Safe treatment and resource recycling system and method for urea hydrolysis wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a safe treatment and resource recycling system and method for urea hydrolysis wastewater, and the system comprises a wastewater tank, a security filter, an electrodialysis device, a thermal decomposition deamination device, an ammonia water tank, a urea dissolving tank and a urea hydrolysis tank which are communicated in sequence; wherein the urea hydrolysis tank is communicated with the wastewater tank; the wastewater tank is communicated with the security filter through a heat exchanger; the electrodialysis device is communicated with the thermal decomposition deamination device through a heat exchanger; the electrodialysis device is also communicated with the urea dissolving tank; and the thermal decomposition deamination device is also connected with an alkali liquor tank. The system can realize efficient cyclic utilization of urea hydrolysis wastewater, meets resource recovery of valuable substances in the wastewater, effectively removes high-concentration harmful ions, reduces energy consumption and the use amount of cooling water and dissolving water, can ensure the characteristics of safety, greenness, low carbon and cycle of the process, and has a wide application prospect. And the production and maintenance cost of a power plant is obviously reduced.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a system and method for safely treating and recycling urea hydrolysis wastewater. Background Art

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

[0003] In the process of urea hydrolysis to produce ammonia, the hydrolysis generator often experiences foaming of the solution, rising of the virtual liquid level, and accumulation of chloride ion concentration, 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, it is necessary to discharge sewage regularly. The sewage 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 to recycle and safely reuse urea hydrolysis wastewater.

[0004] At present, the methods for treating wastewater containing urea and ammonia nitrogen mainly include biological method, chemical method and physical method (such as air stripping method), but each has its limitations. The biological method has limited effect on high-concentration ammonia nitrogen wastewater, usually requires large dilution, increases the amount of water to be treated and the floor space, and the nitrogen element is difficult to recycle. The chemical precipitation method uses chemical agents to precipitate ammonia nitrogen, but the cost of the agents is high, the operation is complicated, and a large amount of sludge needs to be treated. The air stripping method removes ammonia nitrogen through gas, which is suitable for high-concentration ammonia nitrogen wastewater, but it consumes a lot of energy, has low efficiency, and may also cause secondary pollution.

[0005] Therefore, it is very necessary to develop a safe 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 system and method for safely treating and recycling urea hydrolysis wastewater to solve the problems existing in the above-mentioned prior art. The system can remove harmful ions in wastewater to the greatest extent and recover ammonia nitrogen and residual urea at the same time.

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

[0008] In a first aspect, the present invention provides a safe treatment and resource recovery system for urea hydrolysis wastewater, comprising a wastewater tank 1, a security filter 3, an electrodialysis device 4, a thermal decomposition deamination device 5, an ammonia water tank 6, a urea dissolution tank 7 and a urea hydrolysis tank 8 which 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 regularly discharging the insoluble matter that may be contained in the urea hydrolysis wastewater 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 using the above-mentioned safe treatment and resource recovery system for urea hydrolysis wastewater, comprising the following steps:

[0022] The urea hydrolysis wastewater produced 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 the concentrated water from the electrodialysis device 4 enters the heat exchanger 2 for heat exchange;

[0024] The urea hydrolysis wastewater after heat exchange and cooling 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] Fresh water obtained by electrodialysis treatment enters urea dissolution tank 7 for reuse, concentrated water enters thermal decomposition deamination device 5 after heat exchange and temperature increase in heat exchanger 2, and alkali liquid is transported from alkali liquid tank 9 to thermal decomposition deamination device 5, concentrated water generates ammonia water and tower bottom waste water after thermal decomposition treatment, wherein ammonia water enters ammonia water tank 6, and tower bottom waste water is mixed with domestic sewage in the plant area and discharged;

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

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

[0029] Furthermore, 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 deamination device via the concentrated water, achieving the dual purpose of cooling the wastewater and heating the concentrated water, thereby significantly reducing energy consumption and cooling water usage.

[0031] Furthermore, the temperature inside the thermal decomposition deamination 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 deamination device 5 can be reused by the system after entering the urea dissolution tank through the ammonia water tank.

[0033] The invention discloses a system and method for safely treating and recycling urea hydrolysis wastewater, wherein the urea hydrolysis wastewater discharged from the urea hydrolysis tank first enters a pressurized wastewater tank, then is cooled by a heat exchanger, and then is intercepted by a safety filter to remove particulate matter in the urea hydrolysis wastewater (to protect the electrodialysis device, reduce scaling and membrane clogging), and the filtered water enters the electrodialysis device, and fresh water and concentrated water can be obtained through electrodialysis treatment; the fresh water contains a high concentration of undecomposed urea resources, and the harmful ions (chloride ions) in the fresh water have been fully reduced to a reusable standard (chloride ion concentration ≤ 5 mg / L), and can be reused in a urea dissolution tank and enter a urea hydrolysis tank via the urea dissolution tank, without the risk of corrosion to the hydrolysis generator, and the reuse of the fresh water 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 in the urea dissolution tank, so as to achieve the effective reuse of the residual unhydrolyzed urea in the fresh water and reduce the use of urea raw materials. The concentrated water is enriched with ammonia nitrogen, carbonate, chloride ions, etc. in the urea hydrolysis wastewater. After being heated through the heat exchanger and entering the thermal decomposition deamination device, a certain concentration of alkali solution is added to the thermal decomposition deamination device through the alkali solution tank. After the concentrated water reacts in the thermal decomposition deamination device, the ammonia and carbon dioxide produced 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 used again by the urea hydrolysis system to realize the resource recovery of ammonia nitrogen; the total nitrogen concentration of the wastewater in the tower bottom has reached the discharge standard (total nitrogen concentration ≤15mg / L, ammonia nitrogen concentration ≤5mg / L), and the ions in the wastewater are mainly chloride ions and sodium ions, which can enter the plant sewage pool for regulation and then be discharged. Through the application of the heat exchanger, the heat carried by the urea hydrolysis wastewater itself can be effectively transferred to the thermal decomposition deamination device through the concentrated water, achieving the dual purpose of cooling the wastewater and heating the concentrated water, thereby significantly reducing energy consumption and the use of cooling water. Therefore, the safe treatment and resource recovery system of urea hydrolysis wastewater of the present invention can realize the efficient recycling of urea hydrolysis wastewater, effectively remove high-concentration harmful ions while meeting the resource recovery requirements, and ensure the safety, greenness, low carbon and recycling characteristics of the process. The device maximizes the utilization rate of raw materials, realizes the resource recovery of valuable substances in urea hydrolysis wastewater and the separation and removal of harmful ions, thereby significantly reducing the production and maintenance costs of power plants.

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

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

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 The present invention is a schematic diagram of a safe treatment and resource recovery system for urea hydrolysis wastewater, wherein: 1-wastewater tank; 2-heat exchanger; 3-safety filter; 4-electrodialysis device; 5-thermal decomposition deamination device; 6-ammonia water tank; 7-urea dissolution tank; 8-urea hydrolysis tank; 9-alkali solution tank. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may 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 associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

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

[0044] Wherein, the urea hydrolysis tank 8 is connected to the wastewater tank 1;

[0045] The waste water tank 1 and the security filter 3 are connected via a heat exchanger 2;

[0046] The electrodialysis device 4 is connected to the thermal decomposition and deamination device 5 via a heat exchanger 2;

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

[0048] The thermal decomposition and deamination device 5 is also connected to an alkali liquid tank 9 .

[0049] More specifically, 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 security filter 3, the security filter 3 is communicated with the water inlet of the electrodialysis device 4, the concentrate 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.

[0050] As a preferred embodiment of the present invention, a mud 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 resistant and corrosion resistant materials.

[0052] As a preferred embodiment of the present invention, the safety filter 3 contains an automatic backwashing device.

[0053] As a preferred embodiment of the present invention, the thermal decomposition deamination 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 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:

[0055] The urea hydrolysis wastewater produced 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 the concentrated water from the electrodialysis device 4 enters the heat exchanger 2 for heat exchange;

[0057] The urea hydrolysis wastewater after heat exchange and cooling 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] Fresh water obtained by electrodialysis treatment enters urea dissolution tank 7 for reuse, concentrated water enters thermal decomposition deamination device 5 after heat exchange and temperature increase in heat exchanger 2, and alkali liquid is transported from alkali liquid tank 9 to thermal decomposition deamination device 5, concentrated water generates ammonia water and tower bottom waste water after thermal decomposition treatment, wherein ammonia water enters ammonia water tank 6, and tower bottom waste water is mixed with domestic sewage in the plant area and discharged;

[0060] The ammonia water in the ammonia water tank 6 is transported to the urea dissolving tank 7 for reuse (for dissolving urea to obtain urea solution), and the urea solution in the urea dissolving tank 7 enters the urea hydrolysis tank 8 for urea hydrolysis to produce ammonia (the urea solution in the urea dissolving tank 7 is actually a mixed solution of urea and ammonia water, in which both urea and ammonia water can be dissolved 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 120A and the voltage does not exceed 250V. Electrodialysis treatment can significantly reduce harmful ions (Cl -) concentration to below 500 mg / L, thereby effectively preventing subsequent processing equipment from being corroded.

[0064] As a preferred embodiment of the present invention, the temperature inside the thermal decomposition deamination 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 alkali solution is transported from the boundary area to the alkali solution tank 9, and the steam required by the thermal decomposition and deamination device 5 is provided by the boundary area.

[0066] As a preferred embodiment of the present invention, the alkali solution is transported from the alkali solution tank 9 to the thermal decomposition deamination device 5, comprising: transporting the alkali solution at a molar ratio of hydroxide to chloride ion>1.5 while controlling the pH value to be 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 entering the security filter after being cooled by the heat exchanger from the wastewater tank and the liquid entering the thermal decomposition and deamination 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, safety filter, electrodialysis device, thermal decomposition deamination device, ammonia water tank, urea dissolution tank, urea hydrolysis tank and alkali solution tank that constitute the safe treatment and resource recovery system of urea hydrolysis wastewater of the present invention are all products of the prior art. Devices with specific structures not mentioned in the specification of the present invention can use the existing technology and are not the focus of the present invention, so they will not be repeated.

[0069] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments. The following specific embodiments are only references to the specific implementation methods of the present invention. For ordinary technicians in this field, all other embodiments are also within the scope of protection of the present invention. Terms such as "top" and "bottom" are only used for convenience of description and do not limit the actual orientation of the device. The terms "connected" and "connected" should be understood in a broad sense, including fixed or detachable, direct or indirect, etc. The system includes not only the listed elements, but may also include other elements that are not explicitly listed. The specific embodiments are only for illustration, and technicians can modify and apply them according to actual conditions. The scope of the present invention is not limited to these embodiments, but is based on the widest scope of the principles and novel features of the invention.

[0070] Example 1

[0071] A safe treatment and resource recovery system for urea hydrolysis wastewater: comprising a wastewater tank 1, a security filter 3, an electrodialysis device 4, a thermal decomposition deamination device 5, an ammonia water tank 6, a urea dissolution tank 7 and a urea hydrolysis tank 8, which are connected in sequence, and an alkali liquid tank 9 connected to the thermal decomposition deamination device 5;

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

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

[0074] The electrodialysis device 4 and the thermal decomposition deamination device 5 are connected via 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 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 security filter 3, 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 outlet of the fresh water chamber 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;

[0077] A mud 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 resistant and corrosion resistant materials;

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

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

[0081] The method for treating urea hydrolysis wastewater from a thermal power plant using the above-mentioned safe treatment and resource recovery system for urea hydrolysis wastewater comprises the following steps:

[0082] S1, the urea hydrolysis wastewater produced by the urea hydrolysis tank 8 enters the wastewater tank 1 for storage and regulation (the wastewater tank 1 is a pressure tank to prevent ammonia gas from being released and escaping in large quantities);

[0083] S2. The urea hydrolysis wastewater in the wastewater tank 1 enters the heat exchanger 2 (the temperature of the urea hydrolysis wastewater is 120-150°C when entering 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; wherein, 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 after heat exchange and cooling 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, and sets the transmembrane pressure to be less than 0.2MPa. When this value is exceeded, automatic backwashing is performed to remove impurities in the wastewater to protect the electrodialysis device 4 and reduce scaling and membrane clogging; the characteristics of the filtered urea hydrolysis wastewater are as follows: pH = 10.2, TDS = 13360mg / L, total nitrogen = 17500mg / L, CO3 2- =14168mg / L, NH3-N=12370.69mg / L, Cl - =454.12mg / L, urea nitrogen=2431mg / L.

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

[0086] S5. The fresh water obtained by electrodialysis treatment enters the urea dissolution tank 7 for reuse, and the concentrated water enters the thermal decomposition deamination device 5 for thermal decomposition resource treatment after heat exchange in the heat exchanger 2 for heating. At the same time, the alkali solution is transported from the alkali solution tank 9 to the thermal decomposition deamination device 5, and the alkali solution is transported according to the molar ratio of hydroxide and chloride ions>1.5, and the pH is controlled at 9.5-14 to thoroughly distill the ammonium ions and ensure the reaction speed; the internal temperature of the thermal decomposition deamination device 5 is controlled at 120°C, the pressure is controlled at 1.4MPa, 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 tower plate. After multiple gas-liquid phase equilibria, the ammonia concentration in the gas phase is increased, NH3 and CO2 are fully separated from the water, and then enter the condensation-absorption integrated ammonia recovery device from the top of the tower, and are completely liquefied to form ammonia water with a concentration of 9-28wt%, and enter the ammonia water tank 6; at the same time, as ammonia continues to evaporate, the ammonia concentration in the liquid becomes lower and lower. When it reaches the bottom of the tower, the total nitrogen concentration in the remaining wastewater is ≤15mg / L, and the ammonia nitrogen concentration is ≤5mg / L. The ions in the remaining wastewater in the bottom of the tower are mainly chloride ions (460mg / L) and sodium ions (290mg / L), which can be mixed with domestic sewage in the factory area and directly discharged into the pipe.

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

[0088] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A safe treatment and resource recovery system for urea hydrolysis wastewater, characterized in that: It comprises a wastewater tank (1), a security filter (3), an electrodialysis device (4), a thermal decomposition deamination device (5), an ammonia water tank (6), a urea dissolution tank (7) and a urea hydrolysis tank (8) which are connected in sequence; Wherein, the urea hydrolysis tank (8) and the wastewater tank (1) are connected; The waste water tank (1) and the security filter (3) are connected via a heat exchanger (2); The electrodialysis device (4) and the thermal decomposition and deamination device (5) are connected via a heat exchanger (2); The electrodialysis device (4) is also connected to the urea dissolution tank (7); The thermal decomposition and deamination device (5) is also connected to an alkali liquid tank (9).

2. The safe treatment and resource recovery system of urea hydrolysis wastewater according to claim 1, characterized in that: The bottom of the wastewater tank (1) is provided with a mud discharge device and a non-condensable gas absorption device.

3. The safe treatment and resource recovery system of urea hydrolysis wastewater according to claim 1, characterized in that: The heat exchange plates inside the heat exchanger (2) are made of high temperature resistant and corrosion resistant materials.

4. The safe treatment and resource recovery system of urea hydrolysis wastewater according to claim 1, characterized in that: The safety filter (3) contains an automatic backwashing device.

5. The safe treatment and resource recovery system of urea hydrolysis wastewater according to claim 1, characterized in that: The thermal decomposition deamination device (5) contains an alkali pump, a non-condensable gas absorption device and a condensation-absorption integrated ammonia recovery device.

6. A method for treating urea hydrolysis wastewater from a thermal power plant using the safe treatment and resource recovery system for urea hydrolysis wastewater according to any one of claims 1 to 5, characterized in that: The following steps are involved: 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, after being 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; Fresh water obtained by electrodialysis treatment enters the urea dissolution tank (7) for reuse, and concentrated water enters the thermal decomposition deamination device (5) after being heated by heat exchange in the heat exchanger (2). At the same time, alkali liquid is transported from the alkali liquid tank (9) to the thermal decomposition deamination device (5). After thermal decomposition treatment, concentrated water generates ammonia water and tower bottom waste water, of which the ammonia water enters the ammonia water tank (6); The ammonia water in the ammonia water tank (6) is transported to the urea dissolving tank (7) for reuse, and the urea solution in the urea dissolving tank (7) enters the urea hydrolysis tank (8) for urea hydrolysis to produce ammonia.

7. The method for treating urea hydrolysis wastewater from a thermal power plant according to claim 6, characterized in that: The temperature of the urea hydrolysis wastewater entering the heat exchanger (2) is 120-150°C.

8. The method for treating urea hydrolysis wastewater from a thermal power plant according to claim 6, characterized in that: 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).

9. The method for treating urea hydrolysis wastewater from a thermal power plant according to claim 6, characterized in that: The temperature inside the thermal decomposition deamination device (5) is 120° C., the pressure is 1.2-1.6 MPa, and the condensation reflux ratio is 0.1-0.4.

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