Patent Application
20220174808
Oil and gas production processes generate large volumes of liquid waste. For example, hydraulic fracturing of shale utilizes large volumes of high-pressure water to fracture shale formation. The wastewater generated during the drilling phase is called flowback water, whereas the water generated during the production phase is called produced water. Both the flowback and produced waters contain various organic and inorganic components, and discharging produced water can pollute surface and underground water and soil. Since approximately 250 million barrels per day (i.e., ˜30 million m3 per day) of produced water are generated globally (see F. I.-R. Ahmadun et al., “Review of technologies for oil and gas produced water treatment,” J. Hazard. Mater., vol. 170, pp. 530-551, 2009), an amount that is expected to continue increasing for an extended period of time, there is a growing need for new methods to treat large volumes of produced water robustly and efficiently. With volatility in the prices of oil and gas, there is a pressing parallel need to reduce the costs of production, including produced water treatment costs.
A variety of methods are currently utilized to treat produced water for the purposes of discharge as well as for recycling and reuse in subsequent hydraulic fracturing operations. This diverse set of water treatment techniques include de-oiling (removing dispersed oil and grease), removal of soluble organics, disinfection, suspended solid particle removal, dissolved gas removal (including hydrocarbon gases, carbon dioxide, and hydrogen sulfide), desalination (removing sodium and chloride ions), and water-softening (reducing calcium and magnesium hardness), among others (see F. I.-R. Ahmadun et al.).
Plasma arc discharge generates a significantly elevated temperature beyond 2,000 K around the arc (see A. Czernichowski et al., “Spectral and electrical diagnostics of gliding arc,” Acta Physica Polonica-Series A General Physics, vol. 89, pp. 595-604, 1996; and O. Mutaf-Yardimci et al., “Thermal and nonthermal regimes of gliding arc discharge in air flow,” Journal of Applied Physics, vol. 87, pp. 1632-1641, 2000). In addition, plasma discharge generates active plasma species directly in liquid, i.e., OH, O, O3, H2O2, NOx, UV and electric fields. Thus, if one can successfully generate plasma discharge in produced water, the plasma discharge can be applied for the removal of dispersed oil/grease and soluble hydrocarbons (see N. McIntyre et al., “Uses of ultraviolet/ozone for hydrocarbon removal: Applications to surfaces of complex composition or geometry,” J. Vac. Sci. Technol., A: Vacuum, Surfaces, and Films, vol. 9, pp. 1355-1359, 1991), water softening (see Y. Yang et al., “Removal of CaCO3 scales on a filter membrane using plasma discharge in water,” Int. J. Heat Mass Transfer, vol. 52, pp. 4901-4906, 2009; and Y. Yang et al., “Mineral Fouling Control by Underwater Plasma Discharge in a Heat Exchanger,” J. Heat Transfer, vol. 133, p. 054502, 2011), and disinfection (see H.-S. Kim et al., “Concentration of hydrogen peroxide generated by gliding arc discharge and inactivation of E. coli in water,” Int. Commun. Heat Mass Transfer, vol. 42, pp. 5-10, 2013). These active plasma treatment species may be employed for produced and flowback water from oil and gas exploration as well as, more broadly, wastewater streams from municipalities and range of industrial processes.
Generation of plasma discharge requires the use of two or more electrodes, for example, at least one cathode and one anode, positioned relatively close together (e.g., 2-5 mm for discharge in gas). When the voltage between the two electrodes increases to a certain value such as 2 kV, breakdown of gas between the two electrodes takes place, generating a discharge of plasma. Depending on the magnitude of the voltage across the two electrodes and other factors such as the geometry of electrodes, a variety of different types of plasma discharges can be produced and controlled, including corona, spark, and arc.
When one attempts to produce plasma discharges in liquid such as water, it is more complicated. As soon as two electrodes with high voltage are immersed in water, electrolysis occurs, generating gas bubbles at both electrodes. When there are sufficient amounts of gas at the two electrodes, the “breakdown” of water can occur, and subsequently plasma discharge takes place in water. The use of gas bubbles generated from electrolysis can result in breakdown in a small volume of water, for example, as in a beaker. However, in order to treat several gallons of water per minute or more, plasma generation using gas bubbles generated from electrolysis is a method that is neither sufficient nor practical.
Another technical challenge in generating plasma discharge in water treatment applications such as produced water or seawater is their high electric conductivity. The conductivity of produced water is in the range of 100-200 mS/cm due to a large amount of dissolved ions such as sodium, calcium, chloride, magnesium, and others (see F. I.-R. Ahmadun et al.), whereas that of seawater is about 50 mS/cm (see V. L. Snoeyink et al., Water chemistry. New York: John Wiley, 1980). In liquids with such high conductivity, electrons instantly and continually flow from cathode to anode as high electric conductivity water provides an effective path for electrons to flow, a phenomenon that can be referred as electron leakage in liquid. Accordingly, compressed gas is injected at or between the two electrodes to provide a gap to assist breakdown such that plasma is able to be discharged in high conductivity liquid using only a moderately high voltage of ˜1 kV. When gas injection is utilized to assist the generation of plasma discharges in high electric-conductivity liquids, it is essential to have gas bubbles remain in the gap between the two electrodes such that the breakdown of water takes place, leading to the generation of plasma discharge.
At the moment when gas bubbles occupy the space between the two electrodes by displacing liquid, breakdown occurs, generating plasma discharge. However, since gas density is approximately 1,000 times smaller than that of liquid (i.e., water) (see B. Munson et al., Fundamentals of Fluid Mechanics, 7th ed. New York: John Wiley & Sons, Inc, 2013), gas bubbles tend to rise in a liquid-filled plasma reactor due to the buoyancy force created by the density difference between gas and liquid.
As described above, gas needs to surround the high-voltage (HV) electrode for a plasma discharge to occur in liquid. The plasma discharge is typically ignited at the tip of the HV electrode, the tip being the closest point to the ground electrode. As the plasma discharge generates intense heat, the tip of the HV electrode can erode over time during normal operation, potentially affecting the flow rate and/or flow path of gas through the HV electrode, and/or increasing the distance between the HV and ground electrodes, and thereby increasing the impedance between the two electrodes.
Therefore, there is a need in the art to have a large size plasma discharge in a plasma reactor such that there is a relatively large volume of exposure and sufficient contact time between the plasma discharge and water being treated. Further, there is a need to contain, restrict or control the gas bubbles within a small space between the two electrodes. Methods to restrict the motion of the gas injected to plasma reactor are necessary so that gas bubbles stay longer in the plasma reactor, resulting in the steady and stable generation of plasma discharges in liquid. Still further, there is a need for a method of generating plasma discharge in liquid which does not depend on the electric conductivity of the liquid. In addition, there is a need for a high voltage electrode for generating a plasma discharge in liquid that obviates or minimizes the deficiencies described above.
In one embodiment, a system for generating a plasma discharge in liquid includes a first and second electrode spaced apart in an interior space of a vessel, a channel defined at least partially by at least one of the first and second electrodes, and a first inlet in fluid communication with the interior space configured to generate a vortical fluid flow at a tip of the first electrode. In one embodiment, a second outlet in fluid communication with the interior space configured to facilitate the generation of the vortical fluid flow. In one embodiment, the first inlet and the second outlet are positioned to generate a forward vortex liquid flow. In one embodiment, the first inlet and the second outlet are positioned to generate a reverse vortex liquid flow. In one embodiment, the first inlet and the second outlet are positioned to generate a vortex between the first and second electrode. In one embodiment, the first electrode is a high-voltage electrode and the second electrode is a ground electrode. In one embodiment, the first electrode is a positive high-voltage electrode and the second electrode is a negative high-voltage electrode. In one embodiment, the second electrode is coaxially disposed around the first electrode. In one embodiment, the channel is disposed between the first and second electrode. In one embodiment, both the first and second electrodes have a hollow cylindrical geometry, and the second electrode is coaxially disposed around the first electrode. In one embodiment, an insulation structure is disposed between the first and second electrode along a length of the first electrode.
In one embodiment, a method for generating a plasma discharge in liquid is disclosed. The method includes the steps of positioning a first electrode and a second electrode the liquid, where the first electrode is separated from the second electrode by a distance, generating a voltage between the first and second electrode, injecting a gas through a channel defined at least partially by at least one of the first and second electrodes, and generating a vortex in the liquid at a tip of the first electrode. In one embodiment, an increased electrical impedance is generated between the first and second electrode as the liquid in the space between the two electrodes is replaced by gas. In one embodiment, the first electrode is a high-voltage electrode and the second electrode is a ground electrode. In one embodiment, the second electrode is coaxially disposed around the first electrode. In one embodiment, the method includes the step of injecting a gas through a channel disposed between the first and second electrode. In one embodiment, the both the first and second electrodes have a hollow cylindrical geometry, and the second electrode is coaxially disposed around the first electrode. In one embodiment, the method includes the step of injecting a gas through a channel disposed in the first electrode. In one embodiment, an insulation structure is disposed between the first and second electrode along a length of the first electrode. In one embodiment, the vortex is a forward vortex liquid flow. In one embodiment, the vortex is a reverse vortex liquid flow. In one embodiment, the vortex is generated between the first and second electrode. In one embodiment, an increased electrical impedance is generated between the first and second electrode as the liquid in the space between the two electrodes is replaced by gas.
In one embodiment, an electrode assembly includes a high voltage electrode having a proximal end inlet, a distal end outlet and a lumen therebetween, a ground electrode having a proximal and distal end, where the distal end of the ground electrode at least partially surrounds and extends beyond the distal end outlet of the high voltage electrode, and a spacer region between the high voltage electrode and the ground electrode. In one embodiment, the spacer region includes an air gap. In one embodiment, the spacer region includes an insulation structure. In one embodiment, the high voltage electrode is a positive high voltage electrode and the ground electrode is a negative high voltage electrode. In one embodiment, both the high voltage and ground electrode have substantially planar geometries. In one embodiment, the ground electrode is coaxially disposed around the high voltage electrode. In one embodiment, a channel is disposed in the spacer region. In one embodiment, both the high voltage electrode and the ground electrode have a hollow cylindrical geometry. In one embodiment, the high voltage electrode has a hollow cylindrical geometry and the ground electrode has a substantially planar geometry.
In one embodiment, a system for generating a plasma discharge in liquid includes a high voltage electrode having a proximal end inlet, a distal end outlet and a lumen therebetween, a ground electrode, and a vessel for holding a liquid therein, the vessel having at least one liquid inlet and at least one liquid outlet, where the high voltage electrode is positioned within the vessel such that the distal end outlet is submergible in a liquid contained within the vessel. In one embodiment, at least one liquid inlet and at least one liquid outlet are configured to facilitate the generation of a vortical fluid flow of the liquid. In one embodiment, at least one liquid inlet and at least one liquid outlet are positioned to generate a reverse vortex liquid flow. In one embodiment, at least one liquid inlet and at least one liquid outlet are positioned to generate a vortex liquid flow between the high voltage electrode and the ground electrode. In one embodiment, the system includes a spacer region between the high voltage electrode and the ground electrode. In one embodiment, the spacer region includes an air gap. In one embodiment, the spacer region includes an insulation structure. In one embodiment, the high voltage electrode is a positive high voltage electrode and the ground electrode is a negative high voltage electrode. In one embodiment, the ground electrode is coaxially disposed around the high voltage electrode. In one embodiment, a channel is disposed in the spacer region. In one embodiment, both the high voltage electrode and the ground electrode have a hollow cylindrical geometry.
In one embodiment, a method for generating a plasma discharge in liquid is disclosed. The method includes the steps of positioning at least a distal portion of a high voltage electrode in a liquid, the high voltage electrode having a proximal end inlet, a distal end outlet and a lumen therebetween, positioning at least a portion of a ground electrode in the liquid, injecting a gas through the lumen of the high voltage electrode and into the liquid via the distal end outlet, forming a vortex flow pattern between the electrodes within the liquid and generating an electrical voltage between the electrodes to form a plasma within the liquid. In one embodiment, the flow pattern is a forward vortex liquid flow. In one embodiment, the flow pattern is a reverse vortex liquid flow. In one embodiment, the high voltage electrode is a positive high voltage electrode and the ground electrode is a negative high voltage electrode. In one embodiment, the high voltage electrode is surrounded by an insulator structure. In one embodiment, the high voltage electrode has a hollow cylindrical geometry.
In one embodiment, a system for generating a plasma discharge in liquid includes first and second electrodes spaced apart in an interior space of a vessel, a channel defined at least partially by at least one of the first and second electrodes for injecting a gas in a first direction, and a first inlet in fluid communication with the interior space configured to generate a vortical fluid flow in a second direction in the interior space. In one embodiment, a portion of the channel is directed through a sidewall of the first electrode having a tubular geometry. In one embodiment, the portion of the channel is substantially tangential to a longitudinal axis of the first electrode. In one embodiment, the first and second direction are the same direction (for example, both directions are in the clockwise direction). In one embodiment, the first and second direction are opposite directions (for example, one is a clockwise direction, and the other is a counterclockwise direction).
In one embodiment, a method for generating a plasma discharge in liquid includes the steps of positioning at least a distal portion of a high voltage electrode in a liquid, the high voltage electrode having a proximal end inlet, a distal end outlet and a lumen therebetween, positioning at least a portion of a ground electrode in the liquid, injecting a gas through the lumen of the high voltage electrode and into the liquid at a first direction via the distal end outlet, forming a vortex flow pattern in a second direction between the electrodes within the liquid, and generating an electrical voltage between the electrodes to form a plasma within the liquid. In one embodiment, the gas exits the high voltage electrode through a sidewall of the high voltage electrode having a tubular geometry. In one embodiment, the gas exits the high voltage electrode tangentially to a longitudinal axis of the high voltage electrode. In one embodiment, the first and second direction are the same direction. In one embodiment, the first and second direction are opposite directions.
In accordance with one or more embodiments, a system for generating a plasma discharge in liquid includes a liquid inlet and a liquid outlet in fluid communication with an interior space of a liquid vessel, the inlet and outlet both disposed near a top side of the liquid vessel and configured to generate a vortex fluid flow in the interior space of the liquid vessel, and a high voltage electrode and a ground electrode spaced apart, the high voltage electrode i) disposed at a bottom side of the liquid vessel, and ii) including a gas channel for gas injection into the liquid vessel. In some embodiments, the system can further include a liquid reservoir in fluid communication with the interior space of the liquid vessel and a pump that pumps liquid between the liquid reservoir and the liquid vessel. In these embodiments, the system can further include a liquid spray nozzle in the liquid reservoir, the liquid spray nozzle in fluid communication with the liquid outlet. In certain embodiments, the liquid inlet can be disposed tangentially relative to a sidewall of the liquid vessel to generate the vortex fluid flow in the interior space. In some embodiments, the liquid outlet can be disposed at a center of the top side of the liquid vessel to generate a reverse vortex fluid flow in the interior space. In certain embodiments, the system can further include an insulator around the high voltage electrode, and a center tube extension of the liquid outlet into the interior space of the liquid vessel, with a gap between the center tube and the insulator. In some embodiments, the insulator can be one of Teflon, glass-filled Teflon, sapphire, or ceramic. In certain embodiments, the system can further include a photocatalyst coating on the center tube. In some embodiments, the photocatalyst can be titanium dioxide (TiO2). In certain embodiments, the ground electrode can be disposed in the interior space of the liquid vessel. In some of these embodiments, the ground electrode can be disposed coaxially around the high voltage electrode. In certain embodiments, the system can further include an insulator between the high voltage electrode and the ground electrode, along a length of the high voltage electrode. In some embodiments, the insulator can be one of Teflon, glass-filled Teflon, sapphire, or ceramic. In certain embodiments, the ground electrode can be disposed at the top side of the liquid vessel. In certain other embodiments, the ground electrode can be disposed upstream of the liquid inlet in fluid communication with the liquid. In some embodiments, the high voltage electrode can further include an endcap and a plurality of lateral openings in a sidewall of the high voltage electrode having a tubular geometry proximal to the endcap. In certain embodiments, the endcap can include a central opening. In some embodiments, the lateral openings can be disposed radially in the sidewall of the high voltage electrode. In some other embodiments, the lateral openings can be disposed tangentially in the sidewall of the high voltage electrode.
In accordance with one or more embodiments, a method of generating a plasma discharge in liquid includes providing a high voltage electrode and a ground electrode spaced apart, disposing the high voltage electrode at a bottom side of a liquid vessel, the high voltage electrode including a gas channel, generating a vortex fluid flow of gas inside the liquid vessel, injecting gas through the gas channel into the liquid vessel, and applying an electrical voltage between the high voltage electrode and the ground electrode to generate a plasma discharge in the liquid vessel. In some embodiments, generating the vortex liquid flow inside the liquid vessel can include pumping liquid from a liquid reservoir through a liquid inlet into the liquid vessel and out through a liquid outlet out of the liquid vessel. In certain embodiments, the method can further include generating the vortex fluid flow around the high voltage electrode.
In accordance with one or more embodiments, a system for generating a plasma discharge in liquid includes a liquid inlet and a liquid outlet in fluid communication with an interior space of a liquid vessel, the inlet and outlet both disposed near a top side of the liquid vessel and configured to generate a vortex fluid flow in the interior space of the liquid vessel, and a high voltage electrode and a ground electrode spaced apart, the high voltage electrode i) disposed at a bottom side of the liquid vessel, ii) including a gas channel for gas injection into the liquid vessel, and iii) an endcap and a plurality of lateral openings in a sidewall of the high voltage electrode proximal to the endcap, and the ground electrode disposed upstream of the liquid inlet in fluid communication with the liquid. In some embodiments, the endcap can include a central opening. In certain embodiments, the lateral openings can be disposed radially in the sidewall of the high voltage electrode. In certain other embodiments, the lateral openings can be disposed tangentially in the sidewall of the high voltage electrode. In some embodiments, the system can further include an insulator around the high voltage electrode, and a center tube extension of the liquid outlet into the interior space of the liquid vessel, with a gap between the center tube and the insulator. In certain embodiments, the insulator can be one of Teflon, glass-filled Teflon, sapphire, or ceramic. In some embodiments, the system can further include a photocatalyst coating on the center tube. In certain embodiments, the photocatalyst can be titanium dioxide (TiO2).
In accordance with one or more embodiments, a system for generating a plasma discharge in liquid includes a liquid inlet and a liquid outlet in fluid communication with an interior reactor space of a cylindrical liquid vessel having a central axis, the inlet and outlet both disposed near a top side of the liquid vessel and configured to generate a vortex liquid flow in the interior space of the liquid vessel, and a high voltage electrode and a ground electrode spaced apart, the high voltage electrode disposed coaxially with the central axis of the cylindrical liquid vessel at a bottom side of the liquid vessel, and including a central solid cylindrical rod inserted at least partially into and coaxial with a cylindrically-symmetric electrode housing, the electrode housing including a gas channel disposed tangentially to the central solid cylindrical rod along an interior wall of the electrode housing for gas injection into an interior electrode space of the electrode housing, the gas channel configured to generate a vortex gas flow within the interior electrode space around the central solid cylindrical rod. In some embodiments, the liquid inlet and outlet, and gas channel can be configured such that the vortex liquid flow and the vortex gas flow rotate in the same direction. In some other embodiments, the liquid inlet and outlet, and gas channel can be configured such that the vortex liquid flow and the vortex gas flow rotate in opposite directions. In certain embodiments, the electrode housing can be formed of an insulator material. In some embodiments, the electrode housing can be a cylindrical electrode housing, a divergent-cone-shaped electrode housing, a convergent-cone-shaped electrode housing, an hourglass-shaped electrode housing, or a bell-shaped electrode housing. In certain embodiments, the central solid rod can be formed of one of stainless steel, titanium, tungsten, copper, copper tungsten, silver, titanium oxide (TiOx), iron, and carbon. In some embodiments, an end of the central solid rod proximal to the ground electrode can be disposed above a top side of the electrode housing. In certain embodiments, the system can further include a means for slidably adjusting a distance between the end of the central solid rod and the ground electrode. In some embodiments, the ground electrode can be disposed at the top side of the liquid vessel.
In accordance with one or more embodiments, a high voltage electrode for generating a plasma discharge in liquid includes a central solid rod inserted at least partially into and coaxial with a cylindrically-symmetric electrode housing, the electrode housing including a gas channel disposed tangentially to the central solid rod along an interior wall of the electrode housing for gas injection into an interior electrode space of the electrode housing, the gas channel configured to generate a vortex gas flow within the interior electrode housing space around the central solid rod. In certain embodiments, the electrode housing can be formed of an insulator material. In some embodiments, the electrode housing can be a cylindrical electrode housing, a divergent-cone-shaped electrode housing, a convergent-cone-shaped electrode housing, an hourglass-shaped electrode housing, or a bell-shaped electrode housing. In certain embodiments, the central solid rod can be formed of one of stainless steel, titanium, tungsten, copper, copper tungsten, silver, titanium oxide (TiOx), iron, and carbon.
In accordance with one or more embodiments, a method of generating a plasma discharge in liquid includes providing a high voltage electrode and a ground electrode spaced apart, disposing the high voltage electrode at a bottom side of a liquid vessel, the high voltage electrode including a central solid rod inserted at least partially into and coaxial with a cylindrically-symmetric electrode housing, the electrode housing including a gas channel disposed tangentially to the central solid rod along an interior wall of the electrode housing for gas injection into an interior electrode space of the electrode housing for generating a vortex gas flow within the interior electrode space around the central solid rod, generating a vortex liquid flow inside the liquid vessel, injecting gas through the gas channel into the electrode housing, and applying an electrical voltage between the high voltage electrode and the ground electrode to generate a plasma discharge in the liquid vessel. In some embodiments, generating the vortex liquid flow inside the liquid vessel can include pumping liquid from a liquid reservoir through a liquid inlet into the liquid vessel and out through a liquid outlet out of the liquid vessel. In certain other embodiments, the method can further include generating the vortex liquid flow around the high voltage electrode.
The foregoing purposes and features, as well as other purposes and features, will become apparent with reference to the description and accompanying figures below, which are included to provide an understanding of the invention and constitute a part of the specification, in which like numerals represent like elements, and in which:
It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clearer comprehension of the present invention, while eliminating, for the purpose of clarity, many other elements found in systems and methods of plasma discharge in liquid. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.
As used herein, each of the following terms has the meaning associated with it in this section.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
“About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate.
“HV” as used herein means high-voltage, such as a voltage in excess of 1,000 V (1 kV).
Ranges: throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Where appropriate, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.
In certain embodiments, vortex flows of liquid can be clockwise or counterclockwise, and they can move from the bottom-up or top-down in a given reactor. Types of vortex flows are also varied and can include spiral flows, tornado flows, forward vortex flows, reverse vortex flows and vortical flows among others. Plasma water treatment reactors likewise may in certain embodiments be oriented vertical, horizontally, or diagonally. In certain embodiments, multiple cathodes, anodes, and electrode sets may be used, and the electrodes may vary in shape, size, material and construction. In certain embodiments, a coaxial electrode set includes an outer ground electrode jacket and inner high-voltage electrode stem, both constructed of stainless steel, and could easily take a different shape and be made of a wide variety of different materials such as tungsten, titanium alloy or electrically conductive ceramic.
Referring now in detail to the drawings, in which like reference numerals indicate like parts or elements throughout the several views, in various embodiments, presented herein is a system and method for plasma discharge in liquid.
Embodiments described herein introduce methods of gas injection at or between two or more electrodes (i.e., at least one ground electrode and one high-voltage electrode) in liquid such that gas bubbles can be contained within the space between two electrodes. The purpose of this method is to provide a non-liquid, gas gap between two electrodes which permits breakdown at high voltage in a reactor filled with liquid. As a result, plasma such as an arc is able to be discharged with the help of gas bubbles in a liquid volume, even high-conductivity liquid. In certain embodiments, an increased electrical impedance is generated between a first and second electrode as the liquid in the space between the two electrodes is replaced by gas. Either gas or gas-liquid mixtures can be injected. Wide varieties of chemicals or chemical combinations can be selected for injection as gas such as oxygen, nitrogen, hydrogen, or inert gases among others, and as liquid as in the case of water to generate hydrogen peroxide or ferrous sulfate solution to induce Fenton's oxidation.
Certain embodiments utilize a co-axial electrode geometry, which consists of two co-axial cylindrical geometries. In certain embodiments, the outer cylindrical tube forms the ground electrode, whereas the inner cylindrical tube forms the high-voltage (HV) electrode. The inner high voltage electrode can have DC high voltage (i.e., positive or negative) or AC high voltage. In certain embodiments of utilizing AC high voltage, the polarity in the high voltage electrode continuously switches between negative and positive. In the co-axial geometry, gas can be introduced through the inner tube space in the HV electrode or alternatively through the space between the two cylindrical electrodes. Since both electrodes are immersed in liquid, an annulus tube made of insulation material (e.g., glass-filled Teflon, Macor, or borosilicate) is used between the outer ground electrode and the HV center electrode tube so that discharge does not take place except at the tip of the HV electrode. For this purpose, the electric insulation material surrounds the HV electrode except at the tip. Such an insulation protection prevents the leakage of electrons from the HV electrode to liquid. This is particularly important in a high-conductivity liquid as the insulation layer prevents electrons from leakage at the HV electrode.
In order to have the HV electrode surrounded by gas inside a plasma reactor filled with liquid, certain embodiments utilize either forward vortex liquid flow or reverse vortex liquid flow inside the plasma reactor. In certain embodiments, in the case of forward vortex liquid flow, a co-axial electrode system is used for the generation of plasma discharge in liquid, whereas in the case of the reverse vortex liquid flow, two electrodes are positioned on the opposite sides (i.e., top and bottom) of the plasma reactor.
In one embodiment, with reference now to
Referring now to
Referring now to
As plasma arc discharge 44 is produced at the low-pressure zone 36, the compressed gas 18 coming through the channel 28 in the HV electrode 21 pushes the plasma discharge downward, creating arc jet in the middle of rotating liquid 39 along the inner wall of the reactor 63. In other words, the low-pressure zone expands the arc discharge so that the interface surface of the arc 44 is significantly increased, increasing the treatment efficiency of the liquid 10 as the direct contact surface between the arc discharge 44 and liquid increases. In addition, as plasma arc discharge 44 is produced at the low-pressure zone 36, the compressed gas 18 coming through the channel 28 in the HV electrode 21 pushes the plasma discharge downward, creating arc jet in the middle of rotating liquid 39 along the inner wall of the reactor 63. In other words, the low-pressure zone expands the arc discharge so that the interface surface of the arc 44 is significantly increased, increasing the treatment efficiency of the liquid 10 as the direct contact surface between the arc discharge 44 and liquid increases.
With reference now to
In one embodiment of a system 600A, B, with reference now to
In one reverse vortex flow system 700, according to an embodiment, as the centrifugal force produced by the reverse vortex flow 79 creates a low-pressure zone 76 at the middle of the plasma reactor 73, compressed gas 18 fills the low-pressure zone 76. The unique feature of the reactor 73 with the reverse vortex flow 79 is that the low-pressure zone 76 extends all the way to the bottom 82 of the reactor 73. On the contrary, in the reactor 63 with forward vortex flow 39, the low-pressure zone 36 is limited to the upper area near the HV electrode 21 in the reactor 63 as both liquid and gas must leave the reactor 63 through an exit 32 located near the top of the reactor 63. Furthermore, as the density of gas is about 1,000 times smaller than liquid, the gas in the low-pressure zone 36 tends to rise, further limiting the low-pressure zone 36 in the forward vortex flow 39.
The reverse vortex reactor 73 has the HV electrode 74 and the ground electrode 75 positioned at the opposite sides, e.g., top 81 and bottom 82 in the reactor 73, respectively. For example, the HV electrode 74 is positioned at the top 81 of the reactor 73, whereas the ground electrode 75 is positioned at the bottom 82 of the reactor 73. The reverse vortex liquid flow 79 creates an extended air channel 76 between the two electrodes 74 and 75 as shown schematically in
One of the major benefits of the reverse vortex flow 79 in the reactor 73 is that the gas moves downward as the exit for both liquid and gas is located at the bottom of the reactor 73. Consequently, the plasma discharge 45 is extended or stretched downward, increasing the size of the plasma discharge much larger than the plasma discharge 44 in the forward vortex flow 39 in the reactor 63. Furthermore, the gas channel 76 surrounds the HV electrode 74, thus preventing liquid from making contact with the HV electrode 74. In certain embodiments, if the HV electrode 74 makes contact with liquid for more than 0.5 s, then the short circuit occurs between the two electrodes 74 and 75, and plasma will extinguish. Thus, it is preferable to have the HV electrode 74 surrounded by gas at all times. The direction of reverse vortex flow of liquid 79 can be in either clockwise or counterclockwise direction. The embodiments of
Referring now to
In another embodiment of a system 802 shown in
In another embodiment of a system 804 shown in
With reference now to
A method 1000 according to one embodiment is shown in the flow chart of
In accordance with one or more embodiments, in one reverse vortex flow system 1100 for generating a plasma discharge in liquid, shown in
Since the liquid inlet 1133 and the liquid outlet 1134 are disposed near the top 1182T of the liquid vessel 1182, with the liquid outlet 1134 disposed at the center of the top side 1182T of the liquid vessel 1182 and the liquid inlet 1133 disposed tangentially relative to a sidewall 1182S of the liquid vessel 1182, as shown in
The gas pocket 1176 surrounds the HV electrode 1174 near the bottom of the liquid vessel 1182, generating plasma arc discharge 1145 in the liquid vessel 1182. Accordingly, UV radiation and reactive species are generated from the plasma discharge and remain inside the liquid vessel 1182. The reactive species include OH, O, O3, H2O2, and NOx. Since most reactive species have a short half-life (on the order of milliseconds or less), except for ozone (O3) and hydrogen peroxide (H2O2), it is beneficial to generate these reactive species near the liquid or inside the liquid such that the reactive species make direct contact with liquid molecules as the reactive species are generated. Another major benefit of the use of reverse vortex flow 1179 with the HV electrode 1174 at the bottom 1182B of the liquid vessel 1182 is that heat is not accumulated around the HV electrode 1174, reducing erosion of the HV electrode 1174. Furthermore, the gas pocket 1176 surrounds the HV electrode 1174, thus preventing liquid from making contact with the HV electrode 1174. Note that if the HV electrode 1174 makes contact with liquid for more than about 0.5 s, then a short circuit occurs between the two electrodes, and the plasma will extinguish. Thus, it is preferable to have the HV electrode 1174 surrounded by gas at all times. The direction of reverse vortex flow of liquid 1179 can be in either clockwise or counterclockwise direction as viewed from above, with a clockwise direction shown in
As described above, with reference now to
In another reverse vortex flow system 1200 for generating a plasma discharge in liquid, shown in
Since the liquid inlet 1233 and the liquid outlet 1234 are disposed near the top 1282T of the liquid vessel 1282, with the liquid outlet 1234 disposed at the center of the top side 1282T of the liquid vessel 1282 and the liquid inlet 1233 disposed tangentially relative to a sidewall 1282S of the liquid vessel 1282, as shown in
When high-voltage plasma discharge is used for the treatment of liquid (e.g., water, wastewater, seawater, produced water, landfill leachate, etc.), there is often a technical challenge in a mismatch between the size of the plasma discharge and the volume of liquid. For example, the plasma discharge in liquid is a point source, whereas the volume of liquid is very large (i.e., in excess of 1,000 gallons a day). In addition, the contaminants in the liquid (i.e., organic and inorganic chemicals, microorganisms, dissolved metal ions, toxic and carcinogenic molecules, hydrocarbons, etc.) are dispersed in the liquid volume. Therefore, it is desirable to have a system where liquid makes a direct and close contact with the point-source plasma discharge for an efficient treatment. Since liquid in the liquid vessel moves spirally down to the bottom of the liquid vessel before it makes a sharp turn upward, the bottom of the liquid vessel is an ideal location for a plasma discharge to be positioned, as shown in
However, the physical properties of the liquid to be treated can vary widely. For example, wastewater can be contaminated with a large number of suspended particles, organics and/or ions, making it a thick slurry with a high density and viscosity. When the density and viscosity of the liquid increase well beyond those of water, the rotating velocity inside the liquid vessel decreases, and thus the centrifugal force needed to move the liquid down to the bottom of the liquid vessel is diminished. In this case, 100% of the liquid does not move down to the bottom of the liquid vessel. Instead, some part of the liquid entering the liquid vessel through the liquid inlet moves directly toward the liquid outlet at the top of the liquid vessel. Therefore, in order to cause substantially all of the liquid to be treated to move down to the bottom of the liquid vessel, in accordance with one or more embodiments, a system 1210 for generating a plasma discharge in liquid, shown in
In accordance with one or more embodiments,
In accordance with one or more embodiments, a method 1500 of generating a plasma discharge in liquid, shown in
The embodiments disclosed herein provide numerous benefits. One major benefit of the embodiments disclosed herein is that they provide a method to generate a plasma arc discharge in a cylindrical liquid vessel, where a large volume of water passes through at a flow rate in a range of between 10 gpm and 1000 gpm. Both forward and reverse vortex flows of liquid create a low-pressure zone at the center of the liquid vessel, which is extremely useful in the generation of plasma arc discharge in liquid. The low-pressure zone created by the forward and reverse vortex flows of liquid helps the arc discharge to expand as compressed gas pushes the arc from the small space between the two electrodes into the middle of the liquid vessel. Accordingly, the interface surface of the arc with liquid increases, and thus the contact between the arc and water increases, making the plasma treatment more efficient. Further, both forward and reverse vortex flows in the liquid vessel increase the residence time of water in the liquid vessel. Accordingly, the contact time between plasma arc and water, and thus the treatment time of water, increases. In addition, both forward and reverse vortex flows become stronger with increasing liquid flow rate. Thus, the low-pressure zone at the center of the liquid vessel increases with increasing liquid flow rate. Hence, the present method of creating an arc discharge is an ideal method for plasma treatment at a large liquid flow rate. In other words, the present application of forward and reverse vortex flows can be scaled up to very large flow applications.
In accordance with one or more embodiments, as shown in
The electrode housing 1660 includes a gas channel 1670 that, as shown in
The electrode housing is formed of plastic, or other insulator material, into a variety of shapes, as shown in
In certain embodiments, the central solid cylindrical rod can be formed of stainless steel, titanium, tungsten, copper, copper tungsten, silver, titanium oxide (TiOx), iron, carbon, or any other conductive material. Turning back to
A feature of the HV electrode described herein is that conduction heat transfer along the central solid cylindrical rod 1645 is limited by Fourier heat conduction. For example, for a stainless steel central solid rod having a diameter of 0.25″, the maximum heat transfer is about 80 W when the temperature of the plasma at the end 1646 of the central solid rod 1645 is 2000 K. For a plasma arc discharge power of 2 kW, only 80 W can be transferred to the electrode housing 1660 via conduction heat transfer through the central solid cylindrical rod 1645. Therefore, the electrode housing 1660 is not exposed to the high temperature environment of the plasma discharge, and the heat generated by the plasma discharge dissipates to the liquid to be treated, and only a relatively small fraction of the heat from the plasma discharge is conducted to the electrode housing 1660.
In accordance with one or more embodiments, as shown in
The electrode housing is formed of plastic, or other insulator material, into a variety of shapes, as shown in
In accordance with one or more embodiments, as shown in
The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention.
This application is a continuation-in-part of U.S. application Ser. No. 16/258,734 filed on Jan. 28, 2019, which is a continuation-in-part of U.S. application Ser. No. 15/511,425 filed on Mar. 15, 2017, now U.S. Pat. No. 10,793,447 B2 issued on Oct. 6, 2020, which is a national stage filing of International Application No. PCT/US15/50137 filed on Sep. 15, 2015, which claims priority to U.S. provisional application No. 62/050,369 filed on Sep. 15, 2014, all of which are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 62050369 | Sep 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16258734 | Jan 2019 | US |
| Child | 17672858 | US | |
| Parent | 15511425 | Mar 2017 | US |
| Child | 16258734 | US |
