Flow field optimization method for secondary air bellow of opposed firing boiler
By using 3D modeling of the secondary air box and optimization of the baffle plate in the counter-fired boiler, the problem of uneven air volume distribution was solved, improving combustion efficiency and stability, and reducing high-temperature corrosion and coking.
Patent Information
- Application Number
- CN202510911484.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-02
- Publication Date
- 2025-11-18
AI Technical Summary
The secondary air boxes of existing counter-fired boilers generally adopt a large structure, with each burnout air duct sharing a single duct. This results in uneven airflow distribution in each burnout air duct, leading to low combustion efficiency, poor stability, and problems such as flame pulsation, high-temperature corrosion, and coking.
A symmetrical three-dimensional model was used to model the secondary air box. The three-dimensional velocity field distribution was obtained by computational fluid dynamics, the airflow was calculated, and guide vanes in different directions were arranged at appropriate locations to optimize the flow field of the secondary air box.
It significantly improves the uniformity of the flow field in the secondary air box, enhances the combustion efficiency of the boiler, improves combustion stability, and reduces high-temperature corrosion and coking.
Smart Images
Figure CN120974964A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary air supply technology for power plant boilers, specifically, it relates to a flow field optimization method for the secondary air box of a counter-firing boiler. Background Technology
[0002] Front and rear wall opposed combustion boilers can enhance the turbulence and mixing of pulverized coal airflow, increase the airflow filling in the furnace, and make the heat load and flue gas temperature distribution more uniform along the width of the furnace. This design is widely used in thermal power generation technology. The secondary air box is an important component of the boiler combustion system, which collects the air required for combustion and distributes it evenly to each burner and burnout air nozzle.
[0003] However, in actual operation, due to the common use of large air box structures in secondary air boxes and the sharing of a single air duct among multiple burners, air volume distribution deviations are prone to occur in each burner. At this time, it is difficult for the secondary air to mix evenly with the fuel, significantly increasing the loss of unburned carbon, resulting in poor combustion efficiency and reduced combustion stability, leading to flame pulsation and localized high and low temperature zones, which in turn cause high-temperature corrosion, coking, and cracking of the water-cooled walls. Summary of the Invention
[0004] To address the technical problems existing in the prior art, an embodiment of the present invention provides a flow field optimization method for the secondary air box of a counter-firing boiler.
[0005] According to one aspect of the present invention, a flow field optimization method for a secondary air box of a counter-firing boiler includes: modeling the three-dimensional structure of the secondary air box using a symmetrical three-dimensional model to form a three-dimensional model of the secondary air box; obtaining the three-dimensional velocity field distribution of hot air entering the secondary air box based on the three-dimensional model of the secondary air box, and calculating the airflow at each outlet of the secondary air box; and arranging guide plates in different directions at appropriate positions based on the three-dimensional velocity field distribution and the airflow at each outlet.
[0006] In one example of the flow field optimization method provided above, the flow field optimization method further includes: obtaining the three-dimensional velocity field distribution of hot air entering the secondary air box after the baffle is arranged, and calculating the airflow at each outlet of the secondary air box after the baffle is arranged; and arranging baffles at other appropriate locations based on the three-dimensional velocity field distribution of the secondary air box after the baffle is arranged and the airflow at each outlet.
[0007] In one example of the flow field optimization method provided above, the three-dimensional model of the secondary air box includes: an air inlet, a secondary air box sidewall, a secondary air box front wall, a secondary air box rear wall, a first front wall burnout air duct, a second front wall burnout air duct, a first front wall burner duct, a second front wall burner duct, a third front wall burner duct, a first rear wall burnout air duct, a second rear wall burnout air duct, a first rear wall burner duct, a second rear wall burner duct, and a third rear wall burner duct; wherein, the first front wall... The burnout air duct, the second front wall burnout air duct, the first front wall burner air duct, the second front wall burner air duct, and the third front wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the front wall of the secondary air box; the first rear wall burnout air duct, the second rear wall burnout air duct, the first rear wall burner air duct, the second rear wall burner air duct, and the third rear wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the rear wall of the secondary air box; wherein, each layer of burnout air duct has multiple burnout air outlets, and each layer of burner air duct has multiple secondary air outlets.
[0008] In one example of the flow field optimization method provided above, the three-dimensional model of the secondary wind box further includes: a duct center surface, the duct center surface and the secondary wind box side wall facing each other, and the secondary wind box front wall and the secondary wind box rear wall facing each other and located between the duct center surface and the secondary wind box side wall.
[0009] In one example of the flow field optimization method provided above, the method of arranging guide vanes in different directions at appropriate locations based on the three-dimensional velocity field distribution and the airflow of each outlet includes: arranging guide vanes in the +y-axis to -z-axis direction in the first front wall burnout air duct and the first rear wall burnout air duct; arranging guide vanes in the -x-axis to -z-axis direction in the second front wall burnout air duct, the first front wall burner air duct, the second rear wall burnout air duct, and the first rear wall burner air duct; arranging guide vanes in the -y-axis to -z-axis direction in the second front wall burner air duct, the third front wall burner air duct, the second rear wall burner air duct, and the third front wall burner air duct; wherein, the direction from the front wall of the secondary air box to the rear wall of the secondary air box is the +x-axis direction, the direction from the center surface of the air duct to the side wall of the secondary air box is the +y-axis direction, and the directions from the third front wall burner air duct to the first front wall burnout air duct and the third rear wall burner air duct to the first rear wall burnout air duct are both the +z-axis direction.
[0010] In one example of the flow field optimization method provided above, the step of arranging the guide vanes at other appropriate locations based on the three-dimensional velocity field distribution of the secondary air box after the guide vanes are arranged and the airflow of each outlet includes: arranging guide vanes in the -x-axis to +y-axis direction outside the combustion air duct of the first front wall; wherein the width of the external guide vanes is three-eighths of the width of the secondary air box sidewall, and the lower part of the external guide vanes is flush with the lower part of the combustion air duct of the second rear wall; a baffle plate with a 30° arc is arranged at the center of the first outlet and the second outlet on each air duct; wherein the first outlet of each air duct is adjacent to the sidewall of the secondary air box, and the second outlet of each air duct is adjacent to the corresponding first outlet.
[0011] In one example of the flow field optimization method provided above, the guide vanes are composed of two straight plates and a 1 / 4 circular arc plate.
[0012] Beneficial effects: The flow field optimization method for the secondary air box of the present invention can realize the numerical simulation of the three-dimensional flow field distribution through computational fluid dynamics, thereby accurately identifying regions of uneven airflow and then strategically arranging guide vanes, which can significantly improve the flow field uniformity of each air duct in the secondary air box and improve the combustion efficiency of the boiler. Furthermore, the flow field optimization method for the secondary air box of the present invention can be used for secondary air boxes with different original structures, and has a wide range of applications. Attached Figure Description
[0013] The above and other aspects, features, and advantages of embodiments of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:
[0014] Figure 1 This is a flowchart of a flow field optimization method for the secondary air box of a counter-firing boiler according to an embodiment of the present invention;
[0015] Figure 2 This is a schematic diagram of a three-dimensional model of a secondary bellows according to an embodiment of the present invention;
[0016] Figure 3 This is a velocity field distribution diagram of the center surface of the sidewall according to an embodiment of the present invention;
[0017] Figure 4 This is a schematic diagram of a three-dimensional model of the secondary air box after the first arrangement of the guide vanes according to an embodiment of the present invention;
[0018] Figure 5 This is a velocity field distribution diagram of the center surface of the front wall of the secondary air box after the arrangement of the guide vanes according to an embodiment of the present invention;
[0019] Figure 6 This is a schematic diagram of a three-dimensional model of the secondary air box after the second arrangement of the guide vanes according to an embodiment of the present invention. Detailed Implementation
[0020] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can be implemented in many different forms, and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the invention and various modifications suitable for particular intended applications.
[0021] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The terms "based on", "according to", etc., mean "at least partially based on" or "at least partially according to". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term remains consistent throughout the specification.
[0022] Figure 1 This is a flowchart of a flow field optimization method for the secondary air box of a counter-firing boiler according to an embodiment of the present invention.
[0023] Reference Figure 1 In step S110, a symmetrical three-dimensional model is used to model the three-dimensional structure of the secondary wind box to form a three-dimensional model of the secondary wind box.
[0024] Figure 2 This is a schematic diagram of a three-dimensional model of a secondary bellows according to an embodiment of the present invention. (Refer to...) Figure 2 Since the secondary air box of the counter-firing boiler has a symmetrical structure, a symmetrical 3D model is used to model the 3D structure of the secondary air box. The symmetry plane is the xy plane where the center plane 2 of the air duct is located. The 3D model of the secondary air box includes: air inlet 1, secondary air box side wall 3, secondary air box front wall 4, secondary air box rear wall 5, first front wall burnout air duct 6, second front wall burnout air duct 7, first front wall burner air duct 8, second front wall burner air duct 9, third front wall burner air duct 10, first rear wall burnout air duct 11, second rear wall burnout air duct 12, first rear wall burner air duct 13, second rear wall burner air duct 14, and third front wall burner air duct 15.
[0025] The first front wall burnout air duct 6, the second front wall burnout air duct 7, the first front wall burner air duct 8, the second front wall burner air duct 9, and the third front wall burner air duct 10 are arranged in a sequentially spaced-apart stack on the front wall 4 of the secondary air box; the first rear wall burnout air duct 11, the second rear wall burnout air duct 12, the first rear wall burner air duct 13, the second rear wall burner air duct 14, and the third front wall burner air duct 15 are arranged in a sequentially spaced-apart stack on the rear wall 5 of the secondary air box; wherein, each layer of burnout air duct has three burnout air outlets, and each layer of burner air duct has three secondary air outlets.
[0026] The center surface 2 of the air duct and the side wall 3 of the secondary air box are arranged facing each other, and the front wall 4 and the rear wall 5 of the secondary air box are arranged facing each other and located between the center surface 2 of the air duct and the side wall 3 of the secondary air box.
[0027] In step S120, the three-dimensional velocity field distribution of hot air after entering the secondary air box is obtained based on the three-dimensional model of the secondary air box, and the airflow at each outlet of the secondary air box is calculated.
[0028] Specifically, the original three-dimensional structural model of the secondary wind tunnel established in step S110 was meshed using Ansys Fluent meshing software, and the resulting mesh file was imported into Ansys Fluent for numerical simulation. During the calculation, the center plane 2 of the air duct was set as the symmetry plane; air inlet 1 was set as the mass inlet, the air mass flow rate was 250 kg / s, and the physical properties were set to 600 Kelvin (K). At this point, the air density and viscosity were 0.588 kg / m³. 3 and 3×10 -5 Pa·s; Both the combustion air outlet and the secondary air outlet are set as pressure outlets with a back pressure of 0 Pa. The flow rates of each outlet obtained by numerical simulation are shown in Table 1. Among them, the outlets near the secondary air box sidewall 3 in each duct are numbered a, the middle outlets are numbered b, and the outlets near the center surface 2 of the duct are numbered c.
[0029] Table 1. Outlet flow rates of the original secondary air box (unit: kg / s)
[0030]
[0031] As shown in Table 1, the flow rate at the front wall outlet is significantly greater than that at the rear wall outlet, and the flow rates at each duct in the front and rear walls also differ considerably.
[0032] Figure 3 This is a velocity field distribution diagram of the center surface of the sidewall according to an embodiment of the present invention. (Refer to Table 1 and...) Figure 3 It can be observed that, due to inertia and the fact that air inlet 1 is perpendicular to each air duct, only a portion of the air enters the rear wall due to entrainment.
[0033] Furthermore, according to the definition of non-uniformity:
[0034]
[0035] In Equation 1, U represents the non-uniformity, N represents the number of outlets, i is a variable, and Qi represents the flow rate at the i-th outlet. This represents the average flow rate at each outlet. The original secondary air box (without guide vanes) had a flow rate non-uniformity of 14.15% at each outlet, indicating poor uniformity.
[0036] In step S130, guide vanes in different directions are arranged at appropriate locations based on the three-dimensional velocity field distribution and the airflow at each outlet.
[0037] Specifically, guide vanes in the +y-axis to -z-axis direction are arranged in the first front wall burner duct 6 and the first rear wall burner duct 11; guide vanes in the -x-axis to -z-axis direction are arranged in the second front wall burner duct 7, the first front wall burner duct 8, the second rear wall burner duct 12, and the first rear wall burner duct 13; and guide vanes in the -y-axis to -z-axis direction are arranged in the second front wall burner duct 9, the third front wall burner duct 10, the second rear wall burner duct 14, and the third front wall burner duct 15, thereby introducing air from the side walls into each duct. Each guide vane consists of two straight plates and a 1 / 4 arc plate, and the length of each guide vane entering the duct is 1.5m. Figure 4 As shown. Figure 4 This is a schematic diagram of a three-dimensional model of the secondary air box after the first arrangement of the guide vanes according to an embodiment of the present invention.
[0038] In step S140, the three-dimensional velocity field distribution of hot air entering the secondary air box after the baffle is arranged is obtained, and the airflow of each outlet of the secondary air box after the baffle is arranged is calculated.
[0039] In step S140, the same calculation method as in step S120 is used. The outlet flow rates of the secondary air box after the baffle plate is arranged, obtained by numerical simulation calculation, are shown in Table 2, and their numbering meanings are consistent with those in Table 1.
[0040] Table 2. Flow rates at each outlet of the secondary air box after the baffle plate is installed (unit: kg / s)
[0041]
[0042] According to Equation 1, the non-uniformity of the flow rate at each outlet of the secondary air box after the baffle plate is arranged is 9.50%, which is an improvement over the original secondary air box. However, the total flow rate at the outlet of the first rear wall combustion air duct 11 is still significantly lower than that of other ducts, and the flow rate at the outlet a near the side wall is significantly smaller in each duct.
[0043] Figure 5 This is a velocity field distribution diagram of the center surface of the front wall of the secondary air box after the arrangement of the guide vanes according to an embodiment of the present invention. (Refer to...) Figure 5 It can be observed that, due to inertia, the leeward side entrainment effect is weaker at outlet a near the sidewall, resulting in a smaller outlet flow rate.
[0044] From Table 2 and Figure 5 It can be seen that after arranging the guide vanes in step S130, the non-uniformity of the flow rate at each outlet of the secondary air box has been improved. Therefore, as another embodiment of the present invention, steps S140 and S150 may be omitted.
[0045] In step S150, based on the three-dimensional velocity field distribution of the secondary air box after the guide vanes are arranged and the airflow at each outlet, guide vanes are arranged at other appropriate locations.
[0046] Specifically, to increase the total flow rate at the outlet of the first rear wall burnout air duct 11, a guide vane 16 is installed outside the first front wall burnout air duct 6, with its direction from the -x axis to the +y axis. The width of the guide vane 16 is 3 / 8 of the width of the side wall, and the lower part of the guide vane 16 is flush with the lower part of the second rear wall burnout air duct 12. Furthermore, to increase the flow rate at outlet a near the side wall, the length of the guide vane entering the duct is shortened to 0.5m. A baffle plate 17 with a 30° arc (where the center of the arc of the baffle plate 17 faces the side wall) is also arranged at the center of outlet a and outlet b to enhance the leeward side entrainment effect at outlet a. Figure 6 As shown. Figure 6 This is a schematic diagram of a three-dimensional model of the secondary air box after the second arrangement of the guide vanes according to an embodiment of the present invention.
[0047] The flow rates at each outlet of the secondary air box after the baffle optimization (i.e., secondary baffle arrangement) obtained by numerical simulation calculation are shown in Table 3. The meaning of their numbers is the same as that in Table 1.
[0048] Table 3. Flow rates at each outlet of the secondary air box after baffle optimization (unit: kg / s)
[0049]
[0050] Continuing to use Equation 1 for calculation, the non-uniformity of the flow rate at each outlet of the secondary air box after the baffle optimization is 5.55%, which is significantly improved compared with the original secondary air box. It can be considered that the flow field uniformity meets the requirements.
[0051] In summary, the flow field optimization method for the secondary air box according to embodiments of the present invention can achieve numerical simulation of the three-dimensional flow field distribution through computational fluid dynamics, thereby accurately identifying regions of uneven airflow and subsequently arranging guide vanes accordingly. This significantly improves the flow field uniformity of each air duct in the secondary air box, thereby increasing the combustion efficiency of the boiler. Furthermore, the flow field optimization method for the secondary air box according to embodiments of the present invention can be applied to secondary air boxes with different original structures, thus having a wide range of applications.
[0052] The terms “exemplary,” “example,” etc., used throughout this specification mean “serving as an example, instance, or illustration” and do not imply “preferred” or “advantageous” than other embodiments. Detailed descriptions are included for the purpose of providing an understanding of the described techniques. However, these techniques can be practiced without these detailed descriptions. In some instances, well-known structures and apparatuses are shown in block diagram form to avoid obscuring the concepts of the described embodiments.
[0053] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.
Claims
1. A method for optimizing the flow field of the secondary air box in a counter-firing boiler, characterized in that, The flow field optimization method includes: A symmetrical 3D model is used to model the 3D structure of the secondary bellows to form a 3D model of the secondary bellows. The three-dimensional velocity field distribution of hot air after entering the secondary air box is obtained based on the three-dimensional model of the secondary air box, and the airflow at each outlet of the secondary air box is calculated. Based on the three-dimensional velocity field distribution and the airflow at each outlet, guide vanes in different directions are arranged at appropriate locations.
2. The flow field optimization method according to claim 1, characterized in that, The flow field optimization method also includes: The three-dimensional velocity field distribution of hot air entering the secondary air box after the baffles are arranged is obtained, and the airflow at each outlet of the secondary air box after the baffles are arranged is calculated. Based on the three-dimensional velocity field distribution of the secondary air box after the baffles are installed and the airflow at each outlet, baffles are installed at other appropriate locations.
3. The flow field optimization method according to claim 1, characterized in that, The three-dimensional model of the secondary air box includes: air inlet, secondary air box side wall, secondary air box front wall, secondary air box rear wall, first front wall burnout air duct, second front wall burnout air duct, first front wall burner air duct, second front wall burner air duct, third front wall burner air duct, first rear wall burnout air duct, second rear wall burnout air duct, first rear wall burner air duct, second rear wall burner air duct, and third rear wall burner air duct. The first front wall burnout air duct, the second front wall burnout air duct, the first front wall burner air duct, the second front wall burner air duct, and the third front wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the front wall of the secondary air box; the first rear wall burnout air duct, the second rear wall burnout air duct, the first rear wall burner air duct, the second rear wall burner air duct, and the third rear wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the rear wall of the secondary air box. Each layer of burnout air duct has multiple burnout air outlets, and each layer of burner air duct has multiple secondary air outlets.
4. The process optimization method according to claim 3, characterized in that, The three-dimensional model of the secondary air box also includes: a central surface of the air duct, which is arranged facing each other with the side wall of the secondary air box, and the front wall and rear wall of the secondary air box are arranged facing each other and located between the central surface of the air duct and the side wall of the secondary air box.
5. The process optimization method according to claim 4, characterized in that, The method of arranging guide vanes in different directions at appropriate locations based on the three-dimensional velocity field distribution and the airflow at each outlet includes: Guide vanes are arranged in the +y-axis to -z-axis direction in the first front wall combustion air duct and the first rear wall combustion air duct; Guide plates are arranged along the -x axis to -z axis in the second front wall burnout air duct, the first front wall burner air duct, the second rear wall burnout air duct, and the first rear wall burner air duct. Guide vanes are arranged along the -y axis to -z axis in the second front wall burner duct, the third front wall burner duct, the second rear wall burner duct, and the third front wall burner duct. Among them, the direction from the front wall of the secondary air box to the rear wall of the secondary air box is the +x axis direction, the direction from the center surface of the air duct to the side wall of the secondary air box is the +y axis direction, and the direction from the third front wall burner air duct to the first front wall burnout air duct and the direction from the third rear wall burner air duct to the first rear wall burnout air duct are both the +z axis direction.
6. The flow field optimization method according to claim 2, characterized in that, The three-dimensional model of the secondary air box includes: air inlet, secondary air box side wall, secondary air box front wall, secondary air box rear wall, first front wall burnout air duct, second front wall burnout air duct, first front wall burner air duct, second front wall burner air duct, third front wall burner air duct, first rear wall burnout air duct, second rear wall burnout air duct, first rear wall burner air duct, second rear wall burner air duct, and third rear wall burner air duct. The first front wall burnout air duct, the second front wall burnout air duct, the first front wall burner air duct, the second front wall burner air duct, and the third front wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the front wall of the secondary air box; the first rear wall burnout air duct, the second rear wall burnout air duct, the first rear wall burner air duct, the second rear wall burner air duct, and the third rear wall burner air duct are arranged in a sequentially spaced-apart stacked layer on the rear wall of the secondary air box. Each layer of burnout air duct has multiple burnout air outlets, and each layer of burner air duct has multiple secondary air outlets.
7. The process optimization method according to claim 6, characterized in that, The three-dimensional model of the secondary air box also includes: a central surface of the air duct, which is arranged facing each other with the side wall of the secondary air box, and the front wall and rear wall of the secondary air box are arranged facing each other and located between the central surface of the air duct and the side wall of the secondary air box.
8. The process optimization method according to claim 7, characterized in that, The method of arranging guide vanes in different directions at appropriate locations based on the three-dimensional velocity field distribution and the airflow at each outlet includes: Guide vanes are arranged in the +y-axis to -z-axis direction in the first front wall combustion air duct and the first rear wall combustion air duct; Guide plates are arranged along the -x axis to -z axis in the second front wall burnout air duct, the first front wall burner air duct, the second rear wall burnout air duct, and the first rear wall burner air duct. Guide vanes are arranged along the -y axis to -z axis in the second front wall burner duct, the third front wall burner duct, the second rear wall burner duct, and the third front wall burner duct. Among them, the direction from the front wall of the secondary air box to the rear wall of the secondary air box is the +x axis direction, the direction from the center surface of the air duct to the side wall of the secondary air box is the +y axis direction, and the direction from the third front wall burner air duct to the first front wall burnout air duct and the direction from the third rear wall burner air duct to the first rear wall burnout air duct are both the +z axis direction.
9. The process optimization method according to claim 8, characterized in that, The step of arranging guide vanes at other appropriate locations based on the three-dimensional velocity field distribution of the secondary air box after the guide vanes are arranged and the airflow at each outlet includes: A guide plate is arranged outside the combustion air duct of the first front wall in the direction from -x axis to +y axis; wherein, the width of the external guide plate is three-eighths of the width of the secondary air box side wall, and the lower part of the external guide plate is flush with the lower part of the combustion air duct of the second rear wall. A baffle plate with a 30° arc is arranged at the center of the first and second outlets of each air duct; wherein, the first outlet of each air duct is adjacent to the side wall of the secondary air box, and the second outlet of each air duct is adjacent to the corresponding first outlet.
10. The process optimization method according to any one of claims 1 to 9, characterized in that, Each of the guide plates consists of two straight plates and a 1 / 4 circular arc plate.