Gas Turbine System The present invention relates to a gas turbine system com ^¬ prising a burner arrangement having a tubular combustion chamber, a turbine and a transition duct connecting the combustion chamber and the turbine, wherein the transition duct is provided with an axially extending cooling air channel.

Gas turbine systems of the above mentioned kind are known in prior art. During the operation, ambient air is compressed and directed towards the burner arrangement. Inside the burn ^¬ er arrangement the compressed air is mixed with fuel, and the created fuel-air-mixture is ignited within the combustion chamber to generate hot combustion gases, which are directed towards the turbine via the transition duct. The turbine ex ^¬ tracts rotational energy from the hot combustion gases and drives a load, such as a generator.

With increasing operating temperatures it is often necessary to cool components of a gas turbine system in order to coun ^¬ teract a limitation of a useful life of the gas turbine sys ^¬ tem. In this context it is known to provide the transition duct with a cooling air channel extending axially substantially over the entire length of the transition duct and hav ^¬ ing multiple inlets and multiple outlets. As used herein the terms "axial" and "axially" refer to directions and orienta ^¬ tions extending substantially parallel to the longitudinal axis of the transition duct. Such a cooling air channel de ^¬ sign has the drawback that the cooling air distribution has a significant uncertainty due to the multiple inlets and out ^¬ lets, which needs to be covered by additional cooling air. However, additional cooling air negatively affects the aim to meet low NOx emissions.

Starting from this prior art it is an object of the present invention to provide a gas turbine system of the above- mentioned kind having an alternative structure contributing to the aim to meet low NOx emissions over a broad load range.

In order to solve this object the present invention provides a gas turbine system of the above-mentioned kind, character ^¬ ized in that the transition duct is provided with a plurality of axially extending cooling air channels, wherein each cooling air channel is provided with one single inlet opened to the outside of the transition duct and with one single outlet opened to the inside of the transition duct. Thanks to this inventive design of the cooling air channels the reliability of the cooling air distribution is significantly improved, whereby the cooling air consumption is reduced. Accordingly, the cooling air channel design of the present invention posi- tively effects the NOx emissions of the gas turbine system while maintaining an effective cooling.

Preferably, the ends of at least some circumferentially neighboring cooling air channels are arranged with an offset in axial direction such that the cooling air channels partly overlap each other when viewed in the circumferential direc ^¬ tion. Such a staggering of the cooling air channels increases the mechanical robustness of the transition duct. According to one aspect of the present invention at least some of the cooling air channels extend substantially over the entire length of the transition duct.

In addition or alternatively at least some of the cooling air channels are arranged consecutively in axial direction. This design is beneficial for cases with higher heat loads.

According to a further aspect of the present invention, at least some of the cooling air channels, which are consecu- tively arranged in axial direction, are aligned with each other . In addition or alternatively, at least some of the cooling air channels, which are consecutively arranged in axial di ^¬ rection, are arranged with an offset in axial direction in relation to at least one circumferentially neighboring cool- ing air channels.

According to yet a further aspect of the present invention at least some of the cooling air channels have different flow cross sections.

At least some of the cooling air channels may have a co-flow arrangement with respect to the combustion gases directed through the transition duct. In addition or alternatively, at least some of the cooling air channels may have a counter-flow arrangement with respect to the combustion gases directed through the transition duct.

By means of choosing the adequate number of cooling air chan- nels, the adequate length, flow cross section and flow direc ^¬ tion for each cooling air channel, and the adequate relative positions of the cooling air channels, it is possible to lo ^¬ cally adjust the cooling efficiency and the mechanical ro ^¬ bustness of the transition duct.

Preferably, the transition duct comprises a three layer bond ^¬ ed panel design, wherein the middle layer is provided with elongated cutouts defining the cooling air channels, and wherein the outer layer and the inner layer are provided with holes defining the inlets and the outlets of the cooling air channels. Such a structure of the transition duct can easily be produced at low costs.

Advantageously the free end of the combustion chamber is in- serted in the transition duct in order to simplify the assembly of the gas turbine system. Further features and advantages of the present invention will become apparent by means of the following description of dif ^¬ ferent embodiments of gas turbine systems according to the present invention with reference to the accompanying drawings. In the drawings

Figure 1 is a schematical view of an exemplary gas turbine system according to an embodiment of the present invention ;

Figure 2 is a schematical view of a transition duct of the gas turbine system shown in figure 1, wherein the transition duct is provided with a plurality of axially extending cooling air channels;

Figure 3 is a schematic cross-sectional view of cooling air channels as shown in figure 2 formed accord ^¬ ing to a second design of the present invention;

Figure 4 is a schematic cross-sectional partial view of cooling air channels as shown in figure 2 formed according to a third design of the present invention;

Figure 5 is a schematic cross-sectional partial view of cooling air channels as shown in figure 2 formed according to a fourth design of the present invention; ;

Figure 6 is a schematic cross-sectional partial view of cooling air channels as shown in figure 2 formed according to a fifth design of the present invention;

Figure 7 is a schematic cross-sectional partial view of cooling air channels as shown in figure 2 formed according to a sixth design of the present invention; Figure 8 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to a seventh design of the present invention;

Figure 9 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to an eighth design of the present invention;

Figure 10 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to a ninth design of the present invention;

Figure 11 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to a tenth design of the present invention;

Figure 12 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to an eleventh design of the present invention;

Figure 13 is a schematic top partial view of cooling air channels as shown in figure 2 formed according to a twelfth design of the present invention; and

Figure 14 is a schematic top partial view of cooling air channels as shown in figure 2 formed accordingly to a thirteenth design of the present invention.

Figure 1 shows a gas turbine system 1 according to an embodi ^¬ ment of the present invention. The gas turbine system 1 com ^¬ prises a multi-part housing 2, a compressor 3 arranged within the housing 2, a burner arrangement 4, which is fixed to the housing 2 and is provided with a combustion chamber 5, a turbine 6 arranged within the housing 2 and a transition duct 7 connecting the combustion chamber 5 and the turbine 6. During the assembly of the gas turbine system 1, the transition duct 7 is connected to the turbine 6. Moreover, the transition duct 7 is adjusted an fixed to the housing 2 by means of a fixture 8. Subsequently the burner arrangement 4 is inserted in the housing through an associated opening of the housing, whereupon the free end of the combustion chamber 5 is entered in the transition duct 7. Afterwards the combustion chamber 5 and the transition duct 7 are adjusted to each other, and the burner arrangement 4 is fixed to the housing 2.

During operation of the gas turbine system 1 the compressor 3 compresses ambient air and directs the compressed air towards the burner arrangement 4 as shown by means of arrows 9 in figure 1. Within the burner arrangement 4 the compressed air is mixed with fuel, whereupon the resulting fuel-air-mixture is ignited and burned within the combustion chamber 5 of the burner arrangement 4. The hot combustion gases are directed through the transition duct 7 towards the turbine 6 as shown by arrows 10 in order to drive the turbine 6 in known manner.

In order to withstand high operating temperatures, the tran- sition duct 7 is provided with a plurality of axially extend ^¬ ing cooling air channels 11 as shown in figure 2. Each cooling air channel 11 is provided with one single inlet 12 opened to the outside of the transition duct 7 and with one single outlet 13 opened to the inside of the transition duct 7, wherein the inlets 12 and the outlets 13 are formed at op ^¬ posing ends of the cooling air channels 11, respectively. In the shown cooling air channel design, most of the cooling air channels 11, which are provided on the hotter upper part of the transition duct 7, extend substantially over the entire length of the transition duct 7 in order to ensure effective cooling. Most of the cooling air channels 11, which are pro ^¬ vided on the colder lower part of the transition duct 7, merely extend over a part of the length of the transition duct 7 to the downstream end of the transition duct 7. Howev- er, please note that this cooling air channel distribution only serves as an example and is not to be understood con ^¬ strictive. It is rather possible to distribute the cooling air channels 11 over the transition duct 7 in a different manner. The ends of circumferentially neighboring cooling air channels 11 are arranged with an offset a in axial direc ^¬ tion, respectively. This staggering of the cooling air channels 11 increases the mechanical robustness of the transition duct 7. The single cooling air channels 11 may be arranged in a co-flow and/or in a counter-flow arrangement with respect to the combustion gases directed through the transition duct 7, as it is explained in more detail below. The transition duct 7 comprises a three layer bonded panel design, wherein the middle layer 14 is provided with elongated cutouts defin ^¬ ing the cooling air channels 11, and wherein the outer layer 15 and the inner layer 16 are provided with holes defining the inlets 12 and the outlets 13 of the cooling air channels 11. In figure 2, the outer layer 15 is not shown in order to illustrate the cooling air channels 11. However, it should be noted that other designs are possible, too, such as a two layer bond panel design, where one of the layers is twice the thickness of the other, where the cooling air channels are machined into the thick layer and the second layer is bonded to it, and where the inlets are formed in one of the layers and the outlets are formed in the other.

Figures 3 to 13 show different cooling air channel designs according to the present invention, wherein the same refer- ence numerals are used to denote same or similar components or features.

Figure 3 shows a second cooling air channel design according to the present invention. According to this first design two of the cooling air channels 11 are arranged consecutively in axial direction and are aligned with each other. By arranging a plurality of cooling air channels 11 consecutively in axial direction the cooling performance is increased. In the case shown the flow direction of the cooling air, which is repre- sented by arrows 17, and the flow direction of the hot gases passing through the transition duct 7, which is represented by arrow 18, is counter flow. Figures 4 and 5 show a third and a fourth cooling channel de ^¬ sign similar to the one shown in figure 3. However, instead of two cooling channels operated in counter flow with respect to the hot gas flow direction there are provided three or ra- ther four cooling air channels 11 operated in counter flow, which are arranged consecutively in axial direction and are aligned with each other. These designs are beneficial for cases with higher heat loads. Figure 6 shows a fifth cooling channel design similar to the one shown in figure 4 with three cooling air channels 11, which are arranged consecutively in axial direction and are aligned with each other. However, in contrast to the design shown in figure 4 the cooling air channels 11 according to the fifth design are operated in co-flow with respect to the hot gas flow direction.

Figure 7 shows a sixth cooling channel design similar to the one shown in figure 5 with four cooling air channels 11, which are arranged consecutively in axial direction and are aligned with each other. However, seen from the left to the right in figure 7, the first, second and fourth cooling air channel 11 are operated in counter-flow, while the third cooling channel 11 is operated in co-flow with respect to the hot gas flow direction. This set up is especially beneficial if the head load in the region between the second and the third cooling air channel 11 is very high. In such regions it can be of advantage to have two inlets 12 close to each other to achieve a high cooling effectiveness.

Figures 8 to 10 show a seventh, eighth and ninth cooling air channel design according to the present invention, wherein the middle layer 14, the outer layer 15 and the inner layer 16, which are arranged above each other, are depicted trans- parently. These figures illustrate, that axially and circum- ferentially neighboring cooling air channels 11 can be pro ^¬ vided in different co- and counter flow arrangements. The de ^¬ sign according to figure 8 shows three rows cooling air chan- nels 11, which are have a co-flow arrangement. The design ac ^¬ cording to figure 9 also shows three rows cooling air chan ^¬ nels 11, wherein, when seen from the left to the right, the cooling air channels 11 of the first and the third row have a co-flow arrangement, and the ones of the second row have a counter-flow arrangement. The design according to figure 10 comprises three rows of cooling air channels, too, wherein the cooling air channels 11 of each row have co- an counter- flow arrangements. This set up is beneficial because the cooling effectiveness in each cooling air channel 11 is highest close to the inlet 12 due to the impingement effect, the inflow effect and the largest driving temperature difference. So with the shown alternating arrangement the most even cool ^¬ ing is ensured.

Figure 11 shows a tenth cooling air channel design according to the present invention, which is similar to the seventh design shown in figure 8. However the cooling air channels 11 arranged in the first row, when seen from the left, have a smaller flow cross-section compared to the cooling air channels 11 arranged in the second and third row.

Figure 12 shows an eleventh cooling air channel design according to the present invention, which is similar to the ninth design shown in figure 10. However, in the first row only two cooling air channels 11 are provided having a dif ^¬ ferent channel pitch than the cooling air channels 11 of the second and third row. Accordingly, the cooling air channels 11 of the first row are not axially aligned with the ones of the second and third row.

Figure 13 shows a twelfth cooling air channel design accord ^¬ ing to the present invention. Circumferentially neighboring cooling air channels 11 are arranged with an offset a in axi- al direction such that the cooling air channels 11 in suc ^¬ cessive rows partly overlap each other when viewed in the circumferential direction as shown by reference numeral b. Such a staggering of the cooling air channels 11 increases the mechanical robustness of the transition duct, which is in particular useful with respect to a three layer bonded panel design of the transition duct 7. Figure 14 shows a thirteenth cooling air channel design according to the present invention similar to the one shown in figure 8, wherein axially neighboring cooling air channels 11 have different length. It should be noted, that the above-described embodiments only serve as examples and are not constrictive. Moreover, it should be noted, that the cooling efficiency and the mechani ^¬ cal robustness of the transition duct 7 can be locally varied by means of choosing the adequate number of cooling air chan- nels 11, the adequate number of rows of cooling air channels 11 in axial direction, the adequate length, flow cross sec ^¬ tion and flow direction for each cooling air channel 11, and the adequate relative positions of the cooling air channels 11, e.g. with respect to staggering and pitch.