Patent Application
20230150838
This invention relates to the production of potable water by the desalination of saline water. In general, the potable water shortage is becoming more and more acute. Conflicts over potable water are already taking place with increasing frequency. There are continuous efforts to convert more sea or saline water into potable water.
The two common desalination technologies of importance are SWRO (Sea Water Reverse Osmosis) and thermal distillation.
In SWRO, sea water is pumped at high pressure through a water permeable membrane. Water, the product, permeates through the membrane. Soluble salt content in the sea water is retained by the membrane, and the amount of salt in the membrane increases over time. The salt must be discarded when its concentration reaches a high level, typically between 20-50% of the feed water. The entire process is very energy intensive.
Thermal distillation is another process widely employed to produce potable water. The process, as the name implies, consists of boiling sea water, and condensing the vapor (steam) to produce potable water. When water is boiled off, soluble salts are left behind in the remaining seawater. The solution becomes more and more concentrated with salt, which then has to be discarded to prevent damage to the equipment. Typically, around 20% of the feed is used, whereas the balance of around 80% has to be discarded. The process is very energy intensive.
These two commercially significant processes require enormous amounts of energy of either fossil fuels or fossil fuel derived energy. In addition, waste disposal is a significant drawback. Both processes produce very large amounts of waste, i.e., highly saline water that must be discarded. Treating this waste is difficult and expensive. Ocean disposal causes damage to the marine environment.
In a conventional heating process used in distillation, the heat is transferred between two media which are separated by a barrier between them. The barrier, usually a metal or a material such as graphite, enables the heat transfer but prevents the mixing of fluids from opposite sides of the barrier. The present invention eliminates the need for such barrier.
The present invention provides a method and apparatus for desalination of water, using a distillation process which is powered by solar energy. In the present invention, a solid material is heated by solar means, and the solid material heats the saline liquid by direct contact. Thus, the present invention eliminates the use of any barrier between the heated solid material and the liquid to be heated.
The hot solid material is introduced at the top of a chamber or tower and sinks to the bottom, transferring heat to the saline liquid which is pumped upward in the chamber. The solid material is preferably an impervious material such as silicon carbide, quartz, graphite, ceramics etc.
The saline water is heated and evaporates. The water vapor is then guided through pipes and heat exchangers to a barometric condenser. The vacuum created by the barometric condenser not only condenses the vapor, thereby producing water as a product, but also creates the condition in the equipment for the efficient removal and recovery of remaining salts in the saline water.
After having been used to heat the water, the solid material is extracted, renovated, and recycled to continue the process.
The retrograde salts, calcium carbonate and calcium sulfate, precipitate due to a high saline temperature, and are removed by a desludging unit. The halides NaCl and MgCl2 undergo crystallization and finally precipitate in two separate chambers where they can be removed as solidified salts. Therefore, the process is a ZLD (Zero Liquid Discharge) process as there is virtually no liquid discharge at all.
The present invention therefore comprises an efficient and economical process which combines barrier free solar heating and vacuum cooling, while eliminating or substantially mitigating the disadvantages discussed above.
The present invention therefore has the primary object of providing a desalination process which is powered by solar energy.
The invention has the further object of providing a desalination process which uses thermal distillation, and in which saline water is heated by direct contact with a hot solid material.
The invention has the further object of providing an efficient process for desalination, while also producing commercially useful residues from the saline water being treated.
The invention has the further object of producing potable water, and other products of commercial use, while generating a minimum of waste, and while minimizing the overall costs of maintenance and energy.
The invention has the further object of providing an apparatus which performs the above-described functions.
The reader skilled in the art will recognize other objects and advantages of the invention, from a reading of the following brief description of the drawings, the detailed description of the invention, and the appended claims.
In brief, the process of the present invention is as follows. First, solid material (preferably having the form of a plurality of small solid balls) is heated by solar means, outside a vessel or chamber. The heated balls are introduced into the vessel, at or near its top or upper region, while saline liquid is pumped upward within the vessel. The balls fall by gravity through the vessel, while continuously contacting the liquid. The balls heat the liquid so as to cause the liquid to vaporize, thus separating the liquid from the salts carried by the liquid. In this way, the process produces potable water and one or more solid residues which can be commercially useful. The solid balls are recovered from the bottom or lower region of the vessel, and are renovated and then reheated and reintroduced into the vessel without interrupting the process.
The term “renovated”, as used in this specification, means the removal of scale deposits which form on the surfaces of the solid material, as a consequence of the contact between the hot solid material and the saline liquid.
Scales form when soluble salts extracted from saline liquid become deposited on warm surfaces. Such scale formation interferes with heat transfer surfaces, thus reducing the efficiency of heat transfer.
It is expensive and difficult, and time consuming, to remove the scales directly. In the prior art, it has been necessary to shut down the process to remove the scales. In the present invention, scale formed on the surfaces of the solid balls is removed by abrasion created when the balls impact each other, and when they impact the surfaces on which they travel.
In the present invention, the hot surface is provided by the heated solid balls, which are continuously moving through the liquid, and which are continuously removed, renovated, reheated, and re-used. By keeping the solid material in a continuous state of motion, and by renovating the solid material by abrasion, the present invention avoids the problem of scale formation, and the process can be operated continuously, without disruption.
The detailed structure and operation of the apparatus of the present invention will first be described with reference to the schematic diagram of
In this specification, the terms “solid material” and “solid balls” will be used interchangeably, it being understood that a preferred form of solid material is that of solid balls. However, the invention is not limited to use with solids in the form of balls or spheres.
As shown in
The saline water leaves the storage tank ST1 via pipe P1, and flows towards heat exchanger HE1. In this heat exchanger, the saline liquid is preheated by heat exchange with circulating hot potable water.
The now preheated saline water then flows through pipe P2, and is further heated in heat exchanger HE2, which receives heat from vapor or steam created in chamber C1, as will be explained below. The water passing through heat exchanger HE2 then flows through pipe P3, into the raw saline storage tank ST2.
From the storage tank ST2, a now warm saline flows further through pipe P4, into pipe P5, and then upwards into chamber C1. The chamber is preferably insulated. It is in this chamber that the saline liquid is placed in continuous contact with heated solid material, so that heat is transferred from the solid material to the liquid. The solid material preferably has the form of small balls or spheres, indicated symbolically by reference numeral 130. The solid material flows countercurrently relative to the inflow of the saline liquid. That is, in chamber C1, the liquid flows upwardly, and the solid material flows downwardly.
The solid material exits the chamber at the bottom, through pipe P5, and flows into a circulation device CD1, which is more fully illustrated in
Chamber C2, which will also be described later, is similar in construction to that of chamber C1. Solid material flows out of chamber C2 through pipe P19 and into circulation device CD2, also illustrated more fully in
Pipe P5, at the bottom of chamber C1, is similar to pipe P19, at the bottom of chamber C2. Similarly, pipe P8 corresponds to pipe P31, and pipe P6 corresponds to pipe P20. Also, pipe P4 corresponds to pipe P18.
In the case of both chambers C1 and C2, the solid material leaving the chambers, at the bottoms thereof, is renovated and reheated. The details of the renovation and reheating will be described later. For present purposes, it should be understood that the solid material is conveyed to solar heaters SH1 and SH2. These solar heaters receive solar radiation, symbolized by arrows 120 and 121. The heated material is conveyed, through pipes P7 and P30, respectively, into temporary heated storage units TS1 and TS2, before re-entering the upper regions of the respective chambers C1 and C2.
The preferably continuous flow of warm saline into the chamber C1 at its bottom will cause an overflow of saline at its top which then flows through pipe P10 into sludge chamber SC. A minor amount of the saline leaves the sludge chamber at its bottom through pipe P11, and is filtered in the filtration tank FT1 and circulated back into the sludge chamber by pipes P12 and P10. The majority of the saline runs by overflow through pipe P14 into the crystallization spray chamber CSC1.
Inside the sludge chamber SC, retrograde salts such as calcium sulfate and calcium carbonate will precipitate and accumulate. These materials accumulate in the sludge chamber, and are funnelled into pipe P11, then filtered inside filtration tank FT1, and then withdrawn from the process as a product having commercial value.
The remaining filtered saline is pumped back into the sludge chamber SC through pipe P12. The saline enters pipe P10, preferably at the top of the sludge chamber. The continuous overflow of saline in the sludge chamber SC flows into pipe P14 and is released as a spray inside the crystallization spray chamber CSC1, in which the halide sodium chloride is crystallized, preferably under vacuum, and funneled into pipe P16, where it is filtered in filtration tank FT2 and subsequently withdrawn from the process as another product having commercial value.
In the crystallization spray chamber CSC1, the majority of the liquid saline is vaporized, leaving the crystallization chamber CSC1 by pipe P15. A small part of the liquid is drained into the filtration tank FT2, and then fed into pipe P18 and finally pipe P19.
The continuous flow of saline into chamber C2, through pipes P18 and P19, causes an overflow of saline guided by pipe P21 into crystallization spray chamber CSC2, where it is sprayed downwardly, releasing its heat as steam or vapor upwardly into pipe P22 and subsequently pipe P26. The remaining liquid flows through pipe P23, and is filtered to remove the halide magnesium chloride, in filtration tank FT3, and the residue is recovered as a product of commercial value. The remaining saline is pumped back through pipe P24, entering pipe P18, and then flows into pipe P19, so as to be able to return to chamber C2.
The saline which passes filtration tank FT2 is pumped through pipe P18 into pipe P19, which connects chamber C2 with circulation device CD2. The saline flows upwardly, through pipe P19, in the opposite direction to the solid material, and the saline is heated by direct contact with the solar heated solid material flowing downwardly, as was described with respect to chamber C1. The solid material finally drops through pipe P19 into the circulation device CD2, to be described in detail later, from which it is recirculated by pipe P20 into solar heater system SH2, and finally introduced, via solid storage TS2, into the chamber C2 again, from the upper region, thus continuously reheating the saline liquid inside the chamber.
A final circulation of pure potable water takes place at the barometric condenser BC. This barometric condenser creates a vacuum and condenses the incoming steam/vapor from the desalination process to be collected as the end product. The circulating potable water is pumped from the water circulation tank CT via pipe P28 to the heat exchanger HE1 and the barometric condenser BC, and back into the water circulation tank CT. The excess of condensed steam/vapor is finally collected as potable water through pipe P29.
During the desalination process, saline water will thus be split into three components, namely liquid, steam and/or vapor, and salts.
Stated in more detail, the steam leaving chamber C1, through pipe P9, the vapor leaving the crystallization spray chamber CSC1, through pipe P15, and the steam or vapor from the crystallization spray chamber CSC2, flowing through pipe P22, are condensed in the barometric condenser BC, to become potable water. The potable water flows through pipe P27, and enters a circulatory flow into a circulating tank CT, flowing through pipe P28 and passing through heat exchanger HE1, to release heat, and enters the barometric condenser again. The steady inflow of steam and vapor from pipe P26 being condensed by the barometric condenser causes an accumulation and finally an overflow of potable water inside the circulation tank CT which is then collected and withdrawn from the process as a product having commercial value. The potable water is collected through pipe P29.
In summary, in chamber C1, the warm raw saline enters the chamber at the bottom, flowing upwards and heated by contact with the solid material, which counterflows downwards through the chamber. The steam will leave the chamber C1 at the top, through pipe P9, passing through heat exchanger HE2, through pipe P26, and towards the barometric condenser BC.
A secondary flow of steam and/or vapor will exit the crystallization spray chamber CSC1, joining the steam flow from chamber C1, also towards the barometric condenser BC.
A third flow of steam/vapor exiting the crystallization spray chamber CSC2, will again join the previous two streams on their way to the barometric condenser BC.
The steam and/or vapor from each of the chamber C1, the crystallization spray chamber CSC1, and the crystallization spray chamber CSC2, are all accumulated in pipe P26. Inside the barometric condenser BC, the incoming steam/vapor is liquified and finally collected as warm, potable water.
The solid material, typically having the form of solid balls 130, falls out of the chambers C1 and C2, and is conveyed to vibrating sieve 102. The balls are transported in saline liquid, which is moved through the system by liquid circulation pump 107. This means of transport has been found to be dust-free, efficient, and economical.
The solid balls fall onto a conical abrasive screen 103 within the vibrating sieve 102, and are shaken, rolled about, and abraded by the abrasive screen. In this way, the scale material, which has formed and accumulated on the surfaces of the balls, is removed.
The solid balls are then sprayed with saline liquid, by sprayer 104, so as to flush off the debris on the balls, before they roll down a chute (not shown) to begin the reheating process. The conveying saline, the flushing saline, the scale material, and the detritus all flow through the abrasive screen and collect at the bottom of the vibrating sieve, and then drain through the outlet pipe 105 into a settling tank 106 where the solids settle and are removed. The filtered saline returns to the process via pipe P4 and pipe P18 of
Wet abrading is a fast, economical, environmentally friendly process for renovating or reconditioning the solid balls. The scale material and detritus are removed in solid form.
The solid balls may also be renovated or reconditioned by chemical, ultrasonic, or other means.
After the solid balls have been renovated, the balls are ready to be reheated, as represented by solar heaters SH1 and SH2 of
As shown in
The solid balls are therefore transported by a vertical screw conveyor 110 to a secondary heater 111, which comprises a line focus Fresnel reflector heater, where the balls are heated to a very high temperature. The line focus Fresnel reflector heater includes a quartz tube 113 located above an assembly of mirrors 112 which reflect solar radiation and concentrate it on the quartz tube. The quartz tube is supported by rollers and a drive mechanism (not shown) which rotates the tube around its axis, as indicated by arrow 114.
The secondary heater 111 is mounted at an incline. The inlet end 115 of the quartz tube 113 where the solid balls are fed is higher than the outlet end 116. The outlet end 116 is similarly higher than the inlet of temporary storage devices TS1 and TS2 of
Solar radiation heats the solid balls inside the quartz tube. Rotating the quartz tube results in even heating of the solid balls, and facilitates moving the solid balls down the incline from the inlet towards the outlet of the secondary heater, and on to the inlet of the temporary storage devices TS1 and TS2 of
One or both of heaters 108 and 111 can be considered a heating means in the present invention.
The solid balls could also be heated by a parabolic trough, or a flat or curved Fresnel lens concentrator. The quartz tubing can also be non-transparent, metallic, non-metallic such as graphite, for indirect heating of the solid balls.
The chambers C1 and C2 contain a vertical helix 10. As described with respect to
The inside of the chamber may be provided with suitable structures to prolong the contact time of the saline with the solid material. For example, as shown in
In an alternative embodiment, shown in
The solid material leaves the chamber C1/C2 by either of pipes P5 or P19, into the circulation device CD1/CD2, shown in
As shown in
The bottom of the temporary storage tank TS has a feed controller or dispenser 117 which can adjust the amount of solid material released from the temporary storage tank TS.
The solid material then enters chamber C1 or C2 through an inlet chute 25 at the upper side. The solid material storage facilities, the storage tank, and the storage dispenser are designed to store flexible amounts of solid hot material of desired shapes and/or size, to maintain the process heat capacity which is needed in times of insufficient solar radiation, such as on cloudy days, and during night, to ensure overall continuous production.
The highest temperature in chamber C1 or C2 will be at the top surface of the saline liquid inside the chamber, due to the heat exchange while in contact with the hot solid material entering the chamber. Some saline flashes off as steam, which leaves the chamber C1 through pipe P9, and passes through heat exchanger HE2, to heat further the fresh warm raw saline on its way to the storage tank ST2.
In
All process equipment which has a higher or lower temperature than ambient is preferably insulated by suitable insulation materials which prevent heat or cooling losses during the process. The chambers and other equipment are preferably fabricated from thermo plastic and/or saline resistant material.
The solid material used in the present invention preferably is made of solid, round balls which are inert and thermally stable. It is preferred that the solid material have a density substantially greater than that of the saline liquid, to allow easy separation of the solid from the liquid.
Regardless of the shape of the solid material, it is preferable that the material be pourable. That is, the solid material preferably comprises a plurality of pieces each having a sufficiently small diameter that the material can be efficiently poured and/or moved through a pipe or conduit by a liquid. The use of a large number of relatively small pieces also has the advantage of maximizing the amount of surface contact between the solid and the saline liquid.
The solid material may be made of ceramic, such as aluminum oxide, graphite, silicon carbide, or quartz. The preferred diameter of the balls is about 5-25 mm. The balls are easily removed from the vessel, and can be easily renovated by causing rolling and/or vibratory motion.
The solid material could also be non-spherical, and could vary in size from the range described above. The solid could be an alloy, a eutectic liquid or solid, or a liquid such as mercury. The solid material could have a shape like that of a ball bearing. Also, the solid material could include combinations of materials having different compositions, and could include pieces of varying shape and/or size. All such combinations of compositions, shapes, and sizes are within the scope of the present invention.
The present invention also overcomes the problem of scale formation in heat exchangers used in the thermal evaporation of saline liquids.
The spiral upward flow of saline liquid minimizes the mixing between incoming and exiting liquid.
The conical bottom of the chamber allows easy collection, recovery, and transfer of the solid balls to the location where they can be reheated.
The final products of the desalination process include 1) potable water, collected at the circulation tank CT, 2) retrograde products calcium carbonate and calcium sulfate, collected at the filtration tank FT1, 3) the halide sodium chloride at filtration tank FT2, and 4) the halides magnesium and potassium salt at filtration tank FT3.
The invention can be modified in various ways. The number of chambers can be increased or decreased. Although a dual solar heater, as shown, is preferred, there could be as few as one solar heater, or there could be more than two such heaters. There also could be non-solar heat sources, in addition to the solar heaters.
In another embodiment, the storage tank for the hot solid material could be divided into sections, with extra solar heating being directed at one of such sections.
The modifications indicated above, and others which will be apparent to those skilled in the art, should be considered within the spirit and scope of the following claims.
