An SCR flue AIG anti-abrasion system based on boundary layer gas film shielding

Abstract

The embodiment of the present disclosure provides an SCR flue AIG anti-abrasion system based on boundary layer gas film shielding, an AIG support pipe is arranged in the SCR flue, and the anti-abrasion system comprises a micro-hole jet array arranged on the windward surface of the AIG support pipe; the jet axis of the micro-hole jet array and the tangent of the windward surface of the AIG support pipe have an inclination angle, which is used for spraying clean hot air to adhere to and flow in the spanwise direction on the windward surface of the AIG support pipe, so as to form a continuous high-speed gas film boundary layer. The present disclosure realizes flexible interception of high-inertia fly ash by utilizing aerodynamic deflection force, avoids physical abrasion without increasing a physical blocking surface and without changing a local temperature field, and meanwhile, does not destroy the local thermodynamics and fluid mechanics balance of the SCR denitration.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the field of SCR flue AIG anti-wear technology, specifically relating to an SCR flue AIG anti-wear system based on boundary layer gas film shielding. Background Technology

[0002] In ultra-low emission retrofitting of large coal-fired boilers of 660MW and above, SCR (Selective Catalytic Reduction) denitrification reactors are mostly located between the economizer and the air preheater. The flue gas in this zone is a high-dust gas-solid two-phase flow, with fly ash concentrations often reaching 30g / N·m³. 3 ~50g / N·m 3 To ensure thorough mixing of ammonia and flue gas, ammonia injection grids (AIGs) are typically arranged in a dense bundle across a large rectangular flue.

[0003] Because the flue gas velocity is typically as high as 12 m / s to 18 m / s, the windward surface of the AIG tube bundle is subjected to severe forward scouring by high-energy fly ash particles for a long time. Traditional anti-wear methods are passive "physical resistance," which have a short lifespan and are prone to increasing flow resistance; while conventional compressed air purging is very likely to disrupt the temperature balance inside the reactor.

[0004] Specifically, current typical anti-wear technologies mainly rely on traditional physical methods, such as adding an angle steel anti-wear cover in front of the ammonia injection grid. However, this approach further reduces the throttling area within the rectangular flue, increasing system resistance. Furthermore, in high-wear areas, the angle steel is typically worn through within 1-2 major overhaul cycles, exhibiting an absolute upper limit to its physical lifespan, necessitating frequent shutdowns for replacement and increasing maintenance costs. Another method involves using ambient temperature compressed air to purge the windward side of the ammonia injection grid. However, the introduction of a large amount of cold air causes a sudden drop in local flue gas temperature in the AIG area. In an ammonia-rich environment, this easily exceeds the dew point of ammonium bisulfate (ABS), leading to severe viscous condensation and ash accumulation, ultimately causing complete blockage of the ammonia injection orifices. Summary of the Invention

[0005] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide an SCR flue AIG anti-wear system based on boundary layer air film shielding, wherein an AIG support tube is provided in the SCR flue, and the anti-wear system includes a microporous jet array disposed on the windward side of the AIG support tube; The jet axis of the microporous jet array has an inclined angle with the tangent of the windward surface of the AIG support tube, which is used to spray clean hot air that adheres to the windward surface of the AIG support tube and flows longitudinally to form a continuous high-speed air film boundary layer.

[0006] Furthermore, the microporous jet array is staggered along the axial direction of the AIG support tube, with an equivalent hydraulic diameter of 1.5mm to 3.0mm; the tilt angle is 15° to 30°.

[0007] Furthermore, the anti-wear system also includes a clean hot air supply main pipe disposed outside the SCR flue; The AIG support pipe is connected to the clean hot air supply main pipe via a hot air inlet branch pipe.

[0008] Furthermore, the AIG support tube includes an air film chamber and an ammonia injection chamber; the air film chamber and the ammonia injection chamber are separated by a rigid physical partition; The air film cavity is connected to the clean hot air supply main pipe and is used to spray clean hot air upstream of the flue gas through the micro-hole jet array to form an air film. The ammonia injection chamber is connected to the main pipe of the ammonia / air mixture and is used to inject ammonia into the downstream of the flue gas through the ammonia injection hole.

[0009] Furthermore, the clean hot air in the clean hot air supply main pipe is taken from the secondary air or primary air at the outlet of the boiler air preheater, and the air temperature is 300℃~380℃, which is consistent with the flue gas temperature at the inlet of the SCR reactor.

[0010] Furthermore, the anti-wear system also includes a closed-loop control unit; the closed-loop control unit is used to automatically adjust the frequency of the variable frequency booster fan installed on the clean hot air supply main pipe according to the load signal or flue gas flow signal of the boiler distributed control system, so as to maintain a constant blow-off ratio under full load conditions; wherein, The blow-off ratio is the ratio of the momentum flux of the film fluid ejected by the microporous jet array to the momentum flux of the mainstream flue gas.

[0011] Furthermore, the blow-off ratio satisfies the following formula:

[0012] In the formula, and These represent the density and velocity of the film fluid, respectively. and These represent the density and velocity of the mainstream flue gas, respectively.

[0013] Optionally, the SCR flue is a rectangular flue, and multiple AIG support tubes are fixed in the SCR flue and perpendicular to the direction of the mainstream flue gas flow.

[0014] An embodiment of the present disclosure discloses an SCR flue AIG anti-wear system based on boundary layer air film shielding, which introduces the "air film cooling" fluid control mechanism. Through isothermal air film jets at a specific angle, it achieves flexible interception of high-inertia fly ash by utilizing aerodynamic deflection force without increasing any physical obstruction surface or changing the local temperature field. This avoids physical wear and does not disrupt the local thermodynamic and hydrodynamic equilibrium of SCR denitrification. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an SCR flue AIG anti-wear system based on boundary layer air film shielding according to an embodiment of the present disclosure; Figure 2 This is a schematic diagram of the structure of an AIG support tube according to another embodiment of the present disclosure. Detailed Implementation

[0016] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0017] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0018] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily need to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0019] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component discussed below may be referred to as the second component without departing from the teachings of this disclosure. As used in this disclosure, the term "and / or" includes all combinations of any one and more of the associated listed items.

[0020] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing this disclosure, and therefore cannot be used to limit the scope of protection of this disclosure.

[0021] like Figure 1 The diagram shows a pipeline layout of an SCR flue AIG anti-wear system based on boundary layer air film shielding according to an embodiment of this disclosure. The SCR flue (1) is provided with AIG support pipes (2), specifically multiple AIG support pipes (2) are fixed horizontally or vertically in the SCR flue (1) and perpendicular to the direction of the main flue flow (the SCR flue (1) in the figure is viewed from a top or bottom angle).

[0022] For example, such as Figure 1 As shown, the anti-wear system also includes a clean hot air supply main pipe (3) located outside the SCR flue (1) and independent of the AIG support pipe (2). The AIG support pipe (2) penetrates the side wall of the SCR flue (1) through a parallel hot air inlet branch pipe (4) and is connected to the clean hot air supply main pipe (3).

[0023] like Figure 2 As shown, the anti-wear system of this embodiment includes a microporous jet array (21) densely distributed on the windward side of the AIG support tube (2). The jet axis of the microporous jet array (21) has an inclination angle α with the tangent of the windward side of the AIG support tube (2), which is used to spray clean hot air to adhere to and spread outward on the windward side of the AIG support tube (2) to form a continuous high-speed air film boundary layer. This utilizes aerodynamic deflection force to change the normal impact trajectory of high-inertia fly ash particles in dusty flue gas, thereby achieving non-physical contact air film shielding anti-wear.

[0024] The microporous jet array (21) is arranged in a staggered pattern along the axial direction of the AIG support tube (2), with an equivalent hydraulic diameter of 1.5 mm to 3.0 mm and an inclination angle of 15° to 30° to ensure that the air film has sufficient wall adhesion effect (Coanda effect).

[0025] For example, such as Figure 2As shown, the AIG support pipe (2) includes an air film chamber (22) and an ammonia injection chamber (23). The air film chamber (22) is connected to the clean hot air supply main pipe (4) and is used to spray clean hot air upstream of the flue gas through the microporous jet array (21) to form an air film; the ammonia injection chamber (23) is connected to the ammonia / air mixture main pipe and is used to spray ammonia downstream of the flue gas through the ammonia injection hole (25). The air film chamber (22) and the ammonia injection chamber (23) are separated by a rigid physical partition (24), so that the clean hot air supply main pipe (4) and the ammonia pipeline are completely isolated from each other in terms of physical structure and supplied with air independently. Even if the microporous jet array (21) is accidentally blocked, there will be no danger of hot air backflow into the ammonia pipeline. The risk of fluid mixing is avoided by physical isolation through dual channels.

[0026] The clean hot air in the clean hot air supply main pipe (4) is taken from the secondary or primary air at the outlet of the boiler air preheater (air preheater), so that the temperature of the gas film ejected by the micro-perforated jet array (21) matches the flue gas temperature (≈300℃~380℃), avoiding the risk of ammonium bisulfate condensation due to local flue gas temperature reduction, which would block the AIG nozzle. Combined with the streamlined gas film attached to the windward side of the AIG support pipe, which acts as a "virtual aerodynamic fairing", the deformation resistance and wake vortex of the flow around the circular pipe are greatly reduced, effectively reducing the flow resistance of the entire SCR flue (1).

[0027] For example, an SCR flue gas AIG anti-wear system based on boundary layer air film shielding according to an embodiment of this disclosure further includes a closed-loop control unit with built-in variable load adaptive control logic, used to automatically adjust the frequency of the variable frequency booster fan (5) installed on the clean hot air supply main pipe (4) according to the load signal or flue gas flow signal of the boiler distributed control system (DCS) in order to maintain the blow-off ratio under full load conditions. Constant. Wherein, the blow-off ratio The ratio of the momentum flux of the film fluid ejected from the microporous jet array (21) to the momentum flux of the mainstream flue gas. (Blow-off ratio) Specifically, it should satisfy the following formula:

[0028] In the formula, and These represent the density and velocity of the film fluid, respectively. and These represent the density and velocity of the mainstream flue gas, respectively.

[0029] When fly ash particles with high kinetic energy (mass) ,speed When approaching the stagnation point near the AIG pipe wall, it encountered a blow-off ratio. A high-speed air film layer. According to the momentum theorem... The gas film with high normal momentum exerts a strong reverse repulsive force and tangential acceleration force on the fly ash. The trajectory of the fly ash is forcibly "bent" at a distance of 3mm to 5mm from the pipe wall, and it slides along the direction of the gas film, completely eliminating the mechanical cutting and fatigue impact of solid particles on the metal surface, forming a boundary layer isolation with zero rigid collision.

[0030] The following example, using the retrofitting of the denitrification system of a rectangular flue of a 660MW coal-fired unit, illustrates the technical solution disclosed herein.

[0031] 1. Determining dimensions and parameters: The rectangular flue has a cross-sectional dimension of 12m (width) × 10m (height), and the flue gas velocity is... =15m / s, flue gas temperature 330℃, flue gas density ≈0.77kg / m 3 (Operating conditions).

[0032] 2. AIG structural modification: The original single-tube AIG with an angle steel shield was removed and replaced with a non-standard tube consisting of a front air film chamber and a rear ammonia injection chamber. On the front curved surface, laser drilling was used to create jet micro-holes with a diameter of φ2.0mm and an inclination angle α=20°. The hole spacing was set to 8mm, arranged in a staggered, quincunx pattern to ensure seamless connection of the spanwise air film.

[0033] 3. Air source and thermal control: The anti-wear air source is taken from the hot secondary air outlet of the air preheater and led to the outside of the flue through an independent DN300 main pipe. To overcome the resistance of the pipeline system and regulate the hot air volume (or velocity), a high-temperature resistant variable frequency booster fan and a hot air flow meter are installed on the pipeline.

[0034] Calculations were performed to maintain the blow-off ratio. (Assuming that the density is approximately equal under isothermal conditions):

[0035] The initial velocity of the film jet was calculated. The flow rate needs to be maintained above 18.3 m / s. Then, the flow rate of the hot air is calculated based on the number and area of ​​the micropores, and the variable frequency fan is adjusted to achieve the required initial velocity of the air film jet.

[0036] 4. Variable load operation and commissioning: When the unit reduces its load from 660MW to 300MW for peak shaving, the flue gas velocity... The DCS system detects the load signal and instructs the variable frequency booster fan to reduce its speed, thus decreasing the jet velocity. The system descends synchronously, maintaining the optimal blow-drift ratio at all times. This not only ensures wear prevention under low loads but also minimizes plant power consumption, achieving adaptive, maintenance-free operation throughout its entire lifecycle.

[0037] An embodiment of the present disclosure discloses an SCR flue AIG anti-wear system based on boundary layer air film shielding, which introduces the "air film cooling" fluid control mechanism. Through isothermal air film jets at a specific angle, it achieves flexible interception of high-inertia fly ash by utilizing aerodynamic deflection force without increasing any physical obstruction surface or changing the local temperature field. This avoids physical wear and does not disrupt the local thermodynamic and hydrodynamic equilibrium of SCR denitrification.

[0038] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. An AIG anti-wear system for SCR flues based on boundary layer air film shielding, wherein an AIG support tube is provided in the SCR flue, characterized in that, The wear-resistant system includes a microporous jet array disposed on the windward side of the AIG support tube; The jet axis of the microporous jet array has an inclined angle with the tangent of the windward surface of the AIG support tube, which is used to spray clean hot air that adheres to the windward surface of the AIG support tube and flows longitudinally to form a continuous high-speed air film boundary layer.

2. The anti-wear system according to claim 1, characterized in that, The microporous jet array is staggered along the axial direction of the AIG support tube, with an equivalent hydraulic diameter of 1.5mm to 3.0mm; the tilt angle is 15° to 30°.

3. The anti-wear system according to claim 1, characterized in that, The wear-resistant system also includes a clean hot air supply main pipe located outside the SCR flue; The AIG support pipe is connected to the clean hot air supply main pipe via a hot air inlet branch pipe.

4. The anti-wear system according to claim 3, characterized in that, The AIG support tube includes an air-film chamber and an ammonia injection chamber; the air-film chamber and the ammonia injection chamber are separated by a rigid physical partition; The air film cavity is connected to the clean hot air supply main pipe and is used to spray clean hot air upstream of the flue gas through the micro-hole jet array to form an air film. The ammonia injection chamber is connected to the main pipe of the ammonia / air mixture and is used to inject ammonia into the downstream of the flue gas through the ammonia injection hole.

5. The anti-wear system according to claim 3, characterized in that, The clean hot air in the clean hot air supply header is taken from the secondary or primary air at the outlet of the boiler air preheater, and the air temperature is 300℃~380℃, which is consistent with the flue gas temperature at the inlet of the SCR reactor.

6. The anti-wear system according to any one of claims 3 to 5, characterized in that, It also includes a closed-loop control unit; the closed-loop control unit is used to automatically adjust the frequency of the variable frequency booster fan installed on the clean hot air supply main pipe according to the load signal or flue gas flow signal of the boiler distributed control system, so as to maintain a constant blow-off ratio under full load conditions; wherein, The blow-off ratio is the ratio of the momentum flux of the film fluid ejected by the microporous jet array to the momentum flux of the mainstream flue gas.

7. The anti-wear system according to claim 6, characterized in that, The blow-off ratio satisfies the following formula: In the formula, and These represent the density and velocity of the film fluid, respectively. and These represent the density and velocity of the mainstream flue gas, respectively.

8. The anti-wear system according to claim 1, characterized in that, The SCR flue is a rectangular flue, and multiple AIG support tubes are fixed in the SCR flue and perpendicular to the direction of the mainstream flue flow.

Images