Octagonal tangential boiler hot secondary air system and process

Abstract

The application relates to the technical field of boiler air distribution control, and provides an eight-corner tangential Pi-shaped boiler hot secondary air system and a process, which comprises a hearth, the hearth is connected with two hot secondary air systems; the two hot secondary air systems comprise a hot secondary air preparation mechanism, the hot secondary air preparation mechanism is connected with a first rectifying air duct through an air outlet channel, the first rectifying air duct is respectively connected with a front wall secondary air mechanism and a rear wall secondary air mechanism through first branch air ducts, the front wall secondary air mechanism and the rear wall secondary air mechanism are respectively connected with the hearth and symmetrically arranged; the front wall secondary air mechanism is connected with a front wall overfire air mechanism, the rear wall secondary air mechanism is connected with a rear wall overfire air mechanism, and the front wall overfire air mechanism and the rear wall overfire air mechanism are symmetrically arranged with the center line of the hearth. The scheme ensures that the flow is consistent when entering the bifurcated loop, and avoids the serious hot air flow unevenness existing in the traditional arrangement mode during the operation of the unit.

Description

Technical Field

[0001] This invention relates to the field of boiler air distribution control technology, specifically to an octagonal tangent-circle Π-shaped boiler hot secondary air system and process. Background Technology

[0002] Due to the limitations of coal-fired units, especially the duct layout and blower placement of the octagonal Π-shaped furnace, the duct paths entering the large air boxes on the front and rear walls of the boiler are very different, resulting in significant differences in the resistance of each circuit. Later, it is necessary to modify the duct to ensure the balance of air volume entering the air box, so as to ensure a reasonable aerodynamic field inside the furnace.

[0003] Therefore, the design of secondary hot air ducts during the infrastructure phase rarely considers the distribution of secondary hot air volume. The primary design principle remains minimizing material usage and maximizing space utilization. However, this design approach leads to significant problems in boiler combustion later on. Secondary hot air, a crucial component of boiler combustion, plays a vital role in pulverized coal combustion, providing a small portion of oxygen in the initial stages and all of it in the later stages. Therefore, a proper distribution of secondary hot air volume directly impacts boiler combustion quality, pulverized coal burnout, pollutant emissions, and corrosion and coking of the boiler water-cooled walls, among other issues.

[0004] Currently, in order to alleviate or solve the problem of uneven air volume distribution in octagonal tangential Π-shaped boilers, the modification team has tried to add guide plates and resistance orifice plates in some locations. However, this modification scheme often has great uncertainty. The increase in resistance of the orifice plate and the guiding effect of the guide plate often rely on numerical simulation technology and some preliminary test data on site, which will lead to a large gap between the actual effect after the modification and the simulation effect. Furthermore, fixed guide plates and orifice plates do not have room for later adjustment, and the adjustment performance of the baffle gate in the air duct is very poor. Therefore, the expected effect of the modification cannot be achieved.

[0005] In conclusion, the effects of later modifications are very likely to fail to meet the requirements, and the distribution of secondary air volume has a huge impact on boiler combustion. Therefore, adopting a reasonable layout of the hot secondary air duct in the early stage of design is a one-time solution. From the perspective of long-term operation of the unit, excessive focus on saving materials and simple layout in the early stage of design is often counterproductive. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention proposes an octagonal tangential Π-shaped boiler hot secondary air system and process, which ensures consistent flow when entering the bifurcation circuit, avoiding the serious uneven hot air flow that occurs during unit operation in traditional layout methods. This improves boiler combustion efficiency, reduces pollutant emissions, extends boiler service life, and enhances overall boiler performance.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: An octagonal tangent-circle Π-shaped boiler hot secondary air system includes a furnace, the furnace being connected to two hot secondary air systems, the two hot secondary air systems being connected by a connecting air duct and symmetrically arranged along the centerline of the furnace; The hot secondary air system includes a hot secondary air preparation mechanism, which is connected to a first rectifier air duct through an air outlet channel. The first rectifier air duct is connected to a front wall secondary air mechanism and a rear wall secondary air mechanism through a first branch air duct. The front wall secondary air mechanism and the rear wall secondary air mechanism are respectively connected to the furnace and are symmetrically arranged along the centerline of the furnace. The front wall secondary air mechanism is connected to a front wall burnout air mechanism, and the rear wall secondary air mechanism is connected to a rear wall burnout air mechanism. The front wall burnout air mechanism and the rear wall burnout air mechanism are symmetrically arranged along the centerline of the furnace. The front wall burnout air mechanism includes a front second rectifier air duct, which is connected to the furnace through a front second branch air duct; the rear wall burnout air mechanism includes a rear second rectifier air duct, which is connected to the furnace through a rear second branch air duct.

[0008] Furthermore, the front wall secondary air mechanism includes a front wall secondary air duct connected to the first diversion air duct, a front second rectifier air duct connected to the front wall secondary air duct, and the front wall secondary air duct connected to the furnace through a front wall secondary air box; the rear wall secondary air mechanism includes a rear wall secondary air duct connected to the first diversion air duct, a rear second rectifier air duct connected to the rear wall secondary air duct, and the rear wall secondary air duct connected to the furnace through a rear wall secondary air box.

[0009] Furthermore, the first rectifier duct is connected to two first branch ducts via connectors, and the two first branch ducts are symmetrically arranged with respect to the centerline of the first rectifier duct; the front second rectifier duct is connected to two front second branch ducts via connectors, and the two front second branch ducts are symmetrically arranged with respect to the centerline of the front second rectifier duct; the rear second rectifier duct is connected to two rear second branch ducts via connectors, and the two rear second branch ducts are symmetrically arranged with respect to the centerline of the rear second rectifier duct.

[0010] Furthermore, the connector is provided with a flow guiding device, which includes a plurality of flow guiding plates, and the spacing between adjacent flow guiding plates gradually increases from the inner arc to the outer arc.

[0011] Furthermore, the flow guiding device is fixed by flat steel and tie rods, and the tie rods and flat steel are arranged in the direction of airflow.

[0012] Furthermore, the duct design wind speed of the front wall secondary air mechanism and the rear wall secondary air mechanism is selected in the range of 15~30m / s.

[0013] Furthermore, the velocity of each cross-section of the first rectifier duct, the first branch duct, the front second rectifier duct, the front second branch duct, the rear second rectifier duct, and the rear second branch duct is uniform.

[0014] Furthermore, air intakes are provided on the front second rectifier air duct and the rear second rectifier air duct, and the air velocity of the front wall burnout air mechanism and the rear wall burnout air mechanism is selected in the range of 15~30m / s.

[0015] Furthermore, the hot secondary air preparation mechanism includes a blower, which is connected to the air outlet channel through an air preheater, and the air outlet channels of the two hot secondary air systems are connected through the connecting air duct.

[0016] A process for a hot secondary air system for an octagonal tangentially shaped Π-type boiler includes the following steps: The two hot secondary air systems heat cold air into hot secondary air through their respective outlet channels. The hot secondary air from both systems is then connected and mixed via a connecting duct. Simultaneously, the hot secondary air from both systems continues to flow into their respective systems: the hot secondary air enters the first rectifier duct through the outlet channel, then is rectified and enters the first branch duct, where it is split into two streams of hot secondary air with equal flow rates. Finally, these streams are injected into the furnace through symmetrically arranged front and rear wall hot secondary air mechanisms. A stream of hot secondary air is drawn from the secondary air mechanism on the front wall as the burnout air for the front wall and enters the second rectifier air duct. After passing through the second split air duct, it is divided into two streams of hot secondary air with the same flow rate and injected into the furnace. A stream of hot secondary air is drawn from the secondary air mechanism on the rear wall as the burnout air for the rear wall and enters the second rectifier air duct. After passing through the second split air duct, it is divided into two streams of hot secondary air with the same flow rate and injected into the furnace.

[0017] The beneficial effects of this invention are as follows: First, two symmetrically connected secondary hot air systems are connected to the furnace to ensure consistent airflow in both systems. The secondary hot air is rectified by the first rectifier duct and then enters two first branch ducts, which are then connected to the symmetrically arranged front and rear wall secondary hot air mechanisms. This ensures that the duct paths for the front and rear walls are identical, guaranteeing that the secondary air flow rate entering the front wall is the same as that entering the rear wall under any load condition.

[0018] Moreover, the front wall burnout air mechanism and the rear wall burnout air mechanism are symmetrically arranged, and the two burnout air mechanisms are diverted to the second diversion air duct through the second rectifier air duct, ensuring that the flow rate of burnout air entering each corner is the same.

[0019] Secondly, the internal flow guiding device of the connector ensures that the flow rate is consistent when entering different air ducts. The uniform velocity of each air duct section of the first rectifier air duct, the first branch air duct, the front second rectifier air duct, the front second branch air duct, the rear second rectifier air duct, and the rear second branch air duct ensures that the flow field of the hot secondary air is uniform. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall system structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the burnout air system structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the internal flow guiding device in the connector according to an embodiment of the present invention. Figure 1 ; Figure 4 This is a schematic diagram of the internal flow guiding device in the connector according to an embodiment of the present invention. Figure 2 .

[0021] The following are labeled in the diagram: 1. Secondary air box on the rear wall; 2. Furnace; 3. First branch air duct; 4. Connecting air duct; 5. Air preheater; 6. Secondary air box on the front wall; 7. First rectifier air duct; 8. Secondary air duct on the rear wall; 9. Secondary air duct on the front wall; 10. Second rectifier air duct on the front; 11. Second branch air duct on the front; 12. Second rectifier air duct on the rear; 13. Second branch air duct on the rear. Detailed Implementation

[0022] To make the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are merely one implementation method and do not represent all embodiments.

[0023] Combination Figures 1-4 This embodiment provides an octagonal tangent-circle Π-shaped boiler hot secondary air system, including a furnace 2. The furnace 2 is connected to a hot secondary air system. Two hot secondary air systems are connected by a connecting air duct 4 and are symmetrically arranged along the centerline of the furnace 2. The connecting air duct 4 is equipped with a connecting air damper to adjust the air duct pressure. This symmetrical connection layout can ensure that the air volume of the two hot secondary air systems is consistent, which helps to improve the stability of the furnace 2 operation and the uniformity of air volume distribution.

[0024] The hot secondary air system includes a hot secondary air preparation mechanism, which is connected to a first rectifier duct 7 via an air outlet channel. The first rectifier duct 7 is connected to a front wall secondary air mechanism and a rear wall secondary air mechanism via a first branch duct 3. The front wall secondary air mechanism and the rear wall secondary air mechanism are connected to the furnace 2 and are symmetrically arranged along the centerline of the furnace 2. The front wall secondary air mechanism is connected to a front wall burnout air mechanism, and the rear wall secondary air mechanism is connected to a rear wall burnout air mechanism. The front wall burnout air mechanism and the rear wall burnout air mechanism are symmetrically arranged along the centerline of the furnace 2. The front wall burnout air mechanism includes a front second rectifier duct 10, which is connected to the furnace 2 via a front second branch duct 11. The rear wall burnout air mechanism includes a rear second rectifier duct 12, which is connected to the furnace 2 via a rear second branch duct 13.

[0025] The first rectifier duct 7 is connected to two first branch ducts 3 via connectors, and the two first branch ducts 3 are symmetrically arranged about the centerline of the first rectifier duct 7. The front second rectifier duct 10 is connected to two front second branch ducts 11 via connectors, and the two front second branch ducts 11 are symmetrically arranged about the centerline of the front second rectifier duct 10. The rear second rectifier duct 12 is connected to two rear second branch ducts 13 via connectors, and the two rear second branch ducts 13 are symmetrically arranged about the centerline of the rear second rectifier duct 12. Air intakes are also provided on the front second rectifier duct 10 and the rear second rectifier duct 12.

[0026] Preferably, the front wall secondary air mechanism includes a front wall secondary air duct 9 connected to the first diversion air duct 3, a front second rectifier air duct 10 connected to the front wall secondary air duct 9, and the front wall secondary air duct 9 is connected to the furnace 2 through the front wall secondary air box 6; the rear wall secondary air mechanism includes a rear wall secondary air duct 8 connected to the first diversion air duct 3, a rear second rectifier air duct 12 connected to the rear wall secondary air duct 8, and the rear wall secondary air duct 8 is connected to the furnace 2 through the rear wall secondary air box 1.

[0027] This embodiment adopts a symmetrical arrangement to ensure that the air duct paths of the secondary air box 1 entering the boiler rear wall and the secondary air box 6 entering the boiler front wall are the same, and the number and type of burnout air duct bends entering each corner burnout air nozzle are completely consistent. Compared with the traditional arrangement where hot secondary air first enters the secondary air box 1 and the burnout air mechanism on the rear wall, and then is diverted to the secondary air box 6 and the burnout air mechanism on the front wall, this arrangement ensures that under any load condition, the flow rate of the hot secondary air system entering the secondary air box 6 on the front wall is the same as the flow rate entering the secondary air box 1 on the rear wall, and the flow rate of the burnout air entering each corner is the same.

[0028] The hot secondary air preparation mechanism includes a blower. The cold air delivered by the blower is heated by the air preheater 5 to become hot secondary air. The output end of the air preheater 5 is connected to the air outlet channel. As a preferred embodiment, a connecting air duct 4 is set at the air outlet channels of the two hot secondary air systems to ensure that the air volume of the main pipe of the two hot secondary air systems is consistent.

[0029] In this embodiment, other locations where the air ducts change are also provided with connecting parts. The connecting parts include elbows, irregular parts, and flow dividers. The connecting parts are provided with flow guiding devices. The flow guiding devices include several flow guiding plates. The spacing between adjacent flow guiding plates gradually increases from the inner arc to the outer arc. By adjusting the flow direction and flow performance of the hot secondary air, the flow rate is ensured to be consistent when entering different air ducts.

[0030] The design principles of the first rectifying duct 7, the first branching duct 3, the front second rectifying duct 10, the front second branching duct 11, the rear second rectifying duct 12, and the rear second branching duct 13 adopt the flow field optimization principle, rather than the resistance minimization principle, to ensure uniform velocity across each duct cross-section. The flow field optimization principle aims to achieve optimal airflow distribution and flow field state by optimizing the geometry and layout of the ducts. This principle considers factors such as velocity distribution, airflow uniformity, and resistance distribution, achieving optimal flow field performance through reasonable duct design. The resistance minimization principle refers to minimizing resistance loss through duct shape and size design. This principle aims to reduce wind resistance in the duct system to lower system energy consumption and operating costs. Under the resistance minimization principle, the focus is on reducing resistance loss within the duct, but airflow uniformity cannot be guaranteed. Therefore, the flow field optimization principle is adopted in the design to ensure uniform hot secondary airflow.

[0031] The principle of optimal flow field refers to minimizing the standard velocity deviation rate of the cross-section. As an optimal approach, simulation software is used to calculate the velocity distribution of the hot secondary airflow passing through the guide device, thereby obtaining the standard velocity deviation rate of the cross-section after passing through the guide device. By continuously adjusting the spacing and curvature of each guide vane, multiple optimized physical models are generated. These models are then imported into a high-performance computer for numerical simulation calculations. Through iterative calculations, an optimal guide vane arrangement scheme for the flow field is achieved. The current regulations recommend the following methods for calculating the number of guide vanes and the spacing between them: , in, , , , This is the total distance from the inner edge to the outer edge of the elbow. These are the radial widths of the two air ducts connected to the elbow, respectively. To set the number of deflectors, The inner bending radius of the elbow. This is the first spacing on the inner edge of the bend. And so on.

[0032] Compared with the empirical installation method of the guide vane recommended in the regulations, the guide vane installation scheme optimized by numerical simulation is more accurate and has a smaller velocity deviation rate after the flow passes through the guide device.

[0033] The baffle plate is reinforced using flat steel and tie rods. The tie rods and flat steel are positioned in the direction of airflow; support rods are not recommended to prevent uneven distribution of hot secondary air within the duct. The number of tie rods should be 2-4 pieces depending on the duct size, and the number of flat steel pieces should be 1-4 pieces depending on the width of the baffle plate. The structural strength and stability of the duct can be improved by adding reinforcing ribs to the outside of the duct.

[0034] Using the system provided in this example, the design wind speed of the split duct is flexible and does not need to consider the resistance distribution between the front and rear walls. It is only necessary to consider the resistance distribution of the secondary air box 6 entering the front wall, the secondary air box 1 entering the rear wall, and the burnout air mechanism. The optimal selection is made according to the installation space and materials used. Too small a design wind speed can easily cause dust accumulation in the duct. The preferred duct design wind speed range is 15~30m / s.

[0035] This invention also provides a process for a Π-shaped hot secondary air duct for an octagonal tangent-circle boiler, comprising the following steps: The air preheater 5 in the two hot secondary air systems heats the cold air into hot air and then enters the air outlet channel. The hot secondary air of the two systems is connected and mixed through the connecting air duct 4 on the air outlet channel. At the same time, the hot secondary air of the two systems continues to flow into their respective systems: it enters the first rectifier air duct 7 through the flow guide device. After being rectified by the flow guide device, the flow velocity is evenly distributed along the cross section and enters the two first diversion air ducts 3. It is divided into two hot secondary air with the same flow rate, namely the front wall hot secondary air and the rear wall hot secondary air. The front wall hot secondary air enters the front wall secondary air box 6 through the front wall secondary air duct 9 and finally enters the furnace 2 through the secondary air nozzle of the front wall secondary air box 6. The rear wall hot secondary air enters the rear wall secondary air box 1 through the rear wall secondary air duct 8 and finally enters the furnace 2 through the secondary air nozzle of the rear wall secondary air box 1. A stream of burnout air from the front wall secondary air duct 9 enters the front second rectifier air duct 10. After rectification by the flow guiding device, the flow velocity is evenly distributed along the cross-section. After entering the two front second branch air ducts 11, it is divided into two airflows with the same flow rate, and finally injected into the furnace 2 through the burnout air nozzle of the front second branch air duct 11. A stream of burnout air from the rear wall secondary air duct 8 enters the rear second rectifier air duct 12. After rectification by the flow guiding device, the flow velocity is evenly distributed along the cross-section. After entering the two rear second branch air ducts 13, it is divided into two airflows with the same flow rate, and finally injected into the furnace 2 through the burnout air nozzle of the rear second branch air duct 13. It should be noted that flow guiding devices are installed at the transition points of different air ducts in the system to ensure the uniformity of airflow in different air ducts.

[0036] After the hot secondary air from any hot secondary air system enters the furnace 2, it forms a clockwise tangential circle on one side of the furnace 2. After the hot secondary air from another hot secondary air system enters the furnace 2, it forms a counterclockwise tangential circle on the other side of the furnace 2. The two tangential circles are the same size but opposite in direction. This arrangement can ensure that the airflow velocity entering each tangential circle is similar and reaches the design wind speed, which is in line with the theoretical design standard.

[0037] Therefore, the hot secondary air system provided in this embodiment ensures consistent flow when entering the bifurcation circuit, avoiding the serious uneven hot air flow that occurs during unit operation in traditional layouts. This results in better combustion, improved combustion completeness, reduced generation and emission of combustion products, and reduced environmental impact, thereby improving the overall efficiency and environmental performance of the boiler.

[0038] The specific embodiments of the present invention have been described in detail above with reference to the figures, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. An octagonal tangential Π-shaped boiler hot secondary air system, comprising a furnace (2), characterized in that: The furnace (2) is connected to two hot secondary air systems, which are connected by a connecting air duct (4) and are symmetrically arranged along the centerline of the furnace (2). The hot secondary air system includes a hot secondary air preparation mechanism, which is connected to a first rectifier air duct (7) through an air outlet channel. The first rectifier air duct (7) is connected to a front wall secondary air mechanism and a rear wall secondary air mechanism through a first branch air duct (3). The front wall secondary air mechanism and the rear wall secondary air mechanism are connected to the furnace (2) and are symmetrically arranged along the centerline of the furnace (2). The front wall secondary air mechanism is connected to a front wall burnout air mechanism, and the rear wall secondary air mechanism is connected to a rear wall burnout air mechanism. The front wall burnout air mechanism and the rear wall burnout air mechanism are symmetrically arranged along the centerline of the furnace (2). The front wall burnout air mechanism includes a front second rectifier air duct (10), which is connected to the furnace (2) through a front second branch air duct (11); the rear wall burnout air mechanism includes a rear second rectifier air duct (12), which is connected to the furnace (2) through a rear second branch air duct (13). The first rectifier air duct (7) is connected to two first branch air ducts (3) through a connector, and the two first branch air ducts (3) are symmetrically arranged with respect to the center line of the first rectifier air duct (7); the front second rectifier air duct (10) is connected to two front second branch air ducts (11) through a connector, and the two front second branch air ducts (11) are symmetrically arranged with respect to the center line of the front second rectifier air duct; the rear second rectifier air duct (12) is connected to two rear second branch air ducts (13) through a connector, and the two rear second branch air ducts (13) are symmetrically arranged with respect to the center line of the rear second rectifier air duct (12). The connector is equipped with a flow guiding device, which includes several flow guiding plates. The spacing between adjacent flow guiding plates gradually increases from the inner arc to the outer arc.

2. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The front wall secondary air mechanism includes a front wall secondary air duct (9) connected to the first diversion air duct (3), and a front second rectifier air duct (10) connected to the front wall secondary air duct (9). The front wall secondary air duct (9) is connected to the furnace (2) through the front wall secondary air box (6). The rear wall secondary air mechanism includes a rear wall secondary air duct (8) connected to the first diversion air duct (3), and a rear second rectifier air duct (12) connected to the rear wall secondary air duct (8). The rear wall secondary air duct (8) is connected to the furnace (2) through the rear wall secondary air box (1).

3. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The flow guiding device is fixed by flat steel and tie rods, and the tie rods and flat steel are arranged in the direction of airflow.

4. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The duct design wind speed of the front wall secondary air mechanism and the rear wall secondary air mechanism is selected in the range of 15~30m / s.

5. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The velocity of each cross section of the first rectifier duct (7), the first branch duct (3), the front second rectifier duct (10), the front second branch duct (11), the rear second rectifier duct (12), and the rear second branch duct (13) is uniform.

6. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The front second rectifier air duct (10) and the rear second rectifier air duct (12) are also provided with air intakes, and the air duct design wind speed of the front wall burnout air mechanism and the rear wall burnout air mechanism is selected in the range of 15~30m / s.

7. The octagonal tangential Π-shaped boiler hot secondary air system according to claim 1, characterized in that: The hot secondary air preparation mechanism includes a blower, which is connected to the air outlet channel through an air preheater (5). The air outlet channels of the two hot secondary air systems are connected through the connecting air duct (4).

8. The process of a hot secondary air system for an octagonal tangential Π-shaped boiler as described in any one of claims 1-7, characterized in that, Includes the following steps: The hot secondary air preparation mechanisms of the two hot secondary air systems heat the cold air into hot secondary air and then enter their respective air outlet channels. The hot secondary air of the two systems is connected and mixed through the connecting air duct (4) on the air outlet channel. At the same time, the hot secondary air of the two systems continues to flow into their respective systems: the hot secondary air enters the first rectifier air duct (7) through the air outlet channel, and then enters the first diversion air duct (3) after being rectified by the first rectifier air duct (7). It is divided into two hot secondary air streams with the same flow rate, and finally sprayed into the furnace (2) through the symmetrically arranged front wall secondary air mechanism and rear wall secondary air mechanism respectively. A stream of hot secondary air is drawn from the secondary air mechanism on the front wall as the burnout air of the front wall and enters the second rectifier air duct (10). Then, after passing through the second shunt air duct (11), it is divided into two streams of hot secondary air with the same flow rate and injected into the furnace (2). A stream of hot secondary air is drawn from the secondary air mechanism on the rear wall as the burnout air of the rear wall and enters the second rectifier air duct (12). Then, after passing through the second shunt air duct (13), it is divided into two streams of hot secondary air with the same flow rate and injected into the furnace (2).

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