WO2011138525A1

WO2011138525A1 - Method and device for generating a non-isothermal plasma jet

Info

Publication number: WO2011138525A1
Application number: PCT/FR2011/000277
Authority: WO
Inventors: Pavel Koulik; Anatoly Saychenko
Original assignee: Pek 38-40
Priority date: 2010-05-05
Filing date: 2011-05-04
Publication date: 2011-11-10
Also published as: EP2567599B1; CN103229601A; CN103229601B; FR2959906B1; FR2959906A1; EP2567599A1

Abstract

The invention relates to a method for generating an axisymmetric non-isothermal plasma jet by means of a high-voltage electrical discharge of a single-phase or three-phase direct or alternating current into a gas flow, wherein said discharge is initiated by a discharge plasma, propelled by an electromagnetic force and by the drag force exerted by the gas flow and localized at the ends of the electrodes, characterized in that the gas flow propelling the plasma of the discharge is stabilized and laminarized at all points of the resulting plasma jet, and to a device for using the method comprising, in particular, a gas propellant dispenser consisting of elements for the laminarization of the flow in a honeycomb system or an abruptly expanding system, wherein a system of magnetic fields forms the plasma cords and conduits for the introduction of the propulsion and rotation gas components of the propulsion gas flow.

Description

_ _

METHOD AND DEVICE FOR GENERATING A NON-ISOTHERMIC PLASMA UB JET

The present invention consists of a method for controlled generation of non-isothermal plasma jet at a pressure close to atmospheric pressure and a device for implementing this method.

The generation of plasma jets is related to the transformation technologies of matter, especially plasmochemistry, and more particularly the destruction of products and waste.

_^ Plasma generators the best known and most used in practice, particularly in industry and in particular for the destruction of domestic waste, medical, industrial and other, are plasma generators isothermal DC, AC, high frequency , microwave.

By "isothermal" is meant plasmas whose temperatures of the various components, especially heavy particles (molecules, atoms, radicals, ions) Ta, and electrons, Te, are substantially equal. By definition, a plasma is isothermal when, at any point of its volume, the condition is realized:

Te = Ta [1]

The plasmas generated by the generators mentioned above are usually isothermal. This means that the chemical reactions that occur there are local thermodynamic equilibrium relations, described, for example, by the well-known Arrhenius law. The concentration of the components of the isothermal plasma is described by the equation, also well known, of Saha. If the amplitude of the electric field which accelerates the electrons of the plasma and causes them the reactions of excitation and ionization is rather high, it can happen that the plasma becomes non-isothermal, that is to say. than :

Te> Ta [2]

For the relation (2) to take place the amplitude of the electric field E must obey a condition of the type (case of a weakly ionized plasma):

E> kT _a .n _e .Q / e [3] OR

e is the charge of the electron (e = 1.6 × 10 ^-19 C), k is the Boltzmann constant (k = 1.4 × ¹⁹ J / K);

T _a is the temperature of the heavy components (molecules, radicals, atoms, ions) of the plasma (K);

Q. is the cross section of elastic collisions between electrons and neutral plasma components (m ² ); n _e is the concentration of free electrons (m ³ )

If T _has -2000K, n _e ~ 10 ⁺¹⁹ m ^"3 , Q ~ 10 ^{" 18} m ² ,

we have E> 2.10 ⁴ V / m ..

Practical use of non-isothermal plasma can be technologically advantageous. This is the case, for example of the destruction of waste, mentioned above. Indeed, the electrons which, in this case, have a great kinetic energy, favor the formation of excited molecular states and radicals, extremely effective for the destruction of organic molecules.

The state of the art, especially with regard to the destruction of waste, has led the users of the technologies of plasmas that they deem more effective than the traditional methods of incineration, to use generators of jets of isothermal plasmas (ie in a state of thermodynamic equilibrium) at atmospheric pressure, such as DC, AC, radio frequency or microwave arc generators. The temperature of these plasmas is of the order of 6,000-12,000 K depending on the generation conditions.

It is clear that such plasmas are effective in destroying the organic molecules that make up the largest part of the waste mentioned. They are also effective in destroying non-organic molecules.

Accompanied by a plasma quenching process (rapid cooling that prevents the recombination of many harmful molecular states, including dioxins and furans), these technologies have proven advantageous over traditional thermochemical technologies. , ".

(See, for example, Zhukov M. F. Izv.SOAN USSR, Ser.Techn.Nauk, 197U, VI (8) P. 12-18, Burov IS, Ermolaeva EM, Moss AL, Minsk ITMO 1975, p.71-78; see also www.europlasma.com). The stated temperature level (6,000 - 12,000 K) is however superfluous. It is inevitable if an isothermal plasma is used at atmospheric pressure because ^" the temperature level (T = T _a = T _e ) determines the concentration of electrons necessary for the electrical conductivity of the plasma, the latter ensuring the energy balance of the arc. This level of temperature is, however, excessive for the realization of the plasmochemical reactions of destruction of the waste in question.This temperature level leads to enormous energy expenditure which makes the very reasons for the use of the Isothermal plasma generators and make the exploitation of traditional incineration techniques with the addition of extremely expensive, bulky and inefficient filters still today the solution despite all preferable in comparison with jets of isothermal plasmas.

The solution is therefore to use a non-isothermal plasma, the temperature level of the heavy components (T _a ) would be of the order of 2000 - 2500 K, which is sufficient to achieve the intended chemical reactions for example, those necessary for the destruction of waste without the formation of harmful chemical components, while the temperature of the electrons would be of the order of 6 000 - 12 000 K, which would ensure an electric current sufficient to support the mechanism of electric discharge and the energy balance of the plasma jet.

Non-isothermal plasma generators have been proposed, protected by patents, and exploited at the industrial level (see, for example, Engelsht VS, Saichenko AN, Okopnik GM, Musin Nu XI Vsesoyuznaya Konf, Po Generator nizkotemperaturnoy plazmi, Novosibirsk, 1989; P 255, Desiatkov GA, Enguelsht VS, Saichenko AN, Musin NU, and Plasma Jets in the Development of New Materials Technology, Proc.Of the International Workshop 3-9 September, Frunze, USSR Ed., OPSolonenko, AIFedorchenko. VSP, Utrecht, (NL), Tokyo (Japan), pp 499-509, see also www.glidarc.com).

They are based on the use of the principle of the high voltage arc sliding between two electrodes of divergent geometry. Initiated by a discharge where the electrodes are closest to each other, the arc is propelled along these electrodes thanks to the electromagnetic force created by the field magnetic due to the current flowing through the electrode and the current flowing through the arc in a direction substantially perpendicular to the axis of the electrodes. The movement of the ¾rc may be, in addition, biased by a longitudinal stream of propellant gas which contributes to forming the plasma jet downstream of the electrodes. As the arc slides, its length and electrical resistance increase and the intensity of the current decreases. There comes a moment when the current becomes too weak to support the energy balance of the discharge and the arc disappears. A new discharge is then initiated again at the base of the electrodes and the process is repeated. So we have a perpetual movement of "back and forth" of the arc along the electrodes. In its movement, the arc creates around it a "plasma cloud" whose properties, and especially the life time, depend on the nature of the gas in which the discharge takes place, the presence of a hydrodynamic flow of gas , the level of the amplitude of the voltage between the electrodes, and the divergence geometry of the electrodes. This plasma cloud can ensure the existence of a conductive area of electricity in the absence of electric current during its lifetime. It is therefore possible to feed the arc not only with direct current but also with pulse current, if the plasma cloud lifetime is greater than the pause between the voltage pulses between the electrodes. In particular, it is possible to feed the sliding arc with alternating current, for example of frequency 50Hz.

Sliding arcs have been created by DC generators, single-phase and three-phase alternating current. In the latter case, solutions with three electrodes and six electrodes have been proposed and carried out industrially. The use of three and six electrodes (see Engelsht VS, Gurovich V. Ts., Desyatkov GA, Musin NU, Saitchenko AN Experimental investigation and application of the high-voltage low-current arc in gas flow .20 ICPIG.-Barga, 1991 -P.978-979) is proposed in order to standardize as much as possible the plasma area generated, since this plasma is out of thermodynamic equilibrium and therefore contains large concentrations of molecules and radicals in the state metastable. It is the potential energy of these particles (non-thermal effects), and not only their kinetic energy (thermal effects), which make it possible to break down the particles of the products to be destroyed by the plasma.

The processes and generators mentioned have the following disadvantages which make them difficult to apply in practice, or substantially reduce their effectiveness: 1. Spatial non-uniformity of the generated plasma jet.

2. Instability of the generated plasma.

3. Impossibility of control of the process and its parameters.

4. Limited (reduced) dimensions of the plasma area.

5. Plasma-limited plasma generation zone (the presence of electrodes in the plasma zone obstructs the treatment field).

The fact that the sliding arc is by definition in constant motion can be a disadvantage because it conditions the spatial nonuniformity and the instability of the generated plasma.

The authors cited above (Desyatkov et al.) Have also proposed a configuration of the electrodes which fixes the position of the arc in space as soon as it has reached the ends of the electrodes. The current lines then bend subjected, on the one hand, to the drag force of the propulsive gas flow and to the electromagnetic force and, on the other hand, to the hydrodynamic resistance of the arc which tends to maintain its position. in the most ionized area of space. This solution is more advantageous than that of the sliding arc. However, experimental work shows that the arc, and therefore the plasma jet it generates, remains unstable. This instability is mainly due to the turbulent nature of the propellant gas flow. In addition, given the short length of the plasma jet generated, it is difficult to perform object processing work by preventing the jet reflected by the treated object from altering the parts of the generator, including the electrodes. It is therefore highly desirable that the plasma jet be substantially longer. However, it is possible to extend the plasma jet according to existing technologies by increasing the incident power, the energy efficiency of such a generator is very low because the power losses increase almost proportionally to the square of the dimension of the jet, of shape close to the sphere. In the context of the foregoing, an object of the present invention is to develop a stable non-isothermal plasma jet generation method, at a pressure close to atmospheric pressure or above atmospheric pressure, which can be used advantageously for the industrial production of plasmochemical reactions, particularly in the field of the destruction and recycling of waste, in particular organic waste. " ,. "

It is advantageous to use a method for generating a uniform non-isothermal plasma jet in the space of a plasmochemical reactor.

It is also advantageous to operate a method of generating a non-isothermal plasma jet that is stable over time during the entire duration of a plasmochemical treatment.

It is also advantageous to use an elongated plasma jet whose length to diameter ratio is substantially greater than unity. It is all the more advantageous to use a laminarized non-isothermal plasma jet of in order to increase the length thereof while limiting the energy exchanges with the surrounding gaseous medium.

A great advantage is any technology capable of providing variable controlled treatment depending on the composition of the feed gas, the shape, the nature, and the composition of the treated product.

Objects of the invention are achieved by generating a non-isothermal plasma jet, at a pressure close to atmospheric pressure, according to a method of generating an axisymmetric jet of non-isothermal plasma with the aid of a single-phase or three-phase high-voltage direct or alternating current electric discharge in a gas flow, discharge initiated by a breakdown plasma, propelled by an electromagnetic force and by the drag force exerted by the gas flow and located at the ends of electrodes, characterized in that the flow of gas propelling the plasma of the discharge is stabilized at all points of the resulting plasma jet, the relative velocity of the gas, V *, at any point of the propulsive flow, obeying the relation like:

r * <D *: V * (r *) = l.

D * ≤r * ≤l: V * (r *) = 1 - cos [n (r * - 1) / 2 (D * -1)],

and that the condition of hydrodynamic stabilization of the arc is satisfied:

V≤Re * .r) / p. D

or

D * = D / D ₀ ; r * = 2r / D ₀ ;

D and D ₀ are respectively the outer diameter of the jet, and the diameter of the zone of laminarization and that D <D ₀ ;

r is the radius of the jet point where the current velocity V is determined;

V ₀ is the speed of the laminarized flow.

Re * is the critical Reynolds number of the stabilized flux;

η and p are respectively the dynamic viscosity and the density of the gas propelling at the temperature of the propellant flow of the present invention and a .

device for the implementation of a method of generating ^a jet of non-isothermal piasma as above wherein the propelling gas stream enters the forming zone of the arc by means of a distributor of gas comprising an inlet manifold, a velocity profile forming device and a sieve of the present invention.

Other objects, features and advantages of the present invention appear from the drawings, diagrams and illustrations appended to the present invention, in which:

• Figure 1 illustrates the configuration of the high-voltage arc generated between two electrodes in the alternating current regime (50 Hz) conveyed by a gas flow in two cases: fig.la: the flow of gas is turbulent

fig.lb: the flow of gas is organized so that the hydrodynamic pulsations are minimal, in particular, the gas flow is laminarized.

FIG. 1c also illustrates the fact that the stabilized non-thermal plasma jet as proposed by the present invention, in particular laminarized, propagates over a distance substantially greater than the length of the unstabilized flux.

FIG. 2 shows a diagram of embodiment of the device making it possible to implement the present invention ("a") and mentions two variants of cooling of the electrodes: FIG. 2a: cooling in air; fig.2b: cooling with water.

FIG. 3 illustrates a three-electrode non-thermal plasma jet generation system powered by a three-phase power source.

FIG. 4a illustrates a six-electrode non-thermal plasma jet generation system powered by a three-phase power source, in two configurations: fig.4b: star connection; fig.4c: triangle connection;

Fig. 5a illustrates a particular case of application of the present invention when the generator is powered by three-phase alternating current and is provided with three base electrodes and an annular electrode so as to stretch the portion of the excited plasma jet. by the electric current and in this way to control the configuration.

Fig.5b illustrates the case where the annular electrode is cooled by gas or by water.

FIG. 6 illustrates the particular case of the application of a magnetic field to each of the six electrodes supplying a non-thermal jet generator: FIG. 6a: cross section of the device; Fig. 6b: longitudinal section, magnetic field being directed to concentrate the electric discharge in the axial zone of the plasma jet. Fig. 6c: longitudinal section, magnetic field directed to locate the electric discharge in the peripheral area of the plasma jet. Fig 6d: Longitudinal section, the magnetic field is continuous and constant in time. In this case, the electric shock oscillates.

Fig.7 shows a cross-section of a non-isothermal plasma jet generated by six electrodes and rotated about its axis by means of a deflector system and / or a coaxial magnetic field.

FIG. 8 illustrates the particular case where the non-thermal plasma jet is propelled and stabilized by a flow of gas composed of concentric zones of gas, each of which having a flow rate controlled by valves. ·. _,,,,.

• The tig.9 is a graph of. the variation of the rare length generating the non-isothermal plasma jet, for two values of the voltage, as a function of the speed V of the propellant gas introduced to stabilize the non-isothermal plasma jet according to the present invention.

• Fig. configuration of the electrodes with milled central body.

• Figll. electrode configuration with pads. The principle of the proposed method lies in the following:

It is proposed to use as a basis the method of generating a non-isothermal plasma axisymmetric jet using a single or three-phase direct or alternating current high-voltage electric discharge in a gas flow, initiated discharge. by a breakdown plasma, propelled by an electromagnetic force and by the drag force exerted by the gas flow and located at the ends of the electrodes.

The plasma in such a jet is in a non-thermal state as defined by the formulas [1] - [3], which gives principle advantages to the present invention. Unfortunately, in existing applications, the generated plasma jet is turbulent and the advantage of the non-thermal plasma remains practically unused, since the energy exchanges in a turbulent plasma are too intense and it becomes impossible to exploit them: electrons and that of excited particles and free radicals, possibly formed and in a metastable state, are "wasted" and lost in heat.

The present invention makes it possible, on the contrary, to exploit these advantages based on the limitation of the heat losses and the optimization of the use of the excited states of the particles.

The present invention consists in stabilizing the plasma jet by acting on the flow of gas which feeds and propels it. Stabilization is mainly hydrodynamic. It consists in organizing in all points of the flow of gas which coats and propels the plasma jet conditions where the convective exchanges are eliminated and practically only remains the molecular dissipation, in particular thermal conduction and diffusion. The experience of the authors of the present invention has shown that for this: • the relative speed of the gas, V *, at any point of the propulsive flow, must obey the empirical relation of the type:

r * <D *: V * (r *) = l. [1];

D * <r * <l: V * (r *) = l - cos [n (r * - l) / 2 (D * -l)] [2];

• that the hydrodynamic stabilization condition must be satisfied:

V <e * .r | / p. D, [3]

or

D * = D / D ₀ ; r * = 2r / D ₀ ;

D and D ₀ are respectively the outside diameter of the jet

and the diameter of the stabilization zone (D <D ₀ );

r is the radius of the jet point where the current speed is determined

V;

V ₀ is the speed of the laminarized flow;

Re * is the critical Reynolds number of the stabilized flux;

η and p are respectively the dynamic viscosity and the density of the gas propelling at the temperature and the pressure of the flow

propelling.

A Reynolds critical number, Re *, is the value of the Reynolds number at which the flow spontaneously passes from the laminar state to the turbulent state. For a flux in an axisymmetric tube this value is well known and is at the level of 2000. Experience shows that this spontaneous passage is determined by the velocity differences between the adjacent layers of the fluid or more precisely by the gradient of this velocity . It is conceivable, and the experience of the authors of the present invention confirms it, to have a base flow of high velocity and of restricted characteristic dimension for which the character of the exchanges remains molecular even if the Reynolds number is much greater than 2000. Flows of this kind are called pseudo-laminars by the authors of the present invention. Pseudo-laminar fluxes have been observed by the authors of the present invention for Reynolds numbers (formally computed) of up to 100,000. For this purpose, the flux must be embedded in a "sheath" of fluid where the velocity passes. monotonously and as a smooth function of the value of the speed at the heart of the base flow at the speed of the surrounding flow, in particular the zero velocity of a stationary environment. In addition, the experience has shows that for a flow to be pseudo-laminar, it is necessary that the gradient of the flow velocity in the intermediate zone is equal to zero at the boundaries of the intermediate flow with the base flow and the surrounding flow.

The value of Re * can only be determined empirically. The work done by the authors of the present invention has shown that, practically, Re * ~ 1.5.10 ⁴ . This result can be used for all mentioned plasma jet configurations and for all the implementers mentioned in the present invention. For other configurations, in order to remain within the scope of the present invention, it is necessary, before setting the regime and the operating parameters of the plasma jet, to carry out well-known hydrodynamic measurements and classics on the device adopted so as to determine empirically Re * and, subsequently, to choose the value of V according to the formula [3].

When a pseudo-laminar flow baths a plasma bead or an arc, the experience of the authors of the present invention has shown that the pseudo-laminarity condition around the plasma bead is satisfied almost automatically: the plasma bead is not disturbed not. The exchanges with the flow remain laminar.

So that the plasma cord (even if the axis of the latter has a direction perpendicular to the direction of the flow which bypasses it) is not disturbed by the propulsive flow, it is sufficient that this flow is pseudo-laminar .

The relationships [1] - [3] are a practical example of realizing the pseudo-laminarity condition claimed in the present invention. The present invention therefore makes it possible, in particular, to minimize the energy exchanges between the plasma jet and the surrounding medium. Examples have shown that the plasma jet pseudo-laminarized, and thus stabilized, can be very long. It is therefore possible to control and optimize the shape and energy balance so as to optimize heat exchange and mass exchanges with the treated material load.

Such optimization is possible, for example, by applying a magnetic field perpendicular to the direction of the electric current . . ,,,,,

which runs through the plasma cord generating the jet of pia iid. Leb l ur these electromagnetic generate a rotation of the electric arc which stimulates the energy exchanges within the non-thermal plasma jet.

Rotation of the non-thermal plasma jet is also achieved by introducing the propellant gas stream at an angle such that it forms a plasma vortex whereby energy exchanges are stimulated in the plasma jet.

Magnetic fields can also be applied to each of the electrodes which makes it possible to modify the shape of the plasma bead, bringing it closer to the axis of the jet or moving it away according to the direction of application of the magnetic field (traversed by a current alternative) with respect to the direction of the electric current supplying the discharge. A constant magnetic field can widen and shorten the shape of the jet.

Once the plasma jet is stabilized (pseudo-laminarized), it now becomes advantageous to combine the speed of the plasma jet, determining the intensity of the energy exchanges and the formation of non-thermal plasma around the plasma cords, the effects of stabilization and pseudo-laminarization (organization of the propeller gas velocity profile), electromagnetic rotation, hydrodynamic rotation, compression or extension of the shape of the plasma cord (s) which gives the possibility of introducing gaseous mixtures (containing components that decompose into active particles in contact with the non-thermal plasma) in the non-thermal plasma jet and optimizing their state of excitation and their composition, in particular the concentration of free radicals which promote the destruction of organic molecules and the reconstruction of useful components such as syngas, for example.

The principle of the device of the present invention is illustrated in FIG.

Fig.la shows the chaotic nature of the plasma cord 2 from the electrodes 1 of a standard device powered by a turbulent flow of gas, as used in practice and that photographed multiple times by users. We see that the electrodes 1 emit a cord of α3π ^> 2 of indeterminate form, unstable in space and time. The plasma area 3 around the cord is also unstable in time and space. This configuration strongly limits the applications of this type of plasma which can not be called a plasma jet.

Fig.lb shows the result of principle of the use of a propellant gas flow distribution device. The plasma cord 2 is stabilized. The plasma jet 4 is embedded in the jet of gas 5 from the distributor 6. It is of stable and uniform configuration.

The ^f ig. gives a principle comparison of the two cases mentioned above: the plasma cord 2, the plasma zone 3 are substantially stretched and of greater length than in the case of the standard device. Appears a jet of plasma 4 stabilized by the jet of gas 5.

In general, the device for implementing the method of generating a stabilized non-thermal plasma jet as defined in the present invention is illustrated in FIG. A high-voltage discharge in the form of a plasma bead of substantially constant cross section, 2, is initiated between two electrodes 1, parallel or diverging at a given angle relative to the axis of symmetry of the generator, connected by the intermediate metal rods 7 and a metal cone 8 to an AC source 9. The metal cone is connected to the power supply system via a capacitor 10 and can be moved along its axis of in order to vary the distance separating it from the metal rods.

The feed gas, propelling and stabilizing the non-thermal plasma jet 4 is introduced via a conduit 11 provided with a collector 12, a screen-grid 13 and a distribution device. speed (speed) 14.

The manifold is supplied with gas via the inlet conduit 15. Gaseous components, liquid or in the form of sprayed droplets, can be added to the gas flow via the conduit 16.

The flow distributor 14 can be used to predetermine and control the flow distribution of the flow of the gas stream. It may consist, in particular, of a set of small diameter tubes arranged in honeycomb, as shown in fig.2. The profile of the lengths of these tubes ι - _í '·,. ,. , Ι ^ι Ι \? *, I not the profile of the hydrodynamic resistances in τοηαιοη of the radius of the distributor. This makes it possible to create a velocity profile 17 (V (r)) which predetermines the stability of the gas flow and therefore of the resulting flow of plasma. In particular, it is possible in this way to form a gas flow whose central portion 18 of diameter D has a constant speed and the peripheral portion, limited to the diameter D ₀ (19), has a predetermined radial profile (17). Experience shows that such a flux has all the appearances and characteristics of a laminar flow. When this flow baths the plasma cord, it stabilizes it. The exchanges within this jet (zones 4) are molecular exchanges whose intensity is substantially lower than that of the turbulent exchanges. In particular, heat exchange and mass exchange are determined by thermal conductivity and diffusion in the medium and not by thermal exchanges and turbulent mass exchanges. They are therefore of much lower intensity and greater extent. This makes it possible to obtain a plasma jet of large dimensions, especially of great length, that is to say. to transport the plasma at great distance without losing the determining characteristics (enthalpy) as shown in fig. the.

In other words, the device according to the present invention is characterized in that the device for forming the propellant gas flow velocity profile (14) is an axially symmetrical system of coaxial tubes arranged in honeycomb and traversed longitudinally. by the conductive supports of the electrodes, the axis of the tubes being parallel to the flow axis and the current length of the tubes inversely proportional to the local velocity of the gas flow.

The rods 7 are constructed so as to represent a minimum hydrodynamic resistance for the flow of gas so as to disturb only locally the character of the gas flow.

The electrodes 1 which support the heat releases due to the passage of the electric charges from the metal zone to the gas (auto-electronic emission) and are inevitably subjected to erosion can be cooled by a gas flow (the electrode 1 can in this case when it is crossed by a gas channel 20 which traverses them as shown in fig.2 b) or by a stream of water (the electrode 1, in this case, is traversed by a current of water 21 as shown fig.2 c). The metallic cone (8) which allows the initiation of the electrode dc ucnc can be replaced by a longitudinally milled body (35) as shown in Figure 10, which reduces its hydrodynamic resistance. The latter can also be reduced if the metal cone 8 is replaced by radial metal plates (36) fixed on the electrodes and designed so that the distance between the plates is minimal in the part of the electrodes most upstream of the axial flow of gas, as shown in Figure 11

The device operates as follows: at the time of priming ^* discharge, a short arc lights between the cone 8 and the rods 7.

Driven by the electromagnetic forces and the drag of the flow of gas which bathes the plasma cord 2, it moves to the right, reaches the electrodes 1 and is fixed at their ends in position 22. Its stable shape is determined by the equilibrium between the forces mentioned and the thermal resistance force that forces the arc to occupy the created ionized channel rather than moving into a neighboring non-ionized zone. Around the plasma cord is created a zone of non-thermal plasma 4 stable and uniform conditions (2) and (3) take place. The values and temperature gradients (Ta, Te) and concentrations of the plasma components in this area are determined by molecular exchanges (heat conduction, diffusion, electrical conductivity) and condition the extent of the non-thermal plasma area. of the jet.

FIG. 3 illustrates an implementation diagram of the present invention according to which the plasma bead 2 is generated by three electrodes 1 by means of a metal cone 8 connected to a three-phase electric current generator with elements of ballast as inductances 23 which allows a particularly high energy efficiency. The system is stabilized by a flow of gas from a gas distributor 6 for coating the electrodes and the plasma beads with a flow of gas whose radial profile of the flow is predetermined so as to stabilize the discharge and laminarize the plasma jet.

An even more advantageous solution is proposed in FIG. In this case, the plasma cord 2 is generated by six electrodes 1 via the metal cone 8, connected to a generator of ectr that rp as. The electrodes are electrically connected by a laminarized flow of stabilizing gas 5 from a distributor 14. Depending on whether the electrode connections are made in a triangle (as shown by the connection 9 'in FIG 4b) or in a star (as shown in FIG. shows the connection 9 "of Fig. 4c), there is a configuration of centralized plasma cords 24 'or peripheral 24". Depending on the application of the non-thermal plasma jet, one or the other of the solutions is preferable.

Fig.5 illustrates another possible embodiment of the present invention. In this case, the stabilized non-thermal plasma jet 4 is formed by plasma cords 2 connecting the three electrodes fed by a three-phase alternating current source 9 to an annular electrode 5. As shown in FIG. 5c, the annular electrode 25, disposed to overheat due to its contact with the plasma jet, can be cooled, for example by means of a stream of water supplied and discharged through the conduits 26. Protrusions 27 are optionally made to locate and fix the base of the plasma cords.

In this way, the device claimed in the present invention is characterized in that it is provided with an electrode (25) to the ground, circular, coaxial with the laminarized jet and surrounding it inside the zone of laminarization so as to locate the discharge in the laminar zone of the generated jet.

The stabilization (see Fig. 5b) is achieved by a gas flow 5 from a distributor 6 in which the honeycomb device 14 of FIG. 2 is replaced by a sudden expansion system 27 which makes it possible to create a velocity profile 17 of the flow empirically adapted to the diagram of FIG. 5. It can be seen that the propulsion gas introduced into the distributor 6 creates a vortex 29 in the stream of shaped gas directed towards the screen-grid 13, thus forming the desired velocity profile V (r) 17.

FIG. 6a illustrates the case of addition of solenoids 31 creating magnetic fields perpendicular to the plasma cords 2 coming from each of the electrodes 1. The flow of propellant gas issuing from the distributor 6 and stabilizing the plasma jet 4 is organized in a manner to coat the entire configuration of the plasma leads, whether these are concentrated by the AC-generated magnetic field towards the axis of the generator (see Fig. 6 b), or pushed outwards (see fig. 6 c) according to whether the oscillations of the field and the current are in phase or in ase or again, orc s by a c amp m dnt in time, oscillating between the two situations of fig.6 b and fig, 6 c as shown in fig.6 d.

FIG. 7a shows the cross section of another device for implementing the present invention, according to which the flow of propellant gas 28, and consequently the plasma cords 2 coming from the six electrodes 1, after having left the cone 8, are swirled by hydrodynamic deflectors 32 or by a magnetic field generated by a solenoid 31, magnetic field whose oscillations are synchronized with the alternating current supply discharges.

Fig.7 b shows the angle δ between the axis of the baffles and the direction of the flow of propellant gas.

FIG. 7c shows the angle δ 'between the deflector axis and the tangent to the radial attachment circle of the deflectors.

We have δ <90 ° and δ '<90 °.

The device according to the present invention may also be characterized in that it comprises solenoids (31) traversed by a direct or alternating electric current, in particular synchronized with the current supplying the discharge, the solenoids being arranged so as to create a magnetic field directed at an angle β between 0 ° and 90 ° with respect to the direction of the discharge current and at an angle γ between 0 ° and 90 ° with respect to the direction of the laminarized flow.

Fig. 8 shows the longitudinal section of a propellant gas distribution device 28 according to which the position of the plasma bead 2 and the configuration of the plasma zone 3 coming from the electrodes 1 after leaving the metal cone 8 are controlled by a device 33 provided with valves 34 providing a distribution of the propellant gas 28, in portions, along the metal cone, through the electrodes (especially to cool them) and the periphery of the generator.

Fig. 9 illustrates the dependence of the length of the plasma jet, L (m) of the propulsion gas velocity, V (m / s) for different values of the voltage applied to the electrodes. _{For example, it is possible to use the} chemical, plasmochemical and pharmaceutical industries, in particular for the manufacture of powders and in particular of nanopowder.

Non-thermal plasma jet generators can be advantageously used in different industries for instant sterilization of contaminated surfaces.

The use of the present invention is exceptionally effective and advantageous, particularly economically for the destruction of household, industrial medical waste and especially for the incineration of organic waste by plasma. In this case, it makes it possible in particular to eliminate harmful residual gases such as dioxins and furans and to recycle organic waste by transforming it into combustible products such as syngas.

Examples:

1. Atmospheric pressure air-based non-thermal plasma jet generator for the disposal of medical waste.

Power: 100 kW

Pressure: 1 bar

Electrode voltage: 10 kV

Frequency: 50 Hz

Maximum electric current: 10 A

Amount of electrodes: 6

Stabilization device: honeycomb distributor.

Reynolds number of the airflow bathing the plasma arc: varies between 300 and 14,000. The plasma jet retains its quasi-laminar properties thanks to the measures taken to stabilize it.

2. Non-thermal plasma gas jet generator of complex composition with sub-atmospheric pressure applicable for the destruction of medical waste.

Power: 100 kW

Pressure: 1.7 bar.

Electrode voltage: 20 kV

Frequency: 50 Hz

Maximum electric current: 5 A , _{ect ro es} .

Stabilizer: Expansion valve.

In the case of the two examples cited above, the application of a perpendicular magnetic field of 0.11T to the electric current according to FIG. 6 allowed, according to the configuration of this field, to reduce the jet length d 3m to 0, 8 m and increase the diameter from 4.5 cm to 12 cm.

9 illustrates the variation of the length of the arc generating the plasma jet ^no: isothermal depending on the speed of the air flow propelling the non-thermal plasma jet for two voltage values illustrated in two examples above, according to the present invention.

conclusions

1. The implementation of the present invention makes it possible to obtain arc lengths generating the non-isothermal plasma jet of the order of several meters, which is much greater than the extent of the known sliding arcs and unstabilized non-isothermal plasma jets.

2. The plasma jet retains its quasi-laminar properties, even when the Reynolds number is greater than 2000.

3. The claimed method and the device of its implementation as used in the present examples achieves the objects of the present invention. It makes it possible to transport the plasma at a distance greater than that reached in the preceding example, and therefore to project it onto the target that can represent a load of medical waste, without being disturbed by or acting on the parts of the device generating the plasma jet, especially the electrodes.

4. The use of very high voltages is however not recommended considering the probability and the danger of non _f% programmed outside the device. At very high voltage, there are also internal discharges that "shunt" the arc and disturb the jet of plasma. The use of a magnetic field perpendicular to the electric current of the discharge makes it possible to control the configuration of the jet and to optimize the dimensions and the energy balance, which confirms the utility of the invention for practical applications requiring the adaptation of the plasma jet to the load of material to be treated, for example, in the case of the destruction or recycling of waste, including medical.

Claims

1. Method for generating a non-isothermal plasma axisymmetric jet using a single-phase or three-phase direct current or alternating current high-voltage electric discharge in a gas flow, discharged by a breakdown plasma, propelled by an electromagnetic force and by the drag force exerted by the gas flow and located at the electrode ends, characterized in that the flow of gas propelling the plasma of the discharge is stabilized at all points of the resulting plasma jet, the relative velocity of the gas, V *, at any point of the propulsive flow, obeying the relation of the type:

r * <D *: V * (r *) = l.

D * ≤r * ≤l: ^* V * (r *) = l - cos [n (r * - l) / 2 (D * -l)],

and that the condition of hydrodynamic stabilization of the arc is satisfied:

V <e * .q / p. D

or

D * = D / D ₀ ; r * = 2r / D ₀ ;

r is the radius of the jet point where the current velocity V is determined;

V ₀ is the speed of the laminarized flow.

Re * is the critical Reynolds number of the stabilized flux;

η and p are respectively the dynamic viscosity and the density of the gas propelling at the temperature of the propulsive flow.

2. Method according to claim 1 characterized in that the arc is subjected to the action of magnetic fields perpendicular to the electric current.

3. Method according to one of the preceding claims, characterized in that the electric current of the arc or arcs is directed parallel or at angles δ <90 ° with respect to the axis of the propellant gas flow and δ ' <90 ° with respect to the tangent to the circle on which the deflectors are positioned.

4. Method according to one of the preceding claims, characterized in that the flow of propellant gas contains molecular components, for example water vapor, which break down into particles. 2011/138525 ^ i _J - .PCT / FR2011 / 000277 eA metastable and radical tees in non-thermal piasma contact.

5. Device for implementing the method of generating a non-isothermal plasma jet according to one of the preceding claims, characterized in that the flow of propellant gas (28) enters the formation zone of the arc (4) via a gas distributor (6) comprising an inlet manifold (12), a velocity profile forming device (14) and a sieve grid (13).

6. Device according to claim 5, characterized in that the device for forming the velocity profile (14) of the propellant gas flow (28) is an axisymmetric system of coaxial tubes arranged in honeycomb and traversed longitudinally by the supports. conductors of the electrodes, the axis of the tubes being parallel to the axis of the flow and the current length of the tubes inversely proportional to the local velocity of the gas flow as determined in claim 1.

7. Device according to one of claims 5 or 6, characterized in that the device for forming the velocity profile (14) of the propellant gas flow (28) comprises a collector (12), a brutal expansion ring ( 27) and a sieve grid (13).

8. Device according to one of claims 6 or 7, characterized in that it comprises solenoids (31) traversed by a continuous or alternating electric current, in particular synchronized with the current supplying the discharge, the solenoids being arranged so as to creating a magnetic field directed at an angle β between 0 ° and 90 ° with respect to the direction of the discharge current and at an angle γ between 0 ° and 90 ° with respect to the direction of the laminarized flow.

9. Device according to one of claims 5 to 8, characterized in that the collector of the laminarizer device is provided with supply ducts (15,16) components in the form of liquids, sprays or gas.

10. Device according to one of claims 5 to 9, characterized in that it is provided with a ground electrode (25), circular, coaxial with the laminarized jet and surrounding it inside the zone of laminarization of 2011/138525. . .. ,,,. . ,, PCT / FR2011 / 000277. way to locate the discharge in the laminarisanon area to the generated jet.

11. Device according to one of claims 5 to 10, characterized in that the metal cone (8) for priming the discharge between the electrodes (1) is replaced by a longitudinally milled body (35) which allows the reduce its hydrodynamic resistance.

12. Device according to one of claims 5 to 11, characterized in that the metal cone 8 is replaced by radial metal plates (36) fixed on the electrodes (1) and designed so that the distance between the plates is minimal in the part of the electrodes most upstream of the axial flow of gas.