Urea hydrolyzer waste liquid resourceful treatment system and method

Abstract

The invention belongs to the technical field of industrial waste liquid treatment and recycling, and relates to a urea hydrolyzer waste liquid recycling treatment system and method. The pH value of the waste liquid of the urea hydrolyzer is adjusted to 11.2 + / -0.3 in the pH adjusting water tank, and the temperature of the waste liquid to be treated is adjusted by adopting the urea hydrolyzer. The ammonia-containing gas and the stripped wastewater are separated through the filler stripping tower, and the stripping process of the filler stripping tower depends on the heat of the waste liquid, so that energy conservation and consumption reduction are facilitated. The purity of ammonium sulfate generated by the two-stage sulfuric acid absorption tower is greater than or equal to 99%. Denitrifying nitrogen removal and COD degradation are performed on the waste liquid through the A / O-MBR, and COD degradation is further performed by utilizing the electrocatalytic oxidation reactor. The multi-effect evaporator realizes separation of wastewater into condensate water and a concentrated solution, the condensate water is used for recycling, the concentrated solution is used for crystallization separation of Na2CO3, and full utilization of wastewater resources is realized. According to the method, efficient ammonia nitrogen removal and salt resource recycling of the high-salt waste liquid are achieved, and energy conservation and consumption reduction are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial waste liquid treatment and resource utilization, and relates to a urea hydrolyzer waste liquid resource utilization treatment system and method. Background Art

[0002] In industrial production, urea hydrolyzers are widely used to hydrolyze urea solution, producing ammonia and other products for subsequent processes such as denitrification. However, during operation, impurity ions in the urea solution become highly concentrated in the hydrolyzer, especially chloride ions, which can cause localized corrosion of the stainless steel reactor and heat exchange tubes. Regular wastewater discharge is one method to control and reduce the chloride ion concentration in the hydrolyzed solution. However, most power plants struggle with the difficulty of treating wastewater containing high concentrations of ammonia nitrogen, COD, and salt, making it difficult to treat after discharge. This causes the chloride ion concentration in the hydrolyzer to seriously exceed the standard, threatening the stable operation of the hydrolyzer. Direct discharge of the chloride ion would also cause serious environmental pollution.

[0003] Currently, the main treatment methods for wastewater generated by urea hydrolysis include physical, chemical, and biological methods. These methods can only remove insoluble impurities in the wastewater, with limited effects on the removal of ammonia nitrogen and COD. Furthermore, the treatment costs are high and secondary pollution is likely to occur. The existing technologies have the following major problems:

[0004] High energy consumption: The traditional stripping method requires additional steam heating and does not utilize the waste heat of the hydrolysis waste liquid, which is usually 50-80°C, resulting in a 30%-50% increase in operating costs;

[0005] Low ammonia nitrogen recovery rate: Ammonia absorption is insufficient, the recovery rate is less than 80%, and tail gas escape causes secondary pollution;

[0006] Salt is difficult to handle: high salt levels cause scaling and clogging of evaporation crystallizers, and the salt purity is low, usually less than 90%, making it impossible to recycle;

[0007] Incomplete COD degradation: Residues of difficult-to-degrade nitrogen-containing organic matter (such as carbamate) make it difficult for the effluent COD to reach the standard (>100 mg / L) stably.

[0008] In summary, the treatment methods for waste liquid generated by urea hydrolysis have the problems of high energy consumption, low ammonia nitrogen recovery rate, inability to recover salt and incomplete COD degradation. Summary of the Invention

[0009] The purpose of the present invention is to provide a urea hydrolyzer waste liquid resource treatment system and method to solve the technical problems of high energy consumption, low ammonia nitrogen recovery rate, inability to recover salt and incomplete COD degradation in the treatment method of waste liquid generated by urea hydrolysis.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a urea hydrolyzer waste liquid resource treatment system, comprising:

[0012] pH adjustment pool;

[0013] A packing stripping tower, wherein the outlet of the pH adjustment water tank is connected to the inlet of the packing stripping tower through a spiral plate heat exchanger; the packing stripping tower is provided with a gas outlet and a waste liquid outlet, and the gas outlet is connected to an ammonium sulfate storage tank through a two-stage sulfuric acid absorption tower;

[0014] A / O-MBR reactor, the waste liquid outlet is connected to a multi-effect evaporator through the A / O-MBR reactor, the electrocatalytic oxidation reactor, and the evaporator heat pump in sequence, the multi-effect evaporator is provided with a condensed water outlet and a concentrated liquid outlet, and the concentrated liquid outlet is connected to a crystallizer.

[0015] In a second aspect, the present invention provides a method for resource-based treatment of urea hydrolyzer waste liquid, based on a urea hydrolyzer waste liquid resource-based treatment system, comprising the following steps:

[0016] The urea hydrolysis wastewater was passed into the pH adjustment tank to adjust the pH of the wastewater to 11.2±0.3;

[0017] The waste liquid after pH adjustment is passed into the spiral plate heat exchanger for temperature adjustment to ensure that the temperature of the waste liquid after pH adjustment is greater than or equal to 70°C;

[0018] The waste liquid enters the packed stripping tower from the spiral plate heat exchanger for ammonia nitrogen stripping. The ammonia-containing gas generated after stripping enters the two-stage sulfuric acid absorption tower to obtain ammonium sulfate solution, which is stored in the ammonium sulfate storage tank;

[0019] The wastewater after stripping is cooled to 35℃ and enters the A / O-MBR reactor for denitrification and COD degradation;

[0020] The effluent from the A / O-MBR reactor enters the electrocatalytic oxidation reactor for further COD degradation;

[0021] The effluent from the electrocatalytic oxidation reactor enters the multi-effect evaporator to obtain evaporated condensed water and concentrated liquid. The condensed water is reused to replenish the urea hydrolyzer, and the concentrated liquid enters the crystallizer to crystallize and separate Na2CO3. The crystallization mother liquor produced by the crystallizer is refluxed to the inlet of the evaporator heat pump.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention adjusts the pH of the urea hydrolyzer wastewater to 11.2±0.3 in a pH-regulating tank. The urea hydrolyzer is used to adjust the temperature of the wastewater to be treated, ensuring that the wastewater entering the packing stripping tower meets the required temperature and preventing excessive temperature rise. The packing stripping tower separates ammonia-containing gas and stripped wastewater, facilitating subsequent treatment. The stripping process in the packing stripping tower utilizes the wastewater's own heat, facilitating energy conservation and cost reduction. The ammonium sulfate generated by the two-stage sulfuric acid absorption tower has a purity of ≥99%, achieving efficient ammonia nitrogen removal and resource recovery. The wastewater undergoes denitrification and COD degradation in an A / O-MBR reactor, and further COD degradation is performed in an electrocatalytic oxidation reactor, facilitating wastewater recycling. A multi-effect evaporator separates the wastewater into condensate and concentrate, with the condensate used for recycling and the concentrate used for crystallization and separation of Na2CO3, achieving full utilization of wastewater resources. The present invention realizes efficient ammonia nitrogen removal and salt resource recovery and utilization of high-salt waste liquid. The recovered products include ammonium sulfate, Na2CO3 and condensed water. During the wastewater treatment process, the waste heat of the urea hydrolyzer waste liquid is used as the heat source for the packing stripping tower and the multi-effect evaporator, which is conducive to energy saving and consumption reduction.

[0024] The method of the present invention passes the urea hydrolysis waste liquid into a pH adjustment water tank to adjust the pH of the waste liquid to 11.2±0.3, thereby promoting the conversion of ammonium ions into free NH3. The waste liquid after pH adjustment is passed into a spiral plate heat exchanger for temperature adjustment to ensure that the temperature of the waste liquid after pH adjustment is greater than or equal to 70°C, which is convenient for the stripping of ammonia nitrogen. The waste liquid enters the packed stripping tower from the spiral plate heat exchanger for ammonia nitrogen stripping. The ammonia-containing gas generated after stripping enters a two-stage sulfuric acid absorption tower to obtain ammonium sulfate solution, and the ammonium sulfate solution is stored in an ammonium sulfate storage tank. The waste water after stripping is cooled to 35°C and enters the A / O-MBR reactor for denitrification and COD degradation; the effluent from the A / O-MBR reactor enters the electrocatalytic oxidation reactor for further COD degradation, which is beneficial to the comprehensive recovery of the waste liquid. The effluent from the electrocatalytic oxidation reactor enters a multiple-effect evaporator, producing evaporated condensate and concentrated liquid. The condensate is reused to replenish the urea hydrolyzer, while the concentrated liquid enters a crystallizer to separate Na2CO3. The resulting crystallization mother liquor is refluxed to the inlet of the evaporator's heat pump. This invention achieves efficient ammonia and nitrogen removal and salt resource recovery from high-salt wastewater. During the wastewater treatment process, waste heat from the urea hydrolyzer wastewater is used as a heat source for the packing stripping tower and the multiple-effect evaporator, contributing to energy conservation and consumption reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0026] Figure 2 Flow chart of the method of the present invention.

[0027] Among them: 1. pH adjustment water tank; 2. Spiral plate heat exchanger; 3. Booster pump; 4. Packing stripping tower; 5. Two-stage sulfuric acid absorption tower; 6. Ammonium sulfate storage tank; 7. A / O-MBR reactor; 8. Electrocatalytic oxidation reactor; 9. Evaporator heat pump; 10. Multi-effect evaporator; 11. Crystallizer; 12. Control unit; 201. Cooling water inlet; 202. Cooling water outlet; 401. Gas outlet; 402. Waste liquid outlet; 501. Primary absorption tower; 502. Secondary absorption tower; 701. Anoxic tank; 702. Oxygen consumption tank; 703. MBR membrane assembly; 101. Primary multi-effect evaporator; 102. Secondary multi-effect evaporator; 103. Third-stage multi-effect evaporator; 111. Crystal outlet; 112. Crystallization mother liquor outlet. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first," "second," and the like in the description of the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatus.

[0030] The present invention is described in further detail below with reference to the accompanying drawings:

[0031] Example 1:

[0032] See also Figure 1 This embodiment discloses a urea hydrolyzer waste liquid resource treatment system, comprising: a pH adjustment water tank 1, a packing stripping tower 4, a two-stage sulfuric acid absorption tower 5, an ammonium sulfate storage tank 6, an A / O-MBR reactor 7, an electrocatalytic oxidation reactor 8, an evaporator heat pump 9 connected to a multi-effect evaporator 10 and a crystallizer 11;

[0033] The pH of the urea hydrolyzer wastewater is adjusted to pH = 11.2 ± 0.3 in the pH adjustment water tank 1. The outlet of the pH adjustment water tank 1 is connected to the inlet of the packing stripping tower 4 through the spiral plate heat exchanger 2. The wastewater is temperature-adjusted by the spiral plate heat exchanger 2 to ensure that the temperature of the wastewater entering the packing stripping tower 4 meets the requirements and prevents the temperature from being too high. The packing stripping tower 4 is provided with a gas outlet 401 and a waste liquid outlet 402. The ammonia-containing gas and the wastewater after stripping are separated by the packing stripping tower 4 to facilitate the next step of treatment. The stripping process of the packing stripping tower relies on the heat of the wastewater itself, which is conducive to energy saving and consumption reduction. The gas outlet 401 is connected to the ammonium sulfate storage tank 6 through the two-stage sulfuric acid absorption tower 5. The purity of the ammonium sulfate generated by the two-stage sulfuric acid absorption tower 5 is ≥99%, achieving efficient ammonia nitrogen removal and resource recovery. The waste liquid outlet 402 is connected to a multi-effect evaporator 10, which is sequentially connected through the A / O-MBR reactor 7, the electrocatalytic oxidation reactor 8, and the evaporator heat pump 9. The multi-effect evaporator 10 is equipped with a condensate outlet and a concentrate outlet, and the concentrate outlet is connected to a crystallizer 11. The A / O-MBR reactor 7 is used for denitrification and COD degradation of the waste liquid, while the electrocatalytic oxidation reactor 8 further degrades COD, achieving deep COD degradation and facilitating wastewater recycling. The multi-effect evaporator 10 separates the wastewater into condensate and concentrate. The condensate is recycled, and the concentrate is used to crystallize and separate Na2CO3 in the crystallizer 11, achieving full utilization of wastewater resources.

[0034] In the embodiment of the present invention, the spiral plate heat exchanger 2 is provided with a cooling water inlet 201 and a cooling water outlet 202 to prevent the cooling water from entering the packing stripping tower 4;

[0035] A booster pump 3 is provided between the spiral plate heat exchanger 2 and the filler stripping tower 4 .

[0036] In the embodiment of the present invention, the gas-liquid ratio of the packing stripping tower 4 is 4000:1, and the packing stripping tower 4 is filled with ball ring packing.

[0037] In an embodiment of the present invention, the two-stage sulfuric acid absorption tower 5 includes a primary absorption tower 501 and a secondary absorption tower 502. The primary absorption tower 501 and the secondary absorption tower 502 are both provided with a receiving port, a gas discharge port and a liquid discharge port. The gas outlet 401 is connected to the receiving port of the primary absorption tower 501, the gas discharge port of the primary absorption tower 501 is connected to the receiving port of the secondary absorption tower 502, and the liquid discharge ports of the primary absorption tower 501 and the secondary absorption tower 502 are both connected to the inlet of the ammonium sulfate storage tank 6.

[0038] In this embodiment of the present invention, the A / O-MBR reactor 7 includes an anoxic tank 701, an oxygen consumption tank 702 and an MBR membrane assembly 703, the waste liquid outlet 402 is connected to the inlet of the anoxic tank 701, the oxygen consumption tank 702 is located between the anoxic tank 701 and the MBR membrane assembly 703, the MBR membrane assembly 703 is located at the outlet of the A / O-MBR reactor 7, and the outlet of the A / O-MBR reactor 7 is connected to the inlet of the electrocatalytic oxidation reactor 8;

[0039] The anode of the electrocatalytic oxidation reactor 8 is a Ti / PbO2 electrode, and the cathode is loaded with a Fe3O4 / graphene composite catalyst.

[0040] In an embodiment of the present invention, the multi-effect evaporator 10 includes a first-stage multi-effect evaporator 101, a second-stage multi-effect evaporator 102, and a third-stage multi-effect evaporator 103. The first-stage multi-effect evaporator 101, the second-stage multi-effect evaporator 102, and the third-stage multi-effect evaporator 103 are all provided with a first inlet, a second inlet, a condensed water outlet, a steam discharge hole, and a concentrated liquid outlet. The outlet of the evaporator heat pump 9 is connected to the second inlet of the first-stage multi-effect evaporator 101, the steam hole of the first-stage multi-effect evaporator 101 is connected to the second inlet of the second-stage multi-effect evaporator 102, and the concentrated liquid outlet of the first-stage multi-effect evaporator 101 is connected to the second inlet of the second-stage multi-effect evaporator 102. The first inlet of the secondary multi-effect evaporator 102 is connected, the steam hole of the secondary multi-effect evaporator 102 is connected to the second inlet of the tertiary multi-effect evaporator 103, the concentrated liquid outlet of the secondary multi-effect evaporator 102 is connected to the first inlet of the tertiary multi-effect evaporator 103, the concentrated liquid outlet of the tertiary multi-effect evaporator 103 is connected to the crystallizer 11, the condensed water outlets of the primary multi-effect evaporator 101, the secondary multi-effect evaporator 102 and the tertiary multi-effect evaporator 103 are used to connect to the water supply port of the hydrolyzer, and the first inlet of the primary multi-effect evaporator 101 is used to introduce the waste liquid heat source generated by urea hydrolysis.

[0041] In the embodiment of the present invention, the crystallizer 11 is provided with a crystal outlet 111 and a crystallization mother liquor outlet 112 , and the crystallization mother liquor outlet 112 is connected to the inlet of the evaporator heat pump 9 .

[0042] In the embodiment of the present invention, online water quality sensors are arranged in the pH adjustment pool 1 and the two-stage sulfuric acid absorption tower 5, an ORP sensor is arranged in the A / O-MBR reactor 7, and a conductivity sensor is provided at the inlet of the multi-effect evaporator 10.

[0043] See also Figure 2 This embodiment also discloses a method for resource-based treatment of urea hydrolyzer waste liquid, based on a urea hydrolyzer waste liquid resource-based treatment system, comprising the following steps:

[0044] S1, pass the urea hydrolysis wastewater into the pH adjustment pool 1, adjust the pH of the wastewater to 11.2±0.3; promote the conversion of ammonium ions NH 4+ Conversion to free NH3 is as follows:

[0045] Add 30% NaOH solution into pH adjustment pool 1 to adjust the pH of the waste liquid to 11.2±0.3.

[0046] S2, the waste liquid after pH adjustment is passed into the spiral plate heat exchanger 2 for temperature adjustment to ensure that the temperature of the waste liquid after pH adjustment is greater than or equal to 70°C;

[0047] S3, the waste liquid enters the packed stripping tower 4 from the spiral plate heat exchanger 2 for ammonia nitrogen stripping, and the ammonia-containing gas generated after stripping enters the two-stage sulfuric acid absorption tower 5 to obtain ammonium sulfate solution, which is stored in the ammonium sulfate storage tank 6;

[0048] S4, the wastewater after stripping is cooled to 35°C and enters the A / O-MBR reactor 7 for denitrification and COD degradation, as follows:

[0049] The wastewater after stripping is cooled to 35°C and enters the anoxic tank 701 where sodium acetate is added to maintain a carbon-nitrogen ratio of C / N=5:1 and a hydraulic retention time of 6h for denitrification.

[0050] In the oxygen consumption tank 702, the dissolved oxygen is maintained at 3.5 mg / L, and the hydraulic retention time is 12 h.

[0051] S5, the effluent from the A / O-MBR reactor 7 enters the electrocatalytic oxidation reactor 8 for further COD degradation;

[0052] S6, the effluent from the electrocatalytic oxidation reactor 8 enters the multi-effect evaporator 10 to obtain evaporated condensed water and concentrated liquid. The condensed water is reused to replenish the urea hydrolyzer, and the concentrated liquid enters the crystallizer 11 to crystallize and separate Na2CO3. The crystallization mother liquor produced by the crystallizer 11 is refluxed to the inlet of the evaporator heat pump 9, as follows:

[0053] The waste heat of the waste liquid of the urea hydrolyzer is used to preheat the water outlet of the electrocatalytic oxidation reactor 8. The evaporation temperature in the three-stage vacuum multi-effect evaporator 10 is 60°C.

[0054] After the concentrated solution enters the crystallizer 11, the temperature is gradually reduced from 60° C. to 30° C.

[0055] The present invention realizes efficient ammonia nitrogen removal and salt resource recovery and utilization of high-salt waste liquid. The recovered products include ammonium sulfate, Na2CO3 and condensed water. During the wastewater treatment process, the waste heat of the urea hydrolyzer waste liquid is used as the heat source for the packing stripping tower 4 and the multi-effect evaporator 10, which is conducive to energy saving and consumption reduction.

[0056] Example 2:

[0057] See also Figure 1 This embodiment discloses a urea hydrolyzer waste liquid resource treatment system, including a waste heat driven ammonia nitrogen recovery unit, a salt-tolerant bio-electrocatalytic coupling unit, a salt closed-loop regeneration unit and a control unit.

[0058] The waste heat driven ammonia nitrogen recovery unit mainly includes: a pH adjustment water tank 1, a spiral plate heat exchanger 2, a packing stripping tower 4 and a two-stage sulfuric acid absorption tower. The maximum temperature in the packing stripping tower 4 can reach 80°C.

[0059] The specific processing flow is as follows:

[0060] The urea hydrolyzer wastewater with a temperature of 75-80°C is fed into the pH adjustment tank 1, and a 30% concentration of NaOH solution is added to adjust the pH of the urea hydrolyzer wastewater to pH = 11.2 ± 0.3;

[0061] The urea hydrolyzer wastewater passes through a spiral plate heat exchanger 2 and enters a packed stripping tower 4. The gas-liquid ratio of the packed stripping tower 4 is set at 4000:1, and the outlet temperature of the spiral plate heat exchanger 2 is controlled to be greater than 70°C. The ammonia gas after stripping passes through a two-stage sulfuric acid absorber 5. The pH of the primary absorbent in the two-stage sulfuric acid absorber 5 is 3.5, and the pH of the secondary absorbent is 2.0, producing a 20% to 25% ammonium sulfate solution. It should be noted that the ammonia nitrogen removal rate of the packed stripping tower 4 is ≥95%, and the purity of the ammonium sulfate produced by the two-stage sulfuric acid absorber 5 is ≥99%. The waste heat from the urea hydrolyzer wastewater is used to maintain the required stripping temperature, preheat the evaporated feed, and drive the circulation pump of the two-stage sulfuric acid absorber 5.

[0062] The salt-tolerant biological-electrocatalytic coupling unit mainly includes: an A / O-MBR reactor 7 enhanced with salt-tolerant bacteria and an electrocatalytic oxidation reactor 8 (Ti / PbO2 anode + Fe3O4 graphene cathode). The suspended solids concentration (MLSS) of the sludge in the A / O-MBR reactor 7 is maintained greater than or equal to 12000 mg / L.

[0063] The specific processing flow is as follows:

[0064] The wastewater after stripping is cooled to 35°C and enters the A / O-MBR reactor 7 strengthened with salt-tolerant bacteria. It mainly passes through the anoxic tank 701 and the aerobic tank 702. Sodium acetate is added to the anoxic section, with a carbon-nitrogen ratio of C / N=5:1 and a hydraulic retention time of 6 hours to carry out denitrification.

[0065] The dissolved oxygen (DO) in the aerobic section is maintained at 3.5 mg / L, the hydraulic retention time (HRT) is 12 h, COD degradation is carried out, and the effluent COD is degraded to ≤300 mg / L. The MBR membrane assembly intercepts microorganisms and suspended solids to ensure effluent stability.

[0066] The effluent of A / O-MBR reactor 7 is fed with H2O2 at a concentration of 80 mg / L and enters electrocatalytic oxidation reactor 8. The current density is maintained at 15 mA / cm 2 The total reaction time is 40 minutes, and the effluent COD is degraded to ≤50 mg / L.

[0067] The salt closed-loop regeneration unit mainly includes: a multiple-effect evaporator 10 and a crystallizer 11.

[0068] The specific processing flow is as follows:

[0069] The outlet water of the electrocatalytic oxidation reactor 8 enters the multi-effect evaporator 10. The evaporation temperature of the three-stage vacuum multi-effect evaporator 10 is 60°C. The evaporated condensed water is reused for water replenishment in the hydrolyzer. The condensed water reuse rate is ≥95%. The concentrated liquid is seeded with nano-CaCO3 crystals, and the temperature is gradually reduced (60°C to 30°C) to crystallize and separate Na2CO3 (purity ≥98%). The crystallized Na2CO3 can be sold as an industrial raw material.

[0070] The control unit 12 mainly includes: an integrated signal sensor and a PLC controller.

[0071] The signal sensors include water quality sensors and operating parameter sensors;

[0072] The water quality sensor mainly collects parameters such as pH, ORP, and conductivity;

[0073] The operating parameter sensor mainly collects information such as the dosage, fan speed, and evaporation pressure.

[0074] The PLC controller can receive sensor signals and adjust operating parameters such as the dosage, fan speed, and current controller in a coordinated manner.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] a. Efficient ammonia nitrogen removal and resource recovery:

[0077] Ammonia nitrogen removal rate ≥98%: By maintaining the stripping temperature (≥70°C) and precise pH control (11.2±0.3) through waste heat, the ammonia nitrogen removal efficiency is increased by 15% to 20% compared with traditional processes, solving the problem of treating high-concentration ammonia nitrogen (>2000mg / L).

[0078] High-value recovery of ammonium sulfate: The two-stage sulfuric acid absorption tower 5 converts ammonia gas into ammonium sulfate solution with a purity of ≥99%. 15-25 kg of ammonium sulfate can be recovered from each ton of waste liquid and can be sold as an industrial raw material.

[0079] Zero ammonia emission: After the tail gas is absorbed by the second stage of the two-stage sulfuric acid absorption tower 5, the NH3 concentration is ≤5mg / m 3 , meeting emission standards and avoiding secondary pollution.

[0080] b. Deep degradation of COD and stable compliance with standards:

[0081] Bio-electrocatalytic synergistic enhancement: Using salt-tolerant bacteria for enhanced treatment, the COD removal rate is increased to 85% to 90%; electrocatalytic deep oxidation: Ti / PbO2-Fe3O4 / graphene electrode excites OH free radicals at a low current density (15mA / cm), and the degradation rate of difficult-to-degrade nitrogen-containing organic matter (such as carbamate) is ≥85%, and the effluent COD is stable at ≤50mg / L, meeting the emission standards.

[0082] c. Zero discharge of high-salt waste liquid and salt resource utilization:

[0083] The purity of fractionated crystallization is ≥98%: Nano-CaCO3 seeds (50nm) induce directional crystallization of Na2CO3, and the retention rate of Cl- and SO42- impurities is ≥95%. The purity of the crystalline salt is increased from 90% in the traditional process to 98%, and can be directly sold as an industrial raw material.

[0084] Fresh water reuse rate ≥95%: The water quality of multi-effect evaporation condensate meets the standards and is reused for hydrolyzer replenishment, reducing fresh water consumption.

[0085] Anti-scaling design: Gradient cooling (60℃→30℃) and vacuum evaporation (-0.09MPa) synergistically suppress scaling of the multi-effect evaporator 10, extending the maintenance cycle by 3 times.

[0086] d. Energy saving and consumption reduction:

[0087] Multi-stage utilization of waste heat: waste liquid waste heat (75-80°C) directly drives the packing stripping tower 4, eliminating steam heating energy consumption; waste liquid waste heat preheats the feed of the multi-effect evaporator 10, reducing evaporation energy consumption by 20%-30%.

[0088] Double improvement of environmental protection and economic benefits:

[0089] Environmental benefits: Ammonia, wastewater, and salt are recycled throughout the entire process, with no secondary pollutants discharged;

[0090] Reduce CO2 emissions: Utilize waste heat and reduce power consumption, achieving an annual carbon reduction of ≥500 tons. Economic benefits: Revenue from resource-based products (ammonium sulfate, Na2CO3) covers 60% to 70% of operating costs.

[0091] Example 3:

[0092] See also Figure 2 This embodiment discloses a method for resource-based treatment of urea hydrolyzer wastewater, comprising the following steps:

[0093] S1, waste heat driven ammonia nitrogen cascade recovery;

[0094] Step description: Introduce the urea hydrolysis wastewater with a temperature of 75-80℃ into the pH adjustment pool 1, add 30% NaOH solution, obtain the wastewater pH through the online water quality sensor, and adjust the wastewater pH to 11.2±0.3 to promote the ammonium ion (NH 4+ ) is converted into free NH3. The regulated waste liquid passes through the spiral plate heat exchanger 2 to maintain the outlet temperature of the spiral plate heat exchanger 2 ≥70°C. The waste liquid is pressurized by the booster pump 3 and enters the packed stripping tower 4. The gas-liquid ratio of the packed stripping tower 4 is set to 4000:1. The ball ring filler filled in the tower increases the gas-liquid contact area, and the ammonia nitrogen removal rate is ≥95%. The ammonia-containing gas generated after stripping enters the two-stage sulfuric acid absorption tower 5. The first-stage absorption tower uses 20% dilute sulfuric acid (pH=3.5) to capture more than 90% of the ammonia gas, generating an ammonium sulfate solution with a concentration of ≥20%, which is stored in the ammonium sulfate storage tank 6 and then sold outside; the second-stage absorption tower uses 5% sulfuric acid (pH=2.0) to purify the tail gas to ensure that the emission NH3 concentration is <5mg / m3.

[0095] S2, salt-tolerant bio-electrocatalytic synergistic degradation of COD;

[0096] Step description: The wastewater after stripping is cooled to 35°C and enters the A / O-MBR reactor 7. It first enters the anoxic tank with a hydraulic retention time of 6 hours. Sodium acetate is added to maintain the carbon-nitrogen ratio C / N=5:1 to promote denitrification.

[0097] After staying in the anoxic tank for 6 hours, it enters the aerobic tank (DO = 3.5 mg / L, HRT = 12 hours) using salt-tolerant bacteria, with a hydraulic retention time of 12 hours. The sludge suspended solids concentration (MLSS) is maintained at 12,000-15,000 mg / L, and COD is degraded to ≤300 mg / L.

[0098] The MBR membrane assembly uses an anti-pollution membrane with a pore size of 0.1 μm and a membrane flux of ≥20 L / (m 2 h) intercepting microorganisms and suspended solids to ensure effluent stability;

[0099] The effluent from the MBR membrane assembly 703 enters the electrocatalytic oxidation reactor 8. The anode uses a Ti / PbO2 electrode, and the cathode is loaded with a Fe3O4 / graphene composite catalyst. 80 mg / L of H2O2 is added to the inlet of the electrocatalytic oxidation reactor 8, the current density is 15 mA / cm2, and the reaction takes 40 minutes. OH free radicals oxidize the difficult-to-degrade organic matter, and the COD in the water is further reduced to ≤50 mg / L.

[0100] S3, salt closed-loop regeneration unit;

[0101] The electrocatalytic effluent from the electrocatalytic oxidation reactor 8 enters a three-stage vacuum multi-effect evaporator 10. The vacuum level in the three-stage vacuum multi-effect evaporator 10 is -0.09 MPa, the evaporation temperature is 60°C, and the total dissolved solids (TDS) in the evaporated condensate is ≤50 mg / L. The evaporated condensate is reused for hydrolyzer replenishment, with a reuse rate of ≥95%. Nano-CaCO3 seed crystals (50 nm particle size, 0.1% w / w) are added to the concentrate to induce directional crystallization of Na2CO3 and inhibit the precipitation of impurities such as Cl- and SO42-. The concentrate is then cooled gradually (60°C to 30°C) by a cooling coil before entering a crystallizer 11. The separated Na2CO3 crystals have a purity of ≥98% and are sold as industrial raw materials. The mother liquor is then returned to the three-stage vacuum multi-effect evaporator 10 for recycling.

[0102] During wastewater treatment, control unit 12 receives signals from signal sensors and monitors in real time the pH of pH adjustment tank 1 and two-stage sulfuric acid absorption tower 5, the ORP of anoxic tank 701 and oxygen consumption tank 702, and the conductivity of the inlet of multiple-effect evaporator 10. ORP represents the redox potential of water, the redox capacity of the reaction solution. Control unit 12 also adjusts the dosage of NaOH and H2O2, the fan speed of packing stripping tower 4, the gas-liquid ratio of packing stripping tower 4, and the current density of electrocatalytic oxidation reactor 8 based on the influent load. This ensures the entire system operates automatically.

[0103] Example 4:

[0104] See also Figure 2 This embodiment discloses a method for resource-based treatment of urea hydrolyzer wastewater, which is as follows:

[0105] Example Project Background:

[0106] The urea hydrolyzer waste liquid treatment project of a thermal power plant has a daily treatment capacity of 1,000 tons of urea waste liquid. The water quality parameters are shown in Table 1.

[0107] Table 1. Water quality parameters:

[0108] parameter Concentration / value Ammonia nitrogen (NH3-N) 2800mg / L COD 4800mg / L TDS 18000mg / L pH 9.5 temperature 78℃

[0109] Treatment objectives: ammonia nitrogen removal rate ≥98%, COD ≤50mg / L; Na2CO3 recovery rate ≥95%, fresh water reuse rate ≥95%.

[0110] Specific implementation steps and parameters

[0111] S10, waste heat driven ammonia nitrogen cascade recovery;

[0112] S11, pretreatment and pH adjustment:

[0113] The wastewater enters pH adjustment tank 1, where 30% NaOH solution is added. The pH is adjusted from 9.5 to 11.2 using an online pH sensor (Mettler Toledo InPro 3250). After adjustment, the wastewater is passed through spiral plate heat exchanger 2 to maintain an outlet temperature of ≥70°C. The heat exchange area of spiral plate heat exchanger 2 is 200m 2 .

[0114] S12, efficient stripping and absorption:

[0115] The waste liquid enters the packed stripping tower 4, which has a diameter of 3m and a height of 10m. The packing is DN50 ball rings, and the gas-liquid ratio is set at 4000:1. After the stripping, the ammonia nitrogen concentration in the waste liquid drops to 45mg / L, with a removal rate of 98.4%.

[0116] The ammonia gas is blown off and enters the two-stage sulfuric acid absorption tower 5: the first absorption tower uses 20% dilute sulfuric acid, pH = 3.5, to generate ammonium sulfate solution with a concentration of 22% and a daily output of 1.8 tons; the second absorption tower uses 5% sulfuric acid, pH = 2.0, and the tail gas NH3 concentration is ≤3mg / m 3 , measured at 2.8 mg / m 3 .

[0117] S20, salt-tolerant bio-electrocatalytic synergistic degradation of COD;

[0118] S21, treatment process of A / O-MBR reactor 7;

[0119] After stripping, the wastewater is cooled to 35°C and enters the anoxic pool 701. The volume of the anoxic pool 701 is 500m 3 , hydraulic retention time HRT = 6h, sodium acetate was added to maintain C / N = 5:1, denitrification was carried out, and the nitrate concentration dropped from 120mg / L to <5mg / L.

[0120] Salt-tolerant bacteria are added to the oxygen consumption pool 702, and the volume of the oxygen consumption pool 702 is 1000m 3 , hydraulic retention time HRT = 12h, DO = 3.5mg / L, MLSS = 14000mg / L, COD degraded to 280mg / L, and the removal rate was 94.2%.

[0121] The flux of MBR membrane module 703 is maintained at 22L / (m 2 h), transmembrane pressure difference ≤ 30 kPa, MBR membrane component 703 is made of PVDF material with a pore size of 0.1 μm.

[0122] S22, electrocatalytic oxidation process of the electrocatalytic oxidation reactor 8;

[0123] The effluent from the MBR membrane assembly 703 enters the electrocatalytic oxidation reactor 8. The effective volume of the electrocatalytic oxidation reactor 8 is 50m 3 The anode uses Ti / PbO2 electrode, the cathode is loaded with Fe3O4 / graphene catalyst, 80 mg / L H2O2 is added, and the current density is 15 mA / cm 2 , react for 40 minutes.

[0124] The effluent COD is 42 mg / L, the removal rate is 85%, the BOD5 / COD is increased from 0.15 to 0.52, and the biodegradability is significantly improved.

[0125] S30, closed-loop salt regeneration and zero discharge;

[0126] S31, multi-effect evaporation concentration;

[0127] The electrocatalytic effluent enters a three-stage multi-effect evaporator 10. The vacuum level in the three-stage vacuum multi-effect evaporator 10 is -0.09 MPa, and the evaporation temperature is 60°C. The total dissolved solids (TDS) in the evaporated condensate is 45 mg / L. This condensate is directly reused for urea hydrolyzer replenishment, with a reuse rate of 96.5%. The TDS of the concentrate is increased to 180,000 mg / L, and nano-CaCO3 seed crystals (particle size 50 nm, dosage 0.1% w / w) are added.

[0128] S32, fractional crystallization;

[0129] The concentrated liquid is cooled from 60°C to 30°C by gradient cooling and enters the crystallizer 11, where Na2CO3 crystals are separated to obtain Na2CO3 crystals with a purity of 98.3% and a daily output of 0.95 tons; the mother liquor is refluxed to the three-stage multi-effect evaporator 10 for circulation treatment.

[0130] S40, intelligent control and waste heat utilization:

[0131] Sensor and PLC control:

[0132] Based on real-time monitoring data from a pH probe (Mettler Toledo), an ORP sensor (Hach LXV440), and a conductivity meter (Emerson CM444), the PLC controller dynamically adjusts the NaOH dosage, dynamically controls the carbon source dosage in the anoxic tank 701, and optimizes the vacuum degree of the multi-effect evaporator 10.

[0133] The treatment effects and economic benefits are shown in Table 2;

[0134] Table 2, treatment effect data:

[0135] parameter Influent concentration Outlet concentration Removal rate / recovery rate <![CDATA[Ammonia nitrogen (NH3-N)]]> 2800mg / L 45mg / L 98.4％ COD 4800mg / L 42mg / L 99.1％ TDS 18000mg / L 45mg / L (recycled water) 95.2％

[0136] Economic and environmental benefits:

[0137] Resource utilization benefits:

[0138] Ammonium sulfate: 1.8 tons / day × 1,000 yuan / ton = 1,800 yuan / day;

[0139] Na2CO3: 0.95 tons / day × 870 yuan / ton = 826.5 yuan / day;

[0140] Annual income: (540+7600)×330 days=866,700 yuan.

[0141] Environmental benefits:

[0142] Annual CO2 emission reduction: Through waste heat utilization and reduced electricity consumption, carbon emissions are reduced by 620 tons, equivalent to planting 34,000 trees; water conservation: the fresh water reuse rate is 96.5%, saving 348,000 tons of fresh water annually.

[0143] In summary, the system and method for resource-based treatment of urea hydrolyzer waste liquid of the present invention can realize resource-based treatment of urea waste liquid and have certain economic and environmental benefits.

[0144] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. Urea hydrolyzer waste liquid resource treatment system, characterized in that: include: pH adjustment tank (1); A packing stripping tower (4), wherein the outlet of the pH regulating water pool (1) is connected to the inlet of the packing stripping tower (4) via a spiral plate heat exchanger (2); the packing stripping tower (4) is provided with a gas outlet (401) and a waste liquid outlet (402), and the gas outlet (401) is connected to an ammonium sulfate storage tank (6) via a two-stage sulfuric acid absorption tower (5); A / O-MBR reactor (7), the waste liquid outlet (402) is connected to a multi-effect evaporator (10) through the A / O-MBR reactor (7), the electrocatalytic oxidation reactor (8), and the evaporator heat pump (9) in sequence, the multi-effect evaporator (10) is provided with a condensed water outlet and a concentrated liquid outlet, and the concentrated liquid outlet is connected to a crystallizer (11).

2. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: The spiral plate heat exchanger (2) is provided with a cooling water inlet (201) and a cooling water outlet (202); A booster pump (3) is provided between the spiral plate heat exchanger (2) and the filler stripping tower (4).

3. The urea hydrolyzer waste liquid resource treatment system according to claim 1 or 2, characterized in that: The gas-liquid ratio of the packing stripping tower (4) is 4000:1, and the packing stripping tower (4) is filled with ball ring packing.

4. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: The two-stage sulfuric acid absorption tower (5) comprises a primary absorption tower (501) and a secondary absorption tower (502), wherein the primary absorption tower (501) and the secondary absorption tower (502) are both provided with a receiving port, a gas discharge port and a liquid discharge port, wherein the gas outlet (401) is connected to the receiving port of the primary absorption tower (501), the gas discharge port of the primary absorption tower (501) is connected to the receiving port of the secondary absorption tower (502), and the liquid discharge ports of the primary absorption tower (501) and the secondary absorption tower (502) are both connected to the inlet of the ammonium sulfate storage tank (6).

5. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: The A / O-MBR reactor (7) comprises an anoxic tank (701), an oxygen consumption tank (702) and an MBR membrane assembly (703); the waste liquid outlet (402) is connected to the inlet of the anoxic tank (701); the oxygen consumption tank (702) is located between the anoxic tank (701) and the MBR membrane assembly (703); the MBR membrane assembly (703) is located at the outlet of the A / O-MBR reactor (7); and the outlet of the A / O-MBR reactor (7) is connected to the inlet of the electrocatalytic oxidation reactor (8); The anode of the electrocatalytic oxidation reactor (8) adopts a Ti / PbO2 electrode, and the cathode is loaded with a Fe3O4 / graphene composite catalyst.

6. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: The multi-effect evaporator (10) comprises a first-stage multi-effect evaporator (101), a second-stage multi-effect evaporator (102) and a third-stage multi-effect evaporator (103); the first-stage multi-effect evaporator (101), the second-stage multi-effect evaporator (102) and the third-stage multi-effect evaporator (103) are all provided with a first inlet, a second inlet, a condensed water outlet, a steam discharge hole and a concentrated liquid outlet; the outlet of the evaporator heat pump (9) is connected to the second inlet of the first-stage multi-effect evaporator (101); the steam hole of the first-stage multi-effect evaporator (101) is connected to the second inlet of the second-stage multi-effect evaporator (102); the concentrated liquid outlet of the first-stage multi-effect evaporator (101) is connected to the second inlet of the second-stage multi-effect evaporator (102); The first inlet of the secondary multi-effect evaporator (102), the steam hole of the secondary multi-effect evaporator (102) is connected to the second inlet of the third multi-effect evaporator (103), the concentrated liquid outlet of the secondary multi-effect evaporator (102) is connected to the first inlet of the third multi-effect evaporator (103), the concentrated liquid outlet of the third multi-effect evaporator (103) is connected to the crystallizer (11), the condensed water outlets of the first multi-effect evaporator (101), the second multi-effect evaporator (102) and the third multi-effect evaporator (103) are used to connect to the water supply port of the hydrolyzer, and the first inlet of the first multi-effect evaporator (101) is used to introduce the waste liquid heat source generated by urea hydrolysis.

7. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: The crystallizer (11) is provided with a crystal outlet (111) and a crystallization mother liquor outlet (112), and the crystallization mother liquor outlet (112) is connected to the inlet of the evaporator heat pump (9).

8. The urea hydrolyzer waste liquid resource treatment system according to claim 1, characterized in that: Online water quality sensors are arranged in the pH adjustment water pool (1) and the two-stage sulfuric acid absorption tower (5), an ORP sensor is arranged in the A / O-MBR reactor (7), and a conductivity sensor is provided at the inlet of the multi-effect evaporator (10).

9. A method for resource-based treatment of urea hydrolyzer waste liquid, based on the urea hydrolyzer waste liquid resource-based treatment system according to any one of claims 1 to 8, characterized in that: The following steps are involved: The urea hydrolysis wastewater is passed into a pH adjustment tank (1) to adjust the pH of the wastewater to 11.2±0.3; The waste liquid after pH adjustment is passed into the spiral plate heat exchanger (2) for temperature adjustment to ensure that the temperature of the waste liquid after pH adjustment is greater than or equal to 70° C.; The waste liquid enters the packed stripping tower (4) from the spiral plate heat exchanger (2) for ammonia nitrogen stripping. The ammonia-containing gas generated after stripping enters the two-stage sulfuric acid absorption tower (5) to obtain ammonium sulfate solution, which is stored in the ammonium sulfate storage tank (6); The wastewater after stripping is cooled to 35°C and enters the A / O-MBR reactor (7) for denitrification and COD degradation; The effluent from the A / O-MBR reactor (7) enters the electrocatalytic oxidation reactor (8) for further COD degradation; The effluent from the electrocatalytic oxidation reactor (8) enters the multi-effect evaporator (10) to obtain evaporated condensed water and concentrated liquid. The condensed water is reused to replenish the urea hydrolyzer, and the concentrated liquid enters the crystallizer (11) to crystallize and separate Na2CO3. The crystallization mother liquor generated by the crystallizer (11) is refluxed to the inlet of the evaporator heat pump (9).

10. The method for resource recovery of urea hydrolyzer wastewater according to claim 9, characterized in that: The following steps are also included: Add 30% NaOH solution into the pH adjustment tank (1) to adjust the pH of the wastewater to 11.2±0.3; The wastewater after stripping is cooled to 35° C. and enters the anoxic tank ( 701 ) and is added with sodium acetate to maintain a carbon-nitrogen ratio of C / N=5:1 and a hydraulic retention time of 6 hours for denitrification. In the oxygen consumption tank (702), the dissolved oxygen is maintained at 3.5 mg / L and the hydraulic retention time is 12 h; The waste heat of the waste liquid of the urea hydrolyzer is used to preheat the water outlet of the electrocatalytic oxidation reactor (8), and the evaporation temperature in the three-stage vacuum multi-effect evaporator (10) is 60°C; After the concentrated liquid enters the crystallizer (11), the temperature is gradually reduced from 60°C to 30°C.

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