EP1178183A2 - Low pressure steam turbine with multi channel diffuser - Google Patents

Abstract

The axial/radial three-passage diffusor of the LP steam turbine has two deflector plates (8,9) which extend over the diffusor's whole length and are distributed between an inner diffusor ring (4) and outer diffusor ring (5) so that the surface distribution to the three diffusor sections (10-12) in the intake area is unequal. A large part of the flow intake area of the whole diffusor is allotted to the inner and center sections, and a smaller part to the outer section.

Description

Technical field

The invention relates to a low-pressure steam turbine with an axial flow axial / radial multi-channel diffuser and exhaust steam housing for low-loss guidance of the blading evaporation.

State of the art

A diffuser of this type is described in DE 44 22 700. The one revealed there The diffuser has one following the last row of blades Low pressure steam turbine has an axial flow inlet and a radial one Flow outlet on. The diffuser is designed to optimize the Turbine output designed by the greatest possible pressure recovery. For this are the first sections of the inner and outer diffuser ring with respect to the hub or the blade carrier at an articulation angle aligned. This measure serves to make the Total pressure profile over the channel height of the diffuser in the area of the last one Blade row. Furthermore, the diffuser has a radially outward curve Baffle that divides it into an inner and an outer channel. in the outer and inner channels are arranged flow ribs that are radial or flow diagonally. The baffle serves the Redirection and also the management of the outflow. The flow ribs are intended to support the guide plate and in particular to reduce it of the twist in the delay zone, which also optimizes the Contribute to pressure recovery. However, realized flow ribs can only be used for bring about an optimal swirl reduction for a certain operating load. at a different operating load does not necessarily reduce the swirl optimal. A diffuser with this measure therefore only achieves one certain operating load an optimal pressure recovery. Furthermore, the Flow ribs and their attachment to the baffles with a relative great design effort. In addition, the supersonic interferes Crevice flow with the remaining subsonic flow.

EP 581 978, in particular in FIG. 4 of that document, contains a multi-channel exhaust gas diffuser for an axially flow-through gas turbine with an axial flow inlet and radial flow exit disclosed. This multi-channel diffuser points along three zones in length. The first zone is like a bell diffuser trained and extends single-channel from the last row of blades to Exit plane of several flow fins. The diffuser rings also point here Buckling angles, which are set so that a homogenization of the Total pressure profile is reached. The second zone faces downstream from the Flow ribs on flow-conducting guide rings, which have several channels form. The third zone is used to strongly divert the exhaust gas flow into radial Direction and then flows into the chimney of the gas turbine. To this The purpose is the guide rings of the second zone over the length of the third zone continued, where they are curved there. The second zone shows slight Redirection, but high diffuser effect on, the third zone large redirection, however only very modest diffuser effect.

Presentation of the invention

It is the object of the present invention to provide an axial / radial multi-channel diffuser with an exhaust steam housing for a low-pressure steam turbine, which achieves an improved pressure recovery compared to the diffusers of the prior art, as a result of which the efficiency of the low-pressure steam turbine is increased. Furthermore, the multi-channel diffuser should be optimized for as many operating conditions of the steam turbine as possible and be connected with a reduced design effort. Finally, the exhaust steam housing should be matched to the diffuser in terms of turbine performance.
This object is achieved by an axial / radial three-channel diffuser with an evaporator housing according to claim 1. The three-channel diffuser has three partial diffusers, an inner, middle and outer partial diffuser, which are formed by an inner diffuser ring, an outer diffuser ring and two guide plates arranged between the diffuser rings. A first section of the inner diffuser ring is arranged with respect to the hub at an inward angle towards the rotor axis and a first section of the outer diffuser ring is arranged at an angle with respect to the blade channel at the level of the last row of blades, facing away from the rotor axis ,

Extend in the axial / radial three-channel diffuser according to the invention especially the two baffles along the entire length of the diffuser. they are between the inner and outer diffuser ring unevenly distributed, so that the area distribution on the three partial diffusers in the inlet surface of the diffuser is uneven. The majority of Entry area on the inner and middle partial diffuser and a small part of the Entry surface on the outer partial diffuser. The initial tangents continue to educate of the two guide plates together with the rectilinearly approximated hub-side and housing-side limits of the blading duct above the final stage of the Low-pressure steam turbine at least approximately a common one Intersection in the meridian plane. After all, the baffles are as possible located near the last row of blades, the distance between the last row of blades and the leading edges of the baffles through for everyone Operating conditions allowable minimum distance is determined.

This is the characteristics of the diffuser in its interaction zone with the last one Level outlined.

The diffusion zone of the diffuser is characterized by the following features. The ratio of the exit area to the entry area of the individual partial diffusers is greater than two for the middle partial diffuser and greater than three for the outer Part diffuser. For the inner partial diffuser, the corresponding is geometric Area ratio in a range from 1.5 to 1.8.

The ratio of its length to its length is further for the middle partial diffuser Channel height in the entrance area at least four. For the outside Partial diffuser is the ratio of length to channel height in the entry area is at least equal to 10 and for the inner partial diffuser is the corresponding one Ratio at least 2.5. Because of these relatively large length-to-channel height ratios the deflections of the partial diffusers are corresponding relatively gentle.

The ratio of the exit area to the entry area of the entire diffuser is about two.

Finally, the evaporator housing of the diffuser is designed so that the size the area of the parting plane between the upper and lower half of the Evaporator housing to the size of the outlet surfaces of the partial diffusers is coordinated.

The two baffles are used to separate the diffuser channel into three partial diffusers, in which the blading outflow is guided. That caused Flow control is the better, the more partial diffusers for the same Total diffuser are available. On the other hand, there are more friction losses and higher blockages the more baffles are arranged. The one chosen here Number, three partial diffusers and two baffles has the advantage that one optimized flow control with reasonable friction losses on the Surfaces of the baffles and blockages is effected.

The baffles and partial diffusers guide and stabilize the blading outflow and deflect it in a radial direction. Since the baffles extend over the entire length of the diffuser, this guidance is further supported.
The radial extension of the partial diffusers also serves to naturally reduce the tangential speed. The partial diffusers are therefore optimal for all operating conditions with regard to the reduction of the tangential speed. Furthermore, the design effort for the guide plates is relatively small and no further design measures such as deflection and flow ribs are necessary to reduce the tangential speed.

The flow guidance and stabilization is further brought about, in particular, by the distribution of the diffuser inlet area over the three partial diffusers. A large part of the inlet area is accounted for by the inner and middle channel, whereby the major part of the flow is led from the blading to the exhaust steam housing. The small part of the inlet area is accounted for by the outer channel, through which the supersonic gap flow as well as the flow influenced by the gap flow is taken up from the turbine and deflected meridionally and is shielded from the majority of the flow to the evaporation housing. This shielding avoids flow interference between the majority of the flow and the high-energy gap flow, which would impair the diffuser effect.
The minimum distance between the last row of blades and the leading edges of the baffles further helps to optimally shield the gap flow and to avoid flow interference and streamline convergences.
The ratio of length to channel height of each partial diffuser of 2.5 and more enables a gentle deflection from the axial, or diagonal, to the radial flow direction, which prevents the delayed flow from separating, even with a ratio of the outlet area to the inlet area of 1.6.

The guidance and stabilization of the blading outflow through the three Partial diffusers, the shielding of the high-energy gap flow and the gentle deflection due to the length of the channels in relation to theirs Canal heights bring about an overall smoothing and lowering of the Total pressure profile at the level of the last row of blades. The caused by this More power leads to an increase in the efficiency of the Low pressure steam turbine.

The design of the diffuser according to the invention is based on an inverse Design process in which the predominant flow fields be determined. Then the ideal ones are created Flow fields are calculated and the geometry of the diffuser based on this ideal flow fields is determined. In particular, this three-channel diffuser designed for limit load conditions. At limit load was a Flow field determined for which a three-channel diffuser with an orientation of Initial tangent of his guide plates according to the invention the highest Pressure recovery achieved. Through experimental evidence, this is from this Design resulting geometry in the entire operating range of the turbine Superior diffusers of the prior art. This interpretation also provides the advantage that a higher turbine output with the same Capacitor pressure is achieved or that the same turbine output at higher Condenser pressure is achieved and thus a smaller, cheaper Cooling system for the steam turbine is required.

In special embodiments of the invention, further special features of the interaction zone of the diffuser are disclosed below.
In a first particular embodiment of the invention, the initial tangents of the guide plates lie in an angular range around the first kink points of the guide plates and around a reference initial tangent, which at least approximately lead through the first kink point of the guide plate and through the intersection of the rectilinearly approximated boundaries of the blade channel.

In a further special embodiment of the invention, the outer one is used Partial diffuser a share of the total flow inlet area of the diffuser in the Range of 10-12%. The remaining entry area is 55-60% on the inside Partial diffuser and 30-35% distributed in the middle part diffuser.

In a further embodiment, the distance between the leading edges of the guide plates and the trailing edge of the last moving blade is 4% of the total height of the running row.
In a further embodiment, the front edges of the guide plates are profiled at the flow inlet of the diffuser, which causes a gentle acceleration when entering the partial diffusers.

In other versions, the diffusion zone of the diffuser is characterized as follows.
The baffles are each supported by struts or supports that extend from the inner and outer diffuser ring to the two baffles. The middle partial diffuser remains free of supports and therefore has minimal flow disturbances and losses.

In a further, special embodiment of the evaporation zone of the diffuser is on End baffle between the inner and middle partial diffuser in a radial Extending an evaporation baffle. This exhaust steam baffle causes a better flow distribution in the evaporation housing, whereby the Flow losses are minimized and the condenser is charged more evenly becomes.

Brief description of the drawings

Figur 1 einen vertikalen Schnitt eines erfindungsgemässen Diffusors mit Abdampfgehäuse,

Figur 1a ein Detail der zylinderseitigen Interaktionszone des Diffusors,

Figur 1b ein Detail der nabenseitigen Interaktionszone des Diffusors,

Figur 2 ein Detail der profilierten Vorderkanten der Leitbleche am Diffusoreintritt,

Figur 3 ein Querschnitt durch ein Abdampfgehäuse des Diffusors,

Figur 4 eine Sicht auf die Trennebene zwischen der oberen und unteren Hälfte des Diffusors.

Figur 5 einen vertikalen Schnitt einer weiteren Variante des erfindungsgemässen Diffusors mit Abdampfgehäuse,

Figur 6 eine Sicht auf die Trennebene zwischen der oberen und unteren Hälfte der weiteren Variante von Figur 5.

Show it:

FIG. 1 shows a vertical section of a diffuser according to the invention with an evaporation housing,

FIG. 1a shows a detail of the cylinder-side interaction zone of the diffuser,

1b shows a detail of the hub-side interaction zone of the diffuser,

FIG. 2 shows a detail of the profiled front edges of the guide plates at the diffuser inlet,

FIG. 3 shows a cross section through an evaporator housing of the diffuser,

Figure 4 is a view of the parting plane between the upper and lower half of the diffuser.

FIG. 5 shows a vertical section of a further variant of the diffuser according to the invention with an evaporation housing,

6 shows a view of the parting plane between the upper and lower half of the further variant of FIG. 5.

Way of carrying out the invention

Figure 1 shows a three-channel diffuser as part of a low-pressure steam turbine. It leads the blading outflow into an exhaust steam housing 20. The low pressure steam turbine shows the rotor 1 with the rotor axis 2 and a rotor blade 3 of the last row of rotor blades. The three-channel diffuser is delimited by an inner diffuser ring 4 and an outer diffuser ring 5. The outer diffuser ring 4 is connected to the blade carrier 7. The inner and outer diffuser rings 4 and 5 have kink angles  _N and  _Z in the region of the rear edge of the rotor blade, wherein, as shown in FIGS. 1a and 1b, the angle  _N through the first section 4 'of the inner diffuser ring 4 and an extension of the hub 6 and the angle  _{Z are formed} by the extension of the last section 7 'of the blade carrier 7 and the first section 5' of the outer diffuser ring 5. These kink angles are, for example, 10-20 ° and help to ensure that a total pressure profile that is as homogeneous as possible is achieved at the outlet of the last row of blades.

The inside of the diffuser has two guide plates 8 and 9, which divide the diffuser into three subchannels, an inner partial diffuser 10, a central partial diffuser 11 and an outer partial diffuser 12. The baffles are supported by supports 13 which extend from the inner and outer diffuser rings 4 and 5 to the baffles. For reasons of strength, the first supports 13 in the direction of flow are thicker than the second supports and each have a round cross section. The middle partial diffuser 10 is in particular free of supports.
The baffles are distributed over the channel height of the diffuser in consideration of the total pressure profile in such a way that an aerodynamically optimal surface distribution over the three subchannels is achieved. The first guide plate 8 is arranged in such a way that the inner partial diffuser 10 has a flow entry area which is, for example, approximately 60% of the flow entry area of the entire diffuser. The second guide plate 9 is further arranged such that the central partial diffuser 11 has, for example, a flow entry area of approximately 30% of the total flow entry area. As a result, the majority of the total inlet area is attributable to the two first channels 10 and 11. The outer partial diffuser 12, on the other hand, has a flow inlet area of, for example, approximately 10% of the total flow inlet area.
The diffuser exit area is designed such that the ratio of the exit area to the entry area of the entire diffuser, that is to say its upper and lower half, is approximately 2.
In the case of the individual partial diffusers, the geometric relationships from the outlet to the inlet surface are as follows.
For the inner partial diffuser 10, for example, the ratio of the exit area S12 in the upper half of the diffuser to the entry area S11 is approximately 1.3.

The ratio of exit area S13 in the lower half of the diffuser to entrance area S11 is larger and is approximately 1.6. The exit surface S13 of the inner partial diffuser 10 is therefore further out in the lower half of the diffuser than in the upper half. (Although it is actually in the lower half of the diffuser, it is also shown in this figure and in FIG. 4 with S13.)
For the central partial diffuser 11, the ratio of the exit area S22 to the entry area S21 is approximately 2.1.
For the outer partial diffuser, the ratio of outlet area S32 to inlet area S31 is approximately 3.3. Such area ratios are the prerequisite for significantly increasing the efficiency of the turbine.

The diffuser is designed with a view to smoothly guiding the flow low curvature in relation to the channel height. The three Partial diffusers have a large length-to-channel height ratio. This is for the inner partial diffuser 10, for example, greater 2.7 in the lower half of the diffuser. For the middle and outer partial diffuser 11 and 12 are the Ratios greater than 4.4 or greater than twelve in the example shown. The inner and outer diffuser ring as well as the two baffles point in their Cross section for manufacturing reasons several straight sections, due to the large length-to-channel height ratios in gentle Angles of inclination to each other. Allow this gentle angle of inclination improved guidance of the blading outflow. It will Avoided flow interference and flow separation in particular. Due to the relatively large radial extension of the diffuser and the Partial diffusers also become a natural breakdown of tangential speeds without the help of additional flow ribs or other measures Reductions in tangential speeds achieved.

The three partial diffusers have a gentle deflection due to their radial extension. The total deflection of each partial diffuser is indicated by the angles  ₁ ,  ₂ and  ₃ in the center line 15 of the individual partial diffusers 10, 11 and 12, respectively. These angles are, for example, approximately 70 °, 36 ° or 47 °.

The guide plates 8 and 9 are approximately designed so that the extension of their initial tangents form the intersection A. The rectilinearly approximated hub-side and housing-side boundary of the blade channel also runs through this intersection point A. In the exemplary embodiment shown, the starting tangents of the guide plates 8 and 9 are oriented at angles ε ₁ and ε ₂ with respect to the rotor axis 2. In variants of the invention, the intersection A between the linearly approximated hub-side and housing-side limits of the blading duct via the final stage of the turbine and the initial tangents of the guide plates 8 and 9 form an at least approximately common intersection. In the variants, the initial tangent of the guide plate 8 forms an angle in the range of ε ₁ + 8 ° with the straight-line approximated hub-side limit. The initial tangent of the guide plate 9 accordingly forms an angle in the range of ε ₂ ± 4 °.
This geometrical design of the guide plates with regard to the limits of the blading duct also applies to other housing contours and blade types, such as for example for completely conical rectilinear housing contours, for housing contours in which the section runs cylindrical or almost cylindrical over the last row of blades. This geometry can also be used not only for blades with a tip seal, but also for blades with shrouds. In this case, the housing-side boundary of the blade channel runs through the intersection of the rear edge of the last blade and the shroud.

In a real interpretation of the invention, the initial tangents of Baffles 8, 9 in an angular range around the first intersection points B and C Baffles 8 and 9 and around the reference tangents by the Lead intersection points B and C and through intersection point A.

The diffuser rings 4 and 5 and baffles 8 and 9 exist in the example shown from several straight sections that are at small angles to each other are standing together. Instead of sections are also continuous curved baffles and diffuser rings can be realized.

The partial diffusers 10 and 11 are arranged in such a way that a major part of the flow flows from the blading through these two partial diffusers into the exhaust steam housing 20. A stable guidance of the main part of the flow in the area of the middle partial diffuser is most sensitive to obstructions due to the Mach numbers prevailing there. The middle partial diffuser 11, which is free of supports, thus guides that part of the main flow without further disturbances.
The high-energy, supersonic gap flow from the last rotor blade row, on the other hand, reaches the outer partial diffuser 12, the channel height of which is determined in relation to the prevailing gap flow. The gap flow is conducted through the outer partial diffuser 12 separately from the main part of the flow into the exhaust steam housing 20.

The large length-to-channel height ratio stabilize the Diffuser flow and homogenization and lowering of the Total pressure profile at the level of the last row of blades. This will make the Pressure recovery of the diffuser increases and an increase in efficiency whole low pressure steam turbine reached.

The baffles 8 and 9 extend at the entrance to the diffuser up to close to the row of blades. They are preferably arranged as close as the axial, thermal movements of the rotor blade row and a safety distance required for the various operating conditions allow, without causing rubbing. For example, the distance a between the front edges of the guide plates 8 and 9 and the rear edge of the last rotor blades is 3 4% of the total height h _{w of} the last rotor blade row. Furthermore, the front edges of the baffles 8 and 9 are profiled in order to enable a smooth flow entry into the partial diffusers with the lowest possible overspeeds. The front edges are, for example, as shown in FIG. 2, gently tapered, for example according to the shape NACA 65, the profiling length e being three times the thickness δ. Furthermore, the guide plates are made as thin as possible so that the Mach numbers increase as little as possible. For this purpose, their thickness is, for example, approximately 5% of the channel height of the central partial diffuser 11.

The smallest possible distance between the front edges of the guide plates 8 and 9 of the Wear blade row 3 and the gentle profile of the front edges decisive for increasing the pressure recovery. Are baffles further Remotely located, there may be sound fields and flow interference result, which make pressure recovery in this area impossible would.

In the embodiment shown, an exhaust steam guide plate 8 'is arranged on the guide plate 8 between the inner and middle partial diffuser in a radial extension. This exhaust steam guide plate 8 'brings about an improvement in the flow in the exhaust steam housing 20 and a more uniform flow in the condenser. The steam guide plate 8 'has a gentle total deflection  _L of approximately 50 °. In this exemplary embodiment, this deflection is realized by two sections, the total length of which is approximately 0.7 to the channel height in the exit plane.

FIG. 3 shows a cross section through the exhaust steam housing 20 with an upper one Half 21 and a lower half 22 separated by a parting plane 23 are separated. The turbine steam passing through the exit surface of the top half of the diffuser in the upper half 21 of the evaporation housing 20 flows then down through the parting plane 23 into the lower half 22 and from there through the exit surface 24 of the evaporator housing in the connected there Capacitor.

The evaporation housing is designed in coordination with the diffuser so that the Exit surface 24 of the evaporation housing 20 is about 15% larger than that Total outlet area of the diffuser is. This grants an area reserve in the Separation level for any obstructions in the outflow.

According to FIG. 4, the sum of the exit areas of the partial diffusers 11 and 12 is the upper half of the diffuser is approximately equal to the area 25 in the parting plane 23, which between the evaporation housing and the evaporation baffle 8 'of Baffle 8 is formed and hatched in the figure with solid lines is. This means that half the sum of the exit areas S22 and S32 of the partial diffusers 11 and 12 over the entire rotation of the Diffuser is equal to the hatched plane 25 in the figure. Further is half of the exit surface S12 of the inner partial diffuser 10 over the entire Rotation of the diffuser is equal to the area 26 hatched by dashed lines. The alignment of these surfaces causes the diffuser outflow of the Partial diffusers 11 and 12 as they emerge from the diffuser into the exhaust housing the flow area is as large as possible and there are no bottlenecks. This in turn has a positive effect on pressure recovery.

FIG. 5 shows a variant of the three-channel diffuser according to the invention with an exhaust steam housing, which is optimized in comparison to the configuration in FIG. 1. The optimized diffuser with exhaust steam housing is designed, in particular with regard to the inner partial diffuser, in such a way that the outlet surface S12 'of the inner partial diffuser 10 is further defined in comparison to the configuration in FIG. If the exit surface S12 'is further out, as indicated by the dashed line, the ratio of the exit surface to the inlet surface of that partial diffuser increases and the efficiency of the turbine is increased accordingly. For this purpose, the exit area S12 'is defined in such a way that the ratio of its area to the entry area S11 increases to approximately 1.8, which is a significant increase compared to the ratio of approximately 1.3 in the variant of FIG. In order to continue to ensure that the flow area from the diffuser into the exhaust steam housing is as large as possible, the wall 21 'or hood of the upper half of the exhaust steam housing is placed radially further outwards in comparison to the wall 21 of the exhaust steam housing from FIG. At the same time, the baffle 27 'of the exhaust steam housing is placed axially further out. Accordingly, the deflection  ₁ reduced compared to the deflection angle in Figure 1 to about 60 degrees.

FIG. 6 shows this variant in the parting plane 23 between the upper and lower half of the diffuser. This also shows how the dimensions of the exhaust steam housing and the sizes of the outlet surfaces of the partial diffusers are coordinated. The diffuser is designed such that half of the exit surface S12 'of the inner partial diffuser 10 is approximately equal to the hatched area 28 in the parting plane 23 between the upper and lower half of the diffuser over the entire rotation of the diffuser. The surface 28 is formed by the baffle wall 27 'arranged axially further outwards, the hood 21' placed radially further outwards, a wall 31 facing the turbine and the exhaust-gas baffle 8 '. The surface 28 is finally closed by a fictional axially extending line 30 between the exhaust steam guide plate 8 'and the wall 31.
Furthermore, the sum of the exit areas S22 and S32 of the other two partial diffusers is approximately equal to the hatched area 29 in the parting plane. This surface 29 is the evaporation baffle 8 ', formed by the line 30, the wall 31.
Furthermore, the exit surface S13 'in the lower half of the diffuser in this case falls on the same location as the exit surface S12' for the upper half of the diffuser.

LIST OF REFERENCE NUMBERS

1

rotor

2

rotor axis

3

blade

4, 4 '

inner diffuser ring, first section of the inner diffuser ring

5

outer diffuser ring

5 '

first section of the outer diffuser ring

6

hub

7

blade carrier

7 '

last section of the blade carrier

8th

first baffle

8th'

Abdampfleitblech

9

second baffle

10

inner partial diffuser

11

medium partial diffuser

12

outer partial diffuser

13

Support or struts

15

geometric centerline of the partial diffusers

ε ₁ , ε ₂

Angle of inclination of the initial tangents of the guide plates with respect to the rotor axis

 _1,  _2,  ₃

Deflection angle of the partial diffusers

 _N

Kink angle of the inner diffuser ring

 _Z

Kink angle of the outer diffuser ring

 _L

Deflection angle of the steam guide plate

a

Distance from the blade to the front edge of the guide plate

h _w

Length of the last row of blades

e

Profiling length of the leading edge of the baffle

δ

Baffle thickness

20

exhaust steam

21.21 '

upper half of the steam housing, hood or wall

22

lower half of the evaporator housing

23

parting plane

24

Exit surface from the evaporator housing

25

Flow area of the parting plane for partial diffusers 11 and 12

26

Flow area of the parting plane for partial diffuser 10

27.27 '

baffle wall

28

Flow area of the parting plane for partial diffuser 10 in a further variant

29

Flow area of the parting plane for partial diffusers 11 and 12 in another variant

30

Auxiliary separation line

31

wall of the exhaust casing facing the turbine

S11

Entry surface in inner partial diffuser 10

S12

Exit surface from the inner partial diffuser 10 in the upper half of the diffuser

S12 '

Exit surface from the inner partial diffuser 10 in the upper half of the Diffuser in the further variant

S13

Exit surface from the inner partial diffuser 10 in the lower half of the diffuser

S13 '

Exit surface from the inner partial diffuser 10 in the lower half of the Diffuser in the further variant

S21

Entry area into the middle partial diffuser 11

S22

Exit surface from the middle partial diffuser 11

S31

Entry surface into the outer partial diffuser 12

S32

Exit surface from the outer partial diffuser 12

Claims (16)

Axial / radial three-channel diffuser with exhaust steam housing for low-pressure steam turbine, which leads the blading exhaust steam into the exhaust steam housing (20), with an inner diffuser ring (4), an outer diffuser ring (5) and two baffles (8, 9), which separate the diffuser in three Divide partial diffusers, an inner partial diffuser (10), a middle partial diffuser (11) and an outer partial diffuser (12),
the inner diffuser ring (4) being arranged at an articulation angle ( _N ) with respect to the hub of the low-pressure steam turbine and the outer diffuser ring (5) being arranged at an articulation angle ( _Z ) with respect to the last section (7 ') of the blade carrier (7) of the low-pressure steam turbine .
characterized in that the two baffles (8, 9) extend over the entire length of the diffuser, and the two baffles (8,9) are distributed between the inner diffuser ring (4) and the outer diffuser ring (5) in such a way that the surface distribution is distributed over the three Partial diffusers (10, 11, 12) are uneven in the inlet area, wherein a large part of the flow entry area of the entire diffuser is accounted for by the inner and middle part diffuser (10, 11) and a small part of the flow entry area of the entire diffuser is accounted for by the outer part diffuser (12), and the initial tangents of the guide plates (8, 9) together with the linearly approximated hub-side and housing-side limits of the blade channel of the last stage form at least approximately a common intersection (A) and the guide plates (8, 9) are arranged as close as possible to the rear edge of the last row of blades (3), the distance between the last row of blades (3) and the front edges of the guide plates (8,9) being determined by a minimum distance which is permissible for all operating conditions , Axial / radial three-channel diffuser according to claim 1
characterized in that
the ratio of the exit area (S22) to the entry area (S21) of the central partial diffuser (11) is at least two, the ratio of the exit area (S32) to the entry area (S31) of the outer partial diffuser (12) is at least three and the ratio of the exit area (S12) to Entry surface (S11) of the inner partial diffuser (10) is at least in the lower half of the diffuser in the range from 1.5 to 1.8. Axial / radial three-channel diffuser according to claim 2
characterized in that
for each partial diffuser (10, 11, 12) at least in the lower half of the diffuser the ratio of its length to its channel height in the inlet plane is at least 2.5. Axial / radial three-channel diffuser according to claim 3
characterized in that
the ratio of the total exit area to the total entry area of the three-channel diffuser is approximately two. Axial / radial three-channel diffuser according to claim 4
characterized in that
the entry area (S11) of the inner partial diffuser (10) 55-60%, the entry area (S21) of the middle part diffuser (11) 30-35% and the entry area (S31) of the outer part diffuser (12) 10-12% of the total entry area of the Diffuser. Axial / radial three-channel diffuser according to claim 5,
characterized in that
the initial tangents of the guide plates (8, 9) each lie in an angular range of 8 ° around the first break points (B, C) of the guide plates (8, 9) and around a reference start tangent through the first break points (B, C) of the guide plates (8,9) and through the intersection (A) of the rectilinearly approximated hub and housing-side limits of the blade duct of the output stage. Axial / radial three-channel diffuser according to claim 6
characterized in that
the distance (a) between the leading edges of the guide plates (8, 9) and the trailing edge of the last rotor blade is approximately 4% of the total height (h _w ) of the rotor row. Axial / radial three-channel diffuser according to claim 7
characterized in that
the front edges of the guide plates (8, 9) are profiled. Axial / radial three-channel diffuser according to claim 8
characterized in that
the baffles (8, 9) are supported by supports (13) which extend from the inner diffuser ring (4) and outer diffuser ring (5) to the baffle plates (8, 9) and have an increasing diameter downstream, and the middle partial diffuser ( 11) is free of supports. Axial / radial three-channel diffuser according to claim 9
characterized in that
On the guide plate (8), which is arranged between the inner partial diffuser (10) and the middle partial diffuser (11), an exhaust steam guide plate (8 ') is arranged in a radial extension. Axial / radial three-channel diffuser according to claim 10
characterized in that
the baffles (8, 9) have a thickness (δ) which is approximately 5% of the channel height of the central partial diffuser (11). Axial / radial three-channel diffuser according to one of the preceding claims
characterized in that
the size of the outlet surface of the evaporation housing (20) in the parting plane (23) between the upper half (21) and the lower half (22) of the evaporation housing (20) to the size of the outlet surfaces (S12, S22, S32) of the partial diffusers (10 , 11, 12) are coordinated. Axial / radial three-channel diffuser according to claim 12
characterized in that
the sum of the exit area (S22) of the central partial diffuser (11) and the exit area (S32) of the outer partial diffuser (12) is approximately equal to that area (25) in the parting plane (23) between the upper and lower half of the diffuser, which between the hood (21) of the exhaust steam housing (20) and the exhaust steam guide plate (8 ') is formed between the inner partial diffuser (10) and the central partial diffuser (11). Axial / radial three-channel diffuser according to claim 13
characterized in that
the outlet surface (S12) of the inner partial diffuser (10) in the upper half of the diffuser has a ratio of approximately 1.3 to the inlet surface (S11) of the inner partial diffuser (10) and the outlet surface (S12) of the inner partial diffuser (10) over the entire Rotation of the three-channel diffuser is equal to half the area (26) in the parting plane (23) between the upper half (21) and the lower half (22) of the evaporation housing (20) by the baffle (27), the hood (21) of the evaporation housing (20) and the baffle (8) between the inner and middle partial diffuser (11, 12) and the evaporation baffle (8 ') is formed. Axial / radial three-channel diffuser according to claim 12
characterized in that the outlet surface (S12 ') of the inner partial diffuser (10) in the upper half of the diffuser has a ratio of approximately 1.8 to the inlet surface (S11) of the inner partial diffuser (10) and the outlet surface (S12') of the inner partial diffuser (10) in the upper half of the diffuser over the entire rotation of the three-channel diffuser is approximately equal to half of the area (28) in the parting plane (23) between the upper half (21) and the lower half (22) of the evaporation housing (20) from the baffle (27 ') and the hood (21') of the exhaust steam housing (20), from the exhaust baffle (8 ') and an axial line (30) leading from the exhaust baffle (8') to a wall (31) facing the turbine the evaporator housing (20) leads, is formed and the sum of the exit area (S22) of the central partial diffuser (11) and the exit area (S32) of the outer partial diffuser (12) over the entire rotation approximately equal to half of the area (29) in the parting plane (23) between the lower and upper Half of the evaporation housing (20), that through the evaporation baffle (8 '), through the turbine-facing wall (31) of the evaporation housing (20) and through the axial line (30) from the evaporation baffle (8') facing the turbine Wall (31) is formed. Axial / radial three-channel diffuser according to one of the preceding claims 12-15
characterized in that
the total exit area of the three-channel diffuser is approximately 15% smaller than the exit area (24) of the exhaust steam housing (20).

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