WO2012032355A1

WO2012032355A1 - Thermal desalination using breaking jet flash vaporisation

Info

Publication number: WO2012032355A1
Application number: PCT/GB2011/051688
Authority: WO
Inventors: Wessenu Abegaz Maru
Original assignee: Pdx Technologies Ag
Priority date: 2010-09-09
Filing date: 2011-09-09
Publication date: 2012-03-15
Also published as: GB201015012D0; TW201228939A

Abstract

The present invention relates to desalination, specifically to use a breaking jet flash vaporisation injection for desalination, especially Multiple-Effect Distillation (MED) desalination, and an apparatus and a method for such desalination. In one embodiment an apparatus comprises a MED desalination plant; and a fluid mover for moving and treating working fluid with a transport fluid, providing a breaking jet flash vaporisation, wherein the fluid mover is arranged to provide working fluid in to chambers of the MED desalination plant. One embodiment discloses a method of desalination according to a MED process, comprising the steps of heating a saline working fluid; moving the working fluid with a fluid mover using a transport fluid for providing a breaking jet flash vaporisation fluid in to a MED chamber on to an evaporator surface; and separating saline droplets from the working fluid vapour. One embodiment discloses the use of a fluid mover for moving saline working fluid by the use of a transport fluid to create a breaking jet flash vaporisation in a desalination system. Preferably the desalination system may be a MED system. One embodiment comprises the use of a Thermal Fluid Compression (TFC) of the created vapour of the MED system by mixing it with a low volume fraction saturated steam and using it as the transport fluid for the next MED chamber.

Description

Thermal desalination using breaking jet flash vaporisation

The present invention relates to desalination. More specifically, the present invention relates to use a breaking jet flash vaporisation injection for desalination, especially Multiple-Effect Distillation (MED) desalination, and an apparatus and a method for such desalination.

Desalination is generally referred to as the process of removing salt and other minerals from water though it might more correctly be described as the process of removing purer water from increasingly saline brine. The process is most commonly used to make seawater or brackish water drinkable, but it can also be applied to obtain ultrapure water that far exceeds drinking water requirements. Such ultrapure water may, for example, be used for certain industrial processes such as, for example, cleaning of aero engine combustors.

The greater the salinity of the water to desalinate and/or the greater the purity of the desalinated water, the greater the energy required in the desalination process. Salinity is defined according to the total dissolved solids (TDS). This is measured in milligrams per litre (mg/l) or parts per million (ppm). The two units are generally interchangeable in dilute solutions, although ppm is used more commonly in the US. As such the type and quality of water salinity is divided as: Seawater: 15,000-50,000 mg/l TDS, Brackish water: 1 ,500-15,000 mg/l TDS, River water: 500-3,000 mg/l TDS and Pure water: less than 500 mg/l TDS. Most desalination plants use predominantly seawater as the water to desalinate.

Desalination processes aim to separate the saline water into two streams: a fresh water stream containing a low concentration of TDS and a concentrated brine stream. The process is generally energy intensive. Many forms of energy resources (electro-chemical, nuclear, solar, wind etc) are used in the desalination process. The process may use several different technologies for such separations. However, in general, desalination processes may be divided into (i) thermal methods, which involve heating water to produce water vapour, and (ii) membrane processes, which use a membrane to move either water or salt into two zones; one salty and one fresh water.

Among the high desalting capacity thermal techniques, Multi Stage Flash (MSF) and Multiple-Effect Distillation (MED) are the most widely used. While MSF is known to be relatively energy intensive, it has high throughput and had enjoyed a large market share for a long time.

The MED process usually involves the distribution of feed (saline) water onto a surface of an evaporator surface (for example tubes). The saline feed, for example seawater, is taken from its source and is allowed to pass through a heat exchanger. While all of the initial saline feed from the source is used to condense desalinated vapour, it is then split and a large portion of the initial saline feed, now with elevated temperature, is rejected and returned to the source (e.g. to the sea). The amount of saline rejected is a problem when trying to optimise MED plants as the saline reject also carries useful heat that is costly to recover. The return of such elevated temperature water to its source may be an ecological disaster for aquatic life.

MED is touted as the future of thermal desalination due to its potentially high thermal performance compared to MSF and has gained popularity as evidenced by the number of MED plants being built recently. However, the current MED efficiency is bought at the expense of high capital expenditure on high quality materials, especially for the evaporator surfaces. Without the appropriate material properties it would be impossible to create the high heat and mass transfer requirements. Costs are also affected by current stringent emission legislation and high cost of desalination energy, as well as a desire to increase vapour throughput. There is also a desire to increase plant capacity. In addition, all current thermal methods are plagued by scaling and/or fouling problems due to their high temperature operation range. The high temperature operation range is costly due to its high energy requirements and also due to the high capital costs of the materials required. Furthermore the scaling problems arising from the high temperature operating range also carry a significant financial cost due to the chemicals used to remedy the scaling and the plant operation downtime required whilst descaling is performed. Therefore, there is a need for technologies that can shift the conventional heat and mass transfer mechanisms without adversely affecting the plant life due to scaling and incurring huge costs due to plant shut down and high energy bills. In recent years, attention has been given to reducing energy use and increasing throughput.

WO 2004/033920, WO 2006/010949, and WO 2008/062218 may be useful background art for understanding the present disclosure.

It is an object of the present invention to improve desalination plants, especially MED desalination plants. This object can be achieved by the features of the independent claims. Further enhancements are characterized by the dependent claims.

In one embodiment an apparatus comprises

a MED desalination plant; and

a fluid mover for moving and treating working fluid with a transport fluid, providing a breaking jet flash vaporisation, wherein the fluid mover is arranged to provide working fluid in to chambers of the MED desalination plant.

In one embodiment the fluid mover is arranged at the bottom of a MED chamber with an outlet of the fluid mover located above brine collected at the bottom of the MED chamber. Preferably, the fluid mover allows jet break up of the working fluid and its flash vaporisation, producing a homogeneously dispersed mixture of substantially pure water vapour and saline droplets of fine size distribution at the outlet of the fluid mover.

In one embodiment, the fluid mover acts as an inlet to a MED chamber. Preferably, the fluid mover creates a twin fluid flashing plume which is composed of substantially pure water vapour and saline droplets of fine size distributions. Preferably, the fluid mover moves the working fluid from the bottom of a MED chamber and injects the working fluid upwards, in a vertical direction from the bottom to the top of the MED chamber, on to evaporator surfaces of the MED chamber.

Preferably, the outlet of the fluid mover is arranged at a height h that is higher than the height b of the brine. In one embodiment the working fluid is saline feed, for example sea water.

One embodiment comprises a Thermal Fluid Compression (TFC) of substantially pure high enthalpy vapour of the MED chambers for mixing the vapour with a low volume fraction saturated steam and for using it as the transport fluid for the next MED chamber. Preferably, the TFC process may recover waste heat and/or may act as a vacuum pump.

In one embodiment the fluid mover in a desalination system, preferably a MED system, may comprise a hollow body provided with a straight- through passage of substantially constant cross section with an inlet at one end of the passage and an outlet at the other end of the passage for the entry and discharge respectively of a working fluid; a nozzle substantially circumscribing and opening into said passage intermediate the inlet and outlet ends thereof; an inlet communicating with the nozzle for the introduction of a transport fluid; and a mixing chamber being formed within the passage downstream of the nozzle; wherein the nozzle internal geometry and the bore profile of the passage immediately upstream of the nozzle exit are so disposed and configured to optimise the energy transfer between the transport fluid and working fluid that in use through the introduction of transport fluid the jet of working fluid or fluids is broken up and partially atomised to form a dispersed vapour/droplet flow regime with locally supersonic flow conditions. This is being operated at very different operating conditions because of the aim to avoid formation of condensation shock, keeping the fluids as a dispersed vapour/ droplet regime as they exit the fluid mover.

One embodiment discloses a method of desalination according to a MED process, comprising the steps of:

heating a saline working fluid;

moving the working fluid with a fluid mover using a transport fluid for providing a breaking jet flash vaporisation fluid in to a MED chamber on to an evaporator surface; and

separating saline droplets from the working fluid vapour.

In one embodiment, the saline droplets are collected as brine. Preferably, the saline flow may drop in temperature due to meta-stable thermodynamic or flashing phenomena created by the fluid mover while the resulting brine increases its salinity. This is one critical balance the MED system may achieve to avoid scaling, but because of the flashing effect according to the present disclosure, temperature drops and precipitate scales are avoided.

In one embodiment, the fluid mover allows the efficient jet break up of the working fluid and its flash vaporisation, producing a homogeneously dispersed mixture of substantially pure water vapour and saline droplets of fine size distribution at an outlet of the fluid mover. Preferably the fluid mover acts as an inlet to a MED chamber by producing a twin fluid flashing plume which is composed of substantially pure water vapour and saline droplets of fine size distributions. Preferably the fluid mover delivers the saline working fluid as a twin fluid flashing plume from a bottom of a MED chamber and injects the saline working fluid upwards on to evaporator surfaces. In one embodiment the method provides a Thermal Fluid Compression (TFC) of substantially pure high enthalpy vapour of the working fluid by mixing it with a low volume fraction saturated steam and using it as the transport fluid for the next MED chamber. The TFC process may have significant impact on the reduction of energy and capital expenditure costs by recovering waste heat and by acting as a vacuum pump, respectively.

In one embodiment the method provides a homogeneously dispersed mixture flow through an outlet of the fluid mover, whose back pressure is usually sub-atmospheric, further creating intense turbulence and flashing of droplets at a significantly lower saturation temperature than the vapour pressure of the working fluid or below its standard atmospheric temperature and pressure (STP) values. In one embodiment the separation is preferably done by providing a demister allowing vapour of the working fluid to pass via the demister. Preferably the saline working fluid may be seawater. According to one embodiment, a method of moving a working fluid in a desalination system, preferably a MED system, may be provided. The method comprising the steps of: presenting a fluid mover to the working fluid, the mover having a straight-through passage of substantially constant cross section such that the cross-sectional area never decreases below that of the inlet to the fluid mover; applying a substantially circumscribing stream of a transport fluid to the passage through an annular nozzle; breaking up the working fluid jet using flash vaporisation to form a dispersed vapour and droplet flow regime with locally supersonic flow conditions; inducing flow of the working fluid through the passage from an inlet to an outlet thereof as a homogenously dispersed mixture of substantially pure water vapour (substantially pure water may have a TDS less than or equal to 5-10 ppm) and saline droplets of fine size distribution at the outlet of the fluid mover. Hereby no generation of a supersonic condensation shock wave within a passage downstream of a nozzle of a fluid mover by condensation of transport fluid is made; i.e. the condensation shock in the flow passage is avoided.

One embodiment discloses the use of a fluid mover for moving saline working fluid by the use of a transport fluid to create a breaking jet flash vaporisation in a desalination system. Preferably the desalination system may be a Multi-Effect Distillation (MED) system.

One embodiment comprises the use of a Thermal Fluid Compression (TFC) of the created vapour of the MED system by mixing it with a low volume fraction saturated steam and using it as the transport fluid for the next MED chamber.

Embodiments may improve desalination plants, especially MED plants, and/or improve the energy consumption and/or costs associated with desalination plants. The embodiments may reduce energy use as the saline feed is forced to vaporise at a significantly lower saturation temperature than in conventional desalination plants. Embodiments may improve effectiveness since the large surface area produced due to flash atomisation, the heat and mass transfer effectiveness is increased and hence the MED vapour throughput is increased significantly. Embodiments may improve plant life due to reduced scaling and/or reduced costs due to plant shut down and high energy consumption. Embodiments may reduce scaling, since the vaporisation temperature is significantly lower than the saturation temperature of the saline feed, there is less concern with scaling of salt precipitates.

Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from this disclosure. Various embodiments of the present application obtain only a subset of the advantages set forth. No one advantage is critical to the embodiments. Any claimed embodiment may be technically combined with any preceding claimed embodiment(s). The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate, by way of example, presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain, by way of example, the principles of the invention. FIG. 1 shows a schematic exemplary embodiment of a fluid mover. FIG. 2 shows a schematic detail of an exemplary embodiment of a fluid mover.

FIG. 3 shows a further exemplary embodiment of a fluid mover. FIG. 4 shows a schematic layout of a conventional embodiment of a MED process.

FIG. 5 shows a schematic layout of an exemplary embodiment of a first chamber (first Effect) of a MED process.

FIG. 6 shows a schematic layout of an exemplary embodiment of an intermediate chamber (intermediate Effect) of a MED process.

FIG. 7 shows a schematic layout of an exemplary embodiment of a last chamber (last Effect) of a MED process.

FIG. 8 shows an exemplary embodiment of a fluid mover in a chamber of a MED process.

Embodiments relate to the delivery and/or distribution of (saline) feed water on to heated MED evaporator surfaces, for example tubes, of different chambers of a MED system using a fluid mover such as a breaking jet flash vaporisation fluid mover. Such a fluid mover introduces the feed as a liquid breaking jet, which is characterised by a large surface area (or fine droplet size distribution) and flash vaporisation in a sub- atmospheric pressure environment. The process is different from that of spraying of liquids, because its fluid mechanics is significantly different as the process by which vaporisation proceeds efficiently is due to the meta- stable thermodynamic condition that the fluid mover exhibits. In vaporisation, the liquid boiling point must be attained, while flashing vaporisation is due to a reduction in boiling point due to a reduction in vapour pressure. To elucidate the mechanistic behaviour of the process and its use within a MED system, this disclosure first turns to the fluid mover and then to the MED system and how the fluid mover is used within the MED system. The fluid mover may be used in other types of desalination systems.

Turning to the fluid mover used, this disclosure relates to the delivery and/or distribution of (saline) feed water in a MED process using a fluid mover such that the feed is introduced as a liquid breaking jet characterised by large surface area (or fine droplet size distribution) and flash vaporisation in a sub-atmospheric pressure environment. With reference to Figs 1 -3, a fluid mover 10 comprises a working fluid passage 12 having an inlet 14 at one end of the working fluid passage 12 and an outlet 16 at the other end of the working fluid passage 12 for entry and discharge respectively of a working fluid 18. The working fluid 18 is for example a saline feed such as seawater and is the process fluid of the MED. The working fluid passage 12 is a hollow body provided with a substantially straight-through passage of substantially constant fluid dynamic cross section 12a as shown in Fig 2 where the cross-sectional area of the passage 12 never decreases below that of the inlet 14. The fluid mover 10 also comprises a transport fluid nozzle 20 which opens into the working fluid passage 12 intermediate the inlet 14 and outlet 16 thereof. In the embodiment described here, the transport fluid nozzle 20 substantially circumscribes and opens into the working fluid passage 12, such that a high enthalpy and/or high velocity transport fluid 22 is introduced annularly (i.e. in annular form, through an annular passage) into the working fluid passage 12. The transport fluid 22, also called motive fluid 22, transports/moves the working fluid 18. The transport fluid nozzle 20 is generally made of concentric conical cylinder shapes forming the transport fluid nozzle 20 with a transport fluid nozzle exit 26. The transport fluid nozzle 20 has convergent-divergent internal geometry. As illustrated in Fig 2, the convergent-divergent geometry comprises a converging portion 20b, a diverging portion 20c, and a throat portion 20a located between the converging and diverging portions 20b and 20c. In the three embodiments illustrated by Figs 1 -3, the same features have same reference numbers.

For example, in Fig 3, the fluid mover comprises a housing that defines a passage. The passage has an inlet 14 and an outlet 16, and is of substantially constant diameter. The inlet 14 is formed at the front end of a protrusion extending into the housing and defining exteriorly thereof a plenum. The plenum has a transport fluid 22 inlet. The protrusion defines internally thereof part of the passage. The distal end of the protrusion remote from the inlet 14 is tapered on its relatively outer surface and defines a transport fluid nozzle 20 between it and a correspondingly tapered part of the inner wall of the housing. The nozzle 20 is in fluid communication with the plenum and is preferably annular such that it circumscribes the passage. The nozzle 20 has a nozzle inlet, a nozzle outlet and a throat portion intermediate the nozzle inlet and nozzle outlet. The nozzle has convergent-divergent internal geometry, wherein the throat portion has a cross sectional area which is less than the cross sectional area of either the nozzle inlet or the nozzle outlet. The nozzle outlet opens into a mixing chamber defined within the passage.

In operation, the working fluid 18 flows through the inlet 14 into the working fluid passage 12 and a high enthalpy and/or high velocity transport fluid 22 (such as for example supersonic steam or nitrogen) is injected via the transport fluid nozzle 20 into the working fluid passage 12. The internal geometry of the transport fluid nozzle 20, the mixing chamber 12b, the bore profile of the working fluid passage 12 immediately upstream and/or downstream of the transport fluid nozzle exit 26 and the angle of incidence a that the transport fluid nozzle 20 makes with the working fluid passage 12 are disposed and configured to optimise the momentum flux and energy transfer between the high enthalpy and/or high velocity transport fluid 22 and the working fluid 18.

The injection of the high enthalpy and/or high velocity transport fluid 22 creates an aerodynamic bow shock 28 whose front 30 is located at the periphery of the stable but rarefied transport fluid 22. The shock front 30 is characterised by its abrupt change both in thermodynamic and fluid dynamic properties such as pressure, velocity, temperature and entropy. The shock front 30 typically acts as a wall by forming a pseudo-vena contracta or aerodynamic nozzle 34 and exhibits the Fabri choking effect on the working fluid 18. While the rapid rarefaction (or decrease in density) allows the transport fluid 22 to accelerate significantly, it also generates a vacuum region 36 (supersonic flow generates a low pressure or vacuum region) behind the shock front 30 where the working fluid 18 under the Fabri choking condition undergo catastrophic flashing in to the vacuum 36 so created behind the transport fluid shock front 30. There is a catastrophic flashing or break-up of the working fluid 18 under meta-stable thermodynamic conditions. The vacuum region 36 created due to the supersonically expanding transport fluid in such a process is also responsible for the shear induced entrainment (SIE) phenomena that allows the working fluid 18 to accelerate relative to the transport fluid 22 at its shock front 30. The implications are a reduction in the relative velocities of the transport fluid 22 and the working fluid 18 and hence in the lateral shear stress in the working fluid that contributes to the jet break up of the working fluid. Furthermore, due to the direct contact condensation of the transport fluid 22 and direct contact evaporation of the working fluid 18, a stratified vapour flow region develops and acts as an intense mixing layer and/or (in the case of a condensable transport fluid 22) lubricating medium to reduce the lateral shear stress while enhancing the turbulent shear stress.

According to one embodiment, the fluid mover may comprise a hollow body provided with a straight-through passage of substantially constant cross section with an inlet at one end of the passage and an outlet at the other end of the passage for the entry and discharge respectively of a working fluid; wherein the cross-sectional area of the passage never reduces below that of the inlet; a nozzle substantially circumscribing and opening into said passage intermediate the inlet and outlet ends thereof; an inlet communicating with the nozzle for the introduction of a transport fluid; and a mixing chamber being formed within the passage downstream of the nozzle; wherein the nozzle internal geometry and the bore profile of the passage immediately upstream of the nozzle exit are so disposed and configured to optimise the energy transfer between the transport fluid and working fluid that in use through the introduction of transport fluid the working fluid or fluids is induced to flow through the passage from the inlet to the outlet thereof and the working fluid jet is broken up due to flashing and partial atomisation to form a homogenously dispersed mixture of substantially pure water vapour and saline droplets of a fine size distribution with locally supersonic flow conditions, which exits into the MED chamber at the outlet of the fluid mover.

According to one embodiment, a method of moving a working fluid may be provided. The method comprising the steps of: presenting a fluid mover to the working fluid, the mover having a straight-through passage of substantially constant cross section; applying a substantially circumscribing stream of a transport fluid to the passage through an annular nozzle; partially atomising and vaporising the working fluid at the boundary of the pseudo vena contracta (aerodynamic nozzle) and flashing of the working fluid at the core of the pseudo vena contracta immediately after the aerodynamic throat of the vena contracta to form a dispersed vapour and droplet flow regime with locally supersonic flow conditions; inducing flow of the working fluid through the passage from an inlet to an outlet thereof; Hereby avoiding the generation of a supersonic condensation shock wave within the passage downstream of the nozzle by condensation of the transport fluid, as well as avoiding the modulation of the condensation shock wave to vary the working fluid discharge from the outlet.

The combined effects of the above processes creates a homogeneously dispersed or mixture flow 24 through the outlet 16, whose back pressure is usually sub-atmospheric; further creating intense turbulence and flashing of droplets at a significantly lower saturation temperature than at standard atmospheric temperature and pressure. It is this outflow that feeds the MED system's chambers.

The desalination process in a conventional MED system may involve the distribution of feed (saline) water onto the surface of an evaporator in several different chambers (also called Effects or cells) in a thin film to promote evaporation after it has been preheated in an upper section of each chamber. Fig 4 depicts the main process of a conventional MED application with the different chambers. Saline feed, 18a, for example seawater, is taken from its source and is allowed to pass through a heat exchanger usually referred to as pre-heater 50 in Fig 5 (condenser) where its temperature rises due to heat transfer from the desalinated vapour 60a, which in turn condenses. While all of the initial saline feed from the source is used to condense the desalinated vapour 59, the initial saline feed is then split and a large portion of the initial saline feed, now with elevated temperature, is rejected as saline reject 6 and returned to the source (e.g. to the sea). The amount of saline reject 6 is the Achilles heel when trying to optimise MED plants as the saline reject 6 also carries useful heat that is costly to recover. In addition, the return of such elevated temperature water to its source is known to be an ecological disaster for aquatic life.

In a conventional system, the remaining, smaller portion of the saline feed, the working fluid 18, is then allowed to pick up some more heat as it passes through the MED system, starting at the last chamber (Effect) and traversing along the MED process route to the first Effect. Note that one of the key advantages of the MED process is that energy (in the form of an evaporator, external heat) is supplied only in the first Effect, whose pressure is usually maintained at significantly sub-atmospheric conditions. All the processes in the rest of the Effects run as a cascade of this thermodynamic process.

In embodiments of the process of the current invention, the Effects can have several different configurations according to the type of fluid heat transfer surfaces (for example: vertical tube falling film, vertical tube climbing film, horizontal tube falling film, plate heat exchanger) and the direction of brine flow relative to vapour flow (for example: forward, backward, or parallel feed). In all of the technologies, one way to optimise heat and mass transfer may be to increase the liquid surface area. However, in embodiments of the present invention the fluid meets the fluid heat transfer surfaces not as a thin film but in the form of saline droplets and a flashing jet.

Turning to Fig 5, an embodiment of an exemplary configuration of an initial MED chamber or Effect of the current invention is illustrated. The working fluid 18 (for example saline feed such as sea water) passes through various pre-heaters (condensers) as shown in Fig 4 and arrives at the last pre-heater 50, from which it then enters inlet 14 as working fluid 18 of the fluid mover 10. In the initial Effect a pump of some form may be provided to help move the working fluid 18 through the fluid mover. Transport fluid 22 (for example steam) that was generated by a boiler 51 enters transport fluid nozzle 20, passes through transport fluid nozzle throat 20a and interacts with the working fluid 18 as it exits transport fluid nozzle exit 26. The upstream pressure of the transport fluid 22 may be less than 4bar. As described above, the fluid mechanistic behaviour includes both complex fluid dynamics and thermodynamics phenomena and allows the efficient jet break up of the working fluid 18 and its flash vaporisation - producing a homogeneously dispersed mixture 24 of substantially pure water vapour and saline droplets of fine size distribution at the outlet 16 of the fluid mover 10, where it subsequently acts as an inlet to the first MED chamber 52 as a twin fluid flashing plume 53 which is composed of substantially pure water vapour and saline droplets of fine size distributions. Unlike traditional MED systems, the saline feed is delivered as twin fluid flashing plume 53, from the bottom of the first MED chamber 52 and injected upwards in to evaporator surfaces 54 such as tube bundles. While a significant volume and/or surface area of traditional MED chambers 52 is filled with tube bundles 54 to enhance heat transfer efficiency, the present disclosure significantly reduces both the evaporator material usage and the subsequent scaling maintenance cost. Instead, the twin fluid flashing plume 53 with its fine size saline droplets enhances the heat transfer and hence evaporation efficiency and further produces a substantially pure water vapour 60 that is allowed to pass through a demister 55 in to the vapour chamber 56.

The MED chamber 52 is at sub-atmospheric pressure or vacuum condition and therefore, the flashing flow created in the fluid mover 10 due to its own fluid dynamic vacuum condition continues without substantial pressure recovery. For example, with reference to Fig 1 , the pressure P23 downstream of the vena contracta may be less than the pressure P24 at the exit to the fluid mover where P24 is preferably less than or equal to 0.35bar. At the same time, with reference to Fig 5, the twin fluid flashing plume 53 evolution means that the high turbulence dissipation and the increase in density of the saline droplets due to evaporation creates an environment conducive to droplet coalescence. As the droplets get bigger and denser due to increased salinity, they tend to settle at the bottom of MED chamber 52 and form a brine flow 57 that in turn will be delivered as a saline feed or working fluid 18 for the next MED chamber.

The substantially pure water vapour 60 in the vapour chamber 56 may have two components. The first component may be a condensing vapour 60a due to heat exchange with pre-heater 50 while the second component may be a remaining high enthalpy vapour 60b. The significantly pure condensing water vapour 60a in the vapour chamber 56 is driven to the next condensate mixer 59 and forms part of the overall desalinated water. In the traditional MED process, the substantially pure high enthalpy vapour 60b is usually delivered as a heat source for the next chamber evaporator. That process can be followed for this disclosure too. However, a more efficient process is to use a Thermal Fluid Compression (TFC) 61 of the substantially pure high enthalpy vapour 60b by mixing it with a low volume fraction saturated steam and using it as the transport fluid 22 for the next MED chamber. The TFC process is essentially a steam mixing process, for example by using a central or annular steam ejector, to deliver a steam with high pressure values to generate the required transport fluid 22. The TFC process 61 has a significant impact on the reduction of energy and capital expenditure costs by recovering waste heat and by acting as a vacuum pump, respectively. The vacuum pump in a traditional MED system forms a high percentage of the total plant cost. Note that the brine flow 57 has dropped in temperature due to the meta- stable thermodynamic or flashing phenomena while it has also increased its salinity. This is a preferred balance the system is required to achieve to avoid scaling, which could have happened if its temperature has increased. But, thanks to the flashing effect according to the present disclosure, the temperature has dropped and precipitate scales are avoided. Turning to Fig 6, an embodiment of an exemplary configuration of an intermediate MED chamber or Effect is illustrated. The embodiment is similar to that of the initial chamber disclosed above and similar features have similar reference numerals. While the layout may remind one of a standard MED configuration, there are fundamental differences. One such difference is for example the use of the TFC concept 61 disclosed above of the substantially pure high enthalpy vapour 60b by mixing it with a low volume fraction saturated steam and using it as the transport fluid 22 for the next MED chamber. To create a conservation equation for mass, energy and salinity balance, a virtual condensate mixer junction 59 is developed. This device is used for modelling purposes. It collects condensates 60a from the internal side of the vapour chamber 56 and allows in the development of the required balance equations for the three conserved variables. The condensate from the mixer combined with the condensate from the pre-heater are directed towards the next condensate mixer.

Assuming, for example, 14 Effects or chambers in an MED plant, the condensate mixer junction 59 of Effect n receives condensates from previous Effects following an index rule and provides condensates to the next Effect following the index rule. Item 59 in Fig 6 discloses "From n-3 where (n>4, n≠(8,1 1 ))" and "Next 59 Mix n+3 where (n>2; η≠(3,4,5,6,7,9,10))".

Turning to Fig 7, an embodiment of an exemplary configuration of a last MED chamber or Effect is illustrated. While there are similarities with standard MED systems, there are fundamental differences. For example, in the last chamber or Effect, there is no pre-heater 50 and hence no substantially pure condensing water vapour port 60a is available. Instead the vapour is sent to the initial steam condenser unit 67. However, the TFC technology 61 may be used to compress steam and either to send the steam to a condenser or boost the transport fluid 22 in Effect 1 .

Turning to Fig 8, an exemplary embodiment of a fluid mover 10 in a chamber 52 of a MED process is illustrated. In this embodiment the fluid mover 10 is provided at the bottom of the MED chamber 52. This MED chamber 52 is similar to those disclosed above. Between the MED chamber 52 and a vapour chamber 56 is a demister 55. A vacuum pump 71 may be provided to reduce the pressure within the MED chamber 52 to a sub-atmospheric pressure or vacuum condition.

An evaporator surface 54, preferably such as tube bundles 54, may be provided in the MED chamber 52. The evaporator surface 54 may for example be vertical tube falling film, vertical tube climbing film, horizontal tube falling film, and/or plate heat exchanger. Compared with evaporator surfaces of a MED system without the fluid mover 10, the present evaporator surface 54 is reduced in the present embodiment and consequently evaporator material and subsequent scaling maintenance cost are reduced. A brine collector 72 may be provided to collect the brine and forward the brine flow 57. Level b in Fig 8 indicates the amount of brine at the bottom of the MED chamber 52. The brine collector 72 is so arranged that the brine does not reach the outlet 16 of the fluid mover 10. A height h indicates the height of the outlet 16 of the fluid mover 10. The outlet 16 is thus located at the height h that is above the level b of the brine in the MED chamber 52. The twin fluid flashing plume 53 evolution means that the high turbulence dissipation and the increase in density of the saline droplets due to evaporation create an environment conducive to droplet coalescence. As the droplets get bigger and denser due to increased salinity, they tend to settle at the bottom of MED chamber 52 and form a brine flow 57 that in turn will be delivered as a saline feed or working fluid 18 for the next cell. The pure water vapour of plume 53 passes through the demister 55; this is illustrated by the arrow 60 going from the plume 53 to the demister 55 in Fig 8.

The system, method, and use discussed above allow a reduction of the energy and/or costs related to desalination. The invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While the invention has been described and is defined by reference to particular preferred embodiments of the invention, such references do not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts. The described preferred embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the scope of the attached claims, giving full cognizance to equivalents in all respects.

Claims

1 CLAIMS:

1 . An apparatus comprising:

a Multi-Effect Distillation (MED) desalination plant; and

a fluid mover 10 for moving and treating working fluid 18 with a transport fluid 22, for providing a breaking jet flash vaporisation of the working fluid 18, wherein the fluid mover 10 is arranged to provide the working fluid 18 in to chambers of the MED desalination plant. 2. The apparatus according to claim 1 , wherein the fluid mover 10 comprises:

a hollow body provided with a straight-through passage of substantially constant cross section with an inlet 14 at one end of the passage and an outlet 16 at the other end of the passage for the entry and discharge respectively of the working fluid 18;

a nozzle 20 substantially circumscribing and opening into said passage intermediate the inlet 14 and outlet 16 thereof;

an inlet communicating with the nozzle 20 for the introduction of a transport fluid 22; and

a mixing chamber being formed within the passage downstream of the nozzle 20; wherein

the nozzle internal geometry and the bore profile of the passage immediately upstream of the nozzle exit are so disposed and configured to optimise the energy transfer between the transport fluid and working fluid that in use through the introduction of transport fluid the jet of working fluid or fluids is broken up and partially atomised to form a dispersed vapour/droplet flow regime with locally supersonic flow conditions.

2

3. The apparatus according to claim 2, wherein the nozzle 20 comprises a nozzle inlet, a nozzle outlet, and a throat portion intermediate the nozzle inlet and nozzle outlet; and wherein

the nozzle 20 comprises a convergent-divergent internal geometry, wherein the throat portion has a cross sectional area which is less than the cross sectional area of either the nozzle inlet or the nozzle outlet.

4. The apparatus according to any one of the preceding claims, wherein the fluid mover 10 acts as an inlet to a MED chamber 52.

5. The apparatus according to any one of the preceding claims, wherein the fluid mover 10 is configured to allow jet break up of the working fluid 18 and its flash vaporisation, producing a homogeneously dispersed mixture of substantially pure water vapour and saline droplets of fine size distribution at the outlet 16 of the fluid mover 10.

6. The apparatus according to any one of the preceding claims, wherein the fluid mover 10 moves the working fluid 18 from the bottom of a MED chamber 52 and injects the working fluid 18 upwards on to evaporator surfaces 54 of the MED chamber 52.

7. The apparatus according to any one of the preceding claims, wherein the MED desalination plant comprises a Thermal Fluid Compression (TFC) 61 configured for mixing vapour of a MED chamber 52 with a low volume fraction saturated steam and for using it as the transport fluid 22 for the next MED chamber.

8. The apparatus according to any one of the preceding claims, wherein the fluid mover 10 is arranged at the bottom of a MED chamber 3

52 with an outlet 16 of the fluid mover 10 located above brine collected at the bottom of the MED chamber 52.

9. A method of desalination, comprising, for a MED process, the steps of:

heating a saline working fluid 18;

moving the working fluid 18 with a fluid mover 10 using a transport fluid 22 for providing a breaking jet flash vaporisation of the saline working fluid 18 in to a MED chamber 52 on to an evaporator surface 54; and

separating saline droplets from the working fluid vapour.

10. The method according to claim 9, comprising:

providing the fluid mover 10 as an inlet to a MED chamber 52 for producing a homogeneously dispersed mixture of substantially pure water vapour and saline droplets of fine size distribution at an outlet of the fluid mover 10; and

collecting the saline droplets as brine.

1 1 . The method according to claim 9 or 10, comprising:

providing a homogeneously dispersed mixture flow through an outlet 16 of the fluid mover 10, whose back pressure is sub-atmospheric, creating intense turbulence and flashing of droplets at a significantly lower saturation temperature than the vapour pressure of the working fluid 18 or below its standard atmospheric temperature and pressure (STP) values.

12. The method according to any one of the claims 9 to 1 1 , comprising: providing a Thermal Fluid Compression (TFC) 61 for mixing vapour of a MED chamber 52 with a low volume fraction saturated steam and using it as the transport fluid 22 for the next MED chamber; preferably,

the TFC 61 acting as a vacuum pump for the MED chamber 52. 4

13. The method according to any one of the claims 9 to 12, comprising: separating the working fluid 18 by providing a demister 55 allowing vapour of the working fluid 18 to pass via the demister 55.

14. The method according to any one of the claims 9 to 13, for moving a saline working fluid 18 in a desalination system, preferably a MED system, the method comprising the steps of:

providing the fluid mover 10 as an inlet to a MED chamber for the working fluid 18, the mover 10 having a straight-through passage of substantially constant cross section such that the cross-sectional area never decreases below that of an inlet 14 to the fluid mover;

applying a substantially circumscribing stream of a transport fluid 22 to the passage through an annular nozzle 20;

breaking up the working fluid 18 using jet flash vaporisation to form a dispersed vapour and droplet flow regime with locally supersonic flow conditions;

inducing flow of the working fluid 18 through the passage from the inlet 14 to an outlet 16; wherein

the fluid mover 10 is arranged in the MED chamber 52 for ejecting the dispersed vapour and droplet flow towards the evaporator surface 54.

15. The method according to claim 14, further comprising providing the fluid mover 10 to deliver the saline working fluid 18 as a twin fluid flashing plume from a bottom of a MED chamber 52 and injecting the saline working fluid 18 upwards on to evaporator surfaces 54.