A method for treating high ammonia-nitrogen wastewater in production of a catalytic cracking catalyst

Abstract

This invention relates to the field of high ammonia nitrogen wastewater treatment technology, specifically to a method for treating high ammonia nitrogen wastewater generated during catalytic cracking catalyst production. The method includes pretreatment of the high ammonia nitrogen wastewater, impurity and hardness removal, membrane concentration treatment, ammonia nitrogen removal treatment, and falling membrane evaporation crystallization of the deammoniated wastewater. This invention optimizes the treatment steps for high ammonia nitrogen wastewater generated during molecular sieve preparation in catalytic cracking catalyst production, achieving a 50% reduction in the amount of high ammonia nitrogen wastewater requiring ammonia nitrogen removal treatment. It solves the problems of scaling on the trays and packing of the composite stripping ammonia removal tower and overheating of the disc-tube reverse osmosis membrane during summer operation. Simultaneously, it increases the wastewater temperature entering the MVR unit, reduces steam consumption, and significantly lowers the cost of treating high ammonia nitrogen wastewater.

Description

Technical Field

[0001] This invention relates to the field of high ammonia nitrogen wastewater treatment technology, specifically to a method for treating high ammonia nitrogen wastewater produced during catalytic cracking catalyst production. Background Technology

[0002] Molecular sieves are an intermediate product in the production of catalytic cracking catalysts. Their production often results in the generation of large quantities of high-ammonia-nitrogen wastewater. This wastewater is typically acidic and contains high levels of NH4+. + It has a high content and contains a large amount of suspended solids and SO4. 2- Na + and Cl - Substances such as SiO2 not only possess high biotoxicity but also pose potential risks to the ecological environment. Therefore, how to effectively treat wastewater with high ammonia nitrogen levels has become one of the most pressing issues to be addressed in the petrochemical industry.

[0003] Traditional treatment methods utilize ammonium sulfate-ammonia nitrogen treatment units. This process is quite complex, involving multiple stages including a combined stripping ammonia removal tower, an ammonia absorption tower, an ammonium sulfate saturation tower, a tail gas absorption tower, an ammonia distillation tower, and an ammonia removal tower. During treatment, the temperature needs to be maintained at approximately 80°C, which undoubtedly consumes a significant amount of energy. Furthermore, after treatment by the ammonium sulfate-ammonia nitrogen treatment unit, the wastewater must enter a gel pretreatment system for chemical dosing and cooling using an ice machine. Subsequently, the wastewater enters a deep membrane treatment system for concentration, and finally, during evaporation using an MVR unit, it requires heating again. This heating-cooling-heating process results in substantial unnecessary energy waste, increases treatment costs, and is detrimental to sustainable development.

[0004] Therefore, it is necessary to optimize the existing treatment methods for high ammonia nitrogen wastewater in catalytic cracking catalyst production, eliminating the heating-cooling-heating operation to achieve more economical and efficient treatment. Summary of the Invention

[0005] To address the technical problems of existing high-ammonia nitrogen wastewater treatment processes that require heating-cooling-heating, resulting in significant unnecessary energy waste, increased treatment costs, and hindering sustainable development, this invention provides a method for treating high-ammonia nitrogen wastewater in catalytic cracking catalyst production.

[0006] The technical solution of this invention is as follows:

[0007] A method for treating high-ammonia nitrogen wastewater produced in catalytic cracking catalyst production includes the following steps:

[0008] (1) Pretreatment of wastewater with high ammonia nitrogen;

[0009] (2) Removal of impurities and hardness from wastewater with high ammonia nitrogen content;

[0010] (3) Membrane concentration treatment of high ammonia nitrogen wastewater;

[0011] (4) Ammonia nitrogen removal treatment of high ammonia nitrogen wastewater:

[0012] The concentrated high-ammonia-nitrogen wastewater is pumped into a heat exchanger to exchange heat with the ammonia-nitrogen-removed wastewater, and then enters the first heating section of the composite stripping ammonia removal tower.

[0013] A portion of the gas extracted from the secondary flash section of the composite stripping ammonia removal tower is returned to the primary heating section of the composite stripping ammonia removal tower and mixed with the high ammonia nitrogen wastewater in the primary heating section.

[0014] The temperature of the primary heating section is controlled at 51~69℃ and the pressure is ≤-0.07MPa. After heating, the high ammonia nitrogen wastewater is pressurized by the flash feed pump and mixed with the gas extracted from the primary flash section of the composite stripping ammonia removal tower before entering the secondary heating section of the composite stripping ammonia removal tower.

[0015] The secondary heating section is controlled at a temperature of 62~89℃, a pressure of ≤0.045MPa, and a liquid level of <80%. After the high ammonia nitrogen wastewater after the two-stage heating is adjusted to pH 10.5≤13.5, it is pumped into the middle of the stripping section of the composite stripping deammoniation tower. The top temperature of the tower is controlled at ≤107℃, the bottom temperature at 90~105℃, and the pressure at ≤0.095MPa.

[0016] High ammonia nitrogen wastewater flows downwards and comes into countercurrent contact with the steam introduced into the stripping section, causing the ammonia nitrogen content in the water to gradually decrease.

[0017] Wastewater is treated in the first-stage flash evaporation section of the composite stripping ammonia removal tower at a temperature of 78~82℃ and a pressure of ≤-0.045MPa, and in the second-stage flash evaporation section at a temperature of 50~68℃ and a pressure of ≤-0.070MPa. After two flash evaporations to remove ammonia nitrogen, crystallization evaporation is used for desalination.

[0018] (5) Falling film evaporation crystallization after ammonia nitrogen removal from wastewater:

[0019] After ammonia nitrogen removal, the wastewater is fed through a distilled water preheater (temperature controlled at ≥80℃), a non-condensable gas preheater (temperature controlled at ≥85℃), and a fresh steam preheater (temperature preheated to 94~99℃) before entering a first-stage falling film heat exchanger. After material concentration, it is transported by pressure difference to a second-stage falling film heat exchanger for further evaporation and concentration. The distilled water is collected and sent to the production water tank for reuse.

[0020] Furthermore, the untreated high-ammonia nitrogen wastewater had a pH of 3-6, an ammonia nitrogen content of 5000 mg / L, a suspended solids content of 4000 mg / L, a chloride content of 100 mg / L, a sulfate content of 25000 mg / L, a silica content of 200 mg / L, a sodium ion content of 25000 mg / L, and a TDS (total dissolved solids) content of 39945 mg / L.

[0021] Furthermore, step (1) specifically involves:

[0022] The pH value of the high ammonia nitrogen wastewater is adjusted by adding alkali, and then sent to reaction tank one along with a silica removal agent. After stirring, it overflows into clarifier tank one. The supernatant after sedimentation in clarifier tank one is pumped to reaction tank two. Alkali and flocculant are added to reaction tank two, and after stirring, it overflows into clarifier tank two. The supernatant after sedimentation in clarifier tank two has a pH value of 9.5, suspended solids <60mg / L, aluminum <30mg / L, and silica <60mg / L.

[0023] Furthermore, in step (1), alkali is added to the reaction tank to adjust the pH value of the high ammonia nitrogen wastewater to 7.5~8.5;

[0024] The alkali is one or both of sodium hydroxide and sodium carbonate.

[0025] The silicon remover is one or more of lime, magnesium oxide, and sodium aluminate;

[0026] The stirring can be one or both of mechanical stirring and air stirring.

[0027] Furthermore, step (2) specifically involves:

[0028] After pretreatment, the high ammonia nitrogen wastewater is sent to a multi-media filter to remove suspended solids, and then enters an ion exchanger to remove calcium and magnesium ions. Finally, acid is added to adjust the pH using a pipeline mixer. The effluent turbidity is <3 NTU, pH is 6.0~6.5, and calcium is <1 mg / L.

[0029] Furthermore, in step (2), the multi-media filter is filled from bottom to top with a quartz sand pad with a particle size in the range of 1.0~2.0mm, a quartz sand with a particle size in the range of 0.5~1.2mm, and anthracite with a particle size in the range of 0.8~1.8mm.

[0030] The acid is 98% concentrated sulfuric acid.

[0031] Furthermore, step (3) specifically involves:

[0032] In step (2), the treated high ammonia nitrogen wastewater is pumped into the ultrafiltration membrane for external pressure and cross-flow filtration. The ultrafiltration permeate is pumped into the disc tube reverse osmosis membrane and a reducing agent and membrane treatment scale inhibitor are added to control the oxidation-reduction potential of the feed water and prevent membrane scaling. The high ammonia nitrogen wastewater is concentrated by a certain multiple. The disc tube reverse osmosis concentrate is collected and sent to the ammonia nitrogen removal unit.

[0033] Furthermore, in step (3), the ultrafiltration membrane is a tubular membrane or a hollow fiber membrane;

[0034] The reducing agent is sodium bisulfite;

[0035] The concentration factor of disc tube reverse osmosis membrane is 2 to 2.6 times;

[0036] The secondary reverse osmosis membrane is a spiral wound membrane;

[0037] The alkali is 32wt%~35wt% sodium hydroxide.

[0038] Furthermore, in step (3), after the permeate from the disc tube reverse osmosis membrane enters the secondary reverse osmosis membrane filtration, alkali is added to adjust the pH value to achieve the permeate index of turbidity <1NTU, TDS <100mg / L, and pH of 6.8~7.0. The permeate then enters the recycled water tank and is pumped into the production water tank for reuse.

[0039] Furthermore, in step (4), the heat exchanger is a plate heat exchanger or a shell-and-tube heat exchanger.

[0040] Adjust the pH using 32wt%~35wt% sodium hydroxide.

[0041] Furthermore, step (5) also includes:

[0042] The temperature of the liquid in the lower tube box of the first-effect falling film heat exchanger is controlled at 96~100℃, the liquid level at 0.3~2.0m, and the shell-side pressure at 970~1270mbar. The temperature of the liquid in the lower tube box of the second-effect falling film heat exchanger is controlled at 90~94℃, the liquid level at 0.3~2.0m, and the shell-side pressure at 920~960mbar. The concentrated material in the lower tube box is pumped to a forced circulation evaporator for further evaporation, concentration, and crystallization. The further concentrated liquid is then separated by depressurized flash evaporation in a crystallization separator. The vapor pressure in the crystallization separator is controlled at... The concentration of Na2SO4 is ≥35.00%, with a feed temperature of 90-94℃, a liquid level of 0.3-6.0m, and a pressure of 630-720mbar. The concentrated liquid is circulated to a forced circulation evaporator via a forced circulation pump for further concentration. The outlet pressure of the forced circulation pump is 0.1-0.6MPa. When the concentration ratio reaches 25wt%-30wt%, a portion of the concentrated liquid is sent to a thickener and centrifuge via a discharge pump. After centrifugal dehydration, the sodium sulfate crystals are dried in a vibrating fluidized bed and packaged into the product, which can be sold externally.

[0043] Furthermore, in step (5), after the preheated wastewater after ammonia removal enters the double-effect falling film heat exchanger, it undergoes heat exchange and evaporation with the secondary steam after its temperature rises following compression by compressors #1 and #2 of the MVR unit. The entire system reaches thermal balance. Apart from the need for some fresh steam for preheating, the remaining time period only requires the compressor to consume electrical energy to maintain the thermal balance of evaporation in the MVR unit. Compressor #1 controls the outlet pressure to be ≥943mbar, the outlet temperature to be 95~101℃, and the motor frequency to be 15~55Hz. Compressor #2 controls the outlet temperature to be 93~109℃ and the motor frequency to be 15~55Hz.

[0044] Furthermore, in step (5), the distilled water preheater and the non-condensable gas preheater are plate heat exchangers or shell-and-tube heat exchangers.

[0045] The fresh steam preheater, the first-effect falling film heat exchanger, the second-effect falling film heat exchanger, and the forced circulation evaporator are all shell-and-tube heat exchangers.

[0046] The beneficial effects of this invention are as follows:

[0047] This invention optimizes the treatment steps for high ammonia nitrogen wastewater generated during the production of catalytic cracking catalysts due to the preparation of molecular sieves. It reduces the amount of high ammonia nitrogen wastewater requiring ammonia nitrogen removal by half, solves the problems of scaling on the trays and packing of the composite stripping ammonia removal tower, and addresses the issue of overheating of the disc tube reverse osmosis membrane during summer operation. It also increases the temperature of the concentrated brine entering the MVR unit, reduces steam consumption, and significantly lowers the cost of treating high ammonia nitrogen wastewater. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention.

[0050] Figure 2 This is a process flow diagram of the ammonia nitrogen removal treatment in step (4) of Embodiment 1 of the present invention.

[0051] Figure 3 This is a process flow diagram of step (5) of the falling film evaporation crystallization treatment in Embodiment 1 of the present invention. Detailed Implementation

[0052] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0053] Example 1

[0054] During the production of catalytic cracking catalyst, high-ammonia nitrogen wastewater is generated due to the production of molecular sieves. This high-ammonia nitrogen wastewater has a pH of 4, an ammonia nitrogen content of 5000 mg / L, a suspended solids content of 4000 mg / L, a chloride content of 100 mg / L, a sulfate content of 25000 mg / L, a silica content of 200 mg / L, a sodium ion content of 25000 mg / L, and a TDS (total dissolved solids) content of 39945 mg / L.

[0055] The treatment steps for this high-ammonia-nitrogen wastewater are as follows:

[0056] (1) Pretreatment of high ammonia nitrogen wastewater:

[0057] The high-ammonia nitrogen wastewater was collected in an equalization tank, where 32% sodium hydroxide was added to adjust the pH to 8.5. It was then sent to reaction tank one, where 8 ppm sodium aluminate was added as a silica removal agent. After stirring, the wastewater overflowed into clarifier tank one and was pumped to reaction tank two, where 32% sodium hydroxide, polyferric sulfate (flocculator one), and cationic PAM (flocculator two) were added. After mechanical stirring, the wastewater overflowed into clarifier tank two. After pretreatment to remove aluminum, calcium, rare earth ions, and suspended solids from the high-ammonia nitrogen wastewater, the effluent from clarifier tank two had a pH of 9.5, a suspended solids content of 30 mg / L, an aluminum content of 5 mg / L, and a silica content of 20 mg / L.

[0058] (2) Removal of impurities and hardness from wastewater with high ammonia nitrogen:

[0059] The pretreated high-ammonia nitrogen wastewater is sent to a multi-media filter to remove suspended solids. The multi-media filter is filled from bottom to top with a quartz sand cushion layer with a particle size of 1.0~2.0mm, quartz sand with a particle size of 0.5~1.2mm, and anthracite with a particle size of 0.8~1.8mm. Then it enters an ion exchanger to remove calcium and magnesium ions. Finally, 98% concentrated sulfuric acid is added to the pipeline mixer to adjust the pH to 6.0. The effluent turbidity is 1.5 NTU and the calcium content is 0.5 mg / L.

[0060] (3) Membrane concentration treatment of high ammonia nitrogen wastewater:

[0061] After treatment in step (2), the high ammonia nitrogen wastewater is collected and stored in the inlet tank. It is then pumped into a hollow fiber ultrafiltration membrane for external pressure and cross-flow filtration. The ultrafiltration permeate is pumped into a disc tube reverse osmosis membrane with 20% sodium bisulfite solution and membrane treatment-specific scale inhibitor i-A0002 (provided by Xiamen Jiarong Technology Co., Ltd.) added to control the oxidation-reduction potential of the inlet water and prevent membrane scaling. The high ammonia nitrogen wastewater is concentrated to 2.5 times. The concentrated water from the disc tube reverse osmosis membrane is collected and sent to the ammonia nitrogen removal unit. The permeate from the disc tube reverse osmosis membrane enters the secondary reverse osmosis membrane (wound membrane) for filtration. 32% sodium hydroxide is added to adjust the pH value to 7.0. The permeate with a turbidity of 0.5TU, a TDS content of 15mg / L, and a pH value of 7.0 is pumped into the recycling tank and then pumped into the plant's production water tank for reuse.

[0062] (4) Ammonia nitrogen removal treatment of high ammonia nitrogen wastewater:

[0063] The concentrated high-ammonia nitrogen wastewater is pumped into a heat exchanger to exchange heat with the ammonia nitrogen-removed wastewater, and then enters the composite gas ammonia removal tower. The composite gas ammonia removal tower includes a heating section, a stripping section and a flash section. The heating section is divided into a primary heating section and a secondary heating section, and the flash section is divided into a primary flash section and a secondary flash section.

[0064] The high ammonia nitrogen wastewater is first heated in the primary heating section. After being partially stripped from the secondary flash section of the composite stripping ammonia removal tower by a Venturi water ejector and mixed, it enters the primary heating section. The temperature of the primary heating section is controlled at 61.3℃ and the pressure is -0.075MPa. After being heated, the high ammonia nitrogen wastewater is pressurized by the flash feed pump and then mixed with the gas from the primary flash section of the composite stripping ammonia removal tower by a Venturi water ejector and enters the secondary heating section of the composite stripping ammonia removal tower.

[0065] The ammonia-nitrogen-containing wastewater after two-stage heating has a temperature of approximately 80℃, a pressure of 0.045MPa, and a liquid level of 25%. An appropriate amount of 32% sodium hydroxide is added to adjust the pH of the high-ammonia-nitrogen wastewater after two-stage heating to 10.6. This wastewater is then pumped into the middle of the stripping section of the composite stripping ammonia removal tower by a stripping feed pump. The tower top temperature is controlled at 95.6℃, the tower bottom temperature at 98.8℃, and the pressure at -0.0013MPa. In the middle of the stripping section of the composite stripping ammonia removal tower, the high-ammonia-nitrogen wastewater flows downwards and comes into countercurrent contact with the high-temperature steam entering the stripping section. Under alkaline, high-temperature conditions and dynamic action, the ammonia-nitrogen content in the water gradually decreases.

[0066] After ammonia removal, the wastewater undergoes two flash evaporations in the first-stage flash section (82℃, -0.046MPa) and the second-stage flash section (64℃, -0.073MPa) of the composite stripping ammonia removal tower for further ammonia removal. Then, it is sent to the MVR unit for desalination at about 60℃ by the ammonia removal wastewater discharge pump.

[0067] (5) Falling film evaporation and crystallization of wastewater after ammonia nitrogen removal:

[0068] After ammonia nitrogen removal, the wastewater is fed through a distilled water preheater (temperature controlled at 82℃), a non-condensable gas preheater (temperature controlled at 88℃), and a fresh steam preheater (temperature raised to 99℃) before entering the first-effect falling film heat exchanger. The temperature of the liquid in the lower tube box of the first-effect falling film heat exchanger is controlled at 99.6℃, the liquid level at 1.3m, and the shell-side pressure at 992mbar. After the material is continuously concentrated to a high concentration, it is transported by pressure difference to the second-effect falling film heat exchanger for further evaporation and concentration. The temperature of the liquid in the lower tube box of the second-effect falling film heat exchanger is controlled at 93℃, the liquid level at 1.5m, and the shell-side pressure at 920mbar. The material in the lower tube box is concentrated to a high concentration. The solution, nearing saturation, is pumped to a forced circulation evaporator for further evaporation, concentration, and crystallization. The further concentrated solution is then separated by depressurized flash evaporation in a crystallization separator. The crystallization separator controls the gas phase pressure at 700 mbar, the solution temperature at 94°C, the liquid level at 2.2 m, and the Na₂SO₄ concentration at 34.00%. Part of the concentrated solution is circulated back to the forced circulation evaporator via a forced circulation pump for further concentration. The outlet pressure of the forced circulation pump is 0.3 MPa. Once the concentration ratio meets the requirements, a portion of the concentrated solution is sent to a thickener and centrifuge via a discharge pump. After centrifugal dehydration, the sodium sulfate crystals enter a vibrating fluidized bed for drying and are then packaged as the final product. After the preheated wastewater with deammonia nitrogen enters the double-effect falling film heat exchanger, it exchanges heat with the secondary steam that has been compressed and heated by the compressors #1 and #2 of the MVR unit. The entire system reaches thermal equilibrium. Except for the part of fresh steam needed for preheating at start-up, the thermal equilibrium of the MVR unit is maintained by the compressor consuming electrical energy. The #1 compressor controls the outlet pressure to 945 mbar, the outlet temperature to 98℃, and the motor frequency to 48 Hz. The #2 compressor controls the outlet temperature to 106℃ and the motor frequency to 48 Hz.

[0069] Taking the method in Example 1 as an example, the pretreatment system for high ammonia nitrogen wastewater received 336,780 m³ of wastewater in 2023. 3 After membrane concentration of high ammonia nitrogen wastewater by 2.5 times, the concentrate was 126292 m³. 3 The reduction in high ammonia nitrogen wastewater volume was 210,488 m³. 3 The power consumption per unit of the ammonia removal nitrogen removal unit is 4.5761 kWh / m³. 3 Steam consumption is 25 kg / m³ 3 The unit price of steam is 350 yuan / ton, and the unit price of electricity is 0.72 yuan / kW·h. The volume of high-ammonia nitrogen wastewater was reduced by 210,488 m³. 3 This saved 1.842 million yuan in steam and 694,000 yuan in electricity costs. Furthermore, by adding heat exchangers to the inlet and outlet water of the ammonia removal unit, the outlet water temperature decreased from an average of 66.9℃ to 53.5℃, while the inlet water temperature increased from 33.6℃ to 47.2℃, resulting in a 5 kg / m³ decrease in steam consumption. 3 The treatment volume of high ammonia nitrogen wastewater was 126,292 m³.3 This saved 221,000 yuan in steam. After ammonia nitrogen removal, the evaporation and crystallization process increased the influent temperature from the designed 25℃ to 53.5℃, resulting in a 10 kg / m³ decrease in steam consumption. 3 This saved 442,000 yuan in steam. The cumulative efficiency improvement amounted to 3.2 million yuan, demonstrating that the method of this invention, through optimized processing, achieves effective resource utilization, thereby significantly reducing the consumption of electricity and steam.

[0070] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for treating high-ammonia nitrogen wastewater produced during catalytic cracking catalyst production, characterized in that, Includes the following steps: (1) Pretreatment of high ammonia nitrogen wastewater; (2) Removal of impurities and hardness from high ammonia nitrogen wastewater; (3) Membrane concentration treatment of high ammonia nitrogen wastewater; (4) The concentrated high-ammonia nitrogen wastewater is pumped into a heat exchanger to exchange heat with the wastewater after ammonia nitrogen removal, and then enters the first heating section of the composite stripping ammonia removal tower; a portion of the gas extracted from the second flash section of the composite stripping ammonia removal tower is returned to the first heating section of the composite stripping ammonia removal tower and mixed with the high-ammonia nitrogen wastewater in the first heating section; the temperature of the first heating section is controlled at 51~69℃ and the pressure is ≤-0.07MPa. After being pressurized by the flash feed pump, the heated high-ammonia nitrogen wastewater is mixed with the gas extracted from the first flash section of the composite stripping ammonia removal tower and enters the second heating section of the composite stripping ammonia removal tower; the temperature of the second heating section is controlled at 62~89℃ and the pressure is ≤0.045MPa. With a pressure of Pa and a liquid level <80%, the high-ammonia nitrogen wastewater after two stages of heating is adjusted to pH 10.5 ≤ 13.5 and then pumped into the middle of the stripping section of the composite stripping ammonia removal tower. The tower top temperature is controlled at ≤107℃, the tower bottom temperature at 90~105℃, and the pressure at ≤0.095MPa. The high-ammonia nitrogen wastewater flows downward and comes into countercurrent contact with the steam entering the stripping section, causing the ammonia nitrogen content in the water to gradually decrease. The wastewater undergoes two flash evaporation processes in the composite stripping ammonia removal tower: the temperature is controlled at 78~82℃ and the pressure at ≤-0.045MPa in the first-stage flash evaporation section, and the temperature is controlled at 50~68℃ and the pressure at ≤-0.070MPa in the second-stage flash evaporation section. (5) After ammonia nitrogen removal, the wastewater is fed through a distilled water preheater with a temperature control of ≥80℃, a non-condensable gas preheater with a temperature control of ≥85℃, and a fresh steam preheater to a temperature of 94~99℃. Then it enters the first-effect falling film heat exchanger. After the material is concentrated, it is transported to the second-effect falling film heat exchanger by pressure difference for further evaporation and concentration. The distilled water is collected and sent to the production water tank for reuse. The temperature of the liquid in the lower tube box of the first-effect falling film heat exchanger is controlled at 96~100℃, the liquid level at 0.3~2.0m, and the shell-side pressure at 970~1270mbar. The temperature of the liquid in the lower tube box of the second-effect falling film heat exchanger is controlled at 90~94℃, the liquid level at 0.3~2.0m, and the shell-side pressure at 920~960mbar. The concentrated material in the lower tube box of the second-effect falling film heat exchanger is transported by a transfer pump to a forced circulation evaporator for further evaporation, concentration, and crystallization. The concentrated liquid is then separated by depressurization flash evaporation in a crystallization separator. The crystallizer controls the gas phase pressure to be 630~720 mbar, the feed liquid temperature to be 90~94℃, the liquid level to be 0.3~6.0 m, and the mass fraction of sodium sulfate to be ≥35.00%. Part of the concentrated liquid is circulated to the forced circulation evaporator by a forced circulation pump for further concentration. The outlet pressure of the forced circulation pump is 0.1~0.6 MPa. When the concentration ratio reaches the requirement, part of the concentrated liquid is sent to the thickener and centrifuge by the discharge pump. After centrifugal dehydration, the crystals enter the vibrating fluidized bed for drying and are then packaged into products. After the preheated wastewater after ammonia and nitrogen removal enters the first-effect falling film heat exchanger and the second-effect falling film heat exchanger, it exchanges heat with the secondary steam after being compressed and heated by the compressors #1 and #2 of the MVR unit. The whole system reaches thermal balance. Except for the fresh steam required for preheating at start-up, the MVR unit's evaporation thermal balance is maintained by the compressor consuming electrical energy during other periods. Compressor #1 controls the outlet pressure to be ≥943mbar, the outlet temperature to be 95~101℃, and the motor frequency to be 15~55Hz. Compressor #2 controls the outlet temperature to be 93~109℃ and the motor frequency to be 15~55Hz.

2. The processing method as described in claim 1, characterized in that, Step (1) is as follows: The pH value of the high ammonia nitrogen wastewater is adjusted by adding alkali, and then sent to reaction tank one along with a silica removal agent. After stirring, it overflows into clarifier tank one. The supernatant after sedimentation in clarifier tank one is pumped to reaction tank two. Alkali and flocculant are added to reaction tank two, and after stirring, it overflows into clarifier tank two. The supernatant after sedimentation in clarifier tank two has a pH value of 9.5, suspended solids <60mg / L, aluminum <30mg / L, and silica <60mg / L.

3. The processing method as described in claim 2, characterized in that, In step (1), alkali is added to the reaction tank to adjust the pH of the high ammonia nitrogen wastewater to 7.5~8.5; the silica removal agent is one or more of lime, magnesium oxide, and sodium aluminate.

4. The processing method as described in claim 1, characterized in that, Step (2) is as follows: After pretreatment, the high ammonia nitrogen wastewater is sent to a multi-media filter to remove suspended solids, and then enters an ion exchanger to remove calcium and magnesium ions. Finally, acid is added to adjust the pH using a pipeline mixer. The effluent turbidity is <3 NTU, pH is 6.0~6.5, and calcium is <1 mg / L.

5. The processing method as described in claim 4, characterized in that, In step (2), the multi-media filter is filled from bottom to top with a quartz sand pad with a particle size of 1.0~2.0mm, a quartz sand with a particle size of 0.5~1.2mm, and anthracite with a particle size of 0.8~1.8mm.

6. The processing method as described in claim 1, characterized in that, Step (3) is as follows: In step (2), the treated high ammonia nitrogen wastewater is pumped into an ultrafiltration membrane for external pressure and cross-flow filtration. The ultrafiltration permeate is pumped into a disc tube reverse osmosis membrane, where reducing agent and membrane treatment scale inhibitor are added to control the oxidation-reduction potential of the feed water and prevent membrane scaling. The high ammonia nitrogen wastewater is concentrated by a certain factor. The permeate from the disc tube reverse osmosis membrane enters the secondary reverse osmosis membrane for filtration. After adding alkali to adjust the pH value, the permeate reaches the permeate index of turbidity <1 NTU, TDS <100 mg / L, and pH 6.8~7.

0. It enters the recycled water tank and is pumped into the production water tank for reuse. The concentrated water from the disc tube reverse osmosis membrane is collected and sent to the ammonia nitrogen removal unit.

7. The processing method as described in claim 6, characterized in that, In step (3), the reducing agent is sodium bisulfite; the concentration factor of the disc tube reverse osmosis membrane is 2 to 2.6 times.

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