Patent Application
20180050936
Water purification technology is rapidly becoming an essential aspect of modern life as conventional water resources become increasingly scarce, municipal distribution systems for potable water deteriorate with age, and increased water usage depletes wells and reservoirs, causing saline water contamination. Additionally, further contamination of water sources is occurring from a variety of activities, which include, for example, intensive agriculture, gasoline additives, and heavy toxic metals. These issues are leading to increasing and objectionable levels of germs, bacteria, salts, MTBE, chlorates, perchlorates, arsenic, mercury, and even the chemicals used to disinfect potable water, in the water system.
Furthermore, even though almost three fourths of the earth is covered by oceans, only some 3% of this water exists as fresh water resources, and these resources are becoming increasingly scarce as a result of population growth and global warming. Approximately 69% of all fresh water is contained in ice caps and glaciers; with increased global melting, this fresh water becomes unrecoverable, so less than 1% is actually available, with the majority (over 90%) being ground water in aquifers that are being progressively contaminated by human activities and saline incursions. Thus, there is an urgent need for technology that can turn saline water, including seawater and brine, into fresh water, while removing a broad range of contaminants.
Conventional desalination and water treatment technologies, including reverse osmosis (RO) filtration and thermal distillation systems, such as multiple-effect distillation (MED), multiple-stage flash distillation (MSF), and vapor compression distillation (VC), are rarely able to handle the diverse range of water contaminants found in saline environments. Additionally, even though they are commercially available, they often require multiple treatment stages or some combination of various technologies to achieve acceptable water quality. RO systems suffer from the requirement of high-water pressures as the saline content increases, rendering them expensive in commercial desalination, and they commonly waste more than 40% of the incoming feed water, making them progressively less attractive when water is scarce. Moreover, RO installations produce copious volumes of waste brine that are typically discarded into the sea, resulting in high saline concentrations that are deadly to fish and shellfish. Less conventional technologies, such as ultraviolet (UV) light irradiation or ozone treatment, can be effective against viruses and bacteria but seldom remove other contaminants, such as dissolved gases, salts, hydrocarbons, and insoluble solids. Additionally, while most distillation technologies may be superior at removing a subset of contaminants, they rarely can handle all types of contaminants.
Because commercial desalination plants are normally complex engineering projects that require one to three years of construction, they are typically capital intensive and difficult to move from one place to another. Their complexity and reliance on multiple technologies also make them prone to high maintenance costs. Because RO plants are designed to operate continuously under steady pressure and flow conditions, large pressure fluctuations or power interruptions can damage the membranes, which are expensive to replace; the incoming feed water therefore requires extensive pre-treatment to prevent fouling of the RO membrane.
Thermal distillation systems, such as those described by LeGolf et al. (U.S. Pat. No. 6,635,150 B1) include MED systems, which rely on multiple evaporation and condensation steps that operate under vacuum in order to effect evaporation at temperatures lower than the normal boiling point of water. Such technologies are commercially used for desalination in various countries, but they all operate according to different physico-chemical principles. For example, MED, MSF, and VC systems all require vacuum, which means that the product water cannot be sterilized because evaporation occurs at temperatures lower than those needed for sterilization; also, vacuum systems tend to leak and require mechanical reinforcement. In addition, heat transfer and heat recovery in MED, MSF, and VC systems involve heat exchange across membranes or thin metal surfaces, but heat exchangers are prone to fouling and scale formation and require frequent maintenance.
More recently, Thiers (PCT Application No.: US2009/57277, entitled Large Scale Water Purification and Desalination, filed Sep. 17, 2009, and PCT Application No.: US2010/030759, entitled Method and System for Reduction of Scaling in Purification of Aqueous Solutions, filed Apr. 12, 2010) has described a method of pre-treatment that removes scale-forming constituents from a water stream and large scale embodiments for a desalination system. However, the earlier pre-treatment system described by Thiers relies on a final thermal treatment that involves heating to 120° C. for several minutes of residence time, which, while technically effective, represents a significant energy consumption. There is a need for a pre-treatment method that minimizes energy consumption while still removing scale-forming constituents from an aqueous stream. In addition, the embodiments described by Thiers for a large-scale desalination and water treatment fail to address transient phenomena encountered during start-up and shut down operations and do not properly ensure the maintenance of a stable hydraulic head between different boiling stages. There is a need for industrial configurations that are stable during start-up and shut down procedures, in addition to being stable during normal operation.
There is a need for inexpensive and effective pre-treatment methods that eliminate scale-forming compounds. There is a further need for industrial desalination and water treatment systems that are continuous and largely self-cleaning, that resist corrosion and scaling, that are modular and compact, that recover a major fraction of the input water while producing a highly concentrated waste brine that crystallizes into a solid salt cake, and that are relatively inexpensive and low-maintenance.
The present invention describes various industrial embodiments for an improved desalination and water purification system. The system includes a pre-treatment section that prevents scale formation and a desalination section that consists of an inlet, a preheater, a degasser, multiple evaporation chambers and demisters, product condensers, a waste outlet, a product outlet, multiple heat pipes for heat transfer and recovery, and a control system. The control system permits operation of the purification system continuously with minimal user intervention or cleaning. The system is capable of removing, from a contaminated water sample, a plurality of contaminant types including microbiological contaminants, radiological contaminants, metals, salts, volatile organics, and non-volatile organics. In embodiments of the system and depending on the salinity of the incoming water stream, the volume of water produced can range from about 20% to in excess of 95% of a volume of input water. The system comprises a vertical stack arrangement of boiling chambers, condensers, and a preheater that is compact and portable. The system is capable of water production in the range of 1,000 to 50 million gallons per day.
The pre-treatment section precipitates scale-forming compounds by means of pH adjustment. Addition of either caustic or lime initially precipitates magnesium hydroxide, which is subsequently removed by filtration or sedimentation, or both. Next, the concentration of bicarbonate ions is adjusted by dissolving CO2 or adding bicarbonate or soluble carbonate salts to correspond to the stoichiometric composition of the remaining calcium, magnesium, and other divalent cations in solution, and the pH is again adjusted to values of 9.8 and higher in order to precipitate scale-forming compounds as insoluble carbonates. Following filtration or sedimentation to remove precipitates, the clear pre-treated solution then flows into the desalination section.
The desalination section consists of a vertical stack of boilers, condensers, and demisters with a preheating tank, a degasser, and a heat transfer vessel. The preheating vessel raises the temperature of the incoming water to near the boiling point and can be placed on the top or at the bottom of the vertical stack. Water exiting the preheating tank can have a temperature of at least about 96° C. The preheating tank may have a spiral arrangement of vanes such that incoming water circulates several turns in the tank, thus providing sufficient residence time to effect preheating. Incoming feed water enters the preheating tank tangentially, is gradually preheated by heat pipes until the required temperature is achieved, and exits the preheating tank through a downcomer tube that connects either with the degasser or directly with a lower boiling chamber if there is no need for degassing.
A degasser, which is placed near the top of the vertical stack, removes gases and organic contaminants that may be volatile or non-volatile by means of counter-current stripping of the incoming water against low-pressure steam. The degasser can be in a substantially vertical orientation, having an upper end and a lower end. Pre-heated water enters the degasser at its upper end, and degassed water exits the degasser proximate to the lower end. In the system, steam from the highest evaporation chamber can enter the degasser proximate to the lower end and can exit the degasser proximate to the upper end. The degasser can include a matrix adapted to facilitate mixing of water and steam, stripping the inlet water of essentially all organics, volatiles, and gases by counterflowing the inlet water against an opposite directional flow of a gas in a degasser. The gas can be, for example, steam, air, nitrogen, and the like. The matrix can include substantially spherical particles. However, the matrix can also include non-spherical particles. The matrix can include particles having a size selected to permit uniform packing within the degasser. The matrix can also include particles of distinct sizes, and the particles can be arranged in the degasser in a size gradient. Water can exit the degasser substantially free of organics and volatile gases.
The heat-transfer vessel provides the heat energy for the entire system and can consist of a condenser chamber operating with low-pressure waste steam. Alternatively, it can be a combustion chamber that operates with any type of fuel or a vessel that absorbs heat from a working fluid from recuperators, solar heaters, or economizers.
Pre-treated water is first preheated to near the boiling point and enters a degas ser proximate the upper end of the vertical stack, where gases and hydrocarbons are removed. The degassed water then enters an upper boiler, where a portion of the incoming water is turned into steam; a portion of the steam produced in the upper boiler may be used to provide the required steam for degassing, while the balance enters a demister that removes entrained micro-droplets and is condensed into pure water in a condenser chamber immediately above the boiler. As some of the incoming water in the upper boiler evaporates, the balance of the water becomes progressively more concentrated in soluble salts and continuously cascades downward into a series of lower boilers until it exits the lowermost boiler as a heavy brine at near the solubility limit of the salt solution.
Concurrent with incoming water cascading downward, heat is provided at the heat-transfer vessel and is progressively transferred upwards by means of heat pipes. Heat pipes are highly efficient enthalpy transfer devices that operate with a small temperature difference between their hot and cold ends. A number of heat pipes transfer the heat provided at the heat-transfer vessel to the bottom boiler. The steam produced at the bottom boiler is largely recovered as the heat of condensation in the bottom condenser, where another set of heat pipes transfers that heat to an upper boiler, thus progressively re-using the heat for multiple evaporation and condensation chambers.
Embodiments of the invention are disclosed herein, in some cases in exemplary form or by reference to one or more Figures. However, any such disclosure of a particular embodiment is exemplary only and is not indicative of the full scope of the invention.
Embodiments of the invention include systems, methods, and apparatuses for water purification and desalination. Preferred embodiments provide broad spectrum water purification that is fully automated and can operate over very long periods of time without requiring cleaning or user intervention. For example, systems disclosed herein can run without user control or intervention for 2, 4, 6, 8, 10, or 12 months, or longer. In preferred embodiments, the systems can run automatically for 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 years, or more.
Embodiments of the invention thus provide a water purification and desalination system including at least an inlet for saline water, contaminated water, or seawater, a preheater, a degasser, one or more evaporation chambers, one or more demisters, and one or more product condensers with a product outlet, a waste outlet, and a control system, wherein product water exiting the outlet is substantially pure, and wherein the control system permits operation of the purification system continuously without requiring user intervention. In preferred embodiments, the volume of product water produced is at least about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, or 99%, or more, of the volume of input water. Thus, the system is of great benefit in conditions in which there is relatively high expense or inconvenience associated with obtaining inlet water and/or disposing of wastewater. The system is significantly more efficient in terms of its production of product water per unit of input water or wastewater than many other systems.
Substantially pure water can be, in different embodiments, water that meets any of the following criteria: water purified to a purity, with respect to any contaminant, that is at least 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 250, 500, 750, 1000, or more, times greater in purity than the inlet water. In other embodiments, substantially pure water is water that is purified to one of the foregoing levels, with respect to a plurality of contaminants present in the inlet water. That is, in these embodiments, water purity or quality is a function of the concentration of an array of one or more contaminants, and substantially pure water is water that has, for example, a 25-fold or greater ratio between the concentration of these contaminants in the inlet water as compared to the concentration of the same contaminants in the product water.
In other embodiments, water purity can be measured by conductivity, where ultrapure water has a conductivity typically less than about 1 μSiemens, and distilled water typically has a conductivity of about 5. In such embodiments, conductivity of the product water is generally between about 1 and 7, typically between about 2 and 6, preferably between about 2 and 5, 2 and 4, or 2 and 3. Conductivity is a measure of total dissolved solids (TDS) and is a good indicator of water purity with respect to salts, ions, minerals, and the like.
Alternatively, water purity can be measured by various standards, such as, for example, current U.S. Environmental Protection Agency (EPA) standards as listed in Table 1 and Table 2, as well as other accepted standards as listed in Table 2. Accordingly, preferred embodiments of the invention are capable of reducing any of one or more contaminants from a broad range of contaminants, including, for example, any contaminant(s) listed in Table 1, wherein the final product water has a level for such contaminant(s) at or below the level specified in the column labeled “MCL” (maximum concentration level), where the inlet water has a level for such contaminant(s) that is up to about 25-fold greater than the specified MCL. Likewise, in some embodiments and for some contaminants, systems of the invention can remove contaminants to MCL levels when the inlet water has a contamination that is 30-, 40-, 50-, 60-, 70-, 80-, 90-, 100-, 150-, 250-, 500-, or 1000-fold, or more, higher than the MCL or the product water.
While the capacity of any system to remove contaminants from inlet water is to some extent a function of the total impurity levels in the inlet water, systems of the invention are particularly well suited to remove a plurality of different contaminants, of widely different types, from a single feed stream, producing water that is comparable to distilled water and is in some cases comparable to ultrapure water. It should be noted that the “Challenge Water” column in Table 1 contains concentration levels for contaminants in water used in EPA tests. Preferred embodiments of water purification systems of the invention typically can remove much greater amounts of initial contaminants than the amounts listed in this column. However, contaminant levels corresponding to those mentioned in the “Challenge Water” column are likewise well within the scope of the capabilities of embodiments of the invention.
Determination of water purity and/or efficiency of purification performance can be based upon the ability of a system to remove a broad range of contaminants. For many biological contaminants, the objective is to remove substantially all live contaminants. Table 2 lists additional common contaminants of source water and standard protocols for testing levels of these contaminants. The protocols listed in Tables 1 and 2 are publicly available at www.epa.gov/safewater/mcl.html#mcls for common water contaminants, as well as Methods for the Determination of Organic Compounds in Drinking Water, EPA/600/4-88-039, December 1988, revised July 1991. Methods 547, 550, and 550.1 are in Methods for the Determination of Organic Compounds in Drinking Water—Supplement I, EPA/600-4-90-020, July 1990. Methods 548.1, 549.1, 552.1, and 555 are in Methods for the Determination of Organic Compounds in Drinking Water—Supplement II, EPA/600/R-92-129, August 1992. Methods 502.2, 504.1, 505, 506, 507, 508, 508.1, 515.2, 524.2 525.2, 531.1, 551.1, and 552.2 are in Methods for the Determination of Organic Compounds in Drinking Water—Supplement III, EPA/600/R-95-131, August 1995. Method 1613 is titled “Tetra-through Octa-Chlorinated Dioxins and zFurans by Isotope Dilution HRGC/HRMS,” EPA/821-B-94-005, October 1994. Each of the foregoing is incorporated herein by reference in its entirety.
Cryptosporidium
Giardia lamblia
1MCLG = maximum concentration limit guidance
2MFL = million fibers per liter
3pCi/l = pico Curies per liter
4Substantially no detectable biological contaminants
The objective of the pre-treatment system is to reduce scale-forming compounds to a level at which they will not interfere by forming scale in subsequent treatment, particularly during desalination. Water hardness is normally defined as the amount of calcium (Ca++), magnesium (Mg++), and other divalent ions that are present in the water and is normally expressed in parts per million (ppm) of these ions or their equivalent as calcium carbonate (CaCO3). Scale forms because the water dissolves carbon dioxide from the atmosphere, and such carbon dioxide provides carbonate ions that combine to form both calcium and magnesium carbonates; upon heating, the solubility of calcium and magnesium carbonates markedly decreases, and they precipitate as scale. In reality, scale comprises any chemical compound that precipitates from solution. Thus, iron phosphates and calcium sulfate (gypsum) also produce scale. Table 4 lists a number of chemical compounds that exhibit low solubility in water and can thus form scale. In this context, low solubility is defined by the solubility product, that is, by the product of the ionic concentration of cations and anions of a particular chemical; solubility is usually expressed in moles per liter (mol/L).
2.5 × 10−8
6.0 × 10−9
3.1 × 10−7
3.3 × 10−8
9.8 × 10−9
8.5 × 10−9
6.5 × 10−7
4.1 × 10−6
Conventional descaling technologies include chemical and electromagnetic methods. Chemical methods utilize either pH adjustment, chemical sequestration with polyphosphates, zeolites and the like, or ionic exchange; combinations of these methods are typically used. Normally, chemical methods aim at preventing scale from precipitating by lowering the pH and using chemical sequestration, but they are typically not 100% effective. Electromagnetic methods rely on the electromagnetic excitation of calcium or magnesium carbonate so as to favor crystallographic forms that are non-adherent. For example, electromagnetic excitation favors the precipitation of aragonite rather than calcite; the former is a softer, less adherent form of calcium carbonate. However, electromagnetic methods are only effective over relatively short distances and residence times. There is a need for permanently removing scale-forming constituents from contaminated aqueous solutions, seawater, or produced waters that will be subject to be further processing.
Other factors can complicate scale reduction methods, particularly in high-salinity solutions such as seawater or produce water. These include the buffering effects of high ionic strength solutions and ion complexing phenomena that can shield certain cations from reacting.
An embodiment of the present invention provides a method for removing scale-forming compounds from tap water, contaminated aqueous solutions, seawater, and saline brines such as produced water, involving the initial removal of magnesium ions by precipitating magnesium hydroxide (Mg(OH)2) at high pH, then removing the precipitate by either sedimentation or filtering. Ordinarily, Mg(OH)2 precipitates at high pH (around 11.0), although in many cases the bulk of magnesium precipitates at lower pH.
Following Mg(OH)2 precipitation, carbonate ions are added in the form of CO2 sparging, by adding soluble carbonate or bicarbonate salts in nearly stoichiometric amounts so as to subsequently precipitate calcium, barium, and other divalent cations as carbonates by adjusting the pH to about 10.2 or greater. This process has the net effect of permanently sequestering CO2 from the atmosphere, and the precipitates are then removed by either sedimentation or filtering.
A detailed description of this pre-treatment embodiment follows the flowsheet of
Following precipitation of Mg(OH)2 in vessel V101 (40), the clear solution exits near the top and flows into a static mixer M101 (60), where it is mixed with additional clear filtrate from filter F101 (50) and pump P103 (24) and a source of carbonate ions, which can be pressurized CO2 gas from V102 (32) or a solution of soluble carbonates or bicarbonates.
The aqueous solution then flows into a second static mixer M102, where additional caustic or alkali chemicals are added from the variable valve Va101 (45) so as to adjust the pH to about 10.2, at which point most of the divalent cations in solution precipitate as insoluble carbonates. The precipitate slurry then enters mixer-settler V103 (42), where the insoluble carbonates sediment and flow into filter F102 (52), where a second filter cake (68) is removed. The filtrate from filter F102 enters pump P105 (26), which feeds a variable valve Va102 (47) that allows a portion of the descaled water product (70) to recirculate back into the carbonation loop.
In a further aspect, especially when the contaminated water contains excess carbonate or bicarbonate ions, calcium or magnesium can be added in order to provide the stoichiometric requirements for carbonate precipitation. Alternatively, calcium and magnesium can be substituted for other divalent cations, such as barium, cadmium, cobalt, iron, lead, manganese, nickel, strontium, or zinc, that have low solubility products in carbonate form.
In a further aspect, calcium or magnesium additions are substituted for trivalent cations, such as aluminum or neodymium, that have low solubility products in their carbonate or hydroxide forms.
In a further aspect, CO2 sparging is replaced by the addition of soluble bicarbonate ions, such as sodium, potassium, or ammonium bicarbonate.
In a further aspect, carbonate and scale precipitates are removed by means other than sedimentation or filtering, such as centrifuging.
In a further aspect, the permanent sequestration of CO2 from the atmosphere is achieved in conventional desalination systems, such as MSF evaporation systems, MED plants, and VC desalination systems.
In a further aspect, scale-forming salts are permanently removed from conventional desalination systems.
In a further aspect, tap water, municipal water, or well water containing objectionable hard water constituents, such as calcium or magnesium, are descaled in residential water purification systems.
In a further aspect, valuable scale-forming salts, such as magnesium, barium, and other salts, are recovered.
In a further aspect, scale-forming compounds are precipitated in the form of non-adhering, easily filterable or sedimentable solids and ultimately removed.
In a further aspect, CO2 emissions from power plants and similar flue gases are permanently sequestered.
In a further aspect, scale-forming compounds are sequentially precipitated and removed, so they can be utilized and reused in downstream industrial processes.
A further embodiment of the present invention provides a method for removing a scale-forming compound from an aqueous solution, involving: adding at least one ion to the solution in a stoichiometric amount sufficient to cause the precipitation of a first scale-forming compound at an alkaline pH; adjusting the pH of the solution to an alkaline pH, thereby precipitating the first scale-forming compound; removing the first scale-forming compound from the solution; heating the solution to a temperature sufficient to cause the precipitation of a second scale-forming compound from the solution; and removing the second scale-forming compound from the solution.
In a further aspect, the ion is selected from the group including carbonate ions and divalent cations. In a further aspect, the carbonate ion is HCO3−. In a further aspect, the divalent cation is selected from the group including Ca2+ and Mg2+.
In a further aspect, the stoichiometric amount is sufficient to substitute the divalent cation for a divalent cation selected from the group including barium, cadmium, cobalt, iron, lead, manganese, nickel, strontium, and zinc in the first scale-forming compound.
In a further aspect, the stoichiometric amount is sufficient to substitute the divalent cation for a trivalent cation selected from the group including aluminum and neodymium in the first scale-forming compound.
In a further aspect, adding at least one ion comprises sparging the solution with CO2 gas.
In a further aspect, the CO2 is atmospheric CO2.
In a further aspect, adding at least one ion comprises adding a soluble bicarbonate ion selected from the group including sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate to the solution.
In a further aspect, adding at least one ion comprises adding a compound selected from the group including CaO, Ca(OH)2, Mg(OH)2, and MgO to the solution.
In a further aspect, the alkaline pH is a pH of approximately 9.2 or greater.
In a further aspect, the first scale-forming compound is selected from the group including CaCO3 and MgCO3.
Tn a further aspect, adjusting the pH of the solution comprises adding a compound selected from the group including CaO and NaOH to the solution.
In a further aspect, removing the first scale-forming compound comprises at least one of filtration, sedimentation, and centrifuging.
A further embodiment of the present invention provides a method of obtaining scale-forming compounds, involving: providing an aqueous solution; adding alkali chemicals in amounts sufficient to cause the precipitation of a first scale-forming compound at an alkaline pH; adjusting the pH of the solution to an alkaline pH, thereby precipitating the first scale-forming compound; removing the first scale-forming compound from the solution; adding carbonate ions while maintaining an alkaline pH sufficient to cause the precipitation of a second scale-forming compound from the solution; removing the second scale-forming compound from the solution; recovering the first scale-forming compound; and recovering the second scale-forming compound.
In a further aspect, the first and second scale-forming compounds are selected from the group of compounds listed in Table 4.
A further embodiment of the present invention provides a method of sequestering atmospheric CO2, involving: providing an aqueous solution containing at least one ion capable of forming a CO2-sequestering compound in the presence of carbonate ion; adding carbonate ions to the solution in a stoichiometric amount sufficient to cause the precipitation of the CO2-sequestering compound at an alkaline pH; adjusting the pH of the solution to an alkaline pH, thereby precipitating the CO2-sequestering compound; and removing the CO2-sequestering compound from the solution; wherein adding carbonate ions comprises adding either atmospheric or concentrated CO2 (e.g., from a combustion flue gas) to the solution, and wherein the CO2 is sequestered in the CO2-sequestering compound.
In preferred embodiments, such as those shown in
In
Preheated and degassed water that enters the boiler (92) is further heated by heat pipes (78) that transfer the heat of condensation from a condenser (94). The steam produced in the boiler (92) is cleaned in a demister that is described below and is condensed in a condenser (90), and the clean water product exits the system via a pipe (102), which collects clean water product from each condenser. As water is evaporated from the boiler (92), the concentration of dissolved salts increases. The level of boiling water in the boiler (92) is maintained at a constant level by a downcomer tube (101), which allows water to exit the boiler by gravity.
An important element in the vertical arrangement of boilers and condensers is the ability to maintain a slight pressure differential between boilers, so that a lower boiler will have a slightly higher pressure than an upper boiler; therefore, the temperature of the lower boiler will be slightly higher than that of an upper boiler. This pressure differential can be maintained by a pump, but, in a preferred embodiment, it is simply maintained by the hydraulic head of the downcomer tubes (100) and (101), which maintain such pressure differential by means of a lower pressure-actuated valve (103).
A more detailed description of the vertical arrangement of boilers and condensers is provided in
As water boils in the boiler (92), it becomes denser and more concentrated in soluble salts and exits through the downcomer tube (100) into a lower boiler (96). A valve (103) at the bottom of the downcomer tube (100) provides the necessary hydraulic pressure to maintain the lower boiler (96) at a slightly higher pressure and, thus, at a slightly higher temperature than the upper boiler (92).
The tubes (120) and (130) and the intermediate valve (125) serve dual functions. During start-up procedures, the valve (125), which can be controlled by a pressure regulator or a solenoid, is open, allowing steam to travel directly from the lower boiler (96) to the upper boiler (92), thus accelerating start-up procedures. Once the system is operating at the correct temperature, the valve (125) is closed. During shut-down procedures, the heat source is shut off, and the valve (125) is re-opened so as to facilitate draining of all the boilers.
In contrast with water flow, heat travels upward in the system, from the heat input vessel at the bottom (150) ultimately to the preheating vessel at the top (74), by means of multiple stages of heat pipes (78). At each stage, the heat of condensation or, in the case of the heat input vessel at the bottom (150), the latent heat of flue gases or the heat of condensation of waste steam, is absorbed by a series of heat pipes that transfer the heat to an upper boiler and, at the top of the vertical stack, to the upper preheating tank (74).
An important advantage of the system described herein is the mechanism of heat transfer via heat pipes. As shown in a subsequent section, heat pipes provide a means of transferring heat that is nearly thermodynamically reversible, that is, a system that transfers enthalpy with almost no losses in efficiency. Thus, with the exception of the preheating energy, nearly all of the heat provided by the heat input vessel at the bottom (150) is re-used at each of the boiling and condensing stages by minimizing heat losses at the wall separating the condensing side of the heat pipe from the boiling side. Since that distance is defined by the perforated plate (93), which can be very thin or made as an insulator, the amount of heat lost during heat transfer can be close to zero. Therefore, the energy used during multiple stages of boiling and condensing can be readily approximated by dividing the heat of evaporation of water by the number of stages of the system.
However, as the number of stages in the system increases, the amount of steam produced at each stage decreases; with a large number of stages, the amount of heat that condenses at the upper condenser is insufficient to provide the necessary heat for preheating the incoming water and also insufficient for providing the necessary steam required for degassing. Table 5 illustrates these energy requirements for the case of seawater, which is normally devoid of organic contaminants, as a function of the number of stages in the system, but ignoring degassing requirements.
The above estimates presume that the heat available in the hot waste brine at the bottom of the system and the heat contained in the various product water streams is recovered either by means of heat exchangers or heat pipes. In a simple arrangement, most of this heat can be recovered by preheating the incoming water in exchange with each of the product streams as they cascade downward in a vertical system, ending with heat recovery from the waste brine, and then re-pumping this preheated water to the top of the system, where a minimal amount of supplemental heat is required to bring the temperature up to the boiling point.
In alternative embodiments, the product water at each stage can be re-introduced into an upper condenser stage and allowed to flash, thus releasing part of the contained heat. In other embodiments, the incoming pre-treated water can be divided into separate streams and introduced into each separate stage for distillation.
It is advantageous to be able to maximize the number of boiling and condensing stages in the present invention. This is possible through the use of heat pipes, provided the temperature difference between the condensing and boiling ends of such a heat pipe (the ΔT) is sufficient to maintain the maximum heat flux through the heat pipe. Commercially available heat pipes typically have ΔTs of the order of 8° C. (15° F.), although some have ΔTs as low as 3° C. The ΔT defines the maximum number of stages that are practical with a given amount of heat available at a given temperature. Thus, there is a need for heat pipes that can function with as small a ΔT as possible. It is therefore useful to examine the thermal phenomena in a heat pipe.
Experimentally, the largest barriers to heat transfer in a heat pipe include: 1) the layer immediately adjacent to the outside of the heat pipe, 2) the conduction barrier presented by the material of the heat pipe, and 3) the limitation of the wick material to return working fluid to the hot end of the heat pipe.
In
The heat conduction barrier is also minimized by using a very thin metal foil (77) instead of the solid metal tube of most heat pipes. Mechanical support for the metal foil must be sufficient to sustain moderate vacuum and is provided by a metal screen (85), which provides additional functionality by increasing the internal surface area required for providing the necessary heat of condensation/evaporation.
An improved distribution of working fluid is achieved by orienting the wick toward the axis of the heat pipe, thus reducing the thermal interference of condensate with heat transfer across the wall of the heat pipe. The wick material can be any hydrophilic porous medium that can transfer working fluid by capillary action, such as metallic oxides, some ceramics, surface-treated cellulosic materials, and the like.
In some embodiments, the system for descaling water and saline solutions, embodiments of which are disclosed herein, can be combined with other systems and devices to provide further beneficial features. For example, the system can be used in conjunction with any of the devices or methods disclosed in U.S. Provisional Patent Application No. 60/676,870, entitled SOLAR ALIGNMENT DEVICE, filed May 2, 2005; U.S. Provisional Patent Application No. 60/697,104, entitled VISUAL WATER FLOW INDICATOR, filed Jul. 6, 2005; U.S. Provisional Patent Application No. 60/697,106, entitled APPARATUS FOR RESTORING THE MINERAL CONTENT OF DRINKING WATER, filed Jul. 6, 2005; U.S. Provisional Patent Application No: 60/697107, entitled IMPROVED CYCLONE DEMISTER, filed Jul. 6, 2005; PCT Application No: US2004/039993, filed Dec. 1, 2004; PCT Application No: US2004/039991, filed Dec. 1, 2004; PCT Application No: US2006/040103, filed Oct. 13, 2006; U.S. patent application Ser. No. 12/281,608, filed Sep. 3, 2008; PCT Application No. US2008/03744, filed Mar. 21, 2008; and U.S. Provisional Patent Application No. 60/526,580, filed Dec. 2, 2003; each of the foregoing applications is hereby incorporated by reference in its entirety.
One skilled in the art will appreciate that these methods and devices are and may be adapted to carry out the objects and obtain the ends and advantages mentioned, as well as various other advantages and benefits. The methods, procedures, and devices described herein are presently representative of preferred embodiments and are exemplary and are not intended as limitations on the scope of the invention. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the disclosure.
The invention illustratively described herein suitably can be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that the use of such terms and expressions indicates the exclusion of equivalents of the features shown and described or portions thereof. It is recognized that various modifications are possible within the scope of the invention disclosed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art and that such modifications and variations are considered to be within the scope of this invention as defined by the disclosure.
Those skilled in the art will recognize that the aspects and embodiments of the invention set forth herein can be practiced separately from each other or in conjunction with each other. Therefore, combinations of separate embodiments are within the scope of the invention as disclosed herein.
All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.
The approximate chemical composition of seawater is presented in Table 6, below, and is typical of open ocean, but there are significant variations in seawater composition depending on geography and/or climate.
Fifty gallons of ocean seawater were collected and treated in a pilot facility able to continuously handle from 20 to 200 gallons/day. Initially, 50 mL/liter of a 10% sodium hydroxide (caustic) solution was used to raise the pH of the seawater to approximately 11.2 and the resulting precipitate allowed to sediment in a thickener prior to filtering using a 1μ pore filter. The filtrate was then conditioned with 0.9 g/liter of sodium bicarbonate, and the pH was adjusted to 10.2 so as to obtain another precipitate of carbonate salts, which was again allowed to sediment and was subsequently filtered using a micron filter. Chemical analysis of the final filtrate showed a reduction of about 67% of the scale-forming ions, such as calcium and magnesium, with the balance of calcium and magnesium forming soluble chlorides that do not precipitate upon boiling.
In a similar experiment, one liter of ocean seawater was treated with 30 mL of a 10% sodium hydroxide (caustic) solution was used to raise the pH of the seawater to slightly less than 11.0 and the resulting precipitate allowed to sediment in a thickener prior to filtering using a 1μ pore filter. The filtrate was then conditioned with 0.9 g/liter of sodium bicarbonate, and the pH was adjusted to 9.8 by adding another 0.7 g of caustic solution so as to obtain a precipitate of carbonate salts which was allowed to sediment and was subsequently filtered using a 1μ filter. No scale formation compounds were detected in the resulting filtrate.
A special test procedure was developed for ascertaining the degree of descaling in treated solutions. In this test, a sample of treated solution is collected in a glass beaker, and the sample is subjected to boiling in a pressure cooker for up to 5 hours at temperatures of 120° C. under pressure. Following this test procedure, the sample is removed and inspected visually as well as under a microscope to detect any solid precipitate. Since the residence time in the desalinating section that follows is only a couple of hours, the absence of any scale in this particular test proves that no scale will form during desalination. In none of the examples described herein was any scale detected after pre-treatment.
An aqueous waste influent composition obtained as a waste stream from a fertilizer processing facility was treated in the manner described above in order to remove scale-forming compounds, as a pre-treatment to eventual desalination of the product in a separate water purification apparatus in which the formation of scale would be highly undesirable. The throughput of the treatment apparatus was 6 gallons per day (GPD), which was used a pilot apparatus for testing an industrial situation requiring 2000 m3/day (528,401.6 GPD). The composition of the waste influent with respect to relevant elements and ions is given in Table 7 below.
The waste influent had a TDS content of 35,000 ppm (mg/L). As can be seen from Table 7, the waste influent had particularly high concentrations of calcium and magnesium, which tend to give rise to scale.
The waste influent was processed in the manner described above. Because the influent contained little or no hydrocarbons, deoiling and degassing were not conducted. CO2 carbonation and addition of NaOH (to provide hydroxide ions to react with the Mg in solution) were followed by pH adjustment to a pH of 9.3 using additional NaOH. The process resulted in a filtered scale-forming composition (“filter cake”) and an effluent (product). The effluent product was tested for scale formation according to the procedure described above, and no scale or precipitate was detected.
The treatment process of the present disclosure was applied to seawater that had been adjusted to a high level of TDS and a high degree of water hardness, in order to test the capacity of the process to deal with such input solutions as produced water from oil extraction operations or waste water from gas fracking operations. The water was pretreated using the process of the present disclosure before being purified in a water desalination apparatus such as that described in U.S. Pat. No. 7,678,235. As discussed in greater detail below, the seawater subjected to the pretreatment process of the present disclosure showed no formation of scale when used as feed water in the water purification apparatus.
The following amounts of various compounds were added to fresh ocean water to produce the input aqueous solution of the present example: 7 grams/liter of Ca(OH)2 were added to produce a target Cat′ concentration of 7.1 kppm, and 29 grams/liter of NaCl were also added. The TDS of the resulting water sample was 66 kppm.
A first precipitation was conducted at room temperature by adding approximately 5 grams/liter of NaOH as necessary to increase the pH of the solution to greater than 10.5. A milky precipitate containing mainly magnesium hydroxide was precipitated in this first room temperature procedure. The water was filtered to remove the solid precipitates.
A second precipitation was then conducted by adding sodium bicarbonate and sufficient caustic to adjust the pH to 9.8, and a second precipitate containing mainly calcium and other carbonates was obtained. The TDS of the descaled and filtered water was approximately 65 kppm.
The descaled water was used as an influent for a water purification apparatus in accordance with U.S. Pat. No. 7,678,235. The product water was collected from the apparatus, and the TDS of the product water was measured. While the inlet water had a TDS of 65 kppm, the product water of the water purification apparatus was less than 10 ppm. No appreciable development of scale was observed in the boiler of the apparatus.
Fifty gallons of ocean water were first pre-treated according to the procedures described earlier and fed into a pilot desalinator designed for a 50-200 GPD throughput. The product water had a TDS of less than 10 ppm, and no signs of scale formation were detected in any of the boilers.
Fifty gallons of a synthetic produced water containing in excess of 146,000 ppm of TDS and significant alkalinity were first pre-treated according to the procedures described earlier and fed into a pilot desalinator designed for a 50-200 GPD throughput. The product water had a TDS of less than 40 ppm, and no signs of scale formation were detected in any of the boilers.
Fifty gallons of brackish water containing in excess of 3,870 ppm of TDS were first pre-treated according to the procedures described earlier and fed into a pilot desalinator designed for a 50-200 GPD throughput. The product water had a TDS of less than 10 ppm, and no signs of scale formation were detected in any of the boilers.
This application claims priority to U.S. Provisional Patent Application No. 61/532,766, filed Sep. 9, 2011, and the entire disclosure of that application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61532766 | Sep 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14343517 | May 2014 | US |
| Child | 15797534 | US |
