Ammonia production from urea

Abstract

The application provides a urea ammonia production device, which comprises a urea dissolving kettle, a urea solution storage tank, a heat exchanger, a urea hydrolysis reactor, a gas mixer and an ammonia injection grid arranged in a boiler flue in sequence; the boiler is further connected with a steam turbine; the steam turbine is connected with a heat exchange medium input end and a steam input end of the urea hydrolysis reactor through a steam pressure reducing valve; and a heat exchange medium output end of the urea hydrolysis reactor is connected with a shell side of the heat exchanger, a drain tank and the urea dissolving kettle in sequence. The urea ammonia production device provided by the application uses part of the exhaust steam generated after the steam turbine works to generate electricity as a heat source in the urea hydrolysis process, thereby overcoming the problem of uneconomic production process caused by the use of additional heating equipment to produce steam to heat urea solution in the traditional urea hydrolysis ammonia production process.

Description

Technical Field

[0001] This application relates to the field of boiler denitrification technology, and in particular to a urea-to-ammonia device. Background Technology

[0002] Selective catalytic reduction (SCR) flue gas denitrification technology was gradually applied to the removal of NOx from flue gas of coal-fired boilers starting in the early 1980s. Selective catalytic reduction is based on the reduction of NOx in flue gas to N2 and H2O by injected ammonia (NH3) under the action of a metal catalyst.

[0003] There are three methods for preparing SCR denitrification reducing agents: liquid ammonia, ammonia water, and urea. The ammonia water method is limited in application due to its high energy consumption (transportation, storage, and evaporation). The liquid ammonia evaporation method is simple, mature, and inexpensive; however, ammonia is a hazardous material with the potential for explosion, and its layout requires a certain safety distance from surrounding equipment and buildings, resulting in a large footprint; therefore, it is gradually being phased out. The urea method uses urea as its raw material, eliminating the risks of explosion, toxicity, and major hazard sources, and significantly reducing the required safety distance. Due to the safety of urea compared to liquid ammonia, urea decomposition ammonia production technology is increasingly being chosen by more users in China.

[0004] The principle of urea hydrolysis to ammonia production is that a urea solution of a certain concentration undergoes a hydrolysis reaction in a pressure vessel, generating a mixed gas of NH3, CO2, and H2O. This process requires heating the urea solution to 150-160℃ for the reaction to proceed. Currently, electric boilers or similar devices are used to heat water and generate steam at the corresponding temperature as a heat source to heat the urea solution. However, this method requires additional equipment to generate steam, and the heating process consumes extra energy, resulting in high production costs for the plant. Utility Model Content

[0005] This application provides a urea ammonia production apparatus to solve the problem of uneconomical production process caused by using additional heating equipment to produce steam to heat urea solution during urea hydrolysis ammonia production.

[0006] This application provides a urea-to-ammonia apparatus, comprising a urea dissolving kettle, a urea solution storage tank, a heat exchanger, a urea hydrolysis reactor, a gas mixer, and an ammonia injection grid installed in a boiler flue, connected in series. The boiler is also connected to a steam turbine, which is connected to the heat exchange medium input end and the steam input end of the urea hydrolysis reactor via steam pressure reducing valves. The heat exchange medium output end of the urea hydrolysis reactor is connected in sequence to the shell side of the heat exchanger, the condensate tank, and the urea dissolving vessel. A first transfer pump is installed between the urea dissolving vessel and the urea solution storage tank; A metering pump is installed between the urea solution storage tank and the heat exchanger; The urea hydrolysis reactor is connected to the wastewater storage tank; The gas mixer is also connected to a compressed air line.

[0007] Optionally, the wastewater storage tank and the boiler are connected by a second transfer pump.

[0008] Optionally, the urea hydrolysis reactor includes a reactor body; The reactor body contains heat exchange tubes. The reactor body has an ammonia outlet at the top and a urea solution inlet and a steam inlet on the lower side. The urea solution inlet is connected to the heat exchanger, and the steam inlet is connected to the steam pressure reducing valve.

[0009] Optionally, the gas mixer includes a venturi-shaped housing; One end of the shell is closed while the other end is open; The closed end of the housing is penetrated by an air inlet pipe, which extends into the housing and is close to the throat of the housing; An ammonia inlet pipe is provided on one side of the closed end of the shell.

[0010] Optionally, the short output duct of the housing is provided with multiple grids.

[0011] Optionally, an axial fan is provided at the throat of the housing.

[0012] Optionally, the grid plate includes an outer frame that matches the shape of the housing, and multiple baffles are arranged parallel to each other within the outer frame; The baffles between adjacent grid plates are set at a certain angle.

[0013] This application provides a urea-to-ammonia production apparatus. By extracting a portion of the exhaust steam generated after the turbine's operation for power generation as a heat source for the urea hydrolysis process, it overcomes the drawback of the uneconomical production process caused by the use of additional heating equipment to produce steam to heat the urea solution in traditional urea hydrolysis ammonia production processes. Furthermore, in this application's apparatus, a portion of the steam, after being depressurized by the steam pressure reducing valve 100, is directly introduced into the urea hydrolysis reactor 4. This heats the urea solution while simultaneously stripping the ammonia and carbon dioxide produced during the decomposition of the reaction solution, promoting the decomposition of ammonium carboxylate in the reaction, reducing the concentration of ammonium carboxylate, and thus reducing the corrosion of the reactor by ammonium carboxylate. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a urea-to-ammonia apparatus provided in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of a urea hydrolysis reactor provided in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a gas mixer provided in one embodiment of this application; Figure 4 This is a schematic diagram of the structure of a grid plate provided in an embodiment of this application.

[0016] Explanation of reference numerals in the attached figures: 1. Urea dissolving kettle; 2. Urea solution storage tank; 3. Heat exchanger; 4. Urea hydrolysis reactor; 5. Gas mixer; 6. Boiler; 7. Steam turbine; 8. Drainage tank; 9. Compressed air pipeline; 10. First transfer pump; 20. Metering pump; 30. Second transfer pump; 40. Wastewater storage tank; 41. Reactor body; 42. Heat exchange tube; 51. Shell; 52. Air inlet pipe; 53. Ammonia inlet pipe; 54. Grid plate; 55. Axial flow fan; 61. Ammonia injection grid; 100. Steam pressure reducing valve; 401. Ammonia outlet; 402. Urea solution inlet; 403. Steam inlet; 541. Outer frame; 542. Baffle plate. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0018] like Figure 1 As shown, this application provides a urea-to-ammonia apparatus, including a urea dissolving kettle 1, a urea solution storage tank 2, a heat exchanger 3, a urea hydrolysis reactor 4, a gas mixer 5, and an ammonia injection grid 61 installed in the flue of a boiler 6, which are connected in series. Boiler 6 is also connected to steam turbine 7, which is connected to the heat exchange medium input end and steam input end of urea hydrolysis reactor 4 through steam pressure reducing valve 100. The heat exchange medium output end of the urea hydrolysis reactor 4 is connected in sequence to the shell side of the heat exchanger 3, the condensate tank 8, and the urea dissolving vessel 1. A first transfer pump 10 is installed between the urea dissolving vessel 1 and the urea solution storage tank 2; A metering pump 20 is installed between the urea solution storage tank 2 and the heat exchanger 3; Urea hydrolysis reactor 4 is connected to wastewater storage tank 40; The gas mixer 5 is also connected to the compressed air line 9.

[0019] In this application, the principle of the urea hydrolysis ammonia production process is that a urea solution of a certain concentration undergoes a hydrolysis reaction in a pressure vessel, generating a mixed gas of NH3, CO2, and H2O. The decomposition process of urea proceeds in two steps: the first step is the reaction of urea and water to produce ammonium carbamate (commonly known as methylammonium carbamate), and the second step is the decomposition of ammonium carbamate into carbon dioxide and ammonia. Both steps in this reaction are reversible. However, methylammonium carbamate is highly corrosive, and the higher the concentration, the stronger the corrosiveness, which will seriously affect the service life of key components such as the urea hydrolysis reactor. Therefore, in order to reduce the concentration of methylammonium carbamate, it is necessary to promote its decomposition, that is, to remove the ammonia and carbon dioxide generated in the reaction from the reaction system in a timely manner, so that the reaction proceeds in the reverse direction of methylammonium carbamate decomposition. Therefore, in this application, a portion of the steam after being depressurized by the steam pressure reducing valve 100 is directly introduced into the urea hydrolysis reactor 4. While heating the urea solution, it also serves to strip the ammonia and carbon dioxide generated in the reaction solution, thereby promoting the decomposition of methylammonium carbamate and reducing the corrosion of the reactor by methylammonium carbamate.

[0020] In use, the condensate in the condensate tank 8 serves as the water source, supplying the condensate to the urea dissolving kettle 1 (when the condensate temperature is too high or the condensate volume is insufficient, demineralized water at room temperature can be supplied through the demineralized water section in the factory). This condensate is then mixed with urea granules to prepare a urea solution with a concentration of 40-50%. The urea solution prepared in the urea dissolving kettle 1 is transferred by the first transfer pump 10 to the urea solution storage tank 2 for temporary storage (to prevent crystallization during storage, the urea solution storage tank 2 is equipped with electric or steam heating to ensure that the urea solution is maintained at a temperature higher than that at which crystallization occurs, such as 25-30°C). The urea solution in the urea solution storage tank 2 is then quantitatively drawn by the metering pump 20 and, after heat exchange with the steam condensate output from the urea hydrolysis reactor 4 via the heat exchanger 3, is input into the urea hydrolysis reactor 4 for hydrolysis.

[0021] The ammonia gas produced after urea hydrolysis is discharged from the ammonia outlet at the top of the urea hydrolysis reactor 4 and mixed with the compressed air input from the compressed air pipeline 9 in the gas mixer 5.

[0022] The mixed diluted ammonia gas enters the ammonia injection grid 61 and is injected into the flue. Under the action of the catalyst, the nitrogen oxides in the flue gas are reduced to nitrogen gas.

[0023] During the hydrolysis process, the urea solution in urea hydrolysis reactor 4 also undergoes side reactions, forming byproducts such as biuret. Therefore, it is necessary to discharge these byproducts periodically. During periodic wastewater discharge, the wastewater from urea hydrolysis reactor 4 can be discharged into wastewater storage tank 40 for centralized treatment.

[0024] This application provides a urea-to-ammonia production apparatus. By extracting a portion of the exhaust steam generated after the turbine's operation for power generation as a heat source for the urea hydrolysis process, it overcomes the drawback of the uneconomical production process caused by the use of additional heating equipment to produce steam to heat the urea solution in traditional urea hydrolysis ammonia production processes. Furthermore, in this application's apparatus, a portion of the steam, after being depressurized by the steam pressure reducing valve 100, is directly introduced into the urea hydrolysis reactor 4. This heats the urea solution while simultaneously stripping the ammonia and carbon dioxide produced during the decomposition of the reaction solution, promoting the decomposition of ammonium carboxylate in the reaction, reducing the concentration of ammonium carboxylate, and thus reducing the corrosion of the reactor by ammonium carboxylate.

[0025] like Figure 1 As shown, optionally, the sewage storage tank 40 and the boiler 6 are connected by a second transfer pump 30.

[0026] In this application, the second transfer pump 30 can be used to spray it into the boiler furnace at a temperature of 850~900℃ (near the boiler flame deflector, which can be obtained through actual measurement) as an SNCR denitrification agent to achieve zero discharge of urea hydrolysis wastewater.

[0027] like Figure 2 As shown, optionally, the urea hydrolysis reactor 4 includes a reactor body 41; The reactor body 41 is equipped with a heat exchange tube 42 inside the reactor body 41. The reactor body 41 has an ammonia outlet 401 at the top and a urea solution inlet 402 and a steam inlet 403 at the lower side. The urea solution inlet 402 is connected to the heat exchanger 3, and the steam inlet 403 is connected to the steam pressure reducing valve 100.

[0028] In this application, when the urea solution is hydrolyzed in the urea hydrolysis reactor 4, a portion of the high-pressure exhaust steam extracted from the turbine 7 is depressurized by the steam pressure reducing valve 100. Part of this steam enters the heat exchange tube 42 of the urea hydrolysis reactor 4, while the other part enters the reactor body 41 through the steam inlet 403. Both steam and steam together heat the urea solution input through the urea solution inlet 402, causing the urea to undergo a hydrolysis reaction to produce ammonia. The steam input through the steam inlet 403 also acts as a stripping agent, carrying the ammonia dissolved in the urea solution out of the liquid system. The ammonia produced after urea hydrolysis is discharged from the ammonia outlet at the top of the urea hydrolysis reactor 4 and mixed with compressed air input through the compressed air pipeline 9 in the gas mixer 5.

[0029] like Figure 3 As shown, optionally, the gas mixer 5 includes a venturi-shaped housing 51; One end of the housing 51 is closed while the other end is open; The closed end of the housing 51 is passed through by the air inlet pipe 52, which extends into the housing 51 and is close to the throat of the housing 51; An ammonia inlet pipe 53 is provided on one side of the closed end of the housing 51.

[0030] In this application, the gas mixer 5 is venturi-shaped and is a type of jet mixer.

[0031] When mixing occurs in the gas mixer 5, compressed air is input from the air input pipe 52 and output to the throat of the gas mixer 5. At this time, due to the high flow rate of the compressed air, a negative pressure state of suction can be formed at the ammonia input pipe 53 to facilitate the input of ammonia. The input ammonia and air are mixed in a certain proportion (the specific proportion can be achieved by adjusting the compressed air flow rate and the pipe diameters of the air input pipe 52 and the ammonia input pipe 53).

[0032] like Figure 3 As shown, optionally, a plurality of grid plates 54 are provided inside the output short pipe of the housing 51.

[0033] In this application, the grid plate can cut the fluid and create turbulence.

[0034] like Figure 3 As shown, optionally, an axial fan 55 is provided at the throat of the housing 51.

[0035] In this application, the axial fan 55 can be driven to rotate by input ammonia and compressed air, or by a motor. When driven by a motor, care must be taken to ensure that the fan blades generate suction in the direction of the compressed air and the input of the device during rotation. This avoids excessive resistance to the gas while accelerating gas flow and mixing. Furthermore, when driven by a motor, the motor is located outside the housing 51, and the connecting wires must be sealed when passing through the housing 51 to prevent gas leakage from inside the housing 51. Sealing can be achieved, for example, using sealant.

[0036] like Figure 4 As shown, optionally, the grid plate 54 includes an outer frame 541 that matches the shape of the housing 51, and a plurality of baffles 542 are arranged parallel to each other in the outer frame; The baffles 542 between adjacent grid plates 54 are set at a certain angle.

[0037] As air and ammonia pass through the throat of casing 51, they undergo initial mixing due to the cutting action of the blades of axial fan 55. Then, as they pass through grid 54, they are further separated by baffles 542 on the grid 54, creating turbulence. The baffles, arranged at different angles among multiple grids 54, alter the airflow direction, ensuring uniform mixing of ammonia and air. The diluted ammonia then enters the ammonia injection grid 61, where it is injected into the flue gas. Under the action of a catalyst, nitrogen oxides in the flue gas are reduced to nitrogen.

[0038] In this application, the baffles 542 between adjacent grid plates 54 are set at a certain angle, which is an acute angle or a right angle.

[0039] A urea-to-ammonia production device operates as follows: In use, the condensate in the condensate tank 8 serves as the water source, supplying the condensate to the urea dissolving kettle 1 (when the condensate temperature is too high or the condensate volume is insufficient, demineralized water at room temperature can be supplied through the demineralized water section in the factory). This condensate is then mixed with urea granules to prepare a urea solution with a concentration of 40-50%. The urea solution prepared in the urea dissolving kettle 1 is transferred by the first transfer pump 10 to the urea solution storage tank 2 for temporary storage (to prevent crystallization of the urea solution during storage, the urea solution storage tank 2 is equipped with electric or steam heating to ensure that the urea solution is maintained at a temperature higher than the crystallization temperature, such as 25-30°C; similar urea solution delivery pipelines can also use steam or electric heating). The urea solution in the urea solution storage tank 2 is then quantitatively drawn by the metering pump 20 and, after heat exchange with the steam condensate output from the urea hydrolysis reactor 4 via the heat exchanger 3, is input into the urea hydrolysis reactor 4 for hydrolysis.

[0040] When the urea solution is hydrolyzed in the urea hydrolysis reactor 4, a portion of the high-pressure exhaust steam extracted from the turbine 7 is depressurized by the steam pressure reducing valve 100. Part of this steam enters the heat exchange tube 42 of the urea hydrolysis reactor 4, while the other part enters the reactor body 41 through the steam inlet 403. Both steam and steam together heat the urea solution input through the urea solution inlet 402, causing the urea to undergo a hydrolysis reaction to produce ammonia and carbon dioxide. The steam input through the steam inlet 403 also acts as a stripping agent, carrying the ammonia dissolved in the urea solution out of the liquid system and promoting the decomposition of ammonium carboxylate. The ammonia produced after urea hydrolysis is discharged from the ammonia outlet at the top of the urea hydrolysis reactor 4 and mixed with compressed air input from the compressed air pipeline 9 in the gas mixer 5.

[0041] During mixing in the gas mixer 5, compressed air is input from the air inlet pipe 52 and output to the throat of the gas mixer 5. Due to the high flow rate of the compressed air, a negative pressure state is formed at the ammonia inlet pipe 53 to facilitate the input of ammonia. The input ammonia and air are mixed in a certain ratio (the specific ratio can be achieved by adjusting the compressed air flow rate and the pipe diameters of the air inlet pipe 52 and the ammonia inlet pipe 53). When the air and ammonia pass through the throat of the housing 51, they are initially mixed by the cutting action of the blades of the axial flow fan 55. Then, when they pass through the grid 54, they are divided by the baffles 542 on the grid 54 to form turbulence. The baffles set at different angles among the multiple grids 54 change the airflow direction to achieve uniform mixing of ammonia and air. The diluted ammonia after mixing enters the ammonia injection grid 61 and is injected into the flue. Under the action of the catalyst, the nitrogen oxides in the flue gas are reduced to nitrogen.

[0042] During the hydrolysis process, the urea solution in urea hydrolysis reactor 4 undergoes side reactions, forming byproducts such as biuret. Therefore, it needs to be discharged periodically. During periodic wastewater discharge, the wastewater from urea hydrolysis reactor 4 can be discharged into wastewater storage tank 40 and sprayed into the boiler furnace at a temperature of 850~900℃ (near the boiler flame deflector, the exact temperature can be obtained through actual measurement) using the second transfer pump 30 as an SNCR denitrification agent to achieve zero discharge of urea hydrolysis wastewater.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A urea-to-ammonia production device, characterized in that, It includes a urea dissolving vessel (1), a urea solution storage tank (2), a heat exchanger (3), a urea hydrolysis reactor (4), a gas mixer (5), and an ammonia injection grid (61) installed in the flue of the boiler (6). The boiler (6) is also connected to a steam turbine (7), which is connected to the heat exchange medium input end and the steam input end of the urea hydrolysis reactor (4) respectively through a steam pressure reducing valve (100); The heat exchange medium output end of the urea hydrolysis reactor (4) is connected in sequence to the shell side of the heat exchanger (3), the hydrophobic water tank (8), and the urea dissolving vessel (1); A first transfer pump (10) is provided between the urea dissolving vessel (1) and the urea solution storage tank (2). A metering pump (20) is installed between the urea solution storage tank (2) and the heat exchanger (3). The urea hydrolysis reactor (4) is connected to the sewage storage tank (40); The gas mixer (5) is also connected to the compressed air line (9).

2. The urea-to-ammonia apparatus according to claim 1, characterized in that, The wastewater storage tank (40) and the boiler (6) are connected by a second transfer pump (30).

3. The urea-to-ammonia apparatus according to claim 1, characterized in that, The urea hydrolysis reactor (4) includes a reactor body (41). The reactor body (41) is provided with heat exchange tubes (42). The reactor body (41) has an ammonia outlet (401) at the top and a urea solution inlet (402) and a steam inlet (403) at the bottom side. The urea solution inlet (402) is connected to the heat exchanger (3), and the steam inlet (403) is connected to the steam pressure reducing valve (100).

4. The urea-to-ammonia apparatus according to claim 1, characterized in that, The gas mixer (5) includes a venturi tubular housing (51). One end of the housing (51) is closed and the other end is open; The closed end of the housing (51) is passed through by an air inlet pipe (52), which extends into the housing (51) and is close to the throat of the housing (51); An ammonia inlet pipe (53) is provided on one side of the closed end of the housing (51).

5. The urea-to-ammonia apparatus according to claim 4, characterized in that, The housing (51) has multiple grid plates (54) installed inside the short output pipe.

6. The urea-to-ammonia apparatus according to claim 4, characterized in that, An axial fan (55) is provided at the throat of the housing (51).

7. The urea-to-ammonia apparatus according to claim 5, characterized in that, The grid plate (54) includes an outer frame (541) that matches the shape of the housing (51), and a plurality of baffles (542) are arranged parallel to each other in the outer frame. The baffles (542) between adjacent grid plates (54) are set at a certain angle.

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