Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2001-12-10
2003-09-09
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S760000, C165S168000, C165S174000
Reexamination Certificate
active
06615588
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an arrangement for cooling a component, in particular for cooling the combustion chamber of a turbomachine, in which at least one cooling duct is configured between a component wall to be cooled and a plate-shaped element at a distance from the wall, the plate-shaped element having a number of through-openings for a cooling medium and the distance between the plate-shaped element and the wall increasing in the flow direction of a cooling medium flowing through the cooling duct and impinging by means of the through-openings onto the wall.
The present cooling arrangement is particularly suitable for use in cooling a gas turbine combustion chamber, in which the cooling ducts are configured between the plate-shaped element and the combustion chamber wall.
BACKGROUND OF THE INVENTION
The wall segments of combustion chambers are exposed to very high temperatures. A sufficiently long life of the combustion chamber wall can only be ensured if this wall is additionally cooled during operation. In known combustion chamber arrangements in gas turbine installations, the combustion chamber wall has a double-walled embodiment so that a cooling medium can be inserted into the cooling duct formed by the intermediate space. In this connection and particularly in the case of gas turbine installations, it is known art to guide the combustion air compressed by the compressor through this gap or cooling duct along the combustion chamber wall before it is mixed with the fuel and introduced into the combustion chamber.
An example of a gas turbine combustion chamber configured in this way may be derived from U.S. Pat. No. 4,339,925. In this combustion chamber arrangement, the cooling duct is configured by means of the intermediate space between a plate-shaped element and the combustion chamber wall, the plate-shaped element in the form of a perforated plate being matched to the outer contour of the combustion chamber in such a way that a cooling duct of constant height is formed by means of a constant distance between the plate-shaped element and the combustion chamber wall. The cooling air penetrates by means of the through-openings provided in the plate-shaped element into the cooling duct and, in the process, meets the combustion chamber wall approximately at right angles. A particularly effective cooling effect is achieved by such impingement cooling.
In the case of a compact construction of the combustion chamber, the cooling air flows along the combustion chamber wall in the direction opposite to that of the hot gases generated in the combustion chamber after the combustion process (counterflow principle). In general, the whole of the mass flow of the air intended for the combustion is available for cooling the combustion chamber wall. The pressure loss along the cooling duct is predetermined by the pressure loss of the burners, i.e. by the pressure loss during the mixing of the fuel and air. For cooling purposes, an attempt is therefore made to make the best possible use of this given pressure difference between the outlet from the compressor and the combustion chamber in the cooling of the combustion chamber wall.
The impingement cooling technique is suitable for cooling of the combustion chamber wall in a particularly efficient manner. Precisely in the case of the employment of such a cooling technique for combustion chambers, however, there are some limitations which impair the efficiency of the impingement cooling. In this connection, an essential limitation is caused by the limited space relationships on the cooling air side at the interface between the combustion chamber and the turbine which abuts it. These limited space relationships require a reduction in the distance between the plate-shaped element (usually configured as a perforated plate) and the combustion chamber wall to be cooled in the direction toward the turbine stage and therefore lead to a reduction in the cooling duct height in this region.
In order to improve the efficiency of the cooling, impingement cooling geometries were described and investigated in L. W. Florschuetz et al., “Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement with Crossflow”, ASME, 81-GT-77, pages 1-10, in order to evaluate their influence on the cooling efficiency. In this work, different ratios of the distances apart of the through-openings in the perforated plate to the diameter of these through-openings and the different ratios of the cooling duct height to the diameter of these through-openings were selected. In all the variants investigated in this work, the diameter of the through-openings and the cooling duct height were constant over the length of the cooling duct.
In the case of these impingement cooling geometries, it is known that the cooling effect decreases in the direction in which the air flows away over the cooling duct. Tests have now shown that this behavior is not observed in the case of a geometry in which the duct height increases in the flow direction of the cooling duct. The reason for this is the pressure distribution along the cooling duct. The pressure difference across the perforated plate increases in the direction in which the air flows away. This has the result that the major part of the cooling air flows through the rear holes—in the direction of the air flowing away—and, in the process, cools particularly well. This, however, again leads to a non-uniform cooling effect over the length of the cooling duct.
A combustion chamber arrangement for solving this problem is described in U.S. Pat. No. 5,388,412. In this, the distance between the plate-shaped element and the combustion chamber wall to be cooled likewise increases in the flow direction of the cooling duct formed. In order to avoid the non-uniform cooling effect, the through-openings are provided with tube-like protrusion elements in this arrangement. These protrusion elements extend at right angles to the combustion chamber wall in the cooling duct and their outlet ends have the same distance from the combustion chamber wall over the whole length of the cooling duct. A more uniform cooling effect can be achieved in this way over the length of the cooling ducts. In this arrangement, it is likewise proposed to appropriately modify the diameters of the through-openings at certain locations on the cooling duct in order to intensify the cooling at these locations.
SUMMARY OF THE INVENTION
The object of the present invention consists in providing an arrangement for cooling a component, in particular the combustion chamber of a gas turbine, which arrangement can be realized in a simple manner and has a uniform cooling performance over the length of the cooling duct.
The object is achieved by means of the arrangement according to claim
1
. Advantageous embodiments of the arrangement are the subject matter of the sub-claims. In the case of the present arrangement for cooling a component, at least one cooling duct is configured between a component wall to be cooled and a plate-shaped element at a distance from the wall. In this arrangement, the plate-shaped element has a number of through-openings for a cooling medium and its shape is matched to the contours of the wall to be cooled. This plate-shaped element, also designated below as perforated plate in accordance with its preferred configuration, is arranged opposite to the wall to be cooled or is fastened to the latter in such a way that the distance between the plate-shaped element and the wall increases in the flow direction of a cooling medium flowing through the cooling duct and impinging by means of the through-openings onto the wall. In a gas turbine combustion chamber cooled on the counterflow principle, the cooling duct height, which is determined by the distance between the plate-shaped element and the wall, therefore decreases in the direction toward the turbine stage. The present arrangement is therefore characterized by the size of the through-openings in the plate-shaped element increasing with increasing distance between the
Alstom (Switzerland Ltd
Belena John F.
Burns Doane Swecker & Mathis L.L.P.
Freay Charles G.
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