DE102016005155B4 - Oscillating fire reactor with pulsating flame and process for thermal material treatment or material synthesis - Google Patents

Abstract

Device for the thermal treatment of a raw material in an oscillating hot gas flow of an oscillating fire reactor for material treatment or material synthesis, with a burner (1) to which a mass flow (2) is fed via at least one line to form at least one pulsating flame (12), which burns into a combustion chamber that is fluidically connected to the diffuser and there generates the oscillating hot gas flow for the thermal treatment of the raw material, characterized in that the burner (1) is a swirl burner, within which there is a swirl generator (3), so that a mass flow (5) flowing out of a burner outlet (4), which contains combustion air (2), has a tangential velocity component and the flame (12) is a swirl-stabilized flame with an inner central backflow zone (13) and that a diffuser (7) is connected downstream of the burner outlet (4) of the burner (1), wherein the flame (12) outside the burner (1) downstream of the burner outlet (4) burns.

Description

The invention relates to a vibrating furnace for material treatment or material synthesis (pulse dryer, pulse combustor, pulsation reactor), which has at least one burner, at least one pulsating flame, a combustion chamber and at least one resonant gas column (e.g. in the combustion chamber or in a resonance tube) into which a raw material to be treated can be introduced and from which it can be separated again, according to the preamble of the attached main claim, as well as a corresponding method for operating the same.

The vast majority of all technical or industrial combustion plants and combustion systems are designed and operated in such a way that the combustion process is, on average, constant over time, except for small turbulent fluctuations whose size is at least one order of magnitude smaller than the average values of the combustion process (such as average flow velocity, average temperature of the flame or exhaust gas flow, average static pressure in the combustion chamber, etc.). This means that the conversion of the fuel used is continuous over time and - as a result - the heat release from the combustion process and the mass flow of resulting exhaust gases (combustion products) also have constant values over time for a fixed burner setting.

Deviating from this, phenomena or "abnormalities" sometimes occur which are referred to in the literature as combustion chamber oscillations, self-excited combustion instabilities or thermo-acoustic oscillations. These are characterized by the fact that the initially stationary (i.e. time-constant) combustion process suddenly changes automatically when a stability limit is reached into a time-periodic, oscillating combustion process which is self-excited and whose time function can be described as sinusoidal to a good approximation. Along with this change, the heat release rate(s) of the flame(s) and thus the thermal combustion performance of the combustion system as well as the exhaust gas flow in and out of the combustion chamber and the static pressure in the combustion chamber itself become periodic-unsteady, i.e. oscillating.

The occurrence of these combustion instabilities often results in a different pollutant emission behavior compared to stationary operation of the furnace and, in addition to increased noise pollution in the plant environment, also causes a significantly increased mechanical and/or thermal load on the plant structure (e.g. combustion chamber walls, combustion chamber lining, etc.), which can lead to the destruction of the furnace or individual components.

It is therefore easy to see that the undesirable occurrence of the phenomena described above in furnaces designed for a constant combustion process, in which the static pressure in the combustion chamber or in upstream or downstream system components should also have constant values (equal pressure combustion), must be avoided at all costs. This is discussed, for example, in the DE 199 34 612 A1 , the US 2011/0 041 508 A1 or the DE 195 45 310 A1

However, the situation is quite different in a small number of very special combustion systems in which the phenomenon of self-excited, periodic combustion instabilities described above is deliberately induced and used to generate a periodic combustion process with a periodic heat release rate of the flame and a periodic, oscillating exhaust gas flow (pulsating hot gas flow) in the combustion chamber and in downstream system components (e.g. heat exchangers, chemical reactors, etc.).

These oscillating combustion systems can be divided into those in which the heat from the oscillating combustion process is transferred, e.g. to generate heating heat or domestic water or to generate steam (purely thermal use), as is the case in the US 3 276 505 A1 or in oscillating reactors, in which a physical and/or chemical material treatment of a raw material is in the foreground (e.g. drying, calcination, thermally controlled material synthesis, etc.) and which are often referred to as pulse dryer or pulse combustor or pulsation reactor. A corresponding pulsation reactor is disclosed, for example, in the EP 2 092 976 A1 .

The raw material can also be a mixture of raw materials. The raw material or the mixture of raw materials can be in solid, liquid, gaseous or vaporous form.

The advantage of these systems compared to conventional, stationary combustion systems is the periodic, unsteady and turbulent exhaust gas flow in the combustion chamber or in downstream components (e.g. heat exchangers, reaction chambers, resonance tubes, etc.).

Both against solid walls (combustion chamber wall, wall of a heat exchanger, steam Both in comparison with materials that are introduced into the hot gas flow at a defined treatment temperature for treatment, the heat transfer from the hot gas to the walls or material increases significantly by 2 to 5 times compared to an averagely stationary, turbulent flow with the same average flow velocity and the same temperature.

Due to the analogy between convective heat transfer and mass transfer, the above statement also applies to mass transfer: In the case of periodic-unsteady, oscillating flow, the transfer rate of gaseous/vaporous substances from the hot gas to the material to be treated or from the material into the hot gas flow increases by similar values due to the almost complete absence of boundary layers, which are known to form in stationary flows and represent diffusion or transition resistances.

Due to these relationships, the material to be treated experiences high heating gradients in pulsating hot gas flows (“thermal shock treatment”).

In order to ensure safe operation of oscillating combustion systems or pulsation reactors, it is important to keep the two main parameters of the combustion oscillation - oscillation frequency and oscillation amplitude - constant within the possibilities of a large-scale process. If these change significantly during the process, it can be expected that the advantages, e.g. in heat transfer or in material treatment compared to the conventional, stationary process, will be lost and/or the homogeneity of the resulting product will suffer.

With regard to the oscillation frequency that occurs when self-excited combustion instabilities arise due to phase-correct feedback in the burner - flame - combustion chamber - resonator circuit, there is agreement in the literature that this essentially depends on the geometry of acoustically active or resonant volumes (such as the combustion chamber, the resonance tube, etc.) as well as on the gas temperature.

If these two main factors influencing the oscillation frequency are not changed during the process, e.g. heat transfer or material treatment or synthesis, the frequency of the combustion/pressure/flow oscillations also remains constant to a good approximation.

However, other influencing factors must also be taken into account when determining the amplitude of the vibration.

This becomes clear from the following example: If, in a pulsating reactor with a fixed frequency and thus (automatically adjusting in idle operation without material feed) amplitude of the combustion oscillation, raw material is added to the oscillating hot gas in different mass flows (e.g. 50 kg/h and 100 kg/h) for thermal treatment, then different feed rates of raw material cause a different degree of damping of the oscillation amplitude, since the oscillation energy, which originally only had to cause the gas oscillation of the hot gas, then has to be distributed between hot gas with different levels of particle or droplet loading.

In the limiting case, it is even possible to completely stop the oscillation in the reactor by adding a sufficiently large amount of material to be treated per unit of time, whereby the advantages of the periodic-unsteady process for the generation of specific material properties (e.g. particle sizes, specific surfaces, reactivity, etc.) in the product naturally disappear. It should be remembered here again that a reduction in the oscillation amplitude (characterized, for example, as the amplitude of the oscillation of the static pressure in the combustion chamber or the oscillation of the speed of the hot gas flow in the combustion chamber or in the resonance tube) leads to a reduction in the convective heat and mass transfer between the hot gas and the walls or the material to be thermally treated, so that the advantages of the unsteady process with regard to, for example, achievable, specific material properties disappear.

In other words: Any change in the mass flow of the raw materials fed in as well as the specific material properties of different reactants (raw material density, moisture content, particle size distribution, solids content in suspensions, etc.) changes the amplitude of the oscillation of the pulsating hot gas flow when the material is fed in and thus the result of the material treatment.

In order to achieve the greatest possible material throughput when required, it is generally desirable to operate a system with the greatest possible vibration amplitude when idling.

When operating an oscillating combustion system, it must also be taken into account that the pressure or velocity amplitudes occurring in the combustion process are safely limited in order to safely avoid mechanical/thermal overloading of the system structure.

On the other hand, flashbacks or the flame lifting or extinguishing must also be safely avoided in order to ensure stable, continuous operation.

The term flashback is to be understood as follows: In an oscillating combustion system, which is driven by the process described above, in particular by self-excited combustion instabilities (flame oscillations), there is a temporally periodic change in the mass flow of fuel gas/air mixture exiting the burner (e.g. in the case of premix combustion) and thus also a temporally periodic change in the burner exit velocity (axial velocity component), whereas the flame velocity (burning velocity) of the mixture flowing out of the burner has a constant value with a constant composition (and thus constant air ratio of the premix).

If the flow velocity of the outflowing mixture falls below the value of the flame velocity for a period of time during the oscillation period, the flame moves upstream, counter to the outflow direction, into the burner. The phase in which the flow velocity of the outflowing mixture is below the value of the flame velocity increases as the amplitude of the pressure/combustion oscillations increases.

It is now possible that the flame is driven out of the burner again in the phase of the oscillation period in which the flow velocity of the outflowing mixture increases again to its maximum value and thus burns again in the desired axial position outside the burner, i.e. downstream of the burner outlet, at least for a further period of time.

However, it is particularly problematic if the flame, when it moves into the burner, then finds such a stable anchoring position within the burner that it can no longer be driven out of the burner even at the highest flow velocity of the outflowing mixture occurring within the oscillation period of the oscillation of the burner outlet velocity and thus burns permanently within the burner or the burner housing, thermally damaging or destroying the burner.

In summary, the term flashback refers to a momentary or permanent burning of the flame inside the burner and not, as actually desired, in a raised, stable position axially after the burner exit outside the burner.

• Zum einen ist die Stärke also die Amplitude der Schwingung der Heißgasströmung in einer Schwingfeueranlage eine sehr wichtige, sowohl die Eigenschaften des behandelten oder synthetisierten Materials als auch die Homogenität des thermisch behandelten Materials bestimmende Größe. Die Amplitude ist somit ein wesentlicher Einstellparameter bei der thermischen Materialbehandlung/Materialsynthese in Pulsationsreaktoren.

According to the above, the designer and operator of oscillating furnace systems for thermal material treatment or material synthesis have to solve the following problem:

• On the one hand, the strength, i.e. the amplitude, of the oscillation of the hot gas flow in an oscillating furnace is a very important parameter that determines both the properties of the treated or synthesized material and the homogeneity of the thermally treated material. The amplitude is therefore an essential setting parameter in thermal material treatment/material synthesis in pulsation reactors.

Excessively high values of the oscillation amplitude of the material-carrying hot gas oscillation can lead to a flashback and thus to damage/destruction of the reactor, which must then be immediately counteracted by switching off the flame or the burner.

It is understandable that shutting down the plant due to an unwanted flashback also means that the material (product) that was last thermally treated and/or synthesized under undefined thermal conditions must be considered as scrap.

In addition, before restarting the reactor and resuming thermal material treatment or synthesis, a more or less complex cleaning process of the material-carrying reactor sections is required in order to safely remove thermally undefined treated or synthesized material from the reactor.

The present invention is therefore based on the object of specifying a device with which the amplitudes of the oscillation of the hot gas flow in the combustion chamber can assume high values during operation of a pulsation reactor in order to be able to increase, for example, the achievable product throughput rates and thus the reactor throughput, and at the same time effectively avoid the risk of an unwanted flashback of the pulsating flame into the burner. In addition, a method for operating the device is to be proposed.

This object is achieved according to the invention in that the burner for generating a pulsating flame for generating a pulsating hot gas flow has the features according to the appended main claim.

A method according to the invention is thus characterized in that the pulsating fuel/air mixture flowing to the pulsating flame is guided through a swirl burner and a diffuser connected to it, according to the features of the appended claim 5.

The diffuser is in particular a conical diffuser, preferably made of metal, whose free cross-sectional area increases in the axial flow direction.

An opening half-angle of the element according to the invention, referred to as diffuser, can be selected in the range between 3 degrees and 45 degrees.

Depending on the design, the axial extension of the diffuser (diffuser length) can be 0.5 to 10 times the free diameter of the burner outlet.

The diffuser can be positioned directly after a swirl generator on the burner. However, it is also possible to initially provide a cylindrical pipe element at the outlet of the swirl generator, to which the diffuser is then connected in the axial flow direction.

The invention is based on the surprising discovery that when using a pulsating premix swirl flame or a pulsating, rapidly mixing diffusion swirl flame as the "drive" of an oscillating fire or pulsation reactor to generate the pulsating hot gas flow required for material treatment or synthesis, a burner outlet designed as a diffuser can automatically prevent the pulsating flame from flashing back into the burner, i.e. a flame flashback, if the diffuser length and diffuser opening angle are correctly selected - and this even with very high amplitudes of the combustion oscillation in the combustion chamber.

One possible model for explaining the effect of the invention as an auto-adaptive flashback arrester is based on the fact that when the pulsating flame moves upstream in the moments of the oscillation period with a low burner outflow velocity, the flame itself blocks or obstructs part of the free flow cross-sectional area of the diffuser. This is based on the knowledge that in a swirl burner, the area occupied by the flame or the inner backflow zone of the swirl flow, which is subject to the flame (perpendicular to the axial direction) is essentially independent of the outflow velocity of the fuel gas/air mixture in the axial direction of the burner.

This means that the fresh mixture can only flow out of the burner through the free annular gap remaining between the flame or the inner backflow zone of the swirl flow that forms the flame and the diffuser wall. Since the area of this annular gap perpendicular to the burner axis within the diffuser decreases upstream due to its conical geometry while the area occupied by the flame remains the same, i.e. it becomes smaller and smaller, the value of the axial flow velocity of the fresh mixture flow flowing out of the burner increases monotonically for continuity reasons until a value is reached at which the flame can no longer move further upstream due to its limited flame speed, but comes to a standstill and remains in motion.

• Zunächst wird die Flamme in der Phase der Schwingungsperiode, in der die Strömungsgeschwindigkeit des ausströmenden Gemisches bis zu ihrem Maximalwert aufsteigt, zwar aufgrund der ansteigenden Strömungsgeschwindigkeiten der Frischgemischströmung innerhalb des Diffusors stromabwärts verschoben. Dadurch erhöht sich aber gleichzeitig die Größe der freien Ringspaltfläche, die zwischen der zentralen Flamme, die bei einem Drallbrenner ihre Fläche unabhängig von ihrer axialen Position beibeibehält, und der Diffusorwand liegt. Hierdurch sinkt aus Kontinuitätsgründen der Wert der axialen Strömungsgeschwindigkeit wieder ab und dadurch wird letztlich auch einem zu starken Abheben der Flamme vom Brenneraustritt (mit der Konsequenz, dass die Flamme dann sogar ganz erlöschen kann) wirksam entgegengewirkt.

Conversely, the same mechanism also prevents a pulsating flame from lifting too far (and subsequently extinguishing) from the burner outlet at those times in the oscillation period when particularly high, instantaneous axial velocities of the pulsating fresh mixture flow are present:

• Firstly, in the phase of the oscillation period in which the flow velocity of the outflowing mixture rises to its maximum value, the flame is displaced downstream due to the increasing flow velocities of the fresh mixture flow within the diffuser. However, this simultaneously increases the size of the free annular gap area between the central flame, which in a swirl burner maintains its area regardless of its axial position, and the diffuser wall. As a result, the value of the axial flow velocity drops again for continuity reasons and this ultimately effectively counteracts the flame lifting too far away from the burner outlet (with the consequence that the flame can then even go out completely).

It is expressly pointed out at this point that the burning of the pulsating flame within the diffuser is not considered an impermissible flashback.

In particular, it is easy for a specialist to ensure permanently safe operation of the pulsating flame on/in the diffuser by means of a high-temperature-resistant design of the diffuser, for example by means of a ceramic inner lining or by forced cooling by means of a double-shell design of the diffuser with air or water as the cooling medium.

It should also be noted that the problem of unwanted flashback caused by the pulsating flow in an oscillating fire or pulsation reactor is only significant if the flame is fully premixed (fuel and combustion air are molecularly mixed together spatially in front of the burner) or if it burns as a fast-mixing diffusion flame. In the latter case, for example, there is a nozzle mixed flame in which fuel and combustion air are only brought together inside the burner - preferably at the burner outlet.

• 1 Prinzipskizze eines Drallbrenners mit Diffusor;
• 2 die Prinzipskizze eines Diffusors gemäß 1 mit einer pulsierenden Flamme an zwei unterschiedlichen Positionen.

Further advantages and features of the invention will become apparent from the following description of an embodiment.

• 1 Schematic diagram of a swirl burner with diffuser;
• 2 the schematic diagram of a diffuser according to 1 with a pulsating flame in two different positions.

In the 1 one can see a swirl burner 1, to which fuel and combustion air are supplied separately 2 or an already premixed fuel/air mixture 2 via at least one line not shown in detail here.

Fuel is understood to mean, for example, combustible gases such as natural gas, methane, hydrogen or liquid fuels such as alcohol, etc. In the context of the present invention, combustion air is generally understood to mean an oxidizing agent that provides the oxygen required for combustion. In addition to air, this also includes, for example, pure oxygen or air enriched with oxygen, etc.

This combustion air flow or this fuel/air mixture is passed through a swirl generator 3 within the swirl burner 1, so that the mass flow 5 flowing out of the burner outlet 4 has, in addition to a movement in the axial direction, a rotational movement 6 in the circumferential direction (tangential velocity component or “swirl”).

With this rotational movement 6, the mass flow 5 flows into a diffuser 7. The walls of the diffuser have a substantially conical shape with an opening half-angle 8. This opening half-angle 8 lies in a range between 3° and 45° and is measured relative to the axial direction.

The burner outlet 4 has a substantially circular cross-section and can have an axial extension 9 which is preferably approximately in the range between 0 and 0.5 m.

The axial length 10 of the conical or frustoconical diffuser 7 can be approximately 0.1 to 1 m. In relation to the dimensions of the burner outlet 4, it is therefore between approximately 0.5 and 10 times the free diameter of the burner outlet.

Towards the end 11 of the diffuser 7, a swirl flame 12 forms in the mass flow 5 from the outflowing fuel/air mixture.

This swirl flame 12 is particularly characterized by a central backflow region 13, which is an important characteristic of a swirl-stabilized flame.

The flame 12 burns in a pulsating manner into a combustion chamber (not shown in detail here) which is fluidically connected to the diffuser 7 and generates an oscillating hot gas flow there. If necessary, a quantity of material for material treatment or material synthesis can be added to this hot gas flow. After this material has been treated or synthesized in the hot gas flow, it is finally separated again, for example in a cyclone or a hot gas filter, which are also not shown.

The pulsation of the flame 12 is self-excited and acts on the incoming mass flow 5 in the combination of burner - flame - combustion chamber - reaction chamber - separation device.

Due to the mentioned pulsation or oscillation of the hot gas flow, the flame 12 also oscillates and thus also the rotating mass flow 5 flowing into it, which in turn maintains the pulsation, and so on (i.e. the mass flow emerging from the burner has a time-dependent - mostly approximately sinusoidal - temporal progression).

Due to the oscillating mass flow 5, the axial velocity of the burner outlet flow (axial velocity component of the burner outlet flow) changes, while at the same time the flame velocity 14 of the flame 12 that is formed remains constant. The flame velocity is the speed at which the flame 12 propagates in the fuel/air mixture flowing towards it, counter to the outflow direction.

This shifts the axial position of the developing flame: When the outflow velocity of the mass flow 5 decreases, the flame 12 migrates into the diffuser 7, for example, into the 2 As the speed of the mass flow 5 subsequently increases again as a result of the pulsation, the flame is pushed back in the axial direction out of the diffuser 7, for example to the position shown in the 2 shown “Position 2”

Now, however, the flame 12 is essentially constant in its geometrical dimensions transverse to the outflow direction, regardless of its axial position. This is related to the special properties of a swirl-stabilized flame, as already mentioned above.

• Da sich der Querschnitt des Diffusors in Flammenausbreitungsrichtung von der Fläche A₁ zu der Fläche A₂ konisch erweitert, vergrößert sich die freie Ringfläche des Ringspaltes entsprechend, der die Flamme 12 umgibt und der zwischen der Flamme 12 und der Wandung 16 des Diffusors 7 liegt. Dabei wirkt die drallstabilisierte Flamme 12 u.a. wegen der in ihr vorhandenen zentralen inneren Rückströmzone 13 wie ein fester Körper, der von dem Massenstrom 5 von ausströmendem Brennstoff/Luft-Gemisch nicht durchströmt werden kann.

Since in the axial positions 1 and 2 the cross-sectional areas A ₁ and A ₂ available for the flow are of different sizes due to the conical design of the diffuser 7, the ring surfaces 15 and 17 change in size accordingly between positions 1 and 2, which form at these positions between the flame 12 (which remains constant in its geometric extension) and the wall 16 of the diffuser:

• Since the cross-section of the diffuser widens conically in the direction of flame propagation from the area A ₁ to the area A ₂ , the free annular area of the annular gap that surrounds the flame 12 and lies between the flame 12 and the wall 16 of the diffuser 7 increases accordingly. The swirl-stabilized flame 12 acts like a solid body, which cannot be flowed through by the mass flow 5 of the escaping fuel/air mixture, due to the central inner backflow zone 13 present in it.

In position 2, an axial speed U ₂ with an axial pulse current İ ₂ is established due to the free ring surface 15. If the pulsating flame 12 now moves as described within the pulsation or oscillation period due to the initially decreasing burner outlet mass flow M _changing over time and thus decreasing outlet speed U upstream towards burner 1, it reaches the 2 shown position 1.

In position 1, the free ring surface 17 is, as explained, smaller than the free ring surface 15 in position 2 due to the shape of the diffuser 7. Thus, with the same non-flowable area occupied by the swirl-stabilized flame 12 characterized by the central backflow zone in position 1, the axial flow velocity U ₁ increases and thus the axial impulse flow İ ₁ also increases there. The axial impulse flow İ ₁ is thus greater than the axial impulse flow İ ₂ .

Due to the axial flow velocity U ₁ increasing as explained, the flame 12 is prevented from moving further upstream into the diffuser 7 and thus into the burner 4. Rather, the flame 12 maintains approximately this position 1 until the burner outlet mass flow 5, which increases again within the pulsation or oscillation period and the burner outlet velocity also increases accordingly, forces the flame 12 back downstream into the original position 2, which is considered safe.

In this way, it is ensured that the flame 12 cannot migrate to the burner 1 or to the swirl generator 3 and become trapped therein in the event of a fire flashback.

It should be mentioned here that the wall 16 of the diffuser 7 and the wall 18 of the burner outlet 4 are either uncooled or as in the 2 can be seen on the left side, can be provided with a cooling system 19, which can be achieved, for example, by a stream 20 of air or water which is passed through the cooling system 19.

Furthermore, it is possible to protect the walls 16 and 18 with a ceramic lining.

The device described here and its operation make it possible to set the oscillation amplitude of an oscillating fire reactor to high values, in particular when the plant is idling (i.e. without material being fed in), without having to bear the risk of a flame flashback into the burner, since such a flame flashback is reliably prevented by the diffuser provided according to the invention on the swirl burner used.

List of reference symbols

1

Swirl burner

2

Combustion air or fuel/air mixture mass flow

3

Swirl generator

4

Burner outlet

5

Mass flow

6

rotation

7

Diffuser

8th

Opening half angle

9

axial extension of the burner outlet

10

axial extension of the diffuser

11

End of the diffuser

12

Swirl flame

13

Return flow area

14

Flame speed

15

Ring area

16

Wall

17

Ring area

18

Wall

19

cooling

20

Air or water flow

Claims (5)

Device for the thermal treatment of a raw material in an oscillating hot gas flow of an oscillating fire reactor for material treatment or material synthesis, with a burner (1) to which a mass flow (2) is fed via at least one line to form at least one pulsating flame (12), which burns into a combustion chamber fluidically connected to the diffuser and there generates the oscillating hot gas flow for the thermal treatment of the raw material, characterized in that the burner (1) is a swirl burner, within which there is a swirl generator (3), so that a mass flow (5) flowing out of a burner outlet (4), which contains combustion air (2), has a tangential velocity component and the flame (12) is a swirl-stabilized flame with an inner central backflow zone (13) and that a diffuser (7) is connected downstream of the burner outlet (4) of the burner (1), wherein the flame (12) outside the burner (1) downstream of the burner outlet (4) burns. Device according to Claim 1 , characterized in that the diffuser (7) has a conical shape with a cross-sectional area increasing in the axial direction. Device according to one or more of the preceding claims, characterized in that the diffuser has an opening half-angle (8) which is in the range between 3 degrees and 45 degrees. Device according to one or more of the preceding claims, characterized in that the diffuser has an axial extension of between 0.5 times and 10 times the free diameter of the burner outlet (4). Method for the thermal treatment of a raw material in an oscillating hot gas flow of an oscillating fire reactor for material treatment or material synthesis, with a burner (1) to which a mass flow (2) of fuel gas and air is fed via at least one line to form at least one pulsating flame (12) which generates the pulsating hot gas flow for the thermal treatment of the raw material, wherein the flame burns into a combustion chamber which is fluidically connected to the diffuser and to which a reaction chamber is connected, characterized in that the fuel/air mixture (2) flowing to the pulsating flame (12) is guided through a swirl burner (1), within which there is a swirl generator (3), to a burner outlet (4) and a diffuser (7) which is connected to the latter, wherein the mass flow (5) flowing out of the burner outlet (4) has a tangential velocity component, so that the flame (12) which is outside the burner (1) downstream of the burner outlet (4) burns is a swirl-stabilized flame with an inner central backflow zone (13).

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