DE102016002566B4 - Device and method for the thermal treatment of materials - Google Patents

Abstract

Device for the thermal treatment of a raw material (10), with- a combustion chamber (5) which is a first resonator;- a burner (2) with a supply connection for a fuel (3) through which by means of a periodic-transient, oscillating flame (1) a pulsating exhaust gas flow (9) can be generated, the fuel (3) being a combustible gas or a liquid fuel; and- a reaction chamber (7) adjoining the combustion chamber (5) with- a task for the raw material (10) to be treated in the exhaust gas stream (9), from which a hot gas stream (12) is formed; and- an insert (13) through which the hot gas stream (12) can flow and which has a reduced cross-sectional area (14) compared to the reaction chamber (7) and has a length (15) that is shorter than the overall length of the reaction chamber (7), wherein the insert (13) is a second resonator.

Description

The invention relates to a device for the thermal treatment of a raw material, with a combustion chamber in which at least one periodically unsteady, oscillating flame burns on at least one burner to generate a pulsating, oscillating exhaust gas stream, which flows through a reaction space adjoining the combustion chamber 1, and a corresponding method according to claim 5.

A thermal treatment is understood to mean in particular a thermal material treatment or also a thermal material synthesis, in which case the raw material can also be a raw material mixture. The raw material or raw material mixture can be present in solid or liquid form or in gaseous or vaporous form.

By far the largest number of all technical or industrial furnaces and combustion systems are designed and operated in such a way that the combustion process is constant over time on average, except for minor turbulent fluctuations, the size of which is at least one order of magnitude smaller than the mean values of the combustion process (e.g. mean flow velocity , mean temperature of the flame or the exhaust gas flow, mean 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 waste gas (combustion products) also show 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 vibrations, self-excited combustion instabilities or thermo-acoustic vibrations. These are characterized by the fact that the initially stationary (i.e. time-constant) combustion process suddenly changes into a time-periodic, oscillating combustion process when a stability limit is reached, the time function of which 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 firing capacity of the incinerator as well as the exhaust gas flow in and out of the combustion chamber and the static pressure in the combustion chamber itself become periodically non-stationary, i.e. oscillating.

The occurrence of these combustion instabilities often causes a change in pollutant emission behavior compared to stationary operation of the furnace and, in addition to increased noise pollution in the plant environment, also causes significantly increased mechanical and/or thermal stress on the plant structure, e.g. the combustion chamber walls, the combustion chamber lining, etc. These stresses can be up to lead to the destruction of the furnace or individual components. It is therefore easy to see that the undesired occurrence of the phenomena described above in furnaces that are designed for a combustion process that is constant over time, 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.

However, the situation is quite different for a small number of very special firing systems, such as those in U.S. 5,197,399 A is described, which is the starting point of the present invention and in which the above-mentioned phenomenon of self-excited, periodic combustion instabilities is intentionally brought about and used to create a periodic combustion process with periodic heat release rate of the flame and periodic, oscillating exhaust gas flow (pulsating hot gas flow) in the combustion chamber and to be generated in downstream plant components (e.g. heat exchangers, chemical reactors, etc.).

For more than forty years, chemical reactors have been reported in the relevant literature in which a thermal treatment of an input raw material (educt) or a thermally controlled material synthesis from one or more raw materials takes place and which are typically designed as swinging fire reactors, pulse dryers, pulse combustors or pulsation reactors be designated. Corresponding prior art can be found, for example, in DD 114 454 B1 , the DD 155 161 B1 , the DD 245 648 A1 or the DE 10 2006 046 803 A1 .

What all these reactors have in common is that the thermal material treatment takes place in a pulsating, oscillating hot gas flow - i.e. periodically and transiently over time - with both the heat required for the thermal material treatment or material synthesis and the mechanical vibration energy of the pulsating hot gas flow coming from a transient, oscillating Combustion process of a fuel originate. Natural gas, hydrogen, liquid fuels, etc. can be used as fuels.

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

This causes the heat transfer from the hot gas to increase, both to the solid walls (combustion chamber wall, wall of a heat exchanger, steam generator, etc.) and to the material that is introduced into the hot gas flow with a defined treatment temperature for treatment. This increase is very clear and amounts to two to five times compared to a mean steady, turbulent flow with the same mean flow velocity and the same temperature. Due to these relationships, the material to be treated experiences high heating gradients in pulsating hot gas flows (“thermal shock treatment”).

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 or vaporous substances from the hot gas to the material to be treated or from the material to the hot gas flow increases similar values. This is due to the almost complete absence of boundary layers, which are known to occur in stationary flows and represent diffusion or transition resistances.

The reactors described in the prior art, cf DE 10 2006 046 803 A1 , DE 101 09 892 B4 , DE 10 2006 046 880 B4 or DE 10 2006 032 452 B4 or DE 10 2008 006 607 A1 typically consist of a combustion chamber, in which the reaction conversion of the fuel used takes place with the release of the chemically bound heat in a flame or flameless, as well as a reaction chamber connected to it in the direction of flow, which is often referred to as a "resonance tube". It is known to add the raw material to be treated into this reaction space, so that the thermal material treatment takes place in the reaction space. In some special versions, the raw material is already fed into the combustion chamber.

• Da die Schwingung die gesamte strömende Heißgassäule im Reaktor umfasst, d.h. das Abgas in der Brennkammer als auch das Heißgas im Reaktionsraum bis hin zum abschließenden Filter, ist die durch den periodisch-instationären Verbrennungsprozess in Schwingung, d.h. in periodische Bewegung zu versetzende Masse heißer Gase sehr groß. Da gleichzeitig jedoch nur ein sehr geringer Teil der thermischen Energie aus dem Verbrennungsprozess in mechanische Schwingungsenergie der (gesamten) Heißgasströmung umgewandelt wird, sind die auftretenden Amplituden der Heißgasschwingung in den großen Volumina der Brennkammer und des Reaktionsraumes außerordentlich gering und werden durch die Zugabe des (schwingungsenergiefreien) Rohstoffstromes weiter gedämpft.

However, the swing fire reactors according to the prior art have significant disadvantages and technical problems:

• Since the oscillation encompasses the entire flowing hot gas column in the reactor, ie the exhaust gas in the combustion chamber and the hot gas in the reaction space up to the final filter, the mass of hot gases to be set in oscillation, ie in periodic movement, by the periodic-transient combustion process is very large large. However, since at the same time only a very small part of the thermal energy from the combustion process is converted into mechanical vibrational energy of the (entire) hot gas flow, the amplitudes of the hot gas vibrations in the large volumes of the combustion chamber and the reaction space are extremely small and are reduced by the addition of the (vibrational energy-free ) raw material flow further dampened.

In extreme cases, it is even possible to completely dampen the usually self-excited oscillations of the hot gas flow by using sufficiently high raw material feed rates, with the consequence that the thermal material treatment then takes place in a hot gas flow that is no longer oscillating but instead is stationary. This no longer has the benefits of increased heat and mass transfer rates.

For this reason in particular, today's state-of-the-art swinging furnace reactors are severely limited in several respects: The possible raw material feed rates and thus also the product quantities that can be produced per time are very severely limited by the described decrease in the oscillation amplitudes of the hot gas flow, so that the plant capacities are relatively low.

In principle, a significant increase in the educt feed rates would first of all require an increase in the firing capacity required for their treatment, but this would go hand in hand with a corresponding increase in the waste gas volume flow produced. This would also require a large increase in the volume of the reaction space in which the material treatment takes place in order to ensure a constant material treatment time. As a result, the gas mass to be set in motion would increase again and the achievable amplitudes of the oscillation of the hot gas flow for material treatment would decrease again, with the consequence of a decreasing product quality.

The object of the present invention is to overcome these limitations.

According to the invention, this object is achieved with a device which has the features according to claim 1 .

A device according to the invention thus has a periodic, non-stationary, oscillating flame which is at the front in the combustion chamber in the direction of flow and which generates a pulsating, likewise oscillating flow of hot gas or exhaust gas. The insert used in the reaction chamber, which has a reduced cross-section, can now, if its length, the volume and the temperature of the hot gas introduced into the reaction chamber and the raw material to be treated in it are adjusted accordingly, be driven by the oscillation of the static pressure and the exhaust gas flow as well as by the radiated sound waves of the periodically - In the non-stationary combustion process in the combustion chamber, the hot gas flowing through it stimulates a resonance-enhanced oscillation, so that the raw material (educt) is subjected to the desired thermal material treatment here.

Thus, the hot gas, which contains the exhaust gas flow and oscillates, is resonantly excited only in the section of the insert.

• Bei den im Stand der Technik beschriebenen schwingenden Resonatoren liegt in Wirklichkeit überhaupt kein Resonanzphänomen vor, da es keine periodische Anregungsquelle gibt, die das Gas insbesondere im Reaktionsraum, der häufig als Resonanzrohr bezeichnet wird, in periodische Schwingungen versetzt bzw. zur Resonanz anregt. Vielmehr handelt es sich hier um eine Systeminstabilität, die den gesamten Reaktor betrifft und für deren Schwingungsfrequenz das gekoppelte Schwingungsverhalten aller Anlagenkomponenten, (d.h. Brenner, Brennkammer, Reaktionsraum („Resonanzrohr“), Abscheideeinrichtungen (Filter, Zyklon) etc.) verantwortlich ist.

The invention is based on the following finding:

• In the oscillating resonators described in the prior art, there is in fact no resonance phenomenon at all, since there is no periodic excitation source that sets the gas into periodic oscillations or excites it to resonance, particularly in the reaction chamber, which is often referred to as the resonance tube. Rather, it is a system instability that affects the entire reactor and for whose vibration frequency the coupled vibration behavior of all system components (ie burner, combustion chamber, reaction space ("resonance tube"), separation devices (filter, cyclone) etc.) is responsible.

• Bei dem oben beschriebenen Phänomen der selbsterregten Verbrennungsinstabilitäten handelt es sich nämlich um eine Systeminstabilität, bei der das System beim Erreichen einer anlagenspezifischen Stabilitätsgrenze von einem stationären, schwingungsfreien Betriebszustand (stationärer Verbrennungsprozess) schlagartig in einen periodisch-instationären, schwingenden Betriebszustand (periodisch-instationärer Verbrennungsprozess) umschlägt, ohne dass eine Fremderregung des Systems vorliegt.

However, the use of the term "resonance" for the physical effects that occur shows that there is an essential, stubborn error in connection with the causal phenomena on which the generation of the oscillating hot gas flow is based:

• The phenomenon of self-excited combustion instabilities described above is a system instability in which the system suddenly changes from a stationary, vibration-free operating state (steady-state combustion process) to a periodic, non-stationary, oscillating operating state (periodic-transient combustion process) when a plant-specific stability limit is reached. changes without there being any external excitation of the system.

The term "resonance", on the other hand, comes from exactly this physically completely different phenomenon of an externally or forced-excited oscillation: A system capable of oscillating is stimulated by an external, periodic excitation (e.g. periodic force effect due to periodic imbalance, etc.) to "oscillate", i.e. to resonate.

The resulting vibration frequency of the reactor according to the prior art with self-excited combustion instability does not correspond to such a resonance frequency of a component such as e.g. B. the "resonance tube". Thus, with this procedure, an amplitude amplification caused by resonance cannot be used, as is possible with the device according to the invention.

In other words: In the state-of-the-art oscillating furnace reactors for thermal material treatment, the entire hot gas column (hot gas flow) in the reactor must be made to oscillate, even at points where no material treatment takes place at all or where no material treatment process step takes place at this point does not benefit at all from an existing oscillation of the hot gas flow. This goes hand in hand with a low treatment amplitude. It can be seen that with a configuration according to the invention, by providing an insert with a reduced cross-sectional area and a suitable length in it, a resonance of the hot gas flow flowing through the insert can be excited in a targeted manner, so that the sections of the reaction chamber and whose dimensions are of secondary importance.

Another severe limitation in the applicability of swing fire reactors for thermal material treatment according to the prior art is that for a successful thermal treatment of raw materials, a material-specific material treatment time, i.e. a minimum residence time of the raw materials in the hot gas zone that depends on the product to be produced and the desired product properties of the reactor, is absolutely necessary. If this minimum residence time is not reached, the course of the reaction/reaction conversion is not complete and the desired product has not yet been thermally treated "completely".

In the case of swinging fire reactors described in the patent literature, the material treatment typically takes place in the reaction space, which, as mentioned, is often referred to there as the “resonance tube”. The achievable material treatment time in these known reactors thus depends on given Bener flow rate of the hot gas flow, which is determined by the firing capacity and the air ratio of the combustion, as well as any additional addition of cooling air and the raw material feed rate, and with a given cross-sectional area of the tube of the reaction chamber directly on its length. Increasing the material treatment time by lengthening the reaction chamber would simultaneously lower the oscillation frequency of the oscillation of the hot gas flow and also further reduce the achievable amplitudes of the hot gas oscillation due to the increased total mass of the gas column in the reaction chamber that is now to be oscillated.

The technical disadvantages of the reactors according to the current state of the art can easily be seen here: Vibration frequency and amplitude and the material treatment time are coupled to one another and depend on the reactor geometry, in particular on the length of the reaction chamber in the direction of flow. In the prior art, an increase in the residence time is therefore only at the expense of reduced frequencies and amplitudes of the hot gas oscillation and thus at the expense of reduced heat and mass transfer rates from the hot gas to the raw material to be treated and thus also at the expense of the advantages of thermal material treatment in the oscillating hot gas stream.

These problems are also overcome with the design of a vibration reactor according to the invention.

In a further development of the invention, the length of the insert provided in the reaction chamber can be changed.

It is also possible that, alternatively or additionally, the geometry of the combustion chamber can also be changed.

While a reactor according to the invention, as described above, shows the desired resonance in use only at a special operating point of the reactor with very specific boundary conditions, a reactor developed in this way has at least one, possibly also two frequency-tunable resonators. As a result, the reactor can be set to a large number of different operating states or operating points.

In this regard, it should be noted that e.g. the resonance within the insert depends on the speed of sound, which in turn depends on the temperature. The temperature is influenced, among other things, by the combustion temperature, the possible admixture of cooling air, the quantity and the temperature of the raw material/educt, etc.

In a reactor developed as explained, the first resonator in the direction of flow—namely the combustion chamber—can be matched with regard to the boundary conditions, as well as the second resonator in the direction of flow, namely the insert with a reduced cross section.

The first resonator thus has a burner with the associated supply connections for fuel and combustion air, a flame and a combustion chamber that acts as a resonator, which in terms of its geometry and the resulting vibration behavior of the gas column contained in it (exhaust gas from the combustion process of the flame) can be tuned in terms of frequency in the frequency range between 50 and 1,000 Hz. The device is suitable for the targeted generation of self-excited combustion instabilities in the burner-flame-combustion chamber part of the reactor, ie in the first resonator.

Connected by a preferably insulated pipeline, into which cooling air can be added if necessary to set a desired material treatment temperature, the oscillating, i.e. periodically unsteady-flowing, hot gas from the oscillating combustion process of the flame in the combustion chamber, i.e. from the first resonator, is fed to the reaction chamber . In this, the starting material is added and thus also the thermal material treatment, the latter in particular in the second resonator integrated into the reaction space.

By tuning the oscillation frequency of the periodic, unsteady combustion process in the first resonator (self-excited combustion instability with oscillating flame) at the combustion temperature present there, to the resonance behavior of the second resonator with the material treatment temperature present there, which is typically lower than the combustion temperature in the first resonator due to the addition of cooling air and educt Is resonator, there is a tuned resonant excitation of the second resonator by the periodic excitation transmitted to it, which results from the combustion oscillation in the first resonator and is characterized by periodic oscillations of the static pressure and the hot gas flow.

• an die Frequenz der aus dem ersten Resonator austretenden, den zweiten Resonator als Schallwelle anregenden Schwingung. Der an seinen beiden Enden offene Einsatz, also der zweite Resonator besitzt als ½-Wellen-Resonator seine Grundfrequenz-Resonanz bei gegebener Schallgeschwindigkeit (und somit bei gegebener Materialbehandlungstemperatur) genau dann, wenn eine halbe Wellenlänge der Schallwelle bzw. Schwingung in den Einsatz, also den zweiten Resonator passt. Es bildet sich so eine stehende Halbwelle in diesem ½-Wellen-Resonator, die zur Materialbehandlung genutzt wird.

It should be pointed out here that, both alternatively and cumulatively, the second resonator can also be adapted to the frequency of the first resonator by changing the length of the flow through it - or to put it better:

• to the frequency of the vibration emerging from the first resonator and exciting the second resonator as a sound wave. the on The insert is open at both ends, i.e. the second resonator, as a ½-wave resonator, has its fundamental frequency resonance at a given speed of sound (and thus at a given material treatment temperature) exactly when half a wavelength of the sound wave or vibration enters the insert, i.e. the second resonator fits. A standing half-wave forms in this ½-wave resonator, which is used for material treatment.

In contrast to the swinging fire reactors described in the literature, there is a real external or forced excitation with resonance in relation to the vibration generation in the second resonator, i.e. in the actual reaction space of the material treatment. Depending on the tuning of the excitation frequency and vibration damping in terms of frequency, resonance-related excitation increases (amplification) of up to a factor of ten can be set in the second resonator. So here there is actually a possibility of actively influencing the vibration amplitudes in the reaction space during thermal material treatment.

Irrespective of this, the invention solves another problem of the oscillating fire reactors according to the prior art: Regardless of the selection of the excitation frequency from the first resonator, the duration of the material treatment in the reaction chamber or in the second resonator is independent of the oscillation frequency of the hot gas flow present there, as long as the average Throughput or the average flow rate is kept constant, since the length of the second resonator (ie the length of the "resonance tube") does not have to change so that different material treatment frequencies are present there.

Thus, the frequency of the material treatment in the pulsating hot gas flow is physically decoupled from the duration of the material treatment in the reaction space or in the second resonator. Thus, both variables now represent independent process parameters of the thermal material treatment.

In addition, there is the possibility of using this method to directly excite harmonics, i.e. higher harmonic resonance frequencies of the second resonator in the reaction space.

If this resonator is, for example, a ½-wave resonator with, for example, a fundamental frequency of 100 Hz at a given hot gas or material treatment temperature, frequencies of 200 Hz, 300 Hz, 400 Hz ... etc. would be specifically used for thermal Material treatment excitable.

Surprisingly, it has been shown that the material properties achieved in the treated products depend on the product of the treatment frequency and the treatment duration at the same material treatment temperature. This means that with a treatment frequency of 100 Hz and a material treatment time of 400 milliseconds, the same result is achieved in terms of product properties and product quality as with 400 Hz and 100 milliseconds.

One reason for this is assumed to be that the particles of a raw material to be treated experience the same number of oscillation cycles in the reaction space during their treatment in both cases.

If, with a device according to the invention, one is able to significantly increase the frequencies of the thermal material treatment by targeted excitation of the second resonator in the reaction chamber, for example by targeted resonance excitation of the harmonics of the second resonator, one can simultaneously achieve the full thermal treatment of the raw material necessary residence times and thus the size or the volume of the reaction chamber (or the length of the necessary resonance tube with a fixed cross-sectional area) significantly reduce.

At the same time, however, the necessary gas mass that has to be set in motion decreases compared to the devices and methods described in the patent literature, in which the hot gas column of the entire swing fire reactor has to be set in motion with a significantly larger gas mass. With this and with the above-described, resonance-related increase (intensification) of the oscillation amplitude in the second resonator, considerably larger raw material mass flows can be treated there with the same average firing capacity of the reactor than with reactors according to the prior art. The achievable reactor throughput increases accordingly and improves the profitability of the thermal process.

Finally, for the sake of good order, it should be pointed out that the type of resonator (Helmholtz resonator, ½-wave resonator, ½-wave resonator) used as the first resonator and/or as the second resonator is fundamentally irrelevant , as long as it is ensured that the vibration frequencies of the static pressure and the flow velocity of the oscillating hot gas flow resulting from the unsteady combustion process, which are associated with the generation of self-excited combustion instabilities in the first resonator (combustion chamber), are suitable for the second resonator in the reactor tion space for the thermal material treatment to resonate.

In a further preferred embodiment of the invention, the insert proposed in the reaction space can be changed in its axial position within the reaction space.

• Typischerweise besteht eine thermische Materialbehandlung in einem Schwingfeuerreaktor beispielsweise beim Einsatz eines flüssigen Rohstoffes (z.B. Rohstoff-Lösung oder wässrige Suspension mit Feststoffanteil) aus folgenden Einzelschritten:
  • - Zerstäubung des flüssigen Rohstoffes z.B. mit Hilfe einer Zerstäuberdüse
  • - Aufheizung und Verdampfung der Rohstoff-Lösung/Trocknung des Feststoffes
  • - Aufheizen des Rohstoffes auf Materialbehandlungstemperatur
  • - Thermische Behandlung z.B. Kalzination, Ablauf von Festkörperreaktionen, Entgasung
  • - Kristallwachstum/Kristallumwandlungen,
  • - usw.

The advantage of this further development becomes apparent in the following consideration:

• Typically, thermal material treatment in a swing fire reactor, for example when using a liquid raw material (e.g. raw material solution or aqueous suspension with a solid content), consists of the following individual steps:
  • - Atomization of the liquid raw material eg with the help of an atomizer nozzle
  • - Heating and evaporation of the raw material solution/drying of the solid
  • - Heating the raw material to material treatment temperature
  • - Thermal treatment, eg calcination, course of solid-state reactions, degassing
  • - crystal growth/crystal transformations,
  • - etc.

It is very unlikely that all of these physically very different individual stages of thermal material treatment in a swing furnace reactor benefit to the same extent from an oscillation of the hot gas flow around the droplets/particles to be treated compared to thermal treatment in a stationary, non-oscillating hot gas flow.

In the reactors described in the prior art, however, the entire flowing column of hot gas in the entire reactor space is set in motion with the consequence of a large and sluggish gas mass with significant vibration damping and the resulting small vibration amplitudes and low vibration frequencies of the oscillating hot gas flow.

With the particularly preferred development of the invention described here, on the other hand, there is the possibility of accommodating the actual reaction space for the material treatment, i. H. to position the second resonator or the insert at exactly that point at which, according to the individual step or physical sub-process of the thermal material treatment taking place there, the product experiences the greatest change in its achievable material properties compared to thermal treatment in a stationary hot gas flow without oscillations.

Such an optimizing position of the insert can easily be determined in preliminary tests by repeating the material treatment with the insert positioned differently within the reactor chamber based on the measured material properties of product samples manufactured in this way.

As a particular advantage, it should also be mentioned that the material, after undergoing the thermal treatment in the second resonator at high treatment frequencies and short residence times (typically less than 200 milliseconds, preferably less than 100 milliseconds) in the downstream reactor part with an increased reactor diameter and therefore significantly reduced flow velocities, undergoes a thermal Post-treatment undergoes, which can be used for the complete degradation of unwanted residual components of the raw material mixture / raw material solution.

For example, when processing a nitrate-containing raw material, the residual nitrate content in the product or, in the case of organic components in the raw material, the residual carbon content in the product can be significantly reduced or completely avoided. In order to ensure this reliably, after-treatment times in the reaction chamber downstream of the second resonator must be longer than 2 seconds, preferably longer than 3 seconds.

Finally, it should be pointed out that the insert or resonator, which can be displaced in its axial position in the reaction chamber, can be designed such that its resonant frequency can be adjusted, i.e. tuned in terms of frequency, in particular by changing or adjusting its length.

Typically, finely divided particles with an average particle size in the range from 5 nm to 100 μm can be produced with the device according to the invention and the associated method. Finely divided particles, for example in the form of carbides, nitrides, simple oxides, complex mixed oxides, oxides with doping, mixtures of oxides or coated particles, can be produced in a targeted manner by this method according to the invention.

For this purpose, a so-called precursor mixture is produced from educts, which contains at least all components of the solid particles to be formed.

For the special case that only one starting material is required, the term precursor mixture is used below.

The precursor mixture formed from the raw material components can be present as a solid, for example in the form of a finely divided powder or powder mixture, in the form of a solution, a suspension, a dispersion or emulsion, a gel, as a gas or vapor.

Spherical particles in particular result when using liquid raw material mixtures, such as solutions, dispersions or emulsions.

The precursor mixture can be conditioned by a one- or multi-stage wet-chemical intermediate step in such a way that a specific particle shape or size is established in the thermal process, for example a particularly narrow grain size distribution of the particles. Known methods such as, for example, co-precipitation or hydroxide precipitation can be used for the wet-chemical intermediate step.

The forms of the precursor mixture mentioned are introduced into the hot gas flow of the device according to the invention, for example by spraying, introducing or blowing in. The type of precursor application, such as the type, diameter and spray pattern of a multi-component nozzle used for this purpose, the direction of feed (e.g. direction of injection) and the place of feed influence the process control and the resulting thermal treatment regime and are therefore important control variables for the resulting particle properties.

The particles that form are transported through the reactor with the hot gas stream and are thermally treated in this hot gas stream. The properties of the hot gas flow thus significantly influence the thermal treatment and thus the properties of the particles that are formed. The device according to the invention offers a large number of options for the targeted setting of process parameters for the thermal production and/or treatment of these finely divided particles according to the invention. For example, the temperature profile, the maximum process temperature, the dwell time of the gas flow and the dwell time of the particles in the gas flow can be adjusted in a manner known to those skilled in the art.

A special feature of the device according to the invention is that the hot gas flow can be made to oscillate. In oscillating or pulsating hot gas flows, there is a significantly increased heat transfer due to the high flow turbulence. The heat transfer has a significant influence on the reaction and phase formation mechanisms in the material conversion and in the phase formation. By choosing the frequency and amplitude of the pulsating gas flow, the reaction conditions can be precisely adapted to the requirements of the material to be produced.

With the device according to the invention, there is the possibility of stimulating the gas space of the thermal material treatment, i.e. the second resonator, to resonate by an external, periodic excitation. In the case of resonance, this results in an 8-10 times higher amplitude of the gas column oscillation during thermal material treatment within the second resonator than with excitation at frequencies outside of this resonance band. The resulting higher amplitudes significantly increase heat and mass transfer.

Higher frequencies also significantly increase heat and mass transfer. Since the device according to the invention can also generate high harmonics, that is to say very high frequencies, for example in the range greater than 300 Hz, this results in a further setting parameter for a particularly high heat transfer.

The rate of heat transfer decisively defines the heating rate of the precursors or particles and thus the actual temperature profile. Higher amplitudes and higher frequencies of the pulsating gas flow accelerate the reaction and phase formation mechanisms. In this way, for example, a higher degree of reaction conversion of the precursor mixture can be achieved with a comparable residence time, or the activity of, for example, catalytic materials can be increased. The possibility according to the invention for significantly higher amplitudes and higher frequencies than in conventional systems thus expands the possibilities for process control, expands the possible substance spectrum of the materials to be treated, spreads the adjustable particle properties and simplifies process control.

Depending on the material system, the frequency and amplitudes of the oscillating hot gas flow have varying degrees of influence on partial reaction steps such as drying, heating, (chronologically) different phase reactions, cooling, etc. and thus on particle formation and/or thermal particle treatment.

With the device according to the invention and the method according to the invention, the reaction section or reaction sections in which, for example, the desired influence by high amplitudes and frequencies is particularly strong, can be specifically selected by the positioning of the second resonator within the reactor and the feed location is selected according to the precursor mixture.

In a particularly preferred embodiment, particles are at least partially coated by a suitable precursor combination of a prepared precursor mixture in the form of a dispersion. In this case, for example, the solid phase in the case of suspensions or the inner phase in the case of the emulsion contains at least all the components that are required to form the particles to be coated. The liquid phase in the case of the suspension or the outer phase in the case of the emulsion contain at least all of the coating components. By choosing a suitable thermal treatment regime, the solid particles are formed and these particles are at least partially coated.

The finely divided particles produced in the pulsating hot gas stream according to the invention are then separated from the hot gas stream using a suitable separator. The hot gas is optionally cooled before it enters the separating device to a temperature that is required depending on the type of separating device. In a preferred embodiment, the particles formed are separated from the hot gas stream at temperatures above 300° C., preferably above 500° C., particularly preferably above 600° C., for example by a cyclone or a hot gas reactor. This can prevent, for example, highly reactive particles from absorbing hot gas components, such as water. In this embodiment, the hot gas can be cooled after the filter if required.

• 1 die Prinzipskizze einer Vorrichtung zur thermischen Behandlung eines Rohstoffes mit einer Brennkammer, einem Reaktionsraum und einem in dem Reaktionsraum integrierten Einsatz, bei der die Brennkammer in ihrer Geometrie veränderbar ist;
• 2 die Prinzipskizze einer Vorrichtung gemäß 1 mit einer anderen Veränderbarkeit der Brennkammer-Geometrie.

Further advantages and features of the invention result from the following description of exemplary embodiments. It shows:

• 1 the schematic diagram of a device for the thermal treatment of a raw material with a combustion chamber, a reaction space and an insert integrated in the reaction space, in which the geometry of the combustion chamber can be changed;
• 2 according to the schematic diagram of a device 1 with a different variability of the combustion chamber geometry.

In 1 you can see the basic sketch of a reactor for the thermal treatment of a raw material within a periodically non-stationary oscillating hot gas stream. This stream of hot gas is generated by a flame 1 on a burner 2, for which purpose fuel 3 and combustion air 4 are supplied. The flame 1 burns in a combustion chamber 5.

Fuel is understood to mean combustible gases such as natural gas, methane, hydrogen or liquid fuels such as alcohol, etc. Combustion air in the context of this application 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.

In principle, it is possible to operate the flame in an externally excited manner by supplying the flame with a corresponding oscillating supply of a fuel/air mixture that is periodically modulated over time or with a flow of combustion air that is periodically modulated over time. The ability to change the mass flow of the fuel/air mixture is particularly preferred in the case of premixed combustion, and a change in the mass flow of the combustion air is particularly preferred in the case of diffusion combustion.

Otherwise, the combustion is operated in such a way that it has a periodic, transient, oscillating operating state. The frequency of the pulsating combustion is influenced, for example, by the geometry of the combustion chamber and the process temperature.

The pulsating flow of hot gas ultimately generated by the pulsating flame flows through a coupling tube 6 into a reaction chamber 7, the wall 8 of which is gas-tight and heat-tight. The thermal tightness can be ensured in particular by separate insulation.

A raw material 10 to be treated and cooling air 11 are fed into the exhaust gas flow 9 flowing out of the coupling pipe 6. This forms a hot gas flow 12, which flows through the reaction chamber 7 and at the end of which is passed through a hot gas filter or cyclone (not shown here). in which the raw material 10 thermally treated in the reaction chamber 7 is separated from the hot gas stream 12 .

It is now essential that an insert 13 is provided in the reaction space 7 , which has a reduced cross-sectional area 14 compared to the reaction space 7 .

In the example shown here, this insert 13 is designed as a single tube and has an axial length 15 through which flow occurs, which is only a fraction of the total length of the reaction chamber 7 . In addition, the insert 13 is connected to the wall 8 of the reaction chamber 7 in a substantially gas-tight manner, so that the hot gas flow 12 flows completely through the free cross section of the insert 13 lying on the inside in the radial direction, but not laterally past it.

The insert 13 is adjustable in its axial length 15, so that it is possible to adjust its length in such a way that it is tuned to the oscillation frequency of the periodically unsteady combustion process in the combustion chamber 5 so that the periodically unsteady hot gas flow excited by this 12 is resonantly excited when it passes through the insert 13 and thus changes in the area of this insert 13 into an externally or forcedly excited vibration. The excitation peaks that occur due to resonance can go up to a factor of 10.

The resonant frequency within the insert 13 is particularly dependent on the temperature of the hot gas stream 12, since this temperature influences the speed of sound that is relevant for generating resonance.

The insert 13 is also referred to below as the second resonator.

In the example shown here, the combustion chamber 5 can also be adjusted due to the presence of a movable floor 16 . The assembly described to this extent is also referred to below as the first resonator. With the adjustability of the first resonator, one has a further manipulated variable via which real resonance within the second resonator, ie the insert 13, in the reaction space 7 can be adjusted.

• Der erste Resonator mit der Brennkammer 5 soll als ¼-Wellen-Resonator ausgeführt sein mit einer veränderbaren Länge zwischen 0,5 m und 1,0 m. Aufgrund der einstellbaren Brenner-/Flammenparameter (Brenngasmassenstrom, Luftmassenstrom, Luftzahl, Vorwärmtemperatur der Luft, etc.) soll die Flamme 1 stabil schwingend brennen in einem Temperaturbereich der Flamme 1 bzw. des Abgasstromes 9, welcher von der Flamme 1 erzeugt wird, zwischen 800 °C und 1.800 °C. Entsprechend der gewählten Verbrennungstemperatur stellen sich im ersten Resonator Schallgeschwindigkeiten zwischen ca. 630 m/s und 830 m/s ein. (Zur Vereinfachung wird hier nur mit Luft als Medium gerechnet und nicht mit der vollständigen Abgaszusammensetzung.) Gemäß der eingestellten Länge des ersten Resonators entstehen Schwingungsfrequenzen bei Entstehung selbsterregter Verbrennungsschwingungen im ersten Resonator zwischen ca. 160 Hz bis ca. 420 Hz. Die niedrigste Temperatur von ca. 800 °C und die größte Länge des ersten Resonators von 1.0 m ergeben z.B. die niedrigste Frequenz des schwingenden ¼-Wellen-Resonators von ca. 160 Hz. Mit dieser kann der nachfolgende zweite Resonator im Reaktionsraum zu Resonanz angeregt werden.

In order to explain and illustrate the importance and the mode of operation of two frequency-tunable resonators in the reactor described here, an exemplary calculation is presented below, without however wishing to restrict the general validity through this concrete exemplary calculation:

• The first resonator with the combustion chamber 5 should be designed as a ¼-wave resonator with a variable length between 0.5 m and 1.0 m. Due to the adjustable burner/flame parameters (fuel gas mass flow, air mass flow, air ratio, preheating temperature of the air, etc .) The flame 1 should burn in a stable, oscillating manner in a temperature range of the flame 1 or of the exhaust gas flow 9, which is generated by the flame 1, between 800° C. and 1,800° C. Depending on the selected combustion temperature, sound velocities of between approx. 630 m/s and 830 m/s occur in the first resonator. (For the sake of simplification, only air is used as the medium and not the complete exhaust gas composition.) Depending on the set length of the first resonator, oscillation frequencies arise when self-excited combustion oscillations arise in the first resonator between approx. 160 Hz and approx. 420 Hz. The lowest temperature of Approx. 800 °C and the greatest length of the first resonator of 1.0 m result in the lowest frequency of the oscillating ¼-wave resonator of approx. 160 Hz. With this, the following second resonator in the reaction space can be excited to resonance.

In use 13 as the second resonator, which is designed as a ½-wave resonator, thermal material treatment in the temperature range between 200° C. and 800° C. should be made possible with resonant excitation of the second resonator using the adjustable combustion oscillation in the first resonator. The sound velocities in the second resonator are 430 m/s to 630 m/s in the temperature range desired for the material treatment.

If the flow length 15 of the second resonator is 2.0 m, the fundamental resonance frequency would be approx. 160 Hz at the highest material treatment temperature of 800 °C and would therefore just be 800 °C with the lowest, adjustable oscillation frequency in the first resonator Flame/exhaust gas temperature resonantly excitable.

However, if a material treatment temperature of 200° C. was desired in the second resonator, the resonant frequency of the second resonator at this temperature and with a flow length 15 of the second resonator would be approximately 105 Hz Oscillation frequency at 800 °C of 160 Hz resonant to the fundamental oscillation.

In this desired case, the length 15 of the insert 13 as the second resonator would have to be reduced to about 1.34 m in order to achieve a resonant frequency as the fundamental oscillation of about 160 Hz in the second resonator at a material treatment temperature of 200 °C first resonator at whose minimum frequency of 160 Hz could be resonantly excited.

From the example explained, one can easily see the advantages that arise when both resonators can be tuned to one another and to the desired temperatures in terms of frequency via individual geometry settings.

A further aspect of the present invention is that the insert 13 can be positioned as required in its axial position within the reaction space 7 according to the arrows 17 .

Raw material particles conveyed in the hot gas stream 12 are thus first acted upon in the area in front of the insert 13 by the hot gas flow 12 with the frequency and amplitude present in the reaction chamber 7, then within the free cross section 14 of the insert 13 by the hot gas flow 12 flowing there at least at increased speed then again in the hot gas flow 12 flowing at a lower speed in the region of the reaction chamber that is no longer restricted in cross section. With a corresponding coordination of the vibration generated in the combustion chamber 1 and the length 15 of the insert 13, the flow through the insert 13 can be brought into resonance not only with a fundamental but possibly also with a harmonic, which reduces the intensity of the in the area of the insert 13 caused thermal treatment increased accordingly.

If the raw material consists of a raw material mixture for which it makes sense to have different intensities of the thermal treatment in succession, this can be adjusted accordingly by selecting the appropriate axial position of the insert 13 within the reaction chamber 7 as required.

In the 2 is essentially the same device as in 1 shown. In this case, the combustion chamber 5 differs in the way it is tuned as a resonator to the flame 1 burning in it. Instead of changing the volume of the combustion chamber 5 via a sliding floor, as in the 1 is shown, in this embodiment there is a tube insert 18 surrounding the flame 1 on the burner 2 in the radial direction, which can be displaced in the axial direction 19 of the combustion chamber 5 in order to be able to adjust the vibration generated in the combustion chamber 5 to the insert 13 so that so at this a resonance is generated with respect to the hot gas flow 12 flowing through it.

Reference List

1

flame

2

burner

3

fuel

4

combustion air

5

combustion chamber

6

coupling tube

7

reaction space

8th

wall

9

exhaust flow

10

raw material

11

cooling air

12

hot gas flow

13

mission

14

Cross sectional area

15

axial length

16

Adjustable bottom

17

arrows

18

tube insert

19

axial direction

Claims (6)

Device for the thermal treatment of a raw material (10), with - a combustion chamber (5) which is a first resonator; - A burner (2) with a supply connection for a fuel (3) through which a pulsating exhaust gas flow (9) can be generated by means of a periodically unsteady, oscillating flame (1), the fuel (3) being a combustible gas or a liquid fuel ; and - A reaction chamber (7) adjoining the combustion chamber (5). - A task for the raw material to be treated (10) in the exhaust gas stream (9), from which a hot gas stream (12) is formed; and - an insert (13) through which the hot gas stream (12) can flow, with a reduced cross-sectional area (14) compared to the reaction chamber (7), which has a length (15) that is shorter than the overall length of the reaction chamber (7), the Insert (13) is a second resonator. Device according to claim 1 , characterized in that the length (15) of the insert (13) is variable. Device according to claim 1 or 2 , characterized in that the geometry of the combustion chamber (5) can be changed by means of a displaceable base (16). Device according to claim 1 or 2 , characterized in that the geometry of the combustion chamber (5) can be changed in that a tube insert (18) surrounding the flame (1) on the burner (2) in the radial direction can be displaced in the axial direction (19) of the combustion chamber (5). Process for the thermal treatment of a raw material (10) in a periodically unsteady, oscillating hot gas flow (12), in which a periodically unsteady, oscillating exhaust gas flow (9) is generated by a periodically unsteady, oscillating flame (1), in which the exhaust flow (9) after leaving a combustion chamber (5), which is a first resonator, into a reaction chamber (7), with the raw material (10) to be treated and optionally cooling air entering the exhaust gas stream (9) flowing out of the combustion chamber (5). (11) is applied, whereby the hot gas stream (12) is formed, characterized in that the hot gas stream (12) is in an insert (13) provided in the reaction chamber (7) through which the hot gas stream (12) can flow, which is a second resonator , is excited to a resonant oscillation with a cross-sectional area (14) that is reduced compared to the reaction space (7) and a length (15) that is shorter than the total length of the reaction space (7). procedure according to claim 5 , characterized in that the flame (1) can be excited externally to oscillate.

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