Patent Application
20120205320
The exemplary embodiments of the present application relate generally to methods and systems for purifying water. They find particular application in conjunction with water desalination, and will be described with particular reference thereto. However, it is to be appreciated that the exemplary embodiments are also amenable to other like applications.
Conventional water desalination is based on temperature or pressure. With respect to sea water, there are generally two methods used to desalinate the water: thermal distillation (e.g. multi-stage flash distillation) and reverse osmosis. Drawbacks of these processes include high energy costs for flash distillation and the requirement of frequent back flush of the reverse osmosis (RO) membrane as effluent recovery efficiency drops rapidly with usage. With respect to brackish water, Electro-Deionization (ED) is another alternative. Under a system for ED, reduced conductivity of brackish water relative to sea water allows for efficient operation with lower Joule heating.
Recent developments in both energy and pressure recovery have lowered the energy cost of water desalination to 1.7 kWh/m3 (or 6.46 W/gph). Notwithstanding these improvements, however, the energy cost of water desalination is still comparatively high compared to the energy cost of conventional water treatment. Namely, the energy cost of conventional water treatment is 2-4 W/gph. Accordingly, there exists a need for systems and methods for water desalination that have an energy cost more in line with that of conventional water treatment systems.
Energy costs aside, some desalination systems produce environmentally harmful waste water that can be difficult to dispose of. Reverse osmosis, for example, produces brine water as a byproduct of the desalination process. Brine water, because of its high concentration of salt, is generally toxic to both plants and animals. Moreover, because the salt is dissolved within the water, it is generally difficult to remove the salt from the water. Other desalination systems, in addition to, or in alternative to, producing brine water use chemicals to advance the desalination process, whereby waste water (such as brine water) containing such chemicals may be produced. Naturally, the chemicals, similar to a high concentration of salt, may be toxic to plants and animals. Accordingly, it would be advantageous to have systems and methods for water desalination that do not produce environmentally harmful waste water.
Notwithstanding the potential environmental impact of chemicals, discussed above, chemicals also add to the operating expense of a water desalination system. Accordingly, it would be advantageous to have systems and methods for water desalination that do not require chemicals.
Additionally, the waste water from most desalination systems contains high concentrations of salt. As the skilled artisan will appreciate, salt has value in the chemical industry, whereby it could be sold to offset the cost of operating a desalination system. However, one problem thus far has been that the cost of separating the salt from the waste water has proven to be uneconomical. Additionally, even if the salt is separated from the waste water, it contains a mixture of various types of salt. The chemical industry will generally require concentrated amounts of certain types of salts as opposed to a hodgepodge of different salts. Accordingly, it would be advantageous to have a desalination system that allows for the economic recovery of salt from waste water, and further allows the ratio of different types of salt to be adjusted.
From a maintenance standpoint, some desalination systems have to contend with scale build-up that needs to be periodically cleaned for efficient operation. Similarly, in the case of reverse osmosis, the RO membrane requires frequent back flush to clean the membrane. Naturally, periodic cleaning factors into the cost of producing desalinated water, whereby it would be advantageous to have a system that doesn't require frequent cleaning, or has an automated mechanism to clean itself.
Beyond maintenance, zero liquid discharge (ZLD) targets seek to extract 100% of the salt from water. However, some desalination systems, such as reverse osmosis, are directly salt concentration dependent. That is to say, the efficiency of desalination reduces as the salt concentration increases. Accordingly, it would be advantageous to have a desalination system that is not dependent on the concentration of salt dissolved within the water.
The present application contemplates new and improved systems and/or methods which may be employed to mitigate the above-referenced problems and others.
According to one aspect of the present application, a method for treatment of water is provided. The method includes receiving source water having particles therein and generating supercritical water from the source water. The method further includes separating the supercritical water into effluent water and waste water having aggregated particles. The supercritical water is separated using a spiral separator.
According to another aspect of the present application, a system for the treatment of water is provided. The system includes an inlet operative to receive source water having particles therein. The system further includes a supercritical water generator operative to generate super critical water from the source water and a spiral separator operative to separate the supercritical water into effluent water and waste water having aggregated particles therein. The system further includes an outlet operative to provide a path for the effluent water.
According to yet another aspect of the present application, a system for separation of particles from supercritical water is provided. The system includes an inlet to receive at least a portion of the supercritical water containing the particles. The system further includes a spiral channel within which the supercritical water flows in a manner such that the particles flow in a tubular band offset from a center of the channel. The channel is pressurized to at least 22.1 MPa and the supercritical water is heated to at least 647° K. The system further includes a first outlet for the supercritical water within which the tubular band flows and a second outlet for the remaining supercritical water.
The exemplary embodiments use a spiral separator configured to exploit the properties of supercritical water for water desalination. As will be discussed below, by first converting source water to supercritical water, particles disposed therein (e.g., salt) can be more easily separated using a spiral separator.
Supercritical water is achieved at a critical temperature Tc=647° K or greater and a critical pressure pc=22.1 MPa or greater. Compared to water at ambient conditions, supercritical water exhibits properties that more readily facilitate desalination. Among these properties, supercritical water has a viscosity of approximately 1/100 that of normal water. The two orders of magnitude reduction allows fluid to move much more rapidly through a device, whereby the flow rates through the device for a given pressure gradient are approximately 100 times higher. This advantageously allows the device to be reduced in size. Another property of supercritical water, although counter-intuitive, is that the solubility of inorganic salts in supercritical water is basically zero. For example, it drops from 40%/weight at 300° C. to 100 ppm at 450° C.
With reference to
After water has reached a supercritical state, a spiral separator is used to separate the salts which precipitate out of the supercritical water. The spiral separator to which the exemplary embodiments relate is configured in accordance with the spiral separators such as discussed in various ones of the incorporated references, such spiral separators being modified to operate with supercritical water. As should be appreciated, this entails modifying the spiral separator to handle the increased pressure and temperatures necessary for supercritical water. One option for achieving this is placing a spiral separator into a standard Conflat flange system. As the skilled artisan will appreciate, such a system can easily handle the temperatures and pressures of supercritical water. The modified spiral separator, in one embodiment, may be made out of carbon reinforced steel, although other materials which are able to withstand the heat and pressure may also be used.
Additionally, because supercritical water has a viscosity 1/100 that of normal water, the actual volume for the modified spiral separator can advantageously be scaled down by at least a factor of 100 relative to the spiral separator incorporated herein by reference for a given flow rate.
In one embodiment, the spiral separator uses a curved channel of a spiral device to introduce a centrifugal force upon entrained in a fluid, e.g., water, to facilitate improved separation of such particles from the fluid. As these particles flow through the channel, a tubular pinch effect causes the particles to flow in a tubular band. The introduced centrifugal force perturbs the tubular band (e.g. forces the tubular band to flow in a manner offset from a center of the channel), resulting in an asymmetric inertial migration of the band toward the inner wall of the channel. This force balance allows for focusing and compaction of suspended particulates into a narrow band for extraction. The separation principle contemplated herein implements a balance of the centrifugal and fluidic forces to achieve asymmetric inertial equilibrium near the inner sidewall. Angled impingement of the inlet stream towards the inner wall also allow for earlier band formation due to a Coanda effect where wall friction is used to attach the impinging flow.
With reference to
With reference to
Referring still to
With reference to
As mentioned, an exemplary method 400 begins by receiving source water (at 402). Source water, as its name would imply, merely refers to water from a source, such as the ocean or an aquifer. Naturally, as the exemplary methods and systems of the present application are directed towards water desalination, the source water preferably contains salts therein. However, the skilled artisan will appreciate that the teachings of the present application is equally amenable to source water containing particles other than salt, whereby the exemplary methods and systems may be used more generally for water purification. In fact, notwithstanding that salt generally has density greater than that of water, the spiral separator discussed above allows the removal of neutrally buoyant particles.
After receiving source water (at 402), the source water is, again, optionally pre-treated (at 404). The goal of pre-treatment (at 402) is to remove suspensions and/or sub-micron organics contained within the source water. Sub-micron organics include, for example, total organic carbon (TOC) and some viruses and toxins. Pretreatment (402) includes optionally mixing a coagulant with the source water (at 414) and separating the source water from suspensions and submicron organics (at 416). The coagulant causes suspended particles disposed within the source water to clump together. Naturally, the larger the suspensions within the source water, the easier it is to separate the suspensions from the source water. After the coagulant is mixed in the source water (at 414), assuming a coagulant is used, the source water is separated from the suspensions therein (at 416). Essentially, the loose particles floating around in the water are removed (e.g., algae). Preferably, this is accomplished through the use of a spiral separator capable of removing neutrally buoyant particles, such as the spiral separator of U.S. patent application Ser. No. 11/936,729, incorporated herein by reference. Thus, pre-treatment (at 404) serves to produce a higher quality water for desalination, which advantageously reduces the energy requirements for producing the supercritical water because superfluous material is not heated (when generating supercritical water).
Regardless of whether or not there is pre-treatment of the source water (at 504), supercritical water is generated from the source water (at 406) next. The generation of supercritical water (at 406) includes pressurizing the source water (at 418) and heating the source water (at 420). As discussed above, the source water needs to be pressurized beyond the critical pressure pc of 22.1 MPa. Additionally, the source water needs to be heated beyond the critical temperature Tc of 647° K. The result of heating and pressurizing the water beyond critical temperature Tc and the critical pressure pc, respectively, is that salt disposed within the water begins to precipitate out of the water.
As discussed in connection with
Advantageously, one may use this to extract, and sell, salt particles from the supercritical water which have value to the chemical industry. As hinted at above, the extracted salt can help offset the cost of the desalination. As should be appreciated, because the salt is suspended, as opposed to dissolved, in the water it is relatively easy to extract.
Beyond facilitating extraction of salt, the heat and pressure of the supercritical water also advantageously denatures and oxidizes any organic materials disposed within the supercritical water, thereby making the water free of any potential harmful biological entities (such as e.g. potential biological warfare agents) which cannot be filtered out in the optional pre-treatment (at 404). While the supercritical water will generally have enough oxygen to oxidize the organic matter present, in situations where the oxygen content of the supercritical water is low, oxygen may be injected into the supercritical water. For more details pertaining to one process for denaturing of organic contaminants in water through the use of supercritical water and oxygen, see U.S. Pat. No. 7,186,345, incorporated herein by reference.
Assuming supercritical water has been generated from the source water (at 406), the supercritical water may optionally be delayed before sending it through the separator to allow the salt dissolved within the supercritical water to precipitate out (at 408). Delaying the supercritical water (at 406) advantageously allows the salts dissolved therein more time to precipitate, and in turn, allows salt crystals that precipitate out of the supercritical water to grow larger in size. Naturally, the larger the salt crystals suspended within the supercritical water, the easier it is to separate the supercritical water from the salt crystals. Additionally, from a practical standpoint, if an inadequate amount of time is provided for the precipitation of salt out of the supercritical water, the salt crystals may be too small to efficiently separate from the supercritical water, whereby the device separating the supercritical water from the salt may be unable to perform its task. Thus, the amount of delay is dependent upon the rate of precipitation, the desired crystal size and the capabilities of the device separating the salt from the supercritical water. Delay may be achieved by employing a buffing tank or other portable holding area. It is understood that when a holding area is used, the holding area will be in a pressurized and/or heated vessel to maintain the supercritical state of the water.
Regardless of whether the supercritical water is delayed (at 408), the supercritical water is next separated into effluent (or potable) water and waste water containing aggregated particles therein (e.g., salt). As should be appreciated by the discussion heretofore, the supercritical water is separated using spiral separator technology, such as the spiral separator shown in, and discussed in connection with, previous
Preferably, the resulting effluent water may contain approximately 1000 ppm salt to as little as 100 ppm salt. It is understood recovered effluent water may be put to different uses having different requirements. For example, if the recovered water is to be used for irrigation less than 1000 ppm would be acceptable, whereas if the use is for drinking water, 500 ppm is needed. Thus, the present system, as the skilled artisan will appreciate, is capable of generating effluent water well within federal and world standards for different applications. Additionally, the waste water is preferably stored for proper disposal or sent to another system to remove the aggregated salt particles suspended within the waste water.
Advantageously, the spiral separator allows the separation of neutrally buoyant particles from the salt water, whereby supercritical water with a temperature and/or a pressure at or about the critical temperature Tc and/or critical pressure pc, respectively, may be used. As should be appreciated, the lower the temperature and the pressure of the supercritical water, the less energy is required to produce the supercritical water. Additionally, this further allows the spiral separator to efficiently remove salts which precipitate at a slow rate, whereby the spiral separator can remove much smaller salt crystals than a hydroclone, which depends on sedimentation.
Additionally, the use of a spiral separator for separation (at 406) advantageously produces waste water that is easily disposed of. Namely, in contrast with brine water of reverse osmosis, which contains high concentrations of salt dissolved therein, the waste water of the exemplary methods and systems merely contains salt suspended therein. As the skilled artisan will appreciate, the removal of suspensions from water is relatively easy and inexpensive compared to the removal of dissolved materials from water. The exemplary methods and systems discussed herein can also be used to process brine waste water, which, as discussed above, is difficult to dispose of in an environmentally friendly manner.
From the perspective of a zero liquid discharge (ZLD) target, the use of a spiral separator is advantageous. Namely, the goal of a ZLD target is to remove 100% of the salt within water. In the case of reverse osmosis, as the concentration of salt within the water increases, the efficiency of reverse osmosis desalination process decreases. The spiral separator, on the other hand, does not suffer from such a limitation, whereby the efficiency of spiral separator is not dependent upon the concentration of salt within the supercritical water (or at last not to the same degree as reverse osmosis).
After the supercritical water is separated (at 410), heat and/or pressure (collectively referred to as energy) are optionally recovered from the supercritical water (at 412). This recovered energy may then be used for the generation of supercritical water (at 406). This recovered energy advantageously reduces the amount of energy required to be expended for desalination. Naturally, as the efficiency of energy recovery (at 410) increases, the less external energy the exemplary methods and systems require, and the more competitive the exemplary methods and systems become with other desalination systems, such as reverse osmosis.
With reference to
With reference to
The source water 602 may be from an ocean, aquifer, storage tank, another system for processing water, or any other like source of water. Additionally, because the exemplary methods and systems of the present application are directed towards water desalination, the source water preferably contains particles, such as salts, therein. However, as discussed above, the systems and methods of the present application are equally amenable to uses other than water desalination.
The water desalination system 604 receives source water 602 via inlet 606. The water may, for example, be pumped to the water desalination system 604 from the above mentioned sources or other sources. The pretreater 608 then pretreats the water to remove suspensions and submicron organics as discussed at 404 of
Thereafter, the pretreated water is converted to supercritical water within supercritical water generator 610 as discussed at 406 of
The supercritical water is then, in at least one embodiment, stored in a buffer tank 612 until the salt crystals achieve a desired size. The buffer tank serves to introduce the delay discussed at 408 of
Once the supercritical water has been delayed for an amount of time, the water is separated from the salt using spiral separator 614 as discussed at 410 of
The spiral separator 614 may optionally include a flushing system 628 to remove any scale build-up (i.e., salt crystals that have built-up on the channel walls of the spiral separator). The flushing system simply flushes the spiral separator with fresh water. This may, for example, be automated at regular intervals. Generally, the flushing system only needs to be used after the flow through the spiral separator 614 stops. Namely, the flow rate through the spiral separator should generally be sufficiently high to avoid scale build-up.
After separation, the effluent water is directed towards the energy recoverer 616, wherein pressure and/or heat are recovered and used by the supercritical water generator 610 to generate supercritical water. As should be appreciated, this mirrors the discussion at 412 of
With respect to recovering heat, the heating of water to the supercritical phase and back is a reversible process unlike distillation. Namely, the supercritical water isn't doing any work because the heating is done at effectively a constant volume. Consequently, a very good heat exchanger could, in principle, extract heat from the supercritical water after separation (at 408) and preheat the incoming water. However, this is a daunting task because a regenerative heat exchanger will have to be efficient to levels of 50% energy recovery. Regardless of this challenge, there is no thermodynamic reason why regenerative heat exchangers cannot be made 100% efficient.
After the energy is extracted from the effluent water, the potable water is output from desalination system 604 via outlet 620. The waste water may, as shown in
Common types of heat exchangers may be used. One example is a spiral heat exchanger (SHE) wherein a first spiral channel is nested with a second spiral channel. Hot water flows through the first spiral channel and water to be heated flows through the second spiral channel. The spiral heat exchanger is often used in the heating of fluids which contain solids that have a tendency to foul the inside of the heat exchanger. The device has low pressure drop and has a “self cleaning” mechanism, whereby fouled surfaces cause a localized increase in fluid velocity, thus increasing the drag (or fluid friction) on the fouled surface, thus helping to dislodge the blockage and keep the heat exchanger clean.
With respect to recovering pressure, recent advances in the development of pressure exchangers can be used to implement the present device. For example, Energy Recovery, Inc., for example, has an efficient, energy saving, energy recovery solution: the PX Pressure Exchanger® (PX). The PX uses the principle of positive displacement and isobaric chambers to achieve extremely efficient transfer of energy from a high-pressure waste stream, such as the brine stream from a reverse osmosis desalination unit, to a low-pressure incoming feed stream. The PX device is highly efficient, up to 98%, whereby virtually no energy is lost in the transfer.
As illustrated in
Turning now to
The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
This application claims the priority, as a divisional, of U.S. application Ser. No. 12/615,663, filed Nov. 10, 2009, the disclosure of which is incorporated herein by reference in its entirety. The disclosures of U.S. patent application Ser. No. 11/936,729 (U.S. Publication No. 2009/0114607) for “FLUIDIC DEVICE AND METHOD FOR SEPARATION OF NEUTRALLY BUOYANT PARTICLES,” by Lean et al., filed Nov. 7, 2007; U.S. patent application Ser. No. 11/606,460 (U.S. Publication No. 2008/0128331) for “PARTICLE SEPARATION AND CONCENTRATION SYSTEM”, by Lean et al.; U.S. patent application Ser. No. 11/936,753 (U.S. Publication No. 2009/0114601) for DEVICE AND METHOD FOR DYNAMIC PROCESSING IN WATER PURIFICATION”, by Lean et al.; U.S. patent application Ser. No. 11/606,458 (U.S. Publication No. 2009/0050538) for “SERPENTINE STRUCTURES FOR CONTINUOUS FLOW PARTICLE SEPARATIONS”, by Lean et al.; U.S. patent application Ser. No. 11/725,358 (U.S. Publication No. 2008/0230458) for “VORTEX STRUCTURE FOR HIGH THROUGHPUT CONTINUOUS FLOW SEPARATION”, by Lean et al.; and U.S. Pat. No. 7,186,345 for “SYSTEMS FOR WATER PURIFICATION THROUGH SUPERCRITICAL OXIDATION,” by Lee et al., filed May 6, 2004, are each hereby incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12615663 | Nov 2009 | US |
| Child | 13456628 | US |
