WO2017194635A1

WO2017194635A1 - Plasma generation

Info

Publication number: WO2017194635A1
Application number: PCT/EP2017/061234
Authority: WO
Inventors: Anil Patel; Dipam Patel
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-05-11
Filing date: 2017-05-10
Publication date: 2017-11-16
Anticipated expiration: 2018-11-11
Also published as: GB201608288D0; GB2550176A

Abstract

In an example, there is provided a plasma generator comprising: a fluid inlet configured to cause a fluid flow; a first electrode defining an inner space configured to enable the flow of the fluid, and a second electrode having a longitudinal axis and extending in the inner space defined by the first electrode, wherein the second electrode comprises a ridge defining a tapered helix configured to increase a distance from the ridge to the first electrode as the ridge extends away from the fluid inlet along the longitudinal axis of the second electrode, the plasma generator being configured to generate one or more arc discharges between the ridge of the second electrode and the first electrode to generate a plasma in the fluid flow, and cause the one or more arc discharges to glide along the ridge of the second electrode in the fluid flow.

Description

PLASMA GENERATION

Field of Invention

The invention relates to a plasma generator and a method for generating a plasma. The invention also relates but is not limited to a plasma-assisted (or plasma- enhanced) combustion burner and a method for enhancing a combustion with a plasma or to any plasma-assisted reactor and process, such as for gas and/or chemical reforming processes or for material reforming granulation, as non-limiting examples.

Background

A plasma can be generated using two planar electrodes placed in a plane defined by the two electrodes. Each of the planar electrodes comprises a curved edge, and the two edges face each other in the plane defined by the two electrodes. The two electrodes are placed in a gas flow, and the curved edges of the two planar electrodes are diverging with respect to each other in the direction of the gas flow.

Arc discharges are generated across the gas flow between the electrodes, first where the distance between the electrodes is the smallest, and the arc discharges glide towards the wider electrode gap. Gas flow kinetic supports the arc discharges glide, and the gas flow helps the arc discharges to glide along the curved edges of the electrodes in the direction of the gas flow until they disappear. The electrical energy of the arc discharges is transferred to the gas flow via the generated plasma.

Summary of Invention

Aspects and embodiments of the invention are set out in the appended claims. These and other aspects and embodiments of the invention are also described herein. Brief Description of Drawings

Figure 1A schematically illustrates a longitudinal section of an example of a plasma generator;

Figure 1 B schematically illustrates a view in perspective of a first detail of the plasma generator of Figure 1A;

Figure 1 C schematically illustrates a view of a longitudinal section of a second detail of the plasma generator of Figure 1A;

Figure 1 D schematically illustrates a view in perspective of an electrode of the plasma generator of Figure 1 A;

Figure 1 E schematically illustrates a view in perspective of a third detail of the plasma generator of Figure 1 A;

Figure 2A schematically illustrates a longitudinal section of an example of a burner; Figure 2B schematically illustrates a view in perspective of a longitudinal section of the burner of Figure 2A;

Figure 3 schematically illustrates an example of a burner of the Figure 2A connected to a load;

Figure 4 schematically illustrates an example of steps of a method for generating a plasma; and

Figure 5 schematically illustrates an example of steps of a method for enhancing a combustion with a plasma.

Specific Description

The disclosure relates to a plasma generator comprising a pair of electrodes, one of the electrodes being located in an inner space of the other electrode. A fluid may be caused to flow between the pair of electrodes. A plasma may be generated in the fluid flow by one or more arc discharges generated between the two electrodes.

The one or more arc discharges may be caused to glide around a longitudinal axis of the electrode located in the inner space of the other electrode, in the fluid flow. The gliding of the arc discharges around a longitudinal axis of the inner electrode defines three-dimensional pathways of the arc discharges. The fluid interacts with the one or more arc discharges as the discharges are caused to glide around the longitudinal axis of the inner electrode. In some examples, the fluid flow may be caused to whirl in the plasma generator (e.g. in the same orientation as the one or more arc discharges are caused to glide around the longitudinal axis) and interaction between the fluid caused to whirl and the gliding arc discharges may be enhanced.

In some examples, the one or more arc discharges may be caused to rotate around the longitudinal axis at a tip of the electrode located in the inner space of the other electrode, and interaction between the arc discharges caused to rotate around the longitudinal axis at the tip of the inner electrode and the fluid flow may be enhanced.

In some examples, an electromagnetic field may cause a glide and/or a rotation of the arc discharges around the longitudinal axis to be enhanced (e.g. facilitated and/or accelerated). Interaction between the gliding and/or rotating arc discharges and the fluid flow may also be enhanced.

In some examples the generated plasma may process the fluid flowing in the plasma generator, and the processed fluid may be used in numerous applications, such as plasma-enhanced combustion as a non-limiting example.

Figures 1A, 1 B and 1 C illustrate an example of a plasma generator 1 according to the disclosure.

In the example of Figures 1A, 1 B and 1 C, the plasma generator 1 comprises a fluid inlet 2 configured to cause a fluid flow 3.

The plasma generator 1 also comprises a first electrode 4 defining an inner space 5 configured to enable the flow 3 of the fluid.

The plasma generator 1 also comprises a second electrode 6 having a longitudinal axis 7, and extending in the inner space 5 defined by the first electrode 4. In the example of Figures 1A, 1 B and 1 C, the second electrode 6 comprises a ridge 8 defining a tapered helix configured to increase a distance 9 from the ridge 8 to the first electrode 4 as the ridge 8 extends away from the fluid inlet 2 along the longitudinal axis 7 of the second electrode 6. The plasma generator 1 is configured to generate one or more arc discharges 10 between the ridge 8 of the second electrode 6 and the first electrode 4 to generate a plasma in the fluid flow 3. As illustrated by Figure 1 B, the plasma generator 1 is configured to cause the one or more arc discharges 10 to glide along the ridge 8 of the second electrode 6 in the fluid flow 3.

The plasma generator 1 comprises an electrical power source 1 1 connected to the first electrode 4 and the second electrode 6. In the example of Figures 1A, 1 B and 1 C, the plasma generator comprises a controller 12 configured to control the power source 1 1 to generate e.g. voltage pulses. Alternatively or additionally, the controller 12 may be configured to control the power source 1 1 to generate e.g. a voltage constant in time. In the example of Figures 1A, 1 B and 1 C, the fluid inlet 2 may be configured to be connected to an external pump P enabling the flow 3. Alternatively or additionally, the fluid inlet 2 may comprise the pump P and the pump P may form part of the plasma generator 1. In the example of Figures 1A, 1 B and 1 C, the controller 12 is configured to control the flow 3 (such as the rate and/or the pressure) of the fluid (e.g. by controlling operation of the pump P) as a function of the generation of the arc discharges 10 between the electrodes 4 and 6, and may enhance the control of the generation of the plasma. In an example, the rate of the fluid flow may be relatively low compared to a frequency of the gliding of the arc discharges 10 around the longitudinal axis 7, and the fluid flow may further interact with the arc discharges.

In operation, the fluid inlet 2 causes the fluid to flow between the first electrode 4 and the second electrode 6. The controller 12 causes the power source 1 1 to generate an electric field between the first electrode 4 and the second electrode 6, e.g. by generating a voltage pulse applied to one of the first electrode 4 or the second electrode 6. When the electric field between the first electrode 4 and the second electrode 6 reaches a predetermined voltage (sometimes referred to as the "arc breakdown voltage", one or more arc discharges 10 are generated across the fluid flow 3 between the ridge 8 of the second electrode 6 and the first electrode 4, and the plasma is generated in the fluid flow 3. The value of the arc breakdown voltage depends on fluid condition and flow rate.

The generated plasma excites the molecules of the fluid to a higher energy stage. The molecules of the fluid are ionised.

The arc discharges 10 appear first where the distance 9 between the electrodes 4 and 6 is the smallest (see distance 9a in Figure 1 B), i.e. towards the fluid inlet 2. The fluid inlet 2 causes the fluid to flow at a predetermined rate (e.g. due to the operation of the pump P, e.g. controlled by the controller 12). The speed of the discharges 10 depends on:

the input power to the electrodes 4 and 6, and/or on

the fluid composition, and/or on

the flow rate and conditions. In some examples and as described below, the arc discharges 10 move relative to the fluid flow 3 along a helix trajectory, and the fluid flow 3 passes through an ionized ring gliding arc. The ring allows a quasi-uniform activation of the flowing fluid in terms of space and time. The fluid flow 3 helps the arc discharges 10 to be displaced along the ridge 8 in a direction of the fluid flow 3 and in a direction of increasing distance 9 on the tapered helix defined by the ridge 8, i.e. from the distance 9a to distances 9b and 9c illustrated in Figure 1 B. The plasma generator 1 is configured to cause the arc discharges 10 to glide along the ridge 8, i.e. around the longitudinal axis 7 of the second electrode 6 away from the fluid inlet as illustrated by Figure 1 B.

In operation, in a first phase, the discharges 10 have a relatively low power and are in a non-equilibrium state. The discharges 10 transition to a second phase of the gliding, where the generated plasma is close to a thermodynamic equilibrium, because the electrical power delivered by the power source 1 1 is sufficient to compensate for the energy transferred to the fluid flow 3. The ionic energy of the fluid increases and the generated plasma may be qualified as a thermal plasma. However, as a length of the arc discharges increases during the second phase, the length of the arc discharges eventually reaches a length where the electrical power delivered by the power source 1 1 cannot compensate for the energy lost by thermal 5 conduction any longer. The generated plasma enters a third phase of the gliding. The fluid temperature decreases, and the generated plasma may be qualified as a nonthermal plasma, but the temperature of the electron remains approximately the same, and the plasma is at a thermodynamic non-equilibrium during the second phase.

10

The increased length of the arc results in a transition to a non-equilibrium plasma, leading to a more rapid cooling to an intermediate temperature (around 2000-3000 K) and to an increase in electric field temperature (>1eV).

15 In the example of Figures 1A, 1 B and 1 C, the second electrode 6 of the plasma generator 1 comprises a tip 13 connected to the ridge 8.

The tip 13 is configured to cause the one or more arc discharges 10 to rotate around the longitudinal axis 7 of the second electrode 6 as the one or more arc discharges 20 10 are caused to glide from the ridge 8. In the example of Figures 1A, 1 B and 1 C, the tip 13 of the second electrode 6 comprises a disc-shaped extremity 14 (see Figure 1 D), but other shapes for the tip 13 are envisaged, and, in some non-limiting examples, the tip 13 could be non-truncated.

25 In operation, and as illustrated in Figure 1 B, as the arc discharges 10 glide towards the end of the ridge 8 away from the fluid inlet 2, the arc discharges 10 are caused to rotate around the longitudinal axis 7 of the second electrode 6. In some examples, rotation may be caused by a momentum provided by the gliding on the ridge 8 to the arc discharges 10. The arc discharges 10 rotating around the longitudinal axis 7 of

30 the second electrode 6 may create one or more rings 100 of arc discharges 10 around the tip 13 of the second electrode 6 which intersects the fluid flow 3, and may generate additional plasma in the fluid flow 3. Once an arc discharge 10 reaches the tip 13, it has a stable rotating intermediate temperature arc in the fluid flow 3.

The arc discharge rotation frequency at the tip 13 is for example comprised between 5 20Hz and 50Hz. The rotation speed is not affected greatly by the variations in the fluid flow rate. Higher current input results in higher rotational frequency, leading to higher power input.

In the example of Figures 1A, 1 B and 1 C, the fluid inlet 2 is configured to cause a 10 whirling movement of the fluid around the longitudinal axis 7 of the second electrode 6 in the plasma generator 1.

In the example of Figures 1A, 1 B and 1 C, the fluid inlet 2 comprises a helical groove channel 15. The helical channel 15 comprises a shaft 16 having a longitudinal axis 15 17 and comprising a helical thread 18 (see Figure 1 E) configured to fit tightly in an outer cylinder 19 (see Figures 1 A and 1 C).

The longitudinal axis 17 of the shaft 16 is aligned with the longitudinal axis 7 of the second electrode 6 (see Figure 1 C). The helical groove channel 15 is co-axial with 20 the second electrode 6, and the helical channel 15 is configured to cause the whirling movement of the fluid around the longitudinal axis 7 of the second electrode 6 in the plasma generator 1.

In the example of Figures 1A, 1 B and 1 C, the shaft 16 comprises a hollow part 161 25 around the longitudinal axis 17, and enables connection of the second electrode 6 to the power source 1 1. A part of the second electrode 6 may be located in the hollow part of the shaft 16 (see Figure 1 C).

In operation, a fluid flowing in the fluid inlet 2 circulates in the helical groove channel 30 15 defined by the helical thread 18 and is caused to whirl between the first electrode 4 and the second electrode 6 in the plasma generator 1 , around the longitudinal axis 7. A circulation of the whirling fluid flow 3 in the plasma generator is longer, compared to a non-whirling flow, and interaction between the fluid flow 3 and the arc discharges 10 is enhanced.

35 In the example of Figures 1A, 1 B and 1 C, the fluid inlet 2 is configured to cause the whirling movement of the fluid in the plasma generator 1 in a same orientation as the plasma generator 1 is configured to cause the one or more arc discharges 10 to glide along the ridge 8 of the second electrode 6. In other words, if the arc discharges 10 are caused to glide clockwise (see Figure 1 B) along the second electrode 6, away from the fluid inlet 2, the fluid flow 3 is caused to whirl clockwise as well. Similarly, if the arc discharges 10 are caused to glide anti-clockwise (not shown in the Figures), the fluid flow is caused to whirl anti-clockwise as well. In operation, the whirling movement of the fluid around the longitudinal axis 7 of the second electrode 6 in the plasma generator 1 enhances the gliding of the arc discharges 10 along the ridge 8 of the second electrode 6.

In the example of Figures 1A, 1 B and 1 C, a pitch 20 of the helical channel 15 is identical to a pitch 21 of the tapered helix defined by the ridge 8. The helical channel 15 is thus configured to cause the whirling movement of the fluid flow 3 to be aligned with the gliding of the arc discharges 10 along the ridge 8 of the second electrode 6.

In some examples, the pitch 20 may be different from the pitch 21 and generates turbulence pressure undulation in the fluid flow 3.

In operation, the whirling movement around the longitudinal axis 7 with the identical pitch 20 compared to the pitch 21 of the tapered helix defined by the ridge 8 further enhances the gliding of the arc discharges 10 along the ridge 8 of the second electrode 6.

It should be understood that additionally or alternatively to the helical channel 15 described above, the fluid inlet 2 may comprise or may be configured to be connected to any type of tornado generator, such as a generator comprising an inlet tangential to the whirl intended for the flow 3.

The whirling movement of the fluid flow 3 through the plasma generator 1 creates a relatively cool peripheral fluid flow and may extend the operating life of the plasma generator 1. In some examples the whirling movement may be cyclonic and may create a turbulent flow. In the example of Figures 1A, 1 B and 1 C, the plasma generator 1 further comprises a field generator 22 configured to generate an electromagnetic field 23 illustrated in Figure 1 D and configured to cause enhancement of a glide of the one or more arc discharges 10 along the ridge 8. In the example of Figures 1A, 1 B and 1 C, the field generator 22 comprises a coil 24 located around the first electrode 4. In the example of Figures 1A, 1 B and 1 C, the controller 12 is configured to control the field generator 22.

In operation, as illustrated in Figure 1 C, the field generator 22 generates a rotating electromagnetic field 23, which enhances the glide of the one or more arc discharges 10 along the ridge 8, i.e. by acting on the arc discharges 10 in a same orientation as the plasma generator 1 is configured to cause the arc discharges 10 to glide along the ridge 8 of the second electrode 6. In other words, if the arc discharges 10 are caused to glide clockwise (see Figure 1 B) around the longitudinal axis 7 along the second electrode 6, away from the fluid inlet 2, the electromagnetic field 23 acts on the arc discharges 10 clockwise as well (see Figure 1 C). Similarly, if the arc discharges 10 are caused to glide anti-clockwise (not shown in the Figures), the electromagnetic field acts on the arc discharges anti-clockwise as well. Alternatively or additionally, in some examples, the electromagnetic field 23 may cause enhancement of the glide by e.g. accelerating the linear speed of the glide, i.e. of the arc discharges 10 along the ridge 8, e.g. as controlled by the controller 12.

Additionally or alternatively, in the example of Figures 1A, 1 B and 1 C, the field generator 22 may be configured to generate an electromagnetic field 23 configured to cause enhancement of the rotation of the arc discharges 10 around the longitudinal axis 7 of the second electrode 6, at the tip 13 of the second electrode 6. In operation, as illustrated in Figure 1 D, the rotating electromagnetic field 23 enhances the rotation of the one or more arc discharges 10 at the tip 13, i.e. by acting on the arc discharges 10 in a same orientation as the plasma generator 1 is configured to cause the one or more arc discharges 10 to rotate around the tip 13. In some examples, the electromagnetic field 23 may cause enhancement of the rotation by e.g. facilitating the rotation, i.e. by acting on the arc discharges 10 in the same orientation as the rotation (i.e. clockwise or anti-clockwise). Alternatively or additionally, in some examples, the electromagnetic field 23 may cause enhancement of the rotation by e.g. accelerating the rotation speed of the arc discharges 10 around the longitudinal axis 7, e.g. as controlled by the controller 12. In some examples, greater rotation speed of the arc discharges 10 enhances interaction of the fluid flow 3 with the arc discharges 10 and the generation of plasma in the fluid flow 3. In some examples the electromagnetic field 23 may be constant in time, during operation of the plasma generator 1.

The plasma generator requires a relatively low energy input for the generation of the plasma.

In the example of Figures 1A, 1 B and 1 C, the power source 1 1 and the field generator 22 are connected to electrical mains M of a supplier. In that example, the power source 1 1 and the field generator 22 comprise an alternating current - direct current converter 25 and 26, respectively. The alternating current - direct current converter 25 of the power source 1 1 may be configured to provide high voltage rectified pulses. The alternating current - direct current converter 26 of the field generator 22 may be configured to provide a rectified electromagnetic field (such as unidirectional voltage and current), e.g. constant in time during operation of the plasma generator 1.

In some examples, the first electrode 4 and/or the second electrode 6 comprises a conductive ceramic. In some examples, the first electrode 4 comprises one or more metal oxides, such as Si0₂, Sn0₂, Ti0₂, W0₂, A12O3, Zr0₂ as non-limiting examples. In some examples the second electrode 6 comprises a conductive ceramic such as S1O2, Sn0₂, T1O2, WO2, A12O3, Zr0₂ as non-limiting examples. The conductive ceramic of the electrodes 4 and/or 6 may allow a relatively low erosion of the electrodes 4 and/or 6. Other materials, such as metals, may be envisaged. As illustrated in Figure 1A, the plasma generator comprises a plasma outlet 27 configured to cause a flow of plasma-enhanced fluid 28.

As illustrated by Figure 4, the disclosure also relates to a method for generating a plasma comprising, at S1 , generating one of more discharges between a first electrode and a second electrode. In the example of Figure 4, the first electrode defines an inner space and the second electrode has a longitudinal axis and extends in the inner space defined by the first electrode. The method illustrated in Figure 4 also comprises controlling, at S2, the flow of fluid between the first electrode and the second electrode to cause the one or more arc discharges to glide in the fluid flow along the second electrode and around the longitudinal axis of the second electrode to generate a plasma in the fluid flow.

It should be understood that the method illustrated in Figure 4 can be implemented in the plasma generator illustrated in Figures 1A, 1 B and 1 C, as a non-limiting example of plasma generators which can implement the method illustrated in Figure 4. Alternatively or additionally, the method illustrated in Figure 4 can be implemented in other plasma generators.

In some examples, the controller 12 comprises a processor and a memory and is configured to perform, at least partly, one or more steps of operation of the plasma generation described with reference to Figures 1A, 1 B and 1 C and/or one or more steps of the method described with reference to Figure 4.

The generated plasma may have numerous applications. Examples of applications of the generated plasma include, as non-limiting examples: gasification, gas and/or chemical reforming, material reforming granulation, surface treatment for e.g. metals and/or polymers, material and chemical processing, flue gas decontaminating, deodorising of flue emissions, breakdown of hazardous materials. One of the non-limiting examples includes applications for plasma-enhanced combustion. The second phase of the gliding provides both the sufficient fluid flow temperature and the sufficient energy density for ignition and combustion support. The third phase of the gliding enables to keep the NOx emissions at a relatively low level.

The generated plasma may enhance combustion by, for example:

- flame stabilisation, ignition and extinction, allowing a relatively large expansion of an explosion limit and/or a lean flame blow-off limit;

- relatively cool temperature ignition;

kinetics of plasma discharges and ions, allowing pathways for radicals; and reduction of the Lewis number of combustible fluids involved in the combustion. The generated plasma enables the combustible fluids (e.g. a fuel and an oxidant) to react at a significantly accelerated rate of reaction, with relatively low amount of oxidant, with a relatively low risk of blow out and a virtually complete combustion.

Figures 2A and 2B illustrate an example of a plasma-assisted combustion burner 29 according to the disclosure.

In the example of Figures 2A and 2B, the burner 29 comprises a plasma generator 1 according to any aspects of the disclosure and a fluid supply 30 connected to the fluid inlet 2.

In the example of Figures 2A and 2B, the fluid supply 30 is a fuel source, and the fluid inlet 2 of the plasma generator 1 is connected to the fuel supply 30. The fuel fluid can be a gas or a liquid. In some examples, the plasma generator 1 is configured to be connected to gas mains of a supplier. Other examples of fuel supplies include, as non-limiting examples: butane, propane, mine gas, flare gas. The disclosure applies to different types and/or grades and/or mixtures of fuels, such as fuels having a relatively low grade and/or a relatively high amount of contamination. In the example of Figures 2A and 2B, the burner comprises a combustion chamber 31. The combustion chamber 31 comprises a first fluid intake 32 configured to define an inner fluid channel 33, and a second fluid intake 34 extending in the inner fluid channel 33 defined by the first fluid intake 32. In the example of Figures 2A and 2B, the second fluid intake 34 of the combustion chamber 31 is connected to the plasma generator 1. In the example of Figures 2A and 2B, the first fluid intake 32 of the combustion chamber 31 is connected to an oxidant fluid source, such as the atmosphere. Alternatively or additionally, fuel could be introduced at the first fluid intake 32, fuel such as any hydro carbon (gas and/or liquid) fuel, including e.g. contaminated products. It should be understood that the fluids introduced in the intakes 32 and/or 34 may be a gas (such as vaporised liquid oxidant or fuel) and/or a liquid (such as liquid oxidant or fuel).

In the example of Figures 2A and 2B, the first fluid intake 32 is configured to channel a fluid F, such as the oxidant fluid, downstream the second fluid intake 34 enabling intake of the plasma-enhanced fluid 28 (i.e. the fuel fluid flow 3 as processed by the plasma) output from the plasma generator 1. The first fluid intake 32 comprises a housing 35 comprising a tapered inner profile.

In operation, the second fluid intake 34 enables the intake of the flow of plasma- enhanced fluid 28 (such as the plasma-processed fuel) from the plasma generator 1 , and enables intake of fluid F (such as the oxidant fluid) through the first intake 32. In some examples, the flow of plasma-enhanced fluid 28 through the second intake 34 may generate the intake of the oxidant fluid F through the first intake 32 by drawing the oxidant fluid. The channelling caused by the first intake 32 mixes the flow of plasma-enhanced fluid 28 and the oxidant fluid F in the combustion chamber 31 , and creates a plasma-enhanced flow 36 downstream the first fluid intake 32 and the second fluid intake 34, for a plasma-enhanced reaction (e.g. combustion).

It should be understood that the whirling movement of the plasma-enhanced fluid 28 from the plasma generator 1 may extend through the combustion chamber 31 and may be conveyed to the plasma-enhanced flow 36. The whirling movement of the plasma-enhanced flow 36 creates a relatively cool peripheral fluid flow in the combustion chamber 31 and may extend the operating life of the combustion chamber 31. In some examples the whirling movement of the plasma-enhanced flow 36 may be cyclonic and may cause the plasma-enhanced flow 36 to be a turbulent flow. In some examples, the turbulent flow enhances the combustion reaction.

In the example of Figures 2A and 2B, the combustion chamber 31 further comprises an electromagnetic field generator (37, 38) configured to cause a modulated magnetic pinch to the plasma-enhanced flow 36 in the fluid flow, downstream the first fluid intake 32 and the second fluid intake 34. In the example of Figures 2A and 2B, the electromagnetic field generator (37, 38) comprises a coil 38 located around the combustion chamber 31. In the example of Figures 2A and 2B, the controller 12 is configured to control the electromagnetic field generator (37, 38) to generate an electromagnetic field, which may act e.g. as an electromagnet, pulsed in time, e.g. as controlled waveforms. The plasma pinch is caused by Lorentz forces generated by the electromagnetic field. In some examples, the modulated plasma pinch causes the plasma-enhanced flow 36 to be turbulent. In some examples, the turbulent flow enhances the combustion reaction.

In operation, the modulated pinch to the plasma-enhanced flow 36 caused in the fluid flow enhances the mixing of and/or the combustion reaction in the plasma-enhanced flow 36 in the combustion chamber 31.

In the example of Figures 2A and 2B, the electromagnetic field generator (37, 38) is configured to be connected to the electrical mains M of a supplier and comprises an alternating current - direct current converter 39. The alternating current - direct current converter 39 of the electromagnetic field generator (37, 38) may be configured to provide a modulated power, such as relatively low voltage and relatively high current. As illustrated in Figure 3, the combustion is exothermic and the produced thermal energy may be delivered to a load 41 , through an outlet 40 of the combustion chamber 31. In some examples, the load 41 may be a heat diffuser and/or a heat exchanger, or any other type of heat load.

In some examples, information feedback may be obtained from the flue gas emissions through the outlet 40, e.g. via a sensor 42 configured to sense mass flow, energy and/or emission data (such as gas composition i.e. CO, CO₂, O, HC as non- limiting examples). In some examples, the information feedback obtained from the sensor 42 may be fed as an input to the controller 12, e.g. enabling enhanced control of the plasma generation and/or combustion. Alternatively or additionally, at least a part of the flue gas emissions through the outlet 40 may be reintroduced in the combustion chamber 31 , e.g. via the first inlet 32 and/or the second inlet 34, for further improvement of the efficiency of the combustion. In some examples, the combustion chamber 31 comprises one or more nanoparticle ceramics, such as nanoparticle based conductive ceramic Si0₂, Sn0₂, Ti0₂, W0₂, Ai₂0₃, Zr0₂ as non-limiting examples. In some examples, the combustion chamber 31 may be lined with the nanoparticle ceramics acting as a thin layer refractory material. In some examples, the first electrode 4 is configured to be an anode and the second electrode 6 is configured to be a cathode. Alternatively or additionally, the first electrode 4 could be configured to the cathode and the second electrode 6 could be configured to be the anode. As illustrated in Figure 5, the disclosure also relates to a method for enhancing a combustion with a plasma. The method of Figure 5 comprises generating, at S3, a plasma using a method illustrated in Figure 4 in a first fluid (such as comprising a fuel fluid), and, at S4, controlling an intake of a second fluid (such as comprising an oxidant fluid) to be mixed with the generated plasma for combustion.

In some examples, the controller 12 comprises an embedded processor and a memory and is configured to perform, at least partly, one or more steps of operation of the plasma-assisted combustion described with reference to Figures 2A and 2B and/or one or more steps of the method described with reference to Figure 5.

The burner according to any aspect of the disclosure may be used in any system which employs combustion processes, such as burner systems used in households, commercial premises or industries. Non-limiting examples include:

e.g. for households: single dwelling household combination boilers and portable gas heater systems,

e.g. for commercial premises: commercial boilers used in district heating or centralised heating systems for flats or larger premises such as offices, process heating such as industrial dry cleaners, chemical production, food and beverage production,

- e.g. for industries: smelting, steelworks, cement production, incineration systems, process heat generators and steam generators.

Other examples of applications include: external burners, power generators (such as steam turbines, gas turbines or Organic Rankine Cycle (ORC) systems), absorption or adsorption chillers and heat pumps.

The burner according to any aspect of the disclosure may have a relatively small dimension due to the ability to of the burner deliver a relatively high thermal density. The burner according to any aspect of the disclosure may operate at relatively high temperatures, thus allowing a relatively large difference of temperature between the combusted gases and the load 41 and a relatively fast energy transfer to the load 41. The burner according to any aspect of the disclosure may be efficient, i.e. may require a relatively low amount of fuel (e.g. lean combustion) and may allow for relatively low levels of harmful emissions such as NOx and/or unburned hydrocarbons (such as Co or ash HCs). Other advantages include: a relatively low amount of particles due to faster and complete reaction, and scalability of the system, for example from 1 kW to 1 MW (megawatt), and this example range may be extended by having multiple units in the system.

Modifications and Variations

Other variations and modifications of the plasma generator or the burner will be apparent to the skilled in the art in the context of the present disclosure, and various features described above may have advantages with or without other features described above. In the example of Figures 1A, 1 B and 1C, the outer cylinder 19 of the fluid inlet 2 has a straight cylindrical geometry, but it should be understood that any other type of shape is also envisaged.

In the example of Figures 1A, 1 B and 1 C, the fluid inlet 2 is configured to cause a whirl of the fluid flow 3. However it should be understood that the fluid inlet 2 may cause the fluid to flow in a direction substantially parallel to the longitudinal axis 7 of the second electrode 6.

In the examples of Figures 1A, 1 B and 1 C, the tapered helix has a straight conical profile 43 (see Figure 1A), but it should be understood that any type of tapered profile may be envisaged, for example any type of curved profiles are equally envisaged by the present disclosure.

Similarly, in the example of Figures 1A, 1 B and 1 C, the first electrode 4 has a straight cylindrical geometry, but it should be understood that any type of geometry could be envisaged. For example any type of diverging tapered shape (such as conical or curved) could be envisaged for the first electrode 4, as long as the distance from the ridge 8 to the first electrode 4 increases as the second electrode 6 extends away from the fluid inlet 2. In the example of Figures 1A, 1 B and 1C, the power source 1 1 , the field generator 22 and the electromagnetic field generator (37, 38) are connected to the electrical mains M of the supplier, but it should be understood that any one of the power source 1 1 and/or the field generator 22 and/or the electromagnetic field generator (37, 38) could be connected to any other electrical power supply (such as power generators) and/or power storage (such as batteries).

In the example of Figures 1A, 1 B and 1 C the power source 1 1 , the field generator 22 and the electromagnetic field generator (37, 38) are operated using direct current, but it should be understood that the disclosure also applies to any one of the power source, the field generator and the electromagnetic field generator being operated by one or more alternating currents. In the example of Figures 1A, 1 B and 1 C, the controller 12 is configured to control the pump P, the power source 1 1 , the field generator 22 and the electromagnetic field generator (37, 38), but it should be understood that any one or more of the pump P, the power source 1 1 , the field generator 22 and/or the electromagnetic field generator (37, 38) could be controlled by one or more separate controllers.

As one possibility, there is provided a computer program, computer program product, or computer readable medium, comprising computer program instructions to cause a programmable computer to carry out any one or more of the methods described herein.

In example implementations, at least some portions of the activities related to the controller herein may be implemented in software. It is appreciated that software components of the present disclosure may, if desired, be implemented in ROM (read only memory) form. The software components may, generally, be implemented in hardware, if desired, using conventional techniques. In some examples, components of the controller may use specialized applications and hardware. The controller may comprises a server, which should not be understood as a single entity, but rather as a physical and/or virtual device comprising at least a processor and a memory, the memory may be comprised in one or more servers which can be located in a single location or can be remote from each other to form a distributed network (such as "server farms", e.g., using wired or wireless technology).

In some examples, one or more memory elements can store data used for the operations described herein. This includes the memory element being able to store software, logic, code, or processor instructions that are executed to carry out the activities described in the disclosure.

A processor can execute any type of instructions associated with the data to achieve the operations detailed herein in the disclosure. In one example, the processor could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM)), an ASIC that includes digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof. The data received by the controller may be typically received over a range of possible communications networks, at least such as: a satellite based communications network; a cable based communications network; a telephony based communications network; a mobile-telephony based communications network; an Internet Protocol (IP) communications network; and/or a computer based communications network. In some examples, the controller may comprise one or more networks. Networks may be provisioned in any form including, but not limited to, local area networks (LANs), wireless local area networks (WLANs), virtual local area networks (VLANs), metropolitan area networks (MANs), wide area networks (WANs), virtual private networks (VPNs), Intranet, Extranet, any other appropriate architecture or system, or any combination thereof that facilitates communications in a network.

The above embodiments are to be understood as illustrative examples, and further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A plasma generator comprising:

a fluid inlet configured to cause a fluid flow;

a first electrode defining an inner space configured to enable the flow of the fluid, and

a second electrode having a longitudinal axis and extending in the inner space defined by the first electrode,

wherein the second electrode comprises a ridge defining a tapered helix configured to increase a distance from the ridge to the first electrode as the ridge extends away from the fluid inlet along the longitudinal axis of the second electrode, the plasma generator being configured to generate one or more arc discharges between the ridge of the second electrode and the first electrode to generate a plasma in the fluid flow, and cause the one or more arc discharges to glide along the ridge of the second electrode in the fluid flow.

2. The plasma generator of claim 1 , wherein the fluid inlet is configured to cause a whirling movement of the fluid around the longitudinal axis of the second electrode in the plasma generator.

3. The plasma generator of claim 2, wherein the fluid inlet comprises a helical channel.

4. The plasma generator of claim 3, wherein a pitch of the helical channel is identical to a pitch of the tapered helix defined by the ridge.

5. The plasma generator of any one of claims 2 to 4, wherein the fluid inlet is configured to cause the whirling movement of the fluid in the plasma generator in a same orientation as the plasma generator is configured to cause the one or more arc discharges to glide along the ridge of the second electrode.

6. The plasma generator of any one of claims 1 to 5, further comprising:

a controller configured to control the flow of the fluid as a function of a generation of the one or more arc discharges.

7. The plasma generator of any one of claims 1 to 4, wherein the second electrode comprises a tip connected to the ridge and configured to cause the one or more arc discharges to rotate around the longitudinal axis of the second electrode as the one

5 or more arc discharges are caused to glide from the ridge.

8. The plasma generator of claim 7, wherein the tip of the second electrode comprises a disc-shaped extremity.

10 9. The plasma generator of claim 7 or 8, further comprising:

a field generator configured to generate an electromagnetic field configured to cause enhancement of at least one of:

a glide of the one or more arc discharges along the ridge; and/or

a rotation of the one or more arc discharges around the longitudinal axis of

15 the second electrode, at the tip of the second electrode.

10. The plasma generator of claim 9, wherein the field generator comprises:

a coil located around the first electrode.

20 1 1. The plasma generator of claim 9 or 10, further comprising:

a controller configured to control the field generator to generate an electromagnetic field rotating in a same orientation as the plasma generator is configured to cause the one or more arc discharges to glide along the ridge of the second electrode.

25

12. The plasma generator of any one of claims 1 to 1 1 , wherein the first electrode and/or the second electrode comprises a ceramic.

13. The plasma generator of any one of claims 1 to 12, further comprising:

30 a power source connected to the first electrode and the second electrode.

14. The plasma generator of claim 13, further comprising:

a controller configured to control the power source to generate voltage pulses.

15. The plasma generator of claim 9 or 13, wherein the field generator and/or the power source is configured to be connected to electrical mains of a supplier and comprises an alternating current - direct current converter.

5 16. A plasma-assisted combustion burner comprising:

a plasma generator of any one of claims 1 to 15, and

a fluid supply connected to the fluid inlet.

17. The burner of claim 16, further comprising a combustion chamber comprising: 10 a first fluid intake configured to define an inner fluid channel; and

a second fluid intake extending in the inner fluid channel defined by the first fluid intake.

18. The burner of claim 17, wherein the first fluid intake is configured to channel a 15 fluid downstream the second fluid intake.

19. The burner of claim 17 or 18, wherein the first fluid intake comprises a housing comprising a tapered inner profile.

20 20. The burner of any one of claims 16 to 19, wherein the combustion chamber further comprises:

an electromagnetic field generator configured to cause a modulated pinch to a plasma-enhanced flow, downstream the first fluid intake and the second fluid intake.

25 21. The burner of claim 20, wherein the electromagnetic field generator comprises:

a coil located around the combustion chamber.

22. The burner of claim 20 or 21 , wherein the electromagnetic field generator is configured to be connected to electrical mains of a supplier and comprises an 30 alternating current - direct current converter.

23. The burner of claim 20 to 22, further comprising:

a controller configured to control the electromagnetic field generator to generate an electromagnetic field, pulsed in time.

5 24. The burner of any one of claims 16 to 23, wherein the fluid inlet of the plasma generator is configured to be connected to a fuel supply.

25. The burner of claims 24, wherein the plasma generator is configured to be connected to gas mains of a supplier.

10

26. The burner of any one of claims 17 to 25, wherein the second fluid intake of the combustion chamber is connected to the plasma generator.

27. The burner of any one of claims 17 to 26, wherein the first fluid intake of the 15 combustion chamber is connected to an oxidant source and/or a fuel source.

28. The burner of any one of claims 17 to 27, wherein the combustion chamber comprises one or more nanoparticle ceramics.

20 29. The plasma generator of any one of claims 1 to 15 or the burner of any one of claims 16 to 28, wherein the first electrode is configured to be an anode and the second electrode is configured to be a cathode.

30. A method for generating a plasma, comprising:

25 generating one or more arc discharges between a first electrode and a second electrode,

wherein the first electrode defines an inner space and the second electrode has a longitudinal axis and extends in the inner space defined by the first electrode; and

30 controlling a flow of fluid between the first electrode and the second electrode to cause the one or more arc discharges to glide in the fluid flow, along the second electrode and around the longitudinal axis of the second electrode, to generate a plasma in the fluid flow.

31. A method for enhancing a combustion with a plasma, comprising: generating a plasma according to claim 30 in a first fluid;

controlling an intake of a second fluid to be mixed with the generated plasma for combustion.

5

32. The method of claim 31 , wherein:

the first fluid comprises a fuel fluid and the second fluid comprises an oxidant fluid and/or a fuel fluid.

10 33. A computer program, computer program product, or computer readable medium, comprising computer program instructions to:

cause a programmable computer to provide a plasma generator of any one of claims 1 to 15 or a burner of any one of claims 16 to 29; or comprising computer program instructions to:

15 cause a programmable computer to carry out any one or more of the methods according to any one of claims 30 to 32.