An ammonia injection device and an ammonia injection mixing device suitable for SCR denitration

Abstract

The application discloses a kind of ammonia injection device and device suitable for SCR denitration, ammonia injection pipeline designed in the application can reduce the flow resistance of ammonia in pipeline due to the length of each partial branch pipe section is small, and the diameter difference of branch pipe is not big;The main pipe and branch pipe are evenly distributed vertically, the amount of ammonia entering the branch pipe is basically equal, and the pipeline resistance is small, so that the amount of ammonia at the first four nozzles of the branch pipe close to the main pipe is close to consistent, the diameter of the two nozzles close to the edge increases once, the nozzle arrangement is closer to the flue around, which can improve the ammonia concentration around;At the same time, due to the diameter of the nozzle close to the edge is larger, the overall speed difference appears, which causes transverse cyclone in the flue, and can enhance the mixing effect of ammonia and flue gas;Compared with the existing design, the ammonia-flue gas mixing device is divided into four parts by 360°, the application can mix the flue gas at the corners with NH3 well, and improve the denitration efficiency.

Description

Technical Field

[0001] This invention is applied to the field of flue gas denitrification technology for power plant boilers, specifically relating to an ammonia injection device and an ammonia mixing device suitable for SCR denitrification. Background Technology

[0002] The principle of SCR denitrification is to use reducing agents such as ammonia (NH3) and a catalyst to remove nitrogen oxides (NOx) from flue gas. x It is converted into nitrogen N2, which is non-toxic and harmless to the environment. In the SCR denitrification process, the mixing of NH3 with flue gas is one of the most important process technologies. The uniformity of the mixing determines the denitrification efficiency and also affects the safe and stable operation of the downstream air preheater.

[0003] In the existing technology, the common ammonia-flue gas homogenization device is an ammonia injection grid equipped with a circular nozzle or an ammonia injection grid that divides 360° into four equal parts at 90° intervals and is combined with a baffle plate to turbulence. The process is simple, but the ammonia injection of these two types of ammonia injection grids is uneven, the ammonia and flue gas mixing efficiency is low, and it is difficult to achieve a match between the ammonia quantity and the flue gas quantity.

[0004] Therefore, there is an urgent need in this field to design an ammonia injection mixing device to ensure that ammonia gas is fully mixed with flue gas. Summary of the Invention

[0005] The purpose of this invention is to provide an ammonia injection device and an ammonia mixing device suitable for SCR denitrification that can solve the above-mentioned problems, enhance the uniform mixing effect of ammonia and flue gas in a shorter flue, and reduce ammonia injection resistance.

[0006] This invention discloses an ammonia injection device suitable for SCR denitrification, comprising a square ammonia injection straight pipeline, an ammonia injection pipe disposed within the ammonia injection straight pipeline, and an ammonia injection port disposed at the end of the ammonia injection pipe. The ammonia injection pipe includes a diagonal ammonia injection pipe disposed along the diagonal of the ammonia injection straight pipeline and a conventional ammonia injection pipe perpendicular to the inner wall of the ammonia injection straight pipeline; a plurality of ammonia direct injection ports are uniformly disposed on the diagonal ammonia injection pipe and the conventional ammonia injection pipe.

[0007] The diagonal ammonia nozzle includes a first diagonal ammonia nozzle and a second diagonal ammonia nozzle located in the same plane; an ammonia main pipeline is provided at the intersection of the first diagonal ammonia nozzle and the second diagonal ammonia nozzle.

[0008] The conventional ammonia nozzle includes a vertical ammonia nozzle and a horizontal ammonia nozzle that are in the same plane as the diagonal ammonia nozzle; the vertical ammonia nozzle and the horizontal ammonia nozzle intersect at the main ammonia pipeline.

[0009] Furthermore, with the ammonia main pipeline as the center, ammonia direct injection ports symmetrical about the ammonia main pipeline are provided at equal intervals on the first diagonal ammonia injection pipe, the second diagonal ammonia injection pipe, the vertical ammonia injection pipe, and the horizontal ammonia injection pipe; the diameter of the ammonia direct injection port near the ammonia main pipeline is smaller than the diameter of the ammonia direct injection port far from the ammonia main pipeline.

[0010] Furthermore, each of the first diagonal ammonia spray pipe, the second diagonal ammonia spray pipe, the vertical ammonia spray pipe, and the horizontal ammonia spray pipe is provided with 12 ammonia direct injection nozzles. The four sets of ammonia direct injection nozzles adjacent to the main ammonia pipeline have the same diameter, while the two sets of ammonia direct injection nozzles farther away from the main ammonia pipeline have gradually increasing diameters.

[0011] Furthermore, with the ammonia main pipeline as the center, the diameter of the ammonia direct injection port near the ammonia main pipeline gradually decreases.

[0012] Furthermore, the length of the diagonal ammonia spray pipe and the conventional ammonia spray pipe extends close to the inner wall of the ammonia spray straight pipe.

[0013] Furthermore, the ammonia spray nozzle is a circular pipe.

[0014] Furthermore, the diameter ratio of the main ammonia gas pipeline to the diagonal ammonia gas spray pipe is 2:1;

[0015] The diagonal ammonia nozzle has the same diameter as the conventional ammonia nozzle.

[0016] Furthermore, the ammonia spray nozzle occupies 20-25% of the area of ​​the ammonia spray straight pipeline.

[0017] The present invention also discloses an ammonia injection mixing device suitable for SCR denitrification, including any of the above-mentioned ammonia injection devices suitable for SCR denitrification, and an ammonia-flue gas mixing baffle disposed directly behind the outlet direction of the ammonia injection device and arranged parallel to the branch pipeline; the distance between the ammonia-flue gas mixing baffle and the ammonia injection device is less than the distance at which the ammonia gas flow velocity injected by the ammonia injection device is reduced to half.

[0018] The beneficial effects of this invention are:

[0019] The ammonia injection pipeline designed in this invention has a short length of each branch pipe section and a small difference in the pipe diameter of the branch pipes, which can reduce the flow resistance of ammonia in the pipeline. The main pipe and branch pipes are evenly and vertically distributed, and the amount of ammonia entering the branch pipes is basically equal, resulting in low pipeline resistance. This makes the amount of ammonia at the first four nozzles of the branch pipes close to the main pipe almost the same, and the diameter of the two nozzles near the edge increases one at a time. The nozzles are arranged closer to the perimeter of the flue, which can increase the ammonia concentration around the perimeter.

[0020] Meanwhile, due to the increased diameter of the nozzles near the edges, an overall velocity difference occurs, creating a transverse swirling flow within the flue, which enhances the mixing effect of ammonia and flue gas. Compared to existing designs that divide the 360° into four equal parts, this invention can effectively mix the flue gas and NH3 at the corners, improving denitrification efficiency.

[0021] The ammonia injection mixing device designed in this invention is matched with the ammonia injection device for SCR denitrification. The nozzles near the edge of the branch pipe are the high-speed ammonia injection zone, while the upper part of the mixing device is the low-speed flue gas zone due to gravity. The high-speed ammonia injection zone and the low-speed flue gas zone are arranged in an interleaved manner, generating a lateral turbulent vortex. This allows the concentration distribution of ammonia and flue gas to be uniform after a short mixing distance, effectively solving the problem of poor mixing efficiency between ammonia and flue gas when initially injected into the flue, improving denitrification efficiency, and ensuring the safe and stable operation of the unit. The mixing baffle corresponds to the ammonia injection pipeline, and the negative pressure behind the baffle can be used to form a reflux zone, thereby enhancing the turbulence between ammonia and flue gas and improving the mixing uniformity of ammonia and flue gas.

[0022] The six ammonia nozzles on the branch pipeline have diameters that are initially equal from the center outwards, gradually increasing towards the edges. This design takes into account that for the same flow rate, a larger nozzle diameter results in a faster flow rate, thus increasing the uniformity of the cross-sectional flow velocity. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the ammonia injection mixing device applicable to SCR denitrification in this invention.

[0024] Figure 2 This is a schematic diagram of the overall structure of the ammonia injection device applicable to SCR denitrification in this invention.

[0025] Figure 3 This is a schematic diagram of the pipeline distribution of the ammonia injection device in this invention;

[0026] Figure 4 This is a schematic diagram showing the distribution of the ammonia-flue gas mixing baffles in the ammonia injection mixing device of the present invention.

[0027] Figure 5 This is a graph showing the relationship between ammonia concentration and mixing distance in the device of the present invention.

[0028] Figure 6 The images show the NH3 velocity cloud diagrams at a mixing distance of 5m for the ammonia injection device a and the traditional grid-type ammonia injection device b in a specific embodiment of the present invention. Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings:

[0030] like Figure 1-3As shown, an ammonia injection device suitable for SCR denitrification includes a square ammonia injection straight pipeline 1, an ammonia injection pipe 2 disposed within the ammonia injection straight pipeline 1, and an ammonia nozzle 3 disposed at the end of the ammonia injection pipe 2. The ammonia injection pipe 2 is a circular pipe. The ammonia injection pipe 2 occupies 20-25% of the area of ​​the ammonia injection straight pipeline 1. The ammonia injection pipe 2 includes a diagonal ammonia injection pipe 21 disposed along the diagonal of the ammonia injection straight pipeline 1 and a conventional ammonia injection pipe 22 perpendicular to the inner wall of the ammonia injection straight pipeline 1; a plurality of ammonia direct injection nozzles 3 are uniformly disposed on the diagonal ammonia injection pipe 21 and the conventional ammonia injection pipe 22; the pipe lengths of the diagonal ammonia injection pipe 21 and the conventional ammonia injection pipe 22 extend close to the inner wall of the ammonia injection straight pipeline 1. The diameter ratio of the main ammonia pipeline 20 to the diagonal ammonia injection pipe 21 is 2:1; the diagonal ammonia injection pipe 21 and the conventional ammonia injection pipe 22 have the same diameter.

[0031] The diagonal ammonia nozzle 21 includes a first diagonal ammonia nozzle 211 and a second diagonal ammonia nozzle 212 located in the same plane; an ammonia main pipeline 20 is provided at the intersection of the first diagonal ammonia nozzle 211 and the second diagonal ammonia nozzle 212.

[0032] The conventional ammonia nozzle 22 includes a vertical ammonia nozzle 221 and a horizontal ammonia nozzle 222, which are in the same plane as the diagonal ammonia nozzle 21; the vertical ammonia nozzle 221 and the horizontal ammonia nozzle 222 intersect with the main ammonia pipeline 20.

[0033] Centered on the main ammonia pipeline 20, 12 ammonia direct injection nozzles 3 are provided on the first diagonal ammonia injection pipe 211, the second diagonal ammonia injection pipe 212, the vertical ammonia injection pipe 221, and the horizontal ammonia injection pipe 222. The four sets of ammonia direct injection nozzles 3 adjacent to the main ammonia pipeline 20 have the same diameter, while the two sets of ammonia direct injection nozzles 3 farther away from the main ammonia pipeline 20 have gradually increasing diameters. Example

[0034] Figure 1 The diagram shows an ammonia injection mixing device suitable for SCR denitrification, which includes an ammonia injection device and an ammonia-flue gas mixing device 4, with the ammonia-flue gas mixing device 4 located 2m downstream of the ammonia injection device.

[0035] ammonia injection device, such as Figure 1 As shown, it includes a straight ammonia injection pipeline 1, a diagonal ammonia injection pipe 21, a conventional ammonia injection pipe 22, and a circular ammonia injection nozzle 3 on the pipeline.

[0036] The diagonal ammonia nozzle 21 and the conventional ammonia nozzle 22 are staggered, with the pipelines at a 45° angle. The length of the diagonal ammonia nozzle 21 is 1.41 times the length of the conventional ammonia nozzle 22.

[0037] The diameter of the ammonia injection straight pipeline 1 is 100 mm, the length of the ammonia injection straight pipeline 1 is 1 m, and the diameters of the diagonal ammonia injection pipes 21 and the conventional ammonia injection pipes 22 are 50 mm. The length of each pipeline of the conventional ammonia injection pipe 22 is 600 mm, and the length of each pipeline of the diagonal ammonia injection pipe 21 is 840 mm.

[0038] The ammonia direct injection nozzles 3 are 30 mm, 28 mm, and 26 mm respectively. The distance between the ammonia direct injection nozzles 3 and the diagonal ammonia injection pipes is 50 mm. The nozzles are distributed at the same positions on 8 branch pipelines. The upper nozzles on the positive cross are respectively distributed at 75 mm, 150 mm, 250 mm, 350 mm, 450 mm, and 550 mm from the starting point. The upper nozzles on the inclined cross are respectively distributed at 105 mm, 210 mm, 355 mm, 500 mm, 645 mm, and 790 mm from the starting point. There are 6 nozzles on each single branch pipeline of the positive cross and the inclined cross.

[0039] As Figure 1 and 4 shown, the ammonia - flue gas mixing device is a baffle with a certain thickness, installed downstream of the ammonia injection pipeline, 1.5 m away from the ammonia injection pipeline. Its shape is a square baffle corresponding to the "rice" - shaped ammonia injection pipeline branches. The size of each corresponding square baffle is 600×50 mm. The negative pressure area behind the baffle is used to form a backflow, which intensifies the mixing between ammonia and flue gas.

[0040] As Figure 5 shown, from the curve graph of the relationship between ammonia concentration and mixing distance, it can be obtained that the longer the mixing distance, the lower the non - uniformity of ammonia concentration, the better the mixing degree of ammonia and flue gas, and the more uniform the mixing.

[0041] In this embodiment, a set of square ammonia injection mixing devices and the corresponding SCR flue duct are selected as the computational domain for CFD (Computational Fluid Dynamics) numerical simulation calculation. In the boundary conditions, the flue gas inlet velocity is 12 m / s, the temperature is 600 K, and the ammonia inlet velocity is 7 m / s. The ammonia - flue gas mixing effects of the ammonia injection device of the present invention and the traditional grid - type ammonia injection device are compared.

[0042] When the flue gas inlet velocity and the ammonia inlet velocity are the same, the ammonia concentration distribution cloud diagram at a mixing distance of 5 m is shown in Figure 6 , Figure 6 a, which shows the ammonia - flue gas mixing effect of the ammonia injection device of the present invention. The ammonia diffuses relatively fully behind the mixing baffle, the ammonia distribution is relatively uniform, and the non - uniformity is 4.51%.

[0043] Figure 6b demonstrates the ammonia-flue gas mixing effect of a traditional grid-type ammonia injection device. Its ammonia diffusion is poor and the ammonia distribution is obviously uneven. The ammonia concentration is high at the point directly opposite the ammonia injection grid, while the ammonia concentration is very low in other areas. Its ammonia unevenness is 13.21%.

[0044] Therefore, based on the numerical simulation results, the ammonia injection device of this invention is superior to the traditional ammonia injection method in terms of ammonia-flue gas mixing effect, which can greatly improve denitrification efficiency, reduce ash blockage in the air preheater, and improve the safety and stability of boiler operation.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ammonia injection device suitable for SCR denitrification, comprising a square ammonia injection straight pipeline (1), an ammonia injection pipe disposed within the ammonia injection straight pipeline (1), and an ammonia injection port disposed at the end of the ammonia injection pipe, characterized in that: The ammonia spray pipe (2) includes a diagonal ammonia spray pipe (21) arranged along the diagonal of the ammonia spraying straight pipe (1) and a conventional ammonia spray pipe (22) perpendicular to the inner wall of the ammonia spraying straight pipe (1); a plurality of ammonia direct injection ports (3) are evenly provided on the diagonal ammonia spray pipe (21) and the conventional ammonia spray pipe (22). The diagonal ammonia nozzle (21) includes a first diagonal ammonia nozzle (211) and a second diagonal ammonia nozzle (212) in the same plane; an ammonia main pipeline (20) is provided at the intersection of the first diagonal ammonia nozzle (211) and the second diagonal ammonia nozzle (212); The conventional ammonia nozzle (22) includes a vertical ammonia nozzle (221) and a horizontal ammonia nozzle (222) that are in the same plane as the diagonal ammonia nozzle (21); the vertical ammonia nozzle (221) and the horizontal ammonia nozzle (222) intersect with the main ammonia pipeline (20); with the main ammonia pipeline (20) as the center, ammonia direct injection ports (3) symmetrical about the main ammonia pipeline (20) are provided at equal intervals on the first diagonal ammonia nozzle (211), the second diagonal ammonia nozzle (212), the vertical ammonia nozzle (221), and the horizontal ammonia nozzle (222); the diameter of the ammonia direct injection port (3) near the main ammonia pipeline (20) is smaller than the diameter of the ammonia direct injection port (3) far from the main ammonia pipeline (20); Each of the first diagonal ammonia nozzle (211), the second diagonal ammonia nozzle (212), the vertical ammonia nozzle (221), and the horizontal ammonia nozzle (222) is provided with 12 ammonia direct injection ports (3). The four sets of ammonia direct injection ports (3) adjacent to the main ammonia pipeline (20) have the same diameter, while the two sets of ammonia direct injection ports (3) farther away from the main ammonia pipeline (20) have progressively larger diameters. The diameter ratio of the main ammonia pipeline (20) to the diagonal ammonia nozzle (21) is 2:

1. The diagonal ammonia nozzle (21) has the same diameter as the conventional ammonia nozzle (22). The ammonia nozzle (2) occupies 20-25% of the area of ​​the ammonia injection pipeline (1). With the ammonia main pipeline (20) as the center, the diameter of the ammonia direct injection port (3) near the ammonia main pipeline (20) gradually decreases.

2. The ammonia injection device for SCR denitrification according to claim 1, characterized in that: The lengths of the diagonal ammonia nozzle (21) and the conventional ammonia nozzle (22) extend close to the inner wall of the ammonia injection straight pipe (1).

3. The ammonia injection device for SCR denitrification according to claim 1, characterized in that: The ammonia nozzle (2) is a circular pipe.

4. An ammonia injection mixing device suitable for SCR denitrification, characterized in that: Includes the ammonia injection device for SCR denitrification as described in any of claims 1-3, and an ammonia-flue gas mixing baffle (4) arranged directly behind the outlet direction of the ammonia injection device and parallel to the branch pipe; the distance between the ammonia-flue gas mixing baffle (4) and the ammonia injection device is less than the distance at which the ammonia gas flow velocity of the ammonia injection device decreases to half.

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