Ammonia-nitrogen wastewater treatment system coupled with double-tower stripping and heat pump

Abstract

The application belongs to the field of wastewater treatment systems, and discloses an ammonia-nitrogen wastewater treatment system with double-tower stripping ammonia removal coupled with a heat pump, wherein the vapor at the top of the first ammonia removal tower serves as the heat source of the second ammonia removal tower, the vapor at the top of the second ammonia removal tower serves as the heat source of the secondary steam generator (horizontal tube falling film evaporator) of the heat pump system, a two-stage steam compressor is coupled, the temperature difference utilization interval is increased, and the waste heat of the tower kettle water, ammonia water and ammonia tail gas is fully recycled and utilized, compared with the traditional stripping ammonia removal system, the efficiency is further improved and the consumption is reduced, and the stripping ammonia removal system is suitable for a wide range of applications, greatly improves the wastewater treatment flow, is stable and reliable in system operation, has lower energy consumption per ton of water treatment, and is reasonable, flexible and reliable in ammonia recovery method.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment systems, and more specifically, relates to an ammonia nitrogen wastewater treatment system. Background Technology

[0002] The widespread use of ammonia in industries such as chemical engineering, metallurgy, and new energy batteries leads to the generation of large quantities of high-salinity, high-ammonia-nitrogen wastewater. For example, the hydrometallurgical process for tungsten generates 50-100 cubic meters of wastewater (ammonia nitrogen 7-20 g / L, COD 200-2000 mg / L) per ton of APT produced, while the production of ternary lithium battery precursors generates 18-30 tons of wastewater (ammonia nitrogen 2-8 g / L, sodium sulfate 60-120 g / L) per ton. This type of wastewater requires strict treatment to meet the discharge standard of ammonia nitrogen ≤15 mg / L. Currently, the mainstream treatment processes include air stripping and steam stripping, both of which are based on the volatility of free ammonia to achieve separation. However, each has its own drawbacks: after air stripping, the ammonia nitrogen residue is 50-300 mg / L, requiring secondary treatment and easily causing tail gas pollution, and has been gradually phased out; although steam stripping has a good ammonia removal effect, it has extremely high energy consumption, consuming 90-110 kg of steam per ton of water (accounting for more than 90% of the total energy consumption of the system), and 80% of the heat at the top of the tower is wasted by cooling water, resulting in high operating costs. Summary of the Invention

[0003] The purpose of this application is to provide an ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump, so as to solve the technical problems of high energy consumption and low recovery rate of existing ammonia nitrogen wastewater treatment systems.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] A dual-tower stripping ammonia removal coupled with a heat pump is provided for an ammonia nitrogen wastewater treatment system, comprising:

[0006] The system consists of a first ammonia removal tower, a second ammonia removal tower, a first raw water preheater, a second raw water preheater, a third raw water preheater, a fourth raw water preheater, and a steam generator.

[0007] The first batch of raw water is preheated by passing through the first raw water preheater and the third raw water preheater in sequence, and then enters the first ammonia removal tower. After mass transfer with steam in the first ammonia removal tower, the ammonia-containing steam is discharged from the top of the first ammonia removal tower and then enters the second ammonia removal tower.

[0008] The second stream of raw water is preheated sequentially through the second and fourth raw water preheaters before entering the second ammonia removal tower. In the second ammonia removal tower, after mass transfer with steam, the ammonia-containing steam is discharged from the top of the tower and exchanges heat with the steam generator.

[0009] External steam enters the first deammoniation tower, the second deammoniation tower, and the steam generator, respectively; after the primary steam compressor and the secondary steam compressor are started, secondary steam is generated and enters the first deammoniation tower.

[0010] As a further improvement to the above technical solution:

[0011] Optionally, the wastewater treated in the first deammoniation tower is discharged from the bottom via the first discharge pump, and a portion of the wastewater is returned to the first deammoniation tower via the first branch pipe to ensure the optimal flow rate required for evaporation of the falling film evaporator in the first deammoniation tower; the wastewater treated in the second deammoniation tower is discharged from the bottom via the second discharge pump, and a portion of the wastewater is returned to the second deammoniation tower via the second branch pipe to ensure the optimal flow rate required for evaporation of the falling film evaporator in the second deammoniation tower.

[0012] External steam enters the first ammonia removal tower, the second ammonia removal tower, and the steam generator through the third branch pipe respectively; the fluid inside the first falling film reboiler is the wastewater descending inside the tower. After heat exchange with the shell-side steam, the steam required for ammonia stripping is generated inside the tube. The steam rises and undergoes mass transfer with the wastewater, becoming ammonia-containing steam, which is then discharged from the top of the tower.

[0013] Optionally, the ammonia-containing vapor discharged from the top of the first ammonia removal tower enters the shell side of the second falling film reboiler at the bottom of the second ammonia removal tower through the fourth branch pipe, where it exchanges heat with the wastewater in the tube side. After the vapor is condensed, it enters the ammonia condensate tank and is pumped to the upper part of the second ammonia removal tower by the ammonia condensate pump, where it enters the top rectification section for distillation. The fluid in the tubes of the second falling film reboiler is the wastewater descending from the tower. After exchanging heat with the ammonia-containing vapor in the shell side, the steam required for ammonia stripping is generated in the tubes. The steam rises and exchanges mass with the wastewater, and then becomes ammonia-containing vapor in the rectification section before being discharged from the top of the tower.

[0014] The ammonia-containing vapor discharged from the top of the second ammonia removal tower enters the tube side of the horizontal tube falling film evaporator through the fifth branch pipe. The shell side is heated by saturated water delivered by the water circulation pump in the steam generator, and part of it condenses to form ammonia water and uncondensed ammonia-containing vapor.

[0015] Ammonia water enters the intermediate ammonia water tank, and after being pumped by the ammonia water pump, it can be selectively transported back to the second ammonia removal tower, or enter the absorption and concentration tower after passing through the first raw water preheater, or be discharged as finished ammonia water.

[0016] Uncondensed ammonia-containing vapor enters the shell side of the second raw water preheater through the sixth branch pipe, where it exchanges heat with the tube side raw water and is completely condensed. It is then discharged from the bottom of the shell side of the second raw water preheater to the bottom of the absorption and concentration tower. Non-condensable gas is discharged through the seventh branch pipe to the tube distributor at the bottom of the absorption and concentration tower. The non-condensable gas is washed by the circulating liquid inside the tower, and after three stages of absorption, it is discharged from the top of the tower. It is then connected to the inlet of the vacuum pump through the eighth branch pipe, and subsequently discharged at a high point or into the plant's tail gas system.

[0017] Optionally, the condensate from the shell side of the first falling film reboiler at the bottom of the first ammonia removal tower enters the condensate tank and is pumped back to the steam generator by the condensate pump. Then, the saturated water is pumped by the water circulation pump in the steam generator to the shell side distributor of the horizontal tube falling film evaporator, where it exchanges heat with the ammonia-containing steam in the tube side of the horizontal tube falling film evaporator and evaporates. The saturated steam is then returned to the steam generator via the tenth branch pipe for gas-liquid separation. The steam enters the first-stage steam compressor via the eleventh branch pipe, then enters the buffer tank, and then enters the second-stage steam compressor via the twelfth branch pipe. The pressurized saturated steam is discharged to the shell side of the first falling film reboiler at the bottom of the first ammonia removal tower, where it exchanges heat with the fluid in the tube side of the first falling film reboiler, which is the wastewater descending in the tower. The steam required for ammonia stripping is generated in the tube side and serves as the heat source for the distillation of the first ammonia removal tower.

[0018] Optionally, the ammonia-containing vapor produced by the first ammonia stripping tower enters the second falling film reboiler at the bottom of the second ammonia stripping tower, serving as the heat source for the ammonia stripping operation of the second ammonia stripping tower; after condensation, it is fully refluxed back to the second ammonia stripping tower via an ammonia pump, and after being distilled together with the ammonia vapor produced by the ammonia stripping in the second ammonia stripping tower, it is discharged from the fifth branch pipe at the top of the second ammonia stripping tower to the tube side of the horizontal falling film evaporator; the ammonia-containing vapor passes through the shell side of the steam generator, and after the water-containing portion is condensed, the condensate is discharged to the ammonia intermediate tank, and then transported by an ammonia pump for distillation reflux. The ammonia vapor can be either discharged as finished product ammonia water or discharged to the absorption and concentration tower as absorbent replenishment; the remaining ammonia vapor enters the shell side of the second raw water preheater, and after being completely condensed by the tube side raw water, it enters the absorption and concentration tower, either as absorbent replenishment or discharged as finished product ammonia water. The concentrated ammonia vapor is condensed after passing through the second raw water preheater, and the remaining non-condensable gas enters the bottom of the absorption and concentration tower through the branch pipe. The non-condensable gas is washed by the circulating liquid in the tower and discharged from the top of the tower after two-stage separation. It is then connected to the inlet of the vacuum pump through the eighth branch pipe and subsequently discharged from the high point.

[0019] Optionally, the ammonia water circulation discharge pump delivers the bottom liquid of the absorption and concentration tower to the chilled water cooler, where it exchanges heat with the chilled water to cool down. After cooling, it is then delivered to the tube distributors at the top of each packing section of the absorption and concentration tower for spraying to wash away non-condensable gases and concentrate the absorbent. Once the absorbent concentration reaches the required level, it is discharged through the ninth branch pipe via the ammonia water circulation discharge pump.

[0020] Optionally, the first and second deammoniation towers are fed in parallel, with the overhead steam from the first deammoniation tower serving as the heat source for the second deammoniation tower.

[0021] Optionally, the top of the second deammoniation tower is provided with a rectification section to concentrate the ammonia-containing vapor generated by the first and second deammoniation towers through centralized rectification.

[0022] Optionally, the saturated water in the steam generator is heated by the horizontal tube falling film evaporator to generate steam and some residual saturated water. The saturated water flows back to the tube distributor in the steam generator, where a negative pressure is formed under the action of the first-stage steam compressor, promoting the further generation of flash steam.

[0023] Saturated water condensed from the first ammonia removal tower is temporarily stored in a condensate tank and then pumped by a condensate pump to the tube distributor in the steam generator. Under the action of the first-stage steam compressor, a negative pressure is formed, promoting the generation of flash steam.

[0024] Optionally, the primary steam compressor and the secondary steam compressor are connected in series.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled with a heat pump provided in this application uses the top steam of the first ammonia removal tower as the heat source of the second ammonia removal tower, and the top steam of the second ammonia removal tower as the heat source of the horizontal tube falling film evaporator. Coupled with a two-stage steam compressor, the system increases the temperature difference utilization range and fully recovers and utilizes the waste heat of the tower bottom water, ammonia water, and ammonia tail gas. Compared with the traditional stripping ammonia removal system, the actual cost of steam energy consumption is further reduced. Attached Figure Description

[0027] 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, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the ammonia nitrogen wastewater treatment system of the dual-tower stripping deammoniation coupled heat pump of this application.

[0029] The following are the labeling elements in the figure:

[0030] 1. Third raw water preheater; 2. First ammonia removal tower;

[0031] 3. Condensate tank; 4. Fourth raw water preheater; 5. Second ammonia removal tower;

[0032] 6. Ammonia condensate tank; 7. Horizontal tube falling film evaporator; 8. Second raw water preheater; 9. Steam generator; 10. Ammonia intermediate tank; 11. Second stage steam compressor; 12. First stage steam compressor; 13. Buffer tank; 14. First raw water preheater; 15. Absorption and concentration tower; 16. Chilled water cooler; 17. First discharge pump; 18. Condensate pump; 19. Second discharge pump; 20. Ammonia condensate pump; 21. First falling film reboiler; 22. Steam drum water circulation pump; 23. Ammonia pump; 24. Vacuum pump; 25. Ammonia circulation... 26. Discharge pump; 27. First raw water inlet pipe; 28. Second raw water inlet pipe; 29. ​​First discharge pipe; 30. First branch pipe; 31. Second branch pipe; 32. Third branch pipe; 33. Fourth branch pipe; 34. Fifth branch pipe; 35. Sixth branch pipe; 36. Seventh branch pipe; 37. Eighth branch pipe; 38. Thirteenth branch pipe; 39. Fourteenth branch pipe; 40. Ninth branch pipe; 41. Tenth branch pipe; 42. Eleventh branch pipe; 43. Twelfth branch pipe; 44. Fifteenth branch pipe; 51. Second falling film reboiler. Detailed Implementation

[0033] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0034] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0035] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] like Figure 1 As shown, this application provides an ammonia nitrogen wastewater treatment system using a dual-tower stripping ammonia removal coupled heat pump.

[0039] The raw water enters the system in two streams for ammonia removal. The first stream of raw water is preheated by passing through the first raw water preheater 14 and the third raw water preheater 1 from the first raw water inlet pipe 26, and then enters the top of the first ammonia removal tower 2. After sufficient mass transfer through the internal components of the tower and the rising steam, the ammonia and steam are discharged from the top together. The treated wastewater is discharged from the bottom through the first discharge pump 17, then through the third raw water preheater 1, and finally through the first discharge pipe 28. A portion of the wastewater after passing through the first discharge pump 17 can also be selected for reflux through the first branch pipe 29 to ensure the optimal flow rate required for evaporation in the falling film evaporator.

[0040] The second raw water is preheated from the second raw water inlet pipe 27 through the second raw water preheater 8 and the fourth raw water preheater 4, and then enters the upper part of the second ammonia removal tower 5. After sufficient mass transfer through the distribution of internal components and rising steam, ammonia and steam are discharged from the top together. The treated wastewater is discharged from the bottom through the second discharge pump 19, then through the fourth raw water preheater 4, and finally through the second discharge pipe 30. Selectively, a portion of the wastewater is refluxed through the second branch pipe 31 to ensure the optimal flow rate required for evaporation in the second falling film reboiler 51.

[0041] The steam source for the ammonia nitrogen wastewater treatment system is divided into two parts: fresh steam entering the system from the third branch pipe 32 and secondary steam generated by compression and heating of the primary steam compressor 12 and the secondary steam compressor 11. During the start-up phase, the steam source is provided by the third branch pipe 32, which enters the first falling film reboiler 21 at the bottom of the first ammonia removal tower 2 through the third branch pipe 32a, enters the second falling film reboiler 51 at the bottom of the second ammonia removal tower 5 through the third branch pipe 32b, and enters the steam drum through the third branch pipe 32c to replenish the compressor for smooth operation.

[0042] After the primary steam compressor 12 and the secondary steam compressor 11 are started, the heat source is provided by the secondary steam generated in the horizontal tube falling film evaporator 7 and the steam drum through the compressor. The steam compressed by the secondary steam compressor 11 enters the shell side of the first falling film reboiler 21 in the lower part of the first ammonia removal tower 2, where it exchanges heat with the internal wastewater. After the steam is condensed, it enters the condensate tank 3 and is sent back to the steam drum by the condensate pump 18. The fluid in the tubes of the first falling film reboiler 21 is the wastewater descending in the tower. After heat exchange with the shell side steam, the steam required for ammonia stripping is generated in the tubes. This steam rises and, after sufficient mass transfer with the wastewater, becomes ammonia-containing steam, which is discharged from the top of the tower. After passing through the fourth branch pipe 33, it enters the shell side of the second falling film reboiler 51 in the lower part of the second ammonia removal tower 5, where it exchanges heat with the internal wastewater. After the steam is condensed, it enters the ammonia condensate tank 6 and is sent to the upper part of the second ammonia removal tower 5 by the ammonia condensate pump 20. Depending on the operating conditions, it can be selectively sent to the top rectification section for distillation. The fluid inside tube 51 of the second falling film reboiler is the wastewater descending from the tower. After heat exchange with ammonia-containing steam in the shell side, the steam required for ammonia stripping is generated inside the tube. This steam rises and, after sufficient mass transfer with the wastewater, passes through the rectification section and becomes high-ammonia-content steam, which is then discharged from the top of the tower.

[0043] Steam discharged from the top of the second ammonia removal tower 5 enters the tube side of the horizontal falling film evaporator 7 via the fifth branch pipe 34, where it exchanges heat with the saturated drum water supplied by the drum water circulation pump 22 in the shell side, partially condensing to form ammonia water and uncondensed ammonia-containing concentrated steam. The ammonia water enters the ammonia water intermediate tank 10, and is then pumped back to the second ammonia removal tower 5 via the ammonia water pump 23, or enters the absorption and concentration tower 15 after passing through the first raw water preheater 14, or is discharged as finished ammonia water. The uncondensed ammonia-containing concentrated steam enters the shell side of the second raw water preheater 8 via the sixth branch pipe 35, where it exchanges heat with the tube side raw water and is completely condensed. It is then discharged from the bottom of the shell side of the second raw water preheater 8 to the bottom of the absorption and concentration tower 15. The non-condensable gas is discharged via the seventh branch pipe 36 to the lower tube distributor of the absorption and concentration tower 15. The non-condensable gas is washed by the circulating liquid inside the tower, and after three stages of absorption, it is discharged from the top of the tower. It is then connected to the inlet of the vacuum pump 24 via the eighth branch pipe 37, and subsequently discharged at a high point or enters the plant's tail gas system.

[0044] The condensate from the shell side of the first falling film reboiler 21 at the bottom of the first ammonia removal tower 2 enters the condensate tank 3 and is then pumped back to the steam drum by the condensate pump 18. This saturated water is then pumped by the steam drum water circulation pump 22 to the shell side distributor of the horizontal tube falling film evaporator 7, where it exchanges heat with the high-ammonia-content steam in the tube side of the evaporator 7. The resulting superheated water returns to the steam drum via the tenth branch pipe 41 at the bottom for gas-liquid separation. The steam then enters the first-stage steam compressor 12 via the eleventh branch pipe 42, then enters the buffer tank 13, and finally enters the second-stage steam compressor 11 via the twelfth branch pipe 43. After this two-stage compression, the designed steam temperature rise is 46°C. The pressurized saturated steam is discharged to the shell side of the first falling film reboiler 21 at the bottom of the first ammonia removal tower 2, where it exchanges heat with the fluid inside the tubes of the first falling film reboiler 21, which is the wastewater descending within the tower. Steam required for ammonia stripping is generated inside the tubes, serving as the heat source for the distillation of the first ammonia removal tower 2.

[0045] The ammonia vapor produced by the distillation of the first ammonia removal tower 2 enters the reboiler at the bottom of the second ammonia removal tower 5, serving as the heat source for the ammonia removal operation of the second ammonia removal tower 5. After condensation, it is fully refluxed to the second ammonia removal tower 5 through the second discharge pump 19, and after being distilled together with the ammonia vapor produced by the ammonia removal in the second ammonia removal tower 5, it is discharged from the fifth branch pipe 34 at the top of the second ammonia removal tower 5 to the tube side of the horizontal falling film evaporator 7. After the concentrated ammonia vapor is partially condensed by the shell-side steam drum water, the condensate is discharged to the ammonia water intermediate tank, and then transported by the ammonia water pump 23 for distillation reflux, or discharged as finished ammonia water, or discharged to the absorption and concentration tower 15 as absorbent replenishment. The remaining concentrated ammonia vapor enters the shell side of the second raw water preheater 8, and after being completely condensed by the tube-side raw water, the condensed ammonia water has a high concentration and preferentially enters the absorption and concentration tower 15 as absorbent replenishment. The non-condensable gas remaining after the high-concentration ammonia vapor passes through the second raw water preheater 8 enters the bottom of the absorption and concentration tower 15 through the seventh branch pipe 36. The non-condensable gas is washed by the circulating liquid in the tower and discharged from the top of the tower after two-stage separation. It is then connected to the inlet of the vacuum pump 24 through the eighth branch pipe 37 and subsequently discharged at a high point.

[0046] The ammonia water circulation discharge pump 25 transports the bottom liquid of the absorption and concentration tower 15 to the chilled water cooler. After exchanging heat with the chilled water and cooling down, it is transported to the tube distributor at the top of each packing section of the absorption and concentration tower 15 for spraying to wash away non-condensable gas and concentrate the absorbent. After the absorbent concentration reaches the required level, it is discharged through the ninth branch pipe 40 after the ammonia water circulation discharge pump 25.

[0047] This application employs a dual-tower parallel feeding system, with the top steam of the first ammonia removal tower 2 serving as the heat source for the second ammonia removal tower 5. The first ammonia removal tower 2 operates at atmospheric pressure, while the second ammonia removal tower 5 operates under negative pressure. The required steam flow rate of this system can be reduced by approximately half, meaning the power of the compressor can be reduced. Furthermore, the steam compressor in this invention experiences a greater temperature rise, specifically 46°C, resulting in a wider range of waste heat utilization. In practice, the actual comprehensive energy consumption of the system can be reduced by 10-20% compared to similar single-tower heat pump ammonia removal systems.

[0048] According to Henry's Law, under isothermal and isobaric conditions, the solubility of ammonia in a solution is directly proportional to the equilibrium pressure of the solute above the liquid surface. This means that if the ammonia is refluxed back into the raw water pipeline and repeatedly fed into the tower, the amount of ammonia vapor at the top of the tower will inevitably increase, and the top temperature will easily drop. To maintain the outlet temperature at 98-100℃, the demand for steam in the tower bottom will increase dramatically (i.e., fresh steam needs to be added or the compressor selection needs to allow for a margin). Therefore, the first ammonia removal tower 2 has no rectification section, and no ammonia water is refluxed back into the first raw water feed pipe 26 to ensure that the top steam temperature is stable at 98-100℃, while also ensuring a stable steam flow rate and preventing system instability and failure caused by ammonia water reflux.

[0049] The bottom of the first deammoniation tower 2 is designed with a first falling film reboiler 21 and a tower bottom water return port. This reboiler utilizes the gravity flow of wastewater, which is distributed by a secondary distributor and then forms a film before entering the heat exchange tube. Compared with conventional siphon reboilers, no additional equipment is required, and the heat exchange efficiency can be increased by more than 30%.

[0050] The second ammonia removal tower 5 is designed with a rectification section at the top, which centrally rectifys and concentrates the steam generated by the first ammonia removal tower 2 and the second ammonia removal tower 5. By adjusting the reflux ratio and controlling the concentration at the outlet, the tower top temperature is stabilized at 81~83℃, providing a stable heat source for the horizontal tube falling film evaporator 7. The ammonia vapor outlet temperature of this tower is 80℃, and the ammonia content is >15%. The initial concentration of ammonia water is convenient, and it is refluxed to the rectification section according to the operating conditions without affecting the quality of the water effluent from the tower bottom.

[0051] The bottom of the second ammonia removal tower 5 is designed with a second falling film reboiler 51 and a tower bottom water return port. This reboiler utilizes the gravity flow of wastewater, which is distributed by a two-stage distributor and then forms a film before entering the heat exchange tube. Compared with conventional siphon reboilers, no additional arrangement is required, and the heat exchange efficiency can be increased by more than 30%.

[0052] The first deammonia removal tower 2 and the second deammonia removal tower 5 are fed in parallel. The first deammonia removal tower 2 is fed 55% of the total feed, and the second deammonia removal tower 5 is fed 45%. The steam at the top of the deammonia removal tower is reused as a heat source for the second deammonia removal tower 5. That is, when treating the same flow rate of wastewater, the primary steam consumption of this process is 55% of that of a single tower process, and the system energy consumption is significantly reduced.

[0053] The horizontal tube falling film evaporator 7 has a thin liquid film thickness and a heat transfer coefficient that is 1.5-2 times that of the vertical tube falling film evaporator. Due to its small temperature difference, it has high heat transfer efficiency, is suitable for lower evaporation temperatures, has a high thermal conductivity, stronger liquid distribution uniformity, low operating energy consumption, and high evaporation efficiency.

[0054] The steam generator 9 is specifically a steam drum. The water in the steam drum is heated by the horizontal falling film evaporator 7 to produce steam and some unevaporated saturated steam drum water, which flows back to the steam drum tube distributor. Under the action of the first-stage steam compressor, a negative pressure is created, promoting the generation of flash low-pressure steam. Additionally, the saturated water condensed from the first ammonia removal tower 2 at 110-116°C is temporarily stored in the condensate tank 3, and then pumped by the condensate pump 18 to the inner tube distributor of the steam drum. Again, under the suction force of the first-stage steam compressor, a negative pressure is created, promoting the generation of flash low-pressure steam.

[0055] The steam sources for the primary steam compressor 12 and the secondary steam compressor 11 are fresh steam and steam generated by the evaporation of water in the steam drum. They adopt a relatively independent closed-loop system, with the two compressors connected in series to generate a single stream of steam, which is simple and reliable.

[0056] The horizontal tube falling film evaporator 7 shell side, steam drum, first-stage steam compressor 12, buffer tank 13, second-stage steam compressor 11, first ammonia removal tower 2 lower first falling film reboiler 21 shell side, condensate tank 3 and live steam inlet form a steam heating circulation system. It does not come into direct contact with wastewater or ammonia vapor, and the compressor operates smoothly.

[0057] The absorption and concentration tower 15 receives concentrated ammonia vapor from the bottom of the tower via the seventh branch pipe 36. The tower has three sections of high-efficiency corrugated structured packing in its middle section. The lower two sections have ammonia water circulation distribution pipes above them, and a liquid redistributor is located between the two sections. A pure water inlet pipe is located in the middle to keep the third section of packing wet, absorbing escaped ammonia gas and serving as makeup water for the ammonia absorption system (the ammonia water in the intermediate tank 10 is used as qualified ammonia water when discharged by the ammonia water pump 23). A cyclone separator is located in the upper part of the tower to separate the mist from the liquid. A wire mesh is located at the top to capture micron-sized droplets. Non-condensable tail gas is discharged from the top eighth branch pipe 37. The tower is cooled by heat exchange with chilled water through a chilled water cooler 16 to ensure its absorption efficiency.

[0058] The first raw water preheater 14, the second raw water preheater 8, the third raw water preheater 1, and the fourth raw water preheater 4 respectively utilize the waste heat from high-temperature ammonia water, ammonia gas, and wastewater discharged from the tower bottom to heat the feed raw water and recover heat. The temperature of the wastewater discharged after recovery is not higher than 60 degrees Celsius.

[0059] The system provided in this application, which consists of a dual ammonia removal tower coupled with a heat pump, uses the top steam of the first ammonia removal tower 2 as the heat source of the second ammonia removal tower 5, and the top steam of the second ammonia removal tower 5 as the heat source of the secondary steam generator (horizontal tube falling film evaporator 7) of the heat pump system. It is coupled with a two-stage steam compressor to increase the temperature difference utilization range and fully recover and utilize the waste heat of the tower bottom water, ammonia water, and ammonia tail gas.

[0060] Compared to traditional stripping ammonia removal systems and superior comparative and similar ammonia removal systems, taking a 55 cubic meter / h ternary wastewater treatment project in a new energy industry as an example, the ammonia nitrogen content in its wastewater is usually between 3000 and 5000 ppm. The following table compares the operating costs of different treatment methods:

[0061]

[0062] Note: Steam price is 200 yuan / ton, and industrial electricity price is 0.8 yuan / kWh.

[0063] As can be seen from the table above, the ammonia stripping tower coupled with a heat pump has a significant advantage over the traditional stripping ammonia stripping method. Compared with the comparative example, the actual cost of steam energy consumption of the process of this invention is further reduced by more than 20%.

[0064] In addition, the steam system is completely independent, and the compressor and other equipment do not come into direct contact with the wastewater. The operation of the equipment is not affected by the quality of the wastewater. The steam compressors are used in series, and the steam quantity and pressure are stable.

[0065] The first ammonia removal tower 2 does not have a rectification section and no reflux. The ammonia nitrogen content in the feed is relatively stable, so the top temperature of the tower is stable at a high temperature of 98~100℃. This steam serves as a heat source for the falling film reboiler at the bottom of the second ammonia removal tower 5, and the heat is stable.

[0066] The second ammonia removal tower 5 has a rectification section at the top, using high-efficiency perforated plate corrugated packing (such as 450Y), which is more efficient than floating valve trays. Dilute ammonia is centrally distilled without affecting the feed to the second ammonia removal tower 5. During stable operation, the concentration of dilute ammonia at the top of the second ammonia removal tower 5 is 16%~20%, which, after condensation, can meet most of the owner's production needs. This reduces the intensity of downstream absorption operations and avoids the risk of ammonia escaping from the absorption system. The downstream absorption and concentration tower 15 utilizes chilled water for heat exchange to promote absorption, and can further concentrate the ammonia as needed. This process is flexible, stable, and reliable. In contrast, in the comparative single-ammonia stripping tower coupled with a heat pump system, the top rectification section is eliminated, and the ammonia-water mixed raw water is returned to the stripping tower. On the surface, the rectification section is eliminated, but in reality, the separation intensity of the stripping section is doubled due to the ammonia water reflux. The tower diameter, the number of trays, and the tray spacing need to be increased. Moreover, the tower top temperature is greatly affected by the volatilization of inlet ammonia gas. This problem is particularly obvious in the treatment of metallurgical wastewater with high ammonia nitrogen content (ammonia nitrogen in wastewater is greater than 20,000 ppm). In addition, in this process, all ammonia water is recovered from the absorption system. Based on past engineering experience, the problem of ammonia gas escaping from the absorption system frequently occurs in this process. The unabsorbed tail gas needs to be acid washed and absorbed through a spray absorption tower.

[0067] The deammonia removal tower is designed with a falling film reboiler at the bottom and a horizontal tube falling film evaporator for ammonia vapor, among other new equipment. Compared with conventional heat exchange equipment with the same function, its heat exchange efficiency is greatly improved, effectively ensuring the heat exchange efficiency under low temperature difference conditions and ensuring the stable and efficient operation of the system.

[0068] Taking a ternary wastewater treatment as an example, the wastewater treatment capacity is 55t / h, the ammonia nitrogen content is 0.545wt%, the ammonia nitrogen content of the bottom water of the tower is required to be ≤15ppm, and the ammonia water recovery concentration is adjustable from 16% to 22%.

[0069] In the wastewater ammonia removal process: raw water enters the system in two streams for ammonia removal treatment. The first stream has a flow rate of 30 t / h and is preheated by the first raw water preheater 14 and the third raw water preheater 1, reaching a temperature of 96~99℃. It then enters the top of the first ammonia removal tower 2. After sufficient mass transfer through the distribution of internal components and the rising steam, ammonia and steam are discharged together from the top. The top steam outlet temperature is 98~100℃. The treated wastewater is discharged from the bottom through the first discharge pump 17, with a wastewater temperature of approximately 104~106℃. Selectively, a portion of the wastewater is refluxed through the first branch pipe 29 to ensure the optimal film-forming flow rate required for evaporation in the first falling film reboiler 21. The remaining wastewater is then refluxed. After heat exchange and cooling with the raw water, the first raw water is discharged. The second raw water flow rate is 25t / h, which is preheated through the second raw water preheater 8 and the fourth raw water preheater 4 to a temperature of 85~88℃. It then enters the upper part of the second ammonia removal tower 5. After sufficient mass transfer through the distribution of internal components and rising steam, ammonia and steam are discharged together from the top. The top steam outlet temperature is 81~83℃. The treated wastewater is discharged from the bottom through the second discharge pump 19. The wastewater temperature is about 89~91℃. Selectively, a portion of the wastewater is refluxed through the second branch pipe 31 to ensure the optimal film-forming flow rate required for evaporation in the second falling film reboiler 51. The remaining wastewater is discharged after heat exchange and cooling with the raw water. Using this dual-tower feeding method, for the same wastewater treatment capacity of 55t / h, the steam from the outlet of the first ammonia removal tower 2 serves as the heat source for the second ammonia removal tower 5. The required circulating steam consumption of the system is the amount of steam entering the first ammonia removal tower 2, which is the steam required for the treatment of 30t / h of wastewater. Compared to a single-tower coupled heat pump system, the circulating steam consumption is reduced by approximately 45%. This steam has a wider operating temperature range, with a condensation temperature of 70℃ in the horizontal tube falling film evaporator. Furthermore, the dual-tower configuration allows for flexible adjustment of the feed ratio between the two towers to handle different boiling point water qualities, achieving an optimal balance between throughput and energy consumption. In addition, compared to the comparative system, this adds one more tower, effectively doubling the throughput, offering significant advantages for high-flow-rate projects.

[0070] In the steam circulation system: the steam source for this process system is divided into two parts, the same as the comparative example, namely, fresh steam entering the system from the third branch pipe 32 and secondary steam generated by compression and heating by the primary steam compressor and the secondary steam compressor. During the start-up phase, the steam source is provided by the third branch pipe 32, which enters the first falling film reboiler 21 at the bottom of the first ammonia removal tower 2 through 32a, enters the second falling film reboiler 51 at the bottom of the second ammonia removal tower 5 through 32b, and enters the steam drum through 32c to replenish the compressor for smooth operation. After the system starts up, the heat source is provided by the compressor compressing the evaporating steam generated from the horizontal tube falling film evaporator 7 and the flash steam generated in the steam drum. The steam flow rate is 2.4~3 t / h. The initial steam temperature in the steam drum is 70℃, and its negative pressure is maintained by the compressor pumping air. After being compressed by the secondary steam compressor 11, the steam temperature reaches 116℃, that is, the overall temperature rise is 46℃, the steam flow rate is reduced by 45%, so the overall energy consumption is reduced by about 15~20%. The 116°C steam, after being compressed, enters the shell side of the first falling film reboiler 21 at the bottom of the first ammonia removal tower 2, where it exchanges heat with the film-forming wastewater inside the tube side. The tube side wastewater evaporates to produce steam at 104~106°C. The shell side steam condenses into condensate at 110~116°C, which enters the condensate tank 3. It is then transported back to the distributor inside the steam drum by the condensate pump 18 and the fifteenth branch pipe 44 for flash evaporation to produce steam and saturated water. The saturated water is then transported by the steam drum water circulation pump 22 to the shell side distributor of the horizontal tube falling film evaporator 7, where it exchanges heat with the steam exiting the top of the second ammonia removal tower 5 in the tube side, and evaporates to produce secondary steam, which then enters the first-stage steam compressor 12 to realize the circulation of the steam system.

[0071] Ammonia vapor heat and ammonia water recovery: The fluid in the heat exchange tubes of the first falling film reboiler 21 in the lower section of the first ammonia removal tower 2 is the wastewater descending from the tower. After heat exchange with the shell-side steam, 2.3~2.8 t / h of steam at 104~106℃ required for ammonia stripping is generated in the tubes. This steam rises and, after sufficient mass transfer with the wastewater in the tower internals such as the trays / packing, becomes ammonia-containing steam at 98~100℃. It is discharged from the top of the tower and, after passing through the fourth branch pipe 33, enters the shell side of the second falling film reboiler 51 in the lower section of the second ammonia removal tower 5. It exchanges heat with the film-forming wastewater inside the heat exchange tubes. The shell-side ammonia vapor condenses into dilute ammonia water at 92~98℃ and enters the ammonia water condensation tank 6. It is then sent to the top of the second ammonia removal tower 5 for reflux by the ammonia water condensation pump 20. A small portion is used as makeup liquid for the downstream absorption tower. Depending on the operating conditions, it can be selectively sent to the top rectification section for distillation. The fluid inside the second ammonia removal tower 5 and the second falling film reboiler 51 is the descending wastewater. After heat exchange with ammonia-containing steam in the shell side, 2.1~2.5 t / h of steam is generated inside the tubes to produce the steam required for ammonia stripping. This steam rises and passes through the stripping and rectification sections, where it undergoes sufficient mass transfer with the wastewater in the trays / packing and other internal components of the tower, becoming high-ammonia-containing steam at 81~83℃. This steam is discharged from the top of the second ammonia removal tower 5, with an adjustable ammonia concentration of 16~22%. The ammonia-containing steam discharged from the top of the second ammonia removal tower 5 enters the tube side of the horizontal falling film evaporator 7 via the fifth branch pipe 34. There, it exchanges heat with 70℃ saturated drum water supplied by the drum water circulation pump 22 in the shell side. This is adjustable; most of the condensation can be adjusted to form a 16~22% ammonia-containing water product, while the remaining uncondensed concentrated ammonia-containing steam is discharged. Ammonia water enters the intermediate ammonia tank 10, and is then pumped by the ammonia pump 23. It can be selectively returned to the second deammoniation tower 5, or guided through the thirteenth branch pipe 38 to the first raw water preheater 14 and then enters the absorption and concentration tower 15 as makeup liquid, or discharged as 16-22% finished ammonia water. Uncondensed ammonia-containing concentrated vapor enters the shell side of the second raw water preheater 8 through the sixth branch pipe 35, where it is completely condensed by heat exchange with the tube side raw water. Part of it is discharged from the bottom of the shell side of the second raw water preheater 8 to the bottom of the absorption and concentration tower 15, and the other part is discharged through the fourteenth branch pipe 39 to the intermediate ammonia tank 10. Non-condensable gas is discharged through the seventh branch pipe 36 to the lower tube distributor of the absorption and concentration tower 15. The non-condensable gas is washed by the circulating liquid in the tower, and after three-stage absorption, it is discharged from the top of the tower. It is connected to the inlet of the vacuum pump 24 through the eighth branch pipe 37, and then discharged at a high point or enters the plant tail gas system.

[0072] The bottom liquid of the tower is transported to the chilled water cooler by the ammonia water circulation discharge pump 25. After exchanging heat with the chilled water and cooling down, it is transported to the upper tube distributor of each packing section of the absorption and concentration tower 15 for spraying to wash away non-condensable gas and concentrate the absorbent. Optionally, chilled water is used for cooling. The concentration of the absorbent is adjustable from 16% to 28%. After passing through the ammonia water circulation discharge pump 25, it is discharged through the ninth branch pipe 40.

[0073] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A dual-tower stripping ammonia removal coupled with a heat pump system for treating ammonia nitrogen wastewater, characterized in that, include: The system consists of a first ammonia removal tower (2), a second ammonia removal tower (5), a first raw water preheater (14), a second raw water preheater (8), a third raw water preheater (1), a fourth raw water preheater (4), and a steam generator (9). The first raw water is preheated by passing through the first raw water preheater (14) and the third raw water preheater (1) in sequence, and then enters the first deammoniation tower (2). After mass transfer with steam in the first deammoniation tower (2), the ammonia-containing steam is discharged from the top of the first deammoniation tower (2) and then enters the second deammoniation tower (5). The second batch of raw water is preheated sequentially through the second raw water preheater (8) and the fourth raw water preheater (4), and then enters the second ammonia removal tower (5). After mass transfer with steam in the second ammonia removal tower (5), the ammonia-containing steam is discharged from the top of the second ammonia removal tower (5) and exchanges heat with the steam generator (9). External steam enters the first deammoniation tower (2), the second deammoniation tower (5), and the steam generator (9) respectively; after the first-stage steam compressor (12) and the second-stage steam compressor (11) are started, secondary steam is generated and enters the first deammoniation tower (2); The ammonia-containing vapor discharged from the top of the first ammonia removal tower (2) enters the shell side of the second falling film reboiler (51) at the bottom of the second ammonia removal tower (5) after passing through the fourth branch pipe (33). It exchanges heat with the wastewater in its tube side. After the vapor is condensed, it enters the ammonia condensate tank (6) and is sent to the upper part of the second ammonia removal tower (5) by the ammonia condensate pump (20) to enter the top rectification section for distillation. The fluid in the tube of the second falling film reboiler (51) is the wastewater descending in the tower. After exchanging heat with the ammonia-containing vapor in the shell side, the vapor required for ammonia stripping is generated in the tube. After the vapor rises and exchanges mass with the wastewater, it becomes ammonia-containing vapor in the rectification section and is discharged from the top of the tower. The ammonia-containing vapor discharged from the top of the second ammonia removal tower (5) enters the tube side of the horizontal tube falling film evaporator (7) through the fifth branch pipe (34), and exchanges heat with the saturated water transported by the water circulation pump of the steam generator in the shell side, and partially condenses to form ammonia water and uncondensed ammonia-containing vapor; Ammonia water enters the ammonia water intermediate tank (10), and after passing through the ammonia water pump (23), it can be selectively transported back to the second ammonia removal tower (5), or after passing through the first raw water preheater (14), it enters the absorption and concentration tower (15), or it can be discharged as finished ammonia water. Uncondensed ammonia vapor enters the shell side of the second raw water preheater (8) through the sixth branch pipe (35), where it is completely condensed by heat exchange with the tube side raw water. It is then discharged from the bottom of the shell side of the second raw water preheater (8) to the bottom of the absorption and concentration tower (15). The non-condensable gas is discharged through the seventh branch pipe (36) to the lower tube distributor of the absorption and concentration tower (15). The non-condensable gas is washed by the circulating liquid in the tower, and after three stages of absorption, it is discharged from the top of the tower. It is then connected to the inlet of the vacuum pump (24) through the eighth branch pipe (37), and subsequently discharged at a high point or enters the plant tail gas system.

2. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, Wastewater treated in the first deammoniation tower (2) is discharged from the bottom via the first discharge pump (17), and part of the wastewater is returned to the first deammoniation tower (2) via the first branch pipe (29) to ensure the optimal flow rate required for evaporation of the falling film evaporator in the first deammoniation tower (2); Wastewater treated in the second deammoniation tower (5) is discharged from the bottom via the second discharge pump (19), and part of the wastewater is returned to the second deammoniation tower (5) via the second branch pipe (31) to ensure the optimal flow rate required for evaporation of the falling film evaporator in the second deammoniation tower (5); External steam enters the first deammoniation tower (2), the second deammoniation tower (5) and the steam generator (9) through the third branch pipe (32); the fluid in the first falling film reboiler (21) is the wastewater descending in the tower. After heat exchange with the shell side steam, the steam required for ammonia stripping is generated in the tube. After the steam rises and transfers mass with the wastewater, it becomes ammonia-containing steam and is discharged from the top of the tower.

3. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The condensate from the shell side of the first falling film reboiler (21) at the bottom of the first ammonia removal tower (2) enters the condensate tank (3) and is pumped back to the steam generator (9) by the condensate pump (18). The saturated water is then pumped to the shell side distributor of the horizontal tube falling film evaporator (7) by the water circulation pump (22) in the steam generator, where it exchanges heat with the ammonia-containing steam in the tube side of the horizontal tube falling film evaporator (7) to generate saturated steam. The saturated steam is then returned to the steam generator (9) via the tenth branch pipe (41) for gas-liquid separation. The steam enters the first-stage steam compressor (12) via the eleventh branch pipe (42), then enters the buffer tank, and then enters the second-stage steam compressor (11) via the twelfth branch pipe (43). The pressurized saturated steam is discharged to the shell side of the first falling film reboiler (21) at the bottom of the first ammonia removal tower (2), where it exchanges heat with the fluid in the tube side of the first falling film reboiler (21) as the wastewater descending in the tower. The steam required for ammonia stripping is generated in the tube side and serves as the heat source for the distillation of the first ammonia removal tower (2).

4. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The ammonia-containing vapor generated by the distillation of the first ammonia removal tower (2) enters the second falling film reboiler (51) at the bottom of the second ammonia removal tower (5) as the heat source for the ammonia removal operation of the second ammonia removal tower (5); after condensation, it is fully refluxed to the second ammonia removal tower (5) by the ammonia water pump, and after being distilled together with the ammonia vapor generated by the ammonia removal of the second ammonia removal tower (5), it is discharged from the fifth branch pipe (34) at the top of the second ammonia removal tower (5) to the tube side of the horizontal falling film evaporator (7); the ammonia-containing vapor passes through the shell side of the steam generator (9), and after the water-containing part is condensed, the condensate is discharged to the ammonia water intermediate tank, and is transported by the ammonia water pump (23) for distillation reflux, The ammonia vapor can be discharged as finished product ammonia water or discharged to the absorption and concentration tower (15) as absorbent liquid replenishment; the remaining ammonia vapor enters the shell side of the second raw water preheater (8), and after being completely condensed by the tube side raw water, it enters the absorption and concentration tower (15) as absorbent liquid replenishment or as finished product ammonia water discharge. The concentrated ammonia vapor is condensed after passing through the second raw water preheater (8), and the remaining non-condensable gas enters the bottom of the absorption and concentration tower (15) through the seventh branch pipe (36). The non-condensable gas is washed by the circulating liquid in the tower and discharged from the top of the tower after two-stage separation. It is connected to the inlet of the vacuum pump (24) through the eighth branch pipe (37) and then discharged from the high point.

5. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The ammonia water circulation discharge pump (25) transports the bottom liquid of the absorption and concentration tower (15) to the chilled water cooler. After exchanging heat with the chilled water and cooling down, it is transported to the upper tube distributor of each packing section of the absorption and concentration tower (15) for spraying operation to wash the non-condensable gas and concentrate the absorbent. After the absorbent concentration reaches the required level, it is discharged through the ninth branch pipe (40) after passing through the ammonia water circulation discharge pump (25).

6. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The first deammonia removal tower (2) and the second deammonia removal tower (5) are fed in parallel, and the top steam of the first deammonia removal tower (2) is used as the heat source of the second deammonia removal tower (5).

7. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The top of the second deammoniation tower (5) is equipped with a rectification section to concentrate the ammonia-containing vapor generated by the first deammoniation tower (2) and the second deammoniation tower (5).

8. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The saturated water in the steam generator (9) generates steam and some residual saturated water under the heating action of the horizontal tube falling film evaporator (7). The saturated water flows back to the tube distributor in the steam generator (9). Under the action of the first-stage steam compressor (12), a negative pressure is formed, which promotes the further generation of flash steam. Saturated water condensed from the first ammonia removal tower (2) is temporarily stored in the condensate tank (3) and then transported by the condensate pump (18) to the tube distributor in the steam generator (9). Under the action of the first-stage steam compressor (12), a negative pressure is formed to promote the generation of flash steam.

9. The ammonia nitrogen wastewater treatment system with a dual-tower stripping ammonia removal coupled heat pump as described in claim 1, characterized in that, The primary steam compressor (12) and the secondary steam compressor (11) are connected in series.

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