ANNULAR-COMBUSTION-CHAMBER BYPASS

Abstract

An annular combustion chamber (1) for a gas turbine, the chamber having an outer shell (12) which has at least one inlet opening (4) for a burner (3) and an outlet (7) which opens into a turbine chamber (8), wherein ducts (14) which can be closed, which are oriented substantially parallel to the symmetry axis (2) of the annular combustion chamber (1), and through which final compressor air is guided into the annular combustion chamber (1) are provided in the outer shell (12) in the region of the outlet (7). Ring segments around the outer shell have projections selectively movable to at least partially block and open the ducts. A gas turbine is also disclosed.

Description

The invention relates to an annular combustion chamber having a bypass for reducing carbon monoxide emissions in partial load operation, and to a gas turbine having such an annular combustion chamber.

When the gas turbine is operated at partial load, the combustion temperature in the combustion chamber drops. As a consequence, the primary zone temperature which is relevant for carbon monoxide emissions also falls, to below a minimum value, whereby an increased quantity of carbon monoxide is generated and/or emitted. As this is to be avoided, the useful partial load range of the gas turbine is limited.

It is an object of the invention to provide an annular combustion chamber, of the type mentioned in the introduction, which permits a considerable increase in the useful partial load range.

The invention achieves this object by providing that, in such an annular combustion chamber for a gas turbine, having an outer shell which has at least one inlet opening for a burner and an outlet that opens into a turbine space, ducts are provided in the outer shell in the region of the outlet, which ducts are closable and are oriented substantially parallel to the axis of symmetry of the annular combustion chamber, and through these compressor outlet air can be guided into the annular combustion chamber.

By virtue of this measure, it is possible to introduce compressor air into a region at the end of the combustion chamber without it taking part in the combustion, that is to say it is supplied back to the air-fuel mixture only after the combustion process. The effect of this is that the richer mixture can be burnt in the combustion space at higher temperatures, and thus the carbon monoxide emissions during partial load operation can be reduced.

In one advantageous embodiment, the annular combustion chamber comprises a last row of heat-shield plates arranged in the circumferential direction on the outer shell in the region of the outlet in the interior of the annular combustion chamber, and a second-to-last row of heat-shield plates arranged next to the last row in the direction of the at least one inlet opening, wherein a gap is provided between the last and second-to-last rows of heat-shield plates, in the region of the ducts. By virtue of this gap, the compressor outlet air can flow unperturbed into the combustion chamber.

It is further advantageous if an adjustment device, comprising ring segments which form a ring that is oriented coaxially with the annular combustion chamber and may be moved axially with respect to the annular combustion chamber, is provided on the exterior of the outer shell for closing and opening the ducts. The ring segments have the advantage of simpler assembly and/or disassembly.

In this context, it is expedient if the ring of the adjustment device can be moved in a continuously variable manner in order to set, as required, a desired gap width and thus to be able to remove a determined quantity of air from the compressor outlet air prior to the combustion.

In one advantageous embodiment of the invention, the ring segments have, on their side facing away from the turbine, projections for engaging in the ducts. In this context, it is expedient if the projections are of trapezoidal design. By virtue of the projections, in particular by virtue of their trapezoidal shape, the quantity of air to be guided through the ducts can be set with particular precision. The ducts may of course also be entirely closed. In that context, the ring is moved only in the axial direction, by a mechanism. Various possibilities exist for such a mechanism for controlling and moving the ring segments. Specifically, this can be effected using motors, lever or hydraulic mechanisms, etc., which for example displace the ring axially on rails or other movement elements. Optionally, these mechanisms may also be installed inside or outside the housing.

With regard to the high temperatures when the annular combustion chamber is in operation, it is advantageous if the projections of the ring segments have a thermal barrier coating (TBC) on their surfaces exposed to the hot gas of the combustion. For the same reason, it is expedient if the interior of the outer shell also has a thermal barrier coating in the region of the gap, between the last and the second-to-last rows of the heat-shield plates, that is to say between the openings of the ducts into the interior of the combustion chamber. In annular combustion chambers according to the prior art, the last and the second-to-last rows of the heat-shield plates still adjoin one another and the interior of the outer shell was sufficiently protected by the heat-shield plates. The gap resulting from the invention increases the exposure of the outer shell, in this region, to the hot gases of the combustion.

It is furthermore expedient if the last row of heat-shield plates, which is the furthest of all the heat-shield plates from the core region of the combustion, is metallic and the second-to-last row is ceramic as, on one hand, the service temperature of ceramic materials is substantially higher than the maximum service temperature of high-temperature metal alloys and, on the other hand, high-temperature metal alloys are less brittle and have better heat- and temperature-conducting behavior.

Finally, the invention also indicates a novel gas turbine in which an annular combustion chamber according to the invention is integrated.

By virtue of the continuously variable adjusting device according to the invention for feeding compressor outlet air into a region at the end of the combustion chamber, i.e. after the combustion has taken place, it is possible to reduce carbon monoxide emissions in partial load operation since higher combustion temperatures arise on account of a richer mixture.

The consumption of cold air in baseload operation is no greater than with current designs.

Furthermore, the invention is relatively easy to convert as the ring segments, for example two half rings, are simple components which need only be displaced axially.

The invention will be explained in more detail and by way of example with reference to the drawings, which are diagrammatic and not to scale and in which:

FIG. 1 shows a combustion system having an annular combustion chamber according to the invention,

FIG. 2 shows the turbine-facing side of the annular combustion chamber with adjustment device on the outer shell and bypass ducts,

FIG. 3 shows a half ring of the adjustment device for the bypass,

FIG. 4 shows a metallic heat-shield plate according to the prior art,

FIG. 5 shows a metallic heat-shield plate for the annular combustion chamber according to the invention and

FIG. 6 shows the interior of the annular combustion chamber in the region of the outlet.

FIG. 1 shows, schematically and by way of example, the combustion system of an annular combustion chamber 1 according to the invention. The annular combustion chamber 1 consists of a closed ring which is arranged around a rotor axis 2. Burners 3 are arranged in inlet openings 4 in the upper region of the combustion chamber 1. This is where the fuel 5 is mixed with the compressor air 6. The actual combustion takes place in the combustion chamber 1. The hot combustion gases enter the turbine space 8 through the outlet 7 and there impinge upon the first static guide vane 9. In order to protect against scaling, the annular combustion chamber 1 is clad with ceramic heat-shields 10 and metallic heat-shields 11 which are attached to the outer shell 12.

According to the invention, the combustion chamber outer shell 12 is provided with ducts 14 between the last ceramic heat-shield row 13 (i.e. the second-to-last heat-shield row) and the metallic intake shell plate (i.e. the last heat-shield row 11), in the region of the outlet 7, which ducts are oriented substantially parallel to the axis 2 of the annular combustion chamber 1.

In order that these ducts 14 may be closed or opened as required, an adjustment device 15 is provided on the exterior of the outer shell 12, as shown in FIG. 2. The adjustment device 15 has ring segments 16, for example two half rings, one of which is shown in FIG. 3. By means of corresponding projections 17, it is possible to set determined gap widths in the ducts 14 or even to close the latter entirely.

In order to permit this inflow of air into the annular combustion chamber 1, the metallic intake shell plates, that is to say the plates of the last heat-shield row 11 are shorter than a heat-shield plate 18 of the last row of an annular combustion chamber according to the prior art. FIG. 4 shows such a heat-shield plate 18 of the last row of an annular combustion chamber according to the prior art and the shortening undertaken at the broken line so as to obtain a metallic heat-shield plate 11 as shown in FIG. 5 and as required for the present invention.

FIG. 6 shows a view of the interior of the annular combustion chamber 1 with last 11 and second-to-last 13 heat-shield plate rows and the openings 20 of the ducts 14 in the outer shell 12 for the air bypass during partial load.

Since, according to the invention, the last row 11 of the heat-shield plates is shorter than the heat-shield plates according to the prior art and is arranged on the outer shell 12 of the annular combustion chamber 1 such that it no longer directly adjoins the second-to-last row of the heat-shield plates 13, there results a gap 19 in the circumferential direction of the annular combustion chamber 1 without the heat protection which exists hitherto. The ducts 14 open into the interior of the annular combustion chamber 1 in this gap 19. When the annular combustion chamber 1 is in operation, the outer shell 12 is exposed to very high temperatures between these openings 20. In order to protect the outer shell 12 from these temperatures in spite of the gap 19, the interior of the outer shell 12 is provided with a thermal barrier coating in the region of the gap 19 between the last 11 and the second-to-last row 13 of the heat-shield plates, that is to say between the openings 20 of the ducts 14 toward the combustion chamber interior.

The projections 17 of the ring segments 16 also have a thermal barrier coating on their surfaces exposed to the hot gas of the combustion.

Claims

1. An annular combustion chamber for a gas turbine, the combustion chamber having an outer shell and the outer shell has at least one inlet opening for a burner and has an outlet that opens into a turbine space; ducts in the outer shell located in the region of the outlet, the ducts are closable, the ducts are oriented substantially parallel to an axis of symmetry of the annular combustion chamber, and compressor outlet air can selectively be guided through the ducts and into the annular combustion chamber;an adjustment device, comprising a ring that is oriented coaxially with the annular combustion chamber and may be moved axially with respect to the annular combustion chamber, the ring is provided on the exterior of the outer shell and is configured and located for selectively closing and opening the ducts.

2. The annular combustion chamber as claimed in claim 1, comprising a last row of heat-shield plates arranged in the circumferential direction on the outer shell in the region of the outlet from the interior of the annular combustion chamber, and a second-to-last row of heat-shield plates arranged next to the last row in the direction toward the at least one inlet openinga gap between the last and second-to-last rows of heat-shield plates, in the region of the opening of the ducts into the interior of the annular combustion chamber.

3. The annular combustion chamber as claimed in claim 1, wherein the ring is movable in a continuously variable manner for the selective closing and opening of the ducts.

4. The annular combustion chamber as claimed in claim 1, wherein the ring has, on a side thereof facing away from the turbine, projections for engaging in respective the ducts.

5. The annular combustion chamber as claimed in claim 4, wherein the projections engaging in the ducts are of trapezoidal shape.

6. The annular combustion chamber as claimed in either of claim 4, wherein the projections have a thermal barrier coating on surfaces exposed to hot gas.

7. The annular combustion chamber as claimed in claim 6, wherein the interior of the outer shell has a thermal barrier coating in the region of the gap.

8. The annular combustion chamber as claimed in claim 2, wherein the last row of heat-shield plates is metallic and the second-to-last row of heat shield plates is ceramic.

9. A gas turbine having an annular combustion chamber as claimed in claim 2.

10. The annular combustion chamber as claimed in claim 1, wherein the ring is comprised of a plurality of ring segments which together define the ring.