A system for purifying water

Abstract

A system for removing one or more contaminants from water is provided, which may include a hydrate formation chamber assembly, a contaminated water diffusion assembly within the hydrate formation chamber assembly, a space between a wall of the hydrate formation chamber assembly and the diffusion assembly, and a guest compound conduit configured to supply a guest compound into the space and form a hydrate comprising water and the guest compound. A method for removing one or more contaminants from water is provided, which may include supplying a contaminated water mixture and one or more guest compounds, forming a hydrate complex comprising water and the one or more guest compounds, and separating the water from the guest compounds to provide contaminant-reduced water. A mixture is also provided, which may include a liquid component comprising water and at least one contaminant, and a solid component comprising the hydrate complex. One embodiment of the system provides a method for generating excess electricity as a by-product of a desalination process.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 026,329, entitled "Microfluidic Desalination Using Gas Hydrates," filed on May 18, 2020, which is hereby incorporated by reference in its entirety. Statement Regarding Rights to Inventions Made Under Federally Sponsored Research and Development

[0002] This disclosure was made in part with government support under Contract No. DE - AC05 - 76RL01830 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

[0003] This disclosure generally relates to systems, methods, and / or compositions for purifying water, and in more detail, to desalination techniques for water.

Background Art

[0004] Desalination is an important solution for increasing the water supply for municipal and agricultural use, and some consider it an essential technology for purifying water generated from various industrial processes as well as oil and gas exploration. Reverse osmosis (RO) is the commercial reference standard for desalination technology, but such processes generally require inexpensive and uninterrupted power to operate, and membranes that are susceptible to biofouling and require regular maintenance that increases operating costs. Additionally, when working with water obtained from oil and gas well sites, high salt content is often present, and most drilling locations are remote from the grid infrastructure that can supply the power necessary to drive most reverse osmosis processes. [[ID=二十六]]

[0005] Previously developed thermal desalination methods on a pilot scale include multiple-effect distillation (MED), multi-stage flash distillation (MSF), membrane distillation (MD), and forward osmosis (FO). All distillation methods involve the evaporation of water to separate dissolved impurities, which has the following drawbacks: The large heat input (>300 kJ / kg) and heat of vaporization (2260 kJ / kg) required to raise the water temperature to 100°C induce salting-out precipitation on heat exchangers, causing corrosion and adhesion. FO still requires membranes, thus having similar maintenance and limitations as RO.

[0006] Freeze-desalination methods have received little attention. Research has shown little to no cost advantage compared to other methods. An exception is freeze-desalination using gaseous hydrates, which raises the freezing point temperature of the system and thus substantially reduces energy requirements. However, practical desalination systems using gaseous hydrates still have to overcome the significant challenge of the energy required for cooling. Even with the use of electric chillers, there is no energy advantage compared to RO. A suitable refrigerant can be used to keep the pressure low. Gaseous hydrates produced with methane require high pressures, for example, of 1000 psig or more. The final challenge is an effective system and method for separating gaseous hydrate crystals from residual concentrated brine and refrigerant. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, there is a need for advanced desalination systems that can operate to overcome these limitations and be expanded for use in desired locations and configurations. Embodiments that allow the use of solar heat or industrial waste heat to achieve cooling instead of electricity are highly desirable, as they can potentially produce water at substantially lower cost than reverse osmosis, are deployable in more locations, and can even treat highly saline generated water. This description provides information on a novel combination of cooling heat with a microfluidic separation method for performing “desalination on a chip,” which represents a series of significant advances in this field. An auxiliary advantage of the systems and / or methods of this disclosure is the ability of the system in one embodiment to generate surplus electricity in addition to drinking water. [Means for solving the problem]

[0008] A system for removing one or more contaminants from water is provided. The system may include a hydrate-forming chamber assembly, a contaminated water diffusion assembly within the hydrate-forming chamber assembly, a space between the wall of the hydrate-forming chamber assembly and the diffusion assembly, and a guest compound conduit configured to supply a guest compound into the space and form a hydrate containing water and the guest compound.

[0009] A method for removing one or more contaminants from water is also provided. The method may include supplying a contaminated water mixture and one or more guest compounds, forming a hydrate complex containing water and one or more guest compounds, and separating the water from the guest compounds to supply water with fewer contaminants.

[0010] A mixture is also provided which may include a liquid component containing water and at least one contaminant, and a solid component containing a hydrate complex. [Brief explanation of the drawing]

[0011] An embodiment of the present disclosure is described below with reference to the attached drawings. [Figure 1]This is a description of a method for purifying water according to one embodiment of the present disclosure. [Figure 2] This is a description of an assembly used for purifying water, according to one embodiment of the present disclosure. [Figure 3] This is a description of another assembly used for purifying water, according to one embodiment of the present disclosure. [Figure 4] This is a description of yet another assembly used for purifying water, according to one embodiment of the present disclosure. [Figure 5] This is a description of an assembly for use in a system for purifying water and generating electricity, according to one embodiment of the present disclosure. [Figure 6] This is a diagram illustrating an exemplary system for purifying water according to one embodiment of the present disclosure. [Figure 7] This figure illustrates another exemplary system for purifying water according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0012] This disclosure is described with reference to Figures 1 to 7. Referring first to Figure 1, an exemplary method for purifying water is provided, which includes a contaminated water mixture 10 and is then converted into a mixture 12 containing a concentrated contaminated water mixture 16 and a hydrate complex 14. Contaminants in the water are represented as "*", and as shown in the figure, the number of "*" increases from the original water mixture 10 to the water mixture 16.

[0013] According to an exemplary implementation, the mixture 12 may include a solid hydrate 14 and a liquid concentrated contaminated water mixture 16. Thus, the mixture 12 may include both a solid component and a liquid component. According to an exemplary implementation, the solid component and the liquid component can be separated to form a separate mixture of concentrated contaminated water 16 and a separate mixture of the hydrate complex 14 and / or a guest compound, and the hydrate complex 14 can then be dissociated to form separate flows of the guest compound 20 and purified water 18.

[0014] According to exemplary implementations, the contaminated water may contain salt contaminants similar to those found in seawater, and / or the contaminated water may contain other contaminants that may be found in aqueous mixtures or waste containing aqueous mixtures. These contaminants can be found in waste generated during oil and gas processing and / or other industrial processes. Therefore, this disclosure is not limited to the desalination of water but can also be used in other water purification technologies.

[0015] The guest compounds present in the hydrate complex 14 may include, for example, hydrocarbons (e.g., methane, ethane, etc.), fluorocarbons including hydrofluorocarbons (e.g., R134a), and a number of other guest compounds including carbon dioxide, H2S, and / or other refrigerants. Further guest compounds that may be utilized are described in more detail below when referring to specific embodiments of this disclosure.

[0016] Referring next to Figure 2, an assembly of a system for purifying water is provided. According to an exemplary implementation, a hydrate formation chamber assembly 21 is provided which can include a contaminated water diffusion assembly 22 within the hydrate formation chamber assembly 21. The hydrate formation assembly 21 can include a space 24 between the wall 26 of the hydrate formation chamber assembly 21 and the diffusion assembly 22. According to an exemplary implementation, with respect to Figure 2, a single cross-section including at least two spaces 24 is shown. Other configurations are also conceivable which can include a single spatial configuration that allows mixing of a guest compound and contaminated water 10.

[0017] According to an exemplary implementation, contaminated water is supplied to a diffusion assembly 22, which aerosolizes and enters space 24, where it can combine with a guest compound 20 at a specific temperature to produce a solid hydrate 14 and a concentrated contaminant 16. Details of the flow and / or temperature are provided below with reference to specific embodiments of this disclosure.

[0018] Next, referring to FIG. 3, the mixture 12 can then be supplied to a liquid-solid separation assembly 30 configured to separate the solid hydrate from the contaminated concentrate to form a stream of the separated contaminated concentrate and the solid hydrate suspended in the guest compound (G). This separation can be carried out by associating the hydrophobic hydrate / guest compound mixture with a hydrophobic path and the hydrophilic contaminated concentrate with a hydrophilic path within the separator.

[0019] According to an exemplary embodiment, an additional assembly of the system used to purify water is provided with the representation of FIG. 4, and the solid hydrate dissociates in a dissociation assembly 40 to form purified water 18 and a liquid refrigerant guest compound 20. The guest compound can be a liquid refrigerant upon dissociation. This dissociation can be carried out by heating the solid hydrate until it becomes liquid, thus dissociating the hydrate into the guest compound and a water stream.

[0020] According to an exemplary embodiment, the present disclosure can utilize a super-potent hydrate former that forms gas hydrates at a low pressure of 3 to 5 bar (<100 psig), i.e., a guest compound such as R134a or other fluorocarbon refrigerants. When injected into the cooled refrigerant, small gas hydrate crystals are generated, and a large amount of immiscible fluid can be injected to perform atomization in order to separate the gas hydrate crystals from the concentrate and the refrigerant.

[0021] Next, referring to FIG. 5, according to an exemplary embodiment, a flow diagram of the guest compound is provided that includes, for example, heat exchangers 3, 4, and 5 disposed between sub-assemblies of a thermal compressor and an expander / generator, and guest compound streams 1 and 2 entering a hydrate formation chamber assembly, with reference to the configurations of the following embodiments and systems including the assemblies described herein. According to an exemplary embodiment, the guest compound stream can be cooled using the expansion of the guest compound returned after dissociation. By coupling a generator to the expander, electrical power in the form of electricity can be generated.

[0022] Referring next to Figure 6, a system according to at least one exemplary embodiment of the present disclosure is depicted. This system develops the use of gas hydrates, also called inclusion hydrates, for purifying water. As referenced above, these inclusion hydrate materials may be ice-like crystalline "inclusion" compounds formed when water (host compound) comes into contact with hydrophobic small molecules (guest compound) under specific pressure and temperature conditions. When the guest molecule is a component of natural gas, the inclusion hydrate is also called a gas hydrate.

[0023] These gaseous hydrates are formed by cooling the brine feed. This requires only one-fifth the energy compared to heating to evaporate water, such as in conventional thermal desalination. Impurities are removed during the formation of the gaseous hydrates, so that drinking water can be produced when the solids dissociate or melt. Sensitive membranes that are susceptible to biofouling or that need to maintain a positive fluid flow during shutdown, as required in reverse osmosis systems, are not used. The system can operate continuously, is scalable, and is a low-cost process for desalination of seawater and high-salinity generated water.

[0024] When combined with a reactor system that enables the utilization of the desalination properties of gaseous hydrates when formed in brine, such a system can be configured to form a continuous photovoltaic desalination system in combination with thermal vapor compression cooling technology, droplet sprayer technology, and photovoltaic technology. A microfluidic separator incorporating branched hydrophilic and hydrophobic channels can be used to separate the three phases (gaseous hydrate (14), brine concentrate (16), and guest compound (20)) fed into the separator. Energy balance calculations show that this system is <15 kWh th / m 3 This indicates that the cost of thermal equalization (LCOH) is required in kWh. th If the cost per unit is approximately $0.01, the estimated amortization capital and operating costs for this system are based on a water leveling cost (LCOW) of LCOW ≤ $0.50 / m³. 3 This indicates that it will be achieved.

[0025] According to at least one embodiment of the present disclosure, the system can perform a process in which aqueous gas hydrates form around an R134a core (or other refrigerant), separate, and then dissociate the hydrates to obtain pure water (18). The system may include a separator 30 that can define hydrophobic and hydrophilic regions. The gas hydrate 14 can be formed using a brine concentrate 16 as a mixture 12. The mixture 12 may include a solid hydrate complex 14 and a concentrated contaminant mixture 16. The mixture 16 is hydrophilic, while the hydrate complex 14 and guest compounds are hydrophobic. By taking advantage of these different chemical properties, the system may separate the complex from the mixture 16, for example, by returning the brine concentrate to seawater and leaving only the gas hydrate.

[0026] The decomposition of the hydrate yields water and a guest compound (e.g., R134a). Further hydrophilic / hydrophobic separation provides reusable pure water and R134a. According to exemplary implementations, this can be performed using microchannels or microfluidic separators.

[0027] One of the key advantages of gas hydrate desalination processes compared to conventional multiple-effect distillation or vapor compression methods is the significantly reduced (theoretical) energy requirements. Desalination processes involving the vaporization of water require both sensible heat input to raise the water temperature and latent heat input of approximately 2400 kJ / kg. In contrast, the heat of formation of gas hydrates is typically between 300 kJ / kg and 400 kJ / kg, and by selecting a strong hydrate-forming agent, the source fluid only needs to be cooled to 15°C. Thus, gas hydrate desalination processes require only about one-fifth the intrinsic energy input compared to vaporization-based desalination. This is a very significant advantage for solar thermal desalination processes.

[0028] Commercial processes have generally not been developed around gaseous hydrate desalination for several reasons. Firstly, the cooling requirements of these systems are analyzed assuming typical electromechanical vapor compression systems, which offer little to no advantage compared to the power requirements of RO. Secondly, it is assumed that hydrate formation occurs in scaled-up pressure vessels, as well as in the methods researchers use to produce hydrates in the laboratory. The difficulties of this method include the need for large and expensive pressure vessels, the inefficient mechanical separation of hydrate crystals from concentrated salt solutions, the capture of salt solution within hydrate crystal aggregates, and surface contamination and adhesion. None of these problems have yet been effectively solved with conventionally designed systems.

[0029] Referring to Figures 6 and 7, the separation process can be initiated by introducing a three-phase fluid into a channel having opposing hydrophilic and hydrophobic surfaces. Due to the strong opposing surface tension, the aqueous concentrate phase (16) is separated from the hydrate-refrigerant phase (14). The aqueous concentrate (16) can then be discharged through the hydrophilic channel. The hydrate-refrigerant phase (14) then passes through a microchannel heat exchanger, absorbing heat from the inflowing seawater and causing the hydrate crystals to dissociate (degenerate) into liquid water. The two-phase water-refrigerant fluid can then pass through a second T or Y junction having opposing hydrophilic and hydrophobic surfaces to separate the drinking water for discharge from the refrigerant phase for recycling. The discharged refrigerant is cooled via a standard expansion valve before entering the evaporator, where the remaining liquid refrigerant expands to cool the liquid refrigerant exiting the heat compressor. The refrigerant vapor is then returned to the heat compressor to close the cycle.

[0030] The system can utilize adsorbent materials with superhydrophobic properties, i.e., very high sorption capacity and chemical affinity for fluorocarbon refrigerants such as R134a. These properties are leveraged in multi-bed heat exchanger configurations that achieve a compression effect by very efficiently utilizing low-grade heat (90-150°C). This heat compressor can serve as a temporary replacement for electric compressors in typical chiller systems.

[0031] Such a system can realize direct conversion of solar heat into a low-temperature, pressurized refrigerant (such as R134a) flow, which can be used to directly form gaseous hydrates at a moderate temperature and pressure of approximately 10°C and 4 bar. The system's atomizer can be used to overcome motion barriers that inhibit hydrate formation in batch systems. For example, it has been found that atomized seawater droplets that exit the atomizer and become liquid R134a form gaseous hydrates almost instantaneously, thus producing a three-phase system (microhydrate crystals, aqueous concentrate, and refrigerant).

[0032] To effectively separate three-phase gas hydrate-containing fluids, microfluidic separators such as "tips" fabricated from polymers or glass using photolithography can be used to etch the microchannels where chemical reactions take place, or the system can perform fluid separation. A unique feature presented here is the use of a mixture of hydrophilic and hydrophobic channels that effectively divides and directs the flow of the immiscible aqueous and non-aqueous phases within the microchannels.

[0033] Microfluidic separators represent a technical solution to the most challenging aspect of desalination in gas hydrate processes: phase separation. Furthermore, once the flow path design is proven, the chips can be mass-produced at very low cost (less than $5 per plate), allowing desalination systems to be manufactured to support a wide range of needs, from residential to full-scale urban water systems. There are no inherent limitations on the use of seawater for supply. Fluids with higher salinity can also be desalinized in this system by lowering the evaporator temperature and / or increasing the operating pressure.

[0034] The chips may be fabricated from a naturally hydrophilic material (such as silica) and patterned with a series of Y or T junctions having opposing hydrophobic channels. The hydrophobic channels may be fabricated by coating the channel surface with a monolayer of photocleavable nitrobenzyl fluorosilane that strongly attracts fluorocarbon refrigerants. Embodiments of the system may utilize alternative refrigerants with low global warming potential (GWP) as guest compounds such as R32, R1234yf, and R1233zde, for which gas hydrate formation data is limited or has not yet been reported.

[0035] Another embodiment of this disclosure includes a turboexpander or other type of gas expansion engine (i.e., a scroll or piston expander) that can enable the system to generate electricity. An exemplary calculated estimate of the flow rate of R134a (17.6 kg / s) for estimating the power output from the system, assuming a thermal compressor produces R134a at 39 bar and 110°C and discharge from the expander at 8 bar and 35°C. This gives nearly isentropic expansion and generates power between 200 kW and 400 kW depending on parasitic loads in the system. These loads are difficult to refine at this point due to unknown losses in the microfluidic separator by the atomizer. However, even at the lower end of power production, the impact is significant. Assuming electricity sales are only $0.07 / kWh, this cuts the levelized cost of the water produced in half compared to the same system without power generation.

Claims

1. A system for removing one or more contaminants from water, Hydrate formation chamber assembly, A contaminated water diffusion assembly within the hydrate-forming chamber assembly, wherein the contaminated water diffusion assembly is configured to aerosolize the contaminated water and form aerosolized contaminated water, The space between the wall of the hydrate formation chamber assembly and the contaminated water diffusion assembly, A system comprising: a guest compound conduit configured to supply a guest compound into the space and to form a hydrate containing water and the guest compound from the aerosolized contaminated water from the contaminated water diffusion assembly.

2. The system according to claim 1, further comprising a single outlet conduit configured to supply a mixture of solid hydrate and liquid contaminant concentrate.

3. The system according to claim 2, further comprising a separation assembly operably coupled to the single outlet and configured to receive the mixture of solid hydrate and liquid contaminant concentrate.

4. The system according to claim 3, further comprising at least two separation assembly outlet conduits, wherein the first conduit of the at least two separation assembly outlet conduits is configured to carry solid hydrates, and the second conduit of the at least two separation assembly outlet conduits is configured to carry liquid contaminant concentrates.

5. The system according to claim 4, further comprising a hydrate dissociation assembly operably coupled to the first conduit and configured to receive the solid hydrate and dissociate it into water and the guest compound.

6. The system according to claim 5, further comprising a compressor configured to receive the guest compound and to supply the guest compound to the guest compound conduit.

7. The system according to claim 2, further comprising a microfluidic separator configured to separate the hydrate from the contaminant concentrate.

8. The system according to claim 2, further comprising a microfluidic separator configured to dissociate the hydrate.

9. The system according to claim 2, further comprising a microfluidic separator configured to separate water from the guest compound.

10. The system according to claim 1, further comprising an evaporator operably coupled to the guest compound conduit to accelerate the temperature change of the guest compound before it enters the hydrate formation chamber assembly.

11. The system according to claim 8, wherein the guest compound of the hydrate includes methane, ethane, fluorocarbon, R134a, hydrofluorocarbon, carbon dioxide and / or H2S.

12. The system according to claim 11, wherein the microfluidic separator comprises a hydrophilic pathway and a hydrophobic pathway, wherein the hydrates, including methane, ethane, fluorocarbons, R134a, hydrofluorocarbons, carbon dioxide and / or H2S, flow through the hydrophobic pathway, and the contaminants flow through the hydrophilic pathway.

Images