AU2019363347A1

AU2019363347A1 - Seawater desalination system for ships

Info

Publication number: AU2019363347A1
Application number: AU2019363347A
Authority: AU
Inventors: Patrick Wagner
Original assignee: DESSALATOR
Current assignee: DESSALATOR
Priority date: 2018-10-16
Filing date: 2019-10-15
Publication date: 2021-05-13
Also published as: FR3087183A1; EP3867198A1; FR3087183B1; WO2020079361A1

Abstract

The present invention relates to a seawater desalination system comprising a reverse-osmosis cell containing a semipermeable membrane to desalinate the water by passing seawater under pressure through the said membrane, a pump for forcing the seawater under pressure through the said membrane and a mechanism for driving the shaft of the said pump, in which the said drive mechanism comprises a DC motor, powered by a DC voltage, and an AC motor, powered by an AC voltage, characterized in that the said motors are mounted in a position for driving the shaft of the said pump via a belt respectively driving a first and second pulley, the pulley is being positioned one beside the other on the shaft of the pump, in which each pulley is fixed to the shaft of the pump using a clutch of the sprag clutch type.

Description

DESCRIPTION

Seawater desalination system for boats

Technical field

The present invention relates to seawater desalination systems which are installed on boats, in particular sailing boats, and which are intended to provide potable water for the occupants of said boats when they are at sea, and relates in particular to a seawater desalination system that operates equally well by means of alternating current and by means of direct current.

State of the art

Sailing boats of a certain size are increasingly often equipped with a seawater desalination system that makes it possible to provide the necessary potable water for the occupants of the boat when it is at sea for a certain time. Such a desalination system is generally composed of a reverse osmosis membrane device through which the seawater is forced under pressure so that only the potable water passes through the membrane whereas the majority of the mineral salts are blocked by said membrane.

A pump is necessary in order to force the seawater, under relatively high pressure that can reach 65 bar, to pass through the membrane used in order to effect the reverse osmosis. A mechanism for driving the pump is therefore necessary. This drive mechanism is generally a direct current motor powered by the on-board battery. Various devices may be used in order to power said battery, such as a dynamo rotated by a wind turbine. It goes without saying that such a battery, which is sufficient to power the boat's lighting system, discharges rapidly when it is a question of powering a motor. In order to overcome a possible deficiency in the battery, sailing boats have a power generator that provides alternating current. When the battery is discharged or when there is not enough wind to make the wind turbine operate or else when the boat is berthed, it is therefore customary to start the power generator, and to use a charger to convert the 220 volt alternating current into 12 or 24 volt direct current that is capable of powering the motor used for the desalination of the seawater. It is clear that such a system consumes a considerable amount of energy owing to the transformation of the alternating current into direct current and said system is certainly not practical to implement.

European patent EP 1 240 076 discloses a seawater desalination system in which the drive mechanism for the pump can be, equally, either a direct current motor or an alternating current motor, the passage from one to the other taking place automatically without human intervention.

In the system according to document EP 1 240 076, the motors are mounted in a position for driving the axle of the pump via a belt respectively driving a pulley at each of the ends of the axle, each of the belts connecting the drive shaft of the motor corresponding to the axle of the pump so that each of the motors rotates the axle of the pump when it is activated. The drive mechanism comprises clutch release means which result from the freewheel mounting of each of the pulleys on the axle of the pump, so that the pulley corresponding to one of the motors starts freewheeling when the other motor is activated in order to drive the axle of the pump.

Even if the systems according to the prior art, including in particular the one described within document EP 1240 076, have the advantage of a mechanism for driving the pump by, equally, either a direct current motor or an alternating current motor, said systems have drawbacks associated with their configuration. In the system according to document EP 1 240 076, the direct current motor and the alternating current motor are positioned in such a way that they have an axis of rotation substantially parallel to the axle of the pump, said system comprising two motors attached respectively to the opposite ends of said axle of the pump. This configuration has a drawback for maintenance of the system, according to which the two ends of said pump, if they are looked at in the direction of the pump, must be accessible. The system described in the prior art, according to document EP 1 240 076, has another drawback that resides in the fact that the direction of rotation of the direct current motor and that of the alternating current motor must oppose one another so as to enable the motor to pivot the axle of the pump in only one direction.

In practice, this means that one of the two motors must be modified in order to reverse the direction of its direction of rotation before it is installed in the system disclosed in the prior art.

If one considers the fact that the desalination system described above is particularly suitable for use on a boat, it is worth considering the space available on said boat for a desalination system. This available space is, by definition, very limited. Consequently, the aim of the invention is to provide a desalination system that is more compact than the system known from the prior art and that can be installed without the opposing ends of said system being available while it is being used in order to allow this system to be maintained.

Disclosure of the invention

The invention relates to a seawater desalination system comprising a reverse osmosis cell that contains a semi-permeable membrane for performing the desalination of the water by passing seawater under pressure through said membrane, a pump for forcing the seawater under pressure through said membrane and a mechanism for driving the axle of said pump wherein said drive mechanism comprises a direct current motor, powered by a direct voltage and an alternating current motor, powered by an alternating voltage, wherein said motors are mounted in a position for driving the axle of said pump by a belt respectively driving a first and a second pulley, which are positioned one beside the other on the axle of the pump, wherein each pulley is attached onto the axle of the pump by means of a sprag-type clutch.

According to an embodiment of the present invention, the system furthermore comprises selection means for activating only said alternating current motor and thus driving the axle of said pump when the two motors are powered.

According to an embodiment of the present invention, said selection means comprise an electromagnetic relay powered by said alternating voltage when the latter is connected and a switch in the power supply circuit of said direct current motor, said switch normally being closed and moving into the open position when said electromagnetic relay is powered by said alternating voltage so that said direct current motor stops being activated as soon as said alternating voltage is connected.

According to an embodiment of the present invention, said selection means are composed of a control logic such as an electromagnetic board or CMOS technology.

According to an embodiment of the present invention, the system furthermore comprises a tank into which the desalinated water is sent after it has passed through said membrane.

According to an embodiment of the present invention, the system furthermore comprises a solenoid valve for sending the desalinated water into said tank when the quality of said water is satisfactory and for rejecting the desalinated water when its quality is unsatisfactory.

According to an embodiment of the present invention, the system furthermore comprises a water salinity analysis means for providing a potability threshold and a non-potability threshold corresponding to a salinity that is higher than the potability threshold, said water being rejected only when its salinity exceeds the non-potability threshold, and the water being stored in said tank, after it has been rejected for unsatisfactory quality, only when its salinity has decreased again below said potability threshold.

According to an embodiment of the present invention, the system is installed on board a boat such as a sailing boat.

Brief description of the figures

The aim, subject and characteristics of the invention will become more clearly apparent upon reading the following description with reference to the drawings, in which:

[figure 1] shows a diagrammatic view of a boat in which a seawater desalination system has been installed,

[figure 2] depicts a diagrammatic view of the configuration of the seawater desalination system, said configuration showing the pump positioned between the direct current motor and the alternating current motor which are used for driving said pump,

[figure 3] shows a diagrammatic view of the electrical connections of the seawater desalination system, and

[figure 4] depicts an example of a sprag-type clutch used for attaching pulleys onto the axle of the pump.

Detailed description of the invention

Figure 1 shows a diagrammatic view of a boat in which a seawater desalination system has been installed. The desalination system 1 according to the present invention is depicted inside the hull of a boat 10. The desalination of the seawater 100 is performed by means of a reverse osmosis cell 12 comprising a semi-permeable membrane. The seawater 100 is sent under pressure into the reverse osmosis cell 12. The pressure, used within the reverse osmosis cell 12, is typically at least 26 bar. During use, the pressure may reach a level of around 65 bar. According to the desalination principle, water (H 20) may pass through the semi-permeable membrane whereas the mineral salts, which are contained in the seawater 100, cannot do this. This makes it possible to obtain soft water, the salinity level of which is lower than a defined threshold that makes it possible to use said soft water on board the boat 10.

Within the system as shown in figure 1, the seawater 100 to be desalinated is introduced by virtue of a pump 20 that is used to draw in said seawater 100 to be desalinated via the inlet valve 14. This water first of all passes through a filter 16, which is suitable for retaining particles which are of a size that is greater than a threshold determined by said filter 16. During normal use of the system, said filter 16 must be cleaned periodically.

After it has passed into the filter 16, the seawater 100 to be desalinated is then sent, via a pipe 17, to a pump unit comprising a pump 20, a direct current motor 22 and an alternating current motor 24. The two motors 22, 24 are positioned on the side opposite the pump 20 and are connected to the axle of said pump 20 in order to enable the driving of said axle of the pump 20. The configuration and the connections between the pump 20, the direct current motor 22 and the alternating current motor 24 are described in detail in figure 2.

The pump 20, which is driven either by the direct current motor 22 or by the alternating current motor 24, is used in order to force the passage of the seawater 100 to be desalinated through the pipe 26 against the semi-permeable membrane that is situated inside the reverse osmosis cell 12. The soft water thus collected is gathered at the outlet of the reverse osmosis cell 12 and is then transported via the pipe 28 towards a solenoid valve 30. The solenoid valve 30 is used either to send the water, via the pipe 32, into a soft water tank 34, when its level of salinity is lower than a determined threshold, or to evacuate the water to outside the boat, via the pipe 36 and the evacuation valve 37, when its level of salinity is higher than the determined threshold and when the quality of the water does not correspond to the predetermined quality criteria.

The option offering the possibility of sending the water either towards the pipe 32 or towards the pipe 36 by using the solenoid valve 30 is controlled by a control element 38. Said control element 38 may be in the form of a single electronic board produced by virtue of CMOS technology. The command, which is generated and transmitted by the control element 38, takes into account the parameters of the water gathered at the outlet of the reverse osmosis cell 12. These characteristics relate to, amongst other things, the salinity of the water provided by a salinity detector equipped with two electrodes which measure the salinity of the water by electrical resistivity. The salinity detector makes it possible to measure two salinity thresholds. The first salinity threshold is a potability threshold, the second threshold is a non-potability threshold, the two thresholds corresponding to the legal salinity thresholds. When the salinity threshold is lower than the potability threshold, the system, confirming that the water is potable, sends it to the tank 34 via the pipe 32. On the other hand, when the salinity threshold is higher than the potability threshold, the system waits for the non-potability threshold to be crossed in order to reject the water into the sea via the pipe 36. If, subsequently, the salinity level decreases, the water continues to be rejected into the sea until the salinity level passes

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below the potability threshold. At this precise moment, the water which is considered to be sufficiently potable is again directed towards the tank 34 via the pipe 32. This command procedure, which uses the solenoid valve 30 and the control element 38 in three steps, guarantees a production of quality and great reliability.

Figure 2 depicts a diagrammatic view of the pump unit 18 comprising the pump 20, the direct current motor 22 and the alternating current motor 24. The pump 20 has an axle 21 onto which two pulleys are attached. The first pulley 40 is connected to the drive shaft of the direct current motor 22 by a belt 42. The second pulley 44 is connected to the drive shaft of the alternating current motor 24 by a belt 46. Each of the pulleys 40, 44 is mounted on the axle 21 of the pump 20 in a freewheeling manner. When one of the motors 22, 24 rotates the corresponding pulley via the associated belt, the frictional force exerted on the axle 21 of the pump 20 by the other pulley is lower than the frictional force exerted by the other motor at rest. This means that the pulley of the motor that is not rotating starts to freewheel. Thus, if the direct current motor 22 is activated, it rotates the pulley 40 by way of the belt 42 and thus rotates the axle of the pump. Since the frictional force exerted by the shaft of the alternating current motor 24 is higher than the frictional force exerted by the pulley, the pulley 24 starts freewheeling. This means that the belt 46 remains immobile and does not drive the alternating current motor 24. In the same way, when the alternating current motor 24 is activated, the pulley 40 starts freewheeling. The belt 42 remains immobile and does not drive the direct current motor 22. The pulleys 40, 44 are attached onto the axle 21 of the pump 20 by means of sprag-type clutches. The operation of a clutch of this type is explained in detail with reference to figure 4. An attachment of this type makes it possible to guarantee, on the one hand, the driving of the pump by means of one of the two motors 22, 24, and, on the other hand, makes it possible for the pulleys to operate in a freewheeling manner as soon as the corresponding motor is not activated (as explained above).

As shown in figure 2, the pump unit 18 is provided with a support 19, said support being able to be used in order to assemble said pump unit prior to its installation inside a boat. Once it has been assembled by means of the support 19, the pump unit may be introduced into a relatively restricted space and may be displaced in the direction of the arrow, as depicted in figure 2. When the installation is complete, by virtue of the configuration of the pump unit 18, all that is required is that the front face (as shown in figure 2) remains accessible during use of the system 1 according to the invention, in order that maintenance of said pump unit can be carried out. The turning elements and the belts 42, 46 are accessible from the same side as the pump unit 18.

Figure 3 shows a diagrammatic view of the pump unit 18 as well as an electrical connection that enables the operation of the direct current motor 22 and the alternating current motor 24. According to the present invention, only one of the motors 22, 24 is powered if the system 1 has a power supply from a battery 48 and a power supply 50 of 220 volts provided by a power generator. The battery 48 is suitable for a power supply of 12 or 24 volts. In order to ensure that only one of the two motors is powered, the alternating current power supply takes priority, as shown in figure 3, which depicts an embodiment of an electrical system to which the pump unit 18 is connected. Indeed, assuming that the direct current motor 22 is powered by the battery 48, the switch 52 is in the closed position. As soon as the power generator is started, the electromagnetic relay 54 is activated and the switch 52 opens, thus cutting the power supply to the direct current motor 22. Thus, only the alternating current motor 24 is powered. According to an alternative embodiment, the power supply to the direct current motor 22 or to the alternating current motor 24 is controlled by the control element 38 (as shown in figure 1). Said control system 38 could be used in order to optimise the system and control the precise operating mode of the system 1 according to the invention. For example, the control element 38 could serve to manage the different timings, such as a timing of a few seconds, which are implemented prior to being able to gather the potable water in the tank after the desalination system 1 according to the invention has been started.

Figure 4 shows an example of a sprag-type clutch 60, said clutch comprising an inner wheel 61 and an outer wheel 62. Intermediate elements 63 are present between the inner wheel 61 and the outer wheel 62. The presence, and the specific shape of said elements 63, enables a rotation of the inner wheel 61 that brings about the corresponding rotation of the outer wheel 62. The inner wheel 61 may also undergo a rotation without thereby having an effect on the outer wheel 62. As can be seen in figure 4, the intermediate elements 63 are held in place by virtue of a positioning element 64.

If one considers the option according to which the inner wheel 61 undergoes a rotation that brings about a corresponding rotation of the outer wheel 62, the intermediate elements 63 may transmit the driving of the inner wheel 61 to the outer wheel 62 if the inner wheel performs a rotation in the direction of the arrow 70, as shown in figure 4.

If one considers the option according to which the inner wheel 61 undergoes a rotation in the direction of the arrow 70, without thereby having an effect on the outer wheel 62, the outer surface of said inner wheel 61 comes into contact with the intermediate element 63, along a contact point 67. In the same way, the intermediate element 63 comes into contact with the inner surface of the outer wheel 62, along a contact point 66. By virtue of this contact, the rotation of the inner wheel 61 may bring about the corresponding rotation of the outer wheel 62. In the opposite case, if the inner wheel 61 undergoes a rotation in the direction of the arrow 75, as shown in figure 4, the shape of the intermediate elements 63 makes it possible for the sprag-type clutch to start freewheeling. This means that the inner wheel 61 may undergo a rotation in the direction of the arrow 75 without any force being exerted on the outer wheel 62.

The attachment of the pulleys 40, 44 to the axle 21 of the pump 20, as shown in figure 2, makes it possible for said pulleys to be driven by their respective motor or to start freewheeling.

Claims

1. A seawater (100) desalination system (1) comprising a reverse osmosis cell (12) that contains a semi-permeable membrane for performing the desalination of the water by passing seawater under pressure through said membrane, a pump (20) for forcing the seawater (100) under pressure through said membrane and a mechanism for driving the axle (21) of said pump (20) wherein said drive mechanism comprises a direct current motor (22), powered by a direct voltage and an alternating current motor (24), powered by an alternating voltage, characterised in that said motors (22, 24) are mounted in a position for driving the axle (21) of said pump (20) by a belt respectively driving a first (40) and a second pulley (44), which are positioned one beside the other on the axle (21) of the pump (20), wherein each pulley (40, 44) is attached onto the axle of the pump (20) by means of a sprag-type clutch (60).

2. The system (1) according to Claim 1, further comprising selection means for activating only said alternating current motor (24) and thus driving the axle (21) of said pump (20) when the two motors (22, 24) are powered.

3. The system (1) according to Claim 2, wherein said selection means comprise an electromagnetic relay (54) powered by said alternating voltage when the latter is connected and a switch (52) in the power supply circuit of said direct current motor (22), said switch (52) normally being closed and moving into the open position when said electromagnetic relay (54) is powered by said alternating voltage so that said direct current motor (24) stops being activated as soon as said alternating voltage is connected.

4. The system (1) according to Claim 2, wherein said selection means are composed of a control logic such as an electromagnetic board or CMOS technology.

5. The system (1) according to one of Claims 1 to 4, further comprising a tank (34) into which the desalinated water is sent after it has passed through said membrane.

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6. The system (1) according to Claim 5, further comprising a solenoid valve (30) for sending the desalinated water into said tank (34) when the quality of said water is satisfactory and for rejecting the desalinated water when its quality is unsatisfactory.

7. The system (1) according to Claim 6, further comprising a water salinity analysis means for providing a potability threshold and a non-potability threshold corresponding to a salinity that is higher than the potability threshold, said water being rejected only when its salinity exceeds the non-potability threshold, and the water being stored in said tank (34), after it has been rejected for unsatisfactory quality, only when its salinity has decreased again below said potability threshold.

8. The system (1) according to one of the preceding claims, installed on board a boat (10) such as a sailing boat.