A combustion system with adaptive adjustment of fuel nozzle swirl number

Abstract

The present invention discloses a combustion system with adaptive adjustment of the swirl number of a fuel nozzle, comprising an outer wall of a fuel nozzle, an outer wall of a premixed fuel, an outer wall of a duty air, an outer wall of a duty fuel, an outer wall of a purge air, a premixed swirl blade, an outer wall of a duty swirl blade, an annular premixed fuel baffle and an annular duty fuel baffle; wherein the outer wall of the fuel nozzle, the outer wall of the premixed fuel, the outer wall of the duty air, the outer wall of the duty fuel and the outer wall of the purge air are all concentric circular cross-section thin-walled structures. The present invention combines the respective advantages of strong swirl and weak swirl fuel nozzles, and the swirl number of the swirl fuel nozzle can be adaptively adjusted according to the load size of the gas turbine, and the swirl number of the fuel nozzle is increased at low load to enhance combustion stability, and the swirl number of the fuel nozzle is reduced at high load to reduce NOx emissions.

Description

Technical Field

[0001] The invention relates to a dry low-nitrogen staged combustion system, in particular to a dry low-nitrogen staged combustion system with adaptively adjusted swirl number of a fuel nozzle. Background Art

[0002] The swirl fuel nozzle can produce a swirling jet downstream, which can not only enhance the mixing of air and fuel, but also form a stable high-temperature flue gas recirculation zone, thus stabilizing the flame. In addition, because the swirl fuel nozzle can realize premixed combustion, the flame surface equivalence ratio can be adjusted to be close to the lean burnout limit, greatly reducing the flame surface temperature, thereby effectively controlling the generation of thermal NOx pollutants.

[0003] The swirl number is generally used to measure the intensity of the swirling jet downstream of the swirl fuel nozzle. The definition of the swirl number refers to the ratio of the airflow rotational momentum flux to the axial momentum flux. According to the size of the swirl number, the swirl fuel nozzle can be divided into a strong swirl fuel nozzle and a weak swirl fuel nozzle. After the airflow passes through the strong swirl fuel nozzle, a stable recirculation zone can be formed downstream. However, after passing through the weak swirl fuel nozzle, due to the small rotational momentum flux of the airflow, a stable recirculation zone cannot be formed downstream of the nozzle. The rotating jet can only reduce the speed of the central airflow, forming a low-speed flow field area with central divergence, so that the flame is stabilized at the position where the local turbulent flame propagation speed is equal to the local airflow speed. Compared with the strong swirl fuel nozzle, since there is no high-temperature flue gas recirculation zone downstream of the weak swirl fuel nozzle, the residence time of the flue gas in the high-temperature zone of the combustion chamber can be reduced, and it has more advantages in terms of NOx emission performance, but the ignition stability of the weak swirl fuel nozzle is poor at low load.

[0004] Weak swirl combustion is a novel lean premixed combustion technology that emerged in the 1990s. It has not yet been applied to heavy-duty gas turbines, mainly because the combustion stability of weak swirl fuel nozzles is poor when the gas turbine is under low load. Currently, heavy-duty gas turbines in service still generally use strong swirl fuel nozzles with flame stabilization in the recirculation zone. By axially or radially grading the fuel, the duty fuel adopts diffusion or premixed combustion, and the main fuel adopts premixed combustion to control NOx emissions. However, due to the presence of a high-temperature flue gas recirculation zone downstream of the strong swirl fuel nozzle, this will prolong the residence time of some high-temperature flue gases in the combustion chamber, increase the generation of thermal NOx, and thus offset the advantage of premixed combustion in reducing NOx emissions. Summary of the invention

[0005] In order to further reduce the NOx emission of heavy-duty gas turbines and solve the problem that the weak swirl fuel nozzle is prone to unstable combustion when the gas turbine is under low load, the present invention proposes a combustion system with adaptive adjustment of the swirl number of the fuel nozzle. The present invention combines the advantages of strong swirl and weak swirl fuel nozzles. The swirl number of the swirl fuel nozzle can be adaptively adjusted according to the load size of the gas turbine. The swirl number of the fuel nozzle is increased at low load to enhance combustion stability, while the swirl number of the fuel nozzle is reduced at high load to reduce NOx emissions. The principle of adaptive adjustment of the swirl number of the swirl fuel nozzle is that when the load of the gas turbine changes, the aerodynamic force exerted on the swirl blade will change accordingly. The aerodynamic force is small at low load and large at high load. The present invention designs the swirl blade into a spring active hinge connection structure, so that the angle of the swirl blade can change with the aerodynamic force, thereby changing the ratio of the rotational momentum flux to the axial momentum flux after the airflow passes through the swirl blade, so as to achieve the purpose of adaptive adjustment of the swirl number.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A combustion system with adaptive adjustment of swirl number of a fuel nozzle comprises an outer wall of a fuel nozzle, an outer wall of a premixed fuel, an outer wall of a duty air, an outer wall of a duty fuel, an outer wall of a purge air, a premixed swirl blade, an outer wall of a duty swirl blade, an annular premixed fuel baffle and an annular duty fuel baffle; wherein the outer wall of the fuel nozzle, the outer wall of the premixed fuel, the outer wall of the duty air, the outer wall of the duty fuel and the outer wall of the purge air are all thin-walled structures with concentric circular cross sections;

[0008] The premixing swirl blade is located in the annular channel formed by the outer wall of the fuel nozzle and the outer wall of the premixing fuel, and is used to separate the annular channel formed by the outer wall of the fuel nozzle and the outer wall of the premixing fuel into an upstream main combustion air flow channel and a downstream main fuel premixing chamber;

[0009] The duty swirl blade is located in the annular channel formed by the duty air outer wall and the duty fuel outer wall, and is used to separate the annular channel formed by the duty air outer wall and the duty fuel outer wall into an upstream duty air flow channel and a downstream duty fuel premixing chamber;

[0010] The annular premix fuel partition is located between the premix fuel outer wall and the duty air outer wall, and is used to separate the annular channel formed by the premix fuel outer wall and the duty air outer wall into an upstream premix fuel flow channel and a downstream premix combustion cooling air flow channel;

[0011] The annular duty fuel partition is located between the duty fuel outer wall and the purge air outer wall, and is used to separate the annular channel formed by the duty fuel outer wall and the purge air outer wall into an upstream duty fuel flow channel and a downstream duty combustion cooling air flow channel;

[0012] The purge air outer wall is located at the center of the fuel nozzle, and the interior of the purge air outer wall is a purge air flow channel.

[0013] A further improvement of the present invention is that the premixing swirl blade is composed of a blade straight section, a swirl blade and a rotating torsion spring, the blade straight section is a hollow structure, and the swirl blade and the blade straight section are connected by a rotating torsion spring.

[0014] A further improvement of the present invention is that a premixed fuel injection hole is provided at the leading edge of the straight section of the blade.

[0015] A further improvement of the present invention is that a premixed combustion cooling air hole is provided at the rear of the straight section of the blade.

[0016] A further improvement of the present invention is that the swirl blades can rotate freely and adaptively change the swirl number of the fuel nozzle according to the change of the aerodynamic force acting on the swirl blades.

[0017] A further improvement of the present invention is that a duty fuel injection hole and a duty combustion cooling air hole are provided on the duty swirl blade.

[0018] A further improvement of the present invention is that cooling air injection holes are provided in the downstream sections of the premixed combustion cooling air flow channel, the duty combustion cooling air flow channel and the purge air flow channel.

[0019] A further improvement of the present invention is that purge air injection holes are provided in the downstream sections of the premixed combustion cooling air flow channel, the duty combustion cooling air flow channel and the purge air flow channel.

[0020] The present invention has at least the following beneficial technical effects:

[0021] The present invention provides a combustion system with adaptive adjustment of the swirl number of a fuel nozzle, wherein the premixed fuel nozzle is designed to be composed of a straight blade section and a swirl blade, and the swirl blade is connected to the straight blade section by a rotating torsion spring. This design allows the swirl blade to adaptively rotate around the center of the torsion spring. When the load of the gas turbine increases, the aerodynamic force on the swirl blade increases, the swirl blade rotates toward the back of the blade, the angle between the swirl blade and the straight blade section increases, the rotational momentum flux of the airflow after passing through the swirl blade decreases, and the axial momentum flux increases, so that the swirl number adaptively decreases with the load; on the contrary, when the load of the gas turbine decreases, the swirl number of the fuel nozzle will adaptively increase with the load. Therefore, this combustion system with adaptive adjustment of the swirl number of the fuel nozzle combines the advantages of a strong swirl fuel nozzle and a weak swirl fuel nozzle. When the gas turbine is under low load, the swirl number of the fuel nozzle is large, and has the advantages of good ignition and combustion stability of the gas turbine. When the gas turbine is under high load, the swirl number of the fuel nozzle decreases, which can reduce the residence time of the high-temperature flue gas in the combustion chamber, and has the advantage of further reducing NOx emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a structural schematic diagram of a combustion system with adaptive adjustment of swirl number of a fuel nozzle according to the present invention.

[0023] Figure 2 It is a structural schematic diagram of a premixing swirl blade in a combustion system with adaptive adjustment of the swirl number of a fuel nozzle according to the present invention.

[0024] Figure 3 It is a schematic diagram of the maximum and minimum positions of the swirl blades that can be adaptively adjusted according to the present invention.

[0025] Description of reference numerals:

[0026] 1. Outer wall of fuel nozzle; 2. Outer wall of premixed fuel; 3. Outer wall of duty air; 4. Outer wall of duty fuel; 5. Outer wall of purge air; 6. Premixed swirl blade; 7. Duty swirl blade; 8. Premixed fuel injection hole; 9. Premixed combustion cooling air hole; 10. Duty fuel injection hole; 11. Duty combustion cooling air hole; 12. Annular premixed fuel baffle; 13. Annular duty fuel baffle; 14. Main combustion air flow channel; 15. Main Fuel premixing chamber; 16. Premixed fuel flow channel; 17. Premixed combustion cooling air flow channel; 18. Duty fuel flow channel; 19. Duty combustion cooling air flow channel; 20. Duty air flow channel; 21. Duty fuel premixing chamber; 22. Purge air flow channel; 23. Premixed combustion cooling air injection hole; 24. Duty combustion cooling air injection hole; 25. Purge air injection hole; 26. Blade straight section; 27. Torsion spring; 28. Swirl blade. DETAILED DESCRIPTION

[0027] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] See also Figure 1 The present invention provides a combustion system with adaptive adjustment of the swirl number of a fuel nozzle, comprising a fuel nozzle outer wall 1, a premixed fuel outer wall 2, a duty air outer wall 3, a duty fuel outer wall 4, a purge air outer wall 5, a premixed swirl blade 6 and a duty swirl blade 7.

[0029] See also Figure 1In this embodiment, the fuel nozzle outer wall 1 is 500mm long, 220mm outer diameter, and 216mm inner diameter; the premixed fuel outer wall 2 is 500mm long, 118mm outer diameter, and 114mm inner diameter; the duty air outer wall 3 is 500mm long, 94mm outer diameter, and 90mm inner diameter; the duty fuel outer wall 4 is 500mm long, 44mm outer diameter, and 40mm inner diameter; the purge air outer wall 5 is 500mm long, 24mm outer diameter, and 20mm inner diameter; the fuel nozzle outer wall 1, the premixed fuel outer wall 2, the duty air outer wall 3, the duty fuel outer wall 4 and the purge air outer wall 5 are coaxially arranged; the premixed swirl blade 6 is arranged in the annular flow channel formed by the fuel nozzle outer wall 1 and the premixed fuel outer wall 2, and the axial position is 1.5 meters from the fuel nozzle. The left end face is 197.5mm, the number of blades is 10, which are evenly arranged in the circumferential direction, and 7 premixed fuel injection holes 8 with a diameter of 1.5mm are evenly spaced on the back of the leading edge of the straight section of the blade and the blade basin, and a square-section premixed combustion cooling air hole 9 with a length of 5mm and a width of 3mm is opened at the rear of the straight section of the blade; the duty swirl blade 7 is arranged in an annular flow channel formed by the duty air outer wall 3 and the duty fuel outer wall 4, and the axial position is 348mm away from the left end face of the fuel nozzle. The number of blades is 6, which are evenly arranged in the circumferential direction, and 4 duty fuel injection holes 10 with a diameter of 1.5mm are evenly spaced on the back of the leading edge of the straight section of the blade and the blade basin, and a square-section duty combustion cooling air hole 11 with a length of 5mm and a width of 3mm is opened at the rear of the straight section of the blade. The annular premix fuel baffle 12 is arranged in the annular flow channel formed by the premix fuel outer wall 2 and the duty air outer wall 3, and the axial position is 220mm away from the left end face of the fuel nozzle; the annular duty fuel baffle 13 is arranged in the annular flow channel formed by the duty fuel outer wall 4 and the purge air outer wall 5, and the axial position is 365mm away from the left end face of the fuel nozzle. The premix swirl blade 6 divides the annular channel formed by the fuel nozzle outer wall 1 and the premix fuel outer wall 2 into two parts, one is the main combustion air flow channel 14 located upstream of the premix swirl blade 6, and the other is the main fuel premixing chamber 15 located downstream of the premix swirl blade 6. The duty swirl blade 7 divides the annular channel formed by the duty air outer wall 3 and the duty fuel outer wall 4 into two parts, one is the duty air flow channel 20 located upstream of the duty swirl blade 7, and the other is the duty fuel premixing chamber 21 located downstream of the duty swirl blade 7. The annular premix fuel partition 12 divides the annular channel formed by the premix fuel outer wall 2 and the duty air outer wall 3 into two parts, one is the premix fuel flow channel 16 located upstream of the annular premix fuel partition 12, and the other is the premix combustion cooling air flow channel 17 located downstream of the annular premix fuel partition 12. The annular duty fuel partition 13 divides the annular channel formed by the duty fuel outer wall 4 and the purge air outer wall 5 into two parts, one is the duty fuel flow channel 18 located upstream of the annular duty fuel partition 13, and the other is the duty combustion cooling air flow channel 19 located downstream of the annular duty fuel partition 13. The space enclosed by the purge air outer wall 5 is the purge air flow channel 22.On the right end faces of the premixed combustion cooling air flow channel 17, the duty combustion cooling air flow channel 19 and the purge air flow channel 22, a premixed combustion cooling air injection hole 23, a duty combustion cooling air injection hole 24 and a purge air injection hole 25 with a diameter of 1 mm are respectively opened.

[0030] See also Figure 2 In this embodiment, the premixing swirl blade 6 is mainly composed of a blade straight section 26, a torsion spring 27 and a swirl blade 28.

[0031] See also Figure 3 In this embodiment, the maximum and minimum positions of the swirl blade 28 of the premixing swirl blade 6 that can be adaptively adjusted are position 31 and position 29 respectively, and position 30 is located between position 29 and position 31.

[0032] The specific working method of the combustion system with adaptive adjustment of the swirl number of the fuel nozzle in this embodiment is as follows:

[0033] The air involved in combustion enters the fuel nozzle through the main combustion air flow channel 14, the duty air flow channel 20, the purge air flow channel 22 and the premixed combustion cooling air hole 9 respectively; the fuel involved in combustion enters the fuel nozzle through the premixed fuel flow channel 16 and the duty fuel flow channel 18 respectively. The premixed fuel enters the hollow structure inside the premixed swirl blade 6 through the premixed fuel flow channel 16, and is sprayed into the main combustion air flow channel 14 through the premixed fuel injection hole 8, and is mixed with the main combustion air entering the main combustion air flow channel 14. The main combustion air and the premixed fuel flow through the premixed swirl blade 6 while mixing, and a rotating airflow is formed after passing through the premixed swirl blade 6. The main combustion air and the premixed fuel are further mixed in the main fuel premixing chamber 15, and the mixed combustible mixture enters the downstream combustion chamber in the form of a rotating jet for combustion.

[0034] The duty fuel enters the hollow structure inside the duty swirl blade 7 through the duty fuel flow channel 18, and is sprayed into the duty air flow channel 20 through the duty fuel injection hole 10, and is mixed with the duty air entering the duty air flow channel 20. The duty air and the duty fuel flow through the duty swirl blade 7 while being mixed, and a rotating airflow is formed after passing through the duty swirl blade 7. The duty air and the duty fuel are further mixed in the duty fuel premixing chamber 21, and the mixed combustible mixed air enters the downstream combustion chamber in a rotating jet manner for combustion.

[0035] The cooling air for cooling the fuel nozzle enters the fuel nozzle through the premixed combustion cooling air hole 9 on the premixed swirl blade 6, and then is divided into two paths. One path passes through the premixed combustion cooling air flow channel 17 and is ejected from the premixed combustion cooling air injection hole 23 to cool the wall surface between the main fuel premixing chamber 15 and the duty fuel premixing chamber 21; the other path enters the duty combustion cooling air flow channel 19 through the duty combustion cooling air hole 11 on the duty swirl blade 7 and is ejected from the duty combustion cooling air injection hole 24 to cool the wall surface between the duty fuel premixing chamber 21 and the purge air flow channel 22. The purge air passes through the purge air flow channel 22 and is ejected into the combustion chamber through the purge air injection hole 25. By controlling the flow rate of the purge air, the axial position of the recirculation zone in the combustion chamber can be adjusted to prevent the high-temperature recirculation zone from moving forward and burning the fuel nozzle.

[0036] When the combustion system is started, the swirl blade 28 of the premixing swirl blade 6 is at the minimum position 29, and the swirling jet formed by the main combustion air after passing through the premixing swirl blade 6 is the strongest, forming a strong recirculation zone at the head of the combustion chamber, which is conducive to the ignition and start of the combustion chamber; after the ignition is successful, with the increase of the combustion air and fuel flow, the combustion chamber temperature gradually increases, and the stable combustion boundary of the combustion chamber becomes wider. At this time, the aerodynamic force exerted on the swirl blade 28 also increases with the increase of the air flow. Under the action of the aerodynamic force, the swirl blade 28 gradually overcomes the elastic force of the torsion spring 27, and the position of the swirl blade 28 is adaptively adjusted to the larger direction to position 30. When the air flow increases to the maximum, the swirl blade 28 is adaptively adjusted to the maximum position 31. At this time, the swirl number of the fuel nozzle is the smallest, and the swirling jet formed by the main combustion air after passing through the premixing swirl blade 6 is weak. No recirculation zone is formed at the head of the combustion chamber, which can reduce the residence time of the high-temperature flue gas in the combustion chamber and further reduce NOx emissions. When the combustion system stops working, the working process is just the opposite, and the position of the swirl blade 28 of the premixing swirl blade 6 is gradually and adaptively adjusted from the maximum position 31 to the minimum position 29.

[0037] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A combustion system with adaptive adjustment of fuel nozzle swirl number, characterized in that: It includes a fuel nozzle outer wall, a premix fuel outer wall, a duty air outer wall, a duty fuel outer wall, a purge air outer wall, a premix swirl blade, a duty swirl blade, an annular premix fuel baffle and an annular duty fuel baffle; wherein the fuel nozzle outer wall, the premix fuel outer wall, the duty air outer wall, the duty fuel outer wall and the purge air outer wall are all concentric circular cross-section thin-wall structures; The premixing swirl blade is located in the annular channel formed by the outer wall of the fuel nozzle and the outer wall of the premixing fuel, and is used to separate the annular channel formed by the outer wall of the fuel nozzle and the outer wall of the premixing fuel into an upstream main combustion air flow channel and a downstream main fuel premixing chamber; The duty swirl blade is located in the annular channel formed by the duty air outer wall and the duty fuel outer wall, and is used to separate the annular channel formed by the duty air outer wall and the duty fuel outer wall into an upstream duty air flow channel and a downstream duty fuel premixing chamber; The annular premix fuel partition is located between the premix fuel outer wall and the duty air outer wall, and is used to separate the annular channel formed by the premix fuel outer wall and the duty air outer wall into an upstream premix fuel flow channel and a downstream premix combustion cooling air flow channel; The annular duty fuel partition is located between the duty fuel outer wall and the purge air outer wall, and is used to separate the annular channel formed by the duty fuel outer wall and the purge air outer wall into an upstream duty fuel flow channel and a downstream duty combustion cooling air flow channel; The purge air outer wall is located at the center of the fuel nozzle, and the interior of the purge air outer wall is a purge air flow channel; The premixing swirl blade is composed of a blade straight section, a swirl blade and a rotating torsion spring. The blade straight section is a hollow structure, and the swirl blade and the blade straight section are connected by a rotating torsion spring. The duty swirl blades are provided with duty fuel injection holes and duty combustion cooling air holes.

2. A combustion system with adaptive adjustment of swirl number of a fuel nozzle according to claim 1, characterized in that: A premix fuel injection hole is provided at the leading edge of the straight section of the blade.

3. A combustion system with adaptive adjustment of fuel nozzle swirl number according to claim 1, characterized in that: Premixed combustion cooling air holes are provided at the rear of the straight section of the blade.

4. A combustion system with adaptive adjustment of fuel nozzle swirl number according to claim 1, characterized in that: According to the change of the aerodynamic force acting on the swirl blade, the swirl blade can rotate freely and adaptively change the swirl number of the fuel nozzle.

5. A combustion system with adaptive adjustment of fuel nozzle swirl number according to claim 1, characterized in that: Cooling air injection holes are provided in the downstream sections of the premixed combustion cooling air flow channel, the duty combustion cooling air flow channel and the purge air flow channel.

6. A combustion system with adaptive adjustment of fuel nozzle swirl number according to claim 1, characterized in that: The premixed combustion cooling air flow channel, the duty combustion cooling air flow channel and the downstream section of the purge air flow channel are provided with purge air injection holes.

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