GB2463660A

GB2463660A - Radial flow turbine

Info

Publication number: GB2463660A
Application number: GB0817133A
Authority: GB
Inventors: Graham Cox
Original assignee: PCA ENGINEERS Ltd
Current assignee: PCA ENGINEERS Ltd
Priority date: 2008-09-19
Filing date: 2008-09-19
Publication date: 2010-03-24
Anticipated expiration: 2028-09-19
Also published as: GB2463660B; GB0817133D0

Abstract

A radial flow turbine has at least two expansion stages wherein fluid flows through a turbine wheel 11 in a first radial direction in the first stage, and then through the turbine wheel 11 in the opposite radial direction in the second stage, each expansion stage having a variable inlet nozzle 16, 28. Each nozzle 16, 28 may be defined between a fixed member 19, 20 adjacent to the turbine wheel 1, and a slidable member 15, 25 which slides in a circular path around the centre of the turbine wheel 11. A sliding control mechanism 14 may be provided to move each slidable member 15, 25 either independently or together. High pressure fluid may be supplied from outside the turbine wheel 11. Fluid may flow from the final stage of the turbine to an exhaust port 17 radially outwards of the turbine wheel 11. The turbine may be part of a waste heat recovery system using a Rankine cycle and an organic fluid.

Description

FLUID TURBINE

Field of the Invention

This invention relates to a fluid turbine, and in particular to a variable-flow turbine in which the fluid passes through a single row of turbine blades more than once between the inlet and exhaust.

Background to the Invention

In an early form of steam turbine, known as the Elektra turbine, the flow expands radially inwards and outwards through the same rotor via a series of partial admissions, the flow rate being regulated by a single steam control valve at the inlet. A typical configuration of Elektra turbine is illustrated in Figure 1. In this way, multiple expansion stages can be achieved with a single rotor, permit-ting a very compact and economical construction. This is very important when the turbine is to be used for small-scale recovery of energy from waste heat.

Although the Elektra design allows for variable flow rate, the expansion stages are each fixed in dimensions, with the result that the efficiency of the turbine can vary greatly with varying flow rate. In order to minimise energy waste, it is desirable to ensure that there is no significant change in efficiency under conditions of variable load.

Summary of the Invention

According to the invention, there is provided a radial fluid turbine having at least two expansion stages wherein fluid flows through the turbine in a first radial direction in the first stage and then through the turbine in the opposite ra- dial direction in the second stage, each of the expansion stages having a dy-namically variable nozzle in which the flow area can be varied in accordance with the fluid flow rate through the turbine.

The term "dynamically variable nozzle" means a nozzle which can be varied as the flow rate changes while the turbine is operating.

The nozzles are preferably defined between a fixed member adjacent to the turbine, and a slidable member which slides in a circular path around the centre of the turbine. A sliding control mechanism may be provided to move each slidable member independently of the other or in a linked manner, for ex-ample by a geared drive between the different slidable members.

Although typically a small turbine according to the invention may have just two expansion stages, there may be more than two. While it may be con-venient in some circumstances for the initial high pressure fluid supply to be from outside the turbine wheel, it would be possible for the initial high pressure fluid supply to be from within the turbine. Equally, the exhaust fluid may pass to a discharge port within the turbine wheel or exterior to it.

The turbine of the invention is suitably a low specific speed device, and while it will typically be used with compressible fluids, reference being made to "expansion stages", it would be possible to employ the same design with water or other liquids. In the case of liquids, because there is no change in density, all the stages will be the same size and can therefore be linked together in a 1:1 relationship.

Typically applications of the turbine of the invention with compressible fluids are (a) in Rankine cycle machines for recovery of waste heat from smaller-scale applications such as internal combustion engines, (b) smaller steam applications, for example with waste steam, and (c) with industrial gases.

Rankine cycle machines could conveniently use organic refrigerant/air-conditioner gases such as R134A, enabling energy recovery at relatively low temperatures.

Since the turbine can operate at relatively low speeds, it is suitable for small scale applications, for example 1 to 250kW, and can be used to drive al-ternators and the like directly. The ability to maintain efficiency over a range of operating conditions/flow rates ensures that the maximum recovery of energy is achieved.

Brief Description of the Drawings

In the drawings: Figure 1 is a partial sectional view of an example of a prior art "Elektra" turbine; Figure 2 is a diagrammatic sectional view of a turbine according to an exemplary embodiment of the invention, with the nozzles in the open position; Figure 3 is a view corresponding to that of Figure 2, but with the nozzles in the closed position; Figure 4 is a perspective view of the exterior of the turbine shown in Fig-ures 2 and 3; Figure 5 is a view corresponding to that of Figure 4, but with the control slider removed; Figure 6 is a view corresponding to that of Figure 5, but with the upper cover of the turbine removed; Figures 7 and 8 are diagrammatic sectional views of a second embodi-ment of the invention having two stages with feed and exhaust from within the turbine wheel, the figures respectively showing the open and closed positions thereof; Figures 9 and 10 are diagrammatic sectional views of a third embodi- ment of the invention having three stages, with feed from within the ring and ex-haust to the exterior, again respectively showing the open and closed positions of the variable elements; and Figures 11 and 12 are diagrammatic sectional views of a fourth embodi-ment of the invention having three stages, with feed from the exterior of the ring and exhaust from within the ring, respectively in the open and closed positions of the variable elements.

Detailed Description of the Illustrated Embodiment

The "Elektra" steam turbine shown in Figure 1 was first proposed over years ago. It consisted of a radial turbine in which the inlet steam is con-trolled by a needle valve 1 and flows through the turbine into a curved passage 2 within the turbine wheel 3 which directs the steam through a second expan-sion stage 4 outwardly through the turbine, discharging through a second curved passage 5 on the exterior of the turbine, which directs the steam through a third expansion stage 6 inwardly through the turbine and into a third curved passage 7 redirecting the steam outwardly through the turbine again in a fourth expansion stage 8, from where it is exhausted through an outlet port 9. The successive curved passages and expansion stages can be dimensioned such that the pressure drop at each stage is approximately equal for normal operat-ing conditions to maximise efficiency, but it will be appreciated that, if the flow rate is reduced by the needle valve, or increased, to accommodate varying loads, the relationship between the pressure drops in the different stages will not be maintained, resulting in a loss of efficiency.

Referring now to Figure 2 to 6, the radial impulse turbine has a turbine wheel 11 of generally conventional form, mounted on a rotor disc (not shown) which is in turn carried on an output shaft 12 by which the rotational energy of the turbine is transmitted. The shaft 12 is mounted in a bearing housing 13 which can be rotated by means of a first actuator arm 14. The bearing housing 13 has a portion 15 upstanding therefrom for the height of the turbine wheel and serving to define on one side thereof a movable side of the inlet nozzle 16 and on the other side thereof a movable side of the exhaust outlet 17. A fixed cap 18 encloses the turbine and carries an outer guide 19 which conforms with the exterior of the turbine wheel 11 over more than half the circumference thereof and forms at one end thereof the fixed side of the inlet nozzle 16 and at the other end the fixed side of the exhaust outlet 17. Between the cap 18 and the bearing housing 13 and within the turbine wheel 11 are located a fixed guide 20, carried by a fixed disc 21 and secured to a clamp 22 by a central screw 23, the clamp in turn being screwed to the cap 18 by outer screws 24, and a moving guide 25 which is carried by a disc (not shown) which encloses the fluid pas-sage within the turbine wheel and which carries a control pin 26 extending through a curved slot 27 in the cap 18. Movement of the pin 26 along the slot 27 causes rotation of the moving guide 25 relative to the fixed guide 20, chang-ing the shape of the fluid channel 28 defined between them and the length of the opening through the turbine wheel at each stage. The control pin 26 is moved by a second actuator arm 29 sliding in a channel 30 in the side of the clamp 22.

Figure 2 shows the open configuration of the turbine for higher flow of the fluid therethrough. The first actuator arm 14 is rotated anti-clockwise relative to the cap 18, causing the portion 15 to move away from the outer guide in the inlet nozzle. The moving guide 25 is also rotated anti-clockwise by movement of the second actuator arm 29 to minimise the length of the outlet from the tur- bine wheel 11 in the first stage and to maximise the length of the nozzle open-ing to the second stage.

By contrast, Figure 3 shows the closed configuration suited to a lower flow of fluid through the turbine. In this case, the actuators 14 and 29 are moved to cause rotation of the portion 15 and the moving guide 25 in a clock-wise direction to reduce the width of the inlet nozzle 16 and the width of the nozzle at the second stage of the turbine. It will be appreciated that, to achieve the optimum efficiency, the movable components 15 and 25 are movable sepa-rately of each other. The object to be achieved in each case is to achieve equal fluid velocity change at each stage, with the component of velocity of the fluid tangential to the turbine wheel at each nozzle matched as nearly as possible.

Referring now to Figures 7 and 8, a second embodiment of the invention is illustrated in which the pressurised fluid inlet 70 is within the turbine wheel and two expansion stages through the turbine wheel are provided, such that the exhaust discharge from the turbine also occurs within the ring. Figure 7 illus-trates the high flow, open position, while Figure 8 illustrates the lower flow, closed position when the two movable guide components 71 and 72 have moved clockwise relative to the turbine wheel 11.

Figures 9 and 10 illustrate an embodiment in which three stages are pro-vided, with the pressurised fluid inlet 90 being within the ring and the exhaust discharge 91 is external to the wheel 11. Again, the first of the Figures, Figure 9, illustrates the open, high flow position, while the other Figure shows the closed, lower flow position. In this case, three movable components 92, 93 and 94 are required to enable the velocity change at each successive stage to be equalised to maximise efficiency.

Finally, Figures 11 and 12 illustrate an alternative three stage configura- tion, in which the pressurised fluid inlet 110 is external to the ring and the ex-haust discharge 111 is within the wheel 11. Again, three movable components 112, 113, and 114 are provided to control the area of each nozzle admitting flow to the turbine wheel at each stage.

It will be appreciated that the illustrated embodiments are examples of the possible configurations within the scope of the invention.

Claims

CLAIMS1. A radial fluid turbine having at least two expansion stages wherein fluid flows through a turbine wheel in a first radial direction in the first stage and then through the turbine wheel in the opposite radial direction in the second stage, each of the expansion stages having a dynamically variable nozzle in which the flow area can be varied in accordance with the fluid flow rate through the turbine.
2. A radial flow turbine according to Claim 1, wherein each nozzle is defined between a fixed member adjacent to the turbine wheel, and a slidable member which slides in a circular path around the centre of the turbine wheel.
3. A radial flow turbine according to Claim 1 or 2, wherein a sliding control mechanism is provided to move each slidable member independently of the other or in a linked manner.
4. A radial flow turbine according to any preceding claim, wherein high pressure fluid is supplied from outside the turbine wheel.
5. A radial flow turbine according to any preceding claim, wherein fluid flows from the final stage to an exhaust port radially outwards of the turbine wheel.
6. A radial flow turbine, substantially as described with reference to, and/or as shown in, Figures 2 to 6, Figures 7 and 8, Figures 9 and 10, or Fig-ures 11 and 12, of the drawings.
7. A waste heat recovery system consisting of a Rankine cycle in-cluding a radial flow turbine according to any preceding claim.
8. A system according to Claim 7, wherein the working fluid in the Rankine cycle is an organic fluid.