GB2321304A - Burner for a gas turbine - Google Patents

Abstract

A burner for a gas turbine has a series of atomiser nozzles 12 located around a periphery of a swirler 4 on its downstream side, liquid fuel issuing from the nozzles being atomised by high-pressure air introduced into a conduit 10 in which the nozzles are situated. Holes 14 in the swirler wall opposite the nozzle outlets allow the atomised fuel through to the swirler air passages where the air-fuel mixture is mixed with further air. In a dual-fuel version of the invention, the conduit may be used to introduce gas fuel into the swirler instead of liquid fuel, the gas being allowed through by means of the same holes.

Description

BURNER FOR A GAS TURBINE The invention concerns a burner for a gas turbine, and more specifically a burner employing atomisation of liquid fuel supplied to said burner.

In a gas turbine, in order to achieve efficient combustion with low pollution emissions it is essential that the fuel and air supplied to the combustor be properly mixed for each engine running condition. This mixing process is carried out in a burner disposed upstream of the cornbustor, and a number of different kinds of burners and combustion systems have been devised to achieve suitable mixing.

One such system is the airblast atomisation process, whereby liquid fuel is converted into fine droplets, these droplets being then entrained in air supplied to the combustor.

Known airblast atomisers for gas turbine applications are single devices (one per burner assembly) set proximate the central axis of the burner and within sight of the combustion flame. Such an arrangement, whilst having the advantage of simplicity, can suffer from the significant drawback that it is exposed to intense heat generated by the flame, and in particular is subject to so-called coking, i.e. the build-up of carbon on surfaces and orifices due to flarne-heat action on the fuel passing over the surfaces. A deleterious effect of coking is a fall-offin burner performance as carbon deposits build up (such deposits cause a change in the dimensions of critical passageways and orifices), and to counter this the burner must be removed at regular intervals for servicing.

According to the invention there is provided a burner for a gas turbine, comprising a swirler for the mixing of air and fuel, and a plurality of atomiser arrangements disposed, in terms of fuel flow, upstream of said swirler in spaced relationship about a longitudinal axis of said burner, said atomiser arrangements serving to atomise liquid fuel supplied to the burner and to supply said atomised fuel to said swirler for mixture with air.

Providing the burner with a number of atomisers located away from the central part of the burner ensures that the atomisers will be maintained at a lower temperature in an area where there is less likelihood of coking, the result being a longer period between services.

A further advantage is that the fuel is given longer residence time in the ralin airstream entering the swirler, and this promotes more thorough mixing of the fuel with combustion air.

The burner may comprise a liquid-fuel supply inlet and a high-pressure air supply inlet, and said atorssser arrangements may each comprise a nozzle, said nozzle being located in a conduit in communication with said high-pressure air supply inlet, and an opening connecting said conduit and an air-flow region of said swirler, said nozzle being in communication with said liquid-fuel supply inlet. The opening may be substantially in line with a longitudinal axis of said nozzle.

The nozzles may be disposed adjacent a peripheral region of said swirler, which serves to reduce the temperature and risk of coking of the nozzles even further.

The burner may be a dual-fuel bumer, said high-pressure air supply inlet serving optionally to convey fuel gas into said conduit for supply to said swirler by way of said openings.

The liquid fuel may be further atomised in said swirler by a flow of air supplied to said swirler through radial openings in said swirler.

An ernbodiment of the invention will now be described, by way of example only, with reference to the drawings, of which: Figure 1 is a longitudinal section through a gas turbine combustion chamber and a burner in accordance with the invention; Figure 2 is a sectional view of a typical swirler; Figures 3(a) and 3(b) are, respectively, a longitudinal section through, and an endview of, a burner in accordance with the invention, and Figure 4 is a detailed section of a part of the burner of Figure 3 showing the disposition of an atomiser nozzle.

Referring first to Figure 1, a combustion chamber 1 is shown which receives a fuel-air mixture from a burner assembly 2, the latter comprising a burner head arrangement 3 and a swirler 4. Combustion chamber 1 and burner assembly 2 are part of a gas turbine engine and are contained within a casing structure thereof. Air from, for example, a gas turbine compressor driven by the main turbine, surrounds the burner assembly 2, and this air passes radially inwards through passages 5 in the swirler to a central region A of the burner, where the air turns through 90C and moves downstream into the combustion zone B (see arrows in Figure 1). An end-view of the swirler 4 is shown in Figure 2, in which can be seen the usual swirler blades 6 which serve to impart to an essentially radial flow of air 7 a rotational component about the axis 8 of the swirler.

Liquid fuel is supplied to the burner through an inlet 9, while air under pressure is introduced through an inlet 10. An annular gallery 11 is in communication with the air inlet 10 and provides atomising air to a series of atomiser nozzles 12 (see Figures 3 and 4) situated adjacent an upstream wall 13 of the swirler 4. The nozzles 12, which receive liquid fuel from the fuel inlet 9, are spaced at substantially equal distances around a periphery of the swirler wall 13 and face at their fuel-ejection ends a corresponding series of openings 14 which connect the gallery 11 with the internal passageways 5 of the swirler 4 forming an airflow region thereof. In this embodiment a nozzle is allocated to each of the passageways 5 shown in Figure 2.

In operation, liquid fuel under pressure issuing from each nozzle outlet, which is in line with its associated opening 14, is acted upon by the air from gallery 11 which also discharges its air content through the same openings. The interaction between fuel and gallery air through the openings 14 causes the fuel to atomise and a mixture of fuel and air passes into the main airstream flowing through the swirler passages 5 (see Figure 2). This first-stage atomisation/mixing process moves to a second stage which takes place in the swirler passages. Here the discharged mixture is acted upon by the main airstream 7 to further improve fuel atomisation and mixing. The two-stage process in combination with the longer residence time (from swirler inlet to point of combustion) results in excellent fuel atomisation and uniform fuel distribution in the combustion air.

It has been assumed that the burner, as heretofore described, runs off liquid fuel only, with the inlet 10 providing solely air for the atomisation process. It is equally possible, however, for the inlet 10 to be used to convey gas fuel into the gallery 11 for introduction into the swirler 4 through the openings 14, the fuel gas being then mixed with the main airflow 7. The burner then becomes a dual-fuel burner with the inlet 10 and the openings 14 serving the dual function just described. In practical terms, a change-over mechanism (e.g. a two-way valve) is required upstream of the burner to route either high-pressure air or gas to the inlet 10.

The mixture provided by the burner 2 will normally be set for on-load running of the gas turbine. On start-up or at low-loads, however, a particularly fuel-rich mixture is required, and this may necessitate the inclusion of an additional fuelling device. This may take the form of a further liquid- or gas-fuel device positioned at the central area of the burner (position C).

While the preferred embodiment has one nozzle for each swirler passageway 5, an alternative measure is to reduce this to one nozzle for every few passageways. Such an arrangement would allow for larger nozzle sizes for a given total fuel flow, thereby reducing the possibility of blockage. However, fewer fuel nozzles would also give a less uniform fuel distribution in the air-fuel mixture exiting the swirler.

Claims (7)

1. A burner for a gas turbine, comprising a swirler for the mixing of air and fuel, and a plurality of atomiser arrangements disposed, in terms of fuel flow, upstream of said swirler in spaced relationship about a longitudinal axis of said burner, said atomiser arrangements serving to atomise liquid fuel supplied to the burner and to supply said atomised fuel to said swirler for mixture with air.

2. Burner as claimed in Claim 1, comprising a liquid-fuel supply inlet and a highpressure air supply inlet, said atomiser arrangements each comprising a nozzle, said nozzle being located in a conduit in communication with said high-pressure air supply inlet, and an opening connecting said conduit and an air-flow region of said swirler, said nozzle being in communication with said liquid-fuel supply inlet.

3. Burner as claimed in Claim 2, in which said opening is substantially in line with a longitudinal axis of said nozzle.

4. Burner as claimed in Claim 2 or Claim 3, in which said nozzles are disposed adjacent a peripheral region of said swirler.

5. Burner as claimed in any one of the preceding claims, in which said burner is a dualfuel burner, said high-pressure air supply inlet serving optionally to convey fuel gas into said conduit for supply to said swirler by way of said openings.

6. Burner as claimed in any one of the preceding claims, in which said liquid fuel is further atomised in said swirler by a flow of air supplied to said swirler through radial openings in said swirler.

7. Burner substantially as shown in and/or as hereinbefore described with reference to Figures 1, 3 and 4 of the drawings.