DE102016002566A1 - Apparatus and method for thermal material treatment - Google Patents

Abstract

The invention relates to a method and a device for the thermal treatment of a raw material (10), with a combustion chamber (5) in which a periodically unsteady, oscillating flame (1) burns, for generating a pulsating exhaust gas stream (9) by a the combustion chamber (5) adjoining the reaction space (7) flows. In order to achieve that the raw material is treated effectively, it is proposed that in the reaction space (7) a through-flow of the exhaust stream, in the cross-sectional area (14) relative to the reaction space (7) reduced insert (13) is provided, which has a length (15) which is shorter than a total length of the reaction space (7). In particular, the length (15) of the insert (13) and the geometry of the combustion chamber (5) are variable, so that one has two tunable resonators.

Description

The invention relates to a device for the thermal treatment of a raw material, with a combustion chamber in which burns at least one burner at least one periodic-unsteady, oscillating flame to produce a pulsating oscillating exhaust gas stream which flows through a subsequent reaction chamber to the combustion chamber, and a corresponding Method.

Under a thermal treatment is understood in particular a thermal material treatment or a thermal material synthesis, wherein it may also be a raw material mixture in the raw material. The raw material or the raw material mixture can be present both in solid and in liquid 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 on average with the exception of minor turbulent fluctuations whose magnitude is at least an order of magnitude smaller than the average sizes of the combustion process (eg average flow velocity, mean 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 consequence, also the heat release from the combustion process and the mass flow of exhaust gas arising (combustion products) have constant values 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 thermoacoustic oscillations. These are characterized by the fact that the initially steady (ie time-constant) combustion process, when a stability limit is reached, suddenly switches over into a time-periodic, oscillating combustion process, the time function of which can be described in a good approximation as sinusoidal. Along with this change, the heat release rate (s) of the flame (s) and thus the thermal firing performance of the incinerator as well as the exhaust flow into and out of the combustion chamber and the static pressure in the combustion chamber itself become periodically unsteady, i. H. swinging / 1, 2 /.

The occurrence of these combustion instabilities often causes a relation to the stationary operation of the furnace changed pollutant emission behavior and causes not only increased noise pollution of the plant environment but also a significantly increased mechanical and / or thermal stress on the plant structure, eg. As the combustion chamber walls, the combustion chamber lining etc. These loads can lead to destruction of the furnace or individual components. It is therefore easy to see that the undesired occurrence of the phenomena described above in furnaces which are designed for a time-constant combustion process in which the static pressure in the combustion chamber or in upstream or downstream plant components should also have constant values (constant pressure). Combustion), must be avoided.

Quite different, however, is the situation in a small number of very specialized combustion systems, as envisaged in the present invention, where the phenomenon of self-excited, periodic combustion instabilities, as illustrated above, is deliberately induced and utilized, a periodic combustion process with periodic heat release rate the flame and periodic, oscillating exhaust gas flow (pulsating hot gas flow) in the combustion chamber and in downstream plant components (eg heat exchangers, chemical reactors, etc.) to produce.

For more than forty years, the relevant literature has reported chemical reactors in which thermal treatment of a raw material feedstock or thermally controlled material synthesis is from one or more raw materials, typically as vibrating-fire reactors, pulse dryer, pulse combustor or pulsation reactors be designated / 3, 4, 5, 6 /.

All of these reactors have in common that the thermal material treatment in a pulsating, oscillating hot gas flow - ie temporally-instationary - takes place, both the heat required for the thermal material treatment or material synthesis heat and the mechanical vibration energy of the pulsating hot gas flow of a transient, oscillatory 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 consists in the periodic average-transient and turbulent exhaust gas flow in the combustion chamber and in downstream components, eg. B. heat exchangers, reaction chambers, resonance tubes, etc.

This causes the heat transfer from the hot gas increases, both on the solid walls (combustion chamber wall, wall of a heat exchanger, steam generator, etc.) and on the material which is introduced for treatment in the hot gas flow with a defined treatment temperature. This increase is very clear and is two to five times higher than a steady-state, turbulent flow with the same average flow velocity and the same temperature. Due to these relationships, material to be treated undergoes high heating gradients in pulsating hot gas flows ("thermal shock treatment" / 6 /).

Due to the analogy between convective heat transfer and mass transfer, the above statement also applies to the mass transfer: In the case of periodic-transient, oscillating flow, the transition 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 arise in stationary flows and represent diffusion or contact resistance.

The reactors / 6, 7, 8, 9 / described in the prior art typically consist of a combustion chamber, in which the reaction conversion of the fuel used to release the chemically bound therein heat in a flame or flames, and then in the flow direction thereafter a reaction space which is often referred to as a "resonance tube". It is known to add the raw material to be treated to this reaction space so that thermal material treatment takes place in the reaction space. In some special versions, the raw material is already given up in the combustion chamber.

However, the prior art vibrating fire reactors have significant disadvantages and technical problems:
Since the oscillation comprises the entire flowing hot gas column in the reactor, ie the exhaust gas in the combustion chamber as well as the hot gas in the reaction space up to the final filter, the mass of hot gases to be displaced by the periodic-transient combustion process, ie in periodic motion, is very high large. However, since only a very small part of the thermal energy from the combustion process is converted into mechanical vibration energy of the (total) hot gas flow, the amplitudes of the hot gas oscillation occurring in the large volumes of the combustion chamber and the reaction space are extremely low and by the addition of the (vibrational energy ) Commodity flow further subdued.

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

For this reason in particular, today's vibrating-fire reactors are severely limited in several respects: the possible raw material application rates and thus also the producible product quantities per time are very severely limited by the described decrease in the oscillation amplitudes of the hot gas flow, so that also the plant capacities are relatively small.

In principle, a significant increase in the educt feed rates would first of all make it necessary to increase the firing rate required for their treatment, which would, however, be accompanied by a corresponding increase in the resulting exhaust gas volume flow. This would also require a large increase in the volume of the reaction space in which the material treatment takes place so as to ensure a consistent material treatment time. As a result, the gas mass to be vibrated would increase again and the recoverable 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.

This object is achieved in that in the reaction space a flowed through by the exhaust gas flow, in the cross-sectional area opposite the reaction space reduced use is provided, which has a length in the flow or axial direction, which is shorter than a total length of the reaction space.

A device according to the invention thus has a periodically unsteady, oscillating flame in the combustion chamber in front in the flow direction, which generates a pulsating, likewise oscillating, hot gas or exhaust gas flow. The used in the reaction space, reduced in cross-section can now with appropriate tuning of its length, the volume and the temperature of the introduced into the reaction chamber hot gas and the raw material to be treated in this by the vibration of the static pressure and the exhaust gas flow and by radiated sound waves of the periodic - transient combustion process in the combustion chamber at the hot gas flowing therethrough stimulate a resonance-enhanced vibration, so that the discontinued raw material (educt) is here subjected to the desired thermal material treatment.

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

The invention is based on the following finding:
In reality, there is no resonance phenomenon whatsoever in the vibrating resonators described in the prior art, since there is no periodic excitation source which sets the gas in periodic oscillations or stimulates resonance, in particular in the reaction space, which is often referred to as resonance tube. Rather, this is a system instability, which affects the entire reactor and for their vibration frequency, the coupled vibration behavior of all system components, (ie burner, combustion chamber, reaction chamber ("resonance tube"), separating devices (filters, cyclone), etc.) is responsible / 10 /.

However, it can be seen from the use of the term "resonance" for the occurring physical effects that there is a substantial, persistent error in connection with the causative phenomena underlying the generation of the oscillating hot gas flow:
The phenomenon of self-excited combustion instabilities described above is in fact a system instability in which, when a system-specific stability limit is reached, the system abruptly changes from a stationary, vibration-free operating state (stationary combustion process) into a periodically transient, oscillatory operating state (periodic-transient combustion process). turns over without any external excitation of the system.

The term "resonance", on the other hand, comes precisely from this, physically completely different phenomenon of a strange or forced excitation oscillation:
An oscillatory system is stimulated by an external, periodic excitation (eg periodic force due to periodic imbalance, etc.) for "resonating", ie for resonating.

The adjusting oscillation frequency of the prior art reactor with self-excited combustion instability thus does not correspond to such a resonant frequency of a component such. B. of the "resonance tube". Thus, in this procedure also not a resonance-induced amplitude gain can be exploited, as is possible with the device according to the invention.

In other words, in the vibrating-fire reactors for thermal material treatment according to the prior art, the entire, located in the reactor hot gas column (hot gas flow) must be set in vibration, even in places where no material treatment takes place at all or taking place at this point process step of material treatment not benefited at all from a present vibration of the hot gas flow. This goes hand in hand with a low treatment amplitude. It can be seen that, with an embodiment according to the invention, the provision of an insert with a reduced cross-sectional area and suitable length can purposefully excite a resonance of the hot gas flow flowing through the insert, so that the portions of the reaction space upstream and downstream of the insert in the flow direction whose dimensions are of minor importance.

Another strong limitation in the applicability of prior art thermal material handling vibrating fire reactors is that for a successful thermal treatment of raw materials, a material-specific material treatment time, i. H. a dependent on the product to be produced and the desired product properties minimum residence time of the raw materials in the hot gas zone of the reactor, is absolutely necessary. If this minimum residence time is exceeded, the reaction sequence / reaction conversion is not completed and the desired product is not yet "finished" thermally treated.

In the case of vibrating-fire reactors described in the patent literature, the material treatment is typically carried out in the reaction space, which, as mentioned above, is frequently referred to as a "resonance tube". The achievable material treatment time in these prior art reactors thus depends on the flow rate of the hot gas flow, which is determined by the firing capacity and the combustion air number, and optionally additional addition of cooling air and the raw material feed rate, and at a given pipe cross-sectional area of the reaction space directly from the length from. An increase in the material treatment time by an extension of the reaction chamber would simultaneously lower the oscillation frequency of the oscillation of the hot gas flow and also reduce the recoverable amplitudes of the hot gas oscillation by the increased total mass of the now to be vibrated gas column in the reaction chamber.

One recognizes here easily the technical disadvantages of the reactors according to the current state of the art: vibration frequency and amplitude and the material treatment time depend on each other coupled from the reactor geometry, in particular from the length of the reaction space in the flow direction. An extension of the residence time is thus in the prior art 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 of the hot gas to the raw material to be treated and thus at the expense of the advantages of a thermal material treatment in the oscillating hot gas flow.

These problems are also overcome with the inventive design of a vibration reactor.

In a development of the invention, the insert provided in the reaction space can be variable in its flow-through length.

It is also possible that alternatively or additionally, the combustion chamber is variable in its geometry.

While a reactor according to the invention as described so far shows the desired resonance in use only at a specific operating point of the reactor with very specific boundary conditions, such a further developed reactor thus has at least one, possibly also two frequency tunable resonators. This has the consequence that the reactor can be set to a large number of different operating states or operating points.

In this regard, it should be noted that z. B. the resonance within the insert depends on the speed of sound, which in turn is temperature dependent. The temperature is u. a. influenced by the combustion temperature, the possible admixture of cooling air, the amount and the temperature of the raw material / educt, etc.

In the case of a reactor which has been developed as described above, it is thus possible to tune the boundary conditions at the first resonator in the direction of flow - namely the combustion chamber - and at the second resonator in the flow direction, namely the insert reduced in 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, which acts as a resonator, which in terms of their geometry and the resulting vibration behavior of the gas column contained in it (the exhaust gas of the combustion process the flame) in the frequency range between 50 and 1000 Hz frequency tunable. The device is suitable for the targeted generation of self-excited combustion instabilities in the reactor part burner-flame combustion chamber, ie in the first resonator.

Connected by a preferably insulated pipe into which cooling air can be added if necessary to set a desired material treatment temperature, the oscillating, d. H. periodically-instationarily flowing hot gas from the oscillating combustion process of the flame in the combustion chamber, that is supplied from the first resonator, the reaction space. In this then takes place the Eduktzugabe and thus also the thermal material treatment, the latter in particular in the integrated into the reaction chamber second resonator.

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

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 altering its length throughflow - or rather to the frequency of the resonator emerging from the first resonator and exciting the second resonator as a sound wave Vibration. The open at its two ends insert, so the second resonator has as a 12-wave resonator its fundamental frequency resonance at a given speed of sound (and thus at a given material treatment temperature) if and only half a wavelength of the sound wave or vibration in the use, ie fits the second resonator. This forms a standing half-wave in this ½-wave resonator, which is used for material treatment.

In contrast to the vibrating fire reactors described in the literature, there is a genuine external or forced excitation with resonance in relation to the generation of vibrations in the second resonator, ie in the actual reaction space of the material treatment. Depending on the frequency tuning of the excitation frequency and vibration damping can in the second resonator Resonance-related peaks (amplification) of the excitation can be adjusted up to a factor of ten. So here is actually an active ability to influence the vibration amplitudes in the reaction chamber in the thermal material treatment.

Independently of the choice of the excitation frequency from the first resonator, the duration of the material treatment in the reaction space or in the second resonator is independent of the existing there oscillation frequency of the hot gas flow, as long as the middle 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 there are different material treatment frequencies.

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, it is possible to use this method directly harmonic waves, d. H. to specifically excite 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 for a given hot gas or material treatment temperature, then frequencies of 200 Hz, 300 Hz, 400 Hz, etc. would be targeted for the thermal Material treatment excitable.

Surprisingly, it has been shown that the material properties achieved of the treated products at the same material treatment temperature depend on the product of treatment frequency and treatment time. Ie. at 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 at 400 Hz and 100 milliseconds.

One reason for this is presumed 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.

So if you are in a device according to the invention in a position to increase the frequencies of the thermal material treatment by a targeted excitation of the second resonator in the reaction chamber significantly, for example, by a targeted resonant excitation of the harmonics of the second resonator, you can simultaneously for complete thermal treatment of the raw material necessary residence times and thus the size or the volume of the reaction space (or the length of the required resonance tube with a fixed cross-sectional area) significantly reduced.

At the same time, however, the necessary gas mass, which must be vibrated, is reduced in comparison with the devices and methods described in the patent literature, in which the hot gas column of the entire vibrating fire reactor must be vibrated with a significantly greater mass of gas. Thus, and with the above-described resonance-induced elevation (amplification) of the oscillation amplitude in the second resonator, significantly larger raw material mass flows can thus be treated at the same average firing capacity of the reactor than are enforced in state-of-the-art reactors. Accordingly, the achievable reactor throughput increases significantly 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 second resonator 2 is fundamentally not important Therefore, as long as it is ensured that the vibration frequencies of the static pressure and the flow velocity of the unsteady combustion process resulting in the generation of self-induced combustion instabilities in the first resonator (combustion chamber) are suitable for oscillating around the second resonator in the reaction space for thermal material treatment to stimulate.

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.

• – 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, a thermal material treatment in a vibrating fire reactor, for example when using a liquid raw material (eg raw material solution or aqueous suspension with solids content) consists of the following individual steps:

• - Atomization of the liquid raw material z. B. with the aid of a spray nozzle
• - Heating and evaporation of the raw material solution / drying of the solid
• - Heating the raw material to material treatment temperature
• - Thermal treatment z. B. calcination, expiration of solid state reactions, degassing
• - crystal growth / crystal transformations,
• - etc.

It is very unlikely that all of these physically very different single cuts of thermal material treatment in a vibrating fire reactor will equally benefit from oscillation of the hot gas flow around the droplets / particles to be treated versus thermal treatment in a stationary flowing non-oscillating hot gas flow.

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

With the described here, particularly preferred embodiment of the invention, however, it is possible, in the outwardly gas and heat sealed reactor housing the actual reaction space of the material treatment, d. H. to position the second resonator or the insert at exactly the point at which, according to the individual step or physical sub-process of the thermal material treatment taking place there, the product undergoes the greatest change in its material properties that can be achieved compared to a 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 in differently positioned use within the reactor space on the basis of the measured material properties of product samples manufactured in this way.

As a particular advantage, it should also be mentioned that the material after passing through the thermal treatment in the second resonator at high treatment frequencies and short residence time (typically below 200 milliseconds, preferably below 100 milliseconds) in the downstream reactor part with again increased reactor diameter and therefore significantly reduced flow rates a thermal Aftertreatment learns that can be used for the complete removal of unwanted residual components of the raw material mixture / raw material solution.

For example, when processing a nitrate-containing raw material of the residual nitrate content in the product or organic components in the raw material, the residual carbon content in the product significantly reduced or completely avoided. To ensure this safely, after-treatment periods in the reaction space downstream of the second resonator are greater than 2 seconds, preferably greater than 3 seconds.

Finally, it should also be pointed out that the insert or resonator which can be displaced in its axial position in the reaction space can also be configured such that it is adjustable in terms of its resonant frequency, in particular by changing or adjusting its length, that is to say tunable in terms of frequency.

Typically, finely divided particles having 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. By means of this process according to the invention, finely divided particles, for example in the form of carbides, nitrides, simple oxides, complex mixed oxides, doped oxides, mixtures of oxides or coated particles can be produced in a targeted manner.

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

For the special case that only one reactant is needed, the term precursor mixture will nevertheless be used below.

The precursor mixture formed from the raw material components can be present both 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.

When using liquid mixtures of raw materials, such as solutions, dispersions or emulsions result in particularly spherical particles.

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

The mentioned forms of the precursor mixture are introduced into the hot gas stream of the device according to the invention, for example by spraying, introduction or injection. The nature of the precursor task, such as the type, diameter and spray pattern of a multicomponent nozzle used for this purpose, the feed direction (eg injection direction) and the feed location, influence the process control and the resulting thermal treatment regime and are thus important control variables for the resulting particle properties.

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

A special feature of the device according to the invention is that the hot gas stream can be set in vibration. In oscillating or pulsating hot gas flows results in a significantly increased heat transfer due to the high flow turbulence. The heat transfer significantly influences the reaction and phase-forming mechanisms during the transformation or phase formation. By choosing the frequency and amplitude of the pulsating gas flow, the reaction conditions can be adapted exactly to the requirements of the material to be produced.

In the device according to the invention, it is possible, the gas space of the thermal material treatment, d. H. to excite the second resonator by an external, periodic excitation for resonating. In the case of resonance, this results in an 8-10 times higher amplitude of the gas column oscillation in the thermal material treatment within the second resonator than in an excitation with frequencies outside this resonance band. The resulting higher amplitudes significantly increase the heat and mass transfer.

Even higher frequencies increase the heat and mass transfer significantly. Since the device according to the invention also high harmonic frequencies, ie very high frequencies, for example, in the range greater than 300 Hz can be generated, this results in a further adjustment parameters for a particularly high heat transfer.

The rate of heat transfer significantly 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-forming mechanisms. Thus, for example, a higher degree of reaction conversion of the precursor mixture can be achieved with a comparable residence time, or the activity can be increased in, for example, catalytic materials. 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, disseminates the adjustable particle properties and simplifies the process control.

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

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

In a particularly preferred embodiment, at least partial coating of particles takes place by means of 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 emulsion at least includes all components which are necessary for the formation of the particles to be coated. The liquid phase in the suspension or the outer phase in the emulsion contain at least all coating components. By choosing a suitable thermal treatment regime, it is thus possible to form the solid particles and at least partially coat these particles.

The finely divided particles produced in the pulsating hot gas stream according to the invention are finally separated from the hot gas stream with a suitable separator. The hot gas is optionally before entering the Abscheideinrichtung cooled to a temperature required depending on the type of separator. In a preferred embodiment, the separation of the particles formed from the hot gas stream at temperatures above 300 ° C, preferably above 500 ° C, more preferably above 600 ° C, for example by a cyclone or a hot gas reactor. This can be prevented, for example, that highly reactive particles hot gas components, such as water record. The hot gas can be cooled in this embodiment, if necessary after the filter.

Further advantages and features of the invention will become apparent from the following description of exemplary embodiments. Showing:

1 the schematic diagram of an apparatus for the thermal treatment of a raw material with a combustion chamber, a reaction space and an integrated in the reaction space insert, wherein the combustion chamber is variable in geometry;

2 the schematic diagram of a device according to 1 with a different variability of the combustor geometry.

In 1 one recognizes the schematic diagram of a reactor for the thermal treatment of a raw material within a periodically unsteady swinging hot gas stream. This hot gas flow is through a flame 1 on a burner 2 What causes this fuel 3 and combustion air 4 be supplied. The flame 1 it burns in a combustion chamber 5 ,

By fuel is meant fuel gases such as natural gas, methane, hydrogen or liquid fuels such as alcohol, etc. For the purposes of this application, combustion air is generally understood to mean an oxidizing agent which provides the oxygen required for the combustion. In addition to air, this includes, for example, pure oxygen or oxygen-enriched air, etc.

In principle, it is possible to operate the flame in a foreign-controlled manner by means of a corresponding oscillating supply of the flame with a periodically modulated fuel / air mixture or with a temporally periodically modulated flow of combustion air. The variability of the mass flow of fuel / air mixture is particularly preferred in the case of premix combustion or a change in the mass flow of the combustion air, in particular in the case of a diffusion combustion.

Incidentally, the combustion is operated so that it has a periodic-transient, oscillatory operating state. Here, the frequency of the pulsating combustion z. B. influenced by the geometry of the combustion chamber as well as by the process temperature.

The pulsating hot gas flow ultimately generated by the pulsating flame flows through a coupling tube 6 in a reaction room 7 whose wall 8th is gas and heat. The heat-sealing can be ensured in particular by a separate insulation.

In the from the coupling tube 6 outgoing exhaust gas flow 9 becomes on the one hand a raw material to be treated 10 abandoned as well as cooling air 11 , This forms a hot gas stream 12 passing through the reaction space 7 flows through and is passed at the end by a hot gas filter or cyclone, not shown here, in which the in the reaction space 7 thermally treated raw material 10 is separated from the hot gas stream.

It is essential now that in the reaction space 7 an insert 13 is provided, the one opposite the reaction space 7 reduced cross-sectional area 14 having.

In the example shown here is this use 13 formed as a single tube and has a flow-through axial length 15, which is only a fraction of the total length of the reaction space 7 Has. Besides, the use is 13 essentially gas-tight to the wall 8th connected to the reaction space, so that the hot gas flow 12 completely through the radial inside free cross section of the insert 13 flows, but not laterally past this.

The use 13 is adjustable in its axial length 15, so that there is the possibility to adjust it in its length such that it is at the oscillation frequency of the periodically unsteady combustion process in the combustion chamber 5 is tuned so that the excited by this periodic transient hot gas flow 12 as they pass through the insert 13 resonantly excited and so in the field of this use 13 into a foreign or forced excited vibration. The resonances of the excitations can be up to the factor 10 walk.

The resonant frequency within the insert 13 is in particular dependent on the temperature of the hot gas stream 12 since this temperature affects the speed of sound relevant to resonance generation.

The use 13 is referred to below as the second resonator.

In the example shown here is also the combustion chamber 5 by the presence of a sliding floor 16 adjustable. In the following, the assembly described so far is also referred to as the first resonator. With the adjustability of the first resonator has a further manipulated variable on the one real resonance within the second resonator so the use 13 in the reaction room 7 can be adjusted.

To illustrate and illustrate the meaning and operation of two frequency tunable resonators in the reactor described herein, an example calculation is presented below without, however, wanting to limit the generality by this specific example 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 should 1 stable oscillating burning in a temperature range of the flame 1 or the exhaust stream 9 which of the flame 1 is generated, between 800 ° C and 1,800 ° C. Depending on the selected combustion temperature, sound velocities of between about 630 m / s and 830 m / s are established in the first resonator. (For simplicity, only air as the medium is used here and not with the complete exhaust gas composition.) According to the set length of the first resonator, oscillation frequencies occur when self-excited combustion oscillations occur in the first resonator between approx. 160 Hz and approx. 420 Hz. The lowest temperature of 800 ° C and the largest length of the first resonator of 1.0 m give z. B. the lowest frequency of the oscillating ¼-wave resonator of about 160 Hz. With this, the subsequent second resonator can be excited in the reaction chamber to resonance.

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

In the case of a selected through-flow length 15 of the second resonator of 2.0 m, the resonance fundamental frequency would be approximately 160 Hz at the highest material treatment temperature of 800 ° C. and would therefore be just at the lowest, adjustable oscillation frequency in the first resonator at 800 ° C. Flame / exhaust gas temperature resonantly excitable.

If, however, a material treatment temperature in the second resonator of 200 ° C. is desired, then the resonant frequency of the second resonator would be approximately 105 Hz at this temperature and a through-flow length 15 of the second resonator. The second resonator would therefore no longer be through the first resonator with its minimum Oscillation frequency at 800 ° C of 160 Hz resonant to the fundamental vibration excitable.

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

It is easy to see from the illustrated example the advantages that arise when both resonators can be tuned in frequency to one another and to the desired temperatures via individual geometry settings.

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

In the hot gas stream 12 transported commodity particles are thus initially in the field before use 13 with the hot gas flow 12 with the in the reaction room 7 existing frequency and amplitude applied, then within the free cross section 14 of the insert 13 from the flowing there at least at elevated speed hot gas flow and then again in the flowing at a lower speed hot gas flow in no longer limited in cross-section region of the reaction space. It can with a corresponding vote of the in the combustion chamber 1 generated vibration and the length 15 of the insert 13 the flow through the insert 13 not only with a fundamental but possibly also with a harmonic are brought into resonance, reflecting the intensity of the field of use 13 caused corresponding thermal treatment increased accordingly.

If the raw material consists of a mixture of raw materials, in which it makes sense to have different intensities of the thermal treatment in time succession, this can thus be adjusted accordingly by the appropriate axial position of the insert 13 within the reaction space 7 is selected as needed.

In the 2 is a substantially same device as in 1 shown. In this case, the combustion chamber is different 5 by the way he acts as a resonator on the flame burning in him 1 is agreed. Instead of the volume of the combustion chamber 5 To change a sliding floor, as in the 1 is shown, in this embodiment, the flame 1 at the burner 2 radially surrounding tubular insert 18 provided in the axial direction 19 the combustion chamber 5 is displaceable, so in the combustion chamber 5 generated vibration according to the use 13 to tune so that in this a resonance with respect to the flowing through him hot gas flow 12 is produced.

literature

• /1/ AA Putnam and WR Dennis: "Organ Pipe Oscillations in Flamefilled Tubes"; Proc. Comb. Inst. 4, p. 556 ff., 1952
• / 2 / H. Büchner: "Experimental and theoretical investigations of the formation mechanisms of self-excited pressure oscillations in premixed combustion systems"; Dissertation University of Karlsruhe, Shaker-Verlag Aachen, 1992
• / 3 / DD 114 454 B1
• / 4 / DD 155 161 B1
• / 5 / DD 245 648 A1
• / 6 / DE 10 2006 046 803 A1
• / 7 / DE 101 09 892 B4
• /8th/ DE 10 2006 046 880 B4
• / 9 / DE 10 2006 032 452 B4
• / 10 / Chr. Bender: "Measurement and calculation of the resonance behavior coupled Helmholtz resonators in technical combustion systems"; Dissertation Universität Karlsruhe KIT, 2010

LIST OF REFERENCE NUMBERS

1

flame

2

burner

3

fuel

4

combustion air

5

combustion chamber

6

pipe coupling

7

reaction chamber

8th

wall

9

exhaust gas flow

10

raw material

11

cooling air

12

Hot gas stream

13

commitment

14

Cross sectional area

15

Axial length

16

Adjustable bottom

17

arrows

18

tube insert

19

axially

Claims (6)

Device for thermal treatment of a raw material ( 10 ), with a combustion chamber ( 5 ), in which a periodically unsteady, oscillating flame ( 1 ) burns to produce a pulsating exhaust gas flow ( 9 ), which by a to the combustion chamber ( 5 ) subsequent reaction space ( 7 ) flows, characterized in that in the reaction space ( 7 ) flowed through by the exhaust stream, in its cross-sectional area ( 14 ) opposite the reaction space ( 7 ) reduced use ( 13 ) is provided, which has a length (15) which is shorter than a total length of the reaction space ( 7 ). Device according to claim 1, characterized in that the length (15) of the insert ( 13 ) is changeable. Device according to claim 1 or 2, characterized in that the combustion chamber ( 5 ) is variable in geometry. Device according to one or more of the preceding claims, characterized in that the flame ( 1 ) is externally excitable to vibrations. Process for the thermal treatment of a raw material in a periodically transient oscillating exhaust gas flow ( 9 ) caused by a periodically unsteady flame ( 1 ), wherein the exhaust gas flow through a reaction space ( 7 ), characterized in that the exhaust gas flow in a in the reaction space ( 7 ) intended use ( 13 ) with a relative to the reaction space ( 7 ) reduced cross-sectional area and one compared to the total length of the reaction space ( 7 ) shorter length (15) is excited to a resonant oscillation. A process for the production of finely divided particles in which the finely divided particles form from a precursor mixture which comprises at least all components for forming the finely divided particles, wherein the particle formation and / or a thermal particle treatment takes place in a vibrating exhaust gas stream and the particles subsequently formed from Waste gas stream to be separated, characterized in that the oscillating exhaust gas flow is excited in a resonant section.

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