TURBO MACHINE WITH AN INNER HOUSING AND AN OUTER HOUSING

Abstract: The invention relates to a turbo machine (1), especially a steam turbine, having a main axis (2), an inner housing (3), an outer housing (4), a top region (5), and a bottom region (6). Between the outer housing (4) and the inner housing (3), a radial gap (7) is formed, which has a narrow part (8) in said bottom region (6).

Description: 1 Description Turbo machine with an inner housing and an outer housing The invention relates to a turbo machine, especially a steam turbine having an inner housing and an outer housing spaced apart, so that a gap is formed between the inner housing and the outer housing. It is known, as described in German patent application DE 35 22 916 Al that during the operation of a turbo machine, especially a steam turbine, the inner housing, the outer housing as well as the turbine rotor elongate to a different ■ amount due to different temperatures acting on these parts of the turbo machine. It is therefore normal practise to compensate the difference in the axial elongation between the housings and the turbine rotor by translation means. As the temperatures acting on the inner housing and the outer housing are also different, there may arise a temperature gradient in the inner housing and outer housing which may lead to different deformations during operation of the turbo machine as well as during cooling down of the turbo machine. U.K. Patent Specification 740 944 relates to thermal turbi- nes, more specially steam turbines, which comprise an internal housing separated from an external housing by a gap. The turbine is driven by a driving medium, a part of which is branched off and passed through the gap between the internal and the external housing. During the operation of the turbine this part of the driving medium acts as a cooling medium for the external housing, so that the hot inner housing is thermally separated from the cold outer housing. Fins are secured on the inner face of the external housing in order to improve the heat transfer on the outer housing. U.S. Patent 5,388,960 relates to a forced-air-cooling apparatus of a steam turbine in a high temperature state just after an operation shut down of the steam turbine. This apparatus serves for save and quick cooling of the turbine. U.S. Patent 3,746,463 relates to a multi-stage axial flow steam turbine having an inner and an outer casing. The inner casing is mounted within the outer casing in such a manner as to limit relative axial movement and allow free relative radial movement between the inner and outer casing, which is caused by changes in temperature. The inner casing therefore is mounted within the outer casing by a plurality of keys and keyways, fitted pins and axial alignment fits, is obtained by tonk and groove portions which locate the inner casing axial- ly with respect to the outer casing and yet allow free radial movement of the inner casing with respect to the outer ca- sing. It is an object of the invention to provide a turbo machine in which thermal deformations of the outer housing are smaller than a critical value. With the forgoing and other objects in view there is provided, in accordance with the invention, a turbo machine, in particular a steam turbine, having a main axis, an inner housing and an outer housing, a top region and a bottom region wherein said outer housing surrounds said inner housing, so that a radial gap is formed, said gap having a narrow part in that bottom region, further comprising a mounting region for mounting said outer housing on said inner housing and a bla- ding region extending along said main axis, whereby said gap extends along said main axis outside said mounting region and at least partially axially overlaps said blading region. The invention relies on the physical effect that during the shut down of a turbo machine the inner housing and the outer housing remain on different temperatures. Due to this difference in temperature a gaseous medium, like steam in the gap (space) between the inner housing and the outer housing is set in a thermal convection motion (temperature-gradient driven flow) directed from the bottom region to the top region of the turbo machine. This may lead to a temperature difference in the outer housing with a higher temperature in the top region as in the bottom region. Such a temperature gradient in the outer housing across the height of the outer housing may lead to a buckling of the outer housing (outer casing) from the top region to the bottom region after turbine trip. Under some critical conditions this may lead to a radial displacement of the inner housing and a rubbing of the moving blades of the rotor on the inner housing (inner casing) . The narrowing of the gap between the inner housing and the outer housing in the bottom region leads to a better transmission of heat from the inner housing to the outer housing as well as to a higher convection rate, especially a turbulent convection, in the top region. This leads to a super linear temperature profile across the height of the outer ca- sing. This means that the temperture profile in the outer casing has a temperature gradient (change of temperature per unit length ΔT/ΔH) in the bottom area which is greater than 1. The thermal stresses in the outer casing are therefore reduced, so that the chance of buckling of the outer casing along the main axis is reduced. In accordance with another feature of the invention, the inner housing extends in said gap towards that outer housing, so that the gap, the space between inner housing and outer housing, is reduced along the main axis. The invention is also applicable for a turbine, in particular a steam turbine, having a blade career for the guide blades (vanes) instead of an inner housing or in addition to an inner housing. In accordance with a further feature of the invention, a heat contacting extra mass is thermally coupled with said inner housing and situated in said bottom region. The extra mass may consist of the same material as the inner housing. It is possible that this extra mass is part of the inner housing, especially cast as one piece together with the inner housing, welded to the inner housing or fastened to the inner housing in a suitable way. In accordance with again an added feature of the invention, said extra mass or extra part of the inner housing may have approximately a triangular cross section, a rectangular cross section or another cross section which is suitable, according to the special geometry of the inner housing and outer housing as well as the physical parameters for the operation of the turbo machine. The extra mass or extra part of the inner housing is pre- ferably directed along said main axis and provides a rib or fin on the inner housing. In accordance with again an additional feature of the invention, a compensating mass is situated in said top region, especially connected to the inner housing. This compensation mass leads to a contribution of mass of the inner housing, so that the center line of mass coincides with the main axis of the turbo machine. The compensation mass may have a similar shape as the extra mass so that a symmetry of the inner hou- sing will be established. The compensating mass is also preferably directed along the main axis. It is also in principle possible that the outer housing extends towards said inner housing in said bottom region to narrow the gap between inner housing and outer housing. The turbo machinery is preferably a high pressure steam turbine or an intermediate pressure steam turbine. In accordance with again a further feature of the invention, the inner housing comprises two housing parts which are separable from each other along a horizontal plain. Each housing part has preferably a horizontal radially outward directed flange. The housing parts are preferably mechanically fixed together through these flanges. For fastening the flanges together, commonly nuts and bolts or the like can be used. The- se flanges also reduce the gap between the inner housing and the outer housing in a horizontal plain between the top region and the bottom region. A convectional flow of steam from the bottom region to the top region or viceversa is in this case restricted. Under these circumstances a narrowing of the gap in the bottom region due to said narrow part is most effective, in the sense that heat transmission between inner housing and outer housing is improved and the temperature in the outer housing in the bottom region is raised. Although the invention is illustrated and described herein as embodied in a steam turbine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalence of the claims. The invention may be used for all kinds of turbo machines having inner and outer housing, like steam turbines and gas turbines and the like. The construction of the invention, however, together with ad- ditional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings . In the drawing the parts of a turbo machine which are useful to understand the invention are described in detail and those parts commonly used for a turbo machine are not described in detail . The drawing is partly schematic and partly not in scale. It is shown in FIG 1 a sectional view along the main axis of a intermediate steam turbine, FIG 2 different temperature profiles across the height of the outer housing, FIG 3 the thermal deformation along the main axis due to the temperature gradients of figure 2, FIG 4 and 5 a cross sectional view through the steam turbine of figure 1. Referring now to the figures in detail, figure 1 shows a sectional view through a high pressure steam turbine 1 along a main axis 2 of said steam turbine 1. Said steam turbine 1 comprises a turbine rotor 15 which carries the moving blades 17. The turbine rotor 15 is axially and circumferentially surrounded by an inner housing 3 which carries the guide blades 18. Moving blades 17 and guide blades 18 (vanes) are ar- ranged in a blading region 24, which extends along the main axis 2. Said inner housing 3 is surrounded by an outer housing 4. During operation of the steam turbine 1 intermediate pressurized steam flows from an inflow region 13 to an outflow region 14 between which the guide blades 18 and moving blades 17 are situated. The outer housing 4 is mounted on the inner housing 3 in a mounting region 20 located near the inflow region and in a mounting region 20 located near the outflow region. The inner housing 3 comprises two housing parts 3A, 3B. The housing part 3B is located in a bottom region 6 of the steam turbine 1 and the housing part 3A is located in a top region 5 of the steam turbine 1. Between the inner housing 3 and the outer housing 4 a radial gap 7 remains, which gap 7 has a circular ring-like cross section and extends along the main axis 2. The gap 7 is narrowed in the bottom region 6 (narrow part 8, see figure 4, 5) along said main axis 2 at least partially axially overlapping said blading 7 region 24 outside, in particular in between, said mounting regions 20. In figure 2 three different temperature profiles 21, 22, 23 are shown across the height of the outer housing 3. The height of the outer housing 3 is counted from the bottom of the outer casing 3 to the top of the outer casing 3. The height of the outer casing 3 at the top is called H op an ^ the height of the outer casing 3 at the main axis 2 is called H2. The temperature difference between the bottom and the top of the outer casing 3 is called ΔT. The temperature profile 22 is a linear temperature profile. The temperature profile 23 is a super linear temperature profile which means that the temperature difference between bottom and main axis 2 is greater than the temperature difference between main axis and top. Temperature profile 21 is sub-linear, which means that the temperature difference between bottom and main axis 2 is smaller than the temperature difference between main axis 2 and top of the outer casing 3. These temperature profiles lead to a different buckling of the outer casing 3 along the main axis 2. Figure 3 shows the result of a numerical calculation of the buckling of the outer casing 4 for the temperature profiles shown in figure 2. In figures 4 and 5 a cross sectional view through the steam turbine 1 is shown. The inner housing 3 comprises two housing parts 3A, 3B which are fitted together on a horizontal plain 11. Each housing part 3A, 3B has two flanges 12A, 12B which are situated opposite to each other. The outer casing 4 has a circular ring-like cross section. The inner housing 3 (inner casing) has a circular cross section with radially outward directed fins. Two of these fins are formed by the horizontal flangees 12A, 12B. Vertically directed fins are formed by an extra mass 9 which is located in the bottom region 6 of the steam turbine 1. A further vertical fin is formed by a compensation mass 10 located in the top region 5 of the steam turbine 1. Between the outer housing 4 and the inner housing 3 a ring-like radial gap 7 remains. This gap 7 is narrowed in the region of the horizontal plain 11 by the flangees 12A, 12B. Between the outer casing 4 and the flangees 12A, 12B a horizontal narrow part 19 of the gap 7 is provided. A further narrow part 8 of the gap 7 is formed by the extra mass 9 which extends in the gap 7 towards the outer casing 4. In the embodiment according to figure 4, all fins (extra mass 9, compensation mass 10 and flangees 12A, 12B) have approximate- ly a rectangular cross section. Compensation mass 10 and extra mass 9 extend along the main axis at least partially outside said mounting regions 20 (mounting devices) and axially overlapping (at least partially) said blading region 24. In figure 5 the extra mass 9 has approximately a triangular cross section. It is also possible to provide a compensation mass 10 also having approximately a triangular cross section. During shut down and cooling of the turbo machinery 1 a natu- ral convection of gaseous medium, steam, in the gap 7 is started. Due to the extra mass 9 heat from the inner casing 3 is transmitted to the outer housing 4 in such an amount that natural convection occurs also in the gap between the narrow part 8 and the horizontal narrow part 19. Due to this con- vection heat is also transferred to the outer housing 4 so that the temperature T on the inner surface 25 of the outer housing 4 is increased in the region between narrow part 8 and the horizontal plain 11. The temperature of the inner housing 3 on the outer surface 24 does not change very much on the outer surface 24.

Claims: Claims 1. Turbo machine (1), in particular steam turbine, having a main axis (2), an inner housing (3), an outer housing (4), a top region (5) and a bottom region (6), a mounting region (20) for mounting said inner housing (3) on said outer housing (4), a blading region (24) extending along said main axis (2), said outer housing (4) surrounding said inner housing (3) so that a radial gap (7) is formed, said gap (7) ha- ving a narrow part (8) in said bottom region (6) and extends along said main axis (2) outside that mounting region (20) partially overlapping said blading region (24) in the direction of said main axis (2) . 2. Turbo machine (1) according to claim 1, in which said inner housing (3) extends in said gap (7) towards said outer housing (4) to form said narrow part (8) . 3. Turbo machine (1) according to one of the preceeding claims having an extra mass (9), which is heatconducting, thermally coupled with said inner housing (3) and situated in said bottom region (6). 4. Turbo machine (1) according to claim 3 in which said extra mass (9) has approximately a triangular cross-section, a rectangular cross-section or the like. 5. Turbo machine (1) according to claim 3 or 4 in which said extra mass (9) is directed along said main axis (2) . 6. Turbo machine (1) according to one of the preceeding claims in which a compensating mass (10) is situated in said top region (5), especially connected to said inner housing (3) . 10 7. Turbo machine (1) according to one of the preceeding claims in which in said bottom region (6) said outer housing (4) extends towards said inner housing (3). 8. Turbo machine (1) according to one of the preceeding claims being a high pressure steam turbine or an intermediate pressure steam turbine. 9. Turbo machine (1) according to one of the preceeding claims in which said inner housing (3) comprises two housing parts (3A, 3B) , said housing parts (3A, 3B) being separable from each other along a horizontal plain (11). 10. Turbo machine (1) according to claim 9 in which each housing part (3A, 3B) has an horizontal radially outward direc- ted flange (12A, 12B) .

Inventors: CRANE LAURENCE, GOBRECHT EDWIN, HANNON JOE, SIMON VOLKER, CRANE, LAURENCE, GOBRECHT, EDWIN, HANNON, JOE, SIMON, VOLKER
Applicants: CRANE LAURENCE, GOBRECHT EDWIN, HANNON JOE, SIEMENS AG, SIMON VOLKER, CRANE, LAURENCE, GOBRECHT, EDWIN, HANNON, JOE, SIEMENS AKTIENGESELLSCHAFT, SIMON, VOLKER
Application year: 1999
Main classification: F01D25
IPC codes: F01D25