CN112079515B

CN112079515B - Method for recycling TDI industrial wastewater

Info

Publication number: CN112079515B
Application number: CN202011082524.1A
Authority: CN
Inventors: 孙孝天; 杨勇; 尹璐; 张玉胜; 许亮
Original assignee: Jiangsu Maiande Energy Saving Evaporation Equipment Co ltd
Current assignee: Jiangsu Maiande Energy Saving Evaporation Equipment Co ltd
Priority date: 2020-10-12
Filing date: 2020-10-12
Publication date: 2023-04-07
Anticipated expiration: 2040-10-12
Also published as: CN112079515A

Abstract

The invention relates to a recycling treatment method of TDI industrial wastewater, which sequentially comprises the following steps: the method comprises the steps that calcium magnesium ions and bicarbonate radical are removed from mixed miscellaneous salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate through a pretreatment unit; the separation of divalent salt and monovalent salt is realized through a salt separating unit; the divalent salt is re-concentrated to enable the concentration of the sodium sulfate solution to reach 9.86%, and the sodium sulfate solution enters a sodium sulfate freezing and crystallizing unit to be frozen and crystallized at 0 ℃; the monovalent salt mixed solution is concentrated again to ensure that the concentration of sodium chloride reaches 4 percent and the concentration of sodium nitrate reaches 9.9 percent; entering a sodium chloride evaporation and crystallization unit for multi-effect evaporation of a monovalent salt mixed solution to crystallize and separate sodium chloride from a sodium nitrate solution; and after the sodium nitrate solution is subjected to flash evaporation and temperature reduction by the sodium nitrate flash evaporation unit, the sodium nitrate solution enters the sodium nitrate cooling and crystallizing unit and is cooled to normal temperature, so that the sodium nitrate is crystallized. And (3) performing hot melt crystallization on the sodium sulfate, and drying to obtain the sodium sulfate with the purity of 99%. The invention classifies and recovers the mixed miscellaneous salt, has high production rate and good quality of the crystallized salt.

Description

Method for recycling TDI industrial wastewater

Technical Field

The invention relates to an industrial wastewater treatment method, in particular to a TDI industrial wastewater recycling method, and belongs to the technical field of wastewater recycling.

Background

Toluene diisocyanate (TDI for short) is a main chemical raw material in polyurethane industry, is widely applied, and is mainly used for producing polyurethane series products such as sponge, high-grade paint, high-grade adhesive, high-cycle elastomer and the like.

Large amounts of waste water are produced during the production of TDI: red water, hydrogenated water, organic wastewater, inorganic wastewater, acidic water, and the like. The wastewater has the characteristics of high salt content, high aniline concentration, high chromaticity, high content of organic matters which are difficult to degrade and the like.

For such wastewater, a single biochemical method and a conventional chemical method are conventionally adopted for treatment, and a large amount of mixed salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate is generated. At present, mixed miscellaneous salt is already qualified as dangerous waste and needs special treatment, so that the environmental protection pressure of enterprises and the wastewater treatment cost are increased. Therefore, aiming at the TDI industrial wastewater, a salt separation treatment process is developed to improve the productivity of the crystallized salt and the quality of the crystallized salt, and the key point for realizing the resource utilization of the TDI industrial wastewater is realized.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provide a recycling method of TDI industrial wastewater, which can classify and recycle salts in the wastewater, improve the productivity of crystallized salts and improve the quality of the crystallized salts.

In order to solve the technical problems, the invention provides a recycling treatment method of TDI industrial wastewater, which sequentially comprises the following steps: the method comprises the steps that calcium magnesium ions and bicarbonate radical are removed from mixed miscellaneous salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate through a pretreatment unit; the separation of divalent salt and monovalent salt is realized through a salt separating unit; the divalent salt is re-concentrated to enable the concentration of the sodium sulfate solution to reach 9.86%, and the sodium sulfate solution enters a sodium sulfate freezing and crystallizing unit to be frozen and crystallized at 0 ℃; the monovalent salt mixed solution is concentrated again to ensure that the concentration of sodium chloride reaches 4 percent and the concentration of sodium nitrate reaches 9.9 percent; fourthly, enabling the monovalent salt mixed solution to enter a sodium chloride evaporation and crystallization unit for multi-effect evaporation to separate out sodium chloride crystals and separate from a sodium nitrate solution; and after the sodium nitrate solution is subjected to flash evaporation and temperature reduction by the sodium nitrate flash evaporation unit, the sodium nitrate solution enters the sodium nitrate cooling and crystallizing unit and is cooled to normal temperature, so that the sodium nitrate is crystallized.

Compared with the prior art, the invention has the following beneficial effects: calcium ions and magnesium ions in the mixed salt wastewater are removed through the pretreatment unit, bicarbonate radicals are removed, temporary hardness is removed, the risk of system scaling is further reduced, the subsequent membrane concentration system and crystallization operation safety are ensured, and the salt yield purity is improved. After the divalent salt is separated from the monovalent salt, the solubility of the sodium sulfate solution is rapidly reduced along with the reduction of the temperature because the temperature of the sodium sulfate solution is lower than 40 ℃; the system adopts a freezing crystallization method to improve the crystallization efficiency. For sodium nitrate and sodium chloride in monovalent salt, according to the characteristics that the solubility of sodium nitrate is higher and the solubility of sodium chloride is more stable along with the change of temperature, a method of crystallizing sodium chloride by multi-effect evaporation, and then carrying out flash evaporation cooling and cooling crystallization on a sodium nitrate solution is adopted. And because the reduction of the solubility of the sodium nitrate below 20 ℃ is gradual, the sodium nitrate solution is cooled to normal temperature for crystallization, and the production efficiency is improved.

The improvement of the invention comprises the steps of performing freeze crystallization on sodium sulfate, then performing double-effect evaporation crystallization on the sodium sulfate in a sodium sulfate hot-melting crystallization unit, drying and packaging to obtain the sodium sulfate with the purity of 99%. Freezing and crystallizing to obtain sodium sulfate decahydrate, and performing hot melting crystallization to obtain sodium sulfate which meets the first-class standard II in the GB/T6009-2014 industry anhydrous sodium sulfate and can be sold to the outside.

As a further improvement of the invention, after the sodium chloride crystals are separated out in the step four, the sodium chloride crystals are washed by a salt washing unit and then dried and packaged to obtain sodium chloride with the purity of 98%; and fifthly, after the sodium nitrate is crystallized, drying by a sodium nitrate drying unit, and packaging to obtain the sodium nitrate with the purity of 99%. The obtained sodium chloride meets the standard of industrial sodium chloride (secondary industrial dry salt) in GB/T5462-2015 industrial salt and can be sold to the outside; the obtained sodium nitrate meets the standard of general industrial qualified products in GB/T4553-2016 industrial sodium nitrate, and can be sold to the outside.

As a further improvement of the invention, the sodium chloride evaporative crystallization unit comprises a primary-effect salt evaporation unit, a secondary-effect salt evaporation unit and a tertiary-effect salt evaporation unit, wherein the outlet of a multi-effect feed pump is connected with the tertiary-effect salt evaporation unit, the discharge of the tertiary-effect salt evaporation unit is connected with the secondary-effect salt evaporation unit through a tertiary-effect salt transfer pump, and the discharge of the secondary-effect salt evaporation unit is connected with the primary-effect salt evaporation unit through a secondary-effect salt transfer pump; the lower part of an effective salt separator of the effective salt evaporation unit is connected with an inlet of an effective salt circulating pump through an effective salt circulating pipe, an outlet of the effective salt circulating pump is connected with a tube pass inlet of an effective salt evaporator, and a tube pass outlet of the effective salt evaporator is connected with a feeding pipe of the effective salt separator; and a sedimentation separator is arranged on the primary effective salt circulating pipe, an outlet at the top of the sedimentation separator is connected with an inlet of a flash evaporation feed pump, and an outlet of the flash evaporation feed pump is connected with the sodium nitrate flash evaporation unit and the primary effective salt circulating pipe. According to the characteristics, the sodium chloride evaporative crystallization unit adopts triple-effect countercurrent evaporative crystallization, discharges materials at high temperature effectively, and can improve the recovery rate of sodium chloride and the recovery rate of sodium nitrate. Along with heating the evaporation to the mixed solution, sodium chloride is gradually separated out, sodium nitrate is not separated out yet because the solubility improves, the upper portion of first effect salt circulating pipe inserts the inner chamber lower part of sedimentation separator, the diameter ratio of sedimentation separator's diameter and first effect salt circulating pipe is 3.5, sedimentation separator's draw ratio is 1.5:1, the separated sodium chloride crystal slurry flows to the bottom, so that salt separation by a thermal method is realized, the salt recovery rate and the quality are improved, a flash evaporation feed pump pumps out a sodium nitrate solution from the top of the sedimentation separator, and the sodium nitrate solution is sent to a sodium nitrate flash evaporation unit for evaporation or sent back to a single-effect salt circulating pipe for circulation.

As a further improvement of the invention, the bottom of the primary salt separator is provided with a salt leg, the bottom outlet of the salt leg is connected with the inlet of the thick salt tank through a thick salt crystal slurry pump, the bottom outlet of the thick salt tank is connected with the inlet of a thick salt centrifuge, the clear liquid outlet of the thick salt centrifuge and the overflow port of the thick salt tank are both connected with the salt mother liquid tank, and the bottom outlet of the salt mother liquid tank is connected with the inlet of a flash evaporation feed pump through a salt mother liquid pump; the salt discharging port of the coarse salt centrifuge is connected with the salt washing tank, the bottom of the salt washing tank is connected with the inlet of the salt washing pump, the outlet of the salt washing pump is simultaneously connected with the fine salt thick tank and the salt mother liquor tank, the overflow port of the fine salt thick tank is connected with the salt washing tank, the bottom outlet of the fine salt thick tank is connected with the inlet of the fine salt centrifuge, the clear liquid outlet of the fine salt centrifuge is connected with the salt washing tank, and the fine salt outlet of the fine salt centrifuge is connected with the sodium chloride drying unit. And (3) leading the mixed solution to reach a common saturation point through an evaporation process, firstly separating out sodium chloride, and when the solid-liquid ratio of the system reaches 1: after 10, crystal mush in a salt leg at the bottom of the one-effect salt separator is pumped out by a crude salt crystal mush pump, sent into a crude salt thickening tank for temporary storage, sodium chloride concentration in the crude salt thickening tank reaches 91 wt%, then sent into a crude salt centrifuge for solid-liquid separation, high-purity centrifugal mother liquor discharged by the crude salt centrifuge enters a salt mother liquor tank for temporary storage, sent to a sodium nitrate flash evaporation unit by a salt mother liquor pump, and the separated high-purity sodium chloride is discharged from a salt discharge port of the crude salt centrifuge. And (2) feeding the high-purity sodium chloride separated from the coarse salt centrifuge into a salt washing tank, washing away the residual sodium nitrate solution on the surfaces of sodium chloride particles by using clean water, improving the salt quality, feeding the sodium chloride solution into a refined salt thickening tank through a salt washing pump for temporary storage, returning the overflow of the refined salt thickening tank into the salt washing tank, feeding the material at the bottom of the refined salt thickening tank into a refined salt centrifuge for solid-liquid separation again, and feeding the high-purity sodium chloride into a sodium chloride drying unit for drying to obtain a sodium chloride finished product with the purity of 98%. When the salt washing tank operates for a period of time, the impurity concentration is increased, and the washing water is sent back to the salt mother liquor tank by the salt washing pump to be recycled.

As a further improvement of the invention, the sodium nitrate flash unit comprises a flash tank, an inlet of the flash tank is connected with an outlet of the flash feed pump, a sodium nitrate flash pipe at the top of the flash tank is connected with the top of a triple-effect salt separator of the triple-effect salt evaporation unit, and a bottom outlet of the flash tank is connected with an inlet of the flash discharge pump; the sodium nitrate cooling crystallization unit comprises a cooling crystallizer, a cooling heat exchanger and a cooling circulating pump, wherein the outlet of the flash evaporation discharging pump is connected with the inlet of the cooling circulating pump, the outlet of the cooling circulating pump is connected with the inlet of the cooling heat exchanger, the outlet of the cooling heat exchanger is connected with the feeding pipe of the cooling crystallizer, and the circulating liquid outlet of the cooling crystallizer is connected with the inlet of the cooling circulating pump through a cooling circulating pipe; the outlet of the lower part of the side wall of the cooling crystallizer is connected with the inlet of a cooling crystal slurry pump, the outlet of the cooling crystal slurry pump is connected with a cooling thick tank and a cooling circulating pipe, the outlet of the bottom of the cooling thick tank is connected with the inlet of a cooling centrifuge, the solid-phase outlet of the cooling centrifuge is connected with a sodium nitrate drying unit, the liquid-phase outlet of the cooling centrifuge is connected with the upper overflow port of the cooling crystallizer and the inlet of a cooling mother liquid tank, the outlet of the cooling mother liquid tank is connected with a cooling unit mother liquid pipe and the cooling circulating pipe through a cooling mother liquid pump, and the cooling unit mother liquid pipe is connected with the inlet of a multi-effect feeding pump. Sodium nitrate solution separated from the sodium chloride evaporative crystallization unit is fed into a flash tank through a flash feed pump, flash evaporation and temperature reduction are carried out under vacuum suction, a part of sodium nitrate is separated out firstly, and the energy consumption of the sodium nitrate cooling crystallization unit can be reduced; and (4) sending the sodium nitrate salt subjected to flash evaporation into a sodium nitrate cooling crystallization unit by a flash evaporation discharge pump for cooling crystallization. And a flash evaporation discharging pump sends new sodium nitrate into a cooling circulating pipe, the new sodium nitrate and circulating liquid enter a cooling circulating pump together, the cooling circulating pump sends a sodium nitrate solution into a cooling heat exchanger to be cooled to normal temperature, a large amount of sodium nitrate is crystallized and separated out after the sodium nitrate solution enters a cooling crystallizer, and the overflow of the cooling crystallizer continues to enter the cooling circulating pipe for circulation. The shell pass of the cooling heat exchanger is provided with cooling water circulation through a first internal circulation pump, an outlet pipeline of the first internal circulation pump is connected with a first refrigerant cache barrel, an outlet of the first refrigerant cache barrel is connected with an inlet of a first refrigerator through a pump, and an outlet of the first refrigerator is connected with an inlet pipeline of the first internal circulation pump. And pumping the sodium nitrate crystal slurry at the bottom of the cooling crystallizer by a cooling crystal slurry pump, sending the sodium nitrate crystal slurry into a cooling thickening tank for caching, then sending the sodium nitrate crystal slurry into a cooling centrifuge for solid-liquid separation to obtain high-purity sodium nitrate salt and sodium nitrate centrifugal mother liquor, and sending the obtained sodium nitrate salt into a sodium nitrate drying unit for drying to obtain high-purity sodium nitrate finished salt. The sodium nitrate centrifugal mother liquor, the overflow of the cooling thickening tank and the overflow of the top of the cooling crystallizer jointly enter a cooling mother liquor tank for collection, the concentration of sodium chloride in the cooling mother liquor tank is 7.6 percent, the concentration of sodium nitrate is 41 percent, the sodium nitrate is pumped by a cooling mother liquor pump and returns to the inlet of a sodium chloride evaporative crystallization unit from a mother liquor pipe of a cooling unit, and the sodium nitrate centrifugal mother liquor and the overflow of the cooling thickening tank can also return to a cooling circulating pipe for circulation or impurity salt preparation. The solubility of the sodium nitrate is reduced along with the reduction of the temperature, and the reduction of the solubility below 20 ℃ is gradual; the system cools the sodium nitrate solution to normal temperature for crystallization, and can improve the production efficiency.

As a further improvement of the invention, the sodium nitrate drying unit comprises a vibration drying bed, a solid phase outlet of the cooling centrifuge is connected with a feed inlet of the vibration drying bed, a hot air inlet of the vibration drying bed is connected with an outlet of an air heater, a hot air outlet of the vibration drying bed is connected with an air inlet of a cyclone dust collector, a discharge port at the bottom of the cyclone dust collector and a discharge port of the vibration drying bed are connected with sodium nitrate packaging equipment together, an air outlet at the top of the cyclone dust collector is connected with an inlet of a water film dust collector through an induced draft fan, and a liquid discharge port of the water film dust collector is connected with an inlet of the cooling mother liquid tank. And (3) allowing sodium nitrate salt at the outlet of the cooling centrifuge to enter a vibration drying bed for drying, discharging the sodium nitrate salt from the vibration drying bed to obtain finished sodium nitrate salt with the purity of 98%, and packaging the finished sodium nitrate salt in sodium nitrate packaging equipment. After fresh air is sent into an air heater by an air blower to be heated, hot air enters from the lower part of a vibration drying bed, tail gas is discharged from the top of the vibration drying bed, collected materials also enter into a package after being dedusted by a cyclone dust collector, the tail gas is discharged from the top of the cyclone dust collector and enters into a water film deduster for dedusting under the suction of a draught fan, dedusting liquid returns to a cooling mother liquid tank for circulation, the discharge is stopped, and the materials are recovered.

As a further improvement of the invention, the sodium sulfate freezing and crystallizing unit comprises a freezing crystallizer, a freezing heat exchanger and a freezing circulating pump, wherein the outlet of the freezing feed pump is connected with the inlet of the hot side of the precooler, and the outlet of the hot side of the precooler is connected with the inlet of the freezing circulating pump; the outlet of the freezing circulating pump is connected with the inlet of the freezing heat exchanger, the outlet of the freezing heat exchanger is connected with the feeding pipe of the freezing crystallizer, the circulating overflow port of the freezing crystallizer is connected with the inlet of the freezing circulating pump through a freezing circulating pipe, the outlet of the lower part of the side wall of the freezing crystallizer is connected with the inlet of a freezing crystal slurry pump, the outlet of the freezing crystal slurry pump is connected with a freezing thick tank and the freezing circulating pipe, the outlet of the bottom of the freezing thick tank is connected with the inlet of a freezing centrifugal machine, the solid-phase outlet of the freezing centrifugal machine is connected with a sodium sulfate hot melting crystallization unit, the liquid-phase outlet of the freezing centrifugal machine and the upper overflow port of the freezing crystallizer are connected with the inlet of a freezing mother liquid tank together, the outlet of the freezing mother liquid tank is connected with the freezing circulating pipe and the cold-side inlet of the precooler through a freezing mother liquid pump, and the cold-side outlet of the precooler is connected with the outer discharge pipe of the freezing unit. Since the sodium sulfate solution is below 40 ℃, the solubility is rapidly reduced along with the reduction of the temperature; the system adopts a freezing crystallization method to improve the crystallization efficiency. The sodium sulfate solution with the concentration of 9.86 percent by weight at 25 ℃ is pre-cooled to 14 ℃ by a pre-cooler and then is sent into a freezing circulating pipe by a freezing feed pump, the sodium sulfate solution and circulating liquid enter a freezing circulating pump together, the freezing circulating pump sends the sodium sulfate solution into a freezing heat exchanger to be cooled to 0 ℃, a large amount of sodium sulfate is crystallized and separated out after the sodium sulfate solution enters a freezing crystallizer, and the overflow of the freezing crystallizer continues to enter the freezing circulating pipe for circulation. And the shell pass of the refrigerating heat exchanger is provided with refrigerant ethylene glycol circulation by an internal circulation pump II, an outlet pipeline of the internal circulation pump II is connected with a refrigerant cache barrel II, an outlet of the refrigerant cache barrel II is connected with an inlet of a refrigerator II through a pump, and an outlet of the refrigerator II is connected with an inlet pipeline of the internal circulation pump II. And pumping the sodium sulfate crystal slurry at the bottom of the freezing crystallizer by a freezing crystal slurry pump, sending the sodium sulfate crystal slurry into a freezing thickening tank for caching, then sending the sodium sulfate crystal slurry into a freezing centrifuge for solid-liquid separation to obtain sodium sulfate decahydrate and sodium sulfate centrifugal mother liquor, and sending the obtained sodium sulfate decahydrate, namely mirabilite, into a sodium sulfate drying unit for drying to obtain sodium sulfate finished salt. The overflow of the sodium sulfate centrifugal mother liquor and the freezing thick tank and the overflow at the top of the freezing crystallizer jointly enter a freezing mother liquor tank to be collected, the sodium sulfate centrifugal mother liquor is pumped out by a freezing mother liquor pump, and the sodium sulfate centrifugal mother liquor enters a precooler to precool a new sodium sulfate solution, so that residual cold is recycled, the energy consumption of the system is saved, and the heated sodium sulfate centrifugal mother liquor is discharged from an outer discharge pipe of a freezing unit.

As a further improvement of the invention, the sodium sulfate hot melting crystallization unit comprises a primary effect nitrate evaporation unit, a secondary effect nitrate evaporation unit and a nitrate hot melting tank, wherein a solid phase outlet of the freezing centrifuge is connected with an inlet of the nitrate hot melting tank, a bottom outlet of the nitrate hot melting tank is connected with a primary effect nitrate circulating pipe through a nitrate mother liquor pump, an outlet of the primary effect nitrate circulating pipe is connected with an inlet of a primary effect nitrate circulating pump, an outlet of the primary effect nitrate circulating pump is connected with an inlet of a primary effect nitrate evaporator, an outlet of the primary effect nitrate evaporator is connected with a feed inlet of a primary effect nitrate separator, a bottom outlet of the primary effect nitrate separator is connected with the primary effect nitrate circulating pipe, a salt leg outlet of the primary effect nitrate separator is connected with an inlet of a nitrate thick tank through a thick nitrate crystal slurry pump, a bottom outlet of the nitrate thick tank is connected with an inlet of a nitrate centrifuge, a liquid phase outlet of the nitrate centrifuge is connected with an inlet of the nitrate hot melting tank, and a solid phase outlet of the nitrate centrifuge is connected with a sodium sulfate drying unit.

As a further improvement of the invention, the outlet of the nitrate mother liquor pump is connected with a double-effect nitrate circulating pipe, the outlet of the double-effect nitrate circulating pipe is connected with the inlet of a double-effect nitrate circulating pump, the outlet of the double-effect nitrate circulating pump is connected with the inlet of a double-effect nitrate evaporator, the outlet of the double-effect nitrate evaporator is connected with the feed inlet of a double-effect nitrate separator, the bottom outlet of the double-effect nitrate separator is connected with the double-effect nitrate circulating pipe, and the salt leg outlet of the double-effect nitrate separator is connected with the inlet of the nitrate thickening tank through a double-effect nitrate crystal slurry pump; the shell pass inlet of the first-effect saltpeter evaporator is connected with a raw steam pipe, the top steam outlet of the first-effect saltpeter separator is connected with the shell pass inlet of the second-effect saltpeter evaporator, the shell pass outlets of the first-effect saltpeter evaporator and the second-effect saltpeter evaporator are respectively connected with a double-effect condensate water tank, and the outlet of the double-effect condensate water tank is connected with a condensate water recovery pipe through a double-effect condensate water pump; and a steam outlet at the top of the two-effect saltpeter separator is connected with a saltpeter surface cooler.

The saltpeter hot melting tank is a mother liquid tank of the system and also serves as a saltpeter melting tank and a feeding tank, cost is saved, mirabilite obtained by the sodium sulfate freezing and crystallizing unit enters the saltpeter hot melting tank, a sodium sulfate solution with the concentration of 32.6% is pumped out by a saltpeter mother liquid pump and returns to the first-effect saltpeter circulating pipe and the second-effect saltpeter circulating pipe for circulation, secondary steam discharged by the first-effect saltpeter separator serves as a heat source of the second-effect saltpeter evaporator, condensate water of the shell pass of the first-effect saltpeter evaporator and the second-effect saltpeter evaporator enters the double-effect condensate water tank for collection, is pumped out by the double-effect condensate water pump and enters the condensate water recycling pipe for recycling. When the solid-liquid ratio of the system reaches 1: and after 10, pumping the salt slurry into a nitrate thickening tank for caching through a first-effect nitrate crystal slurry pump and a second-effect nitrate crystal slurry pump, separating the salt slurry into a nitrate centrifuge to obtain high-purity sodium sulfate and nitrate centrifugal mother liquor, and delivering the obtained sodium sulfate into a sodium sulfate drying unit for drying to obtain sodium sulfate with the purity of 99%.

As a further improvement of the invention, an outlet of an outer discharge pipe of the freezing unit is connected with a feed inlet of a mixed salt evaporation kettle, a bottom outlet of the mixed salt evaporation kettle is connected with an inlet of a mixed salt centrifuge, a liquid phase outlet of the mixed salt centrifuge is connected with a mixed salt mother liquor temporary storage tank, an outlet of the mixed salt mother liquor temporary storage tank is connected with a reflux port of the mixed salt evaporation kettle through a mixed salt mother liquor reflux pump, and a solid phase outlet of the mixed salt centrifuge is connected with a mixed salt packaging device; and an exhaust port of the miscellaneous salt evaporation kettle is connected with an inlet of a surface cooler II, and an outlet of the surface cooler II is connected with a vacuum pump II. And waste mother liquor discharged from a mother liquor pipe of the cooling unit or an outer discharge pipe of the freezing unit enters a mixed salt evaporation kettle for evaporation and crystallization, then enters a mixed salt centrifuge for solid-liquid separation, and is packed in a solid phase to obtain the marketable mixed salt. The mixed salt centrifugal mother liquor enters a mixed salt mother liquor temporary storage tank for storage, is pumped out by a mixed salt mother liquor reflux pump and returns to the mixed salt evaporation kettle for circulation; the waste mother liquor is solidified, so that the waste water is completely recycled, and the quality of the main product salt is improved. And under the suction of the vacuum pump II, the exhaust steam of the miscellaneous salt evaporation kettle enters the surface air cooler II for condensation, and the miscellaneous salt evaporation kettle is maintained under vacuum to accelerate evaporation. Condensed water of a jacket of the mixed salt evaporation kettle enters a mixed salt condensed water collection tank for collection, and is sent to a condensed water recovery pipe by a mixed salt condensed water pump for recovery.

Drawings

The invention is described in further detail below with reference to the attached drawing figures and the detailed description, which are provided for reference and illustration only and are not meant to limit the invention.

FIG. 1 is a flow chart of a pretreatment unit, a salt separation unit and a divalent salt re-concentration unit according to the present invention.

FIG. 2 is a flow chart of the evaporative sodium chloride crystallization unit and the salt washing unit in the invention.

FIG. 3 is a flow chart of a sodium nitrate flash evaporation unit and a sodium nitrate cooling crystallization unit in the present invention.

Fig. 4 is a flow chart of a sodium nitrate drying unit according to the present invention.

FIG. 5 is a flow diagram of a sodium sulfate freezing and crystallizing unit in the present invention.

FIG. 6 is a flow chart of a sodium sulfate hot-melt crystallization unit according to the present invention.

FIG. 7 is a flow diagram of a miscellaneous salt recovery unit of the present invention.

In the figure: 1. a pre-processing unit; 1a, a raw water pipeline; 1b, a raw water feeding pump; 1c, weak acid resin adsorption bed; 1d, a decarburization feed pump; 1e, a decarbonizing tower; 2. a salt separation unit; a ro feed pump; 2b. Ro devices; 2c.RO thick water tank; 2d, a first-stage nanofiltration high-pressure pump; 2e, a first-stage nanofiltration device; 2f, a first-stage nanofiltration concentrated water tank; 2g, a first-stage nanofiltration water production tank; 3. a divalent salt reconcentration unit; 3a, a secondary nanofiltration high-pressure pump; 3b, a secondary nanofiltration device; 3c, a second-stage nanofiltration concentrated water tank; 3d, a freezing feed pump; 3e, a secondary nanofiltration water production tank; swro high pressure pump; a SWRO device at 3 g; 3h, a reclaimed water recycling pipe; 3j.SWRO concentrated pool; 3k, an electrodialysis feeding pump; 3m, an electrodialysis device; 3n, electrodialysis concentrated water pool; 3p, a multi-effect feed pump; 4. a sodium chloride evaporative crystallization unit; 4a, a primary preheater; 4b, a secondary preheater; 4c1. A three-effect salt separator; 4c2, a triple-effect salt circulating pipe; 4c3, a triple-effect salt circulating pump; 4c4. A triple-effect salt evaporator; 4c5, a triple-effect salt transferring pump; 4d1, a two-effect salt separator; 4d2. A double-effect salt circulating pipe; 4d3, a double-effect salt circulating pump; 4d4. A double-effect salt evaporator; 4d5, a double-effect salt transferring pump; 4e1. A salt separator; 4e2, a one-effect salt circulating pipe; 4e3, a single-effect salt circulating pump; 4e4. A first effect salt evaporator; 4e5, a sedimentation separator; 4e6. Flash feed pump; 4f, raw steam condensation water tank; 4g, a steam condensate pump is generated; 4h, using a sewage condensed water tank; 4j, a sewage condensate pump; 4k, a sewage condensate water discharge pipe; 4m, coarse salt crystal slurry pump; 4n, a thick crude salt tank; 4p, a coarse salt centrifuge; 4q, a salt mother liquor tank; 4r, a salt mother liquor pump; 4s, a first surface cooler; 4t, a first vacuum pump; 5. a salt washing unit; 5a, washing a salt tank; 5b, a salt washing pump; 5c, a refined salt thickening tank; 5d, a refined salt centrifuge; 6. a sodium chloride drying unit; 7. a sodium nitrate flash evaporation unit; 7a, a flash tank; 7b, sodium nitrate flash tube; 7c, a flash evaporation discharge pump; 8. a sodium nitrate cooling and crystallizing unit; 8a, cooling the crystallizer; 8b, cooling the circulating pipe; 8c, a cooling circulating pump; 8d, cooling the heat exchanger; 8e, cooling the crystal slurry pump; 8f, cooling the thick tank; 8g, cooling the centrifuge; cooling the mother liquor tank for 8 h; 8j, a cooling mother liquor pump; 8k, cooling a unit mother liquor pipe; 8m, a first refrigerator; 8n, a first refrigerant buffer barrel; 8p, an internal circulation pump I; 9. a sodium nitrate drying unit; 9a, a blower; 9b, an air heater; 9c, vibrating the drying bed; 9d, a cyclone dust collector; 9e, a draught fan; 9f, a water film deduster; 9g, sodium nitrate packaging equipment; 10. a sodium sulfate freezing and crystallizing unit; 10a, a freezing crystallizer; 10b, a refrigeration circulating pipe; 10c, a refrigeration circulating pump; 10d, freezing a heat exchanger; 10e, freezing a crystal slurry pump; 10f, freezing the thick tank; 10g, freezing a centrifugal machine; freezing the mother liquor tank for 10 hours; 10j, a chilled mother liquor pump; 10k, a precooler; 10m, a refrigeration unit external discharge pipe; 10n, a second refrigerator; 10p, a second refrigerant cache barrel; 10q. an internal circulating pump II; 11. a sodium sulfate hot-melting crystallization unit; 11a, a single-effect nitrate separator; 11b, a one-effect nitre circulating pipe; 11c, a single-effect nitrate circulating pump; 11d, a single-effect saltpeter evaporator; 11e, a first-effect nitrate crystal slurry pump; 11f, a double-effect nitrate separator; 11g, a double-effect nitre circulating pipe; 11h, a double-effect nitrate circulating pump; 11j, a double-effect nitre evaporator; 11k, a double-effect nitrate crystal slurry pump; 11m, a nitre thickening tank; 11n, a nitre centrifuge; 11p, carrying out a nitrate hot melting tank; 11q. a nitre mother liquor pump; 11r, a double-effect condensed water tank; 11s, a double-effect condensate pump; surface cooling device for nitre; 12. a sodium sulfate drying unit; 13. a miscellaneous salt recovery unit; 13a, a miscellaneous salt evaporation kettle; 13b, a miscellaneous salt centrifuge; 13c, temporary storage tank of miscellaneous salt mother liquor; 13d, a miscellaneous salt mother liquor reflux pump; 13e, packaging equipment for miscellaneous salt; 13f, a surface cooler II; 13g, a vacuum pump II; 13h, a miscellaneous salt condensate water collection tank; 13j, a miscellaneous salt condensate pump; G1. a raw steam pipe; G2. a condensate recovery pipe; G3. a cooling water supply pipe; G4. a cooling water return pipe; G5. high-pressure flushing water pipe.

Detailed Description

As shown in fig. 1 to 7, the method for recycling TDI industrial wastewater of the present invention sequentially comprises the following steps: the method comprises the steps that calcium magnesium ions and bicarbonate radical are removed from mixed miscellaneous salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate through a pretreatment unit 1; the separation of divalent salt and monovalent salt is realized through the salting unit 2; the divalent salt is re-concentrated to enable the concentration of the sodium sulfate solution to reach 9.86%, and the sodium sulfate solution enters a sodium sulfate freezing and crystallizing unit 10 to be frozen and crystallized at 0 ℃; the monovalent salt mixed solution is concentrated again to ensure that the concentration of sodium chloride reaches 4 percent and the concentration of sodium nitrate reaches 9.9 percent; the monovalent salt mixed solution enters a sodium chloride evaporation and crystallization unit 4 to be evaporated in a multiple-effect mode, so that sodium chloride is crystallized and separated from a sodium nitrate solution; and after the sodium nitrate solution is subjected to flash evaporation and temperature reduction by the sodium nitrate flash evaporation unit 7, the sodium nitrate solution enters the sodium nitrate cooling and crystallizing unit 8 and is cooled to normal temperature, so that the sodium nitrate is crystallized.

And step three, after sodium sulfate is frozen and crystallized, the sodium sulfate enters a sodium sulfate hot melting crystallization unit 11 to be subjected to double-effect evaporation crystallization, and sodium sulfate with the purity of 99% is obtained after drying and packaging.

Step four, after sodium chloride crystals are precipitated, washing the crystals by a salt washing unit 5, and drying and packaging the crystals to obtain sodium chloride with the purity of 98%; after the sodium nitrate is crystallized, the sodium nitrate is dried by a sodium nitrate drying unit 9, and then the sodium nitrate with the purity of 99% is obtained through packaging.

As shown in fig. 1, the pretreatment unit 1 includes a raw water feed pump 1b connected to a raw water pipe 1a, an outlet of the raw water feed pump 1b is connected to an inlet of a weak acid resin adsorption bed 1c, an outlet of the weak acid resin adsorption bed 1c is connected to an inlet of a decarbonization tower 1e through a decarbonization feed pump 1d, an outlet of the decarbonization tower 1e is connected to an inlet of an RO device 2b through an RO feed pump 2a, an outlet of the RO device 2b is connected to an RO concentrate tank 2c, an outlet of the RO concentrate tank 2c is connected to an inlet of a primary nanofiltration device 2e through a primary nanofiltration high-pressure pump 2d, a concentrate outlet of the primary nanofiltration device 2e is connected to a primary nanofiltration concentrate tank 2f, and a product water outlet of the primary nanofiltration device 2e is connected to a primary nanofiltration product tank 2g.

Sending mixed salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate into a weak acid resin adsorption bed 1c by a raw water feeding pump 1b for sodium ion exchange to remove calcium and magnesium ions; and then the effluent is sent into a decarbonizing tower 1e by a decarbonizing feed pump 1d to remove bicarbonate radical, so that temporary hardness is removed, the risk of system scaling is further reduced, the subsequent membrane concentration system and crystallization operation safety are ensured, and the salt purity is improved.

The RO device 2b and the primary nanofiltration device 2e form a salt separation unit 2, pretreated mixed miscellaneous salt wastewater is sent into the RO device 2b by an RO feed pump 2a, partial clear water is filtered out by a reverse osmosis membrane, the pre-concentrated mixed miscellaneous salt wastewater enters an RO concentrated water tank 2c for temporary storage, then is sent into a primary nanofiltration device 2e for filtration by a primary nanofiltration high-pressure pump 2d, divalent sodium sulfate enters a primary nanofiltration concentrated water tank 2f for temporary storage, and micromolecules, monovalent sodium chloride and sodium nitrate enter a primary nanofiltration water tank 2g for temporary storage, so that the separation of divalent salt and monovalent salt is realized, and a foundation is laid for obtaining single high-purity crystal salt.

An outlet of the first-stage nanofiltration concentrated water tank 2f is connected with an inlet of a second-stage nanofiltration device 3b through a second-stage nanofiltration high-pressure pump 3a, a concentrated brine outlet of the second-stage nanofiltration device 3b is connected with a second-stage nanofiltration concentrated water tank 3c, and the second-stage nanofiltration concentrated water tank 3c is connected with a sodium sulfate freezing crystallization unit 10 through a freezing feed pump 3 d; a water production outlet of the second-stage nanofiltration device 3b is connected with a second-stage nanofiltration water production tank 3 e; the outlet water of the second-stage nanofiltration water production tank 3e is connected with the first-stage nanofiltration water production tank 2g, the outlet of the first-stage nanofiltration water production tank 2g is connected with the inlet of a SWRO device 3g through a SWRO high-pressure pump 3f, the clear water outlet of the SWRO device 3g is connected with a reclaimed water recycling pipe 3h, the brine outlet of the SWRO device 3g is connected with a SWRO concentrated water tank 3j, the outlet of the SWRO concentrated water tank 3j is connected with an electrodialysis device 3m through an electrodialysis feeding pump 3k, the concentrated brine outlet of the electrodialysis device 3m is connected with an electrodialysis concentrated water tank 3n, and the outlet of the electrodialysis concentrated water tank 3n is connected with a sodium chloride evaporation crystallization unit 4 through a multi-effect feeding pump 3p.

A secondary nanofiltration high-pressure pump 3a, a secondary nanofiltration device 3b, a secondary nanofiltration concentrated water tank 3c, a secondary nanofiltration water-producing water tank 3e and the like form a divalent salt re-concentration unit 3; a small amount of monovalent salt still remains in the sodium sulfate solution temporarily stored in the primary nanofiltration concentrated water tank 2f, the sodium sulfate solution is sent to a secondary nanofiltration device 3b by a secondary nanofiltration high-pressure pump 3a for secondary filtration, the concentration of the sodium sulfate solution after the secondary nanofiltration high-pressure pump is concentrated again reaches 9.86 percent by weight, the sodium sulfate solution enters a secondary nanofiltration concentrated water tank 3c for temporary storage, and then the sodium sulfate solution is sent to a sodium sulfate freezing and crystallizing unit 10 by a freezing and feeding pump 3d for freezing and crystallizing; the filtered monovalent salt firstly enters a second-stage nanofiltration water production tank 3e for temporary storage and then is converged into a first-stage nanofiltration water production tank 2g.

The monovalent salt mixed solution in the primary nanofiltration water production tank 2g is sent into a SWRO device 3g by a SWRO high-pressure pump 3f to be concentrated continuously, the SWRO device 3g is a reverse osmosis seawater desalination device, filtered clean water enters a reclaimed water recycling pipe 3h to be recycled, concentrated solution enters a SWRO concentrated water tank 3j to be temporarily stored, then is sent into an electrodialysis device 3m by an electrodialysis feeding pump 3k to be concentrated continuously, concentrated brine enters an electrodialysis concentrated water tank 3n to be temporarily stored, the concentration of sodium chloride is increased to 4 wt, the concentration of sodium nitrate solution is increased to 9.9 wt, and the concentrated solution is sent into a sodium chloride evaporation and crystallization unit 4 by a multi-effect feeding pump 3p to be evaporated and crystallized.

As shown in fig. 2, the sodium chloride evaporative crystallization unit 4 comprises a one-effect, two-effect and three-effect salt evaporation unit, an outlet of a multi-effect feed pump 3p is preheated by a first-stage preheater 4a and a second-stage preheater 4b in sequence and then is connected with a three-effect salt circulation pipe 4c2, an outlet of the three-effect salt circulation pipe 4c2 is connected with inlets of a three-effect salt circulation pump 4c3 and a three-effect salt transfer pump 4c5, an outlet of the three-effect salt circulation pump 4c3 is connected with an inlet of a three-effect salt evaporator 4c4, and an outlet of the three-effect salt evaporator 4c4 is connected with a feed pipe of a three-effect salt separator 4c 1; the outlet of the triple-effect salt transferring pump 4c5 is connected with the double-effect salt circulating pipe 4d2, the outlet of the double-effect salt circulating pipe 4d2 is connected with the inlets of the double-effect salt circulating pump 4d3 and the double-effect salt transferring pump 4d5, the outlet of the double-effect salt circulating pump 4d3 is connected with the inlet of the double-effect salt evaporator 4d4, and the outlet of the double-effect salt evaporator 4d4 is connected with the feeding pipe of the double-effect salt separator 4d 1; the outlet of the double-effect salt transferring pump 4d5 is connected with the single-effect salt circulating pipe 4e2. The lower part of an effective salt separator 4e1 of an effective salt evaporation unit is connected with an inlet of an effective salt circulating pump 4e3 through an effective salt circulating pipe 4e2, an outlet of the effective salt circulating pump 4e3 is connected with a tube pass inlet of an effective salt evaporator 4e4, and a tube pass outlet of the effective salt evaporator 4e4 is connected with a feeding pipe of the effective salt separator 4e 1; a sedimentation separator 4e5 is arranged on the one-effect salt circulating pipe 4e2, the top outlet of the sedimentation separator 4e5 is connected with the inlet of a flash feed pump 4e6, and the outlet of the flash feed pump 4e6 is connected with a sodium nitrate flash unit 7 and the one-effect salt circulating pipe 4e2.

A shell pass inlet of the first-effect salt evaporator 4e4 is connected with the raw steam pipe G1, a shell pass outlet of the first-effect salt evaporator 4e4 is connected with the raw steam condensate tank 4f, an outlet of the raw steam condensate tank 4f is connected with a hot side inlet of the primary preheater 4a through the raw steam condensate pump 4G, and a hot side outlet of the primary preheater 4a is connected with the condensate water recovery pipe G2; the top steam vent of one effect salt separator 4e1 links to each other with the shell side entry of two effect salt evaporator 4d4, the top steam vent of two effect salt separator 4d1 links to each other with the shell side entry of three effect salt evaporator 4c4, the shell side export of two effect salt evaporator 4d4 and three effect salt evaporator 4c4 links to each other with dirty condensate water pitcher 4h, dirty condensate water pitcher 4 h's export links to each other with the hot side entry of second grade preheater 4b through dirty condensate water pump 4j, the hot side export of second grade preheater 4b links to each other with dirty condensate water discharge pipe 4k.

The raw steam is used as a heat source of the first-effect salt evaporator 4e4, the exhaust steam of the first-effect salt separator 4e1 is used as a heat source of the second-effect salt evaporator 4d4, and the exhaust steam of the second-effect salt separator 4d1 is used as a heat source of the third-effect salt evaporator 4c4, so that the gradient utilization of heat energy is realized. Condensed water discharged by the triple-effect salt evaporator 4c4 and the double-effect salt evaporator 4d4 enters a sewage condensed water tank 4h for collection, and is sent to a primary preheater 4a by a sewage condensed water pump 4j for primary preheating of monovalent salt solution, and the monovalent salt solution is heated to 53.4 ℃; condensed water discharged from the primary salt evaporator 4e4 enters a steam generating condensate tank 4f for collection, and is sent to a secondary preheater 4b by a steam generating condensate pump 4g for secondary preheating of monovalent salt solution, and the monovalent salt solution is heated to 72.8 ℃; further realizes the waste heat recovery. The non-condensable gases of the first-effect salt evaporator 4e4, the second-effect salt evaporator 4d4 and the third-effect salt evaporator 4c4 enter the surface air cooler for condensation for 4s under the suction of the vacuum pump for 4t. High-pressure washing water from the high-pressure washing water pipe G5 enters from the tops of the one-effect salt separator 4e1, the two-effect salt separator 4d1, and the three-effect salt separator 4c1, and can wash the separators.

According to the characteristics that the solubility of sodium nitrate is different from that of sodium chloride, the higher the temperature of sodium nitrate is, the higher the solubility is, and the solubility of sodium chloride is stable along with the change of the temperature, the sodium chloride evaporative crystallization unit 4 adopts triple-effect countercurrent evaporative crystallization, discharges materials at high temperature effectively, and can improve the recovery rate of sodium chloride and the recovery rate of sodium nitrate. As the mixed solution is heated and evaporated, sodium chloride is gradually separated out, sodium nitrate is not separated out due to the improvement of solubility, the upper part of the primary salt circulation pipe 4e2 is inserted into the lower part of the inner cavity of the sedimentation separator 4e5, the diameter ratio of the diameter of the sedimentation separator 4e5 to the primary salt circulation pipe 4e2 is 3.5, and the length-diameter ratio of the sedimentation separator 4e5 is 1.5:1, the separated sodium chloride crystal slurry flows towards the bottom, so that salt separation is realized by a thermal method, the salt recovery rate and the quality are improved, a flash evaporation feeding pump 4e6 pumps out a sodium nitrate solution from the top of a settling separator 4e5, and the sodium nitrate solution is sent to a sodium nitrate flash evaporation unit 7 for evaporation or sent back to a primary salt circulating pipe 4e2 for circulation.

An effect salt separator 4e1 bottom is equipped with the salt leg, and the bottom export of salt leg links to each other through thick salt crystal thick liquid pump 4m and thick salt jar 4 n's entry, and thick salt jar 4 n's bottom export links to each other with thick salt centrifuge 4 p's entry, and thick salt centrifuge 4 p's clear solution export and thick salt jar 4 n's overflow mouth all link to each other with salt mother liquor jar 4q, and salt mother liquor jar 4 q's bottom export links to each other through salt mother liquor pump 4r and flash distillation charge pump 4e 6's entry. And (3) leading the mixed solution to reach a common saturation point through an evaporation process, firstly separating out sodium chloride, and when the solid-liquid ratio of the system reaches 1: after 10, the magma in the salt leg at the bottom of the one-effect salt separator 4e1 is pumped out by a crude salt magma pump 4m, sent into a crude salt thickening tank 4n for temporary storage, the sodium chloride concentration in the crude salt thickening tank 4n reaches 91 wt%, then sent into a crude salt centrifuge 4p for solid-liquid separation, the high-purity centrifugal mother liquor discharged from the crude salt centrifuge 4p enters a salt mother liquor tank 4q for temporary storage, sent to a sodium nitrate flash evaporation unit 7 by a salt mother liquor pump 4r, and the separated high-purity sodium chloride is discharged from a salt discharge port of the crude salt centrifuge 4p.

The salt discharge port of the coarse salt centrifuge 4p is connected with the salt washing tank 5a, the bottom of the salt washing tank 5a is connected with the inlet of the salt washing pump 5b, the outlet of the salt washing pump 5b is simultaneously connected with the fine salt thick tank 5c and the salt mother liquor tank 4q, the overflow port of the fine salt thick tank 5c is connected with the salt washing tank 5a, the bottom outlet of the fine salt thick tank 5c is connected with the inlet of the fine salt centrifuge 5d, the clear liquid outlet of the fine salt centrifuge 5d is connected with the salt washing tank 5a, and the fine salt outlet of the fine salt centrifuge 5d is connected with the sodium chloride drying unit 6. High-purity sodium chloride separated from a coarse salt centrifuge 4p enters a salt washing tank 5a, sodium nitrate solution remained on the surface of sodium chloride particles is washed away by clean water, the salt quality is improved, the sodium chloride is sent into a refined salt thick tank 5c through a salt washing pump 5b to be temporarily stored, overflow of the refined salt thick tank 5c returns to the salt washing tank 5a, the bottom material of the refined salt thick tank 5c enters a refined salt centrifuge 5d to be subjected to solid-liquid separation again, the high-purity sodium chloride enters a sodium chloride drying unit 6 to be dried, and then a sodium chloride finished product with the purity of 98% is obtained, meets the industrial sodium chloride (industrial dry salt secondary) standard in GB/T5462-2015 industrial salt and can be sold to the outside. When the salt washing tank 5a is operated for a period of time, the impurity concentration increases, and the washing water is sent back to the salt mother liquor tank 4q by the salt washing pump 5b to be recycled.

As shown in fig. 3, the sodium nitrate flash unit 7 includes a flash tank 7a, an inlet of the flash tank 7a is connected to an outlet of the flash feed pump 4e6, and a sodium nitrate flash pipe 7b at the top of the flash tank 7a is connected to the top of the triple-effect salt separator 4c1 of the triple-effect salt evaporation unit; the bottom outlet of the flash tank 7a is connected to a sodium nitrate cooling crystallization unit 8 via a flash discharge pump 7c. Sodium nitrate solution separated from the sodium chloride evaporative crystallization unit 4 is sent into a flash tank 7a by a flash feed pump 4e6, and is subjected to flash evaporation and temperature reduction under vacuum suction, so that a part of sodium nitrate is separated out firstly, and the energy consumption of a sodium nitrate cooling crystallization unit 8 can be reduced; and sending the sodium nitrate salt subjected to flash evaporation into a sodium nitrate cooling and crystallizing unit 8 by a flash evaporation discharge pump 7c for cooling and crystallizing.

The sodium nitrate cooling crystallization unit 8 comprises a cooling crystallizer 8a, a cooling heat exchanger 8d and a cooling circulating pump 8c, wherein the outlet of the flash evaporation discharging pump 7c is also connected with the inlet of the cooling circulating pump 8c, the outlet of the cooling circulating pump 8c is connected with the inlet of the cooling heat exchanger 8d, the outlet of the cooling heat exchanger 8d is connected with the feeding pipe of the cooling crystallizer 8a, and the circulating liquid outlet of the cooling crystallizer 8a is connected with the inlet of the cooling circulating pump 8c through a cooling circulating pipe 8b. An outlet at the lower part of the side wall of the cooling crystallizer 8a is connected with an inlet of a cooling crystal slurry pump 8e, an outlet of the cooling crystal slurry pump 8e is connected with a cooling thick tank 8f and a cooling circulation pipe 8b, an outlet at the bottom of the cooling thick tank 8f is connected with an inlet of a cooling centrifuge 8g, a solid phase outlet of the cooling centrifuge 8g is connected with a sodium nitrate drying unit 9, a liquid phase outlet of the cooling centrifuge 8g and an upper overflow port of the cooling crystallizer 8a are connected with an inlet of a cooling mother liquid tank 8h together, an outlet of the cooling mother liquid tank 8h is connected with a cooling unit mother liquid pipe 8k and the cooling circulation pipe 8b through a cooling mother liquid pump 8j, and the cooling unit mother liquid pipe 8k is connected with an inlet of a multi-effect feeding pump 3p.

And the flash evaporation discharging pump 7c sends new sodium nitrate into the cooling circulating pipe 8b, the new sodium nitrate and the circulating liquid enter the cooling circulating pump 8c together, the cooling circulating pump 8c sends the sodium nitrate solution into the cooling heat exchanger 8d to be cooled to normal temperature, a large amount of sodium nitrate is crystallized and separated out after the sodium nitrate solution enters the cooling crystallizer 8a, and the overflow of the cooling crystallizer 8a continues to enter the cooling circulating pipe 8b for circulation. The shell side of the cooling heat exchanger 8d is provided with cooling water circulation through an internal circulation pump 8p, an outlet pipeline of the internal circulation pump 8p is connected with a refrigerant cache barrel 8n, an outlet of the refrigerant cache barrel 8n is connected with an inlet of a refrigerator 8m through a pump, and an outlet of the refrigerator 8m is connected with an inlet pipeline of the internal circulation pump 8p. The cooling water supply pipe G3 is connected with a cooling water inlet of the first refrigerator 8m, and a cooling water outlet of the first refrigerator 8m is connected with a cooling water return pipe G4.

And pumping the sodium nitrate crystal slurry at the bottom of the cooling crystallizer 8a by a cooling crystal slurry pump 8e, sending the sodium nitrate crystal slurry into a cooling thickening tank 8f for caching, then sending the sodium nitrate crystal slurry into a cooling centrifuge 8g for solid-liquid separation to obtain high-purity sodium nitrate salt and sodium nitrate centrifugal mother liquor, and sending the obtained sodium nitrate salt into a sodium nitrate drying unit 9 for drying to obtain high-purity sodium nitrate finished salt. The sodium nitrate centrifugal mother liquor, the overflow of the cooling thickening tank 8f and the overflow of the top of the cooling crystallizer 8a enter a cooling mother liquor tank 8h together for collection, the concentration of sodium chloride in the cooling mother liquor tank 8h is 7.6 percent, the concentration of sodium nitrate is 41 percent, the sodium nitrate is pumped out by a cooling mother liquor pump 8j and returns to the inlet of the sodium chloride evaporative crystallization unit 4 from a cooling unit mother liquor pipe 8k, and the sodium nitrate can also return to a cooling circulation pipe 8b for circulation or impurity salt preparation. The solubility of the sodium nitrate is reduced along with the reduction of the temperature, and the reduction of the solubility below 20 ℃ is gradual; the system cools the sodium nitrate solution to normal temperature for crystallization, and can improve the production efficiency.

As shown in fig. 4, the sodium nitrate drying unit 9 includes a vibration drying bed 9c, a solid phase outlet of a cooling centrifuge 8g is connected with a feed inlet of the vibration drying bed 9c, a hot air inlet of the vibration drying bed 9c is connected with an outlet of an air heater 9b, a hot air outlet of the vibration drying bed 9c is connected with an air inlet of a cyclone 9d, a bottom discharge port of the cyclone 9d and a discharge port of the vibration drying bed 9c are connected with a sodium nitrate packing device 9g together, a top air outlet of the cyclone 9d is connected with an inlet of a water film dust collector 9f through an induced draft fan 9e, and a liquid discharge port of the water film dust collector 9f is connected with an inlet of a cooling mother liquid tank 8h.

And sodium nitrate salt at the outlet of the cooling centrifuge 8g enters a vibration drying bed 9c for drying, the discharge material of the vibration drying bed 9c is sodium nitrate finished salt with the purity of 98%, and the sodium nitrate finished salt enters sodium nitrate packing equipment 9g for packing. The product meets the standard of general industrial qualified products in GB/T4553-2016 industrial sodium nitrate and can be sold externally. After fresh air is sent into the air heater 9b by the air blower 9a to be heated, hot air enters from the lower part of the vibration drying bed 9c, tail gas is discharged from the top of the vibration drying bed 9c, collected materials also enter into a package after being dedusted by the cyclone dust collector 9d, the tail gas is discharged from the top of the cyclone dust collector 9d, enters into the water film dust collector 9f to be dedusted under the suction of the draught fan 9e, and dedusting liquid returns to the cooling mother liquid tank 8h to be circulated, so that the discharge is stopped, and the materials are recycled.

As shown in fig. 5, the sodium sulfate freezing and crystallizing unit 10 includes a freezing crystallizer 10a, a freezing heat exchanger 10d and a freezing circulating pump 10c, wherein the outlet of the freezing feed pump 3d is connected with the inlet of the hot side of the precooler 10k, and the outlet of the hot side of the precooler 10k is connected with the inlet of the freezing circulating pump 10 c; the outlet of the freezing circulating pump 10c is connected with the inlet of the freezing heat exchanger 10d, the outlet of the freezing heat exchanger 10d is connected with the feeding pipe of the freezing crystallizer 10a, and the circulating liquid outlet of the freezing crystallizer 10a is connected with the inlet of the freezing circulating pump 10c through the freezing circulating pipe 10 b; an outlet at the lower part of the side wall of the freezing crystallizer 10a is connected with an inlet of a freezing crystal slurry pump 10e, an outlet of the freezing crystal slurry pump 10e is connected with a freezing thick tank 10f and a freezing circulating pipe 10b, an outlet at the bottom of the freezing thick tank 10f is connected with an inlet of a freezing centrifugal machine 10g, a solid phase outlet of the freezing centrifugal machine 10g is connected with a sodium sulfate hot melting crystallization unit 11, a liquid phase outlet of the freezing centrifugal machine 10g and an upper overflow port of the freezing crystallizer 10a are connected with an inlet of a freezing mother liquid tank 10h together, an outlet of the freezing mother liquid tank 10h is connected with the freezing circulating pipe 10b and a cold side inlet of a precooler 10k through a freezing mother liquid pump 10j, and a cold side outlet of the precooler 10k is connected with a freezing unit external discharge pipe 10m.

The new sodium sulfate solution with the temperature of 25 ℃ is pre-cooled to 14 ℃ by a pre-cooler 10k by a freezing feed pump 3d and then is sent into a freezing circulating pipe 10b, the new sodium sulfate solution and circulating liquid enter a freezing circulating pump 10c together, the freezing circulating pump 10c sends the sodium sulfate solution into a freezing heat exchanger 10d to be cooled to 0 ℃, a large amount of sodium sulfate is crystallized and separated out after the sodium sulfate solution enters a freezing crystallizer 10a, and the overflow of the freezing crystallizer 10a continues to enter the freezing circulating pipe 10b for circulation. The shell pass of the refrigerating heat exchanger 10d is provided with refrigerant ethylene glycol circulation by an internal circulation pump II 10q, an outlet pipeline of the internal circulation pump II 10q is connected with a refrigerant cache barrel II 10p, an outlet of the refrigerant cache barrel II 10p is connected with an inlet of a refrigerating machine II 10n through a pump, and an outlet of the refrigerating machine II 10n is connected with an inlet pipeline of the internal circulation pump II 10q.

After being pumped by a frozen crystal slurry pump 10e, the sodium sulfate crystal slurry at the bottom of the frozen crystallizer 10a is sent to a frozen thick tank 10f for caching, and then enters a frozen centrifugal machine 10g for solid-liquid separation to obtain sodium sulfate decahydrate and sodium sulfate centrifugal mother liquor, and the obtained sodium sulfate decahydrate, namely mirabilite, is sent to a sodium sulfate drying unit 12 for drying to obtain sodium sulfate finished salt. The sodium sulfate centrifugal mother liquor, the overflow of the freezing thick tank 10f and the overflow of the top of the freezing crystallizer 10a enter the freezing mother liquor tank 10h together for collection, are pumped out by a freezing mother liquor pump 10j, enter a precooler 10k for precooling a new sodium sulfate solution, realize the recycling of residual cold, save the energy consumption of the system, and discharge the heated sodium sulfate centrifugal mother liquor from a pipe 10m outside the freezing unit.

As shown in fig. 6, the sodium sulfate hot melting crystallization unit 11 includes a first-effect and second-effect saltpeter evaporation units and a saltpeter hot melting tank 11p, a solid phase outlet of a refrigerated centrifuge 10g is connected with an inlet of the saltpeter hot melting tank 11p, a bottom outlet of the saltpeter hot melting tank 11p is connected with a first-effect saltpeter circulating pipe 11b through a saltpeter mother liquor pump 11q, an outlet of the first-effect saltpeter circulating pipe 11b is connected with an inlet of a first-effect saltpeter circulating pump 11c, an outlet of the first-effect saltpeter circulating pump 11c is connected with an inlet of a first-effect saltpeter evaporator 11d, an outlet of the first-effect saltpeter evaporator 11d is connected with a feed inlet of a first-effect saltpeter separator 11a, a bottom outlet of the first-effect saltpeter separator 11a is connected with an inlet of a saltpeter thick tank 11m pump 11e, a bottom outlet of the thick saltpeter thick tank 11m thick tank is connected with an inlet of a saltpeter centrifuge 11n, a liquid phase outlet of the saltpeter centrifuge 11n is connected with an inlet of the saltpeter centrifuge 11p, and a saltpeter centrifuge unit 11n is connected with a solid phase outlet of the saltpeter centrifuge 12 n.

An outlet of the nitrate mother liquor pump 11q is connected with a double-effect nitrate circulating pipe 11g, an outlet of the double-effect nitrate circulating pipe 11g is connected with an inlet of a double-effect nitrate circulating pump 11h, an outlet of the double-effect nitrate circulating pump 11h is connected with an inlet of a double-effect nitrate evaporator 11j, an outlet of the double-effect nitrate evaporator 11j is connected with a feed inlet of a double-effect nitrate separator 11f, a bottom outlet of the double-effect nitrate separator 11f is connected with the double-effect nitrate circulating pipe 11g, and a salt leg outlet of the double-effect nitrate separator 11f is connected with an inlet of a nitrate thickening tank 11m through a double-effect nitrate crystal slurry pump 11 k; a shell pass inlet of the first-effect saltpeter evaporator 11d is connected with a raw steam pipe G1, a steam outlet at the top of the first-effect saltpeter separator 11a is connected with a shell pass inlet of the second-effect saltpeter evaporator 11j, shell pass outlets of the first-effect saltpeter evaporator 11d and the second-effect saltpeter evaporator 11j are respectively connected with a double-effect condensate water tank 11r, and an outlet of the double-effect condensate water tank 11r is connected with a condensate water recovery pipe G2 through a double-effect condensate water pump 11 s; the top steam outlet of the double-effect saltpeter separator 11f is connected with a saltpeter surface cooler 11t.

The mirabilite hot melting tank is a mother liquor tank of the system and also serves as a mirabilite melting tank and a feeding tank, cost is saved, mirabilite obtained by the sodium sulfate freezing and crystallizing unit 10 enters the mirabilite hot melting tank 11p, a sodium sulfate solution with the concentration of 32.6% is pumped out by the mirabilite mother liquor pump 11q and returns to the first-effect mirabilite circulating pipe 11b and the second-effect mirabilite circulating pipe 11G for circulation, secondary steam discharged by the first-effect mirabilite separator 11a serves as a heat source of the second-effect mirabilite evaporator 11j, and condensed water of the shell pass of the first-effect mirabilite evaporator 11d and the second-effect mirabilite evaporator 11j enters the double-effect condensed water tank 11r for collection, is pumped out by the double-effect condensed water pump 11s and then enters the condensed water recovery pipe G2 for recycling. When the solid-liquid ratio of the system reaches 1: after 10, pumping the salt slurry into a nitrate thickening tank 11m for caching through a first-effect nitrate crystal slurry pump 11e and a second-effect nitrate crystal slurry pump 11k, then separating the salt slurry into high-purity sodium sulfate and nitrate centrifugal mother liquor in a nitrate centrifuge 11n, and drying the obtained sodium sulfate in a sodium sulfate drying unit 12 to obtain sodium sulfate with the purity of 99%, wherein the sodium sulfate meets the first-class II standard of 'GB/T6009-2014 industrial anhydrous sodium sulfate', and can be sold externally.

As shown in fig. 7, an outlet of a mother liquor pipe 8k of the cooling unit or an outlet of an external discharging pipe 10m of the freezing unit is connected with a feed inlet of a mixed salt evaporator 13a, an outlet at the bottom of the mixed salt evaporator 13a is connected with an inlet of a mixed salt centrifuge 13b, a liquid phase outlet of the mixed salt centrifuge 13b is connected with a temporary mixed salt mother liquor storage tank 13c, an outlet of the temporary mixed salt mother liquor storage tank 13c is connected with a return port of the mixed salt evaporator 13a through a mixed salt mother liquor reflux pump 13d, and a solid phase outlet of the mixed salt centrifuge 13b is connected with a mixed salt packaging device 13 e; an exhaust port of the miscellaneous salt evaporation kettle 13a is connected with an inlet of a second surface cooler 13f, and an outlet of the second surface cooler 13f is connected with a second vacuum pump 13g.

And waste mother liquor discharged from a mother liquor pipe 8k of the cooling unit or an outer discharge pipe 10m of the freezing unit enters a mixed salt evaporation kettle 13a for evaporation and crystallization, then enters a mixed salt centrifuge 13b for solid-liquid separation, and is packed in a solid phase to obtain the saleable mixed salt. The mixed salt centrifugal mother liquor enters a mixed salt mother liquor temporary storage tank 13c for storage, is pumped out by a mixed salt mother liquor reflux pump 13d and returns to the mixed salt evaporation kettle 13a for circulation; the waste mother liquor is solidified, so that the waste water is completely recycled, and the quality of the main product salt is improved. And under the suction of a second vacuum pump 13g, the exhaust steam of the mixed salt evaporation kettle 13a enters a second surface air cooler 13f for condensation, and the mixed salt evaporation kettle 13a is maintained to accelerate evaporation under vacuum. The condensed water in the jacket of the miscellaneous salt evaporation kettle 13a enters a miscellaneous salt condensed water collection tank 13h for collection, and is sent to a condensed water recovery pipe G2 by a miscellaneous salt condensed water pump 13j for recovery.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention. In addition to the above embodiments, the present invention may have other embodiments, and all technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of the present invention. Technical features of the present invention which are not described may be implemented by or using the prior art, and will not be described herein.

Claims

1. A method for recycling TDI industrial wastewater is characterized by sequentially comprising the following steps: the method comprises the steps that calcium magnesium ions and bicarbonate radical are removed from mixed miscellaneous salt wastewater rich in sodium nitrate, sodium chloride and sodium sulfate through a pretreatment unit; the separation of divalent salt and monovalent salt is realized through a salt separating unit; the divalent salt is subjected to secondary nanofiltration and reconcentration to enable the concentration of the sodium sulfate solution to reach 9.86%, the sodium sulfate solution enters a sodium sulfate freezing and crystallizing unit to be subjected to freezing and crystallizing at 0 ℃, then enters a sodium sulfate hot melting and crystallizing unit to be subjected to double-effect evaporation and crystallization, and is dried and packaged to obtain sodium sulfate with the purity of 99%; the monovalent salt mixed solution is subjected to SWRO reverse osmosis and electrodialysis and then concentrated to ensure that the concentration of sodium chloride reaches 4 percent and the concentration of sodium nitrate reaches 9.9 percent; fourthly, enabling the monovalent salt mixed solution to enter a sodium chloride evaporation and crystallization unit for multi-effect evaporation to separate out sodium chloride crystals and separate from a sodium nitrate solution; washing the precipitated sodium chloride crystals by a salt washing unit, and drying and packaging to obtain sodium chloride with the purity of 98%; fifthly, enabling the sodium nitrate solution to enter a sodium nitrate flash evaporation unit, carrying out flash evaporation and cooling under the vacuum condition, firstly separating out a part of sodium nitrate, then enabling the sodium nitrate solution to enter a sodium nitrate cooling and crystallizing unit to be cooled to the normal temperature to crystallize the sodium nitrate, drying through a sodium nitrate drying unit, and packaging to obtain the sodium nitrate with the purity of 99%.

2. The recycling treatment method of TDI industrial wastewater according to claim 1, which comprises: the sodium chloride evaporation crystallization unit comprises a first-effect salt evaporation unit, a second-effect salt evaporation unit and a third-effect salt evaporation unit, wherein the outlet of a multi-effect feed pump is connected with the third-effect salt evaporation unit, the discharge of the third-effect salt evaporation unit is connected with the second-effect salt evaporation unit through a third-effect salt transfer pump, and the discharge of the second-effect salt evaporation unit is connected with the first-effect salt evaporation unit through a second-effect salt transfer pump; the lower part of an effective salt separator of the effective salt evaporation unit is connected with an inlet of an effective salt circulating pump through an effective salt circulating pipe, an outlet of the effective salt circulating pump is connected with a tube pass inlet of the effective salt evaporator, and a tube pass outlet of the effective salt evaporator is connected with a feeding pipe of the effective salt separator; a sedimentation separator is arranged on the primary effective salt circulating pipe, the diameter ratio of the diameter of the sedimentation separator to the primary effective salt circulating pipe is 3.5:1, the top outlet of the settling separator is connected with the inlet of a flash feed pump, and the outlet of the flash feed pump is connected with the sodium nitrate flash unit and a primary salt circulating pipe.

3. The recycling treatment method of TDI industrial wastewater according to claim 2, which comprises: the bottom of the first-effect salt separator is provided with a salt leg, the bottom outlet of the salt leg is connected with the inlet of the thick salt tank through a thick salt crystal slurry pump, the bottom outlet of the thick salt tank is connected with the inlet of a thick salt centrifugal machine, the clear liquid outlet of the thick salt centrifugal machine and the overflow port of the thick salt tank are both connected with a salt mother liquid tank, and the bottom outlet of the salt mother liquid tank is connected with the inlet of a flash evaporation feed pump through a salt mother liquid pump; the salt discharging port of the coarse salt centrifuge is connected with the salt washing tank, the bottom of the salt washing tank is connected with the inlet of the salt washing pump, the outlet of the salt washing pump is simultaneously connected with the fine salt thick tank and the salt mother liquor tank, the overflow port of the fine salt thick tank is connected with the salt washing tank, the bottom outlet of the fine salt thick tank is connected with the inlet of the fine salt centrifuge, the clear liquid outlet of the fine salt centrifuge is connected with the salt washing tank, and the fine salt outlet of the fine salt centrifuge is connected with the sodium chloride drying unit.

4. The method for recycling TDI industrial wastewater as claimed in claim 3, wherein: the sodium nitrate flash unit comprises a flash tank, an inlet of the flash tank is connected with an outlet of the flash feed pump, a sodium nitrate flash pipe at the top of the flash tank is connected with the top of a triple-effect salt separator of the triple-effect salt evaporation unit, and an outlet at the bottom of the flash tank is connected with an inlet of the flash discharge pump; the sodium nitrate cooling crystallization unit comprises a cooling crystallizer, a cooling heat exchanger and a cooling circulating pump, wherein the outlet of the flash evaporation discharging pump is connected with the inlet of the cooling circulating pump, the outlet of the cooling circulating pump is connected with the inlet of the cooling heat exchanger, the outlet of the cooling heat exchanger is connected with the feeding pipe of the cooling crystallizer, and the circulating liquid outlet of the cooling crystallizer is connected with the inlet of the cooling circulating pump through a cooling circulating pipe; the outlet of the lower part of the side wall of the cooling crystallizer is connected with the inlet of a cooling crystal slurry pump, the outlet of the cooling crystal slurry pump is connected with a cooling thick tank and a cooling circulating pipe, the outlet of the bottom of the cooling thick tank is connected with the inlet of a cooling centrifuge, the solid-phase outlet of the cooling centrifuge is connected with a sodium nitrate drying unit, the liquid-phase outlet of the cooling centrifuge is connected with the upper overflow port of the cooling crystallizer and the inlet of a cooling mother liquid tank, the outlet of the cooling mother liquid tank is connected with a cooling unit mother liquid pipe and the cooling circulating pipe through a cooling mother liquid pump, and the cooling unit mother liquid pipe is connected with the inlet of a multi-effect feeding pump.

5. The recycling treatment method of TDI industrial wastewater according to claim 4, which comprises: the dry unit of sodium nitrate includes the vibration drying bed, cooling centrifuge's solid phase outlet with the feed inlet of vibration drying bed links to each other, the hot-blast import of vibration drying bed links to each other with air heater's export, the hot air exitus of vibration drying bed links to each other with cyclone's air intake, cyclone's bottom discharge mouth with the discharge gate of vibration drying bed links to each other with sodium nitrate baling equipment jointly, cyclone's top air outlet passes through the entry that draught fan and water film deduster and links to each other, water film deduster's leakage fluid dram with the entry of cooling mother liquor jar links to each other.

6. The recycling treatment method of TDI industrial wastewater according to claim 1, which comprises: the sodium sulfate freezing and crystallizing unit comprises a freezing crystallizer, a freezing heat exchanger and a freezing circulating pump, wherein an outlet of the freezing feed pump is connected with an inlet at the hot side of the precooler, and an outlet at the hot side of the precooler is connected with an inlet of the freezing circulating pump; the outlet of the freezing circulating pump is connected with the inlet of the freezing heat exchanger, the outlet of the freezing heat exchanger is connected with the feeding pipe of the freezing crystallizer, the circulating overflow port of the freezing crystallizer is connected with the inlet of the freezing circulating pump through a freezing circulating pipe, the outlet of the lower part of the side wall of the freezing crystallizer is connected with the inlet of a freezing crystal slurry pump, the outlet of the freezing crystal slurry pump is connected with a freezing thick tank and the freezing circulating pipe, the outlet of the bottom of the freezing thick tank is connected with the inlet of a freezing centrifugal machine, the solid-phase outlet of the freezing centrifugal machine is connected with a sodium sulfate hot melting crystallization unit, the liquid-phase outlet of the freezing centrifugal machine and the upper overflow port of the freezing crystallizer are connected with the inlet of a freezing mother liquid tank together, the outlet of the freezing mother liquid tank is connected with the freezing circulating pipe and the cold-side inlet of the precooler through a freezing mother liquid pump, and the cold-side outlet of the precooler is connected with the outer discharge pipe of the freezing unit.

7. The recycling treatment method of TDI industrial wastewater according to claim 6, which comprises: sodium sulfate hot melt crystallization unit includes one imitates, two imitates nitre evaporation unit and nitre hot melt jar, freezing centrifuge's solid phase export with the entry of nitre hot melt jar links to each other, the bottom export of nitre hot melt jar links to each other with an effect nitre circulating pipe through the nitre mother liquor pump, the export of an effect nitre circulating pipe links to each other with the entry of an effect nitre circulating pump, the export of an effect nitre evaporator links to each other with the feed inlet of an effect nitre separator, the bottom export of an effect nitre separator with an effect nitre circulating pipe links to each other, the salt leg export of an effect nitre separator links to each other through the entry of an effect nitre brilliant and nitre thick jar, the bottom export of nitre thick jar links to each other with the entry of nitre centrifuge, the liquid phase export of nitre centrifuge with the entry of nitre hot melt jar links to each other, the solid phase export of nitre centrifuge links to each other with sodium sulfate drying unit.

8. The recycling treatment method of TDI industrial wastewater according to claim 7, which comprises: the outlet of the nitrate mother liquor pump is connected with a double-effect nitrate circulating pipe, the outlet of the double-effect nitrate circulating pipe is connected with the inlet of a double-effect nitrate circulating pump, the outlet of the double-effect nitrate circulating pump is connected with the inlet of a double-effect nitrate evaporator, the outlet of the double-effect nitrate evaporator is connected with the feed inlet of a double-effect nitrate separator, the bottom outlet of the double-effect nitrate separator is connected with the double-effect nitrate circulating pipe, and the salt leg outlet of the double-effect nitrate separator is connected with the inlet of the nitrate thickening tank through a double-effect nitrate crystal pulp pump; the shell pass inlet of the first-effect saltpeter evaporator is connected with a raw steam pipe, the top steam outlet of the first-effect saltpeter separator is connected with the shell pass inlet of the second-effect saltpeter evaporator, the shell pass outlets of the first-effect saltpeter evaporator and the second-effect saltpeter evaporator are respectively connected with a double-effect condensate water tank, and the outlet of the double-effect condensate water tank is connected with a condensate water recovery pipe through a double-effect condensate water pump; and a steam outlet at the top of the two-effect saltpeter separator is connected with a saltpeter surface cooler.

9. The recycling treatment method of TDI industrial wastewater according to claim 6, which comprises: the outlet of the outer discharge pipe of the freezing unit is connected with the feed inlet of a mixed salt evaporation kettle, the outlet at the bottom of the mixed salt evaporation kettle is connected with the inlet of a mixed salt centrifuge, the liquid-phase outlet of the mixed salt centrifuge is connected with a mixed salt mother liquor temporary storage tank, the outlet of the mixed salt mother liquor temporary storage tank is connected with the reflux port of the mixed salt evaporation kettle through a mixed salt mother liquor reflux pump, and the solid-phase outlet of the mixed salt centrifuge is connected with a mixed salt packaging device; and an exhaust port of the miscellaneous salt evaporation kettle is connected with an inlet of a surface air cooler II, and an outlet of the surface air cooler II is connected with a vacuum pump II.