SOLAR OCEAN THERMAL ENERGY SEAWATER DISTILLATION SYSTEM

Apparatus and methods for distilling fresh water from seawater or from impure water by evaporation and condensation, as a system which may be characterized as a direct-heating continuous-flow solar thermal still, with heat supplying an evaporator primarily by solar energy from incident or reflecting sunlight, cooling supplying a condenser primarily by cold seawater piping from deep below the sea surface or from another cold-water source, with evaporator operating in a range of pressures from atmospheric at sea level to a pressure reduced below atmospheric pressure at sea level. The system maximizes the thermal gradient from the hot side of the evaporator to the cold side of the condenser, minimizing the energy flows and mass flows required for a given unit of fresh water output.

This application includes material that is subject to copyright protection.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention is in the field of obtaining fresh water from seawater or from impure water by distillation through the processes of evaporation and condensation.

Access to fresh water for human use has been an increasing concern as population has grown exponentially in recent times. As groundwater, lakes and riverine sources of clean fresh water have grown more expensive and scarce, technologies to desalinate seawater and to obtain pure water out of impure or polluted water have been increasingly used to supplement or replace natural sources of supply.

The cost of obtaining pure fresh water from seawater or impure sources is driven, among other factors, by the cost of the energy required, the efficiency of the technology used, and capital costs for the technology. As the cost of energy has grown with the rising cost of fossil fuel, the use of naturally occurring energy sources (essentially free), such as solar energy, are increasingly being considered as primary sources of energy to drive fresh water production processes.

Description of Related Art

Among technologies used to obtain fresh water by desalinating seawater, two are relevant here: Reverse osmosis, and distillation. Reverse osmosis is a process whereby seawater is forced through a special porous filter that allows the water to pass through but not the salts. In distillation, the water is heated until it vaporizes at a free surface, and the water vapor is condensed out of the wet air in a secondary process. In comparison, reverse osmosis is at least 40% less energy-intensive than distillation, thus has traditionally been the preferred technology, given the same source of energy. Reverse osmosis suffers from problems associated with the eventual clogging of the porous filter medium with salts and other impurities. Distillation suffers from relatively high energy costs. Various strategies have been invoked to solve these issues, but until recently reverse osmosis has remained the favored choice especially in large installations, because of its dramatically lower energy cost. Now with rising energy cost, distillation is getting a second look.

Distillation of fresh water out of seawater by evaporation and condensation is driven by heating seawater until it evaporates and then cooling the wet air until the fresh water condenses out of it. The rate of evaporation depends on how fast heat can be transferred into the water being heated. A primary factor affecting the rate of heat transfer is the temperature difference between the source of heat and the water being heated. On the condensation side, the opposite situation occurs. The rate of condensation depends on how fast heat can be extracted from the wet air, essentially the rate of “cold transfer” from a coolant into the wet air.

Another factor is the pressure at which the evaporative process occurs. Water boils at 212° Fahrenheit at normal atmospheric pressure, but it boils at a significantly lower temperature when the pressure at the free surface of the water is below atmospheric pressure. With a lower temperature required to evaporate water at reduced pressure, less heat needs to be used, at lower energy cost. So reduced-pressure evaporative systems are more cost-efficient than ones operated at atmospheric pressure.

Given these primary factors influencing the energy cost of distillation of water, a wide variety of technologies have been developed to exploit temperature and pressure differences to obtain fresh water cost-effectively. It is useful to compare three classes of technologies utilizing naturally-occurring energy sources to illustrate the motivation for the instant invention disclosed hereunder.

A technology called Ocean Thermal Energy Conversion (OTEC) has been developed to exploit the temperature difference between warm surface seawater found in the tropics, and cold seawater found deep in the ocean even in the tropics. Waters of these two different temperatures are put through a kind of heat exchanger, and a modest amount of the heat is captured and either diverted to drive a power plant (for power-generation), or piped to an evaporator to distill fresh water out of the warm seawater. OTEC suffers from a relatively small temperature difference between its hot side and its cold side, and thus when configured as a distillation system it requires massive amounts of fluid volume to flow through the system for a small amount of resulting fresh water. Recent OTEC embodiments have added solar collectors to increase the temperature difference between the hot and cold sides of the system, somewhat reducing the amount of fluid flows required to produce a given amount of distilled fresh water as a product.

A second technology called Concentrated Solar Power (CSP) uses mirrors to concentrate sunlight focused on a collector system which heat a working fluid. Such mirrors are typically parabolic trough designs, or multi-segmented flat Fresnel equivalent designs. CSP systems have been developed which heat a working fluid which in turn is used to evaporate fresh water out of seawater. The condensation of the fresh water is driven by a coolant, typically additional seawater essentially from the same source as the seawater being evaporated. CSP systems operate at greater temperature differences than OTEC systems, and are thus more energy-efficient.

A third group of water distillation technologies are generically called solar stills. Conventional solar stills operate in principle by sunlight transmitting through a transparent covering into a reservoir of seawater or impure water, heating the seawater or impure so it evaporates. The water vapor rises and collects on the underside of the covering, running down the covering, and collecting in channels or troughs as the product of the system. Simple solar stills are relatively inefficient, but their simplicity is appealing.

A fourth kind of distillation system called Low Temperature Thermal Distillation (LTTD) has been developed with an evaporator operating at a reduced pressure (below atmospheric pressure). As earlier mentioned, water boils at a lower temperature when subject to reduced pressure, so significantly less energy is required to cause evaporation, making such systems arguably more cost-effective than distillation systems operating at atmospheric pressure.

The instant invention described below is a hybrid solar still system, and can be characterized as a Solar OTEC (SOTEC) technology, with additional elements from each of the technologies described above. This novel technology increases the temperature difference between the “hot side” and the “cold side” of a distillation system even further than is the case in current-generation solar OTEC systems, increasing efficiency to a greater degree than other combined distillation technologies. With a reduced-pressure evaporator, this system operates with a smaller amount of fluid flow required to produce a given amount of resulting distilled fresh water than the other technologies mentioned above.

BRIEF SUMMARY OF THE INVENTION

This invention is a desalination/distillation system comprised of hardware systems, fluid flows, and thermodynamic processes for evaporating water vapor out of seawater or impure water, and condensing the water vapor back into the liquid phase as fresh water. The evaporation process is driven by heat, primarily converted from incident or reflected sunlight, focused on an evaporator by a parabolic trough type mirror, or by a flat Fresnel segmented mirror system, equivalent in effect to a parabolic trough mirror. The mirror system is rotated to follow the transit of the sun through the sky throughout the course of the day. The condensation is driven by a coolant liquid, optimally cold seawater obtained from sufficiently below the sea surface that it's temperature is significantly lower than the temperature of the seawater at the surface. Supplemental heat may be from other sources such as process heat from a power plant. Supplemental or alternative coolant may be from other sources, such as cold river water. This invention is characterized as a kind of direct-heating solar still, with no intervening working fluid.

A key feature of this invention is the maximization of the temperature gradient between the hot side of the evaporator and the cold side of the condenser, thereby minimizing the energy required to distill a given unit of fresh water. This is accomplished by using concentrated sunlight on the hot side of the evaporator, and the coldest naturally available water as coolant on the cold side of the condenser, and controlling the fluid flows to maximize the heat flows through the system.

In one embodiment of the invention, the evaporation and condensation processes occur in a single stage configuration wherein the evaporation and condensation occur in a single chamber which is in direct contact with a second chamber containing a coolant liquid. In another embodiment, the invention is comprised of a series of multiple chambers isolating the evaporation process from the condensation process to enhance efficiency. The evaporation process can be further divided into additional multiple stages to also further enhance efficiency. A partial vacuum applied to the evaporation chamber, lowering the boiling point of the water contained therein also enhances efficiency by lowering the energy required for evaporation.

Single-stage system. One embodiment of the invention is a single-stage configuration. This embodiment is comprised of systems and methods for desalinating seawater by evaporation and condensation within a specially shaped set of two chambers. The primary structure of the system is a pair of chambers or pipes, typically one above the other, wherein they share one or several common wall(s). The upper wall(s) of the lower chamber serve as the lower wall(s) of the upper chamber. The lower chamber is approximately shaped like a teardrop in crossection, and the upper chamber is shaped in crossection such that it forms a cap on the upper portion of the lower chamber. The interior upper walls of the lower chamber have one or more catchment gutters affixed, said catchment gutters running longitudinally along the length of the chamber, each such gutter fitted at its end with an exit pipe leading to a collection reservoir of any shape. A coolant liquid, such as cold seawater drawn from the sea far from the sea surface, is pumped through the upper chamber, serving to cool by conduction the top part of the lower chamber. Seawater from the surface of the sea in a liquid state together with ambient air are caused to continuously flow into, through, and finally discharging out of the lower chamber. The air and seawater typically each partially fill the lower chamber. Incident or reflected sunlight is caused to strike the exterior bottom surface of the lower chamber by reflection off a parabolic trough mirror, or a segmented Fresnel equivalent of a parabolic trough mirror, heating the bottom and lower walls of the chamber, thereby heating the seawater in the lower chamber sufficient to cause evaporation of water in the lower chamber, or boiling together with evaporation of water in the lower chamber, into the air in the lower chamber. The water-vapor-laden (wet) air rises toward the top of the lower chamber, striking the cold upper walls of the lower chamber, condensing thereon into a liquid state, and flowing down the upper walls into catchment gutters, then flowing out through exit pipes into a collection reservoir.

Multiple-stage system. Another embodiment of the invention is a multi-stage configuration. Seawater from the surface of the sea in a liquid state and ambient air are caused to flow into, through, and out of an evaporator comprised of a single chamber. The air and seawater in the evaporator each partially fill the evaporator. Incident sunlight or sunlight reflected off a parabolic mirror, or a Fresnel-equivalent of a parabolic mirror, is caused to strike the lower exterior surface of the evaporator, heating the walls of the evaporator and thereby heating the seawater in the evaporator sufficient to cause evaporation of water in the evaporator, or boiling together with evaporation of water in the evaporator into the air in the evaporator. The water-vapor-laden (“wet”) air is forced to flow out of the evaporator, into, through, and out of the first of two chambers of a two-chamber condenser, heating the walls of the first condenser chamber. The first condenser chamber shares one or more surfaces with a second condenser chamber. Cold seawater is obtained through a pipe extending from the sea surface to some depth below where the seawater temperature is relatively colder than at the sea surface, or cold seawater is obtained from some other source. This cold seawater is fed into, through, and out of the second condenser chamber, absorbing the heat in the surfaces shared with the first condenser chamber, causing water to condense from a vapor state into a liquid state on the shared walls in the first condenser chamber, leaving the remaining air in the first condenser chamber relatively drier. The condensed desalinated (“fresh”) water flows by force of gravity down the walls of the first condenser chamber, and is caused by gravity or other means to flow out of the first condenser chamber into any kind of storage container or pipe for delivery as the product of the system.

The remaining concentrated seawater (brine) in the evaporator is caused to flow out of the evaporator and is discharged. The seawater caused to flow out of the second condenser chamber is also discharged. The air caused to flow out of the first condenser chamber is also discharged.

Both single stage and multi-stage embodiments can be further supplemented with an inflow preheater that captures heat from the brine being exhausted from the evaporator to preheat the inflow of seawater into the evaporator. In one embodiment of the invention, such a pre-heater also serves as a heat reservoir enabling the system to continue production of fresh water at night, when no sunlight can drive the evaporation process directly.

Both single and multi-stage embodiments can be further supplemented with pumps which serve to reduce the pressure inside the evaporator to reduce the temperature of the boiling point of the water contained therein, and subsequently to re-pressurize the air and water flowing out of the evaporator. This reduced pressure in the evaporator enables a higher rate of production of fresh water for a given input of energy than is the case for the system operating under ambient (atmospheric) pressure in all stages. In such embodiments of the invention, the system can be characterized as a Low Temperature Thermal Distillation system.

Various embodiments of six variations of this hybrid solar still are considered, (said variations named hereunder as SOTEC I, SOTEC II, SOTEC III, SOTEC IV, SOTEC V, and SOTEC VI), reflecting six variations of mass and energy pathways which characterize them. The said variations are defined as follows.

SOTEC I is defined as: A single-stage system where evaporation and condensation occur in a single chamber.

SOTEC II is defined as: A SOTEC I system, with the addition of a preheater to raise the temperature of inflowing water to be distilled, reducing the additional heat required for evaporation.

SOTEC III is defined as: A SOTEC I or SOTEC II system, with the addition of pressure management subsystems which reduce the pressure inside the chamber, thereby reducing the temperature at which the water contained therein boils, and raising the rate of evaporation.

SOTEC IV is defined as: A multi-stage system where evaporation and condensation occur in separate subsystems.

SOTEC V is defined as: A SOTEC IV system, with the addition of a preheater to raise the temperature of inflowing water to be distilled, reducing the additional heat required for evaporation. The preheater may also serve as a heat reservoir enabling continuous operation of the system even at night when there is no sunlight available as a heat source.

SOTEC VI is defined as: A SOTEC IV or SOTEC V system, with the addition of pressure management subsystems which reduce the pressure inside the evaporator, thereby reducing the temperature at which the water contained therein boils, and raising the rate of evaporation.

DETAILED DESCRIPTION OF THE INVENTION

This invention is a hybrid solar thermal still technology, incorporating features of Ocean Thermal Energy Conversion (OTEC), concentrated Solar Power (CSP), and in some embodiments, features of Low Temperature Thermal Distillation (LTTD).

Note that the Figures are not to any specific scale, and in physical embodiments some structures or substructures may be larger or smaller relative to others in the same Figure or related Figures.

An embodiment of the first variation, SOTEC I, is illustrated schematically in crossection inFIG. 1. In this embodiment of the invention, a single stage structure is used to evaporate water vapor out of seawater or impure fresh water and condense fresh water. The main structure of the system is a tube20extended left-to-right, which resides in ambient air5, near or above the sea surface10and the sea itself15. The main tube20has a second tube25attached to its upper surface. A mirror (or set of mirrors)30is located below the main tube20. Inside the main tube are a set of gutters shown schematically as35that run the length of the tube. Sunlight40reflects off the mirror(s) onto the bottom of the main tube20. Ambient air flows45into the main tube and is resident therein60, flowing slowly left-to-right. Relatively warm surface seawater50flows into the bottom of the main tube and is resident therein55, flowing slowly left-to-right. Relatively cold seawater, typically drawn from deep beneath the surface of the sea65is piped into the upper tube and is resident therein70serving as a heat sink (coolant), flowing slowly left-to-right. The sunlight40reflecting off the mirror(s)30heats the lower surface of the main tube20, said heat transmitting into and heating the resident seawater55sufficient to cause evaporation and/or boiling, generating water vapor75into and warming the resident ambient air60. Said warm and wet resident ambient air rises, and upon contacting the upper surface of the main tube, which is in contact with the lower surface of the upper tube, loses heat80into the coolant, and condensing onto the upper surface of the main tube85, and running down into the gutters60. The warmed coolant is exhausted from the end of the upper tube90, combining with the relatively saline brine95, and is disposed of into the sea at a mid-level100. The relatively dry ambient air is exhausted from the main tube105. The condensed fresh water in the gutters35flow out110into a reservoir115, and being held therein120as the product of the system.

FIG. 2illustrates an embodiment of the SOTEC I system schematically in isometric view. The tubular structure200together comprising the main and secondary tubes shown inFIG. 1as20and25, having below it a parabolic mirror205serving to reflect sunlight onto the lower surface of the structure200. Warm surface seawater210flows into and through the main tube, exhausting at225as brine. Ambient air215enters the main tube, flowing through it and exhausting at240. Cold seawater drawn sourced from deep within the sea220enters the upper tube serving as a heat sink (coolant) and exhausting at230. Condensed fresh water flows out of the end of the tube at240as product of the system.

FIG. 3illustrates another embodiment of the SOTEC I system schematically in isometric view. The tubular structure200together comprising the main and secondary tubes shown inFIG. 1as20and25, have below it a segmented Fresnel mirror array300serving to reflect sunlight onto the lower surface of the structure200. The segments of the mirror array are rotated slightly during the day, following the track of the sun in the sky. Warm surface seawater210flows into and through the main tube, exhausting at225as brine. Ambient air215enters the main tube, flowing through it and exhausting at240. Cold seawater drawn sourced from deep within the sea220enters the upper tube serving as a heat sink (coolant) and exhausting at230. Condensed fresh water flows out of the end of the tube at240as product of the system.

FIG. 4illustrates in a crossection view the thermodynamics of one embodiment of a SOTEC I system. The tubular structure is comprising two tubular sections combined in a teardrop shape with a lower tube405serving as the main chamber and an upper tube410serving as a coolant chamber, the two tubes sharing a thermally conductive common wall445. The main chamber contains at its bottom seawater or impure fresh water415, and also containing in its upper section ambient air420. The water415has a free surface425. The upper tube410contains relatively cold seawater430serving as a heat sink (coolant). The entire tubular structure is exposed to ambient air all around435. The upper surface440of the upper tube is exposed to the ambient air435. Sunlight470reflects off an array of mirror surfaces480onto the exterior of the lower surface of the main tube, said exterior lower surface painted with a high-light-absorption black surface490. Said sunlight heating the water415in the main tube, causing evaporation and/or boiling, in turn causing water vapor450to rise into the air in the main tube420. The warmed wet air in turn rising, contacting the cooling surface445. Heat flowing through surface445, causing condensation of the water vapor450, said condensed water455running down the surface445, collecting in a plurality of gutters460. Said condensed water465residing in the gutters460runs along the gutters exiting the system as the product. The mirror array480is segmented, the segments475differentially rotating485to follow the sun in such as way as to maximize the intensity of light reflected onto the bottom surface of the main tube405. The bottom surface of the main tube405has a selective low-emissivity coating490applied to it, minimizing the energy lost by emission from the surface, and thus maximizing the energy transmitted through the bottom of the main tube405.

Solar energy is also collected and converted to electricity by means of photovoltaic “solar” panel495, mounted on the wall440of the coolant chamber. Said photovoltaic panel495is cooled by coolant430, enhancing the efficiency of operation of said panel. In another embodiment, said photovoltaic panel is mounted on the exterior of the delivery pipe bringing coolant to the coolant tube410. In another embodiment, the exterior wall440of the coolant chamber is a thermal insulator, shielding said coolant430from being heated by incident sunlight.

FIG. 5illustrates in a crossection view the thermodynamics of a second embodiment of a SOTEC I system. The tubular structure is comprising two tubular sections505and510, one inside the other. The outer (main) tube505serves as the distillation chamber, and the inner tub510serves as the heat sink (coolant) tube.

The main tube505contains at its bottom seawater or impure fresh water545, and also contains in its upper section ambient air550. The water545has a free surface547. The coolant tube510contains relatively cold seawater507serving as a heat sink (coolant). The entire tubular structure is exposed to ambient air all around500. Sunlight530reflects off an array of mirror surfaces525onto the exterior of the lower surface of the main tube, said exterior lower surface painted with a high-light-absorption black surface520. Said sunlight heating the water545in the main tube, causing evaporation and/or boiling, in turn causing water vapor555to rise into the air in the main tube505. The warmed wet air in turn rising, contacting the cooling surface of the coolant tube510. Heat flowing through surface510of the coolant tube causing condensation of the water vapor555, said condensed water running down the surface of the coolant tube510as well as the upper surface of the main tube505, collecting in a plurality of gutters515. Said condensed water565residing in the gutters515runs along the gutters exiting the system as the product. The mirror array525is segmented, the segments525differentially rotating570to follow the sun in such as way as to maximize the intensity of light reflected onto the bottom surface520of the main tube505.

The evaporator tube505is fitted with a sun-shield535, mounted above it with an air gap540between the evaporator505and the sunshield535. This protects the upper region of the evaporator tube from being disadvantageously heated by impinging sunlight.

One embodiment of the second variation SOTEC system, that is, SOTEC II, is illustrated schematically in crossectionFIG. 6. This embodiment of the invention is in almost all respects identical to the SOTEC I embodiment illustrated inFIG. 1, but with the addition of a preheater660and665as described below. In this embodiment of the invention, a single stage structure is used to evaporate water vapor out of seawater or impure fresh water and condense fresh water. The main structure of the system is a tube610extended left-to-right, which resides in ambient air600, near or above the sea surface603and the sea itself605. The main tube607has a second tube610attached to its upper surface. A mirror (or set of mirrors)613is located below the main tube607. Inside the main tube are a set of gutters shown schematically as615that run the length of the tube. Sunlight617reflects off the mirror(s) onto the bottom of the main tube607. Ambient air flows620into the main tube and is resident therein627, flowing slowly left-to-right Relatively warm surface seawater623is sourced from near the sea surface, and flows through663a preheater tube660and therefrom flows into the bottom of the main tube607and is resident therein625, flowing slowly right-to-left. Relatively cold seawater, typically drawn from deep beneath the surface of the sea630, or from a cold river, is piped into the upper tube610and is resident therein633serving as a heat sink (coolant), flowing slowly left-to-right. The sunlight617reflecting off the mirror(s)613heats the lower surface of the main tube607, said heat transmitting into and heating the resident seawater625sufficient to cause evaporation and/or boiling, generating water vapor635into and warming the resident ambient air627. Said warm and wet resident ambient air rises, and upon contacting the upper surface of the main tube, which is in contact with the lower surface of the upper tube610, loses heat637into the coolant, and the water vapor contained therein condensing onto the upper surface of the main tube607, and running down into the gutters615. The warmed coolant is exhausted from the end of the upper tube643. The relatively hot brine645flows out of the main tube607into the preheater tube665, residing therein and flowing left-to-right, losing heat to the incoming warm seawater663in the preheater. In one embodiment of the system the preheater is of sufficient size to serve as a heat reservoir, storing enough heat to enable the system to continue operation at night when there is no sunlight available to drive the system. Brine667is exhausted from the preheater, and is combined with exhausted coolant647, and disposed of into the sea at a mid-level670. The relatively dry ambient air is exhausted from the main tube650. The condensed fresh water in the gutters615flow out653into a reservoir655, and being held therein657as the product of the system.

FIG. 7illustrates a crossection AA of the preheater substructure shown schematically inFIG. 6as660and665. The preheater is comprising an outer tube700and an inner tube705, said inner tube fitted with heat transfer fins710. The outer tube contains incoming warm seawater715sourced from near the surface of the sea, and the inner tube contains outgoing hot brine720sourced as the outflow of the main tube shown inFIG. 6as607. The said hot brine720loses heat through the walls of the inner tube705and the heat transfer fins attached thereto710, preheating the incoming warm seawater715. In one embodiment of the preheater, the configuration of the inflow and outflow pipes is interchanged so that the brine exiting the evaporator enters the outer pipe, and the inflowing seawater to be heated flows through the inner pipe. The outer pipe is then configured as a tank of arbitrarily large size, and serves as a heat reservoir, enabling operation of the entire distillation system even at night when sunlight is absent.

The fourth variation, SOTEC IV, is illustrated schematically in crossectionFIG. 8. In this embodiment of the invention, the evaporation process is separated from the condensation process, each occurring in a separate subsystem. The entire system resides in ambient air800above the sea805, and near the surface of the sea803. The evaporator structure of the system is a tube807extended left-to-right, A mirror (or set of mirrors)815is located below the evaporator tube807.

The condenser structure of the system is a conventional cross-flow condenser of a type typically used in swamp coolers, or may be a bespoke configuration comprising a main body817with cooling channels820.

The process flow is as follows. Ambient air flows830into the evaporator tube807and is resident therein810, flowing slowly left-to-right. Relatively warm surface seawater832flows into the bottom of the evaporator tube and is resident therein813, flowing slowly left-to-right. The sunlight827reflecting off the mirror(s)815heats the lower surface of the evaporator tube807, said heat transmitting into and heating the resident seawater813sufficient to cause evaporation and/or boiling, generating water vapor835into and warming the resident ambient air810. Brine flows out of the evaporator tube837and is disposed of at a mid-level in the sea852. Said warm and wet resident ambient air rises, and flows out of the evaporator tube840into the condenser817. Cold seawater is sourced from the sea at depth842and flows into the cooling channels of the condenser and is resident therein825, flowing slowly from right to left. The warm wet air823comes in contact with the walls of the cooling channels820, and pure fresh water condenses therefrom descending into the bottom of the condenser body845, and is resident therein847, and finally flows out860and is collected in a reservoir857and is resident therein as the product of the system. Relatively cool dry ambient air is exhausted from the condenser855.

FIG. 9illustrates an embodiment of a SOTEC IV system evaporator tube shown schematically in isometric view. The tubular structure900comprising the evaporator tube shown inFIG. 8as807, having below it a segmented Fresnel mirror array905serving to reflect sunlight onto the lower surface of the structure900. The segments of the mirror array are rotated during the day, following the track of the sun in the sky. Warm surface seawater910flows into and through the main tube, exhausting at920as brine. Ambient air915enters the evaporator tube900, flowing through it and exhausting hot and wet at925.

FIG. 10illustrates in a crossection view the thermodynamics of one embodiment of a SOTEC IV evaporator subsystem. The tubular structure900contains at its bottom seawater or impure fresh water1000, and also containing in its upper section ambient air1005. The water1000has a free surface1003. Sunlight1010reflects off an array of mirror surfaces905onto the exterior of the lower surface of the evaporator tube. The entire exterior surface of the evaporator tube is painted with a high-light-absorption/selective low emissivity surface1030. Said sunlight heating the water1000in the tube900, causing evaporation and/or boiling, in turn causing water vapor1015to rise into the air in the tube900. The warmed wet air in turn rising, contacting the cooling surface445. The mirror array905is segmented, the segments1020differentially rotating1025to follow the sun in such as way as to maximize the intensity of light reflected onto the bottom surface1030of the evaporator tube900.

FIG. 11illustrates in a crossection view an alternative embodiment of a SOTEC IV evaporator subsystem with a parabolic trough mirror. This view as shown is geographically looking approximately North. The evaporator1040is heated by said parabolic mirror1045, reflecting the sun's rays shown when the sun is at zenith in the sky (approximately noon)1050onto the bottom of said evaporator. Said parabolic mirror follows the sun, rotating1055approximately about its focal point within the evaporator tube, maximizing the intensity of sunlight on the bottom of the evaporator tube. Said parabolic mirror is show in its rotated position around 2 p.m. Said mirror and said evaporator tube may be structurally fixed together, and both rotated following the sun to maximize the intensity of the sun's rays on the bottom of said evaporator throughout the day from morning till night. Similarly, in an alternative embodiment, a Fresnel mirror segment array, functionally equivalent to said parabolic trough mirror, may be rotated1055in its entirety, in addition to individual segments thereof being rotated in coordination as shown at1025inFIG. 10.

FIG. 12illustrates an embodiment of a SOTEC IV condenser (referenced as817inFIG. 8), and its thermodynamics. The condenser body1100contains a set of channels1105which are joined together at their bottoms1107. The condenser body is filled with cold seawater sourced from the sea at a depth where the seawater temperature is significantly below the seawater temperature at the surface, as coolant1110, or cold water from some alternative source such as a cold river, said cold water flowing through the condenser body1105containing wet air1115which is introduced from the evaporator subsystem (referenced as845inFIG. 8). The wet air1115strikes the relatively cold walls of the channels and the water vapor in the wet air condenses thereon1120, running down said channel walls and collecting in the joined section at the bottom of the channels1125, exhausting therefrom as the product of the system.

FIG. 13illustrates the fifth variation, SOTEC V, shown schematically in crossection. This variation is similar in most respects to a SOTEC IV system as illustrated inFIG. 8, except that a brine preheater stage is added to enhance thermal efficiency. As in a SOTEC IV system, in this embodiment of the invention, the evaporation process is separated from the condensation process, each occurring in a separate subsystem. The entire system resides in ambient air1200above the sea1205, and near the surface of the sea1203. The evaporator structure of the system is a tube1207extended left-to-right, A mirror (or set of mirrors)1215is located below the evaporator tube1207.

A brine preheater substructure1217serves to preheat incoming warm seawater. The brine preheater is a tube-within-a-tube structure, comprising an outer tube1223and an inner tube1225. In one embodiment, the preheater may be relatively large and serve as a heat reservoir, enabling the entire distillation system to operate from the stored heat even during nighttime hours when there is no sunlight to reflect onto the evaporator subsystem. The condenser structure of the system is a conventional cross-flow condenser of a type typically used in swamp coolers, or may be a bespoke configuration comprising a main body1229with cooling channels1230.

The process flow is as follows. Ambient air flows1240into the evaporator tube1207and is resident therein1210, flowing slowly left-to-right. Relatively warm surface seawater1243flows through the brine preheater1223, picking up heat from outflowing brine from the evaporator1247transferred through the shared walls of the preheater, flowing therefrom into the evaporator and being resident therein, flowing slowly right to left1213, and exiting therefrom as brine into the brine preheater inner tube1227, and exiting therefrom1263and being disposed of at a midlevel in the sea1265. Sunlight1237reflecting off the mirror(s)1215heats the lower surface of the evaporator tube1207, said heat transmitting into and heating the resident seawater1213sufficient to cause evaporation and/or boiling, generating water vapor1245into and warming the resident ambient air1210. Said warm and wet resident ambient air rises, and flows out of the evaporator tube1250into the condenser1229. Cold seawater is sourced from the sea at depth1253or another cold water source such as a cold river, and flows into the cooling channels of the condenser1230and is resident therein1235, flowing slowly from right to left. The warm wet air1233comes in contact with the walls of the cooling channels1230, and pure fresh water condenses therefrom descending1255into the bottom of the condenser body1229, and is resident therein1257, and finally flows out1273and is collected in a reservoir1270and is resident therein as the product of the system1275. Relatively cool dry ambient air is exhausted from the condenser1267.

FIG. 14illustrates the sixth variation, SOTEC VI, shown schematically in crossection. This variation is similar in most respects to a SOTEC V system as illustrated inFIG. 12, except that the pressure inside the evaporator is reduced, lowering the boiling point of the water contained therein. As in a SOTEC V system, in this embodiment of the invention, the evaporation process is separated from the condensation process, each occurring in a separate subsystem. The entire system resides in ambient air1300above the sea1305, and near the surface of the sea1303. The evaporator structure of the system is a tube1307extended left-to-right, A mirror (or set of mirrors)1315is located below the evaporator tube1307.

A brine preheater substructure1317serves to preheat incoming warm seawater. The brine preheater is a tube-within-a-tube structure, comprising an outer tube1320and inner tube1225. The condenser structure of the system is a conventional cross-flow condenser of a type typically used in swamp coolers, or may be a bespoke configuration comprising a main body1329with cooling channels1330.

The process flow is as follows. Ambient air flows1340through a gate valve1383into the evaporator tube1207and is resident therein1310, flowing slowly left-to-right. Relatively warm surface seawater1343flows through the brine preheater1320, picking up heat from outflowing brine from the evaporator1347transferred through the shared walls of the preheater, flowing therefrom through a gate valve1377into the evaporator and being resident therein, flowing slowly right to left1313, and exiting therefrom through pump1380as brine into the brine preheater inner tube1327, and exiting therefrom1363and being disposed of at a midlevel in the sea1365. Sunlight1337reflecting off the mirror(s)1315heats the lower surface of the evaporator tube1307, said heat transmitting into and heating the resident seawater1313sufficient to cause evaporation and/or boiling, generating water vapor1345into and warming the resident ambient air1310. The evaporator operates at a reduced pressure, so the boiling point temperature of the water contained therein is reduced from the temperature at which it would boil at atmospheric pressure. Said warm and wet resident ambient air rises, and is pumped out of the evaporator by pump1385, being re-pressurized to ambient atmospheric pressure exiting the evaporator tube1350into the condenser1329at ambient atmospheric pressure. Cold seawater is sourced from the sea at depth1353, or sourced from another cold-water source such as a cold river, and flows into the cooling channels of the condenser1330and is resident therein1335, flowing slowly from right to left. The warm wet air1333comes in contact with the walls of the cooling channels1330, and pure fresh water condenses therefrom descending1355into the bottom of the condenser body1329, and is resident therein1357, and finally flows out1373and is collected in a reservoir1370and is resident therein as the product of the system1375. Relatively cool dry ambient air is exhausted from the condenser1367.

FIG. 15illustrates in plan view an SOTEC II distillation plant as a complete system located on land1410, near a shoreline1405of the ocean1410. Various fluid flows pass through an offshore concrete manifold structure1415, anchoring piping to the sea floor. Warm near-surface seawater enters the system by means of a pump1425, said near-surface seawater being piped1420into the system. Coolant seawater sourced from deep within the sea enters the system by means of another pump1433and is piped1430into the system. Both of the aforesaid fluid flows are piped ashore1428, through an onshore concrete anchoring manifold structure1435. The said warm seawater is distributed through a plenum1440and intake pipes1445to an array of evaporator/condensers1450. The aforesaid coolant water is distributed to the evaporator/condensers through a plenum and piping1460. Brine is exhausted from the evaporator/condensers1450through piping and a plenum1465, and exhausted through manifold1415into the midlevel of the ocean1470. In the case where the embodiment shown inFIG. 14is located far from a seacoast, pipes1428, may be quite lengthy, even miles in extent, in which case they are thermally insulated.

FIG. 16illustrates in crossection view a SOTEC V distillation system configured as a floating platform at sea. The system floats on the sea1510at the sea surface1505, exposed above to ambient air1500. The said platform is supported at the sea surface by floats1515. If the platform were viewed in plan view it would be seen as generally round, or rectangular, any other general outline shape. A central hub1535is comprising a condenser1540, an air exhaust chimney1560, a holding tank1545in which fresh water is collected as the product of the system, and inflow and outflow piping from and to the sea, and said hub is surrounded by evaporator tubes1520and related subsystems, each such subsystem comprising a preheater tube1533, said preheater optionally serving as a heat reservoir supporting nighttime system operation when there is no direct sunlight available, a Fresnel array of mirror segments1525, and various piping, said group of substructures arrayed in a configuration such that the inflow end of each evaporator is remote from the condenser at the hub and the outflow end of each evaporator is proximate to the condenser at the hub.

The system operates as follows: Warm near-surface seawater enters the system at the periphery1565, flowing through the preheater1523,1570, then entering and flowing through the lower region of the evaporator tube1586. Ambient air1575enters the evaporator and flows through1580. Sunlight1585is reflected off mirrors1525onto the bottom of the evaporator tube, heating the water in the evaporator tube1586, causing evaporation into the air1580in the upper region of the evaporator tube. The hot wet air is exhausted1588into the condenser. The brine resulting from the distillation process is exhausted into the preheater1533, passing through and exhausting therefrom1590, and being piped1550through the condenser body joining exhaust coolant water and being passed out of the system at a midlevel of the ocean1600.

The condenser is comprising a condenser body1535configured as a tank structure, and a subsystem of coolant pipes1540. Cold seawater1595is sourced from deep within the ocean and piped1555into the coolant pipes of the condenser. The warm wet air1588entering the condenser body strikes the walls1592of the coolant pipes1540, and water condenses on the surfaces of said coolant pipes1598collecting in the base of the tank1599as the product of the system. The relatively dried and cooled air passes through the chimney1560and is exhausted from the system1610. The relatively warmed coolant water is piped downward joining the exhausted brine1550, and exhausted from the system at a mid-level of the ocean1600.