Ammonia injection device and ammonia injection mixing device suitable for SCR denitration

Abstract

The application discloses a kind of suitable for SCR denitration ammonia injection device and device, including ammonia injection pipe and the ammonia injection port of setting at ammonia injection pipe end, ammonia injection pipe includes ammonia main pipeline, branch pipeline and branch pipeline;Along ammonia main pipeline circumferential direction, equidistantly there are several branch pipelines;In branch pipeline, equidistantly and parallelly there are several vertical branch pipeline branch pipelines;Several branch pipelines are in the same plane, plane vertical branch pipeline;In branch pipeline, there is vertical plane ammonia injection port;Ammonia injection port gas outlet direction is same with ammonia main pipeline inner gas flow direction.The ammonia injection device suitable for SCR denitration designed in the application, including branch pipeline and branch pipeline, ammonia injection pipeline because each part branch pipe length is small, and the difference of branch pipeline diameter is not big, so it can reduce the flow resistance of ammonia in pipeline.

Description

Technical Field

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

[0002] To meet environmental protection requirements, most coal-fired power units have adopted the widely used selective reduction (SCR) denitrification technology.

[0003] The principle of SCR denitrification is to use ammonia (NH3) and other reducing agents, under the action of a catalyst, to remove nitrogen oxides (NOx) from the flue gas. x NH3 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.

[0004] In the existing technology, the common ammonia-flue gas homogenization device is an ammonia injection grid equipped with a circular nozzle and a flow guide plate for turbulence. The process is simple, but the ammonia injection resistance is large, the ammonia-flue gas mixing efficiency is low, and it is difficult to achieve a match between the ammonia quantity and the flue gas quantity.

[0005] 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

[0006] 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.

[0007] This invention discloses an ammonia injection device suitable for SCR denitrification, including an ammonia injection pipe and an ammonia nozzle disposed at the end of the ammonia injection pipe. The ammonia injection pipe includes a main ammonia pipeline, branch pipelines, and sub-pipelines. Several branch pipelines are provided at equal intervals along the circumferential direction of the main ammonia pipeline.

[0008] On the main pipeline, a plurality of branch pipelines perpendicular to the main pipeline are arranged at equal intervals and parallel to each other; the plurality of branch pipelines are located in the same plane, and the plane is perpendicular to the main pipeline.

[0009] On the branch pipeline, there is an ammonia nozzle perpendicular to the plane; the direction of gas outlet of the ammonia nozzle is the same as the direction of gas flow in the main ammonia pipeline.

[0010] Furthermore, the ratio of the diameter of the main ammonia pipeline to the diameter of the branch pipeline is 2:1.

[0011] Furthermore, the length of the branch pipe is the same as the length of the sub-pipe; the ratio of the diameter of the branch pipe to the diameter of the sub-pipe is 1.6:1.

[0012] Furthermore, four branch pipelines are provided at equal intervals along the circumference of the main ammonia pipeline.

[0013] Furthermore, on the branch pipeline, three sets of branch pipelines perpendicular to the branch pipeline are arranged at equal intervals and parallel to each other, and an ammonia nozzle is arranged at equal intervals on the branch pipeline.

[0014] Furthermore, the branch pipeline includes a first branch pipeline, a second branch pipeline, a third branch pipeline, and a fourth branch pipeline;

[0015] The first branch pipe is provided with a first branch pipe; the second branch pipe is provided with a second branch pipe; the third branch pipe is provided with a third branch pipe; and the fourth branch pipe is provided with a fourth branch pipe.

[0016] The first branch pipe is parallel to the third branch pipe and perpendicular to the second branch pipe; the second branch pipe is parallel to the fourth branch pipe.

[0017] The present invention also discloses an ammonia injection mixing device suitable for SCR denitrification, comprising an ammonia injection device based on the above-mentioned ammonia injection device 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] Furthermore, the length of the ammonia-flue gas mixing baffle is the same as the length of the branch pipe of the ammonia injection device; the width of the ammonia-flue gas mixing baffle is the same as the diameter of the branch pipe of the ammonia injection device.

[0019] The beneficial effects of this invention are:

[0020] 1. The ammonia injection device for SCR denitrification designed in this invention includes a main pipeline and branch pipelines, which are similar to the shape of a swastika. Because the length of each branch pipeline is small and the difference in pipe diameter between the main pipeline and the branch pipeline is not large, the flow resistance of ammonia in the pipeline can be reduced.

[0021] 2. The ammonia injection device designed in this invention for SCR denitrification has a uniform and vertically distributed main ammonia pipeline and branch pipelines. Therefore, the amount of ammonia entering the branch pipeline from the main pipeline is basically equal, the pipeline resistance is small, and the amount of ammonia at each nozzle is nearly consistent. Moreover, the nozzles are arranged closer to the perimeter of the flue, which can increase the ammonia concentration around the perimeter.

[0022] 3. The ammonia injection device for SCR denitrification designed in this invention has a cross-sectional arrangement of adjacent branch pipes, resulting in an overall velocity difference and creating a transverse vortex in the flue, which can enhance the mixing effect of ammonia and flue gas and improve the denitrification efficiency.

[0023] 4. The ammonia injection mixing device designed in this invention is suitable for SCR denitrification. The ammonia-flue gas mixing baffle corresponds to the ammonia injection pipeline. The negative pressure behind the baffle can be used to form a reflux zone, thereby enhancing the disturbance of ammonia and flue gas and improving the mixing uniformity of ammonia and flue gas.

[0024] 5. The ammonia injection mixing device designed in this invention for SCR denitrification is simple in structure, low in cost, and easy to implement, requiring no complex operation. The ammonia injection device and the ammonia-flue gas mixing baffle are arranged in a crisscross pattern on adjacent branch pipes, with the high-speed ammonia injection zone and the low-speed flue gas zone intersecting, generating lateral turbulent swirling flow. This ensures a uniform concentration distribution of ammonia and flue gas after a short mixing distance, effectively solving the problem of poor initial 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. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the ammonia injection mixing device applicable to SCR denitrification in this invention.

[0026] Figure 2 This is a schematic diagram of the overall structure of the ammonia injection device applicable to SCR denitrification in this invention.

[0027] Figure 3 This is a schematic diagram of the pipeline distribution of the ammonia injection device in this invention;

[0028] 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.

[0029] Figure 5 This is a graph showing the relationship between ammonia concentration and mixing distance in the device of the present invention.

[0030] Figure 6 The following are NH3 velocity cloud maps at a mixing distance of 5m for the ammonia injection device (a) and the conventional grid-type ammonia injection device (b) in a specific embodiment of the present invention. Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings:

[0032] like Figure 2-3 As shown, an ammonia injection device suitable for SCR denitrification includes an ammonia injection pipe and an ammonia nozzle at the end of the ammonia injection pipe. The ammonia injection pipe includes a main ammonia line 1, a branch line 2, and a branch pipe 3. Four branch lines are provided at equal intervals along the circumference of the main ammonia line 1.

[0033] The branch pipeline includes a first branch pipeline 21, a second branch pipeline 22, a third branch pipeline 23 and a fourth branch pipeline 24;

[0034] A first branch pipe 31 is provided on the first branch pipeline 21; a second branch pipe 32 is provided on the second branch pipeline 22; a third branch pipe 33 is provided on the third branch pipeline 23; a fourth branch pipe 34 is provided on the fourth branch pipeline 24;

[0035] The first branch pipe 31 is parallel to the third branch pipe 33 and perpendicular to the second branch pipe 32; the second branch pipe 32 is parallel to the fourth branch pipe 34.

[0036] On the branch pipeline 2, three groups of branch pipelines 3 perpendicular to the branch pipeline are arranged at equal intervals and in parallel, and 6 ammonia injection nozzles are arranged at equal intervals on the branch pipelines. A number of branch pipelines 3 are in the same plane, and the plane is perpendicular to the branch pipeline 4;

[0037] On the branch pipeline 3, an ammonia injection nozzle 4 perpendicular to the plane is provided; the出气方向 of the ammonia injection nozzle is the same as the gas flow direction in the ammonia main pipeline.

[0038] Among them, the ratio of the pipeline diameter of the ammonia main pipeline 1 to the pipeline diameter of the branch pipeline 2 is 2:1. The pipeline length of the branch pipeline 2 is the same as the pipeline length of the branch pipeline 3; the ratio of the pipeline diameter of the branch pipeline 2 to the pipeline diameter of the branch pipeline 3 is 1.6:1.

[0039] Such as Figure 1 、 4 As shown, an ammonia injection mixing device applicable to SCR denitration includes the above-mentioned ammonia injection device applicable to SCR denitration, and an ammonia-gas mixing baffle 5 arranged directly behind the出气方向 of the ammonia injection device and parallel to the branch pipeline; the distance between the ammonia-gas mixing baffle 5 and the ammonia injection device is less than the distance at which the ammonia gas flow rate ejected by the ammonia injection device decays to half.

[0040] The length of the ammonia-gas mixing baffle 5 is the same as the length of the branch pipeline 2 of the ammonia injection device; the width of the ammonia-gas mixing baffle 5 is the same as the pipe diameter of the branch pipeline 2 of the ammonia injection device Embodiment

[0041] Figure 1 As shown is an ammonia injection mixing device applicable to SCR denitration, including an ammonia injection device and an ammonia-gas mixing device. The ammonia-gas mixing device 5 is located 1.5 m downstream of the ammonia injection device and includes a square baffle corresponding to the "卍"-shaped ammonia injection pipeline branch.

[0042] The ammonia injection device is as Figure 1 It should be noted that there is an unclear expression "出气方向" in the original text. It is recommended to clarify this term for a more accurate translation.As shown in the figure, it includes the ammonia injection straight section pipeline 1, the "卍"-shaped branch pipeline 2, the branch pipeline 3, and the circular nozzles 4 on the pipelines. The "卍"-shaped pipeline is composed of 4 groups of exactly the same branch pipelines and the branch pipelines on it. The included angle between adjacent branch pipelines is 90°. 3 branch pipelines extend vertically on the same side of the branch pipeline, and the included angle between them and the branch pipeline is 90°. The distance between the middle of each branch pipeline is 200mm. The length of the branch pipeline is 620mm, and the length of the branch pipeline is 600mm.

[0043] In the "卍"-shaped ammonia injection pipeline, the diameter of the branch pipeline is 50mm, the diameter of the branch pipeline is 30mm, the diameter of the nozzle is 15mm, the length of the straight section pipeline is 1m, and the nozzles are distributed at the same position on 12 branch pipelines. Starting from the connection between each branch pipe and the branch pipeline, the nozzles on the branch pipeline are distributed at 50mm, 150mm, 250mm, 350mm, 450mm, and 550mm from the starting point respectively. There are 6 nozzles on each branch pipeline.

[0044] As Figure 4 shown, the ammonia-gas mixing device is a baffle with a certain thickness, installed downstream of the ammonia injection pipeline, 1.5m away from the ammonia injection pipeline. Its shape is a square baffle corresponding to the branch of the "卍"-shaped ammonia injection pipeline. The size of each corresponding square baffle is 600×15mm. The negative pressure area behind the baffle is used to form a backflow to intensify the mixing between ammonia and flue gas.

[0045] 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 12.18m / s, the temperature is 613K, and the ammonia inlet velocity is 7.32m / s. The ammonia-gas mixing effects of the ammonia injection device of the present invention and the traditional grid-type ammonia injection device are compared.

[0046] 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 5m is shown in Figure 6 , Figure a shows the ammonia-gas mixing effect of the ammonia injection device of the present invention. The ammonia diffuses relatively fully behind the mixing baffle, and the ammonia distribution is relatively uniform, with a non-uniformity of 5.12%;

[0047] Figure b shows the ammonia-gas mixing effect of the traditional grid-type ammonia injection device. The ammonia diffusion is poor, the ammonia distribution is significantly non-uniform, the ammonia concentration is large directly opposite the ammonia injection grid, and the ammonia concentration is very small in other areas. Its ammonia non-uniformity is 16.75%.

[0048] 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.

[0049] 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 mixing device applicable to SCR denitration, comprising an ammonia injection device and an ammonia-gas mixing baffle arranged directly behind the outlet direction of the ammonia injection device, characterized in that: The ammonia injection device includes a main ammonia pipeline, four branch pipelines equidistantly arranged along the circumferential direction of the main ammonia pipeline, and branch pipelines arranged on the branch pipelines; The included angles between adjacent branch pipelines are all 90°; On the same side of each branch pipeline, three groups of branch pipelines perpendicular to the branch pipeline are equidistantly and parallelly arranged, and each branch pipeline is in the same plane, and the plane is perpendicular to the branch pipeline; Six ammonia nozzles are equidistantly arranged on each branch pipeline, the ammonia nozzles are perpendicular to the plane, and the outlet direction of the ammonia nozzles is the same as the gas flow direction in the main ammonia pipeline; The branch pipelines include a first branch pipeline, a second branch pipeline, a third branch pipeline and a fourth branch pipeline; A first branch pipe is provided on the first branch pipeline, a second branch pipe is provided on the second branch pipeline, a third branch pipe is provided on the third branch pipeline, and a fourth branch pipe is provided on the fourth branch pipeline; The first branch pipe is parallel to the third branch pipe and perpendicular to the second branch pipe; the second branch pipe is parallel to the fourth branch pipe; The ammonia-gas mixing baffle is arranged parallel to the branch pipeline and is a square baffle corresponding to the branch pipes of the "卍"-shaped ammonia injection pipeline; The distance between the ammonia-gas mixing baffle and the ammonia injection device is less than the distance at which the ammonia gas flow rate ejected from the ammonia injection device decays to half.

2. The ammonia injection mixing device for SCR denitrification according to claim 1, characterized in that: The length of the ammonia-gas mixing baffle is the same as the length of the branch pipeline; the width of the ammonia-gas mixing baffle is the same as the pipe diameter of the branch pipeline.

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