NO309588B1 - Nozzle device for a free-jet water turbine - Google Patents

Abstract

The invention relates to an open-jet water turbine for powers of over 1kW, especially a Pelton turbine, with a bowl wheel and a plurality of injection nozzles (4, 5) arranged at its periphery and mutually staggered by an angle alpha . Such installations are usually designed with an angle of stagger alpha = 90 DEG because the efficiency falls as the angle of stagger is reduced. Contrary to accepted opinion, however, the efficiency increases once more of the angle of stagger is even smaller than 45 DEG and a flat efficiency curve with high efficiencies over a wide range of load is obtained. In addition, a higher injection can be attained, leading to lower investment costs for a given power.

Description

The present invention relates to a water-driven pelton turbine for outputs above 1 kW, according to the preamble.

Free current water turbines are usually connected to an electric generator to create electricity, where the turbine shaft and the generator shaft are connected to each other. In other words, with a free-jet turbine, the turbine wheel can sit on the generator shaft and, while hanging freely in the air, run around a house. Depending on the amount of flow, from 1 to 6 nozzles are applied tangentially with the water from a pressure pipeline with a mean jet circle diameter Ds. The adjustable needle nozzles are placed evenly offset around the outside, i.e. the offset angle of the nozzles to e.g. a 4-nozzle device is practically always 90°. The center line of the nozzle lies in the plane of the axial turbine wheel center, so that the water jet runs equally distributed in both bowls of a pair and is deflected equally distributed to both sides by almost 180° (J. Raabe: "Hydraulische Maschinen und Anlagen", VDI Verlag, 2. Auflage, Dusseldorf 1989, pp. 453 ff.). To make the generator small, the speed of the turbine must be as high as possible. At a given water jet velocity, this can only be achieved with a small turbine diameter. In order to keep the diameter of the free-jet turbine relatively small, the turbine is made from a specific flow rate, i.e. from a specific number of revolutions nq = 10 with a 2-nozzle injection system (nq = n Q1/2/H<3/4>, see J. Raabe : "Hydraulische Maschinen und Anlagen", VDI Verlag, 2nd Auflage, Dusseldorf 1989, p. 184 and p. 278). The shaft of the generator is usually lying here. In order to process even larger amounts of water, a second impeller with a 2-nozzle injection system is additionally mounted on the same axle (see e.g. Achenseekraftwerk der TIWAG, Tirol). Only for very large plants and at least 4 injection nozzles do you switch to technically expensive but flow-favorable vertical generator shafts (see, for example, Kraftwerk Silz in TIWAG, Tirol).

The invention has the task of improving the area of use for the tube inlet wheel. This task is solved in that between the injection nozzles there is at least one forslcyvning angle a among them which is 44° or less.

According to the state of the art, the assumption applies that the water from two spray nozzles must not interfere with each other. Based on experience, this applies to existing 6-nozzle turbines, where the offset angle for the jets is a constant 60°. The efficiency is not optimal here, as the residual water from the previous jet hits the water from the following jet at an angle of 60° and deflects it relatively much. It was therefore the lesson so far, which was based on experiments, that if you start from a displacement angle a of 90° with a reduction of the displacement angle, the efficiency also becomes worse.

The invention now shows that with a continued reduction of the displacement angle a, there is no constant reduction of the efficiency, but on the contrary that the efficiency after reduction below a certain displacement angle a again rises to high values. The explanation for this lies in the fact that the jets at displacement angles a, which keep getting smaller, finally unite into a kind of spiral seam with radial components, much like in the spiral housing of a Francis turbine. The losses due to the mutual beam deflection become smaller. At the same time, per bowl, a higher pressure is achieved with less loss.

The advantages described above are achieved with the turbine according to the present invention as defined by the features stated in the claims.

It is advantageous to combine several injection nozzles into a nozzle group with No offset angle a, whereby an increase in efficiency already begins at an offset angle of 38° and less, while an optimum can be between 29° and 20°, for example 27°. The nozzle group in and of itself increases the lifetime of the turbine, as the turbine bowls are no longer exposed to a load change per nozzle, but only per nozzle group. Fatigue fractures therefore occur less frequently.

Another advantage is the lower noise level. The especially noisy cutting of the water jet with the foremost entry cut into an empty bowl now only takes place once per nozzle group and no longer at each nozzle. Several such nozzle groups can be distributed on the outside in such a way that the radial forces in the turbine bearing are mostly canceled out.

The device relating to the invention allows a high water pressure on the turbine, as with the small offset angle, up to 12 injection nozzles can be distributed around the outside of the turbine, whereby the shaft then has to be positioned vertically. Especially with highly varying amounts of water, the free-jet wheel with the injection system according to this invention would displace slow-moving Francis turbines to a specific speed of around nq =35.

By purposefully connecting and disconnecting the affected external injection nozzles in a nozzle group, the efficiency proceeds almost over the entire range of the water variation during one nozzle's operation, i.e. from 1/4 of the water quantity at full load with four nozzles to full load as a very flat curve with a high maximum value .

Another advantage is the structural simplification for the water supply and the jet switch. The supply pipes are shorter and the curvatures are weaker, whereby the degree of nozzle deflection is improved. The space required for the injection system is significantly reduced and the mechanism for the nozzle regulation is close at hand.

The high water pressure makes it possible with a turbine wheel to produce significantly higher outputs. The investments during construction are therefore smaller in terms of turbine size, space requirements and water supply in relation to performance.

Instead of a normal 2-wheel plant with 2 injection nozzles each for the range riq = 14 to 20, a single-wheel plant with 4 injection nozzles can be built without expensive ring lines and a standing axle. The turbine can be fed by up to 6 injection nozzles, with the preservation of an inexpensive horizontal shaft arrangement. No additional ventilation losses or bearing friction losses occur with a second impeller. The structural simplification was mentioned above.

In an earlier two-nozzle system with a horizontal shaft, the pipe bends for the water supply mostly do not lie in a plane, whereby the water is set in rotation. This well-known problem leads to atomization of the free jet by centripetal forces and thus to a reduction of the efficiency. In the nozzle group that relates to the invention, the strong curvature from the first to the second nozzles disappears. In addition, the atomization of the jet is smaller, as the pipe curvature due to the small construction space can mostly be carried out in a plane.

In the following, the invention is described using design examples. Here, figure 1 schematically shows a turbine impeller which is pressurized from a 4-nozzle nozzle group where the displacement angle a = 27°, figure 2 schematically shows the tightening amount of water QB for a bowl at a revolution U of 360° and the previous pressure from a 4-nozzle system with an offset angle a = 90°, and Figure 3 schematically shows the tightening amount of water QB for a bowl with a revolution U of 360° and pressure from a 4-nozzle nozzle group, where the offset angle a = 27°.

The application subject will be explained using a 4-nozzle turbine.

Usually, the angle of inclination of 4 injection nozzles is constant a = 90°. Each bowl on the turbine is filled and emptied 4 times for each revolution of the wheel (= 360°, figure 2). With the device relating to the invention, the injection nozzles in a nozzle group come so close to each other that the bowl is first filled when the first water jet engages, and then immediately pressured by the next injection nozzle when the bowl is emptied of the water from the first injection nozzle (figure 3) . The offset angle a to the nozzle center line is chosen so that the contour curve for the total water pressure shows a most constant upper part. This is achieved at a = 30°.

When all 4 nozzles follow one another, the amount of water in the turbine bowls rises only once for each revolution of the wheel and also only drops once after the fourth nozzle jet.

If the arrangement of the nozzles in a single nozzle group results in excessively high bending moments in the shaft, several nozzle groups can also be distributed evenly around the outside. There then follows an increase and a decrease in the amount of water for each nozzle group.

In the area around the maximum bowl pressure, the turbine works with the best degree of efficiency, as the hydraulic radius of the jet rh is then the largest (rtl = water's cross-sectional area/fiction surface area; see "Hiitte, des Ingenieurs Taschenbuch", Verlag von Wilhelm Ernst & Sohn, 27th edition , Berlin 1941, p. 472 or J. Raabe, "Hydraulische Maschinen und Anlagen", VDI Verlage, 2nd edition, Dusseldorf 1989, p. 808). The hydraulic loss due to friction and vortex formation in the bowl is then the smallest in relation to the impulse force of the water. The small amounts of water at the inlet (E) and outlet (A) of the jet from the bowl (shaded surfaces (E) and (A) in figure 2) are changed with a lower degree of efficiency, as the jet is then extended flat over the bowl. Its impulse force is small compared to the friction surface.

These beginning and end areas where the degree of efficiency is poor occur with the usual nozzle arrangement once per nozzle (in the example in Figure 2 exactly eight times), but with the nozzle arrangement relating to the invention only once for each nozzle group (2 shaded surfaces (E) and ( A) in figure 3).

The collection of the jets relating to the invention is shown in the water quantity diagram (figure 3) as a constant upper curve, which means that the vanes process the largest quantity of water with the best degree of efficiency. This causes an improvement in the hydraulic efficiency of the turbine.

An ordinary needle nozzle is used as the injection nozzle. The nozzle center line is tangent to the normal jet circle diameter of the turbine Ds, (ie no changes are to be made on the turbine). The supply pipe 6 to each nozzle group now consists of a single curved pipe 8, which tapers in the discharge direction. As usual, the individual nozzle necks are welded to this piece of pipe. On a turbine with a specific number of revolutions per nozzle of nqo = 3 (slow moving), the optimal nozzle displacement angle according to this invention is a = 1<9>° (<nq>D<=> n Qd<1/2> / H<374>, where Qd is the flow per nozzle, see J. Raabe, "Hydraulische Maschinen und Anlagen", VDI Verlage, 2nd edition, Dusseldorf 1989, p. 292). For n^ = 7, a = 27°, and for rv = 11, a = 35° would be the optimal displacement angle. Other angles can be interpolated for each specific number of revolutions.

Figure 1 shows an example of the arrangement of the injection nozzles. The turbine has a specific number of revolutions of n^ = 14. According to experience, a turbine has the best degree of efficiency when n^ = 7 approximately. From the formula nq = (iD iR)<1/2> nq0 (with iD = number of nozzles and iR = number of wheels) it becomes a favorable device when one chooses iD = 4 and iR = 1. This 4-nozzle, one-wheel device becomes constructed with a nozzle offset angle of a = 27° which relates to the invention.

Claims (10)

1. Water-driven pelton turbine for outputs above 1 kW, with a vane wheel 1 (2) having at least three times as many injection nozzles (4) as vanes arranged around the circumference, where the nozzle center lines (7) of neighboring nozzles are offset by an offset angle a relative to each other and where more than two nozzles (4) are united to form a nozzle group to improve the vane efficiency, CHARACTERIZED BY the fact that the forslcyvning angles a in a nozzle group are the same and less than 44°, and that a vane passing two neighboring nozzles in a nozzle group receives no less than 50% of a nozzle's effect. 2. Turbine according to claim 1, CHARACTERIZED IN THAT the displacement angles a in a nozzle group are 38° or less. 3. Turbine according to claim 2, CHARACTERIZED IN THAT the displacement angles a in a nozzle group are between 29 and 20°, preferably 27°. 4. Turbine according to the preceding claim, CHARACTERIZED IN THAT a nozzle group's injection nozzles (4) are fed through a common curved pipe (8). 5. Turbine according to claim 4, CHARACTERIZED IN that several nozzle groups are distributed around the circumference. 6. Turbine according to the preceding claim, CHARACTERIZED BY the fact that injection nozzles (4) can be switched on and off separately to change the effect. 7. Turbine according to the preceding claim, CHARACTERIZED IN THAT the jets from the injection nozzles (4) can be regulated to change the effect. 8. Turbine according to the preceding claim, CHARACTERIZED IN THAT the specific number of revolutions per irm spray nozzle n^, respectively Di/B2 is between 5 to 11, and that the offset angle a in a nozzle group is between 20° and 40°. 9. Turbine according to claim 1, CHARACTERIZED IN THAT nine to fifteen injection nozzles are placed evenly distributed with the same offset angle a to each other along the circumference. 10. Turbine according to claims 4-9, CHARACTERIZED IN THAT only the outer injection nozzles (4) in each nozzle group can be connected and disconnected in order to maintain a contour curve with a high vane pressure in the areas between the currently active injection nozzles in a group in the event of a change in power demand .