WO2016008007A1

WO2016008007A1 - Apparatus and systems for solar pumping and water purification

Info

Publication number: WO2016008007A1
Application number: PCT/AU2015/050395
Authority: WO
Inventors: Trevor Powell
Original assignee: Trevor Powell
Priority date: 2014-07-16
Filing date: 2015-07-14
Publication date: 2016-01-21

Abstract

The present invention provides a pumping system comprising: a collector configured to absorb thermal energy from the sun, a converter configured to convert the thermal energy absorbed by the collector into mechanical energy, and a pump in mechanical connection with the converter, wherein the system is configured such that the thermal energy absorbed from the sun is converted to mechanical energy, the mechanical energy in turn driving the pump. It is found that the efficiencies in pumping systems including a solar thermal energy collector are improved where thermal energy is not used to generate electricity, but instead used to directly drive the pump.

Description

APPARATUS AND SYSTEMS FOR SOLAR PUMPING AND WATER PURIFICATION

FIELD OF THE INVENTION

The present invention is broadly directed to the field of liquid pumping. More particularly, although not exclusively, the invention relates to pumping systems for use in large scale agriculture, municipal water supply, mining and water purification processes such as desalination. BACKGROUND TO THE INVENTION

The pumping of water and other fluids and semisolids is an energy intensive process required in many industrial settings. The cost of energy required for pumping processes can dramatically affect the economic viability of a commercial enterprise.

In agriculture, pumps for irrigation are typically driven by electric motors (for grid-connected applications), or diesel engines (for remote or off-grid applications).

Large-scale pumping applications such as municipal water supply, in placer mining or resources processing, (for example, mine dewatering or for the movement of tailings), may require flow rates of the order of multi Ml/hr in order to properly service the operation

Commercial desalination processes require the pumping of vast quantities of seawater into the desalination plant, process intermediates through the plant, the resultant brine to waste, and the desalinated water to storage reservoirs.

There have been attempts in the prior art to limit the consumption of fossil fuels in industrial pumps. With the increasing effects of climate change and depletion of fossil fuel reserves, solar energy has been extensively explored. One approach for smaller scale agricultural applications has been the use of photovoltaic (PV) cells to power electric pump motors. One disadvantage relates to the relatively low efficiencies of PV cells, resulting in the requirement for large numbers of cells to power even a small pump. The input cost is therefore high, and generally not economically viable for large-scale industrial processes. Another approach has been in the use of solar collectors which absorb thermal energy from the sun. A collector fluid passes through the collector and is heated, with the heated fluid then being used to generate steam. The steam is ultimately used to drive a turbine which is coupled to a generator to produce electrical energy which is used to power an electric pump motor. This process requires large collector areas for practical viability. The economies of installing large collectors mean that such installations are not widely used.

It is an aspect of the present invention to overcome a problem of the prior art to provide a pumping system which is powered by solar energy, the system having improved efficiencies over those of the prior art. It is another aspect of the present invention to provide a useful alternative to pumping systems of the prior art.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a pumping system comprising: a collector configured to absorb thermal energy from the sun, a converter configured to convert the thermal energy absorbed by the collector into mechanical energy, and a pump in mechanical connection with the converter, wherein the system is configured such that the thermal energy absorbed from the sun is converted to mechanical energy, the mechanical energy in turn driving the pump.

In one embodiment, the system does not require electrical energy for pumping, and may furthermore be devoid of an electrical generator or an electric pump.

In one embodiment, the collector is configured to heat a heat transfer fluid passing through the collector.

In one embodiment, the collector comprises a reflector. In one embodiment, the converter is a turbine, and may be an expansion turbine.

In one embodiment, the heat transfer fluid directly or indirectly drives the turbine.

In one embodiment, the turbine directly or indirectly drives the pump.

In one embodiment, the system comprises a mechanical transmission which may be operatively interposed between the turbine and the pump.

In a second aspect, the present invention provides a water purification system comprising a pumping system as described herein.

In one embodiment of the system of the second aspect, the purification method of the purification system requires the input of thermal energy. The purification method of the purification may be a distillation method such as a multiple-effect distillation method.

In one embodiment, the system of the second aspect is configured such that waste heat from the pumping system is conveyed to a heat-energy requiring component of the desalination system, such as a heat exchanger. The waste heat may be captured from a converter of the pumping system. Where the converter is a turbine, the waste heat may be inherent in or captured from a turbine exhaust.

In one embodiment, the system of the second aspect comprises one or more conduits for conducting the turbine exhaust, or waste heat captured from the turbine exhaust to a heat-energy requiring component of the purification method.

In one embodiment, the system of the second aspect is configured to desalinate water. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic representation of an exemplary solar pumping system of the present invention. The solid arrowed lines represent the flow of fluids and steam through the system, while the arrowed dotted lines indicated the flow of mechanical energy. The dashed line between 30 and 18 represents the feedback function between those components. P, pump; GB, gear box; SG, speed governor; G, generator; V, valve.

Fig. 2 is a schematic representation of an exemplary water desalination system comprising an exemplary solar pumping system of the present invention. Components common to the systems of Fig. 1 and Fig. 2 are numerically marked identically. The solid arrowed lines represent the flow of fluids and steam through the system, while the arrowed dotted lines indicated the flow of mechanical energy. The dashed line between 30 and 18 represents the feedback function between those components. P, pump; GB, gear box; SG, speed governor; G, generator; V, valve, Heat Ex; heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION

After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects apply to specific exemplary embodiments, and not necessarily to all embodiments covered by the claims.

Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may.

The present invention is predicated at least in part on Applicant's finding that the efficiencies in pumping systems including a solar thermal energy collector are improved where thermal energy is not used to generate electricity, but instead used to directly drive the pump. Accordingly, in a first aspect the present invention provides a pumping system comprising:

a collector configured to absorb thermal energy from the sun,

a converter configured to convert the thermal energy absorbed by the collector into mechanical energy, and

a pump in mechanical connection with the converter,

wherein the system is configured such that the thermal energy absorbed from the sun is converted to mechanical energy, the mechanical energy in turn driving the pump.

The present invention is a significant departure from prior art systems which use the thermal energy of the sun to vaporize water, with the attendant volume expansion of water driving a mechanical turbine. The turbine in prior art systems is connected to a generator which generates electrical energy which is used to power an electrical pump. Applicant has recognized that significant efficiency losses occur at the steps of (i) converting the mechanical energy of the turbine into electrical energy at the generator, (ii) converting the electrical energy back into mechanical energy at the pump, and also (iii) transmission losses through the electricity grid. The efficiency losses may be decreased or completely obviated where the system is configured to have no requirement for electrical energy, and mechanical power is generated local to the pumping operation. Applicant has found that by the mechanical coupling of a turbine to a pump, the efficiency losses due to the conversion of mechanical energy to electrical energy, and the subsequent conversion of electrical energy to mechanical energy of prior art systems are obviated.

The collector of the present system may be any apparatus or system capable of absorbing thermal energy from the sun. The skilled person is familiar with a large number of collectors suitable for use in the present systems. Any collector capable of being utilized in a system for driving a turbine is potentially useful in the present systems.

Typically, the collector comprises an absorber through which an absorber fluid is passed, the absorber fluid being heated in passage through the absorber. The absorber may be a conduit or a chamber through which the fluid may pass. In some cases the absorber fluid is water, which is directly vaporized in the absorber with the vaporized water being channel to a turbine. In other cases, the absorber fluid circulates in a closed loop, with thermal energy stored in the fluid being transferred via a heat exchanger to water which is in turn vaporized and channeled to a turbine. The skilled person is also familiar with the many means available to direct or concentrate solar energy onto an absorber.

The solar collector of the present system may be of the non-concentrating or concentrating type. In the non-concentrating type, the collector area (i.e., the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). In these types of collector the entire solar panel absorbs solar energy. By contrast, concentrating collectors have a large concentrator and a relatively smaller absorber.

The collector of the present system may be flat-plate collector. These collectors typically consist of a dark flat-plate absorber, a transparent cover that reduces heat losses, a heat-transport fluid to remove heat from the absorber, and a heat insulating backing. The absorber generally consists of a thin absorber sheet (often fabricated from a thermally stable polymer, aluminium, steel or copper, to which a matte black or selective coating is applied) often backed by a grid or coil of fluid tubing placed in an insulated casing with a glass or polycarbonate cover. The collector of the present system may be a vacuum tube collector. Evacuated heat pipe tubes (EHPTs) are composed of multiple evacuated glass tubes each containing an absorber plate fused to a heat pipe. The heat is transferred to the heat transfer fluid in a heat exchanger which is wrapped in insulation and covered by a protective sheet metal or plastic case.

Alternatively, the collector of the present system may be a solar bowl. This is a type of solar thermal collector that operates similarly to a parabolic dish, but instead of using a tracking parabolic mirror with a fixed receiver, it has a fixed spherical mirror with a tracking receiver.

The collector of the present invention may be a parabolic dish collector, wherein one or more parabolic dishes concentrate solar energy at a single focal point. The shape of a parabola means that incoming light rays which are parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive.

The collector of the present systems may be a solar power tower. A power tower comprises a large tower surrounded by tracking mirrors (heliostats). These mirrors are aligned to focus sunlight on the receiver at the top of the tower, with collected heat being transferred to a power station below. This design reaches very high temperatures. The solar collector of the present system may be a parabolic trough. This type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or a heat pipe, placed at the focal line, containing a heat transfer fluid which transfers heat from the collectors to a steam generator in the power station.

Given the benefit of the present disclosure, the skilled person is able to identify or conceive of many types of solar thermal collectors useful in the context of the present systems.

The use of solar thermal energy as the energy source for high volume pumping (and particularly in systems where the solar thermal energy is converted into rotational mechanical energy) provides for opportunities not realized by prior artisans. For example, pumped hydro power as off-peak storage was conceived many years ago, but has never been commercially viable in systems reliant on photovoltaic panels as the energy source. The present systems exploit a high volume pump driven by a low cost renewal energy source to provide for a useful and commercially important advance in the art.

In one embodiment, the pumping system does not require electrical energy for pumping, or an electrical generator, or an electric pump. These embodiments of the invention are distinguished from prior art solar pumping systems whereby a solar thermal collector is used to generate electrical energy. Prior art systems typically involve a steam driven turbine which in turn drives an electrical generator, the output of the generator used to drive an electric pump. The present invention is completely operable without electricity or electric devices, with the thermal energy of the sun being converted to mechanical energy without the need for an intermediate step requiring electrical energy.

It will be understood, however, that particular embodiments of the present system may include the use of electrical energy and/or electrical devices such as generators and electrically driven pumps. Such an embodiment is disclosed as a preferred embodiment herein, and in which a generator is used to power pumps involved in auxiliary systems such as the recirculation of heat transfer fluid through the solar collector and cold water through a condenser.

It will be understood that even the non-auxiliary pump of the system may be assisted in some way by electrical energy, with such embodiments not being excluded from the ambit of this invention. The converter of the present system may be any rotary or non-rotary apparatus that extracts energy from a fluid flow (the fluid being a liquid, a gas, or a vapor) and coverts that energy to useful work. While the converter may be non-rotary (such as a piston), combination rotary and non-rotary (such a piston driving a crankshaft), the converter is more typically a rotary apparatus.

Turbines are commonly used rotary energy converters useful in the present systems. The turbine of the present system may be a turbomachine with a rotor assembly to which a shaft or drum with blades is attached. Moving fluid (typically steam) acts on the blades so that they move and impart rotational energy to the rotor.

The turbine may be an impulse turbine and/or a reaction turbine. Some steam turbines employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery.

In one embodiment, the turbine is an expansion turbine (also known as a turbo-expander, or screw expander). These turbines are centrifugal or axial flow turbines through which a high pressure gas is expanded to produce mechanical work. Expansion turbines are preferred in the context of the present invention given the ability of these contrivances to utilize energy for saturated steam at high efficiency and at relatively low temperatures. By contrast, non-expansion turbines (such as those typically used in coal-fired steam turbine based plants) require an input quality of the steam in the range of about 0.95-0.98. This means that the input saturated steam will have 95-98% steam and 2-5% liquid water droplets. These droplets are erosive and lead to significant reduction in turbine life. This in turn leads to substantial loss of the latent heat of vaporization of water and hence less efficiency in these conventional steam turbines. In the case of an expansion turbine, the input saturated steam quality can fall to 1 0-20% level depending upon the operation conditions. Hence more of the latent heat is utilized thereby leading to significantly higher efficiencies. Where the solar thermal collector utilizes a heat transfer fluid, the heat transfer fluid may indirectly drive the converter. The skilled person will be familiar with many types of heat exchangers that will be useful in that regard. A simple and useful heat exchanger is a boiler, whereby the heat transfer fluid is pushed through a metal coil. The coil directly contacts water entering the boiler, with the water being converted into steam. The boiler is a substantially sealed vessel, and so pressure is created within. The pressurized steam exits the boiler through an outlet, and is typically conveyed via a pipe to the converter where the mechanical energy is created.

The output of the converter may be rotary, non-rotary or a combination of rotary and non-rotary. More typically the output of the converter is rotary, generally provided by a drive shaft rotated by a turbine.

As will be immediately appreciated by the skilled person, the rotary output may be used to directly or indirectly operate a mechanical pump. Where the converter is a turbine, it is likely that the speed of the rotor will be in excess of that useful to drive a mechanical pump. Further, the output of a turbine may have insufficient torque to properly drive a mechanical pump. For at least one of these reasons, the system may comprise speed-reduction gearing of the type well known to the skilled artisan. The gearing is operatively disposed between the converter output and the mechanical pump input.

With regards to the mechanical pump of the present system, the skilled person is enabled to select an appropriate type based on a number of parameters such as application, capacity, viscosity of fluid to be pumped, output pressure required, and the like. Typically, the pump is configured to be driven by a rotational input.

The present solar pumping system may be used in any application, such as for pumping water, oil, slurries and the like. Accordingly, there is further provided by the present invention a method of pumping a fluid comprising the step of providing a pumping system as described herein. Typically, an input conduit is operably connected between the fluid to be pumped and the pump input, and an output conduit operably connected between the pump output and the desired destination of the fluid.

Efficiencies of the pumping systems of the present invention may be calculated. An efficiency for the pumping system described above (based on solar energy input with reference to mechanical energy output) is estimated to be at least about 10, 15, 20, 25, 30, 35, 40, 45 or 50%; and in one embodiment about 45%.

Applicant has further discovered that the present pumping systems provide particular advantage in the pumping of water in water purification systems and methods. Thus, in a further aspect, the present invention provides a water purification system comprising a pumping system as described herein.

It will be appreciated that the present pumping systems may be used in systems and methods to remove any type of contaminant from water including elemental species, organic and inorganic compounds, ionized species, bacteria, viruses, parasites, aquatic life forms, microscopic and macroscopic structures and the like. Greater advantage will be provided where the efficiency gains (over the prior art) are higher such as in purification systems requiring the pumping of substantial volumes of fluid.

For example, pumping the massive volumes of seawater in a commercial desalination installation is a major energy input of the desalination process. Typically, electrical pumps are utilized which consume huge amounts of electrical power. Typically, the electrical power is provided by coal fired power stations, and thus the efficiency losses in converting the mechanical power of a turbine into electricity is immediately inherent in the powering of desalination pumps. This efficiency issue is further worsened due to the losses inherent in the long distance transmission of electrical power through power lines. Further losses are seen where the electrical power is converted again to mechanical power needed to drive the pumps. For large desalination plants, the distance issue can be at least partially offset by co-locating the power generation and the desalination plant, however that is not always possible. In all circumstances however, the inherent efficiency losses due to the conversion to and from electrical power is unavoidable. Use of the pumping systems of the present invention overcomes those efficiency losses to improve not only the economic viability of a desalination process, but also the carbon footprint. The present pumping system may be incorporated into any or all pumping processes of a water purification system, for the removal of salt or any other undesired contaminant. Where the water purification system is a desalination system, suitable points for incorporating a pumping system of the present invention include bulk salt water intake, bulk fresh water output, as well as any subsidiary pumping requirements of the system such as conveying process intermediates, clean- in-place processes and the like.

An alternative or additional advantage provided through use of the present systems in water purification, is that waste heat from the present pumping system is useful as input thermal energy in a purification system. As will be appreciated, many types of purification processes require an input of thermal energy. In particular, processes which operate on the basis of distillation (such as desalination processes) require significant inputs of energy to evaporate the solvent (water).

Distillation processes commonly used to produce fresh water from salt water, include multistage flash (MSF), and multiple effect (MED) processes. While these processes generally operate on the principle of reducing the vapor pressure of water within the unit to permit boiling to occur at lower temperatures, they still require the addition of heat. While distillation units typically use designs that conserve as much thermal energy as possible by interchanging the heat of condensation and heat of vaporization within the units, input thermal energy is nevertheless required. The major energy requirement in the distillation process is generally providing the heat for vaporization to the feed water. Typically, the heat of vaporization is input via a heat exchanger.

In some embodiments, the waste heat is initially stored before use in the water purification process. It will be appreciated that the use of heat storage means allows the potential for an increase in daily yield of a solar thermal field, balances energy output and may effectively enable base load capacity. Heat storage media potentially useful in the context of the present invention include: water, molten salt, masses of earth or bedrock; aquifers; water-filled gravel pits, and phase-change materials. In some embodiments the waste heat of the converter (in whatever form) may be in excess of that required by the water purification process. For example a MED process may require heat energy input of about 80 to 85 degrees Celsius, while the exhaust of a turbine may be 100 to 130 degrees Celsius. Accordingly, in some embodiments of the invention the turbine exhaust is actively or passively cooled before conveyance to the water purification process.

It is preferable that in the present water purification systems, the converter of the pumping system is an expanding converter, such as an expansion turbine. These turbines operate essentially as a compressor in reverse; expanding the fluid (steam) which in turn rotates the turbine. The heat that would otherwise be lost to the atmosphere as a result of the expansion of the steam (or any indeed any other low temperature organic fluid in the turbine) is harvested for use in the water purification system.

Considering the example of MED process (which is typically used for desalination), the system comprises a set of heat exchangers. The MED system and the pumping system may be operably connected such that waste heat from the turbine of the pumping system is conveyed to the heat exchangers of the MED system. This conveyance may be achieved by any manner conceivable by the skilled person, however in one embodiment the condensate from the turbine exhaust is simply conducted (via any suitable conduit) to a heat exchanger of the MED system. The turbine exhaust is typically heated water, but may comprise heated air or water vapor.

The hot discharge fluid from the pumping system turbine at circa 1 00°C (i.e. not the distillate) is passed through the radiator tubes and the heat so captured will drive the MED process. The outlet water from the MED then starts the process again as feed water to the solar field.

The present pumping systems may be utilized in non-distillation water purification processes such as reverse osmosis of the present application. In such applications the mechanical pump of the pumping system is capable of pumping water at higher pressures than those typically required for distillation-based methods such as MED. For example, where a reverse osmosis (RO) method is used, the pressure provided by the pump must be sufficient to overcome the osmotic pressure of the solutes (such as salts) in the water to be treated. For seawater desalination typical pumping pressures of from about 800 to about 1 ,180 psi (say 7000 kN/m2) are used. In the prior art, these high pressures required for RO are provided by specialized electric pumps requiring significant amounts of power to function.

The present pumping systems may replace high pressure pumps used in reverse osmosis water purification systems. Given the benefit of the present specification the skilled person is enabled to select a mechanically driven high pressure pump for use in the present systems. For example, multi-stage pumps are known to be capable of developing the pressures required for RO desalination processes from the rotational mechanical output of a converter of the present pumping system. A suitable pump may be capable of generating a pressure of at least about 800 psi (and in some circumstances over 1000 psi), optionally at a flow rate of about 80 m³/hr. Kirloskar Brothers Limited (Pune, India) produce multistage pumps, of type MN, MHA MLA, and RKB potentially suitable in the present methods.

For instance, at 500m (50bar) working pressure, a multistage pump can supply 0.51 ML/8hr day to a RO desalination process. Given that typically 20% to 40% of supplied water is recoverable, 0.1 to 0.2ML/day fresh water can be recovered (in this case no energy is recovered from the output waste stream). By comparison, well designed prior art systems comprising energy recovery but reliant on specialized electrically powered pumps typically require 3KWH energy per m³ of water, while 7.5KWH/m³ is typically required for a RO plant without an energy regeneration system.

The present invention will now be more fully described by reference to the following preferred embodiment.

PREFERRED EMBODIMENTS OF THE INVENTION

Turning to Fig. 1 there is shown generally a solar pumping system of the present invention useful in an irrigation system in a large-scale water pumping application of the type useful in an agricultural setting. The system comprises a closed heating circuit 10, for the circulation of a heat transfer fluid (HTF) through a series of solar thermal collectors 12 of the trough reflector type. The reflector surface area is about 400 m². The heating circuit 10 comprises a heat exchanger 14. HTF is circulated around the low pressure circuit by the pump 16 (4.5 kW, 30 m head). HTF exits the solar collectors 12 and enters the heat exchanger 14 at a temperature of about 220°C, depending on conditions such as the amount of incident solar radiation, ambient temperature, and the configuration and input requirements of the turbine which in this preferred embodiment is a screw expander turbine.

The heat exchanger 14 is a liquid/liquid heat exchanger (such as a boiler) which transfers heat to incoming water to produce steam at the rate of about 0.5 kg/sec to about 2.8 kg/sec, depending on the temperature of the incoming HTF. The steam is conducted via a valve 18 to a turbine 20, which in this embodiment is a twin screw expander turbine. The turbine typically produces rotary mechanical output of at least about 1 ,400 rpm.

The mechanical energy of the turbine 20 is transferred via a drive shaft to a gear box 22, comprising speed reduction gears. The rotational speed of the output shaft of the gearbox 22 is about 1500 to 3000 rpm.

A generator 26 (20 kW at 200 V) is driven by the output shaft of the gearbox 22, the generator output connected to the electric pumps 16, 34 and 36. The output shaft of the gear box is connected to the input shaft of an agricultural water pump 28, (which may be rotary, centrifugal pump). The pump 28 draws water from the reservoir 24 for distribution to the land under irrigation.

A speed control subsystem is provided to ensure the input speed into the pump is not excessive. Cavitation at the pump may be caused by excessive speeds. The subsystem consists of a speed governor 30 which provides feedback (shown as a dashed line in the drawing) to the valve 18. Thus, excessive rotational speed as detected by the governor 30 causes the valve 18 to partially close thereby restricting the volume of steam entering the turbine 20, which in turn slows the turbine output speed.

It is generally desirable for the pump to be run at a speed selected to maximize efficiency Hence the system may be configured to increase the supply of steam where pump RPM falls below a certain threshold.

The present systems may be required to operate under a broad range of solar thermal energy input given the large variations in available sunlight throughout the day, and also across the year. The skilled person therefore understands that steam volume (and also the characteristics of the steam) may vary, and therefore the system may be configured so as to best utilize the available steam. Accordingly, the system may not be configured so as to operate under any predetermined condition or parameter as typical in convectional steam machines/engines. Given the benefit of the present description, the skilled person will however be capable of routinely investigating the influence of an alteration to any condition under which the present systems are operable, or to provide alternative configurations. For example, in some cases it may be desirable or necessary to provide a further valve to differentially mix hot water from the boiler with the steam from the boiler to control the steam quality being fed to the screw expander.

The steam exiting the turbine 20 may be passed through a condenser 32, with the condensate being conducted by the pump 34 (7.5 kW, 160 m head, 60 litres/min) to the heat exchanger 14 for boiling in the production of steam. The condenser 32 is cooled by water drawn from the reservoir 24 by the pump 36 (2 kW, 5 m head, 20 litres/min). Water exiting the condenser 32 is returned to the reservoir. In some embodiments, the system may comprise a cyclone separator (or similar contrivance) disposed after the condenser and the feed water pump 34 so as to separate any vapor steam that may escape from the condenser. This may be required so as to avoid any problem of cavitation in the pump, and optionally to maximize the efficiency with which the pump works

The use of a condenser may be avoided where an open system is used, and wherein water for boiling is drawn directly from the reservoir 24 by the pump 36 and conducted to the heat exchanger 14. In that case, the components 38 are not required. By this system, the agricultural pump 28 is capable of an output of about 100KW after consideration of all the losses. Since the output power is fixed for the system the actual flow rate will depend on the pressure head at which water is to be pumped. Typically for a pressure head of 5m the flow rate would be 23.5 mega liters per day and for a pressure head of 1 5m about 1 5.5 mega liters per day, based on 4 to 6 hours of operation. The flow rate for other pressure heads can be calculated in a similar manner.

Modeling total water flow per day achievable with the present pumping systems (as detailed in Table 1 ) shows unexpectedly high flow rates. As expected, flow rate decreases as head increases.

An exemplary desalination system comprising a pumping system as described above is shown in Fig. 2. The desalination system is a multiple-effect distillation (MED) system 50, consisting of multiple stages 52 or "effects". In each stage the feed water is heated by steam in tubes. Some of the water evaporates, and this steam flows into the tubes of the next stage, heating and evaporating more water. Each stage essentially reuses the energy from the previous stage. Water evaporation in each stage 52 is effected by a heat exchanger 54.

It will be seen from Fig. 2 that the MED system 50 is fed ocean water 24 by the pump 28. The pump 28 is mechanically driven by an expander turbine 20 which is in turn driven by steam produced by the closed low pressure heating circuit 10 (more fully defined in Fig. 1 ). The exhaust from the turbine 20 (being heated water) is conveyed via insulated pipes to the heat exchangers 54. Thus, the waste heat from the turbine 20 is used to assist in the heating of water within each stage 52, thereby decreasing the overall energy requirements of the MED process 50. The remaining energy required for the MED plant may be provided by additional solar collector unit 10 with a heat exchanger inside the first stage of the MED plant in place of the steam generator 14. It will be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, the skilled person is enabled (with only routine optimization methodology) to configure any of the pumping and/or water purification systems described herein to operate at any desired scale.

Claims

CLAIMS:

1 . A pumping system comprising :

a collector configured to absorb thermal energy from the sun,

a pump in mechanical connection with the converter

2. The pumping system of claim 1 that does not require electrical energy for pumping.

3. The pumping system of claim 1 or claim 2 which is devoid of an electrical generator or an electric pump.

4. The pumping system of any one of claims 1 to 3 wherein the collector is configured to heat a heat transfer fluid passing through the collector.

5. The pumping system of any one of claims 1 to 4 wherein the collector comprises a reflector.

6. The pumping system of any one of claims 1 to 5 wherein the converter is a turbine.

7. The pumping system of any one of claims 1 to 6 wherein the turbine is an expansion turbine.

8. The pumping system of claim 6 or claim 7 wherein the heat transfer fluid directly or indirectly drives the turbine.

9. The pumping system of any one of claims 6 to 8 wherein the turbine directly or indirectly drives the pump.

1 0. The pumping system of any one of claims 6 to 9 comprising a mechanical transmission.

1 1 . The pumping system of claim 10 wherein the transmission is operatively interposed between the turbine and the pump.

12. A water purification system comprising a pumping system according to any one of claims 1 to 1 1 .

13. The water purification system of claim 12 wherein the purification method of the purification system requires the input of thermal energy.

14. The water purification system of claim 13, wherein the purification method of the system is a distillation method.

15. The water purification system of claim 14 wherein the distillation method is a multiple- effect distillation method.

16. The water purification system of claim 15 configured such that waste heat from the pumping system is conveyed to a heat-energy requiring component of the purification method.

17. The water purification system of claim 16 wherein the heat-energy requiring component of the purification method is a heat exchanger.

18. The water purification system of claim 16 or claim 17 wherein the waste heat is captured from a converter of the pumping system.

19. The water purification system of claim 18 wherein where the converter is a turbine, the waste heat is inherent in or captured from a turbine exhaust.

20. The water purification system of claim 19 comprising one or more conduits for conducting the turbine exhaust, or waste heat captured from the turbine exhaust.

21 . The water purification system of any one of claims 12 to 20 configured to desalinate wate