GR1009109B - Solar desalination arrangement furnished with a low-cost collector - Google Patents

Abstract

The invention relates to an arrangement meant for seawater or brackish water desalination, comprising a reverse-osmosis desalination unit 20 and a natural or artificial or adequately- modified lake 10 containing a high-concentration salt solution. A supply of high-concentration salt solution current flows out from said lake and returns thereto in a lower salt concentration state. The lake’s water evaporation -which is mainly achieved by solar energy-ensures the approximately constant long-term salt concentration. Practically, the lake 10 operates as a low-cost solar collector. The required compression of the seawater or brackish water that enter from one side of the semi-permeable membranes of the pressure containers 22 of the reverse-osmosis desalination unit 20 is obtained by displacement due to the volume increase of the high-concentration salt solution current coming from the lake 10 and returning thereto under a diluted condition. The increase of the high-concentration salt solution current occurs under high-pressure conditions as this current absorbs water from another seawater current through semi-permeable membranes contained in the respective pressure containers of an additional osmosis unit 40 which operates under the direct-osmosis principle.

Description

Solar desalination device using low cost collector

The invention relates to a solar desalination device using a low-cost collector.

Given the imperative and growing need for clean water, various desalination technologies have been developed and a large number of desalination plants have been constructed.

The most important seawater or brackish water desalination methods that have been adopted commercially can be classified mainly into two groups according to the technology they use: The membrane group and the thermal group (or thermal imitation group). The first group mainly includes reverse osmosis (RO), forward osmosis (FO) and electrodialysis methods, while the second group mainly includes multistage flash (MSF), multistage distillation (MED) and vapor compression (VC).

A common feature of all desalination technologies and their associated commercial applications is the significant amount of energy (either electrical or thermal, depending on the technology applied) required to operate the desalination unit. Consequently, the cost of energy is the main factor in the operating cost of a typical desalination plant, resulting in the relatively high price of the desalinated water produced.

Desalination, powered by renewable energy sources, is challenging for both economic and environmental reasons. Various technologies have been developed and many research projects have been implemented, however, these methods have not been widely applied commercially, mainly due to the high required investment costs. From a commercial point of view, one of the most popular desalination methods is reverse osmosis desalination powered by photovoltaic panels and typically found applications in small-scale installations. Since the solar power is less than 1 KW / m2 and the efficiency of the solar panels is low, (about 18%), the area of the panels required for such an application is very large, resulting in high investment costs.

The desalination technology that seems to be the most commercially attractive in recent years is reverse osmosis (RO), mainly due to the remarkable reduction in the cost of the semi-permeable osmosis membranes used according to this technology. The major operating cost of this method is the cost of electricity required to operate the high pressure pumps that compress the seawater into the pressure vessels containing the semi-permeable osmosis membranes. In addition, in places not connected to the electricity grid, (as for example on some islands), the actual cost of producing electricity is much higher compared to the nominal one, resulting in the also very high cost of reverse osmosis desalination and the discouragement of such choices.

The reverse osmosis desalination according to the present invention is powered by renewable sources and therefore, does not need electric high pressure pumps, eliminating the associated energy costs. Briefly, it includes a reverse osmosis desalination unit and additionally a natural or artificial solar pond containing a highly concentrated salt solution. A supply of highly concentrated salt solution flows out of said pond and returns to it having a lower salt concentration. Evaporation of water from the lake, mainly due to incident solar radiation, ensures the approximately constant salt concentration in said lake. In fact, this pond acts as a large-scale and low-cost solar collector. The required compression of the seawater entering the semi-permeable membranes of the said desalination unit is achieved by the displacement due to an increase in volume and under very high pressure of the supply of the highly concentrated salt solution, originating from the aforementioned lake, as it absorbs water from another supply of sea water through semi-permeable membranes contained in the corresponding pressure vessels of an additional direct osmosis unit, provided for this purpose.

The design and operation of a desalination unit according to the present invention can be based either on a continuous flow process or on a batch basis. The continuous flow process has been developed and described below for practical purposes, however, the batch process approach is an alternative and is based on similar principles and operating characteristics to the continuous flow process.

The desalination process according to the present invention can be based on a single stage operation, however, the multistage process increases efficiency and is therefore the one adopted in what is described below. Brief description of designs:

In Figure 1, which refers to a multi-stage continuous flow desalination process according to the present invention, the following can be seen:

- The low-cost solar collector, i.e. the highly concentrated salt solution pond (10).

- The desalination unit (20), which works according to the principle of reverse osmosis, with the pressure vessels (22), the inlet ducts (23) and outlet (27) respectively of the desalinated sea or brackish water and the outlet ducts of the desalinated water.

- The compression unit (40) which works according to the principle of direct osmosis, with the pressure vessels (42), the inlet ducts (44) and outlet (47) respectively of the highly concentrated salt solution and the inlet ducts (46) and outlet (45) respectively of seawater or brackish water compression. - The pressure / flow conversion unit (60) with the pairs of cylinders (61) / (71), the inlet (47) and outlet (44) ducts respectively of the highly concentrated salt solution and the inlet (27) and outlet ducts (23 ) respectively of desalinated sea or brackish water.

- The seawater filtration and processing units (31) and high concentration salt solution (48) respectively.

- The desalinated water storage tank (28).

- The pumps for advancing seawater (32) and (49), highly concentrated salt solution (71), desalinated water (29), desalinated sea or brackish water discharge (72) and compression sea or brackish discharge discharge ( 51).

In Figure 2, which refers to the compression unit (60), the following is shown:

- The pair of two cylinders (61), which includes cylinder (611) and cylinder (612). Each of the cylinders (611) and (612) consists of the container (or body) of the cylinder (62), the piston (63), the rod (64) and the inlet / outlet ports of the two spaces (parts) of cylinder (62), which are separated from the piston (63).

- The flow control valves (65) and (66) of the highly concentrated salt solution to and from the vessels (42) of the compression unit and the flow control valves (67) and (68) of the unsalted sea or brackish water menu to and from the containers (22) of the desalination unit.

- The line (47) of high concentration salt solution from the pressure vessel (42) of one stage of the compression unit to the flow control valves (65) / (66) and the line (44) of high concentration salt solution from the flow control valves ( 65) / (66) to the pressure vessel (42) of the next stage of the compression unit.

- The pipe (27) of the desalinated water from the pressure vessel (22) of one stage of the compression unit to the flow control valves (67) / (68) and the pipe (23) of the desalinated water from the flow control valves (67) / (68) to the pressure vessel (22) of the previous stage of the desalination unit.

Four supply streams (hereinafter referred to as "feed streams" or simply "streams"), are included in the processes according to the present invention: - The highly concentrated salt solution stream (hereinafter for brevity DAUS) in the compression unit (40).

- The stream of brackish water, or seawater, or concentrated seawater (hereafter, for brevity's sake, THNA) in the desalination unit (20).

- The stream of brackish water, or seawater, or condensed seawater (hereafter for brevity TNS) in the compression unit (40).

- The desalinated water stream (hereafter AN for brevity) in the desalination unit (20).

The term "solution concentration" mentioned in this text corresponds to the term "solution content" found in the relevant Greek literature.

As for the direction of flow of each of the four aforementioned flow streams from one stage to another, any combination may be chosen, however, in the following description, the adopted flow directions are: streams THNA and THNS entering the last stage of the units and exit from the first. The DAUS current, located in counter-flow with respect to the aforementioned currents, enters the first stage of the units and exits from the last.

The units or components included in said desalination process according to the present invention are described in detail below, with reference to drawing 1:

The - at least one - low-cost solar collector, which is actually a natural or artificial, or suitably shaped pond or pool (10), containing DAUS which feeds the compression unit (40) mentioned below and returns diluted, resulting reducing the concentration of the salt solution in the lake or pool. This reduction is compensated mainly by solar radiation which evaporates water from the lake, increasing the concentration of the salt solution it contains. Consequently, with appropriate adjustment of the outflow and inflows of the DAUS solution to and from the lake (10), depending on the size of the lake, the local climate and other local conditions, the salinity concentration of the solution in the lake remains approximately constant over time.

Said pond or pool (10) is preferably shallow. However, one or more shallower regions may form in the lake, so that the deeper layers of these regions develop high temperatures in the DAUS due to the effect of stratification of high salinity solution in a solar lake. The DAUS stream feeding the compression unit (40) is preferably drawn from the depth of these shallower regions.

Dark-colored gravel, stones, or other suitable materials are preferably placed on the bottom of the lake, improving the absorption of solar radiation and, therefore, contributing to the increase in the rate of evaporation of water from the lake and the concentration of DAUS in it. Dark colored semi-submersible particles or structures may also optionally be selected for the same reason.

Alternatively, very high concentration salt solution or salt slurry from salt flats or similar areas, or even dry salt, can be used to produce DAUS, mixed in the appropriate proportion with the medium or low concentration salt solution that either exits the due to compression unit, whether it comes from anywhere else. For example, when one Kgr of 70% strength salt slurry is mixed with five Kgr of 10% strength salt solution leaving the compression unit, then six Kgr of 20% strength salt solution are produced and can re-feed the compression unit with DAUS.

The desalination unit (20) is similar to existing reverse osmosis desalination units and includes at least one desalination stage. Each desalination stage (for example stage number "k"), includes at least one pressure vessel (22), containing semi-permeable membranes of any type, and:

- The inlet pipe (23) which supplies a high-pressure DHW stream to one surface of the semi-permeable membrane of the pressure vessel (22), coming from the next stage of the desalination unit (stage numbered "(K 1)" ) through the pressure / flow conversion unit (60). In case the stage numbered "k" is the last stage of the unit, then said high pressure stream THNA comes through the feed line (24) and the feed pump (32). The high pressure of the THNA supply stream is achieved thanks to the compression unit (40) and the pressure/flow conversion unit (60) described below, and its value exceeds the osmotic pressure value, developed for the specific conditions (temperature, concentration salt, etc.) of the TNA supply current. Therefore, clean, desalinated water (AN) from said feed stream THNA permeates the semi-permeable membrane, and via the local outlet AN (25), the central outlet AN (26) and the pump (29) is stored in desalinated water tank (28).

- The concentrated solution outlet pipe (27) which drains from the pressure vessel (22) the THNA supply stream, which has a higher concentration and a lower flow rate, compared to those of the THNA supply stream entering the specific pressure vessel (22) through of the intake duct (23) mentioned above.

The compression unit (40), the purpose of which is to increase the supply under pressure in the DAUS stream, so that this pressure is transferred through the pressure / supply conversion unit (60) to the TNA supply stream and displaces it in the pressure vessels ( 22) of the desalination unit (20), compressed to the required level, so that the desalination process is possible through the semi-permeable membranes of said pressure vessels (22). During the aforementioned process, which is carried out through the pressure/flow conversion unit (60), the two aforementioned streams DAUS and THNA are not mixed. Said compression unit (40) operates according to the principle of direct osmosis and comprises at least one compression stage, while each compression stage comprises at least one pressure vessel (42), containing semi-permeable membranes of any suitable type.

It also includes:

- The inlet duct (44) of the high pressure DAUS supply stream to the first side of the semi-permeable membrane of said pressure vessel (42). The DAUS supply current comes from the previous compression stage (stage number "(k-1)"). In the event that stage number "k" is the first stage of the unit, then the said DHW supply stream is from the high concentration salt solution pond (10) through the filtration / treatment unit (48) and the advance pump ( 71). Said high pressure DAUS supply stream exits the pressure vessel (42) through the outlet pipe (47) and compresses the same stage (numbered "k") DHW stream of the desalination unit, through the compression cylinders of the same stage (numbered "k") of the pressure / flow conversion unit (60). At each stage, said high concentration salt solution (HBS) leaves the pressure vessel (42) through the outlet pipe (47) having a lower concentration and higher flow, compared to those of the incoming HBS solution through the inlet pipe (44). .

- The inlet pipe (46) to the second side of the semi-permeable membrane of the pressure vessel in question (42) of the same stage (under number "k") of the THS supply stream coming from the next stage (under number "k+1") of the compression unit (40). In case the stage numbered "k" is the last stage of the unit, then the said DHW supply stream comes from the DHW supply pipe (46) through the pump (49). The aforementioned THNS stream leaves the pressure vessel (42) of the previous stage (stage numbered "(K-1)") through the outlet pipe (45). In the event that the stage numbered "(K)" is the first stage of said compression unit, (40), then said high pressure THS stream leaves the pressure vessel (42) and through the return pipe (50 ) and of the propulsion pump (51) returns to the sea, having a higher concentration and lower flow, compared to those of the incoming THNS in the pressure vessel (42) through the inlet pipe (46) mentioned above. Since, in each particular stage, the concentration of DAUS on the first side of the semi-permeable membrane of the pressure vessel (42) of said stage is much higher than the concentration of THNS on the second side of said semi-permeable membrane of the aforementioned pressure vessel (42), water originating from the TNS current penetrates the semi-permeable membrane, and enters the circulation of the MYS increasing its volume and its supply. This increase in flow is used to compress the THNA entering the corresponding stage of the desalination unit (20).

The pressure/flow conversion unit (60), the purpose of which is to transfer the high pressure achieved in the stream MYS within a stage of the compression unit (40) to the stream THNA of the corresponding stage of the desalination unit (20), so that the pressure of THNA to be at the required design level for the reverse osmosis process, without the mixing of the two aforementioned streams MYS and THNA. The aforementioned transfer of pressure can be carried out in various ways and methods, such as with any type of turbine (for the MYS stream) and pump (for the THNA stream) pair, with a pressure vessel containing a suitable flexible membrane that separates the volume of it into two separate / sections of variable volume, etc. For the purposes of describing the present invention, the cylinder pair method is adopted without affecting generality.

The pressure/flow conversion unit (60) in each of its stages and with reference to drawing 2 includes:

- The pair of two cylinders (61), including cylinder (611) and cylinder (612). Each of the cylinders (611) and (612) consists of the container (or body) of the cylinder (62), the piston (63), the rod (64) and the inlet / outlet ports of the two spaces (parts) of cylinder (62), which are separated from the piston (63). There may even be more than one pair of rollers in each tier. - The flow control valves (65), (66), (67) and (68). These valves can be of any type. The type of valves shown in drawing 2 is purely indicative. The design form prevailing in the design of hydraulic power systems has been used, without loss of generality. Four valves are shown in figure 2: Two to control the flow of the DAUS supply stream to and from the cylinder pair and two more to control the TNA supply stream to and from the cylinder pair. However, depending on the design and type of valves, fewer (or more) of the four valves could be used, more or less complex respectively.

- Instruments and other control equipment not shown in drawing 2.

At each stage of the pressure/flow conversion unit (60), (for example at stage number "k"), and with reference to drawing 2: The supply stream DAUS leaves the pressure vessel (42) of the given stage (sub< 1>number "k") of the compression unit (40) and through the pipe (47) and the valve (65) enters the right part of the first cylinder (611) and, being under high pressure, forces the piston (63) of the cylinder (611) to move to the left, displacing (also under pressure) the TNA contained in the left part of the cylinder (611). This stream of THNA is led through the valve (67) and the pipe (23) to the pressure vessel (22) of the said stage (numbered "k") of the desalination unit (20). Said DAUS supply current cannot reach the second cylinder (612), because it is blocked by the valve (66) which is closed for it. In the same way, the supply stream THNA cannot reach the second cylinder (612), because it is blocked by the - closed for it - valve (68). At the same time, the supply stream THNA leaves the pressure vessel (22) of the next stage (stage numbered "(k 1)") of the desalination unit (20) and through the pipe (27) and the valve (68) enters the left part of the second cylinder (612) and, being under high pressure, causes its piston (63) to move to the right, displacing (also under pressure) the DAUS contained in the right part of the cylinder (612) causing it to it ends through the valve (66) and the pipe (44) in the pressure vessel (42) of the next stage (stage numbered "(k 1)") of the compression unit (40). The aforementioned supply stream THNA cannot reach the first cylinder (611) since it is blocked by valve (67). In the same way, the DAUS supply stream cannot reach the first cylinder (611), since it is blocked by valve (65). When the pistons of the cylinders reach the end of their travel, the four valves change position, causing the first cylinder (611) and second cylinder (612) to switch roles, thus ensuring continuous operation of the desalination unit.

An additional cylinder pair (70) is included in said pressure/flow conversion unit (60), before the first stage, and operates in a similar manner to the other cylinder pairs of said pressure/flow conversion unit (60). The purpose of this additional pair of cylinders (70) is to use the DHW supply stream exiting the first stage of the desalination unit (20) under high pressure, so as to pressurize the DAUS and force it into the pressure vessel ( 42) of the first stage of the compression unit (40). While one cylinder of the cylinder pair (70) operates in the manner described above, the other cylinder is filled in one section with a low-pressure flow of DHW through the pump (71), displacing at low pressure the THNA contained in the other part of said second cylinder and discharging it back into the sea via the pump (72).

In each cylinder (611), (612) of any stage of the pressure/supply conversion unit (60) and the complementary pair of cylinders (70) the cross-sections of the two sections into which the cylinder is divided by the piston (63) may be equal, i.e. there is no bacter, and the piston moves due to the developing pressure, so the supply of one current entering the cylinder is equal to the supply of the other current leaving the cylinder. It is preferable, however, to have a bacter and the cross-sections of the two sections into which the cylinder is divided by the piston (63) are not equal, due to the bacter. Consequently, the supply of input current to one part of the cylinder differs from the supply of output current from the other part of the cylinder. In this way, the pressure/flow conversion unit (60) does not simply function as a pressure transporter from the DAUS stream to the THNA stream, but optimizes the pressure/flow relationships of said streams with the goal of minimum final cost. The desired ratio of the input - output benefits of the aforementioned two currents in the cylinders of each stage is achieved by the appropriate selection of the ratio of the diameter of the rod to the internal diameter of the cylinder.

When a cylinder of one stage (for example the stage numbered "k") is in operation, it receives from that particular stage of the compression unit (40) a high-pressure DAUS input stream in its section having the smallest cross-section (which is that which contains the bacter (64)), as a result of which the piston (63) is forced to move and compress and displace under pressure towards the specific stage of the desalination unit (20) the THNA located in the other part of the cylinder, i.e. of the one that has the largest cross-section and does not contain the bacterium.

The following simple relationship applies: RDAUS * FDAUS * n = ΦΘNA * FΘNA, where:

- η is the efficiency factor, which is generally very high, (very close to the value "1"), since the losses are extremely low.

- PDAUS and FDAUS are the pressure and the supply respectively of the current AUS that enters into the cylinder. The formula applies: RDAUS = (ROSMDAUS - ROSMTHNS) - DRDAUS, where: ROSMDAUS is the osmotic pressure of the flow ADAUS on one side of the semi-permeable membrane of the pressure vessel (42) of the said stage (stage numbered "k" ) of the compression unit (40), for the specific conditions (solution concentration, temperature, type of dissolved salt, etc.) of the stage in question.

ROSSMTHNS is the osmotic pressure of the TNS stream on the other side of the semi-permeable membrane of the pressure vessel (42) of the said stage (stage numbered "k") of the compression unit (40), for the specific conditions (solution concentration, temperature, type of dissolved salt, etc.) of that grade.

DRDAUS is the pressure drop during the passage of water through the semi-permeable membrane contained in the pressure vessel (42) of said stage of the compression unit (40). The aforementioned water comes from seawater or brackish water compression and through the semi-permeate it ends up in the highly concentrated salt solution.

High values of DRDAUS result in low value of the pressure PRDAUS. - PΘNA and FΘNA are the pressure and the supply respectively of the stream ΘNA leaving the cylinder. The formula applies: PTHNA = ROSSMTHNA DPΘNA, where:

ROSSMTHNA is the osmotic pressure of the stream THNA on one side of the semi-permeable membrane of the pressure vessel (22) of the said stage (stage numbered "k") of the desalination unit (20), for the specific conditions (solution concentration, temperature, type of dissolved salt, etc.) of that grade. DPQNA is the pressure drop during the passage of water through the semi-permeable membrane contained in the pressure vessel (22) of said desalination unit stage (20). The aforementioned water comes from sea or brackish desalination water.

A high value of DPQNA leads to a high value of PTHNA.

The above-mentioned detailed description applies to the cases that normally apply, i.e. to those in which the value of the pressure of the PDAUS is greater than that of the pressure of the PTHNA, which means that the difference in the concentrations of the DAUS and THNS currents is relatively large and the concentration of the THNA current relatively small. However, there is a case in some, or even in all stages of the unit, where a relatively low salt concentration DAUS current is used, with the result that the value of the pressure of the PDAUS is lower than that of the pressure of the PTHNA. In this case, the unit works in the opposite way to the one described above, in order to increase the pressure of the DHW stream to the desired level for the desalination process. More specifically, the DAUS current is led to the part of the cylinder with the largest cross-section (the one that does not contain the bacter) and the ΘNA current is led to the part of the cylinder with the smallest cross-section (the one that contains the bacter), so the supply of the ΘNA current exiting each stage of the pressure conversion unit (60) is less than that of the DAUS stream entering it.

The aforementioned process can be implemented in other ways than this pair of scrolls, such as with a pair of turbine (for the highly concentrated salt solution stream) and pump (for the seawater stream). In each stage, the ratio of the supply of the highly concentrated salt solution stream into the turbine to the supply of the seawater stream into the pump is that required to operate the particular stage of the desalination unit (20) and is achieved, either by selecting a turbine and a pump with an appropriate displacement / embolization ratio coupled on a common axis, either by choosing a turbine and a pump with displacements / embolization not necessarily related to each other but coupled with the intervention of a reducer of a suitable transmission ratio or other corresponding drive device, (such as pulleys and belts), also of suitable gear ratio.

The values of THRDAUS and DPΘNA but also the possible range of their change in each stage of the desalination (20) and compression (40) units are chosen according to the nature and properties of the semi-permeable membranes used and other technical and economic factors. Also, during the design of the installation, in each stage of the desalination (20) and compression (40) units, the functional characteristics of the DAUS, THNA and THNS solutions (concentrations, supplies, etc.) of each operating stage are selected appropriately, in order to achieve the best possible technical and economic result, naturally within the limits imposed by the relevant balances of benefits and power. However, in this way, it is very possible that in one or more stages of the desalination (20) and compression (40) units, the pressure of the THNA stream, which comes from the next stage of the desalination unit (20) and enters the left part of the cylinder (612) of the specific stage is not strong enough to displace the piston (63) and displace the DAUS contained in the right part of the cylinder (612) towards the next stage of the compression unit (40), i.e. some additional power to carry out said displacement of the piston (63) and the displacement of the DAUS. This additional required power is provided by an external source and is preferably applied directly to the rod (64) of the aforementioned roller (612), with the help of suitable equipment, such as for example a toothed rule which is fitted on the rod and monitors its movement and with a gear cooperating with said rule and rotated - through a reducer of a suitable transmission ratio - by an engine supplied with the aforementioned additional power. The above also applies to the complementary pair of cylinders (70). It is also possible, in one or more stages of said units, that the opposite happens, that is, the above-mentioned pressure of the THNA stream which comes from the next stage of the desalination unit (20) and enters the left part of the cylinder (612) of the specific stage to be greater than that required for the movement of the piston (63) and the displacement of the DAUS contained in the right part of the cylinder (612) towards the specific stage of the compression unit (40), i.e. there should be some power surplus. And in this case, the surplus power is received with the help of - corresponding to the aforementioned - equipment, (toothed rule adjusted on the rod, gear, etc.). The above also applies to the complementary pair of cylinders (70).

What is usually expected is to observe a surplus of power in some grades and a deficit in others. The preferred approach to deal with the above is to interconnect all said tiers in any way, such as: electrical, hydraulic, mechanical, etc., or a combination of the aforementioned. If electrical interconnection is selected, then the respective cylinder of each stage is connected (for example via a rule / gear / reducer) to a small generator / motor, which is electrically connected to the corresponding pumps / motors of the remaining stages of the installation using of the necessary electrical equipment and the required electrical characteristic adapters. In this way, the generators/motors of the overpowered stages act as generators supplying power to the system, while the generators/motors of the underpowered stages act as motors, drawing power from the system. The above also applies to the complementary pair of cylinders (70). Because (by design) the total power balance of all stages can rarely be zero, a (relatively small) total power deficit or surplus is usually expected. If it is a deficit, then this is covered with an additional motor supplied electrically by external power, if it is not a surplus, this surplus is preferably used for the other needs of the installation. Instead of the aforementioned electrical interface, a hydraulic interface can be used and its function is equivalent to that of the electric one, with the difference that, instead of generators / motors, hydraulic pumps / hydraulic motors are used, connected to hydraulic oil pipes of a small hydraulic unit including the necessary operating and flow control equipment. If mechanical linkage is selected, then the corresponding cam of each cylinder of each stage has a gear rack, which is mechanically connected by means of one or more gears of suitable transmission ratio and the corresponding shafts, to the gear racks of the cams of the remaining cylinders. The combination of two or more of the aforementioned ways can be implemented, as for example in the following selected way: The two toothed rules of the parallel bars of the two cylinders (611), (612) of a pair of cylinders (61) are bridged by a rotating gear about a non-moving axis, and interposed between the toothed rules, so that the movement of one rod is of equal value and opposite direction to the movement of the other rod. The above applies to all pairs of cylinders (61) and all said gears are connected to each other, either electrically, hydraulically or mechanically, as described above.

The aforementioned additional required power, which is necessary to cover the total power deficit of the interconnected cylinder banks, can be conventional, such as for example electric power, or even come from an additional equipment, which is provided for the reason this (and not shown in drawings 1 and 2). The additional equipment in question includes a compression sub-unit supplied with both DAUS current, originating either from the lake (10), or from anywhere else, and with THNS current from the sea, and operates in a manner similar to that of the compression unit ( 40), ensuring a supply of DAUS under pressure, which is driven to a turbine connected to a generator or hydraulic pump and produces energy which it appropriately distributes to as many cylinders as required, in order to cover the corresponding power deficit.

An additional DAUS stream can be channeled not only to the first stage of the compression unit (40), but also to one or more of the following stages, mixing with the - relatively diluted - DAUS solution that enters the said stage from the previous one, with possibly removing some of the diluted DAUS before mixing. In this way, the concentration and therefore the osmotic pressure of DAUS increases in the specific stage, but also in the following ones, in relation to the corresponding ones that would apply if there was no aforementioned addition of DAUS. Regardless of whether an additional stream of highly concentrated solution is fed to subsequent (other than the first) stages of the compression unit (40) as mentioned above or not, an additional stream of seawater may be fed not only to the latter but also to one or more of the previous stages of either the compression unit (40) or the desalination unit (20) respectively, or both, mixing with the - relatively concentrated - compression seawater solutions (SWW) and/or desalination seawater (SWW) that enter the specific stage of the compression (40) and desalination (20) units, respectively, from the next stage, with possible removal of some amount of the relatively concentrated THNS and / or THNA solutions before the respective mixing. In this way, the concentration and therefore the osmotic pressure of TNS and/or TNA is reduced in the specific grade, but also in the previous ones, in relation to the corresponding ones that would apply if there was no aforementioned addition of TNS and/or TNA.

Claims (6)

1. Arrangement for desalination of sea or brackish water, including: Desalination unit (20), which operates with the reverse osmosis process, with continuous flow and includes one or more stages of operation. Each stage of operation includes one or more containers (22), containing semi-permeable osmosis membranes, to which the water to be desalinated is led, after previously being compressed to a pressure greater than its osmotic pressure. Compression unit (40), which operates with the process of direct osmosis, with continuous flow and includes one or more stages of operation. Each stage of operation includes one or more vessels (42) containing semi-permeable osmosis membranes. On one side of said membranes a flow stream of highly concentrated salt solution is led, while on the other side a flow stream of compressed sea or brackish water (which is not related to the water to be desalinated) is led. The highly concentrated salt solution absorbs (through the semi-permeable membranes, by the process of direct osmosis) water from the sea or brackish compression flow stream, thereby increasing its supply and then compressing the water to be desalinated towards the corresponding stage of the desalination unit (20), without mixing the highly concentrated salt solution with the water to be desalinated Characterized by the fact that It includes at least one natural or artificial or suitably modified lake (10), which acts as a solar collector and contains a highly concentrated salt solution. Supply of highly concentrated salt solution, originating from this lake (10) feeds the aforementioned compression unit (40). The highly concentrated salt solution after being used in the compression unit (40) returns back to the lake (10), with a larger flow and having a lower salt concentration, to be gradually re-condensed within the lake, due to the constant evaporation of water from the lake, due to mainly due to the incident solar radiation. The values of the aforementioned supplies of highly concentrated salt solution to and from the lake - and consequently the size of the desalination (20) and compression (40) units - are determined by the size of the lake (10), the climate and other peculiarities of the area , with the aim of maintaining the value of the concentration of the salt solution within the lake at the desired constant level, over time. It also includes a pressure/flow conversion unit (60), which is interposed between the aforementioned desalination (20) and compression (40) units, and in each of its operating stages it has at least one pair of cylinders (61) and flow control valves. The internal space of each cylinder (611), (612) is divided by the piston (63) into two separate spaces. In each stage of operation, one cylinder of the pair of cylinders (61) expels from one of its spaces the water to be desalinated towards the corresponding stage of the desalination unit (20), due to the pressure it receives from the high-concentration and high-pressure salt solution, which is channeled into its other space, coming from the corresponding stage of the compression unit (40). At the same time, the other cylinder of the pair (61) receives a stream of desalination seawater from the next stage of the desalination unit (20) and displaces a stream of highly concentrated solution to the next stage of the compression unit (40). The two cylinders of each pair constantly change roles with the help of the flow control valves, so as to ensure continuity in the operation of the unit (60). In each cylinder (611), (612) of each stage of operation of the pressure/supply conversion unit (60), the ratio of the cross-section of the space of the cylinder receiving the highly concentrated salt solution to the cross-section of the space receiving the seawater to be desalinated or brackish water - and consequently the ratio of the supply of the highly concentrated salt solution to the supply of the sea or brackish water to be desalinated - is equal to: (1 / n)* (PTHNA / PDAUS ), where: - η is the coefficient of performance and takes a value slightly less than unity. - RDAUS is the pressure of the stream of highly concentrated salt solution entering the cylinder from the compression unit (40). - PTHNA is the pressure of the seawater or brackish water stream to be desalinated that exits the cylinder and goes to the desalination unit (20). In each pair of cylinders, the rods (64) of the two cylinders are mechanically, electrically or hydraulically connected to each other. In the same way, the rods of each pair of cylinders are connected to the rods of the pairs of cylinders of the remaining stages of the unit. 2. A sea or brackish water desalination device as described in claim 1, Characterized by the fact that Either occasionally or on a permanent basis, very high concentration salt solution or salt slurry, or even dry salt, are mixed in the appropriate proportion with a stream of medium or low concentration salt solution exiting the compression unit (40) or originating elsewhere; resulting in a highly concentrated salt solution being produced at the required concentration and feeding the compression unit (40). 3. Desalination arrangement as described in claim 1, Characterized by the fact that The reverse osmosis (20), compression (40) and pressure/supply conversion (60) desalination units do not operate in continuous flow but in batches, in one or more stages. 4. Desalination arrangement as described in claim 1, Characterized by the fact that The transfer and adjustment of the high pressure transferred from the stream of highly concentrated salt solution exiting a stage of the compression unit (40), to the stream of desalination sea water entering the corresponding stage of the desalination unit (20), is done by a pair of turbines ( for the highly concentrated salt solution stream) and pump (for the seawater stream). At each stage, the ratio of the supply of said high-concentration salt solution stream into the turbine to the supply of said desalination seawater stream into the pump is equal to: (1 / n)* (PTHNA / PDAUS ), where the quantities "n", "RTHNA" and "RDAUS" are as defined in claim 1. 5. Desalination arrangement as described in claim 1, Characterized by the fact that An additional stream of high-concentration salt solution is fed, not only to the first stage of the compression unit (40) but also to one or more of the following stages, mixing with the - relatively diluted - high-concentration salt solution entering the particular stage from the previous one , possibly removing some of the highly concentrated diluted solution prior to mixing. Regardless of whether an additional stream of highly concentrated salt solution is fed to subsequent (other than the first) stages of the compression unit (40), as mentioned above, or not, an additional stream of seawater may - if so selected - be fed not only to the last but and in one or more of the remaining stages, either of the compression unit (40), or of the desalination unit (20) respectively, or of both, mixing with the - relatively concentrated - compression seawater and/or desalination seawater solutions that they enter the specific stage of the compression (40) or desalination (20) units, respectively, from the next stage, with possible removal of some amount of the relatively concentrated solutions before the respective mixing. 6. Desalination arrangement as described in claims 1 and 4, Characterized by the fact that The additional power, which may be necessary to cover the total power shortfall of the interconnected cylinder banks, or turbine/pump pairs, is either conventional, such as for example electric power, or - preferably - derived from an additional equipment , comprising a compression sub-unit operating in a manner similar to that of the compression unit (40), fed both with a stream of highly concentrated solution from the lake (10), or anywhere else, and with a stream of seawater. In this way, a supply of highly concentrated solution under pressure is achieved, which is channeled into a turbine connected to the pairs of cylinders or turbines / pumps of the various stages, compensating for the aforementioned power deficit.