CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims benefit of the priority of U.S. Provisional Patent Application Serial No. 61/540,592, filed on September 29, 201 1, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present disclosure relates to sea-water desalination, and more particularly to desalination by reverse osmosis powered by wave-energy-conversion devices. Desalinated water is often needed in coastal areas where conventional power sources are unavailable, costly, or environmentally problematic, producing both noise and undesirable exhaust. In such areas, desalination powered by captured wave energy is especially attractive.

[0003] Among the technologies available for sea-water desalination, reverse osmosis is simple and efficient. But, reverse osmosis is power intensive, because the sea-water flowing through a reverse-osmosis chamber must be highly pressurized. Thus, powering reverse- osmosis desalination with wave power is symbiotic.

[0004] Figure 1 is a schematic drawing showing the elements of a reverse-osmosis desalination system 100 powered by wave energy. The reverse-osmosis desalination system 100 includes a reverse-osmosis desalination device 101 that includes a chamber 114 and receives a pressurized water flow to be desalinated 102 which is divided by the reverse- osmosis device 101 into two flows, a desalinated water flow 103 and a brine flow 108 of increased salinity. The system comprises two fluid flows, both of which enter the system from the ocean. One flow comprises the fluid to be desalinated (water flow 102). A substantial fraction of this flow leaves the system as desalinated water 103; the remainder is returned to the ocean (water flow 108). The second flow 111 also enters the system from the ocean, is pressurized by the wave-energy-conversion (WEC) subsystem 109, powers the primary pump 104 that pressurizes the water flow to be desalinated 102 and then returns to the ocean 108. The WEC subsystem 109 is powered by oceans waves. The water flow to be desalinated 102, is pressurized in two steps, initially by a primary pump 104 powered by the wave power subsystem 109 and then by a booster pump 105 powered by a recovery turbine 107 that recovers energy from the concentrated brine 108 leaving the reverse-osmosis device 101. The two-step pressurization provides three pressure levels, atmospheric, high enough for reverse osmosis to occur and an intermediate pressure. Water flow 102 is under atmospheric pressure when it is input into filter 106. Further, water flow 102 is under high pressure when inputted into the reverse osmosis device 101, and is under intermediate or medium pressure between the primary 104 and booster 105 pumps.

[0005] The reverse-osmosis desalination system shown in Figure 1 is powered by a so- called surge -type wave-energy converter (WEC) in the WEC subsystem 109, such as those described by WO 2011/079199, which is hereby incorporated by reference in its entirety.

[0006] Further, reverse osmosis consumes power by forcing saline sea water through a membrane comprising passages sufficiently small to block the passage of salt, thereby dividing the water flow to be desalinated 102 into two portions, a desalinated flow 103 and a brine flow 108. The pressure of the brine flow 108 exiting from the reverse-osmosis chamber 114 is almost as high as that in the flow at the entrance to the chamber 114 of the reverse- osmosis device 101. This high pressure is available to contribute to powering the

pressurization of the flow input to the reverse-osmosis chamber 114. Exploitation of the high pressure of the brine exiting the reverse-osmosis chamber is called "recovery." The recovery turbine 107 of Figure 1 uses the high pressure brine flow output 108 of the reverse-osmosis device 101 to power the booster pump 105, as noted above.

[0007] Figure 1 also includes a device called an accumulator 113 that reduces fluctuations in the pressure of the water flow to be desalinated 102. The accumulator 113 is an energy storage device that stores energy when the pressure in the flow is high, and returns the stored energy to the flow when the pressure in the flow is low. A typical accumulator is described in the patent GB 1,104,527 and in the more recent international patent application

WO 2004043576, each of which are hereby incorporated by reference in their entirety. In certain embodiments, the accumulator functions by allowing a flow to occupy a flexible bladder whose expansion and contraction changes the volume available to a fixed quantity of compressible gas. Pressure fluctuations in the incompressible flow are thereby reduced.

[0008] The generic desalination system shown in Figure 1 comprises two fluid flows, the flow to be desalinated 102 which passes through the reverse-osmosis chamber 114 and a WEC-PTO flow 111 produced by the WEC subsystem 109. Figure 1 shows the flow to be desalinated 102 being filtered upstream of being pressurized. This filtering may be provided by a so-called beach well which exploits passage of the sea water to be desalinated through the soil (usually sand) near the shore to inexpensively remove particulate matter present in the sea water.

[0009] Further, the width of the flow lines in each of Figures 1 - 5 reflects the relative magnitudes of the flows. In particular, the reverse-osmosis device 101 is shown to desalinate approximately half of the flow 102 that is input to the device.

[0010] The following publications are hereby incorporated by reference in their entirety: 1) Cruz, Joao, Ocean Wave Energy: Current Status and Future Perspectives (Green Energy and Technology), Springer, 1st edition , 2008 and 2) Cipollina, et al, Seawater Desalination: Conventional and Renewable Energy Processes (Green Energy and Technology), Springer, 1st Edition, 2009.

SUMMARY OF THE INVENTION

[0011] According to one embodiment a desalination system partially submerged in a body of salt water is provided. The desalination system includes a reverse-osmosis device configured to remove salt from an input sea-water flow to be desalinated and to produce an output flow of desalinated water. The desalination system further includes a primary pump configured to pressurize the sea-water flow to be desalinated that passes through the reverse- osmosis device, and a booster pump downstream from the primary pump and configured to additionally pressurize the sea-water flow to be desalinated. In addition, the system includes a filter upstream of the primary and booster pumps configured to receive water from the body of salt water as the sea-water flow to be desalinated and remove particles from the sea-water flow to be desalinated. In the disclosed embodiment, a recovery device downstream from the reverse-osmosis device configured to power the booster pump by reducing the pressure of concentrated brine leaving the reverse-osmosis device, and a plurality of conduits that guide the sea- water flow to be desalinated from the body of salt water to the filter, from the filter to the primary pump, from the primary pump to the booster pump, from the booster pump to the reverse-osmosis device, from the reverse-osmosis device to the recovery device, and from the recovery device back to the body of salt water. The desalination system further includes a wave-energy-conversion (WEC) subsystem, that includes a structure that moves with the wave-induced local water motion of the body of salt water, as well as a power-takeoff subsystem, connected to the structure that moves with the wave-induced local water motion, configured to produce a WEC-PTO pressurized flow of water, independent of the sea-water flow to be desalinated, from the body of salt water and supply the WEC-PTO pressurized flow of water to a turbine. The wave-energy-conversion (WEC) subsystem further includes a turbine configured to power the primary pump by rotating in response to the WEC-PTO pressurized flow of water supplied by the power-takeoff subsystem, as well as a plurality of conduits guiding the WEC-PTO pressurized flow of water from the body of salt water to the power-takeoff subsystem, from the power-takeoff subsystem to the turbine, and from the turbine back to the body of salt water. The disclosed embodiment includes an accumulator attached to the conduit between the primary and booster pumps and configured to reduce pressure fluctuations in the sea- water flow to be desalinated.

[0012] According to another disclosed embodiment, the conduit that guides the WEC-PTO pressurized flow of water from the turbine back to the body of salt water merges with the conduit that guides the sea- water flow to be desalinated from the recovery device back to the body of salt water.

[0013] According to yet another disclosed embodiment, a filter is provided upstream of the primary and booster pumps configured to receive water from the body of salt water as the sea-water flow to be desalinated and a WEC-PTO pressurized water flow. The filter removes particles from both water flows.

[0014] According to a further embodiment, the power-takeoff subsystem pressurizes the sea water flow to be desalinated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a diagram of a conventional WEC-powered reverse-osmosis desalination system.

[0016] Figure 2 illustrates an embodiment of the present disclosure in which the accumulator has been moved to the intermediate-pressure portion of the flow to be desalinated.

[0017] Figure 3 illustrates an embodiment of the present disclosure in which the flow leaving the WEC-PTO turbine is combined with the flow exiting the reverse-osmosis chamber so as to dilute the increased salinity of the flow exiting the reverse-osmosis chamber.

[0018] Figure 4 illustrates an embodiment of the present disclosure in which the flow entering the power-takeoff subsystem is filtered.

[0019] Figure 5 illustrates a single-flow embodiment of the present disclosure in which the power-takeoff subsystem provides the pressurized flow to be desalinated.

DETAILED DESCRIPTION

[0020] Figure 1 describes a reference base system configuration to which several improvements illustrated by Figures 2 through 5 and explained in their accompanying disclosure, are made. Figure 1 illustrates a WEC-powered reverse-osmosis desalination system 100 that includes a reverse-osmosis device 101 that removes salt from a sea-water flow to be desalinated 102 and outputs both desalinated water 103 and a brine flow 108 of increased salinity. The reverse-osmosis desalination system 100 includes a primary pump 104 that pressurizes the sea-water flow to be desalinated 102 that passes through the reverse- osmosis device 101. The system also includes a booster pump 105 which further increases the pressure of the sea- water flow 102 to be desalinated. A filter 106 is provided to receive water from a body of salt water as the sea-water flow to be desalinated 102 and to remove particles from the sea-water flow to be desalinated 102. The filter 106 is upstream from the primary and booster pumps 104 and 105. The system 100 also includes a recovery device 107 downstream from the reverse-osmosis device 101 which powers the booster pump 105 by reducing the pressure of concentrated brine 108 leaving the reverse-osmosis device 101. In some embodiments, the recovery device 107 is a turbine. A plurality of conduits guide the sea-water flow to be desalinated 102 from the from the body of salt water to the filter 106, from the filter 106 to the primary pump 104, from the primary pump 104 to the booster pump 105, from the booster pump 105 to the reverse-osmosis device 101, from the reverse-osmosis device 101 to the recovery device 107, and from the recovery device 107 back to the body of salt water. The system 100 also includes a wave-energy-conversion (WEC) subsystem 109.

[0021] The wave-energy-conversion (WEC) subsystem 109 includes a power-takeoff subsystem 110 including a surge-type wave-energy converter (WEC) powered by wave energy as a structure that moves with the wave-induced local water motion of the body of water in which the desalination system 100 is disposed. The power-takeoff subsystem 110 produces an independent WEC-PTO pressurized flow of water 111 from the body of salt water and provides the WEC-PTO pressurized flow of water 111 to a turbine 112. The turbine 112 rotates in response to the supplied WEC-PTO pressurized flow of water 111 and powers the primary pump 104. An additional plurality of conduits are provided that guide the WEC-PTO pressurized flow of water 111 from the body of salt water to the power-takeoff subsystem 110, from the power-takeoff subsystem 110 to the turbine 112, and from the turbine 112 back to the body of salt water with its salinity unchanged. As noted above, various types of wave energy converters may be used for the WEC subsystem 109 in the disclosed desalination system 100.

[0022] Figure 2 illustrates an embodiment of the present disclosure in which the accumulator 113 has been moved to the intermediate -pressure portion of the sea- water flow to be desalinated 102. Reverse-osmosis membranes operate most effectively when the pressure fluctuates very little. The purpose of an accumulator is to minimize undesirable pressure fluctuations. Pressure fluctuations can be present in an input fluid flow and/or in the power that drives a pressurized pump that delivers a water flow to the reverse-osmosis device 101.

[0023] In the system illustrated in Figure 2, certain power is provided by the capture of intrinsically fluctuating wave action by the wave-energy-conversion (WEC) subsystem 109 that includes a surge-type wave-energy converter (WEC). The WEC subsystem 109 is used to power the primary pump 104 which pressurizes the sea-water flow to be desalinated 102 that is ultimately desalinated by the reverse-osmosis desalination device 101. Because a surge-type wave-energy WEC oscillates with the ocean wave action, and because wave amplitudes vary, the pressure in the fluid flow it generates varies; the accumulator 113 reduces the pressure variation. As such, locating the accumulator 113 downstream of the primary pump 104 that pressurizes water 102 that flows to the reverse-osmosis device 101 minimizes undesirable pressure fluctuations. In contrast to Figure 1, Figure 2 shows the accumulator 113 downstream from the primary pump 104 that pressurizes the sea- water flow to be desalinated 102 and is powered by the WEC subsystem 109. Placing the accumulator between the primary pump 104 and the booster pump 105 allows undesirable pressure fluctuations to be minimized downstream from the primary pump 104 after initial

pressurization powered by the WEC subsystem 109. [0024] In Figures 3-5, the accumulator 113 is not shown in order to simplify the diagrams. However, an accumulator may be used in any of the embodiments of the present disclosure illustrated in Figures 3-5 in either of the configurations illustrated in Figure 1 and Figure 2.

[0025] Further, in the system illustrated by Figure 2, as well as those illustrated and described with respect to Figures 3-5, other types wave energy converters may be used in the wave-energy-conversion (WEC) subsystem 109. For example, a wave-energy-conversion (WEC) subsystem 109 may include at least one "point" absorber as a structure that moves with the wave-induced local water motion of the body of water in which the desalination system 100 is disposed. In such an embodiment, the point absorber is attached to the power- takeoff subsystem 110. A simple point absorber to which the present disclosure applies is a buoy moored to the sea-bed by three cables forming a tripod with each cable connected to its own power-takeoff which together comprise the disclosed power-takeoff subsystem 110. Such absorbers can capture wave-induced motion of the buoy in any of the three possible directions, up and down with the "heave" of wave motion, and horizontally with the "surge" of wave motion. In other embodiments, a "line-like" wave energy converter may be used in the wave-energy-conversion (WEC) subsystem 109, in which one of the three dimensions of the is significantly greater than the other two.

[0026] Figure 3 illustrates an embodiment of the present disclosure in which the flow leaving the WEC-PTO turbine 112 is combined with the flow exiting the reverse-osmosis chamber 114 so as to dilute the increased salinity of the flow exiting the reverse-osmosis chamber 114. The system configuration shown in Figure 3 comprises two fluid flows, the sea-water flow to be desalinated 102, which flows through the reverse-osmosis chamber 114 of the revise-osmosis device 101 and the pressurized flow 111 produced by the WEC subsystem 109 Figure 3 illustrates various conduits through which these flows are guided, and illustrates a merger of these two flows downstream of their passage through their respective turbines 112 and 107. The configuration of Figure 3 is advantageous because certain environmental regulations may dictate the level of the salinity of water that may be reintroduced by a system of the present disclosure.

[0027] Figure 4 illustrates an embodiment of the present disclosure in which the flow entering the power-takeoff subsystem 110 is filtered. In particular, desalination systems are frequently deployed near the sea shore, where beach wells can provide effective, inexpensive filtration. That is, beach wells and other near shore water sources provide an initially filtered source of water filtered by the land comprising the shore. Figure 4 illustrates exploitation of this resource in certain embodiments.

[0028] Figure 5 illustrates an embodiment of the present disclosure in which the power- takeoff subsystem 110 provides the pressurized flow that is desalinated 102. That is, whereas the generic system configuration shown in Figure 1 comprises two distinct fluid flows for the reverse-osmosis chamber 114 of the reverse-osmosis device 101 and power-takeoff subsystem 110, Figure 5 illustrates a configuration in which a single fluid flow passes through both the power-takeoff subsystem 110 and the reverse-osmosis chamber 114 of the reverse-osmosis device 101. In contrast to Figures 1-4, the power-takeoff subsystem 110 in Figure 5 is providing both the fluid flow and its pressurization. In some embodiments, the flow that is desalinated 102 is filtered upstream from the wave-energy-conversion (WEC) subsystem 109 by a filter 501. Thus the relative amounts of flow and pressure provided by the power-takeoff subsystem 110 in Figure 5 may differ from those required by the configurations shown in Figures 1 - 4. In other embodiments of the system disclosed in Figure 5, an accumulator may be used as illustrated in Figures 1 and 2 and their

accompanying disclosure. Further, in other embodiments, further filters may be used.

[0029] The foregoing description of embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated.