Annular type gas turbine combustor

Abstract: A side duct (10) for regulating air flow distribution is disposed slidably in axial direction at a terminal end of a pre-diffuser (1) and as the slide duct (10) is moved, air flow supplied downstream to a swirler (4) is regulated so as to obtain a desired fuel-air ratio. In this way the air flow distribution can be regulated to obtain a desired fuel-air ratio to limit the generation of NO x . The regulating device is not influenced by the high temperature of the flames in the combustion chamber.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to an annular type combustor applied to a gas turbine. Description of the Prior Art: One example of an annular type gas turbine combustor in the prior art is described with reference to Figs. 4 to 6. Fig. 4 is a schematic cross sectional view of a combustor, taken on a vertical plane including a turbine central axis, which shows an upper half portion only of the turbine central axis. That is, an annular type combustor forms a combustor which is concentric with the turbine central axis and annular (like a doughnut shape) surrounding the turbine central axis, together with a lower half portion (not shown) of the turbine central axis. In Fig. 4, numeral 1 designates a pre-diffuser, numeral 2 designates a diffuser case, numeral 3 designates a fuel injector, numeral 4 designates a swirler, numeral 5 designates a liner, numeral 6 designates a dilution hole, numeral 7 designates a cooling hole and numeral 8 designates a rotating ring. In such combustor as so constructed, air passes through the pre-diffuser 1 and enters a combustion region surrounded by the liner 5 via the swirler 4, the dilution hole 6, the cooling hole 7, etc. In said combustor, level of NO x included in an emission gas is influenced by a ratio of fuel to air passing through the swirler 4 (hereinafter referred to as "fuel-air ratio"), and generally as the fuel-air ratio is lowered, the NO x level becomes lower. Thus, in order to attain a low NO x level under every operation condition of gas turbine, there is needed a mechanism for regulating said-fuel-air ratio. In the prior art combustor, therefore, a rotary type flow regulating mechanism, employing the rotating ring 8, is provided at the swirler 4, by which opening cross sectional area of the swirler is changed and the fuel-air ratio is regulated. As shown in Figs. 5 and 6, the rotating ring 8 has an approximately same structure as the swirler 4 and is constructed by swirling blades, each having a certain thickness. Air flow is regulated by the rotating ring 8 which is rotated so that a relative phase to the swirler 4 is changed. That is, if air passage of the rotating ring 8 coincides with air passage of the swirler 4 at a contact plane, the opening cross sectional area becomes maximum and as the relative phase is caused to deviate from this state, as shown in Fig. 6, the opening cross sectional area can be reduced corresponding to the amount of such deviation. According to change of the opening cross sectional area, flow rate of air passing through the swirler 4 is increased or decreased with result that the fuel-air ratio can be regulated. In said prior art combustor, the rotating ring which is a movable portion for regulating the fuel-air ratio is disposed at a position which is easily influenced by flames thus there is a problem that the rotating ring is heated to a high temperature so as to lose its durability and reliability. Also, in such arrangement, there is a problem that a complicated mechanism of the movable portion is needed as a countermeasure for thermal expansion etc. Another prior art combustor for a gas turbine described in US-A-3 905 192 has a movable bell mouth piece positioned at a forward end of a fuel atomizer or nozzle. The bell mouth piece is axially slidable and retractable to open or close an air duct section downstream of the nozzle. Thus, the air flow distribution regulating device is positioned directly in a fuel-air mixing region of the combustor and therefore in a zone which is exposed to considerably high temperatures. SUMMARY OF THE INVENTION: It is an object of the present invention to provide an annular type gas turbine combustor of high reliability which is able to solve the problems in the prior art with a simple construction and provides possibility to regulate the fuel-air ratio safely and securely. In order to attain said object, the present invention provides an annular type gas turbine combustor as defined in claim 1. Preferred embodiments of the combustor are defined in the dependent claims. In this combustor, when air supplied downstream from the pre-diffuser passes through the air flow distribution regulating device at the terminal end of the pre-diffuser, the air flow distribution regulating device is slid in the axial direction and distribution of the air flowing downstream is regulated in a desired direction so as to obtain an optimized combustion. And said air flow distribution regulating device is disposed at the terminal end of the pre-diffuser, as mentioned above, which is apart from flames so as not to be influenced by the flames, thus there is no fear of lowering of durability due to high temperature flames. The present invention also provides an annular type gas turbine combustor in which the air flow distribution regulating device is in the form of a slide duct surrounding the pre-diffuser and said slide duct is divided into a plurality of parts which are divided in the circumferential direction and the divided parts are slidable in the axial direction independent of each other. Thereby each of the divided parts can be slid to various sliding patterns so as to effect appropriate regulations of distribution of the air flowing downstream from the pre-diffuser to meet operation conditions. The present invention also provides an annular type gas turbine combustor in which a roller is disposed between the pre-diffuser and the air flow distribution regulating device, thereby relative movement of the pre-diffuser and the air flow distribution regulating device is done smoothly by the effect of rolling of the roll and the distribution of air flow-can be regulated securely and easily. The present invention also provides an annular type gas turbine combustor in which each of the pre-diffuser and the air flow distribution regulating device has a circular cross sectional shape and is disposed concentrically with each other, thereby the supplied air flows in a concentrically distributed form and the air flow distribution in the radial direction becomes uniform, so that a regular combustion can be attained. The present invention also provides an annular type gas turbine combustor in which each of the pre-diffuser and the air flow distribution regulating device has a polygonal cross sectional shape and is disposed concentrically with each other, thereby even if the pre-diffuser is formed in a polygonal cross sectional shape, the air flow distribution regulating device can well conform to that shape and the distribution of air flow can be regulated securely. The present invention also provides an annular type gas turbine combustor in which the air flow distribution regulating device has its end face formed in a wave shape, thereby there occurs a differential position in the axial direction between a tip position and a bottom position of the wave shape and making use of said differential position, flow-out position of the supplied air is caused to change in the axial direction, so that the distribution of air flow in the circumferential direction can be regulated finely. The present invention also provides an annular type gas turbine combustor in which the air flow distribution regulating device is constructed so as to be rotatable around a gas turbine center axis, thereby the air flow distribution regulating device is rotated in addition to movement in the axial direction and a fine and appropriate regulation of the air flow distribution can be effected further. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a schematic cross sectional view of a combustor of a first embodiment according to the present invention. Fig. 2 is an explanatory view of regulation status of the combustor of Fig. 1. Fig. 3 is a schematic cross sectional view of a combustor of a second embodiment according to the present invention. Fig. 4 is a schematic cross sectional view of a prior art combustor. Fig. 5 is a cross sectional view taken on line A-A of Fig. 4. Fig. 6 is a cross sectional view taken on line B-B of Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS: A first embodiment according to the present invention is described with reference to Figs. 1 and 2. It is to be noted that same portions as those in the above-mentioned prior art are denoted with same numerals in the figures and characteristic features of the present embodiment are described with repetitive description being omitted. The air flow distribution regulating device of the present embodiment employs a slide duct 10, which slide duct 10 is disposed at an end portion of a pre-diffuser 1 concentrically with the pre-diffuser 1 so as to surrounded an outer circumferential surface of the pre-diffuser 1. Although the figure does not show details, the slide duct 10 is constructed integratedly by two divided objects, one being an outer side portion shown in an upper part of Fig. 1 and the other being an inner side portion shown in a lower part of Fig. 1, with a strut 14 being interposed between said two divided objects. Between the slide duct 10 and the pre-diffuser 1, a roller 13 is disposed, and an actuator 15 which connects to outside is connected to a portion of the slide duct 10, so that the slide duct 10, when pushed or pulled by the actuator 15, is movable in the axial direction of the pre-diffuser 1. It is to be noted that the slide duct 10 as shown here is of two divided objects, upper and lower in the figure or outer and inner around the gas turbine axis, but it is not limited to the two divided objects but can be of a single unit or of objects divided into a plurality of more than 2 in a circumferential direction according to convenience of manufacture. Further, the integrated slide duct may summarily be of a cross sectional shape conformable to, and slidable in the axial direction on, the shape of the pre-diffuser, whether circular or polygonal. In the present embodiment as so constructed, as shown by broken lines in Fig. 2, if the slide duct 10 is moved to a downstream side (rightwardly in the figure), air led to the swirler 4 becomes dominant of straight flow components as shown by arrows parallel to the axial direction, thus amount of air that concentrates toward the swirler 4 increases with result that the fuel-air ratio becomes lower and NO x can be reduced, especially at the time of a high load operation. Contrary thereto, as shown by continuous lines in Fig. 2, if the slide duct 10 is moved to an upstream side (leftwardly in the figure), air component which flows outwardly as shown by arrows in a dispersing direction in the figure increases, thus the air led to the swirler 4 decreases with result that the fuel-air ratio becomes higher and unstableness of combustion at the time of low load operation can be avoided. That is, the air flow distribution to the outward direction and the axial direction changes and the fuel-air ratio at the swirler 4 where the air flow distribution decreases becomes higher. Next, description is made on a second embodiment according to the present invention with reference to Fig. 3. It is to be noted that same portions as those in the above-mentioned prior art and first embodiment are denoted with same numerals in the figure and repetitive description is omitted. In an annular type combustor using a slide duct 10 as an air flow distribution regulating device according to the second embodiment, while the slide duct 10 of the first embodiment is formed integratedly by the outer and inner divided objects which are connected by the strut 14, said strut 14 is removed and each one actuator 15a, 15b is provided to the outer slide duct and the inner slide duct, respectively, so that each of said slide ducts is movable in the axial direction independently. In the second embodiment, the outer slide duct and the inner slide duct are-moved independent of each other and distribution of air flow led to an outer shroud passage 11 and an inner shroud passage 12 is regulated. Thereby, a ratio of flow rate of an outer dilution air and an inner dilution air can be changed and a temperature distribution of combustion gas at an outlet portion 9 of the combustor can be optimized. It is to be noted that although a downstream side end face of the slide duct 10 is flat both in the first and second embodiments, an arbitrary shape of end face, such as uneven end face of wave-shape, for example, can be employed and also it is possible that the air flow distribution can be regulated in a circumferential direction. Further, if said end face is formed other than in a flat one and the slide duct 10 is moved not only in the axial direction but also rotationally around the gas turbine axis, then a fine and appropriate regulation of air flow distribution can be effected further. While embodiments of the present invention have been described above with reference to accompanying figures, the present invention is not limited thereto but may naturally be added with various changes in the concrete structure within the scope of the appended claims. According to the present invention, by use of a very simple structure that the air flow distribution regulating device which is slidable in the axial direction is disposed at the terminal end of the pre-diffuser, distribution of air flow led to the downstream swirler can be regulated, and by this flow regulation, fuel-air ratio can also be regulated with result that the fuel-air ratio is lowered at the time of high load operation and NO x can be reduced. Also, at the time of low load operation, the fuel-air ratio is enhanced so that a stable combustion can be attained. And yet, the air flow distribution regulating device is disposed in a close vicinity of the pre-diffuser, thus it is not influenced by flames, its movable portions can be made simpler and an apparatus of high durability and reliability can be provided. Also, according to the present invention, the air flow distribution regulating device is circumferentially divided into a plurality of parts and each of the divided parts is made movable independent of each other, thereby a fine regulation of air flow corresponding to combustion state becomes possible and a combustion gas temperature distribution at the outlet portion of the combustor can be optimized. Further, according to the invention, partial variations, such as a construction that the roller is disposed between the pre-diffuser and the air flow distribution regulating device, a construction that the pre-diffuser and the air flow distribution regulating device, each, has a circular or polygonal cross sectional shape and is disposed concentrically with each other, a construction that the air flow distribution regulating device has its end face formed in a wave-shape and a construction that the air flow distribution regulating device is constructed rotatively around the gas turbine axis, are appropriately selected and added, thereby distribution of supplied air flow can be finely regulated in the axial direction and circumferential direction.

Claims: An annular type gas turbine combustor comprising: an annular combustor casing (2) containing a fuel-air mixing region; a pre-diffuser (1) provided at an inlet end of said combustor casing (2) for supplying air to said fuel-air mixing region of the combustor downstream of said pre-diffuser (1), said pre-diffuser (1) having a terminal end; an air flow distribution regulating device (10) disposed at a terminal end of said pre-diffuser (1) and upstream of said fuel-air mixing region and being slidable in an axial direction of said pre-diffuser (1) for regulating the air flow downstream of said pre-diffuser (1). An annular type gas turbine combustor as claimed in claim 1, wherein said air flow distribution regulating device (10) is in the form of a slide duct surrounding the outer circumferential surface of said pre-diffuser (1) and comprising a radially outer side duct part and a radially inner side duct part. An annular type gas turbine combustor as- claimed in claim 2, wherein said radially outer side duct part and said radially inner side duct part are integrally connected with each other and are connected to an actuator (15) for effecting the sliding movement of the duct in the axial direction of the pre-diffuser (1). An annular type gas turbine combustor as claimed in claim 2, wherein said radially outer side duct part and said radially inner side duct part are respectively connected to an actuator (15a,15b) for independently effecting the sliding movement of the duct parts in the axial direction of the pre-diffuser (1). An annular type gas turbine combustor as claimed in any one of claims 2 to 4, wherein said slide duct is divided into a plurality of parts in the circumferential direction and the divided parts are slidable in the axial direction independent from each other. An annular type gas turbine combustor as claimed in anyone of claims 1 to 5, wherein a roller (13) is disposed between said pre-diffuser (1) and said air flow distribution regulating device (10). An annular type gas turbine combustor as claimed in anyone of claims 1 to 6, wherein said air flow distribution regulating device (10) has a cross sectional shape conforming to the shape of the pre-diffuser (1). An annular type gas turbine combustor as claimed in claims 7, wherein said pre-diffuser (1) and said air flow distribution regulating device (10) respectively have a circular or a polygonal cross sectional shape and are disposed concentrically with each other. An annular type gas turbine combustor as claimed in anyone of claims 1 to 8, wherein said air flow distribution. regulating device (10) has its downstream axial end face formed in a wave shape. An annular type gas turbine combustor as claimed in claim 6, wherein said air flow distribution regulating device (10) is constructed so as to be rotatable around a gas turbine center axis.

Inventors: NAKAE TOMOYOSHI, NAKAE, TOMOYOSHI, Nakae, Tomoyoshi, c/o Mitsubishi Heavy Ind., Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1997
Main classification: F23R3
IPC codes: F23R3, F23L1, F23C99