Patent Application
20090232651
The subject matter disclosed herein relates generally to turbines. More particularly, the present invention relates to a gas turbine configuration having an improved mounting arrangement between the inner and outer shells which enables thermal expansion and contraction of the inner shell relative to the outer shell in both the radial and circumferential directions.
In prior U.S. Pat. No. 5,685,693 of common assignee herewith, there is illustrated an industrial gas turbine having inner and outer shells. The inner shell has a pair of axially spaced circumferential arrays of radially outwardly projecting pins terminating in reduced sections having flats on opposite circumferential sides thereof. Generally, cylindrical sleeves project inwardly and about access openings in the outer shell and have threaded bolt holes extending in circumferential directions. Bolts extend through the holes to engage the flats on the sides of the pins. By adjusting the bolts, the inner shell is adjustable externally of the outer shell to locate the inner shell about the rotor axis. During turbine operation, the inner shells may expand or move out of roundness and concentricity with respect to the outer shell when the shells respond to thermal and physical loads. Since turbine efficiency is affected by the roundness and concentricity of the inner shell with respect to the outer shell, this allowed realignment of the shells without disassembling the turbine. Roundness and concentricity determine the gap between the turbine buckets (attached to the rotor) and the bucket shrouds (attached to the turbine shell) which in turn determines the amount of gas that bypasses the bucket. Since no work is extracted from this bypass gas by the bucket, gas turbine performance is inversely proportional to this clearance gap.
This problem was further addressed in U.S. Pat. No. 6,457,936, which is hereby incorporated by reference in its entirety, with an improved mounting arrangement between the inner and outer shells using support pins loaded only in the circumferential or tangential direction. The circumferentially spaced support pins are disposed through access openings in the outer shell and have projections received in recesses of the inner shell to engage the two shells in a manner that supports the inner shell against radial and circumferential movement relative to the outer shell and enables thermal expansion and contraction of the inner shell relative to the outer shell in radial and axial directions. By controlling the thermal expansion and contraction of the inner turbine shell, the clearance gap between the bucket tips and the shrouds is controlled during the operation of the gas turbine, resulting in improved efficiency.
Recent simulations of the support pins, however, show that concentricity and roundness of the inner turbine shell are affected by how the pins initially are gapped during assembly. Specifically, for an inner turbine shell radially supported by multiple support pins, a minimum of at least two pins must support the gravitational loading when the rotor engine is at rest. When the engine starts, the support pins counteract the applied torque generated by the nozzles carried by the inner shell. The two gravitational loaded pins are exposed simultaneously to the gravitational and counteracting torque loadings, which leads to loss of roundness and concentricity when the shells differentially expand during turbine operation. Moreover, one of the pins is exposed to a gravitational loading in the opposite direction as the counteracting torque loading. When the turbine runs, this pin and the next adjacent pin push the inner shell segment between them against each other. Consequently, when the segment of the inner shell expands during operation, this segment becomes pinched between the two pins, which causes the entire inner turbine shell to be eccentric and out of roundness. One way of addressing these problems is to relax the initial gaps of the support pins, but such configuration reduces turbine efficiency.
Simulations also show that the surface profile of the contact line between the pin and the inner shell affects the concentricity and roundness of the inner shell during turbine operation. Accordingly, there remains a need for a more advanced configuration arrangement between the inner and outer shells in advanced gas turbine design.
To mitigate the gravity pin support dilemma, embodiments encompassed by the present disclosure provide a turbine comprising an outer shell, an inner shell connected to and surrounded by the outer shell in generally concentric relation therewith, at least one turbine rotor housed within the inner shell, a plurality of nozzles and shrouds carried by the inner shell, a plurality of connecting elements engaging the inner and outer shells and for aligning the inner shell about the rotor, and at least one compliant support. In a particular embodiment, the connecting elements have circumferentially facing arcuate sides engaging the inner shell along line contacts whose planer faces are directed radially to the rotor centerline.
Embodiments of the present disclosure also encompass a turbine comprising an outer structural shell, an inner shell connected to and surrounded by the outer structural shell in generally concentric relation therewith, wherein the inner shell has a plurality of recesses spaced circumferentially thereabout, a plurality of nozzles and shrouds carried by the inner shell, a turbine rotor housed within the inner shell, wherein the inner shell comprises two radial outward projections protruding in opposite directions along a horizontal split line of the rotor, a plurality of pins engaging between the inner and outer shells to align the inner shell about the rotor, wherein each pin engages each recess with a first circumferential clearance in the direction of the applied torque loading generated by the nozzles and a first circumferential clearance in the direction of the counteracting torque loading to enable differential growth and contraction of the inner shell relative to the outer shell, the outer shell further comprising two brackets to receive portions of the two radial outward projections to provide horizontal support for the inner shell during turbine assembly, wherein each radial outward projection engages each bracket with a second circumferential clearance in the direction of the applied torque loading generated by the nozzles and a second circumferential clearance in the direction of the counteracting torque loading to enable differential growth and contraction of the inner shell relative to the outer shell; and a spring affixed to one of the brackets to maintain the second circumferential clearance in the direction of the applied torque loading of that bracket at greater than about 0 mils.
Embodiments of the present disclosure also encompass a method for configuring a turbine with improved efficiency. The method includes providing an outer shell with at least two brackets, an inner shell with a plurality of recesses spaced circumferentially thereabout, the inner shell connected to and surrounded by the outer shell in generally concentric relation therewith by a plurality of connecting elements, a plurality of nozzles and shrouds carried by the inner shell, a turbine rotor housed within the inner shell, wherein each recess engages each connecting element to maintain a first circumferential clearance in the direction of the applied torque loading generated by the nozzles and a first circumferential clearance in the direction of the counteracting torque loading to enable differential growth and contraction of the inner shell relative to the outer shell in a circumferential direction of the rotor to enable differential growth and contraction of the inner shell relative to the outer shell, engaging the plurality of recesses with a plurality of pins, wherein each recess receives a portion of each pin with a first circumferential clearance in the direction of the applied torque loading generated by the nozzles and a first circumferential clearance in the direction of the counteracting torque loading, engaging two brackets of the outer shell with two radial outward projections of the inner shell protruding in opposite directions along a horizontal split line of the rotor during turbine assembly, wherein each bracket receives a portion of each radial outward projection with a second circumferential clearance in the direction of the applied torque loading generated by the nozzles and a second circumferential clearance in the direction of the counteracting torque loading, and affixing a compliant support to one of the brackets to maintain the second circumferential clearance in the direction of the applied torque loading of greater than about 0 mils.
Other objects, features, and advantages of this invention will be apparent from the following detailed description and claims.
As summarized above, embodiments of the present invention encompass a turbine with an improved turbine efficiency and a configuration method for improving turbine efficiency by reducing the loss of roundness and concentricity of the inner shell with respect to the outer shell when the turbine is in operation.
In particular embodiments the turbine comprises an outer shell, an inner shell connected to and surrounded by the outer shell in generally concentric relation therewith, at least one turbine rotor housed within the inner shell, a plurality of nozzles and shrouds carried by the inner shell, a plurality of connecting elements engaging between the inner and outer shells aligning the inner shell about the rotor, and at least one compliant support.
A particular embodiment of a turbine section is illustrated in
According to an embodiment illustrated in
Those of ordinary skill in the art should appreciate that the turbine may comprise any suitable number of connecting elements. Theoretically, an infinite number of connecting elements would be most desirable; however, those skilled in the art will appreciate that an infinite number of connecting elements is impractical and that the maximum number of connecting elements therefore will depend on the manufacturing and cost considerations. For example, in particular embodiments the turbine comprise any number of connecting elements from two (2) to thirty six (36) more particularly from 4 to 16, and still more particularly from 6 to 10. For example, in a particular embodiment illustrated in
The inner shell 12 may further comprise at least two radial outward projections 35 and 36 protruding in opposite directions from the inner shell. In particular embodiments, the at least two radial outward projections 35 and 36 comprise pins 31 such as those described hereinabove. In a particular embodiment, the radial outward projections 35 and 36 are positioned along the horizontal split line 37 to provide horizontal support for the inner shell 12 during turbine assembly. The outer shell 11 may further comprise at least two support brackets 38 and 39 for receiving portions of the projections 35 and 36, respectively. In a particular embodiment, illustrated in
Those of ordinary skill in the art will appreciate that when the turbine is turned on, the nozzles will generate an applied torque loading on the rotor as well as the inner and outer shells. Not wishing to be bound by any theory, it is believed that the support pins counteract the torque loading to reduce loss of roundness and concentricity of the inner shell with respect to the outer shell. For example, referring to
Using the same example in which the applied torque from the nozzles is counterclockwise, the circumferential clearances 34 and 41 are gaps “in the direction of the applied torque loading” because the clearances are narrowed when the applied torque loading pushes the inner shell against the pins. In one embodiment, the one or more circumferential clearances in the direction of the applied torque loading are configured to be between about 5 mils and about 20 mils during turbine assembly. In another embodiment, the one or more circumferential clearances in the direction of the applied torque loading are configured to be between about 8 mils and about 15 mils during assembly. In yet another particular embodiment, the one or more circumferential clearances in the direction of the applied torque loading are configured to be about 13 mils at assembly.
Generally, the sum of the circumferential clearances 33 and 34 or 40 and 41 (the total circumferential clearance) should be greater than the greatest thermal expansion of the connecting elements 31 and the recesses 20 to prevent these components from binding during engine operation. As such, the range for these circumferential clearances will depend on the size of the particular engine, the particular recess, and the particular connecting element which are being used.
In the embodiments described above, the two radial outward projections 35 and 36 and their respective support brackets 38 and 39 are able to counteract the inertial load of the inner shell 12 during turbine assembly (
For example, referring to
In an alternative embodiment, illustrated in
In alternative embodiments, the connecting element which is exposed to the gravitational and counteracting torque loadings in opposite directions can be repositioned during turbine operation by an external mechanism.
According to particular embodiments, the compliant support comprises a spring, bellows, crest or wave spring, or any other suitable biasing device such as a force displacement device or constant force device (e.g. a pneumatic piston). Those of ordinary skill in the art should appreciate that the material for the compliant support will depend on the application of the turbine, and should take into consideration factors which include, but are not limited to, operating temperature, magnitude of the applied forces, and cyclic loading. Non-limiting examples of suitable materials for the complaint support include ferrous alloys, and non ferrous alloys, including stainless steel, phosphor bronze, and beryllium copper.
It also has been discovered that contact surface profile of the connecting elements with the inner shell affects the concentricity of the inner and outer turbine shells about the rotor axis. In particular embodiments, the support pins 31 illustrated in
According to a particular embodiment, the arcuate surfaces of each side 75 of the support pins 31 bear in line contact along the sides of the recesses of the inner shell in the circumferential direction. The line contact extends in an axial direction. In a particular embodiment, illustrated in
As illustrated in
It will be appreciated that the embodiments of the support pins provided herein enable the inner shell to thermally expand and contract in radial, circumferential and axial directions while maintaining roundness and concentricity about the rotor axis. When the turbine starts, the inner shell may be expanded radially outwardly relative to the outer shell by heating the inner shell. Similarly, upon the inner shell may be cooled to contract relative to the turbine rotor to control bucket to shroud clearances on demand. With the foregoing arrangements of the pins and their configuration, one pin or projection can simultaneously accept the torque loading and the gravitational loadings without pinching the segment of inner shell between the pins or projections. The pin surface contact profile also maintains concentricity of the inner shell relative to the outer shell and to the axis of the rotor. Further, because the recesses are larger in axial dimension than the axial dimension of the ledges and the ledges are located intermediate the recesses, differential growth of the inner shell in an axial direction is not taken up by the support pins.
The invention is further illustrated by the following example, which is not to be construed in any way as imposing limitations on the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggestion themselves to those skilled in the art without departing from the spirit of the present invention and/or scope of the appended claims.
A turbine comprising eight pins circumferentially spaced about the inner shell with two radial outward projections received by two brackets of the outer shell was first configured so that all clearances between pins and recesses and all clearances between brackets and projections were about 6.5 mils at assembly. After running an experiment measuring the temperatures and forces as a function of time, the resulting Fourier coefficients were extracted from the thermal/structural finite element analysis. The turbine was reconfigured so that the clearances in the direction of the counteracting torque loading were closed and the clearances in the direction of the applied torque loading were about 13 mils at assembly. The same experiment was run and the resulting Fourier coefficients were extracted. Comparison of the test results showed a 43 percent improvement of roundness in the second configuration when compared to the first configuration.
It should be understood that the foregoing relates to a particular embodiment of the present invention, and that numerous changes may be made therein without departing from the scope of the invention as defined from the following claims.
