Axially actuated steam turbine

Abstract

An axially driven steam turbine (10) with a turbine casing (18) containing a turbine stage (12), comprising a series of static blades (24) and a series of movable blades (28) arranged behind the static blades (24) in a turbine passage, wherein the movable blades (28) have radially outer shielding plates (34) which cooperate sealingly with an outer wall section of the turbine passage, wherein a circumferentially and radially extending passage (46) is provided in the outer wall section in front of the series of movable blades (28) in order to deflect solid particles from the steam flow during the operation of the steam turbine (10), wherein the turbine housing (18) contains a circumferential collecting channel (48) between the adjacent turbine stages (12, 14) for collecting solid particles deflected by the circumferential passage (46), wherein the circumferential collection channel (48) further contains several circumferentially spaced flow barriers (54) which are designed to minimize the circumferential flow of solid particles within the circumferential collection channel (48), wherein each of the circumferentially spaced flow barriers (54) further extends axially over the circumferential collection channel (48) such that the circumferential collection channel (48) is divided into several circumferential chambers (48a), characterized by that the circumferential collection channel (48) contains a lining (52) to minimize the erosion of the turbine housing (18) by the circumferential passage (46) into the circumferential collection channel (48) and solid particles deflected into the circumferential collection channel (48), and that the flow barriers (54) are integrally formed with the lining (52).

Description

Field of invention

[0001] The present invention relates to axially actuated steam turbines, and in particular to axially actuated steam turbines with reduced susceptibility to damage due to solid particle erosion (SPE). To achieve the reduced susceptibility of the steam turbine to solid particle erosion, embodiments of the present invention relate to the extraction of solids from the steam stream as it expands through the turbine. General state of the art

[0002] GB 314 496 A and JP 2002 - 250 205 A describe a device for removing water droplets from a steam turbine.

[0003] A common problem associated with steam turbines, and especially intermediate-pressure steam turbines, is solid particle erosion (SPE). Solid particle erosion occurs when solid particles within the steam flowing through the turbine impinge on the rotating and stationary turbine components. These solid particles tend to cause erosion of the static blades (or nozzles), rotating blades (or buckets), and tip sealing devices that seal against the shielding plates at the tips of the rotating blades. While solid particle erosion can occur at any point along the steam flow path through a steam turbine, it can be particularly prevalent in the early turbine stages of an intermediate-pressure (MP) steam turbine.

[0004] Erosion of the trailing edge region of the static blades of a turbine stage can be a particular problem and is known to be caused by rebound of solid particles from the rotating blades of that turbine stage in a direction opposite to the steam flow through the turbine. Known solutions for reducing this particular type of solid erosion are described in US 4,776,765 A. One solution is to provide a coating or layer of protective material on the trailing edge of the static blades of a turbine stage to minimize the susceptibility of these blades to solid erosion due to rebound from the adjacent rotating blades of the turbine stage.Another solution, which can be used alone or in combination with the aforementioned protective material, is to increase the distance between the static blades and the rotating blades of a turbine stage in order to reduce the momentum of any rebounding solid particles.

[0005] The solutions proposed in US 4,776,765 A only attempt to address the problem of erosion at the trailing edge of the rotating blades of a turbine stage, whereas, as mentioned above, solid erosion can occur at any point along the steam flow path through the turbine. While an ideal solution to the problem of reducing solid erosion at any point in the steam flow path through a steam turbine would be to eliminate the solid particles from the steam flow before the steam reaches the turbine, this is impractical. Therefore, other solutions must be proposed.

[0006] A solution described in US 4,726,813 A uses electromagnets arranged on the piping connecting the boiler to the turbine to generate a magnetic field and thereby deflect solid metal particles within the steam flow to a desired location where they are collected. The steam then proceeds to the steam turbine for expansion through the turbine stages.

[0007] Another solution, described in US 7,296,964 B2, involves diverting a portion of the solid particle-containing steam flowing through the steam turbine away from the main steam flow path to the turbine's feedwater heater. The diverted steam thus bypasses downstream rotating components. Holes and passages are generally provided in the component parts of the steam turbine to permit the necessary diversion of a portion of the solid particle-containing steam, and in one embodiment, holes and passages are provided in the radially outer static ring of the first turbine stage. These holes and passages communicate with a passage in the radially outer static ring of the second downstream turbine stage to divert a portion of the steam away from the rotating blades and blade tip sealing devices of the first turbine stage into a steam extraction passage to the feedwater heater.

[0008] The solutions described in both US 4,726,813 A and US 7,296,964 B2 are complex and may not always provide a sufficient reduction in the concentration of solid particles in the steam flow. The complexity of the solution proposed in US 7,296,964 B2 stems in part from the fact that holes and passages must be formed through the radially outer static rings and the tip seals of several stages of the steam turbine. Furthermore, because the holes and passages in the radially outer static ring are provided only at predetermined circumferential positions, the ability to deflect steam containing solid particles is limited, thus restricting the effectiveness of the proposed solution.

[0009] In the turbine according to US 5 271 712 A, a space for storing particulate material is provided in the turbine casing at the tips of the rotor blades.

[0010] The steam turbine according to US 7 296 964 B2 has a channel for removing particles from the steam turbine.

[0011] DE 12 20 204 A describes a turbine with a collection chamber for capturing suspended particles from the working fluid of the turbine.

[0012] There remains a need for improved extraction of solid particles from axially driven steam turbines to make them less susceptible to damage resulting from solid particle erosion (SPE). Brief presentation of the Revelation

[0013] The object of the invention is solved by the axially actuated steam turbine according to claim 1.

[0014] In general terms, our concept provides the following: an axially driven steam turbine with a turbine casing containing a turbine stage comprising a series of static blades and a series of movable blades arranged behind the static blades, wherein the movable blades have radially outer shielding plates that cooperate sealingly with an outer wall section of the turbine passage, wherein a circumferentially extending passage is provided in the outer wall section in front of the series of movable blades in order to deflect solid particles from the steam flow during the operation of the steam turbine.

[0015] One aspect involves the provision of an axially driven steam turbine, which includes the following: a rotor, a turbine casing and several turbine stages, each turbine stage comprising the following: a radially outer static membrane ring that is mounted in the turbine housing, a radially inner static membrane ring and a circumferential series of static blades extending between the radially outer and radially inner static membrane rings; and a circumferential row of movable blades positioned at and behind the circumferential row of static blades, each of the movable blades comprising a foot section held by the rotor and a tip section containing a shielding plate; wherein at least one turbine stage downstream of the first stage of the turbine has an annular axial extension of its radially outer static diaphragm ring, the extension extending in the upstream axial direction to the radially outer static diaphragm ring of a preceding adjacent turbine stage to form an outer wall section of the turbine passage in the preceding turbine stage, the annular axial extension supporting a circumferential sealing device which cooperates with the shielding plates of the circumferential row of movable blades of the preceding turbine stage, an upstream end of the annular axial extension being axially spaced from the radially outer static diaphragm ring of the preceding turbine stage, such that a circumferential passage is defined between them in the preceding turbine stage.which, during the operation of the steam turbine, deflects solid particles from the steam flow through the turbine passage in front of the circumferential row of movable blades of the preceding turbine stage.

[0016]

[0011] Providing a circumferential passage upstream of the circumferential row of movable blades of the "preceding" turbine stage (e.g., the first stage of the turbine) makes it possible to extract solid particles from the steam before they are directed from the circumferential row of static blades to the immediately adjacent downstream circumferential row of movable blades. This advantageously minimizes the rebound of the solid particles from the movable blades onto the trailing edges of the static blades of the first turbine stage.

[0017]

[0012] By performing the circumferential passage continuously in the circumferential direction, it is possible to extract a larger proportion of solid particles from the steam flowing through the first turbine stage than is possible in the prior art described in US 7,296,964 and discussed above. Damage from solid erosion is thus significantly reduced.

[0018]

[0013] Whatever the exact structural features of the turbine may be, it is envisaged that the circumferentially extending passage is provided in at least the first stage of the turbine. It may also be advantageous to provide such a passage in the second stage and perhaps also in one or more subsequent stages. In our preferred turbine structure, the passage in the first stage is formed between a radially outer static membrane ring of the first stage of the turbine and an annular axial extension of a radially outer static membrane ring of the second stage of the turbine. Analogously, a passage in the second stage would be formed between a radially outer static membrane ring of the second stage of the turbine and an annular axial extension of a radially outer static membrane ring of the third stage of the turbine, and so on.

[0019]

[0014] Such an arrangement offers the advantage that solid particles which have not been deflected by the circumferential passage between the circumferential rows of static and movable blades of the first turbine stage and which are still contained in the steam flowing through the second turbine stage can be deflected by the circumferential passage defined between the circumferential rows of static and movable blades of the second turbine stage in front of the circumferential row of movable blades of the second turbine stage, etc. Solid erosion is thus advantageously further reduced.

[0020]

[0015] In some embodiments, the annular axial extension can be integral with the radially outer static diaphragm ring of the second turbine stage (that is, it is manufactured as part of the radially outer static diaphragm ring of the second turbine stage). In other embodiments, the annular axial extension can comprise a ring that is attached to the radially outer static diaphragm ring of the second turbine stage, for example, by mechanical fasteners.

[0021]

[0016] Preferably, the turbine casing includes a circumferential collection channel between the adjacent turbine stages for collecting solid particles deflected by the circumferential passage. The circumferential collection channel serves to collect solid particles that have been deflected by the steam flow upstream of the circumferential row of movable blades of the turbine stage through the circumferential passage. Solid particles deflected by the circumferential passage enter the circumferential channel and can be extracted from it, thereby minimizing the probability of the solid particles re-entering the steam flow through the circumferential passage. The circumferential collection channel also ensures that the collected solid particles are removed from the vicinity of the circumferential sealing device, thus reducing the risk of erosion of the tip sealing device.

[0022]

[0017] The circumferential passage can communicate with an inlet area of ​​the circumferential collecting channel in a generally radial direction.

[0023]

[0018] The circumferential passage can have an inclined surface that acts to direct solid particles from the circumferential passage into the circumferential collection channel. In our preferred turbine structure, the inclined surface can advantageously be provided by an upstream end of the annular axial extension. This inclined surface can slope away from the radially outer static membrane ring of the first turbine stage in a radially outward direction toward the circumferential collection channel. Furthermore, the upstream end of the annular axial extension can include a radially outwardly extending shoulder to impede the re-entry of collected solid particles from the circumferential collection channel into the circumferential passage and thus into the steam flowing through the turbine.

[0024]

[0019] For each turbine stage to which the invention is applied, it is preferred that the circumferential passage is substantially aligned with the leading edges of the movable blades. Thus, the upstream end of the annular axial extension and the leading edges of the movable blades and shielding plates of the turbine stage would generally be radially aligned with each other to maximize the number of solid particles that are deflected into the circumferential passage by the tangential motion of the steam flow.

[0025]

[0020] The circumferential collection channel in the turbine housing can contain a lining to minimize or prevent erosion of the turbine housing by solid particles that are deflected into the circumferential collection channel through the circumferential passage. Providing a lining in the circumferential channel is advantageous because solid particles collected in the circumferential collection channel tend to cause erosion of the lining rather than the turbine housing, and repairing or replacing the lining is easier than repairing or replacing the turbine housing. The lining can comprise several semi-annular lining segments that, when assembled in the circumferential collection channel, cooperate to form a circumferential lining.

[0026]

[0021] The circumferential collection channel can contain several flow barriers spaced around its circumference, arranged to block the circumferential migration of solid particles within the circumferential collection channel. This helps to retain collected solid particles in the circumferential collection channel.

[0027]

[0022] Each of the circumferentially spaced flow barriers can extend axially across the circumferential collection channel, and the circumferential collection channel can thus be divided into several circumferential collection chambers. The flow barriers can be formed integrally with the lining.

[0028]

[0023] In some embodiments, the circumferential collection channel can be dimensioned to have adequate capacity for accumulating collected solid particles over a predetermined period of time.

[0029]

[0024] In other embodiments, the steam turbine may include a particle extraction arrangement (e.g. a suction pipe) with at least one inlet that communicates with the circumferential collection channel to extract solid particles from the circumferential collection channel.

[0030]

[0025] For embodiments in which the circumferential collection channel is continuous or in which the flow barriers (if provided) are not designed to completely block the circumferential migration of the particles, the at least one inlet of the particle extraction arrangement can communicate with a lower circumferential region of the circumferential collection channel. Such an arrangement is advantageous because solid particles collected in the upper circumferential region of the circumferential collection channel generally migrate to the lower circumferential region of the circumferential collection channel under the influence of gravity and other forces.

[0031]

[0026] For embodiments in which the circumferential collection channel is divided into several chambers, each chamber can be provided with at least one inlet of the particle extraction arrangement.

[0032]

[0027] The steam turbine can include a fluid inlet arrangement for injecting fluid such as air into the circumferential collection channel. Introducing fluid can be advantageous because it can dislodge solid particles that have accumulated in the circumferential collection channel and make it easier for the accumulated solid particles to be extracted by the particle extraction arrangement. Brief description of the drawings Fig. Figure 1 is a schematic cross-sectional view of a part of an axially actuated steam turbine according to an embodiment of the present invention; Fig. Figure 2 is an enlarged schematic cross-sectional view of a part of the axially actuated steam turbine shown in Figure 1 and Fig. Figure 3 is a schematic view of a lining that forms part of the axially actuated steam turbine shown in Figures 1 and 2. Detailed description of embodiments of the invention

[0033]

[0031] Embodiments of the present invention will now be described only by way of example and with reference to the accompanying drawings.

[0034]

[0032] Fig. Figure 1 shows part of an embodiment of an axially driven steam turbine 10, with the direction of steam flow through the turbine 10 indicated by arrow S. The steam turbine 10 comprises several turbine stages through which steam expands during operation of the turbine 10. Two complete turbine stages, namely the first and second turbine stages 12 and 14, are shown in Figure 1, but only part of a third turbine stage 60 is shown. It is self-evident that the second turbine stage 14 is located immediately adjacent to and downstream of the first turbine stage 12, and that the third turbine stage 60 is located adjacent to and immediately downstream of the second turbine stage 14.

[0035]

[0033] The steam turbine 10 comprises a rotor 16, of which only a part is shown, and a turbine casing 18. Each of the first, second, and third turbine stages 12, 14, 60, comprises a radially outer static diaphragm ring 20a, 22a, 62a, which is mounted in the turbine casing 18, and a corresponding radially inner static diaphragm ring 20b, 22b, 62b. Rows of circumferentially extending static blades 24, 26, 64 (also known as stator blades or nozzle partitions) extend between the radially outer static diaphragm rings 20a, 22a, 62a and the radially inner static diaphragm rings 20b, 22b, 62b of the first, second, and third turbine stages 12, 14, 60, respectively.

[0036]

[0034] Each turbine stage 12, 14 comprises a circumferential row of movable blades 28, 30, arranged alongside and immediately behind its associated circumferential row of static blades 24, 26. Each of the movable blades 28, 30 comprises a root section 28a, 30a, which is attached by pins or other suitable means to disks 32 formed on the rotor 16. Each of the movable blades 28, 30 also comprises a tip section 28b, 30b, which carries a shielding plate 34, 36, and the shielding plates of the individual movable blades 28, 30 work together to form a continuous shielding plate ring.

[0037]

[0035] The radially outer static membrane ring 22a of each stage downstream of the first stage, in particular the second turbine stage 14, includes an annular axial extension 38 that extends in the axially upstream direction to the radially outer static membrane ring 20a of the preceding or first turbine stage 12, thereby forming an outer wall of the turbine passage. In the illustrated embodiment, the annular axial extension 38 comprises an extension ring that is mechanically or by welding attached to the radially outer static membrane ring 22a of the second turbine stage 14.

[0038]

[0036] As in Fig. As can be seen more clearly in Figure 2, the radially outer shielding plates 34 of the movable blades of the first stage act as a seal against the outer wall of the turbine passage, as defined by the annular axial extension 38. This is because the extension 38 carries a circumferential sealing device 40, which cooperates with the shielding plates 34 of the movable blades of the first turbine stage 12 to minimize steam leakage between the shielding plates and the annular axial extension 38. The sealing device 40 can assume any suitable shape, but in the illustrated embodiment it comprises a rib-like labyrinth seal, which includes several axially spaced and circumferentially extending sealing strips 42 with hook ends that are pressed into the annular axial extension 38.

[0039]

[0037] A triangular sealing rib 44 extending over the circumference, pressed back into the annular axial extension 38, is also provided.

[0040]

[0038] To divert solid particles from the steam flow during the operation of the steam turbine, a circumferential and radially extending passage 46 is provided in the outer wall of the turbine passage, wherein the passage is generally radially aligned with the leading edges of the movable blades 28 and their shielding plates 34.

[0041]

[0039] More precisely, the annular axial extension 38 includes an axially upstream end 38a, which is axially spaced from the radially outer static membrane ring 20a of the first turbine stage 12. The circumferential passage 46 is thus defined between the upstream end 38a of the annular axial extension 38 and the radially outer static membrane ring 20a. During operation of the steam turbine 10, solid particles contained within the steam flowing through the first turbine stage 12 are directed into the circumferential passage 46 upstream of the circumferential row of movable blades 28 of the first turbine stage 12 due to the tangential motion of the steam flow, and these solid particles are then deflected away from the steam flow by the generally radial orientation of the circumferential passage 46.The erosion of the circumferential rows of static and movable blades 24, 28 of the first turbine stage 12 is thus advantageously reduced due to the reduction of solid particles within the steam flowing through the first turbine stage 12.

[0042]

[0040] To reduce the probability that any deflected solid particles re-enter the steam flowing through the steam turbine 10, the turbine housing 18 includes a circumferential collection channel 48 in which solid particles deflected from the steam flowing through the first turbine stage 12 by the circumferential passage 46 are collected and accumulated. The circumferential collection channel 48 is located in the turbine housing 18 between the radially outer static diaphragm rings 20a, 22a of the adjacent first and second turbine stages 12, 14.

[0043]

[0041] To assist in deflecting the solid particles from the circumferential passage 46 into the circumferential collection channel 48, the upstream end 38a of the annular axial extension 38 includes an inclined annular surface 38b. The inclined annular surface 38b slopes down from the radially outer static membrane ring 20a of the first turbine stage 12 in a generally radially outward direction towards the circumferential collection channel 48.

[0044]

[0042] During operation of the turbine, particles deflected into the circumferential collection channel 48 generally circulate within it, driven by the flow entering through the circumferential passage 46. To minimize the re-entry of solid particles from the circumferential collection channel 48 into the circumferential passage 46 and thus into the steam flowing through the first turbine stage 12, the annular axial extension 38 has a circumferentially extending, radially outwardly projecting shoulder 50 at its upstream end 38.

[0045]

[0043] In one embodiment, the circumferential collection channel 48 can be formed directly in the turbine housing 18. However, a disadvantage of this arrangement is that the turbine housing 18 will generally be subject to erosion by the solid particles deflected into the circumferential collection channel 48. In other embodiments, the circumferential collection channel 48 can therefore include a lining 52, which is generally formed by several cooperating partial circumferential lining segments. The lining 52 can be made of the same material as the turbine housing 18, in which case it acts as a sacrificial material that will be subject to erosion by the solid particles, or alternatively, it can be made of a material that is harder than the turbine housing 18 and thus less susceptible to erosion by the collected solid particles.In any case, the lining 52 could then simply be replaced as required during an overhaul of the steam turbine 10 or at another suitable time in the event of an unacceptable level of erosion caused by the collected solid particles.

[0046]

[0044] Due to the tangential movement of the steam within the circumferential collecting channel 48, solid particles deflected into the circumferential collecting channel 48 by the circumferential passage 46 tend to move circumferentially around the circumferential collecting channel 48. To reduce this circumferential movement and thereby reduce the probability that the collected solid particles re-enter the circumferential passage 46 and thus the steam flowing through the first turbine stage 12, the circumferential collecting channel 48 can contain several flow barriers 54 spaced apart around its circumference. In some embodiments, the flow barriers 54 are integrally formed with the lining 52 or lining segments, as best illustrated in Fig. 3 can be seen.

[0047]

[0045] Each flow barrier 54 typically extends axially over the entire width of the circumferential collection channel 48, and the flow barriers 54 thus divide the circumferential collection channel 48 into several individual partial circumferential collection chambers 48a.

[0048]

[0046] In some embodiments, the circumferential collection channel 48 can be dimensioned such that sufficient space exists to accommodate solid particles accumulated over a period of time. This period of time could be the normal overhaul interval for the steam turbine 12 or any other suitable period of time, and after a suitable period of time, the accumulated solid particles could be removed from the circumferential collection channel 48 and / or the lining 52 could be replaced. Replacement of the lining 52 would be necessary in situations where there has been erosion of the lining 52 and any integrally formed associated flow barriers 54 by the accumulated solid particles.

[0049]

[0047] In other embodiments, one or more extraction tubes 56 may be provided to extract collected solid particles from the circumferential collection channel 48. It is assumed that solid particles collected within the upper and possibly lateral circumferential regions of the circumferential collection channel 48 may tend to move towards the lower circumferential region of the circumferential collection channel 48 under the influence of gravity and possibly other forces. If the circumferential collection channel 48 is circumferentially continuous, that is, it is not divided into separate chambers 48a, it may therefore be sufficient to provide one or more extraction tubes 56 in the lower circumferential region of the circumferential collection channel 48. However, each circumferential collection chamber 48a would preferably be equipped with a corresponding extraction tube 56.

[0050]

[0048] It is also considered that one or more inlet tubes could be provided in addition to the one or more extraction tubes 56 to introduce fluid such as air into the circumferential collection channel 48. The introduction of fluid can dislodge accumulated solid particles and therefore make it easier for those dislodged solid particles to be extracted by the one or more extraction tubes 56.

[0051]

[0049] In the illustrated embodiment, the radially outer static diaphragm ring 62a of the third turbine stage 60 also includes an annular axial extension 66, which extends in the axially upstream direction to the radially outer static diaphragm ring 22a of the second turbine stage 14. Like the annular axial extension 66, the illustrated annular axial extension 66 comprises an extension ring that is attached to the radially outer static diaphragm ring 62a of the third turbine stage 60.

[0052]

[0050] The annular axial extension 66 carries a circumferential tip sealing device 68, which cooperates with the shielding plates 36 of the movable blades 30 of the second turbine stage 14 to minimize the escape of steam between the tip sections 30b of the movable blades 30 and the annular axial extension 66. The tip sealing device 68 can be as described above.

[0053]

[0051] The annular axial extension 66 also includes an axially upstream end which is axially spaced from the radially outer static membrane ring 22a of the second turbine stage 14, and a circumferential passage 70 is thus defined between the upstream end of the annular axial extension 66 and the radially outer static membrane ring 22a.

[0054]

[0052] During operation of the steam turbine 10, solid particles contained in the steam flowing through the second turbine stage 14 are deflected into the circumferential passage 70 upstream of the circumferential row of movable blades 30 of the second turbine stage 14 due to the tangential motion of the steam flow, and these solid particles are then deflected away from the steam flow by the circumferential passage 70. The circumferential passage 70 directs the solid particles into a circumferential collection channel 72, which generally contains all of the features described above.

[0055]

[0053] The erosion of the circumferential row of movable blades 30 of the second turbine stage 14 is thus advantageously reduced due to the reduction of solid particles in the steam flowing through the circumferential row of movable blades 30 of the second turbine stage 14.

[0056]

[0054] The radially outer static membrane rings of subsequent turbine stages can also be equipped with particle extraction agents as described above.

[0057]

[0055] Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it is understood that various modifications can be made to those examples without deviating from the scope of protection of the present invention as claimed.

[0058]

[0056] For example, the annular axial extension 38, 66 can be an integral part of the radially outer static membrane ring 22a, 62a of the respective second or third turbine stage 14, 60, instead of being designed as a separate extension ring as above.

[0059]

[0057] The circumferential tip sealing device 40 can comprise any suitable sealing arrangement such as sealing strips, ribs, labyrinth seals, brush seals or blade seals to prevent or at least minimize steam leakage past the tip sections 28b of the movable blades 28 of the first turbine stage 12.

[0060]

[0058] The illustrated steam turbine 10 is designed as an impulse turbine, in which the majority of the turbine stage pressure drop occurs in the rows of static blades 24, 26, 64. However, the concepts described in this specification can be applied equally to pressure turbines, in which a significant proportion of the pressure drop occurs across the rows of movable blades 28, 30.

[0061]

[0059] Although the first, second, and third turbine stages 12, 14, 60 are shown to be the first three expansion stages of the steam turbine 10 (i.e., stages “1”, “2”, and “3”), it is understood that they could be later stages of the steam turbine 10. For example, the first turbine stage 10 mentioned above could be stage “2”, with the second and third turbine stages 14, 60 being stages “3” and “4”, respectively.

Claims

[1] An axially driven steam turbine (10) with a turbine casing (18) containing a turbine stage (12), comprising a series of static blades (24) and a series of movable blades (28) arranged behind the static blades (24) in a turbine passage, wherein the movable blades (28) have radially outer shielding plates (34) which cooperate sealingly with an outer wall section of the turbine passage, wherein a circumferentially and radially extending passage (46) is provided in the outer wall section in front of the series of movable blades (28) in order to deflect solid particles from the steam flow during the operation of the steam turbine (10), wherein the turbine housing (18) contains a circumferential collecting channel (48) between the adjacent turbine stages (12, 14) for collecting solid particles deflected by the circumferential passage (46), wherein the circumferential collection channel (48) further contains several circumferentially spaced flow barriers (54) which are designed to minimize the circumferential flow of solid particles within the circumferential collection channel (48), wherein each of the circumferentially spaced flow barriers (54) further extends axially over the circumferential collection channel (48) such that the circumferential collection channel (48) is divided into several circumferential chambers (48a), characterized by , that the circumferential collection channel (48) contains a lining (52) to minimize the erosion of the turbine housing (18) by solid particles deflected through the circumferential passage (46) into the circumferential collection channel (48), and that the flow barriers (54) are integrally formed with the lining (52). [2] Steam turbine (10) according to claim 1, wherein the circumferential passage (46) communicates in a generally radial direction with an inlet area of ​​the circumferential collecting channel (48). [3] Steam turbine (10) according to claim 2, wherein the circumferential passage has an inclined surface (38b) which operates to direct solid particles from the circumferential passage (46) into the circumferential collecting channel (48). [4] Steam turbine (10) according to one of claims 1 to 3, wherein the circumferential passage (46) is substantially aligned with the leading edges of the movable blades (28). [5] Steam turbine (10) according to any one of claims 1 to 4, wherein the steam turbine (10) includes a particle extraction arrangement (56) which communicates with the circumferential collection channel (48) to extract collected solid particles from it. [6] Steam turbine (10) according to claim 5, wherein at least one inlet of the particle extraction arrangement (56) communicates with a lower circumferential region of the circumferential collection channel (48). [7] Steam turbine (10) according to claim 5, wherein at least one inlet of the particle extraction arrangement (56) communicates with the circumferential collection channel (48) between each pair of circumferentially adjacent flow barriers (54). [8] Steam turbine (10) according to any one of claims 1 to 7, further comprising a fluid inlet designed to inject fluid into the circumferential collecting channel (48), thereby removing accumulated solid particles from the circumferential collecting channel (48).

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