Patent Publication Number: US-6209326-B1

Title: Gas turbine combustor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gas turbine combustor. 
     2. Related Art 
     Gas turbine combustors of the prior art will be described with reference to FIGS. 5 and 6. 
     In a gas turbine combustor of the prior art, as shown in FIGS. 5 and 6, there is arranged at the center of the section of the combustor a pilot fuel nozzle  104  for producing a flame portion. Around this pilot fuel nozzle  104 , there is a cylindrical outer cylinder  106 , on which there are arranged a plurality of main fuel nozzles  102  for producing a premixed gas of a fuel and air. 
     The pilot fuel nozzle  104  is provided with a pilot swirler  103 . Each of the main fuel nozzles  102  is provided with main swirlers  101  which are arranged around the main fuel nozzle  102  and extend to the outer cylinder  106 . A plurality of nozzle ports  105  are opened in the nozzle body wall face of the main fuel nozzle  102  downstream of the main swirlers  101 . 
     In the construction described above, the air and the fuel flow in the directions, as indicated by arrows in FIGS. 5 and 6, so that the air and the fuel are fed from a plurality of main swirlers  101  and one pilot swirler  103 , and from a plurality of main fuel nozzles  102  and one pilot fuel nozzle  104 , respectively, to the combustion zone. 
     The fuel thus fed from the main fuel nozzle  102  is injected from the nozzle ports  105  in the nozzle body wall face so that it is mixed with the air flowing through the main swirlers  101  around the nozzle outer circumference to prepare a premixed gas. 
     In the combustor of the prior art, the main fuel nozzle  102 , the main swirlers  101  and the outer cylinder  106  construct a main fuel nozzle device. 
     The main fuel nozzle device of the gas turbine combustor of the prior is of the type in which the fuel is injected from the nozzle ports formed in the wall face of the nozzle body, as described hereinbefore. 
     This system has a problem in that the premixture to be prepared in the vicinity of the exits of the main swirlers has a tendency to become a gas having a higher fuel concentration at its center portion. Another problem is that the pressure for feeding the fuel has to be set at a high level for establishing a fuel penetration necessary for mixing the fuel, injected from the main fuel nozzles, efficiently with the air flow. 
     Another example of the gas turbine combustor of the prior art is shown in FIG.  7 . 
     In a gas turbine combustor  201  of the prior art, as shown in FIG. 7, there is formed a combustion chamber  212  which is enclosed and defined by both an axially symmetrical cylindrical upstream inner cylinder  206  and a downstream inner cylinder  207  connected at its leading end portion to the rear end portion of the upstream inner cylinder  206 . 
     The downstream inner cylinder  207  forming the combustion chamber  212  together with the upstream inner cylinder  206  is composed of a plurality of cylinders, with these cylinders increasing in diameters from the inner cylinder  206  to a downstream-most cylinder. A clearance is formed at the joint between adjacent inner cylinders  207  so that compressed air flowing outside of the upstream inner cylinder  206  and the downstream inner cylinder  207  may flow as cooling air  217  through this clearance into the downstream inner cylinder  207 , and then may flow further along the inner circumference of the downstream inner cylinder  207  to cool the downstream inner cylinder  207  from its inside to then protect it from the combustion gas which is at a high temperature and under a high pressure. Air as indicated by arrows  204  and  210  flows respectively through swirlers  203  and  209 . 
     In the gas turbine combustor  201  of the prior art, as has been described hereinbefore, a pilot nozzle  202  and a main nozzle  208  are arranged in the upstream inner cylinder  206  on the upstream side of the combustion chamber  212 . A pilot fuel  213  and a main fuel  215 , i.e. the fuels necessary for the operation of the gas turbine, are fed to the upstream side of the combustion chamber  212 . As a result, the ratio of the unburned fuel to the fed fuel has a high value on the upstream side but gradually lowers toward the downstream side, as plotted in the distribution of the unburned fuel in the axial direction of the combustor in FIG.  8 . 
     Specifically, the ratio of the fuel being burned in a section in the combustion chamber  212 , i.e., the so-called “sectional load factor” is high on the upstream side, but a certain unburned fuel ratio is maintained even within a range on the downstream side so that the sectional load factor is shared. As a result, the combustion in the combustion chamber  212  can maintain a stable combustion and a low NOx emission. 
     Gas turbines have been demanded in recent years to have a high temperature and a high pressure of the combustion gas for a larger size and a higher efficiency. However, the reaction rate of the fuel, as fed to the combustion chamber  212 , is increased by the high temperature and pressure of the combustion gas. If 100% of the fuels  213  and  215  required for running the gas turbine are fed on the upstream side, therefore, they are instantly burned on the upstream side, and the unburned gas has a small distribution on the downstream side. As a result, the sectional load factor rises on the upstream side and causes problems of an unstable combustion state and an increase in the NOx emission. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a gas turbine combustor which is enabled to prepare a homogeneous premixture, to thereby suppress an NOx emission by mixing a main fuel and air homogeneously without requiring a high fuel feeding pressure. 
     Another object of the invention is to provide a gas turbine combustor which can eliminate the disadvantage of the instability in the combustion state or the increase in the NOx emission caused when 100% of fuel is fed to the upstream side of the combustion chamber, as in the gas turbine of the prior art. When this gas turbine is demanded to have high temperature and pressure of the combustion gas for a large size and a high efficiency. 
     In order to solve the above-specified problems, according to the invention, there is provided a gas turbine combustor comprising: a cylindrical outer cylinder into which air is fed; main swirlers disposed in the outer cylinder; and an annular fuel feed manifold disposed on the outer circumference of the outer cylinder on the upstream or downstream side of the main swirlers, and having a plurality of nozzle ports communicating with the inside of the outer cylinder. 
     In the invention, the fuel is injected from the outer circumference to the center of the air flowing in the outer cylinder so that a more homogeneous premixture than that of the device of the prior art can be prepared to suppress the NOx emission. 
     On the other hand, it is possible to lower the high fuel feed pressure which has been demanded in the device of the prior art for the fuel to reach the outer circumference of the air flow. 
     In order to solve the aforementioned problem in the gas turbine combustor having the combustion chamber formed by the upstream inner cylinder and the downstream inner cylinder, according to the invention, the main fuel is divided to be fed in the direction of the flow of the burning air in the combustion chamber which is formed by the upstream inner cylinder and the downstream inner cylinder. 
     As a result, even in the gas turbine in which the high temperature and pressure of the combustion gas are demanded for the larger size and the higher efficiency so that the reaction rate of the fuel fed to the inside of the combustion chamber is raised by the high temperature and pressure of the combustion gas, the unburned fuel ratio of the fuel fed to the inside of the combustion chamber can obtain a distribution in which the ratio gently fluctuates in the flow direction of the burning air flowing in the combustion chamber. 
     That is to say, the sectional load factor can be prevented from locally rising especially on the upstream side, to thereby stabilize the combustion state in the combustion chamber and to reduce the NOx emission accompanying the combustion. 
     The main nozzles for dividing the feeding the main fuel to the inside of the combustion chamber are extended at the individual feed positions through the upstream inner cylinder and the downstream inner cylinder. 
     As a result, in addition to the above-specified operations and effects, the distribution of the unburned fuel in the axial direction of the combustion chamber can be individually controlled by controlling the fuels to be injected from the individual main nozzles, to make the combustion state stabler and to reduce the NOx emission effectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In FIGS.  1 ( a )- 1 ( c ) explaining a main fuel nozzle device of a gas turbine combustor according to a first embodiment of the invention, FIG.  1 ( a ) is a side sectional view, ( b ) a sectional view taken in the direction of arrows A—A of FIG.  1 ( a ), and FIG.  1 ( c ) a sectional side elevational view of the gas turbine combustor; 
     FIG. 2 is an explanatory diagram of a modified example of the first embodiment of the invention; 
     FIG. 3 is a partial sectional view showing a gas turbine combustion according to a second embodiment of the invention; 
     FIG. 4 is a diagram illustrating an unburned fuel ratio of a main fuel, as taken in the axial direction of the combustion chamber shown in FIG. 3; 
     FIG. 5 is a sectional side elevational view of a gas turbine combustor of the prior art; 
     In FIGS.  6 ( a ) and  6 ( b ) explaining a main fuel nozzle device in a gas turbine combustor of the prior art, FIG.  6 ( a ) is a sectional side elevational view, and FIG.  6 ( b ) is a sectional view taken in the direction of arrows B—B of FIG.  6 ( a ); 
     FIG. 7 is a longitudinal sectional view showing a portion of another gas turbine combustor of the prior art; and 
     FIG. 8 is a diagram plotting the ratio of an unburned fuel of a main fuel, as taken in the axial direction of the combustion chamber shown in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A gas turbine combustor according to the embodiments of the invention will be described with reference to the accompanying drawings. 
     [First Embodiment] 
     All first embodiment will be described with reference to FIG.  1 . 
     A gas turbine combustor is constructed to include: a cylindrical outer cylinder  106 ; a swirler supporting member  109  of a hollow rod shape disposed in the central axis portion of the outer cylinder  106 ; main swirlers  101  formed between the supporting member  109  and the outer cylinder  106 ; and an annular fuel feed manifold  110  disposed on the downstream side of the main swirlers  101  and on the outer circumference of the outer cylinder  106 , and having a plurality of nozzle ports  111  communicating with the inside of the outer cylinder  106 . 
     The feed of the fuel to the fuel feed manifold  110  is effected, as shown in FIG.  1 ( c ), by forming a bypass passage  112  at the swirler supporting member  109 , used as the main fuel nozzle in the device of the prior art, and by connecting the fuel feed manifold  110  to the bypass passage  112 . 
     With this construction, the fuel is injected from the plurality of nozzle ports  111 , as formed in the fuel feed manifold  110 , into the outer cylinder  106  and is mixed With the air, as fed from the main swirlers  101 , to prepare a premixture. 
     In this embodiment, the fuel, as fed from the nozzle ports  111 , is injected from the outer circumference to the center of the flow of the air fed from the main swirlers  101 , so that the fuel concentration can be homogenized to prepare a homogeneous premixture and thereby suppress the NOx emission to a low level. 
     In the case of the device of the prior art, on the other hand, a high fuel feed pressure is required for enabling the fuel reach to the outer circumference of the air flow. 
     In this embodiment, the fuel feed manifold  110  is arranged on the downstream side of the main swirlers  101  but may be arranged on the upstream side of the main swirlers  101 , as shown in FIG.  2 . In this modification, a better premixture can be prepared, although a dangerous flashback may occur so that countermeasures for preventing this danger have to be undertaken. 
     As has been described hereinbefore in connection with the first embodiment, the gas turbine combustor of the invention is constructed to include: an outer cylinder having the main swirlers therein and adapted to be fed with the air; and an annular fuel feed manifold disposed on the upstream or downstream of the main swirlers and at the outer circumference of the outer cylinder, and having a plurality of nozzle ports communicating with the inside of the outer cylinder. The fuel is injected from the outer circumference to the center of the air flow in the outer cylinder so that the homogeneous premixture can be prepared to suppress the NOx emission and to lower the fuel feed pressure. 
     [Second Embodiment] 
     A gas turbine combustor according to a second embodiment will be described with reference to FIG.  3 . 
     In FIG. 3, the members identical or similar to those of the gas turbine combustor of the prior art shown in FIG. 7 will be designated by the common reference numerals, and their description will be omitted. 
     In a gas turbine combustor  220  of this embodiment, as shown in FIG. 3, a combustion chamber  212  is enclosed and defined by an upstream axially symmetrical inner cylinder  206 , and a downstream inner cylinder  207  connected at its leading end portion to the rear end portion of the upstream inner cylinder  206 . A pilot nozzle  202  is mounted at the center portion on the upstream wall portion of the combustion chamber  212 . At the same time, the pilot nozzle  202  is equipped at a circumferentially equal pitch on its outer circumference with pilot swirlers  203 , which are fixed at their roots on the outer circumference of the pilot nozzle  202  for establishing a swirling flow in the burning air  221  to be fed to the front of the pilot nozzle  202 . 
     On the inner cylinders  206  and  207  on the downstream side of the pilot swirlers  203 , there are arranged a plurality of main nozzles  222  or main nozzles  222   a  to  222   f,  which are extended through the upstream inner cylinder  206  and the downstream inner cylinder  207  in a spaced axial relationship through which the burning air  221  is to flow. 
     In the gas turbine combustor  220  of this embodiment, a pilot fuel  213  is fed from the pilot nozzle  202 , and the burning air  221  is fed, while being swirled by the pilot swirlers  203 , to the combustion chamber  212 . 
     In front of the pilot nozzle  202 , therefore, a flame holding recirculation zone  214  is established on the upstream side of the combustion chamber  212  to hold the flame as in the gas turbine combustor  201  of the prior art. 
     At a light load time of the gas turbine, moreover, the combustion gas to be produced in the combustion chamber  212  has a low temperature so that a main fuel  215  to be fed from the main nozzles  222  to the inside of the combustion chamber  212  has a low reaction rate. As a result, the main fuel  215  is fed exclusively from the pilot nozzle  202  and the main nozzle  222   a  formed through the upstream inner cylinder  206 , so that it may be fed entirely on the upstream side of the combustion chamber  212 . 
     At a heavy load time of the gas turbine, on the other hand, the main fuel  215  is additionally fed from the main nozzles  222   b  to  222   f  formed through the downstream inner cylinder  207 , so that the main fuel  215  may also be fed to the downstream side of the combustion chamber  212  so as to disperse in the axial direction of the combustion chamber  212 . 
     At the light load time of the gas turbine, more specifically, the unburned ratio of the main fuel  215  in the axial direction in the combustion chamber  212  is plotted by the solid line in FIG. 4 by feeding 100% of the main fuel  215  to the upstream side of the combustion chamber  212 . At the high load time of the gas turbine, the unburned ratio of the main fuel  215  in the axial direction of the combustion chamber  212  is plotted by dotted lines in FIG. 4 by feeding the main fuel  215 , as demanded for running the gas turbine, in a manner to distribute it from the upstream side to the downstream side of the combustion chamber  212 . 
     Thus in the gas turbine combustor  220  of this embodiment, at the light load time of the gas turbine when the combustion gas has a low temperature and a low pressure, the reaction rate of the main fuel  215  is so low that the safe combustion state is realized by feeding the main fuel  215  wholly from the upstream side of the combustion chamber  212  to hold the flame with in the recirculation zone  214 . 
     In short, the operations are basically identical to those of the combustor  201  of the prior art. 
     At the heavy load time of the gas turbine when the combustion gas has a high temperature and a high pressure, on the contrary, the reaction rate of the main fuel  215  is raised so that the sectional load factor on the upstream side of the combustion chamber  212  increases to make the combustion state unstable if 100% of the main fuel  215  is fed from the upstream side of the combustion chamber  212 . 
     This increase in the sectional load factor forms a hot gas zone locally in the combustion chamber  212  to increase the NOx emission. 
     At the heavy load time, therefore, the main fuel  215  is divided and also fed to the downstream side of the combustion chamber  212  so that the sectional load factor on the upstream side of the combustion chamber  212  can be lowered and distributed to the downstream side of the combustion chamber  212  to realize the stable combustion state and to eliminate the load hot gas zone in the combustion chamber  212 , and to thereby suppress the NOx emission. 
     When the combustion gas takes such high temperature and pressure conditions for the gas turbine load satisfying the spontaneous ignition conditions of the main fuel  215 , moreover, the stable burning state can be realized without any feed of the pilot fuel  213  to the recirculation zone  214 , by extremely reducing or interrupting the feed of the pilot fuel  213  from the pilot nozzle  202 . At the same time, the NOx emission can be suppressed by decreasing the local hot gas zone which will be established according to the combustion of the pilot fuel  213 . 
     On the other hand, the air passage for feeding the combustion chamber  212  with the air necessary for the combustion is composed, in the prior art, of two lines: a pilot air passage  205  and a plurality of main air passages  211 . However, air flow can be sufficient by providing only one burning air passage  223 , so that it becomes unnecessary to provide main swirlers  209  which have been assigned to each of the main air passages  211 . 
     The cooling air  217 , although not described in this embodiment, for protecting the downstream inner cylinder  207  from the gas of high temperature and pressure is introduced, as in the construction shown in FIG. 7, into the combustion chamber  212  and is guided along the inner circumference of the downstream inner cylinder  207  to cool the inner cylinder  207 . 
     In the gas turbine combustor according to the second embodiment of the invention thus far described, the main fuel, which is ignited for the main combustion with the flame held by the pilot nozzle arranged on the axis of the axially symmetrical cylindrical upstream inner cylinder, is divided and fed in the flow direction of the burning air in the combustion chamber, through which the burning air is swirled and fed by the swirler arranged at the outer circumference of the pilot nozzle. 
     As a result, even if the reaction rate of the main fuel fed to the inside of the combustion chamber is increased as in recent years by the combustion gas of high temperature and pressure at the high load time of the gas turbine, the unburned fuel ratio of the main fuel fed to the inside of the combustion chamber can obtain a distribution in which the ratio gently fluctuates in the flow direction of the burning air flowing in the combustion chamber. As a result, the sectional load factor can be prevented from locally increasing on the upstream side, to thereby stabilize the combustion state and to reduce the NOx emission. 
     When the combustion gas takes a high temperature and a high pressure so that the gas turbine load satisfies the spontaneous ignition conditions for the main fuel, moreover, the stable combustion state can be realized, and the local hot gas zone can be reduced to suppress the NOx emission without extremely reducing the pilot fuel to be fed by the pilot nozzle or by interrupting the feed of the pilot fuel to the recirculation zone. 
     In the gas turbine combustor of the invention, the main nozzles for feeding the main fuel to the inside of the combustion chamber are extended through the upstream inner cylinder and the downstream inner cylinder forming the combustion chamber at their feed positions which are divided in the flow direction of the burning air. 
     As a result, the distribution of the unburned fuel in the axial direction of the combustion chamber can be freely controlled by controlling the fuels to be injected from the individual main nozzles, to thereby make the combustion state stabler and to reduce the NOx emission more effectively.