EP2728258A1

EP2728258A1 - Gas Turbine

Info

Publication number: EP2728258A1
Application number: EP12191049.1A
Authority: EP
Inventors: Andrea Ciani; Adnan Eroglu
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2012-11-02
Filing date: 2012-11-02
Publication date: 2014-05-07

Abstract

A gas turbine (30) comprises a compressor, a first combustor downstream of said compressor, a first turbine, a second combustor (15, 15a) downstream of said first turbine, and a second turbine (16) downstream of said second combustor (15, 15a), whereby said second combustor (15, 15a) comprises a plurality of burners (15) having a mixing section (32), which opens downstream into a wider combustion chamber (24).

The emissions of the gas turbine are improved by providing a continuous transition between the mixing section (32) and the combustion chamber (24).

Description

BACKGROUND OF THE INVENTION

The present invention relates to the technology of gas turbines. It refers to a gas turbine according to the preamble of claim 1.

PRIOR ART

Fig. 1 shows in a perspective view a stationary gas turbine of the applicant of the well-known type GT26.
The gas turbine 10 of Fig. 1 comprises a rotor 11 surrounded by a casing, a compressor 13, which compresses air entering the gas turbine 10 through an air intake 12, a ring of first burners 14 with a first fuel supply 14a, a first (high pressure) turbine 16, a ring of second burners 15 with a second fuel supply 15a, a second (low pressure) turbine 16', and an exhaust gas outlet 17 for releasing the exhaust gas either into a stack or a heat recovery steam generator of an associated water/steam cycle in case of a combined cycle power plant CCPP.
A gas turbine of the type shown in Fig. 1 is called to have a sequential combustion, due to the sequential arrangement of a first and a second combustion chamber with first and second burners.
A typical design of the second burner/combustion chamber (second combustor) arrangement, which is known in the art (see for example document EP 2 169 314 A2 or EP 2 423 599 A2 ) is illustrated in Fig.2.
The second (SEV) combustor of Fig. 2 comprises a second burner/injector 15 axially connected to a combustion chamber 18. In particular, the hot gas flow entering the burner section (from the left side in Fig. 2; see arrow) is fed with fuel by means of fuel supply 15a via the injector (e.g. a lance) through injection holes 15b, flows along a mixing section 32, and leaves the burner section at its exit to expand into the combustion chamber 18.
The interface between the burner section 15, 32 and combustion chamber 18 is characterized by a sudden cross-sectional area change (i.e. backward facing step) comprising a perpendicular front panel 19 extending from the exit of the burner section to inner liner 21 and outer liner 20. The mechanical interface is at the front panel seal, separating the burner front panel 19 from the liners 20 and 21.
The transition between burner section 15, 32 and combustion chamber 18 is located at the periphery of the burner front panel 19. The front panel 19 is flat and a large portion of the combustion chamber 18 is therefore occupied by recirculation bubbles 22.
The two main drawbacks of this current concept are:

(1) The sudden expansion (backward facing step) causes a large pressure drop due to the large recirculation zones associated with it.
(2) The leakages 23 at the burner section/liner interface and between adjacent burners are entering into the combustion chamber 18 in the recirculation bubbles 22, without participating in combustion, i.e. the leakage air is bypassing the flame, which needs to be at higher temperature to fulfil the target combustion chamber exit temperature. Higher flame temperature increases NOx emissions. At part load, CO emissions may increase because of local quenching of the flame.

Thus, although the transition between the second (SEV) burner and combustion chamber with its large backward facing step is a key element for stabilising the flame, it has nevertheless a negative impact on the SEV pressure drop and emissions associated to the leakages 23 between the burner front panel 19 and liners 20, 21.
In the past, it has been proposed to design the burner with a diffuser in its mixing section to minimise the front panel area and therefore the pressure drop.
According to another proposal the leakages were minimised with seals between front panel 19 and liners 20, 21. However, as already said, they are completely bypassing the flame and the decreased turbine inlet temperature due to bypassing air needs to be compensated with higher flame temperature. The leakages may also locally quench the flame and increase the part load CO emissions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a gas turbine with sequential combustion, which avoids the drawbacks of the prior art second burner/combustion chamber arrangement and has reduced emissions.
This object is obtained by a gas turbine according to claim 1.
The gas turbine according to the invention comprises a compressor, a first combustor downstream of said compressor, a first turbine, a second combustor downstream of said first turbine, and a second turbine downstream of said second combustor, whereby said second combustor comprises a plurality of burners having a mixing section, which opens downstream into a wider combustion chamber. It is characterized in that the transition between the mixing section and the combustion chamber is continuous.
According to an embodiment of the invention the transition between the mixing section and the combustion chamber is streamlined.
According to another embodiment of the invention the mixing section and the combustion chamber are assembled from at least two parts, which are joined at a split plane.
Specifically, said split plane is located at the exit of said mixing section.
Specifically, said split plane is located upstream of the exit of said mixing section.
More specifically, said burners inject fuel in an injection plane perpendicular to the flow direction within said mixing section, and that said split plane coincides with said injection plane.
According to a further embodiment of the invention said combustion chamber has an annular layout.
According to just another embodiment of the invention said combustion chamber has a can layout.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

Fig. 1: shows in a perspective view a stationary (or industrial) gas turbine with sequential combustion;
Fig. 2: shows a sectional view of a secondary burner/combustion chamber arrangement according to the state of the art;
Fig. 3: shows a sectional view of a secondary burner/combustion chamber arrangement according to one embodiment of the invention; and
Fig. 4: shows a sectional view of a secondary burner/combustion chamber arrangement according to another embodiment of the invention.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

A basic idea of the present invention is to minimize the second (SEV) burner pressure drop and associated emissions by means of a smoother transition between burner section and combustion chamber. An additional measure is to move the split plane and hence the position of the associated leakages upstream.
According to Fig. 3, the transition between burner mixing section 32 and combustion chamber 24 of a gas turbine 30 with sequential combustion is done with a smoothed, especially streamlined, geometry of the outer liner 25 and inner liner 26.
In addition, the split between burner 15, mixing section 32 and combustion chamber 24 can be located at the mixing section 32 exit (split plane 29), so that leakages 27 are entering into the flame and participate in the fuel/air reaction.
However, there are two measures that may be separated:

(1) The upstream shift of leakages (by shifting the split plane 29 upstream); and
(2) The smoothing of the liner shapes of the inner and/or outer liner (26, 25).

Both measures can be used separately or in combination. Both measures can be applied to combustion chambers with annular or can layout.
According to another embodiment of the invention, as shown for a gas turbine 30' in Fig. 4, the split could be even positioned at the injection plane 31, with the leakages 28 being mixed with the injected fuel, which is particularly suitable for a can layout.

LIST OF REFERENCE NUMERALS

10,30,30': gas turbine
11: rotor
12: air intake
13: compressor
14,15: burner
14a,15a: fuel supply
16,16': turbine
17: exhaust gas outlet
18,24: combustion chamber
19: front panel
20,25: outer liner
21,26: inner liner
22: recirculation bubble
23,27,28: leakage
29: split plane
31: injection plane (split plane)
32: mixing section

Claims

Gas turbine (10, 30, 30'), comprising a compressor (13), a first combustor (14, 14a) downstream of said compressor (13), a first turbine (16), a second combustor (15, 15a) downstream of said first turbine (16), and a second turbine (16') downstream of said second combustor (15, 15a), whereby said second combustor (15, 15a) comprises a plurality of burners (15) having a mixing section (32), which opens downstream into a wider combustion chamber (18, 24), characterized in that the transition between the mixing section (32) and the combustion chamber (24) is continuous.
Gas turbine according to claim 1, characterized in that the transition between the mixing section (32) and the combustion chamber (24) is streamlined.
Gas turbine according to claim 1, characterized in that the mixing section (32) and the combustion chamber (24) are assembled from at least two parts, which are joined at a split plane (29, 31).
Gas turbine according to claim 3, characterized in that said split plane (29) is located at the exit of said mixing section (32).
Gas turbine according to claim 3, characterized in that said split plane (31) is located upstream of the exit of said mixing section (32).
Gas turbine according to claim 5, characterized in that said burners (15) inject fuel in an injection plane (31) perpendicular to the flow direction within said mixing section (32), and that said split plane coincides with said injection plane (31).
Gas turbine according to one of the claims 1-6, characterized in that said combustion chamber (24) has an annular layout.
Gas turbine according to one of the claims 1-6, characterized in that said combustion chamber (24) has a can layout.