WO2018069810A1

WO2018069810A1 - Device for desalinating water by means of locally produced green energy

Info

Publication number: WO2018069810A1
Application number: PCT/IB2017/056217
Authority: WO
Inventors: Tim Carlos L. MAEYENS
Original assignee: Rent A Port Utilities, Naamloze Vennootschap
Priority date: 2016-10-12
Filing date: 2017-10-09
Publication date: 2018-04-19
Also published as: BE1024630A1; BE1024630B1

Abstract

Device for the desalination of water (1) by means of green energy, with which a reverse osmosis desalination device (12, 13) is powered that converts salt or brackish water (44} into product water (28), characterised in that this device has its own local green energy production and is independently controlled by a central control unit (18) that matches the production of product water with the local needs and expectations and with the fluctuating and expected local green energy production.

Description

Device for desalinating water by means of locally produced green energy.

The present invention concerns a device for desalinating water by means of locally produced green energy.

More in particular, the invention is intended for desalinating seawater or river water to obtain desalinated water as potable water or irrigation water for agriculture or even demineralised water. Further in this document we will refer to this desalinated water as product water.

It is known that climate change is increasing the average temperature on earth, due to which annual precipitation in certain areas is increasing and in other areas it is decreasing, but the sea level is rising everywhere. As a result, the seawater is penetrating further inland and is salinating many freshwater sources and the ground water, particularly in coastal areas.

A shortage of freshwater sources is occurring in coastal areas in a number of countries in Southeast Asia, Africa, India and South America. This problem has a negative effect on agricultural activities and on the living conditions of the local inhabitants.

In addition, high population growth in developing countries in Africa, Southeast Asia, India and South America is causing a higher demand for product water, while its supply is diminishing . The scarcity of water is also threatening the lives of Africans in areas such as Mauritania and Namibia. There is insufficient potable water, with health problems as a consequence .

The salt level in the water and the dryness of the land depend on the location and the season in the area concerned. The salt level for example reaches its highest values in coastal areas, but the salination problem is particularly concerning in the dry season because of reduced precipitation. Local desalination devices must therefore be available to tackle this problem.

A known technique for desalinating seawater or brackish water is reverse osmosis, whereby the seawater or brackish water is put under pressure against a membrane, after which salt- free product water is transported through the membrane with this product water appearing on the low-pressure side, while the dissolved substances such as salt ions cannot pass through .

Reverse osmosis requires no thermal energy, but it does use electrical energy to obtain the pressure increase. Reverse osmosis is therefore a relatively low-energy process. Energy consumption has now fallen to approximately 3 kWh/m³ water (Reverse Osmosis, Wikipedia) , but it does require an electrical energy source.

CN 104649478 B describes a desalination device for seawater by means of reverse osmosis and an electrodialysis unit, powered by wind energy. The desalination device is provided with a diesel generator for delivering electricity in order to start up the device or when insufficient green energy is available .

In many remote areas of Africa, Southeast Asia, India and South America there is no access to a public electricity supplying grid, and definitely no access to green renewable energy which is preferable to reduce greenhouse gas emissions.

Should one use green energy, produced by a wind farm for example, through an electricity supplying grid to power a local desalination device with a battery system this would require the following five stages:

1- The conversion of alternating current (AC) from the windmill alternator to direct current (DC) ;

2- The conversion of direct current (DC) to a stabilised alternating current (AC) in an electricity supply network;

3- The conversion of the stabilised alternating current to a direct current (DC) for a local battery;

4- The conversion of the local battery direct current (DC) to a stable alternating current to power a local desalination device;

5- The conversion for each of the pumps of the desalination device of the stable alternating current to a direct current and back to a frequency controlled alternating current. Each of the five stages involves energy losses that make the desalination process less energy efficient. By generating green energy on location with a local windmill, for example, the above mentioned stages 2, 3 and 4 for the conversion of electricity are superfluous, so that the number of stages involving an energy loss is reduced from five to two (stages 1 and 5) .

A problem arising with the local generation of green energy is that it is highly subject to fluctuations. A windmill or wind turbine provides more, less or no electricity depending on whether there is much, little or no wind. A photovoltaic cell supplies a current depending on whether there is much or little sunlight, with no power being generated at night. Hydraulic turbines using the flow in a river or tidal flows supply energy that is dependent on the flow speed or the tides and thus are also subject to fluctuations.

This fluctuating power supply makes the locally generated green energy unsuitable for powering a reverse osmosis desalination device, because the latter requires a stable energy source. An interruption of the power supply can damage the device with the sudden stoppage of the desalination process .

The delicate membranes between the salty water under pressure and the product water that is pressed through the membrane can become defective due to the sudden loss of pressure. In the absence of pressure, transport through the membrane will reverse and allow fresh water to pass to the salty water under the influence of the ordinary osmotic pressure with undesired consequences for the membranes. An additional problem is that a locally established desalination device cannot be moved, while the need for potable water or irrigation water can depend on time and location. The need for irrigation water can depend on the season and can be lower in the rainy season, while the need for potable water can be higher in coastal areas during a dry season, such that the local desalination device in such cases would need to be easily transportable.

The purpose of the present invention is to offer a solution to the above mentioned and other disadvantages, by providing a device for the desalination of water by means of green energy, with which a reverse osmosis desalination device is powered that converts salty or brackish water into product water, whereby this device has its own local green energy production and is independently controlled by a central control unit that matches the production of product water with the local needs and expectations and with the fluctuating and expected local green energy production.

Preferably, the means for the local generation of green energy comprise windmills, wind turbines, photovoltaic solar cells or hydraulic turbines.

An advantage of these means for the local generation of green energy is that they make the mobile device autonomous and thus no longer dependent on access to an electricity supplying grid. An advantage of such a device is that it only consumes green energy that it generates itself so no greenhouse gases are produced .

Another advantage is that this device with local green energy production works more energy-efficiently than with green energy taken from an electricity supplying grid.

In a preferred embodiment the device for the desalination of water, along with the means for the local generation of green energy is built on a movable platform that can be transported over land or water.

An advantage of such a mobile device is that it is transportable to places where it is most needed, depending on the location but also depending on the season and this without requiring access to a public electricity supplying grid . The mobile device is preferably built on a floating platform, such that the platform can be moved over water to coastal areas or over rivers where there is a need for product water. The floating platform can be towed or can have its own autonomous means of propulsion.

Such a floating platform preferably has two main pontoons connected to each other by three detachable connecting pontoons that can be easily detached from each other and moved along the coast or a navigable waterway depending on the need for product water. Preferably, the connected pontoons form a stable platform, whereby each main pontoon is provided with a windmill for the production of green energy, and a pump assembly for pumping up salty or brackish water to a desalination device.

These windmills can be erected pivoting them by means of an electric winch or hydraulic jack present on the mobile device without needing a crane, because the windmills are limited in size, with a hub that for example protrudes 30 metres above the platform and with which limited electrical power (e.g. 100 kW) can be generated. Such windmills can be erected or lowered without a crane, for example in stormy weather.

An advantage of such windmills is that they allow local green electricity to be generated as off average wind speeds of 5.5 m/s .

Another advantage is that these windmills require no mechanical transmission, but directly generate a variable alternating current that is fed through an integrated rectifier as direct current to storage batteries, the desalination device with reverse osmosis and the irrigation system. An additional advantage of these windmills is that they allow the generation of sufficient energy for the independent powering of the floating platform, so a connection to an electricity supply network or a diesel motor for energy production is not required. Such a windmill generates an unstable alternating current (AC) depending on the wind strength, which is converted to a direct current (DC) that is distributed to storage batteries, and to frequency controllers where it is converted to alternating current (AC) to power the pumps for irrigation and the desalination device with reverse osmosis.

Preferably, the central control unit controls energy management by means of a device driver on the device, whereby the central control unit is connected to the energy source, in this case the windmill (s) , to the electrical storage system, in this case the batteries, to the desalination device, in this case the reverse osmosis equipment, to the storage tanks for product water, and to the irrigation system, in this case the pumps that distribute the irrigation water over the plots of land to be irrigated.

The device driver of the central control unit analyses the incoming data from all components to which the control unit is connected, and attributes a sufficient amount of energy from the batteries to the desalination device in the form of a safe, stable power supply, but also to the electronic equipment of the device. The device driver of the central control unit will stop the desalination system in a controlled manner in due time if insufficient green energy is produced to continually power the reverse osmosis system. The device driver of the central control unit uses an autonomous and self-learning module for weather prediction, that is part of the desalination device, and is based on the local wind patterns and on its own wind measurements, but also on other meteorological parameters such as air pressure, precipitation and humidity, with which an accurate and precise local wind prediction is possible and the expected green energy production can be forecasted at any time.

Moreover, the central device driver of the central control unit uses a module for irrigation analysis, that is part of the desalination device, and that forecasts the desired quantity of irrigation water based on local precipitation statistics and other data such as the soil type, local water regimes and the irrigation techniques used, so the central device driver can at any time optimise efficiency of use of the generated energy and the potential of the desalination device, and match them with each other based on the meteorological conditions and expectations, the condition and the characteristics of the windmills, and with the available stock and the expected need of product water.

In addition, the device driver of the central control unit at any time ensures a safe margin of available electrical energy for kick-starting the windmills after stoppage, and for the controlled reduction of the activity of the desalination device if insufficient energy production is anticipated .

The floating platform preferably consists of two floating main pontoons positioned end to end and that are connected to each other by means of three detachable connecting pontoons to form a stable platform and that are each provided with a windmill and a pump assembly to pump up salty or brackish water to its own desalination device.

An advantage of such connected main pontoons is that they offer greater stability for the windmills so they can better stay in their vertical position. The wind exerts a force on the blades and the hub of the windmill that stands perpendicular on the windmill mast and can bring this out of balance and have it incline.

On land this force is neutralised because the foot of the windmill mast is assembled in a heavy base and also because this force is neutralised by the shrinkage or elongation of the mast itself. On a floating pontoon the base is movable and the force on the windmill can cause the floating pontoon to incline. Then the centre of gravity of the windmill mast becomes out of balance potentially causing the mast to incline even further. To prevent this effect, the main pontoons are connected by smaller connecting pontoons, so it is a lot harder for one main pontoon to incline because the second main pontoon would have to be lifted from the water or pushed under water. The length of the connecting smaller pontoons is selected depending on the characteristics of the windmills and the associated forces, such that the floating platform is hydrodynamically able to accommodate the reaction to the incline of a windmill and keep this stable within the tolerances of the windmill. Each desalination device consists of at least one filtering device followed by one or more streets for reverse osmosis, whereby the number of streets to be switched on, if there are a number of streets, can be dynamically controlled by the central control unit depending on the available energy and the desired quantity of product water.

With the intention of better showing the characteristics of the invention, some preferred embodiments of a mobile device for the desalination of water by means of green energy according to the invention are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein: figure 1 schematically shows a perspective view of an device for desalinating water according to the invention;

figure 2 schematically shows the data streams from and to the central control unit of the device;

figure 3 shows a side view of figure 1 along the shortest side of both main pontoons;

figure 4 shows figure 3 but now along the longest side of both main pontoons;

figure 5 shows a top view of figure 1 with desalination devices according to the invention;

figure 6 schematically shows a desalination device with reverse osmosis ;

figure 7 schematically shows the management of the energy household of the desalination device. Figure 1 shows a view in perspective of a mobile device for the desalination of water 1 by means of green energy according to the invention, consisting of two main pontoons 2, 3 positioned next to each other head to tail, that by means of three detachable connecting pontoons 4, 5/ 6 are connected to each other to form a stable platform, each provided with a windmill 7, 8 and a pump assembly 9, 10 to pump up salty or brackish water 11 to a desalination device 12, 13 for reverse osmosis, that supplies product water to a storage tank 14, 15 from where the product water is sent in this case by an irrigation pump 16 to an irrigation 17 pipe, all under the control of a central control unit 18. The pontoons float on a river from which salty water is pumped up to the desalination devices 12, 13 on board the mobile device, for the irrigation of plants on the land 19 with product water.

Figure 2 schematically shows the data streams 20 from and to the central control unit 18, whereby the central control unit 18 is connected to the local production of green energy 21, in this case with the windmills 7, 8; to the storage system for electrical energy 22, in this case the storage batteries 23 with their control unit 24; to the production system 25 for product water, in this case a desalination device 26 with reverse osmosis with its supply of salty water 27 and the discharge of product water 28 and brine water 29; to the storage system for product water 28, in this case the storage tanks 31 for product water 28; to the irrigation system 32, in this case the irrigation pumps and distribution means 33; to an HMI interface 34 to provide access to the central control unit 18 by means of a screen and keyboard; and to a meteorological module 35, in this case a weather predictor .

The device driver of the central control unit 18 communicates with the local production system for energy 21 through an energy production control unit 36; with the storage system for electrical energy 22 through a battery status interface 37; with the production system 25 for product water 28 through a product water production control unit 38; with the storage system 30 for product water 28 through a storage tank status interface 39; and with the irrigation system 32 through an irrigation analysis module 40.

Figure 3 shows a side view along the shortest side of a mobile device for the desalination of water 1 by means of green energy according to the invention consisting of two main pontoons 2, 3 positioned next to each other head to tail and each provided with a desalination device 12, 13, and that by means of three connecting pontoons 4, 5, 6, which connected to each other form a stable platform. Each main pontoon 2, 3 has two storage tanks 41 for product water, each divided into four compartments 42 and each provided with a double bottom 43. Figure 4 shows the same device as shown in figure 3 in side view, but now along the longest side whereby the distance between the windmills 7, 8 is clearly visible. The central control unit 18 is located on one main pontoon 2 on which the irrigation pumps and distribution means 33 are also centrally located to pump irrigation water on land. Figure 5 shows a top view of a mobile device for the desalination of water 1 according to the invention, with two main pontoons 2 , 3 each with a desalination device 12, 13 in which at least one or up to four lines for reverse osmosis are installed. Both desalination devices 12, 13 receive salty river water through the inlet 44 for river water at one end of the main pontoons 2, 3 that is taken through the supply pipes 45 to the desalination devices 12, 13 that, after purification with reverse osmosis to form product water 28 discharge the remaining brine water through the discharge pipes 46 to the drain 47 for brine water at the other end of the main pontoons 2, 3 downstream with the flow of the river.

Figure 6 schematically shows the internal structure of one desalination device 12 with reverse osmosis with its supply of salty water 27 and discharge of product water 28 and brine water 29, whereby a first pump 48 takes the salty water to a pump assembly 49 for pre-treatment, after which the filtered salty water is pumped by at least one or more pumps 51, 52, 53 through a system of one or more shut-off valves 54, 55, 56, 57 to at least one or more reverse osmosis streets 58, 59, 60, 61 and the purified product water 28 is taken further through at least one or more shut-off valves 62, 63, 64, 65 to the product water 28 outlet. The optional reverse osmosis streets 59, 60, 61 are represented by a dotted line.

The remaining brine water 29 in the reverse osmosis streets 58, 59, 60, 61 can be pumped away per osmosis street to the discharge point for brine water 29. When one osmosis street is set to inactive, it is flushed with purified product water 28 to protect the membrane against deterioration.

Figure 7 schematically shows the management of the energy household. One direct current main distribution rail 66 links the local green energy production 21, in this case the windmills 7,8 with their inclusive electronic voltage- current frequency regulation 67a, 67b of which the converters 41a, 41b are part; with a battery system 22 with a pack of batteries 23 and with its electronic control unit 24; with an electronically controlled alimentation 72 for a pump 48 that leads the salty water to a filter assembly; with the electronically controlled alimentations 68,69,70,71 of the four or more pumps 50, 51, 52, 53 that pump the filtered salty water to the respectively one or more osmosis-streets; with the electronically controlled alimentation 73 of the irrigation pumps 33; with the electronically controlled alimentations 74, 75 of the one or more pumps 50', 58' for rinsing the osmosis streets, and with the alimentations of auxiliary devices.

The auxiliary devices comprise the general lighting in and around the device as well as the entrance to it, the mechanical ventilation and cooling of the battery room and of the spaces for the desalination device, the fire protection of the device and the alimentations of the electronic equipment and of the communication systems, the alarm systems, the emergency lighting, the navigational lighting and the alimentation of the equipment for lowering and raising the wind mills. The operation of the mobile device 1 for the desalination of water by means of green energy is autonomous and works as follows . The mobile device 1 for the desalination of water by means of green energy is towed with lowered and disassembled windmills 7, 8 to a position where there is an acute need for product water. The main pontoons and the connecting pontoons are disconnected from each other and towed separately.

Once at the required location, the pontoons 2, 3 are connected to each other by the connecting pontoons 4, 5, 6 of which the draught can be adjusted with ballast water, so the fastenings for this purpose with the main pontoons 2, 3 are at the correct height above the water level and can be attached to the main pontoons without requiring the use of a crane. In this way, a stable floating platform 1 is created, and the necessary electrical, data and fluid connections can now be connected between the two main pontoons 2, 3. Then the platform 1 is moored against a bank near the land to be irrigated 19.

Now the windmills 7, 8 are erected by pulling them up with an electric winch or hydraulic jack, which takes its energy from the reserve stored in the storage batteries 23 of the device. This reserve is also sufficient to start the windmills 7, 8, with a kick-start when they are erected and Π unfolded after which they are driven by the prevailing wind at a height of 30 m.

Once the windmills 7, 8 are operating, they can continually top up the energy reserves in the batteries 23, and are further controlled by the central control unit 18, that continually receives information on the windmills 7, 8 through the control unit 36 of the energy production unit 21 being the windmills 7, 8.

The central control unit 18 also continuously receives information from the energy storage system 22 with storage batteries 23, with their own control unit 24, which sends data through the battery status interface 37 on the amount of energy available in the batteries and on the speed at which these are being discharged or charged. The alternating current (AC) generated by the windmills 7, 8 is converted by a converter to direct current (DC) with which the batteries 23 are being charged.

The central control unit 18 also continuously receives information from the production system 25 for product water 28 through a production control unit 38 for product water 28 that sends information on the energy consumption of the reverse osmosis streets 26, on the number of streets in use and on the flow rate and the quality of the product water 28 that is produced, and on the brine water 29 that is discharged . In addition, the central control unit 18 also continuously receives information from the storage system 30 for product water 28 through a storage tank status interface 39 that sends data on the stock of product water 28 in the storage tanks 31 and on the flow rate of the supply and the discharge of product water 28.

Finally, the central control unit 18 also continuously receives data from the irrigation system 32 through an irrigation analysis module 40 that sends data on the irrigation pumps 16 and on the distribution means 33 for product water.

The central control unit 18 also continuously receives data from the weather prediction module 35 that, based on the local wind patterns and on its own wind measurements, and on meteorological parameters such as air pressure, precipitation and humidity, makes an accurate and precise local wind prediction possible.

The device driver of the central control unit 18 optimises the efficiency of use of the generated energy and the potential of the desalination device 12, 13 at any time, based on the meteorological conditions and expectations, the condition and the characteristics of the windmills 7, 8 and of the storage batteries 23, whereby the device driver matches the production of product water with the generation of green energy by regulating the pumping rate of the pumps 50, 51, 52, 53 of the desalination device 12 and their consumption of electrical energy as a function of the available green energy produced by the wind mills 7, 8 and of the charging level of the battery 23. The device driver of the central control unit 18 governs the pumping rate of the salty water to the osmosis-streets 58, 59, 60, 61 by controlling the pumps 50, 51, 52, 53 through the frequency control 68, 69, 71 of their driving engine in order to adjust the capacity of the desalination plant at any moment to the energy that is being furnished by the windmills 7,8, so that all available wind energy is continuously converted into product water thereby reaching the highest possible production efficiency of the device.

The energy that is produced by windmills fluctuates continuously. Very temporary and small fluctuations are flattened by the support of the battery group 23 which allows the production capacity of the desalination device to be kept stable at a certain level and during a certain time.

The supporting capacity of the battery group to compensate for small temporary fluctuations is limited. The device driver of the central control unit 18 communicates continuously with the battery group through the battery status-interface 37 to guard the condition of the battery group. As soon as the compensating capacity of the battery has sunk to a determined threshold, the central device driver will automatically determine if and to what extent the production capacity must be lowered or raised and if one of the osmosis streets has to be started up or shut down.

The device driver thereby also takes into account the instantaneous and local expected increase or decrease of the wind speeds so as to keep the frequency of starting and stopping low. The device driver communicates to that end with the meteorological module 35 to know continuously the instantaneous and local increase or decrease of the expected wind speeds. The frequency of starting and stopping the osmosis streets strongly determines the lifetime of the osmosis membranes and frequent starting and stopping is detrimental.

To optimise the lifetime of the membranes, the device driver keeps the frequency of starting and stopping as low as possible on the basis of the instantaneous and local expectations of wind speeds as forecast by the meteorological module 35 and continuously transmitted to the device driver. The device driver of the central control unit 18 also ensures that a safe margin of available energy remains available to kick-start the windmills 7, 8 at any time after a stoppage, and for the controlled reduction of the activity of the desalination device 12, 13 if insufficient green energy production is anticipated.

The device driver of the central control unit 18 continuously governs the storage system of electrical energy 22 by loading and unloading the storage batteries 23 through their control unit 24. While governing the loading and unloading as a function of the available wind energy of the windmills 7, 8, or of the solar energy of photovoltaic cells, and of the wind speeds or hours of sunshine expected by the meteorological module 35 and of the number of osmosis streets 58, 59, 60, 61 in use, enough energy is being kept available in the storage system of energy 22 to enable the controlled shutting down in activity of the desalination device 12, 13 including the rinsing of the membranes and of the restart of the windmills 7,8. After a period of inactivity of the windmills 7, 8, for example with no wind or with lowered windmills during a typhoon, the windmills must again be started up with a kick- start using electrical energy, after which the rotation of the blades by the wind can be ensured again.

The device driver of the central control unit 18 ensures that the mobile device for the desalination of water 1 by means of locally generated green energy can function autonomously at all times, and no external energy source such as for example a diesel motor for the generation of power with the undesired production of greenhouse gases is required.

The device driver of the central control unit 18 also ensures that the desalination devices 12, 13 are shut down in a controlled way if the expected energy production is too low to keep them operational.

Each desalination device comprises one or more streets for reverse osmosis, where the salty water is put under pressure and forced through a membrane with the formation of purified product water 28. Each of these one or more streets can be separately stopped by closing a valve 54, 55, 56, 57 so the supply of salty water to the street for reverse osmosis is stopped. Subsequently all pipework in the street concerned is flushed with purified product water 28 to remove all impurities, and the flushing water is drained away through the discharge conduit for brine water 29, so that the membrane is not damaged due to the stopping of the purification process and so that it can be used again later.

The device driver can gradually reduce the capacity of the purification system 12 or build it up again by switching on or off one street 58 or more streets 59, 60, 61 if more than one street is available for reverse osmosis and this depending on the expected available green energy and the expected need for product water. This control is required to protect the purification system for reverse osmosis against damage as a result of fluctuations in green energy production.

The device driver of the central control unit 18 manages the energy household of the device and to that end uses one direct current main distribution rail 66, that connects the local production of green energy, in this case generated by the wind mills 7,8 , to the inclusive electronic voltage- current control 67a, 67b of which the converters 41a, 41b are a part; to the battery system 22 with its battery pack 23 and its electronic control unit 24; to the electronically controlled alimentation 72 of a pump 48 that carries the salty water to a filter assembly; to the electronically controlled alimentations 68, 69, 70, 71 of the one to four pumps 50, 51, 52, 53 that pump the filtered salty water to the respectively one or more osmosis streets; to the electronically controlled alimentation 73 of the irrigation pumps 33; to the electronically controlled alimentations 74, 75 of the one to two pumps for rinsing of the osmosis streets, and to the alimentation of the auxiliary devices.

The auxiliary devices comprise the general lighting in and around the device as well as the entrance to it, the mechanical ventilation and cooling of the battery room and of the spaces for the desalination device, the fire protection of the device and the alimentations of the electronic equipment and of the communication systems, the alarm systems, the emergency lighting, the lighting for navigational security and the alimentation of the equipment for lowering and raising the wind mills.

The device driver of the central control unit 18 communicates to this end with the electronic voltage-current frequency regulators 67a, 67b; with the electronic control unit 24; and with the electronically controlled alimentations 68, 69, 70, 71, 72, 73, 74, 75.

An advantage of the distribution by means of one main distribution rail 66 on direct current, is that the distribution of the electric energy generated by wind mills, photovoltaic cells, or other green energy sources, is more efficient than on alternative current, since a conversion of ACn(Hz net) / DC with the frequency controlling for the alimentation of the pump engines is avoided and saved, and no use is made of AC transformers for the conversion to the required voltages. This distribution on direct current (DC) means a rise in efficiency compared with a distribution on alternative current (AC n) of a desalination device as described in CN 104649478 B. This patent describes a main distribution rail with a separate transformer 4, 7, 10, 13 for the battery group and for every group of consumers. The frequency control 8 of the pumps 9 happens through a double conversion AC n (Hz net) / DC/AC m (Hz motor) .

The isolated electrical network of the present invention is not coupled to a grid or component with a large mass inertia and therefore cannot reckon on the large mass inertia that such as a big public electric grid or generator can offer to stabilise the network.

In order to nonetheless ensure a desired stability of the isolated network of this invention a mass inertia is emulated by the device driver of the central control unit 18 that by power-electronic means manages the network instantaneously and dynamically taking into account the production of energy, the storage of energy, and the charges on the isolated network. This is necessary to prevent the unwanted failure of the isolated network, given its small inertia to compensate fluctuations in available voltage and current.

This assurance of the stability by the device driver of the central controlling unit 18 delivers an improvement of the cost efficiency of the present device compared with a device such as described in CN 104649478 B. In this patent the PLC- control unit 17 manages only the starting values for the working of the different components of the net, that aside from this also uses an auxiliary generator 2 and a dumpcharge 3 that offer more inertia to the net and partly compensate for the lack of mass inertia of a large grid. The device according to the present invention works without an auxiliary generator and without a dump charge, thereby saving the investment and operational cost of these.

Another additional advantage of the present invention is that the device uses exclusively locally generated green energy without any expulsion of greenhouse gases.

Yet another advantage of the present invention is that the pumping of salty water 27 to the filter assembly 49 by a pump 48 as well as the pumping of productwater to the irrigation system 32 by the irrigation pumps 33 happens by means of green energy through the direct current main distribution rail 66. In CN 104649478B, the pre-treatment subsystem nor the product water distribution are coupled to the distribution rail 16 and hence do not use the available green energy in the system.

Another additional advantage of the present invention is that the distribution of product water to the irrigation system 32 is an integral part of the device and is controlled by the device driver of the central control unit 18 in function of the irrigation condition and the available and forecasted wind energy, while in CN 104 649 478 B the needs and capacities for the consumption of desalinated water are not taken into account for the dynamic control of the desalination capacity. The device driver of the central control unit 18 controls the flow of product water to the irrigation system 32 through the frequency control 73 of the irrigation pumps 33.

The central control unit 18 communicates with the irrigation system through the irrigation analysis module 40 in order to also take the irrigation condition into account to control the production capacity of the desalination device 26. The device driver then controls the pumping rate of the irrigation pumps and distribution means 33 as a function of the irrigation condition.

The device driver of the central control unit 18 controls at any moment the production of product water 28 by controlling the pumps 50, 51, 52 and 53 of the osmosis streets of the desalination device 12 by regulating the rate of pumping or eventually by switching the pumps on or off. The central control unit 18 regulates the consumption of electrical energy by the desalination device 12 by controlling the pumps 50, 51, 52, 53 that is continuously adjusted to the available green energy produced by the wind mills 7,8 and to the charge level of the battery 23. The present invention is by no means limited to the embodiments described as an example in the drawings, but a device for the desalination of water by means of local green energy production according to the invention can be realized in all kinds of variants and dimensions, without departing from the scope of the invention. Hence the device can not only be installed on a fixed location, but also on a movable platform that is transportable by land or on waterways.

So besides using windmills, green energy can also be generated by wind turbines, photovoltaic solar panels or hydraulic turbines.

It is obvious that the number of reverse osmosis streets is not limited to four, and can comprise more streets.

In any case the device for the desalination of water must be provided with a central control unit 18, that can match the fluctuating green electricity production with the need for a stable current for powering the pumps and the desalination device itself, and with the need for a prior gradual reduction of the desalination in the device for reverse osmosis, if the device for the desalination of water must be stopped due to a lack of energy or a lack of demand for desalinated water in the form of potable water or irrigation water for agriculture.

Claims

Claims .

1. - Device for the desalination of water (1) by means of green energy, with which a reverse osmosis desalination device (12, 13) is powered that converts salt or brackish water (44) into product water (28), characterised in that this device has its own local green energy production and is independently controlled by a central control unit (18) that matches the production of product water with the local needs and expectations and with the fluctuating and expected local green energy production.

2. Device for the desalination of water (1) according to claim 1, characterised in that together with the means for the local generation of green energy it is built on a movable platform that can be moved over land or water.

3. Device for the desalination of water (1) according to claim 1 or 2, characterised in that the means for the local generation of green energy can consist of windmills (7, 8), wind turbines, photovoltaic solar cells or hydraulic turbines .

4.- Device for the desalination of water (1) according to claim 2, characte ised in that the mobile device is built on a floating platform, so the platform can be moved over water to coastal areas or over rivers, where there is a requirement for product water, whereby the floating platform is towed or has its own autonomous means of propulsion.

5. - Mobile device according to claim 4, characterised in that the floating platform comprises two main pontoons (2, 3) positioned next to each other, which are connected to each other by means of three detachable connecting pontoons (4, 5, 6) to form a stable platform and whereby each main pontoon (2, 3) is provided with a windmill (7, 8) for the production of green energy and a pump assembly (9, 10) to pump up salty or brackish (41) water to a desalination device (12, 13).

6. - Mobile device according to claim 4, characterised in that the length of the detachable connecting pontoons (4, 5, 6) is selected according to the dimensions and characteristics of the windmills (7, 8) and the associated forces on the masts of the windmills, so the floating platform is hydrodynamically able to accommodate the reaction to the inclination of a windmill (7, 8} and keep it stable within the tolerances of the windmill.

7.- Mobile device according to claim 5, characterised in that the windmills (7, 8) can be erected or lowered pivoting by means of an electric winch or a hydraulic jack on the mobile device without requiring a crane. 8.- Mobile device according to claim 5, characterised in that each windmill (7,

8) generates an unstable alternating current (AC) depending on the wind strength, that is converted to direct current (DC) and stored in storage batteries (23) , after which the current from the batteries is converted to alternating current (AC) for powering the pumps for irrigation (33) and the desalination system with reverse osmosis (12, 13).

9. - Device for the desalination of water according to claim 1, characterised in that the central control unit (18) uses a device driver for energy management for the device (1), whereby the central control unit (18) is connected to the energy source (21), in this case the windmills (7, 8), to the electrical storage system (22), in this case the batteries (23), to the desalination device (25), in this case the reverse osmosis equipment (26) , to the storage tanks

(31) for desalinated water, and to the irrigation system

(32) , in this case the pumps (33) that distribute the product water (28) over the plots of land (19) to be irrigated.

10. - Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) analyses the incoming information from all parts to which the central control unit is connected and assigns a sufficient amount of energy from the batteries to the desalination devices (12, 13) in the form of a safe stable power supply but also to the electronic equipment of the device and stops desalination in due time in a controlled way if insufficient green energy production is expected to permanently power the reverse osmosis system (58, 59, 60, 61) .

11. - Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) uses an autonomous and self-learning module for weather prediction (35), that is part of the device and that, based on the local wind patterns and on its own wind measurements, but also on other meteorological parameters such as air pressure, precipitation and humidity, an accurate and precise local wind prediction and the expected green energy production at any time.

12.- Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) uses a module for irrigation analysis (40), that is part of the desalination device, and that forecasts the desired quantity of product water {28) based on local precipitation statistics and other information such as the soil type, local water regimes and the irrigation techniques used, so the central device driver can at any time optimise efficiency of use of the generated energy and the potential of the desalination device, and match them with each other based on the meteorological conditions and expectations and the condition and the characteristics of the windmills.

13. - Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) communicates with the local production system for energy (21) through an energy production control unit (36) with the storage system for electrical energy (22) through a battery status interface (37); with the production system (25) for product water (28) through a product water production control unit (38); with the storage system for product water (30) through a storage tank status interface (39) ; and with the irrigation system (32) through an irrigation analysis module (40) .

14. - Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) at any time matches green energy production with the production of product water (28) by regulating the pumping rate of the pumps {50, 51, 52, 53) of the desalination device (12) and their consumption of electrical energy as a function of the available green energy produced by the wind mills (7,8) and of the charge level of the battery (23) .

15. - Device for the desalination of water according to claim 9, characterised in that the device driver of the central control unit (18) also ensures a safe margin of available energy to kick-start the windmills (7, 8) at any time, and for the controlled reduction of the activity of the desalination device (12, 13) if insufficient green energy production is anticipated.

16. - Device according to claim 9, characterised in that each desalination device (12, 13) consists of at least one pump assembly (49) followed by one or two reverse osmosis streets (58, 59, 60, 61), whereby the number of osmosis streets switched on is dynamically controlled by the device driver of the central control unit (18) depending on the available green energy and the desired quantity of product water (28) .

17. - Device according to claim 1, characterised in that the local production of green energy (21) , in this case generated by wind mills (7, 8) with their inclusive electronic voltage- current frequency regulation 67a, 67b of which the converters 41a, 41b are part, are linked by one direct current main distribution rail (66) to a battery system (22) with a pack of batteries (23) and with its electronic control unit (24); to an electronically controlled alimentation (72) for a pump (48) that leads the salty water to a filter assembly; to the electronically controlled alimentations (68, 69, 70, 71) of the one or more pumps (50, 51, 52, 53) that pump the filtered salty water to the respectively one or more osmosis-streets; with the electronically controlled alimentation (73) of the irrigation pumps (33) ; with the electronically controlled alimentations (74, 75) of the one or more pumps (50', 52') for rinsing the osmosis streets, and with the alimentations of auxiliary devices.

18. - Device according to claim 17, characterised in that the auxiliary devices comprise the general lighting in and around the device as well as the entrance to it, the mechanical ventilation and cooling of the battery room and of the spaces for the desalination device, the fire protection of the device and the alimentations of the electronic equipment and of the communication systems, the alarm systems, the emergency lighting, the lighting for navigational security and the alimentation of the equipment for lowering and raising the wind mills.

19. - Device according to claim 17, characterised in that the stability of the isolated network is ensured by the device driver of the central control unit (18) that emulates a mass inertia of the local network by means of power electronics that manage the network instantaneously and dynamically taking into account the production of energy, the storage energy, and the loads on the isolated network .