Gas turbine combustor

Abstract: In gas turbine combustor constructed by combustion chamber (10) and steam-cooled peripheral wall (2) thereof, there is bored air hole (1) for injecting dilution air therethrough in the peripheral wall (2) on upstream side of the combustion chamber (10), thereby the air is supplied through the air hole (1) into the vicinity of inner surface of the peripheral wall (2) to form film flow of air and increase of fuel concentration there is suppressed. The dilution air is preferably supplied from gas turbine compressor (6).

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a combustor of gas turbine, specifically to a combustor of which peripheral wall is cooled by steam, e.g. as described in US Patent No 4 819 438 A. Description of the Prior Art: Fig. 3 is a constructional view of conventional gas turbine plant. In Fig. 3, numeral 6 designates a compressor, numeral 7 designates a combustor, numeral 8 designates a gas turbine connected to the compressor 6 coaxially and numeral 9 designates an exhaust gas boiler for recovering energy of exhaust gas after used for driving the gas turbine 8. In operation of the gas turbine plant constructed as mentioned above, combustion air which has been compressed by the compressor 6 driven coaxially with the gas turbine 8 is led into the combustor 7. In the combustor 7, fuel is injected for combustion into the combustion air so compressed as above. Combustion gas therefrom is led into the gas turbine 8 for expansion work and then is led into the exhaust gas boiler 9. It is to be noted that, although not shown in the figure, a generator is connected to an output shaft of the gas turbine 8 to be driven by the gas turbine 8. In the exhaust gas boiler 9, water is heated by the exhaust gas sent from the gas turbine 8 to generate steam. This steam is led into a steam turbine (not shown) for drive thereof. Also, a portion of the steam is led into the combustor 7 as a cooling steam to be used for cooling of a peripheral wall of the combustor 7. Fig. 4 is a cross sectional view of main part of one example of a prior art combustor, in which a peripheral wall of the combustor is cooled by cooling steam. In Fig. 4, a combustor 7 of a steam-cooled system is a combustor for generating a combustion gas of high temperature of about 1,500°C at gas turbine inlet. Numeral 2 designates a peripheral wall, which is a steam-cooled wall constructed such that steam flows in the wall for cooling of wall surface, said steam having been generated at the exhaust gas boiler 9 to do expansion work at a steam turbine (not shown) and thus temperature-reduced to a certain level to be used as a cooling steam. Numeral 10 designates a combustion chamber, which is surrounded by the peripheral wall 2 and constructed such that a combustion air from the compressor 6 is led thereinto through a wall portion 20 on an upstream side thereof. Also, in the wall portion 20 on the upstream side of the combustion chamber 10, there is provided a pilot nozzle 4 at a central portion thereof and also provided are a plurality of main nozzles 3, arranged with equal intervals along a circumferential direction of the combustor 7, on an outer side of the pilot nozzle 4. Numeral 2a designates a combustion gas outlet. In operation of he combustor 7 constructed as mentioned above, fuel is injected from the pilot nozzle 4 into the combustion air in the combustion chamber 10 to be ignited and then main fuel is injected from the plurality of main nozzles 3 into the flame so ignited to be mixed and burned with the air in the combustion chamber 10 and generate combustion flame 5. Combustion gas so generated flows out of the outlet 2a of the combustion chamber 10 to be sent to the gas turbine 8 for drive thereof. There are, however, shortcomings as mentioned below in the prior art gas turbine combustor of steam-cooled system shown in Fig. 4. That is, there is formed a low velocity zone of fuel and air flow in the vicinity of inner surface of the peripheral wall 2 on an upstream side in the combustion chamber 10 and fuel concentration in this low velocity zone, which is shown as "B" in Fig. 4, is liable to become higher (thicker). Hence, the flame 5 generated at the low velocity zone B spreads toward the upstream side, that is, toward the nozzles 3, 4, along the vicinity of the inner surface of the peripheral wall 2, so that there is caused there a combustion in which mixing of fuel and air is incomplete or a combustion in which a cross sectional combustion load is high. As the result, in the gas turbine using the prior art combustor 7, there arise problems of increase of discharge of NO x (nitrogen oxides) due to elevation of combustion temperature, increase of combustion vibration due to rapid combustion, etc. in the combustion chamber 10. SUMMARY OF THE INVENTION: It is therefore an object of the present invention to provide a gas turbine combustor, having a steam-cooled wall of combustion chamber, in which increase of fuel concentration at a low velocity zone of flow of fuel and air mixture in the vicinity of inner surface of the steam-cooled wall can be suppressed so as to reduce NO x discharge as well as combustion vibration there can be suppressed. In order to attain said object, a first means provided by the present invention is a gas turbine combustor having a combustion chamber of which peripheral wall is a steam-cooled wall, characterized in being constructed such that there is bored an air hole for injecting air therethrough in said peripheral wall on an upstream side of said combustion chamber and air is supplied through said air hole to the vicinity of an inner surface of said peripheral wall. Also, a second means provided by the present invention is a gas turbine combustor as mentioned in the first means, characterized in being constructed such that there is connected an air tube to an inlet side of said air hole and air supplied from a gas turbine compressor is led into said air hole through said air tube. In the combustion chamber of the gas turbine combustor mentioned above, combustion air is supplied thereinto from the compressor and fuel is injected into the combustion air through a pilot nozzle and main nozzles and, at this time, there is formed a low velocity zone of fuel and air flow in the vicinity of the inner surface of the peripheral wall on the upstream side of the combustion chamber, that is, near the nozzles and fuel concentration at this low velocity zone becomes higher (thicker). Nevertheless, in the present invention, air for dilution is supplied into this low velocity zone of fuel and air flow in the combustion chamber, hence there is formed a film flow of this dilution air in the vicinity of the inner surface of the peripheral wall in the low velocity zone and, due to this film flow, fuel and air are accelerated to be mixed and increase of fuel concentration there is suppressed. Also, the flame developing from a central portion of the combustion chamber is thereby prevented from spreading toward the upstream side along the inner surface of the peripheral wall, hence increase of combustion temperature due to spreading of the flame and increase of NO x discharge accompanying therewith can be suppressed and combustion vibration due to rapid increase of combustion pressure and temperature can be also prevented from occurring. According to the second means of the present invention, the dilution air to be led into the air hole is supplied from the gas turbine compressor, thus there is no need of providing a specific compressed air supply means, such as an exclusive air compressor, and the dilution air of high pressure can be obtained by the means of simple construction and low cost. According to the present invention constructed as above, the effect thereof is summarized as follows: that is, the dilution air is supplied through the air hole into the low velocity zone of fuel and air flow in the vicinity of the inner surface of the peripheral wall on the upstream side of the combustion chamber, thereby mixing of fuel and air is accelerated and increase of fuel concentration in the low velocity zone can be suppressed. Thus, the combustion flame is prevented from spreading to the low velocity zone, and increase of combustion temperature due to spreading of the flame and increase of NO x discharge accompanying therewith are suppressed and also occurring of combustion vibration due to rapid increase of combustion pressure and temperature is prevented. Accordingly, in the present invention, by use of the very simple and low cost means to provide the air hole in the peripheral wall of the combustion chamber, there is obtained a gas turbine in which NO x discharge is reduced and occurring of combustion vibration is prevented. Also, by supplying the dilution air to be led into the air hole from the gas turbine compressor, there is no need of providing a specific air supply means, such as an air compressor, and the dilution air can be obtained by the very simple and low cost means. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a cross sectional view of main part of gas turbine combustor of an embodiment according to the present invention. Fig. 2 is an enlarged cross sectional view of portion "A" of Fig. 1. Fig. 3 is a constructional view of conventional gas turbine plant. Fig. 4 is a cross sectional view of main part of one example of a prior art gas turbine combustor. DESCRIPTION OF THE PREFERRED EMBODIMENTS: In Fig. 1 which shows an embodiment according to the present invention, numeral 2 designates a peripheral wall, which is a steam-cooled wall constructed such that steam flows in the wall for cooling of wall surface, said steam having been generated at the exhaust gas boiler 9, shown in Fig. 3, to do expansion work at a steam turbine (not shown) and thus temperature-reduced to a certain level to be used as a cooling steam. Numeral 10 designates a combustion chamber, which is surrounded by the peripheral wall 2 and constructed such that a combustion air from the compressor 6, shown in Fig. 3, is led thereinto through a wall portion 20 on an upstream side thereof. Also, in the wall portion 20 on the upstream side of the combustion chamber 10, there is provided a pilot nozzle 4 at a central portion thereof and also provided are a plurality of main nozzles 3, arranged with equal intervals along a circumferential direction of the combustor 7, shown in Fig. 3, on an outer side of the pilot nozzle 4. Numeral 2a designates a combustion gas outlet. Above-mentioned construction is same as that in the prior art shown in Fig. 4. In the present invention, the peripheral wall 2 of the combustor 7, is improved as follows, that is, as shown in Figs. 1 and 2, Fig. 2 being an enlarged view of portion "A" of Fig. 1, there are bored a plurality of air holes 1 in the peripheral wall 2 with appropriate intervals therebetween along a circumferential direction of the combustor 7 at position on an upstream side of the peripheral wall 2 of the combustor 7, that is, at position on an outer side of the main nozzles 3. The air holes 1 are provided in one row or in plural rows (two rows in the present embodiment) and each thereof is provided with an air tube 11 connecting to an outlet of the compressor 6 so that a pressurized air from the outlet of the compressor 6 is led therethrough to be injected into the combustion chamber 10 via the air holes 1. In operation of the combustor 7 constructed as mentioned above, fuel is injected from the pilot nozzle 4 into the combustion air in the combustion chamber 10 to be ignited and then main fuel is injected from the plurality of main nozzles 3 into the flame so ignited to be mixed and burned with the air in the combustion chamber 10 and generate combustion flame 5. Combustion gas so generated flows out of the outlet 2a of the combustion chamber 10 to be sent to the gas turbine 8 for drive thereof. While combustion is being made in the combustion chamber 10, there is formed a low velocity zone of fuel and air flow in the vicinity of inner surface of the peripheral wall 2 on the upstream side of the combustion chamber 10, that is, near the nozzles 3, 4. So, in the prior art combustor, fuel and air are not mixed sufficiently together in this low velocity zone and fuel concentration becomes higher (thicker) there. In the combustor of the present invention, however, air for dilution is supplied into the low velocity zone of fuel and air flow via the plurality of air holes 1 bored in the peripheral wall 2, as shown in Fig. 2, hence there is formed a film flow of this dilution air in the vicinity of the inner surface of the peripheral wall 2 in the low velocity zone and, due to this film flow, fuel and air are accelerated to be mixed and increase of fuel concentration in the low velocity zone is suppressed. According to the present embodiment, the flame developing from a central portion of the combustion chamber 10 is prevented from spreading toward the upstream side, hence increase of combustion temperature due to spreading of the flame and increase of NO x discharge accompanying therewith can be suppressed. Also, combustion vibration due to rapid increase of combustion pressure and temperature can be prevented from occurring. Further, according to the present embodiment, the air to be led into the air hole is supplied from the compressor 6 of the gas turbine, hence there is no need of providing a specific compressed air supply means, such as an exclusive air compressor, and moreover the air of high pressure can be supplied. The invention has been described by use of the embodiments as illustrated in the figures, but the invention is not limited thereto but can be added with various modifications to the structure within the scope of the claims as hereafter appended.

Claims: A gas turbine combustor having a combustion chamber (10) of which peripheral wall (2) is a steam-cooled wall, characterized in being constructed such that there is bored an air hole (1) for injecting air therethrough in said peripheral wall (2) on an upstream side of said combustion chamber (10) and air is supplied through said air hole (1) to the vicinity of an inner surface of said peripheral wall (2). A gas turbine combustor as claimed in Claim 1, characterized in being constructed such that there is connected an air tube (11) to an inlet side of said air hole (1) and air supplied from a gas turbine compressor (6) is led into said air hole (1) through said air tube (11).

Inventors: AKAMATSU SHINJI, MANDAI SHIGEMI, OHTA MASATAKA, TANAKA KATSUNORI, AKAMATSU, SHINJI, MANDAI, SHIGEMI, OHTA, MASATAKA, TANAKA, KATSUNORI, Akamatsu, Shinji c/o Takasago Machinery Works, Mandai, Shigemi, Takasago Research &amp; Dev. Center, Ohta, Masataka, Takasago Research &amp; Dev. Center, Tanaka, Katsunori c/o Takasago Machinery Works
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F23R3
IPC codes: F23R3, F02C7