GB2422874A

GB2422874A - Gas turbine burner expansion bar structure

Info

Publication number: GB2422874A
Application number: GB0502437A
Authority: GB
Inventors: Andrew Rowell Faulkner
Original assignee: Alstom Technology AG
Current assignee: GE Vernova GmbH
Priority date: 2005-02-05
Filing date: 2005-02-05
Publication date: 2006-08-09
Also published as: GB0502437D0

Abstract

An expansion bar structure 6 for attaching a burner hood 2 to the engine structure (26, figure 1) in a gas turbine engine 1, the expansion bar structure 6 comprising first and second expansion bars 12, 13, each pivotally connected to a surface of one of the burner hood 2 and the engine structure 26, at one of their ends, by first and second fixings 14, 15, respectively, and pivotally connected together and to a surface of the other of the burner hood 2 and the engine structure 26 by a third fixing 16, and wherein the first and second expansion bars 12, 13 expand and contract proportionally more than the surface of the burner hood 2 or the engine structure 26 between the first and second fixings 14, 15 during the operation of the gas turbine engine 1. This may be achieved by the expansion bars 12, 13 having a higher coefficient of thermal expansion than the surface of the burner hood 2, or engine structure 26, between the first and second fixings 14,15, which may be insulated. The expansion bars 12, 13 may be made of stainless steel.

Description

* 2422874

TITLE

Expansion bar structures

DESCRIPTION

Technical Field

The invention relates to gas turbine engines and provides an expansion bar structure for attaching a burner hood of the gas turbine engine to a part of the engine structure.

pcicground Art During the operation of a gas turbine engine, fuel is burnt in a combustion chamber extending between the burner hood and the turbine stage(s). The burner hood and combustion chamber are situated within an annular plenum chamber that is circumferentially enclosed by an outer casing of the engine. The combustion chamber is normally defined by radially inner and outer combustor liners that extend between the burner hood and the turbine outlet so as to form a chamber where the combustion may be controlled by the progressive addition of air and where vortices may be created to provide flame stability. The ignition of fuel within the combustion chamber produces a large amount of heat and the liners are forced to operate at very high temperatures. In addition, the liners are normally relatively thin to avoid high thermal stresses and therefore have a low thermal inertia. When the gas turbine engine is not in use, the inside of the combustion chamber is at approximately ambient temperature. The changes in the temperature of the gases in the combustion chamber during start up and shut down, as well as during operation of the gas turbine engine, cause the combustor liners to expand and contract rapidly and severely relative to those parts of the engine structure to which they are located. To acconmiodate axial differential expansion, some form of sliding expansion joint is normally included.

The burner hood assembly may be attached to the static structure of the engine by a number of individual circumferentially spaced bars, one of whose functions is to minimise the above-mentioned axial differential thermal expansion, while allowing free radial expansion of the burner hood. The part of the engine static structure to which the expansion bars are connected will vary depending on the detailed design of the gas turbine engine. For example, the expansion bars may be connected to the turbine vane carrier, the outer casing or to some other component part. The term "engine structure" is therefore used throughout this specification to describe any suitable part or component of the engine's static structure to which the expansion bars may be connected.

The individual expansion bars are simple metal bars attached to the engine structure at one end by a first pivoting joint and attached to the burner hood at the opposing end by a second pivoting joint such that they are located in the annular plenum chamber that surrounds the combustion chamber. The expansion bars expand and contract lengthwise faster than the engine structure in accordance with changes of temperature within the plenum chamber to move the burner hood backwards and forwards in the axial direction in a maimer which more closely matches the combustion liners and thus minimises the seal movement at the turbine sealing interfaces.

However, in practice the expansion bars are not able to fully compensate for the expansion and contraction of the combustor liners because the temperature of the air in the plenum chamber is considerably lower than the temperature of the gases inside the combustion chamber. Moreover, the thermal expansion characteristics of the expansion bars and the combustor liners are likely to be substantially different through differences in thermal mass.

One way of overcoming this problem is by ducting cooling air onto or into the various components to control their temperature and reduce the amount of thermal expansion and contraction in accordance with movement of the gas turbine engine seals. This can be done by providing an active or passive control system. However, such active and passive control systems are complicated and require the additional introduction of cooling air into the gas turbine engine.

Summary of the Invention

The present invention offers a solution to the problems mentioned above by providing an expansion bar structure for attaching a burner hood to an engine structure in a turbine engine, for example the outer casing or the turbine vane carrier, the expansion bar structure comprising first and second expansion bars, each pivotally connected to a surface of one of the burner hood and the engine structure at one of their ends by a first and second fixing, respectively, and pivotally connected together and to a surface of the other of the burner hood and the engine structure by a third fixing, and wherein the first and second expansion bars expand and contract proportionally more than the surface of the burner hood or the engine structure between the first and second fixings during the operation of the turbine engine.

Relative to the known type of expansion bar, the expansion bar structure of the invention provides an amplified thermal expansion and contraction during start up, shut down and operation of the gas turbine engine, thereby enabling the movement of the burner head to more closely match the thermal expansion and contraction of the radially inner and outer combustor liners.

The expansion bar structure has a generally triangular construction with the first and second bars forming two sides of the triangle and the surface of the burner hood or engine structure between the first and second fixings forming the third side or base.

The sides of this triangular construction are able to pivot relative to the base. As the sides thermally expand proportionally more than the base when the expansion bar structure experiences an elevation in temperature a distortion occurs in the triangular shape of the expansion bar structure. In a preferred embodiment of the invention the first and second expansion bars are of equal length and identical construction and the distortion is therefore an elongation in a direction perpendicular to the base. Likewise, when the expansion bar structure experiences a decrease in temperature the distortion produced is a contraction in the length of the structure in the direction perpendicular to the base. n

The linear expansion or contraction produced by a conventional individual expansion bar of length, L1 is described by the equation: X1 - L1aAT Where X, is the expansion or contraction; L1 is the length of the conventional individual expansion bar; a is the overall coefficient of linear thermal expansion of the conventional individual expansion bar; and AT is the change in temperature experienced.

For the purposes of a comparison, the magnitude of the elongation or contraction of an expansion bar structure of the present invention which is of the same overall length L1, experiences the same temperature change AT and whose first and second bars have the same coefficient of thermal expansion, a as the above conventional individual expansion bar may be estimated by assuming that the thermal expansion of the base is negligible. This elongation or contraction is described by the following equation: X2 = [ ( L hot) A2}"2 - [ L2 - A2 J'12 Where X2 is the thermal elongation; L2 is the length of the first (or second) bar, L2 = (L1 / sin 0); A is th@ half the length of the base of the structure, A = ( L1 / tan 9); 0 is the angle the first and second bars each form with the base; and L2 hot is the length of the first (or second) bar at the elevated temperature, L2 hot = L2 ( I + a AT).

The approximate elongation of the expansion bar structure of the present invention is a magnification of the expansion or contraction of a conventional individual expansion bar. The magnitude of the magnification is given by: M = In an embodiment of the invention and conventional individual expansion bar where: L1==lm, a=l3xlO6K", AT=450K and 045 X1 is 5.85 x lO m, X2 is 11.7 x iO m and the magnification, M is therefore 2. In other words, this particular embodiment of the expansion bar structure produces an elongation that is approximately twice that produced by the conventional individual expansion bar. By controlling the elongation and contraction of the expansion bar structure a better match to the expansion and contraction of the radially inner and radially outer combustion liners can be achieved, thereby reducing the seal movement at the turbine sealing interfaces.

The elongation and contraction may be controlled by making the first and second expansion bars have a higher coefficient of thermal expansion than the engine structure between the first and second fixings.

The elongation and contraction may additionally or alternatively be controlled by changing the shape of the expansion bar structure within the constraints imposed by the structure's use to alter the angle that the first and second expansion bars form with the surfaces to which they are attached.

The elongation and contraction may be further controlled by making the surface of the engine structure between the first and second fixings experience a lower temperature than the first and second expansion bars during the operation of the gas turbine engine. This will occur by default if the engine structure is part of the external casing, as this will experience nearly ambient temperatures on its outside surface. This may be emphasised by the insulation of the surface between the first and second fixings from the plenum chamber with a lagging material, for example. -Th

The first and second expansion bars may be made of stainless steel such as STG1 IT or 18/8 stainless steel having a coefficient of thermal expansion of 10.2 x 1 06 K' and x 106 K, respectively.

Drawings Figure 1 is a partial radial cross section through an axial flow gas turbine containing an embodiment of the claimed expansion bar structure; Figure 2 shows a plan view of the expansion bar structure in isolation; and Figure 3 shows another plan view of the expansion bar structure in isolation, illustrating its expansion on heating.

Referring first to Figure 1, there is shown a radial cross section through a gas turbine engine 1 showing the burner hood 2, combustion chamber 3 and turbine 4 all encased within an outer pressure casing 5. The expansion bar structure 6 is attached at one end to the engine structure 26 at or near the turbine inlet and at the other to the burner hood 2, and is located in the burner plenum chamber 7 between the combustion chamber 3 and the outer pressure casing 5. The expansion bar structure 6 occupies a plane that extends generally axially of the turbine and is approximately parallel to the longitudinal extent of the combustion chamber 3. The combustion chamber 3 is bounded by radially inner and radially outer combustor liners 8 and 9. The liners 8 and 9 are attached to the turbine vane carrier 4C by an outer liner turbine seal 10 and by inner and outer sliding expansion joints 27 and 28. At their other ends, the liners 8 and 9 are attached to the burner hood 2 by inner and outer sliding expansion joints 29 and 30.

During the operation of the gas turbine engine 1, fuel is injected via burners 11 into the combustion chamber 3 and is ignited. The combustion of fuel in the combustion chamber 3 causes the radially inner and radially outer combustor liners 8 and 9 to experience an elevated and fluctuating temperature. The radially inner and radially outer combustor liners 8 and 9 thermally expand and contract to a size dependent upon the temperature they experience, their design and the coefficient of thermal expansion of their components. The radially inner and radially outer combustor liners 8 and 9 insulate and bound the combustion chamber 3 so that the air in the burner plenum chamber 7 is at a much lower temperature than the combustion gases in the combustion chamber 3 during operation of the gas turbine engine 1. The expansion bar structure 6 experiences this lower temperature and thermally expands and contracts to a size determined by its design, the coefficient of thermal expansion of its components and the lower temperature, thereby moving the burner hood 2 backwards and forwards in a manner that reduces the amount of sliding movement in the expansion joints 27-30.

Figure 2 shows a plan view of the stainless steel expansion bar structure 6. The structure comprises first and second rigid bars 12 and 13 of the same length and construction and first, second and third joints 14, 15 and 16. The first and second bars 12 and 13 are each individually attached to the engine structure 26 at one of their ends by the first and second joints 14 and 15, respectively. The first and second bars 12 and 13 are allowed to pivot in the plane in which they both lie by the first and second joints 14 and 15, respectively. The first and second bars 12 and 13 are attached together and to the burner hood 2 at their other end by the third joint 16. The third joint 16 allows the first and second bars 12 and 13 to pivot in the plane in which they both lie. Thus, the expansion bar structure 6 forms a generally triangular structure, with the surface of the engine structure between the first and second joints 14 and 15 forming the base 17 of the triangle.

The triangular expansion bar structure 6 may be in the opposite orientation with respect to the turbine vane carrier 4 and the burner hood 2 without affecting its function. In other words, the surface of the burner hood 2 may form the base of the triangle and the first and second bars 12 and 13 may be attached together and to the engine structure 26.

Figure 3 shows operation of the stainless steel expansion bar structure 6 on heating.

On experiencing an increase in temperature, for example during start up of the gas turbine engine, the expansion bar structure 6 and its components thermally expand in all directions. In particular, the first and second bars 12 and 13 will expand parallel to their length (as shown by arrows 18 and 19) and the base 17 will expand along its length (as shown by arrow 20). The first and second bars 12 and 13 expand more than the base 17 because they experience a higher temperature and/or have a higher coefficient of thermal expansion and/or a lower thermal inertia. This causes the overall shape of the expansion bar structure 6 to change. The first and second bars 12 and 13 pivot away from the base 17 at the first and second joints 14 and 15 respectively (as shown by arrows 21 and 22) and pivot together at the third joint 12 (as shown by arrows 23 and 24). This produces an overall thermal expansion (represented in Figure 3 by arrow 25) of the expansion bar structure 6 perpendicular to the base 17 that is greater than the thermal expansion of any of the individual components of the expansion bar structure 6. On experiencing a reduction in temperature, the expansion bar structure 6 and its components contract in all directions and the structure undergoes a reversal of the above process.

Claims

I. An expansion bar structure for attaching a burner hood to an engine structure in a turbine engine, the expansion bar structure comprising first and second expansion bars, each pivotally connected to a surface of one of the burner hood and the engine structure at one of their ends by a first and second fixing, respectively, and pivotally connected together and to a surface of the other of the burner hood and the engine structure by a third fixing, and wherein the first and second expansion bars expand and contract proportionally more than the surface of the burner hood or the engine structure between the first and second fixings during the operation of the turbine engine.
2. An expansion bar structure according to claim 1, wherein the first and second expansion bars have a higher coefficient of thermal expansion than the surface of the burner hood or the engine structure between the first and second fixings.
3. An expansion bar structure according to claim I or claim 2, wherein the first and second expansion bars are made from stainless steel.
4. A method of attaching a burner hood to an engine structure in a turbine engine using an expansion bar structure according to any preceding claim, wherein the temperature of the surface of the burner hood or the engine structure between the first and second fixings is controlled to be lower than the temperature of the first and second expansion bars during the operation of the turbine engine.
5. A method according to claim 4, wherein the temperature is controlled by insulating the surface of the burner hood or the engine structure between the first and second fixings.
6. An expansion bar structure for attaching a burner hood to an engine structure in a turbine engine substantially as described herein and with reference to the drawings.