WO2004089830A2

WO2004089830A2 - Solvent extraction system and method

Info

Publication number: WO2004089830A2
Application number: PCT/IL2004/000319
Authority: WO
Inventors: Moshe Schaffer
Original assignee: Moshe Schaffer
Priority date: 2003-04-11
Filing date: 2004-04-08
Publication date: 2004-10-21
Also published as: WO2004089830A8; WO2004089830A3

Abstract

A distillation system (1) for extracting solvent from a reservoir of solvent containing solute dissolved therein: comprising a pool (14) containing a saturated solution of the solute in the solvent coupled to the reservoir of solvent and further coupled to a pool of clean solvent (23), by a vapour bridge (10) including a conduit (12) having an open end submerged in the pool of saturated solution coupled by a closed bridge having air evacuated therefrom to a conduit having an open end submerged in the pool of clean solvent; the system including a heat exchange subsystem for pumping heat from the vapour over the column of clean solvent to the column of saturated solution.

Description

SOLVENT EXTRACTION SYSTEM AND METHOD FIELD OF THE INVENTION

The present invention relates to a system and method for extracting a solvent from a solution, that is particularly applicable to extracting pure water from contaminated water such as from sea water or from sewage. BACKGROUND OF THE INVENTION

An acute problem in much of the populated world is an inadequate supply of fresh water of a quality fit for human consumption. Another problem is the safe disposal of sewage. Indeed, the problems are often linked, where sewage seeping into the fresh water supply may cause cholera and other health problems.

There have been several attempts to purify raw sewage, including biological systems reliant on reed beds and appropriate bacteria.

Sea water, on the other hand, has been purified in the past by desalination.

Distillation per se. is known. Distillation systems allow the controlled evaporation and condensation of the water content of contaminated water.

Energy must be supplied to cause the water content of contaminated water to evaporate, and saturated vapor must be cooled to cause the water vapor therein to condense for collection. Prior art systems for desalinating sea water and for distilling the water content of sewage have typically been expensive to set up and costly to operate. Typically such systems occupy large areas of land, which is generally at a premium in regions having high population densities.

The present invention is directed to providing a comparatively cheap to build, compact and economical to run solution to obtaining pure water from sea water or sewage. SUMMARY OF THE INVENTION

In a first aspect, there is provided a distillation system for extracting solvent from a reservoir of solution comprising a solvent containing solute dissolved therein, comprising a pool containing a saturated solution of said solute in said solvent coupled to said reservoir of said solution by a connection; said pool of saturated solution being coupled to a pool of clean solvent by a vapor bridge comprising a first conduit having a first open end submerged in said pool of saturated solution and a second conduit having a second open end submerged in said pool of clean solvent; said first conduit being coupled to said second conduit by a closed bridge having all air evacuated therefrom; said first conduit being sufficiently high that a column of saturated solution is formed therein supported by atmospheric pressure; said second conduit being sufficiently high that a column of clean solvent is formed therein supported by atmospheric pressure; said columns being linked by solvent vapor in said closed bridge; said system including a heat pump for pumping heat from said vapor over said column of clean solvent to said column of saturated solution above pool of saturated solution for cooling vapor over said column of fresh solvent and heating said column of saturated solution; said connection being an inverted U shaped conduit, acting as a siphon, and having a void above fluid surface in bend of said U tube; said connection further comprising a vacuum pump connected to said void for out-gassing purposes.

Preferably, the distillation system further comprises an inner sleeve within the column of saturated solution for facilitating convection heating therein. Preferably, the closed bridge includes a separation valve for dividing said closed bridge into two separate sections, and one way gas release valves in each section at the bend, for evacuating said sections and for filling the closed bridge with liquids when initiating the distillation system.

Preferably, the distillation system further comprises a secondary pump coupled to a spray nozzle for pumping fresh clean solvent and injecting it as a spray into said saturated vapor above said column of clean solvent to seed said saturated vapor and encourage it to condense.

In preferred embodiments, the distillation system further comprises a system for pumping saturated solution of solvent from saturated solvent pool, through a heat exchange grid situated in second conduit above second column of pure solvent and back into column of saturated solution, for cooling solvent vapor on said heat exchange grid thereby warming saturated solution therein.

Preferably, all pumps are driven by a generator which is cooled by a circulating fluid cooling system having a heat exchanger in said column of saturated solution for heating thereof.

Preferably, hot exhaust gases from said generator are exhausted via an exhaust pipe that passes through said column of saturated solution for further heating said saturated solution.

In preferred embodiments, the solvent is water. In one such preferred embodiment, the solute is salt, the saturated solution is brine and the reservoir is a reservoir of filtered sea water coupled via a filtration system to the sea.

Optionally, the pool of brine is covered with an oil layer to further prevent gas adsorption thereinto.

In another preferred embodiment where the solvent is water, the saturated solution is a saturated solution of brine and sewage water and the reservoir is a reservoir of filtered sewage coupled via a filtration system and settling tanks to a sewage main. Here a crust of sewage forms on the saturated brine solution, which may be skimmed off and harvested.

In a second aspect there is provided a method for extracting solvent from a reservoir of solvent containing solute dissolved therein (solution), comprising:

(a) Coupling said reservoir of dilute solution, comprising solvent and solute, to a pool containing a saturated solution of said solute in said solvent by a connection;

(b) Coupling said pool of saturated solution to a pool of clean solvent via a closed vapor bridge comprising a first conduit having a first open end submerged in said pool of saturated solution coupled by a closed bridge having all air evacuated therefrom to a second conduit having a second open end submerged in said pool of clean solvent, said first conduit containing a first column of saturated solution and said second conduit containing a second column of clean solvent; (c) Pumping saturated solution from pool of saturated solution through a heat exchange grid situated over the column of clean solvent and back into said column of saturated solvent, for cooling vapor over said second column of solvent and heating said first column of saturated solution.

(d) pumping heat from a cold plate to a hot plate via a heat pump, said cold plate being situated in conduit over column of clean solvent and further cools the vapors therein, encouraging their condensation;

Said hot plate being situated in the column of saturated solution and serves to further heat said saturated solution.

Preferably, the method further comprises the step of activating a secondary pump coupled to a spray nozzle for pumping fresh clean solvent from pool of clean solvent and injecting it as a spray into said saturated vapor above said column of clean solvent to seed said saturated vapor and encourage it to condense.

Preferably, all pumps are driven by a generator, and the method includes the step of cooling said generator by a circulating fluid cooling system having a heat exchanger in said column of saturated solution thereby further heating the saturated solution in said column thereof.

Preferably, where the generator emits exhaust gases, wherein said exhaust gases are exhausted via an exhaust pipe that passes through and further heats said column of saturated solution.

In preferred embodiments, the method is applied to the extraction of water. In one such preferred embodiment, the solute is salt, the saturated solution is brine and the reservoir is a reservoir of filtered sea water coupled via a filtration system to the sea.

In preferred embodiments, the method is applied to extraction of water from aqueous solutions.

For example, where said solute is salt, said saturated solution is brine and said reservoir is a reservoir of filtered sea water coupled via a filtration system to the sea.

Or, where said saturated solution is a saturated solution of sewage and brine, and said reservoir is a reservoir of filtered sewage coupled via a filtration system and settling tanks to a sewage main.

The saturated solution will typically include precipitated salt which may be pumped away and washed, providing a useful byproduct. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further understood and appreciated from the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a simplified illustration of an open vessel vacuum distillation system in accordance with the present invention, showing the flow of materials therethrough.

Fig. 2 is a schematic illustration of one type of open vessel vacuum distillation system in accordance with the present invention showing the essential engineering details.

Fig. 3 is a schematic illustration of the left leg of the open vessel vacuum distillation system of figure 2, with a cylindrical sleeve therein.

Fig. 4 is a flow chart illustrating the steps involved in using the system illustrated in Figure 2.

DETAILED DESCRIPTION OF THE INVENTION

For clarity, the invention will be described with reference to an exemplary embodiment of a desalination plant. Although described in relation to desalinating sea water, it will be appreciated that, with minor modifications, the equipment portrayed is equally applicable to the treatment of sewage or other types of contaminated or brackish water. Furthermore, other embodiments of the invention having appropriate modifications, such as size and the like, may be used for the selective distillation (fractionation) and refining of chemicals such as oil. Thus, the exemplary embodiments describe an apparatus and method particularly useful for obtaining pure water from sea water or from sewage by distillation. With reference to Fig. 1, the heart of the apparatus includes a vapor bridge 10, which typically resembles an inverted 'U', having a hot side 12 submerged in a pool of concentrated sea water (brine) 14 and a cold side 16 submerged in a pool of fresh water 18. Solvent (water) is evaporated from the concentrated solution in the hot side 12 and condensed at the cold side 16. Fresh solution may be pumped in 20, and precipitated solute (salt) may be pumped out 22. The clean solvent (water) may be removed 23 and used. To drive the system, heat must be supplied to the hot side 12 and removed from the cold side 16. First arrow 26 shows the flow of solvent vapor through the vapor bridge 10, and second arrow 28 shows the flow of heat pumped from the cold side 16 to the hot side 12, which drives the system.

One important feature of the exemplary embodiment is that the distillation takes place in vacuum over an open vessel. A second important feature is that on the hot side of the vapor bridge, water is evaporated from a saturated solution 14 (in case of sea water, brine), and not from regular contaminated (sea water) water, at normal concentration. In this manner, the concentration of dissolved gases in the fluid at the contaminated side is minimized, and thus the vapor pressure over the contaminated water is reduced. Consequently, less energy need be supplied to cause the water content thereof to evaporate. In this manner, the efficiency of the system is enhanced, and significant energy savings are made.

Referring now to Fig. 2, there is shown a schematic representation of an open vessel vacuum distillation system 1 in accordance with a first embodiment of the present invention. The heart of the open vessel vacuum distillation system is an open pool of concentrated brine 14 connected to a pool of fresh water 18 by a closed vapor bridge 10, consisting generally of a 22 meter high, inverted U shaped conduit whose first and second legs 30, 32 are immersed in the brine pool 14 and fresh pool 18, respectively. Brine pool 14 is connected by a connection 34 that is generally an inverted U shaped conduit, to a pool of filtered sea water 36, which is further connected, via a series of filters and / or settling tanks (not shown) to the sea (not shown).

The closed vapor bridge 10 includes a separation valve 38 for dividing the closed vapor bridge 10 into two separate sections 40L, 40R, and valves, such as one-way gas release valves 42L, 42R in the sections 40L, 40R, at the highest points thereof. When initiating the distillation system, the separation valve 38 is first closed and then saturated solution and solvent may be pumped into the two sections 40L, 40R respectively, displacing the air within the closed vapor bridge 10, which may be evacuated via the valves 42L, 42R. In this manner, the two sections 40L, 40R may be filled liquid. Once pumping stops and separation valve 38 is opened, the heights of the columns of water 44, 46 in the legs 30, 32 of the inverted U tube are allowed to stabilize.

In this manner, a water barometer is created, with the heights of the columns of water 44, 46 exactly balancing the weight of the atmosphere, and thereby being a measure of atmospheric pressure. Normal (standard) atmospheric pressure at sea-level is equivalent to 760 mm (29.9213 in) of mercury or 1.03323 kg/sq cm (14.6960 lb/sq in). Since liquid mercury is 13.6 times as heavy as water, the column of fresh water sustained by normal atmospheric pressure is about 10.5 meters high and that of the denser brine solution is about 8 meters high.

The void above the columns of water 44, 46, at the bend of the U tube 10 is filled with saturated water vapor, which, because the fluid at the contaminated water side is a saturated solution, the quantity of dissolved gases and other impurities in the water vapor is kept to a minimum.

An important feature of the preferred embodiment is the addition of a sleeve 48 within the left leg 30 of the vacuum conduit 10. The sleeve 48 is situated in the left leg 30, above the open pool 14 of concentrated brine, and distanced from it. The sleeve 48 has a narrower diameter than that of the left leg 30 itself, and, as shown in expanded view in Fig. 2, allows convection of the saturated solution therein, enabling the solution 44 within the left leg 30 of the vacuum conduit 10 to be heated up without the saturated solution in leg 30 below the sleeve 48 and within the saturated pool 10 itself being heated. In this manner, the saturated solution 44 within the left leg 30 can be brought to boiling by supplying only a relatively small amount of energy.

There are, in fact, four distinct heating systems that are contemplated for heating the column of saturated solution (brine) 44, and powering the open vessel distillation system disclosed herein:

Firstly, a heat pump 50 connected to a hot plate 52 situated within the sleeve 48, and a corresponding cold side heat sink 54 situated in the right conduit 32 above the column of clean solvent 46 therein may be provided. This first system pumps heat from the cold side heat sink 54 to the hot plate 52, heating the saturated solution in column 44, and cooling vapor in right conduit 32.

Secondly, saturated (brine) solution may be pumped out of the pool of saturated solution 14, via pipework 56 connected to a simple mechanical liquid pump 58 and through a heat exchange grill 60 situated within the right conduit 32 at the fresh water side of the vapor bridge 10, over the column of clean solvent 46. The concentrated solution pumped therethrough, cools the steam in the right conduit 32, encouraging it to condense and join the column of clean solvent 46 (fresh water) therein. Likewise, the concentrated solution pumped through the pipe work 56, in passing through the heat exchange grill 60 and cooling the clean solvent vapor, tends itself, to get heated thereby, and eventually raises the temperature of the concentrated solution in the column of saturated solution 44 (brine) making it easier to heat it further. Thirdly, the heat produced by the generator 62 that powers all the pumps 50, 58... may be cooled via a recirculating liquid cooling system, that transfers the heat generated by the generator 62 to a heat exchange grill 64 that is situated within sleeve 48 and further heats the column of saturated solution 44. Fourthly, the generator 62 will typically be fueled by an organic fuel and will emit exhaust gases. Preferably these exhaust gases will be exhausted via an exhaust pipe 66 or chimney that also is preferably passed through a heat exchange grid 68 in the saturated solution 44 column providing further heat for heating the saturated solution therein. The details provided hereinabove are given by way of example only, and for providing the best mode contemplated for the preferred embodiment. It will be appreciated, however, that the design considerations are inherently flexible and are governed, inter alia, by the type of solvent to be extracted, the solution to be purified, the operating temperature, required throughput, price of fuel, space available and the like. For example, where several heating elements are provided therein 52, 64, 68, apertures 70 may be provided in the wall of the sleeve 48 to facilitate convection therethrough, and to allow controlled heating without reverse thermal gradients.

Referring back to Figure 2, the connection 34, as shown, is an inverted U-shaped conduit, whose legs 72, 74 are immersed in the sea water pool 36 and brine pool 14. Since atmospheric pressure can easily support the weights of the columns of water in the legs 72, 74 of the connection 34, the legs 72, 74 remain full of liquid, and the liquid in the two legs 72, 74, is connected via a liquid connection 76. A vacuum pump 78 is provided to help attain and maintain a vacuum 80 in the bend of the U tube 34 above the liquid connection 76. The vacuum pump 78 serves to out-gas the liquid passing through the liquid connection 76, and, due to the vacuum 80 created, the liquid passes across the connection 34 being driven by the siphon effect.

It will be appreciated that heating the column of saturated solution 44 in the conduit 30 over the pool of brine 14 and cooling the solvent vapor in the column 32 over the pool of fresh solvent 18 encourages solvent (water) to vaporize from the saturated solution (brine) column 44 and condense on the clean solvent (fresh water) side 32 of the vapor bridge 10. To encourage condensation at the cooler, clear solvent side 32 a water atomizing system 82 is provided to spray the water vapor with a mist (fine spray) 84 of droplets of solvent. The droplet mist 84 'seeds' the solvent vapor within the right conduit 32, causing the solvent (water) to condense out of the vapor as droplets; essentially rain-like precipitation. The water atomizing system 82 includes an uptake pipe 86 connected by a pump 87 and a vacuum pump 88 to the clean solvent reservoir 18 for drawing clean solvent (fresh water) therefrom, via pump 87, and releasing it as a fine spray 84, through an atomizer nozzle 90 situated within the clean solvent leg 32 of the U tube 10.

Operation of the system shown for distilling sea water, results in salt 92 crystallizing out of solution in the brine pool 14 as fresh water is withdrawn by evaporation through the vapor bridge 10, and filtered sea water is added through connection 34. The salt 92 may be scooped out, dried and used for other purposes.

Referring now to Figure 4, and with further reference to Fig. 2, there is shown a method of purifying sea water, i.e. extracting solvent (water) from a reservoir 36 (sea water pool) of solvent (water) containing solute (salt) dissolved therein, comprising the steps of: (a) coupling the reservoir 36 (sea water pool) of solvent (water) to a pool 14 containing a saturated solution (brine) of said solute (salt) in said solvent (water) by a connection 34 - Step 1; (b) Coupling the pool 14 of saturated solution (brine) to a pool 18 of clean water via an inverted U tube vapor bridge 10 comprising a first conduit 30 having a first open end 31 submerged in the pool 14 of saturated solution (brine), coupled by a closed bridge 10 having all air evacuated therefrom, to a second conduit 32 having a second open end 33 submerged in the pool 18 of clean solvent (fresh water), the first conduit 30 containing a first column 44 of saturated solution (brine) and the second conduit 32 containing a second column 46 of solvent (water) - Step 2;

The distillation is encouraged by causing an appropriate vapor pressure gradient in the vacuum bridge 10. To achieve this, the brine solution in the first column 44 is preferably heated, and in preferred embodiments, a cylindrical sleeve 48 is provided within the first column 30, to assist efficient convection heating of the brine. The generator 62 used for powering all the pumps 50, 58, 88... may be cooled by a cooling system, such as a circulating liquid cooling system including a heat exchange grill 64 that passes through the brine solution in the first column 30 thereby heating that solution and cooling the circulating liquid in so doing. Additionally, where the generator 62 is powered by an organic fuel for example, such as diesel, petroleum or oil for example, the exhaust gases emitted by the generator 62 may be run through an exhaust pipe 66 that is also passed through the brine solution in the first column 44, thereby heating that solution and cooling the exhaust gases in so doing. To facilitate the heating of the column 44 of saturated solution in the left leg 32 of the vapor bridge 10 and to cool the clean solvent vapor above the column of clean water 46 in right leg 32 there may also be provided a further heat pump 50 connected to a cold plate 54 situated in the right leg 32 above the column of clean water 46, and a hot plate 52 situated in the left leg 30 in the column of saturated solution 44 serving to further heat the solution therein. Heat pump 50 pumps heat from the cold side heat sink 54 to the hot plate 52, the cold side heat sink 54 further cools the clean solvent vapors, encouraging their condensation. Optionally, the heating / cooling includes the further step of pumping the saturated solvent from saturated solvent pool 14, through a closed pipe 56, through a liquid pump 58 and on to a heat exchange grid 60 situated in the second conduit 32 above the second column 46 of clean solvent, and back through pipe 61 into the column 44 of saturated solution, thereby cooling the solution vapor on the heat exchange grid 60 and warming the saturated solution therein - Step 4. Preferably, the method includes the further step of pumping cold clean solution from said pool of clean solution 18 and ejecting it, via appropriate nozzle 90, as a spray into the vapor within said second conduit 32 above the second column 46 of clean water to seed the vapor and encourage it to condense - Step 5.

Although described in relation to desalinating sea water, it will be appreciated that, with minor modifications, the equipment portrayed is equally applicable to the treatment of sewage. Furthermore, other embodiments of the invention, having appropriate modifications of size, may be used for the selective distillation (fractionation) and refining of chemicals such as oil.

It will be appreciated that the invention is not limited to what has been described hereinabove merely by way of example. Rather, the invention is limited solely by the claims which follow, in which the word "comprise", and variations thereof, such as "comprising", "comprised" and the like, indicate that the specified components or steps are included, but not generally to the exclusion of other components or steps.

Claims

1. A distillation system for extracting solvent from a reservoir of solvent containing solute dissolved therein, comprising a pool containing a saturated solution of said solute in said solvent coupled to said reservoir of said solvent by a connection; said pool of saturated solution being coupled to a pool of clean solvent by a vapor bridge comprising a first conduit having a first open end submerged in said pool of saturated solution and a second conduit having a second open end submerged in said pool of clean solvent; said first conduit being coupled to said second conduit by a closed bridge having all air evacuated therefrom; said first conduit being sufficiently high that a column of saturated solution is formed therein supported by atmospheric pressure; said second conduit being sufficiently high that a column of clean solvent is formed therein supported by atmospheric pressure; said columns being linked by solvent vapor in said closed bridge; said system including a heat exchange subsystem for pumping heat from said vapor over said column of clean solvent to said column of saturated solution above pool of saturated solution for cooling vapor over said column of fresh solvent and heating said column of saturated solution; said connection being an inverted U shaped conduit, acting as a siphon, and having a void above fluid surface in bend of said U tube; said connection further comprising a vacuum pump connected to said void for out-gassing purposes.

2. The distillation system of Fig. 1 further comprising an inner sleeve within the column of saturated solution for facilitating convection heating therein.

3. The distillation system of claim 1, wherein the closed bridge includes a separation valve for dividing said closed bridge into two separate sections, and one-way gas release valves in each section at the bend, for evacuating said sections and for filling the closed bridge with solution when initiating the distillation system.

4. The distillation system of claim 1, further comprising a secondary pump coupled to a spray nozzle for pumping fresh clean solvent and injecting it as a spray into said saturated vapor above said column of clean solvent to seed said saturated vapor and encourage it to condense.

5. The distillation system of claim 1, further comprising a system for pumping saturated solution of solvent from saturated solvent pool, through a heat exchange grid situated in second conduit above second column of pure solvent and back into column of saturated solution, for cooling solvent vapor on said heat exchange grid thereby warming saturated solution therein.

6. The distillation system of claim 1, wherein all pumps are driven by a generator which is cooled by a circulating fluid cooling system having a heat exchanger in said column of saturated solution for heating thereof.

7. The distillation system of claim 1, wherein hot exhaust gases from said generator are exhausted via an exhaust pipe that passes through said column of saturated solution for further heating said saturated solution.

8. The distillation system of claim 1, wherein the solvent is water.

9. The distillation system of claim 8, wherein, the solute is salt, the saturated solution is brine and the reservoir is a reservoir of filtered sea water coupled via a filtration system to the sea.

10. The distillation system of claim 8, wherein the pool of brine is covered with an oil layer to further prevent gas adsorption thereinto.

11. The distillation system of claim 8, wherein the solvent is water, the saturated solution is a saturated solution of brine and sewage water and the reservoir is a reservoir of filtered sewage coupled via a filtration system and settling tanks to a sewage main. Here a crust of sewage forms on the saturated brine solution, which may be skimmed off and harvested.

12. A method for extracting solvent from a reservoir of solvent containing solute dissolved therein, comprising:

(a) Coupling said reservoir of solvent to a pool containing a saturated solution of said solute in said solvent by a connection;

(b) Coupling said pool of saturated solution to a pool of clean solvent via a closed vapor bridge comprising a first conduit having a first open end submerged in said pool of saturated solution coupled by a closed bridge having all air evacuated therefrom to a second conduit having a second open end submerged in said pool of clean solvent, said first conduit containing a first column of saturated solution and said second conduit containing a second column of solvent;

(c) Pumping saturated solution from pool of saturated solution through a heat exchange grid situated over the column of clean solvent and back into said column of saturated solvent, for cooling vapor over said second column of solvent and heating said first column of saturated solution;

(d) pumping heat from a cold plate to a hot plate via a heat pump, said cold plate being situated in second conduit over column of clean solution and further cools the vapors therein, encouraging their condensation; said hot plate being situated in the column of saturated solution of solvent and serves to further heat said solution.

13. The method of claim 12 further comprising the step of activating a secondary pump coupled to a spray nozzle for pumping fresh clean solvent from pool of clean solvent and injecting it as a spray into said saturated vapor above said column of clean solvent to seed said saturated vapor and encourage it to condense.

14. The method of claim 13, all pumps being driven by a generator, the method including the step of cooling said generator by a circulating fluid cooling system having a heat exchanger in said column of saturated solution thereby further heating the saturated solution in said column thereof.

15. The method of claim 14, the generator emitting exhaust gases, wherein said exhaust gases are exhausted via an exhaust pipe that passes through and further heats said column of saturated solution.

16. The method of claim 13, being applied to the extraction of water from aqueous solutions.

17. The method of claim 16, the solute being salt, the saturated solution being brine and the reservoir being a reservoir of filtered sea water coupled via a filtration system to the sea.

18. The method of claim 17, the pool of brine is covered with an oil layer to further prevent gas adsorption thereinto.

19. The method of claim 16, the saturated solution being a saturated solution of brine and sewage water and the reservoir being a reservoir of filtered sewage coupled via a filtration system and settling tanks to a sewage main; wherein a crust of sewage forms on the saturated brine solution which may be skimmed off and harvested.

20. The method of claim 16, salt being precipitated from the saturated solution, said salt being harvestable as a useful byproduct.