A safe treatment and resource recovery system and method for urea hydrolysis wastewater

Abstract

The present invention relates to the technical field of wastewater treatment, and in particular to a safety treatment and resource recovery system and method for urea hydrolysis wastewater, including a wastewater tank, a security filter, an electrodialysis device, a thermal decomposition and ammonia removal device, an ammonia water tank, a urea dissolution tank, and a urea hydrolysis tank connected in sequence; wherein, the urea hydrolysis tank is connected to the wastewater tank; the wastewater tank and the security filter are connected through a heat exchanger; the electrodialysis device and the thermal decomposition and ammonia removal device are connected through a heat exchanger; the electrodialysis device is also connected to the urea dissolution tank; the thermal decomposition and ammonia removal device is also connected to an alkali solution tank. This system can achieve the efficient recycling of urea hydrolysis wastewater, effectively remove high-concentration harmful ions while meeting the resource recovery of valuable substances in the wastewater, reduce energy consumption, as well as the usage amounts of cooling water and dissolved water, ensure the safety, greenness, low-carbon and recycling characteristics of the process, and significantly reduce the production and maintenance costs of power plants.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a safety treatment and resource recovery system and method for urea hydrolysis wastewater. Background Art

[0002] Thermal power generation is the main way of power generation. Selective catalytic reduction (SCR) is a commonly used flue gas denitrification process in the thermal power generation process. Ammonia gas is used as a reducing agent and is prepared from aqueous ammonia, liquid ammonia or urea. Urea hydrolysis to ammonia has become the mainstream technology due to its low energy consumption and simple maintenance.

[0003] In urea hydrolysis to ammonia, phenomena such as solution foaming, false liquid level rising, and chloride ion concentration accumulation often occur in the hydrolysis generator, which affect the operation of the denitrification system. The accumulation of chloride ions may also cause equipment corrosion and threaten safe operation. To prevent this phenomenon, regular sewage discharge is required. The sewage wastewater contains high concentrations of urea and chloride ions, and direct discharge wastes resources and pollutes the environment. Therefore, there is an urgent need for a technical means for resource utilization and safe reuse of urea hydrolysis wastewater.

[0004] Currently, the methods for treating wastewater containing urea and ammonia nitrogen mainly include biological methods, chemical methods and physical methods (such as stripping method), but each has its limitations. The biological method has limited effect on high-concentration ammonia nitrogen wastewater and usually requires large-fold dilution, increasing the treatment water volume and floor area and making it difficult to recycle nitrogen elements. The chemical precipitation method uses chemical agents to precipitate ammonia nitrogen, but the agent cost is high, the operation is complex, and a large amount of sludge needs to be treated. The stripping method removes ammonia nitrogen through gas, which is suitable for high-concentration ammonia nitrogen wastewater, but has high energy consumption, low efficiency, and may cause secondary pollution.

[0005] Therefore, it is very necessary to develop a safety treatment and resource recovery system and method for urea hydrolysis wastewater to achieve efficient resource treatment of urea hydrolysis wastewater in thermal power plants and reduce the production cost of power plants. Summary of the Invention

[0006] The purpose of the present invention is to provide a safety treatment and resource recovery system and method for urea hydrolysis wastewater to solve the problems existing in the above-mentioned prior art. This system can remove harmful ions in the wastewater to the greatest extent, and at the same time recover ammonia nitrogen and residual urea.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] In a first aspect, the present invention provides a safety treatment and resource recovery system for urea hydrolysis wastewater, including a wastewater tank 1, a security filter 3, an electrodialysis device 4, a thermal decomposition ammonia removal device 5, an ammonia water tank 6, a urea dissolution tank 7 and a urea hydrolysis tank 8 that are connected in sequence;

[0009] wherein, the urea hydrolysis tank 8 is connected to the wastewater tank 1;

[0010] The waste water tank 1 and the security filter 3 are connected via a heat exchanger 2;

[0011] The electrodialysis device 4 is connected to the thermal decomposition and deamination device 5 via a heat exchanger 2;

[0012] The electrodialysis device 4 is also connected to the urea dissolution tank 7;

[0013] The thermal decomposition and deamination device 5 is also connected to an alkali liquid tank 9 .

[0014] Furthermore, the electrodialysis device 4 includes a concentrated water chamber and a dilute water chamber.

[0015] Further, the outlet of the wastewater tank 1 is communicated with the shell-side fluid inlet of the heat exchanger 2, the shell-side fluid outlet of the heat exchanger 2 is communicated with the inlet of the security filter 3, the outlet of the security filter 3 is communicated with the water inlet of the electrodialysis device 4, the concentrated water chamber outlet of the electrodialysis device 4 is communicated with the tube-side fluid inlet of the heat exchanger 2, the tube-side fluid outlet of the heat exchanger 2 is communicated with the feed inlet of the thermal decomposition deamination device 5, the top outlet of the thermal decomposition deamination device 5 is communicated with the inlet of the ammonia water tank 6, the outlet of the ammonia water tank 6 is communicated with the inlet of the urea dissolution tank 7, the fresh water chamber outlet of the electrodialysis device 4 is communicated with the inlet of the urea dissolution tank 7, the outlet of the urea dissolution tank 7 is communicated with the inlet of the urea hydrolysis tank 8, the outlet of the urea hydrolysis tank 8 is communicated with the inlet of the wastewater tank 1, and the outlet of the alkali liquid tank 9 is communicated with the thermal decomposition deamination device 5.

[0016] Furthermore, a mud discharge device and a non-condensable gas absorption device are provided at the bottom of the wastewater tank 1 .

[0017] The sludge discharge device is convenient for discharging the insoluble matter that may be contained in the urea hydrolysis wastewater regularly after static sedimentation. At the same time, the ammonia gas that may escape from the wastewater tank can be absorbed by the non-condensable gas absorption device to ensure that the on-site gas emissions meet the standards.

[0018] Furthermore, the heat exchange plates inside the heat exchanger 2 are made of high temperature resistant and corrosion resistant materials to prevent corrosion caused by the high content of harmful ions in the original urea hydrolysis wastewater and the high temperature of the original urea hydrolysis wastewater.

[0019] Furthermore, the security filter 3 contains an automatic backwashing device to efficiently remove impurities, protect the normal operation of subsequent equipment and achieve long-term stable operation.

[0020] Furthermore, the thermal decomposition deammonification device 5 contains an alkali pump, a non-condensable gas absorption device and a condensation-absorption integrated ammonia recovery device to achieve efficient recovery of ammonia and qualified discharge of residual water.

[0021] In a second aspect, the present invention provides a method for treating urea hydrolysis wastewater from a thermal power plant by using the above-mentioned safe treatment and resource recovery system for urea hydrolysis wastewater, comprising the following steps:

[0022] The urea hydrolysis wastewater generated by the urea hydrolysis tank 8 enters the wastewater tank 1 for storage and regulation;

[0023] The urea hydrolysis wastewater in the wastewater tank 1 enters the heat exchanger 2, and at the same time, the concentrated water from the electrodialysis device 4 enters the heat exchanger 2 for heat exchange;

[0024] The urea hydrolysis wastewater cooled by heat exchange in the heat exchanger 2 enters the security filter 3 for filtration;

[0025] The filtered urea hydrolysis wastewater enters the electrodialysis device 4 for electrodialysis treatment to obtain concentrated water and fresh water;

[0026] The fresh water obtained by electrodialysis treatment enters the urea dissolution tank 7 for reuse, and the concentrated water is heated by heat exchange in the heat exchanger 2 and then enters the thermal decomposition and ammonia removal device 5. At the same time, the lye is transported from the lye tank 9 to the thermal decomposition and ammonia removal device 5. After thermal decomposition treatment, the concentrated water generates ammonia water and bottom kettle wastewater. The ammonia water enters the ammonia water tank 6, and the bottom kettle wastewater is mixed with the plant domestic sewage and discharged;

[0027] The ammonia water in the ammonia water tank 6 is transported to the urea dissolution tank 7 for reuse (for dissolving urea to obtain urea solution), and the urea solution in the urea dissolution tank 7 enters the urea hydrolysis tank 8 for urea hydrolysis to produce ammonia (the urea solution in the urea dissolution tank 7 is actually a mixed solution of urea and ammonia water, and both urea and ammonia water in it can dissolve to produce ammonia gas).

[0028] Further, the temperature of the urea hydrolysis wastewater flowing into the heat exchanger 2 (from the wastewater tank 1) is 120 - 150 °C.

[0029] Further, the urea hydrolysis wastewater is cooled to 30 - 50 °C after heat exchange in the heat exchanger 2, and the concentrated water from the electrodialysis device 4 is heated to 30 - 50 °C after heat exchange in the heat exchanger 2.

[0030] Through the action of the heat exchanger, the heat in the urea hydrolysis wastewater is effectively transferred to the thermal decomposition and ammonia removal device via the concentrated water, achieving the dual purposes of wastewater cooling and concentrated water heating, thereby significantly reducing energy consumption and the usage amount of cooling water.

[0031] Further, the temperature inside the thermal decomposition and ammonia removal device 5 is 110 - 140 °C, the pressure is 1.2 - 1.6 MPa, and the condensation reflux ratio is 0.1 - 0.4.

[0032] The ammonia water produced by the thermal decomposition and ammonia removal device 5 can be reused by the system after entering the urea dissolution tank via the ammonia water tank.

[0033] The safety treatment and resource recovery system and method for urea hydrolysis wastewater of the present invention. Among them, the urea hydrolysis wastewater discharged from the urea hydrolysis tank first enters a pressurized wastewater tank, and then after being cooled by a heat exchanger, it is intercepted by a security filter to remove particulate matter in the urea hydrolysis wastewater (to protect the electrodialysis device and reduce fouling and membrane blockage). The filtered effluent enters the electrodialysis device, and through electrodialysis treatment, fresh water and concentrated water can be obtained; the fresh water contains a high concentration of undecomposed urea resources, and the harmful ions (chloride ions) in the fresh water have been sufficiently reduced to the reuse standard (chloride ion concentration ≤ 5 mg / L), and it can be reused in the urea dissolution tank and enter the urea hydrolysis tank through the urea dissolution tank, without the risk of corrosion to the hydrolysis generator. Reusing it can not only significantly reduce the consumption of fresh water resources in the production process, but also the remaining urea in the fresh water can be supplemented into the urea dissolution tank to realize the effective reuse of the residual unhydrolyzed urea in the fresh water and reduce the usage amount of urea raw materials. The concentrated water enriches ammonia nitrogen, carbonate, chloride ions, etc. in the urea hydrolysis wastewater. After being heated by a heat exchanger and entering the thermal decomposition and ammonia removal device, and a certain concentration of alkali solution is added to the thermal decomposition and ammonia removal device from the alkali solution tank. After the concentrated water reacts in the thermal decomposition and ammonia removal device, the generated ammonia and carbon dioxide enter the condensation-absorption integrated ammonia recovery device from the top of the tower to form reusable ammonia water, which enters the urea dissolution tank through the ammonia water tank and can be reused by the urea hydrolysis system again to realize the resource recovery of ammonia nitrogen; the total nitrogen concentration of the bottom wastewater has reached the discharge standard (total nitrogen concentration ≤ 15 mg / L, ammonia nitrogen concentration ≤ 5 mg / L), and the main ions in the wastewater are chloride ions and sodium ions, and it can enter the factory sewage pool for adjustment and then be discharged into the pipe network. Through the application of the heat exchanger, the heat carried by the urea hydrolysis wastewater itself can be effectively transferred to the thermal decomposition and ammonia removal device through the concentrated water, achieving the dual purposes of wastewater cooling and concentrated water heating, thereby significantly reducing energy consumption and the usage amount of cooling water. Therefore, the safety treatment and resource recovery system for urea hydrolysis wastewater of the present invention can realize the efficient recycling of urea hydrolysis wastewater, effectively remove high-concentration harmful ions while meeting resource recovery, and ensure the safety, greenness, low-carbon and recycling characteristics of the process. This device maximally improves the raw material utilization rate, realizes the resource recovery of valuable substances in the urea hydrolysis wastewater and the separation and removal of harmful ions, thereby significantly reducing the production and maintenance costs of the power plant.

[0034] The present invention discloses the following technical effects:

[0035] The safety treatment and resource recovery system for urea hydrolysis wastewater of the present invention selects treatment units with a specific composition and arrangement order, which can achieve the efficient recycling of urea hydrolysis wastewater. While meeting the resource recovery of valuable substances (ammonia nitrogen and residual urea) in the wastewater, it can effectively remove high-concentration harmful ions, reduce the energy consumption in the thermal decomposition process, and reduce the usage of cooling water and urea dissolution water for urea hydrolysis wastewater, ensuring the safety, green, low-carbon and circular characteristics of the process, and significantly reducing the production and maintenance costs of power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0037] Figure 1 It is a schematic diagram of the safety treatment and resource recovery system for urea hydrolysis wastewater of the present invention. Among them, 1 - wastewater tank; 2 - heat exchanger; 3 - security filter; 4 - electrodialysis device; 5 - thermal decomposition and ammonia removal device; 6 - ammonia water tank; 7 - urea dissolution tank; 8 - urea hydrolysis tank; 9 - alkali liquid tank. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0039] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0040] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0041] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the specification of the present invention, which will be obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention will be obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0042] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0043] As Figure 1 shown, the present invention provides a safety treatment and resource recovery system for urea hydrolysis wastewater, including a wastewater tank 1, a security filter 3, an electrodialysis device 4, a thermal decomposition deammoniation device 5, an ammonia water tank 6, a urea dissolution tank 7, and a urea hydrolysis tank 8 that are connected in sequence;

[0044] Among them, the urea hydrolysis tank 8 and the wastewater tank 1 are connected;

[0045] The wastewater tank 1 and the security filter 3 are connected through a heat exchanger 2;

[0046] The electrodialysis device 4 and the thermal decomposition deammoniation device 5 are connected through a heat exchanger 2;

[0047] The electrodialysis device 4 is also connected to the urea dissolution tank 7;

[0048] The thermal decomposition deammoniation device 5 is also connected to an alkali solution tank 9.

[0049] More specifically, the outlet of the wastewater tank 1 is connected to the shell-side fluid inlet of the heat exchanger 2, the shell-side fluid outlet of the heat exchanger 2 is connected to the security filter 3, the security filter 3 is connected to the water inlet of the electrodialysis device 4, the concentrated water chamber outlet of the electrodialysis device 4 is connected to the tube-side fluid inlet of the heat exchanger 2, the tube-side fluid outlet of the heat exchanger 2 is connected to the feed port of the thermal decomposition deammoniation device 5, the top outlet of the thermal decomposition deammoniation device 5 is connected to the inlet of the ammonia water tank 6, the outlet of the ammonia water tank 6 is connected to the inlet of the urea dissolution tank 7, the fresh water chamber outlet of the electrodialysis device 4 is connected to the inlet of the urea dissolution tank 7, the outlet of the urea dissolution tank 7 is connected to the inlet of the urea hydrolysis tank 8, the outlet of the urea hydrolysis tank 8 is connected to the inlet of the wastewater tank 1, and the outlet of the alkali solution tank 9 is connected to the thermal decomposition deammoniation device 5.

[0050] As a preferred embodiment of the present invention, a sludge discharge device and a non-condensable gas absorption device are provided at the bottom of the wastewater tank 1.

[0051] As a preferred embodiment of the present invention, the heat exchange plates inside the heat exchanger 2 are made of high-temperature and corrosion-resistant materials.

[0052] As a preferred embodiment of the present invention, the inside of the security filter 3 is provided with an automatic backwashing device.

[0053] As a preferred embodiment of the present invention, the inside of the thermal decomposition deammoniation device 5 contains an alkali pump, a non-condensable gas absorption device, and a condensation-absorption integrated ammonia recovery device.

[0054] The present invention also provides a method for treating the urea hydrolysis wastewater of a certain thermal power plant by using the above-mentioned safety treatment and resource recovery system for urea hydrolysis wastewater, comprising the following steps:

[0055] The urea hydrolysis wastewater generated by the urea hydrolysis tank 8 enters the wastewater tank 1 for storage and regulation.

[0056] The urea hydrolysis wastewater in the wastewater tank 1 enters the heat exchanger 2, and at the same time, the concentrated water from the electrodialysis device 4 enters the heat exchanger 2 for heat exchange.

[0057] The urea hydrolysis wastewater cooled by heat exchange in the heat exchanger 2 enters the security filter 3 for filtration.

[0058] The filtered urea hydrolysis wastewater enters the electrodialysis device 4 for electrodialysis treatment to obtain concentrated water and fresh water.

[0059] The fresh water obtained by electrodialysis treatment enters the urea dissolution tank 7 for reuse, and the concentrated water is heated by heat exchange in the heat exchanger 2 and then enters the thermal decomposition deammoniation device 5. At the same time, the alkali solution is transported from the alkali solution tank 9 to the thermal decomposition deammoniation device 5. After thermal decomposition treatment, the concentrated water generates ammonia water and bottom kettle wastewater. The ammonia water enters the ammonia water tank 6, and the bottom kettle wastewater is mixed with the plant domestic sewage for discharge.

[0060] The ammonia water in the ammonia water tank 6 is transported to the urea dissolution tank 7 for reuse (for dissolving urea to obtain a urea solution), and the urea solution in the urea dissolution tank 7 enters the urea hydrolysis tank 8 for urea hydrolysis to produce ammonia (the urea solution in the urea dissolution tank 7 is actually a mixed solution of urea and ammonia water, and both the urea and ammonia water therein can dissolve to produce ammonia gas).

[0061] As a preferred embodiment of the present invention, the temperature of the urea hydrolysis wastewater entering the heat exchanger 2 is 120 - 150 °C.

[0062] As a preferred embodiment of the present invention, the urea hydrolysis wastewater is cooled to 30 - 50 °C after heat exchange in the heat exchanger 2, and the concentrated water from the electrodialysis device 4 is heated to 30 - 50 °C after heat exchange in the heat exchanger 2.

[0063] As a preferred embodiment of the present invention, the current of the electrodialysis treatment does not exceed 120 A, and the voltage does not exceed 250 V. The electrodialysis treatment can significantly reduce the harmful ions (Cl -)The concentration is reduced to below 500 mg / L, thereby effectively preventing the subsequent treatment equipment from being corroded.

[0064] As a preferred embodiment of the present invention, the temperature inside the thermal decomposition and deammoniation device 5 is 110 - 140 °C, the pressure is 1.2 - 1.6 MPa, and the condensation reflux ratio is 0.1 - 0.4.

[0065] As a preferred embodiment of the present invention, the lye is transported from the battery limit to the lye tank 9, and the steam required by the thermal decomposition and deammoniation device 5 is provided by the battery limit.

[0066] As a preferred embodiment of the present invention, the transportation of the lye from the lye tank 9 to the thermal decomposition and deammoniation device 5 includes: controlling the transportation of the lye according to the molar ratio of hydroxide ions to chloride ions > 1.5 and simultaneously controlling the pH = 9.5 - 14.

[0067] It should be noted that the heat exchanger used in the present invention is a non-contact heat exchanger. The liquid that enters the security filter after being cooled by the heat exchanger from the wastewater tank and the liquid that enters the thermal decomposition and deammoniation device after being heated by the heat exchanger from the electrodialysis device do not contact each other.

[0068] It should be noted that the wastewater tank, heat exchanger, security filter, electrodialysis device, thermal decomposition and deammoniation device, ammonia water tank, urea dissolution tank, urea hydrolysis tank, and lye tank that constitute the safe treatment and resource recovery system for urea hydrolysis wastewater of the present invention are all products of the prior art. For the devices whose specific structures are not mentioned in the specification of the present invention, the prior art can be used, which is not the focus of the present invention, so it will not be elaborated here.

[0069] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following specific embodiments are only for reference of the specific implementation manners of the present invention. For those of ordinary skill in the art, all other embodiments are also within the protection scope of the present invention. Terms such as "top" and "bottom" are only for convenience of description and do not limit the actual orientation of the device. Terms "connected" and "coupled" should be understood in a broad sense, including fixed or detachable, direct or indirect, etc. The system not only includes the listed elements but may also include other elements not explicitly listed. The specific embodiments are only illustrative, and those skilled in the art can modify and apply according to the actual situation. The scope of the present invention is not limited to these embodiments, but is the broadest scope according to the principles and novel features of the invention.

[0070] Example 1

[0071] A safe treatment and resource recovery system for urea hydrolysis wastewater: It consists of a wastewater tank 1, a security filter 3, an electrodialysis device 4, a thermal decomposition and deammoniation device 5, an ammonia water tank 6, a urea dissolution tank 7, and a urea hydrolysis tank 8 that are connected in sequence, and a lye tank 9 that is connected to the thermal decomposition and deammoniation device 5;

[0072] Among them, the urea hydrolysis tank 8 is connected to the wastewater tank 1;

[0073] The wastewater tank 1 and the security filter 3 are connected through the heat exchanger 2;

[0074] The electrodialysis device 4 and the thermal decomposition deammoniation device 5 are connected through the heat exchanger 2;

[0075] The electrodialysis device 4 is also connected to the urea dissolution tank 7;

[0076] More specifically, the outlet of the wastewater tank 1 is connected to the shell-side fluid inlet of the heat exchanger 2, the shell-side fluid outlet of the heat exchanger 2 is connected to the security filter 3, the security filter 3 is connected to the water inlet of the electrodialysis device 4, the concentrated water chamber outlet of the electrodialysis device 4 is connected to the tube-side fluid inlet of the heat exchanger 2, the tube-side fluid outlet of the heat exchanger 2 is connected to the feed inlet of the thermal decomposition deammoniation device 5, the top outlet of the thermal decomposition deammoniation device 5 is connected to the inlet of the ammonia water tank 6, the outlet of the ammonia water tank 6 is connected to the inlet of the urea dissolution tank 7, the fresh water chamber outlet of the electrodialysis device 4 is connected to the inlet of the urea dissolution tank 7, the outlet of the urea dissolution tank 7 is connected to the inlet of the urea hydrolysis tank 8, the outlet of the urea hydrolysis tank 8 is connected to the inlet of the wastewater tank 1, and the outlet of the alkali solution tank 9 is connected to the thermal decomposition deammoniation device 5;

[0077] A sludge discharge device and a non-condensable gas absorption device are provided at the bottom of the wastewater tank 1;

[0078] The heat exchange plates inside the heat exchanger 2 are made of high-temperature and corrosion-resistant materials;

[0079] The security filter 3 contains an automatic backwashing device and a pressure detection device inside;

[0080] The thermal decomposition deammoniation device 5 contains an alkali pump, a non-condensable gas absorption device, and a condensation-absorption integrated ammonia recovery device inside.

[0081] The method for treating the urea hydrolysis wastewater of a thermal power plant by using the above-mentioned safety treatment and resource recovery system for urea hydrolysis wastewater is as follows:

[0082] S1. The urea hydrolysis wastewater generated by the urea hydrolysis tank 8 enters the wastewater tank 1 for storage and regulation (the wastewater tank 1 is a pressure-bearing tank to prevent a large amount of ammonia from being released and escaping);

[0083] S2. The urea hydrolysis wastewater in the wastewater tank 1 enters the heat exchanger 2 (the temperature of the urea hydrolysis wastewater when entering the heat exchanger 2 is 120 - 150 °C), and at the same time, the concentrated water from the electrodialysis device 4 enters the heat exchanger 2 for heat exchange; among them, the pressurized urea hydrolysis wastewater is cooled to 30 - 50 °C after heat exchange in the heat exchanger 2, and the concentrated water from the electrodialysis device 4 is heated to 30 - 50 °C after heat exchange in the heat exchanger 2.

[0084] S3. The urea hydrolysis wastewater cooled by heat exchange in the heat exchanger 2 enters the security filter 3 for filtration. The security filter 3 controls automatic backwashing through its own pressure detection device, with the transmembrane pressure set less than 0.2 MPa. When this value is exceeded, automatic backwashing is carried out to remove impurities in the wastewater to protect the electrodialysis device 4 and reduce scaling and membrane blockage. The filtered urea hydrolysis wastewater has the following characteristics: pH = 10.2, TDS = 13360 mg / L, total nitrogen = 17500 mg / L, CO3 2- = 14168 mg / L, NH3-N = 12370.69 mg / L, Cl - = 454.12 mg / L, urea nitrogen = 2431 mg / L.

[0085] S4. The filtered urea hydrolysis wastewater enters the electrodialysis device 4 for electrodialysis treatment. During operation, the operating parameters of the electrodialysis device 4 are strictly controlled. Among them, the current set value is 120 A, the voltage set value is 250 V, and the equipment membrane area is 320 m 3 , and the set values of the fresh water flow rate, concentrated water flow rate, and electrode water flow rate are all 0.5 m 3 / h, and the electrode water uses 30 g / L sodium sulfate. During the electrodialysis process, under the action of a direct current electric field, using the selective permeability of the ion exchange membrane, the cations and anions in the water migrate to the positive and negative electrodes respectively, thus forming a concentrated water chamber and a fresh water chamber between the partition layers, realizing the separation of water and salt, and generating a concentrated water with a higher salt content and a fresh water with a lower salt content. Among them, the TDS in the fresh water = 783.2 mg / L, which has been reduced to a lower level, the chloride ion concentration has been reduced to 1.75 mg / L, and CO3 2- = 14168 mg / L, NH3-N = 12370.69 mg / L, and the urea nitrogen is well retained, with a concentration of 2153 mg / L; the concentrated water is enriched with ammonia nitrogen, carbonate, chloride ions, sulfate ions, etc. in the original urea hydrolysis wastewater. Specifically, TDS = 12760 mg / L, total nitrogen = 5100 mg / L, CO3 2- = 7629 mg / L, NH3-N = 4211.77 mg / L, Cl - = 446.79 mg / L, urea nitrogen = 197 mg / L; the electrodialysis treatment significantly reduces the concentration of harmful ions in the wastewater, thus effectively preventing the subsequent treatment equipment from being corroded.

[0086] S5. The fresh water obtained by electrodialysis treatment enters the urea dissolution tank 7 for reuse. The concentrated water is heated through heat exchange in the heat exchanger 2 and then enters the thermal decomposition and ammonia removal device 5 for thermal decomposition and resource treatment. Meanwhile, the lye is transported from the lye tank 9 to the thermal decomposition and ammonia removal device 5, and the lye is transported according to the molar ratio of hydroxide ion to chloride ion > 1.5 and by controlling the pH = 9.5 - 14 to completely rectify the ammonium ions and ensure the reaction rate. The internal temperature of the thermal decomposition and ammonia removal device 5 is controlled at 120 °C, the pressure is controlled at 1.4 MPa, and the condensation reflux ratio is 0.2. During the thermal decomposition process, since the relative volatility of NH3 and CO2 is greater than that of water, more NH3 and CO2 enter the gas phase under the action of steam and establish a new gas-liquid equilibrium with the liquid flowing down from the upper tray. After multiple gas-liquid equilibria, the ammonia concentration in the gas phase is increased, and NH3 and CO2 are fully separated from the water. Then, they enter the condensation-absorption integrated ammonia recovery device from the top of the tower, are completely liquefied to form ammonia water with a concentration of 9 - 28 wt%, and enter the ammonia water tank 6. At the same time, as ammonia continuously volatilizes, the ammonia concentration in the liquid becomes lower and lower. When reaching the bottom of the tower, the total nitrogen concentration in the remaining wastewater ≤ 15 mg / L, and the ammonia nitrogen concentration ≤ 5 mg / L. The main ions in the remaining wastewater at the bottom of the tower are chloride ions (460 mg / L) and sodium ions (290 mg / L), which can be directly discharged into the sewer after being mixed with the domestic sewage in the factory area.

[0087] S6. The ammonia water in the ammonia water tank 6 is transported to the urea dissolution tank 7 for reuse (for dissolving urea to obtain urea solution). The urea solution in the urea dissolution tank 7 enters the urea hydrolysis tank 8 for urea hydrolysis to produce ammonia (the urea solution in the urea dissolution tank 7 is actually a mixed solution of urea and ammonia water, and both urea and ammonia water can dissolve to produce ammonia gas).

[0088] The above embodiments are only described for the preferred mode of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A safety treatment and resource recovery system for urea hydrolysis wastewater, characterized in that, It includes a wastewater tank (1), a security filter (3), an electrodialysis device (4), a thermal decomposition and deammoniation device (5), an ammonia water tank (6), a urea dissolution tank (7) and a urea hydrolysis tank (8) which are connected in sequence; Among them, the urea hydrolysis tank (8) is connected to the wastewater tank (1); The wastewater tank (1) and the security filter (3) are connected through a heat exchanger (2); The electrodialysis device (4) and the thermal decomposition and deammoniation device (5) are connected through a heat exchanger (2); The electrodialysis device (4) is also connected to the urea dissolution tank (7); The thermal decomposition and deammoniation device (5) is also connected to an alkali solution tank (9); The steps of treating the urea hydrolysis wastewater of a thermal power plant by using the above-mentioned safety treatment and resource recovery system for urea hydrolysis wastewater include: The urea hydrolysis wastewater generated by the urea hydrolysis tank (8) enters the wastewater tank (1) for storage and regulation; The urea hydrolysis wastewater in the wastewater tank (1) enters the heat exchanger (2), and at the same time, the concentrated water from the electrodialysis device (4) enters the heat exchanger (2) for heat exchange; The urea hydrolysis wastewater cooled by heat exchange in the heat exchanger (2) enters the security filter (3) for filtration; The filtered urea hydrolysis wastewater enters the electrodialysis device (4) for electrodialysis treatment to obtain concentrated water and fresh water; The fresh water obtained by electrodialysis treatment enters the urea dissolution tank (7) for reuse. The concentrated water is heated by heat exchange in the heat exchanger (2) and then enters the thermal decomposition and deammoniation device (5). At the same time, the alkali solution is transported from the alkali solution tank (9) to the thermal decomposition and deammoniation device (5). After thermal decomposition treatment, the concentrated water generates ammonia water and bottom kettle wastewater, and the ammonia water enters the ammonia water tank (6); The ammonia water in the ammonia water tank (6) is transported to the urea dissolution tank (7) for reuse, and the urea solution in the urea dissolution tank (7) enters the urea hydrolysis tank (8) for urea hydrolysis to produce ammonia.

2. The safety treatment and resource recovery system for urea hydrolysis wastewater according to claim 1, wherein, A sludge discharge device and a non-condensable gas absorption device are arranged at the bottom of the wastewater tank (1).

3. The safety treatment and resource recovery system for urea hydrolysis wastewater according to claim 1, wherein, The heat exchange plates inside the heat exchanger (2) are made of high-temperature and corrosion-resistant materials.

4. The safety treatment and resource recovery system for urea hydrolysis wastewater according to claim 1, wherein, The security filter (3) is internally provided with an automatic backwashing device.

5. The safety treatment and resource recovery system for urea hydrolysis wastewater according to claim 1, wherein The thermal decomposition and deammoniation device (5) internally contains an alkali pump, a non-condensable gas absorption device and a condensation-absorption integrated ammonia recovery device.

6. The safety treatment and resource recovery system for urea hydrolysis wastewater as claimed in claim 1, wherein The temperature of the urea hydrolysis wastewater entering the heat exchanger (2) is 120 - 150 °C.

7. The safety treatment and resource recovery system for urea hydrolysis wastewater as claimed in claim 1, wherein The urea hydrolysis wastewater is cooled to 30 - 50 °C after heat exchange in the heat exchanger (2), and the concentrated water from the electrodialysis device (4) is heated to 30 - 50 °C after heat exchange in the heat exchanger (2).

8. The safety treatment and resource recovery system for urea hydrolysis wastewater according to claim 1, wherein, The internal temperature of the thermal decomposition and deammoniation device (5) is 120 °C, the pressure is 1.2 - 1.6 MPa, and the condensation reflux ratio is 0.1 - 0.4.

Images