Mixer

Abstract

A mixer having a housing, a duct within the housing, a first and a second injector arranged to inject a fluid at a centre zone of the duct, a third and a fourth injector arranged to inject the fluid at a wall zone of the duct. The first/third injectors are at a distance D1=v/2f.sub.1 or odd integer multiples of it from the second/fourth injectors in the absence of an acoustic node between them, or at a distance D1=λ.sub.conv=v/f.sub.1 or full wave length integer multiples of it in the presence of an acoustic node between them. Advantageously f.sub.1 is greater than f.sub.2.

Claims

1. A method of dampening oscillating frequencies in a gas turbine mixer, the gas turbine mixer comprising a housing, a duct within the housing, a first injector and a second injector, each arranged to inject a fluid at a center zone of the duct, a third injector and a fourth injector, each arranged to inject the fluid at a wall zone of the duct, the method comprising: either: (a) injecting the fluid through the first injector at a distance D1=v/2f.sub.1, or odd integer multiples of D1, from the second injector in the absence of an acoustic node between the second injector and the first injector, or (b) injecting the fluid through the first injector at a distance D1=v/f.sub.1, or full wave length integer multiples of D1, in the presence of an acoustic node between the second injector and the first injector, and either: (c) injecting the fluid through the third injector at a distance D2=v/2f.sub.2, or odd integer multiples of D2 from the fourth injector in the absence of an acoustic node between the third injector and the fourth injector, or (d) injecting the fluid through the third injector at a distance D2=v/f.sub.2 from the fourth injector in the presence of an acoustic node between the third injector and the fourth injector, wherein f.sub.1 is an oscillating frequency to be damped at the wall zone of the duct, f.sub.2 is an oscillating frequency to be damped at the center zone of the duct, v is a fluid flow speed through the duct, and f.sub.1 is greater than f.sub.2.

2. The method of claim 1, wherein both f.sub.1 and f.sub.2 are lower than 150 Hz.

3. The method of claim 1, wherein the first injector and/or the second injector and/or the third injector and/or the fourth injector comprise a plurality of rows of nozzles close to one another.

4. The method of claim 3, wherein nozzles of different rows of nozzles of the first injector, the second injector, the third injector, or the fourth injector have different penetration.

5. The method of claim 3, wherein nozzles of a same row of nozzles have different penetration.

6. A method of operating a gas turbine, wherein the gas turbine comprises a compressor, a first combustion chamber, a second combustion chamber fed with combustion gases coming from the first combustion chamber, a turbine and a mixer between the first combustion chamber and the second combustion chamber, wherein the mixer comprises a housing, a duct within the housing, a first injector and a second injector, each arranged to inject a fluid at a center zone of the duct, a third injector and a fourth injector, each arranged to inject the fluid at a wall zone of the duct, the method comprising: either: (a) injecting the fluid through the first injector at a distance D1=v/2f.sub.1, or odd integer multiples of D1 from the second injector in the absence of an acoustic node between the second injector and the first injector, or (b) injecting the fluid through the first injector at a distance D1=v/f.sub.1, or full wave length integer multiples of D1 in the presence of an acoustic node between the second injector and the first injector, and either: (c) injecting the fluid through the third injector at a distance D2=v/2f.sub.2, or odd integer multiples of D2, from the fourth injector in the absence of an acoustic node between the third injector and the fourth injector, or (d) injecting the fluid through the third injector at a distance D2=v/f.sub.2 from the fourth injector in the presence of an acoustic node between the third injector and the fourth injector, wherein f.sub.1 is an oscillating frequency to be damped at the wall zone of the duct, f.sub.2 is an oscillating frequency to be damped at the center zone of the duct, v is a fluid flow speed through the duct, and f.sub.1 is greater than f.sub.2.

7. The method of claim 6, wherein both f.sub.1 and f.sub.2 are lower than 150 Hz.

8. The method of claim 6, wherein at least one of the first injector, the second injector, the third injector or the fourth injector comprises a plurality of rows of nozzles close to one another.

9. The method of claim 8, wherein nozzles of different rows of nozzles of the first injector, the second injector, the third injector, or the fourth injector have different penetration.

10. The method of claim 8, wherein nozzles of a same row of nozzles have different penetration.

11. A method of operating a gas turbine, comprising: combusting a fuel in a first combustion chamber, thereby producing a hot gas; flowing the hot gas through a mixer; and either: (a) injecting a fluid in the mixer at a first injection location at a distance D1=v/2f.sub.1, or odd integer multiples of D1, from a second injection location if there are no acoustic nodes between the second injection location and the first injection location, or (b) injecting the fluid at the first injection location at a distance D1=v/f.sub.1, or full wave length integer multiples of D1, if there is at least one acoustic node between the second injection location and the first injection location, and either: (c) injecting the fluid at a third injection location at a distance D2=v/2f.sub.2 or odd integer multiples of D2, from a fourth injection location if there are no acoustic nodes between the third injection location and the fourth injection location, or (d) injecting the fluid at the third injection location at a distance D2=v/f.sub.2 from the fourth injection location if there is at least one acoustic node between the third injection location and the fourth injection location, wherein f.sub.1 is an oscillating frequency to be damped at a wall zone of a duct of the mixer, f.sub.2 is an oscillating frequency to be damped at a center zone of the duct, v is a fluid flow speed through the duct, and f.sub.1 is greater than f.sub.2.

12. The method of claim 11, wherein injecting the fluid in the mixer at the first injection location includes injecting the fluid at the center zone of the duct.

13. The method of claim 11, wherein injecting the fluid at the third injection location includes injecting the fluid at the wall zone of the duct.

14. The method of claim 11, comprising directing a mixture of the hot gas and the injected fluid to a second combustion chamber of the gas turbine.

15. The method of claim 11, wherein both f.sub.1 and f.sub.2 are lower than 150 Hz.

16. The method of claim 11, wherein the mixer comprises at least a first injector, a second injector, a third injector and a fourth injector and wherein at least one of the first injector, the second injector, the third injector or the fourth injector comprises a plurality of rows of nozzles close to one another.

17. The method of claim 16, wherein nozzles of different rows of nozzles of the first injector, the second injector, the third injector, or the fourth injector have different penetration.

18. The method of claim 16, wherein nozzles of a same row of nozzles have different penetration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics and advantages will be more apparent from the description of a preferred but non-exclusive embodiment of the mixer, illustrated by way of non-limiting example in the accompanying drawings, in which:

(2) FIG. 1 schematically shows a gas turbine;

(3) FIG. 2 schematically shows the first combustion chamber, mixer and second combustion chamber of the gas turbine of FIG. 1;

(4) FIG. 3 shows a longitudinal section of a mixer;

(5) FIG. 4 shows a different embodiment of the gas turbine;

(6) FIGS. 5 and 6 show the distance between the first, second, third, fourth injectors, in relation with the pressure within the mixer itself; in those figures the reference 0 identifies the nominal pressure within the mixer;

(7) FIG. 7 shows an example of injectors comprising more rows of nozzles, and

(8) FIG. 8 shows a different embodiment of the mixer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) With reference to the figures, these show the gas turbine 1 with the compressor 2, the first combustion chamber 3, the second combustion chamber 4 fed with a fluid coming from the first combustion chamber 3, the turbine 5. Between the first combustion chamber 3 and the second combustion chamber 4 it is provided the mixer 7. In addition, between the first combustion chamber 3 and the second combustion chamber 4 (upstream or downstream of the mixer 7), a high pressure turbine can be provided (FIG. 4, turbine 9).

(10) The mixer 7 comprises a housing 10, a duct 11 within the housing 10, a first injector 12 arranged to inject a fluid at the centre zone of the duct 11, a second injector 13 arranged to inject a fluid at the centre zone of the duct 11, a third injector 14 arranged to inject a fluid at the wall zone of the duct 11 and a fourth injector 15 arranged for injecting a fluid at the wall zone of the duct 11. Additional injectors can also be provided.

(11) Each injector can comprise a row of nozzles 16 extending over the circumference or perimeter of the duct 11; in addition each injector can comprise a plurality of rows of nozzles close to one another. Additionally, nozzles 16 of different rows of nozzles of a same injector can have same or different penetration and/or nozzles 16 of a same row of nozzles can have different penetration.

(12) For example, FIG. 3 shows an embodiment with injectors arranged for injecting the fluid at the centre zone and at the wall zone of the duct 11 that are provided close to one another.

(13) In order to inject the fluid at the centre zone 18 of the duct 11 the first and second nozzles 12, 13 have a deep penetration into the duct 11; likewise in order to inject the fluid at the wall zone 17 of the duct 11 the third and fourth nozzles have a small penetration into the duct 11; generally the first and second injectors 12, 13 have a deeper penetration into the duct 11 than the third and fourth injectors 14, 15.

(14) The relative position of the injectors can be any, i.e. any injector can be upstream and/or downstream of any other injector (upstream and downstream are referred to the fluid circulation direction identified by the arrow F in the figures).

(15) The distance between the first injector 12 and the second injector 13 is, in case there is no acoustic node between them (i.e. in the absence of an acoustic node)
D1=λ.sub.conv/2=v/2f.sub.1

(16) or an odd integer multiple of it. In case there is an acoustic node between the first and second injectors 12, 13 (i.e. in the presence of an acoustic node) the distance D1 is
D1=λ.sub.conv=v/f.sub.1

(17) or a full wave length integer multiple of it.

(18) Likewise, the distance between the third injector 14 and the fourth injector 15 is, in case there is no acoustic node between them (i.e. in the absence of an acoustic node)
D2=λ.sub.conv/2=v/2f.sub.2

(19) or an odd integer multiple of it. In case there is an acoustic node between the third injector 14 and the fourth injector 15 (i.e. in the presence of an acoustic node) the distance D2 is
D2=λ.sub.conv=v/f.sub.2

(20) or a full wave length integer multiple of it.

(21) In the above formulas:

(22) f.sub.1 is the oscillating frequency (pressure oscillation) to be damped at the wall zone 17 of the duct 11, i.e. at zones within the duct 11 that are close to the wall, e.g. at the outer part of the flame,

(23) f.sub.2 is the oscillating frequency (pressure oscillations) to be damped at a centre zone 18 of the duct 11, e.g. at the inner or centre part of the flame,

(24) λ.sub.conv is the convective wave length, i.e. the flow velocity v through the duct divided by the frequency that should be addressed with the concept,

(25) v is the fluid flow speed through the duct 11.

(26) Acoustic node defines the change of sign of the pressure with reference to the nominal pressure.

(27) In addition, the distances D1 and D2 are measured between the axes of the nozzles 16 of the injectors 12, 13, 14, 15 or, in case an injector comprises more rows of nozzles 16 (all injecting into the same zone being the centre or the wall zone), with reference to an average position between the two or more axes of the nozzles 16 of this injector (see e.g. FIG. 7).

(28) As an example, FIG. 5 shows one wall of the duct 11 and the pressure in relation to an axial coordinate thereof. From this figure it can be acknowledged that the distance of the first injector 12 from the second injector 13 is D1=λ.sub.conv/2=v/2f.sub.1 and likewise the distance of the third injector 14 from the fourth injector 15 is D2=λ.sub.conv/2=v/2f.sub.2 because in this example between the first and second injectors 12, 13 and third and fourth injectors 14, 15 no acoustic nodes are present.

(29) FIG. 6 is similar to FIG. 5; from this figure it can be acknowledged that the distance of the first injector 12 from the second injector 13 is D1=λ.sub.conv/2=v/2f.sub.1 because there is no acoustic node between them and the distance of the third injector 14 from the fourth injector 15 is D2=λ.sub.conv=v/f.sub.2 because an acoustic node is provided between them (the acoustic node being identified by reference 22).

(30) Advantageously, f.sub.1 is greater than f.sub.2. Both f.sub.1 and f.sub.2 are low frequencies e.g. below 150 Hz.

(31) The operation of the mixer and gas turbine having such a mixer is apparent from that described and illustrated and is substantially the following.

(32) Air is compressed at the compressor 2 and is supplied into the burner 3a where fuel is supplied and mixed with the compressed air, generating a mixture that combusts in the combustor 3b with a flame 20a; the hot gas generated through this combustion passes through the transition piece 3c and enters the mixer 4 (in particular the duct 11 of the mixer 4).

(33) At the mixer 4 air is injected into the hot gas via the first, second, third, fourth injectors 12, 13, 14, 15 and via possible additional injectors.

(34) This configuration allows a selective cancellation of the mass flow oscillations, because different zones of the cross section of the duct 11 are responsible for generating pulsations of different frequency. In particular, as indicated above, the zones closer to the duct wall have a higher frequency while the zones farther from the duct walls (i.e. at the centre of the duct) have a lower frequency.

(35) FIG. 8 shows an example of a mixer having a plurality of injectors (more than four).

(36) Naturally the features described may be independently provided from one another. For example, the features of each of the attached claims can be applied independently of the features of the other claims.

(37) In practice the materials used and the dimensions as well as the injector shapes can be chosen at will according to requirements and to the state of the art.

REFERENCE NUMBERS

(38) 1 gas turbine 2 compressor 3 first combustion chamber 3a first burner 3b combustor 3c transition piece 4 second combustion chamber 4a second burner 4b combustor 5 turbine 7 mixer 8 lance 9 turbine 10 housing 11 duct 12 first injector 13 second injector 14 third injector 15 fourth injector 16 nozzles 17 wall zone 18 centre zone 20a, 20b flame 22 acoustic node D1 distance D2 distance F flow λ.sub.conv convective wave length v fluid flow speed through the duct