An online purging device for flue gas denitrification catalyst

Abstract

This invention discloses an online purging system for flue gas denitrification catalysts, comprising: a compressed air tank, a purging pipe, and a purging mechanism; the compressed air tank is connected to the inlet of the purging mechanism, and the outlet of the purging pipe is used to cooperate with the catalyst bed. In this application, the air in the purging pipe is first preheated by high-temperature flue gas, and then the honeycomb catalyst module is subjected to online pulse purging in the direction of flue gas flow (from bottom to top) through the holes of the purging pipe, while room temperature air is simultaneously injected into the other end (upper end) of the catalyst module. Utilizing the temperature difference between the gases injected into the catalyst ends to create a chimney effect, the room temperature air at the upper end rapidly sinks along the channels of the catalyst module, accelerating the upward movement of the purging gas at the lower end. This high-speed convection improves the effect of purging catalyst dust and solves the problem of physical poisoning of the catalyst by highly viscous dust.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and in particular to an online purging device for flue gas denitrification catalyst. Background Technology

[0002] Existing patent application CN202211380899.5 discloses a selective catalytic reduction (SCR) denitrification device for heated flue gas purification, relating to the field of flue gas purification technology. Specifically, it is a heated flue gas purification device using SCR, comprising a boiler. A cooling assembly is installed on the top of the boiler. The right end of the cooling assembly is connected to a first pipe, and the right end of the first pipe is connected to a dust removal assembly. A second pipe is connected to the right side of the boiler, and the right end of the second pipe is connected to the bottom of the first pipe. This heated flue gas purification device, by using a cooling assembly, opens the first pipe and closes the second pipe when the flue gas temperature is too high, allowing the flue gas to pass through the cooling assembly. Cooling water enters the interior of the cooling assembly from the inlet, cooling the flue gas and reducing its temperature, thus preventing excessively high flue gas temperatures that could cause catalyst sintering and failure.

[0003] Catalytic denitrification is currently the best denitrification process for reducing NOx emissions in my country's flue gas treatment. However, dust in the flue gas easily adheres to the catalyst surface, causing physical poisoning. Therefore, it is necessary to purge the catalyst to remove dust from its surface. Traditional SCR denitrification catalyst soot blowing technology mainly involves designing a purge pipe at one end (lower end) of the honeycomb catalyst module, with holes drilled in the purge pipes corresponding to each catalyst module, and then using high-pressure air from these holes to purge the catalyst modules. However, some industrial flue gases contain alkali metal dust, which is highly viscous, and engineering practice has shown that it is difficult to remove it simply by blowing it away. Summary of the Invention

[0004] The purpose of this invention is to provide an online purging device for flue gas denitrification catalysts, which utilizes gas with a certain temperature difference injected into both ends of the catalyst module to generate a chimney effect, allowing the purging gas to generate high-speed convection in the channels of the catalyst module, thereby improving the catalyst dust purging effect and solving the problem of physical poisoning of the catalyst by high-viscosity dust.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention provides an online purging device for flue gas denitrification catalyst, comprising a housing, a flue gas inlet box and a flue gas outlet box disposed on the housing;

[0007] A medium-temperature denitrification catalytic bed is provided in the shell near the flue gas inlet box, and a low-temperature denitrification catalytic bed is provided in the shell near the flue gas outlet box.

[0008] Purge pipes are respectively provided inside the shell corresponding to the medium-temperature denitrification catalyst bed and the low-temperature denitrification catalyst bed;

[0009] A cold air duct is installed in the shell section containing the medium-temperature denitrification catalytic bed;

[0010] Hot air ducts are installed in the shell section containing the low-temperature denitrification catalytic bed;

[0011] The hot air duct passes through the interior of the housing for heat exchange, and its outlet air temperature is higher than that of the cold air duct.

[0012] Furthermore, the cold air duct and the hot air duct are connected to an air source via a tee, and control valves are respectively installed on the cold air duct and the hot air duct;

[0013] Furthermore, the cold air duct and the hot air duct are respectively connected to an air source;

[0014] Furthermore, the air source is a compressed air tank;

[0015] Furthermore, the air source is a blower.

[0016] Furthermore, a hot air heat exchange pipe connected to the hot air pipe is installed inside the flue gas inlet box;

[0017] Or / and, the hot air heat exchange tube has a spiral winding structure.

[0018] Furthermore, a gas distribution cylinder communicating with the interior is provided on the side wall of the housing, the hot air pipe is connected to the gas distribution cylinder, and a solenoid valve that is adjusted and controlled by a controller is provided on it.

[0019] Furthermore, an inverted U-shaped flue gas flow channel is provided inside the housing.

[0020] Furthermore, regarding the design methods for cold air ducts;

[0021] To determine the strength of the convection effect, a physical quantity—wall shear stress—is introduced to characterize the intensity of the chimney effect under different conditions. Its specific expression is as follows:

[0022]

[0023] V—The shear force acting on the calculated section;

[0024] A — Calculate the cross-sectional area;

[0025] b—width of the cross section; h—height of the cross section.

[0026] Under turbulent conditions, the continuity equation is:

[0027]

[0028] In the formula, ui is the time-averaged velocity component of the fluid in the xi direction; ρ is the fluid density; and xi is the spatial coordinate system.

[0029] The catalyst column employs a porous media model, considering the influence of the solid on the fluid through parameters such as the flow resistance added to the fluid and the diffusion coefficient in the modified conservation equations. The single-phase flow conservation equations in the porous media model are as follows.

[0030] mass conservation equation

[0031]

[0032] Momentum conservation equation

[0033]

[0034] In the formula, ρ, u, and ε represent the fluid density, actual flow velocity, and porous medium porosity, respectively. The porous medium porosity ε is determined based on the geometry of the catalyst column; P is the pressure; Γm is the momentum diffusion coefficient; g is the gravitational acceleration; and Rf is the porous medium resistance source term.

[0035] The momentum equation for the porous medium model is superimposed with a velocity-dependent momentum source term, expressed as follows:

[0036]

[0037] In the formula: Si is the source term of the momentum equation; μ is the dynamic viscosity; v is the velocity value; D and C are specified matrices; the first term is the viscous drag loss, and the second term is the inertial drag loss.

[0038] The calculations guide the design of the cooling duct, showing that the gas will accelerate within the catalyst column channels, providing the gaseous power for purging sticky dust. However, the convection effect varies depending on the location of the cooling duct, requiring simulation results to determine the optimal placement.

[0039] Similarly, the speed and temperature of the cold air being blown in, as well as the diameter and number of the cold air ducts, all affect the convection effect caused by the chimney effect. It is necessary to compare the convection effects under different boundary conditions to determine the optimal result.

[0040] Furthermore, a cold air duct is installed at a distance of 0-75 mm from the top of the catalyst column and 25-105 mm from the right side. The cold air duct is equipped with cold air with the following parameters: temperature of 25℃ and gas flow rate of 3.5 m / s. When the gas flows through the catalyst channel, the average wall shear stress inside the catalyst column channel is 0.086 Pa to 0.146 Pa according to simulation calculations.

[0041] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0042] In order to enhance the dust blowing intensity, cold (room temperature) gas is injected into one end of the catalyst bed of the integrated catalytic denitrification and waste heat utilization device. The temperature difference between the gas and the hot gas at the other end of the catalyst module creates a chimney effect in the channels of the honeycomb catalyst, allowing the gas to generate high-speed convection in the channels of the catalyst module, thereby increasing the dust blowing intensity of the catalyst. Attached Figure Description

[0043] The present invention will be further described below with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of the online purging device for flue gas denitrification catalyst of the present invention;

[0045] Figure 2 This is a schematic diagram showing the location of the cold air duct in the online purging device for the flue gas denitrification catalyst of the present invention.

[0046] Explanation of reference numerals in the attached drawings: 1. Compressed air tank; 2. Cold air duct; 2a. Location of cold air duct; 3. Hot air heat exchange duct; 3a. Hot air duct; 4. First purge duct; 4a. Second purge duct; 5. Shell; 5a. Flue gas inlet box; 5b. Flue gas outlet box; 6. Gas distribution cylinder; 7. Controller; 8. Steam drum; 9. Heat exchange duct; 10. Medium-temperature denitrification catalytic bed; 10a. Low-temperature denitrification catalytic bed. Detailed Implementation

[0047] This embodiment discloses an online purging device for flue gas denitrification catalyst, including a housing 5, a flue gas inlet box 5a and a flue gas outlet box 5b installed on the housing 5;

[0048] A medium-temperature denitrification catalytic bed 10 is installed in the shell 5 near the flue gas inlet box 5a, and a low-temperature denitrification catalytic bed 10a is installed in the shell 5 near the flue gas outlet box 5b.

[0049] The first purge pipe 4 and the second purge pipe 4a are respectively connected to an ammonia gas source;

[0050] Purge pipes are installed inside the shell 5 corresponding to the medium-temperature denitrification catalytic bed 10 and the low-temperature denitrification catalytic bed 10a, respectively; a cold air pipe 2 is installed in the section of the shell 5 containing the medium-temperature denitrification catalytic bed 10, wherein... Figure 2 As shown, the cross-sectional view of the cold air duct at position 2a is shown.

[0051] A hot air duct 5a is installed in section 5 of the shell containing the low-temperature denitrification catalytic bed 10a;

[0052] The hot air duct 5a passes through the interior of the housing 5 for heat exchange, and its outlet air temperature is higher than that of the cold air duct 2.

[0053] The shell is designed with an inverted U-shaped flue gas flow channel; the flue gas passes sequentially through a heat exchanger (not labeled), a first purge pipe 4, a medium-temperature denitrification catalytic bed 10, a cold air pipe 2 jet area, another heat exchanger (not labeled), a second purge pipe 4a, a low-temperature denitrification catalytic bed 10a, and a hot air pipe 3a jet area.

[0054] In this embodiment, the cold air duct 2 and the hot air duct 3a are connected to an air source through a tee, and control valves are installed on the cold air duct 2 and the hot air duct 3a respectively;

[0055] Specifically, the cold air duct 2 and the hot air duct 3a are respectively connected to an air source; the air source is a compressed air tank 1; or the air source is a blower.

[0056] As shown in the figure, a hot air heat exchange pipe 3 connected to the hot air pipe 3a is installed in the flue gas inlet box 5a; the hot air heat exchange pipe 3 has a spiral winding structure to improve heat exchange efficiency.

[0057] In this embodiment, a gas distribution cylinder 6 communicating with the interior is installed on the side wall of the housing 5, and the hot air pipe 3a communicates with the gas distribution cylinder 6, and a solenoid valve that is adjusted and controlled by the controller 7 is installed on it.

[0058] The air in the purge pipe is first preheated by high-temperature flue gas, and then used to purge the honeycomb denitrification catalyst module online in the direction of flue gas flow (from bottom to top and / or from top to bottom) through the holes of the purge pipe. At the same time, room temperature air is injected into the other end (top) of the catalyst module. The compressed air tank is connected to the cold air duct and is used to blow room temperature gas into the upper part of the catalyst reaction bed. The purge mechanism includes a header and a purge pipe. The header is a control system, including a gas distribution cylinder. The gas distribution cylinder is connected to the pneumatic control valve. The resistance monitoring mechanism is communicatively connected to the controller of the gas distribution cylinder. The compressed air tank is also connected to the inlet of the purge mechanism, and the outlet of the purge mechanism is connected to the purge pipe. The gas in the purge pipe is preheated and blown into the lower part of the catalyst bed. The purge pipe has nozzles in the same direction as the flue gas to purge the catalyst.

[0059] The overall design of this application includes a shell 5, a flue gas denitrification unit and a waste heat recovery unit installed within the shell; wherein the shell is equipped with a flue gas inlet box and a flue gas outlet box; the flue gas denitrification unit includes a medium-temperature denitrification catalytic bed and a low-temperature denitrification catalytic bed installed within the shell; wherein the medium-temperature denitrification catalytic bed is injected with ammonia through a first purge pipe; the low-temperature denitrification catalytic bed is injected with ammonia through a second purge pipe; the waste heat recovery unit includes a heat exchanger placed within the shell, an inlet water pipe and an outlet water pipe connected to the heat exchanger.

[0060] In this embodiment, the convection effect manifests as a chimney effect, where hot and cold air flows at high speed within the catalyst column pores under the influence of a pressure difference. To compare the strength of the convection effect, a physical quantity—wall shear stress—is introduced to characterize the intensity of the chimney effect under different conditions. Its specific expression is as follows:

[0061]

[0062] V—The shear force acting on the calculated section;

[0063] A — Calculate the cross-sectional area;

[0064] b—width of the cross section; h—height of the cross section.

[0065] Under turbulent conditions, the continuity equation is:

[0066]

[0067] In the formula, u i For fluid in x i The time-averaged velocity component in the direction; ρ is the fluid density; x i It is a spatial coordinate system.

[0068] The catalyst column employs a porous media model, considering the influence of the solid on the fluid through parameters such as the flow resistance added to the fluid and the diffusion coefficient in the modified conservation equations. The single-phase flow conservation equations in the porous media model are as follows.

[0069] mass conservation equation

[0070]

[0071] Momentum conservation equation

[0072]

[0073] In the formula, ρ, u, and ε represent the fluid density, actual flow velocity, and porosity of the porous medium, respectively, with the porosity ε determined based on the geometry of the catalyst column; P is the pressure; Γm is the momentum diffusion coefficient; g is the gravitational acceleration; and R... f This is a source term for resistance in porous media.

[0074] The momentum equation for the porous medium model is superimposed with a velocity-dependent momentum source term, expressed as follows:

[0075]

[0076] In the formula: S i is the source term of the momentum equation; μ is the dynamic viscosity; v is the velocity value; D and C are specified matrices; the first term is the viscous drag loss, and the second term is the inertial drag loss.

[0077] The enhanced convection effect is due to the introduction of low-temperature gas. The low-temperature gas has high pressure and high density, while the high-temperature gas has low pressure and low density. Under the pressure difference between hot and cold, the hot and cold gases convect at high speed in the catalyst channels, thereby enhancing the purging effect.

[0078] The calculations show that in the case of adding a cooling duct, the gas accelerates within the catalyst column channels, providing the gaseous power for purging sticky dust. The convection effect varies depending on the location of the cooling duct, requiring simulation analysis to determine the optimal position. Similarly, the velocity and temperature of the injected cooling air, as well as the diameter and number of cooling ducts, all affect the convection effect of the chimney effect. Comparison of convection effects under different boundary conditions is necessary to determine the optimal result.

[0079] In this embodiment, taking a simplified scaled-down model of a selected unit catalyst column as an example, the gas flowing through the fluid domain is air, the temperature of the gas entering the catalyst column module is 320℃, and the temperature of the gas blown out of the purge nozzle is 300℃; the velocity of the gas entering the catalyst column is 3.5m / s, and the pressure of the purge gas is 600kPa; the velocity of the cold air blown out of the duct is 3.5m / s, and the temperature is 25℃; the unit catalyst column size is 150mm*150mm, and the length is 800mm; the diameter of the purge pipe is 25mm, the diameter of the purge pipe nozzle is 1.25mm, and the installation position is 40mm from the bottom of the catalyst and 55mm from the left side. The catalyst has a depth of 75mm, a length of 200mm, a nozzle height of 12mm, and a nozzle distance of 15mm from the bottom of the catalyst. The catalyst pores have a diameter of 30mm, a spacing of 8.2mm, a wall thickness of 1.4mm, a total of 16 pores, and a porosity of 0.64. The cold air duct has a diameter of 45mm, a length of 200mm, and is installed 25mm from the top of the catalyst and 75mm from the right side. All pipes are made of No. 20 steel with a thermal conductivity of 48 W / m·°C and a specific heat capacity of 0.473 KJ / Kg°C. The inlet and outlet areas of the fluid domain are both 150mm x 150mm, and the height is 1600mm. A geometric model was created using Space Claim, imported into ICEM, and meshed using ICEM to create an unstructured mesh. Simultaneously, the fluid domain was created. After meshing, the mesh file was imported into Ansys Fluent, and different boundary conditions were set in Fluent for solving. Based on the final exported data, as well as pressure cloud maps, the quality of the convection effect is judged, and the design is refined accordingly.

[0080] Implementation Cases

[0081] Case 1: Without adding a cooling duct, when gas flows through the catalyst channel, the average wall shear stress inside the catalyst column channel is 0.0866 Pa according to simulation calculations.

[0082] Case 2: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 45mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channel, the average wall shear stress inside the catalyst column channel is 0.1284pa according to the simulation calculation.

[0083] Case 3: In such Figure 2At the location shown (0mm from the top of the catalyst column and 25mm from the right side), a cold air duct (45mm in diameter and 200mm in length) is added. The relevant parameters for the cold air are set (temperature 25℃ and gas flow rate 3.5m / s). When the gas flows through the catalyst channel, the average wall shear stress inside the catalyst column channel is 0.1003pa according to the simulation calculation.

[0084] Case 4: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1423pa according to the simulation calculation.

[0085] Case 5: In such Figure 2 At the location shown (50mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.0953pa according to the simulation calculation.

[0086] Case 6: In such Figure 2 At the location shown (75mm from the top of the catalyst column and 105mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.0930pa according to the simulation calculation.

[0087] Case 7: In such a way Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (65mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1452pa according to the simulation calculation.

[0088] Case 8: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 55℃, gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1176pa according to the simulation calculation.

[0089] Case 9: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 85℃ and gas flow rate 3.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1084pa according to the simulation calculation.

[0090] Case 10: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 6.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1123pa according to the simulation calculation.

[0091] Case 11: In such Figure 2 At the location shown (25mm from the top of the catalyst column and 75mm from the right side), a cold air duct (45mm in diameter and 200mm in length) was added. The relevant parameters for the cold air were set (temperature 25℃, gas flow rate 9.5m / s). When the gas flows through the catalyst channels, the average wall shear stress inside the catalyst column channels is 0.1042pa according to the simulation calculation.

[0092] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An online purging device for flue gas denitrification catalyst, comprising a housing, a flue gas inlet box and a flue gas outlet box disposed on the housing; A medium-temperature denitrification catalytic bed is provided in the shell near the flue gas inlet box, and a low-temperature denitrification catalytic bed is provided in the shell near the flue gas outlet box. A purge pipe is respectively provided inside the shell corresponding to the medium-temperature denitrification catalytic bed and the low-temperature denitrification catalytic bed; characterized in that: A cold air duct is installed in the shell section containing the medium-temperature denitrification catalyst bed. The cold air duct is installed at a distance of 0~75mm from the top of the catalyst column and 25~105mm from the right side. When the gas flows through the catalyst channel, the average wall shear stress inside the catalyst column channel is 0.093pa~0.146pa. Hot air ducts are installed in the shell section containing the low-temperature denitrification catalytic bed; The cold air duct (2) and the hot air duct (3a) are respectively connected to an air source; the air source is a compressed air tank (1) or a blower; The hot air duct passes through the inside of the housing for heat exchange, and its outlet air temperature is higher than that of the cold air duct. The housing is provided with an inverted U-shaped flue gas flow channel; The purging pipe has nozzles that are aligned with the flue gas to purge the catalyst.

2. The online purging device for flue gas denitrification catalyst according to claim 1, characterized in that: The cold air duct and the hot air duct are connected to an air source via a tee, and control valves are respectively installed on the cold air duct and the hot air duct.

3. The online purging device for flue gas denitrification catalyst according to claim 1, characterized in that: A hot air heat exchange pipe connected to the hot air pipe is installed inside the flue gas inlet box. Or / and, the hot air heat exchange tube has a spiral winding structure.

4. The online purging device for flue gas denitrification catalyst according to claim 1, characterized in that: An air distribution cylinder is provided on the side wall of the housing, which is connected to the interior of the housing. The hot air pipe is connected to the air distribution cylinder and is equipped with a solenoid valve that is adjusted and controlled by a controller.

5. The online purging device for flue gas denitrification catalyst according to any one of claims 1 to 4, characterized in that: Design methods for cold air ducts; To determine the strength of the convection effect, a physical quantity—wall shear stress—is introduced to characterize the intensity of the chimney effect under different conditions; its specific expression is as follows: V—The shear force acting on the calculated section; A — Calculate the cross-sectional area; b—width of the cross section; h—height of the cross section; Under turbulent conditions, the continuity equation is: In the formula, ui is the time-averaged velocity component of the fluid in the xi direction; ρ is the fluid density; and xi is the spatial coordinate system. The catalyst column adopts a porous media model, and the influence of the solid on the fluid is considered by parameters such as the flow resistance added to the fluid and the diffusion coefficient in the modified conservation equation; the single-phase flow conservation equations in the porous media model are as follows; In the formula, ρ, u, and ε represent the fluid density, actual flow velocity, and porous medium porosity, respectively, with the porous medium porosity ε determined based on the geometry of the catalyst column; P is the pressure; Γm is the momentum diffusion coefficient; g is the gravitational acceleration; and Rf is the porous medium resistance source term. The momentum equation for the porous medium model is superimposed with a velocity-dependent momentum source term, expressed as follows: In the formula: Si is the source term of the momentum equation; μ is the dynamic viscosity; v is the velocity value; D and C are specified matrices; the first term is the viscous drag loss, and the second term is the inertial drag loss; The calculation results guide the design of the cooling duct. The gas will accelerate its flow within the catalyst column channels, providing gaseous power for blowing away sticky dust. At the same time, the convection effect caused by placing the cooling duct in different positions will also vary, and the optimal position needs to be determined based on the simulation results. Similarly, the speed and temperature of the cold air being blown in, as well as the diameter and number of the cold air ducts, all affect the convection effect caused by the chimney effect. It is necessary to compare the convection effects under different boundary conditions to determine the optimal result.

6. The online purging device for flue gas denitrification catalyst according to claim 5, characterized in that: The cooling air duct is configured with the following parameters: temperature 25℃ and gas flow rate 3.5m / s.

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