Mixed salt recovery system in wastewater treatment process

Abstract

The utility model discloses a mixed salt recovery system in a wastewater treatment process. The mixed salt recovery system comprises a nanofiltration salt separation device, a sodium chloride falling film concentrator, a sodium chloride evaporative crystallization device, a sodium sulfate falling film concentrator, a sodium sulfate evaporative crystallization device, a sodium sulfate freezing crystallizer and a mixed salt treatment unit. The connecting structure has the advantages that the connecting structure is simple and easy to implement, and the resource utilization rate is increased; meanwhile, separation of sodium chloride and sodium sulfate is achieved on the premise that mixed salt is not separated through a nanofiltration salt separation device, the service life of the nanofiltration salt separation device is prolonged, long-term stable operation of the system is guaranteed, and economic burdens of enterprises are reduced.

Description

Technical field:

[0001] The utility model relates to the technical field of wastewater treatment, in particular to a mixed salt recovery system in a wastewater treatment process. Background technology:

[0002] In order to reduce the output of impure salts in conventional wastewater treatment systems, a mixed salt evaporation device is usually installed after the sodium chloride evaporation crystallization device and the sodium sulfate evaporation crystallization device. The mother liquor after evaporation and crystallization of the sodium chloride evaporation crystallization device and the sodium sulfate evaporation crystallization device is sent to the mixed salt evaporation device for evaporation and crystallization to recover the sodium sulfate and sodium chloride that have not evaporated in the mother liquor. The mixed salt evaporated from the mixed salt evaporation device will return to the front end of the nanofiltration salt separation device, and the sodium chloride and sodium sulfate will be separated again by the nanofiltration salt separation device and then evaporated and crystallized and recovered by the sodium chloride evaporation crystallization device and the sodium sulfate evaporation crystallization device respectively to improve the resource utilization rate. However, in the actual operation of the system, the amount of mixed salt recovered will be relatively large, which greatly increases the cleaning frequency and pressure of the nanofiltration salt separation device, and ultimately causes the service life of the nanofiltration salt separation device to be far less than the designed life, increasing the burden on the enterprise. Utility model content:

[0003] The utility model aims to provide a mixed salt recovery system in a wastewater treatment process, which has a simple connection structure, improves resource utilization, and prolongs the service life of a nanofiltration salt separation device.

[0004] The utility model is implemented by the following technical scheme: The purpose of this patent is to provide a mixed salt recovery system in a wastewater treatment process, which includes a nanofiltration salt separation device, a sodium chloride falling film concentrator, a sodium chloride evaporation crystallization device, a sodium sulfate falling film concentrator, a sodium sulfate evaporation crystallization device, a sodium sulfate freezing crystallizer and a mixed salt treatment unit; the water production outlet of the nanofiltration salt separation device is connected to the liquid inlet of the sodium chloride falling film concentrator, and the liquid outlet of the sodium chloride falling film concentrator is connected to the liquid inlet of the sodium chloride evaporation crystallization device; the concentrated water outlet of the nanofiltration salt separation device is connected to the liquid inlet of the sodium sulfate falling film concentrator, and the liquid outlet of the sodium sulfate falling film concentrator is connected to the liquid inlet of the sodium sulfate evaporation crystallization device; the mother liquor outlets of the sodium chloride evaporation crystallization device and the sodium sulfate evaporation crystallization device are both connected to the liquid inlet of the sodium sulfate freezing crystallizer, and the clear liquid outlet of the sodium sulfate freezing crystallizer is connected to the liquid inlet of the mixed salt evaporation crystallization device of the mixed salt treatment unit.

[0005] Furthermore, the mother liquor outlet of the mixed salt centrifuge of the mixed salt treatment unit is connected to the liquid inlet of the sodium chloride falling film concentrator.

[0006] Further, the mixed salt treatment unit includes the mixed salt evaporation and crystallization device, the mixed salt thickener, and the mixed salt centrifuge that are connected in sequence according to the flow direction of the mixed salt material; the mixed salt outlet of the mixed salt centrifuge is connected to the feed inlet of the mixed salt dissolution tank, and the liquid outlet of the mixed salt dissolution tank is connected to the liquid inlet of the sodium chloride falling film concentrator; the liquid outlet of the mixed salt centrifuge is connected to the liquid inlet of the drum dryer.

[0007] Further, it also includes a mirabilite thickener and a mirabilite centrifuge; the material outlet of the sodium sulfate freezing crystallizer is connected to the feed inlet of the mirabilite thickener, and the discharge outlet of the mirabilite thickener is connected to the feed inlet of the mirabilite centrifuge; the mirabilite outlet of the mirabilite centrifuge is connected to the feed inlet of the sodium sulfate evaporation and crystallization device.

[0008] Further, it also includes a sodium sulfate thickener, a sodium sulfate centrifuge, and a sodium sulfate fluidized bed dryer that are connected in sequence according to the material flow direction; the salt liquid outlet of the sodium sulfate evaporation and crystallization device is connected to the liquid inlet of the sodium sulfate thickener.

[0009] Further, it also includes a sodium chloride thickener, a sodium chloride centrifuge, and a sodium chloride fluidized bed dryer that are connected in sequence according to the material flow direction, and the salt liquid outlet of the sodium chloride evaporation and crystallization device is connected to the liquid inlet of the sodium chloride thickener.

[0010] Advantages of the present utility model: The connection structure of the present utility model is simple and easy to implement. The mother liquor generated by evaporation and crystallization in the sodium chloride evaporation and crystallization device and the mother liquor generated by evaporation and crystallization in the sodium sulfate evaporation and crystallization device enter the sodium sulfate freezing crystallizer for freezing crystallization to remove most of the sodium sulfate in the mother liquor. The clarified liquid containing most of the sodium chloride and a small amount of sodium sulfate after freezing is processed by the mixed salt treatment unit to obtain a mixed salt solution. The mixed salt solution is then concentrated by the sodium chloride falling film concentrator and evaporated and crystallized by the sodium chloride evaporation and crystallization device to recover most of the sodium chloride. The content of sodium sulfate in the mother liquor produced by the sodium chloride evaporation and crystallization device increases, and then the above-mentioned sodium sulfate is recovered through the sodium sulfate freezing crystallizer, improving the resource utilization rate; at the same time, it enables the separation of sodium chloride and sodium sulfate without using a nanofiltration salt separation device, prolongs the service life of the nanofiltration salt separation device, ensures the long-term stable operation of the system, and reduces the economic burden of the enterprise. Description of the Drawings:

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0012] Figure 1 This is a schematic diagram of the overall structure of the present utility model.

[0013] Nanofiltration salt separation device 1, sodium chloride falling film concentrator 2, sodium chloride evaporation crystallization device 3, sodium sulfate falling film concentrator 4, sodium sulfate evaporation crystallization device 5, sodium sulfate freezing crystallizer 6, mixed salt treatment unit 7, mixed salt evaporation crystallization device 71, mixed salt thickener 72, mixed salt centrifuge 73, mixed salt dissolution tank 74, drum dryer 75, mirabilite thickener 8, mirabilite centrifuge 9, sodium sulfate thickener 10, sodium sulfate centrifuge 11, sodium sulfate fluidized drying bed 12, sodium chloride thickener 13, sodium chloride centrifuge 14, sodium chloride fluidized drying bed 15. Specific implementation manner:

[0014] Example: As Figure 1 shown, a mixed salt recovery system in a wastewater treatment process includes a nanofiltration salt separation device 1, a sodium chloride falling film concentrator 2, a sodium chloride evaporation crystallization device 3, a sodium sulfate falling film concentrator 4, a sodium sulfate evaporation crystallization device 5, a sodium sulfate freezing crystallizer 6, a mixed salt treatment unit 7, a mirabilite thickener 8 and a mirabilite centrifuge 9; the water production outlet of the nanofiltration salt separation device 1 is communicated with the liquid inlet of the sodium chloride falling film concentrator 2, and the liquid outlet of the sodium chloride falling film concentrator 2 is communicated with the liquid inlet of the sodium chloride evaporation crystallization device 3; the concentrated water outlet of the nanofiltration salt separation device 1 is communicated with the liquid inlet of the sodium sulfate falling film concentrator 4, and the liquid outlet of the sodium sulfate falling film concentrator 4 is communicated with the liquid inlet of the sodium sulfate evaporation crystallization device 5; the mother liquor outlets of the sodium chloride evaporation crystallization device 3 and the sodium sulfate evaporation crystallization device 5 are both communicated with the liquid inlet of the sodium sulfate freezing crystallizer 6, and the clear liquid outlet of the sodium sulfate freezing crystallizer 6 is communicated with the liquid inlet of the mixed salt evaporation crystallization device 71 of the mixed salt treatment unit 7; the mother liquor outlet of the mixed salt centrifuge 73 of the mixed salt treatment unit 7 is communicated with the liquid inlet of the sodium chloride falling film concentrator 2.

[0015] The mixed salt treatment unit 7 includes a mixed salt evaporation crystallization device 71, a mixed salt thickener 72 and a mixed salt centrifuge 73 that are sequentially communicated according to the flow direction of the mixed salt material; the mixed salt outlet of the mixed salt centrifuge 73 is communicated with the feed inlet of the mixed salt dissolution tank 74, the liquid outlet of the mixed salt dissolution tank 74 is communicated with the liquid inlet of the sodium chloride falling film concentrator 2; the liquid outlet of the mixed salt centrifuge 73 is communicated with the liquid inlet of the drum dryer 75.

[0016] The material outlet of the sodium sulfate freezing crystallizer 6 is communicated with the feed inlet of the mirabilite thickener 8, the discharge outlet of the mirabilite thickener 8 is communicated with the feed inlet of the mirabilite centrifuge 9; the mirabilite outlet of the mirabilite centrifuge 9 is communicated with the feed inlet of the sodium sulfate evaporation crystallization device 5.

[0017] The sodium sulfate thickener 10, the sodium sulfate centrifuge 11, and the sodium sulfate fluidized drying bed 12 are connected in sequence according to the material flow direction; the salt solution outlet of the sodium sulfate evaporation and crystallization device 5 is connected to the liquid inlet of the sodium sulfate thickener 10.

[0018] The sodium chloride thickener 13, the sodium chloride centrifuge 14, and the sodium chloride fluidized drying bed 15 are connected in sequence according to the material flow direction; the salt solution outlet of the sodium chloride evaporation and crystallization device 3 is connected to the liquid inlet of the sodium chloride thickener 13.

[0019] Working principle:

[0020] 1) After the industrial wastewater is subjected to impurity removal and hardness removal by the front-end conventional pretreatment system, it enters the nanofiltration salt separation device 1 for salt separation, obtaining produced water and concentrated water.

[0021] 2) On the sodium chloride side: The produced water is concentrated by falling film through the sodium chloride falling film concentrator 2 and then enters the sodium chloride evaporation and crystallization device 3 for concentration and crystallization. The evaporation and crystallization temperature is 96 °C. The sodium chloride is evaporated to obtain a salt solution, and the sodium sulfate remains in the mother liquor and the concentration of sodium sulfate in the mother liquor is increased until it is close to saturation. Then, the evaporation and crystallization is stopped. The obtained salt solution enters the sodium chloride thickener 13 for thickening, and then enters the sodium chloride centrifuge 14. The salt obtained by centrifugation enters the sodium chloride fluidized drying bed 15 for drying to obtain sodium chloride crystal salt.

[0022] 3) On the sodium sulfate side: The concentrated water is evaporated and falls film through the sodium sulfate falling film concentrator 4 and then enters the sodium sulfate evaporation and crystallization device 5 for concentration and crystallization. The evaporation and crystallization temperature is 100 °C. The sodium sulfate is evaporated to obtain a salt solution, and the sodium chloride remains in the mother liquor until it is close to saturation. Then, the evaporation and crystallization is stopped. The obtained salt solution enters the sodium sulfate thickener 10 for thickening, and then enters the sodium sulfate centrifuge 11. The salt obtained by centrifugation enters the sodium sulfate fluidized drying bed 12 for drying to obtain sodium sulfate crystal salt.

[0023] The mother liquor generated by evaporation and crystallization in the sodium chloride evaporation and crystallization device 3 and the mother liquor generated by evaporation and crystallization in the sodium sulfate evaporation and crystallization device 5 enter the sodium sulfate freezing crystallizer 6 for freezing crystallization. The obtained mirabilite solution enters the mirabilite thickener 8 for thickening, and then enters the mirabilite centrifuge 9 to centrifuge out sodium sulfate decahydrate (mirabilite). The sodium sulfate decahydrate is sent to the sodium sulfate evaporation and crystallization device 5 for evaporation and crystallization.

[0024] 4) Mixed salts: The clarified liquid after freezing in the sodium sulfate freezing crystallizer 6 enters the mixed salt evaporation and crystallization device 71 for evaporation and crystallization, then enters the mixed salt thickener 72 for thickening, and then enters the mixed salt centrifuge 73 to centrifuge out the mixed salts. Since the mixed salts contain most of sodium chloride and a small part of sodium sulfate, the mixed salts are sent to the mixed salt dissolution tank 74 to be dissolved in water. After dissolution, it enters the sodium chloride falling film concentrator 2 for concentration, and then enters the sodium chloride evaporation and crystallization device 3 for evaporation and crystallization to recover the sodium chloride in the mixed salts.

[0025] Since the mixed salts also contain a small amount of sodium sulfate, after evaporation and concentration by the sodium chloride evaporation and crystallization device 3, the content of sodium sulfate in the mother liquor produced increases. Therefore, the mother liquor of the sodium chloride evaporation and crystallization device 3 goes to the sodium sulfate freezing crystallizer 6, and most of the sodium sulfate in the mother liquor is frozen and crystallized by the sodium sulfate freezing crystallizer 6, realizing the separation and crystallization of sodium sulfate and sodium chloride in the mixed salts as a whole, and greatly improving the resource utilization rate of the system.

[0026] 5) Miscellaneous salts: The mother liquor centrifuged out by the mixed salt centrifuge 73 enters the drum dryer 75 for drying to obtain miscellaneous salts.

[0027] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mixed salt recovery system in a wastewater treatment process, characterized in that: It comprises a nanofiltration salt separation device, a sodium chloride falling film concentrator, a sodium chloride evaporation crystallization device, a sodium sulfate falling film concentrator, a sodium sulfate evaporation crystallization device, a sodium sulfate freezing crystallizer and a mixed salt treatment unit; the produced water outlet of the nanofiltration salt separation device is communicated with the liquid inlet of the sodium chloride falling film concentrator, and the liquid outlet of the sodium chloride falling film concentrator is communicated with the liquid inlet of the sodium chloride evaporation crystallization device; the concentrated water outlet of the nanofiltration salt separation device is communicated with the liquid inlet of the sodium sulfate falling film concentrator, and the liquid outlet of the sodium sulfate falling film concentrator is communicated with the liquid inlet of the sodium sulfate evaporation crystallization device; the mother liquor outlets of the sodium chloride evaporation crystallization device and the sodium sulfate evaporation crystallization device are both communicated with the liquid inlet of the sodium sulfate freezing crystallizer, and the clear liquid outlet of the sodium sulfate freezing crystallizer is communicated with the liquid inlet of the mixed salt evaporation crystallization device of the mixed salt treatment unit.

2. A mixed salt recovery system in a wastewater treatment process according to claim 1, characterized in that: The mother liquor outlet of the mixed salt centrifuge of the mixed salt treatment unit is communicated with the liquid inlet of the sodium chloride falling film concentrator.

3. A mixed salt recovery system in a wastewater treatment process according to claim 2, characterized in that: The mixed salt processing unit includes the mixed salt evaporation and crystallization device, the mixed salt thickener and the mixed salt centrifuge which are connected in sequence according to the direction of the mixed salt material; the mixed salt outlet of the mixed salt centrifuge is connected to the feed port of the mixed salt dissolving tank, and the liquid outlet of the mixed salt dissolving tank is connected to the liquid inlet of the sodium chloride falling film concentrator; the liquid outlet of the mixed salt centrifuge is connected to the liquid inlet of the drum dryer.

4. The mixed salt recovery system in the wastewater treatment process according to claim 1, characterized in that: It also includes a Glauber's salt thickener and a Glauber's salt centrifuge; the material outlet of the sodium sulfate freezing crystallizer is connected to the feed inlet of the Glauber's salt thickener, the discharge port of the Glauber's salt thickener is connected to the feed inlet of the Glauber's salt centrifuge; the Glauber's salt outlet of the Glauber's salt centrifuge is connected to the feed inlet of the sodium sulfate evaporation crystallization device.

5. The mixed salt recovery system in the wastewater treatment process according to claim 4, characterized in that: It also includes a sodium sulfate thickener, a sodium sulfate centrifuge and a sodium sulfate fluidized drying bed which are connected in sequence according to the direction of the materials; the salt solution outlet of the sodium sulfate evaporation and crystallization device is connected with the liquid inlet of the sodium sulfate thickener.

6. The mixed salt recovery system in the wastewater treatment process according to claim 1, characterized in that: It also includes a sodium chloride thickener, a sodium chloride centrifuge and a sodium chloride fluidized drying bed which are connected in sequence according to the direction of the materials. The salt solution outlet of the sodium chloride evaporation and crystallization device is connected with the liquid inlet of the sodium chloride thickener.

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