Burner

Abstract: A burner comprises at least one swirl member (5) for mixing a fuel with an air previously to burning of the fuel, and at least one eddy generating device (6) which is arranged in a flow of a mixture of the fuel and air to generate an eddy (8) in the flow so that the eddy maintains a shape of a flame of the burned fuel and which is arranged apart from a downstream end of the swirl member (5) by a fixed sufficient distance so that the shape of the flame maintained by the eddy is prevented from moving toward the downstream end of the swirl member (5).

Description: The present invention relates to a burner with a swirl member and an eddy generating device, particularly to a premix burner in which a fuel is mixed with air before the fuel is burned. As disclosed by Publications of Japanese Patent Unexamined Publication Nos. 64-54122 and 2-40418, a well-known burner has generally a two-step burner system for decreasing a density of NO x so that the fuel is mixed with the air previously to burning of the fuel, when a rated output is obtained. The fuel is mixed with the air previously to burning of the fuel in a second burner by a premix swirl of a premixing device. In order to decrease the density of NO x , an even mixing of the fuel-and-air and a low density of fuel in the mixture are effective. Therefore, the mixing of the fuel-and-air proceeds in a large space and the premix swirl in the premix device accelerates the even mixing. An eddy generating device or flow obstructor member, that is, a flame keeper is arranged close to a downstream side of the premix swirl as disclosed in Publication of Japanese Patent Unexamined Publication No. 64-54122 or is movable longitudinally at the downstream side of the premix swirl according to a variation of temperature in the burner as disclosed in Publication of Japanese Patent Unexamined Publication No. 2-40418, and the swirl extends in the premix device to mix the fuel and the air between upstream and downstream sides of the premix device. In the conventional premix burner, a flame is formed and extinguished alternately at a downstream end of the premix swirl so that a vibration is generated in the premix burner and an operation of the premix burner is not stable. The object of the present invention is to provide a burner and a gas turbine in which vibrations are not generated and a stable operation can be realized. The object is solved according to the features of the independent claims. The dependent claims show advantageous embodiments and further developments of the invention. The burner according to the invention is provided with at least one swirl member for mixing a fuel with an air previously to burning of the fuel, and at least one eddy generating device which is arranged in a flow of an air/fuel-mixture to generate an eddy flow in the flow so that the eddy maintains or restrains a shape of a flame of the burned fuel. The eddy generating device can be arranged apart from a downstream end of the swirl member by a fixed sufficient distance so that the shape of the flame is not deformed toward the downstream end of the swirl member. Since the eddy generating device is arranged apart from the downstream end of the swirl member by the fixed sufficient distance although an eddy flow is generated by a termination of the swirl member at the downstream end of the swirl member to maintain the shape of the flame, a force applied to the flame from the eddy flow by the termination of the swirl member for drawing the shape of the flame from the eddy generating device toward the downstream end of the swirl member is small and is always constant in spite of the variation of temperature in the burner so that the shape of the flame is not changed toward the downstream end of the swirl member. Therefore, the vibration of the flame is not generated and the operation of the burner is stable. The following drawings showing examples of embodiments of the invention describe the invention in more detail, in which Fig. 1 is a cross-sectional view showing a part of a burner according to the present invention, Fig. 2 is an oblique projection and partly-sectional view showing the burner of Fig. 1, Fig. 3 is a cross-sectional view showing a burner system accommodating a burner according to the present invention, Fig. 4 is a cross-sectional view showing a part of another burner according to the present invention, Fig. 5 is an oblique projection and partly-sectional view showing the burner of Fig. 4, Fig. 6 is a cross-sectional view showing a part of another burner according to the present invention, Fig. 7 is an oblique projection and partly-sectional view showing the burner of Fig. 6, Fig. 8 is a cross-sectional view showing a part of another burner according to the present invention, Fig. 9 is a diagram showing relations among a NO x density rate, a burning vibration amplitude rate, and a position of a flame keeper. As shown in Figs. 1 to 3, a burner system includes a main burning chamber R1, a supplementary burning chamber R2, fuel nozzles 3a, 3b, 3c, and a premix device 4. Gas turbine vanes 16 are arranged at a downstream side of the main burning chamber R1, and a compressor 1 is arranged at an upperstream side thereof. The premix device 4 is arranged at an upperstream radially outside of the main burning chamber R1 and accommodates swirl members 5 for accelerating a mixing between a fuel and an air. A flame keeper (an eddy generating device) 6 is arranged at a downstream side of the premix device 4. A flow path area of the premix device 4 is smaller than that of the flame keeper 6 and a flow speed of the mixture in the premix device 4 is larger than that at the flame keeper 6. The flame keeper 6 is supported on a periphery of an end of the premix device 4 and includes a tapered portion 6a and a steep expansion surface 6b arranged at a downstream side of the tapered portion 6a. The mixture flows toward the flame keeper 6 as shown by an arrow of AF, and the steep expansion surface 6b operates as an eddy starting point 6c to generate an eddy 8 at a downstream side of the steep expansion surface 6b so that a shape of the flame is maintained or restrained by the eddy 8. A cooling air path 6d is arranged at an outer periphery of the flame keeper 6 and a cooling air CA flows in the cooling air path 6d to cool the flame keeper 6 and to be supplied to the main burning chamber R1. It is important that the flame keeper 6 is fixed in relation to the swirl members 5 and the eddy starting point 6c is apart from downstream end surfaces 5a of the swirl members 5 by a fixed distance 1. In other words, a space is formed between the eddy starting point 6c and the downstream end surfaces 5a of the swirl members 5. A high-pressure air from the compressor 1 flows into a liner 2 forming the main burning chamber R1 after a flow direction of the high-pressure air is changed in a U-shaped manner. In the burner system, the fuel is supplied to three burning steps through a first step fuel path 3a, a second step fuel path 3b and a start assisting fuel path 3c to be burned. The fuel from the first step fuel path 3a is burned mainly in the supplementary burning chamber R2. The fuel from the second step fuel path 3b is injected by a second step fuel nozzle 4b into the premix device 4 to be mixed with the air flowing from an outer periphery of the premix device 4 and is burned in the main burning chamber R1. The fuel from the start assisting fuel path 3c is used only when the burner is started. A gas generated from the main burning chamber Rl flows through a back tube 7 to the gas turbine vanes 16 so that a gas turbine is rotated. The fuel from the first step fuel path 3a is burned in a diffusion combustion so that a burning thereof is stable althrough a density of NOx is high. The fuel from the second step fuel path 3b is burned in a premixing combustion so that the density of NOx is low. The fuel from the first step fuel path 3a and from the start assisting fuel path 3c is used between a start of burning and a predetermined output of the burner. The fuel from the first step fuel path 3a and from the second step fuel path 3b is used between the predetermined output of the burner and a rated output thereof. In order to decrease the density of NOx, it is necessary that a rate of the fuel from the second step fuel path 3b for the premixing to a whole of the fuel is large and a rate of the whole of the fuel to the air supplied for the burning is small. When the mixture AF flows out of the swirl members 5 to be burned in the main burning chamber R1, the mixture AF forms an eddy at the downstream side of the flame keeper 6 so that the shape of the flame is maintained by the eddy. Since the eddy starting point 6c of the steep expansion surface 6b is fixed in relation to the swirl members 5 and is arranged apart from the downstream ends of the swirl members 5 by the fixed sufficient distance, the flame burning in the main burning chamber R1 cannot move toward the eddy formed at the downstream ends of the swirl members 5. Therefore, the flame burning in the main burning chamber R1 is stable. An angle of the tapered portion 6a may be changed variously. If the tapered portion 6a faces to the supplementary burning chamber R2, it is easy to transmit the flame in the supplementary burning chamber R2 to the main burning chamber R1 when the burning in the main burning chamber R1 is started. In any case, it is important that the eddy 8 is generated by the steep expansion surface 6b. A root portion of a flexible seal 9 includes a cooling air path 10 to cool a reverse surface of the flame keeper 6. The cooling air flowing out of the flame keeper 6 is injected into the liner 2 without a contact with the eddy 8 so that the eddy 8 is not disturbed. A separating wall 11 guides the cooling air to effectively cool the flame keeper 6. As shown in Figs. 4 and 5, the flame keeper 6 may be extends in the premix device 4. In this case, a distance 1 is formed between the steep expansion surface 6b of the flame keeper 6 and the downstream end surfaces 5a of the swirl members 5. Since the flow direction of the mixture is changed in the premix device 4 with a high flow speed thereof before the mixture flows into the burning chambers, the mixture is effectively oriented radially inwardly by the premix device 4. A wall of the premix device 4 includes an air intake path 13 through which the cooling air flows into the flame keeper 6 to flow it. A narrow clearance 12 is arranged at a reverse wall of the flame keeper 6 so that the flow speed of the cooling air is accelerated to obtain an effective cooling. The burner may includes a plurality of the flame keepers 6 arranged longitudinally or radially. As shown in Figs. 6 and 7, two of the flame keepers 6 and 14 are arranged longitudinally or radially. A ring 14 as the flame keeper generates the eddy of the mixture at the downstream end thereof to maintain a flame B. The flame keeper 6 also generates the eddy 8 of the mixture at the downstream end thereof to maintain a flame A. A distance is formed between the downstream end of the ring 14 and the downstream end surfaces 5a of the swirl members 5. The burner may include a plurality of the rings 14, and the ring 14 may be V-shaped. As shown in Fig. 8, the flame keeper 6 may be integrally mounted at the inside of the premix device 4. The swirl members 5 terminate with a clearance from a forward end of the premix device 4 so that the distance 1 is formed between the downstream end of the flame keeper 6 and the downstream end surfaces 5a of the swirl members 5. The shape of the flame keeper 6 may be changed variously, and the- premix device 4 may have a cylindrical shape instead of an annular shape. In Fig. 9, a NOx density rate is a rate of a NOx density by the burner according to the present invention to a NOx density by the conventional burner, a burning vibration amplitude rate is a rate of a vibration amplitude of the burner according to the present invention to a vibration amplitude of the conventional burner, and a position of a flame keeper is a distance between the downstream end of the flame keeper 6 and the downstream end surfaces 5a of the swirl members 5. In the conventional burner, the position of the flame keeper is 0. A line A show an actual relation between the position of the flame keeper and the NOx density rate, and a line B shows an actual relation between the position of the flame keeper and the burning vibration amplitude rate. These actual relations were measured when an outer diameter of the liner 2 is 350 mm and a height of the swirl members 5 is 22 mm. The larger the position of the flame keeper is, the smaller the NOx density rate and the burning vibration amplitude rate are. When the position of the flame keeper is 10 to 15 mm, the NOx density rate, the size of the burner is small and the operation of the burner is stable.

Claims: Burner, comprising at least one swirl member (5) for mixing a fuel with air before burning the fuel, and at least one eddy generating device (6) which is arranged apart from a downstream end (5a) of the swirl member (5) in a flow of an air/fuel-mixture to generate an eddy in the flow so that the eddy maintains a shape of a flame of the burned fuel, characterized in that an eddy starting point (6c) of the at least one eddy generating device (6) is arranged to the swirl member (5) at a fixed distance so that the shape of the flame maintained by the eddy is kept apart from the downstream end (5a) of the swirl member (5) with a fixed distance. Burner according to claim 1, characterized in that the eddy generating device (6) and the premix device (4) have a circular cross-section, and are arranged coaxially with a burning chamber (R1, R2). Burner according to claim 1 or 2, characterized in that the eddy generating device (6) is longitudinally fixedly connected to the swirl member (5). Burner according to claim 2, characterized in that the burner has a plurality of the eddy generating devices (6) radially and/or longitudinally spaced within the burner. Burner according to claim 4, characterized in that the eddy generating device (6) arranged at the most radially outward portion generates the largest diameter of the eddy. Burner according to claim 4, characterized in that sizes of the eddies respectively formed by the eddy generating devices (6) are different from each other so that sizes of the flames respectively maintained by the eddies are different from each other. Burner according to claim 1, characterized in that the eddy generating device has an outer surface which is in contact with the fuel/air mixture and an inner surface on which a cooling air path is provided. Burner according to claim 7, characterized in that the cooling air emerges on a downstream side of the eddy generating device (6) after cooling the eddy generating device (6). Gas turbine, comprising at least one swirl member (5) for mixing a fuel with air before burning the fuel, at least one eddy generating device (6) which is aranged apart from a downstream end (5a) of the swirl member (5) in a flow of an air/fuel-mixture to generate an eddy in the flow so that the eddy maintains a shape of a flame of the burned fuel, and gas turbine blades driven by a gas generated from the burned fuel, characterized in that an eddy starting point (6c) of the at least one eddy generating device (6) is arranged to the swirl member (5) at a fixed distance so that the shape of the flame maintained by the eddy is kept apart from the downstream end (5a) of the swirl member with a fixed distance.

Inventors: AZUHATA SHIGERU, IIZUKA NOBUYUKI, ISHIBASHI YOJI, KUMATA KAZUHIKO, KURODA MICHIO, MORITOMO YOSHIKAZU, OHMORI TAKASHI, SASADA TETSUO, SATO ISAO, TORIYA HAJIME, URUSHIDANI HARUO, AZUHATA, SHIGERU, IIZUKA, NOBUYUKI, ISHIBASHI, YOJI, KUMATA, KAZUHIKO, KURODA, MICHIO, MORITOMO, YOSHIKAZU, OHMORI, TAKASHI, SASADA, TETSUO, SATO, ISAO, TORIYA, HAJIME, URUSHIDANI, HARUO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1991
Main classification: F23R3
IPC codes: F23R3