Method and reactor for carrying out chemical reactions

Abstract

The present invention relates to a method for carrying out chemical reactions using a reactor (100-400), in which a reaction tube (2) arranged in a reaction vessel (1) is heated during the reaction period to a reaction tube temperature level between 400° C. and 1500° C. using radiant heat provided by one or more electric heating elements (3) arranged in the reaction vessel (1), with the proviso that in at least a part of the reaction vessel (1) provided with the heating element (3), a gas atmosphere is provided during the reaction period, said gas atmosphere having a defined volume fraction of oxygen. The corresponding reactors (100-400) are also part of the present invention.

Description

[Technical field]

[0001] The present invention relates to a process for carrying out chemical reactions and to a corresponding reactor according to the preambles of the independent claims. [Background technology]

[0002] Many processes in the chemical industry use reactors in which one or more reactants pass through heated reaction tubes where they react catalytically or non-catalytically. Heating serves in particular to exceed the activation energy required for a chemical reaction to occur and, in the case of endothermic reactions, to provide the energy required for the chemical reaction. The reaction may proceed entirely endothermically or, after the activation energy has been exceeded, exothermically. The present invention is particularly concerned with strongly endothermic reactions, as will be further explained below.

[0003] Examples of such processes are steam cracking, various reforming processes, in particular steam reforming, dry reforming (carbon dioxide reforming), mixed reforming processes, alkane dehydrogenation processes, etc. In steam cracking, the reaction tube is led through the reactor in the form of a coil with at least one reverse bend in the reactor, while in steam reforming, tubes that pass through the reactor without a reverse bend are usually used. The invention can also be used in connection with so-called "millisecond" or single-pass reactors, which are characterized by very short residence times.

[0004] Further applications of the present invention are reactors for carrying out the reverse water gas shift (RWGS) reaction of carbon dioxide with hydrogen to form carbon monoxide and water, the dehydrogenation of oxygenates such as the reaction of methanol to formaldehyde and hydrogen, the decomposition of ammonia to give gaseous nitrogen and hydrogen, the dehydrogenation of so-called liquid organic hydrogen carriers (LOHC) known to those skilled in the art, and the reforming of methanol and glycerol (unless already included in the term "reforming" used above).

[0005] The present invention is suitable for all such processes and reactor tube embodiments. By way of example only, reference is made to the articles "Ethylene", "Gas Production" and "Propene" in the Ullman Encyclopedia of Industrial Chemistry, e.g. DOI: 10.1002 / 14356007.a10_045.pub2 dated April 15, 2009, DOI: 10.1002 / 14356007.a12_169.pub2 dated December 15, 2006 and DOI: 10.1002 / 14356007.a22_211 dated June 15, 2000.

[0006] The reaction tubes of the corresponding reactor are customarily heated using burners, for which purpose they are led through a combustion chamber in which the burners are also arranged.

[0007] However, there is now a growing demand for synthetic products such as olefins, but also for synthesis gas and hydrogen produced with zero or reduced local carbon dioxide emissions. This demand cannot be met by processes using combustion reactors, as they usually use fossil fuels. Other processes are practically ruled out, for example, due to their high costs.

[0008] It has therefore been proposed to support or replace the burners in the corresponding reactors by electric heating means. In addition to direct electric heating, in which an electric current is applied to the reaction tubes themselves, for example in the known star (point) circuit, and other types of heating that are not described in detail here, there are also concepts in particular for so-called indirect electric heating, which is also used in the context of the present invention. Regardless of the specific type of heating or the heating concept implemented in the process, a suitably heated reactor is also called a "furnace".

[0009] Such indirect electrical heating can be carried out, for example, as described in WO 2020 / 002326, using electrically operated radiant heating elements ("radiant heaters") suitable for heating to the high temperatures required for the mentioned reactions, which are arranged in the furnace so as not to be in direct contact with the reaction tubes. Heat transfer occurs mainly or exclusively in the form of radiant heat. Therefore, in the following, terms such as "indirect heating", "heating by radiant heat" are used synonymously. The properties of the corresponding heating elements are described below.

[0010] The present invention has the object of providing provisions which allow advantageous operation of a reactor of the type described, which is indirectly electrically heated using a suitable heating element. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2020 / 002326 [Non-patent literature]

[0012] [Non-Patent Document 1] DOI:10.1002 / 14356007.a10_045.pub2, April 15, 2009 [Non-Patent Document 2] DOI:10.1002 / 14356007.a12_169.pub2, December 15, 2006 [Non-Patent Document 3] DOI:10.1002 / 14356007.a22_211, June 15, 2000 [Non-Patent Document 4] J.Min.Metall.B55,2019,55 [Non-Patent Document 5] Surf.Coat.Technol.135,2001,291 Summary of the Invention

[0013] Against this background, the invention proposes a process for carrying out a chemical reaction and a corresponding reactor with the features of the independent claims. Embodiments of the invention are the subject of the dependent claims and the following description.

[0014] The present invention relates to a process for carrying out chemical reactions, in which a reactor is used in which a reaction tube arranged in a reaction vessel is heated during the reaction period using radiant heat provided by one or more electric heating elements arranged in the reaction vessel. The heating is carried out to reach a temperature level, hereinafter referred to as the "reaction tube temperature level", in particular on the reaction tube surface and / or within the reaction tube, between 400°C and 1500°C, in particular between 450°C and 1300°C, more particularly between 500°C and 1,200°C, and even more particularly between 600°C and 1,100°C. During the reaction period, one or more combustible components pass through the reaction tube. The temperature of the reaction tube can be selected to be the same or comparable to the temperature selected for the calcination furnace or other electrically heated furnace. The reaction tube temperature covers a relatively wide temperature range, since a considerable temperature gradient always occurs in the corresponding reaction tube (in particular at the "cold" inlet and the "hot" outlet where coking increases). If radiant heating elements are used, even higher heating element temperatures are necessary to provide the above-mentioned reaction tube temperature levels.

[0015] The invention can be used as mentioned above, in particular in connection with the production of olefins and / or other synthesis products by steam cracking, as mentioned at the outset, or in connection with the production of synthesis gas or hydrogen by steam reforming, but the invention is in principle suitable for all types of reactions in which a feed mixture, in gaseous state, passes through a reaction tube heated from the outside to a suitable temperature level and thereby reacts.

[0016] The reaction tubes are led through the reaction vessel in all conceivable ways, in particular with or without one or more reversal points or reverse bends. In particular, the reaction tubes can be arranged in a row in a vertically arranged plane and heated by radiant heating elements arranged on both sides of the plane. A multi-row arrangement in the intermediate region between the two planes and corresponding heating from outside the intermediate region are also possible. In particular, the reaction tubes have a length of 5 to 100 m and / or a diameter of 20 to 200 mm. Furthermore, the individual reaction tubes can be designed in sections of two or more parallel strands, in which the tube diameter is smaller compared to a single tube. Preferably, the multi-strand section is arranged near the entrance to the furnace in order to provide this region with a length-specific reaction tube wall area that is as high as possible. Further downstream of this configuration, the parallel strands are first combined into a common strand, preferably with a larger tube diameter. In this example, the reaction tube is composed of two or more parallel strands, in particular joints including fittings and connecting strands. Conversely, in principle it is also possible to provide a multi-strand design at the end or middle part of the reactor tube, with intermediate divisions and, if necessary, additional joints. In general, the embodiments of the invention allow for the division and combination of tubes in any conceivable manner. Depending on the type of reaction, the reactor tubes can be filled with suitable catalytic and / or inert materials or can be provided in empty form.

[0017] The present invention provides for heating of the reaction tubes using electrically provided radiant heat, however, this does not exclude the use of other types of heating as well, for example direct heating, in which the reaction tube itself is used as an electrical resistance to generate heat, induction heating or heating using burners in further reaction vessels of the reactor. In any case, in addition to the radiant heat, a portion of the heat provided by suitable heating elements can also be transferred convectively to the reaction tubes.

[0018] Thus, when reference is made in this specification to the use of indirect electric heating, i.e. the use of radiant heat provided by an electric heating element, this does not exclude the presence of additional electric or non-electric heating. It may also be envisaged to vary the contribution of the electric heating, and in particular the non-electric heating types, over time, for example as a function of the supply and price of electricity or of the supply and price of non-electric energy sources.

[0019] A "reaction vessel" is understood in the present specification to mean an enclosure that is partially or completely insulated from the outside and that may in particular be lined with a material that is heat-resistant at the temperatures mentioned. The reaction vessel is in particular surrounded to a large extent, i.e. at least 90%, 95%, 99%, 99.5% or 99.8%, by (solid) walls that have thermal insulating properties. These walls may comprise a tight-fitting, continuous or impermeable lining, such as a metal sheet, and one or more insulating layers. The figures given for the proportion of the reaction vessel "surrounded by insulating walls" may in this context be understood as the proportion of the entire housing of the reaction vessel that is in particular composed of a solid structure that has thermal insulating properties, i.e. that is covered with, made from or contains insulating material. Openings or ports of the reactor housing are usually not completely insulated, but may not be included in the figures given for a "largely enclosed" reaction vessel. As understood in the present specification, any part of the reactor wall that is provided as being "thermal" may have a thermal insulation resistance of 2 W / m 2 K or less, especially 1.5 W / m 2 Less than K, 1 W / m 2 Less than K, 0.5 W / m 2 Less than K or 0.2 W / m 2The term "thermal transmittance" is intended to express that the values ​​indicated by the relevant figures refer (only) to the conductive heat transfer coefficient in solid structures (in particular excluding the radiative and convective heat transfer components inside and outside the walls). For example, as indicated above, if the reactor vessel is surrounded by at least x% by insulated walls, then no more than x% of these wall areas may be configured to have a thermal transmittance as just indicated. As mentioned above, openings or ports in the reactor housing may be correspondingly uninsulated and therefore may have a higher thermal transmittance or may not represent a thermal barrier at all, for example in the case of permanent openings. To provide a reactor wall of an insulated configuration, the wall may be composed of, contain or be coated with an insulating material, such as, but not limited to, ceramic fibers, heat-reflective metal foils, minerals and polymer foams, or any combination thereof, as mentioned above. In particular, different insulating materials may be provided in response to the local temperatures present and to different thermal resistances.

[0020] As mentioned above, the invention is not limited to using exactly one reaction vessel, but can in particular also be used in an apparatus with differently heated reaction vessels. Further details regarding the corresponding reaction vessels, their equipment with gas supply devices and, if applicable, gas extraction devices and their connections to stacks etc. are further described below. In this specification, the terms (outlet) "stack" and "chimney" are used synonymously and both relate to a structure with the (main) function of providing a fluid connection to a safe outlet location, e.g. to the atmosphere, preferably at a sufficient height above ground level.

[0021] In the context of the present invention, the reaction vessel does not have to be designed to be airtight, i.e. at least not completely airtight. According to an embodiment of the present invention, the reaction vessel is provided to be sufficiently airtight in particular so that the oxygen level in the vessel can be substantially controlled. As mentioned above in this specification, a defined oxygen concentration is particularly advantageous at the heating element, and therefore the airtightness of the reaction vessel is particularly important in the vicinity of the heating element. The walls of the reaction vessel may therefore be provided to be less airtight in the vicinity of the heating element. However, this is not provided in all embodiments of the present invention. For the avoidance of doubt, the airtightness may not concern a gas intentionally introduced, even if this gas flows under the effect of a pressure difference between the outside and the inside of the reaction vessel, i.e. across the wall.

[0022] In this specification, the term "reaction period" is understood to mean the period during which the reaction to be carried out occurs and during which the reactants necessary for the reaction pass through the reaction tubes, or a portion of the corresponding period. During the reaction period, combustible components, especially hydrocarbons, usually pass through the reaction tubes, since they are contained in the process feed gas. During periods other than the reaction period, such as regeneration or inerting periods, such combustible components usually do not pass through the reaction tubes.

[0023] As is generally known, processes of the type described may also include, in particular, a decoking operation, in which deposits formed in the reaction tubes after a corresponding reaction period are removed, for example by "burning off" with an oxygen-containing gas or gas mixture. This is particularly true in the case of purely gas-phase reactions without catalysts. Before the corresponding decoking operation, the reaction tubes are usually cleaned of reactants and in particular a precooling or subsequent heating is carried out. Not only decoking operations, but also corresponding periods of standby operation, in which, for example, pure steam is added to the reaction tubes to avoid (excessive) cooling (so-called "hot steam standby operation"), and periods of cooling or heating, are not counted as part of the reaction period in the understanding used herein, nor are, for example, maintenance periods or periods during which a catalyst bed is replaced or regenerated.

[0024] According to the invention, in at least a part of the reaction vessel provided with a heating element, a gas atmosphere is provided in the reaction vessel during the reaction period during which at least the combustible components pass through the reaction tube, or during a part of the reaction period. The gas atmosphere comprises, in particular, one or more known inert gases, such as nitrogen or carbon dioxide, or one or more noble gases, such as argon, as well as oxygen, with a volume fraction adjusted between 500 ppm and 10%, in particular between 1000 ppm and 5% or between 5,000 ppm and 3%. Herein, for a (feedback) control structure implemented in a control device or system that adjusts the oxygen volume fraction, a lower limit value can be used to define a lower threshold value and an upper limit value can be used to define an upper threshold value.

[0025] In summary, the present invention proposes to provide a gas atmosphere that includes controlling oxygen within a "sweet spot" window during the reaction period where both safety and device life criteria are met, as further explained below. During periods other than the reaction period, i.e., periods when preferably no flammable components are passing through the reaction tube, an oxygen content outside this window can be used, or in other embodiments, the same oxygen content can be used.

[0026] According to an embodiment of the invention, by keeping the volume fraction oxygen content within limit values, on the one hand it is possible to increase the durability of the corresponding heating element and, on the other hand, to ensure a high level of operational safety.

[0027] The heating elements used for the indirect heating of the corresponding reaction tubes usually comprise electrically conductive metallic or non-metallic heating structures of a given shape, for example straight or otherwise shaped rods, wires or strips, the metallic heating structures being preferably made in particular from alloys containing at least the elements Fe, Cr and Al. Alternatively or additionally, the metallic heating structures can also be made at least partially from nickel-chromium alloys, copper-nickel alloys or nickel-iron alloys.

[0028] It is known that in the indirect heating of reaction tubes, especially steam cracking, extremely high heat flux densities at high temperatures are necessary for economical operation, and therefore the heating elements or heating structures must be operated close to their upper temperature limit. However, just close to this limit, the heating elements and heating structures become very sensitive to the furnace atmosphere. In particular, a certain minimum oxygen content is advantageous to avoid or slow down the rapid or slow deterioration of the heating elements or heating structures. For example, the use of metallic heating structures, including aluminum, allows the maintenance of a stable aluminum oxide layer present on the surface of the heating structure, which protects the material from uncontrolled corrosion and other damage mechanisms. The invention therefore achieves a long durability of the heating elements or their heating structures by using an appropriate minimum oxygen content.

[0029] It is known that FeCrAl-based heating elements are damaged when exposed to atmospheres containing high concentrations of nitrogen and low concentrations of oxygen at high temperatures, resulting in a lower maximum operating temperature in such atmospheres compared to the maximum allowable operating temperature in air. Without being bound by theory, it is believed that this damage is related to the formation of nitrides that prevent the formation of a protective aluminum oxide layer on the element surface, leading to corrosion that significantly reduces the life of the heating element. The extent and rate at which such damage occurs is related to the concentration of oxygen and oxygen-containing species in the atmosphere in contact with the heating element and the heating element temperature. For example, a study documented in J.Min.Metall.B55,2019,55 shows that when FeCrAl material is heated to 1,200 °C in a 99.996% nitrogen atmosphere (with oxygen and water impurity levels less than 10 ppm), corrosion proceeds through the formation of localized subsurface nitrided regions consisting of AlN phase particles. Conversely, as documented in Surf. Coat. Technol. 135, 2001, 291, it was observed that for FeCrAl alloys, there was no significant morphological difference between the oxide scales obtained by oxidation in air or in gas atmospheres containing 2 or 10% by volume of oxygen.

[0030] Again, without being bound by theory and without limiting the scope of the invention, it is believed that the oxygen concentration required at the surface of the heating element to prevent accelerated deterioration of the heating element depends on the operating conditions, such as the temperature and thermal history of the heating element, which determine the thickness and quality of the protective oxide layer. In favorable situations, a very low oxygen concentration (for example, 100 ppm) is sufficient to prevent accelerated deterioration, but taking into account situations in which the surface of the heating element is more susceptible to nitriding treatments and, as a consequence, the uneven distribution of oxygen in the furnace, which may locally result in the concentration of oxygen being below the target concentration, it is wise to target a higher oxygen concentration in the furnace atmosphere. Thus, a practical lower limit for the oxygen concentration in the furnace or reaction vessel atmosphere is considered to be 0.1% oxygen by volume, although 500 ppm can also be selected. Upper concentration values ​​such as 0.2% oxygen by volume, or even higher concentration values ​​such as 0.5% by volume, can provide additional safety margins in less favorable furnace conditions or more pronounced uneven distribution of oxygen, and can be selected according to the invention. Conversely, a low oxygen concentration in the vicinity of the heating element may be beneficial, since the oxidation rate of common heating element materials is known to increase with oxygen concentration, as long as a minimum oxygen concentration to prevent nitride corrosion is met, which may also depend on temperature and heating element composition.

[0031] The provision of a gas atmosphere as provided according to the invention is advantageous with respect to the metal alloys mentioned, but in principle is also advantageous for use with other materials, for example based on MoSi2 or SiC, regardless of the damaging effects observed in each case.

[0032] An important consideration in determining the maximum amount of oxygen allowed is the flammability limits of the feed and product gases. In the flammability envelope of all flammable gases there is an oxygen concentration, commonly called the limiting oxygen concentration (LOC), below which a flammable mixture cannot form. For example, the LOC of ethylene at 25 °C and 1 atm is 10% oxygen. At these conditions, a mixture of ethylene, nitrogen and oxygen that does not contain at least 10% oxygen cannot produce a self-propagating flame. Combining literature data and temperature adjustment procedures, the LOCs of ethane and ethylene at 830 °C, a common steam cracking temperature, can be estimated to be 4.1% and 3.6%, respectively. If the oxygen concentration in the reaction vessel is lower than these limits, a flammable mixture will not form even if the coil bursts.

[0033] While there is some uncertainty in calculating the same limits for a complex mixture such as naphtha, estimates place hexane at 4.2% of its LOC, so ethylene is expected to be the reactant / product with the lowest LOC. Although 830°C is above the autoignition temperature of all these hydrocarbons, even if spontaneous combustion were to occur, being kept below the LOC would be expected to prevent shock wave generation.

[0034] Based on these observations, oxygen levels are proposed according to the present invention.

[0035] In general, a heating element used in the context of the present invention may have a base, for example made of a non-conductive heat-resistant material (for example ceramic), on or within which a heating structure, for example in the form of a heating wire or heating ribbon, is guided, for example in a meandering manner. Alternatively, one or more straight and / or curved heating structures with a holder associated with the heating element may also be used. For example, so-called heating cartridges may be used, which may be fixed to a suitable connection by plug-in or bayonet connection or the like. Typically, a multi-phase alternating current (AC), in particular a three-phase alternating current, is used for heating, and the heating wires may be connected in groups to the corresponding phases of the alternating current, although direct current (DC) heating may also be used. The present invention allows for, and is not limited to, any grouping, arrangement and operation mode of the corresponding heating elements.

[0036] In the context of the present invention, corresponding heating elements can be arranged in particular on the walls of the reaction vessel, from which heat can be radiated to the reaction tubes. These walls can be straight or curved, for example in the form of a paraboloid. These walls can have any combination of wall shapes and can also have straight wall sections, which can be arranged, for example, at an angle to one another or at any angle.

[0037] The provision of a gas atmosphere according to the invention ensures that the mentioned oxygen content is prevalent in the area in which the heating elements are located.

[0038] The invention has the result that, due to the proposed upper oxygen limit, the operational safety of the corresponding reaction vessel is improved, in particular in the case of damage to the reaction tubes ("coil rupture"). In the event of corresponding damage, one or more reaction tubes may in particular be completely cut off, but the invention is also advantageous against small leaks. In the event of corresponding damage, flammable gases may suddenly or gradually leak into the reaction vessel, which is largely sealed for thermal insulation reasons.

[0039] Such damage is less of a safety problem in conventional combustion reactors than in the device according to the invention, where at least one reaction vessel is exclusively heated electrically, because in a combustion reactor, the flammable gases escaping from the reaction tubes, for example in the form of a hydrocarbon / steam mixture, can be converted in a controlled manner by combustion occurring in the reaction vessel or in the corresponding combustion chamber, or can be safely discharged in the exhaust gas stream. Furthermore, the gas chamber surrounding the reaction tube is already essentially "inerted", since the oxygen content is significantly reduced by the already regular combustion of the fuel gas. In contrast, in the case of purely electrical heating, the corresponding flammable gases can accumulate in the reaction vessel and reach the explosion or explosion limit, for example, at temperatures above the normal oxygen content and autoignition temperature of air. Even in the case of combustion without explosion or explosion, complete or incomplete combustion can release energy and cause overheating. Complete or incomplete combustion, together with the amount of gases leaving the reaction tubes, can cause a particularly undesirable pressure rise. The present invention reduces such pressure rise because combustion of the gas mixture is limited by the low oxygen concentration, and therefore the low oxygen inventory, in the reactor chamber.

[0040] The present invention is therefore particularly preferred for indirectly electrically heated reactors where the process gas temperature approaches or exceeds the autoignition temperature of the components contained in the process gas, particularly the hydrocarbons.

[0041] By the proposed measures, the invention creates a containment vessel with a regulated atmosphere, which serves to maintain the protective oxide surface on the heating elements and to provide safety-related protection of the high-temperature reaction vessel with electrically energy input. Within the scope of the invention, in particular a full electric heating of the correspondingly operated reaction vessel may be provided, i.e. advantageously the heating of at least the reaction tubes in this reaction vessel is carried out predominantly or exclusively by electric heating, with at least 90, 95 or 99% of the heat introduced therein, in particular of the total heat introduced therein, being carried out by electric heating means. Since heat input via the gas mixture passing through the reaction tube or tubes is not taken into account here, this proportion relates in particular to the heat transferred in the reaction vessel from the outside to the wall of the reaction tube or tubes or generated in the reaction vessel at the wall or catalyst bed.

[0042] In a particular embodiment of the invention, hereinafter also referred to as the "first group of embodiments", one or more gases or gas mixtures used to provide the gas atmosphere can be fed into the reaction vessel while a part of the gas atmosphere is discharged from the reaction vessel. This in particular results in a continuous flow through the reaction vessel, in this way, for example, heat accumulation or local concentration or depletion of gas components can also be avoided. In this way, it is particularly easy to control the oxygen content in the gas atmosphere by adjusting the feed accordingly. In this first group of embodiments, in particular the outflow opening or openings (hereinafter only partially in the singular form is used for simplicity) from the reaction vessel, through which a connection can be established with a stack, for example an emergency stack, are permanently open. This means that the outflow opening or openings do not oppose any mechanical resistance to the outflow or inflow of fluids into or out of the reaction vessel, except for possible constrictions present in the flow cross section. The opening or openings are therefore not sealed, at least during the reaction period.

[0043] In this case, the stack openings or the connections to the stack or further outflow openings also serve to vent excess gases, in particular flammable hydrocarbons, in case of damage to the reaction tubes. In this case, the stack can have structural elements (so-called velocity seals or confusers), in particular in the region of the stack walls, to prevent backflow (for example by free convection) into the reaction vessel.

[0044] In another embodiment, hereinafter also referred to as "second group of embodiments", one or more outflow openings (hereinafter only partially used in the singular for the sake of simplicity) from the reaction vessel, in particular the stack openings or the connections to the stack, can be designed to open only above a predefined pressure level, for example by closing the outflow opening via a pressure flap, or a rupture disk or a corresponding valve. In this case, the outflow openings are normally closed, i.e. below the predefined pressure level, but serve for the discharge of excess gases or, in particular, of flammable hydrocarbons in case of damage to the reaction tubes, if the corresponding pressure increases due to the release of the corresponding stack cross section. In this case, temporary or permanent openings can be provided when a predefined pressure level is reached. In the present context, a "permanent" opening is understood to mean in particular an irreversible opening, which therefore in this embodiment is not resealed after the pressure has fallen below the predefined pressure level by subsequently releasing the gas. In the case of a "temporary" opening, on the other hand, reclosing takes place.

[0045] To open at a given pressure level, one or more outlet openings can have, for example, one or more spring-loaded or weight-loaded flaps with opening resistance defined by a spring or load characteristic, so that they only open at a corresponding pressure, or more precisely, a pressure difference across the opening. Examples of flap configurations suitable for rectangular duct openings are discussed in connection with Figures 6A to 6D below. If the axis of rotation of the flap is offset from the duct wall, the pressure increase at which the flap opens can be tuned by adjusting the thickness and / or density of the material on either side of the axis. Similar configurations can be used for circular duct openings.

[0046] In addition to the above-mentioned use of burst disks or (mechanical) pressure relief valves, known per se, it is also possible, for example, to detect pressure values ​​by means of a sensor and, if a predefined threshold is exceeded, to activate any type of opening mechanism, for example a firing mechanism or an electric actuator drive, which makes it possible, if necessary, to create an opening with a sufficiently large cross-section within a short response time and which can be kept closed during normal operation in the manner described.

[0047] In this case, i.e. in the second group of embodiments, the stack openings, which are closed during normal operation, can be bypassed via corresponding bypass line openings into the stack in order to remove the gas atmosphere or to flush the reaction vessel. In this way, the use of fluidic technology devices in the bypass lines allows a particularly controlled, e.g. time-controlled, removal.

[0048] In general, the removal of gas from the reactor chamber can result in a change in the composition of the gas atmosphere and / or cooling. The gas removed from the reactor chamber can be cooled and / or regenerated in order to be used again (recycled) to provide the gas atmosphere. In the course of cooling, heat integration can be performed, i.e. the heat removed from the gas can be transferred to further streams and / or steam in the steam system, especially in a heat exchanger.

[0049] For supplying one or more gases or gas mixtures used to provide the gas atmosphere, gas supply means in the form of or including supply nozzles or supply openings, as well as gas reservoirs connected thereto, are provided and used, which can be designed to be controllable, in particular by means of known fluid technology.

[0050] The supply and / or extraction can be carried out continuously or discontinuously, subject to control based on the desired oxygen content, in particular complying with the first and second limit values ​​used according to the invention.

[0051] In other words, in the context of the present invention, a continuous or discontinuous supply of one or more gases or gas mixtures used to provide the gas atmosphere is made into the reaction vessel, and a removal of at least a portion of the gas atmosphere from the reaction vessel may furthermore be made, in which case the removal can be made at least partially simultaneously with the supply or at least partially delayed from the supply.

[0052] Within the scope of the present invention, a pressure level below atmospheric pressure can be provided in the reaction vessel. This can be done by regulating the supply and withdrawal, especially in the case of simultaneous supply and withdrawal in the described manner, in particular in the case of embodiments with a permanently open connection from the reaction vessel to the (emergency) stack or to other measures previously provided in connection with the first group of embodiments. In this case, a static negative pressure is generated in the reaction vessel due to the high temperatures in the stack and in the reaction vessel and, as a result, the reduced density of the contained gas volume. In this context, for example, the use of a fan to induce a draft ("suction") can also be provided until a corresponding static negative pressure is formed.

[0053] By operating the reaction vessel at a pressure level below atmospheric pressure, it is possible to ensure that undesirable components, possibly harmful, corrosive or flammable, are prevented from escaping from the reaction vessel at all times. However, the inflow of air or secondary air can occur, which can be limited by a well-sealed design and / or compensated for by appropriate controls.

[0054] Therefore, when the reactor is operated at subatmospheric pressure levels, the reactor walls are preferably particularly tight to prevent uncontrolled ingress of air, i.e. oxygen, into the reactor. In an embodiment, the furnace walls have a relative air ingress rate of 0.5 Nm per furnace inner wall surface area and per average pressure difference (as an absolute value) between the reactor interior and the surrounding outside atmosphere (at the same altitude). 3 / (h×m 2 × mbar), less than 0.25 Nm 3 / (h×m 2 × millibars), or 0.1 Nm 3 / (h×m 2 × millibars), where Nm 3 is standard cubic meter at 0° C. and atmospheric pressure. In this specification, the inner wall surface area of ​​the furnace is defined as the sum of the hot surface areas of the thermal box or reactor insulation that bounds the inner box volume in all directions (i.e., sides, top, bottom), not including the surface area of ​​radiant heating elements or other structures protruding from the insulation into the inner box volume. These values ​​are selected to allow a reasonable inert gas feed rate (minimizing utility consumption and convective heat losses through the stack) while maintaining the resulting oxygen concentration inside the reactor below a specified upper limit. In preferred embodiments, the average pressure difference (in absolute terms) between the inside of the reactor vessel and the surrounding outside atmosphere (at the same altitude) is less than 10 mbar, less than 5 mbar, or less than 3 mbar, depending mainly on the stack design (e.g., height, diameter, insulation), and optionally, the provision of a fan or similar device. As a general design rule, the tightness of the reactor wall is given priority when lower oxygen limits are specified and / or operating costs need to be minimized and / or the absolute pressure difference across the reactor wall to the environment is increased.

[0055] However, in an alternative which may be used in particular in connection with the second group of embodiments described above, a superatmospheric pressure level may also be established within the reaction vessel. Thus, as explained, it is preferable to be able to provide a superatmospheric pressure level when the stack openings to the reaction vessel are closed or only formed for openings above a predefined pressure level.

[0056] In particular, the gas atmosphere can be provided by supplying one or more gases or gas mixtures used to provide the gas atmosphere to the reaction vessel, without simultaneously removing part of the gas atmosphere from the reaction vessel, as in the previously described embodiment. In this case, the corresponding gas or gas mixture can be injected up to a superatmospheric pressure level, which pressure level is lower than the opening pressure of the mentioned and above described outlet opening. Advantageously, the corresponding design allows in particular a reduction in the amount of gas required, since the gas atmosphere can be supplied only at the start or intermittently during the reaction phase and then maintained without further measures.

[0057] However, a superatmospheric pressure level can also be set in embodiments that are supplied with a gas or gas mixture for providing the gas atmosphere and simultaneously removing part of the gas atmosphere from the reaction vessel, preferably by providing a suitably controlled and / or dimensioned bypass line that ensures a corresponding pressure level in the reaction vessel. See above. In other words, a superatmospheric pressure level can be set in the reaction vessel even in the case of a permanently open outlet opening or an outlet opening with, for example, an adjustable flow rate, provided that the amount of gas supplied and / or the amount of gas exiting through the outlet opening is adjusted accordingly.

[0058] In particular, a controlled supply can provide a superatmospheric pressure level to the reaction vessel to prevent the inflow of ambient air which would increase the oxygen content in an uncontrolled manner. In this embodiment, measurement of the oxygen content after the initial conditioning is performed may not be necessary since the oxygen content cannot subsequently increase.

[0059] In this specification, the term "subatmospheric pressure level" is intended to refer to any pressure below the standard atmospheric pressure of 101.325 Pa, in particular at least 10, 50, 100 or 200 mbar below this pressure. Similarly, the term "superatmospheric pressure level" is intended to refer to any pressure above the standard atmospheric pressure of 101.325 Pa, in particular at least 10, 50, 100 or 200 mbar above this pressure.

[0060] In an embodiment of the invention, the wall of the reaction vessel does not comprise an inspection port for visual inspection of the inner space of the reaction vessel open to the atmosphere, or comprises only an inspection port for visual inspection of the inner space of the reaction vessel hermetically closed with a transparent material, in particular a heat-resistant transparent material. That is to say, in an embodiment of the invention, in particular in the form of an (open) inspection port, there is no heat and / or gas leakage in the reactor wall, so that the gas atmosphere in the reactor can be adjusted in a particularly controlled manner. In an embodiment, a glazed and sealed observation window is provided, i.e. an inspection port for visual inspection of the inner space of the reaction vessel hermetically closed with a transparent material. The outside of the window is preferably fitted with a movable insulating cover or blind, which limits heat loss when the window is not used for observation. In an embodiment of the invention, a camera can be provided that allows observation of the reaction tube, but in a manner in which hermeticity is maintained, i.e. behind a transparent window or inside the reactor. In the case of providing a camera installed inside the reactor, any cable can be passed through the reactor wall via a hermetic port.

[0061] In embodiments of the present invention, open ports in the reactor wall can be omitted, particularly since electric heating provides heat in a much more controlled manner as compared to burners, reducing or eliminating the need to monitor the temperature of the reactor tubes.

[0062] To summarise the above, the gas atmosphere may be provided by injecting one or more gases or gas mixtures used to provide the gas atmosphere in the reaction vessel without simultaneously removing a portion of the gas atmosphere from the reaction vessel, or while simultaneously removing a portion of the gas atmosphere from the reaction vessel.

[0063] For the sake of clarification only, it should be emphasized again that operation at subatmospheric pressure levels is feasible, especially when there is a (relatively) large-area connection between the reaction vessel and the stack outlet (i.e. low flow-related pressure losses) and a sufficiently tall stack is filled with hot (i.e. light) gas. In this case, the pressure drop caused by the flow is smaller than the geodetic pressure difference between the hot gas and the cold outside air that occurs over the height of the stack, resulting in a negative pressure difference between the inner gas atmosphere and the outside atmosphere at the same geodetic height. Also, as mentioned above, a blower can be used to provide a subatmospheric pressure level. Blowers can be provided in the main stack line and in the bypass line.

[0064] Conversely, especially if the connection between the reaction vessel and the stack outlet (during normal operation) is completely closed or reduced in size, e.g. via a bypass line, superatmospheric pressure levels will occur, resulting in a pressure loss greater than the geodetic pressure difference between the hot gas and the cold outside air, and consequently, the height of the stack or the bypass line.

[0065] Thus, in the first and second group of embodiments, the invention can be implemented with subatmospheric or superatmospheric pressure levels in the reaction vessel. In the first group of embodiments, it is preferred that subatmospheric pressure levels can be provided by appropriately dimensioning and positioning the outlet opening and / or by using a blower.

[0066] According to a particularly advantageous embodiment, the method according to the invention comprises the use of a plurality of gases or gas mixtures for providing the gas atmosphere, comprising a first gas or gas mixture having a first volume fraction of oxygen and a second gas or gas mixture having a second volume fraction of oxygen lower than the first volume fraction, which can be used as described below.

[0067] In one embodiment of the invention, it can be provided that at least a portion of the first gas or gas mixture is fed to at least one first region of the reaction vessel, while at least a portion of the second gas or gas mixture is fed therefrom separately to at least one second region of the reaction vessel. This embodiment in particular makes it possible to adjust the spatial distribution of the oxygen content in a particularly advantageous manner depending on the local requirements. It is also possible that the feeding to the first and second regions is carried out simultaneously, in particular in an adjustable amount in each case, or not simultaneously. For example, at least temporarily, the gas or gas mixture can be fed only to one of these regions, for example at subatmospheric pressure levels, when the air intake (and therefore the inflow of oxygen) is very high and only nitrogen or another inert gas is fed. A defined air intake can also be ensured, for example via adjustable or non-adjustable inflow openings, such as ventilation slots, flaps or closable holes. In order to be able to adjust the amount of incoming ambient air in this way, the corresponding inflow openings can be designed to be openable and closable, in particular in a variable number or with an adjustable flow cross-section. A corresponding adjustment of the inflow can therefore be understood within the meaning of the present invention as a further defined supply of the gas mixture, i.e. ambient air.

[0068] In this context, it is also possible to permanently supply a gas or gas mixture (whether premixed or not, as will be explained below) only to one area (for example, by means of supply means provided only at certain points of the reactor wall, as explained above, or also by inlet openings for air). Supply "to" the corresponding area or areas is performed in such a way that the corresponding gas or gas mixture (or the respective part) reaches the area or areas, which are for example below or to the side, so that the gas or gas mixture flows in the reactor vessel due to a defined flow in the reactor vessel, due to thermal effects or simply due to inflow impingement. Supply within these areas is also possible. However, in another embodiment of the invention, clean "instrument" air is used instead of the air leaking into the reactor. Advantages of using clean air include less ingress of dust, moisture and possible contaminants that may affect the life of the elements.

[0069] In particular, the heating elements may be arranged in at least one first region of the reaction vessel and the reaction tubes in at least one second region. By the described gas supply or the intake of ambient air, in particular a relative increase in the oxygen content in the region of the heating elements (to avoid deterioration / damage in the described manner) and a relative decrease in the oxygen content in the region of the reaction tubes (to minimize reactive conversion of components that may escape) can be achieved.

[0070] In particular, since the first and second regions are not separated from each other by any kind of separation device, such an arrangement can be used in particular when the corresponding first and second gases or gas mixtures can be continuously fed through the corresponding elements. The continuous feeding and drawing that occurs in this case allows the concentration gradient to be maintained, whereas intermittent feeding may rather lead to mixing over time. This embodiment of the invention is therefore advantageously used in the continuous case.

[0071] In addition to or instead of the previously described embodiment with separate feeds, at least a portion of the first gas or gas mixture and at least a portion of the second gas or gas mixture are fully or partially premixed outside the reactor and fed to the reactor in a fully or partially premixed state. Such an embodiment is particularly suitable when the reactor does not have a continuous flow. This alternative interconnection allows to minimize concentration gradients in large-volume reactors, especially in the case of distributed metering at the bottom and / or side walls and / or ceiling of the reactor. The advantage of targeted oxygen enrichment in the region of the heating elements, which is possible with the previously described design, is then traded off for a significantly more uniform distribution and a reduced risk of unfavorable local imbalances (e.g., local too little oxygen in some heating elements or too high oxygen concentration near the reactor tubes).

[0072] A combination of corresponding measures is also possible, such as, for example, separate feeding of premixed and non-premixed gases. In this case, for example, a mixture of nitrogen and air can be fed to the wall of the reaction vessel, while nitrogen can be fed to the center of the reaction vessel. In this way, a moderate oxygen enrichment can be achieved in the vicinity of the heating element, while at the same time, concentration gradients can be limited by partial premixing.

[0073] In principle, in various embodiments of the invention, the feed can be made to various locations in the reaction vessel, in particular to multiple points.

[0074] The first gas or gas mixture may be or may contain air, a gas mixture enriched or depleted in oxygen compared to air, or oxygen, and the second gas or gas mixture may be or may contain a gas mixture depleted in oxygen compared to air, nitrogen, carbon dioxide, or another inert gas. In principle, the first gas or gas mixture may contain oxygen in a volume fraction of more than 1%, 5%, 10%. Known processes, for example air separation, can be used to provide the corresponding gas or gas mixture. The term "inert gas" is understood in this specification to mean a gas that does not participate as a reactant in the oxidation reaction, in particular under the conditions prevailing in the reaction vessel. As mentioned above, it is also possible to supply only one gas or gas mixture, in particular with respect to the second gas or gas mixture, having the composition described above.

[0075] In all cases, the actual volume fraction of oxygen in at least one region of the reaction vessel can be detected during the reaction period and / or at the start of the reaction period, and the supply of one or more gases or gas mixtures used to provide the gas atmosphere can be regulated or controlled based on the detection, in particular by relative and / or absolute changes in amount. The detection can in particular be performed in predetermined periods or (quasi-)continuously.

[0076] In embodiments of the invention where there is continuous flow through the reaction vessel, detection of oxygen content can preferably be performed downstream of the outlet from the reaction vessel (e.g., in a stack or bypass line, etc.). Additionally or alternatively, oxygen content can be measured at one or more locations within the reaction vessel. Any suitable method of measuring oxygen content can be used, for example, tunable laser diodes, zirconium oxide probes, gas chromatography, paramagnetism, etc.

[0077] If the reaction vessel is intermittently pressurized, the oxygen content can similarly be measured in the corresponding purge gas exhaust line and / or in the reaction vessel itself.

[0078] In all embodiments of the invention, if the oxygen concentration exceeds a maximum allowable level, any kind of safety-related function can be initiated. If the oxygen level falls below a minimum allowable level, operational measures can be initiated to re-establish the desired oxygen content in the reactor. Too low an oxygen concentration is not considered a safety concern, but as mentioned above, it may affect the life of the heating elements.

[0079] Unacceptable leakage of gas from the reaction tube can also be detected, in particular via a pressure measuring sensor in the reaction vessel, so that, for example, the injection of reactants can be immediately blocked or stopped on the basis of a corresponding switching signal.

[0080] The content of one or more reactants (in particular as carbon monoxide equivalents) can also be measured continuously in the purge stream to detect minor damage to the reaction tubes (leaks without a sudden or measurable pressure rise). Unacceptable values ​​can also lead to a rapid halt to the supply of reactants.

[0081] If suitable measurement methods are used (e.g. laser, gas chromatography), for example the content of hydrocarbons or their combustion products can additionally or alternatively be measured with the same sensor in the region of the reaction vessel for all the designs described.

[0082] In embodiments of the present invention, leak detection may be achieved particularly in the presence of moisture since reactor tubes typically contain significant amounts of steam.

[0083] Thus, more generally, the invention may involve determining a value indicative of a gas leak from one or more reactor tubes based on pressure and / or hydrocarbon measurements and / or moisture detection, and initiating one or more safety measures if the value exceeds a predetermined threshold.

[0084] Furthermore, in certain embodiments, the present invention provides means for carrying out possible pre-heating of the conditioning gas prior to its free flow into the reactor vessel, such pre-heating can be carried out in particular in heat exchange with gases withdrawn from the reactor chamber.

[0085] In other words, the gas or gas mixture, or at least one of the two or more gases or gas mixtures, used to provide the gas atmosphere may be preheated before being supplied to the reaction vessel.Embodiments of the invention may include waste heat recovery, particularly including preheating achieved via heat exchange with gases exiting the reaction vessel.

[0086] In particular, when injecting the corresponding gas or gas mixture close to the wall, it may be advantageous to preheat the corresponding gas or gas mixture, for example by first passing it through a pipe passage of sufficient length through the interior of the coil box, i.e. the reaction vessel, and then leading it to the injection device. In this way, it is possible to avoid the occurrence of undesired cooling of the heating element by the cooling conditioning gas, which may impair the target power of the heating element.

[0087] In particular, the injection device can be placed directly at the end of the heated pipe passage, or the heated conditioning gas can be first led back from the coil box into a pipeline (preferably an insulated pipeline) and then be an injection device from outside. Alternatively, an external heat source can be used to preheat the conditioning gas (electricity, steam, hot oil, hot water, etc.).

[0088] The gas injection means used in the corresponding embodiment of the invention may therefore comprise one or more preheating devices and one or more injection devices. In the present context, "injection" is intended to refer in particular to the release of a gas or gas mixture into the reaction vessel via the corresponding injection device.

[0089] In other words, in a particularly preferred embodiment of the present invention, means may be provided for transferring sensible heat in or from the interior of the reaction vessel to a corresponding gas or gas mixture.

[0090] The invention further proposes a reactor for carrying out chemical reactions, comprising a reaction vessel, a reaction tube arranged in the reaction vessel and means adapted to heat the reaction tube, during the reaction period, to a reaction tube temperature level between 400° C. and 1500° C., using radiant heat provided by one or more electric heating elements arranged in the reaction vessel. The reactor is characterized by means adapted to provide, during the reaction period, in at least a part of the reaction vessel provided with the heating element, a gas atmosphere with a volume fraction of oxygen adjusted between a first limit value and a second limit value, the first limit value and the second limit value being selected as indicated above for the process proposed according to the invention.

[0091] In particular, explicit reference is made to the above description for further embodiments of corresponding reactors which may be configured to carry out the process of any of the embodiments described above.

[0092] The features and advantages of the present invention and its advantageous embodiments are explained again below.

[0093] The proposed concept of filling an almost completely sealed reaction vessel with a specific gas atmosphere allows the oxygen content to be reduced compared to the outside ambient air. As can be utilized according to the invention, the conversion of the escaping hydrocarbons in case of failure of one or more reaction tubes and the resulting additional volume expansion (as a result of the heat input of the reaction) are correlated in a first approximation with the oxygen partial pressure. This correlation is summarized in Table 1 below, where xO2 is the oxygen mole fraction and V reak is the volumetric inertia associated with the reaction. The values ​​shown below are examples and are not intended to provide generally valid quantitative information.

[0094] The maximum oxygen content in the reaction vessel (ie the second limit value used in particular according to the invention) can be specified based in particular on the dimensioning of the outlet stack.

[0095] Table 1 TIFF2024514553000002.tif82170

[0096] Maximum allowable pressure in the reaction vessel p max is determined by the mechanical stability of the respective chamber or surrounding containment. This is because the pressure p box must be at least as high as the volume of the chamber involved, V Box , diameter of outlet stack D stack , and the oxygen mole fraction, p max ≧p box =f(V Box ,D stack ,xO2) Depends on.

[0097] This requirement is the design criterion for dimensioning the outlet stack. This relationship is explained with reference to Figure 5. For example, if a maximum allowable pressure increase of 20 mbar is used as a criterion, as illustrated by dashed lines 51 and 52, the reaction-related volume increase must be a maximum of about 10 mbar to be able to use a stack (dashed line 51) with a diameter of 500 mm. 3 / sec, which gives a maximum oxygen content of approximately 1%. Looking at this inversely, if you want to use the maximum 1% oxygen content you need to use a stack diameter of at least 500mm.

[0098] To be able to use a stack with a diameter of 900 mm (dashed line 52), the volume ratio is about 42 m 3 / sec or less, which translates to a maximum oxygen content of approximately 4%. Conversely, similar to the explanation above, if a maximum oxygen content of 4% is used, a stack diameter of at least 900mm should be used.

[0099] The lower the oxygen content in the reaction vessel, the smaller the increase in volume. The diameter of the outlet stack, which needs to dissipate the additional volume, can therefore also be smaller. The determining factor for effectively limiting the oxygen content is always to have a sufficiently good seal against the environment, particularly under subatmospheric pressure conditions inside the reaction vessel, to sufficiently prevent or minimize the uncontrolled ingress of oxygen-containing air. However, as explained, a perfect seal is not necessary in this case.

[0100] The present invention will now be further described with reference to the prior art and with reference to the accompanying drawings which show embodiments of the invention in comparison with the prior art. [Brief description of the drawings]

[0101] [Figure 1] FIG. 1 is a schematic diagram of a reactor for carrying out chemical reactions, according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a reactor for carrying out chemical reactions, according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic diagram of a reactor for carrying out chemical reactions, according to one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a reactor for carrying out chemical reactions, according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic diagram illustrating the basic principles of stack sizing according to one embodiment of the present invention. [Figure 6A] FIG. 6A is a schematic diagram of an example pressure flap device, according to an embodiment of the present invention. [Figure 6B] FIG. 6B is a schematic diagram of an example pressure flap arrangement, in accordance with an embodiment of the present invention. [Figure 6C] FIG. 6C is a schematic diagram of an example of a pressure flap arrangement, in accordance with an embodiment of the present invention. [Figure 6D] FIG. 6D is a schematic diagram of an example pressure flap arrangement, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0102] In the drawings, structurally or functionally corresponding elements are illustrated with the same reference numerals and are not repeatedly described for the sake of clarity. Where components of a device are described below, the corresponding description also refers in each case to the processes carried out using the device and vice versa.

[0103] In the reactor illustrated in Figure 1 and generally designated 100, illustrated in very simplified form, a reaction tube 2 designed as described above is placed in a reaction vessel 1 also designed as described above. A heating element 3 of the same type described above is placed in the wall of the reaction vessel 1, which indirectly heats the reaction tube 2 using radiant heat.

[0104] In the illustrated example, gas supply means 4 are arranged at the bottom of the reaction vessel 3, which allows for the supply of gases or gas mixtures with different oxygen contents, as illustrated herein with arrows 4.1 and 4.2. In the embodiment illustrated herein, these gases or gas mixtures are supplied separately, whereby in particular a gas or gas mixture 4.1 with a higher oxygen content than gas or gas mixture 4.2 can be supplied in the region of the reaction tube 2, in order to provide a higher oxygen content in the region of the heating element 3.

[0105] Herein, gas extraction means 5 in the form of a permanently open stack opening to the stack 6, with simultaneous supply via gas supply means 4, allows a continuous flow through the reaction vessel 1 to be achieved with the advantages previously mentioned. This allows the reaction vessel 1 to be operated at sub-atmospheric pressure levels due to the lower density of the hot gas atmosphere in the stack compared to ambient air. The air inlet is illustrated by an unlabelled curved arrow.

[0106] The reactor 200 illustrated in FIG. 2 is essentially different in that the gases or gas mixtures 4.1, 4.2 are already mixed externally to form a gas mixture 4.3, which is supplied to the reaction vessel 1 by gas supply means 4.

[0107] Also, as previously mentioned, all of the illustrated embodiments can be operated or provided with the supply of only a single gas or gas mixture, either temporarily or permanently.

[0108] The reactor 300 illustrated in FIG. 3 differs from the previously described designs in that the stack opening is closed by a rupture disk 7 or by other suitable means that only open the stack cross section if a certain reactor pressure is exceeded. Also, a gas extraction means, shown here as 5, establishes a bypass connection to the stack 6 and can in particular be appropriately regulated and / or dimensioned. In this way, a superatmospheric pressure level can be set in the reactor 1 with the advantages described. The gases used to provide the reactor 1 with the desired oxygen content can be premixed or fed separately, as shown here by dashed arrow 4.3 for illustrative purposes. Undetermined gas losses from the reactor 1 are shown with curved arrows.

[0109] A further embodiment of the reactor 400 illustrated in Fig. 4 does not have any permanently open gas extraction means, so that here no flow-through can be set up and preferably the reaction vessel 1 can be pressurized with a suitable gas atmosphere at the start or at regular time intervals. As before, the reaction vessel 1 is operated in particular at superatmospheric pressure level.

[0110] FIG. 5 shows, in diagram form, a schematic representation of the basic principle of stack dimensioning according to one embodiment of the invention, where the oxygen content in percentage is shown on the horizontal axis and the volume uncertainty factor (m 3The time required for a maximum pressure increase of 20 mbar is shown on the vertical axis ( / sec). Graph 51 represents the relationship already explained above with reference to Table 1. Dashed line 52 shows the value required for a maximum pressure increase of 20 mbar for a stack diameter of 500 mm and dashed line 53 shows the corresponding value for a stack diameter of 900 mm. Explicit reference is made to the above explanations.

[0111] 6A to 6D show schematic examples of pressure flap devices according to embodiments of the invention. As mentioned above, the flap devices are configured to close or partially close rectangular openings in the reactor wall, but circular openings or openings of different shapes in the reactor wall can be provided with such flap devices as well.

[0112] In either case, the flap arrangement comprises a first flap 601 and a second flap 602. In the embodiment shown in Figure 6A, the flaps 601, 602 are shaped to leave a circular opening 603 in the closed state to allow a defined gas flow, but according to the embodiment shown in Figures 6B and 6D, the flaps 601, 602 can also be sized to leave a slit-like opening 604 for the same purpose. In the embodiment shown in Figure 6C, a further opening 605 is provided for the same purpose. The flaps 601, 602 may be hinged to a portion of the reactor wall and may be provided in a spring or weight biased configuration. According to the embodiment shown in Figures 6C and 6D, the flaps 601, 602 themselves may be provided with a hinge, as shown at 606, or in other embodiments, a predetermined break line or notch. These or the biasing spring or weight forces may be configured such that the flaps 601, 602 open above a predetermined pressure.

Claims

1. 1. A method for carrying out chemical reactions using a reactor (100-400), in which a reaction tube (2) arranged in a reaction vessel (1) is heated from the outside to a reaction tube temperature level between 400° C. and 1500° C. during a reaction period using radiant heat provided by one or more electric heating elements (3) provided in the reaction vessel (1), during which one or more combustible components pass through the reaction tube (2), characterized in that in at least a part of the reaction vessel (1) provided with the electric heating element (3), during the reaction period or during a part of the reaction period, a gas atmosphere is provided, which gas atmosphere comprises, in addition to one or more known inert gases or one or more noble gases, a volume fraction of oxygen between 500 ppm and 10%, the mentioned oxygen content prevailing in the area in which the electric heating element is arranged.

2. 2. The method of claim 1, wherein the gas atmosphere comprises a volume fraction of oxygen between 1,000 ppm and 5%, or between 5,000 ppm and 3%.

3. 2. The method according to claim 1, wherein a continuous or discontinuous supply of one or more gases or gas mixtures is carried out which are used to provide the gas atmosphere to the reaction vessel (1) and / or to remove at least a portion of the gas atmosphere from the reaction vessel (1).

4. 4. The method according to claim 3, wherein the reaction vessel (1) is provided with a subatmospheric pressure level.

5. 4. The method according to any one of claims 1 to 3, wherein the reaction vessel (1) is provided with a superatmospheric pressure level.

6. 5. The method according to claim 1, wherein the wall (1) of the reaction vessel (1) does not have an inspection port for visual inspection of the inner space of the reaction vessel (1) or only has an inspection port for visual inspection of the inner space of the reaction vessel (1) that is hermetically closed with a transparent material.

7. 5. The method of claim 1, wherein one, two or more gases or gas mixtures are used to provide the gas atmosphere.

8. 8. The method of claim 7, wherein two or more gases or gas mixtures are used, including a first gas or gas mixture having a first volume fraction of oxygen and a second gas or gas mixture having a second volume fraction of oxygen that is lower than the first volume fraction.

9. 9. The method according to claim 8, wherein at least a portion of the first gas or gas mixture is supplied to at least a first region of the reaction vessel (1) and at least a portion of the second gas or gas mixture is supplied separately from the first region to at least a second region of the reaction vessel (1).

10. 5. The method according to claim 2, wherein a gas or gas mixture is used that is injected into a second region of the reaction vessel while no gas or gas mixture is injected into the first region of the reaction vessel.

11. 10. The method according to claim 9, wherein the heating element (3) is arranged in at least one of the first regions and the reaction tube (2) is arranged in at least one of the second regions of the reaction vessel (1).

12. 9. The method according to claim 8, wherein at least a portion of the first gas or gas mixture and at least a portion of the second gas or gas mixture are mixed outside the reaction vessel (1) and supplied in a mixed state to the reaction vessel (1).

13. 5. The method according to claim 2, wherein during and / or at the start of the reaction period, an actual volume fraction of oxygen is detected in at least one area of ​​the reaction vessel and / or stack, a bypass, or a purge line connected to the bypass, and the supply of the one or more gases or gas mixtures used to provide the gas atmosphere is regulated or controlled based on said detection.

14. 5. The method according to claim 3 or 4, wherein at least one of the gas or gas mixture or two or more gases or gas mixtures used to provide the gas atmosphere is preheated before injection into the interior of the reaction vessel (1).

15. A reactor (100-400) for carrying out chemical reactions, comprising a reaction vessel (1), a reaction tube (2) arranged in said reaction vessel (1) and means arranged for heating said reaction tube (2) from the outside during the reaction period up to a reaction tube temperature level between 400 °C and 1500 °C using radiant heat provided by one or more electric heating elements (3) arranged in said reaction vessel (1), said reactor being characterized by means adapted for providing a gas atmosphere during the reaction period or during a part of the reaction period to at least a part of said reaction vessel (1) provided with said electric heating element (3), said gas atmosphere comprising, in addition to one or more known inert gases or one or more noble gases, a volume fraction of oxygen between 500 ppm and 10%, said oxygen content mentioned prevailing in the area in which said electric heating elements are arranged.

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