EP2347177B1 - Device for burning a fuel/oxidant mixture - Google Patents

Description

The invention relates to a device for combustion of a fuel / oxidant mixture in a highly exothermic reaction consisting of a reactor with a combustion chamber containing at least a first porous material and at least one second porous material in separate zones, wherein the zones are designed so that an exothermic reaction can take place only in the second zone and is provided with one or more supply lines for the fuel and for the oxidizing agent.

In the documents DE 43 22 109 C2 and DE 199 39 951 C2 Devices are described which are designed as so-called pore burners.
The combustible gas mixture then first flows through a region, hereinafter referred to as zone A, which has such small, effective pore diameters that do not permit stationary flame propagation, ie, the first porous zone is effectively similar to a flashback flame arrester. However, the subsequent actual combustion region, hereinafter referred to as zone C, has pore sizes large enough to permit steady state combustion. As a criterion for the flame propagation inside a porous matrix is in the literature (for example Babkin et al. in "Combustion and Flame", Vol. 87, pp. 182-190, 1991 ) indicates a critical Péclet number of Pe> 65.
As a porous combustion chamber filling of pore reactors for chemical industrial plants materials such. As alumina, zirconia, silicon carbide, among others, are used, which in addition to high temperature resistance also have sufficient corrosion resistance. Preferably used to produce the porous combustion chamber beds of temperature-resistant, ceramic balls, saddles and similar bodies, such as, for example used as a disordered packing for thermal separation processes. Beds are preferred because they allow a simple cleaning of deposits, for example, in the hydrogen chloride synthesis resulting salt residues, which originate from the fuel gases. Also for pore burners to produce hydrogen chloride zones of different pore structure or size according to DE 43 22 109 C2 arranged. This is done by using differently sized fillers for zones A and C. In addition, structured packings and foams in zones A and B can also be used.

According to the document DE 199 39 951 C2 can be arranged between the formed with packing, porous structures of the two zones with different pore size preferably another support grid, which prevents the discharge of smaller filler of the zone A in the interstices of the larger packing of the zone C. Also, at the gas outlet from the zone C is in burners, in which the gases do not emerge vertically upwards, another, gas-permeable carrier grate which closes the combustion chamber. This makes it possible to arrange the reactor in any position despite loose bulk of the packing in the combustion chamber.

The porous reaction space is preferably surrounded by a corrosion-resistant, cooled wall, which consists for example of graphite impregnated with synthetic resin. The cooling can be done by cooling water, air or the fuel gases themselves. Between the cooled wall and the combustion chamber is then preferably an insulating intermediate layer of high-temperature resistant, corrosion-resistant and thermally insulating materials, which prevents heat loss and ensures that prevails in the combustion chamber at any point the desired combustion chamber temperature. According to the document DE 199 39 951 C2 A strong insulation allows a nearly adiabatic process control, which does not affect the temperature of the cooled wall due to the combustion process. The adiabatic process allows, for example, a simple scale-up of such chemical reactors, since the heat transport properties to the cooled walls are irrelevant and the entire process in the flow direction can be viewed almost one-dimensionally.
In a pore reactor, the reaction is carried out within a porous matrix of temperature-resistant material. Unlike conventional reactor devices, it is not necessary to arrange the reactor in a voluminous combustion chamber or downstream of such. From the reactor itself flow the hot reaction products without direct flame formation.
In the DE 43 22 109 C2 It is proposed to use a significantly lower and for the combustion zone a significantly higher than the critical Péclet number of Pe = 65 for the first zone.

If the pore reactor is ignited, the combustion stabilizes at the interface between the two zones. Due to the small pore dimensions in the first zone, there is no combustion in this region in the stationary state but only preheating of the gas mixture. This property also meets the stringent safety requirements for a risk of re-ignition in chemical plants.

Due to the excellent heat transfer between gas and solid phase within the porous matrix, these are approximately in thermal equilibrium. The approximate thermal equilibrium between the gas phase and the solid phase and the intensive mixing within the pore body substantially causes the disappearance of free flames in the combustion zone equipped with larger pores. The combustion process now takes place in an extended reaction area, which can be characterized more as a combustion reactor than as a combustion chamber with free flames.

According to the document DE 199 39 951 C2 the premixing chamber is a component and safety-relevant component of the device described.

A disadvantage of the known designs is the localized temperature detection in the reaction zone by thermocouples. Another disadvantage of pore reactors, the porous layers of which are composed of bulk solids, is that the bulk material are entrained in a larger or suddenly increased gas flow from the gas stream and thus lead to changes in bulk density and the Peclet number. A safe process under heavily varying gas flow conditions, especially for the controlled burning of large amounts of halogen-containing gases in case of accidents is possible only to a very limited extent.
Furthermore, from the DE 197 29 718 A1 a burner for a burner for gaseous fuels known. This burner body has porous material with interconnected hollow bodies and is divided in the gas flow direction into at least two zones.
The object of the invention is to provide a reactor which allows the abovementioned exothermic chemical reactions while reducing the disadvantages described in more detail above.

The object of the invention is achieved with a device having the features of claim 1. In a preferred embodiment of the device is provided that the combustion chamber and the porous materials are made of materials that withstand a temperature of 1000 ° C to 2400 ° C.

Advantageously, a temperature monitoring device and an ignition device are arranged in the zone B. The temperature monitoring device is preferably an infrared sensor that detects a range of 2 to 200 cm ² at the interface to the zone C. A detection over the specified range is not possible according to the known prior art. According to the invention, the device is arranged vertically and the zone A is above the zones B and C. The bulk bodies of the zones A and C are arranged on supporting grids. A loosening or swirling of the bulk material and a change in the flow resistance and thus the Peclet number is prevented by the weight of the bulk body and the supporting grates. In addition, by arranging the zone A above the zone C loosening of the loose layer is avoided in principle, because the bed C is thereby pressed in the direction of gravity against the support grid.
According to another embodiment of the invention, it is provided in the method that the fuel / oxidant mixture and the additionally supplied gas are at least partially mixed in a premixing device, which is connected upstream of the reactor. A corresponding device according to this development is that it has a premixing chamber for the fuel / oxidant mixture, from which this fuel / oxidant mixture flows into the combustion chamber.
The premix chamber used here according to the invention enables a much better mixing and a more effective conversion of the reactants, which, for example, allows a reduction of the required methane content in the hydrogen chloride synthesis.
In particular, in an advantageous development of the invention, it is provided that the premixing chamber is designed such that the component of the flow velocity of the mixture in the premixing chamber relative to the combustion chamber is greater than the flame velocity in the combustion chamber. As a result, the premixing chamber is dimensioned such that a flame which possibly arises in the premixing chamber is blown out in the event of inadvertent ignition over the entire operating range, for example during startup.

A further improvement in this respect is achieved in a development of the invention by means of a cooling of the premixing chamber.

According to another advantageous development, provision is made for a porous material with contiguous cavities which are large enough for flame development to be provided in the combustion chamber.

In particular, the porosity of the coherent voided material in the direction of flame evolution changes to larger pores, with a Péclet critical number at an inner pore size interface above which flame evolution occurs and below which it is suppressed.

Combustion stabilization is achieved by increasing the pore size in the direction of flow, with a critical Péclet number in one zone of the porous pore size material above which flame evolution occurs and below which it is suppressed.

The application of this technique for the production of chemical products, such as hydrogen chloride, or for post-combustion of noxious gases, such as halogen-containing gases, not only has an advantageous effect on the combustion itself, but also allows those plant parts in which the pore reactor is integrated to design and arrange advantageous.

The premixing chamber is preferably made of corrosion-resistant materials, eg. B. made of resin-impregnated graphite. Enamelled or fluoroplastic-lined steel parts can also be used to construct a mixing chamber. From the premixing chamber, the premixed gases preferably enter the zone A of the pore reactor through a grid of corrosion-resistant material, for example silicon carbide, aluminum oxide or the like. As previously mentioned, a number of chemical reactants, such as. As chlorine and methane, under the influence of UV radiation for auto-ignition. The auto-ignition in the premix chamber should but for security reasons be avoided. A grate and the design of zone A is chosen so that no or only very little UV radiation from the zone A or C reaches the premixing chamber, which could lead to the ignition of the gas mixture of chlorine and methane into the premixing chamber.

Particularly noteworthy is the stability of the combustion in the described pore reactor. Compared with the hydrogen chloride reactors designed according to the prior art, which react very sensitively to pressure and volume fluctuations of the gases, in which case the flame can easily extinguish, the combustion reaction in the pore reactor, by contrast, by the heat capacity of the packing in zone C even in short-term failure Gases ignited immediately. For safety reasons, however, it is expedient to turn off the other gas in the event of failure of one of the gases and to connect an inert gas purging. Even after several minutes, the reactor can then be put back into operation without delay even after an inert gas purge without delay.

The ignition and preheating of the reactor can be done with a fuel gas (hydrogen, methane, etc.) and air. However, this can also be a conventional ignition device, which is common for such chemical reactors used. After complete heating of the zone C can be gradually or immediately to the reactants, such as chlorine, methane and air, converted.

Sudden load fluctuations up to 50% of the rated load, which can occur in such systems can be controlled with the described pore reactors without difficulty.

The scale-up for technical systems is surprisingly simple due to the technical teaching for the dimensioning of pore reactors, especially in the previously described, adiabatic process management, must be complied with regardless of the size defined flow conditions in the zones A and C.

The pore reactors described below and modified for chemical processes are parts of process plants for the production of hydrochloric acid or for the afterburning of halogen-containing, preferably chlorine-containing compounds.

Such a system has, for example, a modified pore reactor, a heat exchanger for the cooling of the reaction products or for the use of their heat content and depending on the type of plant and an absorber, scrubber or scrubber at transition pieces between the apparatus, pumps, piping and the usual safety, measuring - and control devices on. Due to the reaction and the good mixing of the gases in the pore reactor, a voluminous combustion chamber is not required compared to the prior art. The reactor can be directly attached to the following apparatuses, e.g. As a heat exchanger, a quencher with absorber or other devices are connected. After cooling the reaction products flowing out of the reactor in a heat exchanger or after a quench, a partial stream of the cooled gas or gas mixture, as described above, is returned to the reactor. Alternatively, as described, another gas, for. As water vapor, are added.

Depending on the requirements of the product, only parts of the process plant can be required, for. As reactor and gas cooler or reactor and quench, depending on whether the product is gaseous or dissolved in water required as hydrochloric acid.

Another embodiment of a plant for the production of hydrogen chloride used as a hydrogen supplier hydrocarbon gases, eg. As natural gas, methane, propane, etc., chlorine and air. The combustion takes place according to the highly simplified illustrated reaction equations (1) and (2):

CH ₄ + O ₂ + Cl ₂ -> CO + 2HCl + H ₂ O (1),

CO + 1 / 2O ₂ -> CO ₂ (2).

This combustion is difficult to achieve in systems according to the prior art, since unfavorable boundary conditions can cause soot, which pollutes the system and the acid. The described special properties of the pore reactor unexpectedly allow a stable, soot-free combustion even for this critical application.
Pore reactors for the afterburning of halogen-containing exhaust gases or vaporizable or gaseous, halogen-containing, organic compounds are, as will become clearer later with reference to embodiments, carried out so that the oxidizing agent and fuel gas are preferably premixed injected into the premixing chamber. Due to the high reaction enthalpy of oxidant and fuel gas, a stable support flame is generated in the combustion zone C. The nachverbrennende gas or gas mixture is injected via an inlet pipe in the premixing preferably via a support grid in front of the zone A of the pore reactor and mixed with the fuel / oxidant mixture. To control the temperature of the post-combustion process, it is preferable to use a corresponding excess of the oxidizing agent, in particular air. To control the temperature in the zone C of the pore reactor, the temperature is measured for example by means of an infrared pyrometer and further processed the signal for the oxidant control. The subsequent post-combustion facilities differ from the plant components described above, depending on the halogen content of the exhaust gases. At low halogen content, in which the extraction of hydrochloric acid is not in the foreground, only a quencher and a scrubber is generally followed. Other accompanying substances, eg. B. sulfur compounds o. Ä., Can also be subjected to the described facilities a harmless disposal. This also applies in principle to halogen-containing or sulfur-containing vaporizable substances or mixtures. Since the described post-combustion with pore reactor do not require a combustion chamber in the conventional sense, such systems can be made very compact and inexpensive.

• erfindungsmäßig weist der Brennraum mindestens zwei Zonen mit Material unterschiedlicher Porengröße auf, zwischen denen die Porengröße die kritische Péclet-Zahl ergibt;
• erfindungsmäßig weist das Material mit zusammenhängenden Hohlräumen zumindest teilweise eine Schüttung von Körpern auf, wie sie für Festkörperschüttungen oder geordnete Packungen bei thermischen Trennverfahren eingesetzt werden, wie Kugeln oder Sattelkörper;
• erfindungsmäßig ist an der Grenzfläche für Zonen unterschiedlicher Porosität ein Tragrost vorgesehen, um einen Austrag der Körper aus einer Zone in die andere zu vermeiden, wobei der Tragrost gekühlt ist;
• vorzugsweise ist die Brennkammer für Flammenstabilität bei Über- und Unterdruck ausgelegt;
• vorzugsweise werden die zugeführten Produktgase alle oder nur zum Teil vorgewärmt, um nach Zumischung von kühlenden Dämpfen wie z.B. Wasserdampf ein Auskondensieren in der Vormischkammer vermeiden (auskondensierte Bestandteile würden den Reaktionserfolg erheblich verschlechtern und zur Bildung von unerwünschten Nebenprodukte führen);
• vorzugsweise wird die Vormischkammer nicht gekühlt, sondern deren Wände werden gezielt über Taupunkttemperatur der Gasmischung gehalten, um so ein Auskondensieren von Gasbestandteilen zu verhindern.

Die Brennkammer kann nun auch für Flammenstabilität bei Über- oder Unterdruck ausgelegt werden, was im vorbekannten Stand der Technik nur zu ungenügender Flammenstabilität geführt hätte. Aufgrund der Erfindung und ihrer Weiterbildungen steht aber ein wesentlich größerer Druckbereich zur Verfügung, so dass eine entsprechende Auslegung für einen großen Druckbereich in einer dem Fachmann geläufigen Weise, insbesondere auch für Über- oder Unterdruck, zu einer wesentlichen Erhöhung der Flammenstabilität führen kann. Regelungen können dabei weitgehend entfallen.Due to the foregoing, detailed embodiments, the following features of the invention result:

• According to the invention, the combustion chamber has at least two zones of material of different pore sizes, between which the pore size gives the critical Péclet number;
• According to the invention, the material with contiguous cavities at least partially a bed of bodies, as they are used for solid beds or ordered packings in thermal separation processes, such as balls or caliper body;
• erfindungsmäßig a support grid is provided at the interface for zones of different porosity to avoid discharge of the body from one zone to the other, wherein the support grid is cooled;
• Preferably, the combustion chamber is designed for flame stability at positive and negative pressure;
• Preferably, the product gases supplied are all or only partially preheated to avoid condense in the premixing chamber after admixture of cooling vapors such as water vapor (condensed components would significantly reduce the success of the reaction and lead to the formation of unwanted by-products);
• Preferably, the premixing chamber is not cooled, but its walls are selectively maintained above the dew point temperature of the gas mixture so as to prevent condensation of gas constituents.

The combustion chamber can now also be designed for flame stability under positive or negative pressure, which would have led to insufficient flame stability in the prior art. Due to the invention and its developments but a much larger pressure range available, so that a corresponding design for a large pressure range in a familiar to the expert way, especially for over or under pressure, can lead to a significant increase in flame stability. Regulations can be included largely eliminated.

In particular, in a preferred development of the invention, a combustion chamber insulation is provided for an approximately adiabatic combustion guidance without wall effects. Adiabatic combustion management is particularly advantageous for increasing the conversion rate.

In addition to the combustion, it is also possible to obtain reaction products, for example in the hydrogen chloride gas combustion for hydrogen chloride synthesis. For this purpose, it is provided in a preferred development of the invention that the device has a device for obtaining or separating reaction products from the combusted fuel / oxidant. In particular, for the synthesis of hydrogen chloride is provided that the device is designed for a chlorine-containing compound in the fuel and methane in the oxidizing agent for burning the hydrogen chloride and has a procedural device for the recovery of hydrogen chloride or hydrochloric acid behind the combustion chamber. The named design is known to the person skilled in the art. In particular, it should be noted that the corresponding safety devices are taken into account and the materials are correspondingly corrosion-resistant to chlorine.

As already explained above, the invention can be used not only for burning and for hydrogen chloride synthesis, but also as a device for post-combustion of exhaust gases and, in particular, for cleaning. For example, it is possible for some in the embodiments shown in the following description, nachverbrennen proportions of chlorine-containing organic compounds without problems and thus to dispose of harmless.

• Fig. 1 Teildarstellung einer Porenreaktor-Anlage

Other measures and features of the invention will become apparent from the following description of an embodiment with reference to the accompanying drawings. Show it:

• Fig. 1 Partial representation of a pore reactor plant

For the following embodiment, the above-explained in more detail pore reactor 1 was selected, which has particular advantages over other types of reactor with which the invention can be formed. The essential feature of the invention is that the flame is cooled by supplying an additional gas to the fuel / oxidant mixture, which can be realized in all conceivable reactor types. Therefore, the following description of the embodiment alone based on the pore reactor 1 is not to be considered as limiting.

An embodiment of a pore reactor 1 according to the invention is shown in FIG Fig. 1 shown. The housing of the pore reactor 1 consists of a thin-walled, high temperature resistant ceramic inner lining 8 of oxide ceramic with a thickness of 2 mm to 50 mm, a Graphitstützmantel 9 and a spaced therefrom outer steel shell 10. Between the Graphitstützmantel 9 and the steel shell 10 cooling water is passed, which leaves the pore reactor 1 at the nozzle 12. Further, the defined zones A - 2, the zone B - 4 and the zone C - 3 are shown. The zone C - 3 acts as a combustion zone, in which the combustion takes place. In Zone A - 2, ignition is avoided by appropriate dimensioning. The combustion zone C - 3 is filled with packing for this purpose, whereas the zone A - 2 is filled with pore bodies which act as a flame barrier. Zone A - 2 and Zone C - 3 are spaced by Zone B - 4. At the interface between the zone B - 4 and the zone C - 3, the large-area temperature monitoring is carried out by access of a temperature sensor in the temperature measuring socket 6. About the premixing chamber 5, the gas mixture is passed from above into the pore reactor 1. The reaction of the reaction mixture takes place in the zone C - 3, which is arranged on the support grid 7 and is additionally cooled by the heat exchanger 11 arranged underneath. The wall temperature of the reaction zone C - 3 is monitored by a wall temperature sensor 13.

LIST OF REFERENCE NUMBERS

1

pores reactor

2

Zone A

3

Zone C

4

Zone B

5

premix

6

Socket for temperature sensor

7

support grid

8th

ceramic interior lining

9

Graphitwandung

10

Stahlaußenwandung

11

heat exchangers

12

Cooling medium connection

13

Wall temperature sensor

Claims (10)

1. Device for burning a fuel/oxidant mixture in a highly exothermic reaction, the device consisting of a reactor (1) comprising one or more feed lines for the fuel and for the oxidant, which lines are arranged such that the fuel/oxidant mixture is guided into the reactor (1) from above, and comprising a combustion chamber that contains at least one first porous material in a zone A (2) and at least one second porous material in a separate zone C (3), wherein zones A (2) and C (3) are of different porosities, wherein the zones are configured such that the first zone A (2) is located above zone C (3), which zone C functions as a combustion zone whereas ignition is prevented in zone A (2) by appropriate dimensioning, and wherein zones A (2) and C (3) are separated by a zone B (4) such that a distance is formed between zone A (2) and zone C (3) which is arranged before zone C (3) in the flow direction of the fuel/oxidant mixture and is from 10 mm to 4000 mm, wherein an additional gas is fed to the fuel/oxidant mixture such that the flame is cooled by feeding the additional gas to the fuel/oxidant mixture, wherein at least one support grate (7) is cooled, which grate is provided at the interface for the zones of different porosities, and wherein the porous materials are at least partially formed as a filling of bodies, as are used as packed beds or structured packing in thermal separation processes.
2. Device according to claim 1, wherein the distance formed by zone B (4) between zone A (2) and zone C (3) is from 20 mm to 500 mm.
3. Device according to either claim 1 or claim 2, wherein the combustion chamber and the porous materials consist of materials that are resistant to a temperature of from 1000°C to 2400°C.
4. Device according to claim 3, wherein a temperature monitoring device (6) and optionally an ignition device are arranged in zone B (4).
5. Device according to claim 4, wherein the temperature monitoring device (6) is an infrared sensor.
6. Device according to claims 1 to 5, wherein a premixing chamber (5) for the fuel/oxidant mixture is provided.
7. Device according to claim 6, wherein the premixing chamber (5) is configured such that the component of the flow speed of the mixture in the premixing chamber (5) that is related to the direction towards the combustion chamber is greater than the flame speed in the combustion chamber.
8. Device according to either claim 6 or claim 7, wherein the premixing chamber (5) is cooled.
9. Device according to at least one of claims 1 to 8, wherein the combustion chamber is configured for flame stability during overpressure and/or negative pressure.
10. Device according to at least one of claims 1 to 9, wherein the combustion chamber is temperature-controlled for carrying out combustion approximately adiabatically without thermal wall effects.

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