Abstract:
This invention aims to suppress the occurrence of smoke, for example, during a light load operation of a gas turbine, by adopting an air blast method for a pilot nozzle in a dual fuel combustion low NO x  combustor. A gas turbine combustor of the present invention is that in a gas turbine furnished with a dual fuel combustion low NO x  combustor having a pilot nozzle capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively, and a plurality of main nozzles disposed around the pilot nozzle and being capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively, wherein the pilot nozzle has a gas nozzle portion for injecting the gaseous fuel, and a liquid nozzle portion for injecting the liquid fuel, adopts an air blast method for the liquid nozzle portion, uses combustion air as air for an air blast, and throws the combustion air at a liquid film formed in the liquid nozzle portion to atomize the liquid fuel by use of a velocity difference.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a dual fuel combustion low NO x  combustor of a gas turbine. 
   2. Description of the Related Art 
   In recent years, various improvements have been made on a combustor, etc. in a gas turbine to decrease NO x  and raise the temperature of the gas turbine (raise the inlet temperature of the turbine), thereby achieving a high efficiency. 
   As shown in  FIG. 4 , for example, a fuel F, which has been injected through a pilot nozzle  102  provided at the center of a combustor inner tube  101 , and a plurality of main nozzles  103  provided around the pilot nozzle  102 , and compressed air PA, which has been discharged from a compressor  104  and introduced to an upstream side of the combustor inner tube  101 , are mixed in a combustor  100  of a gas turbine. Then, the mixture is combusted in a combustion zone on a downstream side of the combustor inner tube  101  or an upstream side of a combustor transition pipe  105 , and is introduced as a high temperature, high pressure combustion gas CG into the turbine equipped with stationary blades  106  and moving blades  107 . In the turbine, the combustion gas CG is expanded to serve as a driving force, which drives the compressor  104  and outputs a surplus driving force to the outside. 
   The ratio between the compressed air PA and the fuel F introduced into the combustor inner tube  101  (i.e., fuel-air ratio) needs to be controlled to take an optimal value according to the operating state of the gas turbine (namely, the amount of fuel charged). For this purpose, not all of the compressed air PA is introduced into a combustion section of the combustor  100 , but part of the compressed air PA is bypassed and flowed from a turbine casing  108  into the combustor transition pipe  105 . A bypass valve  109  is provided for this purpose, and allows part of the compressed air PA to be flowed and supplied into the combustor transition pipe  105  from an opening portion of a bypass pipe  110  provided in the turbine casing  108 . 
   In such a combustor  100 , the upstream side of the combustor inner tube  101  is allocated as a first stage combustion zone, and the downstream side of the combustor inner tube  101  is allocated as a second stage combustion zone. A relatively small amount of fuel is injected through the pilot nozzle  102  into the first stage combustion zone to generate a high temperature combustion gas. With this combustion gas as a flame (trigger), a large amount of a lean premixed fuel mixture is injected through the main nozzles  103  into the second stage combustion zone, whereby the generation of a locally high temperature combustion gas is prevented, and NO x  is kept to a minimum (see, for example, Japanese Patent Application Laid-Open No. 2000-130756). 
   As the combustor  100  mentioned above, a so-called dual fuel combustion low NO x  combustor is known which has the pilot nozzle  102  capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively, and the plurality of main nozzles  103  disposed around the pilot nozzle  102  and being capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively. 
   The pilot nozzle  102  is taken as an example for illustration, as shown, for example, in  FIG. 5 . The pilot nozzle  102  has a liquid nozzle portion  112  of a pressure spraying type, provided at the center of a nozzle body  111 , for spraying a liquid fuel, and a plurality of gas nozzle portions  113 , concentrically surrounding the liquid nozzle portion  112 , for injecting a gaseous fuel obliquely outwardly. 
   In such a dual fuel combustion low NO x  combustor, the pilot nozzle  102  renders varieties of fuels available, and can use different fuels in combination, thereby actualizing diffusive combustion with excellent stability of combustion, while the main nozzles  103  can use many fuels, thereby making it possible to decrease the amount of a pilot fuel used in diffusive combustion, and achieve pre-mixed combustion involving a minimal NO x  concentration (see, for example, Japanese Patent Application Laid-Open No. 1997-264536). 
   In the above-described dual fuel combustion low NO x  combustor, however, a pressure spraying type nozzle is used as the liquid nozzle portion  112  for injecting a liquid fuel in the pilot nozzle  102 . This has posed the problem that if an operation with a high pilot ratio (a high ratio of the amount of the liquid fuel injected from the pilot nozzle  102  to the amount of the liquid fuel injected from the main nozzles  103 ) is performed to ensure combustion stability, for example, during a light load operation of the gas turbine, smoke (black smoke) occurs, causing pollution. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to suppress the generation of smoke, for example, during a light load operation of the gas turbine, by adopting an air blast method for the pilot nozzle in the dual fuel combustion low NO x  combustor. 
   To attain the above object, the gas turbine combustor of the present invention is a gas turbine combustor in a gas turbine furnished with a dual fuel combustion low NO x  combustor having a pilot nozzle capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively, and a plurality of main nozzles disposed around the pilot nozzle and being capable of injecting a gaseous fuel and a liquid fuel simultaneously or selectively, 
   wherein the pilot nozzle has a gas nozzle portion for injecting the gaseous fuel, and a liquid nozzle portion for injecting the liquid fuel, adopts an air blast method for the liquid nozzle portion, uses combustion air as air for an air blast, and throws the combustion air at a liquid film formed in the liquid nozzle portion to atomize the liquid fuel by use of a velocity difference between the combustion air and the liquid film. 
   The gas turbine combustor is characterized in that the liquid nozzle portion is formed in an annular shape in order to inject the liquid fuel in an annular liquid film state, and further has a first air blast nozzle portion for producing an air blast along an inner surface of a film of the liquid fuel injected in the annular liquid film state, and a second air blast nozzle portion for producing an air blast along an outer surface of the film of the liquid fuel. 
   The gas turbine combustor is also characterized in that an air passage for supplying the combustion air at least to the first air blast nozzle portion is branched into a plurality of sections in a circumferential direction of the pilot nozzle, a gas passage for supplying the gaseous fuel to the gas nozzle portion, and a liquid passage for supplying the liquid fuel to the liquid nozzle portion are each similarly branched into a plurality of sections in the circumferential direction of the pilot nozzle, and the plural sections of the air passage and the plural sections of the gas passage and/or the plural sections of the liquid passage are alternately disposed in the circumferential direction of the pilot nozzle. 
   The gas turbine combustor is also characterized in that the air passage is disposed at an angle with respect to a radial line of the pilot nozzle in order to generate a swirl in the first air blast nozzle portion. 
   The gas turbine combustor is also characterized in that the second air blast nozzle portion is formed in an annular shape for producing the air blast in an annular form. 
   The gas turbine combustor is also characterized in that the second air blast nozzle portion has a swirler disposed in an interior thereof. 
   The gas turbine combustor is also characterized in that the liquid nozzle portion is provided inside a swirler which is disposed inside an air blast nozzle portion formed in an annular shape for producing the air blast in an annular form. 
   The gas turbine combustor is also characterized in that the liquid nozzle portion is oriented such that the liquid fuel is injected along an exterior of the air blast produced in an air blast nozzle portion. 
   The gas turbine combustor is also characterized in that an air passage for supplying the combustion air to the air blast nozzle portion is branched into a plurality of sections in a circumferential direction of the pilot nozzle, a gas passage for supplying the gaseous fuel to the gas nozzle portion is similarly branched into a plurality of sections in the circumferential direction of the pilot nozzle, and the plural sections of the air passage and the plural sections of the gas passage are alternately disposed in the circumferential direction of the pilot nozzle. 
   The gas turbine combustor is also characterized in that the first air blast nozzle portion is provided at a center of the pilot nozzle, and the combustion air within a turbine casing is supplied to the first air blast nozzle portion via external piping through an air passage penetrating a nearly central portion of the pilot nozzle. 
   The gas turbine combustor is also characterized in that the first air blast nozzle portion has a swirler disposed in an interior thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 1 of the present invention. 
       FIG. 2  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 2 of the present invention. 
       FIG. 3  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 3 of the present invention. 
       FIG. 4  is a sectional view of the surroundings of a conventional gas turbine combustor. 
       FIG. 5  is a sectional view of essential parts of a conventional pilot nozzle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The gas turbine combustor according to the present invention will now be described in detail by embodiments with reference to the accompanying drawings. 
   Embodiment 1 
     FIG. 1  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 1 of the present invention. 
   As shown in  FIG. 1 , a pilot nozzle  10  of a dual fuel combustion low NO x  combustor in a gas turbine comprises a rod-shaped nozzle body  11  fitted into a tubular nozzle cover  12 . 
   The nozzle body  11  has a gas nozzle portion  13  for injecting a gaseous fuel such as LNG, and a liquid nozzle portion  14  for injecting a liquid fuel such as a light oil or kerosene. An air blast method is adopted for the liquid nozzle portion  14 , and combustion air (pressurized air) is used as air for an air blast. The combustion air is thrown at a liquid film formed in the liquid nozzle portion  14  so that the liquid fuel is atomized by use of a velocity difference between the combustion air and the liquid film (a shearing force works). 
   A plurality of the gas nozzle portions  13  are provided in an outer peripheral portion of the tip of the nozzle body  11  in such a manner as to pass through the nozzle cover  12 , and are adapted to inject the gaseous fuel obliquely outwardly of the nozzle body  11 . 
   The liquid nozzle portion  14  has a front side formed in a tapered annular shape for injecting the liquid fuel in an annular liquid film state, and further has a first air blast nozzle portion  15   a  for producing an air blast (a stream of violently blown air) along the inner surface of the film of the liquid fuel injected in the annular liquid film state, and a second air blast nozzle portion  15   b  for producing an air blast along the outer surface of the film of the liquid fuel. 
   The first air blast nozzle portion  15   a  is formed as a horizontally elongated cavity at the center of the nozzle body  11 . An air passage  16  for supplying pressurized air to the first air blast nozzle portion  15   a  is branched into a plurality of sections in the circumferential direction of the nozzle body  11 . Similarly, a gas passage  17  for supplying the gaseous fuel to the gas nozzle portions  13 , and a liquid passage  18  for supplying the liquid fuel to the liquid nozzle portion  14  are each branched into a plurality of sections in the circumferential direction of the nozzle body  11 . The plural sections of the air passage  16  and the plural sections of the gas passage  17  and/or the plural sections of the liquid passage  18  are alternately disposed in the circumferential direction of the nozzle body  11 . Moreover, the air passage  16  has an introduction end portion open to the outer periphery of an intermediate portion of the nozzle body  11 , and is disposed at an angle with respect to the radial line of the nozzle body  11  in order to generate a swirl in the first air blast nozzle portion  15   a.    
   The second air blast nozzle portion  15   b  has a front side formed in a tapered annular shape for producing an air blast in a tapered annular form. The numeral  19  in the drawing denotes a nozzle cap fitted over the front end of the nozzle body  11 , and the nozzle cap  19  has an inner surface formed as a taper surface. An air passage (air introduction hole)  20  for supplying pressurized air to the second air blast nozzle portion  15   b  is branched into a plurality of sections in an outer peripheral portion of the nozzle body  11 , and has an introduction-side end portion open to the outer periphery of an intermediate portion of the nozzle body  11 . The second air blast nozzle portion  15   b  has a straight part, inside which a plurality of vane-shaped swirlers  21  are disposed in the circumferential direction. 
   The liquid nozzle portion  14  is divided into a front-stage liquid nozzle portion  14   a  having a first-half part formed in a tapered annular shape, and a rear-stage liquid nozzle portion  14   b  formed in a straight annular shape. The front-stage liquid nozzle portion  14   a  and the rear-stage liquid nozzle portion  14   b  are brought into communication by a plurality of swirl ports  14   c  provided in the circumferential direction of the nozzle body  11 . Inside the front-stage liquid nozzle portion  14   a,  a step  14   d  for generating a swirl is formed in the shape of a rib. 
   Other features of the dual fuel combustion low NO x  combustor are the same as those in  FIG. 4 , and duplicate explanations are omitted by reference to  FIG. 4 . 
   Because of the above configuration, if a gaseous fuel is used as the fuel for the dual fuel combustion low NO x  combustor during the operation of the gas turbine, in the pilot nozzle  10 , the gaseous fuel from a gaseous fuel supply source (not shown) passes through the gas passage  17  branched into plural sections in the circumferential direction of the nozzle body  11 , and is injected obliquely outwardly from the gas nozzle portions  13  provided at the front ends of the plural sections. 
   If a liquid fuel is used simultaneously with, or selectively instead of, the gaseous fuel, the liquid fuel from a liquid fuel supply source (not shown) passes through the liquid passage  18  branched into plural sections in the circumferential direction of the nozzle body  11 , and is supplied to the liquid nozzle portion  14  formed in an annular shape. From there, the liquid fuel is fed and, while being swirled by the swirl port  14   c  and the step  14   d,  is injected in an annular liquid film state from the tapered annular part of the front-stage liquid nozzle portion  14   a.    
   At the same time, pressurized air from a pressurized air supply source (not shown; air discharged from the compressor of the gas turbine) is supplied to the first air blast nozzle portion  15   a  after passing through the air passage  16  branched into plural sections in the circumferential direction of the nozzle body  11 , and is likewise supplied to the second air blast nozzle portion  15   b  past the air passage  20 . The pressurized air supplied to the first air blast nozzle portion  15   a  is injected to the outside while being swirled because of the inclination of the air passage  16 , thereby forming an air blast running along the inner surface of the film of the liquid fuel injected in an annular liquid film state from the liquid nozzle portion  14 . The pressurized air supplied to the second air blast nozzle portion  15   b  is injected to the outside while being swirled by the swirlers  21 , thereby forming an air blast running along the outer surface of the film of the liquid fuel injected in an annular liquid film state from the liquid nozzle portion  14 . 
   As shown above, air blasts are formed along the inner and outer surfaces of the film of the liquid fuel injected in an annular liquid film state from the liquid nozzle portion  14 . Thus, the atomization and evaporation of the liquid fuel are promoted to obtain a satisfactory state of combustion. Thus, even if an operation at a high pilot ratio is performed to ensure combustion stability, for example, during a light load operation of the gas turbine, the occurrence of smoke (black smoke) can be kept down. 
   In the present embodiment, the air passage  16 , which supplies pressurized air to the first air blast nozzle portion  15   a  formed as a horizontally elongated cavity at the center of the nozzle body  11 , is branched into a plurality of sections in the circumferential direction of the nozzle body  11 . Similarly, the gas passage  17  for supplying the gaseous fuel to the gas nozzle portion  13 , and the liquid passage  18  for supplying the liquid fuel to the liquid nozzle portion  14  are each branched into a plurality of sections in the circumferential direction of the nozzle body  11 . The plural sections of the air passage  16  and the plural sections of the gas passage  17  and/or the plural sections of the liquid passage  18  are alternately disposed in the circumferential direction of the nozzle body  11 . Thus, the complicatedness of the passage structure in the nozzle body  11  can be effectively avoided. In other words, the pilot nozzle  10  adopting the air blast method can be produced easily and inexpensively. 
   Embodiment 2 
     FIG. 2  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 2 of the present invention. 
   The present embodiment is an embodiment in which the first air blast nozzle portion  15   a  in Embodiment 1 is abolished; only an annular air blast nozzle portion  15 A corresponding to the second air blast nozzle portion  15   b  in Embodiment 1 is provided; and the front end of a liquid nozzle portion  14 A formed in the shape of a port and communicating with the annular front-stage liquid nozzle portion  14   a  is open to each of vane-shaped swirlers  21  provided in the air blast nozzle portion  15 A. Since other features are the same as those in Embodiment 1, the same members as those shown in  FIG. 1  are assigned the same numerals as in  FIG. 1 , and duplicate explanations are omitted. 
   According to the present embodiment, the liquid fuel injected from the liquid nozzle portions  14 A forms a liquid film spreading along the outer circumferential wall surface of the air blast nozzle portion  15 A, and an air blast by the air blast nozzle portion  15 A is produced inside this liquid film, thereby promoting the atomization of the liquid fuel. 
   Thus, the same actions and effects as those in Embodiment 1 are obtained. Furthermore, the first air blast nozzle portion  15   a  in Embodiment 1 is abolished. This brings the advantage that the passage and nozzle structures in the nozzle body  11  can be simplified as compared with Embodiment 1. 
   Embodiment 3 
     FIG. 3  is a sectional view of essential parts of a pilot nozzle, showing Embodiment 3 of the present invention. 
   The present embodiment is an embodiment in which the air passage  16  for supplying pressurized air to the first air blast nozzle portion  15   a  in Embodiment 1 is formed as a single air passage  16 A penetrating the center of the nozzle body  11 , and external piping is connected to the air passage  16 A so that pressurized air within the turbine casing is supplied to the first air blast nozzle portion  15   a  (see a pressurized air outlet  30  formed in the turbine casing  180  of  FIG. 4  and having external piping connected thereto). Also, a swirler  28  is mounted inside the first air blast nozzle portion  15 . Since other features are the same as those in Embodiment 1, the same members as those shown in  FIG. 1  are assigned the same numerals as in  FIG. 1 , and duplicate explanations are omitted. 
   According to the present embodiment, the liquid fuel injected from the liquid nozzle portion  14  is atomized to a higher degree by air blasts generated in a sandwich form. Thus, the same actions and effects as those in Embodiment 1 are obtained. Furthermore, the single air passage  16 A offers the advantage that the passage structure in the nozzle body  11  can be simplified as compared with Embodiment 1. 
   It goes without saying that the present invention is not limited to the foregoing embodiments, but various changes and modifications, such as a change in the structure of the swirler and a change in the shape of the nozzle portion, can be made without deviating from the subject matter of the present invention.