GB2403162A - Desalination of sea water by barometric vacuum distillation - Google Patents

Abstract

In a desalination apparatus, seawater is raised barometrically to a level BH dependent on atmospheric pressure, Volume X, above which is a barometric vacuum, Volume Y. The system is heated, preferably by solar energy, and water evaporates from volume X at reduced boiling point. Cool seawater enters through Input B, leaves through Output A, and condenses the pure water, which is collected. The apparatus comprises a column consisting of concentric tubes. The apparatus further comprises a number of valves, pumps and heat exchangers. Further embodiments of the invention are able to float or may be land based, by placing in a hole in the ground.

Description

24031 62 Evaporative Seawater Desalinator This invention is based upon a

novel method of separating sea-, salt-, brackish and other impure water into brine and pure water.

A headline across the top of page 10 of the London Observed on Sunday 1st June 2003 reads PA billion thirst for clean watery This is followed by Across the globe it (Safe water) is a matter of life and deaths An objective of this invention is to provide clean, distilled water from seawater using, preferably, local and cheap fomms of energy such as that obtained from wind, waves and the sun.

A method of distilling seawater using barometric vacuum to lower the boiling point and thus use less and local atmospheric fomms of energy. The "Free" atmospheric vacuum is used to lower the boiling point of seawater so that energy hitherto used to raise the temperature of the water to its normal boiling point is not needed.

Heat is still needed to raise the temperature of the water from its ambient temperature to its lowered boiling point and it is envisaged that a large proportion of this heat would be taken from the wamm output of brine and pure water. This heat would be re-used to heat the incoming water. Heat from other sources, possibly waste" heat from other processes could and should be utilised.

An atmospheric or Torricellian vacuum may obtained, using mercury, which is some 12 times more dense than water, by submersing a glass tube some 120 cm long, closed at one end, fully, horizontally so that it is submerged, in a bath of mercury. If the closed end is raised until the tube is vertical, the air pressure, pressing down on the surface of the mercury, will maintain the column up to a certain height only. Above that height will be a vacuum. The height will vary from day to day and will be about 11 Ocm. The same principle will apply to an inverted U-tube. The same effect will occur if water is substituted for the mercury with alteration that the tube will now have to be over 13m long and the daily variations would be much greater.

If, then, using a water-filled U-tube a barrier is put in a pool so that each leg of the tube is, in effect, in a separate pool we could apply heat at the vacuum surface level at one side and take heat away (Cool it) from the other. The effect would be that water would boil or evaporate from the heated side and condense on the cooled side. If the heated side contained salty water only pure water would evaporate and be condensed.

A possible embodiment of the invention will have three discrete parts, viz., the upper, middle and lower sections. The product is circular or polygonal when viewed from above.

High pressures would exist and the stays, struts, ties, supports and stringers needed to give the structure strength and rigidity to perform its work, have been left out. Fig 1 is cross section of the upper part through input B of one segment and output A of the opposite one.

The significant parts of the design of the upper part are: The evaporation surface exists at the meeting of Volumes X and Y. It is monitored by a float Detector A (Compare this with a flushing lavatory cistern or a car fuel gauge tank sender) at the Torricellian, barometric height (BH) above the surface level. At this level, the seawater which had not evaporated would just overflow into the brine extraction route i. e. through Output C. Seawater would arrive at this level and be maintained there by air pressure up through Input A. Water heated by, and from, wamm brine and distilled pure water, and solar energy, (and possibly other external sources) would be maintained at just above this level so that it would boil at a temperature below 100 degrees C. Heat pumps and exchangers would extract as much heat as is feasible to be used to heat the incoming seawater. The surface below the boiling seawater would be matt black to absorb radiant energy from the sun and would also have electrical heating elements upon its surface to supply heat obtained from wind and wave generators. In addition, if there were a local source, electricity from an external source could be utilised. The brine could be released back into the sea, downstream of any current, if there were no demand for evaporated sea salt or its use was not needed for further processing. There would have to be a non- return valve (Valves C and D) on the brine and distilled water outputs to protect the vacuum.

The Torricellian barometric vacuum volume exists above the evaporation surface (Volume O. It is subject to the greenhouse effect from the sun's rays entering from above. Its state, initially, will be one of near vacuum. It will then vary up to saturated water pressure and beyond until it is filled with air boiled out of the seawater. Detector B' a barometer in effect, would monitor this. The air dissolved in water is a problem and it, when boiled out of the seawater, will degrade the vacuum. It will be removed when required. See later.

The area above the vacuum consists of two shallow layers (Conical in the round) of glass, plastic or other transparent material. In the volume between the two layers would flow the input volume of fresh seawater, which would be pumped from the coolest stratum of the sea. The fresh, relatively cool seawater would enter through Input B and leave through Output A. It would have to be pumped for it would have to rise above the level of its barometric height. The lower surface of the lower layer would be ribbed to allow water vapour to condense and then flow down the lower surface for collection. This level could be made in separate sectors so that fresh seawater could flow up from the edge to the top go round and go down the other half of that sector (Fig 2).

The column consists of concentric tubes and has two purposes. It must hold the surface of the evaporating water at the barometric height and also provide heat exchange from the hot brine and the distilled water to the incoming seawater. Additional supporting columns must be provided to ensure that structural rigidity and stability is maintained. If it is decided to leave the column out, other means of support must be found for the upper part and an alternative method of heat exchange employed. Fig 3 shows the seawater-floating version with its column which supports the upper part and transports and allows heat exchange between the liquids. Other supporting structures must be employed.

The base, in addition to supporting the weight off all the above whilst floating, must also maintain the correct barometric height of the evaporating surface. It does this by pumping air into Volume Z through Pump A under the control of Detector A. The role of Pump B is to pump the pure, cool seawater up and over the vacuum in Volume Y to offer a condensation surface for warm water vapour in the vacuum. Valves C and D are non-return valves in the output pipes for brine and distilled water. They are there to maintain of both in one direction (Out) and to prevent external air pressure from destroying the vacuum.

Two possible examples of the invention are shown as Fins 3 and 4. The floating version is shown in Fig 3, After the apparatus had been manufactured and tested, Volume Z would be filled with air from Pump A so that it would float with Valves A and B closed. When the apparatus had arrived at the place of use it would be towed into seawater deep enough to immerse the whole thing. A hose, the other end of which was held above the surface of the sea, would be attached to Pump A and Valves A and B would be opened. Pump D would be bypassed by Valve F which would be opened, temporarily, to allow seawater to flood into all of the invention driving the air within out of Valves A and B. The whole thing would sink under its own weight with all parts being filled with seawater. When Valves A and B were at the level of the sea surface Valves A, B and C would be closed. Pump A would then pump air from the surface (Through the hose) into Volume Z which would cause the apparatus to rise in the water and float. The rise would cease and Pump A would cease working when Detector A (Effectively a float valve) detected that water had reached its barometric level.

Volume Y would contain a vacuum. Pump A would work with Detector A to maintain this level by pumping air into Volume Z. Pump D would then pump seawater from below Volume _ up, over Volume Y through the outemmost of a series of the concentric pipes which Seawater contains dissolved air and this would be boiled out and would eventually destroy the vacuum in Volume Y. When this happened, detected by Detector B. the process as described when the apparatus was commissioned (Towing out into deeper water opening and closing Valves A and B etc.) would have to be executed. The air will accumulate in Volume Y and will have to be released through Valve B. Not much air will need to be released through Valve A but it will have to be done because air has a lesser cooling effect than water.

Additional heat would increase the evaporation of the seawater in Volume X. This could be provided by wave generators of electricity around the outer circumference around Volume Z together with wind generators and solar power panels on the shore. This electricity need not be of high quality as its use would be to provide heat on the lower blackened surface (To absorb the radiant sunlight through the glass above Volume Y) through electrically resistant wires. Some electricity would be stored in accumulators to operate the pumps. The more heat provided the greater will be the output of pure water.

Fig 4 shows a land-based embodiment of the invention envisaged to be placed at the top of the beach in a hole six or seven metres deep. The invention, in this manifestation, would be unstable and would have to be supported in the upright position by posts with wheels to allow for its vertical movement. It is irrelevant which type of upper part were used. When the apparatus had been fully built and tested in its hole, the hole would be flooded with seawater by Pump C. Valve E would be opened and Pumps D and B operated. Valves A and B would be opened to allow the air to escape as seawater was pumped in. When detector E showed water had reached its working level, Valves C and D would be opened to clear the output pipes of air. When air ceased to exit, being replaced by seawater, these valves would close. Pump D would continue to operate until seawater came out of Valves A and B. Then Pump D would be fumed off and Valves A. B and E would be closed. Pump B would continue to operate. The whole apparatus would be full of water.

Pump A would then start to pump air into Volume Z. and would continue to do so until detector A registered that the evaporation surface was at the correct level. Pump A would stop then because evaporation into the vacuum of Volume Y would have started. Pump A. a bi-directional air pump would then pump air into and out of Volume Z under the control of Detector E. This would maintain the evaporation surface at the maximum level until Detector B detected that the air boiled out of the seawater had degraded the sufficiently to warrant that the apparatus required flooding once more.

Subsequent to each flooding the water output would be contaminated by the saltwater left in the pipes. This could be at such a low level as to be ignored. The salt could be detected by testing with silver nitrate or by tasting it. One possible solution could be to alter Valve C into a switching valve, as well as being a non return valve, which would divert the output back into the hole for a period sufficient to deal with the seawater content left in the pipes.

Claims (1)

1. An objective of this invention is to provide clean, distilled water from seawater using preferably local and cheap forms of energy such as that obtained from wind, waves and the sun. The system operates by evaporation. The boiling point of the water is reduced by utilising the free, natural vacuum achieved by lifting the water, in a closed vessel to its barometric height. The cost reduction will result from a lower energy input due the envisaged average boiling point being around an envisaged average of 70 degrees C., An objective has been to use locally available materials and methods of construction. The realization of the method will vary from area to area depending upon local resources and skills.

   An objective is to utilise Waste heat from electricity generating stations, refineries etc. if they are close, to cool their outputs usefully