Method for cooling a gas turbine and gas turbine for conducting said method

Abstract

A method is disclosed for cooling a gas turbine having a turbine, wherein a rotor, which rotates about a machine axis, carries a plurality of rotating blades, which are mounted by blade roots and extend with their airfoils into a hot gas path of the gas turbine. The rotor is concentrically surrounded by a turbine vane carrier carrying a plurality of stationary vanes, whereby the rotating blades and the stationary vanes are arranged in alternating rows in axial direction. An extended lifetime with external cooling is achieved by providing first and second cooling systems for the turbine.

Claims

1. A method for cooling a gas turbine, the gas turbine including a compressor, a turbine, and a rotor, the method comprising: passing a first flow of cooling air through a high pressure cooling air channel that extends from an exit of the compressor; passing the first flow of cooling air, after the first flow of cooling air has passed through the high pressure cooling air channel, to a first bore of a heat shield provided on the rotor opposite to a plurality of stationary vanes of the turbine, thereby cooling the heat shield; cooling airfoils of rotating blades of the turbine using the first flow of cooling air after the first flow of cooling air has passed through the first bore of the heat shield; passing a second flow of cooling air through a low pressure cooling air channel that is connected to the compressor at a location that is upstream from the exit of the compressor and, as the second flow of cooling air passes through the low pressure cooling air channel, cooling the rotor using the second flow of cooling air; passing the second flow of cooling air to a second bore of the heat shield after the second flow of cooling air has passed through the low pressure cooling air channel, thereby further cooling the heat shield, wherein the heat shield is connected to the rotor via a first fir tree part and a second fir tree part, the first fir tree part and the second fir tree part being separated by a gap, wherein passing the second flow of cooling air to the second bore comprises passing the second flow of cooling air through the gap and into the second bore; cooling the blade roots of the rotating blades using the second flow of cooling air of the low pressure cooling air channel after the second flow of cooling air has passed through the second bore of the heat shield; and wherein the low pressure cooling air channel is separate from the high pressure cooling air channel and is positioned so that, in a radial direction, the low pressure cooling air channel is closer to a machine axis about which the rotor rotates than the high pressure cooling air channel, the second flow of cooling air passing through the low pressure cooling air channel has a temperature that is lower than a temperature of the first flow of cooling air passing through the high pressure cooling air channel, and the second flow of cooling air passing through the low pressure cooling air channel has a pressure that is lower than a pressure of the first flow of cooling air passing through the high pressure cooling air channel.

2. The method of claim 1, wherein the low pressure cooling air channel reduces a temperature of the cooling air passing therethrough.

3. The method of claim 1, wherein the compressor has multiple stages and the low pressure cooling air channel is connected to an intermediate stage of the compressor upstream of a last stage of the compressor, the exit of the compressor being in fluid communication with the last stage of the compressor.

4. The method of claim 1, wherein cooling the rotor using the second flow of cooling air comprises cooling a drum of the rotor using the second flow of cooling air prior to the second flow of cooling air passing through the second bore of the heat shield.

5. The method of claim 1, further comprising: using a radial turbine of the low pressure cooling air channel to reduce the temperature of the second flow of cooling air passing through the low pressure cooling air channel and to reduce the pressure of the second flow of cooling air passing through the low pressure cooling air channel prior to cooling the blade roots using the second flow of cooling air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows part of a gas turbine with rows of rotating blades and stationary vanes, which are exposed to hot gas from an adjacent combustor and are cooled by a cooling scheme according to an embodiment of the invention;

(3) FIG. 2 shows a single rotating blade being cooled by two separate cooling air flows of different pressure and temperature according to an embodiment of the invention;

(4) FIG. 3 shows a view of a divided cooling air supply from a compressor to the turbine according to an embodiment of the invention;

(5) FIG. 4 showssimilar to FIG. 3a view of a divided cooling air supply from a compressor to the turbine using a radial turbine (FIG. 4b) for the low temperature, low pressure flow according to another embodiment of the invention;

(6) FIG. 5 shows the supply of both kinds of cooling air to the first row of rotating blades by means of a special heat shield upstream of said blades according to a further embodiment of the invention; and

(7) FIG. 6 shows in a perspective view (FIGS. 6a and 6c) the design of a heat shield according to FIG. 5, and the two separated cooling air paths within said heat shield (FIG. 6b).

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

(8) As shown in FIG. 1, the present application focuses on the cooling within the turbine section 15 of a gas turbine engine 10, which is enclosed by a casing 14. The cooling is split into two distinct systems A and B: A high pressure cooling system A is used to feed the blades 16 and vanes 17 and the turbine vane carrier (TVC) 13. A low pressure cooling system B is isolated through high pressure seals from the high pressure cooling system A and the hot gas path through the turbine section 15.

(9) The low pressure cooling system B focuses on cooling the rotor 11 and the blade fir trees (blade roots 37 in FIG. 2). The rotor 11 and rotor fir trees 37 require low temperature air but do not require high pressure air. In contrast, the blades 16 and vanes 17, i.e. their airfoils 36 (FIG. 2), require high pressure air but are not as sensitive to the temperature of the air as the rotor 11. This system enables considerably more favourable operating conditions for the heavily loaded fir trees 37 of blades 16.

(10) The respective cooling concept thus employs the primary high pressure air system (A) to cool the blades 16 (airfoils 36) and turbine vane carrier 13, with the inclusion of a secondary isolated cooling system (B) that pumps air of a lower temperature and pressure along the rotor core (11) to the turbine blade fir trees (37) and vane heat shields (e.g. 34a in FIG. 3).

(11) FIG. 2 illustrates a detailed view of how the two systems are split at the blade level of a rotating blade 17. One system focuses on the blade airfoil 36 where high pressure cooling air HCA of higher temperature is introduced below the platform of the blade 17 and enters the airfoil 36 exits the blade as leakage air LA and is used for film cooling (high pressure), while the second system takes care of the temperatures within the rotor 11 and rotor fir trees (blade root 37) and receives low pressure cooling air LCA of lower temperature through a low pressure cooling air channel 18, which low pressure cooling air LCA exits through a cooling air vent 19.

(12) FIG. 3 illustrates one embodiment of the proposed cooling scheme: Air, at a low pressure and temperature, is extracted from a compressor 20a of a gas turbine 10a at one of the earlier compressor stages, is subsequently passed through the rotor 11a in a low pressure cooling air channel 21a, reducing the temperature further due to the change in radius, and is directed towards the rotor turbine 15a and rotor turbine fir trees of rotating blades 17a (first row) and 26a (second row) through branches 24a and 25a after passing a pre-swirler 23a. In addition, heat shield 34a of second row vane is cooled by this air.

(13) This cooling scheme enables fir tree survival under heavily loaded operating conditions. At the compressor end (20a), part of the (high pressure) air is directed through high pressure cooling air channel 22a, which is farer from machine axis 35 in radial direction than low pressure cooling air channel 21a, towards the blades 17a of the first row (blade one) and can be employed to prevent hot gas ingestion, or tuned to be of sufficient magnitude to have the focused job of cooling turbine blade one (its airfoil) entirely.

(14) FIG. 4a illustrates a flow configuration in a gas turbine 10b similar to FIG. 3, taking air from the end of compressor 20b through a radial turbine 38 (FIG. 4b) to cool the rotor drum (11b) and turbine fir trees of first and second row blades 17b and 26b.

(15) The change in radius and the radial turbine 38 reduce the fluid temperature and pressure of the air, which air cools the rotor drum (11b) and subsequently passes through a pre-swirler 23b before entering branches 24b and 25b and cooling the blade fir trees. The second flow path (high pressure cooling air channel 22b) takes air and prevents hot gas ingestion at vane one 16b and blade one 17b giving some redundancy to the seal in this location. This secondary flow could be tuned to have the focused job of cooling blade one 17b entirely.

(16) FIG. 5 illustrates a gas turbine 10c with compressor 20c and turbine section 15c with a cooling scheme similar to that of FIG. 3, but including a rotor heat shield 28 that is placed before the first blade of turbine 15c. High pressure cooling air is extracted at the end of compressor 20c and supplied to the heat shield 28 through high pressure cooling air channel 22c at rotor 11c. Low pressure cooling air flows from an earlier compressor stage through low pressure cooling air channel 21c and rotor cavities 27a,b to heat shield 28. Heat shield 28, which can be cast out of advanced materials reducing the weight, provides separate flow paths (31, 32 in FIG. 6b) for the high and low pressure cooling air flows so that the fir tree or blade root 37 and airfoil 36 of the first blade can be cooled separately.

(17) FIGS. 6a and 6c provide a more detailed look at one of the possible configurations of such a heat shield 28. The heat shield 28 is attached to the rotor (11c in FIG. 5) via a fir tree 30 in a fashion similar to the blade fixations. Above fir tree 30 a triangular body 29 with a slant 33 contains two bores or flow paths 31, 32 for the high pressure and low pressure cooling air, respectively. The fir tree 30 is axially divided into two parts 30a and 30b, which are separated by a gap. Through this gap the low pressure cooling air enters flow path 32. Flow path 31 has its entrance in first part 30a of fir tree 30.

(18) Thus, two internal flow paths 31, 32 are available within the heat shield 28one (32) for the low pressure low temperature air and a second bore (31) that directs the high pressure high temperature air for the blade (airfoil) cooling. While one segment of the rotor heat shield is shown, said heat shield could comprise a number of segments in one piece.

(19) Characteristic features and advantages of the present solution are: Employment of two pressure sources to decouple the hot gas path cooling (of the blades and vanes specifically) from the cooling requirement of the rotor and the attachment (fir trees) of said blades and vanes to the rotor; The lifetime of the attachment areas, the fir trees, are highly dependent on the temperature and the load of the blades; enabling a reduced temperature at the fir trees allows for larger lifetime values, and a more robust product, that can operate under a wider range of operational configurations; The solution can enable rotor cooling without the requirement of an external cooler.

LIST OF REFERENCE NUMERALS

(20) 10,10a-c gas turbine 11,11a-c rotor 12 combustor 13,13a,b turbine vane carrier (TVC) 14 casing 15,15a-c turbine 16,16a,b (first) vane 17,17a-c (first) blade 18 low pressure (LP) cooling air channel 19 cooling air vent 20a-c compressor 21a-c low pressure (LP) cooling air channel 22a-c high pressure (HP) cooling air channel 23a,b pre-swirler 24a,b branch 25a,b branch 26a,b (second) blade 27a,b cavity 28 heat shield 29 body 30 fir tree 30a,b fir tree section 31,32 flow path (bore) 33 slant 34a,b vane heat shield 35 machine axis 36 airfoil 37 blade root (e.g. fir tree) 38 radial turbine A,B cooling system LA leakage air HCA high pressure cooling air LCA low pressure cooling air