Exhaust steam casing for an expansion turbine with optimized flow divider

Abstract

The invention relates to an exhaust steam housing (1) for an expansion turbine comprising at least an inlet area (3) which is essentially ring-shaped relative to the turbine axis (2), a guide apparatus extending in the direction of flow and comprising a funnel-shaped widening area (4) for deflecting a working fluid flowing through the exhaust housing (1) and an angled, preferably at an angle of approximately 90° to the turbine axis (2) outlet area (5), In the funnel-shaped widening region (4), a circumferential flow divider (6) extending essentially in the main flow direction during load operation is arranged, which divides the funnel-shaped region (4) into a radially outer flow region (7) and a radially inner flow region (8).

Description

[0001] The present invention relates to an exhaust steam housing for an expansion turbine, according to the preamble of independent claim 1.

[0002] Expansion turbines are well-known from the prior art and are widely used in various applications to convert the energy contained in a working fluid into usable mechanical work. A key component of an expansion turbine is the exhaust casing, which has to fulfill several functions: - Flow guidance: The exhaust steam casing directs the working fluid exiting the last stage of the expansion turbine (hereinafter also referred to as steam) to the condenser. It ensures that the steam is directed in the correct direction and at the appropriate speed. - Pressure reduction: The shape of the exhaust steam casing, which usually widens into a funnel shape, further reduces the static steam pressure as it exits the turbine, leading to an increase in turbine power. - Energy conservation: By efficiently directing the steam to the condenser and minimizing flow losses, the exhaust housing helps to ensure that as much of the thermal energy still present in the steam as possible can be used.

[0003] During partial load operation, and especially during load changes while the turbine is running, turbulence and backflow in the exhaust casing area can cause transient aerodynamic excitation of the rotor blades in the low-pressure range, leading to impermissible vibration amplitudes. To reduce these vibrations, it may be necessary to decrease the transient aerodynamic excitation during partial load operation.

[0004] Another problem associated with turbulence and backflow in the exhaust housing is the erosion of the trailing edge of the final stage rotor blades. This occurs when temperatures rise during partial load operation and liquid water is injected into the exhaust section for cooling. The water droplets are then carried by turbulence and can strike the trailing edge, causing damage or wear to the final stage rotor blades.

[0005] To prevent impermissible vibration amplitudes, rotor blades are currently often equipped with damping elements (such as coupling wires, coupling pins, or support wings). These elements dampen the vibration of the rotor blades, but always lead to a reduction in efficiency. To prevent erosion at the trailing edge of the rotor blades, the cooling water in the exhaust housing is used very selectively; however, this only marginally increases the service life. The rotor blades must therefore be regularly inspected and replaced if necessary.

[0006] Based on the prior art, the object of the invention is to provide an evaporation housing which solves or at least reduces the problems described above.

[0007] The problem is solved by the features of independent claim 1.

[0008] Further advantageous embodiments of the invention, which can be used individually or in combination with one another, are the subject of the dependent claims.

[0009] The exhaust steam casing according to the invention for an expansion turbine, comprising at least one inlet region formed in a substantially ring-shaped manner relative to the turbine axis, a guide apparatus adjoining it in the flow direction, and a funnel-shaped widening region for deflecting a working fluid flowing through the exhaust steam casing, and an outlet region arranged at an angle, preferably at an angle of approximately 90°, to the turbine axis, is characterized in that a circumferential flow divider extending substantially in the main flow direction during load operation is arranged in the funnel-shaped widening region, which divides the funnel-shaped region into a radially outer flow region and a radially inner flow region.

[0010] The primary function of the flow divider is to prevent or reduce flow momentum transfer in the partial load range between the outer flow region, with at least partially pronounced axial flow, and the inner flow region, with largely stagnant flow or, due to the suction effect of the low-pressure blade on the hub side in the partial load range, moderate backflow. The flow divider creates a flow separation while maintaining fluidic connection. Any deflection of the flow plays only a minor role in this respect. The flow divider is essentially oriented in the main flow direction (during load operation).

[0011] One embodiment of the invention provides that the flow divider is designed as a conical shell with a constant opening angle. Such a design is particularly simple and cost-effective to manufacture.

[0012] An advantageous embodiment of the invention provides that the flow divider is designed as a conical shell with an opening angle that changes around its circumference. The change in the opening angle preferably takes into account the main flow direction during load operation. For this purpose, in a particularly advantageous embodiment, a bulge or a further conical shell can be provided at the end of the conical shell, following the main flow direction.

[0013] A further embodiment of the invention provides that the flow divider has a varying length around its circumference. The vortex-generating effect is of varying intensity within the flow geometry; thus, in the upper region of a downward-directed outflow, a shorter flow divider would favor the flow. The length is defined here as the length of the flow divider in the direction of the main flow direction.

[0014] Regarding vortex formation in the inner region, it is also beneficial to create a boundary between the inner and outer regions, which induces the formation of a boundary layer on both sides. This effect is beneficial, allowing the flow divider to be made shorter overall or to be interrupted in certain circumferential sections. This limits losses during operation under load.

[0015] Further embodiments and advantages of the invention are explained below using exemplary embodiments. It shows: - Fig. 1: An exhaust housing in axial section according to the state of the art; - Fig. 2: A first exhaust housing according to the invention with a symmetrically designed flow divider; - Fig. 3: A second embodiment of an exhaust housing according to the invention with a flow element whose length changes over the circumference; - Fig. 4: A third embodiment of an exhaust steam housing according to the invention in which a further conical shell with a larger opening angle is arranged at the flow-side end of the flow divider designed as a conical shell.

[0016] The figures represent only a schematic and simplified depiction of the evaporation housing, showing essentially only the components necessary for the invention. Identical or functionally equivalent components are identified by the same reference numerals across all figures.

[0017] Fig. Figure 1 shows an axial section through an exhaust steam casing 1 according to the current state of the art. The exhaust steam casing 1 is designed to direct the steam exiting the last stage 10 of the expansion turbine to a condenser (not shown). The steam flows into the exhaust steam casing 1 through an inlet section 3, formed by the turbine rotor 11 and the exhaust steam casing 1, which is essentially annular in relation to the turbine axis 2. The steam then flows through a guide vane assembly, which extends in the direction of flow and includes a funnel-shaped widening section 4, and is deflected by 90° relative to the turbine axis 2. Finally, the steam exits the exhaust steam casing 1 through the outlet section 5 located in the lower part of the exhaust steam casing 1, heading towards the condenser.

[0018] The funnel-shaped extension 4 of the exhaust steam casing 1 reduces the steam pressure at the turbine exit, thus optimizing condensation. To conserve energy and efficiently direct the steam to the condenser, a flow through the exhaust steam casing 1 with minimal loss is desirable. During partial load operation, and especially during load changes while the turbine is running, turbulence and backflow can occur in the area of ​​the exhaust steam casing 1. This turbulence and backflow cause transient aerodynamic excitations of the rotor blades in the low-pressure section of the turbine, which can lead to unacceptable vibration amplitudes at the final stage rotor blades 12. Another problem associated with the turbulence and backflow in the area of ​​the exhaust steam casing 1 is the erosion of the trailing edge of the final stage rotor blades.This occurs when temperatures rise during partial load operation and liquid water is injected into the exhaust section for cooling. The water droplets are then carried by turbulence and can strike the trailing edge of the final stage rotor blades 12, where they cause damage or wear to the final stage rotor blades 12.

[0019] Fig. Figure 2 shows a first embodiment of an exhaust housing 1 with a flow divider 6. The basic structure of the exhaust housing 1 corresponds to that shown in Figure 2. Fig. 1 described evaporation housing 1, to whose detailed description reference is therefore made here. In contrast to the evaporation housing according to Fig. In the funnel-shaped widening section 4, a circumferential (rotationally symmetrical) flow divider 6 is arranged, extending essentially in the main flow direction during load operation. This divider divides the funnel-shaped section 4 into an outer flow region 7 and an inner flow region 8. The opening angle largely corresponds to the opening angle of the funnel-shaped widening section 4 of the exhaust steam housing.

[0020] The main function of the flow divider 6 is to prevent or reduce the flow momentum transfer between the outer flow region 7, with at least partially pronounced axial flow, and the inner flow region 8, with largely stagnant flow or, due to a hub-side suction effect of the low-pressure blade in the partial-load region, moderate backflow, in the partial-load range. The flow divider 6 ensures flow separation, while maintaining a fluidic connection, i.e., the outer flow region 7 and the inner flow region 8 merge again into a common space. The length of the flow divider 6 can be individually determined; it can extend only over the length of the funnel-shaped widening region 4, or, as in the exemplary embodiment, project beyond it. The length is defined as the direction in the main flow direction.

[0021] Fig. Figure 3 shows a second embodiment of an exhaust housing 1 according to the invention with a flow divider 6 whose length varies around its circumference. The basic structure of the exhaust housing according to the invention and the function of the flow divider were already described in the embodiment according to Figure 3. Fig. 2 explained. The difference to the exemplary embodiment according to Fig. 2 consists in the fact that the flow divider 6 has a different length around its circumference. The vortex-driving effect is of varying intensity within the flow geometry, whereby in the upper region of a downward-directed outflow, a shorter length of the flow divider 6 promotes the flow guidance within the exhaust steam housing 1 and ensures lower flow losses.

[0022] Fig. Figure 4 shows a further embodiment of an evaporation housing 1 according to the invention, which differs from the embodiment according to Fig.2 differs in that, at the flow-side end of the conical flow divider 6, a further conical shell 13 with a larger opening angle is arranged. The change in the opening angle takes into account the main flow direction under load and thus, in turn, reduces flow losses. A similar effect can also be achieved by bulging the flow-side end of the conical shell. Furthermore, the flow divider can also have an opening angle that changes around its circumference and / or additional openings can be provided in certain circumferential regions to further reduce flow losses under load.

[0023] In principle, within the scope of the invention it is possible to combine the described measures with each other in different ways, insofar as technically possible.

Claims

[1] Exhaust steam casing (1) for an expansion turbine comprising at least an inlet area (3) which is essentially ring-shaped relative to the turbine axis (2), a guide apparatus comprising a funnel-shaped widening area (4) extending in the direction of flow for deflecting a working fluid flowing through the exhaust housing (1) and an outlet area (5) arranged at an angle, preferably at an angle of approximately 90°, to the turbine axis (2), characterized by , that in the funnel-shaped widening area (4), a circumferential flow divider (6) extending essentially in the main flow direction during load operation is arranged, which divides the funnel-shaped area (4) into a radially outer flow area (7) and a radially inner flow area (8). [2] Evaporation housing (1) according to claim 1, characterized by, that the flow divider (6) is designed as a conical shell with a constant opening angle. [3] Evaporation housing (1) according to claim 1, characterized by , that the flow divider (6) is designed as a conical shell with an opening angle that changes over the circumference. [4] Evaporation housing (1) according to claim 2 or 3, characterized by , that at the flow-side end of the flow divider (6) the conical shell is curved or another conical shell (9) with a larger opening angle is arranged. [5] Evaporation housing (1) according to any one of the preceding claims, characterized by , that the flow divider (6) has a different length around its circumference. [6] Evaporation housing (1) according to any one of the preceding claims, characterized by , that the flow divider (6) is interrupted in certain circumferential regions.

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