WO2008060159A2

WO2008060159A2 - Hydraulic reaction turbine

Info

Publication number: WO2008060159A2
Application number: PCT/NO2007/000355
Authority: WO
Inventors: Anders Wedmark
Original assignee: Andritz Technology And Asset Management Gmbh
Priority date: 2006-11-16
Filing date: 2007-10-10
Publication date: 2008-05-22
Also published as: WO2008060159A3; NO20065275L; CA2669840C; CA2669840A1; NO325508B1

Abstract

Hydraulic reaction turbine comprising a runner; a draft tube (1) downstream of the runner; injection means (4,10) for introducing water into the draft tube in order to reduce pressure fluctuations therein; and control means (6) for the injection of water. The said control means comprise at least one movable element (6) incorporated in said injection means (4,10) and located closely adjacent to the draft tube wall (1a).

Description

HYDRAULIC REACTION TURBINE

In the draft tube downstream of the runner in Francis turbines and other hydraulic reaction turbines with fixed runner blades there have been problems in connection with vibrations and pulsations when operated at higher and/or at lower loads than the load for highest efficiency. Various methods are known for the purpose of reducing these pressure fluctuations, that are related to an undesired rotational component of the water in the draft tube when the unfavourable load conditions occur.

Mechanical means are known for reducing or eliminating the above problems . One example of a mechanical solution is found in US patent publication 2004/0037698, describing fixed stay vanes after the runner.

Other prior art solutions resort to air or gas injection for the same purpose, as for example described in JP-02238177 and US-2004/0265117.

Moreover, injection of water into the draft tube in order to reduce pressure fluctuations therein has been described in WO-2006/043824.

Mention may further be made of JP-61178563, where also introduction of water through the draft tube wall is shown. However, this is for suppressing exfoliation in a Kaplan-type of turbine in which there is not any problem with pressure pulsations of the kind contemplated here. Such problems occur regularly at certain load conditions in reaction turbines having a runner with fixed blades, whereas Kaplan-type turbines have adjustable pitch blades. By injecting water, the unfavourable flow vortex formation that may occur, will be impeded or destroyed, thereby making it possible to operate the turbines over a broader range of loads .

More specifically the injection of water (under high pressure) will serve to eliminate the rotational or vortex component mentioned above, occurring in the water leaving the turbine runner. Thus, the downstream flow will be more close to axial, and the undesired pressure fluctuations will no longer represent a serious problem. It may, however, be considered to be a certain drawback that injection of water under pressure will require some energy, which may reduce the total efficiency of such turbines .

The present invention aims at improving the water in- jection apparatus in reaction turbines as mentioned above. Thus, the invention in a general aspect is directed to a hydraulic reaction turbine comprising a runner, a draft tube downstream of the runner, injection means for introducing water into the draft tube in order to reduce pressure fluctuations therein, and control means for the amount of water to be injected. The novel and specific features according to the invention primarily consist therein that said control means comprise at least one movable element incorporated in said injection means and located closely adjacent to the draft tube wall.

A substantial advantage obtained with this solution, is that no energy is lost by controlling or restricting the injection water flow upstream of the point of introducing the water through the draft tube wall, for example by means of a valve located at some distance from the draft tube as done according to prior art. Since by means of the present invention such loss of energy is avoided, the total operating efficiency is increased. This may be very important in many turbine installations, - existing installations as well as new plants to be designed.

The invention will now be explained more in detail with reference to various embodiments thereof, as illustrated in the accompanying drawings, where: Fig. 1 is a simplified cross-section of a draft tube with a slot-like water injection opening, Fig. IA shows the shape of the water injection opening as seen according to arrows A-A in Fig. 1, Fig. 2 in a similar cross-sectional view as Fig. 1, shows a second embodiment with a number of water injection openings distributed around the periphery of the draft tube,

Fig. 3 shows a simplified vertical cross-section at one of the water injection openings in Fig. 2,

Fig. 4 in cross-section shows a further embodiment with a water injection nozzle arranged at an inclination horizontally with respect to the draft tube wall, Fig. 4A shows the fundamental shape of a water injection opening that may be established with the nozzle structure in fig. 4, Fig. 5 shows an injection nozzle that may be taken as a modification of the one in Fig. 4, Fig. 5A shows the end face of the nozzle in Fig. 5,

Fig. 6 shows a further modification from the embodiment in Fig. 5, as a more typical nozzle that has a circular cross-sectional shape,

Fig. 7 is a schematic overview illustration in axial cross-section, showing essential parts of a reaction turbine, including the runner and the draft tube as well as a water injection apparatus .

Looking first at Fig. 6, there is illustrated a conventional Francis turbine with a runner 100 and a draft tube 1, with an axis of rotation 100a, being also the central axis of draft tube 1 immediately downstream of the runner 100. In the wall of draft tube 1 there is schematically indicated an injection apparatus 10 for water to be introduced so as to reduce pressure fluctuations as discussed above.

Fig. 1 being a cross-sectional view as indicated at I-I in Fig. 6, illustrates a first embodiment where control means for the injection of water comprises a movable element 6 located closely adjacent to the draft tube wall Ia. Moreover, in this embodiment the injection apparatus comprises a water distribution chamber 4 external to the draft tube wall Ia and in communication with a slot or opening 10 in the wall. The slot-like injection opening 10 is adjustable by means of the movable member 6, that may be moved in translation as illustrated by arrows 1Ox so that an edge portion 6e of this element may establish a smaller or larger outflow cross-sectional area in nozzle 10. As will be understood, the movable element 6 during such adjustment will be moved in a direction closely parallel to the draft tube wall Ia at the position of the nozzle or slot opening 10.

As illustrated in Fig. IA, the opening 10 has a substantially elongated shape, whereby the above mentioned edge portion 6e of the movable element 6 will form one long side or limitation of opening 10. This structure will provide for an advantageous control of the amount of water injected through nozzle opening 10 from chamber 4. In the embodiment of Fig. 2 a comparatively large number of slot-like openings 20 are provided and evenly distributed along the circumference of draft tube wall Ia. It will be understood that although complete coverage of the whole circumference as illustrated in Fig. 2, is favourable, there may be modifications where some portions of the circumference do not have such injection openings. This may be in order to ensure that the water has the proper angle relative to the axis of the draft tube when it enters the draft tube. Water is supplied under pressure through a conduit 2 and distributed around the draft tube by means of an external, closed channel 3. Thus, water injection will take place as indicated with two arrows 25, through all openings 20. There is a further advantageous structural feature being common to the embodiments illustrated in Figs 1 and 2: As will be seen, the openings 10 and 20 diverge outwards through the wall Ia, thus reducing the velocity of the injected water while flowing from chambers 4 and 5, respectively, into the draft tube 1. During such flow most of the energy in this water will be maintained, which is beneficial to the total efficiency of the turbine.

The cross-sectional detail of Fig. 3 shows how control of the water injection can take place in this embodiment. From an annular chamber 5 formed by channel structure 3, an opening 20 at draft tube wall Ia is formed in part by a movable element 7 that is adapted to be adjusted as indicated by arrows 2Ox, ie. in a substantially vertical direction. Preferably the movable element 7 is part of an integral structure extending around the complete circumference of the draft tube 1. Thus, the integral assembly of such movable elements 7 may be adjusted in common in an axial direction as indicated. At 7e there is shown an edge portion of the movable element 7, being effective in defining the opening 20 in an upward direction and thereby the amount of water injected.

In the embodiment of Fig. 4 there is a tubular nozzle 40 arranged at an angle in the horizontal plane, to the draft tube wall Ia and having a rectangular cross- sectional shape. This is due to a structure of plate parts, comprising at one (inner) side a plate member 41 and at the other side a plate member 42 being adjustable by translatory movements so as to constitute a control element. Plate member 42 during adjustment may be moved outwards or inwards with respect to the wall Ia, ie. between a forward position where the injection opening is almost closed, and a retracted position, indicated at 42', that will result in a maximum outflow cross-sectional area. In the latter position the spacing between the plate members 41 and 42 is indicated at 44. The corresponding shape of the opening is illustrated in Fig. 4A. Reference numeral 42e denotes the edge portion of plate member 42 being effective in defining the injection opening together with the inner surface of plate member 41. In the structure shown, this function is related to the fact that plate member 42 as a movable control element is adapted to be adjusted in a direction closely parallel to the longitudinal direction of the nozzle 40. In contrast to the embodiment of Fig. 4, the one illustrated in Fig. 5 is based on a tubular nozzle 50 having a circular cross-sectional shape. Here, there is provided a movable sleeve 52 that cooperates with a cone- shaped, stationary insert member 51. This is dimensioned so as together with sleeve 52 more or less to restrict the flow cross-sectional area at the outlet of the nozzle. In the fully forward position as shown, the sleeve 52 serves to almost block for any water injection, whereas more retracted positions of the sleeve 52 gradually will result in an increased flow cross-sectional area of the nozzle. In a maximum retracted position as indicated at 52' there will be a maximum amount of water injected through the nozzle. In other words this movable element in the form of a sleeve-like tip 52 of the tubular nozzle 50, is adapted to be adjusted telescopically on the nozzle, and the outwardly diverging insert member 51 is provided and shaped for cooperation with outer end portions 52e of the sleeve or tip 52.

As seen from Fig. 5A the end face of the circular cross-section nozzle structure in Fig. 5 will be of a substantially elliptical shape in view of the angle between nozzle 50 and draft tube wall Ia.

In Fig. 6 there is again a form of control of the amount of water injected through the draft tube wall Ia, based on relative movement of an element 62 and outer end portions 6Oe of a tubular nozzle 60. Element 62 is here generally rod-shaped and provided with an outer end member 64 for cooperating with the end portions 6Oe. Like nozzle 50 in Fig. 5, nozzle 60 in Fig. 6 has a circular cross- sectional shape. Nozzle orifice or end portions 6Oe will normally have an elliptical shape in view of the inclined position of nozzle 60 in relation to the wall Ia. The end member 64 will be correspondingly shaped and in addition is diverging outwards so as preferably to be able to completely close nozzle orifice 6Oe. This is illustrated in a retracted position shown at 62' in Fig. 6.

On the other hand end member 64, because of the diverging or conical shape will have a favourable effect of spreading the injected water into a large volume of the main, vertical water flow from the runner 100 (Fig. 1) .

It will be understood that in many of the embodiments described, the movable control elements may be exposed to the main water flow in the draft tube, at least in some of the adjusted positions of the movable elements.

Whereas some practical embodiments according to the invention have been described and schematically illustrated in the drawings, various modifications may be possible, such as in the number and shape of nozzles or injection openings or the direction of water injection, depending on the requirements in individual hydraulic reaction turbines where pressure fluctuations in the draft tube may be a problem.

Claims

C l a i m s

1. Hydraulic reaction turbine comprising - a runner (100) ,

- a draft tube (1) downstream of the runner,

- injection means (4,10,5,20,30,40,50) for introducing water into the draft tube in order to reduce pressure fluctuations therein, - and control means (6,7,11,42,52) for the amount of water to be injected, c h a r a c t e r i s e d in that said control means comprise at least one movable element

(6,7,11,42,52,62) incorporated in said injection means (4,10,5,20,30,40,50,60) and located closely adjacent to the draft tube wall (Ia) .

2. Turbine according to claim 1, wherein said injection means comprise at least one slot-like opening (10,20) in the draft tube wall (Ia) for said water injection, and said movable element (6,7) is adapted to be adjusted in a direction closely parallel to the draft tube wall (Ia) at the position of the slot-like opening (10,20).

3. Turbine according to claim 2, wherein one edge portion (6e,7e) of said movable element (6,7) forms a longer side of said slot-like opening (10,20).

4. Turbine according to claim 1, 2 or 3 , wherein a plurality of said slot-like openings (20) are evenly distributed around a substantial portion of the periphery of said draft tube (1) .

5. Turbine according to claim 4, wherein said movable element (7) is an integral element common to said plurality of slot-like openings (20) and preferably is adapted to be adjusted in an axial direction with respect to the draft tube (1) .

6. Turbine according to claim 1, wherein said injection means comprise at least one tubular nozzle (40,41,42,50,60) directed at an angle through the draft tube wall (Ia), and said movable element (42,52,62) is adapted to be adjusted in a direction closely parallel to the axial direction of the tubular nozzle.

7. Turbine according to claim 6, wherein said tubular nozzle (40,41,42) has a generally rectangular cross- sectional shape and is provided with a slot-like opening (44) for said water injection and an edge portion (42e) of said movable element (42) forms a longer side of said slot-like opening (44) .

8. Turbine according to claim 6, wherein said movable element forms a sleeve-like tip (52) of said tubular nozzle (50) and is adapted to be adjusted telescopically in axial relation to the tubular nozzle, and an outwardly diverging insert member (51) is provided and shaped for cooperation with outer end portions (52e) of said sleeve- like tip (52) .

9. Turbine according to claim 6, wherein said movable element comprises an axially extended rod (62) being adjustable in its longitudinal direction within the tubular nozzle (60) and having an outer end member (64) adapted to cooperate with outer end portions (6Oe) of the nozzle (60) .

10. Turbine according to claim 9, wherein said end member (64) has an outwardly diverging shape.

11. Turbine according to any one of claims 1-5, wherein said injection means (4,10,5,20) comprise at least one opening (10,20) in the draft tube wall Ia having an outwardly diverging flow cross-sectional area.