the first-effect evaporator and the two-effect evaporator both use raw steam to provide heat, and the three-effect evaporator uses secondary steam generated by the two-effect evaporator to provide heat; S5, cooling and slicing, when the concentration of the high-salt wastewater after multi-effect evaporation reaches the required level, it enters the crystallization slicer, and the calcium chloride in the high-salt wastewater is cooled, crystallized and sliced ​​out by the crystallization slicer to obtain calcium chloride crystals; Among them, the heat source of the multi-stage preheater in step S2 includes exhaust steam condensate and live steam condensate. The exhaust steam condensate is produced by condensing the secondary steam generated by the first-effect evaporator and the exhaust steam generated by the three-effect evaporator in step S4, and the live steam condensate is the condensate generated by the first-effect evaporator and the second-effect evaporator in step S4.

2. The water resource reuse process of a wastewater treatment process in the polysilicon industry according to claim 1, characterized in that: The following steps are also included: S6, the secondary steam generated by the first-effect evaporator and the exhaust steam generated by the three-effect evaporator in step S4 are condensed in exhaust steam condensers to obtain exhaust steam condensed water, the condensed water is collected in an exhaust steam condensed water tank and pumped into a multi-stage preheater for heat exchange with high-salt wastewater, and the exhaust steam condensed water after heat exchange is returned to the reclaimed water reuse pool.

3. The water resource reuse process of a wastewater treatment process in the polysilicon industry according to claim 1, characterized in that: The pretreatment equipment in step S1 is a multi-media filter.

4. The water resource reuse process for wastewater treatment in the polysilicon industry according to claim 2, characterized in that: In step S3, the MVR evaporation system includes an MVR evaporation concentrator and an MVR steam compressor. The MVR evaporation concentrator is used to evaporate and concentrate high-salt wastewater, and the MVR steam compressor is used to compress and heat the exhaust steam generated by the MVR evaporation concentrator so that it is reused in the MVR evaporation concentrator to obtain MVR exhaust steam condensate.

5. A water resource reuse process for wastewater treatment in the polysilicon industry according to claim 4, characterized in that: The MVR exhaust steam condensate can be collected in an exhaust steam condensate water transfer tank.

6. The water resource reuse process for wastewater treatment in the polysilicon industry according to claim 1, characterized in that: The raw steam used by the first-effect evaporator in step S4 is saturated steam of 1.0 MPa.

7. The water resource reuse process for wastewater treatment in the polysilicon industry according to claim 1, characterized in that: The raw steam used by the second-effect evaporator in step S4 is saturated steam of 0.2 MPa.

8. The water resource reuse process for wastewater treatment in the polysilicon industry according to claim 2, characterized in that: The following steps are also included: S7, collecting the raw steam condensate produced by the first-effect evaporator and the second-effect evaporator in step S4 into a raw steam condensate tank and pumping it into a multi-stage preheater for heat exchange with high-salt wastewater, and the raw steam condensate after heat exchange is transported to the outside for reuse.

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