Precise ammonia injection SCR denitration system

Abstract

The utility model discloses a kind of precision ammonia injection SCR denitration systems, the system includes flue, ammonia injection mixer, rotary denitration box and control system.Ammonia injection mixer is located in flue, including multiple ammonia injection mixing units, each unit is equipped with reducing pipe, coil pipe, cavity, ammonia gas distribution pipe and nozzle.Catalyst grid plate rotatable is equipped in denitration box, is divided into denitration chamber and replacement chamber by partition plate, cooperation sealing assembly realizes catalyst replacement without stopping machine.The utility model is compact in structure, ammonia injection is uniform, and it is strong to prevent blockage, and catalyst online replacement can be realized, suitable for coal-fired power plant, industrial boiler and the like flue gas denitration scene.

Description

Technical Field

[0001] This utility model relates to the field of flue gas treatment technology, and more specifically, to a precision ammonia injection SCR denitrification system. Background Technology

[0002] Nitrogen oxides (NO) x NOx is a major component of air pollution, and its emission control is a key focus in environmental protection. Selective catalytic reduction (SCR) technology is currently the most widely used and technologically mature flue gas denitrification technology. Its basic principle is to inject a reducing agent (such as ammonia) into the flue gas under the action of a catalyst, thereby reducing NOx. x It is reduced to harmless nitrogen and water.

[0003] SCR denitrification systems mainly include ammonia injection systems, mixing systems, and catalytic reaction systems. Among these, the ammonia injection and mixing stage is crucial for ensuring denitrification efficiency and controlling ammonia slip. Traditional ammonia injection often uses an ammonia injection grid (AIG) combined with a static mixer. However, this method suffers from problems such as uneven mixing, high ammonia slip, high system resistance, and large installation space requirements. Its application is particularly limited in existing old boiler renovation projects where vertical space in the flue is limited.

[0004] To address the aforementioned problems, existing technologies have proposed various improvement solutions. For example, Chinese invention patent CN116510501B discloses an ammonia injection mixer and a flue gas denitrification system. This technology integrates the functions of an ammonia injection grid and a static mixer, proposing a mixer with multiple ammonia injection mixing units. Each unit includes a reducing pipe, a coil, a cavity, and an ammonia nozzle. The ammonia gas is first preheated by the heat of the flue gas through the coil located inside the reducing pipe, preventing low-temperature condensation of ammonium bisulfate (ABS) from clogging the nozzles. The preheated ammonia gas enters the cavity and is then injected into the throat or inlet of the reducing pipe through a distribution pipe and nozzles to mix with the flue gas. This structure effectively reduces the installation height and, through preheating and structural design, alleviates the nozzle clogging problem to some extent.

[0005] However, this technical solution still has certain limitations. Another maintenance challenge of the SCR system lies in the replacement and cleaning of the catalyst module. During long-term operation, the catalyst can become deactivated due to fly ash blockage, alkali metal poisoning, arsenic poisoning, etc., requiring periodic replacement or regeneration. In traditional SCR reactors, the catalyst is installed in a fixed catalyst bed; replacement requires system shutdown, a time-consuming and labor-intensive process that severely impacts the continuous operation of the production line. Therefore, developing an SCR denitrification system that can achieve precise ammonia injection and uniform mixing, as well as online catalyst replacement and minimize system downtime, is of great significance for improving the economic operation of the entire denitrification system. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a precise ammonia injection SCR denitrification system. This system integrates efficient ammonia injection mixing and online catalyst replacement functions, ensuring high denitrification efficiency under low ammonia slip conditions while enabling non-stop catalyst maintenance. It is particularly suitable for industrial kiln flue gas treatment scenarios with limited installation space and requiring continuous operation. To achieve the above objectives, the technical solution of this utility model is as follows: A precision ammonia injection SCR denitrification system includes a flue, an ammonia injection mixer, a rotary denitrification box, and a control system. The ammonia injection mixer is located in the flue, and the rotary denitrification box is located downstream of the flue. The rotary denitrification box includes a box body, a rotary motor, a drive wheel, a partition plate, and a sealing assembly. The box body is divided into a denitrification chamber and a replacement chamber by the partition plate. The rotary motor is located on the top of the box body, and its output shaft is connected to a drive shaft. The drive wheel is fixed to the drive shaft, and at least two catalyst grid plates are circumferentially spaced on the drive wheel. The partition plate has slotted holes for the catalyst grid plates to pass through. The sealing assembly is located at the slotted holes and is used to seal or open the slotted holes. The control system is electrically connected to the ammonia injection mixer, the rotary motor, and the sealing assembly.

[0007] As an improvement of this utility model, the ammonia injection mixer includes multiple ammonia injection mixing units. Each ammonia injection mixing unit includes two or more reducing pipes, an ammonia inlet pipe, a coil, an ammonia distribution pipe, and an ammonia nozzle. The reducing pipe is a Venturi or Laval tube structure. The inlet or outlet of the reducing pipe is provided with a straight pipe section for flue gas rectification. The area between the reducing pipes is closed to form a cavity. The coil is located inside the reducing pipe, with one end connected to the ammonia inlet pipe and the other end connected to the cavity. One end of the ammonia distribution pipe is connected to the cavity, and the other end is connected to several branch pipes. The branch pipes extend to the flue gas inlet end of the reducing pipe. The ammonia nozzle is located at the end of the branch pipe and faces the same direction as the flue gas flow.

[0008] As an improvement of this utility model, the coil is a spiral coil, and the outer wall of the coil is provided with anti-flow elements or guide vanes to enhance the heat exchange and mixing effect.

[0009] As an improvement of this utility model, the sealing assembly includes a drive motor, a screw, and a sealing plate. The drive motor drives the screw to rotate, causing the sealing plate to move up and down to close or open the strip hole.

[0010] As an improvement of this utility model, the replacement chamber is equipped with an inlet fan and an outlet fan to discharge residual flue gas when replacing the catalyst, thereby ensuring operational safety.

[0011] As an improvement of this utility model, the catalyst grid plate of the denitrification box is fixed to the fixed plate of the transmission wheel by bolts, which facilitates disassembly and replacement.

[0012] The precision ammonia injection SCR denitrification system of this invention has the following beneficial effects: This invention combines high-efficiency ammonia injection mixing technology with a rotary catalyst replacement structure. When a batch of catalyst needs to be replaced, it can be switched to the replacement chamber simply by rotating the system. This allows for maintenance, cleaning, or replacement without shutting down the system, completely solving the industry pain point of traditional SCR systems where catalyst replacement requires shutdown and affects the continuous operation of the main equipment. It is particularly suitable for industrial production lines that cannot be easily shut down, significantly improving annual operating hours and economic efficiency.

[0013] This invention inherits the advantages of the Venturi-type ammonia injector mixer. Ammonia gas is preheated by the coil, effectively preventing low-temperature condensation of ammonium bisulfate and nozzle clogging. The nozzle is located at the center of the Venturi tube inlet, utilizing the Venturi effect to achieve uniform micro-scale mixing of ammonia and flue gas under high-speed turbulent flow. This ensures a high degree of uniformity in the ammonia-nitrogen molar ratio at the catalyst inlet cross-section, thereby significantly reducing the risk of ammonia escape while maintaining high denitrification efficiency and mitigating corrosion and clogging of downstream equipment such as the air preheater. Furthermore, compared to the traditional "AIG + static mixer" model, the integrated design results in a smaller system pressure drop and lower operating energy consumption. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 This is a schematic diagram of the sealing assembly structure.

[0015] List of identifiers in attached diagrams: 10. Reducing pipe; 11. Ammonia inlet pipe; 12. Ammonia nozzle; 16. Cavity; 17. Coil; 200. Flue; 31. Partition plate; 311. Strip hole; 313. Limiting plate; 32. Denitrification chamber; 33. Replacement chamber; 334. Inlet fan; 337. Outlet fan; 4. Rotary motor; 41. Drive shaft; 42. Drive wheel; 43. Catalyst grid plate; 51. Drive motor; 52. Screw; 53. Sealing plate. Detailed Implementation

[0016] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. It should be noted that the terms "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the accompanying drawings, and the terms "inner" and "outer" refer to the directions toward or away from the geometric center of a specific component, respectively.

[0017] Furthermore, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0018] As shown in the figure, this utility model provides a precision ammonia injection SCR denitrification system, which consists of two main parts: an ammonia injection mixing module and a denitrification reaction module, both of which are located within the flue 200. The core of the ammonia injection mixing module is an ammonia mixer, which is composed of multiple identical ammonia injection mixing units arranged side by side, spanning the entire cross-section of the flue 200. Each ammonia injection mixing unit mainly includes two Venturi-structured reducing pipes 10 (the number can be increased or decreased according to the width of the flue 200). The reducing pipe 10 consists of a reduced diameter section, a straight pipe section, and an expanded diameter section. The area between the two reducing pipes 10 is completely sealed, forming a shared sealed cavity 16. Each reducing pipe 10 has an inlet straight pipe section welded to its flue gas inlet end and an outlet straight pipe section welded to its outlet end for rectifying the flue gas.

[0019] Ammonia inlet pipe 11 is welded and passes through the top of flue 200, with its lower end connected to the top of cavity 16, for introducing ammonia-air mixture into cavity 16. Inside each reducer 10, a spiral coil 17 is provided, which is made of high-temperature resistant stainless steel tube. The lower end of coil 17 passes through the top wall of reducer 10 and connects to cavity 16, while the upper end is closed. Multiple metal anti-flow fins (not shown separately in the figure) are welded to the outer wall of coil 17 to enhance heat transfer.

[0020] Inside cavity 16, an ammonia distribution pipe is installed, with its inlet connected to cavity 16. The ammonia distribution pipe branches downwards into two branch pipes, each branch pipe passing downwards through the bottom plate of cavity 16 and the top plate of the corresponding inlet straight pipe section, extending to the central axis of the inlet straight pipe section. Each branch pipe has an ammonia nozzle 12 threadedly connected to its end, with its nozzle pointing vertically downwards, aligned with the flue gas flow direction. Approximately 5 cm directly above each ammonia nozzle 12, an umbrella-shaped dust-blocking element is installed. This dust-blocking element is made of thin 310S stainless steel sheet and welded to the branch pipe via a thin stainless steel fixing rod.

[0021] The core of the denitrification reaction module is a rotary denitrification box, which is a vertical rectangular tower. Inside, a vertically welded partition plate 31 divides the internal part of the box into two chambers: a denitrification chamber 32 (connected to the flue gas inlet 200) and a replacement chamber 33.

[0022] A rotary motor 4 is fixedly mounted on the top of the housing via a bracket. Its output shaft points vertically downwards and is connected to a drive shaft 41 via a coupling. This drive shaft 41 passes through the top of the housing via a bearing housing and extends into the housing. Multiple drive wheels 42 (two are shown in the diagram) are fixed vertically at intervals on the drive shaft 41. Two sets of catalyst support units are symmetrically fixed to the circumference of each drive wheel 42 via bolts. Each support unit includes two fixing plates, upper and lower, with a catalyst grid plate 43 clamped between them and secured with bolts.

[0023] A slotted hole 311 is formed in the partition plate 31, its height and width slightly larger than the catalyst grid plate 43, allowing it to pass through. A sealing assembly is installed on the side of the partition plate 31 facing the replacement chamber 33. This assembly includes a drive motor 51 fixed to the partition plate 31 via a base, a screw 52 driven by the drive motor 51, and a sealing plate 53 connected to the screw 52 via a threaded sleeve. The sealing plate 53 is larger than the slotted hole 311 and can be driven up and down by the drive motor 51 to close or open the slotted hole 311. To ensure smooth movement of the sealing plate 53 without rotation, a guide rod is welded to its upper part, which is slidably connected to a limiting plate 313 fixed to the partition plate 31. To further ensure sealing accuracy, a photoelectric switch is installed on the sealing plate 53, and a sensing strip is affixed to the partition plate 31 at the position where the sealing plate 53 is fully closed; the two work together to achieve closed-loop control.

[0024] An air inlet and an air intake fan 334 are installed at the top of the replacement chamber 33, and an air outlet and an exhaust pipe are connected to its bottom. An exhaust fan 337 is installed on the exhaust pipe, and its outlet pipe is connected to the flue 200 upstream of the ammonia injection mixer. In addition, a mounting port with a sealing strip is provided on the side wall of the replacement chamber 33, and a heavy-duty sealing door is installed by a hinge.

[0025] Specifically, the working principle of this utility model is as follows: Flue gas flows into flue 200 and passes through the ammonia injector mixer. Ammonia (or ammonia-air mixture) enters cavity 16 through ammonia inlet pipe 11. Part of the ammonia first enters coil 17, where it is heated by the high-temperature flue gas as it flows through reducer 10, thus raising its temperature and preventing the formation of viscous ammonium bisulfate due to reaction with SO3 at low temperatures during subsequent injection. The heated ammonia returns to cavity 16, mixes with the ammonia directly entering cavity 16, and then passes through ammonia distribution pipe and branch pipes before finally being injected into the flue gas flow through ammonia nozzle 12. Because the nozzle is located at the center of the straight pipe section at the venturi inlet, the high-speed ammonia is thoroughly mixed with the flue gas accelerated by the Venturi effect, resulting in excellent mixing. The mixed ammonia-nitrogen gas then enters the downstream rotary denitrification box.

[0026] When catalyst replacement is required, the control system activates the drive motor 51 of the sealing assembly, which rotates the screw 52, ​​causing the sealing plate 53 to rise and open the slotted hole 311 on the partition plate 31. Then, the rotary motor 4 is activated, rotating the drive shaft 41 and drive wheel 42 180° to rotate the saturated or clogged catalyst grid plate 43 in the denitrification chamber 32 to the replacement chamber 33. Simultaneously, the cleaned or replaced new catalyst grid plate 43 in the replacement chamber 33 is rotated to the denitrification chamber 32. Subsequently, the sealing plate 53 descends to reseal the slotted hole 311. The ventilation unit activates, purging the residual flue gas in the replacement chamber 33 to the main flue 200. The operator can then open the sealing door to safely maintain the catalyst in the replacement chamber 33. The entire process requires no system shutdown, achieving online replacement.

[0027] The accompanying drawings merely illustrate the technical concept of this utility model and should not be construed as limiting the scope of protection of this utility model. For those skilled in the art, various improvements and modifications can be made without departing from the principle of this utility model, and all such improvements and modifications fall within the scope of protection of the claims of this utility model.

Claims

1. A precision ammonia injection SCR denitrification system, comprising a flue, an ammonia injection mixer, a rotary denitrification box, and a control system, wherein the ammonia injection mixer is located in the flue, characterized in that: The rotary denitrification box is located downstream of the flue. The rotary denitrification box includes a box body, a rotary motor, a transmission wheel, a partition plate, and a sealing assembly. The box body is divided into a denitrification chamber and a replacement chamber by the partition plate. The rotary motor is located on the top of the box body. The output shaft of the rotary motor is connected to the transmission shaft. The transmission wheel is fixed to the transmission shaft. At least two catalyst grid plates are arranged circumferentially on the transmission wheel. The partition plate has a slotted hole. The sealing assembly is located at the slotted hole. The control system is electrically connected to the ammonia injection mixer, the rotary motor, and the sealing assembly.

2. The precision ammonia injection SCR denitrification system according to claim 1, characterized in that: The ammonia injection mixer includes multiple ammonia injection mixing units. Each ammonia injection mixing unit includes two or more reducing pipes, an ammonia inlet pipe, a coil, an ammonia distribution pipe, and an ammonia nozzle. The reducing pipe is a Venturi or Laval tube structure. The inlet or outlet of the reducing pipe has a straight pipe section. The area between the reducing pipes is closed to form a cavity. The coil is located inside the reducing pipe, with one end connected to the ammonia inlet pipe and the other end connected to the cavity. One end of the ammonia distribution pipe is connected to the cavity, and the other end is connected to several branch pipes. The branch pipes extend to the flue gas inlet end of the reducing pipe. The ammonia nozzle is located at the end of the branch pipe and faces the same direction as the flue gas flow.

3. The precision ammonia injection SCR denitrification system according to claim 2, characterized in that: The coil is a spiral coil, and the outer wall of the coil is provided with anti-flow elements or guide vanes.

4. The precision ammonia injection SCR denitrification system according to claim 1, characterized in that: The sealing assembly includes a drive motor, a screw, and a sealing plate. The drive motor drives the screw to rotate, causing the sealing plate to move up and down to close or open the strip hole.

5. The precision ammonia injection SCR denitrification system according to claim 1, characterized in that: The replacement chamber is equipped with an air inlet fan and an air outlet fan.

6. The precision ammonia injection SCR denitrification system according to claim 1, characterized in that: The catalyst grid plate of the denitrification box is fixed to the fixed plate of the drive wheel by bolts.

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