Self-regulating vacuum still

A self-regulating vacuum still (8) has a fluid reservoir (10), a boiler (28), a vapor separator (46), a condenser (33), and a condensate reservoir (58). The boiler (28) receives fluid from the fluid reservoir (10) in liquid form and heats the fluid to generate fluid vapor, preferably using evacuated solar tubes (44). The vapor separator (46) receives the fluid vapor from the boiler (28) and separates entrained moisture. Preferably a packing (50) is provided by structured wire mesh which is disposed in a vapor outlet (49) from the vapor separator (46). The condenser (33) receives the fluid vapor from the vapor separator (46), and cools the fluid vapor to a condensate. The condenser (3) has a collection section (34), a condensate section (35) and an outlet (16) which is proximate to the collection section (34) and the condensate section (35). An airlock (20) is connected to the outlet (16) for venting air and fluid vapor from the condenser (33) when a preselected pressure is exceeded. A condensate reservoir (58) is connected to the condenser (33) for receiving condensate.

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates in general to vacuum stills, and in particular to vacuum stills which use the weight of a fluid column to create a vacuum and which, at least in part, drives distillation.

BACKGROUND OF THE INVENTION

Clean water is necessary for human health and well being. Evaporating and condensing of water, in natural processes such as the water cycle and in the man-made processes of distillation and desalination, cleans water of most or all impurities. However, the high specific heat of water and other liquids of moderate volatility means an expensive expenditure of energy is required, for distillation and desalination.

Many inventions have used a vacuum to reduce vapor pressure and achieve evaporation with less energy for heating. These include use of a barometric column of condensate, a technique derived from barometers and the ancient observation that water cannot be siphoned at a height exceeding 10.3 meters—“nature abhors a vacuum,” as Aristotle theorized. In these inventions, the barometric column of condensate has been used to pull an initial vacuum, and/or as a pulling counter-weight to slow the loss of vacuum in an evaporative stage, and in other novel manners.

Many inventions have used solar energy and ambient temperature differences, alone or in combination with vacuums, to increase the heat-energy efficiency of evaporation. Related inventions have used various mechanical devices, series of chambers, stop-cocks and valves, gauges and timing sequences to achieve greater efficiency of evaporation and condensation. Some have used vents, for filling the system initially, and for periodic evacuation of air entrained in water, usually using mechanical vacuum pumps. The Newcomen engine used a “snifting clack,” a valve so-named because it sounded like a congested man breathing out his nose, to relieve air entrained in water that built up in his vacuum-driven piston cylinder. Some of the inventions require a high degree of oversight and control in their operation, and most need periodic system purges and maintenance of various pumps and active devices.

There may be a need and a market for a simple system that is self-starting and self-stopping. Preferably, such a system would not require either energy-consuming devices for its operation or need for regular oversight to function. The system would also use the force of gravity working on a column of condensed water to create vacuums and reduce heat energy expenditure. Preferably, the thermal “delta” or difference would create an evaporation region and a condensation region which could be established passively, with low-cost or free energy. A system is needed that incorporates all the aforementioned features and yet still scales well, to be affordable to private citizens as well as public utilities or private corporations. A system, finally, designed to use natural changes in outdoor temperature to its advantage, would be robust, forgiving, and desirable.

SUMMARY OF THE INVENTION

A novel self-regulating vacuum still is disclosed having a fluid reservoir, a boiler, a vapor separator, a condenser, and a condensate reservoir. The boiler has a fluid section which includes a liquid portion and a vapor portion. The liquid portion is in fluid communication with the fluid reservoir for receiving the fluid from the fluid reservoir with the fluid disposed in liquid form in the liquid portion of the fluid section. A one-way flow control valve preferably disposed there-between the fluid reservoir and the fluid section of the boiler. The fluid is heated in the boiler to generate fluid vapor, preferably using heat provided by evacuated solar tubes which is conducted to the fluid section. The vapor separator receives fluid vapor from the boiler along with moisture entrained with the fluid vapor, and separates the entrained moisture from the fluid vapor. The vapor separator has an inlet with an end segment having perforations for passing the fluid vapor, with the perforations preventing foaming of the fluid vapor. The vapor separator further includes an enclosure which has a cross-sectional area which is larger than a cross-sectional area of the vapor portion of the fluid section of the boiler. A vapor outlet is located between the vapor separator and the condenser, and structured wire mesh is disposed in the vapor outlet for capturing the moisture entrained in the fluid vapor.

The condenser has a vapor collection section and a condensate section which sequentially receive the fluid vapor from the boiler and the vapor separator, and then cool the fluid vapor to a condensate and receive the condensate in the condensate section. A condensate level is defined between the fluid vapor and the condensate, and the condensate level is located beneath the vapor collection section. An outlet is disposed in the condenser, proximate to the collection section and the condensate section. An airlock is connected to the outlet for selectively venting fluid vapor from the condenser when a preselected pressure is exceeded within the condenser. A condensate reservoir is disposed in fluid communication with the condensate section of the condenser for receiving condensate. The condensate reservoir has a dispensing valve for selectively passing the condensate therefrom.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures,FIG. 1graphs an exemplary cycling of the system, its two phases, stages, and several periodic iterations that complete and comprise one cycle. System pressure, represented qualitatively but not quantitatively by the Y-axis, is graphed along a solid line against time on the X-axis. Above the line is positive pressure and below the line is a vacuum. The rate of evaporation, represented qualitatively but not quantitatively by the secondary right-hand Y-axis, is graphed along a soft dotted line, also against time on the X-axis. The graphs are here provided to explain stages typical in operation.

The system starts where it had ended in the previous cycle, in a full and pressure-positive stage6, where evaporation is still and thus the system is at equilibrium. The default assumption is a constant amount of heat, such as from sunlight, entering the system. To begin the cycle, here we dispense along region1the full column of condensed water, forming a vacuum. With heat entering the system, and a vacuum now formed, evaporation generates vapor which begins to fill the vacuum along curve2until near-atmospheric pressure is reached at region3. Evaporation continues steadily as excess pressure is vented along region3, as will be described below, until heat is removed in section7. This stage of cooling shown by section7could be caused, as examples, by diurnal temperature variation, by cloud cover, by rain, or by a removal of the heat source. Here it is shown as a consistent cooling duration and amount. It induces a drop in pressure in region4, as gas expanded by heat now contracts. As the cooling period of section7ends, this trough in pressure in region4ends, and evaporation resumes while venting along section3.

Once the system fills up with condensate, the cycle enters the next phase, demarcated at point5. Here pressure rises beyond near-atmospheric for the first time, rising until it reaches a maximum at point6. This is the full phase of the cycle, wherein evaporation has mostly subsided. A very modest amount of evaporation may continue after drops in pressure along region4due to cooling in section7; once heat resumes, however, this evaporation eventually stops once the system is completely full of condensate.

Now referring toFIG. 2, a schematic diagram of a self-regulating vacuum still8shows the parts of a basic embodiment. Water level32and condensate level37are shown as they would correspond to specific numbered stages of the cycle inFIG. 1. A reservoir10for the water supply is preferably open to atmospheric pressure. The vacuum still8has boiler28and a condenser33. Water is contained in the boiler28within a fluid section29, which has a liquid portion30and a vapor portion31. The interface between the liquid portion30and the vapor portion31defines a liquid level32. The lower end of the fluid section29is preferably sealed with a cap26, which may be provided by a plug, cap, or valve, provided it is air-tight. The condenser33has a collection section34and a condensate section35. Water vapor from the boiler28enters the condenser33and is collected in the collection section24. A vapor leg14is defined to extend from the vapor portion of the fluid section29of the boiler28, through the collection section24of the condenser33and into the condensate section35, terminating above the condensate column36. The interface of the vapor leg14and the condensate column36define the condensate level37.

The condenser33further has an outlet16which is located in an upper portion of the condensate section35, proximate to the collection section34. A tube18has an interior terminal end which extends from the outlet16to define a chamber for collecting air entrained in the water from reservoir10and water vapor. An airlock20is mounted on the exterior terminal end of the tube18to provide a one-way valve for venting the collected air and water vapor when excess pressure is encountered within the vacuum still8. In some embodiments, the airlock20may be replaced by a check valve which is configured to vent air and water vapor when the preselected pressure is exceeded. A dispensing valve22allows the condensate column36to be drained, or dispensed, via the U-shaped pipe type gas trap24.

Water is available through a gently rising water inlet12to the vertical section comprising the vapor leg14of the system. The boiler28is preferably a region where heat is applied to the fluid section29. Heat is preferably provided by sunlight striking the exterior of a tube or other structure providing the fluid section of the boiler28, in order to achieve evaporation. The water evaporates from the surface of liquid level32and fills the vapor leg16, including both the vapor portion31of the fluid section29and the collection section34of the condenser33. The water vapor in the collection section34of the condenser33is then cooled and condensed to a liquid condensate, and the condensate is received in the condensate section35and collected in the condensate column36. The liquid condensate then fills the condensate column30, raising the condensate level36, depicted as a height range. The condensate column36is the stacked volume of condensate.

Now the cycle will be explained in detail, referring toFIG. 2and as it corresponds toFIG. 1. During the filling phase, to the left of demarcation at point5inFIG. 1, the liquid level32is free to rise or fall modestly as pressure in vapor leg14varies. Opening the dispensing valve22will drop the condensate column36until it reaches the bottom marking of the height range for condensate level37, as it balances a vacuum created in the vapor leg14inside the system with atmospheric pressure outside. This vacuum-forming event is marked by region1on the graph inFIG. 1.

As heat is applied around region28, liquid evaporates, fills the system with its gas pressure, and condenses, filling the condensate column36and raising the condensate level37. First the vacuum is filled by evaporate, as marked along curve2on the graph ofFIG. 1, then evaporate gas in excess of the back pressure of a liquid-filled airlock20will vent out, as marked at part3inFIG. 1and also depicted inFIG. 2. In other embodiments where a one-way check valve is used in place of an airlock20, evaporate gas will vent when the cracking pressure of the one-way check valve is exceeded. With heat removed in region7of the graph ofFIG. 1, evaporation stops and pressure drops to point4, as depicted by the drop in the graphed rate of evaporation, and much condensate forms, in both the boiler28and the condenser33. The system remains as depicted inFIG. 2during these stages, until the condensate level37fills to its top marking.

Now referring toFIG. 3, the condensate column30has risen to close the outlet16. The collection section34is now sealed off from the outlet16and the airlock20. Referring toFIG. 1, the system is now in the full phase of the cycle, graphed to the right of demarcation5. Pressure can now build above atmospheric, as marked at the maximum pressure point6on the graph. During cooling in region7, pressure can still drop in troughs4, with a very slow rate of evaporation occurring. Now referring toFIG. 3, the pressure build above atmospheric raises the vapor pressure in the vapor leg14, shutting off evaporation as heat input and heat loss remain steady. This pressure build up can also push the height of condensate in the outlet level37up to its top marking. If pressure in the vapor leg14pushes the top outlet level38high enough, condensate will flow freely out of the airlock20, thus acting as an emergency pressure relief valve for the vapor leg14. Due to the increased air pressure, liquid level32may sit lower in the fluid section29. With the condensate section35full of the condensate, the condensate column36is ready to be dispensed again, back to the region1of the curve inFIG. 1.

FIG. 4is a schematic of a second self-regulating vacuum still40which produces sterile distillate. The vacuum still40has a boiler28, a vapor separator46and a condenser33. The boiler28has a heated enclosure42which houses a fluid section29and evacuated solar tubes44. Preferably, the enclosure has a window that allows light through, but as with a greenhouse, traps the heat in the enclosure42. Note that the enclosure42may be provided by an insulated glass enclosure, for example, or it could also be of another type such as a heating chimney connected to a combustion stove, that opens to the atmosphere just below the vapor separator46. Fourteen evacuated solar tubes44are shown, but a different number may be used. Further, the evacuated solar tubes44could be substituted for a vertically stacked series of parabolic trough solar collectors, to provide heating for the boiler28. Impurities, saline slurry, and substances that are not evaporated will accumulate in the drain54. In the case of desalination, the drain54can be partly opened to separate out concentrated saline slurry, for example out a U-shaped pipe outlet onto an evaporating pool for salt production or disposal.

The fluid section29of the boiler28is preferably an elongate tube which includes a liquid portion30and a vapor portion31, with a liquid level32defined at the interface between the liquid portion30and the vapor portion31. As noted above, the volume of the respective liquid portion30and the vapor portion31will vary along with the liquid level32during various evaporative cycles for the vacuum still40, as noted above in reference toFIG. 1. The evacuated solar tubes44are preferably in direct contact with the fluid section29for conducting solar heat to the fluid disposed in the fluid section29. In embodiments where metal piping is used to provide the fluid section29, the evacuated solar tubes44would have direct metal contact with the piping and other structure providing the fluid section29for conducting collected solar heat. The fluid section29includes a liquid portion30and a vapor portion31. Impure water is added into the water supply reservoir10and can flow up through a check valve41and the rising water inlet12into the fluid section29for heating to become a vapor. The water level32will settle at some height until it is heated above boiling point for a particular pressure within the fluid section29, and individual columns of water vapor as steam will push up the fluid section29through a porous and capped end segment47into an inlet45for the vapor separator46.

The vapor separator46has an enclosure48which preferably has a larger cross-sectional area than the structure of the vapor portion31of the fluid section29. The larger cross-sectional area allows moisture droplets entrained in the vapor to more readily drop out of the vapor. The enclosure48also allows sufficient surface area for water to vaporize properly, without constraint by surface tension effects along pipes and provides enough volume to prevent vacuums from siphoning water up the fluid section29. The larger cross-sectional area of the enclosure48also enables distillation through evaporating up and condensing back down the fluid section29. The end segment47is capped to stop foaming or shooting up, and is porous to be a drain down the fluid section29as well as the inlet. The vapor separator46has an outlet49which passes water vapor from the enclosure48to the condenser33. A packing50is disposed in the outlet49to remove moisture droplets from the water vapor. The packing50is preferably a structured wire mesh. The vapor separator46also has an emergency pressure relief valve52.

Evaporate leaves vapor separator46and passes into the condenser33where it is cooled in the collection section34and the condensate section35, and then collected as part of the fluid column36located in the lower end of the condensate section35. If air pressure exceeds the vent pressure of the airlock20, the pressure will release through the outlet16, the drape pipe56to exit the airlock20into atmospheric pressure outside. The drape pipe56drapes the airlock20so that air is released downwards. This has the advantage known to those skilled in sterile technique in biological laboratories, namely that less dust and microbial particulate will have a chance to enter an orifice upwards against gravity. This also has the advantage that no rain water can pool on its outside surface. At the lower end of the condensate section35of the condenser33is a condensate reservoir58. This is where clean water is stored. Evaporate condenses and fills until the condensate level36surpasses the outlet16and pressure builds until boiling ceases and it enters the full phase of the cycle.

The condensate level60in the reservoir58is depicted in an early stage of filling, where the condensate level37is only a short height above the condensate leg drain62where it enters the reservoir58. As the condensate column36fills higher and higher in the condensate section35, the reservoir level60will also rise. The pressure will also rise in the ullage64of the reservoir58, which will push and hold the condensate column36up. Note that it is possible for the pressure in the ullage64to push the fluid level60of the reservoir58down below the condensate leg drain62pipe entrance. This pressurized air in the ullage64would release up the condensate column36and into the vapor leg inside the condenser33. Note that it is also possible for pressure in the ullage64to entrain all of its air into water dispensed over time through the dispensing valve22, until there is no longer an air pocket in the ullage64, but rather only a liquid phase volume of condensate.

Mineral rock66is added to the condensate reservoir58to make the condensed distillate into drinking water. Preferably the self-regulating still40ofFIG. 4as depicted would produce sufficient water for one household's drinking water needs. Note that the condensate reservoir58could also be connected at a distance by pipe to the condensate leg drain62, for example inside a building, to serve as a water-cooler. When drinking water is dispensed through a spigot such as the dispensing valve22, condensate reservoir58has the advantage of being pressurized and self-filling, regardless of the stage or phase of the system cycle. The condensate reservoir58, and every component of the system that contacts the evaporate and especially the condensate, are preferably comprised of a material with a low solids leach-rate, such as a vitrified ceramic, glass, or low-oxidizing metal, whose interior surfaces may be further sealed with a wax or inert polymer.

The vacuum still of the present disclosure provides advantages of a self-starting and self-regulating vacuum still for producing clean water. The pressure outlet provides the advantage of self-starting, as long as there is a thermal gradient to sustain evaporation in the boiler and condensation in the condenser. Another advantage it provides is the self-filling of the barometric column of condensate in the condensate section. Another advantage is that air entrained in liquid and released under vacuum, which builds up in the condenser, is also vented by the pressure outlet through an airlock or a one-way check valve, which takes out the maintenance requirement of purging the system. If the height of the condensate section were to significantly exceed 10.3 meters, then this system would additionally have the efficiency-improving advantage that the condensate column provides a counter-weight and full vacuum, i.e. constitutes a barometric leg, during most of the filling phase. However, as the system is driven primarily by the temperature gradient, the vacuums formed by gravity and cooling are used to increase the rate of evaporation during the filling phase and thus serve a supporting role in production of condensate. Positive pressure build-up is designed into the system to allow it the advantage of being self-stopping during the full phase.