GB2103718A

GB2103718A - Gas turbine plant

Info

Publication number: GB2103718A
Application number: GB08222302A
Authority: GB
Inventors: Costantino Vinciguerra
Original assignee: Nuovo Pignone SpA
Current assignee: Nuovo Pignone SpA
Priority date: 1981-08-03
Filing date: 1982-08-02
Publication date: 1983-02-23
Also published as: IT8123336A0; FR2510656B1; SE8204552L; JPS6340241B2; DE3228799C2; JPS5827803A; CA1187809A; SE8204552D0; DE3228799A1; GB2103718B; IT1137783B; FR2510656A1

Abstract

The plant has an intermediate connection member (4) between a gas generator (3) and a power stage (7), which member (4) acts as a heat- exchanger for the stator box (6) of the power stage (7) with which lt is thermally in contact at its downstream end (4''). The member (4) is provided with an electric heating coil (15) embedded in its external surface and with an inner annular chamber (17) within which cooling air is caused to flow along a helical path from the downstream end to the upstream end of the chamber. Heating by coil (15) during start-up causes the stator box (6) to expand, thus permitting a reduction in clearance between the rotor discs and box (6). When elevated temperatures have been attained, the cooling air can cause appropriate cooling to ensure efficient operation. Valves 19, 22 can control the cooling air. <IMAGE>

Description

SPECIFICATION A gas turbine having a stator box integrated with a heat-exchanger This invention relates to a gas turbine having a stator box which is integrated with a heatexchanger, for permitting adequately the preheating of the stator box prior to starting the turbine and then the efficient cooling of the stator box. The intention is to reduce the problems associated with the transient states of the gas turbine and thus to obtain high efficiencies in such turbines with lower costs and simpler constructional arrangements.

As is known in a gas turbine and more particularly in the power stage of a gas turbine high temperatures are experienced which cause considerable thermal expansions in various component parts. However, whereas the rotor, which has its vanes directly acted upon by the hot gases, expands immediately once the turbine is started, the stator box, with its considerable thickness and its more external position subjected to more cooling, takes a longer time to become heated and thus to expand.

Thus, in order to prevent, during transient states, the rotor portions, when expanded, from scraping against the fixed stator portions with the possible attendant damage to the vanes and/or the sealing members, the clearances between the rotor and the stator in current gas turbines are made sufficiently wide but the result is a decrease in the efficiency of the turbine.

There is therefore a need to reduce this defect and thus to provide a turbine having a high efficiency inasmuch as it becomes possible to have only narrow clearances between the rotor and the stator in the power stage.

According to the present invention, there is provided a gas generator connected coaxially to an upstream end of an intermediate connection member or transition piece, the downstream end whereof is in its turn in heat-exchanging contact, frontally and coaxially, with a stator box of a power stage, the intermediate connection member supporting in the region of its upstream end a plurality of radial tubes for air intended to cool rotor discs of the power stage, which air may in use be drawn under pressure from a compression stage of the gas generator; wherein the intermediate connection member or transition piece is equipped with an electrically actuable heating coil embedded in its outer surface region and with an internal annular chamber in the interior of which a plurality of radial gills defines a helical pathway for the cooling air which in use may be conveyed from the downstream end of the chamber to the upstream end and to the plurality of radial tubes.

Thus with the present invention the stator box of the power stage can be preheated and caused to expand even before starting the turbine, so that no obstacle need hinder the expansion of the rotor in spite of the fact that the clearances between the stator and the rotor are kept to a minimum both under cold conditions and in steady operating conditions.

The preheating of the stator box is not carried out directly, but indirectly by conduction. This is of benefit because the present invention also makes it possible to improve the cooling in steady operating conditions of the stator box, and a direct heating of the stator box, due to the presence of heating appliances, would make the attainment of the latter objective both intricate and cumbersome.

In contrast, a more efficient cooling of the stator box under steady operational conditions is required by the intention of minimizing as far as practicable the expansion of the stator box due to the temperature differential between the preheating temperature and the steady operational temperature, so as to minimize the clearances between the stator and the rotor under steady operational conditions and also to obtain beneficial results as to constructional economy and simplification since a cold stator box is not difficult to build and can be made with cheap steel alloys, that is, materials which are not too expensive. Also, this improvement in cooling is then obtained, rather than by directly acting upon the stator box, in an indirect way by conduction.

In summation, both the preheating and the subsequent improvement of the cooling of the stator box of the gas turbine are obtained, according to the present invention, by acting upon the intermediate connection member, or transition piece, which contacts thermally the stator box in the downstream section and is heated by an electric coil embedded therein, and is, conversely, cooled by an air stream under pressure drawn from a compression stage of the gas generator and helically conveyed within an annular chamber of the transition piece in the direction from upstream to downstream thereof.

According to a further feature of the present invention, provision exists for the inner annular chamber of the intermediate connection member or transition piece to be fed with cooling air also in the region of its upstream end, the two feeding streams, upstream and downstream, respectively, being governed by specially provided halves. By so doing, that is by properly calibrating the valves, the magnitude of the airflow for cooling, which flows through the chamber of the intermediate connection member, and thus the cooling of the stator box of the power stage can also be adjusted.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows mainly a side elevation view, but with part in vertical section, of a gas turbine incorporating the heat-exchanger integrated with the stator box according to the present invention; and Figure 2 is a vertical section, on a considerably enlarged scale, of the heat-exchanger and adjacent regions of other components, of the arrangement shown in Figure 1.

Referring now to the drawings, there is shown a gas turbine which includes an air-inlet casing 2 which supports the upstream end of a gas generator 3, the other end of which is secured to the upstream end 4' of an intermediate connection member, or transition piece, 4, the latter having a substantially cylindrical outline. The downstream end 4" of the member 4, in its turn, is secured, by bolts such as 5, to a stator box 6, of a power stage 7, the box 6 supporting stator vanes 8, whereas rotor discs 9, mounted on a power shaft 10, of the stage 7, are cooled by a cooling air stream fed thereto through a set of radial tubes 11, the tubes 11 being supported by the transition piece 4 at the upstream end 4' thereof.

Figure 1 shows, also, a diffuser 12, and exhaust box 13, and a pipe 14 which conveys, to the radial tubes 11, air which has been withdrawn, under pressure, from a compression stage (intermediate) of the gas generator 3.

The cylindrical transition piece 4 is equipped with an electric heating coil 15, embedded bodily near an outer surface of piece 4 and enclosed on its exterior by an annular insulating member 16.

In its interior, the cylindical piece 4 has an annular chamber 17, as well as a set of radial gills 18, which, in the illustrated section, partition the chamber 1 7 into a number of sub-chambers, referenced 1 i' 172, 1 73, 1 74, respectively, which are so serially and mutually connected as to provide a helical pathway. The most downstream chamber 171 is connected, via a regulation valve 19, to the pipe 14 for conveying the cooling air stream, whereas the most upstream chamber 1 74 communicates, via a set of bores 20, with an annular chamber 21 into which the radial tubes 11 open, and is connected to the pipe 14 through a regulation valve 22.

By this arrangement the intermediate connection member or transition piece 4, can act like a heat-exchanger for the stator box 6, inasmuch as it, when being heated by the electric coil 15, will administer heat, through an annular contact surface 23, to the stator box 6 which will therefore be heated, whereas the same transition piece 4, when cooled by forced circulation of cooling air flowing from the annular chamber 17 to the annular chamber 21, will take heat away from the stator chamber 6, also via the annular contact surface 23, whereby the stator box is cooled.

In order further to improve the magnitude of the heat exchange between the transition piece 4 and the stator box 6, the latter can be constructed so as to have a small mass, whereby a small thermal inertia is achieved, whereas the central body and the downstream end 4" of the transition piece 4 are built massively to encourage the heat transfer therethrough and, lastly, the annular contact surface 23 can be made very wide so as to encourage the heat exchange.

Claims

1. A gas turbine comprising a gas generator connected coaxially to an upstream end of an intermediate connection member of transition piece, the downstream end whereof is in its turn in heat-exchange contact, frontally and coaxially, with a stator box of a power stage, the intermediate connection member supporting in the region of its upstream end a plurality of radial tubes for air intended to cool rotor discs of the power stage, which air may in use be drawn under pressure from a compression stage of the gas generator; wherein the intermediate connection member or transition piece is equipped with an electrically actuable heating coil embedded in its outer surface region and with an internal annular chamber in the interior of which a plurality of radial gills defines a helical pathway for the cooling air which in use may be conveyed from the downstream end of the chamber to the upstream end and to the plurality of radial tubes.

2. A gas turbine as claimed in Claim 1 , wherein provision exists for the internal annular chamber of the intermediate connection member or transition piece to be fed with cooling air also in the region of its upstream end, the two feeding stream, upstream and downstream, respectively, being regulated by corresponding valves.

3. A heat-exchanger integrated with the stator box of a gas turbine, substantially as hereinbefore described with reference to, and illustrated in, the accompanying drawings.