Patent Description:
As known, a gas turbine assembly for power plant comprises a compressor unit, a combustor unit and a turbine unit. The compressor unit is configured for compressing incoming air supplied at a compressor inlet. The compressed air leaving the compressor unit flows into a closed volume (called "plenum") and from there into the combustor unit. This combustor unit comprises usually a plurality of burners configured for injecting fuel (at least one type of fuel) into the compressed air flow. The mixture of fuel and compressed air enters a combustion chamber where this mixture ignites. The resulting hot gas flow leaves the combustion chamber and flows by the turbine unit performing a rotating work on a rotor connected to a generator. Usually the same rotor, that could be made as a single piece or in form of a plurality of adjacent rotor disks, supports also the rotating parts of the compressor assembly and it defines the main axis of the system. As known, the turbine unit and the compressor unit comprise a plurality of rows of rotating blades that are interposed by a plurality of rows of stator vanes. The rotating blades are supported by the rotor whereas the stator vanes are supported by a casing (called "vane carrier") that is concentric and surrounding the gas turbine assembly.

In order to achieve a high efficiency, the hot gas flow has to have a very high turbine inlet temperature. However, in general this high temperature involves an undesired high NOx emission level. In order to reduce this emission and to increase operational flexibility without decreasing the efficiency, a so called "sequential" gas turbine is particularly suitable. In general, a sequential gas turbine performs two combustion stages in series. Today at least two different kinds of sequential gas turbines are known. According to a first embodiment, the gas turbine comprises a first combustor and a second combustor that are annular shaped and are physically separated by a turbine, called high pressure turbine. Downstream the second combustor a second turbine is provided (called low pressure turbine).

According to a second embodiment, the sequential gas turbine is not provided with the high-pressure turbine and the combustor assembly is realized in form of a plurality of can-combustors wherein each can-combustor comprises a first combustor and a second combustor arranged directly one downstream the other inside a common casing can-shaped. These two examples of gas turbine assemblies have been cited only as non-limiting examples wherein the present invention can be applied. Indeed, as preferred example of gas turbine suitable to be improved by the present invention, the gas turbine assembly may involve a single stage of combustion with a single annular combustion chamber.

As known in this technical field, the terms "circumferential, radial, axial, outer and inner" refer to the rotor or assembly axis (that is parallel to the main air/hot gas flow). The terms "downstream and upstream" refer to the main direction of the air/hot gas flowing from the compressor to the turbine.

For cooling reasons it is common practice to use part of the compressed air wherein this cooling air by-passes the combustor and is fed to some hot components to be cooled. According to the prior art practice, that can be represented for instance by the enclosed <FIG> disclosing an Applicant solution or by the disclosure of the prior art document <CIT>, the compressed air is fed by the compressor outlet to a diffuser and from there to a plenum before entering the combustor. According to the prior art practice, part of the compressor air flowing into the diffusor is spilled from the main flow and directed by a swirl line towards an annulus extending from the compressor to the turbine and provided between the rotor and a rotor cover. With the term "swirl line" we mean a plurality of channels configured to apply a swirl to the spilled air flow that before leaving the compressor has been axially forced by the two last row of compressor vanes. According to <FIG>, the a line is provided to connect a guide tube, arranged between the diffuser and a plenum, to the annulus. The annulus of <FIG> is closed downstream and upstream by seals that are configured for allowing a leakage of air respectively towards the last and/or the second last row of compressor vanes for purging purposes and towards the first row turbine vanes for sealing purposes. From the annulus the swirled spilled air is fed to a volume obtained inside the rotor and from there is directed to the first row of turbine blades. As disclosed in <FIG>, the rotor comprises a plurality of adjacent disks wherein each couple of adjacent disks (at least between the compressor and the turbine) form a cooling volume. In this example, the swirled spilled air is fed to a rotor volume substantially arranged in a middle position of the rotor and from there via axial channels flow towards the rotor disk supporting the first row of blades. A discharge line is provided for feeding the air to the blades from this cooling volume.

According to the disclosure of <CIT>, the annulus extending from the compressor to the turbine is divided in two adjacent sub-annulus volumes divided by a seal. As for the previous example, the downstream end of the downstream sub-annulus is provided with a seal configured for allowing a leakage of the air towards the first row of turbine vanes. This downstream sub-annulus is connected to the plenum by a first swirl line (reference <NUM>) so that the compressed air fed into the plenum by the diffusor can enter the downstream sub-annulus. A downstream discharge line (reference <NUM>) is provided for connecting the downstream sub-annulus to a rotor volume obtained in the rotor disk supporting the first row of turbine blades. Indeed, from this rotor volume the air reached the first row of turbine blades. The upstream sub-annulus is connected to the plenum by an upstream or second swirl line (reference <NUM>) so that the compressed air fed into the plenum by the diffusor can enter the upstream sub-annulus. The upstream end of the upstream sub-annulus is connected to the compressor so that, after cooling the rotor, the air is again introduced in the main flow leaving the compressor.

Thus, in both prior art disclosures above described the diffusor or the plenum are in fluid connection via swirl lines to the annulus. The fact of providing the assembly with these swirl lines involves some drawbacks in terms of mechanical processing required. Moreover, the high numbers of deviations imposed to the air flow between the compressor to the turbine generates an high pressure loss that implies an higher amount of air to be used for cooling.

<CIT> relates to a guide vane element for use in a turbo compressor of such an engine and to a method for cooling components of the engine.

<CIT> relates to gas turbine systems, and more particularly to inducers for supplying cooling medium to various components in a gas turbine system.

<CIT> relates to the technology of gas turbines, in particular to a method for cooling a gas turbine.

<CIT> relates a system for cooling a gas turbine, which is capable of improving the efficiency of a gas turbine by individually supplying cooling air to each of a plurality of turbine disks.

The invention relates to a gas turbine assembly for power plant according to claim <NUM>.

Preferably, the compressor comprises an outlet and a diffuser downstream connected to the compressor outlet. This diffuser is configured for guiding the air leaving the compressor towards a combustor unit. Usually the two last rows of vanes (the last row is called "outlet guide vanes") are configured for forcing the flow along the axial direction. The single annulus of the invention is directly connected to the compressor in an upstream position with respect to the compressor outlet (preferably downstream the last rotating row of compressor blades) and both the diffuser and the plenum are fluidly separated from the single annulus (no line is present between diffuser/plenum and the single annulus). Thus, according the invention the air is fed to the annulus directly spilled from the compressor and not from the diffuser or the plenum downstream the compressor. In this way the air used for cooling is itself provided with a swirl and therefore no additional swirl lines or devices are required for this scope.

Preferably, the compressor outlet comprises two rows of vanes configured for axially guiding the air before leaving the compressor. In this configuration, the single annulus is connected to the compressor in a position directly upstream with respect to these two last rows of vanes.

Preferably, the rotor comprises a plurality of adjacent disks and the cooling volume foregoing mentioned is obtained between two adjacent rotor disks wherein the downstream disk of this couple supports the first row of turbine blades.

Preferably, the single annulus comprises a curved inlet portion upstream connected to the compressor.

The invention has been foregoing described in structural terms. However, the invention is also defined in terms of a method of operating the gas turbine assembly according to claim <NUM>.

This method allows to understand the differences between the invention and the prior art. In the cited prior document the annulus is fluidly connected to the compressor but this connection is used to fed air from the annulus into the compressor and not vice-versa as the present invention.

Thus, as a not limiting list of the advantage of the invention, the cooling of the rotor or rotor disks between the compressor and the turbine are improved and a less amount of air is required for cooling the first row of turbine blades due to a higher swirl preserved from the compressor to the turbine. Indeed, a higher swirl means a lower relative temperature of the air with respect to the rotating parts of the assembly.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims.

The features of the invention believed to be novel are set forth with particularity in the appended claims.

The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:.

In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to preferred embodiments, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention.

Reference will now be made to the drawing figures to describe the present invention in detail.

Reference is made to <FIG> which is a schematic view of a not-limiting example of a gas turbine assembly for power plant that can be improved by the present invention. In <FIG> the gas turbine assembly <NUM> comprises a compressor unit <NUM>, a combustion unit <NUM>, a turbine unit <NUM> and a generator (for simplicity, not shown in the attached figures). The rotating parts of the compressor <NUM>, turbine <NUM> and generator are supported by a common rotor <NUM>, which is housed in a casings <NUM> and extends along an axis A. In <FIG>, the rotor <NUM> comprises a front shaft <NUM>, a rear shaft <NUM> and in between a plurality of adjacent rotor disks <NUM> clamped as a pack by a central tie rod <NUM>. As an alternative, the rotor disks may be welded together. Each rotor disk <NUM> supports a row of blades <NUM>. The casing <NUM> comprises a plurality of stator rows of vanes <NUM> alternated with the rotating rows of blades <NUM>.

Reference is made to <FIG> that is a schematic enlarged view of the portion II of <FIG>. This view refers to the prior art practice. <FIG> discloses a downstream portion of the compressor <NUM> and an upstream portion of the turbine <NUM>. In particular, <FIG> discloses the two last rows of compressor vanes <NUM>, the last row of compressor blades <NUM>, the first row of turbine vanes <NUM> and the first row of turbine blades <NUM>. As known, the two last rows of compressor vanes <NUM> are configured for axially guiding the air flow leaving the compressor. Downstream the compressor <NUM> a diffusor <NUM> is provided for guiding the compressed air towards the combustor. Reference <NUM> refers to a guide pipe configured for guiding part of the compressed air into a plenum <NUM> wherein the air can reach the first row of turbine vanes <NUM> for cooling reason. <FIG> also discloses part of a rotor <NUM> in form of a plurality of adjacent disks. References <NUM> and <NUM> refer respectively to a rotor disk supporting the last row of compressing blades <NUM> and to a rotor disk supporting the first row of turbine blades <NUM>. In the portion between the compressor outlet and the turbine inlet, the rotor <NUM> is coupled to a rotor cover <NUM>. This rotor cover and the corresponding portion of the rotor <NUM> defines an annulus <NUM>, i.e. a volume closed upstream by an upstream seal <NUM> and downstream by a downstream seal <NUM>. The annulus <NUM> is fed by cooling air and these seals <NUM><NUM> are configured for allowing an air leakage towards the last row of compressor vanes <NUM> and downstream the first row of turbine vanes <NUM> respectively for purging and sealing purposes. The cooling air fed in the annulus <NUM> is part of the compressed air passing by the pipe <NUM>. Indeed, between the pipe <NUM> and the annulus <NUM> a swirl line <NUM> is provided for feeding the air to the annulus <NUM> and for imposing to the air a swirl effect. As disclosed in <FIG>, each couple of adjacent rotor disks are shaped to define cooling volumes <NUM>. Reference <NUM> refers to the cooling volume partially obtained in the rotor disk <NUM> supporting the first row of turbine blades <NUM>. Between this cooling volume <NUM> and the upstream cooling volumes <NUM> axially channels are provided <NUM> for allowing the cooling air entering an upstream cooling volume <NUM> to reaches the cooling volume <NUM> and from there the first row of blade <NUM> via a discharge line <NUM>. Reference <NUM> refers to a line connecting the annulus <NUM> to an upstream cooling volume <NUM>.

Reference is now made to <FIG> that is a schematic enlarged view of the portion II of <FIG> duly modified according to the present invention. In this sense the same components disclosed in <FIG> have been represented in <FIG> with the same numerical referral. According to <FIG>, and to the invention, the annulus <NUM> and the diffuser <NUM>/plenum <NUM> are not in fluid connection. Indeed, the annulus <NUM> is fed by compresses air spilled directed from the compressor, in this example directly upstream the last two rows of vanes <NUM> and downstream the last compressor row of blades <NUM>. Preferably, as presented, the inlet portion <NUM> of the annulus <NUM> is curved for minimizing the pressure loss. The cooling volume <NUM> obtained in the rotor disk <NUM> supporting the turbine blades <NUM> is directly fed by air leaving the annulus <NUM> and not coming from the upstream volumes <NUM> as per the previous figure. Indeed, reference <NUM> refers to a discharge line connecting the cooling volume <NUM> to the annulus <NUM>. The first turbine vanes <NUM> are fed with air via the seal <NUM> as per the previous figure.

Finally, <FIG> discloses a different embodiment of a gas turbine not part of the invention. The same elements discloses in <FIG> and <FIG> have been represented with the same numerical referral. The two different independent solutions refer respectively the upstream portion and the downstream portion of the annulus <NUM>, i.e. the gap fed by cooling air obtained between the rotor (in form of a plurality of rotor disks) and the rotor cover. At the downstream portion, the discharge line <NUM> have been removed and the annulus <NUM> has been prolonged up to the first rotor turbine disk where a radial space <NUM> is present between the firs turbine vane row <NUM> and the firs turbine blade row <NUM>. As disclosed the seal <NUM> has been replaced in this radial space <NUM>. In <FIG> the first firs turbine blade row <NUM> is fed by air coming directly from the prolonged portion of the annulus <NUM> via the discharge line <NUM> and not more from the volume <NUM> (that become as the volumes <NUM> of <FIG>). Indeed, in <FIG> the line <NUM> is obtained in the first turbine disk <NUM> connecting directly the prolonged portion of the annulus <NUM> to the firs turbine blade row <NUM>. The second difference at the upstream portion of the annulus <NUM> refer the inlet portion <NUM>. In this case inlet portion <NUM> is no more fed by air directly downstream the last compressor blade row <NUM> but it is fed by air directly downstream the second last compressor blade row <NUM>'. In this case the inlet portion <NUM> is realized in form of a line (i.e. a plurality of holes for instance) obtained in the last rotor compressor disk <NUM>. As foregoing mentioned, these upstream and downstream solutions are independent, i.e. may be together or individually implemented.

Claim 1:
A gas turbine assembly for power plant, the gas turbine (<NUM>) comprising:
- a rotor (<NUM>) having an axis (A);
- a compressor (<NUM>);
- a turbine (<NUM>);
- a rotor cover (<NUM>);
- a single annulus (<NUM>) between the rotor (<NUM>) and the rotor cover (<NUM>);
wherein
the single annulus (<NUM>) is connected upstream to the compressor (<NUM>) for being fed by air spilled from the compressor (<NUM>) and downstream to discharge lines (<NUM>, <NUM>, <NUM>) for feeding the compressor air to the turbine (<NUM>);
characterized in that
a first discharge line (<NUM>) is downstream connected to a cooling volume (<NUM>) obtained inside the rotor (<NUM>) and from there the air is fed to the turbine (<NUM>) via a second discharge line (<NUM>);
wherein the turbine (<NUM>) comprises a first row of vanes (<NUM>); at the downstream end of the single annulus (<NUM>) between the rotor (<NUM>) and the rotor cover (<NUM>) being provided a seal (<NUM>) configured for allowing leakage of air from the annulus (<NUM>) towards a stator-rotor cavity between the first row of turbine vanes (<NUM>) and the first row of turbine blades (<NUM>).