WO2022233740A1

WO2022233740A1 - Plasma reactor apparatus and method thereof

Info

Publication number: WO2022233740A1
Application number: PCT/EP2022/061586
Authority: WO
Inventors: Michael Maughan
Original assignee: Mac Scitech Limited
Priority date: 2021-05-06
Filing date: 2022-04-29
Publication date: 2022-11-10

Abstract

A plasma reactor having a reaction chamber containing a central electrode and a radially outer annular electrode. A plurality of magnets are positioned immediately adjacent an internal plasma chamber to control and optimise plasma creation and motion within the plasma chamber.

Description

PLASMA REACTOR APPARATUS AND METHOD THEREOF

Field of invention

The present invention relates to a plasma reactor and in particular although not exclusively, to apparatus and methods of generating plasma within a chamber as a means of reacting and in particular disassociating a gas such as carbon dioxide.

Background

Carbon dioxide is ubiquitous within climate change models and targets set out to reduce greenhouse emissions and prevent global warming. Methods for the cost-effective, energy efficient and scalable processing of carbon dioxide are increasingly being sought and amongst these are the conversion of carbon dioxide to carbon monoxide by selective reduction. Current technologies include electrolysis and gas-shift reactions over metallic catalysts. Such processes can involve high temperatures and pressures and are challenging energetically, environmentally (through reliance on fossil fuels as feedstock), and from an engineering perspective (using complex high temperature solid electrolytes or fluidized bed catalyst reactors having very specific catalyst compositions and high operating temperatures and pressures).

The processing of carbon dioxide to carbon monoxide and oxygen is also gaining interest as various space programs look toward longer duration manned exploration of space and most particularly manned missions and habitation development of Mars. With the Martian atmosphere comprising 95% carbon dioxide and with very little readily available hydrogen, methods for the processing of carbon dioxide into fuels for energy storage and propulsion and synthesis of oxygen for breathing and propulsion are necessities.

Current methods for converting carbon dioxide or other gases into desirable products such as oxygen include use of plasma torches as a means to dissociate the carbon dioxide into carbon monoxide which may then be hydrogenated to form hydrocarbons and/or alcohols.

WO 2009/073048 A1 describes a system and process for high temperature, high speed dissociation of carbon dioxide using plasma gas dissociation.

K. Arita and S. Iizuka (Hydrogenation of CO2 to C¾ using a low-pressure cross-field pulse discharge with hydrogen; 22nd International Symposium on Plasma Chemistry; July 5-102015; Antwep, Belgium) describes the decomposition of carbon dioxide within a discharge chamber containing electrodes and an arrangement of magnets. The magnetic field is created by the magnets to intersect with electric field of the powered electrodes.

However, there exists a need for improved plasma reactors offering enhanced reaction rate efficiency and scalability with minimised energy demand and processing time.

Summary of the Invention

It is an objective of the present invention to provide a plasma reactor, system, apparatus and method suitable for use in the conversion and/or dissociation of a target gas into a desired alternate form and/or for the creation of desirable by-products. It is a specific objective to provide a plasma reactor configured to create and maintain a plasma at a localised region within a reactor chamber so as to provide a concentrated reaction zone into which a target gas may be supplied and/or circulated. It is a further specific objective to provide a scalable energy efficient apparatus and system to reduce (dissociate) carbon dioxide into carbon monoxide and to generate oxygen.

The objectives are achieved via a plasma reactor having a plurality of electrodes and an array of magnets to create and maintain an electrically generated and magnetically manipulated plasma within a reactor chamber. The reactor chamber is provided with respective gas flow inlet and outlet ports to allow introduction of a process gas and then output of a desired reaction product and/or by-products via reaction with the controlled plasma. The present apparatus and system provides a means of controlling and monitoring operation parameters of the plasma reactor and associated components via control of any one or a combination of electrical power supplied to at least one of the electrodes, a magnetic field strength generated by the magnets, reactant gas flow into the reactor, plasma motion, temperature, reaction rate and energy efficiency of the reaction sequence. Operational characteristics may be controlled via moderation of the frequency and/or polarity of the electric and/or the magnetic field.

Reference within this specification to a ‘ plasma ’ encompasses alternative terms such as an ionised gas or gas-plasma. The present apparatus and system is compatible and configured for the reaction (dissociation) of a process gas, such as carbon dioxide, via a variety of different plasma creation mechanisms including arc discharge, coronal discharge or electrostatic discharge. The plasma referred to herein may be considered to have motion and the electric and magnetic fields as created within the present apparatus and system are configured to control plasma motion via a circulating, vortex or other processional motion within a plasma region defined between a pair of opposing electrodes. The creation and maintenance of the plasma motion is achieved via a specific array of electrodes and magnets at the plasma region that in turn acts to increase the effective reaction volume, increase the surface area of the plasma boundary and/or increase the path length by which carbon dioxide or other target gas may be dissociated/reduced. According to a first aspect of the present invention there is provided a plasma reactor comprising: a reactor chamber having at least one gas flow inlet and at least one outlet; a central electrode positioned on a central longitudinal axis and an annular electrode centred on and extending around the central electrode such that the central and annular electrodes are orientated opposed to one another and define a plasma region therebetween, the central and annular electrodes both located on a common electrode plane; a plurality of primary magnets centred on and extending around the longitudinal axis, at least one first magnet located at a first site of the common electrode plane and extending around the longitudinal axis and at least one second magnet located at a second opposite side of the common electrode plane and extending around the longitudinal axis; the magnetic poles of the first and second magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

Preferably, at least a part of the first and second magnets are positioned opposed to and either side of the annular electrode. Preferably, the reactor further comprises a plurality of secondary magnets centred on and extending around the longitudinal axis, at least a third magnet of the secondary magnets located at the first side of the common electrode plane and extending around the longitudinal axis and at least one fourth magnet of the secondary magnets located at the second side of the common electrode plane and extending around the longitudinal axis, the magnetic poles of the third and fourth magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

Preferably, an orientation of the north and south poles of the magnets as described herein is such that the orientation of the poles of a magnet a first side of the common electrode plane is opposite or inverted relative to the corresponding magnet at the alternate/opposite side of the common electrode plane. Accordingly, in the longitudinal axis direction, the polarity of the first magnet of the primary pair is N-S and the polarity of the second magnet of the primary pair is S-N. Where the plasma reactor comprises a pair of secondary magnets, the north and south poles of the third magnet of the secondary pair is S-N and S-N for the fourth magnet of the secondary pair. Preferably, the secondary magnets are positioned in a radial direction between the primary magnets and the longitudinal axis and wherein a separation distance from the common electrode plane in the longitudinal axis direction is greater than that of the primary magnets.

Preferably, the polarity of the magnetic poles of the first and/or third magnet that is positioned facing and opposed to the common electrode plane is different to that of the respective second and/or fourth magnet positioned facing and opposed to the common electrode plane so as to create said magnetic circuit with flux lines aligned generally perpendicular or oblique to the common electrode plane at the plasma region.

Optionally, the first and second magnets and/or the third and fourth magnets comprise any one or a combination of: a plurality of rod, bar or block magnets; a continuous annular magnet or an arrangement of part annular arcuate magnet segments.

Preferably, the central electrode comprises a disc-shape configuration. Preferably, the annular electrode comprises an annular ring-shape configuration that extends continuously around the longitudinal axis.

Preferably, a radially inner portion of the annular electrode and/or a radially outer portion of the inner electrode comprises a sharpened or tapered annular edge.

Preferably, the plasma reactor further comprises at least one magnet mounting to mount the plurality of magnets in fixed position relative to the longitudinal axis, the magnet mounting comprising a material that is generally non-porous and/or electrically insulating.

Optionally, the magnet mounting comprises a first half and a second half mated together to at least partially encapsulate the magnets. Optionally, the magnet mounting is annular or at least part annular and defines an internal plasma chamber containing the inner electrode and at least a radially inner portion of the annular electrode. Preferably, the plasma reactor further comprises an electrode mounting to mount the annular electrode at a fixed position relative to the longitudinal axis and the electrode mounting comprises a material that is electrically conducting.

Preferably, the plasma reactor further comprises at least one sensor having at least a portion located within the reactor chamber and/or the plasma chamber. Optionally, the sensor may comprise any one or a combination of: a fibre optic, a piezoelectric sensor, a thermoelectric sensor, a photoelectric sensor, or a magnetometer; the sensor configured to sense or monitor any one or a combination of the following set of: pressure, temperature, gas flow rate, a gas reaction status, a plasma status, a voltage, a current, or a magnetic field strength.

Optionally, the plasma reactor may comprise at least one drain port provided at a wall of the reactor chamber. Preferably the reactor comprises a plurality of drain ports.

Optionally, the magnets may comprise permanent magnets or electromagnets. Such magnets may be formed as continuous annular bodies or may comprise an array of individual magnet bodies positioned in close proximity of one another as an annular array extending around the longitudinal axis each with a respective magnetic axis that is aligned generally parallel or nearly parallel to the longitudinal axis. Where the magnetic bodies are electromagnets, respective electrical connections may be provided to the magnetic bodies. Such electrical connections may be formed as a common disc or other common electrical connection or separate individual electrical connections may be provided to each body, with each connection connectable to a single or a common power source.

Optionally, the plasma reactor comprises a single pair of the central and annular electrodes mounted within the reactor chamber. Optionally, the plasma reactor may comprise a plurality of respective pairs of the central and annular electrodes mounted within the single reactor chamber. Optionally, the plasma reactor further comprises a spectrophotometer to enable spectrophotometric analysis of a plasma generated within the plasma region. Preferably, the plasma reactor comprises a control unit having at least an electronic circuit board, a processor, a memory and data storage utility, the control unit connected to and configured for the control of any one or a combination of: a supply of electrical power to the central and annular electrode, a gas flow rate into the reactor chamber, a voltage and/or current provided at the magnets, a magnetic field strength generated by the magnets, at least one sensor within the reactor chamber, or an analysis of data and/or readings generated by a sensor within the reactor chamber.

Preferably, the plasma reactor comprises at least two gas flow inlets, a first gas flow inlet connected to or provided in communication with a supply of carbon dioxide and a second gas flow inlet connected to or provided in communication with a supply of a secondary gas. Preferably the secondary gas is hydrogen.

According to a further aspect of the present invention there is provided plasma reactor apparatus comprising: a plurality of plasma reactors as claimed in any preceding claim connected in gas flow communication via their respective gas flow inlets and outlets; wherein each of the plasma reactors are connected in-series to define an in-series gas flow pathway through the plasma reactor apparatus.

Preferably, the apparatus comprises a single control unit coupled to each of the respective plasma reactors. Preferably, the apparatus comprises a single spectrophotometer connected or connectable to the control unit.

According to a further aspect of the present invention there is provided a method of dissociating carbon dioxide using a plasma reactor or the apparatus as claimed herein comprising: introducing carbon dioxide into the reactor chamber via the gas flow inlet; applying an electric current to and/or creating a potential difference across the central electrode and the annular electrode; generating a magnetic field at the plasma region using the plurality of primary magnets; reacting carbon dioxide within the reactor chamber with a plasma created between the central and annular electrodes.

According to a further aspect of the present invention there is provided a method of creating and maintaining a plasma within a plasma reactor comprising: introducing at least one gas into a reactor chamber via at least one gas flow inlet; applying an electric current to and/or creating a potential difference between a central electrode positioned on a central longitudinal axis and an annular electrode centred on and extending around the central electrode such that the central and annular electrodes are orientated opposed to one another and define a plasma region therebetween, the central and annular electrodes both located on a common electrode plane; generating a magnetic field at the plasma region using a plurality of primary magnets centred on and extending around the longitudinal axis, at least one first magnet located at a first site of the common electrode plane and extending around the longitudinal axis and at least one second magnet located at a second opposite side of the common electrode plane and extending around the longitudinal axis, the magnetic poles of the first and second magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

Optionally, the method further comprises controlling a plasma generated in the plasma region using the control unit to control any one or a combination of: a voltage at or between the central and annular electrodes, a current at or between the central and annular electrodes, a magnetic field strength at the plasma region.

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure l is a schematic illustration of a plasma reactor system including a plasma reactor to receive a flow of a gas and selected processing components to convert the input gas to one or more reactant products according to a specific implementation of the present invention;

Figure 2A is an external side view of the plasma reactor of figure 1;

Figure 2B is a cross sectional side view of the plasma reactor of figure 2A; Figure 3 is a cross sectional view of selected core components of the plasma reactor of figures 2A and 2B including a pair of electrodes and an array of magnets;

Figure 4 is an external view of the core components of figure 3;

Figure 5 is a perspective cross sectional view of the core components of figure 4;

Figure 6 is a cross sectional view of some of the core components of figures 4 and 5;

Figure 7 is a perspective cross sectional view through the magnetic array and selected other components of the plasma reactor core of figures 4 to 6 illustrating the magnetic circuit lines created by the array of magnets;

Figure 8 is a cross sectional view through the magnetic array and selected other components of the plasma reactor core of figures 4 to 6 illustrating the magnetic circuit lines created by the array of magnets;

Figure 9 is a schematic view of an array of plasma reactors housed within a single or common reactor chamber forming part of plasma reactor apparatus according to further a specific implementation of the present invention;

Figure 10 is a schematic illustration of a plurality of plasma reactors of the type of figures 2A to 2B connected in-series to provide plasma reactor apparatus according to further a specific implementation of the present invention.

Detailed description of preferred embodiment of the invention

Referring to figure 1, the present plasma reactor system and apparatus is configured for the magnetically manipulated creation and control of a plasma within a reactor chamber and for the reactive plasma processing (reaction, conversion or dissociation) of a gas to generate a desired reaction product. The present apparatus and system is also configured for reaction status monitoring of gaseous products and/or the plasma via spectrophotometric analysis (such as emission and/or absorption spectroscopy) to provide a system adapted for precise control of throughput reactant gas and product generation. Referring to figure 1, the present plasma reactor system comprises a main reactor vessel 18 in which reactor wall (18a, figure 2B) define an internal reactor chamber 19. The plasma reactor comprises a core 11 having a first central or inner electrode 14; a second annular or outer electrode 15; an array of magnets 16, 17 and a core mounting arrangement indicated generally by reference 12. An internal region of the core 11, as defined by the core mounting arrangement 12 defines an internal plasma chamber 44 that may be considered a partially enclosed volume or region within the main reactor chamber 19 and within which a plasma is created and maintained. The plasma chamber 44 is provided in open gas flow communication with the surrounding reactor chamber 19. Reactor vessel 18 comprises a first gas flow inlet port 20a, a second gas flow inlet port 20b and a gas flow outlet port 21. A first gas flow control valve 23a is provided in the gas flow direction upstream of inlet port 20a and a corresponding gas flow control valve 23b is positioned upstream of second inlet port 20b. An output valve 22 is positioned in the gas flow direction downstream of outlet port 21. Reactor vessel 18 further comprises a liquid drain port 37 having a respective valve 38. Outer electrode 15 and inner electrode 14 are coupled electrically to a power supply 27 via respective electric conduits 34a, 34b. System 10 further comprises an electrical current sensor 28 connected to the power supply 27 via electrical connection 34c. Central electrode 14 is connected to the power supply 27 via conduit 34b and an elongate rod 13 that extends through the wall (18a) of reactor vessel 18 via a surrounding insulator sleeve 43. System 10 further comprises a control unit 24 configured to control the various electrical, magnetic, mechanical, electromagnetic and electromechanical components within the system 10. Control unit 24 may comprise computer hardware including in particular a printed circuit board, a CPU, memory, data storage, a user interface, software running on the computer apparatus and communication modules for wired and wireless communication with other components within the system 10 and for wireless remote or wired connection to remote servers, cloud architectures and the like. In particular, control unit 24 is coupled electrically to valves 23a, 23b via respective electrical connectors 30a, 30b to provide the controlled inflow of gas into reactor chamber 19 via inlet ports 20a, 20b. Control unit 24 is further connected to power supply 27 (via connection 32); to electrical current sensor 28 (via connection 31) and to a suitable pressure gauge 26a (via connection 33). Pressure gauge 26a is further provided with a pressure sensor or pressure sensing tip 26b mounted within reactor chamber 19. A spectrophotometer 25 is also connected to control unit 24 and comprises a fibre optic 29a having a fibre optic tip or head 29b mounted within plasma chamber 44 in close proximity to central electrode 14. Control unit 24 is also coupled to valve 22 via connection 30c and may also be coupled to drain valve 38 via suitable electrical connection (not shown).

Referring to figures 2A and 2B, the plasma reactor part of the overall system 10, of figure 1 is illustrated as an external side view and then in cross section through A-A. Reactor vessel 18 may comprise a generally cylindrical wall 18a and formed from a material which is non-porous and impervious to gas and liquid (i.e. water). Reactor wall 18a is capable of withstanding elevated pressures and defines internal chamber 19 that may have a desired volume ratio relative to plasma chamber 44. Wall 18 is centred on a longitudinal axis 45 of reactor 58. Two reactor end plates 39 are mounted at each terminal end of wall 18a.

End plates 39 comprise the respective ports 20a, 20b, 21 and 40 for the inflow and outflow of gas in addition to the mounting of a pressure sensor (manometer) within chamber 19. Each end plate 39 may comprise plastic, a metal or ceramic with such materials being compatible with gaseous and aqueous reaction components and suitable of withstanding the high reaction pressures. End plates 39 may be formed integrally with vessel wall 18a or may be separate components connected via a liquid and gas tight seal. Reactor 58 further comprises an annular electrode mounting plate 46 to mount the outer annular electrode 15 such that a radially inner region of the electrode is positioned within reactor chamber 19. In addition, a radially inner edge of electrode 15 is positioned within plasma chamber 44. Plate 46 comprises a material that is electrically conductive and is beneficial to transfer heat energy from the annular electrode 15 whilst also providing electrical connection to power supply 27.

Reactor 58 further comprises respective annular electrode mounting plate insulating seals 35a, 35b. Seals 35a, 35b sit between the reactor wall 18a and annular electrode mounting plate 46 so as to form an electrically insulating barrier between wall 18a and plate 46.

Seals 35a, 35b may comprise suitable insulating materials such as polytetrafluoroethylene (PTFE) or another polyfluoroalkyl (PFA). The present plasma reactor 58 is compatible for use with electromagnets or permanent magnets 16, 17. Where reactor 58 comprises electromagnets, suitable electrical connections 36 provide an electrical coupling to power supply 27. Electrical connections 36 also provide connection to respective magnetic sensors (not shown) mounted in close proximity to plasma chamber 44. Plasma core 11 also comprises a first magnet housing 42 to positionally secure magnets 16 and a second magnet housing 41 to positionally secure magnets 17 at the core mounting arrangement 12. Each magnet housing 42, 41, in part, defines the plasma chamber 44 at the core mounting arrangement 12. Each housing 42, 41 comprises a material that is non-porous, electrically insulating and configured to withstand the forces associated with the interaction between the first and second magnets 16, 17. Additionally, each respective housing 42, 41 is formed from two components (a first and second half) which are mated together to form a seal enclosure around the respective electromagnetic coil(s), the magnets and/or magnetic sensors (not shown). As appropriate, electrical connections (not shown) are incorporated at the respective housings 42, 41 (at a respective periphery of each housing with regard to the first housing 42), with such connections running through the annular electrode mounting plates 46. Power supply 27 via the associated connections and the electrical couplings provide electrical potential to the inner electrode 14 and outer electrode 15. Parameters such as voltage, frequency, polarity, pulse width, or duty cycle of the electrical potential may be adjusted to control the shape, volume, temperature and motion of the plasma generated within the plasma chamber 44 so as to optimise the reaction profile and rate. Spectrophotometric analysis of the plasma is achieved via the fibre optic sensor head 29b at the plasma chamber 44 in close proximity to inner electrode 14. Data from the fibre sensor head 29b may be used to define the parameters of the electrical potential. Control unit 24 comprising the plasma monitoring system is capable of reading data from: the spectrophotometer 25, magnetic field sensors (not shown and typically referred to as magnetometers or gauss sensors), temperature sensors, other pressure sensors, and voltage and current sensors that also form part of system 10. When implemented as a continuous flow or automated system, the sensor readings from such sensors is processed by control unit 24 to moderate one or more reaction parameters, as indicated, including for example flow regulation of reacting gases into chamber 19, plasma power supply parameters and electromagnetic flux parameters to control and optimise the plasma reaction process. The respective electrical connections 34a, 34b (and inner electrode rod 13) enable the application of an electrical potential to outer annular electrode 18 relative to inner electrode 14 to affect the generation of plasma within plasma chamber 44. The electrical potential is generated via control unit 24 and moderated through control of wave form, frequency, pulse width and polarity. Fibre optic 29a, and head 29b, are capable of desired transmission of key frequency components of the spectral emission from the plasma to the spectrophotometer 25. The internal pressure within chamber 19 may be moderated via control unit 24 using pressure gauge 26b (inserted through port 40) to moderate the flow rates of the inlet and outlet gases within chamber 19. A volume of the plasma chamber, as indicated, is enclosed by arrangement 12 including magnet housings 42, 41 with the shape also defined by inner and outer electrodes 14, 15, annular electrode mounting plate 46 and respective seals 35a, 35b.

Referring to figures 3 to 6, preferably, a radially outer edge 48 of inner electrode 14 is tapered or sharpened. Similarly, a radially inner edge 49 of outer electrode 15 is tapered or sharpened. Such profiling is advantageous to increase the localised electric field and to promote arc discharge between the respective electrodes 14, 15. Each electrode 14, 15 comprises a conductive material such as stainless steel, aluminium or copper and is removable and replaceable at the core 11. Inner electrode rod 13 functions to support and align inner electrode 14 relative to the annular outer electrode 15 and comprises a conductive material such as stainless steel, copper or aluminium.

Fibre optic head 29b comprises an optically transparent window which collects emitted radiation from the gaseous plasma and an orifice to accept the optical fibre. The head 29b is positioned in the centre of an opening of the inner plasma chamber 44 and orientated into the space between the central and annular electrodes, 14, 15. The window may be made from a compatible material such as quartz.

The set of first magnets 16 and the set of second magnets 17 are each positioned to extend annularly and adjacent the annular outer electrode 15 and plasma chamber 44. That is, one half of magnets 16 and 17 are positioned at a first side 44a of a common electrode plane 47 that bisects the inner and outer electrodes 14, 15. Similarly, a second half of magnets 16,

17 are located at an opposite side 44b of the common electrode plane 47. The magnetic poles of the respective magnets 16, 17 are orientated relative to the electrodes 14, 15 and the common electrode plane 47 so as to create a magnetic circuit that bisects and is specifically focussed to a plasma region 50. Plasma region 50 is positioned at or in close proximity to the common electrode plane 47 at a position radially between electrodes 14 and 15 and in particular their respective edges 48, 49. In particular and referring to figure 7 and 8, magnets 16 and 17 at first side 44a comprise respective south poles that are inward facing and are positioned closest to the common electrode plane 47 with respective north poles being outward facing away from the common electrode plane 47 (and the plasma chamber 44). Similarly, the magnets 16 and 17 at the second side 44b comprise respective north poles that are orientated to be inward facing towards the common electrode plane 47 with corresponding south poles orientated to be outward facing away from the common electrode plane 47. Such a configuration provides a magnetic circuit having field/flux lines 56a that bisect the plasma region 50 and are perpendicular or oblique to the common electrode plane 47 within which the inner and outer electrodes 14, 15 are held. Each set of magnets 16, 17 is arranged as a respective pair of magnets with one of the magnets of each pair located at each respective side 44a, 44b or the common electrode plane 47. Each set of magnets 16, 17 is arranged annularly around longitudinal axis 45 with the set of first magnets 16 positioned closest and either side of annular outer electrode 15 (that is effectively sandwiched between the pair of first magnets 16). The second pair of magnets 17 are positioned generally opposed to the plasma region 50 at a radial position corresponding to the gap between the respective electrode edges 48, 49. Additionally, the second pair of magnets 17 are positioned in a radial direction (relative to axis 45) between the central electrode 14 and the set of first magnets 16. The magnetic field lines 56a generated via the pair of first magnets 16 are supplemented by the corresponding magnetic flux generated by the set of second magnets 17. As indicated, magnets 16, 17 may be implemented as electromagnets or permanent magnets. The net interaction and juxtaposition of the magnets 16, 17 relative to the electrodes 14, 15 is designed to direct and reinforce the magnetic flux into an arrangement aligned generally perpendicular or at least oblique to the applied electric field (between the inner and outer electrodes 14, 15 in the common electrode plane 47). Moderation of the strength and position of the magnets 16, 17 can be achieved during assembly (when implemented with permanent magnets) or by alteration of the current and polarity when implemented as electromagnets (electromagnetic coils) with respect to the electromagnetically generated fields. The net effect of the magnetic field and in particular flux lines 56a is to create a stable angular acceleration of the charged plasma particles around axis 45 at the region of the common electrode plane 47. Such an arrangement is effective to increase the effective instantaneous volume and turbulence within the plasma chamber 44 and enhance the reaction of the gas inflow with the plasma as well as allowing moderation of the effective average plasma temperature and accordingly reaction rate and profile.

Referring to figure 7 (and figure 8) and according to the specific implementation, each pair of first and second magnets 16, 17 comprises a respective annular magnetic body having a generally ring-shaped configuration. As will be appreciated, according to further embodiments, each magnet 16, 17 may be formed from a plurality of individual rod or bar magnets (arranged in an annular array around axis 45) with each rod or bar aligned such that their respective north and south poles are orientated as illustrated in figure 7 and 8.

The pair of first magnets 16a, 16b positioned respectively at either side of outer annular electrode 15 is configured to generate a primary magnetic circuit having flux or field lines 56a that extend within the plasma chamber 44 (figure 3). The orientation of the north and south poles of magnets 16a, 16b are configured such that flux lines 56a in the plasma region 50 extend parallel or generally parallel to longitudinal axis 45 and also perpendicular or generally perpendicular to the common electrode plane 47. Regions of the flux lines 56 outside or in close proximity to plasma chamber 44, are also aligned parallel or nearly parallel with axis 45. Such a configuration is achieved as first primary magnet 16a comprises a north pole surface 52 positioned furthest from annular electrode 15 and a corresponding south pole face 53 positioned facing electrode 15. Similarly, a north pole 61 of primary magnet 16b is positioned facing electrode 15 whilst the opposite south pole surface 62 is orientated away from electrode 15. Similarly, and referring to the pair of secondary magnets 17a, 17b, a south pole face 63 of magnet 17a is orientated away from plasma chamber 44 whilst a corresponding north pole face 64 is orientated to be facing towards plasma chamber 44 and common electrode plane 47. The opposite secondary magnet 17b comprises a corresponding north pole face 65 orientated to be facing inwardly into the plasma chamber 44 and common electrode plane 47 whilst the opposite north pole face 66 is orientated away from plasma chamber 44. Accordingly, in the direction of longitudinal axis 45 and from left to right of figure 7, the orientation of the poles of the primary magnets 16a, 16b is N-S N-S and the orientation of the poles of the secondary magnets 17a, 17b in the direction of longitudinal axis 45 is S-N S-N. As will be appreciated, the alternate configuration of the poles of primary magnets 16a, 16b could be S-N S-N and for the secondary magnets 17a, 17b, N-S N-S.

Each of the magnets 16a, 16b, 17a, 17b, as indicated may be formed from a continuous respective single body so as to be continuous in a circumferential direction around axis 45. Alternatively, each of the magnets 16a, 16b, 17a, 17b may be formed as an assembly or array of discreet rod or bar magnets arranged in ring in the circumferential direction around axis 45. Optionally, the annular magnetic rings 16, 17 may be formed from curved or arcuate segments connected, coupled or mounted end-to-end so as to form a segmented continuous ring. However, in all configurations, the orientation of the magnetic poles corresponds to the north and south pole relationship as described herein and as illustrated generally in figure 7 and 8.

Referring again to figure 3, central electrode 14 and the radially outer annular electrode 15 are positioned on central axis 45 so as to define a uniform electrode gap or spacing (between respective edges 48, 49). Outer electrode 15 extends continuously and has an uninterrupted solid body around central electrode 14 that comprise a circular or disc-shape configuration. The electrode gap corresponding to the plasma region 50 together with the arrangement of magnets 16, 17 ensures that the plasma discharge/arc forms in the region of highest magnetic flux density and linearity. As indicated, the magnets are arranged on either side 44a, 44b of the common electrode plane 47 and preferably comprises the dual inner and outer magnetic rings 16, 17 with respective inverted poles that in turn, create a combined and reinforced magnetic field within plasma chamber 44. Separation of the opposing inner magnets 16 is such that the distance between a face of the opposing magnets is no larger than 1/2000 times the Gauss strength at the face of each magnet multiplied by the radial width of the magnet face. As an example, for a magnet of strength 3000 and radial width of face being 10mm, a maximum magnetic separation would be 15 mm.

In operation, and where electromagnets are utilised, a magnetic field is generated by power supply 27 capable of delivering 10 to 40 kV of electrical potential. A flyback-style transformer with a frequency voltage modulation may be used. Equally, a charge-pump- type power supply with variable voltage output from 10 to 40 kV and high voltage output switching may be employed to generate the necessary frequency and voltage control. Spectrophotometric analysis of the plasma is performed by a diode array UV/Vis spectrophotometer optically coupled to the fibre optic cable 29a. The pressure of the reaction is monitored by a suitable diaphragm pressure transducer (26a). Control unit 24 is configured to read data from the spectrophotometer, pressure sensors and power supply sensors to control gas flow in and out of reactor chamber 19. A power supply voltage and frequency may then be modulated to maintain optimal reaction conditions.

In a batch -process, reactor chamber 19 and plasma chamber 44 (being in gas flow communication with one another) are charged to a desired pressure with a known volume of reactant gas in particular carbon dioxide and hydrogen via inflow ports 20a, 20b. The magnetic field is applied. If the magnet field is created by electromagnets, the plasma is initiated by application of an electric field to generate an arc between electrode edges 48, 49. The magnetic field and plasma conditions are monitored and controlled in order to maintain and optimise the plasma motion and containment within plasma chamber 44. Water produced as a by-product is collected and recycled via drain port 37. Carbon monoxide as a gas product of the reaction with the plasma at plasma region 50 is collected from gas outflow port 21.

In particular, and according to a batch-process, the plasma reactor system 10 may be implemented according to the following processing stages. In a first stage, the reactor 58 is purged with carbon dioxide to an absolute pressure of 0.1 MPa (1 bar). Hydrogen gas is introduced into the purged reactor to a stoichiometric mixture of 0.95: 1 hydrogemcarbon dioxide with or without the presence of nitrogen as a plasma promotor. In a second stage, the reaction is initiated by purging the system with reactant gasses followed by application of the magnetic field, if generated by electromagnets. In a third stage, the plasma is initiated by application of an electric field which is moderated by the variation of voltage and frequency and the motion of which is controlled by the application of external magnetic fields. The progress of the reaction is followed by monitoring pressure, temperature change and optical spectroscopy and the plasma control conditions adjusted to maintain the optimal reaction process. The system is allowed to reach equilibrium and the plasma generator is shut down. In a fourth stage, the reactor is discharged to a pre-set residual pressure of 0.1 MPa (1 bar). In a fifth stage, the reactor is then charged with 1 :0.95 mixture of carbon dioxide and hydrogen to 0.2 MPa (2 bar) pressure with or without a nitrogen as a promotor. In a sixth stage, the plasma is initiated by application of an electric field which is moderated by the variation of voltage and frequency and application of external magnetic fields. The progress of the reaction is followed by monitoring pressure change and optical spectroscopy and the plasma control conditions adjusted to maintain the optimal reaction process. The system is allowed to reach equilibrium. In a seventh stage, the reactor contents are discharged to a pre-set residual pressure. Stages 4-7 are repeated sequentially, and the product gas collected for processing. Throughout the reaction water is condensed on the reactor sides and removed from ports in the base of the reactor for recycling.

A further specific implementation of the plasma reactor 58 is described referring to figure 9. According to the further embodiment, a plurality of plasma cores 11 are housed within a common reactor chamber 19. Each core 11 comprises those components and function as described referring to figures 1 to 8. In addition, suitable electrical connections 57 provide connection of the respective inner electrodes 14. In particular, a first inner electrode 14a is coupled to a third inner electrode 14c and a second electrode 14b is coupled to a fourth inner electrode 14d. Similarly, a first outer electrode 15a is connected to power supply 27a via connection 34a, a second outer electrode 15b is connected to a second power supply 27b via connection 34c; a third outer electrode 15c is connected to the first power supply 27a via connection 34a and a fourth outer electrode 15d is connected to the second power supply 27b via electrical connection 34c. According to the further embodiment of figure 9, four interconnected cores 11 (each comprising respective electrodes and magnets) are mounted within chamber 19. The reactor array of figure 9 may be operated and functions as described referring to figures 1 to 8 involving inflow of two reactant gases via ports 20a and 20b and the outflow of a gas product via output port 21.

A further arrangement of a plasma reactor is illustrated referring to figure 10. According to this arrangement, a plurality of reactors 58a, 58b, 58c are arranged in-series such that the outlet port 21 of first reactor 58a is coupled to a respective inlet port 59 of second reactor 58b and a corresponding outlet port 21 of second reactor 58b is connected to an inlet port 60 of third reactor 58c. Each reactor 58a, 58b, 58c, comprises a respective liquid (water) drain port 37a, 37b, 37c each with a respective electrically controlled valve 38a, 38b, 38c. As will be appreciated any number of reactors may be coupled in-series.

According to a continuous process, the system of figure 10 is purged with carbon dioxide to a pre-determined starting operating pressure as a first stage. As a second stage, a 1 : 1 mixture of hydrogen and carbon dioxide is added to the first chamber to a predetermined pressure. As a third stage, the plasma in each chamber is initiated by application of an electric field which is moderated by the variation of voltage and frequency and application of external magnetic fields. The progress of the reaction is followed by monitoring pressure, temperature change and optical spectroscopy and the plasma control conditions adjusted to maintain the optimal reaction progression. As a fourth stage, product gas is removed from the final chamber at a pre-determined rate calculated from the inlet gas flow rate and outlet gas temperature and pressure and with reference to the in-process spectroscopic analysis such that a stable equilibrium is held in each of the sequential reaction chambers. After start-up the initial product stream of carbon monoxide gas will contain an excess of carbon dioxide until the continuous flow reactor reaches a state of equilibrium and as such can be discarded or recycled. As a fifth stage, once equilibrium has been attained the flow of gas into and out of the reactor chambers are continued at a steady a rate determined by the whole reactor system and desired equilibrium position in each reactor. Water is condensed throughout the reaction and collected for recycling.

Where necessary flow regulators can be employed between chambers to vary pressure throughout the reactor system. Accordingly, the in-series arrangement of figure 10 may be implemented as a continuous process in which the reactors 58a, 58b, 58c process sequentially the reactant gases to produce a continuous output flow of reactant gas (e.g. carbon monoxide) from a continuous input stream of the reactant gases (carbon dioxide and hydrogen). Each respective reactor 58a, 58b, 58c may comprise the respective sensors 29b, 26b so as to monitor the various reaction condition parameters for responsive control by the control unit 24. As will be appreciated, optimum reaction profile and plasma motion, temperature, reaction rate and energy efficiency are controlled through moderation of the frequency and/or polarity of the electric field and/or the magnetic field. Monitoring of the plasma condition can be achieved using Hall-effect sensors, current, voltage sensors, as well as spectrophotometric analysis of the plasma emission spectrum at each plasma reactor 58 and also 58a, 58b, 58c according to the batch or continuous processing reaction apparatus.

Claims

1. A plasma reactor comprising: a reactor chamber having at least one gas flow inlet and at least one outlet; a central electrode positioned on a central longitudinal axis and an annular electrode centred on and extending around the central electrode such that the central and annular electrodes are orientated opposed to one another and define a plasma region therebetween, the central and annular electrodes both located on a common electrode plane; a plurality of primary magnets centred on and extending around the longitudinal axis, at least one first magnet located at a first site of the common electrode plane and extending around the longitudinal axis and at least one second magnet located at a second opposite side of the common electrode plane and extending around the longitudinal axis; the magnetic poles of the first and second magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

2. The reactor as claimed in claim 1 wherein at least a part of the first and second magnets are positioned opposed to and either side of the annular electrode.

3. The reactor as claimed in claims 1 or 2 comprising a plurality of secondary magnets centred on and extending around the longitudinal axis, at least a third magnet of the secondary magnets located at the first side of the common electrode plane and extending around the longitudinal axis and at least one fourth magnet of the secondary magnets located at the second side of the common electrode plane and extending around the longitudinal axis, the magnetic poles of the third and fourth magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

4. The reactor as claimed in claim 3 wherein the secondary magnets are positioned in a radial direction between the primary magnets and the longitudinal axis and wherein a separation distance from the common electrode plane in the longitudinal axis direction is greater than that of the primary magnets.

5. The reactor as claimed in claims 3 or 4 wherein the polarity of the magnetic poles of the first and/or third magnet that is positioned facing and opposed to the common electrode plane is different to that of the respective second and/or fourth magnet positioned facing and opposed to the common electrode plane so as to create said magnetic circuit with flux lines aligned generally perpendicular or oblique to the common electrode plane at the plasma region.

6. The reactor as claimed in any one of claims 3 to 5 wherein the first and second magnets and/or the third and fourth magnets comprise any one or a combination of: a plurality of rod, bar or block magnets; a continuous annular magnet or an arrangement of part annular arcuate magnet segments.

7. The reactor as claimed in any preceding claim wherein the central electrode comprises a disc-shape configuration.

8. The reactor as claimed in any preceding claim wherein the annular electrode comprises an annular ring-shape configuration that extends continuously around the longitudinal axis.

9. The reactor as claimed in any preceding claim comprising at least one magnet mounting to mount the plurality of magnets in fixed position relative to the longitudinal axis, the magnet mounting comprising a material that is generally non-porous and/or electrically insulating.

10. The reactor as claimed in claim 9 wherein the magnet mounting comprises a first half and a second half mated together to at least partially encapsulate the magnets.

11. The reactor as claimed in claims 9 or 10 wherein the magnet mounting is annular or at least part annular and defines an internal plasma chamber containing the inner electrode and at least a radially inner portion of the annular electrode.

12. The reactor as claimed in any preceding claim comprising an electrode mounting to mount the annular electrode at a fixed position relative to the longitudinal axis and the electrode mounting comprises a material that is electrically conducting.

13. The reactor as claimed in any preceding claim when dependent on claim 11 comprising at least one sensor having at least a portion located within the reactor chamber and/or the plasma chamber.

14. The reactor as claimed in claim 13 wherein the sensor comprises any one or a combination of:

• a fibre optic,

• a piezoelectric sensor,

• a thermoelectric sensor,

• a photoelectric sensor, or

• a magnetometer; the sensor configured to sense or monitor any one or a combination of the following set of:

• pressure,

• temperature,

• gas flow rate,

• a gas reaction status,

• a plasma status,

• a voltage,

• a current, or

• a magnetic field strength.

15. The reactor as claimed in any preceding further comprising at least one drain port provided at a wall of the reactor chamber.

16. The reactor as claimed in any preceding claim wherein a radially inner portion of the annular electrode and/or a radially outer portion of the inner electrode comprises a sharpened or tapered annular edge.

17. The reactor as claimed in any preceding claim wherein the magnets comprise any one or a combination of:

• permanent magnets, or

• electromagnets.

18. The reactor as claimed in any preceding claim comprising a single pair of the central and annular electrodes mounted within the reactor chamber.

19. The reactor as claimed in any preceding claim comprising a plurality of respective pairs of the central and annular electrodes mounted within the single reactor chamber.

20. The reactor as claimed in any preceding claim further comprising a spectrophotometer to enable spectrophotometric analysis of a plasma generated within the plasma region.

21. The reactor as claimed in claim 20 further comprising a control unit having at least an electronic circuit board, a processor, a memory and data storage utility, the control unit connected to and configured for the control of any one or a combination of:

• a supply of electrical power to the central and annular electrode,

• a gas flow rate into the reactor chamber,

• a voltage and/or current provided at the magnets,

• a magnetic field strength generated by the magnets,

• at least one sensor within the reactor chamber, or

• an analysis of data and/or readings generated by a sensor within the reactor chamber.

22. The reactor as claimed in any preceding claim comprising at least two gas flow inlets, a first gas flow inlet connected to or provided in communication with a supply of carbon dioxide and a second gas flow inlet connected to or provided in communication with a supply of a secondary gas.

23. The reactor as claimed in claim 22 wherein the secondary gas is hydrogen.

24. Plasma reactor apparatus comprising: a plurality of plasma reactors as claimed in any preceding claim connected in gas flow communication via their respective gas flow inlets and outlets; wherein each of the plasma reactors are connected in-series to define an in-series gas flow pathway through the plasma reactor apparatus.

25. The apparatus as claimed in claim 24 comprising a single control unit coupled to each of the respective plasma reactors.

26. A method of dissociating carbon dioxide using a plasma reactor or the apparatus as claimed in any preceding claim comprising: introducing carbon dioxide into the reactor chamber via the gas flow inlet; applying an electric current to and/or creating a potential difference across the central electrode and the annular electrode; generating a magnetic field at the plasma region using the plurality of primary magnets; reacting carbon dioxide within the reactor chamber with a plasma created between the central and annular electrodes.

27. A method of creating and maintaining a plasma within a plasma reactor comprising: introducing at least one gas into a reactor chamber via at least one gas flow inlet; applying an electric current to and/or creating a potential difference between a central electrode positioned on a central longitudinal axis and an annular electrode centred on and extending around the central electrode such that the central and annular electrodes are orientated opposed to one another and define a plasma region therebetween, the central and annular electrodes both located on a common electrode plane; generating a magnetic field at the plasma region using a plurality of primary magnets centred on and extending around the longitudinal axis, at least one first magnet located at a first site of the common electrode plane and extending around the longitudinal axis and at least one second magnet located at a second opposite side of the common electrode plane and extending around the longitudinal axis, the magnetic poles of the first and second magnets orientated to create a magnetic circuit having a portion with flux lines that bisect the plasma region and are aligned generally perpendicular or oblique to the common electrode plane.

28. The method as claimed in claim 27 further comprising controlling a plasma generated in the plasma region using the control unit to control any one or a combination of:

• a voltage at or between the central and annular electrodes,

• a current at or between the central and annular electrodes,

• a magnetic field strength at the plasma region.