An energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water

Abstract

The embodiment of the present invention discloses an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water. The present invention utilizes the volatility difference of COD-generating substances in the high-salt wastewater system to physically separate the COD in the ammonia nitrogen wastewater from the product, and recycle the ammonia nitrogen in the wastewater into high-purity liquid ammonia or ammonia water. At the same time, the steam circulation recovery process is coupled to the recovery process, which greatly saves the use of circulating water while reducing steam energy consumption, thereby achieving low energy consumption and high returns. The process flow is simple, the equipment investment cost is low, the operating cost is low, the operation is simple, the degree of automation is high, and the operation is stable.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of wastewater treatment technology, and specifically to an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water. Background Art

[0002] During the production process of ternary new materials, rare earth, battery recycling and other industries, a large amount of high-salt wastewater containing COD and ammonia nitrogen is generated. The general practice is to input this type of wastewater into the stripping distillation device for deammoniation and recovery of ammonia water. However, due to the introduction of a large amount of organic matter in the raw materials or production process, such as low-boiling-point, volatile oil substances, some oils are dissolved in the wastewater and are not easy to be removed before distillation. Therefore, the recovered ammonia water will contain a high concentration of COD, which affects the purity and quality of the ammonia water, making it difficult to reuse or sell it at a low value. Due to the difficulty of purifying COD from this type of wastewater, it is difficult to use this ammonia nitrogen wastewater to prepare high-purity liquid ammonia products that are more valuable than ammonia water. In addition, the removal of COD from this type of wastewater and the preparation of liquid ammonia or ammonia water often face the problems of high operating costs and high energy consumption, which is also one of the constraints for the resource recovery of this part of wastewater.

[0003] Patent CN220609159U discloses a device for preparing liquid ammonia from ammonia-nitrogen wastewater. The device uses a stripping tower, a mixer, and a heater. However, the device does not consider the purification of organic pollutants present in the ammonia-nitrogen wastewater. The purity of the prepared liquid ammonia is difficult to guarantee, and it is easily mixed with hexamethyldisiloxane organic matter generated during the production process, resulting in high COD in the recovered liquid ammonia, low liquid ammonia purity, and limited reuse.

[0004] Patent CN110921832B discloses a novel treatment device for high-ammonia nitrogen wastewater. Through a special structural design, the aerobic zone is divided into a first aerobic zone with decarbonizing bacteria as the dominant bacterial community and a second aerobic zone with nitrifying bacteria as the dominant bacterial community. COD degradation is carried out in the first aerobic zone, and nitrification and denitrification are carried out in the second aerobic zone, thereby reducing the inhibitory effect of decarbonizing bacteria on nitrifying bacteria and improving the nitrification and denitrification effect. However, the device cannot achieve resource recovery and utilization of ammonia nitrogen, nor can it treat high-salt ammonia-containing wastewater.

[0005] Patent CN220376509U discloses a high-COD and high-ammonia nitrogen wastewater treatment system, in which wastewater containing COD and ammonia nitrogen flows through a pretreatment system, a sand filtration system, and an ultrafiltration system in sequence to remove hardness and turbidity from the wastewater and filter out suspended matter, solid precipitation, etc. in the water; the filtrate of the ultrafiltration system enters a vibrating membrane system for filtration, and its concentrated water is preheated by a primary preheating system and a secondary preheating system. Through two-stage preheating, the wastewater can be heated to the requirements of a wet catalytic oxidation system, saving steam use. The wet catalytic oxidation system is then used to remove COD and ammonia nitrogen from the water. The wet catalytic oxidation system is placed before the evaporation crystallization system, which can reduce the preheating process in the evaporation crystallization system. Finally, crystalline salts and miscellaneous salts are obtained through the evaporation crystallization system, and the condensed water basically does not contain COD and ammonia nitrogen. However, a large amount of miscellaneous salts generated during the treatment process are difficult to treat as solid waste / hazardous waste, and the treatment cost is high and the investment is large.

[0006] The various existing technologies cannot effectively solve the problems of high energy consumption and high operating costs in the treatment process of high-salt wastewater containing COD and ammonia nitrogen, and it is difficult to recycle ammonia nitrogen into liquid ammonia or ammonia water. There is an urgent need for an energy-saving process for recycling ammonia nitrogen from high-salt wastewater containing COD and ammonia nitrogen to prevent volatile oil substances from entering liquid ammonia or ammonia water and affecting product quality. Summary of the Invention

[0007] To this end, the present invention proposes an energy-saving process for recycling high-purity liquid ammonia or ammonia water from high-salinity wastewater containing COD and ammonia nitrogen. By utilizing the volatility difference between COD-generating substances and ammonia gas in the high-salinity wastewater system, the COD in the ammonia nitrogen wastewater can be physically separated from the ammonia product, and the ammonia nitrogen in the wastewater can be recycled as a resource in the form of high-purity liquid ammonia or ammonia water. Simultaneously, a steam recycling process is coupled to the recycling process, significantly reducing the use of circulating water while reducing steam energy consumption, achieving low energy consumption and high returns. The process is simple, with low equipment investment and operating costs, simple operation, a high degree of automation, and stable operation.

[0008] In order to achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0009] An energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water, characterized in that the process comprises the following steps:

[0010] (1) The raw water is divided into two streams. One stream enters the first heat exchanger to exchange heat with the hot stream at the bottom of the stripping distillation tower to obtain the first raw water. The other stream enters the second heat exchanger to exchange heat with the steam condensate from the reboiler to obtain the second raw water and the cold stream.

[0011] (2) The first raw water and the second raw water are combined, and the obtained heated raw water is adjusted in pH, and then enters a stripping distillation tower with steam for stripping to obtain overhead gas, a tower bottom hot stream, and a tower bottom side stream. The tower bottom hot stream returns to step (1) and enters a first heat exchanger for heat exchange;

[0012] (3) The hot side outlet stream of the second heat exchanger in step (1) is combined with the liquid phase from the gas-liquid separator, and then enters a heat recovery device for heat exchange with the tower top gas to obtain condensate, the first non-condensable gas and low-temperature low-pressure steam, and the condensate is returned to the stripping distillation tower;

[0013] (4) The low-temperature, low-pressure steam is separated into a gas phase and a liquid phase by a gas-liquid separator, the liquid phase is returned to step (3) and enters a heat recovery device for heat exchange, the gas phase is compressed by a compressor to obtain compressed steam, the compressed steam and the bottom side stream of step (2) enter a reboiler for heat exchange, the obtained gas-liquid mixture is returned to step (2) and enters a stripping distillation tower for stripping, and fresh steam is used to supplement the heat when the heat is insufficient. The obtained steam condensate is returned to step (1) and enters a second heat exchanger for heat exchange, and the liquid phase is returned to step (3) and merged with the hot side outlet stream of the first heat exchanger and enters a heat recovery device for heat exchange;

[0014] (5) The first non-condensable gas enters the organic phase separator and is exchanged with the cooling medium as the cold source to obtain COD-containing ammonia water and a second non-condensable gas. The second non-condensable gas is purified to obtain pure ammonia water or liquid ammonia product.

[0015] Furthermore, in step (1), the first heat exchanger or the second heat exchanger is a plate heat exchanger;

[0016] The temperature of the first raw water is 85-95°C, the temperature of the second raw water is 85-95°C, and the temperature of the cold logistics is 45-60°C.

[0017] Furthermore, in step (2), the temperature of the heated raw water is 85-95°C, and the pH after adjusting the pH is 12 or above;

[0018] The stripping conditions are: atmospheric distillation, steam is saturated steam with a pressure of 0.3MPaG~0.6MPaG and a temperature of 130~160℃, and the vapor-liquid mass ratio of the required steam to the raw water entering the tower is 1:15~1:30;

[0019] The temperature of the tower top gas is 85-100°C, the temperature of the tower bottom hot flow is 105-110°C, and the temperature of the tower bottom side flow is 105-110°C.

[0020] Furthermore, in step (3), the temperature of the liquid phase is 50-85°C;

[0021] The heat recovery device is a shell and tube evaporator;

[0022] The temperature of the low-temperature and low-pressure steam is 50-85°C and the pressure is 30-80 kPaA;

[0023] The temperature of the condensate is 50-85°C;

[0024] The temperature of the first non-condensable gas is 55-90°C.

[0025] Furthermore, in step (4), the temperature of the compressed steam is 110-120°C and the pressure is 140-200 kPaA;

[0026] The temperature of the gas-liquid mixture is 105-110°C and the pressure is 120-140 kPaA;

[0027] The temperature of the steam condensate is 105-110°C.

[0028] Furthermore, in step (5), the organic phase separator is a shell and tube heat exchanger;

[0029] The cooling medium is low-temperature water or other low-temperature medium, and its temperature is 5~32℃;

[0030] The temperature of the COD-containing ammonia water is 15-20°C;

[0031] The temperature of the second non-condensable gas is 15-20°C.

[0032] Furthermore, in step (5),

[0033] The purification comprises: passing the second non-condensable gas into a composite purifier filled with a COD removal material or a drying material.

[0034] Furthermore, the process further comprises: using a COD removal device to perform COD removal treatment on the COD-containing ammonia water obtained in step (5), wherein the COD removal device is a filter using a resin filler / filter membrane.

[0035] The embodiments of the present invention have the following advantages:

[0036] 1) The present invention effectively solves the problem that high-salt wastewater containing COD, ammonia nitrogen and nitrogen cannot be recycled as a resource. By utilizing the properties of each component in the wastewater and through reasonable process design, the source components that produce COD in the wastewater are physically separated and concentrated. The volume of wastewater that the system needs to treat COD is reduced to about 1-10% of the original treatment volume, and the COD treatment load is greatly reduced. In addition, more than 85% of the ammonia nitrogen can be recovered as high-purity liquid ammonia or high-purity concentrated ammonia water, and the ammonia nitrogen content in the bottom effluent can be reduced to below 10 mg / L.

[0037] 2) This invention addresses the high steam and circulating water consumption associated with recovering aqueous or liquid ammonia. A heat recovery unit recovers most of the system's heat, generating secondary steam. This steam is then converted into high-grade compressed steam, consuming a small amount of electricity. This steam serves as the heat source for the stripping distillation column, replacing some of the fresh steam consumed. This reduces the overall energy consumption, operating costs, and carbon emissions of the device. The steam-to-raw water mass ratio required for stripping distillation is reduced from 1:10-1:7 to 1:15-1:30.

[0038] 3) The present invention reduces the heat load required for cooling the entire system by recovering the heat from the tower top, saves the use of circulating water, and reduces equipment investment and floor space.

[0039] 4) In the heat recovery system designed by the present invention, raw water enters the stripping distillation tower after undergoing multiple heat exchanges, fully utilizing the heat within the system and reducing the temperature of the water discharged from the system to the process design value. This reduces the investment in heat preservation and anti-scalding equipment and improves safety performance.

[0040] 5) The present invention prepares high-purity liquid ammonia or ammonia water by condensing the gas phase at the top of the tower. The process is simple, the equipment investment and space occupation are small, the degree of automation is high, and the ammonia water / liquid ammonia has high purity and controllable concentration. Almost no non-condensable gas is generated, thus avoiding the waste of ammonia resources and air pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0042] Figure 1 The present invention provides an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water;

[0043] In the figure: 1-raw water tank; 2-raw water pump; 3-first heat exchanger; 4-second heat exchanger; 5-alkali solution pipeline; 6-stripping distillation tower; 7-heat recovery device; 8-separation reflux pipeline; 9-gas-liquid separator; 10-compressor; 11-reboiler; 12-organic phase separator; 13-COD-containing ammonia pipeline; 14-COD-containing ammonia buffer tank; 15-COD removal device; 16-composite purifier; 17-ammonia recovery device; 18-ammonia product pipeline. DETAILED DESCRIPTION

[0044] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0045] See also Figure 1 The present invention provides an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water, comprising:

[0046] (1) High-salt wastewater containing COD and ammonia nitrogen is conditioned in the raw water tank 1 and then divided into two streams by the raw water pump 2. One stream passes through the first heat exchanger 3 and exchanges heat with the hot stream from the bottom outlet of the stripping distillation tower 6 to increase the temperature of the raw water, thereby obtaining the first raw water with a temperature of 85-95°C and the first cold stream with a temperature of 45-60°C. The first cold stream mainly contains salt, water and trace COD, and can be sent to the park pipeline network for salt production or zero-discharge treatment. The other stream enters the second heat exchanger 4 and exchanges heat with the steam condensate from the outlet of the reboiler 11 to increase the temperature of the raw water, thereby obtaining the second raw water with a temperature of 85-95°C and the second cold stream with a temperature of 45-60°C.

[0047] (2) The first raw water and the second raw water are combined, and the resulting heated raw water with a temperature of 85-95°C is adjusted for pH and then enters the stripping distillation tower 6 with a saturated steam with a temperature of 130-160°C and a pressure of 0.3MPaG-0.6MPaG at a vapor-liquid mass ratio of 1:15-1:30. The steam is stripped under atmospheric distillation conditions to obtain a tower top gas with a temperature of 85-100°C (mainly including ammonia vapor, water vapor and organic gas), a tower bottom hot flow with a temperature of 105-110°C (mainly composed of salt and water), and a tower bottom side flow with a temperature of 105-110°C (mainly composed of salt and water). The tower bottom hot flow returns to step (1) and enters the first heat exchanger 3 for heat exchange with the raw water. The steam comes from the gas-liquid mixture generated by the reboiler 11, and fresh steam is used to supplement it when it is insufficient.

[0048] Before the combined heated raw water enters the stripping distillation tower, a NaOH solution with a mass concentration of 30% to 50% is added to the raw water through the alkali liquid pipeline 5 to adjust the raw water pH to ≥ 12, so that the ionic ammonia nitrogen is converted into molecular ammonia nitrogen.

[0049] (3) The gas generated at the top of the stripping distillation tower 6 is heat-exchanged with the condensed water in the system in the heat recovery device 7 to obtain a first condensate, a first non-condensable gas and low-temperature, low-pressure steam. The condensate has a temperature of 50-85°C and is a mixture of the condensate at the hot side outlet of the second heat exchanger in step (1) and the liquid phase separated by the gas-liquid separator 9. The low-temperature, low-pressure steam is produced by the condensate being vaporized in the heat recovery device 7 by heat-exchanging with the steam generated at the top of the stripping distillation tower 7. The steam temperature is 50-85°C and the pressure is 30-80 kPaA. The first condensate is the condensate generated after the gas generated at the top of the stripping distillation tower 6 releases heat in the shell side of the heat recovery device 7. The main components of the condensate are water, a very small amount of ammonia and a very small amount of organic matter, and its temperature is 50-85°C (because the condensate temperature is higher than the volatility of ammonia and organic gas, ammonia and organic gas cannot be dissolved in the condensate). The condensate is refluxed into the stripping distillation tower 6 through the separation reflux line 8. The temperature of the first non-condensable gas is 55~90℃, and its components are ammonia, organic gas produced at the top of the tower, and a small amount of water vapor.

[0050] (4) The low-temperature, low-pressure steam generated by the heat recovery device 7 is separated by the gas-liquid separator 9 (a vertical separator with a demisting and defoaming device) to obtain a gas phase with a temperature of 50-85°C and a liquid phase with a temperature of 50-85°C. The gas phase is compressed by the compressor 10 (a centrifugal or positive displacement compressor) to obtain compressed steam with a temperature of 110-120°C and a pressure of 140-200 kPaA. The compressed steam is used as a heat source to heat the bottom side stream obtained in step (2) in the reboiler 11. The resulting gas-liquid mixture with a temperature of 105-110°C and a pressure of 120-143 kPaA is returned to step (2) to heat and strip the heated raw water.

[0051] (5) The first non-condensable gas enters the organic phase separator 12 and is cooled using the cooling medium as a cold source to obtain ammonia water containing COD and the second non-condensable gas.

[0052] The first non-condensable gas discharged through the top outlet of the heat recovery device 7 enters the shell side inlet of the organic phase separator 12. Under the indirect cooling effect of the cooling medium at 5~25℃, 80%~90% of the oil / COD in the hot side gas phase will be condensed together with 5~15% ammonia and more than 99% of water to form a second condensate. The main components of the second condensate are water, ammonia and COD, and the total COD accounts for 80%~90% of the COD in the tower top gas. The condensate enters the COD ammonia buffer tank 14 through the COD ammonia pipeline 13. The COD ammonia can be treated as a waste liquid after reduction. In some preferred embodiments, the COD ammonia can be further sent to the COD removal device 15 for de-COD treatment to meet the COD standard of its effluent. Among them, the COD removal device 15 is a filter using a resin filler / filter membrane. The resin filler can use a domestically mature resin material for COD removal / organic gas removal, and the filter membrane can use a relatively mature PP or PA membrane on the market. It removes organic matter / oil particles from the ammonia water through adsorption or precision filtration. The filter is a vertical container with a bottom-inlet and top-outlet structure. It is filled with a dedicated COD removal resin. The resin filler / filter membrane is an organic polymer material. Because it generally has a large specific surface area and a rich pore structure, it can effectively adsorb organic pollutants, inorganic pollutants, and odorous substances in the exhaust gas. It has the advantages of fast adsorption speed, large adsorption capacity, easy regeneration and reuse, and is widely used in the field of exhaust gas treatment.

[0053] The second non-condensable gas is the uncondensed gas from the shell side of organic phase separator 12, where COD is significantly removed. This gas enters composite purifier 16. Composite purifier 16 is a composite packing purifier containing selective water-absorbing and drying materials and selective COD removal materials. The selective water-absorbing and drying materials can be alkaline drying materials such as quicklime or hydrated lime particles, or activated alumina or molecular sieves. The selective COD removal materials can be domestically produced resin materials for COD and organic gas removal. This composite purifier is a vertical vessel with bottom-inlet and top-outlet configuration. It is layered with specialized COD removal materials (located in the upper section) and drying materials (located in the lower section). The gas is adsorbed by the drying and COD removal materials, removing any remaining moisture and COD. The outlet of composite purifier 16 is pure ammonia with an oil content of less than 0.001%. This gas enters ammonia recovery unit 17, where the cooling medium reduces the temperature to below 10°C, producing high-purity liquid ammonia with a COD removal rate of 90-99%. This is then discharged and collected via ammonia product pipeline 18. If the system needs to recover aqueous ammonia rather than liquid ammonia, the purifier can be loaded with only COD removal material, without the drying material. Pure water can be added to adjust the ammonia concentration during aqueous ammonia recovery. The ammonia nitrogen recovered from the purified aqueous ammonia or liquid ammonia in this device accounts for over 85% of the total ammonia nitrogen recovered from the wastewater. Example

[0054] This embodiment provides an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water:

[0055] (1) High-salt wastewater containing COD and ammonia nitrogen, with a treatment capacity of 3 m 3 / h, with a COD content of 3000 mg / L, primarily low-boiling-point organic matter, an ammonia nitrogen content of 50 g / L, and a salt content of 30 g / L. After conditioning in raw water tank 1, this wastewater is divided into two streams by raw water pump 2. One stream passes through a first heat exchanger 3, where it exchanges heat with a hot stream at 105°C from the bottom outlet of a stripping distillation tower 6, raising the raw water temperature to produce first raw water at 90°C and a first cold stream at 45°C. The other stream enters a second heat exchanger 4, where it exchanges heat with steam condensate at 110°C from the outlet of a reboiler 11, raising the raw water temperature to produce second raw water at 90°C and a second cold stream at 45°C.

[0056] (2) The first raw water and the second raw water are combined, and the resulting heated raw water with a temperature of 90°C is adjusted to a pH of 12 or above by adding alkali, and then mixed with saturated steam with a temperature of 160°C and a pressure of 0.6 MPaG, and enters the stripping distillation tower 6 at a vapor-liquid mass ratio of 1:20. The stripping is carried out under the condition of atmospheric distillation to obtain a tower top gas with a temperature of 85°C, a tower bottom hot stream with a temperature of 105°C, and a tower bottom side stream with a temperature of 105°C. The tower bottom hot stream returns to step (1) and enters the first heat exchanger 3 for heat exchange with the raw water. The steam comes from the gas-liquid mixture generated by the reboiler 11, and fresh steam is used to supplement it when it is insufficient.

[0057] (3) The second cold stream of step (1) at a temperature of 45°C is combined with the liquid phase separated by the gas-liquid separator 9 at a temperature of 70°C, and then heat exchanged with the overhead gas in the heat recovery device 7 to obtain a first condensate at a temperature of 70°C, a first non-condensable gas at a temperature of 70°C, and low-temperature, low-pressure steam at a temperature of 70°C and a pressure of 31 kPaA. The first condensate is refluxed through the separation reflux line 8 into the stripping distillation tower 6.

[0058] (4) The low-temperature, low-pressure steam is separated into a gas phase at a temperature of 70°C and a liquid phase at a temperature of 70°C by a gas-liquid separator 9 (a vertical separator with a demisting and defoaming device). The gas phase is compressed by a compressor 10 (a centrifugal or positive displacement compressor) to obtain compressed steam at a temperature of 110°C and a pressure of 140 kPaA. The compressed steam is used as a heat source to heat the bottom side stream obtained in step (2) in a reboiler 11. The resulting gas-liquid mixture with a temperature of 105°C and a pressure of 120 kPaA is returned to step (2) to strip the heated raw water. The liquid phase is combined with the second cold stream of step (3) and enters a heat recovery device 7 for heat exchange.

[0059] (5) The first non-condensable gas enters the organic phase separator 12 and is cooled using a cooling medium at 5-25°C as a cold source, producing ammonia water containing COD and a second non-condensable gas. The COD-containing ammonia water has an ammonia mass concentration of 20% and enters the COD-containing ammonia water buffer tank 14 through pipeline 13. It is then sent to the COD removal device 15 for COD removal treatment, so that the effluent COD meets the process requirements.

[0060] The second non-condensable gas, which remains uncondensed in the shell side of organic phase separator 12, enters composite purifier 16 for deep COD removal and drying before entering the shell side of ammonia recovery unit 17. The ammonia recovery unit uses 5°C cooling water as the medium in the tube side. The second non-condensable gas undergoes indirect condensation in the shell side, resulting in liquid ammonia, which is discharged and collected via ammonia product pipeline 18. The product liquid ammonia has an NH3 mass fraction of ≥99.9%, an H2O content of ≤1000 ppm, and an oil content of ≤5 mg / kg, meeting the liquid ammonia quality standard GB / T 536-2017.

[0061] Beneficial effects of this embodiment:

[0062] 1) Recovery of ammonia water containing a small amount of COD (ammonia mass fraction 20%): 136.5 kg / h, which can be used for internal production circulation;

[0063] 2) Recovered high-purity liquid ammonia: 154.85 kg / h, which can be sold as a high-value product, equivalent to a reduction of 773.5 kg / h of COD-containing ammonia water (ammonia mass fraction 20%). The ammonia recovery rate of the entire process reaches 99.9%, and the ammonia recovery rate of the pure liquid ammonia product reaches more than 85% of the overall ammonia recovery rate;

[0064] 3) Steam consumption: 50 kg steam / m 3 water, saving 50~80 kg steam / m 3 Water; that is, the mass ratio of steam to raw water required for stripping distillation is reduced from 1:10~1:7 to 1:20.

[0065] 4) Cooling water consumption is reduced from 150m3 in conventional process 3 / h reduced to 50m 3 / h.

[0066] 5) The ammonia nitrogen index of the tower bottom effluent is consistent with the conventional process, and the ammonia nitrogen can reach below 15 mg / L, meeting the national emission standards. Example

[0067] This embodiment provides an energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water:

[0068] (1) High-salt wastewater containing COD and ammonia nitrogen, water volume 50 m 3 / h, with an ammonia nitrogen content of approximately 10 g / L, a salt content of 120 g / L, and a COD content of 1000 mg / L. After conditioning in raw water tank 1, it is divided into two streams by raw water pump 2. One stream passes through the first heat exchanger 3, where it exchanges heat with the hot stream at 106°C from the bottom outlet of the stripping distillation tower 6, raising the raw water temperature to produce first raw water at 90°C and a first cold stream at 50°C. The other stream enters the second heat exchanger 4, where it exchanges heat with steam condensate at 108°C from the outlet of the reboiler 11, raising the raw water temperature to produce second raw water at 92°C and a second cold stream at 60°C.

[0069] (2) The first raw water and the second raw water are combined, and the resulting heated raw water with a temperature of 91°C is adjusted to pH ≥ 12 with a 30% NaOH solution, and then enters the stripping distillation tower 6 with a vapor-liquid mass ratio of 1:25 with fresh saturated steam at a temperature of 150°C and a pressure of 0.5 MPaG. Stripping is performed under atmospheric distillation conditions to obtain a tower top gas with a temperature of 93°C, a tower bottom hot stream with a temperature of 106°C, and a tower bottom side stream with a temperature of 108°C. The tower bottom hot stream returns to step (1) and enters the first heat exchanger 3 for heat exchange with the raw water. Among them, the steam is partly derived from the gas-liquid mixture generated by the reboiler 11, and partly from the fresh steam.

[0070] (3) The second cold stream of step (1) at a temperature of 60°C is combined with the liquid phase separated by the gas-liquid separator 9 at a temperature of 85°C, and then heat exchanged with the overhead gas in the heat recovery device 7 to obtain a first condensate at a temperature of 80°C, a first non-condensable gas at a temperature of 88°C, and low-temperature, low-pressure steam at a temperature of 80°C and a pressure of 47 kPaA. The first condensate is refluxed through the separation reflux line 8 into the stripping distillation tower 6.

[0071] (4) The low-temperature, low-pressure steam is separated into a gas phase at a temperature of 80°C and a liquid phase at a temperature of 80°C by a gas-liquid separator 9 (a vertical separator with a demisting and defoaming device). The gas phase is compressed by a compressor 10 (a centrifugal or positive displacement compressor) to obtain compressed steam at a temperature of 118°C and a pressure of 180 kPaA. The compressed steam is used as a heat source to heat the bottom side stream obtained in step (2) in a reboiler 11. The resulting gas-liquid mixture at a temperature of 110°C and a pressure of 143 kPaA is returned to step (2) and stripped with the heated raw water. The liquid phase is combined with the second cold stream of step (3) and enters a heat recovery device 7 for heat exchange.

[0072] (5) The first non-condensable gas enters the organic phase separator 12 and is cooled using a 10°C cooling medium as a cold source, producing COD-containing ammonia water and a second non-condensable gas. The COD-containing ammonia water enters the COD-containing ammonia water buffer tank 14 through the COD-containing ammonia water pipeline 13 and is then sent to the COD removal device 15 for COD removal treatment, so that the effluent COD meets the standard. The effluent is ammonia water with a concentration of 25%.

[0073] The second non-condensable gas is the uncondensed gas from the shell side of organic phase separator 12, where COD is significantly reduced. It enters composite purifier 16 for deep COD removal and then enters ammonia recovery unit 17, where it is condensed using a 32°C cooling medium and the concentration is adjusted by adding pure water. The resulting product is 15% pure ammonia water, which is discharged and collected via ammonia product pipeline 18. The quality standards for pure ammonia water meet the standards shown in Table 1.

[0074] ,

[0075] Beneficial effects of this embodiment:

[0076] 1) Recovery of ammonia water containing a small amount of COD (ammonia mass fraction 20%): 455.25 kg / h, which can be used for internal production circulation;

[0077] 2) Recovered high-purity ammonia: 3439.67 kg / h (ammonia mass fraction 15%), which can be sold as a high-value product. This is equivalent to reducing the amount of COD-containing ammonia (ammonia mass fraction 15%) by 3439.67 kg / h. The ammonia recovery rate of the entire process reaches 99.9%, and the ammonia recovery rate of the pure liquid ammonia product reaches over 85% of the total ammonia recovery.

[0078] 3) Steam consumption: 40 kg steam / m 3 water, saving 60~90 kg steam / m 3 Water; that is, the mass ratio of steam to raw water required for stripping distillation is reduced from 1:10~1:7 to 1:25.

[0079] 4) Cooling water consumption is reduced from 1000m3 in conventional process 3 / h reduced to 400m 3 / h.

[0080] 5) The ammonia nitrogen index of the tower bottom effluent is consistent with the conventional process, and the ammonia nitrogen can reach below 10 mg / L.

[0081] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water, characterized in that: The process comprises the following steps: (1) The raw water is divided into two streams. One stream enters the first heat exchanger to exchange heat with the hot stream at the bottom of the stripping distillation tower to obtain the first raw water. The other stream enters the second heat exchanger to exchange heat with the steam condensate from the reboiler to obtain the second raw water and the cold stream. (2) The first raw water and the second raw water are combined, and the obtained heated raw water is adjusted in pH, and then enters a stripping distillation tower with steam for stripping to obtain overhead gas, a tower bottom hot stream, and a tower bottom side stream. The tower bottom hot stream returns to step (1) and enters a first heat exchanger for heat exchange; (3) The hot side outlet stream of the second heat exchanger in step (1) is combined with the liquid phase from the gas-liquid separator, and then enters a heat recovery device for heat exchange with the tower top gas to obtain condensate, the first non-condensable gas and low-temperature low-pressure steam, and the condensate is returned to the stripping distillation tower; (4) The low-temperature, low-pressure steam is separated into a gas phase and a liquid phase by a gas-liquid separator, the liquid phase is returned to step (3) and enters a heat recovery device for heat exchange, the gas phase is compressed by a compressor to obtain compressed steam, the compressed steam and the bottom side stream of step (2) enter a reboiler for heat exchange, the obtained gas-liquid mixture is returned to step (2) and enters a stripping distillation tower for stripping, and fresh steam is used to supplement the heat when the heat is insufficient. The obtained steam condensate is returned to step (1) and enters a second heat exchanger for heat exchange, and the liquid phase is returned to step (3) and merged with the hot side outlet stream of the first heat exchanger and enters a heat recovery device for heat exchange; (5) The first non-condensable gas enters the organic phase separator and performs heat exchange with a cooling medium as a cold source to obtain COD-containing ammonia water and a second non-condensable gas. The second non-condensable gas is purified to obtain the high-purity liquid ammonia or ammonia water; In step (1), the first heat exchanger or the second heat exchanger is a plate heat exchanger; the temperature of the first raw water is 85-95°C, the temperature of the second raw water is 85-95°C, and the temperature of the cold stream is 45-60°C; In step (2), the temperature of the heated raw water is 85-95°C, and the pH after adjusting the pH is 12 or above; the stripping conditions are: atmospheric distillation, the steam is saturated steam with a pressure of 0.3MPaG-0.6MPaG and a temperature of 130-160°C, and the required steam to tower raw water vapor-liquid mass ratio is 1:15-1:30; the temperature of the tower top gas is 85-100°C, the temperature of the tower bottom hot flow is 105-110°C, and the temperature of the tower bottom side flow is 105-110°C; In step (3), the temperature of the liquid phase is 50-85°C; the heat recovery device is a shell and tube evaporator; The temperature of the low-temperature and low-pressure steam is 50-85°C, and the pressure is 30-80 kPaA; the temperature of the condensate is 50-85°C; and the temperature of the first non-condensable gas is 55-90°C.

2. The energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water according to claim 1, characterized in that: In step (4), The temperature of the compressed steam is 110-120°C and the pressure is 140-200 kPaA; The temperature of the gas-liquid mixture is 105-110°C and the pressure is 120-140 kPaA; The temperature of the steam condensate is 105-110°C.

3. The energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water according to claim 1, characterized in that: In step (5), The organic phase separator is a shell and tube heat exchanger; The cooling medium is low-temperature water or other low-temperature medium, and its temperature is 5~32℃; The temperature of the COD-containing ammonia water is 15-20°C; The temperature of the second non-condensable gas is 15-20°C.

4. The energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water according to claim 1, characterized in that: In step (5), The purification comprises: passing the second non-condensable gas into a composite purifier filled with a COD removal material or a drying material.

5. The energy-saving process for recycling high-salt wastewater containing COD and ammonia nitrogen into high-purity liquid ammonia or ammonia water according to claim 1, characterized in that: The process further comprises: The COD-containing ammonia water obtained in step (5) is subjected to COD removal treatment using a COD removal device, wherein the COD removal device is a filter using a resin filler / filter membrane.

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