GB2210107A

GB2210107A - Device for deriving energy from a liquid flow

Info

Publication number: GB2210107A
Application number: GB8822192A
Authority: GB
Inventors: R Geoffrey Norman Bullock
Original assignee: SECRETARY ENERGY BRIT
Current assignee: SECRETARY ENERGY BRIT
Priority date: 1987-09-21
Filing date: 1988-09-21
Publication date: 1989-06-01
Also published as: GB8822192D0; GB8722218D0

Abstract

A butterfly gate valve 16 diverts liquid flow alternately into and out of a pair of chambers 11, 12. By careful shaping and dimensioning of the components flow past the gate valve 16 merges smoothly with swirling flow within the chambers 11, 12 and hydrodynamic pressures assist the switching movement of the gate valve 16; the movement can even be fully flow actuated. The opposed rise and fall of liquid level in the chambers can be used to drive air through a turbine (21, Fig 2) and thus convert, for example, a water pressure head into electrical energy. <IMAGE>

Description

Low head liquid energy conversion device The invention relates to a device for the conversion into a useful or useable form of the energy in a supply of liquid at a low pressure head. More particularly the invention relates to a low head water engine and a flow actuated gate valve there for.

Several forms of engine have been proposed for extracting energy from sources of water at relatively low pressure heads, such as rivers or tidal flow. A number are based upon one or more chambers provided with gate valves which are opened and closed appropriately to cause the chamber repeatedly to fill and then empty. The rise and fall of the water level in the chamber provides the drive for a power output component. This may be an air turbine driven by air forced to flow to and fro by the movement of the water level, as for example described in "Hydropneumatic approach to harnessing tidal energy" by A M Gorlov - June 1982 conference on New Approaches to Tidal Power, Bedford Institute of Oceanography, Dartmouth, Nova Scotia.In another arrangement, the rise and fall of water level acts on a float mechanically coupled to hydraulic pistons, as described by E M Wilson, D E Basett and I D Jones in a paper entitled "Two New Machines for Hydraulic Power from Low Heads" presented to the 12th IAHR Symposium, Stirling, August 1984.

A problem for engines of this type is to provide a flow path and gate valve and control arrangement which is effective whilst being simple and economical not only in terms of manufacturing and maintenance costs but also in terms of the proportion of energy taken up in moving and controlling gate valves.

According to the invention, there is provided apparatus for liquid flow control comprising a first chamber and a second chamber, each chamber having a port opening for liquid flow into and out of the chamber, a pivoted gate valve being positioned to control liquid flow alternately into and out of the chambers so that whilst liquid flows into the first chamber liquid flows out of the second chamber and vice versa, the chambers having a shape in horizontal section and locations relative to the gate valve such as to generate a swirling flow of liquid in the chambers which swirling flow, in the region of the respective ports, merges substantially smoothly with the flow of liquid past the gate valve.

Preferably the said shape in horizontal section and locations relative to the gate valve of the chambers, and the shape of the gate valve are such that the general direction of flow of liquid flowing into or out of a chamber past the gate valve is substantially tangential to the flow line of the swirling liquid within the chamber at the periphery thereof.

Preferably the gate valve is so pivoted intermediate its ends for movement about an axis transverse to the direction of liquid flow, and the port openings are so dimensioned and located that hydrodynamic pressures automatically provide forces appropriate for causing or assisting alternating switchover of the gate valve whenever a predetermined substantial difference in liquid level between the chambers is reached.

With certain configurations fully automatic flow actuated operation is possible. In general, however, it may be desirable to provide a releasable latch mechanism for temporarily holding the gate valve in one or more predetermined positions. A suitably controlled independent power source may be coupled to the gate valve. This may be desirable for optimising economic or power output performance, or in an apparatus in which the forces provided by hydrodynamic pressures are alone insufficient to move the gate valve as required.

Preferably the port openings are facing one another and define therebetween a space through which, but for the gate valve, liquid would flow between the chambers from an upstream to a downstream side thereof when the apparatus is in use, the gate valve being positioned between the port openings and pivotable between a first position in which the port in the first chamber is open to inflow of liquid from the upstream side but closed to outflow of liquid to the downstream side, whilst the port in the second chamber is closed to inflow of liquid from the upstream side but open to outflow of liquid to the downstream side, and a second position in which the open and closed conditions of the respective ports are reversed.

For deriving power from the apparatus, a turbine is connected to be driven by air or other suitable gas caused to flow through the turbine by the reciprocating movement of the liquid levels in the chambers. In this case, to maintain a trapped volume of air in the chambers and turbine duct, the top of the port opening of each chamber is below the lowest liquid level reached in the chamber in the vicinity of the port when the apparatus is in normal use.

Specific constructions of apparatus embodying the invention will now be described by way of example and with reference to the drawings filed herewith, in which: Figure 1 is a diagrammatic plan view of an apparatus, Figure 2 is a diagrammatic elevation in the direction of arrow A in Figure 1, Figure 3 is a diagrammatic horizontal sectional view of part of the apparatus, and Figure 4 is a diagrammatic horizontal sectional view of part of a modified apparatus.

The apparatus of this example, referred to as a pneumatic water engine, is intended for harnessing sources of hydropower with a very low pressure head, such as is too low to be harnessed economically by conventional water driven turbines. A differential head of the order of 3 m across the apparatus is assumed.

Two chambers 11, 12 are provided by a pair of cylinders whi-ch form part of a barrage 13 positioned acrossthe water flow the direction of which is indicated by arrow A in Figure 1.

The cylinders are arranged side by side with their axes vertical. A short section of the wall at the bottom of each cylinder is cut away to form ports 14, 15 facing each other across the narrowing region between the two cylinders. The barrage 13 extends across the space between the cylinders and upwardly from the level of the top of the ports 14, 15.

A butterfly gate valve 16 is mounted on a pivot 17 which, in this example, extends vertically and is transverse to the direction of water flow. As may best be seen from Figure 3, the gate valve 16 can move about the pivot 17 between two principle positions: a first position in which port 15 is open to inflow of water from the upstream side of the barrage, but closed to outflow of water to the downstream side, whilst port 14 is closed to inflow of water from the upstream side of the barrage, but open to outflow of water to the downstream side: and a second position in which the open and closed conditions of the ports 14, 15 are reversed.

To prevent water flowing over the gate valve 16 from the upstream to downstream side, a cover plate 18 extends over the top of the gate valve 16.

The two chambers 11 and 12 are intercommunicating at the top through a turbine duct 19 in which is mounted a non-directional air turbine 21 such as a Wells turbine.

Various relative dimensions of the ports 14, 15 and the gate valve 16 are important and the dimensions marked in Figure 3 are as follows: Width of opening of the ports 14, 15 = Lu + Ld where Lu is the distance of the upstream edge of the port to a line transverse to the direction of flow through the axis of the pivot 17 and passing symmetrically through the ports 14, 15. Ld is the corresponding distance from this line to the downstream edge of the port.

Length of gate valve 16 = Gu + Gd where Gu is the length of the gate valve 16 extending upstream from the pivot 17 and Gd is the length of the gate valve 16 extending downstream from the pivot.

In operation, with the gate valve 16 in the first position shown in Figure 3, chamber 12 fills while chamber 11 empties. When a predetermined difference in water levels in the chambers is reached, the gate valve is pivoted across to the second position, chamber 11 then filling whilst chamber 12 empties. The gate valve 16 is then returned to the first position and the cycle repeats.

It will be evident that the sequence creates a reciprocating flow of air through the turbine 21 which can be coupled to a generator to convert energy from the water head into electricity.

It should be noted that the positioning of the ports 14, 15, the gate valve 16 and the use of circular section chambers provides for (a) one gate valve 16 to serve two chambers reducing cost as compared with arrangements requiring a separate gate valve for each chamber (b) gate valve 16 closes onto the edges of the ports 14, 15 substantially tangentially to the cylinder walls, thus providing good entry and exit flow conditions and generating a swirling flow of liquid in the chambers.

The general direction of liquid flow past the gate valve 16 is substantially tangential to the flow line of the swirling liquid within the chamber so that the flows merge smoothly (c) thus flow is effectively in a spiral into and (in the same sense) out of the chamber so that there should be minimal loss of both kinetic energy and inertia (d) spiralling flow tends to create a central depression in the water in the chambers, reducing the risk of splashing into the turbine duct 19, and can be arranged to impart useful pre-swirl to the air entering the turbine (e) zzess for Lc. mainter.ance/replacement of the gate valve is easily provided.

By careful design of the gate valve 16 and the dimensions and positioning of the ports 14, 15, it is possible to achieve self starting, flow actuated movement of the gate valve 16.

Experiments have been carried out on a model apparatus, with a chamber height of 40 cm, and a simple throttle valve for mimicking the effect of the turbine 21.

The model was tested in a flume 61 cm wide capable of containing up to 40 cm depth of water. Typically the tests were carried out with 28 cm depth of water upstream and 13 cm downstream, giving a head of about 15 cm water across the model. The model is thus at a scale of 1:20 of an apparatus intended to work on a 3m pressure head.

In the model the height of the gate valve 16 is 8 cm and the gate moves through a 450 arc. The size of the ports 14, 15 can be varied by changing insert pieces 22, 23 (see Figure 3).

In general, an external force has to be applied to the gate, depending upon the design, either to move it from the first position to the second position and vice versa, or to hold it fully "closed" in these positions whilst the water levels within the chambers vary over the range of available head.

However, configurations have been found in which the gate operates satisfactorily actuated by the flow alone.

These are characterised as follows, the arc angle being the angle through which the gate moves: Gate Length Arc Angle Gu Gd Lu Ld GL (mm) (Degrees) (mm) (mm) (mm) (mm) 120 45 30 90 25 60 130 45 30 100 25 63 130 45 40 90 35 65 140 45 40 100 35 60 155 45 40 115 33 70 120 55 30 90 27 60 130 55 30 100 27 65 140 55 40 100 36 66 155 55 40 115 36 70 170 55 50 120 45 70 190 55 50 140 47 75 190 (30 mm x 65 50 140 47 73 10 mm Fin) The criteria adopted for satisfactory gate valve operation for a water engine are that:: 1. the gate valve must remain firmly closed while the water levels in the chambers vary over more or less the full range of available pressure head 2. once the water level has approximately equalised across the gate valve opening, the gate must move smoothly and rapidly from one "closed" position to the other.

In the examples in which operation met these criteria, the pivot 17 has to be offset towards the upstream edge of the gate, ie Gu Gd. Once the water level in the filling chamber exceeds that in the emptying chamber, hydrostatic pressure across the gate acts increasingly in the sense tending to rotate the gate away from its existing closed position. Evidently this tendency is opposed by hydrodynamic forces which, in the configurations of the examples, hold the gate "closed" against the hydrostatic pressure until the in flowing water approaches the level of the upstream water level.

An important aspect of the configuration in this respect is that it generates a swirling flow of water in the chambers which, in the region of the respective ports, merges substantially smoothly with the flow of water past the gate valve. The general direction of flow of water past the gate valve is substantially tangential to the flow line of the swirling water within the chamber at the periphery thereof. The design avoids flow separation which could diminish or eliminate the desirable hydrodynamic forces.

To achieve operation satisfying the two criteria mentioned above, the relative magnitudes of Gu, Gd and Ld have to be chosen with some care. The effect of varying Ld can be illustrated with reference to Example 1 above which opoperates best with Ld = 70 mm. The gate valve 16 operates with varying degrees of success at any value opf Ld between 65 mm and 75 mm. The effect of reducing Ld to the lower value is that the gate remains "closed" in one position until a higher water level is reached in the filling chamber before the gate swings across to the other position. Conversely, increasing Ld to the higher value has the effect that the gate swings back and forth between the two "closed" positions with a reduced rise and fall (20 - 30 mm in the example) of water levels in the chambers 11, 12.

It will be appreciated that the characteristics of the ports 14, 15 and gate valve 16 offer a wide choice of variables which, by careful adjustment can provide for fine tuning of the operation.

Thus, some arrangements tested showed a tendency for the gate to oscillate rapidly as it approached one or other of its "closed" positions, causing chatter as the gate knocks against the sides of the cylinders. Such chatter has been eliminated by provision of fins near the downstream edge of the gate and/or aerofoils near the upstream edge of the gate. This is illustrated in Figure 4 in which fins are referenced 24 and aerofoils 25.

In addition, or as an alternative to the provision of fins and/or aerofoils, shaping of the gate valve in its horizontal cross section and/or shaping of the vertical edges of the ports 14, 15 can be expected to provide further scope for tuning the performance.

A further advantage of fins and/or aerofoils is a more positive gate movement, with a reduced tendency for the gate to hesitate or hover in-between its two "closed" positions.

A releasable latch mechanism may be provided for temporarily holding the gate at one or more positions.

Thus, a useful capability is to provide for releasably latching the gate at each of its closed positions and at the position symmetrically in-between the two "closed" positions. In this way, with a suitable latch control, release of the gate for movement from one "closed" position to the other may be controlled at least partly independently of the hydrodynamic forces acting on the gate. In particular, the gate may be held in a "closed" position until a higher water level is reached in the filling chamber than might occur in the absence of the latch.

Latchinq in the intermediate position, in which case the apparatus functions as a simple sluice, is useful during construction, maintenance and times of flood.

It may be desirable to provide an independent power source, suitably controlled, coupled to the gate, where, for example, reliance cannot be placed upon a configuration in which gate movement is fully flow actuated; or use of an independent power source in this way may give better results in economic or power output terms. It is important that the water assists rather than opposes the independently powered gate movement.

The invention is not restricted to the details of the foregoing examples. For instance, the examples show 450, 550, and 650 gate movement but it is envisaged that operation at other angles is practicable. The height of the gate valve is limited in that it must remain substantially submerged at all times during operation. A gate valve with a horizontal top is unlikely to be substantially higher than the downstream depth of water.

For a given head of water, increased volume flow may thus be achieved by sloping or stepping the gate valve so that its height is greater at its upstream end. The use of right circular cylinders for the chambers 11, 12 has a number of advantages in terms of flow paths, but, given satisfactory shaping of flow passageways, other shapes of chamber may be used.

There may be more than one pair of chambers in a particular installation. One air turbine could serve more than one pair of chambers. A non-directional air turbine 21 need not necessarily be used; a directional turbine could be used if fed from suitably valved additional air flow passages. In certain circumstances it may prove useful to provide a separate turbine for each chamber and not link the chambers through the turbines in pairs - ie having the other side of the turbine venting to atmosphere.

Certain advantages, as explained above, have been identified in using chambers of circular cross-section formed in right circular cylinders. However, variations in both internal (chamber) and external shape are possible.

For example, we have found that operation of the model giving satisfactory gate valve switching actuated by the flow alone was maintained in spite of the following modifications to the chambers: 1) Conversion of the chambers to a semi-circular shape in cross-section by insertion of a planar, vertical, dividing wall across the diameter of the chambers, the dividing wall being aligned with the general direction of water flow as indicated by arrow A in Figure 1.

2) Conversion of the chambers to a shape in cross-section in which three sides are rectangular and the fourth side containing the ports 14, 15 is semi-circular. The side of the rectangular part transverse to the general direction of fldw A was about 300 mm in the model and the side parallel with the direction A was 273 mm, this corresponding with the diameter of the chambers.

It should be noted that the configuration of the inflow/outflow paths are unaffected by these modifications and a swirling of the flow of water within the chambers was maintained such as to provide the desired smooth merging of the flow directions of water passing the gate valve and that within the chambers adjacent the ports.

In a further modification, for example, the horizontal section through the cylinders may vary with height. The tops may be shaped to operate as a weir. The barrage 13 may be of adjustable height, eg by the use of stoplogs to form a weir.

The examples relate to extraction of useful energy from natural sources of water flow at relatively low pressure heads. However the apparatus is useful for any application, such as metering, where liquid flow is to be switched.

Claims

1. Apparatus for liquid flow control comprising a first chamber and a second chamber, each chamber having a port opening for liquid flow into and out of the chamber, a pivoted gate valve being positioned to control liquid flow alternately into and out of the chambers so that whilst liquid flows into the first chamber liquid flows out of the second chamber and vice versa, the chambers having a shape in horizontal section and locations relative to the gate valve such as to generate a swirling flow of liquid in the chambers which swirling flow, in the region of the respective ports, merges substantially smoothly with the flow of liquid past the gate valve.

2. Apparatus as claimed in claim 1, wherein the said shape in horizontal section and locations relative to the gate valve of the chambers, and the shape of the gate valve are such that the general direction of flow of liquid flowing into or out of a chamber past the gate valve is substantially tangential to the flow line of the swirling liquid within the chamber at the periphery thereof.

3. Apparatus as claimed in claim 1 or claim 2, wherein the gate valve is so pivoted intermediate its ends for movement about an axis transverse to the direction of liquid flow, and the port openings are so dimensioned and located that hydrodynamic pressures automatically provide forces appropriate for causing or assisting alternating switchover of the gate valve whenever a predetermined substantial difference in liquid level between the chambers is reached.

4. Apparatus as claimed in any of the preceding claims, wherein there is provided a releasable latch mechanism for temporarily holding the gate valve in one or more positions.

5. Apparatus as claimed in any of the preceding claims, wherein a controlled independent power source is coupled to the gate valve to cause the required alternating switchover of the gate valve assisted by hydrodynamic pressures in the flowing liquid.

6. Apparatus as claimed in any of the preceding claims, wherein the port openings are facing one another and define therebetween a space through which, but for the gate valve, liquid would flow between the chambers from an upstream to a downstream side thereof when the apparatus is in use, the gate valve being positioned between the port openings and pivotable between a first position in which the port in the first chamber is open to inflow of liquid from the upstream side but closed to outflow of liquid to the downstream side, whilst the port in the second chamber is closed to inflow of liquid from the upstream side but open to outflow of liquid to the downstream side, and a second position in which the open and closed conditions of the respective ports are reversed.

7. Apparatus as claimed in any one of the preceding claims, wherein the top of the port opening of each chamber is below the lowest liquid level reached in the chamber in the vicinity of the port when the apparatus is in normal use.

8. Apparatus as claimed in claim 7, wherein a gas turbine is connected to be driven by air or other suitable gas caused to flow through the turbine by the reciprocating movement of the liquid levels in the chambers.

9. Apparatus as claimed in claim 8, wherein the turbine is in a duct extending from an upper part of the second chamber, means being provided for directing the air (or gas) flow through the turbine so that the turbine rotates in one sense even although the direction of air (or gas) flow from one chamber to the other reverses.

10. Apparatus substantially as hereinbefore described with reference to, and illustrated in, Figures 1 to 3, or Figure 4, of the drawings filed herewith.