Patent Application
20200062617
This disclosure relates to the field of water treatment, particularly to methods and apparatus for the treatment of mineral-containing brine to separate minerals contained in the brine from water, and for the treatment of wastewater from gas and oil wells.
In one embodiment, a method for the separation of water and minerals from a mineral-containing wastewater stream is disclosed. The method includes the steps of passing the wastewater stream at substantially ambient pressure and at a temperature of at least about 40° C. through a membrane assembly comprising a pervaporation membrane separating a retentate volume from a permeate volume, where water from the wastewater stream diffuses through the pervaporation membrane to form a substantially mineral-free water vapor. Pressure is reduced in the permeate volume of the membrane assembly to below ambient pressure to enhance the flow of the water vapor out of the membrane assembly. A mineral-rich product is removed from the membrane assembly comprising minerals from the wastewater.
The foregoing method may be characterized as having different implementations, refinements and/or additional steps, which may be employed alone or in any combination. In one implementation, the mineral-rich product comprises a retentate stream formed in the retentate volume of the membrane assembly. In one refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not greater than about 0.5 bar. In another refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not greater than about 0.4 bar. In yet another refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not less than about 0.3 bar. In yet another refinement, the wastewater stream has a temperature of at least about 50° C. during the step of passing the mineral-containing wastewater stream through the membrane assembly. In a further refinement, the wastewater stream has a temperature of at least about 60° C. during the step of passing the mineral-containing wastewater stream through the membrane assembly.
In one implementation, the mineral-rich product comprises a solid phase that deposits within the permeate volume of the membrane assembly. In one refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not greater than about 0.3 bar. In another refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not less than about 0.1 bar. In yet another refinement, the step of reducing the pressure in the permeate volume of the membrane assembly comprises reducing the pressure to not less than about 0.2 bar. In another refinement, the step of passing the mineral-containing wastewater stream through the membrane assembly comprises passing the wastewater stream at a temperature of at least about 65° C. In a further refinement, the step of passing the mineral-containing wastewater stream through the membrane assembly comprises passing the wastewater stream at a temperature of not greater than about 90° C. In one particular refinement, the step of passing the mineral-containing wastewater stream through the membrane assembly comprises passing the wastewater stream at a temperature of at least about 70° C. and not greater than about 80° C.
In another implementation, wherein the step of reducing the pressure in the permeate volume of the membrane assembly comprises using a vacuum pump that is operatively connected to the permeate volume of the membrane assembly. In one refinement, the vacuum pump is a venturi vacuum pump.
In another implementation, the method includes the step of heating the mineral-containing wastewater stream before the step of passing the mineral-containing wastewater stream through the membrane assembly. In one refinement, the heating step comprises heating the mineral-containing wastewater stream using natural gas as an energy source.
In another implementation, the pervaporation membrane is an inorganic membrane. In one refinement, the membrane is a ceramic membrane. In another implementation, the pervaporation membrane is a mesoporous membrane. In one refinement, the pervaporation membrane has a pore size of at least about 2 nanometers. In another refinement, the pervaporation membrane has a pore size of not greater than about 20 nm. In one implementation, the membrane assembly comprises a tubular membrane assembly.
In another implementation, the method includes the step of chilling the water vapor to condense the water vapor into liquid water. In one refinement, the chilling step comprises chilling the water vapor to not greater than about 10° C. In another refinement, the chilling step comprises chilling the water vapor to not greater than about 5° C. In one implementation, at least about 80% of water from the mineral-containing wastewater stream is recovered with the liquid water. In another implementation, the liquid water condensed from the water vapor has a purity of at least about 99.9%.
In one implementation, the mineral-containing wastewater stream comprises a natural brine. In one refinement, the natural brine comprises at least about 30 g/L dissolved salts. In another refinement, the natural brine comprises at least about 30 g/L sodium chloride. In yet another refinement, the natural brine comprises at least about 75 ppm lithium. In a further refinement, the mineral-rich retentate stream comprises at least about 375 ppm lithium, and in yet a further refinement, the mineral-rich retentate stream comprises at least about 750 ppm lithium.
In one implementation, the mineral-containing wastewater stream comprises produced water from an oil/gas extraction operation. In one refinement, the mineral-containing wastewater stream comprises hydrocarbons, and the method includes the step of removing the hydrocarbons from the wastewater before passing the wastewater stream through the membrane assembly. In a further refinement, the hydrocarbons are separated from the wastewater stream before being passed through the membrane assembly. In yet another refinement, the mineral-containing wastewater stream comprises at least about 50 ppm lithium. In a further refinement, the mineral-rich retentate comprises at least about 250 ppm lithium.
In one implementation, the mineral-containing wastewater stream comprises an aqueous solution recovered from an in-situ leaching process. In one refinement, the aqueous solution comprises uranium. In one particular refinement, the aqueous solution comprises at least about 50 ppm uranium. In another refinement, the mineral-rich product comprises at least about 250 ppm uranium. In yet another refinement, the mineral-rich product comprises at least about 500 ppm uranium.
In another implementation, the wastewater stream includes particulate solids and the method includes the step of separating at least a portion of particulate solids from the wastewater stream before passing the wastewater stream through the membrane assembly. In yet another implementation, the mineral-containing wastewater stream has a pH of at least about pH 6 when the wastewater stream is passed through the membrane assembly. In another implementation, the mineral-containing wastewater stream has a pH of not greater than about pH 8 when the mineral-containing wastewater stream is passed through the membrane assembly.
In another embodiment, an apparatus that is configured for the treatment of a mineral-bearing wastewater stream is disclosed. The apparatus includes a membrane assembly, the membrane assembly comprising a pervaporation membrane separating a retentate volume from a permeate volume. A mineral-bearing wastewater stream source is fluidly connected to the membrane assembly to provide a mineral-bearing wastewater stream to the membrane assembly. A heater is configured to heat the mineral-bearing wastewater stream to a temperature above ambient temperature before being passed to the membrane assembly. A chiller is fluidly connected to the membrane assembly and is configured to chill a permeate stream extracted from the permeate volume, and a vacuum pump is operatively connected to the permeate volume and is configured to maintain the permeate volume at a pressure below ambient pressure.
The foregoing apparatus may be characterized as having different configurations, characterizations and/or additional components, which may be employed alone or in any combination. In one configuration, the pervaporation membrane is an inorganic membrane. In another configuration, the membrane is a ceramic membrane. In yet another configuration, the pervaporation membrane has a pore size of at least about 2 nanometers. In a further configuration, the pervaporation membrane has a pore size of not greater than about 20 nm. In another configuration, the water heater is configured to burn methane gas to heat the wastewater stream.
The present disclosure is directed to methods and systems (e.g., apparatus) for the treatment of wastewater (e.g., aqueous solutions) to separate high quality (e.g., high purity) water from the other components of the wastewater. For example, the wastewater may be a brine solution and the method may include the formation of a useful concentrate of the other brine components, such as minerals (e.g., metal salts), that may be treated to recover salable compounds from the concentrate. Other sources of wastewater-containing streams that may be treated and purified include hydrometallurgical leach solutions, mine drainage and produced water that is a by-product of oil and gas extraction operations.
The methods and systems disclosed herein include the use of a membrane assembly, and in particular a membrane assembly that includes a pervaporation membrane. Pervaporation membranes exhibit different permeabilities towards different components of a mixture, and this functionality is utilized to selectively transport one component through the membrane as a vapor (e.g., water vapor), and leave the other components in the retentate, e.g., to dehydrate the mixture. This is in contrast to reverse osmosis (RO), which uses an applied pressure to overcome the osmotic pressure and reverse the natural flow of the solvent (e.g., water) through the membrane. RO is costly to operate, in part due to the high pressures that are necessary to overcome the osmotic pressure.
As is noted above, the wastewater may be the by-product of an industrial process, such as produced water from oil and/or natural gas extraction, effluent from mining operations, effluent from power plant cooling towers, etc. The wastewater may also be a natural product, such as a natural brine or seawater, including natural brines that are extracted by in-situ mining techniques or brine mining techniques. Although the following description refers to the wastewater to be treated as a brine (e.g., a brine solution), it is to be appreciated that the methods and apparatus may be used to treat any type of wastewater or other aqueous solution, including but not limited to the foregoing.
Broadly characterized, the disclosed embodiments include a method for the treatment of a brine solution. Referring to
According to the present disclosure, the brine solution is passed through a membrane system 150. Before being passed through the membrane system 150, the brine solution 110 may be passed through a heating system 130 to raise the temperature of the brine solution 110 to a desired temperature, e.g., a temperature above the ambient temperature.
The heating system 130 may include any device that is configured for the heating of a liquid, e.g., the heating of an wastewater stream. One embodiment of a heating system according to the present disclosure is illustrated in
Referring back to
In one embodiment, the pervaporation membrane is a mesoporous membrane. For example, the pervaporation membrane may have a pore size of at least about 1 nanometer, such as at least about 1.5 nanometers or even at least about 2 nanometers. In another embodiment, the pervaporation membrane has a pore size of not greater than about 20 nanometers, such as not greater than about 10 nanometers, such as not greater than about 7 nanometers. In one particular characterization, the pervaporation membrane has a pore size range of from about 2.5 nanometers to about 5 nanometers.
Referring back to
In one embodiment, the chiller is configured (e.g., is operated) to reduce the temperature of the permeate vapor 414v to not greater than about 12° C., such as not greater than about 10° C., such as not greater than about 2° C. In another embodiment, the chiller 474 is operated to ensure that at least about 95% of the water in the vapor 414v is converted to liquid water 4141, such as at least about 98%, such as at least about 99% or even at least about 99.5%. In some embodiments, the recovered water (e.g., in tank 480) may be have a high purity, and in particular may be substantially free of other brine components from the brine solution 410. For example, the liquid water 4141 may have a purity of at least about 95%, such as at least about 98%, such as at least about 99% or even at least about 99.5%. Further, the amount of water recovered from the brine solution may be at least about 50%, such as at least about 60%, such as at least about 70%, such as at least about 75% or even at least about 80% or at least about 90%. Thus, a large quantity of high purity water may be recovered from the brine solution.
In addition, the system 400 illustrated in
The compression system 582 may compress the air to a pressure of at least about 5 bar, such as at least about 8 bar, such as at least about 10 bar or even at least about 12 bar. Typically, it will not be necessary to compress the air to more than about 30 bar, such as no more than about 25 bar, or no more than about 20 bar. The compression system 582 may also include a particle filter 588 and/or a dryer 590 to remove particulates and/or to dry the air after compression. After compression, the compressed air is supplied to a venturi vacuum pump 592. The compressed air is supplied to the venturi vacuum pump 592 at a relatively high pressure and relatively low velocity, and exits the venturi vacuum pump at a lower pressure and a higher velocity. As a result, the venturi vacuum pump 592 draws a vacuum through a vacuum port 594 that is operatively connected to the membrane modules, e.g., to the permeate side of the membranes, to draw permeate vapor from the membrane modules.
According to certain embodiments of the present disclosure, the composition of the permeate stream and the retentate stream can be controlled through the selection and application of process variables such as the membrane pore size, the temperature of the heated brine entering the membrane system and the value of the reduced pressure on the permeate side of the membrane modules. In one embodiment, minerals from the brine solution are recovered in the retentate stream extracted from the membrane assembly. According to this embodiment, the minerals remain in the retentate and only water vapor is passed through the pervaporation membrane and recovered as the permeate. Broadly characterized, this embodiment includes heating the brine solution to a relatively low temperature and applying a relatively weak vacuum (e.g., higher pressure) to the permeate. In this manner, the minerals (which have a relatively larger molecule size than the water) from the brine solution remain in the retentate. Thus, two product streams are recovered: a mineral-rich retentate and relatively pure water.
For example, the heating system 130 (
In another embodiment, the brine solution is heated to a relatively higher temperature and/or the vacuum applied to the permeate is relatively stronger (e.g., the pressure is lower) as compared to the embodiment described above for the separation of minerals in the retentate. In this manner, a substantial portion of the minerals are drawn through the pervaporation membrane. It has been found that when operating in this manner, the minerals form a solid (e.g., crystalline) phase on the permeate side of the pervaporation membrane (e.g., in the permeate volume), while the permeate vapor is substantially free of minerals.
According to this embodiment, the heating system 130 (
It has been found that another factor influencing the transport of the minerals through the pervaporation membrane is the flow rate of the feed, e.g., the flow rate of the brine solution into the membrane system. A higher flow rate will tend to force the minerals through the pervaporation membrane, even at temperatures below 75° C., such as in the range of about 50° C. to 60° C. Conversely, relatively low flow rates will require the use of higher temperatures and lower permeate pressures to transport the minerals through the pervaporation membrane.
Referring to
Another embodiment of a system and method for the separation of minerals and water from a brine solution is illustrated in
Referring first to
As illustrated in
By way of example only, the elements and minerals in a feed brine solution may be partitioned as shown in Table I.
It is noteworthy that a substantial portion of the LiCl from the brine (e.g., at least about 90%) is recovered in the solid phase, whereas a smaller amount of MgCl2 from the brine (e.g., not greater than 50%) stays in the retentate. This is beneficial to downstream processing to separate Li from Mg, as these two elements are known to be difficult to separate.
As is noted above, the brine solution may come from a variety of sources including natural or artificial brines. In some embodiments, the brine may include at least about 50,000 ppm, minerals, such as at least about 5,000 ppm minerals, or even at least about 500 ppm minerals. Typically, the brine will include not greater than about 1500 ppm minerals. For example, in some embodiments the brine minerals may include lithium, e.g., in concentrations of at least about 5 ppm, 50 ppm, 150 ppm or higher. The recovery of a mineral-rich product having a high concentration of lithium is advantageous for the production of batteries, e.g., lithium-ion batteries. The brine may also include uranium (e.g., from an in-situ leaching process) and the methods and systems described herein may be used to concentrate the uranium for subsequent recovery.
A sample (Sample 1) of wastewater from a fracking operation is obtained. Sample 1 is first filtered to remove particulate matter, and is treated to remove hydrocarbons and residual oil using known techniques. After filtering and removal of hydrocarbons, the solution is rich in common alkaline salts of potassium, sodium and calcium. The solution also includes some fluorides, iron and some heavy metals. The solution has a density of 1.0988 g/cm3, and the concentrations of salt species and metals listed in Table II. All metal salts are in chloride form and total chloride concentration is about 77.8 g/L, or about 77,800 ppm. The dominant species is sodium.
About 4 liters of the solids-free and crude oil-free wastewater solution is placed in a holding tank from which it is pumped to a pervaporation membrane assembly. The membrane assembly (e.g., module) includes four tubes of a silica-based pervaporation membrane (Pervatech BV, Netherlands). The process circuit includes the holding tank for supplying the solution to the feed side (e.g., retentate side) of the membrane using a feed pump, while a vacuum pump connected to the permeate port. The wastewater is recycled back to the feed tank after passing through the membrane repetitively until most of the freshwater is recovered. The final solution retained in the tank is rich in metal chloride salts and may be disposed of, or may be beneficiated for valuable metals. A second tank with additional wastewater replaces the first tank with the highly concentrated salts and the process is repeated.
In this example, the wastewater solution is heated to about 61° C. and the feed pump is activated to begin circulating the solution through the assembly at a rate of about 190 liters/hr. At the same time, the vacuum pump is turned on and is set to reduce the pump gauge pressure to about 0.45 mbar, resulting in a suction pressure on the membrane of about 0.4 bar. The initial flux of water through the pervaporation membrane is about 9.5 kg/[m2·hr]. After a period of time, the feed pump is stopped and about 760 ml of liquid permeate is collected (“Permeate 1-1”). The feed pump is restarted, and this intermittent process is continued with subsequent permeate volumes of 720 ml (“Permeate 1-2”), 320 ml (“Permeate 1-3”) and 100 ml (“Permeate 1-4”) being collected. The assays are shown in Table III.
To illustrate the efficacy of the method, the combined the data from Table I and Table IV for chlorides and sodium (e.g., the dominant salt species of sodium chloride) is shown:
Table IV illustrates that the method was effective to remove a high purity water permeate having significantly reduced chloride concentration. It is believed that the concentration of chloride increased with subsequent permeate samples as a result of chloride salts (e.g., NaCl) forming on the permeate side of the membrane. This is also evidenced by the flux through the membrane decreasing from an initial flux of about 9.5 kg/[m2·hr] to about 6.5 kg/[m2·hr] near the end of the sampling procedure.
After Permeate 1-3 (320 ml) is removed, about 190 ml of deionized water is used to flush the permeate side of the membrane. The resulting flush water was assayed, and the results are shown in Table V.
At the same time (i.e., after Permeate 1-3 was collected), the retentate contained a concentration of 152000 mg/kg chloride and 87100 mg/kg sodium.
Table VI illustrates the assay of a small sample of the crystalline layer that develops along the external surface (permeate side) of the pervaporation membrane taken after completion of the testing.
It is clear from the assays shown in Table V and Table VI that sodium is selectively diffused through the pervaporation membrane and is retained in the crystalline phase on the permeate side of the membrane, while heavy metals remain in the retentate. This is evidenced by partition of 88-95% of sodium to the crystal phase while less than 1% of each of the metals reports the crystalline phase. This result signifies the ability to recover water selectively through the permeate and specific metal crystals such as sodium chloride and lithium chloride to the crystal phase. A small volume of backwash water is applied to recover crystals from membrane surfaces at ambient or otherwise moderate temperature. This practice mimics solvent extraction, where the membrane serves as a media for separating sodium or lithium from bulk metal elements in a feed liquor to a third phase. The crystals are stripped by a small volume of electrolyte to produce a sufficiently concentrated electrolyte suitable for subsequent reduction to the metal by electrolysis or precipitation.
Another sample (“Sample 2”) of wastewater solution from a fracking process is obtained having a density of 1.031 g/ml and a concentration of salt species and metals listed in Table VII. The total metal chloride concentration is about 25.2 g/L or about 25,200 ppm. The dominant species is sodium.
In a manner similar to that described above for Sample 1, about 4 liters of the solution is placed in a pervaporation membrane assembly. The membrane assembly includes multiple silica-based pervaporation membrane tubes (Pervatech BV, Netherlands). The assembly also includes a tank for supplying the solution to the feed side of the porous membrane tubes using a feed pump and a vacuum pump is connected to the permeate port. The solution is heated to about 61° C. and the feed pump is activated to begin circulating the solution through the assembly at a rate of about 190 liters/hr. At the same time, the vacuum pump is turned on and is set to a gauge pressure of about 0.45 mbar, resulting in a suction pressure on the permeate side of the membrane of about 0.4 bar. The initial flux of water through the pervaporation membrane is about 8.45 kg/[m2·hr]. After a period of time, the feed pump is stopped and about 690 ml of liquid permeate is collected (“Permeate 2-1”). The feed pump is restarted, and this intermittent process is continued with subsequent permeate volumes of 710 ml (“Permeate 2-2”), 250 ml (“Permeate 2-3”) 210 ml (“Permeate 2-4”) and 430 ml (“Permeate 2-5”) being collected. The assays are shown in Table VIII.
To illustrate the efficacy of the method, the combined the data from Table VII and Table VIII for chlorides and sodium (e.g., the dominant salt species of sodium chloride) is shown.
Table IX illustrates that the method was effective to remove a high purity water permeate having significantly reduced chloride concentration.
While various embodiments of a method and system for the separation of water and minerals from a wastewater have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations in energy recycle, membrane configurations and backwash of crystals, vacuum generation system, retentate recycle, non-traditional wastewater sources, continuous bulk fresh water recovery etc. are within the spirit and scope of the present disclosure.
This application claims the priority benefit of U.S. Provisional Patent Application No. 62/720,308 by Kasaini and filed on Aug. 21, 2018, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62720308 | Aug 2018 | US |
