Internal structure and design method of an SCR denitrification system

Abstract

The present invention relates to an internal structure of an SCR denitrification system and a design method thereof. The structure includes a flue gas inlet and outlet connected by a first horizontal channel, a first vertical channel, a second horizontal channel, and a second vertical channel. An ammonia injection grid, a mixer, a rectifying grid, and a catalyst bed are sequentially arranged between the flue gas inlet and the flue gas outlet. A first flow guide is installed in the first horizontal channel, a second flow guide is installed at the first straight bend, a third flow guide is installed at the second straight bend, and a fourth flow guide is installed at the third straight bend. The rectifying grid is located between the fourth flow guide and the catalyst bed. The fourth flow guide includes a plurality of arc-shaped guide plates of equal size and equidistant spacing, each with guide holes formed on the arc-shaped guide plates. Compared with the prior art, the present invention can optimize the flue gas flow direction, improve the uniformity of flue gas distribution on the upper layer of the catalyst bed, prevent localized excessive erosion of the catalyst bed, and improve denitrification efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of denitration in coal-fired power plants, and in particular to an internal structure of an SCR denitration system and a design method thereof. Background Art

[0002] SCR selective catalytic reduction denitrification technology is widely used in the production process of large coal-fired power plants. SCR denitrification devices have the characteristics of high denitrification rate, relatively mature technology and no secondary pollution to the environment. The factors that have a decisive influence on the denitrification efficiency in SCR denitrification devices include the flue gas flow field, the mixing effect of the reducing agent and the distributed temperature field. These factors will affect the long-term safe and stable operation of the denitrification device.

[0003] Current denitrification systems commonly suffer from uneven NH3 concentration and velocity distribution, leading to varying degrees of catalyst wear and reduced denitrification efficiency. The use of guide plates enhances flow uniformity and improves flue gas flow direction, making the flow field above the catalyst bed uniform. This not only ensures NOx removal efficiency, but also reduces local flue gas velocity, minimizing erosion of the catalyst bed and extending catalyst life.

[0004] By searching the existing technologies, it was found that the existing guide plate arrangement mainly changes the arrangement position of the guide plate. Although it can improve part of the flow field, after actual operation after installation, there is still the problem of flue gas gathering on the side near the flue, which makes the flue gas flow field above the catalyst bed and between the guide plate have a large velocity deviation, resulting in local excessive erosion of the catalyst bed, affecting the service life of the catalyst and reducing the denitrification efficiency. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide an internal structure of an SCR denitrification system and a design method thereof. By improving the guide plate structure, the deviation of the flue gas velocity flow field in the area above the catalyst bed and between the guide plates is reduced, thereby avoiding local excessive erosion of the catalyst bed, extending the service life of the catalyst, and improving the denitrification efficiency.

[0006] The objectives of the present invention can be achieved by the following technical solutions: an internal structure of an SCR denitration system, comprising a flue gas inlet and a flue gas outlet, wherein an ammonia injection grid, a mixer, a rectifying grid and a catalyst bed are sequentially arranged between the flue gas inlet and the flue gas outlet, the flue gas inlet is connected to the flue gas outlet through a first horizontal channel, a first vertical channel, a second horizontal channel and a second vertical channel, the first horizontal channel is connected to the first vertical channel through a first straight bend, the first vertical channel is connected to the second horizontal channel through a second straight bend, the second horizontal channel is connected to the second vertical channel through a third straight bend, and the second vertical channel is connected to the flue gas outlet;

[0007] A first guide device is installed in the first horizontal channel, a second guide device is installed at the first straight bend position, the ammonia injection grid and the mixer are both installed in the first vertical channel, and the mixer is located above the ammonia injection grid. A third guide device is installed at the second straight bend position, and a fourth guide device is installed at the third straight bend position. The rectifying grid and the catalyst bed are both installed in the second vertical channel, and the rectifying grid is located between the fourth guide device and the catalyst bed. The fourth guide device includes a plurality of arc-shaped guide plates of the same size and equally spaced, and guide holes are provided on the arc-shaped guide plates.

[0008] Furthermore, the arc radius of the arc guide plate is 600 mm and the arc angle is 90°.

[0009] Furthermore, the upper end of the arc-shaped guide plate is connected to a horizontal straight plate, and the lower end of the arc-shaped guide plate is connected to a vertical tail wing.

[0010] Furthermore, the length of the horizontal straight plate is 100 mm, and the length of the vertical tail wing is 500 mm.

[0011] Furthermore, the arc-shaped guide plate is provided with a plurality of guide holes at equal intervals.

[0012] Furthermore, the diameter of the guide hole is 60 mm.

[0013] Furthermore, the arc-shaped guide plate is made of high-temperature resistant material.

[0014] Furthermore, the first guide device includes a plurality of parallel guide plates parallel to each other in the vertical direction.

[0015] A method for designing the internal structure of an SCR denitration system comprises the following steps:

[0016] S1. Construct a simulation model corresponding to the internal structure of the SCR denitration system. In this case, no diversion holes are provided on the multiple curved plates of the fourth diversion device. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth diversion device is obtained through numerical simulation, and the initial flue gas velocity deviation value is determined.

[0017] S2. For the fourth guide device, guide holes are sequentially and evenly spaced on the first curved guide plate near the inner side of the third straight bend. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth guide device is sequentially obtained through numerical simulation, that is, multiple corresponding flue gas velocity deviation values ​​are obtained. If any of the multiple flue gas velocity deviation values ​​is less than or equal to a preset deviation value, the guide hole arrangement scheme corresponding to the flue gas velocity deviation value is the optimized scheme for the internal structure. Otherwise, proceed to step S3.

[0018] S3. For the fourth guide device, starting from the second curved guide plate near the inner side of the third straight bend, guide holes are opened at equal intervals on each curved guide plate in sequence, and multiple corresponding flue gas velocity deviation values ​​are obtained in sequence through numerical simulation until a flue gas velocity deviation value that is less than or equal to the preset deviation value is obtained. The guide hole opening scheme corresponding to the flue gas velocity deviation value is the optimization scheme of the internal structure.

[0019] Furthermore, the preset deviation value is specifically 15%.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The present invention is designed to punch holes in the arc-shaped guide plate above the rectifier grid in the internal structure of the SCR denitrification system, and the guide holes are mainly opened on the arc-shaped guide plate near the inner side of the third straight bend, which can effectively disperse the high-speed flue gas at the front side of the flue. The windward surface of the guide holes on the guide plate surface can instantly change the movement direction of the high-speed flue gas, causing the high-speed area at the front side of the flue to shift toward the rear side of the flue, making the velocity field of the flue gas in the area between the catalyst bed and the guide plate more evenly distributed, avoiding local erosion of the catalyst bed by the high-speed flue gas at the front side of the flue, thereby extending the service life of the catalyst and improving the denitrification efficiency.

[0022] 2. The present invention optimizes the design of the diversion hole opening scheme by combining a simulation model with numerical simulation, which can intuitively and accurately analyze the flow field distribution of the internal structure of the SCR denitrification system. Without changing the actual internal structure of the denitrification system, the diversion hole opening scheme can be quickly and accurately obtained, thereby improving the efficiency of the optimization design of the internal structure of the SCR denitrification system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the internal structure of the SCR denitration system of the present invention;

[0024] Figure 2 Schematic diagram of the three-dimensional structure of the arc-shaped guide plate of the fourth guide device in the embodiment;

[0025] Figure 3 Schematic diagram of the cross-sectional structure of the arc-shaped guide plate of the fourth guide device in the embodiment;

[0026] Explanation of the marks in the figure: 1. Flue gas inlet end, 21. First guide device, 22. Second guide device, 23. Third guide device, 24. Fourth guide device, 3. Ammonia injection grid, 4. Mixer, 5. Rectifier grid, 6. Catalyst bed, 7. Flue gas outlet end. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Example

[0029] like Figure 1 As shown, an internal structure of an SCR denitration system includes a flue gas inlet end 1 and a flue gas outlet end 7. An ammonia injection grid 3, a mixer 4, a rectifying grid 5, and a catalyst bed 6 are sequentially arranged between the flue gas inlet end 1 and the flue gas outlet end 7. The flue gas inlet end 1 is connected to the flue gas outlet end 7 through a first horizontal channel, a first vertical channel, a second horizontal channel, and a second vertical channel. The first horizontal channel is connected to the first vertical channel through a first straight bend, the first vertical channel is connected to the second horizontal channel through a second straight bend, the second horizontal channel is connected to the second vertical channel through a third straight bend, and the second vertical channel is connected to the flue gas outlet end;

[0030] A first guide device 21 is installed in the first horizontal channel, a second guide device 22 is installed at the first straight bend position, the ammonia injection grid 3 and the mixer 4 are both installed in the first vertical channel, and the mixer 4 is located above the ammonia injection grid 3. A third guide device 23 is installed at the second straight bend position, and a fourth guide device 24 is installed at the third straight bend position. The rectifying grid 5 and the catalyst bed 6 are both installed in the second vertical channel, and the rectifying grid 5 is located between the fourth guide device 24 and the catalyst bed 6. Among them, the first guide device 21 includes a plurality of parallel guide plates parallel to each other in the vertical direction, and the second guide device 22 and the third guide device 23 are both composed of a plurality of arc-shaped guide plates, and the number of arc-shaped guide plates of the second guide device 22 is less than the number of arc-shaped guide plates of the third guide device 23.

[0031] like Figure 2 As shown, the fourth flow guide device 24 comprises a plurality of equally sized, equally spaced arcuate flow guide plates. The arcuate flow guide plate located near the inner side of the third straight bend has flow guide holes. In this embodiment, the diameter of the flow guide holes is 60 mm, the center spacing of the holes is 80 mm, and 11 flow guide holes are provided on each arcuate flow guide plate.

[0032] In this embodiment, Figure 3 As shown, nine identically sized curved guide plates made of high-temperature-resistant material are installed at the third straight bend, above the rectifying grid at the third straight bend. Each of these nine curved guide plates is a 90-degree arc with a radius of 600mm. Each of these nine curved guide plates is connected to a 100mm-long horizontal straight plate at its upper end and a 500mm-long vertical tail at its lower end, further improving the even distribution of flue gas.

[0033] The present invention mainly designs a hole for the arc-shaped guide plate at the third straight bend position, so as to achieve uniform velocity distribution at the front side of the flue and an optimal uniform flow field at the rear side of the flue through the holes, so that the denitrification system can adapt to the changing characteristics of the working conditions in the flue, improve the denitrification efficiency, and reduce catalyst wear, blockage and ammonia escape effects.

[0034] In practical applications, the present invention mainly determines the optimal diversion hole opening scheme by constructing a simulation model and combining it with numerical simulation. The specific process is as follows:

[0035] S1. Construct a simulation model corresponding to the internal structure of the SCR denitration system. In this case, no diversion holes are provided on the multiple curved plates of the fourth diversion device. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth diversion device is obtained through numerical simulation, and the initial flue gas velocity deviation value is determined.

[0036] S2. For the fourth guide device, guide holes are sequentially and evenly spaced on the first curved guide plate near the inner side of the third straight bend. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth guide device is sequentially obtained through numerical simulation, that is, multiple corresponding flue gas velocity deviation values ​​are obtained. If any of the multiple flue gas velocity deviation values ​​is less than or equal to a preset deviation value, the guide hole arrangement scheme corresponding to the flue gas velocity deviation value is the optimized scheme for the internal structure. Otherwise, proceed to step S3.

[0037] S3. For the fourth guide device, starting from the second curved guide plate near the inner side of the third straight bend, guide holes are opened at equal intervals on each curved guide plate in sequence, and multiple corresponding flue gas velocity deviation values ​​are obtained in sequence through numerical simulation until a flue gas velocity deviation value that is less than or equal to the preset deviation value is obtained. The guide hole opening scheme corresponding to the flue gas velocity deviation value is the optimization scheme of the internal structure.

[0038] In this embodiment, the preset deviation value is specifically 15%.

[0039] The perforated arc guide plate device obtained through optimized design can optimize and analyze the NOx concentration and velocity deviation under different working conditions, effectively improve the uneven distribution of gas velocity, and improve the uniformity of the flue gas flow field in front of the catalyst, thereby reducing the wear and deactivation of the catalyst bed, extending the service life of the catalyst, and ensuring the efficiency of the SCR denitrification device.

[0040] In summary, the present invention provides an internal structure of a guide plate and a design method thereof for improving the uniformity of the flow field of an SCR denitration system. By combining numerical simulation with a cold simulation model, the existing denitration system is numerically simulated, the flow field distribution is analyzed, and the drilling optimization simulation of the arc-shaped guide plate above the catalyst bed is performed. After continuously improving the flow field distribution, the optimal drilling scheme is determined. This design method can reduce engineering construction and financial investment without changing the existing guide plate layout of the denitration system. It can achieve the effect of uniform velocity field distribution in order to address the problem of excessive velocity at the front side of the flue caused by long-term use of dust accumulation in the denitration system. It can also avoid local excessive erosion of the catalyst bed and extend the service life of the catalyst.

[0041] By punching holes in the arc-shaped guide plate above the rectifier grid in the denitrification system, not only can the gas flow direction be optimized, but the velocity at the front of the flue can also be more evenly distributed to the rear of the flue through the pores, thereby achieving an optimal uniform flow field and enabling the denitrification system to adapt to the changing operating conditions in the boiler flue, thereby reducing the wear and deactivation, blockage and ammonia escape effects of the catalyst layer, effectively extending the service life of the catalyst, and improving the denitrification efficiency. Without the need for major changes to the existing boiler flue, it meets the requirements of environmental protection, economy, safety, and energy saving.

Claims

1. A method for designing the internal structure of an SCR denitrification system, characterized in that: The internal structure of the SCR denitration system comprises a flue gas inlet end (1) and a flue gas outlet end (7), wherein an ammonia injection grid (3), a mixer (4), a rectifying grid (5) and a catalyst bed (6) are sequentially arranged between the flue gas inlet end (1) and the flue gas outlet end (7), wherein the flue gas inlet end (1) is connected to the flue gas outlet end (7) via a first horizontal channel, a first vertical channel, a second horizontal channel and a second vertical channel, wherein the first horizontal channel is connected to the first vertical channel via a first straight bend, the first vertical channel is connected to the second horizontal channel via a second straight bend, the second horizontal channel is connected to the second vertical channel via a third straight bend, and the second vertical channel is connected to the flue gas outlet end (7); A first flow guide device (21) is installed in the first horizontal channel, a second flow guide device (22) is installed at the first straight bend position, the ammonia injection grid (3) and the mixer (4) are both installed in the first vertical channel, the mixer (4) is located above the ammonia injection grid (3), a third flow guide device (23) is installed at the second straight bend position, a fourth flow guide device (24) is installed at the third straight bend position, the rectifying grid (5) and the catalyst bed (6) are both installed at the second straight bend position. In the vertical channel, the rectifying grid (5) is located between the fourth guide device (24) and the catalyst bed (6), and the fourth guide device (24) includes a plurality of arc-shaped guide plates of the same size and distributed at equal intervals, wherein a plurality of equally spaced guide holes are opened on the arc-shaped guide plate close to the inner side of the third straight bend, the arc radius of the arc-shaped guide plate is 600 mm, the arc angle is 90°, the upper end of the arc-shaped guide plate is connected to a horizontal straight plate, and the lower end of the arc-shaped guide plate is connected to a vertical tail wing; The design method of the internal structure of the SCR denitrification system includes the following steps: S1. Construct a simulation model corresponding to the internal structure of the SCR denitration system. In this case, no diversion holes are provided on the multiple curved plates of the fourth diversion device. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth diversion device is obtained through numerical simulation, and the initial flue gas velocity deviation value is determined. S2. For the fourth guide device, guide holes are sequentially and evenly spaced on the first curved guide plate near the inner side of the third straight bend. The flow field distribution of the flue gas in the area between the catalyst bed and the fourth guide device is sequentially obtained through numerical simulation, that is, multiple corresponding flue gas velocity deviation values ​​are obtained. If any of the multiple flue gas velocity deviation values ​​is less than or equal to a preset deviation value, the guide hole arrangement scheme corresponding to the flue gas velocity deviation value is the optimized scheme for the internal structure. Otherwise, proceed to step S3. S3. For the fourth guide device, starting from the second curved guide plate near the inner side of the third straight bend, guide holes are opened at equal intervals on each curved guide plate in sequence, and multiple corresponding flue gas velocity deviation values ​​are obtained in sequence through numerical simulation until a flue gas velocity deviation value that is less than or equal to the preset deviation value is obtained. The guide hole opening scheme corresponding to the flue gas velocity deviation value is the optimization scheme of the internal structure.

2. The method for designing the internal structure of an SCR denitration system according to claim 1, characterized in that: The length of the horizontal straight plate is 100 mm, and the length of the vertical tail wing is 500 mm.

3. The method for designing the internal structure of an SCR denitration system according to claim 1, characterized in that: The diameter of the guide hole is 60 mm.

4. The method for designing the internal structure of an SCR denitration system according to claim 1, characterized in that: The arc-shaped guide plate is made of high-temperature resistant material.

5. The method for designing the internal structure of an SCR denitration system according to claim 1, characterized in that: The first flow guiding device (21) comprises a plurality of parallel flow guiding plates parallel to each other in a vertical direction.

6. The method for designing the internal structure of an SCR denitration system according to claim 1, characterized in that: The preset deviation value is specifically 15%.

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