Ammonia spraying mixing unit and denitration system using same

Abstract

The invention discloses an ammonia spraying and mixing unit, which is applied to a flue gas denitration system without dust or with low dust content, is mounted in a flue, and comprises a main pipe, an ammonia spraying and mixing unit, an ammonia spraying and mixing unit, an ammonia spraying and mixing unit, an ammonia spraying and mixing unit, an ammonia spraying and mixing unit and an ammonia spraying and mixing unit, and is characterized in that the main pipe is arranged in the flue in the direction vertical to the flue gas flow direction; the plurality of branch pipes are communicated with the main pipe and extend along the flue gas direction; the distribution pipes are arranged at the positions, close to the free ends, of the branch pipes, and the distribution pipes are evenly distributed in the circumferential direction of the branch pipes; the distribution pipe is provided with a plurality of ammonia gas spraying holes of which the spraying direction is the same as that of the flue gas; and the rotational flow blade is fixedly connected to the middle part of the branch pipe in the flue and is used for converting axial airflow into radial rotational airflow in the mixing process of the flue gas and the ammonia gas. According to the invention, uniform mixing of ammonia gas and flue gas can be realized in a short distance, and the device is suitable for a flue gas denitration device which has a low allowable installation height and does not contain dust or has a low dust amount in denitration transformation of an old boiler.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas denitration, and in particular to an ammonia spraying mixing unit and a denitration system using the unit. Background Art

[0002] Existing flue gas denitrification methods mainly include selective catalytic reduction (SCR) technology, selective non-catalytic reduction (SNCR) technology, SNCR / SCR combined flue gas denitrification technology, etc. Among them, SCR technology has the advantages of mature technology, high denitrification efficiency, stable operation, etc., and has become the most widely used flue gas denitrification technology at home and abroad. The main principle of SCR technology is to spray the reducing agent ammonia into the flue gas and mix it evenly. Under the action of the SCR denitrification catalyst, ammonia (NH3) converts nitrogen oxides (NO x ) is reduced to non-toxic and pollution-free nitrogen and water, thereby removing NO from flue gas. x purpose.

[0003] For SCR denitrification technology, the mixing effect of ammonia and flue gas is the key and difficulty in the design and operation of SCR devices. It is also the key factor to ensure the complete denitrification reaction of SCR, improve the denitrification efficiency and ammonia utilization rate, and control the low ammonia escape rate. x Where the ammonia escape rate is too high, the ammonia escape rate will increase; x The denitrification efficiency cannot be guaranteed in places where the temperature is too low. DL / T 296-2011 Technical Guidelines for Flue Gas Denitrification in Thermal Power Plants stipulates that the NH3 / NO ratio in the flue gas at each location in the flue cross section of 100% of the flue gas at 500mm before the inlet of the first layer of the SCR reactor is x The deviation of the molar ratio is preferably -10% to 10%.

[0004] The mixing effect of ammonia and flue gas is mainly determined by the ammonia injection mixing system. In the "Ammonia Injection Mixing System for Coal-fired Flue Gas Denitrification" (GB / T 34339-2017), the ammonia injection mixing system is divided into an ammonia injection grid (AIG) and an ammonia injection static mixer. The AIG is an injection device that injects ammonia into the flue in the form of a grid pipe, including an ammonia injection pipe, a nozzle, a support and accessories; the static mixer is a device that uses certain fixed parts to change the flow state of ammonia and flue gas to achieve full mixing. Typical ammonia injection static mixers have vortex, swirl, longitudinal vortex, V-type and other structural forms.

[0005] The ammonia injection grid and the ammonia injection static mixer are separate devices, both of which require a certain installation space (height); and the ammonia injection mixing system of the above structure requires a longer mixing distance. However, most of the existing boilers were built a long time ago. When they were built, the environmental protection standards were relatively loose, and there was no demand for flue gas denitrification. Therefore, there was no denitrification space reserved in the boiler, and the layout was relatively compact. The free installation height / space was limited, and it was difficult to use the above ammonia injection mixing system for denitrification transformation.

[0006] For example, Chinese patent application CN112742232A discloses an ammonia injection static mixer, which is a single layer or multiple layers, arranged in the flue, each layer of mixers is composed of multiple static mixer units and is distributed in a matrix, and the static mixer units include: a reduced diameter section, which is a tubular structure with a small top and a large bottom, used to increase the flow rate of the mixed gas of ammonia and flue gas; a turbulent section, which is located above the reduced diameter section and connected to the reduced diameter section, and the turbulent section is provided with a turbulent component for diverting the mixed gas, so that the mixed gas forms a vortex on the back of the turbulent section. Although this type of static mixer can significantly reduce the gas velocity distribution deviation and ammonia concentration distribution deviation on the same cross section of the flue, there are still certain requirements for the distance required for mixing; and this type of ammonia injection static mixer has a large pressure drop, and is mainly for dust-containing flue gas, and is not suitable for flue gas denitrification of heating furnaces, gas-fired power furnaces, ethylene cracking furnace flue gas, alkylation waste acid regeneration flue gas and other chemical equipment that do not contain dust or have a low dust content and have more stringent pressure drop requirements.

[0007] Therefore, there is an urgent need for an ammonia spray mixing unit and a denitrification system using the unit, which can achieve uniform mixing of ammonia and flue gas within a shorter distance, and is suitable for the lower allowable installation height in the denitrification transformation of old boilers and for flue gas denitrification devices that do not contain dust or have a low dust content.

[0008] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0009] The object of the present invention is to provide an ammonia spray mixing unit and a denitrification system using the unit, which can achieve uniform mixing of ammonia and flue gas within a shorter distance, and is suitable for the lower allowable installation height in the denitrification transformation of old boilers and for flue gas denitrification devices that do not contain dust or have a low dust content.

[0010] To achieve the above-mentioned purpose, according to a first aspect of the present invention, an ammonia spray mixing unit is provided, which is applied to a flue gas denitrification system that does not contain dust or has a low dust content and is installed in a flue, comprising: a main pipe, which is arranged in a direction perpendicular to the direction of the flue gas flow and passes ammonia or an ammonia-air mixture into the flue; a plurality of branch pipes, which are connected to the main pipe and extend along the direction of the flue gas; a distribution pipe, which is arranged near the free end of the branch pipe and is evenly distributed along the circumference of the branch pipe; a plurality of ammonia spray holes with a spray direction in the same direction as the flue gas are provided on the distribution pipe; and a swirl blade, which is fixedly connected to the middle of the branch pipe in the flue, and is used to convert the axial airflow into a radial rotating airflow during the mixing process of the flue gas and ammonia.

[0011] Furthermore, in the above technical solution, the swirl blade may adopt a curved surface structure corresponding to the position of the ammonia injection hole, and the curved surface structure guides the axial airflow into a radial swirling airflow.

[0012] Furthermore, in the above technical solution, there may be four distribution pipes arranged in a cross shape, or a larger number of distribution pipes may be arranged in a cross shape or a star shape.

[0013] Furthermore, in the above technical solution, multiple layers of distribution pipes may be provided, and each layer of distribution pipes is evenly arranged on a circle centered on the branch pipe; and the projections of each layer of distribution pipes on the cross section of the flue do not overlap.

[0014] Furthermore, in the above technical solution, two layers of distribution pipes may be provided, and the projections of the two layers of distribution pipes on the cross section of the flue are evenly spaced.

[0015] Furthermore, in the above technical solution, there may be multiple main pipes and they may be evenly spaced in the flue, or the main pipes may extend into multiple rows through connecting pipes; the overall structure consisting of multiple main pipes, multiple branch pipes on each main pipe or connecting pipe, and multiple distribution pipes on each branch pipe fully covers the flue cross-section.

[0016] Furthermore, in the above technical solution, the installation height of the overall structure can be controlled between 0.5 meters and 1 meter.

[0017] Furthermore, in the above technical solution, the system pressure drop of the ammonia spray mixing unit of the present invention is less than 100Pa; NO in the flue gas after denitrification x <30mg / Nm 3 .

[0018] According to a second aspect of the present invention, there is provided a denitrification system suitable for denitrification of flue gas containing no dust or with a low dust content, comprising any of the aforementioned ammonia injection mixing units.

[0019] Furthermore, in the above technical solution, the ammonia spray mixing unit can be arranged upstream of the denitrification unit in the flue.

[0020] Furthermore, in the above technical solution, a flow meter and a flow regulating valve may be provided on the extension pipeline of each main pipe of the ammonia injection mixing unit.

[0021] Furthermore, in the above technical solution, the gas source of each main pipe can be provided by an ammonia injection main pipe, and an ammonia-air mixer is provided on the ammonia injection main pipe. The ammonia-air mixer can provide air through a dilution air duct.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The ammonia spray mixing system installed in the flue of conventional flue gas SCR denitrification generally includes an ammonia spray grid and an ammonia spray static mixer, which requires a relatively high installation height; the present invention converts the axial airflow into a radial rotating airflow, which can significantly reduce the installation height required for the ammonia spray mixing unit in the flue while achieving sufficient mixing, and is particularly suitable for the denitrification transformation of old boilers / process heating furnaces / cracking furnaces that have been in operation for many years; since the existing ammonia spray grid and ammonia spray static mixer are replaced, the weight of the equipment required to be added in the flue is greatly reduced, and at the same time, the boiler foundation and frame do not need to be changed, but only need to be reinforced, which is particularly suitable for the denitrification transformation of old boilers that have been in operation for many years, and can significantly reduce the transformation cost;

[0024] 2. The distribution pipe of the present invention distributes ammonia uniformly in an annular manner on the circumference of the branch pipe as the center line, and then causes ammonia and flue gas to rotate around the branch pipe through the swirl blades, which can effectively strengthen the mixing of flue gas and ammonia, and improve the distribution uniformity of ammonia on the same plane (a plane perpendicular to the flow direction of flue gas), thereby shortening the distance required for uniform mixing of ammonia or ammonia-air mixture with flue gas;

[0025] 3. The ammonia spray mixing unit of the present invention is applied to a flue gas denitration system that does not contain dust or has a low dust content. Therefore, ammonia spray holes with small apertures and a large number can be set on the distribution pipe. The gas velocity of the sprayed ammonia or ammonia-air mixed gas can be higher. After being matched with the swirl blades, the swirl effect is better. Experiments have shown that it can fully achieve the effect of the high-precision ammonia nozzle in the existing ammonia spray mixing system and can replace the existing expensive ammonia spray equipment.

[0026] 4. The ammonia spray mixing unit of the present invention makes the system pressure drop lower, and is particularly suitable for flue gas denitration of heating furnaces, ethylene cracking furnaces, and gas-fired power furnaces that are sensitive to pressure drop. The pressure drop increased by the ammonia spray mixing unit of the present invention is within the flexible range of furnace operation, so there is no need to reinforce the furnace or replace the fan;

[0027] 5. The ammonia spray mixing unit of the present invention has a relatively simple structure and can be manufactured in modular batches, effectively reducing production and installation costs.

[0028] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, and to make the above and other purposes, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the first embodiment of the ammonia injection mixing unit of the present invention (without a connecting pipe).

[0030] Figure 2 yes Figure 1 Schematic diagram of the arrangement of multiple ammonia injection mixing units in the flue.

[0031] Figure 3 yes Figure 1 AA schematic diagram in (showing the arrangement of ammonia injection holes).

[0032] Figure 4 It is a schematic structural diagram of a second embodiment of the ammonia injection mixing unit of the present invention (by providing connecting pipes, multiple rows of branch pipes can be provided on the basis of one main pipe).

[0033] Figure 5 yes Figure 4 Schematic diagram of the arrangement of multiple ammonia injection mixing units in the flue.

[0034] Figure 6 yes Figure 4 AA schematic diagram in (showing the arrangement of ammonia injection holes; only one branch pipe is shown).

[0035] Figure 7 It is a schematic diagram of the layout of the denitration system of the present invention.

[0036] Figure 8 It is a control schematic diagram of the ammonia spray mixing unit in the denitration system of the present invention.

[0037] Description of main reference numerals:

[0038] 10-flue; 20-ammonia spray mixing unit, 21-main pipe, 22-branch pipe, 23-distribution pipe, 24-ammonia spray hole, 25-swirl blade, 26-connecting pipe; 30-denitrification unit, 31-denitrification catalyst bed; 41-ammonia spray main pipe, 42-ammonia-air mixer, 43-dilution air pipeline, 44-first flow regulating valve, 45-second flow regulating valve, 46-first flow meter, 47-second flow meter. DETAILED DESCRIPTION

[0039] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0040] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0041] In this document, for the convenience of description, spatial relative terms such as "below", "below", "down", "above", "above", "upper", etc. may be used to describe the relationship between one element or feature and another element or feature in the accompanying drawings. It should be understood that the spatial relative terms are intended to include different orientations of the object in use or operation in addition to the orientation depicted in the figure. For example, if the object in the figure is turned over, the element described as being "below" or "below" other elements or features will be oriented "above" the element or feature. Therefore, the exemplary term "below" can include both below and above. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatial relative terms used in this document should be interpreted accordingly.

[0042] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit a specific position or relative relationship. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable.

[0043] The ammonia spraying grid and / or ammonia spraying static mixer installed in the flue for conventional flue gas SCR denitration require a relatively high installation height. The ammonia spraying mixing unit used in the present invention can significantly reduce the installation height required for the ammonia spraying mixing system in the flue, and is particularly suitable for the denitration transformation of old boilers / process heating furnaces / cracking furnaces that have been in operation for many years. The ammonia spraying mixing unit of the present invention replaces the conventional ammonia spraying grid and ammonia spraying static mixer, and the weight of the equipment required to be added in the flue is greatly reduced. At the same time, the boiler foundation and frame do not need to be modified, but only need to be reinforced.

[0044] like Figures 1 to 3 As shown, the present invention provides an ammonia spray mixing unit of the first embodiment, which is applied to a dust-free flue gas denitration system and installed in a flue, and includes a main pipe 21, a branch pipe 22, a distribution pipe 23 and a swirl blade 25. Among them, the main pipe 21 is arranged in the direction perpendicular to the flue gas flow direction in the flue 10 and passes ammonia or ammonia-air mixed gas; there are multiple branch pipes 22, which are connected to the main pipe 21 and extend along the flue gas direction; the distribution pipe 23 is arranged near the free end of the branch pipe 22, and the distribution pipe 23 is evenly distributed along the circumference of the branch pipe 22; the distribution pipe 23 is provided with a plurality of ammonia spray holes 24 (refer to Figure 3 ); The swirl blade 25 is fixedly connected to the middle of the branch pipe 22 in the flue, and is used to convert the axial airflow into a radial swirling airflow during the mixing process of the flue gas and ammonia. Figure 1 , Figure 2 As shown, the flue gas runs downward in the figure, and the opening direction of the ammonia injection hole 24 is downward, so that the flue gas and the ammonia gas or the ammonia-air mixture all run downward in the same direction. When the airflow runs downward to the swirl blade 25, the axial airflow can be converted into a radial rotating airflow by the guiding effect of the swirl blade 25 fixed on the branch pipe. In this way, the distribution pipe 23 can realize annular uniform distribution of ammonia gas or ammonia-air mixture on the circumference of the branch pipe 22 as the center line, and then the ammonia gas and the flue gas rotate around the branch pipe 22 through the swirl blade 25, so as to strengthen the mixing of the flue gas and ammonia gas, and improve the distribution uniformity of ammonia gas on the same plane (a plane perpendicular to the flow direction of the flue gas), thereby shortening the distance required for the uniform mixing of ammonia gas or ammonia-air mixture gas and flue gas, thereby reducing the overall installation height of the ammonia injection mixing unit.

[0045] Further Figures 1 to 3 As shown, the swirl blade 25 adopts a curved surface structure corresponding to the position of the ammonia injection hole 24, and the curved surface structure can guide the axial airflow into a radial swirling airflow. The inventor has found through research that the ammonia injection mixing unit of the present invention is applied to a flue gas denitration system that does not contain dust or has a low dust content, so ammonia injection holes 24 with small apertures and a large number can be set on the distribution pipe 23. After cooperating with the swirl blade 25, the effect of the high-precision ammonia nozzle in the existing ammonia injection mixing system can be fully achieved. Due to the simple structure and light weight, it has a good economic advantage.

[0046] Figures 1 to 3 In the first embodiment shown in FIG. 1 , there may be four distribution pipes 23 arranged in a cross shape. Alternatively, a cross-shaped or star-shaped arrangement may be adopted, for example Figure 4 When the distribution pipe is in one layer, the number of the mother pipes 21 can be set to multiple and evenly spaced in the flue 10 ( Figure 2 The overall structure composed of multiple main pipes, multiple branch pipes on each main pipe and multiple distribution pipes on each branch pipe fully covers the cross section of the flue (reference Figure 2 ). In this way, the flue gas and ammonia in the flue 10 can be fully mixed to the maximum extent. At the same time, the distribution pipe 23 of one layer can control the overall installation height of the unit to about 0.5-0.7 meters on the basis of ensuring a certain mixing efficiency.

[0047] The present invention also provides another embodiment of the ammonia injection mixing unit, such as Figures 4 to 6As shown, the distribution pipes 23 are arranged in multiple layers, and each layer of the distribution pipes 23 is evenly arranged on the circumference of the branch pipe 22 as the center; the projections of each layer of the distribution pipes 23 on the flue cross section do not overlap, so that the ammonia gas or ammonia-air mixed gas injected can be more dense, and the ammonia gas injected from each ammonia injection hole does not interfere with each other and can be normally mixed and contacted with the flue gas. Preferably, but not restrictively, the distribution pipes 23 are arranged in two layers (as shown in the figure), and the projections of the two layers of the distribution pipes 23 on the flue cross section are evenly spaced (refer to Figure 6 ).

[0048] In this embodiment, the mother tube can be extended into multiple rows through the connecting tube (refer to Figure 4 ), in this way, compared with the first embodiment in which each row corresponds to one main pipe, the weight of the unit can be further reduced, and the installation is more convenient. The overall structure composed of multiple main pipes, multiple branch pipes on the connecting pipe and multiple distribution pipes on each branch pipe also fully covers the cross section of the flue (refer to Figure 5 ). By adopting the implementation method of two or more layers of distribution pipes, the installation height of the overall unit structure can be controlled to be about 0.7 meters to 1 meter.

[0049] Experiments have shown that the ammonia spraying and mixing units using the above two implementations can meet the following index requirements: the pressure drop of the ammonia spraying and mixing unit is less than 100Pa; the NO in the flue gas after denitrification is less than 100Pa; x <30mg / Nm 3 The ammonia spray mixing unit of the present invention can be manufactured in modular batches due to its simple structure, thus effectively reducing production and installation costs.

[0050] like Figure 7 As shown, the present invention also provides a denitration system using the aforementioned ammonia spray mixing unit, which is suitable for denitration of flue gas that does not contain dust or has a low dust content. A denitration unit 30 is provided in the flue 10 of the system, and a denitration catalyst bed 31 is provided in the denitration unit 30 (the present invention preferably uses two layers of denitration catalyst), and the ammonia spray mixing unit 20 of the present invention is arranged upstream of the denitration unit 30 in the flue 10. The flue gas first passes through the ammonia spray mixing unit 20 to mix the flue gas with ammonia or ammonia-air mixture, and then enters the denitration catalyst bed for further denitration treatment. The main pipe 21 of the ammonia spray mixing unit 20 is supplied with gas through the ammonia spray main pipe 41 outside the flue.

[0051] Further Figure 8As shown, a flow meter and a flow regulating valve are provided on the extension pipeline of each main pipe of the ammonia spray mixing unit. Specifically, a first flow meter 46 is provided on the three main pipes 21 of the ammonia spray mixing unit 20, and a second flow meter 47 is provided on the ammonia spray main pipe 41. A first flow regulating valve 44 is provided on the three main pipes 21 of the ammonia spray mixing unit 20, and a second flow regulating valve 45 is provided on the ammonia spray main pipe 41. An ammonia-air mixer 42 is provided on the ammonia spray main pipe 41, and the ammonia-air mixer 42 is connected to the dilution air pipeline 43 to mix ammonia with dilution air so that the ammonia concentration in the ammonia-air mixture injected into the flue is away from its explosion limit. By independently controlling the flow of the main pipe and the dilution of ammonia, the system can control the uniform mixing degree of ammonia and flue gas in the flue according to the needs of the site, while ensuring the safety of the system.

[0052] Example 1

[0053] refer to Figure 1-3 The ammonia injection mixing unit of this embodiment includes 7 main pipes 21, each main pipe 21 is connected to 5 branch pipes 22 arranged perpendicularly thereto, 4 distribution pipes 23 are arranged near the free end of each branch pipe 22 (the end away from the main pipe 21), the 4 distribution pipes 23 are located on the same plane and are evenly distributed on the circumference centered on the branch pipe 22, and each distribution pipe 23 is provided with 9 ammonia injection holes 24 on the side facing the main pipe 21. Four swirl blades 25 are arranged on the branch pipe 22 between the distribution pipe 23 and the main pipe 21.

[0054] A heating furnace was modified for denitration. The installation height required for other conventional ammonia spray mixing systems was 2.0m, while the installation height required for the ammonia spray mixing unit of this embodiment was only 0.5m, which greatly reduced the installation height. The pressure drop of the ammonia spray mixing unit of this embodiment was <100Pa, which was much lower than the 200-300Pa of the conventional ammonia spray mixing system. The ammonia and flue gas mixed well, and NO in the flue gas after denitration x <30mg / Nm 3 , ammonia escape <1mg / Nm 3 .

[0055] Example 2

[0056] refer to Figure 4-6The ammonia spraying and mixing unit of this embodiment includes three main pipes 21, each of which is connected to 12 branch pipes 22 arranged perpendicularly thereto, of which four branch pipes 22 are directly connected to the main pipe 21, and the remaining eight branch pipes 22 are connected to the main pipe 21 through connecting pipes 26. Two layers of distribution pipes 23 are arranged at one end of the branch pipe 22 away from the main pipe 21, and each layer of distribution pipes 23 is composed of 10 distribution pipes 23. The 10 distribution pipes 23 are located on the same plane and are evenly distributed on the circumference of the branch pipe 22 as the center, and the two layers of distribution pipes 23 are staggered in the direction of flue gas flow (that is, the projections on the cross section of the flue do not overlap). Eight ammonia spraying holes 24 are arranged on the side of each distribution pipe 23 facing the main pipe 21. Four swirl blades 25 are arranged on the branch pipe 22 between the distribution pipe 23 and the main pipe 21.

[0057] In a flue gas denitration device of a gas-fired power furnace, the installation height required for other conventional ammonia spray mixing systems is 2.0m, while the installation height required for the ammonia spray mixing unit of this embodiment is only 0.7m, which greatly reduces the installation height; the pressure drop of the ammonia spray mixing unit of this embodiment is <100Pa, which is much lower than the 200-300Pa of the conventional ammonia spray mixing system; the mixing effect of ammonia and flue gas is good, and the NO after denitration is x <25mg / Nm 3 , ammonia escape was not detected.

[0058] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. Any simple modifications, equivalent changes and modifications made to the above exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. An ammonia spray mixing unit, characterized in that: Applied in dust-free flue gas denitrification systems and installed in flues, including: A main pipe is arranged in the flue in a direction perpendicular to the flue gas flow direction and is fed with ammonia or ammonia-air mixture; A plurality of branch pipes, which are connected to the main pipe and extend along the direction of the smoke; A distribution pipe is arranged near the free end of the branch pipe and is evenly distributed along the circumference of the branch pipe; the distribution pipe is provided with a plurality of ammonia injection holes whose injection direction is the same as that of the flue gas; The swirl blade is fixedly connected to the middle of the branch pipe in the flue and is used to convert the axial airflow into a radial swirling airflow during the mixing process of the flue gas and ammonia.

2. The ammonia spray mixing unit according to claim 1, characterized in that: The swirl blade adopts a curved surface structure corresponding to the position of the ammonia injection hole, and the curved surface structure guides the axial airflow into a radial swirling airflow.

3. The ammonia spray mixing unit according to claim 1, characterized in that: There are four distribution pipes arranged in a cross shape.

4. The ammonia spray mixing unit according to claim 3, characterized in that: The distribution pipes are arranged in multiple layers, and the distribution pipes in each layer are evenly arranged on a circle centered on the branch pipe; and the projections of the distribution pipes in each layer on the cross section of the flue do not overlap.

5. The ammonia spray mixing unit according to claim 4, characterized in that: The distribution pipes are arranged in two layers, and the projections of the two layers of distribution pipes on the cross section of the flue are arranged at even intervals.

6. The ammonia spray mixing unit according to claim 1, characterized in that: There are multiple main pipes and they are evenly spaced in the flue, or the main pipes extend into multiple rows through connecting pipes; the overall structure consisting of multiple main pipes, multiple branch pipes on each main pipe or connecting pipe, and multiple distribution pipes on each branch pipe fully covers the cross section of the flue.

7. The ammonia spray mixing unit according to claim 6, characterized in that: The installation height of the overall structure is 0.5 meter to 1 meter.

8. The ammonia spray mixing unit according to claim 1, characterized in that: The system pressure drop of the ammonia spray mixing unit is less than 100Pa; NO in the flue gas after denitrification x <30mg / Nm 3 .

9. A denitration system, characterized in that: The invention is suitable for denitrification of dust-free flue gas, comprising an ammonia spray mixing unit as claimed in any one of claims 1 to 8.

10. The denitration system according to claim 9, characterized in that: The ammonia injection mixing unit is arranged upstream of the denitrification unit in the flue.

11. The denitration system according to claim 10, characterized in that: A flow meter and a flow regulating valve are provided on the extension pipeline of each main pipe of the ammonia injection mixing unit.

12. The denitration system according to claim 11, characterized in that: The air source of each main pipe is provided by an ammonia injection main pipe, on which an ammonia-air mixer is provided, and the ammonia-air mixer provides air through a dilution air pipeline.

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