Flow measuring device for optimizing flow field uniformity and resistance reduction of secondary air distribution box of boiler

Abstract

The application discloses a boiler secondary air distribution box flow field uniform flow resistance reduction optimization and flow measurement device, and relates to the technical field of a boiler secondary air distribution box.The device comprises a main pipeline and two elbow pipelines which are communicated with the main pipeline, the end of the elbow pipeline is provided with a transition chamfer for reducing air resistance, and the inside of the elbow pipeline is provided with a grid plate and a uniform flow assembly for promoting uniform distribution of secondary air flow, and the grid plate and the uniform flow assembly are arranged side by side.The uniform flow assembly comprises a guide plate which is fixedly installed on the inner wall of the elbow pipeline.The grid plate and the uniform flow assembly are arranged in the elbow pipeline, the distribution of the secondary air flow field can be optimized, the secondary air can be uniformly distributed, the air resistance in the elbow pipeline can be reduced by the transition chamfer, the stability and uniformity of the airflow in the pipeline are improved, the accuracy of the measurement of the air measurement element is improved, and the uniformity of the overall air distribution of the boiler is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of boiler secondary air distribution box, and particularly relates to a flow measurement device for optimizing flow field uniformity and resistance reduction of a boiler secondary air distribution box. BACKGROUND

[0002] The existing boiler secondary air system is usually composed of two parts, namely, a burnout air box and a burner secondary air box, for providing secondary air supply required for furnace combustion. The burnout air pipe and the burner secondary air are both arranged with flow measurement points to monitor the distribution of the secondary air volume. However, due to the short straight pipe section, the uneven flow field distribution and the easy interference, the measurement accuracy of the flow measurement points is poor, and the system is difficult to accurately control the deviation of the secondary air volume at the inlet of each corner air box of the front and back walls. Due to the poor flow measurement accuracy of each secondary air distribution box, the overall air distribution of the boiler is uneven, which causes the deterioration of the furnace combustion condition, the uneven distribution of the furnace heat load, the over-temperature of the furnace pipe wall, the high-temperature corrosion, and the poor steam temperature regulation characteristics of the unit. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a flow measurement device for optimizing flow field uniformity and resistance reduction of a boiler secondary air distribution box, which solves the technical problems proposed in the background.

[0004] To solve the above technical problems, the present application provides the following technical scheme: a flow measurement device for optimizing flow field uniformity and resistance reduction of a boiler secondary air distribution box, comprising a main pipe and two elbow pipes installed in communication with the main pipe, the end of the elbow pipe is provided with a transition chamfer for reducing air resistance, and the inside of the elbow pipe is installed with a grid plate and a flow uniformity assembly for promoting uniform distribution of secondary air flow, the grid plate and the flow uniformity assembly are arranged side by side.

[0005] The flow uniformity assembly comprises a guide plate fixedly installed on the inner wall of the elbow pipe, a plurality of funnel-shaped guide holes are formed in the guide plate, and a support rod is installed at each of the four corners of the guide plate, a ventilation plate is fixedly arranged between the four support rods, a plurality of flow uniformity rods with triangular cross sections are rotatably installed in the inside of the ventilation plate, longitudinal air distribution plates are arranged on the left and right sides of the ventilation plate, horizontal air distribution plates are arranged on the upper and lower sides of the ventilation plate, and a driving member is arranged on the ventilation plate to drive the flow uniformity rods, the longitudinal air distribution plates and the horizontal air distribution plates to swing synchronously.

[0006] Further, the grid plate is provided with a hollow part and a solid part, and the guide holes are aligned with the solid part.

[0007] Further, the area of the hollow part accounts for 60%-75% of the total area of the grid plate, and the opening area of the guide holes accounts for 70%-90% of the total area of the guide plate.

[0008] Further, the center line of the ventilation plate coincides with the center line of the guide plate, and the area of the ventilation plate is 40-60% of the area of the guide plate.

[0009] Further, the driving member comprises a servo motor fixedly installed on the side surface of the ventilation plate, the output end of the servo motor is fixedly connected with the end of one of the current sharing rods, the ends of the current sharing rods away from the servo motor are fixedly connected with pulleys one, and the outer portions of the pulleys one are jointly provided with a synchronous belt one.

[0010] Further, the end of one of the horizontal wind dividing plates is fixedly connected with a rotating shaft one, the rotating shaft one is provided with a first transmission member, the first transmission member comprises a pulley two fixedly sleeved on the outer portion of the rotating shaft one, the bottom of the ventilation plate is rotatably installed with a rotating shaft two, the outer portion of the rotating shaft two is fixedly sleeved with a pulley three and a gear one, the outer portions of the pulley two and the pulley three are jointly installed with a synchronous belt two, and the end of the other horizontal wind dividing plate is fixedly connected with a gear two engaged with the gear one.

[0011] Further, the back surface of the ventilation plate is provided with a second transmission member, the second transmission member comprises a fixed rod fixedly installed on the back surface of the ventilation plate, the top of the fixed rod is slidably connected with a sliding frame, the two ends of the sliding frame are rotatably installed with connecting rods, the ends of the connecting rods are rotatably connected with connecting seats, and the connecting seats are slidably installed on the side surface of the vertical wind dividing plate.

[0012] Further, the back surface of the ventilation plate is rotatably installed with a rotating shaft three, the outer portion of the rotating shaft three is fixedly sleeved with a cam, and the sliding frame and the ventilation plate are installed with two symmetrically arranged connecting springs.

[0013] Further, the ends of the rotating shaft one and the rotating shaft three are fixedly connected with pulleys four, the axis of one of the pulleys one is fixedly connected with a pulley five, and the outer portions of the pulley five and the two pulleys four are jointly installed with a synchronous belt three.

[0014] By the above technical scheme, the application provides a flow measurement device for optimizing the flow field uniformity and resistance reduction of a secondary wind box of a boiler, which has at least the following beneficial effects:

[0015] 1. By arranging the grid plate and the current sharing assembly in the elbow pipe, the application can optimize the distribution of the secondary wind flow field, realize uniform distribution of the secondary wind, reduce the airflow resistance in the elbow pipe, improve the stability and uniformity of the airflow in the pipe, and thus improve the accuracy of the measurement of the wind measurement element and help optimize the uniformity of the overall wind distribution of the boiler.

[0016] 2. By controlling the proportion and layout of the hollow part and the guide hole, the application helps the stable flow of the airflow, ensures the uniform passage of the airflow through the guide plate and the grid plate, reduces the pressure drop and resistance of the airflow on the surfaces of the two plates, and improves the airflow passing rate.

[0017] 3、The present application can guide part of the airflow in the center area of the elbow pipe to the edge of the guide plate through the longitudinal and transverse air distribution plates, so that the airflow can pass through the guide plate uniformly, reduce the flow difference between the airflow in the center area of the elbow pipe and the airflow near the inner wall, and realize uniform distribution of the airflow. BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0019] Figure 1 is a schematic diagram of the overall structure of the present application;

[0020] Figure 2 is a schematic diagram of the internal structure of the elbow pipe of the present application;

[0021] Figure 3 is a schematic diagram of the flow uniformizing assembly structure of the present application;

[0022] Figure 4 is a schematic diagram of the flow uniformizing assembly structure of the present application;

[0023] Figure 5 is a schematic diagram of the flow uniformizing assembly structure of the present application; Figure 4 is an enlarged view of A shown in the drawing;

[0024] Figure 6 is a sectional view of the ventilation plate of the present application;

[0025] Figure 7 is a schematic diagram of the grid plate and the guide plate structure of the present application;

[0026] Figure 8 is a sectional view of the grid plate and the guide plate of the present application.

[0027] In the drawing:

[0028] 1, main pipe;

[0029] 2, elbow pipe;

[0030] 3, grid plate; 31, hollow part; 32, solid part;

[0031] 4, flow equalization assembly; 41, flow guide plate; 42, flow guide hole; 43, support rod; 44, ventilation plate; 45, flow equalization rod; 46, longitudinal partition plate; 47, transverse partition plate; 481, servo motor; 482, pulley one; 483, synchronous belt one; 484, rotating shaft one; 485, first transmission member; 4851, pulley two; 4852, rotating shaft two; 4853, pulley three; 4854, synchronous belt two; 4855, gear one; 4856, gear two; 4861, fixed rod; 4862, sliding bracket; 4863, connecting rod; 4864, connecting seat; 4865, rotating shaft three; 4866, cam; 4867, connecting spring; 489, pulley four; 4810, pulley five; 4811, synchronous belt three;

[0032] 5, transition chamfer. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application. Embodiment one

[0034] Because the straight pipe section of the existing secondary air distribution box is short, the flow field distribution is uneven and is easily disturbed, the measurement accuracy of the flow measurement point is poor, and the system is difficult to accurately control the deviation of the secondary air volume of each corner air box inlet of the front and back walls. Due to the poor flow measurement accuracy of each secondary air distribution box, the overall air distribution of the boiler is uneven, which causes the deterioration of the combustion condition of the furnace, the uneven distribution of the furnace heat load, the over-temperature of the furnace pipe wall, the high-temperature corrosion, and the poor steam temperature regulation characteristics of the unit.

[0035] To solve the defects of the air distribution box of the above-mentioned device in use, please refer to Figures 1-8The application provides a flow measuring device for optimizing flow field uniformity and resistance of a boiler secondary air distribution box, which can optimize secondary air flow field distribution and improve the accuracy of flow point measurement without changing the original secondary air duct arrangement. The secondary air distribution box takes a main pipeline 1 and two elbow pipelines 2 communicated with the main pipeline 1 as the basis, a plurality of wind measuring elements are arranged in the main pipeline 1 and the elbow pipeline 2, the wind measuring element is prior art, and the measurement principle is not described in detail here, the plurality of wind measuring elements can realize multi-point measurement, compared with the traditional single-point measurement, the accuracy of measurement can be improved, the end of the elbow pipeline 2 is provided with a transition chamfer 5 for reducing the wind resistance, and the inside of the elbow pipeline 2 is provided with a grid plate 3 and a flow uniformity assembly 4 for promoting the uniform distribution of the secondary air flow, and the grid plate 3 and the flow uniformity assembly 4 are arranged side by side. Wherein the flow guide plate 41 is fixedly installed on the inner wall of the elbow pipeline 2, a plurality of funnel-shaped flow guide holes 42 are formed in the flow guide plate 41, and a supporting rod 43 is installed on each of the four corners of the flow guide plate 41, a ventilation plate 44 is fixedly arranged between the four supporting rods 43, a plurality of flow uniformity rods 45 with triangular cross sections are rotatably installed in the inside of the ventilation plate 44, and the air flow entering the main pipeline 1 from the elbow pipeline 2 sequentially passes through the ventilation plate 44, the flow guide plate 41 and the grid plate 3. When the air flow passes through the ventilation plate 44, it can be preliminarily divided by the flow uniformity rod 45, and the divided air flow passes through the flow uniformity rod 45 and enters the flow guide hole 42, the diameter of the flow guide hole 42 gradually decreases from front to back, the flow guide hole 42 can fully collect the air flow and uniformly guide the air flow to the grid plate 3, and then uniformly release the air flow through the grid plate 3 and enter the main pipeline 1 through the transition chamfer 5. The setting of the transition chamfer 5 can help the air flow to smoothly and stably transition to the main pipeline 1, thereby improving the flow efficiency.

[0036] In order to realize the effect that the air flow uniformly passes through the grid plate 3, the grid plate 3 is provided with a hollow part 31 and a solid part 32, the flow guide hole 42 is aligned with the solid part 32, the air flow entering the flow guide hole 42 can flow to the solid part 32 and then uniformly disperse to the hollow part 31 around the solid part 32, thereby realizing the effect that the air flow uniformly passes through the hollow part 31.

[0037] Since the grid plate 3 and the flow guide plate 41 may increase the wind resistance, the area of the hollow part 31 accounts for 60%-75% of the total area of the grid plate 3, the opening area of the flow guide hole 42 accounts for 70%-90% of the total area of the flow guide plate 41, the median line of the ventilation plate 44 and the median line of the flow guide plate 41 coincide, and the area of the ventilation plate 44 is 40%-60% of the area of the flow guide plate 41. By controlling the proportion and layout of the hollow part 31 and the flow guide hole 42, the air flow can flow as smoothly as possible, the air flow can uniformly pass through while reducing the pressure drop and resistance of the air flow on the surface of the component, and the air flow passing rate is improved. Embodiment two

[0038] Since when the air flow flows in the elbow pipe 2, most of the air flow will pass from the center of the guide plate 41, and a small part of the air flow will pass from the edge of the guide plate 41, which causes the flow rate and flow of the center of the elbow pipe 2 to be different from the flow rate and flow of the inner wall of the elbow pipe 2, and affects the detection accuracy of the wind measuring element. In order to solve this technical problem, the longitudinal flow dividing plate 46 is arranged on the left and right sides of the ventilation plate 44, and the transverse flow dividing plate 47 is arranged on the upper and lower sides of the ventilation plate 44. When the air flow in the center of the elbow pipe 2 passes through the ventilation plate 44, the longitudinal flow dividing plate 46 and the transverse flow dividing plate 47 can guide part of the air flow to the inner wall of the elbow pipe 2, reduce the flow difference between the air flow in the center of the elbow pipe 2 and the air flow in the inner wall of the elbow pipe 2, and the arrangement of the flow equalizing rod 45 can on the one hand make the air flow in the center of the elbow pipe 2 pass uniformly, and on the other hand can reduce the flow rate of the air flow in the center of the elbow pipe 2, thereby reducing the flow rate difference between the air flow in the center of the elbow pipe 2 and the air flow in the inner wall of the elbow pipe 2, improving the consistency and uniformity of the flow rate and flow of the air flow in the elbow pipe 2, and thereby ensuring the accuracy of the measurement of the wind measuring element.

[0039] In order to make the ventilation plate 44 uniformly send the air flow to the guide plate 41, the drive member for driving the flow equalizing rod 45, the longitudinal flow dividing plate 46 and the transverse flow dividing plate 47 to swing synchronously is further arranged on the ventilation plate 44. The drive member is a servo motor 481 fixedly installed on the side surface of the ventilation plate 44. The output end of the servo motor 481 is fixedly connected with the end of one of the flow equalizing rods 45. The end of the flow equalizing rod 45 away from the servo motor 481 is fixedly connected with a pulley one 482. The plurality of pulley ones 482 are externally provided with a synchronous belt one 483. The servo motor 481 can drive one of the flow equalizing rods 45 to swing. The flow equalizing rod 45 drives the corresponding pulley one 482 to swing. The pulley one 482 drives the plurality of synchronous belts one 483 to swing synchronously through the synchronous belt one 483. The plurality of synchronous belts one 483 can drive the plurality of flow equalizing rods 45 to swing synchronously. The swing of the flow equalizing rod 45 can change the air outlet direction of the ventilation plate 44, thereby uniformly sending the air flow to the guide plate 41.

[0040] In order to send the airflow to the edge position of the guide plate 41, that is, the inner wall of the elbow pipe 2, a rotating shaft one 484 is fixedly connected to the end of one of the horizontal air distribution plates 47, a first transmission member 485 is arranged on the rotating shaft one 484, the first transmission member 485 comprises a belt pulley two 4851 which is fixedly sleeved on the outside of the rotating shaft one 484, a rotating shaft two 4852 is rotatably installed at the bottom of the air distribution plate 44, a belt pulley three 4853 and a gear one 4855 are fixedly sleeved on the outside of the rotating shaft two 4852, a synchronous belt two 4854 is jointly installed on the outside of the belt pulley two 4851 and the belt pulley three 4853, the end of the other horizontal air distribution plate 47 is fixedly connected to a gear two 4856 which is engaged with the gear one 4855, the rotating shaft one 484 can drive the horizontal air distribution plate 47 to rotate, and at the same time, the rotating shaft two 4852 can be driven to rotate through the belt pulley two 4851, the belt pulley three 4853 and the synchronous belt two 4854, the rotating shaft two 4852 drives the gear one 4855 to rotate, the gear one 4855 drives the gear two 4856 to rotate in the opposite direction, and the gear two 4856 drives the other horizontal air distribution plate 47 to rotate in the opposite direction, so as to realize the reciprocating swing of the two horizontal air distribution plates 47, and the airflow can flow along the horizontal air distribution plate 47 to the upper and lower sides of the guide plate 41 when passing through the horizontal air distribution plate 47, thereby increasing the airflow flow rate on the upper and lower sides of the guide plate 41 and reducing the flow rate difference in the elbow pipe 2.

[0041] At the same time of distributing part of the airflow to the upper and lower sides of the guide plate 41, part of the airflow also needs to be distributed to the left and right sides of the guide plate 41, therefore, a second transmission member is arranged on the back of the air distribution plate 44, the second transmission member comprises a fixed rod 4861 which is fixedly installed on the back of the air distribution plate 44, a sliding frame 4862 is slidably connected to the top of the fixed rod 4861, connecting rods 4863 are rotatably installed at the two ends of the sliding frame 4862, connecting seats 4864 are rotatably connected to the ends of the connecting rods 4863, the connecting seats 4864 are slidably installed on the side of the vertical air distribution plate 46, a rotating shaft three 4865 is rotatably installed on the back of the air distribution plate 44, a cam 4866 is fixedly sleeved on the outside of the rotating shaft three 4865, the cam 4866 abuts against the side of the fixed rod 4861, two connecting springs 4867 which are symmetrically arranged are installed between the sliding frame 4862 and the air distribution plate 44, the rotating shaft three 4865 can drive the cam 4866 to rotate, the cam 4866 can extrude the fixed rod 4861 to slide, and the reciprocating sliding of the fixed rod 4861 can be realized by the elastic force of the connecting springs 4867, the reciprocating rotation of the connecting rods 4863 can be realized by the reciprocating sliding of the fixed rod 4861, and the reciprocating swing of the two vertical air distribution plates 46 can be realized by the reciprocating rotation of the connecting rods 4863, so as to guide part of the airflow to the left and right sides of the guide plate 41 and realize the uniform distribution of the airflow.

[0042] In order to realize the synchronous rotation of the rotating shaft three 4865 and the rotating shaft one 484, the pulley four 489 is fixedly connected to the end of the rotating shaft one 484 and the rotating shaft three 4865, the axis of one pulley one 482 is fixedly connected with the pulley five 4810, the pulley five 4810 and the outer part of the two pulley four 489 are jointly installed with the synchronous belt three 4811, the synchronous rotation of the rotating shaft three 4865 and the rotating shaft one 484 can be driven by the pulley five 4810, the pulley four 489 and the synchronous belt three 4811 through the rotation of the uniform flow rod 45, the synchronous swing of the horizontal air baffle 47 and the vertical air baffle 46 is realized, part of the airflow in the elbow pipe 2 is distributed to the edge of the guide plate 41, and the flow field distribution is optimized.

[0043] The control mode of the present application is automatically controlled through a controller, the control circuit of the controller can be realized through simple programming by those skilled in the art, the power supply also belongs to the common knowledge in the art, and the present application is mainly used for protecting mechanical devices, therefore, the control mode and the circuit connection of the present application will not be explained in detail.

[0044] It should be noted that, in the present text, relational terms such as first and second and the like can only be used to distinguish one entity or action from another entity or action, without necessarily requiring or implying that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or apparatus that comprises a list of elements does not only include those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, article, or apparatus.

[0045] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flow measuring device for optimizing the flow field uniformity and resistance of a secondary air distribution box of a boiler, comprising a main pipe (1) and two elbow pipes (2) installed in communication with the main pipe (1), a plurality of air flow measuring elements are arranged in the main pipe (1) and the elbow pipes (2), characterized in that: The end of the elbow pipe (2) is provided with a transition chamfer (5) for reducing wind resistance, and the inside of the elbow pipe (2) is provided with a grid plate (3) and a flow uniformizing assembly (4) for promoting uniform distribution of secondary air flow, and the grid plate (3) and the flow uniformizing assembly (4) are arranged side by side; The flow uniformizing assembly (4) comprises a flow guide plate (41) fixedly installed on the inner wall of the elbow pipe (2), a plurality of funnel-shaped flow guide holes (42) are formed in the flow guide plate (41), and a supporting rod (43) is installed at each of the four corners of the flow guide plate (41), a ventilation plate (44) is fixedly arranged between the four supporting rods (43), a plurality of flow uniformizing rods (45) with triangular cross sections are rotatably installed in the ventilation plate (44), longitudinal air distribution plates (46) are arranged on the left and right sides of the ventilation plate (44), and horizontal air distribution plates (47) are arranged on the upper and lower sides of the ventilation plate (44), and a driving member is arranged on the ventilation plate (44) to drive the flow uniformizing rods (45), the longitudinal air distribution plates (46) and the horizontal air distribution plates (47) to swing synchronously. The grid plate (3) is provided with a hollow part (31) and a solid part (32), the flow guide holes (42) are aligned with the solid part (32), the area of the hollow part (31) accounts for 60-75% of the total area of the grid plate (3), the opening area of the flow guide holes (42) accounts for 70-90% of the total area of the flow guide plate (41), the median line of the ventilation plate (44) coincides with the median line of the flow guide plate (41), and the area of the ventilation plate (44) is 40-60% of the area of the flow guide plate (41), the driving member comprises a servo motor (481) fixedly installed on the side surface of the ventilation plate (44), the output end of the servo motor (481) is fixedly connected with the end of one of the flow uniformizing rods (45), and the other ends of the plurality of flow uniformizing rods (45) away from the servo motor (481) are fixedly connected with pulleys (482), and the outer portions of the plurality of pulleys (482) are jointly provided with a synchronous belt (483).

2. The flow measurement device for the flow field uniformity and resistance reduction optimization of the boiler secondary air box of claim 1, wherein: The end of one of the horizontal air distribution plates (47) is fixedly connected with a rotating shaft (484), the rotating shaft (484) is provided with a first transmission member (485), the first transmission member (485) comprises a pulley (4851) fixedly sleeved on the outer portion of the rotating shaft (484), the bottom of the ventilation plate (44) is rotatably installed with a rotating shaft (4852), the outer portion of the rotating shaft (4852) is fixedly sleeved with a pulley (4853) and a gear (4855), the outer portions of the pulley (4851) and the pulley (4853) are jointly provided with a synchronous belt (4854), and the end of the other horizontal air distribution plate (47) is fixedly connected with a gear (4856) engaged with the gear (4855).

3. The flow measurement device for the flow field uniformity and resistance reduction optimization of the boiler secondary windbox of claim 2, wherein: The back of the ventilation plate (44) is provided with a second transmission element, the second transmission element comprises a fixed rod (4861) fixedly installed on the back of the ventilation plate (44), the top of the fixed rod (4861) is slidably connected with a sliding frame (4862), both ends of the sliding frame (4862) are rotatably installed with connecting rods (4863), the end of the connecting rod (4863) is rotatably connected with a connecting seat (4864), and the connecting seat (4864) is slidably installed on the side of the longitudinal partition plate (46).

4. The flow measurement device for the flow field uniformity and resistance reduction optimization of the boiler secondary windbox of claim 3, wherein: The back of the ventilation plate (44) is further rotatably installed with a rotating shaft three (4865), the outside of the rotating shaft three (4865) is fixedly sleeved with a cam (4866), and two symmetrically arranged connecting springs (4867) are installed between the sliding frame (4862) and the ventilation plate (44).

5. The flow measurement device for the flow field uniformity and resistance reduction optimization of the boiler secondary windbox of claim 4, wherein: The ends of the rotating shaft one (484) and the rotating shaft three (4865) are fixedly connected with pulleys four (489), the axis of one of the pulleys one (482) is fixedly connected with a pulley five (4810), and the outside of the pulley five (4810) and the two pulleys four (489) are jointly installed with a synchronous belt three (4811).

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