WO1999041192A1

WO1999041192A1 - Tube furnace for carrying out continuous endothermic gas reactions and use of same

Info

Publication number: WO1999041192A1
Application number: PCT/EP1999/000228
Authority: WO
Inventors: Heiko Mennerich; Eberhard Aufderheide; Rudolf Jeschar; Andreas Birtigh; Ernst Gail; Hans-Hermann Kriegeris; Ralf Jennes
Original assignee: Degussa-Hüls Aktiengesellschaft
Priority date: 1998-02-11
Filing date: 1999-01-16
Publication date: 1999-08-19
Also published as: DE19805481A1; AU2279699A; ZA991067B

Abstract

The invention relates to a tube furnace (10) for continuous endothermic gas reactions, comprising one or more chambers (100), each of which (100) is divided into a heating chamber (101), in which reaction tubes (110) are placed in which reaction gases are able to circulate, and a combustion chamber (102) with at least one assigned burner (120). The burner(s) (120) are arranged in such a way that the combustible gases produced during operation flow into the assigned heating chamber (101) and from the outside heat the reaction tubes (110) positioned in said heating chamber to the temperature required for the reaction. At least one element for circulating the combustible gases is arranged in the chamber (100). According to the invention, at least one flue gas outlet device which is preferably configured as a heat recovery unit (121) and through which the combustible gases leave the reactor is positioned directly adjacent to the burner(s). The preferred circulating element is a combination of burner free jet (134) and diffuser (135). The tube furnace is suitable for the production of hydrocyanic acid according to the 'hydrocyanic acid - methane - ammonia' method.

Description

1

Tube furnace for carrying out continuous endothermic gas reactions and its use

description

The invention relates to a tube furnace or tube reactor for carrying out gas reactions and its use for the production of gaseous substances. In particular, the tubular reactor according to the invention is used for the production of blue acid according to the BMA process (blue acid methane ammonia process) in ceramic tube bundles.

In particular, the invention is directed to a tube furnace for continuous endothermic gas reactions, comprising one or a plurality of chambers with ceramic tubes arranged freely suspended in the respective chamber, through which reaction gases can flow, and with at least one burner assigned to the respective chamber, the or the burner is or are arranged so that the combustion gases generated during operation flow into the associated chamber and the ceramic tubes therein are brought from the outside to the temperature required for the desired reaction, the individual components in the reactor according to the invention energetic, process and emission aspects are arranged in a special way to each other and side by side.

The previously known tube furnace for carrying out gas reactions, especially at temperatures above 900 ° C, for. B. at temperatures between 1000 and 1500 ° C, consist of a series of parallel chambers, which are equipped with freely suspended ceramic tubes or tube bundles. Each of these chambers is heated on its own. The flue gas is extracted via a separate branch duct, which is connected to the individual chambers via extraction hoods 2

is. The vertically arranged tubes, the interior of which represents the actual reaction space, are supplied with the heat required for the reaction through the tube walls, for which the chambers have to be lined appropriately temperature-resistant. The heat is generated by gas or oil burners. The combustion air is heated up recuperatively. The burners, of which two are required per chamber, are arranged in the lower area of the chamber, so that the entire length of the reaction tubes can be brought to the required reaction temperature if possible. The heat of the escaping flue gases can be used for air preheating and / or for steam generation. Such tube furnaces are described for example in DE-PS 10 00 791 and 10 41 476.

In the case of several furnaces, it is possible to connect two furnaces to a common branch duct, which is then arranged between these two furnaces, and to utilize the heat content of the flue gas in a waste heat boiler to produce steam via a collecting duct with the aid of an induced draft fan.

The recuperators for preheating the combustion air are each arranged between two chambers.

A disadvantage of these aforementioned furnaces is their rather large outer surface, which leads to energy losses.

To a certain extent this disadvantage is avoided by the furnaces according to DE-A-31 34 851.

DE-A 31 34 851 discloses a tube furnace for carrying out gas reactions, in particular for the production of hydrocyanic acid according to the BMA process, in ceramic tube bundles which are arranged freely suspended in heating chambers within the bricked furnace, which is provided with a metal construction on the outside are the main components of the burner, a flue gas 3

Branch duct and recuperators, the furnace being in the form of a cuboid or cube, which receives at least two heating chambers arranged in a twin-like manner with recuperators arranged adjacent to the center of the furnace, as well as a flue gas branch duct arranged between the recuperator rooms in the form of a structural unit, and each heating chamber to a maximum has only one burner. Finally, the furnace according to DE-A-31 34 851 is preferably designed such that one or more heat exchangers for the combustion air are arranged in the flue gas branch duct.

Although some of the aforementioned disadvantages can be avoided in this way, in this type of tube furnace it is still disadvantageous that, due to the durability of the material of the recuperators, only temperatures of

Air preheating of up to approx. 500 ° C can be achieved. This is not without problems, because it means that large amounts of energy in the hot flue gas can only be used to generate steam.

Another disadvantage is generally the uneven distribution of the heat-transporting flue gases between the tubes of the ceramic reactor tube bundle. The uneven distribution in the horizontal direction leads to an uneven distribution of the temperature in the individual reaction tubes, which results in a loss of yield.

The unequal distribution of the horizontal tube temperature is supported in today's reactor in that the tube bundle is flowed from the narrow side, which worsens the energy input into the middle tubes of the tube bundle.

A generally unfavorable energy input present in the entire known prior art also has the consequence that very high heating gas temperatures are necessary. Because of these high temperatures Nitrogen oxides are formed, which make aftertreatment of the heating exhaust gases necessary.

In addition to the tube furnaces or tube reactors mentioned, monolithic cocurrent or countercurrent reactors are known for carrying out gas reactions, in particular for carrying out the BMA process, as described, for example, in German patent applications DE-A 195 24 158, DE-A 196 53 989, DE- A 196 53 991 are described.

Here, the heating and reaction channels are combined in a monolithic arrangement, whereby they are in intimate contact. These reactors require significantly less energy than the tube furnaces or tube reactors described above. However, a disadvantage of these monolithic reactors is that they have a peak in the middle of the reactor in the temperature profile. As is realized in the invention, the aim is a continuously falling temperature profile in the axial pipe direction.

DE-PS 884 348 (Lonza) teaches a generic tube furnace for the production of hydrogen cyanide from ammonia and methane. The tube furnace comprises a two-part chamber, one part of which is designed as a heating chamber with reaction tubes arranged therein and the other part of which is designed as a combustion chamber, and allows the combustion gases to be circulated. The combustion chamber comprises a diffuser, and the burner free jet sucks combustion gases out of the heating chamber through a connecting channel ((5) in FIG. 1). The combustion gases are drawn off laterally in the upper part of the heating chamber. A disadvantage of this tube furnace is that the arrangement of the exhaust opening for the combustion gases ((7) in Fig. 1) - on the side at the upper end of the heating chamber (= tube chamber) - increases the negative pressure on the flue gas exhaust and thus prefers the combustion gas in the heating chamber along the chamber wall on which the discharge opening is located, upwards flows. This creates an uneven flow and temperature profile and reduces the yield. Furthermore, the spatial separation of the exhaust opening for the combustion gases (= flue gases) and the burner free jet counteracts an intensive exchange of impulses and thus the combustion gas circulation.

In view of the prior art specified and discussed herein, it was therefore an object of the invention to provide a tube furnace or tube reactor of the type mentioned at the outset which allows endothermic gas reactions, in particular the BMA process, to be carried out in good yield.

The new reactor should be suitable for large-scale use, be as little polluting as possible and at the same time be inexpensive to implement with relatively simple means.

Furthermore, it was an object of the invention to provide a reactor which has a low specific energy consumption.

Another object of the invention was to provide a tube furnace with the lowest possible horizontal

Has temperature gradients within the tube bundle, so that a uniform temperature profile is achieved, which is conducive to a high yield.

Furthermore, the reactor to be created should have a modular design, so that several reactor modules, each with one or more bundles, can be heated with the aid of one or more combustion chambers.

In addition, the new reactor should be able to release less nitrogen oxide (NO _x ) exhaust gases compared to conventional reactors.

Another object of the invention was the use of the new reactor for carrying out gas reactions. It was also an object of the invention to provide a method for producing gaseous substances.

These tasks, as well as other tasks that are not listed individually and verbatim, but which can be derived or inferred from the contexts discussed in the introduction, are solved by a tube furnace or tube reactor of the type mentioned at the outset, which has the feature of the characterizing part of claim 1. A tube furnace (10) for continuous endothermic gas reactions was thus found, comprising one or one

A plurality of chambers (100), the respective chamber (100) being divided into a heating chamber (101) with reaction tubes (110) arranged therein, through which reaction gases can flow, and into a combustion chamber (102) with at least one assigned burner (120) The burner (s) (120) is or are arranged in such a way that the combustion gases generated during operation flow into the associated heating chamber (101) and the reaction tubes (110) located therein from the outside to the temperature required for the desired reaction bring and in the chamber (100) is arranged at least one means for circulating the combustion gases, which is characterized in that in the immediate vicinity of the burner or burners (120) at least one flue gas outflow device (123) is arranged through which the combustion gases leave the reactor . Appropriate modifications of the reactor according to the invention are protected under the subclaims which are referred to claim 1. Uses belonging to the invention, that is to say processes for carrying out endothermic gas reactions, are likewise the subject of claims for protection.

Characterized in that at least one means for effectively circulating the combustion gases is arranged in the chamber and in the immediate vicinity of the burners at least one flue gas outflow device through which the 7

Combustion gases escape from the reactor, arranged, it is possible to specify a tube furnace or tube reactor that allows the implementation of endothermic gas reactions, in particular the BMA process, in an excellent manner with high yield.

The burners of a preferred tubular reactor according to the invention are equipped with a heat recovery unit which serves to preheat the air, the fuel gas or the air / fuel gas mixture by means of the extracted combustion gas and is combined with the flue gas outflow device.

The hot combustion gases, which are generated during operation of the burner, are used several times, e.g. B. circulated three times between the combustion chamber and the heating chamber before they leave the reactor through a flue gas discharge device in the area of the burner. The circulation according to the invention is carried out by a fan or preferably by the impulse, the gases emerging from the burners and the additional formation of a driving pressure drop, which is generated by the diffuser according to a preferred variant of the invention. Due to the spatial proximity of the outflow device for the combustion gases and the burner and thus the burner free jet, there is an intensive pulse exchange between those leaving the reactor

Combustion gases and the burner free jet and thus to a stronger circulation (circulation) of the combustion gases (also called flue gases or heating gases) than is the case due to the pure injector effect of the burner free jet.

In particular, the reactor of the present invention has the following advantages: 1. The new reactor is suitable for large-scale use, less polluting and at the same time inexpensive to implement with relatively simple means.

2. Furthermore, the reactor specifically uses less energy because of the recirculation and

Flow management and arrangement of the flue gas outlet according to the invention has a low horizontal temperature gradient within the tube bundle, so that a uniform temperature profile is achieved, which is necessary for a high yield.

3a. The position of possible flow control profiles is variable and can be positioned in the heating chamber depending on the desired temperature profile.

3b. Furthermore, the reactor enables a modular

Construction so that several bundles of reaction tubes can be heated with the help of one or more combustion chambers.

4. As a result of the circulation of the combustion gases, in addition to the more uniform heating, a known reduction of the nitrogen oxides by recycling of combustion gas is achieved in one process step.

5. The mixture of combustion gas generated in the combustion chamber and low-temperature gas drawn in from the heating chamber results in a reduction in temperature peaks in the combustion zone, which suppresses nitrogen oxide formation.

6. The new reactor releases fewer nitrogen oxides compared to conventional reactors from the prior art, so that post-treatment of the discharged combustion gases can be largely avoided. A tubular reactor according to the invention is used to carry out gas reactions. For the production of hydrocyanic acid according to the BMA process, ceramic tube bundles are arranged within a heating chamber of the preferably bricked reactor, which is provided with a metal structure on the outside, usually freely suspended. The anchoring of the ceramic tubes freely suspended in or in the furnace chambers is done, for. B. m the way that the reaction tubes are attached in a cooling head equipped as Kuhlorgan. A specific embodiment of a cooling head which can be used with the invention is disclosed, for example, in DE 33 09 394 C2.

The aforementioned advantages are surprisingly achieved simply by the multiple circulation of the combustion gases and the uniform horizontal temperature level in the heating chamber caused by the outflow device arranged according to the invention.

In a particularly preferred modification of the invention, the tube furnace is characterized in that the means or means for multiple circulation of the combustion gases are one

Represent a combination of one or more burner free jets and one or more diffusers. The free jet emerging from the burner (s) entrains flue gas from the environment (water jet pump principle / injector principle), so that the mass flow required by the free jet increases along its length. In order to better overcome the pressure loss that the circulated flow generates in the reactor, a diffuser is preferably installed at a distance between 0.2 and 1 m from the entry of the free steel into the combustion chamber. As a result, the kinetic energy present in the free jet at the location of the diffuser is converted into an increase in pressure.

A diffuser in the sense of the invention is, in particular, a flow-comparing installation in a chamber 10

understood the reactor. The diffuser is arranged in such a way that it can predominantly absorb the fast combustion gases emerging from a burner. By predominantly in the context of the invention is meant that more than 50% of a burner free jet volume gets into the diffuser. Preferably, more than 90% was taken up by the diffuser. The free jet volume of the burner particularly expediently reaches the diffuser. In an expedient embodiment, the opening angle of the diffuser is to be selected at 3-7 ° per half angle so that there is no detachment of the flue gas from the reactor wall in order to keep the pressure loss of the tubular reactor small. An asymmetrical design of the diffuser inlet side is particularly preferred, as will also be shown with reference to FIG. 6.

Another embodiment of the invention provides that the means for improving the circulation of the gases in the reactor is a ceramic fan. This also enables better thermostatting of the tube bundle. By installing moving elements in the reactor, the combustion gas can be directed or directed onto the tube bundle from reaction tubes.

In addition to means for circulation, a tube reactor according to the invention in each case has burners and reaction tubes arranged in bundles, preferably ceramic tubes. Both the tube bundle and the burner or burners can be located in one chamber. A tube bundle which extends through the reactor preferably defines a heating chamber which is connected to one another with a combustion chamber or a combustion chamber in the form of a structural unit. The reactor itself can be constructed in a modular manner from several such units, for example from a series of cuboid elements. A so-called combustion chamber with inserted burners and a heating chamber with integrated tube bundles are then present in each element 11

there is no actual separation of the chambers. A structural separation of the heating chamber (= heating chamber) and the combustion chamber (= combustion chamber) is, however, favorable for the flow of the combustion gases along the entirety of the tube bundle or contact tube.

Any device familiar to a person skilled in the art for this purpose is suitable as a burner. For example, it can be a gas or an oil burner. One or more burners can be used per module, depending on the desired output. The burner can be positioned both on the top and on the side of the combustion chamber, partially projecting into the combustion chamber. The burner free jet is then arranged so that it sucks and accelerates combustion gases from the heating chamber through its impulse. The burner is then preferably positioned so that by a

Intake opening between the combustion chamber and the heating chamber combustion gases are sucked out of the heating chamber through the free jet and entrained. Here the ceramic tubes are heated in direct current.

In another embodiment of the reactor according to the invention, the flue gases are circulated in the reverse flow direction, so that the ceramic tubes are heated in countercurrent if this is favorable for the gas phase reaction taking place. The burner is built into the combustion chamber from below or laterally, and a flow guiding element can be installed on the chamber head. The diffuser is adjusted accordingly.

The height and width of the diffuser can be varied within wide limits depending on the special requirements. The exact position results from the pressure drop required for the circulation. The diffuser works in particular according to the reverse nozzle principle. The diffuser increases the pressure drop driving the circulation within the reactor while reducing the gas velocity of the incoming combustion gases. A 12

Asymmetrical design of the diffuser outlet end leads to an improved suction of the combustion gas from the heating chamber.

In a particularly advantageous modification of the tubular reactor according to the invention, the diffuser is at least partially integrally formed with one or more walls of the chamber of the reactor. This means, for example, that the brick walls of the combustion chamber are designed to give the shape of a diffuser.

A further advantageous embodiment of the device according to the invention is that the combustion chamber and the heating chamber or the combustion chamber and the heating chamber are dimensioned such that temperature peaks in the combustion chamber are reduced by a sufficiently high circulation of combustion gases, as a result of which the thermal load on the lining and ceramic pipes is reduced. In addition, nitrogen oxide formation is largely prevented. An aftertreatment of the combustion gases withdrawn from the reactor is thereby largely unnecessary. In addition, the revolution will improve

Energy distribution in the tube bundle is achieved, which increases the yield.

Finally, in the device according to the invention it is also advantageous if, based on the direction of flow of the combustion gases, there is at least one flow guide element downstream of the diffuser which improves or optimizes the flow onto the ceramic tubes by combustion gases emerging from the diffuser. This means in particular that the flow within the reactor space, i.e. the heating chamber, is additionally distributed by the installation of flow guiding elements, for example guide plates and the like, so that the gases which result from the combustion of the fuel gas make the tube bundle more uniform 13

flow around, since this results in a more uniform heating of the pipes and higher yield.

In a particularly advantageous embodiment, the invention provides that the diffuser has an inlet end which is adjacent to the burner and an outlet end and a flow profile is used as the flow guide element which is adjacent to the outlet end; this profile is arranged outside the diffuser so that it projects into the heating chamber. As a result, combustion gases which leave the diffuser can be conducted particularly favorably directly in the direction of the tube bundle arranged in the heating chamber.

In the BMA process, for which the tubular reactor according to the invention is particularly suitable, the actual conversion of the reaction gases (starting materials are, for example, methane and ammonia) takes place in the tube bundles made of ceramic tubes. All ceramics made of oxides, carbides and nitrides and mixtures thereof are suitable as materials for the reaction tubes in the context of the invention. If the ceramics used are porous materials, the walls of the reaction tubes must be coated gas-tight. The reaction tubes are preferably made of I or K aluminum oxide. Due to the manufacturing process, this material may also contain other oxides to a small extent.

The reaction tubes to be used according to the invention can be produced from the ceramic materials with the aid of known extrusion techniques and with any other technique known to the person skilled in the art. The reaction tubes are typically at least 2 m long and have an inner diameter of approximately 16-18 mm.

The reaction tubes are provided on their inner surface with a catalytically active coating which is known per se to the person skilled in the art. A preferred catalytic 14

Coating contains platinum and aluminum nitride. EP 0 407 809 B1 describes a particularly advantageous process for producing these catalytically active coatings, the process described being characterized in that highly active coatings are obtained even with loads of only 2 mg of platinum per cm ^{2 of} the inner surface of the reaction tubes.

The reactors according to the invention can be assembled in modular form to form larger reactors. This reduces the space required for individual reactors, since the distance between two furnaces can be reduced or omitted entirely, because heating is no longer carried out from both sides of the chambers, but rather only from one side. Furthermore, the heat radiation is reduced.

The invention also relates to the use of the

Reactor as described herein for performing endothermic catalytic gas reactions. Among the endothermic gas reactions in question, the catalytic conversion of methane and ammonia to hydrocyanic acid is particularly preferred. This is, for example, in Ullmanns

Encyclopedia on Industrial chemistry, 5th edition (1987), Vol. A 8, pages 162-163.

In addition, the invention also includes a process for the production of gaseous substances, in which gaseous starting materials are converted to gaseous products, the process being characterized in that a reactor is used as described hereinbefore.

In a preferred embodiment of the process according to the invention, the starting materials are ammonia and methane, which leads to the products hydrocyanic acid and hydrogen. 15

To illustrate, further advantageous embodiments are now explained in more detail with the aid of figures.

The figures show:

1 shows a section through a schematic diagram of an embodiment of a particularly preferred reactor according to the invention;

FIG. 2 shows a section along the plane AB from FIG. 1;

FIG. 3 shows a section along the plane CD from FIG. 1;

FIG. 4 shows a section through a schematic diagram of a further embodiment of a reactor according to the invention, in which a burner is positioned on the bottom side;

Figure 5 is a plan view of two exemplary modular arrangements of several reactors to larger reactor units (variant A, variant B);

6 shows a section through a combustion chamber with an asymmetrical design of the diffuser.

FIG. 1 shows a schematically drawn cross section through a tube furnace reactor 10 according to the invention, which has a single actual chamber 100. This chamber 100 can be divided into two rooms 101 and 102. 101 is called the boiler room or heating chamber, while 102 is called the combustion chamber or combustion chamber. It can be seen that in the example chosen, the construction described describes a parallel arrangement of combustion chamber 102 and heating chamber 101. Both rooms are not actually separated from each other, but are connected to each other.

In FIG. 1, 10 denotes the cuboid basic element of the tube furnace according to the invention, from which the reactor is constructed, consisting of the lining with heat-resistant refractory material and one 16

Sheathing, e.g. B. made of sheet metal, 120 the burner, 121 the heat recovery unit, which also as

The outflow device acts, 134 the burner free jet, 135 the lining of the combustion chamber designed as a diffuser, 150 a flow guiding element in the form of a plate for equalizing the supply of combustion gas into the heating chamber 101. Such any number of such elements can be arranged in series or side by side in a row. In the example shown, the element 150 is arranged adjacent to the outlet end 132 of the diffuser and projects into the heating chamber.

The device according to the invention, as can be seen in FIG. 1, is operated as follows:

The educt stream is introduced into the tube bundle (s) 110 from below, the educts being converted into the desired product in the tube bundles. The product emerging from the top of the reaction tube bundle is cooled and removed in the cooling head 111, which is only indicated. It is particularly important here that the product stream can be cooled quickly during insulation, since in most cases the product is only metastable. Devices which are suitable for this are known to the person skilled in the art.

The heating gases are generated in the burner 120 and introduced into the heating chamber 101 via the diffuser 135, which is located in the combustion chamber 102 and optionally via a flow guide plate 150. Here, they heat the reaction tubes 110 in which the actual conversion takes place. After repeated circulation, the combustion gases acting as heating gas leave the reactor 10 through those acting as heat recovery unit 121

Flue gas discharge device, which is located on the burner 120.

FIG. 2 shows a schematic longitudinal section along the AB plane through the reactor. Figure 2 illustrates 17

in particular the arrangement of the tube bundle (s) 110, as well as the combustion chamber shaft 102 can be clearly seen. The diffuser 135 is arranged in the shaft 102. The guide element 150 can be seen both in the shaft 101 and in the shaft 102.

FIG. 3 illustrates a section along the line C-D from FIG. 1. The passage or the connection between the heating chamber 101 and the combustion chamber 102 can be seen. Pipe bundles 110 can also be seen.

FIG. 4 shows the arrangement of the burner 120 on the bottom of the tube furnace 10. This enables operation according to the countercurrent principle.

Figure 5 shows several variants for the arrangement of reactor modules to larger reactor units.

In variant A, two module units 10 are connected to one another in such a way that one of the two heating chambers shown is adjacent to two combustion chambers. This enables the ceramic tubes to be heated from two sides with simultaneous flow from two sides.

Variant B from FIG. 5 illustrates another one

Embodiment of the invention, wherein in variant B the modules 10 are arranged so that the cuboid units are combined with each other both in the longitudinal and in the transverse direction. This allows particularly good use of the available resources in a small space. Energy savings are possible due to the reduced radiation area.

FIG. 6 illustrates how the asymmetrical design of the inlet side 131 of the diffuser 135 is designed to enable an improved circulation of the flue gases.

FIG. 6 shows the combustion chamber 102 with the burner 120, the flue gas outflow device arranged around the burner 18th

123, the burner nozzle 122, the diffuser 135 with the inlet end 131, outlet end 132 and the constriction 133. The inlet side of the diffuser forms an opening angle α _H κs on the heating chamber side and an opening angle α _{Aws on the outer wall side} . The flue gas from the combustion chamber 102 flows through the transition 104 into the heating chamber 101, not shown, and passes back into the heating chamber via the transition 103. α _H κs is generally in the range from 0 to less than 20 °, in particular 0 to 5 °; α _AWS is generally in the range from 20 to 45 °, in particular 25 to 40 °. The asymmetrical shape of the diffuser inlet end leads to an improved suction of the combustion gas sucked in from the heating chamber via the transition 103 by the free jet 134, because a vortex formation which occurs when entering the combustion chamber 102 is suppressed.

Reference list

10 tube furnace

100 chamber

101 heating chamber, boiler room

102 combustion chamber, combustion chamber

103 transition from the heating chamber to the combustion chamber 104 transition from the combustion chamber to the heating chamber

110 tubes, tube bundle

111 cooling heads

120 burners

121 heat recovery unit 122 burner nozzle

123 Flue gas discharge device

130 circulating agents

131 diffuser inlet end

132 Diffuser outlet end 133 Diffuser necking

134 Burner free jet

135 diffuser 140 chamber wall

150 flow guiding element

Claims

19 patent claims

1. tube furnace (10) for continuous endothermic gas reactions, comprising one or a plurality of chambers (100), the respective chamber (100) in a heating chamber (101) with reaction tubes (110) arranged therein, through which reaction gases can flow, and is divided into a combustion chamber (102) with at least one assigned burner (120), the burner or burners (120) being arranged such that the combustion gases generated during operation flow into and into the assigned heating chamber (101) bring the reaction tubes (110) located from outside to the temperature required for the desired reaction and at least one means for circulating the combustion gases is arranged in the chamber (100), characterized in that in the immediate vicinity of the burner or burners

(120) at least one flue gas outflow device (123) is arranged through which the combustion gases

Leave the reactor.

2. Pipe furnace according to claim 1, characterized in that the flue gas outflow device (123) as in the burner (120) integrated heat recovery unit

(121) is formed.

3. Pipe furnace according to claim 1 or 2, characterized in that the means for circulating the combustion gases (130) is a combination of a burner free jet (134) and a diffuser (135), the free jet sucking combustion gas from the heating chamber according to the injector principle and the diffuser (135) predominantly receives the fast combustion gases emerging from the burner (120) and the intake combustion gases and 20th

whose kinetic energy is at least partially converted into pressure with the generation of an additional pressure gradient.

4. Pipe furnace according to claim 3, characterized in that the diffuser (135) is at least partially integrally formed with one or more walls (140) of the chamber (100).

5. Tube furnace according to claims 3 or 4, characterized in that the heating chamber (101) arranged in the chamber (100), which is traversed by the reaction tubes (110), and the combustion chamber (102) are connected to one another in the form of a structural unit .

6. Tube furnace according to one of claims 3 to 5, characterized in that the one or more burners (120) and

Flue gas outflow device (s) (123) are placed on top and partially in the respective combustion chamber (102).

7. Tube furnace according to one of claims 3 to 6, characterized in that based on the flow direction of the combustion gases downstream of the diffuser (135) at least one flow control element (150) is arranged, which the flow against the reaction tubes (110) through from the diffuser (135 ) Optimized combustion gases.

8. Pipe furnace according to claim 7, characterized in that the diffuser (135) has an inlet end (131) and an outlet end (132) and the flow guide element (150) the outlet end (132) 21

is arranged adjacent to the outside of the diffuser (135) so that it projects into the heating chamber (101).

9. Tube furnace according to one of claims 3 to 8, characterized in that the diffuser (135) at the inlet end (131) is asymmetrical, the heating chamber opening angle α _H κs 0 to less than 20 °, in particular 0 to 5 °, and the Opposing (outside wall) opening angles α _A ws 20 to 45 °, in particular 25 to 40 °.

10. A process for the production of gaseous substances, in which gaseous starting materials are converted to gaseous products, in particular for carrying out endothermic catalytic gas reactions, characterized in that a tube furnace according to one of claims 1 to 9 is used.

11. The method according to claim 10, characterized in that hydrocyanic acid is produced from ammonia and methane, using a tube furnace with freely hanging ceramic tubes as reaction tubes.