Rotary kinetic fluid motors or pumps – Casing and spaced housing with space vented to working fluid
Reexamination Certificate
1998-10-13
2001-04-10
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Casing and spaced housing with space vented to working fluid
C415S001000, C415S220000, C415S214100
Reexamination Certificate
active
06213710
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method and an apparatus on a turbomachine with an outer casing and an inner casing or blade carrier for thrust compensation. In particular, the area of application of the invention is in the field of turbo engines of pot-type construction, where a pressure of a fluid flowing through the turbomachine causes an axial force in the longitudinal direction of the shaft, at least on the inner casing.
It is known that, in the case of turbomachines with a high internal pressure, the casing is divided into an inner casing and an outer casing. A multi-channel casing of a steam turbine for high steam pressures and steam temperatures is described in Published, Non-Prosecuted German Patent Application DE 2 218 500 A, corresponding to U.S. Pat. No. 3,844,675. In the present configuration of the high-pressure turbine of pot-type construction, live steam enters the inner casing at a high pressure. After an expansion of about 20% of the total pressure drop of the part-turbine, the steam is passed through holes into the outer casing and thus compresses the inner casing in the region of the joints in the course of its further expansion. In subcritical steam conditions, the configuration with a blade carrier is chosen. Here, the full live-steam pressure is present in the space between the inner casing and the outer casing and thus presses the two halves of the carrier together. In the rest of the description, the term “inner casing” also includes the blade carrier in all cases. Given their superimposition, the pressures acting on various surfaces also ensure a resultant thrust on components, and this has to be absorbed by corresponding devices on the inner casing and/or outer casing and/or on the shaft. For this purpose, it is furthermore known for the interspace between the inner casing and the outer casing to be sealed off from the outlet side of the fluid flowing through the turbomachine, so that the pressure difference between the inlet and the outlet has to be accepted by the inner casing, while the outer casing has to withstand the outlet pressure on the outflow side and the pressure between the outer and inner casing relative to atmospheric pressure on the inflow side. The pressures present in the various spaces of a turbomachine ensure high axial forces, which must be transmitted via corresponding devices such as, for example, bayonet rings, threaded rings, Uhde-Brettschneider fasteners or screwed fastenings, to the outer casing or other suitable devices. In addition to possible large deformations, the forces also give rise to high surface pressures on corresponding supports.
The Published, Non-Prosecuted German Patent Application DE 2 218 500 A, for example, discloses a multi-shell casing of a steam turbine for high steam pressures and steam temperatures. An inner shell is clamped against the outer casing by a supporting ring and thus fixed axially. U.S. Pat. No. 3,754,833, in turn, and its priority document, German Patent DE 20 54 465 B2, describes a device for mounting and centering of shaft seal housings on the outer casing shells of turbomachines in a manner which allows thermal movement in a radial and concentric fashion. The turbine illustrated there has a pot-type casing with a joint normal to the axis. An inner casing carrying the fixed blades is inserted into the pot-type casing at a bearing and centering location. This centering location is formed by an Uhde-Brettschneider fastener. In the region of the shaft lead-throughs through the pot-type casing there are shaft seal housings on which sealing covers are mounted. Bypass passages in the inner casing serve for axial thrust compensation.
The constructional outlay in the case of turbomachines for absorbing the axial forces is, as explained above, very high overall. Since the efficiency of a turbomachine is greatly influenced by flow losses, the thrust forces must furthermore be absorbed in such a way that, given corresponding thermal expansions of the shaft and of the inner and outer casing, the radial gaps at the blade ends are as small as possible.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and an apparatus for thrust compensation on a turbomachine which overcomes the above-mentioned disadvantages of the prior art methods and devices of this general type, which compensate for axial forces in the longitudinal direction of a shaft.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for providing an axial thrust compensation on a turbomachine, which includes: providing a turbomachine having an outer casing, a shaft, and an inner casing with an exterior region, a part of the exterior region of the inner casing defining at least one first area having two partial areas; separating the two partial areas with at least one separating means for providing a compensating axial thrust; and subjecting the turbomachine to a fluid flow having a pressure flowing through the turbomachine causing an axial force in a longitudinal direction of the shaft acting at least on the inner casing, subjecting each of the two partial areas of the at least one first area to different pressures for generating the compensating axial thrust, and a separation between the different pressures brought about by the at least one separating means.
The invention provides that in at least one first area of the exterior of a part of the inner casing is divided for axial thrust compensation into two partial areas for axial thrust compensation, each of which is subjected to a different pressure. The separation between the two pressures being brought about by at least one means, in particular a seal. The exterior of a part of the inner casing is preferably subjected to a pressure for axial thrust compensation that is at least as great as the outlet pressure of the fluid, and preferably approximately as great as the inlet pressure.
In an advantageous embodiment of the invention, the pressure for axial thrust compensation counteracts the axial force of the outlet pressure on the inner casing. The superimposition of the two pressures results in a reduced resultant pressure and this thus causes less thrust. The axial thrust compensation can be carried out, in particular, at the inner casing of the turbomachine. This ensures that the high constructional outlay required hitherto for fixing the inner casing can be reduced. The surface pressures occurring at the fixing elements are therefore lower and hence also lead to less severe deformation. In an advantageous development of the invention, the pressure on the outer part of the inner casing is set in accordance with the operating conditions, for example full load or part load. The axial thrust occurring at the inner casing can then be set by appropriate control of the pressure.
In addition to subjecting an outer part of the inner casing to a pressure for axial thrust compensation, the limitation of the dimensions of the outer part is furthermore carried out by the suitable means, preferably a seal. As a result, the axial thrust compensation at the inner casing can be influenced not only via the pressure but also via the effective area available to the pressure for the formation of an axial force. The effective area, as a first area, is divided by the means into the two partial areas. The effective area preferably includes at least one part of the outer end face of the inner casing. Depending on the construction of the machine, there is therefore the possibility of suitable dimensioning of the outer part of the inner casing for axial thrust compensation, in order to keep the thrust as small as possible. In accordance with the respective steam parameters of a part-turbine, the axial thrust can likewise be set by variation of the areas, defined by the diameter of one or two I-ring seals. The seal itself is thus subjected to pressure and, in particular, subjected to loading. By virtue of the seal, it is also possible for the respective pressure act
Greenberg Laurence A.
Lerner Herbert L.
Look Edward K.
Siemens Aktiengesellschaft
Stemer Werner H.
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