Ammonia injection mixing unit and denitrification system using this unit

Abstract

The application discloses a kind of ammonia injection mixing units, be applied to the flue gas denitration system without dust or lower dust content and install in flue, comprising: main pipe, it is laid in the direction of vertical flue gas flow direction in flue and is connected with ammonia or ammonia air mixture;Branch pipe, the number is multiple, the branch pipe is communicated with main pipe and extends along the direction of flue gas;Distribution pipe, it is arranged in branch pipe near free end, the distribution pipe is evenly distributed along the circumference of branch pipe;Multiple ammonia injection orifices with the same direction as flue gas are provided on distribution pipe;Swirl vane, it is fixedly connected in the middle of branch pipe in flue, for converting axial airflow into radial rotating airflow in the process of flue gas and ammonia mixing.The application can realize the uniform mixing of ammonia and flue gas in a short distance, and is suitable for lower allowable installation height in old boiler denitration reconstruction and flue gas denitration device without dust or lower dust content.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification technology, and in particular to an ammonia injection mixing unit and a denitrification system using the unit. Background Technology

[0002] Existing flue gas denitrification methods mainly include selective catalytic reduction (SCR) technology, selective non-catalytic reduction (SNCR) technology, and combined SNCR / SCR flue gas denitrification technology. Among them, SCR technology has the advantages of mature technology, high denitrification efficiency, and stable operation, and has become the most widely used flue gas denitrification technology both domestically and internationally. The main principle of SCR technology is to inject the reducing agent ammonia into the flue gas and mix it evenly. Under the action of the SCR denitrification catalyst, ammonia (NH3) reduces nitrogen oxides (NOx) in the flue gas. x It is reduced to non-toxic and non-polluting nitrogen and water, thereby achieving the removal of NO from flue gas. x The purpose.

[0003] For SCR (Selective Catalytic Reduction) denitrification technology, the mixing effect of ammonia and flue gas is a key focus and challenge in the design and operation of SCR units. It is also a crucial factor in ensuring complete SCR denitrification, improving denitrification efficiency and ammonia utilization, and controlling a low ammonia slip rate. (In NH3 / NO...) x In areas with excessively high concentrations of NH3 / NO, the ammonia slip rate will increase; x At excessively low temperatures, denitrification efficiency cannot be guaranteed. DL / T 296-2011, "Technical Guidelines for Flue Gas Denitrification in Thermal Power Plants," stipulates that the NH3 / NO3 concentration at various points in the flue gas at 100% cross-section of the flue gas 500mm before the inlet of the first catalyst layer in the SCR reactor should be within acceptable limits. x The deviation of the molar ratio should preferably be -10% to 10%.

[0004] The mixing effect of ammonia and flue gas is mainly determined by the ammonia injection mixing system. The standard "Ammonia Injection Mixing System for Coal-fired Flue Gas Denitrification" (GB / T 34339-2017) classifies the ammonia injection mixing system into two types: AMG (Ammonia Injection Grille) and static ammonia mixer. An AMG is an injection device that injects ammonia into the flue gas duct in the form of a grille pipe, including the injection pipe, nozzle, support, and accessories. A static mixer utilizes fixed components to change the flow state of ammonia and flue gas, achieving thorough mixing. Typical static ammonia mixers include vortex, swirl, longitudinal vortex, and V-type structures.

[0005] Ammonia injection grilles and static ammonia mixers are separate devices, each requiring a certain amount of installation space (height); furthermore, the aforementioned ammonia injection mixing systems require a relatively long mixing distance. However, most existing boilers were built a long time ago, and due to more lenient environmental standards at the time of construction, there was no need for flue gas denitrification. Consequently, no denitrification space was reserved within the boilers, resulting in a compact layout and limited available installation height / space. This makes denitrification retrofitting using the aforementioned ammonia injection mixing systems quite challenging.

[0006] For example, Chinese patent application CN112742232A discloses an ammonia-injected static mixer. This mixer is one or more layers located in a flue. Each layer of the mixer consists of multiple static mixer units arranged in a matrix. Each static mixer unit includes: a narrowing section, a tubular structure with a smaller top and larger bottom, used to increase the flow velocity of the ammonia-flue gas mixture; and a turbulence section, located above and connected to the narrowing section, equipped with turbulence components to divert the mixed gas, causing the mixed gas to form a vortex on the back side of the turbulence section. While this type of static mixer can significantly reduce the deviation in gas velocity distribution and ammonia concentration distribution on the same cross-section of the flue, there are still certain requirements for the mixing distance. Furthermore, this type of ammonia-injected static mixer has a large pressure drop and is mainly designed for flue gas containing dust. It is not suitable for flue gas denitrification in heating furnaces, gas-fired furnaces, ethylene cracking furnaces, alkylation waste acid regeneration flue gas, and other chemical plants where there is no dust or low dust content and the pressure drop requirements are stringent.

[0007] Therefore, there is an urgent need for an ammonia injection mixing unit and a denitrification system that uses this unit, which can achieve uniform mixing of ammonia and flue gas over a short distance. This system is suitable for denitrification retrofitting of old boilers at lower allowable installation heights and for flue gas denitrification devices that are dust-free or have low dust content.

[0008] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to provide an ammonia injection mixing unit and a denitrification system using the unit, which can achieve uniform mixing of ammonia and flue gas over a shorter distance. It is suitable for denitrification retrofitting of old boilers with lower allowable installation heights and for flue gas denitrification devices with no dust or low dust content.

[0010] To achieve the above objectives, according to a first aspect of the present invention, an ammonia injection mixing unit is provided, applied in a flue gas denitrification system with no dust or low dust content and installed in a flue, comprising: a main pipe, which is arranged in the flue gas duct perpendicular to the flue gas flow direction and through which ammonia or ammonia-air mixture is introduced; multiple branch pipes, which are connected to the main pipe and extend along the flue gas direction; a distribution pipe, which is disposed near the free end of the branch pipe and is uniformly distributed along the circumference of the branch pipe; the distribution pipe is provided with multiple ammonia injection holes with the injection direction in the same direction as the flue gas; and swirl vanes, which are fixedly connected to the middle of the branch pipe in the flue gas duct, for converting the axial airflow into a radial rotating airflow during the mixing process of flue gas and ammonia.

[0011] Furthermore, in the above technical solution, the swirl blades can 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 rotating airflow.

[0012] Furthermore, in the above technical solution, the distribution pipes can be four in a cross shape, or more in a star or star-shaped arrangement.

[0013] Furthermore, in the above technical solution, the distribution pipe can be set in multiple layers, with each layer of distribution pipe evenly distributed on the circumference centered on the branch pipe; the projections of each layer of distribution pipe on the cross-section of the flue do not overlap.

[0014] Furthermore, in the above technical solution, the distribution pipe can be set in two layers, 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 can be multiple main pipes that are evenly spaced in the flue, or the main pipes can 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 forms a complete coverage of 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 using the ammonia injection mixing unit of the present invention is <100Pa; the NO content in the flue gas after denitrification is <100Pa. x <30mg / Nm 3 .

[0018] According to a second aspect of the present invention, the present invention provides a denitrification system suitable for denitrification of flue gas containing no dust or with low dust content, including an ammonia injection mixing unit of any of the foregoing.

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

[0020] Furthermore, in the above technical solution, each extension pipe of the main pipe of the ammonia injection mixing unit can be equipped with a flow meter and a flow regulating valve.

[0021] Furthermore, in the above technical solution, the air source for each main pipe can be provided by the ammonia injection main pipe, which is equipped with an ammonia-air mixer. The ammonia-air mixer can provide air through the dilution air duct.

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

[0023] 1. Conventional flue gas SCR denitrification systems typically include an ammonia injection grid and a static ammonia mixer, requiring a relatively high installation height. This invention transforms axial airflow into radial rotating airflow, significantly reducing the installation height required for the ammonia injection mixing unit within the flue while ensuring thorough mixing. This is particularly suitable for denitrification retrofitting of older boilers / process heating furnaces / cracking furnaces that have been in operation for many years. Since it replaces the existing ammonia injection grid and static ammonia mixer, the weight of the additional equipment required in the flue is greatly reduced. At the same time, the boiler foundation and frame do not need to be modified, only reinforced. This is especially suitable for denitrification retrofitting of older boilers that have been in operation for many years, significantly reducing retrofitting costs.

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

[0025] 3. The ammonia injection mixing unit of the present invention is applied in a flue gas denitrification system with no dust or low dust content. Therefore, ammonia injection holes with small diameter and large number can be set on the distribution pipe, and the gas velocity of the injected ammonia or ammonia-air mixture can be higher. After being combined with the swirl blades, the swirl effect produced is better. Tests have shown that it can completely achieve the effect of high-precision ammonia nozzles in the existing ammonia injection mixing system and can replace the existing expensive ammonia injection equipment.

[0026] 4. The ammonia injection mixing unit of the present invention results in a low system pressure drop, which is especially suitable for denitrification of flue gas from heating furnaces, ethylene cracking furnaces and gas-fired power furnaces that are sensitive to pressure drop. The pressure drop increased by the ammonia injection mixing unit of the present invention is within the operating flexibility range of the furnace body, so there is no need to reinforce the furnace body or replace the blower.

[0027] 5. The ammonia mixing unit of the present invention has a relatively simple structure and can be modularly mass-produced, effectively reducing production and installation costs.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the first embodiment of the ammonia mixing unit of the present invention (without connecting pipes).

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

[0031] Figure 3 yes Figure 1 The diagram above shows the arrangement of the ammonia injection holes.

[0032] Figure 4 This is a schematic diagram of the structure of the second embodiment of the ammonia mixing unit of the present invention (by setting a connecting pipe, multiple rows of branch pipes can be set on the basis of a main pipe).

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

[0034] Figure 6 yes Figure 4 The diagram above shows the arrangement of the ammonia injection holes; only one branch pipe is shown.

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

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

[0037] Explanation of key figure labels:

[0038] 10-Flue duct; 20-Ammonia injection mixing unit; 21-Main pipe; 22-Branch pipe; 23-Distribution pipe; 24-Ammonia injection port; 25-Swirl vane; 26-Connecting pipe; 30-Denitrification unit; 31-Denitrification catalyst bed; 41-Ammonia injection main pipe; 42-Ammonia-air mixer; 43-Dilution air duct; 44-First flow regulating valve; 45-Second flow regulating valve; 46-First flow meter; 47-Second flow meter. Detailed Implementation

[0039] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0040] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprising" shall be understood to include the stated elements or components without excluding other elements or other components.

[0041] In this document, for ease of description, spatial relative terms such as “below,” “under,” “down,” “above,” “over,” “up,” etc., are used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different orientations of an object in use or operation, in addition to those depicted in the figures. For example, if an object in the figure is flipped, an element described as “below” or “under” another element or feature would be oriented “above” that element or feature. Thus, the exemplary term “below” can encompass both the downward and upward orientations. An object may also have other orientations (rotated 90 degrees or other orientations), and the spatial relative terms used herein 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 define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0043] Conventional flue gas SCR denitrification systems require relatively high installation heights for ammonia injection grilles and / or static ammonia mixers within the flue. The ammonia injection mixing unit used in this invention significantly reduces the required installation height of the ammonia injection mixing system within the flue, making it particularly suitable for denitrification retrofitting of older boilers / process heating furnaces / cracking furnaces that have been in operation for many years. This invention's ammonia injection mixing unit replaces conventional ammonia injection grilles and static ammonia mixers, greatly reducing the weight of additional equipment required within the flue. Simultaneously, the boiler foundation and frame require no modification, only reinforcement.

[0044] like Figures 1 to 3 As shown, the present invention provides an ammonia injection mixing unit according to a first embodiment. This unit is applied in a dust-free flue gas denitrification system and installed in a flue. It includes a main pipe 21, branch pipes 22, distribution pipes 23, and swirl vanes 25. The main pipe 21 is arranged in the flue 10 perpendicular to the flue gas flow direction and is used to introduce ammonia or an ammonia-air mixture. Multiple branch pipes 22 are connected to the main pipe 21 and extend along the flue gas direction. The distribution pipes 23 are located near the free ends of the branch pipes 22 and are evenly distributed circumferentially along the branch pipes 22. The distribution pipes 23 are provided with multiple ammonia injection holes 24 whose injection direction is the same as that of the flue gas (see reference). Figure 3 The swirl vane 25 is fixedly connected to the middle of the branch pipe 22 inside the flue, and is used to convert the axial airflow into a radial rotating airflow during the mixing of flue gas and ammonia. Figure 1 , Figure 2 As shown, the flue gas flows downwards, and the opening direction of the ammonia injection port 24 is downwards, so that the flue gas and ammonia or ammonia-air mixture both flow downwards in the same direction. When the airflow reaches the swirl vane 25, the axial airflow can be converted into a radial rotating airflow by the guiding action of the swirl vane 25 fixed on the branch pipe. In this way, the distribution pipe 23 can achieve a uniform annular distribution of ammonia or ammonia-air mixture around the circumference of the branch pipe 22. Furthermore, the swirl vane 25 causes the ammonia and flue gas to rotate around the branch pipe 22, which enhances the mixing of flue gas and ammonia and improves the uniformity of ammonia distribution on the same plane (the plane perpendicular to the flue gas flow direction). This shortens the distance required for uniform mixing of ammonia or ammonia-air mixture with flue gas, thereby reducing the overall installation height of the ammonia injection mixing unit.

[0045] Further as Figures 1 to 3 As shown, the swirl vane 25 adopts a curved surface structure corresponding to the position of the ammonia injection port 24. This curved surface structure can guide the axial airflow into a radial rotating airflow. The inventors have discovered that the ammonia injection mixing unit of the present invention can be applied in flue gas denitrification systems with no dust or low dust content. Therefore, the distribution pipe 23 can be provided with a large number of ammonia injection ports 24 with small diameters. After being combined with the swirl vane 25, it can achieve the effect of high-precision ammonia nozzles in existing ammonia injection mixing systems. Due to its simple structure and light weight, it has good economic advantages.

[0046] Figures 1 to 3 In the first embodiment illustrated, the distribution pipes 23 can be four in a cross shape. Alternatively, they can be arranged in a star or other pattern, for example... Figure 4 The method is as follows. When the distribution pipe is in one layer, the number of main pipes 21 can be set to multiple and evenly spaced in the flue 10. Figure 2 The structure consists of 8 main pipes, multiple branch pipes on each main pipe, and multiple distribution pipes on each branch pipe, forming a complete coverage of the flue cross-section (see reference). Figure 2 This method ensures the maximum possible mixing of flue gas and ammonia in the flue 10. Simultaneously, the single-layer distribution pipe 23 allows the overall installation height of the unit to be controlled at approximately 0.5-0.7 meters while maintaining a certain mixing efficiency.

[0047] The present invention also provides another embodiment of the ammonia mixing unit, such as... Figures 4 to 6As shown, the distribution pipe 23 is configured in multiple layers, with each layer of distribution pipe 23 evenly distributed on the circumference centered on the branch pipe 22; the projections of each layer of distribution pipe 23 on the flue cross-section do not overlap. This ensures a denser injection of ammonia or ammonia-air mixture, while also preventing interference between the ammonia emitted from each injection hole, allowing for proper mixing and contact with the flue gas. Preferably, but not limitingly, the distribution pipe 23 is configured in two layers (as shown in the figure), with the projections of the two layers of distribution pipe 23 on the flue cross-section evenly spaced (see reference). Figure 6 ).

[0048] In this embodiment, the main pipe can extend into multiple rows via connecting pipes (see reference). Figure 4 In this way, compared to the first embodiment where each row corresponds to one main pipe, the unit's weight can be further reduced, and installation is more convenient. The overall structure, consisting of multiple main pipes, multiple branch pipes on the connecting pipes, and multiple distribution pipes on each branch pipe, also provides full coverage of the flue cross-section (see reference). Figure 5 With the implementation of two or more layers of distribution pipes, the installation height of the overall unit structure can be controlled to be approximately 0.7 meters to 1 meter.

[0049] Tests have shown that both of the aforementioned ammonia injection mixing units can meet the following requirements: pressure drop of the ammonia injection mixing unit <100Pa; NO in the flue gas after denitrification x <30mg / Nm 3 The ammonia mixing unit of this invention has a simple structure and can be modularly mass-produced, effectively reducing production and installation costs.

[0050] like Figure 7 As shown, the present invention also provides a denitrification system using the aforementioned ammonia mixing unit, which is suitable for denitrification of flue gas that is dust-free or has a low dust content. The system includes a denitrification unit 30 in the flue duct 10, and a denitrification catalyst bed 31 (preferably using two layers of denitrification catalyst) within the denitrification unit 30. The ammonia mixing unit 20 is located upstream of the denitrification unit 30 in the flue duct 10. The flue gas first passes through the ammonia mixing unit 20 to mix with ammonia or an ammonia-air mixture before entering the denitrification catalyst bed for further denitrification. The main pipe 21 of the ammonia mixing unit 20 is supplied with gas through an external ammonia injection main pipe 41.

[0051] Further as Figure 8As shown, each extension pipe of the ammonia injection mixing unit is equipped with a flow meter and a flow regulating valve. Specifically, the three main pipes 21 of the ammonia injection mixing unit 20 are equipped with a first flow meter 46, and the ammonia injection main pipe 41 is equipped with a second flow meter 47. The three main pipes 21 of the ammonia injection mixing unit 20 are equipped with a first flow regulating valve 44, and the ammonia injection main pipe 41 is equipped with a second flow regulating valve 45. The ammonia injection main pipe 41 is equipped with an ammonia-air mixer 42, which is connected to the dilution air pipe 43 and is used to mix ammonia gas with dilution air, so that the ammonia concentration in the ammonia-air mixture injected into the flue is far away from its explosion limit. Through the independent flow control of the main pipes and the dilution of ammonia gas, the system can control the degree of uniform mixing of ammonia gas 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 seven main pipes 21, each main pipe 21 is connected to five branch pipes 22 arranged perpendicularly to it, and four distribution pipes 23 are arranged near the free end (the end away from the main pipe 21) of each branch pipe 22. The four distribution pipes 23 are located on the same plane and are evenly distributed on the circumference centered on the branch pipe 22. Each distribution pipe 23 has nine ammonia injection holes 24 on the side facing the main pipe 21. Four swirl vanes 25 are arranged on the branch pipes 22 between the distribution pipes 23 and the main pipes 21.

[0054] A heating furnace underwent denitrification retrofitting. While other conventional ammonia injection mixing systems require an installation height of 2.0m, the ammonia injection mixing unit of this embodiment requires only 0.5m, a significant reduction in installation height. The pressure drop of the ammonia injection mixing unit in this embodiment is <100Pa, far lower than the 200-300Pa of conventional ammonia injection mixing systems. The ammonia and flue gas mixing effect is excellent, and the NO content in the flue gas after denitrification is low. x <30mg / Nm 3 Ammonia escape <1mg / Nm 3 .

[0055] Example 2

[0056] refer to Figure 4-6The ammonia injection mixing unit in this embodiment includes three main pipes 21, each with 12 branch pipes 22 connected perpendicularly to it. Four branch pipes 22 are directly connected to the main pipes 21, while the remaining eight branch pipes 22 are connected to the main pipes 21 via connecting pipes 26. Two layers of distribution pipes 23 are provided at one end of each branch pipe 22 furthest from the main pipe 21. Each layer of distribution pipes 23 consists of 10 distribution pipes 23, which are located on the same plane and evenly distributed around the circumference of the branch pipe 22. The two layers of distribution pipes 23 are staggered in the flue gas flow direction (i.e., their projections on the flue gas cross-section do not overlap). Each distribution pipe 23 has eight ammonia injection holes 24 on the side facing the main pipe 21. Four swirl vanes 25 are provided on the branch pipes 22 between the distribution pipes 23 and the main pipe 21.

[0057] The installation height required for a flue gas denitrification device in a gas-fired boiler using other conventional ammonia injection mixing systems is 2.0m, while the installation height required using the ammonia injection mixing unit of this embodiment is only 0.7m, a significant reduction. The pressure drop of the ammonia injection mixing unit in this embodiment is <100Pa, far lower than the 200-300Pa of conventional ammonia injection mixing systems; the mixing effect of ammonia and flue gas is excellent, and the NO₂ after denitrification is low. x <25mg / Nm 3 Ammonia escape was not detected.

[0058] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. Any simple modifications, equivalent changes, and alterations made to the foregoing exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. An ammonia injection mixing unit characterized by, The application is applied to a dust-free flue gas denitration system and installed in a flue, comprising: a main pipe arranged in the flue in the direction of the vertical flue gas flow and supplied with ammonia gas or ammonia-air mixed gas; a plurality of branch pipes in communication with the main pipe and extending along the flue gas flow direction; a plurality of distribution pipes arranged at the free ends of the branch pipes and uniformly distributed along the circumferences of the branch pipes; each distribution pipe is provided with a plurality of ammonia injection holes with the same direction as the flue gas flow; each distribution pipe is arranged in multiple layers and uniformly arranged on the circumference of the branch pipe; the projections of the distribution pipes on the flue cross section do not overlap; a plurality of swirl vanes fixedly connected to the middle portions of the branch pipes in the flue for converting the axial gas flow into radial rotational gas flow during the mixing of the flue gas and the ammonia gas.

2. The ammonia injection mixing unit of claim 1, wherein The swirl vanes adopt a curved surface structure corresponding to the positions of the ammonia injection holes, which guides the axial gas flow into radial rotational gas flow.

3. The ammonia injection mixing unit of claim 1 wherein, The distribution pipes are four in number and arranged in a cross shape.

4. The ammonia injection mixing unit of claim 1, wherein The distribution pipes are arranged in two layers, and the projections of the two layers of distribution pipes on the flue cross section are uniformly and separately arranged.

5. The ammonia injection mixing unit of claim 1 wherein, The main pipes are in multiple numbers and uniformly and separately arranged in the flue, or the main pipes are extended in multiple rows through connecting pipes; the overall structure formed by the multiple main pipes, the multiple branch pipes on each main pipe or connecting pipe, and the multiple distribution pipes on each branch pipe fully covers the flue cross section.

6. The ammonia injection mixing unit of claim 5 wherein, The installation height of the overall structure is 0.5-1 m.

7. The ammonia injection mixing unit of claim 1, wherein The system pressure drop using the ammonia injection mixing unit is less than 100 Pa; the NOx in the flue gas after denitration is less than 30 mg / Nm x <30 mg / Nm 3 .

8. A denitration system characterized by, The application is suitable for dust-free flue gas denitration and comprises the ammonia injection and mixing unit according to any one of claims 1-7.

9. The deNOx system according to claim 8, characterized by The ammonia injection and mixing unit is arranged upstream of the denitration unit in the flue.

10. The de-NOx system according to claim 9, characterized by A flow meter and a flow regulating valve are arranged on the extension pipeline of each main pipe of the ammonia injection and mixing unit.

11. The de-NOx system according to claim 10, characterized by The gas source of each main pipe is provided by an ammonia injection header pipe, which is provided with an ammonia-air mixer, and the ammonia-air mixer is provided with air through a dilution air pipeline.

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