Combustor

Abstract: Combustor comprising pilot fuel nozzle and plurality of main premixing nozzles disposed therearound for forming premixture of air and fuel supplied from main fuel nozzle is improved so as not to cause vibratory combustion. Pilot fuel nozzle unit 104 comprises plurality of pilot fuel nozzles 103. Plurality of main premixing nozzles 102 are disposed on coaxial circumference of the pilot fuel nozzle unit 104. The pilot fuel nozzles 103 are arranged irregularly in circumferential direction of the pilot fuel nozzle unit 104, thereby formed is portion 105 where there is no pilot fuel nozzle 103. Premixture in the main premixing nozzles 102 positioned corresponding to the pilot fuel nozzle 103 burns with comparatively short flames. Premixture in the main premixing nozzles 102 positioned corresponding to the portion 105 of no pilot fuel nozzle 103 burns with long flames because of flame spreading from adjacent main fuel nozzles. Thus, by differences in flame length, heat generation rate distribution is dispersed.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates generally to a combustor and more specifically to a combustor which is appropriate for use as a gas turbine combustor. Description of the Prior Art: One example of a premixed flame type combustor which is used as a prior art gas turbine low NOx type combustor is shown in Fig. 9, wherein Fig. 9(a) is a longitudinal cross sectional view of the combustor and Fig. 9(b) is a cross sectional view taken on line C-C of Fig. 9(a). In Fig. 9, within a combustor 201 which is provided to a gas turbine cylinder, there are provided a plurality, eight pieces in this case, of main burners 202 around a central axis of the combustor 201. Each of the main burners 202 comprises therein a main fuel nozzle 203 of same shape for all the main burners 202 and a main swirler 204 of likewise same shape. Also, provided in a portion surrounded by the plurality of main burners 202 and along the central axis of the combustor 201 is a pilot burner 207, which comprises therein a pilot fuel nozzle 206 and a pilot swirler 205 provided around the pilot fuel nozzle 206. Combustion air flowing inside of an outer periphery of the combustor 201 turns in the angle of 180° at an air inflow portion 208 to flow in the combustor 201 passing through the main swirler 204 each of the main burners 202 and the pilot swirler 205 of the pilot burner 207. In the pilot burner 205, pilot fuel supplied from the pilot fuel nozzle 206 is burned by the combustion air which has passed through the pilot swirler 205. In the main burner 202, main fuel supplied from the main fuel nozzle 203 and the combustion air which has passed through the main swirler 204 are mixed to form a premixture, which is fired by pilot flame of the pilot fuel so that a low NOx combustion is effected in the combustor 201. The premixture formed in the main burner 202 is fired by the pilot flame of the pilot fuel, as mentioned above, and in this case, as there is substantially a regularity in a mixing state of the premixture between each of the plurality of main burners 202, combustion state in each of the main burners 202 becomes regular, which results also in a regularity in heat generation distribution all around in the combustor 201 along the central axis direction thereof and there occurs a constant area where there is concentrated a large heat generation in the combustor 201. For this reason, vibratory combustion is prone to occur due to such concentrated heat generation to cause a non-stability of the combustion, which results in a problem that a low NOx combustion is hampered. Various prior art combustors for a gas turbine which respectively have a pilot burner provided on a central axis and a plurality of main burners provided around the pilot burner and each having a main fuel nozzle and a main swirler disposed around the main fuel nozzle are described in JP 08-285 240, EP 0 691 511 A and WO 98/12478 A. SUMMARY OF THE INVENTION: It is an object of the present invention to provide a combustor in which a more averaged heat generation distribution is formed in an axial direction of the combustor so that a heat generation may be less concentrated on a constant area, a stable combustion my be attained with less vibratory combustion an a low NOx combustion may be hampered. In order to solve this object the present invention provides a combustor as defined in claim 1. Preferred embodiments are defined in the dependent claims. According to the combustor of the present invention, two or more types of the main burners having different numbers of fuel injection ports of the main fuel nozzle are provided in the combustor on a circumference surrounding the pilot burner so that a same type of said types may not be adjoined each other, thereby the premixture does not become a constant state all around in the combustor, the portion where the heat generation rate is high is dispersed in the central axis direction of the combustor, a vibratory combustion caused by the concentrated heat generation is avoided and a stable combustion is attained, hence a low NOx combustor in which a low NOx combustion is not hampered can be obtained. According to a preferred embodiment of the combustor of the present invention, two or more types of the main burners having different fitting angles of swirler vanes relative to the main swirler central axis direction are provided in the combustor on a circumference surrounding the pilot burner so that a same type of said types may not be adjoined each other, thereby the premixture does not become a constant state all around in the combustor and the portion where the heat generation rate is high is dispersed to be averaged in the central axis direction of the combustor. Hence, a vibratory combustion caused by the concentrated heat generation is avoided, a stable combustion is attained and a low NOx combustor in which a low NOx combustion is not hampered can be obtained. In this respect the present invention provides a combustor in which a plurality of types of said main burners in which two or more types of said main burners having different numbers of fuel injection ports of said main fuel nozzle and two or more types of said main burners having different fitting angles of swirler vanes relative to a central axis direction of said main swirler are combined are provided in a circumferential direction of the combustor so that a same one of said types may not be adjoined each other. According to the combustor of the present invention, the heat generation rate distribution is further dispersed to be averaged, thereby a vibratory combustion due to the concentrated heat generation is avoided and a stable combustion is attained, hence a low NOx combustor in which a low NOx combustion is not hampered can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a view showing a low NOx combustor of an embodiment according to the present invention, wherein Fig. 1(a) is a longitudinal cross sectional view and Fig. 1(b) is a half cross sectional view taken on line A-A of Fig. 1(a). Fig. 2 is an enlarged view of a nozzle of X-portion of Fig. 1(a), wherein Fig. 2(a) is a longitudinal, partly cut away, view of an N1 type nozzle, Fig. 2(a1) is a cross sectional view taken on line D-D of Fig. 2(a), Fig. 2(a2) is a cross sectional view taken on line E-E of Fig. 2(a), Fig. 2(b) is a longitudinal, partly cut away, cross sectional view of an N2 type nozzle and Fig. 2(b1) is a cross sectional view taken on line F-F of Fig. 2(b). Fig. 3 is an explanatory view of fuel concentration distribution in the combustor of the embodiment, wherein Fig. 3(a) shows that at a main burner 221 outlet and Fig. 3(b) shows that at a main burner 222 outlet. Fig. 4 is a conceptual view of heat generation rate in the combustor of the embodiment. Fig. 5 is a view showing an example of a low NOx combustor which serves to explain certain features of another embodiment according to the present invention, wherein Fig. 5(a) is a longitudinal cross sectional view and Fig. 5(b) is a half cross sectional view taken on line B-B of Fig. 5(a). Fig. 6 is an enlarged view of a main swirler of Y-portion of Fig. 5(a), wherein Fig. 6(a) is a view showing those of an S1 type main swirler, Fig. 6(a1) is a view seen from line G-G of Fig. 6(a), Fig. 6(b) is a view showing those of an S2 type main swirler and Fig. 6(b1) is a view seen from line H-H of Fig. 6(b). Fig. 7 is an explanatory view of fuel concentration distribution in this combustor, wherein Fig. 7(a) shows that at a main burner 223 outlet and Fig. 7(b) shows that at a main burner 224 outlet. Fig. 8 is a conceptual view of heat generation rate in this combustor. Fig. 9 is a view showing an example of a low NOx combustor in the prior art, wherein Fig. 9(a) is a longitudinal cross sectional view and Fig. 9(b) is a half cross sectional view taken on line C-C of Fig. 9(a). Next, a combustor of an embodiment according to the present invention will be described with reference to Figs. 1 to 4. In Fig. 1, a main swirler 204, a pilot swirler 205, a pilot fuel nozzle 206, a pilot burner 207 and an air inflow portion 208 are same as those of the prior art described in Fig. 9. But in a combustor 201 of the present embodiment, in place of the main fuel nozzle 203 having a same common shape as shown in Fig. 9, there are provided two types of main burners 221, 222 comprising therein main fuel nozzles 231, 232, respectively, having mutually different shapes. That is, the main burner 221 of one type thereof comprises an N1 type main fuel nozzle 231 as shown in Fig. 2(a) and the main burner 222 of the other type comprises an N2 type main fuel nozzle 232 as shown in Fig. 2(b), and these two types of the main burners 221, 222 are arranged alternately on a circumference surrounding the pilot burner 207 in the combustor 211 as shown in Fig. 1(b). The main swirler 204 is of a same shape both for the main burners 221, 222. As shown in Fig. 2(a), the N1 type main fuel nozzle 231 has two sectional planes of positions where fuel injection ports 231a are provided, one of said planes taken on line D-D of Fig. 2(a) being shown in Fig. 2(a1) and the other taken on line E-E of Fig. 2(a) being shown in Fig. 2(a2). As seen there, there are provided four fuel injection ports 231a in each of said planes and directions of the fuel injection ports 231a alternate mutually between the two planes. On the other hand, as shown in Fig. 2(b), the N2 type main fuel nozzle 232 has one sectional plane of position where fuel injection ports 232a are provided, said plane taken on line F-F of Fig. 2(b) being shown in Fig. 2(b1). As seen there, there are provided four fuel injection ports 232a in said plane. Accordingly, the number of the fuel injection ports 231a of the N1 type main fuel nozzle 231 is double of that of the fuel injection ports 232a of the N2 type main fuel nozzle 232, but a total injection port area of the fuel injection ports 231a of the N1 type main fuel nozzle 231 is made equal to that of the fuel injection ports 232a of the N2 type main fuel nozzle 232, thereby the construction is made such that the fuel flow rate from each type of the main fuel nozzles becomes equal. In the mentioned embodiment, the main burner 221 comprises the N1 type main fuel nozzle which has many of the fuel injection ports 231a, thereby fuel injection rate per fuel injection port 231a is small, so that penetrating force of the fuel is lowered. Hence, the premixture there is so formed that the fuel concentration becomes high in a central portion of outlet of the main burner 221 and low in outer peripheral portions of same, as shown by fuel concentration distribution of Fig. 3(a). On the other hand, the main burner 222 comprises the N2 type main fuel nozzle 232 which has less number of the fuel injection ports 232a, thereby fuel injection rate per fuel injection port 232a is large, so that penetrating force of the fuel becomes high as compared with the fuel injection port 231a. Hence, the premixture there is so formed that the fuel concentration becomes high in outer peripheral portions of outlet of the main burner 222 reversely, as shown by the fuel concentration distribution of Fig. 3(b). The premixture which has come out of the main burner is fired by peripheral pilot flames as heat source. If the fuel concentration is low in the outer peripheral portions of the burner outlet, like in the main burner 221, the combustion speed is slow and flames become longer and then if the flames spread to the central portion of the premixture, as the fuel concentration there is high, a strong heat generation occurs suddenly in the area comparatively apart from the outlet of the main burner 221. On the other hand, if the fuel concentration is high in the outer peripheral portions of the burner outlet, like in the main burner 222, the combustion speed becomes higher and flames become shorter, and a strong heat generation occurs in the area comparatively near the outlet of the main burner 222. In any case, if the main burners comprising the main fuel nozzles of same type would be arranged on an entire circumference of the combustor 211, like in the prior art case, it is so considered that there would be concentrated a high heat generation in a constant area of the combustor and there would occur the mentioned vibratory combustion due to this concentrated heat generation. Fig. 4 is a conceptual view showing distribution of heat generation rate in the combustors corresponding to the types of the main burners mentioned above, wherein the vertical axis shows heat generation rate and the horizontal axis shows distance from the main burner outlet in the combustor central axis direction. In Fig. 4, broken line a shows the heat generation rate of a combustor in which only the main burners 221, each having therein the N1 type main fuel nozzle 231, are provided, and broken line b shows the heat generation rate of a combustor in which only the main burners 222, each having therein the N2 type main fuel nozzle 232, are provided, wherein both of these combustors correspond to the mentioned combustor 201 in the prior art and there occurs the concentrated heat generation in the area of a constant distance in the combustor central axis direction resulting in the problem of vibratory combustion. In the present third embodiment, as mentioned above, the main burner 221 comprising the N1 type main fuel nozzle 231 and the main burner 222 comprising the N2 type main fuel nozzle 232 are provided alternately on a circumference surrounding the pilot burner 207 in the combustor 211, and the premixture is prevented from becoming a regular state all around in the combustor 211. Thereby, as shown by solid line c in Fig. 4, there are formed mixedly an area where the combustion speed is fast in the combustor central axis direction and an area where it is slow in the same direction and the portion where the heat generation rate is high is dispersed. Thus, a vibratory combustion caused by the concentrated heat generation is avoided and a stable combustion is attained, so that a low NOx combustor in which a low NOx combustion is not hampered can be obtained. It is to be noted that although the main fuel nozzle has been described with respect to two types of the N1 type main fuel nozzle 231 and the N2 type main fuel nozzle 232 in the present embodiment, it is not necessarily limited to these two types. Also, the number, arrangement and direction of the fuel injection ports of the respective main fuel nozzles are not limited to those shown in Fig. 1 or 2 but may be decided arbitrarily. That is, the main burner may be made in plural types wherein the main fuel nozzle has different numbers of the fuel injection ports. Also, the number of the main burners is not limited to eight in total as illustrated but two or more types of the main burners may be arranged on a circumference surrounding the pilot burner 207 in the combustor 211 so that a same type may not be adjoined each other and what is important is to avoid the concentrated heat generation. A combustor of another embodiment will be described with reference to Fig. 5. In Fig. 5, a main fuel nozzle 203, a pilot swirler 205, a pilot fuel nozzle 206, a pilot burner 207 and an air inflow portion 208 are same as those of the prior art described in Fig. 9. But in a combustor 212 of the present embodiment, in place of the main swirler 204 having a same common shape as shown in Fig. 9, there are provided two types of main burners 223, 224 comprising therein main swirlers 241, 242, respectively, having mutually different shapes. In the above, an S1 type main swirler 241 has its swirler vane 241a fitted inclinedly with an angle of 25° to an axial direction of the S1 type main swirler 241 as shown in Fig. 6(a) and an S2 type main swirler 242 has its swirler vane 242a fitted inclinedly with an angle of 35° to an axial direction of the S2 type main swirler 242 as shown in Fig. 6(b). That is, the main burner 223 of one type comprises the S1 type main swirler 241 shown in Fig. 6(a) and the main burner 224 of the other type comprises the S2 type main swirler 242 shown in Fig. 6(b), and these two types of the main burners 223, 224 are arranged alternately on a circumference surrounding the pilot burner 207 in the combustor 212 as shown in Fig. 5(b). The main fuel nozzle 203 is of a same shape both for the main burners 223, 224. In the present example, the main burner 223 comprises the S1 type main swirler 241 wherein fitting angle of the swirler vane 241a is made smaller, thereby premixing of the fuel is in a comparatively irregular state and the premixture there is so formed that the fuel concentration becomes high in a central portion of outlet of the main burner 223 and low in outer peripheral portions of same, as shown by fuel concentration distribution of Fig. 7(a). on the other hand, the main burner 224 comprises the S2 type main swirler 242 wherein fitting angle of the swirler vane 242a is made larger, thereby premixing of the fuel is in a comparatively good and regular state, as shown by fuel concentration distribution of Fig. 7(b). Fig. 8 is a conceptual view showing distribution of heat generation rate in the combustors corresponding to the types of the main burners comprising-the main swirlers mentioned above, wherein the vertical axis shows heat generation rate and the horizontal axis shows distance from the main burner outlet in the combustor central axis direction. In Fig. 8, broken line a shows heat generation rate of a combustor in which only the main burners 223, each having therein the S1 type main swirler 241, are provided, and broken line b shows heat generation rate of a combustor in which only the main burners 224, each having therein the S2 type main swirler 242, are provided, wherein both of these combustors correspond to the mentioned combustor 201 in the prior art and there occurs the concentrated heat generation in the area of a constant distance in the combustor central axis direction resulting in the problem of vibratory combustion. In the present example, as mentioned above, the main burner 223 comprising the S1 type main swirler 241 and the main burner 224 comprising the S2 type main swirler 241 are provided alternately on a circumference surrounding the pilot burner 207 in the combustor 212, and the premixture is prevented from becoming a regular state all around in the combustor 212. Thereby, as shown by solid line c in Fig. 8, there are formed mixedly an area where the combustion speed is fast in the combustor central axis direction and an area where it is slow in the same direction and the portion where the heat generation rate is high is dispersed. Thus, a vibratory combustion caused by the concentrated heat generation is avoided and a stable combustion is attained, so that a low NOx combustor in which a low NOx combustion is not hampered can be obtained. It is to be noted that although the main swirler has been described with respect to two types of the S1 type main swirler 241 and the S2 type main swirler 242 in the present embodiment, it is not necessarily limited to these two types. Also, the fitting angle, number, arrangement and direction of the swirler vane of the respective main swirlers are not limited to those shown in Fig. 5 or 6 but may be decided arbitrarily. That is, the main swirler may be made in plural types wherein the swirler vane has different fitting angles of the vane to the main swirler central axis direction. Also, the number of the main burners is not limited to eight in total as illustrated but two or more types of the main burners may be arranged on a circumference surrounding the pilot burner 207 in the combustor 212 so that a same type may not be adjoined each other and what is important is to avoid the concentrated heat generation. As a preferred embodiment in accordance with the invention, a combustor may be constructed such that a plurality of various types of the main burner are arranged on a circumference surrounding a pilot burner so that a same type may not be adjoined each other, wherein the main burner is made by combination of such of the plural types of the main fuel nozzle as described in the first embodiment and such of the plural types of the main swirler as described in the above example. According to this embodiment, in addition to the effect of the first embodiment, the heat generation rate distribution in the combustor central axis direction is further dispersed to be averaged, so that a vibratory combustion due to the concentrated heat generation is prevented and a stable combustion is attained and a low NOx combustor in which a low NOx combustion is not hampered can be obtained.

Claims: A combustor comprising: a pilot burner (207) provided on a central axis of the combustor (211); and a plurality of main burners (221,222) provided around said pilot burner (207), each having therein a main fuel nozzle (231,232) disposed on a central axis of each of said main burners (221,222) and a main swirler (204) disposed around said main fuel nozzle (231,232), characterized in that said plurality of main burners (221,222) comprise two or more types having different numbers of fuel injection ports (231a,232a) of said main fuel nozzle (231,232) provided alternately in a circumferential direction of the combustor (211). The combustor according to claim 1, characterized in that a total injection port area of the fuel injection ports (231a,232a) of the two or more types of main burners (221,222) is made equal. The combustor according to claim 1 or 2, characterized in that said plurality of main burners (221,222,223,224) comprise two or more types of main burners (223,224) having different fitting angles of swirler vanes (241a,242a) relative to a central axis direction of said main swirler (241,242) provided in a circumferential direction of the combustor (211) so that same ones of said types are not adjoining each other.

Inventors: AKAMATSU SHINJI, AKITA EIJI, KOBAYASHI KAZUYA, MANDAI SHIGEMI, NISHIDA KOICHI, OTA MASATAKA, SATO YOSHICHIKA, TANIMURA SATOSHI, AKAMATSU, SHINJI, AKITA, EIJI, KOBAYASHI, KAZUYA, MANDAI, SHIGEMI, NISHIDA, KOICHI, OTA, MASATAKA, SATO, YOSHICHIKA, TANIMURA, SATOSHI, Akamatsu, Shinji, c/o Mitsubishi Heavy Ind.,Ltd., Akita, Eiji, c/o Mitsubishi Heavy Ind.,Ltd., Kobayashi, Kazuya, c/o Mitsubishi Heavy Ind.,Ltd., Mandai, Shigemi, c/o Mitsubishi Heavy Ind., Ltd., Nishida, Koichi, c/o Mitsubishi Heavy Ind., Ltd., Ota, Masataka, c/o Mitsubishi Heavy Ind., Ltd., Sato, Yoshichika, c/o Mitsubishi Heavy Ind.,Ltd., Tanimura, Satoshi, c/o Mitsubishi Heavy Ind.,Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: F23D23
IPC codes: F23D23, F23M99