Patent Publication Number: US-2011048920-A1

Title: Adsorbent - Adsorbate Desalination Unit and Method

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a device and method for the desalination of seawater, and in particular to an improved adsorbent—adsorbate desalination unit optimized for use in the desalination of seawater. 
     The present invention utilizes an economizing heat exchanger situated outside the pressure vessel of an adsorption device utilizing a silica gel—water working pair adsorbent—adsorbate. The economizing heat exchanger utilizes the heat produced by the adsorption/desorption process to pre-heat the incoming source water to be desalinated, thus increasing the efficiency of the process over the prior art. 
     The introduction of the seawater to be desalinated into the evaporator at an elevated temperature relative to the seawater&#39;s ambient temperature greatly enhances the evaporation process, resulting in an increase of the efficiency of the desalination device over prior adsorption-desalination units. 
     The present invention also utilizes the water leaving the adsorption heat exchanger chamber during desorption to heat the evaporator heat exchanger to increase the efficiency of vaporization of the source seawater. 
     The present invention also utilizes a mist eliminator intermediate the evaporator and the adsorbent heat exchanger chambers to facilitate efficient vaporization of the source seawater without fouling of the adsorption-desalination unit. 
     BACKGROUND OF THE INVENTION 
     Existing desalination technology uses significant energy to separate sea-salt from seawater. The two commercially available processes are thermal desalination and reverse osmosis desalination. Both of these technologies are widely used. 
     Thermal desalination uses large amounts of heat to vaporize seawater. The vaporized water is run through a heat exchanger where the phase reversal to distillate occurs. 
     In reverse osmosis desalination, large amounts of electrical energy drive seawater at high pressure through reverse osmosis membranes to separate ions from the water to produce a concentrated seawater and permeate of fresh water. 
     The present invention relates to the use of an adsorption process for the desalination of seawater. WIPO Application No. PCT/SG2006/000157 (“WIPO &#39;157”) discloses a water desalination system comprising an evaporator for evaporating saline water to produce water vapor; an adsorption means in selective communication with the evaporator for reversibly adsorbing the water vapor from the evaporator; said adsorption means in selective vapor communication with a condenser; and desorbing means for desorbing the adsorbed water vapor from the adsorption means for collection by the condenser; said condenser adapted to condense the water vapor to desalinated water. However, the device and process disclosed in WIPO &#39;157 embodies several inefficiencies that are rectified in the current invention. For example, the process described in WIPO &#39;157 is inefficient because it utilizes only a cooling tower as the source of cooling-water to cool the adsorbent. Also, chilled water is produced in the evaporator which does not optimize the vaporization of the source seawater. 
     The invention of the present disclosure provides an additional method of cooling the fluid used to cool the adsorbent during the adsorption cycle. As it is routed through an economizing heat exchanger, the source seawater is used to cool the fluid used to cool the adsorbent during the adsorption cycle. Further the heat from the adsorbent is, in turn, used to warm the source seawater to be desalinated, enhancing its vaporization energy. This disclosure also includes a method of using the heat remaining in the water leaving the adsorption heat exchanger to heat the evaporator to increase the efficiency of the source seawater. Finally, this disclosure also includes a tortured path mist eliminator to avoid contamination of the adsorbent by the seawater. 
     Seawater temperatures vary considerably based primarily upon the season and the latitude of the location. For the purpose of this disclosure, we expect that the seawater near population centers might range from about 5° C. (41° F.) to about 30° C. (86° F.). For the sake of discussion and illustration purposes only, and not intended as a limitation, this disclosure will use an example source seawater temperature of 15° C. (60° F.) in the description of the present invention and its function. It should be recognized, however, that a wide range of source seawater temperatures may be utilized in connection with the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an improved, efficient method and device for the desalination of seawater using a switchable cycle adsorption-desorption process using an adsorbent/adsorbate working pair such as silica-gel and water. A novel aspect of the invention is the transference of the isosteric heat of adsorption generated in the adsorption cycle to the incoming source seawater to be distilled. The economizing heat exchanger uses heat from the adsorption cycle to raise or increase the temperature of the incoming seawater a total of between about 8° C. (14.4° F.) to about 18° C. (32.4° F.) above the temperature at which it enters or is input into the economizing heat exchanger. For example, the economizing heat exchanger of the present invention raises seawater input at an ambient temperature of 15° C. (60° F.) to between about 23° C. (73.4° F.) and about 33° C. (91° F.) before it is injected into the evaporator to begin the desalination process. 
     The present invention relates to an adsorption-desalination unit providing improved efficiencies over prior adsorption-desalination units through the use of an economizing heat exchanger to remove the heat accumulated in the cooling-water circuit and transfer that heat to the incoming seawater to be desalinated. By the same process, the temperature of the fluid in the cooling-water circuit is lowered by between about 5° C. (11.3° F.) to about 13° C. (23.4° F.) as it passes through the economizing heat exchanger. This cooling reduces the overall demand for external cooling of the fluid in the cooling-water circuit. 
     A further novel aspect of the present invention is the utilization of the heat remaining in the hot water after it powers the desorption cycle. As hot water exits the evaporator heat exchanger in the desorption cycle, the present invention transfers the latent heat remaining in the water to heat the evaporator heat exchanger. The addition of heat to the evaporator heat exchanger increases the efficiency of vaporization of the incoming source seawater to be distilled. The addition of waste heat from the desorption cycle to raise or increase the efficiency of the evaporator will result in increased vaporization of the incoming seawater a total of between about 20%-40% above that expected from the process described in WIPO &#39;157. 
     To combat potentially undesirable effects that may result from injecting pre-heated seawater into a heated evaporator, a tortured-path mist eliminator is also used intermediate the evaporator and the adsorbent heat exchanger chambers. 
     It is therefore an object of the present invention to provide an improved water desalination system. The water desalination system of the present invention is optimized to more efficiently utilize the heating and cooling capacities of an adsorption/desorption process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a schematic drawing of the adsorption-desalination unit of the present invention. 
         FIG. 2  is a schematic drawing of an alternate, single-cycle adsorption-desalination unit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a schematic drawing of a preferred embodiment of the adsorption-desalination unit  10  of the present invention. The adsorption-desalination unit  10  uses an adsorbent  11  which can be regenerated. The presently preferred adsorption means is a silica gel—water working pair adsorption device. The presently preferred adsorbent is a silica gel, though other adsorbents may be useful in the adsorption means. The present invention uses water vapor generated from the source seawater or brine to be desalinated as the adsorbate. 
     The adsorption-desalination unit  10  of the present invention offers improved efficiencies over prior adsorption-desalination units through the use of an economizing heat exchanger  30 , the injection of pre-heated seawater into an evaporator chamber  17 , utilization of waste heat from the desorption cycle to heat the evaporator, and a mist eliminator  12 . 
     An adsorption-desalination unit  10  comprises in principle a pressure vessel  14  divided into a plurality of chambers, at least one, but commonly a pair (two) or more of adsorbent heat exchanger chambers  15 ,  16  located between or positioned intermediate an evaporator chamber  17  containing an evaporator  47  and an upper condenser chamber  18  containing a condenser  48 . The evaporator chamber  17  is typically located below the adsorbent heat exchanger chambers  15 ,  16 , and the condenser chamber  18  is typically located above the adsorbent heat exchanger chambers  15 ,  16 , though alternate arrangements are within the contemplation of this invention. The adsorbent heat exchanger chambers  15 ,  16  are each connected to the condenser chamber  18  and evaporator chamber  17  by one or more valves  19   a,    19   b  and  20   a,    20   b,  respectively. 
     The adsorption-desalination unit  10  of the present invention further comprises a fluid circulation system  22  comprising interconnected tubing or piping to carry fluid to the different chambers  15 ,  16 ,  17 ,  18 . Appropriate valves in the circulation system  22  are provided to selectively direct relatively hot and relatively cold fluid (typically water) through different sections or portions of the fluid circulation system  22  in the appropriate sequence to drive the adsorption process. Fluid circulation system  22  comprises adsorption heat exchanger circuit  23 , cooling-water circuit  61 , and evaporator-heating circuit  60 . Adsorption heat exchanger circuit  23  comprises portions  23   a,    23   b  passing through adsorbent heat exchanger chambers  15  and  16 , respectively. Cooling-water circuit  61  passes through the condenser chamber  18  to drive the condenser  48 . Evaporator-heating circuit  60  passes through the evaporator chamber  17  to drive the evaporator  47 . Fluid circulation system  22  further comprises an economizing heat exchanger loop  50  for passing fluid through an economizing heat exchanger  30 . The economizing heat exchanger loop  50  comprises a portion of the cooling-water circuit  61  and is also interconnected with the adsorption heat exchanger circuit  23 . 
     Many alternative plumbing layouts with various configurations of tubing and valves are well known in the adsorption art, and their use is within the contemplation of the present invention. To practice the present invention, the plumbing must be suitable for directing hot water through one of the adsorbent heat exchanger chambers  15  or  16  and evaporator  47  while directing cooling water through the economizing heat exchanger  30  and the other adsorbent heat exchanger chamber  15  or  16  and, alternatively, the condenser  48 , and for the flows of hot and cooling water to the adsorbent heat exchanger chambers  15  and  16  to be switchable. 
     The fluid circulation system  22  further comprises a pumping means for moving the fluid through the circuit. Pumping means may comprise one or more pumps  34 . 
     The portions  23   a,    23   b  of adsorption heat exchanger circuit  23  within adsorbent heat exchanger chambers  15 ,  16  are surrounded by or packed with an adsorbent  11 , preferably silica gel. 
     The incoming or source solution to be desalinated, such as seawater or brine, is carried, such as by a pumping means like pump  35 , from a source  25 , which may be the ocean, a storage tank (not shown) or any other source of brine, through an inlet line  27  and into the evaporator chamber  17 . The brine is introduced into the evaporator chamber  17  where it is evaporated into a pure or distilled water vapor, leaving behind the salt and other impurities in a more concentrated brine. To increase the rate of evaporation across the evaporator tubes  32  of the evaporator  47 , the solution to be desalinated is preferably dispersed throughout the evaporator chamber  17  by dispersing means, such as a series of spray nozzles  28 . 
     The concentrated brine in the evaporator chamber  17  is collected in a collection area  29 . The concentrated brine may then be removed through a vacuum trap or other pressure-maintaining drain  38  designed to allow removal of the concentrate without significantly changing the water vapor pressure within the evaporator chamber  17 . The concentrated heated brine is directed, such as by a pumping means like pump  36 , through appropriately plumbed tubing, either back into inlet line  27 , thereby providing an additional source of pre-heating of the incoming solution, or, alternately, to a waste outlet  39 . A portion of the concentrated heated brine must be dumped periodically to prevent super-saturation of the solution and formation of insoluble solid deposits on the evaporator tubes  32 . 
     In a preferred embodiment, a mist eliminator  12  is interposed between the evaporator chamber  17  and the adsorbent heat exchanger chambers  15 ,  16 , preferably between the evaporator  47  and the valves  19   a,    19   b  that communicate between the evaporator chamber  17  and the adsorbent heat exchanger chambers  15 ,  16 . The mist eliminator  12  functions to prevent passage of water droplets from the evaporator chamber  17  into the adsorbent heat exchanger chambers  15 ,  16  and to collect water droplets from the air and vapor stream and divert the liquid to an appropriate drain  13  for return to the evaporator  12 . The mist eliminator also functions as a low-efficiency particulate filter. A mist eliminator  12  provides a large surface area in a small volume to collect liquid without substantially impeding air or vapor flow. Unlike filters, which hold particles indefinitely, mist eliminators  12  coalesce (merge) fine droplets and allow the liquid to drain away. 
     Mist eliminator  12  may comprise any number of physical structures known in the art for creating a tortured path for an air stream to follow, thereby providing ample surface areas upon which water droplets in the air stream can collect. The results achieved by a mist eliminator will depend on proper specification of mist eliminator type, such as mesh, vane or fiber bed (or a combination of types), orientation, thickness, internal details, support and spacing in the vessel, vapor velocity and flow pattern, and many other considerations. The mist eliminator  12  of the present invention may be designed in one or more elements or screens for easy removal from the pressure vessel  14  through a pressure-sealed opening (not shown) for cleaning or replacement. 
     When the adsorption-desalination unit  10  is first started, the pressure vessel  14  is evacuated to create a vacuum using an evacuation pump  56 . Once started, an adsorption-desalination unit  10  operates automatically on a four step cycle. In a desorption cycle, hot water is introduced into one of the adsorbent heat exchanger chambers (shown as  16  in  FIG. 1 ) through heat exchanger circuit portion  23   b.  This heating of the silica gel  11  forces water within the gel  11  into vapor (desorption), raising the water vapor pressure within the chamber  16  which, in turn, pushes open one-way valve  20   b  (and keeps one-way valves  19   b  and  20   a  closed). The difference in water vapor pressures between adsorbent heat exchanger chamber  16  and condenser chamber  18  creates an air flow or draw of air and the water vapor in chamber  16  moves through the valve  20   b  and into the condenser chamber  18 . 
     Water vapor in the condenser chamber  18  contacts the condenser  48  which condenses the vapor back into pure desalinated water. This potable water is then collected in a collecting area or condenser well  21  and removed through a vacuum trap  42  or other pressure-maintaining drain and passed through an outlet line  43  to a storage tank  44  or other end use. 
     When the drying of the adsorbent  11  in the adsorbent heat exchanger chamber  16  is complete, in a first switching cycle, the water flowing through the adsorbent heat exchanger circuit  23   b  is switched from hot water to cooling water by means of conventional plumbing such as by the appropriate manipulation of a plurality of control valves, manifolds and pumps (not shown). Typically conventional plumbing is located outside of the pressure vessel  14  of the adsorption-desalination unit  10 . A programmable logic control system or computer (not shown) may be employed to control the positions and timing of the control valves and manifolds of the plumbing. 
     This begins the adsorption cycle. Cool, dry silica gel  11  has a large affinity to capture water vapor and will capture all of the available water vapor from the adsorbent heat exchanger chamber  16 , reducing the pressure in this chamber, closing valve  20   b  and allowing the valve  19   b  to be opened by the pressure of the water vapor being generated by the evaporator  47 . 
     Water evaporates in a vacuum at room temperature and thereby extracts heat from its surroundings. The evaporation of seawater introduced into the evaporator chamber  17  cools the water flowing through the evaporator tubes  32  in the evaporator-heating circuit  60 . The output of this water in the evaporator-heating circuit  60  is returned to the heat source (not shown) for heating and re-routing for the next desorption cycle. 
     In  FIG. 1 , adsorbent heat exchanger chamber  15  is illustrated as being in the adsorption cycle. The evaporated water passes through a mist eliminator  12  and an open or communicating, one-way valve  19   a  into adsorbent heat exchanger chamber  15  and is adsorbed into the adsorbent silica gel  11 . Cool water is circulated in this chamber  15  through the adsorption heat exchanger circuit  23   a  to remove the heat generated by the isosteric heat of adsorption in this chamber  15 . The adsorption process creates a slight decrease in pressure, creating a small vacuum differential between the evaporator chamber  17  and adsorbent heat exchanger chamber  15  that pulls water vapor from the evaporator  17  through valve  19   a  and into the adsorbent heat exchanger chamber  15 . This decrease in pressure in adsorbent heat exchanger chamber  15  also pulls one-way valve  20   a  closed. 
     When adsorbent heat exchanger chamber  15  is in the adsorption cycle, adsorbent heat exchanger chamber  16  is in the desorption cycle, and vice versa; water in chamber  16  that has been adsorbed into the adsorbent  11  is driven from the adsorbent  11  by the circulation of hot water through the portion  23   b  of adsorbent heat exchanger circuit  23  running through chamber  16 . The desorbed water vapor rises and exits adsorbent heat exchanger chamber  16  through opened valve  20   b,  entering the condenser  18  where it is condensed by the cool water circulating through the cooling-water circuit  61 . As will be explained in more detail below, it is important to note that the cool water in the cooling-water circuit  61  gains heat through the condensing process. The cool water has also gained heat as it was run through the portion  23   a  of the adsorbent heat exchanger circuit  23  running through the chamber  15  in the adsorption cycle. The present invention is specially configured to take novel advantage of this heat in the economizing heat exchanger  30 . Similarly, it is important to note that while the hot water circulated through the portion  23   b  of adsorbent heat exchanger circuit  23  loses heat through the desorption process, it still retains some residual heat when it exits the adsorbent heat exchanger chamber  16  in which the desorption cycle is occurring. Rather than simply returning this water to the heat source for reheating, the present invention is specially designed to take advantage of the residual heat in this water by routing it to the evaporator-heating circuit  60  where it is utilized to help heat the evaporator  47 . 
     When an adsorbent heat exchanger chamber  15  is in the adsorption cycle, the pressure in that chamber  15  is slightly lower than in the evaporator chamber  17 , accordingly, a portion of the seawater to be desalinated evaporates and is pulled into the adsorbent heat exchanger chamber  15 . At the same time, the pressure in the other adsorbent heat exchanger chamber  16  in the desorption cycle, is slightly elevated as the water vapor is driven from the silica gel  11 . That desorbed water vapor is pulled into the condenser chamber  18  which has a lower pressure as vapor in that chamber  18  is being condensed back into water. 
     When the silica gel  11  in the adsorption cycle chamber  15  is saturated with water and the silica gel  11  in the desorption cycle chamber  16  is dry, the programmable logic control system of the adsorption-desalination unit  10  automatically switches the adsorbent heat exchanger chambers  15  and  16  between adsorbing and desorbing cycles by exchanging the flows of hot and cool water. In one of two switching cycles, the flow of hot water through the adsorption heat exchanger circuit  23  is switched from flowing through the portion  23   b  of the adsorbent heat exchanger chamber  16  to flowing through the portion  23   a  to begin the desorption process in adsorbent heat exchanger chamber  15 . Cool water that was running through the portion  23   a  of the adsorbent heat exchanger chamber  15  is switched to flow through portion  23   b  of adsorbent heat exchanger chamber  16  to begin the adsorption process. Valves  19   a,    19   b,    20   a  and  20   b  are preferably one-way valves which are actuated to their opposite condition (i.e., opened or closed) based upon changes in the water vapor pressure differentials in the chambers on opposing sides of the valves. For example, when heat exchanger chamber  16  is in the desorption cycle, valve  20   b  is pushed open by the increase in water vapor pressure within heat exchanger chamber  16  due to the desorption of water from the gel  11 , but valve  19   b  is held closed by this same pressure. As an adsorption cycle begins in heat exchanger  16 , the adsorption of water from the vapor creates a partial vacuum which pulls closed the valve  20   b  between the adsorption cycle chamber and the condenser chamber  18  but pulls open the valve  19   b  between the evaporator chamber  17  and heat exchanger chamber  16 , thereby allowing for the proper flow of vapor through the adsorption-desalination unit  10 . Thus it can be seen that the adsorption-desalination unit  10  requires only the switching of the flow of hot and cool water to function, but does not otherwise require the application of any external power source to drive the functioning of the valves  19   a,    19   b,    20   a  and  20   b.    
     Once put into operation, an adsorption-desalination unit  10  operates continuously, switching the adsorption and desorption cycles between the available adsorbent heat exchanger chambers  15 ,  16 . The invention is scalable; adsorption-desalination units  10  having a plurality of adsorbent heat exchanger chambers may increase the volume of seawater that can be desalinated during each cycle. 
     An adsorption-desalination unit  10  is capable of operating with a wide range of temperatures for the hot, the cool and the cold water. Cycles are generally run for pre-determined amounts of time, depending on the conditions presented, such as pressure, temperature, size and number of adsorbent heat exchanger chambers, amount and nature of adsorbent in the adsorbent heat exchanger chambers, and other factors known in the art. In a presently preferred embodiment, peak performance is obtained when the hot water used in the desorbing cycle to run through portion  23   b  of the adsorption heat exchanger circuit  23  is about 90° C. (194° F.), and the cooling water used in the adsorbing cycle to run through portion  23   a  of the adsorption heat exchanger circuit  23  is as cool as possible, perhaps as cool as about 21° C. (70° F.) when the incoming source seawater is at a temperature of about 15° C. (60° F.). 
     A novel feature of the present invention is the pre-heating of the incoming brine by means of an economizing heat exchanger  30 . At the source  25 , seawater or brine will be at the ambient seawater temperature, assumed, for discussion purposes, to be about 15° C. (60° F.), and might, depending on the weather, geographic location and other influencing factors, be introduced into the inlet line  27  having a temperature between about 5° C. (40° F.) to about 30° C. (86° F.). Rather than pre-heating the incoming brine using an external source of heat, the inlet line  27  passes the incoming seawater through an economizing heat exchanger  30 . The economizing heat exchanger  30  of the present invention raises the temperature of the incoming brine by transferring to it the isosteric heat of adsorption from the adsorbent  11  or the heat of condensation from the condenser  48 , or, preferably, both. This is accomplished by directing all or a portion of the fluid output from the adsorbent heat exchanger chambers  15  or  16  in the adsorption cycle and the condenser  48  through the economizing heat exchanger  30 . The economizing heat exchanger  30  utilizes the isosteric heat of adsorption gained by the fluid during the adsorption cycle and the heat of condensation from the condenser  48  to increase the temperature of the incoming seawater from the source  25  from between about 8° C. (14.4° F.) to about 18° C. (32.4° F.) above its ambient temperature before it is introduced or injected into the evaporator  47 . As an example for illustration purposes only and not as a limitation, source seawater input into the economizing heat exchanger  30  at about 15° C. (60° F.) is raised to approximately 23° C. (74° F.) before it is introduced into the evaporator chamber  17 . 
     As part of this heat transfer within the economizing heat exchanger  30 , the temperature of the cooling-fluid from the cooling-circuit input into the economizing heat exchanger  30  is decreased before it is output into the portion  23   a  or  23   b  of the adsorption heat exchanger circuit  23  driving the adsorption cycle at that time. The economizing heat exchanger  30  reduces the temperature of the fluid in the cooling-water circuit by between about 5° C. (11.3° F.) to about 13° C. (23.4° F.) as it passes through the economizing heat exchanger. Continuing the example based on source seawater at 15° C. (60° F.), the cooling-water would be cooled from about 40.5° C. (105° F.) to about 29.4° C. (85° F.). 
     Preferably, all or a portion of the fluid output from the adsorbent heat exchanger chamber  15  or  16  in the adsorption cycle is passed through the condenser  48  via the cooling-water circuit  61  prior to being passed into and through the economizing heat exchanger  30  via the economizing heat exchanger loop  50 . This allows the fluid from the adsorption cycle to gain further heat as it passes through the condenser  48 , and this heat, together with the heat of adsorption can then be transferred through the economizing heat exchanger  30  into the incoming source seawater to be desalinated. 
     Any type of heat exchanger providing efficient heat transfer from one fluid medium to another is suitable for the economizing heat exchanger  30  of the present invention. The presently preferred economizing heat exchanger  30  for use in the present invention is a flat plate type heat exchanger. 
     The utilization of an economizing heat exchanger  30  allows the seawater being desalinated to be injected into the evaporator chamber  17  at a higher temperature than previously known in the art without the application of an external source of heat. As previously stated, the temperature of the ambient seawater can be raised from about 8° C. (14.4° F.) to about 18° C. (32.4° F.) above its starting temperature due to the effect of the economizing heat exchanger  30 . This serves to increase the efficiency and speed of seawater vaporization. By entering into the evaporator chamber  17  (which is in a vacuum) at a higher temperature, the incoming source seawater boils or evaporates into water vapor more quickly and vigorously. 
     Rather than or in addition to heating the evaporator  47  using an additional external source of heat, the present invention efficiently utilizes the heat remaining in the hot water utilized in the desorption cycle by directing all or a portion of such the fluid output from the adsorbent heat exchanger chambers  15  or  16  in the desorption cycle to the evaporator  47  through the evaporator-heating circuit  60 . Returning to our example of source seawater at 15° C. (60° F.), the heating fluid enters the adsorbent heat exchanger chamber in the desorbing cycle (shown in  FIG. 1  as chamber  16 ) through portion  23   b  at a temperature of about 90° C. (194° F.). In the desorbing process, a portion of the heat from the heating fluid is transferred to the adsorbate (water) in the adsorbent (silica gel  11 ), and the heating fluid exits the adsorbent heat exchanger chamber  16  at a temperature of about 85° C. (186° F.). Rather than returning this still hot fluid directly to the heat source (not shown), it can be directed to the evaporator-heating circuit  60  to drive the evaporator  47 . The operation of the evaporator  47  utilizing the heating fluid having a temperature of above about 85° C. (186° F.) creates a temperature gap between the pre-heating incoming source seawater and the evaporator  47 , further catalyzing vaporization of the incoming source seawater. After exiting the evaporator  47 , the heating fluid has been further cooled from about 85° C. (186° F.) to about 78° C. (172° F.). After exiting the evaporator chamber  17 , the heating fluid is returned to an external heat source (not shown) to be reheated. 
     Because of the operation of the evaporator  47  at higher temperatures, a mist eliminator  12  is interposed between the evaporator chamber  17  and the adsorbent heat exchanger chambers  15 ,  16 , preferably between the evaporator  47  and the valves  19   a,    19   b  that communicate between the evaporator chamber  17  and the adsorbent heat exchanger chambers  15 ,  16 . The mist eliminator  12  functions to prevent passage of water droplets from passing from the evaporator chamber  17  into the adsorbent heat exchanger chambers  15 ,  16  and to collect water droplets from an air stream and divert the liquid to an appropriate drain  13  for return to the evaporator  12 . In practice, performance of the adsorption-desalination unit  10  may be optimized by mathematically determining optimum parameters of adsorbent mass, adsorption/desorption cycle time, heating fluid flow and cooling fluid flow for loading into the programmable logic control system. 
       FIG. 2  illustrates an alternative embodiment of a single-cycle adsorption-desalination unit  70  according to the present invention comprising a pressure vessel  71 , divided into a plurality of chambers, said chambers comprising an adsorbent heat exchanger chamber  72 , located between an evaporator chamber  73  containing an evaporator  74  and a condenser chamber  75  containing a condenser  76 . The adsorbent heat exchanger chamber  72  is connected to the condenser chamber  75  by one or more one-way valves  77  and to the evaporator chamber  73  by one or more one-way valves  78 . 
     The single-cycle adsorption-desalination unit  70  further comprises a fluid circulation system  91  comprising interconnected tubing or piping to carry fluid to the different chambers  72 ,  73 , and  75 . Appropriate valves in the circulation system  91  are provided to selectively direct hot and cold fluid (typically water) through different sections or portions of the fluid circulation system  91  in the appropriate sequence to drive the adsorption process. Fluid circulation system  91  comprises adsorption heat exchanger circuit  92 , cooling-water circuit  80 , and evaporator-heating circuit  79 . Adsorption heat exchanger circuit  92  further comprises portion  93  passing through adsorbent heat exchanger chamber  72 . Cooling-water circuit  80  passes through the condenser chamber  75  to drive the condenser  76 . Evaporator-heating circuit  79  passes through the evaporator chamber  73  to drive the evaporator  74 . Fluid circulation system  91  further comprises an economizing heat exchanger loop  82  for passing fluid through an economizing heat exchanger  83 . The economizing heat exchanger loop  82  comprises a portion of the cooling-water circuit  80  and is also interconnected with the adsorption heat exchanger circuit  92 . 
     The fluid circulation system  91  further comprises a pumping means for moving the fluid through the circuit. Pumping means may comprise one or more pumps  81 . 
     The portion  93  of adsorption heat exchanger circuit  92  within adsorbent heat exchanger chamber  72  is packed with an adsorbent  84 , preferably silica gel. 
     The incoming source seawater is carried, such as by a pumping means like pump  85 , from the source  25 , through an inlet line  86  and into the evaporator chamber  73 , where it is evaporated into a pure or distilled water vapor. This leaves behind the salt and other impurities in a more concentrated brine in the collection area  87  where it may be removed and reintroduced into the inlet line  86  or discarded as waste. 
     The inlet line  86  passes the incoming seawater through an economizing heat exchanger  83  for pre-heating. The cooling-water circuit  80  also passes through the economizing heat exchanger  83 . 
     A mist eliminator  88  is interposed between the evaporator chamber  73  and the adsorbent heat exchanger chamber  72 . 
     In operation, a single-cycle adsorption-desalination unit  70  can be switched between the adsorption cycle and the desorption cycle. The Programmable logic control system (not shown) can be appropriately programmed to control the plumbing to start, stop or otherwise manage the flows of source seawater and hot, cool and cold water throughout the various circuits and portions of the fluid circulation system  91  to optimize performance of the single-cycle adsorption-desalination unit  70 . 
     In practice, two or more single-cycle adsorption-desalination units  70  can be operated in parallel, making the system scalable over multiple units  70  to increase the rate and volume of seawater desalinated. Because there is only an adsorbent heat exchanger chamber  72  within a single-cycle adsorption-desalination unit  70 , such units  70  are less complicated and expensive to manufacture and thus may present a cost savings over the standard adsorption-desalination unit  10  (shown in  FIG. 1 ) when the method of the present invention is practiced on an industrial scale. 
     Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.