Patent Application
20140360862
The invention relates to devices and methods for chemical processing. More specifically, the invention relates to energy efficient and scalable device based on non-equilibrium (non-thermal) plasma for the treatment of a gas, including steam, at atmospheric pressure without the need for diluting the steam with some inert carrier gas by the use of a surface plasma reactor.
Plasma formation in steam is generally difficult due to the rate of electron attachment by water molecules being higher than other molecular gases, and dissociative recombination of H30+ with electrons. Consequently, plasma in steam is typically not stable, the current flowing through the plasma is typically low, and the rates of chemical reactions initiated by the high energy electrons are also typically low. A summary of different approaches through which plasma in steam has been stabilized by different research groups in the past is the following: (1) dilute the water vapor with inert gas, as plasma is easier to form in inert gases; (2) employ below atmospheric pressure in the discharge chamber; (3) allow plasma channels (streamers) to transition into arc, as the arc draws huge current; and (4) form plasma in close proximity to a dielectric surface, as additional electrons emitted by the surface through photo- or thermionic emission.
The first two approaches are not preferred in industrial applications due to low throughput and added complications due to the requirement of an inert gas supply or vacuum system. The third approach, i.e., arc discharge, is thermal plasma where the temperature of the working gas is extremely high and significant heat losses occur. Due to very high temperature of gas, the arc discharge cannot be used for partial oxidation reactions, such as conversion of hydrocarbons in fuels into oxygen containing organic compounds like aldehydes, ketones, alcohols, carboxylic acids or nitrogen containing organic compounds. The fourth approach, i.e., plasma in close proximity to dielectric surface, allows atmospheric pressure non-equilibrium plasma formation in pure water vapor but energy density in the plasma still needs to be increased for treating large volumes relevant to practical applications.
In a first embodiment of the invention, a method for the treatment of a gas is provided. The method includes providing the at least one device including first and second dielectric plates facing each other and defining a discharge region, at least one first electrode, at least one second electrode, and a conductive layer, the at least one first electrode and the at least one second electrode each including elongate electrodes disposed on an inner surface of the first dielectric plate and arranged substantially in parallel, the conductive layer disposed beneath the inner surface and extending over at least the portion of the first dielectric plate between the at least one first electrode and the at least one second electrode, and the conductive layer electrically coupled to the at least one second electrode and electrically isolated from the at least one first electrode. The method also includes directing a first gas into at least one device, generating a plurality of voltage pulses between the at least one first electrode and the at least one second electrode to generate a substantially non-thermal plasma in a first gas in the discharge region to yield a second gas, and directing the second gas from the at least one device. In the method, the generating includes selecting a voltage, a repetition rate, and a pulse width for the plurality of voltage pulses based on a thickness and a permittivity of the first dielectric plate and a gap between the at least one first electrode and the at least one second electrode.
In the method, the providing includes selecting the thickness of the first dielectric plate to be between 1 μm and 1 cm.
In the method, the generating can also include selecting the voltage for the plurality of voltage pulses to be between about 100V and about 300 kV, such as between about 10 kV and about 50 kV, or about 30 kV.
In the method, the generating can further include selecting the pulse repetition rate to be between about 1 Hz and about 10000 Hz, such as between about 200 Hz and about 500 Hz, or about 250 Hz.
In the method, the generating can also include selecting the pulse width to be between about 1 ns and about 1000 ns, such as about 150 ns.
The first gas can be contaminated air or a mixture of air with other gases, where the contaminant in the contaminated air is one of a toxic volatile organic compound, a biological agent, or an odor-causing compound.
In one configuration, the method can include selecting the first gas to be a mixture of steam and benzene, selecting the plurality of voltage pulses to cause the non-thermal plasma to generate radicals from the steam that react with at least a portion of the benzene to produce phenol in the second gas, condensing the second gas to generate a liquid, distilling the liquid to separate liquid phenol and a third gas including steam and benzene. Further, the method can include directing the third gas into the at least one device.
In another configuration, the method can include selecting the first gas to be a mixture of tritium-contaminated heavy water molecules and hydrogen containing deuterium, and selecting the plurality of voltage pulses to cause the non-thermal plasma to result in a hydrogen isotopic exchange between the tritium-contaminated heavy water molecules and the hydrogen containing deuterium.
A second embodiment of the invention provides a system. The system includes at least one device and a circuit. The at least one device includes one or more dielectric portions defining at least one elongate and substantially continuous inner surface with an inlet and an outlet, at least one first electrode, at least one second electrode, and at least one a conductive layer, the at least one first electrode and the at least one second electrode disposed on the inner surface and the at least one conductive layer beneath the inner surface and substantially surrounding a discharge region defined by the inner surface, the at least one conductive layer electrically coupled to the at least one second electrode and electrically isolated from the at least one first electrode. In the system, the circuit is in communication with the at least one device and configured for generating a plurality voltage pulses between the at least one first electrode and the at least one second electrode.
In the system, each of the at least one first electrode and the at least one second electrode can be elongate electrodes disposed on the inner surface of a tubular dielectric parallel to each other. Further, the elongate electrodes can extend substantially parallel to an axial direction of the inner surface. The elongate electrodes can alternatively be disposed at the inlet and the outlet of the tubular dielectric.
In some configurations, the inner surface can be a substantially cylindrical surface.
In other configurations, the at least one device can be a plurality of devices, where a first of the plurality of devices is disposed with the discharge region of a second of the plurality of devices, and where the at least one conductive layer of the second of the plurality of devices is not exposed to the discharge region of the first of the plurality of devices.
In still other configurations, the at least one device includes a plurality of devices, and the discharge region of first of the plurality of devices is connected in parallel with the discharge region of a second of the plurality of devices. Alternatively, the discharge region of first of the plurality of devices is connected in series with the discharge region of a second of the plurality of devices.
In a third embodiment of the invention, a system for the treatment of a surface is provided. The system can include a first dielectric portion with a first inner surface and a first outer surface. The system can also include a second dielectric portion with a second inner surface and a second outer surface, the second dielectric portion disposed adjacent to the first dielectric portion such that the first inner surface faces the second inner surface and defines a discharge region. Further, the system can include a first electrode disposed at an inlet end of the discharge region on the first inner surface, and at least one second electrode disposed at an outlet end of the discharge region, the at least one second electrode disposed on at least one of the first inner surface and the second inner surface. Additionally, the system can include at least one conductive layer extending over the first outer surface and the second outer surface, where the at least one conductive layer electrically coupled to the at least one second electrode and electrically isolated from the at least one first electrode. Finally, the system can include a circuit in communication with the at least one device and configured for applying a series of voltage pulses between the at least one first electrode and the at least one second electrode.
In one configuration, the system can include a slit cover coupled to the outlet end having at least one slit. In some cases, the at least one slit has a length between 1 cm and 10 cm and a width between 0.01 cm and 1 cm. In some cases, the at least one slit includes a plurality of slits.
In another configuration, the first dielectric portion and the second dielectric portion can be substantially rectangular dielectric plates, the dielectric plates arranged substantially in parallel and substantially overlapping each other. Further a spacing of the dielectric plates can be between 0.01 cm and 1 cm.
The system can further including a source of air or other gases or mixtures thereof coupled to the inlet end. Alternatively, the system can include a source of steam coupled to the inlet end.
In the system, the voltage pulses delivered by the circuit can be between 100V and 500 kV. Further, the voltage pulses delivered by the circuit can be delivered with a repetition rate between 1 Hz and 1000 Hz.
In a fourth embodiment of the invention, a method of treatment of a surface is provided. The method includes providing a device including at least one dielectric portion defining discharge region with an inlet and an outlet, at least one first electrode, at least one second electrode, and at least one a conductive layer, the at least one first electrode and the at least one second electrode disposed on a major surfaces of the dielectric portions facing the discharge region, the at least one conductive layer substantially surrounding the discharge region and electrically coupled to the at least one second electrode and electrically isolated from the at least one first electrode. The method also includes directing a gas into the inlet, generating a plurality of voltage pulses between the at least one first electrode and the at least one second electrode to generate an activated gas, and applying the gas at the outlet against a surface to be treated. In the method, the plurality of voltage pulses can be selected to generate a corona discharge primarily including surface streamers.
In some configurations, the gas can be air, steam, a mixture of air with other gases, or a mixture of steam with other gases.
In some configurations, the device further including a slit cover coupled to the outlet end of the device and including at least one slit. Thus, the method further includes exposing the surface to be treated to gas at the outlet via the at least one slit.
In the method, the generating further can include selecting the plurality of voltage pulses to be between 100V and 500 kV. The generating further can include selecting the plurality of voltage pulses to be applied with a repetition rate between 1 Hz and 1000 Hz.
The present invention is described with reference to the attached figures, wherein like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.
Further, various non-limiting examples and exemplary results will be presented throughout that serve to illustrate selected embodiments of the invention. It will be appreciated that variations in proportions and alternatives in elements of the components shown will be apparent to those skilled in the art and are within the scope of embodiments of the invention.
The terms “substantially” as used herein with respect to a value, refer to being within 20% of the stated value. As used herein with respect to a condition or property, the term “substantially” refers to matching the stated condition or property to a large extent.
Additionally, although the various embodiments will be described with respect to the treatment of specific gases using specific species, the various embodiments are not limited in this regard. Rather, the various embodiments can be adapted for the treatment of any other types of gases or combinations of gases (e.g., air). As such, the specific example of gases and combinations thereof are provided solely for ease of illustration and not by way of limitation.
The reactor 102 can include gas inlet/outlet portions 103 to allow gases to travel through space 104, as indicated by direction 105. In the various embodiments, gas inlet/outlet portions 103 can be configured in a variety of ways with respect to reactor 102. For example, gas inlet/outlet portions 103 can be configured based on the source or destination of the gases.
In one exemplary configuration of system 100, the reactor 102 can be constructed using glass, acrylic, or other dielectric materials. For example, the reactor 102 can be fabricated from ceramic, such as cordierite, silicon carbide, or alumina, to name a few. However, the various embodiments are not limited in this regard and other types of dielectric materials can be used. Further, although reactor 102 is illustrated in
System 100 further includes an electrode assembly 106 disposed in the space 104. The electrode assembly 106 includes a first dielectric sheet or plate 108, a second dielectric sheet or plate 109, an anode electrode 110, at least one cathode electrode 112, and a conductive layer 116. As shown in
As shown in
In one exemplary configuration of electrode assembly 106, it can be constructed using substantially flat or planar sheets or films, consisting of glass, acrylic, or other dielectric materials, as dielectric plates 108 and 109. As used herein with respect to a measure, property, or the like, the term “substantially” means being within 20% of the stated value. A stainless steel wire can provide anode electrode 110 and aluminum strips can provide cathode electrode(s) 112. However, the various embodiments are not limited to the exemplary materials described above. For example, dielectric surface 104 can be fabricated from ceramic sheets, such as machineable glass ceramics, cordierite, silicon carbide, or alumina, to name a few. An exemplary machineable glass ceramic is MACOR machineable glass ceramic available from Corning Incorporated of Corning, N.Y. The dielectric can also consist of coating e.g. deposited onto the conductive layer through a sputtering process. Further, the electrodes 110 and 112 can be fabricated from any electrically conducting or semi-conducting materials. However, metals, such as stainless steel, copper, silver, tungsten, or alloys thereof would provide superior performance. Further, the materials can be selected so as to provide little or no reactivity with the gases being treated.
Further, the various embodiments are not limited to the wire-to-strip configuration of
Further, the roles of the electrodes in the various embodiments can be reversed. That is, anode electrode 110 and cathode electrode(s) 112 can be switched to provide a cathode electrode at electrode 110 and anode electrodes at electrodes 112.
In addition to the dielectric plates 108 and 109 and the electrodes 110 and 112 and as noted above, the electrode assembly 106 also includes a conductive region 116 disposed on a second major surface or an outer surface (with respect to space 104) of the dielectric plate 108 and electrically coupled to the cathode electrode(s) 112. As shown in
In some embodiments, the conductive region 116 can be configured to extend over substantially the entire second major surface of the dielectric plate 106. However, the various embodiments are not limited in this regard. For example, as shown in
In the various embodiments, the conductive region 116 can be fabricated from any electrically conducting or semi-conducting materials. However, metals, such as stainless steel, copper, silver, tungsten, or alloys thereof would provide superior performance. Further, the materials for the conductive region 116, the connector portions 118, and the cathode electrode(s) 112 can be the same or different.
In addition to reactor 102 and electrode assembly 106, the system 100 can further include a power supply system or circuit 120 for applying a pulsed electric field between anode electrode 110 and cathode electrode(s) 112. In particular, a first output terminal 122 of the circuit 120 can be electrically coupled to the anode electrode 110 and the second output terminal 124 of the circuit 120 can be electrically coupled to the cathode electrode(s) 112. The circuit 120 can be configured to provide a pulse electric field by providing a series of voltage pulses. The voltage pulses can be configured to have a voltage between about 100V and about 50 kV, such as between about 10 kV and about 50 kV. In one configuration a voltage of about 30 kV can be used. The voltage pulses can be applied using a pulse repetition rate that is between about 1 Hz and 10000 Hz, such as between about 50 Hz and 500 Hz. In one configuration the pulse repetition rate can be about 250 Hz. Further, the voltage pulses can have a pulse width between about 1 ns and 1000 ns, such as between about 100 ns and 200 ns. In one configuration, the pulse width can be about 150 ns. However, the various embodiments can be utilized with other parameters for the voltage pulses, depending on the application.
In the various embodiments, the electrical coupling of the second output terminal 124 to the cathode electrode(s) 112 need not be direct. Rather, as shown in
The advantages of the configuration of the electrode assembly of
The structure of
As noted above, the configuration described herein allows for the stacking or combining of multiple reactors. This configuration is illustrated with respect to
The main difference between system 100 and system 400 is that reactor 402 include a first electrode assembly 406A and a second electrode assembly 406B. Like the electrode assembly 106 in system 100, electrode assembly 406A also includes a first dielectric plate 408A and a second dielectric plate 409A defining a space 404A. The dielectric plate 408A is disposed on first surface of a conductive region or plate 416A, electrodes 410A and 412A disposed on the dielectric plate 408A and coupled to conductive region 416A via connecting portions 118. Similarly, electrode assembly 406B also includes a first dielectric plate 408B and a second dielectric plate 409B defining a space 404B. The dielectric plate 408B is disposed on first surface of a conductive region or plate 416B, electrodes 410B and 412B disposed on the dielectric plate 408B and coupled to conductive region 416B via connecting portions 118. As shown in
Thus, the arrangement of the conductive regions 416A, the connecting portions 118, and the electrodes 410A and 412A define a first glide region 414A, similar to the arrangement of components in system 100 for defining electrode assembly 106. Similarly, the arrangement of the conductive regions 416B, the connecting portions 118, and the electrodes 410B and 412B define a first glide region 414B.
As a result of the foregoing structure, a plasma with a larger treatment volume can be provided, as each glide region in each assembly will generate a separate plasma. More importantly, the plasma generated at each of glide regions 414A and 414B will operate substantially independently of each other. In particular, since the conductive region 416A (and thus electrodes 412A and 412B) are coupled to ground, the conductive region 416A effectively operates as a shield portion that prevent accumulation of charges on portions of dielectric regions 408A and 408B opposite the glide regions 414A and 414B, respectively, that could inhibit formation of plasma in either of the glide regions. Thus, the volume of plasma to effect treatment can be increased.
It is worth noting that although electrodes 410A and 410B are shown as being coupled to the same power supply in
The reactors described above, and specifically the configuration of electrodes, 112 and conductive region with respect to dielectric sheet, generates sliding surface discharges in the gas phase. The gas phase may be air, steam (water vapors) or mixtures thereof or any other gas. The conductive layer on the outer surface of the dielectric sheet is an extension of the electrodes and leads to re-distribution of electric field (as shown in
The first effect leads to increase in the probability of plasma channels (streamers) initiation. The second effect keeps the plasma firmly attached to the surface, increasing plasma surface interaction that includes intensification of the plasma through secondary electron emissions from the surface through photo/thermionic emissions or through bombardment of charged particles on the surface. These effects allow to increase energy going into the plasma by about forty times what air is as the working gas and by about twenty times what steam (water vapors) is as the working gas, without losing efficiency for chemical reactions, such as NO conversion in the case of air or hydrogen production in the case of steam.
As a result, the design parameters for such reactors can be selected so increase their effectiveness. In particular, the design parameters can be selected to reduce the amount of voltage required for forming a particular charge on the dielectric plate, or correspondingly, to generate the same plasma. Such selection of parameters is critical since this can reduce power requirements and thus reduce the cost of manufacture and operation of a system.
There are three distinct phases of gliding discharge plasma formed using the electrode assembly described herein. First is the streamer propagation phase, i.e., starting from initiation of streamers from the high voltage electrode until the streamers reach the counter electrode. The second phase is the glow discharge phase, i.e. after bridging the inter-electrode gap, the plasma still remains non-thermal but draws a significantly higher amount of current (energy) compared to the streamer propagation phase. Since, it is still a non-thermal plasma, so it remains energy efficient for chemical reactions with the advantage of higher energy density, i.e., higher throughput. The third phase is a spark discharge, which draws a huge amount of current. But it is not desirable as it is close to a thermal plasma that is usually not energy efficient for chemical reactions, particularly not suitable for partial oxidation of hydrocarbons to obtain partially oxygenated compounds.
One parameter that can thus be adjusted is the inter-electrode gap. When the gap is small, shorter streamers are generated. The shorter streamers formed at lower applied voltages carry less energy per individual streamer and they are more efficient for utilizing the energy for chemical reactions. It is also desirable that the total energy density in the reactor not decrease as it will decrease the treatment volume (throughput). Thus, by reducing the gap length it is also possible to reduce the size of the reactor without affecting the total energy density. Further, the inter-electrode gap needs to be adjusted such that the streamer phase (streamers propagate at lower speed for lower voltage), and the glow phase coincides with the electrical pulse duration. If the electrical pulses are longer, or if the voltage is higher, a glow to spark transition would occur.
In some configurations, the reduction of the inter-electrode gap can be beneficial, but other modifications can be necessary. Referring now to
A second parameter that can be adjusted is the capacitance. For increased capacitance dielectric plates (thin, high permittivity) streamer density can be increased and the glow discharge mode (second phase) may be reached at a lower applied voltage, especially at lower gap lengths. In the various embodiments, the thickness of the dielectric layer can be varied between 1 μm (thin layers can be obtained by placing a dielectric coating on the shielding metal plate) to 1 cm. The dielectric constant or relative permittivity can be varied from 1 to 1,000,000. For example, there are extremely high permittivity materials now available, e.g. calcium copper titanate has relative permitivities greater than 250,000.
However, the design parameters need to be selected carefully and can require adjustment of both the dielectric and the gap length. For example, as noted above, a glow discharge mode can be obtained at lower voltages as the gap length is decreased and capacitance is increased. However, if the gap length is too low, the spark mode will take over. Accordingly, a reduction in capacitance can require an optimization of gap length or vice versa to prevent entering the spark mode.
Thus, enhancements can be obtained by selection of the permittivity or thickness of the dielectric sheets or by selection of the gap between opposing electrodes. Alternatively, the configuration of the voltage pulses can be selected so that low voltage streamers are preferably formed.
As noted above, the discharge chamber geometry is not limited to that illustrated in
Other theoretical aspects and details regarding of electrode assemblies similar to those shown in 1A and 1B and other electrode assemblies and configurations described herein are discussed in greater detail in International Publication NO. WO 2012/044875, published Apr. 5, 2012, the contents of which are herein incorporated by reference in their entirety.
The resulting reactors provided by the configurations shown in
A reactor in accordance with the various embodiments allow for increasing the energy density and increasing the chemical reactions in pulsed corona discharges in steam at atmospheric pressure that can treat much larger volumes of the process gas. Further, such reactors provide dissociation of water molecules and hydrogen molecules forming atomic hydrogen, making feasible hydrogen isotope exchange between hydrogen and water molecules needed in the tritium extraction process. The extracted tritium can then be enriched by an accompanying technique of cryogenic distillation or diffusion process. The process of tritium extraction using a system as described with respect to
A second possible application is the steam reforming of fuels or conversion of the hydrocarbons in the fuel into oxygenated hydrocarbons, including reforming of methane, bio-gas, gasoline and diesel. Traditionally, steam reforming of fuel with non-equilibrium plasmas has been carried out by diluting the steam and fuel mixture with some inert gas or by allowing the steamers to transition to arc (i.e., a thermal plasma) or by outright use of thermal plasmas. However, in a reactor in accordance with the various embodiments, there is no need to dilute the working gas in the case of fuel reforming, which is a major advantage over other non-equilibrium plasma reactors. Further, such reactors are more energy efficient, as non-equilibrium plasma is generally more energy efficient than thermal plasma. The experimental conditions can be optimized to obtain partially oxygenated hydrocarbons, which is difficult to do with thermal plasmas. Additionally, as discussed above processing of large volumes of working gas will be possible in the proposed reactor. Also, increased rates of reaction are possible with a reactor in accordance with the various embodiments due to a larger current going through the plasma.
A third possible application is in the field of providing surface treatments. The hydroxyl radicals produced as a first step in the dissociation of water molecules (H20+e*→OH+H+e) are generally useful for surface treatment of polymers and other materials. The intense plasma formed in working gases other than steam will also be effective for this application.
A fourth and related application is the sterilization of surfaces and related medical applications. The plasma jet that is usually formed in tubular dielectrics and employed for sterilization of surfaces and other related medical applications is generally low intensity plasma. A reactor in accordance with the various embodiments allows the forming of more intense plasma. Also, it also allows increasing the area of the plasma zone by operating multiple plasma reactors in parallel. For example, plasma formed in multiple dielectric tubes bundled together, with the plasmas decoupled by extending the electrodes forming a conductive layer around the dielectric tube, as discussed above and below. Consequently, the increase in current going through the plasma through the multiple tubes will increase the rates of production of reactive species needed for the treatments.
A fifth possible application is the synthesis of chemical compounds by the reactions of reactive species produced by the plasma. For example, the hydroxyl radicals produced by the plasma in steam can be employed to synthesize phenol from benzene, as illustrated in
A schematic of an experimental setup of a reactor vessel in accordance with the various embodiments is illustrated in
For the experimental setup, steam was produced by boiling water in the reaction vessel to displace air from the reaction vessel. The water vapors were condensed in the condenser and recycled. The product gases formed as a result of the action of the plasma on the water molecules passed through the condenser. Flow rates of the product gases were measured by bubble flow meter and the composition of the product gases was analyzed by gas chromatography.
Three configurations of electrodes and dielectric were utilized to evaluate the electrode assembly described above. The first configuration uses a conventional pulsed corona configuration that discharges in steam (i.e., plasma is not in contact with dielectric surface). This configuration is illustrated in
In the experimental setup, the applied voltage was 30 kV, the voltage rise time (10% to 90%) was 50 ns, pulse duration was 300 ns, and pulse repetition rate was 250 Hz. The peak current and electrical power were 2 A and 0.50 W in the case of plasma in steam in the absence of dielectric (
The results described in the previous paragraph clearly show that both the current going through the plasma and the electric power increase by an order of magnitude in the proposed reactor (
A second experimental setup was employed to evaluate the performance of using multiple reactors in accordance with the various embodiments in parallel. This is shown in
The energy efficiency in
The parameters related to the hydrogen production in the case of a system in accordance with the various embodiments are compared in Table 1 to the case of non-equilibrium plasma reactors employed by other research groups in the past. It can be observed from the 7th column in Table 1 that the energy yield in the present study (row number 6) is significantly higher than reported in the case of other reactors (row numbers 1 to 5). The value closest to that of the present study is that shown in row number 5, where a combined system of plasma and catalyst was employed. However, as noted above, hydrogen was generated in the absence of any catalyst in the reactor. Nonetheless, the use of a catalyst is possible in the various embodiments, which can further enhance the rate of hydrogen production.
aThe subscript ‘g’ represents water vapor and ‘l’ represents liquid water;
bDBD is dielectric barrier discharge reactor, FPR is ferroelectric pellet packed bed reactor, PCD is pulsed corona discharges, SD is sliding discharges on dielectric layer with a conductive layer on the opposite side of the dielectric (proposed reactor), MHC is micro-hollow cathode discharges, MJPC is micro-discharges in porous ceramic;
cThe plasma + catalysis by electrodes made of gold was employed to enhance the rate of hydrogen production;
d25° C. is mentioned when the initial temperature of operation was reported to be room temperature.
The energy yields in the case of row number 7, 8, and 9 are higher than that in the proposed reactor. The plasma in the case of reactors of row number 7, 8, and 9 was formed in tiny holes going through a dielectric layer. Such plasma through holes in a dielectric inherently has low power. This can be verified by the low power values and, consequently, low rates of hydrogen generation as shown in 4th and 6th columns, respectively, in Table 1. In general, plasma in holes through a dielectric or in dielectric tubes is difficult to scale up. As previously noted, this is because the plasma in neighboring discharge gaps becomes coupled with adverse effects on each other. The plasma leaves charges on the dielectric surface, which induces the charges of opposite polarity on the other side of the dielectric. The induced charges have adverse effects on the plasma formation in the neighboring chambers when they are operated in parallel. This is discussed below with respect to
The effect of shield portions separating the dielectric tubes on increasing power and scalability by operating multiple plasma reactors in parallel is demonstrated by employing the setup shown in
The advantage of multiple chambers is further illustrated in
The improved efficiency of the various embodiments is readily ascertainable when compared to other comparable treatment systems. This is shown in Table 2 (row 6 is a reactor in accordance with the various embodiments):
aFPR is ferroelectric pellet packed bed reactor, DBD is dielectric barrier discharge or silent discharge reactor, PCD is pulsed corona discharges, SD is sliding discharges on dielectric with a conductive layer on the opposite side of the dielectric (proposed reactor), MHC is micro-hollow cathode discharges, GA is GlidArc, and MICP is micro-discharges in porous ceramics,
bgas was bubbled through the liquid water during the plasma operation,
cthe effects of the plasma were combined with catalysis by the electrode made of gold, and
dtemperature in the reactor is not known but the feed mixture was at room temperature. As shown in the table above, significantly higher rates of hydrogen generation, higher hydrogen concentrations, and higher energy yields were obtained using a reactor in accordance with the various embodiments.
In some embodiments, the materials and thicknesses thereof can affect the amount of species generated. For example, in the case of steam, the amount of hydrogen and hydrogen peroxide can be affected by the type of dielectric material for the dielectric sheets and the thicknesses thereof. Various materials and thicknesses thereof were evaluated, as shown in Table 3:
For each of these cases, peak voltage ˜30 kV, rise time of the voltage (10% to 90%) ˜50 ns and pulse width at half maximum ˜150 ns. The results for these cases are shown in
In summary, the foregoing datasets show that the energy deposition in the plasma can be increased by increasing the capacitance of the plasma-dielectric-conductive layer. This can be achieved by: (1) reducing the thickness of the dielectric layer; or (2) increasing the permittivity of the dielectric (this has been shown by using Macor and glass, with glass having a higher permittivity than Macor). The energy yield for hydrogen is not affected by variations in input power, treatment time and thickness or material of the dielectric. The energy yield for hydrogen peroxide is dependent on material of the dielectric—higher for Macor than for glass. In the case of Macor it is dependent on the thickness of the dielectric indicating a major role of surface mediated reactions which lead to the generation of hydrogen peroxide.
Additionally, treatment time can have an effect as well.
In addition to the foregoing variables, the polarity can affect efficiency. This is shown in
In the foregoing discussion, the various embodiments have been described as including electrodes positioned such that the streamers propagate in a direction relatively perpendicular to the direction of the gas flow. In particular, the electrode are substantially parallel to the direction of gas flow, as shown in
System 2000 can be operated in substantially a same manner as system 100 in
In some configurations, the system 2000 can include a slit cover 2018 with at least one slit. The slit can be between 0.01 cm and 10 cm in length and between 0.01 cm and 1 cm in width. Further, multiple slits can be provided in the slit cover 2018. Alternatively, the glass sheets can be spaced apart to provide a spacing between 0.01 cm and 1 cm and thus define one or more slits.
The resulting streamers for system 2000 are shown in
Despite the change in orientation of the streamers, no adverse effects on gas treatment are observed. Rather, a plasma reactor assembled using the system 2000 results in an increase in electrical energy deposition in non-thermal plasma by an order of magnitude compared to conventional cold plasmas. Rates of production of chemically active species and the chemical reactions driven by them were found to increase in proportion to the energy deposition in the plasma. Thus, such a reactor design not only allows generation of an energetic plasma in air, it can also be used to generate a scalable and energetic plasma in the presence any gas, e.g. in air and water vapor mixtures of any proportions. In one example, water vapor in a process gas can be used for treatments. Such a configuration is advantageous as the formation of strong antibacterial agents like hydroxyl radicals and hydrogen peroxide, generated in water vapor plasma, makes this non-thermal plasma ideally suited for bacterial decontamination.
In the various embodiments, a system, such as that of system 2000 or any other system described herein, can allow plasma-activated gas to exit through a slit, as illustrated in
The current and voltage waveforms and the cumulative energy per pulse (with air as a working gas) for the system 2000 are shown in
In order to determine the influence of the slit width or the distance between the dielectric layers (glass) in the discharge chamber, respectively, a device with a narrower slit was constructed and studied. In this case the cold plasma is generated in a discharge chamber of 2.6 cm×2.0 cm×0.029 cm. The plasma-activated gas (either air or air with water vapor) exits at the bottom through a slit which is 2.6 cm×0.029 cm. The appearance of the plasma formed in the smaller slit device is similar to that generated in the larger slit device. The average power of ˜5 W was lower than in the earlier device (˜10 W).
When the discharge was operated with positive high voltage pulses applied to the inner electrode (electrode 2010), cathode-directed streamers in the discharge gap were generated at an applied voltage of ˜25 kV. When the polarity was reversed, with the inner electrode is configured as the cathode, anode-directed streamers were generated at a lower applied voltage (˜22 kV) and with reduced energy consumption (˜2.5 W). This result indicates that a considerable reduction in voltage and energy can be achieved with discharges which generate anode-directed streamers, rather than cathode-directed streamers. Although the energy consumption was different for differently biased electrodes, the ozone concentration in the treated gas was not affected by the change in polarity. This is illustrated in
Further, the gram-negative Escherichia coli and the gram-positive Staphylococcus epidermidis were used as model microorganisms for opportunistic pathogens in this study. Overnight nutrient-rich broth cultures of E. coli and S. epidermidis were serially diluted to a final concentration of 104 cells/mL. 100 μL of each bacterial suspension was uniformly spread on Brain Heart Infusion agar plates. No polymicrobial cultures were used in these experiments; instead bacterial species were treated separately. Seeded plates were air-dried to insure proper adherence of cells to the solid medium.
The plasma wand or slit was positioned laterally across the seeded petri dish at a constant distance of 10 mm from the agar's surface. This orientation divided the plate into two equal hemispheres, ensuring an approximately similar treatment necessary for establishing the boundaries of a potential bystander effect. The applied voltage was 25 kV, repetition rate was 250 Hz and the duration of treatment for these exposures was 3 minutes. Post-treatment, agar plates were incubated overnight at 28° C. and subsequent bacterial recovery determined compared to an untreated control. The result of such treatments are shown in
Results from the Smaller Slit plasma wand device suggest the smaller area opening to have greater efficacy when operated at lower flow rates than experimentally used for the Larger Slit device. At flow rates of 5 and 10 SLM, the Smaller Slit plasma wand reduced the seeded E. coli inoculum by roughly 0.5 Log10 across the entire plate. Although slightly less effective, at these same operating flow rates the Smaller Slit plasma wand reduced the seeded S. epidermidis inoculum by approximately 0.25 Log10 considering the whole plate (
Both of these wand devices show efficacy against inactivation of surface contaminations of E. coli and S. epidermidis. We observed little killing differences between these two model gram-negative and gram-positive microorganisms, suggesting the possibility of broad-spectrum specificity when using this device; although the lack of pathogenicity of these bacteria is noted. The inclusion of the recovered growth across the entire plate demonstrates the need for multiple adjacent slits for the treatment of larger areas.
The configurations described above rely on the placement of a planar dielectric electrode device disposed in a cylindrical chamber, where the discharges are generated in the gas or vapor space between electrode and counter-electrode, along the planar dielectric. However, the various embodiments are not limited to solely the configurations described above. Rather, non-planar configurations can be used in the various embodiments. In particular, the electrodes can be positioned on the wall of the cylindrical chamber. Some examples of such alternate configurations are illustrated below with respect to
Although in these examples we have shown reactor assemblies with a small number of individual discharge chambers, it is obvious that these geometries can be expanded to include multiple, stacked discharge chambers.
Referring now to
As shown in
In some embodiments, computing system can include a user interface 3302. User interface 3302 can be an internal or external component of computing device 3300. User interface 3302 can include input devices, output devices, and software routines configured to allow a user to interact with and control software applications installed on the computing device 3300. Such input and output devices include, but are not limited to, a display screen 3304, a speaker (not shown), a keypad (not shown), a directional pad (not shown), a directional knob (not shown), and a microphone (not shown). As such, user interface 3302 can facilitate a user-software interaction for launching software development applications and other types of applications installed on the computing device 3300.
System interface 3322 allows the computing device 3300 to communicate directly or indirectly with the other devices, such as an external user interface or other computing devices. Additionally, computing device can include hardware entities 3314, such as microprocessors, application specific integrated circuits (ASICs), and other hardware. As shown in
While the computer-readable storage medium 3318 is shown in an exemplary embodiment to be a single storage medium, the term “computer-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure.
The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to solid-state memories (such as a memory card or other package that houses one or more read-only (non-volatile) memories, random access memories, or other re-writable (volatile) memories), magneto-optical or optical medium (such as a disk or tape). Accordingly, the disclosure is considered to include any one or more of a computer-readable storage medium or a distribution medium, as listed herein and to include recognized equivalents and successor media, in which the software implementations herein are stored.
System interface 3322 can include a network interface unit configured to facilitate communications over a communications network with one or more external devices. Accordingly, a network interface unit can be provided for use with various communication protocols including the IP protocol. Network interface unit can include, but is not limited to, a transceiver, a transceiving device, and a network interface card (NIC).
As noted above, those skilled in the art will recognize that such a plasma reactor may not only be used with conventional gas treatment, but also for decontamination, odor control, etc. While the description above refers to particular embodiments of the invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the invention.
Applicants present certain theoretical aspects above that are believed to be accurate that appear to explain observations made regarding embodiments of the invention. However, embodiments of the invention may be practiced without the theoretical aspects presented. Moreover, the theoretical aspects are presented with the understanding that Applicants do not seek to be bound by the theory presented.
While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.
Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”
Unless otherwise defined, all terms (including 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. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
This application claims the priority U.S. Provisional Patent Application No. 61/566,372 filed Dec. 2, 2011, the contents of which are hereby incorporated in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/67606 | 12/3/2012 | WO | 00 | 6/2/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61566372 | Dec 2011 | US |
