The combustion device according to the present invention is described in the following in connection with a combustion chamber for a gas turbine. However, the combustion device is applicable also to combustion chambers for other purposes.

Traditionally, such gas turbine combustion chambers are defined by a combustion chamber wall having a great number of holes to permit cooling air to enter the combustion chamber and to form a thin cooling air layer on the inside surface of the combustion chamber wall.

However, such introduction of cooling air will reduce the temperature of the combustion gases at the inlet of the turbine, and to compensate for such a temperature reduction, the temperature of the flame is raised, since the efficiency of the gas turbine is determined by the temperature of the combustion gases at the inlet of the turbine. However, if

the temperature of the flame is raised, the formation of NOx is significantly increased. In order to meet the environment requirements, it is consequently desirable to maintain a flame temperature which is as low as possible to keep the NOx-emissions on a low level.

Although, it has been proposed to dispense with the cooling air introduction through the combustion chamber wall, such a solution is not commercialised due to the problems to provide sufficient cooling of the combustion chamber wall.

JP-A-09041991 discloses a combustion device comprising a wall arrangement having a first inner wall defining a combustion chamber. A second wall is provided outside the first inner wall and forms a space between the first wall and the second wall. The second wall comprises a great number of holes arranged to direct jets of a cooling fluid onto a main part of the outer surface of the first wall. The first wall comprises inlet apertures for conveying combustion air into the combustion chamber.

SUMMARY OF THE INVENTION The object of the present invention is to provide a combustion chamber, in which the cooling of the combustion chamber wall is improved.

This object is obtained by a combustion device comprising a wall arrangement having a first inner wall member, defining a combustion chamber, and a second wall member, provided outside the first inner wall member and forming a space between the first and second wall members, the second wall member comprising a great number of holes arranged to direct jets of a cooling fluid onto a main part of the outer surface of the first inner wall member, wherein the first inner wall member is essentially continuous. By means of

such jets of a cooling fluid onto almost the complete combustion chamber wall, it is possible to provide full convection cooling of the combustion chamber so that the first wall member may remain essentially continuous or closed, i. e. to dispense with essentially all introduction of air into the combustion chamber except through the burner. The jets of cooling fluid will impinge onto the outer surface and thus provide a high cooling effect in relation to the mass flow. Preferably the first inner wall member may be formed by an essentially continuous metal sheet.

According to an embodiment of the invention, the second wall member comprises a number of outlet passages arranged to convey said fluid away from said space into at least one collecting channel. By such passages, the cooling fluid may be removed from said space in a convenient manner, improving the cooling effect of the jets of cooling fluid. Such a collecting channel may be arranged to convey at least a main part of said fluid to a burner of the combustion chamber in such a manner that the fluid, which contains oxygen, is introduced into the combustion chamber through the burner. In particular, the combustion chamber is essentially closed and comprises an outlet for combustion gases and a number of burners arranged to convey essentially all of said oxygen- containing fluid to the interior of the combustion chamber.

Consequently, all cooling fluid may be employed as combustion air in the combustion zone of the combustion chamber. Furthermore, said collecting channel may be arranged to convey said fluid in a direction essentially opposite to the flow direction within the combustion chamber.

According to a further embodiment of the invention, the second wall member comprises wall portions through which said holes extend and between which said passages extend.

Such perforated wall portions may have an elongated shape and extend essentially in parallel to each other and to the flow direction within the combustion chamber, i. e. in the longitudinal direction of the combustion chamber.

According to a further embodiment of the invention, a number of distributing channels are arranged to distribute said fluid to the holes of the respective wall portion and are each partly defined by such a wall portion. Thus, a distributing channel is provided radially outside each such wall portion, which ensures an efficient supply of the cooling fluid to said space via the holes in the wall portion. Moreover, a number of collecting channels may be provided, wherein the collecting channels and distributing channels extend essentially in parallel to each other. Thereby, the collecting channels and the distributing channels may advantageously extend in such a manner that every second channel is a distributing channel, supplying cooling fluid, and every second channel is a collecting channel, removing used cooling fluid.

According to a further embodiment of the invention, the second wall member comprises a metal sheet shaped in a meander-like manner to form said distributing and collecting channels and to be resilient in a direction perpendicular to the direction of the channels. Such a meander-like or bellow-like metal sheet is flexible in a tangential direction in such a manner that it may expand and thus follow the thermal expansion of the combustion chamber during operation thereof. A normal external overpressure will keep the metal sheet and thus the second wall member tight against the first inner wall member defining the combustion chamber. By means of such a meander-shaped second wall member, inlet passages may be provided to introduce said fluid into the distributing channel and extend in parallel to the direction of the channels, in such a manner

that such an inlet passage extends between every second collecting channel. Preferably, essentially each distributing and collecting channel has a rectangular shape seen in a cross-section perpendicular to the direction of the channels.

According to another embodiment of the invention, said distributing channel comprises a conduit member separated from the conduit member of adjacent distributing channels.

Such a conduit member may be shaped as a separate, longitudinal box, one side wall of which forms said perforated wall portion. Thereby, an inlet opening may be provided in an end area of the conduit member.

Advantageously, the cross-sectional area of said conduit member is decreasing from said inlet opening along the extension of the distributing channel. By such a feature it is possible, if the pressure changes along the combustion chamber, to keep the pressure drop between the distributing channel and the collecting channel essentially constant. Thereby, a third wall member is provided outside said conduit members, wherein said collecting channel is defined by the first and third wall members.

According to a further embodiment of the invention, distance members are provided between the second wall member and the first inner wall member, and arranged to determine the distance from said holes to the outer surface of the first inner wall member. By such distance members, the cooling effect of different parts of the combustion chamber may be adjusted. Thereby, said distance members may be attached to the wall portions and slideable in relation to the first inner wall portion. Consequently, the first inner wall member may be self-supported without any fix, for instance welded, connections to the surrounding second wall member.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is now to be explained in connection with different embodiments, merely described by way of examples, and with reference to the drawings attached.

Fig 1 discloses a longitudinal sectional view of a combustion device according to the invention.

Fig 2 discloses a cross-sectional view along the line II-II in Fig 1.

Fig 3 discloses a cross-sectional view along the line III-III in Fig 1.

Fig 4 discloses a cross-sectional view along the line IV-IV in Fig 1.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS Fig 1 discloses a combustion device comprising a first inner wall 1 defining an inner space forming a combustion chamber 2. The first inner wall 1 comprises a metal sheet having an inner ceramic layer 1', see Figs 2-4. The combustion chamber 2 is intended to produce hot combustion gases for a turbine of a gas turbine plant.

The combustion chamber 2 has an inlet portion supporting a burner 3 which is supplied with combustion air through apertures 4 and with fuel through fuel conduits 5. Moreover, the combustion chamber 2 has an outlet 6 forming the inlet of the turbine. The first inner wall member 1 is essentially continuous in such a manner that the combustion chamber 2 is essentially closed, i. e. essentially all air supplied enters the combustion chamber 2 through the burner 3.

The combustion chamber 2 may have any suitable shape, for instance the combustion chamber 2 may be annular, forming a torus-like space about a rotational axis of a gas turbine

rotor, or combustion chamber 2 may be shaped as a cylinder. In case the combustion chamber is annular, a number of burners may be provided distributed around the rotational axis.

Fig 1 illustrates two embodiments of the invention, a first embodiment is disclosed in the upper part of the Fig 1 and in Fig 2, and a second embodiment is disclosed in the lower part of Fig 1 and in Figs 3 and 4. However, it is to be noted that a single one of these embodiments may be applied to a combustion device, although it is also possible that these different embodiments may be applied to different parts of one combustion device, as disclosed in Fig 1, for instance the first embodiment to the outer periphery of an annular combustion chamber and the second embodiment to the inner periphery of such an annular combustion chamber.

With reference to the first embodiment and Figs 1 and 2, a second wall member 7 is provided and forms a space 8 between the second wall member 7 and the first inner wall member 1. The second wall member 7 comprises a metal sheet plastically bent to a meander-like or bellow-like shape in such a manner that distributing channels 9 and collecting channels 10 are formed, wherein every second channel is a distributing channel 9 and every second channel is a collecting channel 10. Seen in a cross-sectional view, the distributing channels 9 and the collecting channels 10 have an essentially rectangular shape. The metal sheet 7 has wall portions 11, each forming a side wall of such a distributing channel 9 and having a great number of holes or being perforated, as appears from the figures. The wall portions 11 are essentially parallel to the first inner wall member 1 and provided at certain distance from the first wall member 1. Due to the shape of the metal sheet 7, the wall portions 11 are separated from each other in such a manner that an outlet passage 12 is formed between every second wall

portion 11 and distributing channel 9. Each outlet passage 12 connects the space 8 to a respective collecting channel 10. Moreover, an inlet passage 13 is formed between every second collecting channel 10 and connects the surrounding space to the distributing channel 9. As appears from Fig 1, the collecting channels end in a collecting chamber 14 surrounding the burner 3.

The distributing channels 9, the collecting channels 10, the wall portions 11, the outlet passages 12 and the inlet passages 13 all have an elongated shape extending in parallel to each other, to an longitudinal axis x of the combustion chamber 2, and to the main gas flow direction within the combustion chamber 2.

The second wall member 7, i. e. the wall portions 11, is arranged at a determined distance from the outer surface of the first inner wall member 1 by means of distance members 15 provided between the second wall member and the first inner wall member. The distance members 15 are attached to the wall portions 11 and slideable in relation to the first inner wall portion 1. By such a distance members 15, the distance from the holes of the wall portions 11 to the outer surface of the first inner wall member 1 may be maintained on a certain level ensuring a certain cooling effect.

Outside the second wall member 7, a third outer wall member 16 is provided to enclose the second wall member 7, forming a intermediate wall member, so that an intermediate space is formed therebetween. The third wall member 16 comprises at least one inlet opening 17 arranged in a forward part of the combustion device to convey the combustion air into said intermediate space.

In a gas turbine application, combustion air will be supplied, via the inlet opening 17, to said intermediate

space surrounding the combustion device by means of a compressor (not disclosed) in such a manner that the combustion air has a higher pressure than within the combustion device. Consequently, combustion air is forced from the surrounding intermediate space into the distributing channels 9 via the inlet passages 13. From the distributing channels 9, the combustion air is conveyed through the holes of the wall portions 11 into the space 8 in such a manner that the jets of air impinge the outer surface of the first inner wall member 1. From the space 8, the combustion air is conveyed or forced into the collecting channels 10 via the outlet passages 12. The collecting channels 10 convey the combustion air in a direction opposite to the direction of the main gas flow within the combustion chamber 2 into the collecting chamber 14. From the collecting chamber 14, the combustion air is forced into the combustion chamber 2 via the apertures 4 and the burner 3.

Due to the shape of the metal sheet 7, the second wall member 7 has a substantial resiliency in a tangential direction or a direction perpendicular to said direction of the channels 9,10. Thus, the second wall member 7 may expand when the first inner wall member 1 expands due to a raised temperature during operation of the combustion device. In order to maintain the distance members 15 in contact with the outer surface of the first inner wall member 1, a circumferential band or wire in combination with a spring may be arranged around the outer periphery of the second wall member 7.

With reference to the second embodiment, disclosed in the lower part of Fig 1 and in Figs 3 and 4, the third outer wall member 16 is provided outside the first inner wall member 1 in such a manner that said intermediate space is formed therebetween. In the intermediate space, conduit

members 18 are provided separately and at a distance from each other in such a manner that the conduit members 18 form the second wall member 7 defining the space 8 and have a box-like shape and are essentially rectangular seen in a cross-sectional view. Furthermore, the conduit members 18 are elongated and extend in a direction parallel to the longitudinal axis x.

Each conduit member 18 defines a distributing channel 9 and has a side wall forming a perforated wall portion 11 being essentially parallel to the first inner wall member 1 as in the first embodiment. Each conduit member 18 has an open end facing away from the burner 3 and forming an inlet passage 13 for the combustion air, which is forced through the third outer wall member 16 via the inlet opening 17.

The intermediate space, in which the conduit members 18 are positioned, defines a collecting channel 10 between an outer side wall of the conduit members 18 and the inner surface of the third outer wall member 16. The spaces between adjacent conduit members define the outlet passages 12.

The cross-sectional area of each conduit member 18 decreases from the inlet passage 13 along the extension of the conduit member 18.

In the second embodiment of a gas turbine application, combustion air will be forced through the inlet opening 17 into the distributing channels 9 of the conduit members 18.

From the distributing channels 9, the combustion air is conveyed through the holes of the wall portions 11 into the space 8 in such a manner that the jets of air impinge the outer surface of the first inner wall member 1. From the space 8, the combustion air is conveyed or forced into the collecting channel 10 defined by the third wall member 16 via the outlet passages 12 between adjacent conduit members

18. The collecting channel 10 convey the combustion air in a direction opposite to the direction of the main gas flow within the combustion chamber 2 into the collecting chamber 14 in a similar manner as in the first embodiment.

The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims. It is to be noted that if the combustion chamber has an annular shape, each of the first wall member, the second wall member and the third wall member comprises an inner wall part extending around a centre axis and an outer wall part extending around said centre axis concentrically with regard to the inner wall part.