Field of the Invention
The invention relates to a heat-shield component which is part of a hot-gas wall to be cooled. The invention furthermore relates to a heat-shield configuration which lines a hot-gas space, in particular a combustion chamber of a gas-turbine plant, and has a plurality of heat-shield components. The invention additionally relates to a heat-shield assembly.
Due to high temperatures which prevail in hot-gas passages or other hot-gas spaces, it is necessary for an inner wall of a hot-gas passage to be constructed in the best possible manner in terms of temperature-resistance. On one hand, high-temperature-resistant materials, such as, for example, ceramics, are suitable for that purpose. The disadvantage of ceramic materials lies both in their great brittleness and in their unfavorable heat and temperature conductivity. A suitable alternative to ceramic materials for heat shields is high-temperature-resistant metal alloys on an iron, chromium, nickel or cobalt basis. However, since the service temperature of high-temperature-resistant metal alloys is markedly below the maximum service temperature of ceramic materials, it is necessary to cool metallic heat shields in hot-gas passages.
One possibility is proposed, for example, in U.S. Pat. No. 4,838,031 to Cramer, dated Jun. 13, 1989. Cramer proposes a panel which is formed of four components and is to be mounted on the inside of a combustion-chamber casing. In that case, a first or top layer facing the hot-gas space is made of a refractory metal, but may also be formed by a ceramic material. That is followed underneath by a second layer of steel-wool-like metallic filaments. Those filaments rest on a relatively large number of column-like supports. Those column-like supports and cavities in between form a third layer. The column-like supports are attached to a fourth metallic layer. The steel-wool-like metallic filaments of the second layer absorb heat energy from the overlying layer forming the inner burner wall and transfer that heat energy to an air flow directed between the column-like supports. In that case, the cavities of the third layer are connected, through passages which lead through the fourth layer and the burner casing, to a space outside the burner, and that space is fed with air through a compressor. The compressed air can pass as a coolant through those passages into the cavity formed by the layers.
In addition, a second type of passage is distributed over a front and center region of the combustion chamber. The air originating from the exterior of the combustion chamber passes through such passages through the combustion-chamber casing and the layered panels into the combustion chamber.
The proposal by Cramer has the disadvantage of causing cool air to flow into the combustion chamber over the entire region of the latter without having participated in the combustion. As a consequence thereof, the temperature at an outlet of the combustion chamber drops.
A heat-shield configuration, in particular for structural parts of gas-turbine plants, is described in European Patent 0 224 817 B1. The heat-shield configuration has an inner lining which is made of heat-resistant material and is composed of heat-shield elements in such a way as to cover the surface. The heat-shield elements are anchored to the supporting structure. Those heat-shield elements are disposed next to one another while leaving gaps for the throughflow of cooling fluid and they are thermally movable. Each of those heat-shield elements has a cap part and a shank part shaped like a mushroom. The cap part is a flat or spatial, polygonal plate body having straight or curved boundary lines. The shank part connects a central region of the plate body to the supporting structure. The cap part preferably has a triangular shape, as a result of which an inner lining of virtually any geometry can be produced by identical cap parts. The cap parts as well as other parts of the heat-shield elements, if need be, are made of a high-temperature-resistant material, in particular a steel. The supporting structure has bores through which a cooling fluid, in particular air, can flow into an intermediate space between the cap part and the supporting structure and can flow from there through the gaps, which are intended for the throughflow of the cooling fluid, into a spatial region, for example a combustion chamber of a gas-turbine plant, surrounded by the heat-shield elements. That cooling fluid flow reduces the ingress of hot gas into the intermediate space.
A wall, in particular for gas-turbine plants, which has cooling-fluid passages, is described in German Published, Non-Prosecuted Patent Application DE 35 42 532 A1. In gas-turbine plants, the wall is preferably disposed between a hot space and a cooling-fluid space. The wall is assembled from individual wall elements and each of the wall elements is a plate body made of a high-temperature-resistant material. Each plate body has parallel cooling passages which are distributed over its surface area and communicate at one end with the cooling-fluid space and at the other end with the hot space. The cooling fluid, flowing into the hot space and directed through the cooling-fluid passages, forms a cooling-fluid film on that surface of the wall element and/or adjacent wall elements which faces the hot space.
In summary, all of those heat-shield configurations, in particular for gas-turbine combustion chambers, are based on the principle that compressor air is utilized as a cooling medium for the combustion chamber and its lining as well as for sealing air.
The cooling and sealing air enters the combustion chamber without having participated in the combustion. That cold air mixes with the hot gas. As a result, the temperature at the outlet of the combustion chamber drops. Therefore, the output of the gas turbine and the efficiency of the thermodynamic process decrease. Partial compensation may be carried out by a higher flame temperature being set. However, that then results in material problems, and higher emission values have to be tolerated. It is likewise a disadvantage with the configurations specified that, in the case of the air fed to the burner, pressure losses result due to the entry of the cooling fluid into the combustion chamber.
International Publication No. WO 98/13645 A1, which was published subsequently to the priority date of the instant application, describes a heat-shield component with cooling-fluid return, having a hot-gas wall to be cooled, an inlet passage for cooling fluid, and an outlet passage for the cooling fluid. The inlet passage is directed towards the hot-gas wall and widens in the direction of the hot-gas wall. The inlet passage is largely surrounded by the outlet passage. The supporting structure is constructed as a twin-wall structure, having an outer wall and an inner wall disposed parallel to and adjacent the outer wall while leaving an intermediate space. In order to permit fastening to the supporting structure, the heat-shield component, at the outlet passage, has a fastening part with which the outlet passage is put onto the outer wall and fastened to the latter. Inside the outlet passage, the outer wall has an opening through which the inlet passage is directed while leaving a gap. The inner wall has a further opening into which the inlet passage is pushed over a short length. Cooling fluid can be fed to the heat-shield component through the inlet passage and discharged through the outlet passage. The inlet passage is covered with a cover wall which has impingement-cooling openings. Cooling fluid fed from the inlet passage can pass through the impingement-cooling opening and strike the hot-gas wall, in the course of which the latter is cooled.