Positive and negative rotation combined partition mixing ammonia spraying method and system

Abstract

The invention discloses a positive and negative rotation combined partitioned mixed ammonia spraying method and system, and the positive and negative rotation combined partitioned mixed ammonia spraying method comprises the following steps: carrying out obliquely upward partitioned ammonia spraying in a manner of positive rotation and forming an angle of 15-35 degrees with the horizontal direction in a vertical flue at an inlet of a denitration device; and meanwhile, mixing of the flue gas and the ammonia is enhanced in a manner of reversely rotating and forming an angle of 60-80 degrees with the horizontal direction at a position which is 0.5-0.7 time of the equivalent diameter of the vertical flue at the downstream of an ammonia spraying outlet. Through cooperation of forward-rotation upward ammonia spraying and reverse-rotation mechanical mixing, low pressure loss and high mixing uniformity are both considered, the risk of blockage of an ammonia spraying opening is reduced, and the device is simple and stable in structure, easy to transform and suitable for upgrading and reconstruction of an old boiler.

Description

Technical Field

[0001] This invention relates to a method and system for zoned mixing and ammonia injection that combines forward and reverse swirl, belonging to the field of flue gas denitrification technology. Background Technology

[0002] Selective catalytic reduction (SCR) flue gas denitrification technology is a NOx emission reduction technology that uses a reducing agent (such as liquid ammonia, urea, and ammonia water) in the presence of a catalyst to selectively react with NOx in flue gas, generating pollution-free N2 and H2O. Due to its advantages such as mature technology, high denitrification efficiency, and stable operation, SCR flue gas denitrification technology has become the most widely used flue gas denitrification technology both domestically and internationally.

[0003] In SCR flue gas 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 reaction, improving denitrification efficiency and ammonia utilization, and controlling a low ammonia slip rate. Excessively high NH3 / NOx ratios lead to increased ammonia slip, causing a series of problems such as downstream air preheater blockage, corrosion, and excessive emissions, as well as energy waste. Conversely, excessively low NH3 / NOx ratios result in substandard local denitrification efficiency. Furthermore, changes in coal type, mill combination, and burner adjustments can significantly alter the NOx concentration distribution and flow field at the SCR inlet, leading to a marked deterioration in the uniformity of the ammonia-nitrogen molar ratio.

[0004] To improve the uniformity of ammonia-flue gas mixing, existing technologies employ multi-stage mixing devices downstream of the ammonia injection unit. For example, patent CN218981091U discloses an ammonia injection mixing system for SCR flue gas denitrification in a coal-fired power plant. This system sequentially installs a primary baffle plate, a primary airflow distribution plate, a secondary baffle plate, and a secondary airflow distribution plate downstream of the ammonia injection pipe. The primary baffle plate consists of upper and lower rows of plates, while the secondary baffle plate consists of upper, middle, and lower rows of plates. This structure is complex, difficult to install, and offers limited mixing efficiency. Furthermore, existing ammonia injection methods often involve downward injection, which can cause airflow convection and system pressure loss. Summary of the Invention

[0005] This invention provides a method for zoned mixing and ammonia injection that combines forward and reverse swirl. By using forward swirl ammonia injection in conjunction with reverse swirl to enhance mixing, the uniformity of the mixing of flue gas and ammonia is effectively improved, while pressure loss and fan energy consumption are reduced. Moreover, the structure is simple and easy to install and modify.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for zoned ammonia injection combining forward and reverse rotation involves injecting ammonia distilled in a forward rotation at an angle of 15-35° to the horizontal in the vertical flue at the inlet of a denitrification unit. Simultaneously, at a position 0.5-0.7 times the equivalent diameter of the vertical flue downstream of the ammonia injection outlet, a reverse rotation at an angle of 60-80° to the horizontal is used to enhance the mixing of flue gas and ammonia.

[0008] This application employs a forward-swirl, upward-sloping ammonia injection method, forming a diffused spiral upward airflow. This avoids flue gas collisions and localized vortex dead zones, significantly reducing system pressure loss and fan energy consumption compared to downward-sloping injection methods. Simultaneously, upward injection reduces dust deposition at the nozzle outlet, significantly lowering the risk of nozzle clogging. Furthermore, the direct forward-swirl injection of ammonia at a specific angle balances the diffusion angle of the injected ammonia with its mixing with the flue gas. This, combined with downstream counter-swirl injection at a specific angle to enhance mixing, generates a shear layer vortex, enabling rapid mixing of flue gas and ammonia. The counter-swirl design also effectively corrects the vortex center offset generated by the forward swirl, resulting in more uniform ammonia distribution and a shorter mixing section.

[0009] When injecting ammonia, it is rotated obliquely upward at an angle of 15-35° to the horizontal direction, which can effectively ensure the diffusion range. At the same time as injecting ammonia, it achieves uniform mixing with flue gas, which significantly simplifies the structure and reduces installation costs and difficulties. Then, it is rotated counterclockwise at 60-80° to enhance mixing, which can effectively ensure the uniformity of mixing between flue gas and ammonia.

[0010] To further improve the mixing effect, two or more arc-shaped guide plates are installed at equal intervals along the height direction at the top bend of the vertical flue at the inlet of the denitrification unit.

[0011] A combined forward and reverse swirl ammonia injection system includes a forward swirl ammonia injection mixing device and a reverse swirl enhanced mixing device installed in the vertical flue at the inlet of a denitrification unit. The reverse swirl enhanced mixing device is located downstream of the forward swirl ammonia injection mixing device, and the interval between the forward swirl ammonia injection mixing device and the reverse swirl enhanced mixing device is 0.5 to 0.7 times the equivalent diameter of the vertical flue. The forward swirl ammonia injection mixing device injects ammonia obliquely upward in a forward swirl at an angle of 15 to 35° with respect to the horizontal direction, while the reverse swirl enhanced mixing device enhances the mixing of flue gas and ammonia in a reverse swirl at an angle of 60 to 80° with respect to the horizontal direction.

[0012] The upstream-to-downstream direction of this application is consistent with the flue gas flow direction.

[0013] The above-mentioned mechanical structure design significantly improves the uniformity of ammonia mixing and avoids the problem of easy damage and failure of electrical control equipment under high temperature environment. It is simple, stable and reliable.

[0014] To facilitate assembly and ensure ammonia injection and mixing effects, the positive swirl ammonia injection mixing device includes 4 to 6 sets of identical positive swirl ammonia injection mixing components arranged in a straight line within a vertical flue. Adjacent sets of positive swirl ammonia injection mixing components are separated by partition plates to form partitioned ammonia injection. The partition plates are vertically set, with the bottom of the partition plates flush with the bottom of the ammonia injection port on the positive swirl ammonia injection mixing components. The height of the partition plates is 30 to 40 cm.

[0015] For ease of manufacturing, as one specific implementation, the swirl ammonia injection mixing assembly includes a first conveying pipe, a second conveying pipe, and a swirl ammonia injection assembly;

[0016] The number of the second conveying pipes and the positive swirl ammonia injection components are both three or more, and the number of the two is equal and corresponds one-to-one; each of the second conveying pipes is evenly distributed and connected to the periphery of the outlet end of the first conveying pipe (the inlet end of the second conveying pipe is connected to the periphery of the outlet end of the first conveying pipe); each positive swirl ammonia injection component has the same structure.

[0017] The positive swirl ammonia injection assembly includes ammonia injection pipes and swirl blades. There are more than five ammonia injection pipes and swirl blades, and they correspond one-to-one. The ammonia injection pipes are evenly distributed around the outlet of the corresponding second conveying pipe and are connected to the outlet of the second conveying pipe at an angle of 15-35° with the horizontal direction (the inlet end of the ammonia injection pipe is connected to the periphery of the outlet end of the second conveying pipe). The ammonia injection pipes are inclined upwards from the inlet to the outlet, and the outlet of the ammonia injection pipe is the ammonia injection port. The swirl blades are welded to the gas flow (flue gas) side of the outlet end of the ammonia injection pipe, and the outlet end of the ammonia injection pipe is located at the center of the swirl blades. The swirl blades around the same second conveying pipe are arranged in a positive swirl, similar to the arrangement of fan blades, except that the swirl direction is required to be positive.

[0018] The positive swirl ammonia injection components of each group of positive swirl ammonia injection mixing components are located on the same horizontal plane.

[0019] To further improve the mixing effect, a spiral groove is provided on the inner side of the ammonia injection pipe. By combining the upward tilting ammonia injection method with the swirling core design, the uniformity of the mixing between flue gas and ammonia is effectively improved.

[0020] To facilitate assembly and control, and to ensure the spraying effect, the inlet end of the first delivery pipe of each positive-swirl ammonia spraying mixing component passes through the flue and connects to the same ammonia spraying main pipe; the inner diameter of the first delivery pipe is 1 / 3 of the inner diameter of the ammonia spraying main pipe, the inner diameter of the second delivery pipe is 1 / 3 of the inner diameter of the first delivery pipe, and the inner diameter of the ammonia spraying pipe is 1 / 3 of the inner diameter of the second delivery pipe.

[0021] As one specific implementation scheme, the aforementioned swirl blades are square with a side length of 20~30cm.

[0022] To further improve the mixing effect, the aforementioned swirl blades are equipped with circular holes with a diameter of 3-5 mm, and the porosity of the swirl blades is 45-50%. The aforementioned percentages are surface area percentages. A regulating valve is installed on each of the first delivery pipes between the flue and the ammonia injection main pipe.

[0023] To simplify the structure and facilitate preparation and installation, the anti-swirl enhanced mixing device is horizontally arranged in the flue. The anti-swirl enhanced mixing device is provided with inclined holes at an angle of 60 to 80° to the horizontal direction. The inclined holes are arranged in an anti-swirl pattern, and the axial length of the inclined holes is 5 to 10 cm.

[0024] To ensure throughput and reduce resistance, adjacent inclined holes are separated by inclined metal plates with a thickness of 1 to 2.5 mm. The cross-section of the aforementioned inclined holes is square.

[0025] To improve the synergistic effect of reverse swirl enhancement and forward swirl ammonia injection, and to further enhance the mixing uniformity of flue gas and ammonia, the reverse swirl enhancement mixing device is equipped with 4 to 6 sets of reverse swirl oblique holes. Each set of forward swirl ammonia injection mixing components corresponds to a set of reverse swirl oblique holes, and the reverse swirl oblique holes are vertically opposite to their corresponding forward swirl ammonia injection mixing components.

[0026] The structures of the above-mentioned groups of reverse-rotation oblique holes are the same.

[0027] To further improve the uniformity of mixing, the anti-rotating oblique hole assembly includes anti-rotating baffles and anti-rotating blades. The anti-rotating baffles are centered at one end and curled in the opposite direction at the other end to form a reverse spiral structure, with a gap between adjacent turns of the anti-rotating baffles. There are more than six anti-rotating blades, each inclined in the anti-rotating direction and spaced between adjacent turns of the anti-rotating baffles. The space between adjacent anti-rotating blades and anti-rotating baffles forms an oblique hole. The oblique holes on the same anti-rotating oblique hole assembly are inclined in the anti-rotating direction.

[0028] To further improve the uniformity of the mixing of flue gas and ammonia, the top bend of the vertical flue at the inlet of the denitrification device is equipped with two or more arc-shaped guide plates that are parallel and evenly spaced along the height direction.

[0029] Any techniques not mentioned in this invention are based on existing technologies.

[0030] This invention relates to a combined forward and reverse swirl zoned mixing ammonia injection system and method. By injecting ammonia upwards in a forward swirl in conjunction with mechanical mixing in a reverse swirl, it balances low pressure loss and high mixing uniformity, reduces the risk of ammonia injection port blockage, has a simple and stable structure, is easy to modify, and is suitable for upgrading and retrofitting old boilers. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the positive swirl ammonia mixing component of the present invention;

[0032] Figure 2 for Figure 1Enlarged view of point I in the middle;

[0033] Figure 3 for Figure 2 C-axis view;

[0034] Figure 4 for Figure 1 A-direction view;

[0035] Figure 5 for Figure 4 View from direction B;

[0036] Figure 6 This is a schematic diagram of the anti-rotation enhanced mixing device;

[0037] Figure 7 For Figure 6 View from D direction;

[0038] Figure 8 This is a schematic diagram of a zoned mixing ammonia injection system that combines forward and reverse rotation.

[0039] Figure 9 for Figure 8 A three-dimensional image;

[0040] Figure 10 The diagram shows the flue gas flow pattern in the depth direction of the SCR inlet flue in Example 11 (in the figure, (a) is the BMCR operating condition, (b) is 248MW, and (c) is 190MW).

[0041] Figure 11 The diagram shows the flue gas flow pattern in the width direction of the SCR inlet flue in Example 11 (in the figure, (a) is the BMCR operating condition, (b) is 248MW, and (c) is 190MW).

[0042] Figure 12 The diagram shows the flue gas flow path in the width direction of the SCR reactor in Example 11 (in the figure, (a) is the BMCR condition, (b) is 248MW, and (c) is 190MW).

[0043] Figure 13 The flue gas flow pattern in the depth direction of the SCR inlet flue in Comparative Example 1 (BMCR operating condition).

[0044] Figure 14 The flue gas flow diagram in the width direction of the SCR inlet flue in Comparative Example 1 (BMCR operating condition).

[0045] Figure 15 The flue gas flow diagram in the width direction of the SCR reactor in Comparative Example 1 (BMCR condition).

[0046] In the figure, 1 is a vertical flue, 2 is the first arc-shaped guide plate, 3 is a forward-swirling ammonia injection mixing device, 4 is a reverse-swirling enhanced mixing device, 5 is a partition plate, 6 is the ammonia injection main pipe, 7 is the first conveying pipe, 8 is a regulating valve, 9 is the second conveying pipe, 10 is the ammonia injection pipe, 11 is a spiral groove, 12 is a swirl blade, 13 is a round hole, 14 is a reverse-swirling blade, 15 is an oblique hole, and 16 is a reverse-swirling partition plate. Detailed Implementation

[0047] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0048] The directional terms used in this application, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," are based on the orientation or positional relationship shown in the accompanying drawings or in the usage state, and are only for the convenience of describing this application. They are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application.

[0049] Example 1

[0050] like Figure 8-9 As shown, a method for zoned ammonia injection combining forward and reverse rotation is described. In the vertical flue at the inlet of the denitrification unit, ammonia is injected obliquely upward in a forward rotation at an angle of 25° to the horizontal direction. At the same time, at a position 0.6 times the equivalent diameter of the vertical flue downstream of the ammonia injection outlet, the mixing of flue gas and ammonia is enhanced by a reverse rotation at an angle of 70° to the horizontal direction.

[0051] The above method employs a forward-swirl, upward-sloping ammonia injection, forming a diffused spiral upward airflow. This avoids flue gas collisions and localized vortex dead zones, significantly reducing system pressure loss and fan energy consumption compared to downward-sloping injection. Simultaneously, upward injection reduces dust deposition at the nozzle outlet, significantly lowering the risk of nozzle clogging. Furthermore, the direct forward-swirl injection of ammonia at a specific angle balances the diffusion angle of the injected ammonia with its mixing with the flue gas. This, combined with downstream counter-swirl injection at a specific angle to enhance mixing, generates a shear layer vortex, enabling rapid mixing of flue gas and ammonia. The counter-swirl design also effectively corrects the vortex center offset generated by the forward swirl, resulting in more uniform ammonia distribution and a shorter mixing section.

[0052] Example 2

[0053] Based on Example 1, the following improvements were made: two first arc-shaped guide plates, which are arranged parallel and equally spaced along the height direction, are used to guide the flow at the top bend of the vertical flue at the inlet of the denitrification device.

[0054] Example 3

[0055] like Figure 8-9 As shown, a combined forward and reverse swirl ammonia injection system includes a forward swirl ammonia injection mixing device and a reverse swirl enhanced mixing device installed in the vertical flue at the inlet of a denitrification unit. The reverse swirl enhanced mixing device is located downstream of the forward swirl ammonia injection mixing device, and the interval between the forward swirl ammonia injection mixing device and the reverse swirl enhanced mixing device is 0.6 times the equivalent diameter of the vertical flue. The forward swirl ammonia injection mixing device injects ammonia obliquely upward in a forward swirl at an angle of 25° to the horizontal direction, while the reverse swirl enhanced mixing device enhances the mixing of flue gas and ammonia in a reverse swirl at an angle of 70° to the horizontal direction.

[0056] During ammonia injection, a forward-rotating ammonia mixing device is used to inject ammonia diagonally upward in a forward-rotating manner at an angle of 25° to the horizontal direction. At the same time, a reverse-rotating enhanced mixing device is used to enhance the mixing of flue gas and ammonia in a reverse-rotating manner at an angle of 70° to the horizontal direction.

[0057] The above-mentioned mechanical structure design significantly improves the uniformity of ammonia mixing and avoids the problem of easy damage and failure of electrical control equipment under high temperature environment. It is simple, stable and reliable.

[0058] Example 4

[0059] Based on Example 3, such as Figure 1-5 As shown, the following improvements were made: the positive swirl ammonia injection mixing device includes 5 sets of positive swirl ammonia injection mixing components arranged in a straight line in the vertical flue and with the same structure; adjacent sets of positive swirl ammonia injection mixing components are separated by partition plates to form partitioned ammonia injection, the partition plates are set vertically, the bottom of the partition plates is flush with the bottom of the ammonia injection port on the positive swirl ammonia injection mixing components, and the height of the partition plates is 35cm.

[0060] Example 5

[0061] Based on Example 4, the following improvements were made: Figure 1-5As shown, the swirl ammonia injection mixing assembly includes a first conveying pipe, a second conveying pipe, and a swirl ammonia injection component; there are 5 second conveying pipes and 5 swirl ammonia injection components, and they correspond one-to-one; each second conveying pipe is evenly distributed and connected to the periphery of the outlet end of the first conveying pipe; each swirl ammonia injection component has the same structure; each swirl ammonia injection component includes an ammonia injection pipe and swirl blades, and there are 6 ammonia injection pipes and 6 swirl blades, and they correspond one-to-one; the ammonia injection pipes are evenly distributed around the outlet of the corresponding second conveying pipe and are connected to the outlet of the second conveying pipe at a 25° angle to the horizontal direction; the ammonia injection pipes are inclined upwards from the inlet to the outlet, and the bottom of the partition plate is flush with the bottom of the ammonia injection pipe outlet (ammonia injection port); the swirl blades are welded to the gas-facing side of the outlet end of the ammonia injection pipe, and the outlet end of the ammonia injection pipe falls at the center of the swirl blades; the swirl blades around the same second conveying pipe are arranged in a swirl; the swirl ammonia injection components of each group of swirl ammonia injection mixing assemblies are located on the same horizontal plane.

[0062] Example 6

[0063] Based on Example 5, the following improvements were made: a spiral groove was provided on the inner side of the ammonia injection pipe. By combining the upward-sloping ammonia injection method with the swirling core design, the mixing uniformity of flue gas and ammonia was effectively improved.

[0064] Example 7

[0065] Based on Example 6, the following improvements were made: the inlet end of the first conveying pipe of each positive swirl ammonia injection mixing component passes through the flue and is connected to the same ammonia injection main pipe; the inner diameter of the first conveying pipe is 1 / 3 of the inner diameter of the ammonia injection main pipe, the inner diameter of the second conveying pipe is 1 / 3 of the inner diameter of the first conveying pipe, and the inner diameter of the ammonia injection pipe is 1 / 3 of the inner diameter of the second conveying pipe.

[0066] Example 8

[0067] Based on Example 7, the following improvements were made: the swirl blades are square with a side length of 25cm, and the swirl blades have circular holes with a diameter of 3.5mm distributed on them, resulting in a porosity of 48%. A regulating valve is installed on each of the first delivery pipes between the flue and the ammonia injection main pipe.

[0068] Example 9

[0069] Based on Example 8, the following improvements were made: The anti-swirl enhanced mixing device is horizontally arranged in the flue, and the anti-swirl enhanced mixing device is provided with oblique holes at an angle of 70° to the horizontal direction (the angle between the axis of the oblique hole and the horizontal direction is 70 degrees), and the oblique holes are arranged in an anti-swirl pattern, with an axial length of 8 cm. Adjacent oblique holes are separated by inclined stainless steel plates with a thickness of 1.5 mm, and the cross-section of the oblique holes is square.

[0070] Example 10

[0071] Based on Example 9, the following improvements were made: the anti-rotation enhanced mixing device is provided with 5 sets of anti-rotation oblique holes with the same structure. Each set of positive rotation ammonia injection mixing components corresponds to a set of anti-rotation oblique holes, and the anti-rotation oblique holes are vertically opposite to their corresponding positive rotation ammonia injection mixing components.

[0072] Example 11

[0073] Based on Example 10, the following improvements were made: Figure 6-7 As shown, to further improve the uniformity of mixing, the anti-rotating oblique hole assembly includes anti-rotating baffles and anti-rotating blades. The anti-rotating baffles are centered at one end and curled in the opposite direction at the other end to form a reverse spiral structure, with a gap between adjacent turns of the anti-rotating baffles; the number of anti-rotating blades is more than 6, each blade is inclined in the anti-rotating direction and is spaced between adjacent turns of the anti-rotating baffles, and the space between adjacent anti-rotating blades and anti-rotating baffles forms oblique holes. Figure 6 As shown, the oblique holes on the same anti-rotation oblique hole group are inclined in the anti-rotation direction.

[0074] The top bend of the vertical flue at the inlet of the denitrification unit is equipped with two first arc-shaped guide plates arranged parallel to each other along the height direction at equal intervals. The bottom bend of the vertical flue at the inlet of the denitrification unit is equipped with four second arc-shaped guide plates arranged parallel to each other along the height direction at equal intervals. A flow guiding component is located upstream of the second arc-shaped guide plates, and a turbulence-disrupting component is located downstream of the first arc-shaped guide plates. Based on CFD simulation, this example scheme is applied to the upgrade and retrofit of a 300MW unit, and the boundary conditions are shown in Table 1.

[0075] Table 1

[0076] unit BMCR 248MW 190MW temperature ℃ 342 326 305 density kg / m3 0.575 0.590 0.611 Isobaric specific heat capacity J / (kg.K) 1140 1135 1128 heat transfer coefficient W / (mK) 5.204×10-2 5.067×10-2 4.888×10-2 Dynamic viscosity Pa·s 2.988×10-5 2.929×10-5 2.851×10-5 flue inlet speed m / s 4.93 3.84 2.79 Equivalent diameter of flue inlet m 8.25 8.25 8.25 Equivalent diameter of flue outlet m 5.27 5.27 5.27

[0077] The CV values ​​of the ammonia-nitrogen molar ratio distribution 0.5m upstream of the first catalyst layer under BMCR, 248MW, and 190MW operating conditions were 2.4%, 2.7%, and 2.1%, respectively. The temperature deviation 0.5m upstream of the first catalyst layer under different operating conditions was less than 6℃.

[0078] Comparative Example 1

[0079] The difference from Example 10 is that the forward-swirling ammonia injection mixing device and the reverse-swirling enhanced mixing device are replaced with existing ammonia injection grids and vortex mixers. All other aspects are the same as in Example 10.

[0080] Comparative Example 2

[0081] The difference from Example 10 is that the ammonia injection pipe is inclined downwards from the inlet to the outlet, that is, in this example, the ammonia is injected in a downward section at an angle of 25° to the horizontal direction. All other aspects are the same as in Example 10.

[0082] Comparative Example 3

[0083] The difference from Example 10 is that the ammonia injection pipe is connected to the outlet of the second delivery pipe at a 50° angle to the horizontal direction, and the ammonia injection pipe is inclined upwards from the inlet to the outlet. All other aspects are the same as in Example 10.

[0084] Comparative Example 4

[0085] The difference from Example 10 is that the ammonia injection pipe is connected to the outlet of the second delivery pipe at a 70° angle to the horizontal direction, and the ammonia injection pipe is inclined upwards from the inlet to the outlet; the anti-swirl enhanced mixing device is provided with an oblique hole at a 25° angle to the horizontal direction. The rest are the same as in Example 10.

[0086] Example 12

[0087] The difference from Example 10 is that no circular holes are provided on the swirl blades. All other aspects are the same as in Example 10. Table 2 compares the examples under BMCR conditions.

[0088] Table 2

[0089] ammonia injection method Pressure loss (Pa) Catalyst inlet ammonia-nitrogen ratio distribution CV value % Ammonia slip (ppm) Example 11 70~80 2.4 ＜1 Comparative Example 1 (Spraying downwards) 140~150 6.5 4.2 Comparative Example 2 (slanted downwards) 130~140 3.2 ＜2 Comparative Example 3 120~130 3.2 2.8 Comparative Example 4 100~110 4.6 3.3 Example 12 65~75 2.8 ＜2

Claims

1. A method for zoned mixing and ammonia injection combining forward and reverse rotation, characterized in that: In the vertical flue at the inlet of the denitrification unit, ammonia is injected obliquely upward in a forward rotation at an angle of 15-35° to the horizontal. At the same time, at a position 0.5-0.7 times the equivalent diameter of the vertical flue downstream of the ammonia injection outlet, the mixing of flue gas and ammonia is enhanced by a counter-rotation at an angle of 60-80° to the horizontal.

2. The method for combined forward and reverse rotation ammonia injection in zoned mixing according to claim 1, characterized in that: At the top bend of the vertical flue at the inlet of the denitrification unit, two or more arc-shaped guide plates are set at equal intervals along the height direction to guide the flow.

3. A zoned mixing ammonia injection system combining forward and reverse rotation, characterized in that: This includes a positive swirl ammonia injection mixing device and a negative swirl enhanced mixing device installed in the vertical flue at the inlet of the denitrification unit; The reverse swirl enhanced mixing device is located downstream of the forward swirl ammonia injection mixing device, and the interval between the forward swirl ammonia injection mixing device and the reverse swirl enhanced mixing device is 0.5 to 0.7 times the equivalent diameter of the vertical flue. The forward-rotating ammonia injection mixing device injects ammonia obliquely upward in sections at a forward rotation angle of 15-35° to the horizontal direction, while the reverse-rotating enhanced mixing device enhances the mixing of flue gas and ammonia at a reverse rotation angle of 60-80° to the horizontal direction.

4. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 3, characterized in that: The positive swirl ammonia injection mixing device includes 4 to 6 sets of positive swirl ammonia injection mixing components arranged in a straight line in a vertical flue and having the same structure; adjacent sets of positive swirl ammonia injection mixing components are separated by partition plates to form partitioned ammonia injection, the partition plates are set vertically, the bottom of the partition plates is flush with the bottom of the ammonia injection port on the positive swirl ammonia injection mixing components, and the height of the partition plates is 30 to 40 cm.

5. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 4, characterized in that: The positive swirl ammonia injection mixing assembly includes a first conveying pipe, a second conveying pipe, and a positive swirl ammonia injection assembly; The number of the second conveying pipes and the positive swirl ammonia injection components are all three or more, and the number of the two is equal and corresponds one-to-one; each of the second conveying pipes is evenly distributed and connected to the periphery of the outlet end of the first conveying pipe; each positive swirl ammonia injection component has the same structure. The positive swirl ammonia injection assembly includes an ammonia injection pipe and swirl blades, with more than five ammonia injection pipes and swirl blades, and each corresponding to one another. The ammonia injection pipes are evenly distributed around the outlet of the corresponding second conveying pipe and are connected to the outlet of the second conveying pipe at an angle of 15-35° with the horizontal direction. The ammonia injection pipes are inclined upward from the inlet to the outlet. The swirl vanes are welded to the airflow side of the outlet end of the ammonia injection pipe, and the outlet end of the ammonia injection pipe falls at the center of the swirl vanes. The swirl vanes around the same second conveying pipe are arranged in a positive swirl. The positive swirl ammonia injection components of each group of positive swirl ammonia injection mixing components are located on the same horizontal plane.

6. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 5, characterized in that: The inner side of the ammonia injection pipe is equipped with a spiral groove.

7. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 5, characterized in that: The inlet end of the first conveying pipe of each positive swirl ammonia injection mixing component passes through the flue and connects to the same ammonia injection main pipe; the inner diameter of the first conveying pipe is 1 / 3 of the inner diameter of the ammonia injection main pipe, the inner diameter of the second conveying pipe is 1 / 3 of the inner diameter of the first conveying pipe, and the inner diameter of the ammonia injection pipe is 1 / 3 of the inner diameter of the second conveying pipe.

8. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 5, characterized in that: The swirl blades are square with a side length of 20-30cm, and have circular holes with a diameter of 3-5mm distributed on them. The porosity of the swirl blades is 45-50%. Each of the first conveying pipes between the flue and the ammonia injection main pipe is equipped with a regulating valve.

9. The combined forward and reverse swirl zoned mixing ammonia injection system according to any one of claims 3-8, characterized in that: The anti-swirl enhanced mixing device is horizontally arranged in the flue. The anti-swirl enhanced mixing device is provided with inclined holes at an angle of 60 to 80° to the horizontal direction. The inclined holes are arranged in an anti-swirl pattern and the axial length of the inclined holes is 5 to 10 cm. Adjacent inclined holes are separated by inclined metal plates with a thickness of 1 to 2.5 mm.

10. The combined forward and reverse swirl zoned mixing ammonia injection system according to claim 9, characterized in that: The anti-swirl enhanced mixing device is equipped with 4 to 6 sets of anti-swirl inclined holes. Each set of positive swirl ammonia injection mixing components corresponds to a set of anti-swirl inclined holes. The anti-swirl inclined holes and their corresponding positive swirl ammonia injection mixing components are vertically opposite each other. The top bend of the vertical flue at the inlet of the denitrification device is equipped with two or more arc-shaped guide plates that are parallel and equally spaced along the height direction to guide the flow. Each set of anti-rotation oblique hole groups has the same structure; the anti-rotation oblique hole group includes anti-rotation baffles and anti-rotation blades. The anti-rotation baffles are centered at one end and curled in the opposite direction at the other end to form a reverse spiral structure. There is a gap between two adjacent anti-rotation baffles. There are more than 6 anti-rotation blades. Each anti-rotation blade is inclined in the opposite direction and is spaced between two adjacent anti-rotation baffles. The space between two adjacent anti-rotation blades and anti-rotation baffles forms an oblique hole.

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