Method and reactor arrangement for carrying out chemical reactions

Abstract

The invention relates to a method for carrying out a chemical reaction using a reactor device (100 to 400) in which a reaction tube (2) is arranged in a reactor vessel (1). During one or more first operating modes, one or more reactants are supplied to the reaction tube at a first mass flow rate. During the one or more second operating modes, the one or more reactants are not supplied to the reaction tube or the one or more reactants are supplied to the reaction tube at a second mass flow rate, which is lower at least over time average. During one or more first operating modes, radiant heat is provided at a first heat flow rate by one or more electrical heating elements (3) in the reactor vessel (1), and during one or more second operating modes, radiant heat is not provided or is provided at a second heat flow rate, which is lower at least over time average. In at least a portion of the reactor vessel (1) provided with one or more heating elements (3), a gaseous atmosphere is provided in which the oxygen content is adjusted to a predetermined volume fraction. During one or more first operating modes, the volume fraction of oxygen is adjusted between a first limit value not less than 500 ppm and a second limit value not greater than 10%, and during one or more second operating modes, the volume fraction of oxygen is adjusted between a first limit value not less than 500 ppm and a second limit value not greater than 10%. The volume fraction of oxygen is adjusted to a value that is at least on a time average basis that is higher than during the one or more first operating modes. The object of the invention also comprises the provision of a corresponding reactor device (100 to 400).

Description

Technical Field

[0001] The invention relates to a method for carrying out a chemical reaction and to a corresponding reactor device according to the preamble of the independent claim. Background Art

[0002] In many processes in the chemical industry, reactors are used, wherein one or more reactants are passed through heated reaction tubes, in which the reactants undergo catalytic or non-catalytic reactions. Heating is particularly useful for overcoming the activation energy required for a chemical reaction to occur, and in the case of an endothermic reaction, for providing the energy required for the chemical reaction. The reaction may be carried out as a whole in an endothermic manner, or in an exothermic manner after overcoming the activation energy. The present invention particularly relates to strongly endothermic reactions, as discussed further below.

[0003] Examples of such processes include steam cracking, various reforming processes, in particular steam reforming, dry reforming (carbon dioxide reforming), hybrid reforming processes, alkane dehydrogenation processes, etc. In steam cracking, the reaction tubes are passed through the reactor in the form of coils, the reaction tubes having at least one reverse bend in the reactor, while in steam reforming, tubes are usually used which pass through the reactor without reverse bends. The invention can also be used in conjunction with so-called "millisecond" or "single-pass" reactors, which are characterized by extremely short residence times.

[0004] Other applications of the invention are reactors for carrying out the reverse water gas shift (RWGS) reaction of carbon dioxide and hydrogen to produce carbon monoxide and water, the dehydrogenation of oxygen-containing compounds, such as the reaction of methanol to produce formaldehyde and hydrogen, the decomposition of ammonia to produce 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 (insofar as the term "reforming" as used above is not already included).

[0005] The present invention is applicable to all such processes and embodiments of the reaction tube. As examples only, reference may be made to the articles on "ethylene", "gas production" and "propylene" in the Ullmann Encyclopedia of Industrial Chemistry, for example, published on April 15, 2009, with a digital object identifier (DOI) of 10.1002 / 14356007.a10_045.pub2, published on December 15, 2006, with a DOI of 10.1002 / 14356007.a12_169.pub2, and published on June 15, 2000, with a DOI of 10.1002 / 14356007.a22_211.

[0006] The reaction tubes of the corresponding reactors are usually heated by using burners. For this purpose, the reaction tubes pass through a combustion chamber in which the burners are also arranged.

[0007] However, there is currently an increasing demand for synthetic products such as olefins, as well as for synthesis gas and hydrogen, and the requirement to produce these products with zero or reduced local CO2 emissions. Processes using combustion reactors cannot meet this demand, as they usually use fossil fuels. Other processes, for example, are virtually ruled out due to their high costs.

[0008] Therefore, it is proposed to supplement or replace the burners in the corresponding reactors with electric heating devices. In addition to direct electric heating (e.g. in the known star (neutral point grounded) circuit, the current is applied to the reaction tube itself) and other types of heating that are not described in detail here, there are also so-called indirect electric heating schemes. This scheme is also used within the scope of the present invention. Regardless of the specific type of heating and the heating scheme implemented in the process, a suitably heated reactor is also referred to as a "furnace".

[0009] As described in WO 2020 / 002326 A1, this indirect electric heating can be carried out using an electrically operated radiant heating element ("radiant heater") suitable for heating to the high temperature required for the above-mentioned reaction. This heating element is arranged in the furnace in a manner that the heating element is not in direct contact with the reaction tube. Heat transfer is mainly or entirely carried out in the form of radiant heat. Therefore, the terms "indirect heating", "heating by radiant heat", etc. are used synonymously below. The characteristics of the corresponding heating element are described below.

[0010] Some other examples of prior art documents are discussed below, but it is not admitted that these documents in any way anticipate, suggest or otherwise relate to various aspects of the present invention and its following embodiments.

[0011] According to WO 2019 / 133215 A1, a method and system for optimizing a pyrolysis reaction using temperature measurements obtained from a compact insulated skin thermowell are provided. In the system and method disclosed in the document, the upstream temperature and upstream pressure of the pyrolysis reactor are measured by adiabatic restriction in the inlet manifold of the parallel tube assembly to provide an absolute upstream temperature and upstream pressure. The downstream temperature of the pyrolysis reactor is also measured after adiabatic restriction to provide an absolute downstream temperature. Then, the downstream pressure is determined by multiplying the absolute upstream pressure by the power of (k / k-1) of the quotient of the downstream temperature divided by the upstream temperature, where k is the ratio of the constant pressure specific heat (Cp) to the constant volume specific heat (Cv) of the fluid.

[0012] In US2019 / 002389 A1, a process for continuously preparing tert-butyl ester of olefinically unsaturated carboxylic acid is disclosed, which is carried out by the following steps: a) reacting an olefinically unsaturated carboxylic acid with isobutylene in the presence of an acidic catalyst to obtain an esterification mixture; b) removing the acidic catalyst; c) removing low-boiling components; and d) supplying a liquid containing tert-butyl ester to a distillation apparatus and purifying and distilling the liquid in the distillation apparatus. wherein d1) in a distillation apparatus, the liquid containing tert-butyl ester is separated into a gaseous top product containing tert-butyl ester and a liquid bottom product containing carboxylic acid; d2) the gaseous top product containing tert-butyl ester is at least partially condensed and part of the condensate is recycled to the distillation apparatus as reflux; d3) the liquid bottom product containing carboxylic acid is at least partially recycled to step a); d4) the liquid bottom product containing carboxylic acid is removed and fed to a heater, a superheated liquid recycle stream is removed from the heater and the superheated recycle stream is discharged downwardly into the distillation apparatus; and d5) at least in the top region of the distillation apparatus, the walls of the distillation apparatus which are in contact with the vapor at least in a subregion are heated and / or insulated. In this process, the separation of tert-butyl ester from unreacted carboxylic acid is carried out at a particularly low level of concomitant polymerization of both tert-butyl ester and carboxylic acid.

[0013] According to EP 1 273 552 A2, a hydrogen production device is provided for supplying at least one type of material to a reaction part together with air, oxygen or an oxidant to produce hydrogen through a specific chemical reaction, wherein, for at least one type of material, the supply amount of each material is set by selecting one of two or more set values ​​predetermined corresponding to the required hydrogen production volume, and for air, oxygen or an oxidant, the supply amount of air, oxygen or an oxidant is changed and controlled so that the temperature of the reaction part is within a preset temperature range.

[0014] EP 4 056 892 A1 discloses a steam cracking method using a steam cracking system, the steam cracking system comprising a first steam cracking furnace unit or a plurality of first steam cracking furnace units and a second steam cracking furnace unit or a plurality of second steam cracking furnace units, wherein each of the first steam cracking furnace unit or the plurality of first steam cracking furnace units comprises one or more fired steam cracking furnaces, each of the second steam cracking furnace unit or the plurality of second steam cracking furnace units comprises one or more electric steam cracking furnaces, and each of the first steam cracking furnace unit or the plurality of first steam cracking furnace units comprises a device for preheating at least a portion of the combustion air supplied to its fired steam cracking furnace to a temperature level of at least 100°C.

[0015] EP 3 862 076 A1 relates to a reactor for carrying out a chemical reaction, which has a reactor container and one or more reaction tubes. In this case, several tube sections of the one or more reaction tubes extend between a first region and a second region in the reactor container, respectively, and in this case, in order to heat the tube sections, each tube section can be electrically connected to a phase terminal of a multiphase AC power supply in the first region. According to the document, the tube sections are connected to one another in an electrically conductive manner in the second region as a whole via a single rigid connecting element or in groups via a plurality of rigid connecting elements, which are integrally connected to the single or multiple reaction tubes and are arranged in the reactor container.

[0016] WO 2020 / 002326 A1 relates to a reactor configuration, comprising at least one electrically heated furnace, which defines a space, at least one reaction tube is placed in the furnace space, and the reaction tube has an outlet and an inlet outside the reactor furnace. In addition, the furnace is also provided with: at least one electric radiation heating element suitable for heating to a high temperature in the range of 400 to 1400°C, the heating element is located in the furnace so that the heating element is not in direct contact with at least one reactor tube; and a plurality of inspection ports in the furnace wall so that the condition of at least one reactor tube can be visually inspected from each opposite side of the reactor tube during operation, the total number of inspection ports is sufficient to inspect the full length and circumference of all reactor tubes in the furnace, and wherein the heating load of the furnace is at least 3MW. The electrically heated process requires heat flow and temperature distribution. In many applications, the heat flow is large when the process enters the furnace, but with a lower temperature. When approaching the outlet, the heat flow is low, but with a higher temperature. The present invention can meet this requirement. The reactor is used in many industrial-scale high-temperature gas reforming and heating technologies.

[0017] US2020 / 299131 A1 discloses a liquid fuel catalytic partial oxidation (CPOX) reformer and a fuel cell system, which may include a plurality or a group of spaced CPOX reactor units, each reactor unit including an elongated tube having a permeable wall with an inner surface and an outer surface. The wall surrounds a smooth gas flow channel. At least a portion of the wall is provided with a CPOX catalyst, and / or the structure of the wall is formed by a CPOX catalyst. The structure of the catalyst-containing wall and the open gas flow channel surrounded by the wall define a gas-phase CPOX reaction zone, and the portion of the catalyst-containing wall is permeable to allow the gaseous CPOX reaction mixture to diffuse into the wall and allow the hydrogen-rich product reformate to diffuse out of the wall. The liquid fuel CPOX reformer may also include an evaporator, one or more igniters, and a liquid reformable fuel source. The hydrogen-rich reformate can be converted into electrical energy in a fuel cell unit integrated with the CPOX reactor unit.

[0018] The object of the present invention is to provide measures which enable advantageous operation of a reactor of the type described above which is indirectly electrically heated using suitable heating elements. Summary of the invention

[0019] Against this background, the present invention proposes a method for carrying out a chemical reaction and a corresponding reactor device comprising the features of the independent claims. Embodiments of the invention are subject matter of the dependent claims and of the following description.

[0020] The present invention relates to a method for carrying out a chemical reaction, wherein a reactor device is used, in which a reaction tube arranged in a reactor vessel is provided. During one or more first operating modes, one or more reactants are supplied to (and through) the reaction tube at a first mass flow rate, and during one or more second operating modes, these reactants are not supplied to (and through) the reaction tube, or during these one or more second operating modes, these reactants are supplied to (and through) the reaction tube at a second mass flow rate, and the second mass flow rate is lower than the first mass flow rate at least on a time-averaged basis. "Time-averaged basis" means that the flow rate can fluctuate within a specific time period, but the average flow rate within this time period is characterized as being lower in the second operating mode. The time basis can be one or each of a plurality of second operating modes, in particular compared to one or each of a plurality of first operating modes, or compared to a corresponding time-averaged basis. Compared to the first operating mode, other reactants can also be used in one or more second operating modes, such as air in a decoking mode. Different reactants can also be used between different second operating modes.

[0021] In this regard, the one or more first operating modes may correspond to, or be performed during, one or more reaction time periods described in more detail below. The one or more second operating modes may correspond to, or be performed during, one or more heating, cooling, load change, decoking, or standby time periods also discussed below.

[0022] The present invention is particularly advantageous in that it is able to handle (severe) load changes. Such load changes may occur between a first operating mode and a second operating mode, or between different second operating modes, as referred to above in the term "load change period". In particular, load changes associated with different power outputs of the heating element may result in a particularly high load on the heating element. The present invention solves this problem, as further explained below.

[0023] According to the invention, during one or more first operating modes, radiant heat is provided by one or more electrical heating elements arranged in the reactor vessel, the radiant heat is supplied to the reaction tube at a first heat flow rate, and during one or more second operating modes, no radiant heat is supplied to the reaction tube, or during one or more second operating modes, radiant heat is supplied to the reaction tube at a second heat flow rate, which is lower than that of the first operating mode, at least on a time-averaged basis. With regard to the meaning of "time average", reference is made to the above description. As above, the corresponding time can be one or more time periods for executing one or more second operating modes, in particular compared with one or more time periods for executing one or more first operating modes, or again corresponding to time average. As described below, the reaction tube can thereby be kept at a temperature within different temperature ranges. In particular, the first heat flow rate can be provided by operating one or more heating elements with a constant or substantially constant power input or current, and the second heat flow rate can be provided by operating one or more heating elements with a lower power input or current (at least on a time-averaged basis), which lower power input or current can also vary accordingly over time. For the present invention, it is not necessary for one or more heating elements to provide any heat flow rate in one or more second operating modes. In contrast, in one or more second operating modes, a so-called "hot steam standby" can also be implemented, for example in which steam is passed through the reaction tubes to keep the steam at a specific temperature, i.e., to keep the steam at a predetermined temperature or within a predetermined temperature range, but the heating elements are set to low power consumption or current, or optionally completely stopped.

[0024] The reaction tube temperature reached by using the first heat flow at the reaction tube can be selected to be the same as or equivalent to a combustion furnace or other electric heating furnace. This temperature covers a wide range because a considerable temperature gradient ("cold" inlet and "hot" outlet, especially when coking is aggravated) always occurs in the corresponding reaction tube. When using a radiation heating element, due to the need for a high heat flow, the temperature level of the above-mentioned reaction tube requires a higher temperature of the heating element. In short, the average temperature of the heating element is usually "floating" above the average temperature level of the reaction tube, and the "floating height" between these temperatures is proportional to the density of the heat flow required for the process during operation. The higher the density of the required average heat flow, the greater the average temperature difference between the heating element and the reaction tube. However, the local temperature of a specific heating element surface position will vary and is caused by a complex thermal equilibrium process at a given position, which involves all relevant heat transfer mechanisms (radiation, convection, conduction) and Joule heat caused by current.

[0025] As mentioned above, the invention can be used in particular for the production of olefins and / or other synthetic products by steam cracking or for the production of synthesis gas or hydrogen by steam reforming, as described at the beginning. However, the invention is applicable in principle to all types of reactions in which the feed mixture is passed in the gaseous state through reaction tubes heated from the outside to a suitable temperature level and reacts.

[0026] The reaction tube can pass through the reactor vessel in any conceivable way, in particular with or without one or more reversal points or reversal bends. In particular, the reversal tube can be arranged in a single 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 middle region between the two planes and corresponding heating from the outside of the middle region are also possible. In particular, the reaction tube length is 5m to 100m and / or the diameter is 20mm to 200mm. In addition, each reaction tube can be designed as two or more parallel sections, and the diameter of the tube is smaller than that of a single tube. Preferably, the multi-strand tube section is arranged near the entrance of the furnace to provide the area of ​​the reaction tube wall with the highest possible length in this area. Further downstream of this arrangement, the initial parallel strands are combined into a common strand with a preferably larger diameter. In this example, the reaction tube consists of two or more parallel strands, in particular a connection portion including a connecting fitting, and a combined strand. On the contrary, in principle, a multi-strand design of the reaction tube can also be provided at the end or middle section of the reaction tube, with an intermediate partition and additional connectors when necessary. Generally, in embodiments of the invention, the tubes can be divided and combined in any conceivable manner. Depending on the type of reaction, the reaction tubes can also be filled with suitable catalyst materials and / or inert materials, or remain in the form of empty tubes.

[0027] The invention provides for heating the reaction tubes using electrically provided radiant heat. However, this does not exclude the use of other types of heating in addition thereto, such as direct heating using the reaction tubes themselves as resistors to generate heat, induction heating, or heating using burners in other reactor vessels of the reactor apparatus. In either case, in addition to radiant heat, part of the heat provided by suitable heating elements can also be transferred to the reaction tubes by convection.

[0028] Therefore, if reference is made herein 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. In particular, it is also conceivable that the contribution ratio of the electric heating type and in particular the non-electric heating type is adjusted over time, for example depending on the supply and price of electricity or the supply and price of non-electric energy sources.

[0029] A "reactor vessel" is understood herein as a shell that is partially or completely insulated from the outside, and in particular may be lined with a material that is heat-resistant at the above-mentioned temperatures. In particular, the reactor vessel is mainly, i.e. at least 90%, 95%, 99%, 99.5% or 99.8%, surrounded by (solid) walls with insulating properties. These walls may include a tight, continuous or impermeable backing layer, such as a metal sheet, and one or more insulating layers. The figures given for the proportion in which the reactor vessel is "surrounded by insulating walls" may in this regard be understood in particular as the proportion of the entire shell of the reactor vessel that is composed of a solid structure with insulating properties, i.e., the solid structure is coated with insulating material or is made of insulating material or includes insulating material. The openings or ports of the reactor shell, which are generally not provided as completely insulating, may not be included in the proportion values ​​given for the "mainly surrounded" reactor vessel. As understood herein, any part of the reactor wall provided as "insulated" may have a thermal insulation resistance of less than 2 W / m2K, in particular less than 1.5 W / m 2 K, 1W / m 2 K, 0.5W / m 2 K or 0.2W / m 2 The term "heat transfer coefficient" is intended to mean that the value designated by the relevant figure refers (only) to the conduction heat transfer coefficient in the solid structure (in particular excluding radiation and convection heat transfer components on the inside and outside of the wall). For example, if the reactor vessel is surrounded by at least x% of the insulating wall as described above, these x% or less of the wall area can be configured to have the above-mentioned heat transfer coefficient. As described above, the openings or ports of the reactor shell may not be correspondingly insulated, so the heat transfer coefficient of the opening or port may be higher, or, for example, in the case of permanent openings, the opening or port may not constitute insulation at all. In order to provide a reactor wall with an insulating configuration, the wall can be made of, include, or be coated with an insulating material as described above, such as but not limited to ceramic fibers, heat-reflecting metal foils, minerals and expanded polymers or any combination thereof. In particular, different insulating materials can be provided depending on the local temperatures and different thermal resistances present.

[0030] As mentioned above, the invention is not limited to the use of only one reactor vessel, but in particular can also be used for combinations of reactor vessels with different heating. Further details about the respective reactor vessel, the gas feed device of the reactor vessel, the gas extraction device if applicable, and the connection of the gas extraction device to a chimney or the like will be explained in detail later. In this article, the terms (outlet) "stack" and "chimney" are synonymous, both referring to a structure whose (primary) function is to provide a fluid connection to a safe exit location, for example to the atmosphere, and which exit location is preferably at a sufficient height from the ground.

[0031] Within the scope of the present invention, the reactor vessel does not need to be designed to be airtight, or at least not completely airtight. According to an embodiment of the present invention, a reactor vessel with sufficient airtightness is particularly provided to be able to actually control the oxygen level in the container. As described herein, the concentration of defined oxygen is particularly advantageous at the heating element, so the airtightness of the reaction vessel near the heating element is particularly relevant. Therefore, near the heating element, the wall of the reactor vessel can be set with lower airtightness. However, not all embodiments of the present invention are so arranged. To avoid ambiguity, airtightness may not involve any intentionally introduced gas, even if the gas flows under the influence of the pressure difference between the outside and the inside of the reactor vessel, i.e., through the wall of the reactor vessel.

[0032] "Reaction period" is understood herein to mean the time period or a portion of the corresponding time period during which the reaction is carried out and the reactants required for the reaction are passed through the reaction tubes. This corresponds in particular to the first operating mode. Typically, during the reaction period, combustible components, in particular hydrocarbons, are contained in the process feed gas and therefore pass through the reaction tubes. In periods other than the reaction period, for example in the regeneration period or inertization period (i.e., in particular in the second operating mode), such combustible components are generally not passed through the reaction tubes.

[0033] In an embodiment of the invention, the reaction tubes are heated to the reaction tube temperature level in the time period before the actual reaction period, in the reaction period the reaction tubes are kept at the reaction tube temperature level and / or, in each case during the cooling period after these reaction periods, are cooled from this reaction tube temperature level. The reaction time period is in particular a time period during which "one or more first operating modes" are carried out in the sense understood herein, while the heating or cooling time period is in particular a time period during which "one or more second operating modes" are carried out in the sense understood herein, as described above. The heating is carried out in particular after a (temporary) shutdown of the reactor plant, for example for cleaning, decoking, repair and / or maintenance. Accordingly, the cooling is carried out before the (temporary) shutdown and may comprise active or passive cooling (i.e. "natural cooling" of the reactor).

[0034] As is generally known, a process of the type described may in particular also comprise a decoking operation, in which, after a corresponding reaction period, the deposits formed in the reaction tubes are removed, for example by "burning off" with the aid of an oxygen-containing gas or gas mixture. This applies in particular to pure gas-phase reactions without the use of a catalyst. Before a corresponding decoking operation, the reaction tubes are generally purged of reactants and in particular precooling or subsequent heating is carried out. The corresponding time periods of the decoking operation, as well as corresponding time periods of standby operation, in which pure steam is added to the reaction tubes to avoid (excessive) cooling (so-called "hot steam standby operation") and time periods of cooling or heating are not counted as part of the reaction period in the understanding used herein. That is, the "one or more first operating modes" are not carried out during the corresponding time periods, just as they are not carried out during maintenance periods or during time periods for replacing or regenerating the catalyst bed. These time periods are time periods in which the "one or more second operating modes" are carried out.

[0035] To summarize the above, during one or more second operating modes, the reaction tubes may be operated in at least one of the following modes: in at least one steam standby mode, wherein the reaction tubes are maintained at a predetermined temperature or temperature range by passing steam through the reaction tubes; in a decoking mode, wherein the reaction tubes are decoked by passing steam and air through the reaction tubes; and in a transient cracking mode, wherein the reaction feed load passing through the reaction tubes and / or the process gas temperature at the reaction tube outlet are changed over time. The heating elements may be operated or not operated depending on the specific operating mode. In particular, in the steam standby mode, the heating elements may be stopped, but may also be operated in a "hot" steam standby. In the decoking mode, the heating elements may be operated specifically, while in the transient cracking mode, the load of the heating elements may be changed according to the reaction feed load and / or the process gas temperature at the reaction tube outlet.

[0036] In the context of the present invention, "first" and "second" operating modes may refer to general operating modes of a reactor device or reactor vessel. These modes may include: (i) one or more modes with or without gas flow through the reactor tubes; (ii) one or more modes with a hydrocarbon-containing mixture passing through the reactor tubes, in particular in cracking operation of a reactor device arranged for steam cracking; (iii) one or more modes with steam passing through the reactor tubes in standby operation; (iv) one or more modes with a mixture containing air passing through the reactor tubes, in particular for decoking; or (v) one or more modes of other startup and shutdown operations involving gas flow, in particular nitrogen, air or similar "start-up media". These modes may also be specified based on, for example, the detected operating time of the reactor device or reactor vessel after a specific event (e.g. since the last decoking cycle).

[0037] Whether the first or second operating mode is online or in execution can also be specified alternatively or additionally on the basis of instantaneous measurement data, for example based on temperature measurements in the region of the heating element, in or on the reaction tube, or on the temperature of the process gas at the reaction tube outlet. Accordingly, it is also possible to obtain, for example, current quantity measurements, in particular in the feed line of the reaction tube (for recording flow rates and current composition), oxygen measurements in the reactor vessel and / or in a connected chimney or in a chimney exhaust, pressure measurements in the reactor vessel, analytical measurements downstream of the reaction tube outlet (for determining the composition of the product and, on this basis, for example, determining the gradient sharpness), heating power, measured values ​​of the applied voltage and / or current intensity, as well as pressure measurement data upstream and / or downstream of the reaction tube or pressure difference measurements across the reaction tube, etc.

[0038] In some embodiments, the present invention may include any process controls, which will be further described below. In particular, these process controls may be: (i) based on or used to set temperature set points (e.g., process gas temperature at the outlet of the reaction tube); (ii) specifications for flow control, in particular in the feed line of the reaction tube (for determining flow rate and current composition); (iii) set points for heating power, applied voltage and / or current intensity; and (iv) set points for heating rate or cooling rate. At any time, the acquired measurement data or set points can be evaluated over time and taken into account accordingly, and the time rate of change of the measured values ​​can also be determined (e.g., the average rate of change over a specific time period), and the time variability of the measured values ​​can be quantified (e.g., by obtaining the standard deviation of the measured values ​​over a specific time period). By using the time rate of change averaged over a meaningful time period, a signal with less noise can be obtained in particular.

[0039] In the scope of the present invention, during the reaction period or "first" operation mode described herein, one or more reactants for chemical reaction are supplied to the reaction tube, and during the heating period and / or cooling period or other corresponding "second" operation mode, one or more reactants are not supplied to the reaction tube, or one or more reactants are supplied to the reaction tube in an amount less than the reaction period. During the second operation mode, typical reactants, particularly hydrocarbons, are not used or are used in a smaller amount than during the first operation mode. Other reactants may include water (steam), oxygen and other compounds.

[0040] Within the scope of the invention, one or more second operating modes can also be applied during the reaction period, preferably during a sub-period in which a load change is carried out, for example by changing the feed rate, the product gas temperature and / or the product gas composition. Such a load change is accompanied by a change in the temperature level of the reaction tube and a change in the current or power input to the heating element, which in turn leads to a change in the temperature of the heating element.

[0041] According to the invention, a gas atmosphere is provided in at least a portion of the reactor vessel in which one or more heating elements are arranged.

[0042] A gas atmosphere is provided in at least a portion of the reactor vessel in which one or more heating elements are arranged, the gas atmosphere being separated from one or more reactants supplied to the reactor tubes, in particular by the tube wall of the reactor tubes. In other words, the oxygen content adjusted according to the invention relates in particular to the "gas space" of the reactor, i.e., the gas atmosphere is not in contact with the process gas passing through the reactor tubes containing the one or more reactants, except in the case of a coil rupture. However, the gas space is in direct contact with the outer surface of the heating element and the outer surface of the tube wall of the gastight reactor tube. Thus, the gas atmosphere surrounds the reactor tubes, but is not provided in the reactor tubes.

[0043] As mentioned above, the second operating mode can be a decoking operation, in which a decoking gas stream, for example a mixture of air and steam, is passed through the reaction tubes. The oxygen content of the gas atmosphere provided in at least a portion of the reactor vessel in which the one or more heating elements are arranged is adjusted, in particular independently of the oxygen content of the decoking gas stream. However, this can include simultaneously or temporally related increasing of the oxygen content in the gas space outside the reaction tubes.

[0044] According to embodiments of the invention, the amount of radiant heat supplied to the reaction tubes by one or more electrical heating elements in the reactor vessel may account for more than 90% of the total amount of heat supplied to the reaction tubes in the reactor vessel, in particular may be the entire amount of heat. That is, according to these embodiments of the invention, the reactor does not contain any (additional) combustion in addition to the electrical heating, or such combustion contributes only a small amount to the heat supply to the reaction tubes.

[0045] Therefore, in such an embodiment, the oxygen content set in the gas space outside the reaction tube has no significant effect on the heat input to the reaction tube. Therefore, oxygen control is only used for safety and service life protection, not for process control. In addition, unlike combustion furnaces, where the temperature of the combustion chamber is affected by the oxygen content and thus also the heat input to the reaction tube, the energy consumption of the electric furnace is not affected by the oxygen content. It should also be mentioned that the oxygen content in the coil box has no significant effect on pollutant emissions during normal operation of the electric furnace. Only the aging process of the heating element surface is affected, and aging here refers to slow reactions with very low conversion rates.

[0046] In particular, the gas atmosphere comprises an oxygen content in addition to one or more known inert gases such as nitrogen or carbon dioxide or one or more rare gases. According to the invention, the oxygen content is dynamically adjusted during operation to obtain a predetermined volume fraction value and / or value range of oxygen that varies over time. According to the invention, the adjustment is such that during one or more first operating modes, the volume fraction of oxygen is adjusted between a first limit value and a second limit value, the first limit value being between 500 ppm and 0.5% by volume, and the second limit value being higher than the first limit value and between 3% and 10% by volume. The first limit value may also be between 500 ppm and 0.1% by volume, between 0.1% by volume and 0.2% by volume, between 0.2% by volume and 0.3% by volume, between 0.3% by volume and 0.4% by volume, between 0.4% by volume and 0.5% by volume, or any continuous combination of two or more of these ranges. The second limit value may also be between 3% and 4% volume fraction, between 4% and 5% volume fraction, between 5% and 6% volume fraction, between 6% and 7% volume fraction, between 7% and 8% volume fraction, between 8% and 9% volume fraction, between 9% and 10% volume fraction, or any continuous combination of two or more of these ranges.

[0047] According to the invention, during one or more second operating modes, the volume fraction of oxygen is set to a higher value, at least on a time-averaged basis (in the sense explained above), than during one or more first operating modes. Herein, for a (feedback) control structure implemented in a control device or system for regulating the volume fraction of oxygen, a lower value may be used to define a lower threshold value and a higher value may be used to define an upper threshold value.

[0048] In particular, within the scope of the invention, during one or more second operating modes, the volume fraction of oxygen can be adjusted between a third limit value and a fourth limit value, wherein the third limit value is higher than the first limit value, the fourth limit value is higher than the second limit value, and / or wherein the third limit value is higher than the second limit value. The third and / or fourth limit value can be changed during one or more second operating modes, in particular over time. Therefore, for the (higher) oxygen content during one or more second operating modes, a corresponding threshold-based setting can also be performed, wherein the specifically set value can also be changed continuously or stepwise during one or more second operating modes, so as to correspond, for example, to a gradual increase in temperature and / or a gradual increase in the amount of reactant feed.

[0049] Generally, within the scope of the present invention, within the above-mentioned restrictions, a maximum oxygen content can be specified, in particular to be equal to or lower than the oxygen content in the atmosphere, i.e., in particular to a volume fraction of less than 20%, 15% or 10%. In one or more second operating modes, the time-averaged oxygen content at one or more locations in the reactor vessel is in particular higher than in one or more first operating modes by more than 0.1, 0.5, 1, 2 or 5 percentage points. Preferably, in transient cracking operation, or generally in any other second operating mode in which a combustible gas component is supplied to the reaction tubes, the time-averaged oxygen content at one or more locations in the reactor vessel is higher than in one or more first operating modes by 0.1 to 5 percentage points or between 0.5 and 2 percentage points, but remains lower than the oxygen content in the atmosphere or lower than a lower, safety-oriented maximum oxygen content. Preferably, in steam standby operation, decoking operation or generally in any other second operating mode in which no combustible gas component is supplied to the reaction tubes, the time-averaged oxygen content at one or more locations in the reactor vessel is higher than in one or more first operating modes by more than 1, 2 or 5 percentage points and can increase to the level of the oxygen content in the atmosphere.

[0050] According to an embodiment of the invention, by maintaining the oxygen content between variable limit values, the durability of the corresponding heating element can be increased on the one hand, and a higher level of operating safety can be ensured on the other hand. A relatively low oxygen content during one or more first operating modes ensures that a dangerous (flammable or explosive) atmosphere is reliably prevented from forming in the reactor vessel, or even if reactants leak from the reaction tube, the extent of combustion can be limited. By using a relatively high oxygen content during one or more second operating modes, it is reliably avoided that the heating element is particularly sensitive to damage to its surface protective oxide layer due to thermal expansion effects during these phases, or by improving the oxygen supply in the reoxidized atmosphere, defects occurring in the oxide layer can be repaired more quickly.

[0051] Providing the possibility of controlling the oxygen over time maximizes the durability of the heating element on the one hand and ensures always safe operation on the other hand. Therefore, within the scope of the present invention, various possibilities for dynamic atmosphere regulation that meet the above requirements can be implemented. In particular, the dynamic control can include dynamically adjusting the lower limit and / or upper limit of the oxygen content of the gas atmosphere in the reactor vessel depending on the instantaneous operating mode (being in the first or second operating mode) and the operating conditions. During this regulation process, the lower / upper limit shut-off limit value, the alarm limit value, the process switching value (especially in the case of floating control) and / or the process set point value (in the case of continuous control) can be changed.

[0052] The heating element for indirectly heating the respective reaction tube usually comprises an electrically conductive metal or non-metal heating structure having a given shape, such as a straight or other shaped rod, wire or strip, wherein the metal heating structure can preferably be made of an alloy containing at least the elements iron (Fe), chromium (Cr) and aluminum (Al). Alternatively or additionally, the metal heating structure can also be made at least partially of a nickel-chromium alloy, a copper-nickel alloy or a nickel-iron alloy.

[0053] It has been found that for indirect heating of reaction tubes, in particular in steam cracking, extremely high heat flux densities are required at high temperatures in order to achieve economical operation, so that the heating element or heating structure must be operated near its upper temperature limit. However, it is precisely near this temperature limit that the heating element and heating structure are highly sensitive to the furnace atmosphere. In particular, in order to avoid or slow down the rapid or gradual degradation of the heating element or heating structure, a certain minimum oxygen content is advantageous. For example, when using an aluminum-containing metal heating structure, a stable aluminum oxide layer can be maintained on the surface of the heating structure, which aluminum oxide layer can protect the material from uncontrolled corrosion and other damage mechanisms. Therefore, the present invention achieves a long durability of the heating element or its heating structure by using an appropriate minimum oxygen content.

[0054] It has been found that heating elements based on iron-chromium-aluminum (FeCrAl) are damaged when exposed to an atmosphere containing a high concentration of nitrogen and a low concentration of oxygen at high temperatures, resulting in a lower maximum operating temperature in such an atmosphere than the maximum operating temperature allowed in air. Without being limited to theory, it is believed that this damage is related to the formation of nitrides, which interfere with the formation of a protective aluminum oxide layer on the surface of the element and cause corrosion, which can significantly shorten the service life of the heating element. The extent and speed at which this damage occurs are related to the concentration of oxygen and oxygen-containing species in the atmosphere in contact with the heating element and the element temperature. For example, research recorded in the Journal of Mining and Metallurgy B - Metallurgy (J.Min.Metall.B) 2019 Vol. 55 showed that heating FeCrAl materials to 1200°C in an atmosphere of 99.996% nitrogen (with oxygen and water impurity levels below 10 ppm) resulted in the development of corrosion, which occurred through the formation of local subsurface nitrided areas consisting of AlN phase particles. In contrast, as reported in Surf. Coat. Technol., 2001, Vol. 135, p. 291, for FeCrAl alloys, no obvious morphological differences were observed between the scales obtained by oxidation in air or in a gas atmosphere containing 2% or 10% (volume fraction) oxygen.

[0055] Again, without being bound by theory and without limiting the scope of the invention, it is believed that the concentration of oxygen required at the surface of the heating element to prevent accelerated degradation of the element depends on the operating conditions, such as temperature and the thermal history of the heating element, which determine the thickness and quality of any protective oxide layer. Although in favorable circumstances, a relatively low oxygen concentration (e.g., 100 ppm) may be sufficient to prevent accelerated degradation, it is prudent to set the target oxygen concentration in the furnace atmosphere higher to take into account the situation where the surface of the heating element is more susceptible to nitridation, and to take into account the situation where the oxygen distribution in the furnace is not uniform, which may result in the oxygen concentration in the furnace being lower than the target concentration. Therefore, a practical lower limit for the oxygen concentration in the furnace or reactor vessel atmosphere appears to be 0.1% oxygen by volume, but 500 ppm may also be selected. Higher limiting concentration values, such as 0.2% oxygen by volume or higher, such as 0.5% or 1% by volume, may provide additional safety margins in less favorable furnace conditions or where the oxygen distribution is more significantly non-uniform, and may be selected in accordance with the invention. Conversely, low oxygen concentrations near the heating element may be beneficial as long as a minimum oxygen concentration is met to prevent nitride corrosion, since the oxidation rate of typical heating element materials is known to increase with increasing oxygen concentration. The minimum oxygen concentration may depend on the temperature as well as the composition of the heating element.

[0056] In view of the complexity of the underlying physical mechanisms in such a furnace and the wide range of operating conditions, it is particularly important to foresee the possibility of controlling the oxygen content over time and to adjust the gas atmosphere according to the requirements of the present invention.

[0057] The gas atmosphere provided according to the invention is advantageous for the above-mentioned metal alloys, but in principle it can also be used in conjunction with other materials, for example materials based on MoSi2 or SiC, even though the damage effects observed in each case are different.

[0058] An important consideration in determining the maximum oxygen content allowed is the flammability limits of the feed and product gases. Within the flammability range of all combustible gases, there is an oxygen concentration, commonly referred to as the limiting oxygen concentration (LOC), below which a flammable mixture cannot form. For example, at 25°C and 1 atmosphere, the LOC for ethylene is 10% oxygen. Under these conditions, any 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 conditioning procedures, the LOCs for ethane and ethylene at a typical steam cracking temperature of 830°C can be estimated to be 4.1% and 3.6%, respectively. If the oxygen concentration in the reactor vessel is below these limits, then a flammable mixture will not form in the event of a coil rupture.

[0059] While there is some uncertainty in calculating the same limit for a complex mixture like naphtha, the LOC for hexane is estimated to be 4.2%, so ethylene is expected to be the reactant / product with the lowest LOC. Although 830°C is above the autoignition temperature of all of these hydrocarbons, staying below the LOC is expected to prevent the formation of a shock wave even if autoignition occurs.

[0060] Based on these observations, the oxygen levels for the first and second operating modes of the present invention can be selected for any operating mode in which a combustible component is supplied to the process tube. It should also be noted that for one or more second operating modes in which a combustible component is not supplied to the process tube, the maximum oxygen level can be temporarily increased to the oxygen level in the atmosphere.

[0061] Typically, the heating element used within the scope of the present invention can have a substrate, for example, made of a non-conductive heat-resistant material (such as ceramic), on which a heating structure in the form of, for example, a heating wire or a heating belt is arranged, for example, in a zigzag manner, on or inside the substrate. Alternatively, one or more straight and / or curved heating structures with a bracket associated with the heating element can also be used. For example, a so-called heating cartridge can be used, which can be fixed to a suitable connection site by means of a plug-in or bayonet connection, etc. Typically, multiphase alternating current (AC), in particular three-phase alternating current, is used for heating, and the heating wires can be connected in groups to each phase of the corresponding alternating current, but direct current (DC) heating can also be used. The present invention allows any combination, arrangement and operating mode of the corresponding heating elements, without being limited thereto.

[0062] By using the invention, i.e. using a relatively high oxygen content, in particular during the heating and / or cooling phase or the respective other "second" operating mode, excessive aging of the heating element can be reliably avoided even during the respective heating and / or cooling process or in other operating modes that are (more) prone to this. For example, during the heating process, cracks can occur in the heating element, in particular due to different thermal expansions of the metallic base material of the heating element and the protective oxide layer formed thereon. The higher oxygen content can inhibit the formation of such cracks and contribute to the rapid regeneration of the intact protective oxide layer. At the same time, it is less important to ensure a low-oxygen atmosphere in the reactor vessel during the heating phase, in which, for example, steam is introduced into the respective reaction tube, but no combustible reactants, for example, hydrocarbons, have yet been introduced. The invention takes this into account.

[0063] Thus, before the above (particularly combustible) reactants, especially hydrocarbons, are introduced, the heating element may be heated to a relatively high temperature during a corresponding heating period, during which a relatively high oxygen content may still be maintained. The oxygen set point may then be reduced continuously or stepwise to a sufficiently low level to allow the introduction of reactants to begin. When steady state operation is achieved, a further reduction may be achieved.

[0064] In one embodiment of the invention, it is characterized by a plurality of individually controllable regulating gas injection points. For example, by adjusting the premix ratio at the injection point close to the wall, a reduction in the oxygen content can be achieved, so that the content in the region of the reaction tube remains essentially unchanged. During the cooling process after the reaction operation, the oxygen content in the reaction vessel can be increased accordingly by the reverse procedure.

[0065] As mentioned above, during one or more second operating modes, the volume fraction of oxygen can be varied continuously or stepwise, and during one or more second operating modes, the volume fraction of oxygen can be adjusted as a function of the reaction tube temperature, the heater temperature and / or the amount of reactants fed into the reaction tube, in particular can be varied continuously or stepwise. In this way, within the scope of the invention, the previously mentioned objectives (e.g. avoiding damage to the heating element and avoiding the formation of an explosive atmosphere) can always be achieved to the greatest extent possible.

[0066] As mentioned above, during one or more first operating modes, at least one section of the reaction tube can be kept at a certain reaction tube temperature level, so that the reaction tube temperature level of this section varies only within a predetermined range, in particular not more than 10 K, 30 K or 50 K. During one or more first operating modes, the heating element can also be energized, in particular with a constant or substantially constant effective current, wherein the substantially constant current refers to an operation in which the power consumption does not vary by more than 5%, 10%, 30% during one or more first operating modes. The power consumption in this context is preferably understood to be the effective power consumption averaged over a period of at least 10 s, 30 s, 1 min or 5 min, in order to filter out any short-term fluctuations, in particular related to power control operations (e.g. pulse control or phase angle control in thyristors).

[0067] On the other hand, in one or more second operating modes, for example, during the heating period or the cooling period, the temperature of the reaction tube may vary significantly. During the heating period, the reaction tube can be heated from an initial temperature level, for example, in the range of -50°C to 700°C, to a final temperature level, for example, in the range of 500°C to 1200°C, and vice versa during the cooling period. The temperature of the heating element will also vary accordingly, with the initial temperature level during the heating period also being, for example, between -50°C and 700°C, and the final temperature level being, for example, between 600°C and 1400°C. In all cases, according to the present invention, special consideration can be given to this by using different oxygen contents. Such a heating period can be carried out with or without energizing one or more heating elements installed in the furnace. For example, the initial heating stage can be completed by only an external preheating medium (such as steam, air and / or nitrogen) flowing through the reaction tubes in the furnace. Alternatively, the furnace can be at least partially heated by energizing one or more heating elements without any fluid flowing through the reaction tubes. In a preferred embodiment, at least a portion of the heating period includes flowing an external preheating medium (e.g., steam, air, nitrogen, and / or hydrocarbons) while simultaneously energizing one or more heating elements to gradually raise the temperature of at least a portion of the furnace. The cooling period can be operated in a similar manner, i.e., by varying the composition, flow rate, and / or preheating temperature of the fluid medium flowing through the reaction tubes, and / or varying the current passed through one or more heating elements in the furnace.

[0068] In a more general formulation, during one or more second operating modes, the volume fraction of oxygen may be varied at least temporarily or intermittently, while the second mass flow of one or more reactants may also be varied at least intermittently, and / or during one or more second operating modes, the flow of the second radiant heat may also be varied at least intermittently. The term "intermittently" means that such variation does not necessarily occur over the entire time that the corresponding operating mode is executed, but may be interrupted by periods of no variation. During one or more second operating modes, the at least intermittent variation of the volume fraction of oxygen may be performed with (at least) consideration of at least intermittent variation of the second volume flow of one or more reactants, and / or with consideration of at least intermittent variation of the second heat flow of radiant heat during one or more second operating modes. Other embodiments and criteria for executing the first and second operating modes have been described.

[0069] In other words, as also explained above, during one or more first operating modes, at least a portion of each reaction tube can be maintained at a reaction tube temperature in a first temperature range and during one or more second operating modes at a reaction tube temperature in a second temperature range. The first temperature range can in particular be 400° C. to 1500° C., further in particular 450° C. to 1300° C., 500° C. to 1200° C., or 600° C. to 1100° C., in particular on the reaction tube surface and / or in the reaction tube. The second temperature range is defined, for example, by a temperature difference to the first temperature range, in particular a temperature difference of at least 1 K, 10 K, 50 K or 100 K. In certain cases, this temperature difference can also be small, for example near the inlet of the reaction tube. In certain cases, this temperature difference can also be locally negative, for example when an elevated inlet temperature is used in the second operating mode. As mentioned above, the second temperature range can in particular also be achieved by appropriate pure steam flow standby operation.

[0070] In the context of the invention, the corresponding heating elements can be arranged in particular on the wall of the reactor vessel and radiate heat from there to the reaction tubes. The wall can be straight or curved, for example in the shape of a parabola. The wall can have any combination of wall shapes and, for example, can also have straight wall sections that can be arranged at an angle to one another or at any angle. The gas atmosphere provided according to the invention ensures that the mentioned oxygen content prevails in the region in which the heating elements are arranged.

[0071] The invention improves the operating safety of the corresponding reactor vessel due to the regulation of the upper oxygen limit during one or more first operating modes, in particular in the event of damage to the reactor tubes ("coil rupture"). In the event of corresponding damage, one or more reactor tubes can be cut off, in particular completely. However, the invention is also advantageous for leaks of smaller scale. In the event of corresponding damage, the combustible gas can suddenly or gradually leak into the reactor vessel, which is largely sealed due to thermal insulation reasons.

[0072] Compared with the device according to the invention, such damage is less of a safety problem in conventional combustion reactors. In the device according to the invention, at least one reactor container is heated only electrically, because in a combustion reactor, the combustible gas leaking from the reaction tube, for example in the form of a hydrocarbon / steam mixture, can be converted in a controlled manner by combustion occurring in the reactor container or the corresponding combustion chamber, or can be safely discharged in the exhaust gas flow. In addition, since the conventional combustion of the fuel gas leads to a significant reduction in the oxygen content, the gas chamber surrounding the reaction tube is essentially "inert". In contrast, in the case of purely electrical heating, the corresponding combustible gas may accumulate in the reactor container and reach the explosion or detonation limit, for example, at the normal oxygen content of air and at a temperature above the autoignition temperature. Even in the case of combustion without explosion or detonation, complete or incomplete combustion can lead to energy release, which can lead to overheating. Complete or incomplete combustion, coupled with the gas volume flowing out of the reaction tube, can particularly lead to an undesirable pressure increase. The invention reduces this pressure increase because the combustion of the gas mixture in the reactor chamber is limited by a low oxygen concentration and thus by a low oxygen inventory.

[0073] The invention is therefore particularly suitable for use in indirectly electrically heated reactors in which the process gas temperature is close to or above the autoignition temperature of the components contained in the process gas, in particular hydrocarbons.

[0074] By means of the proposed measures, the invention creates a closed space with a conditioned atmosphere for maintaining protective oxide surfaces on the heating elements and for safety-related protection of high-temperature reactors with electrical energy input. In particular, the use of the invention also increases the durability of the heating elements, and the higher oxygen content protects the heating elements in particular during heating and cooling, during load changes, or during decoking or standby. Within the scope of the invention, in this way, in particular, a completely electrically heated reactor vessel can be provided, i.e. at least in this reactor vessel, the heating of the reaction tubes advantageously takes place predominantly or completely by electrical heating, i.e. at least 90%, 95% or 99% of the heat input, in particular the total heat input in this context, takes place by means of an electrical heating device. The heat input of the gas mixture through the reaction tube or tubes is not taken into account in this context, so that the proportion relates in particular to heat transferred from the outside to the wall of the reaction tube or tubes in the reactor vessel, or to heat generated in the wall or catalyst bed in the reactor vessel.

[0075] In certain embodiments of the present invention, also referred to below as "first group of embodiments", one or more gases or gas mixtures for providing the gaseous atmosphere can be fed to the reactor vessel during one or more first operating modes and / or during one or more second operating modes or at any stage thereof, while a portion of the gaseous atmosphere is simultaneously discharged from the reactor vessel. This can lead in particular to a continuous flow of gas in the reactor vessel, so that, for example, heat accumulation or local enrichment or depletion of gas components can also be avoided in this way. In this way, it is particularly easy to control the oxygen content in the gaseous atmosphere by adjusting the feed accordingly.

[0076] In this first group of embodiments, one or more outflow openings (hereinafter only singular form is used in part for simplification) from the reactor vessel, in particular, can be connected to a chimney, such as an (emergency) chimney, and are permanently open during one or more first operating modes and / or during one or more second operating modes or at any stage thereof. This means that one or more outflow openings, except for the contraction of the possible flow cross section, do not produce any mechanical resistance to the inflow or outflow of fluid into the reactor vessel. Therefore, at least during the reaction, one or more openings are unsealed.

[0077] In this case, the chimney opening or a connection to the chimney or another outflow opening also serves to discharge excess gases, in particular combustible hydrocarbons, in the event of damage to the reaction tube. In this case, the chimney can have structural elements (so-called velocity seals or spoilers), in particular in the chimney wall region, to prevent (for example due to free convection gas flow) a backflow into the reactor vessel.

[0078] In other embodiments, also referred to below as "second group of embodiments", one or more outflow openings from the reactor vessel (hereinafter only the singular form is used in part for simplification), in particular chimney openings or connections to the chimney, can be designed to open only above a predetermined pressure level, for example by closing the outflow openings by means of pressure flaps, bursting discs or corresponding valves. In this case, the outflow openings are usually closed, i.e. below the predetermined pressure level, but in the case of damage to the reaction tube, are used to discharge excess gases, in particular combustible hydrocarbons, when the corresponding pressure increases due to the release of the corresponding chimney cross section. In this case, intermittent or permanent openings can be provided when the predetermined pressure level is reached. In this context, a "permanent" opening is particularly to be understood as an irreversible opening, so that in this embodiment, it is not resealed after the pressure has subsequently dropped below the predetermined pressure level by releasing the gas. On the other hand, in the case of an "intermittent" opening, it can be closed again.

[0079] In order to open at a predetermined pressure level, one or more outflow openings can, for example, have one or more spring-loaded or load-loaded valve flaps, which have an opening resistance defined by the spring or load characteristics and therefore only open at a corresponding pressure, or more precisely, at a pressure difference across the opening. For possible embodiments, reference can be made, for example, to the international patent application PCT / EP2022 / 059330, in particular Figures 6A to 6D therein and the corresponding description on page 28, which are incorporated herein by reference to the extent permitted by law. In addition to the use of bursting discs or (mechanical) pressure relief valves known per se, it is also possible to detect the pressure value, for example by means of a sensor, and to trigger any type of opening mechanism, such as an ignition mechanism or an electric actuator drive, when a predetermined threshold is exceeded. This makes it possible, if necessary, to create an opening with a sufficiently large cross-section for a short period of time, which remains closed in the manner described during normal operation.

[0080] In this case, i.e. in the second embodiment group, the chimney opening which is closed during normal operation can be bypassed by a corresponding bypass line to the chimney in order to remove the gas atmosphere or flush the reactor vessel. In this way, by using fluid technology devices in the bypass line, a particularly controllable, for example time-controlled, discharge operation can be carried out.

[0081] Typically, the gas is removed from the reactor chamber to change the composition of the gas atmosphere and / or to achieve cooling. The gas removed from the reactor chamber can be cooled and / or regenerated in order to be used again (recycled) to provide a gas atmosphere. During the cooling process, heat integration can be performed, i.e., the heat extracted from the gas can be transferred to another stream and / or to steam in a steam system, in particular in a heat exchanger.

[0082] In order to deliver one or more gases or gas mixtures for providing a gas atmosphere during one or more first operating modes and / or during one or more second operating modes or at any stage thereof, a gas feed device, in particular in the form of a feed nozzle or feed opening or comprising such a device, and a gas reservoir connected thereto can be provided and used. These devices can in particular be designed to be controlled by known fluid technology means.

[0083] The feeding and / or withdrawal can be carried out continuously or discontinuously, in particular according to a control based on the required oxygen content to comply with the first and second limit values ​​used according to the invention and / or any other set points or limit values, such as the third and fourth limit values ​​used in one embodiment of the invention.

[0084] In other words, within the scope of the present invention, during one or more first operating modes and / or during one or more second operating modes or any stage thereof, one or more gases or gas mixtures for providing a gas atmosphere can be continuously or discontinuously fed into the reactor vessel, and at least a portion of the gas atmosphere can also be withdrawn from the reactor vessel, wherein the withdrawal can be carried out at least partially simultaneously with the feeding, or at least partially lagging behind the feeding.

[0085] Within the scope of the present invention, during one or more first operating modes and / or during one or more second operating modes or any stage thereof, a pressure level below atmospheric pressure can be provided in the reactor vessel. This can be achieved in particular with simultaneous feeding and extraction in the manner described, and in particular, by coordinating the feeding and extraction in an embodiment with a permanently open connection from the reactor vessel to the (emergency) chimney, or by other measures previously provided in connection with the first group of embodiments. In this case, due to the high temperatures in the chimney and the reactor vessel and the resulting lower density of the contained gas volume, a static negative pressure will be generated in the reactor vessel. In this case, a ("suction") fan can also be provided to generate an air flow, for example until a corresponding static negative pressure is formed.

[0086] By operating the reactor vessel at a pressure level below atmospheric pressure during one or more first operating modes and / or during one or more second operating modes or any phase thereof, an outflow of undesirable components that may be harmful, corrosive or flammable from the reactor vessel can always be reliably prevented. However, an inflow of air or secondary air may occur, but this can be limited by a sufficiently tight design and / or compensated by appropriate controls.

[0087] Therefore, when operating the reactor vessel at a pressure level below atmospheric pressure, the walls of the reactor vessel are preferably particularly airtight to prevent uncontrolled air and thus oxygen from entering the reactor vessel. In one embodiment, the furnace walls are constructed so that the relative air inlet rate per unit of furnace wall surface area and per unit of average pressure difference (in absolute value) between the interior of the reactor vessel and the surrounding external atmosphere (at the same altitude) is limited to less than 0.5 Nm 3 / (h×m 2 ×mbar), less than 0.25Nm 3 / (h×m 2 ×mbar) or less than 0.1Nm 3 / (h×m 2 × mbar) value, where Nm 3It is a standard cubic meter at 0°C and standard atmospheric pressure. The surface area of ​​the furnace inner wall is defined herein as the sum of the thermal surface areas of the hot box or reactor vessel insulation, which defines the internal box volume in all directions (i.e., the sides, top and bottom), excluding the surface area of ​​radiant heating elements or other structures protruding from the insulation into the internal box volume. These values ​​are selected to enable a moderate inert gas feed rate (to minimize utility consumption and convective heat loss through the chimney) while keeping the resulting oxygen concentration inside the reactor vessel below the specified upper limit. In a preferred embodiment, the average pressure difference (in absolute value) between the interior of the reactor vessel and the surrounding external atmosphere (at the same altitude) is less than 10mbar, less than 5mbar or less than 3mbar, which depends primarily on the chimney design (e.g., height, diameter, insulation) and whether a fan or the like is optionally provided. As a general design rule, when a lower oxygen upper limit is defined and / or when operating costs are to be minimized and / or when the absolute pressure difference between the reactor vessel wall and the environment increases, the airtightness of the reactor vessel wall is preferentially improved.

[0088] However, as an alternative, which can be used in particular in combination with the second group of embodiments described above, a pressure level above atmospheric pressure can also be set in the reactor vessel during one or more first operating modes and / or during one or more second operating modes or at any stage thereof. Thus, as explained, a pressure level above atmospheric pressure can preferably be provided if the chimney opening to the reactor vessel is closed or is designed to open only above a predetermined pressure level.

[0089] In particular, the gaseous atmosphere can be achieved by feeding one or more gases or gas mixtures for providing the gaseous atmosphere into the reactor vessel, but, in contrast to the embodiment just described, a portion of the gaseous atmosphere is not simultaneously removed from the reactor vessel. In this case, the corresponding gas or gas mixture can be fed to a pressure level above atmospheric pressure, but below the opening pressure of the outflow openings described above and described above. A corresponding design makes it possible in particular to reduce the amount of gas required, since the gaseous atmosphere can advantageously be fed only at the beginning of the reaction phase or intermittently and can then be maintained without further measures.

[0090] However, during one or more first operating modes and / or during one or more second operating modes or at any stage thereof, in embodiments in which a gas or a gas mixture is fed in to provide a gas atmosphere and a portion of the gas atmosphere is simultaneously withdrawn from the reactor vessel, it is also possible to set a pressure level above atmospheric pressure, preferably by providing a suitably controlled and / or appropriately dimensioned bypass line to ensure a corresponding pressure level in the reactor vessel. Reference is made to the above description. In other words, even if there is a permanently open outflow opening or, for example, an outflow opening with an adjustable flow rate, a pressure level above atmospheric pressure can be set in the reactor vessel if the amount of feed gas and / or the amount of gas flowing out through the outflow opening is adjusted accordingly.

[0091] If during the one or more first operating modes and / or during the one or more second operating modes or at any stage thereof a pressure level above atmospheric pressure is provided in the reactor vessel, in particular by controlled feeding, an uncontrolled inflow of external air leading to an increase in the oxygen content can be prevented. In this embodiment, it may not be necessary to measure the oxygen content, since there is no possibility of a subsequent increase.

[0092] In the present context, the term "pressure level below atmospheric pressure" refers to any pressure below the local atmospheric pressure prevailing at a location in the surroundings near the furnace during the considered operating time, in particular at least 1 mbar, 3 mbar, 5 mbar, 10 mbar, 50 mbar or 100 mbar below said atmospheric pressure. Correspondingly, the term "pressure level above atmospheric pressure" refers to any pressure above the local atmospheric pressure prevailing at a location in the surroundings near the furnace during the considered operating time, in particular at least 1 mbar, 3 mbar, 5 mbar, 10 mbar, 50 mbar or 100 mbar above said atmospheric pressure.

[0093] In an embodiment of the present invention, the wall of the reactor vessel does not include an inspection port open to the atmosphere for visual inspection of the interior space of the reactor vessel, or only includes an inspection port for visual inspection of the interior space of the reactor vessel that is sealed airtight with a transparent material, in particular a heat-resistant transparent material. That is, in an embodiment of the present invention, in particular, there is no heat and / or gas leakage provided in the form of an (open) inspection port on the reactor wall, so that the gas atmosphere in the reactor can be adjusted in a particularly controllable manner. In some embodiments, a glass and sealed observation window is provided, i.e., an inspection port for visual inspection of the interior space of the reactor vessel that is sealed airtight by a transparent material. These windows are preferably equipped with removable insulating covers or shutters on the outside, which can limit heat loss when the windows are not used for observation. In some embodiments of the present invention, a camera capable of observing the reaction tube can be provided, and the camera is installed in a manner to maintain an airtight seal, i.e., installed behind a transparent window or inside a reactor. In the latter case, any cable can pass through the reactor wall through the airtight port.

[0094] In some embodiments of the invention, open ports in the reactor wall may be omitted, particularly since electrical heating reduces or eliminates the need to monitor the temperature of the reactor tubes as compared to burners, since heat is provided in a more controlled manner.

[0095] To summarize the above, during one or more first operating modes and / or during one or more second operating modes, or at any stage thereof, a gas atmosphere can be provided in the following manner: by injecting one or more gases or gas mixtures for providing a gas atmosphere into the reactor vessel without simultaneously withdrawing a portion of the gas atmosphere from the reactor vessel, or by simultaneously withdrawing a portion of the gas atmosphere from the reactor vessel.

[0096] Just for the sake of clarity, it should be emphasized again that, in particular, if there is a (relatively) large-area connection between the reactor vessel and the chimney outlet (i.e., low flow-related pressure losses), and if a sufficiently high chimney is filled with hot (i.e., light) gases, it is possible to operate at a pressure level below atmospheric pressure. In this case, the pressure drop caused by the flow is less than the geodetic pressure difference generated between the hot gases and the external cold air within the chimney height, so that at the same geodetic height, a negative pressure difference is generated between the internal gas atmosphere and the external atmosphere. In addition, as mentioned above, fans can be used to provide a pressure level below atmospheric pressure. Fans can be arranged in the main chimney duct as well as in the bypass duct.

[0097] On the contrary, pressure levels above atmospheric pressure will arise, in particular if the connection between the reactor vessel and the chimney outlet (during normal operation) is completely closed or reduced in size, for example by means of a bypass duct, so that the pressure loss is greater than the geostatic pressure difference arising between the hot gases within the height of the chimney or the bypass duct and the cold outside air.

[0098] Thus, in the first and second groups of embodiments, the present invention can be practiced at a pressure level below atmospheric pressure or above atmospheric pressure within the reactor vessel during one or more first modes of operation and / or during one or more second modes of operation or any stage thereof. In the first group of embodiments, a pressure level below atmospheric pressure can also be provided by appropriately determining the size of the outlet opening and / or using a fan.

[0099] According to a particularly advantageous embodiment, the method according to the invention comprises providing a gas atmosphere using a plurality of gases or gas mixtures during one or more first operating modes and / or during one or more second operating modes or any stage thereof, including a first gas or gas mixture having a first volume fraction of oxygen, and a second gas or gas mixture having a volume fraction of oxygen lower than the first volume fraction. These gases or gas mixtures can be used as described below.

[0100] In one embodiment of the invention, it can be provided that during one or more first operating modes and / or during one or more second operating modes or at any stage thereof, at least a portion of the first gas or gas mixture is fed into at least a first region of the reactor vessel, while at least a portion of the second gas or gas mixture is fed separately into at least a second region of the reactor vessel. This embodiment makes it possible in particular to adjust the spatial distribution of the oxygen content in a particularly advantageous manner according to local requirements. It can also be provided that the feeding into the first and second regions can be carried out simultaneously, in particular also in an adjustable amount in each case, or not simultaneously. For example, at least intermittently, a gas or gas mixture can be fed into only one of the regions, for example, if the air introduction (and the resulting oxygen inflow) is so high at a pressure level below atmospheric pressure that only nitrogen or another inert gas can be fed. During one or more first operating modes and / or during one or more second operating modes or at any stage thereof, it can also be ensured that a limited amount of air is introduced by adjustable or non-adjustable inflow openings such as ventilation slots, valve flaps or closable holes. The corresponding inflow openings can be designed to be openable, in particular in a variable number or with an adjustable flow cross section, so that the amount of ambient air flowing in can be adjusted in this way. In the sense of the invention, a corresponding adjustment of the inflow amount can be understood as a further defined feed of the gas mixture, i.e. the ambient air.

[0101] During one or more first operating modes and / or during one or more second operating modes or during any phase thereof, it is also possible in this context to permanently feed a gas or a gas mixture (premixed or not, as described below) only to one zone (e.g., by means of a feed device arranged only at certain points on the reactor wall, or also the inlet openings for the air just described). The "feeding" into the respective one or more zones is carried out in such a way that the respective gas or gas mixture (or a respective part thereof) reaches these zones, for example, below or to the side, so that due to thermal effects, by a defined gas flow in the reactor vessel, or simply by the inflow impulse, the gas or gas mixture will flow there. It is also feasible to feed in these zones. However, in another embodiment of the invention, clean "instrument" air is used instead of the air leaking into the reactor. The advantages of using clean air include the introduction of less dust, moisture and contaminants that may affect the life of the components.

[0102] In particular, the heating element can be arranged in at least one first region of the reactor vessel and the reaction tubes can be arranged in at least one second region of the reactor vessel. By feeding the above-mentioned gases or introducing ambient air, in particular a relative increase in the oxygen content in the region of the heating element (in order to avoid aging / damage in the above-mentioned manner) and a relative reduction in the oxygen content in the region of the reaction tubes (in order to minimize the reaction conversion of possible leaking components) can be achieved.

[0103] In particular, the first region and the second region are not separated from each other by any type of separation device, and therefore, in particular, such an arrangement can be adopted when the respective first and second gases or gas mixtures can be continuously fed through the respective elements. In this case, the concentration gradient can be maintained by continuous feeding and withdrawal operations, while intermittent feeding may lead to mixing over time. Therefore, this embodiment of the invention is advantageously used in the former cases.

[0104] In addition to the embodiment of the separate feed just described, or as an alternative thereto, during one or more first operating modes and / or during one or more second operating modes or any stage thereof, at least a portion of the first gas or gas mixture and at least a portion of the second gas or gas mixture can be completely or partially premixed outside the reactor vessel and fed into the reactor vessel in a completely or partially premixed state. This embodiment is particularly suitable for situations where there is no continuous flow in the reactor vessel. By this alternative interconnection, the concentration gradient in the large volume reactor vessel can be minimized, especially in the case of distributed metering at the bottom and / or sidewalls and / or top of the reactor vessel. In this case, the advantages of the previously described design that may be achieved in the area of ​​the heating element are replaced by a more significant uniform distribution and a reduced risk of unfavorable local imbalances (e.g., too little local oxygen at certain heating elements or too high oxygen concentration near the reaction tube).

[0105] Combinations of corresponding measures are also possible, for example during one or more first operating modes and / or during one or more second operating modes or any phase thereof, premixed gas and non-premixed gas are fed separately. In this case, for example, a nitrogen-air mixture can be fed at the wall of the reactor vessel, while nitrogen is fed in the center of the reactor vessel. In this way, a moderate oxygen enrichment can also be achieved in the vicinity of the heating element, and at the same time, partial premixing can limit concentration gradients.

[0106] In principle, in various embodiments of the present invention, the feed can enter the reactor vessel at a wide variety of locations, in particular at a plurality of points.

[0107] The first gas or gas mixture can be or contain air, a gas mixture rich in oxygen or lacking oxygen relative to air, or oxygen, and the second gas or gas mixture can be or contain a gas mixture lacking oxygen relative to air, nitrogen, carbon dioxide or other inert gases. In principle, the first gas or gas mixture can include oxygen with a volume fraction greater than 1%, 5% or 10%. Known processes, such as air separation, can be used to provide the corresponding gas or gas mixture. The term "inert gas" herein is understood to refer to a gas that does not participate in the oxidation reaction as a reactant under the conditions that prevail in the reactor vessel, in particular. As previously mentioned, it is also possible to only feed a gas or gas mixture, which then specifically has the composition just described for the second gas or gas mixture.

[0108] In all cases, during and / or at the beginning and / or at the end of one or more first operating modes and / or during and / or at the beginning and / or at the end of one or more second operating modes, or at any stage thereof, the actual volume fraction of oxygen in at least one zone of the reactor vessel can be detected, and the feed of one or more gases or gas mixtures for providing the gas atmosphere, in particular the relative and / or absolute change of the throughput, can be regulated or controlled based on this detection. This detection can be carried out in particular during one or more first operating modes and / or during one or more second operating modes or at any stage thereof, in a predetermined periodic or (pseudo) continuous manner.

[0109] In embodiments of the invention having continuous flow through the reactor vessel, it may be preferred to detect the oxygen content downstream of the reactor vessel's effluent (e.g., at a chimney or bypass line, etc.). Additionally or alternatively, the oxygen content may be measured at one or more locations within the reactor vessel. Any suitable method may be used to measure the oxygen content, such as a tunable laser diode, a zirconium oxide probe, gas chromatography, paramagnetic methods, etc.

[0110] In case the reactor vessel is intermittently pressurized, the oxygen content can similarly be measured in the corresponding purge gas discharge line and / or in the reactor vessel itself.

[0111] In all embodiments of the invention, during one or more first operating modes and / or during one or more second operating modes, or at any stage thereof, if the oxygen concentration exceeds the maximum permitted level, any type of safety-related function may be initiated. If the oxygen content falls below the minimum permitted level, operational measures may be initiated to reestablish the desired oxygen content in the reactor. As previously mentioned, too low an oxygen concentration is not considered a safety issue, but may affect the life of the heating element.

[0112] In particular, an inadmissible leakage of gas in the reaction tube can also be detected by a pressure measuring sensor in the reactor vessel. In this way, for example, the injection of reactants can be immediately prevented or stopped based on a corresponding switching signal.

[0113] In order to detect minor damage to the reaction tubes (leakage flow without a sharp or measurable pressure increase), the content of one or more reactants can also be measured continuously in the purge flow (especially as carbon monoxide equivalent). Impermissible values ​​can also trigger a rapid shutdown of the reactant feed.

[0114] If suitable measuring methods (eg laser, gas chromatography) are used, the content of hydrocarbons or their combustion products in the region of the reactor vessel can also be measured additionally or alternatively with the same sensor for all described designs.

[0115] In embodiments of the present invention, since the reaction tubes usually contain a large amount of steam, leak detection can be achieved in particular by the presence of moisture.

[0116] Thus, more generally, the invention may include 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 when the value exceeds a predetermined threshold.

[0117] Furthermore, in certain embodiments, the present invention provides means for possible preheating of the conditioning gas before it flows freely into the reactor vessel. Such preheating can be achieved in particular by heat exchange with the gas exhausted from the reactor chamber.

[0118] 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 prior to being fed to the reactor vessel during the one or more first operating modes and / or during the one or more second operating modes, or at any stage thereof. Embodiments of the present invention may include waste heat recovery, particularly preheating by heat exchange with gases leaving the reactor vessel.

[0119] In particular in the case of near-wall injection of the respective gas or gas mixture, it may be advantageous to preheat the gas or gas mixture, for example by first passing the gas or gas mixture through a sufficient length in a pipe inside the coil box (i.e. the reactor vessel) before conducting the gas or gas mixture to the injection device. In this way, it is possible to avoid undesirable cooling of the heating element by the cooler conditioning gas, which could impair the target power output of the element.

[0120] It is possible that the injection device is located directly at the end of the heating tube channel, or that the heated conditioning gas is first led out of the coil box through a pipeline (preferably in an insulated tube) and then enters the injection device from the outside. Alternatively, an external heat source can be used to preheat the conditioning gas (electricity, steam, hot oil, hot water, etc.).

[0121] Thus, the gas injection device used in respective embodiments of the present invention may comprise one or more preheating devices and one or more injection devices. "Injection" here is intended to refer in particular to the release of a gas or a gas mixture into the reactor vessel via respective injection devices.

[0122] In other words, in a particularly preferred embodiment of the present invention, means can be provided for transferring sensible heat in or from the interior of the reactor vessel to the corresponding gas or gas mixture.

[0123] The invention also provides a reactor device for carrying out a chemical reaction, specific embodiments of which are expressly referred to the corresponding independent claims.

[0124] With regard to further embodiments of corresponding reactor apparatuses, which can in particular be configured for carrying out the process in any of the above-described embodiments, reference is expressly made to the above description.

[0125] Features and advantages of the invention and its advantageous embodiments are explained again below.

[0126] By means of the proposed concept of an almost completely sealed reactor vessel filled with a specific gas atmosphere, the oxygen content can be reduced compared to the external ambient air. According to the invention, it can be used that in the event of failure of one or more reaction tubes, the conversion of the discharged hydrocarbons and the resulting additional volume expansion (as a result of the reaction heat input) are related to the oxygen partial pressure in a first approximation. This correlation is summarized in Table 1, where xO2 is the oxygen mole fraction, V reak is the volume inertia rate associated with the reaction. The values ​​shown in the table below are examples and are not generally valid quantitative information.

[0127] The maximum oxygen content in the reactor vessel, ie the second limit value used in particular according to the invention, can be determined in particular on the basis of the size of the outlet chimney.

[0128] Table 1

[0129] <![CDATA[xO2 [volume %]]]> <![CDATA[V reak [m 3 / s]]]> 21 218 15 156 10 104 5 52 3 31 1 10 0.1 (almost inert) 1

[0130] The maximum permissible pressure in the reaction vessel is p max Depends on the mechanical stability of the corresponding chamber or surrounding containment. This pressure must be at least equal to the pressure p at which a tube rupture or other safety-related event would occur. box , and p box which in turn depends on the volume V of the relevant chamber Box , outlet chimney diameter D stack and oxygen mole fraction:

[0131] p max ≥ pb ox =f(V Box ,D stack ,xO2)

[0132] This requirement forms the basis for the design of the dimensions of the outlet chimney. Figure 5If, for example, a maximum permissible pressure increase of 20 mbar is taken as the basis, as shown by dashed lines 51 and 52, then in order to be able to use a chimney with a diameter of 500 mm (dashed line 51), the reaction-related volume increase rate must not exceed approximately 10 mbar. 3 / s, which results in a maximum oxygen content of about 1%. On the other hand, if a maximum oxygen content of 1% is to be used, a chimney with a diameter of at least 500 mm must be used.

[0133] In order to be able to use a chimney with a diameter of 900 mm (dashed line 52), the volume rate must not exceed about 42 m 3 / s, resulting in a maximum oxygen content of about 4%. Conversely, similar to the above, if a maximum oxygen content of 4% is to be used, a chimney with a diameter of at least 900 mm must be used.

[0134] The lower the oxygen content in the reactor vessel, the smaller the volume growth. Therefore, the outlet chimney diameter for the discharge of the additional volume can also be smaller. The decisive factor for effectively limiting the oxygen content is always sufficient sealing to the environment, so that uncontrolled ingress of oxygen-containing air is prevented or minimized in an adequate manner, especially when the interior of the reactor vessel is under subatmospheric pressure. However, as mentioned above, complete sealing is not necessary in this case.

[0135] The invention is further explained below with reference to the accompanying drawings, which show embodiments of the invention with reference to and in comparison with the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0136] Figures 1 to 4 A reactor apparatus for performing a chemical reaction according to one embodiment of the present invention is schematically shown.

[0137] Figure 5 The mode of operation according to one embodiment of the invention is schematically illustrated. DETAILED DESCRIPTION

[0138] In the drawings, structurally or functionally corresponding elements are indicated with the same reference numerals and are not described again for the sake of brevity. If components of an apparatus are described below, the corresponding description also applies in each case to the method performed therewith, and vice versa.

[0139] exist Figure 1 In the reactor device shown, which is generally designated 100, a reaction tube 2, which is shown in greatly simplified form and is designed in the above-described manner, is arranged in a reactor vessel 1, which is also designed in the above-described manner. A heating element 3, which is also of the above-described type, is arranged on the wall of the reactor vessel 1 and heats the reaction tube 2 indirectly by radiant heat.

[0140] In the example shown, a gas feed device 4 is arranged at the bottom of the reactor vessel 1, through which gas or gas mixtures with different oxygen contents can be fed in, as indicated by arrows 4.1 and 4.2 in the figure. In the embodiment shown here, these gases or gas mixtures are fed in separately, so that in order to provide a higher oxygen content in the region of the heating element 3, in particular a gas or gas mixture 4.1 can be fed in in the region of the reaction tube 2, which has a higher oxygen content than the gas or gas mixture 4.2.

[0141] By means of the gas extraction device 5, here in the form of a permanently open chimney opening leading to the chimney 6, a continuous flow through the reactor vessel 1 with the aforementioned advantages can be achieved with simultaneous feeding via the gas feed device 4. Due to the lower density of the hot gas atmosphere in the chimney compared to the ambient air, the reactor vessel 1 can therefore be operated at a subatmospheric pressure level. The inlet for the air is indicated by an unlabeled curved arrow.

[0142] Figure 2 The reactor arrangement 200 shown differs therefrom essentially in that the gases or gas mixtures 4 . 1 and 4 . 2 are already mixed externally to form a gas mixture 4 . 3 and are fed into the reactor vessel 1 via a gas feed device 4 .

[0143] As mentioned above, all the shown embodiments can also be operated or provided by intermittent or permanent feeding of only one gas or a gas mixture.

[0144] Figure 3 The reactor device 300 shown differs from the previously described designs in that the chimney opening is closed by a bursting disc 7 or other suitable device, which opens the chimney cross section only when a certain reactor vessel pressure is exceeded. The gas extraction device, also referenced as 5, establishes a bypass connection to the chimney 6, which connection can in particular be appropriately adjusted and / or dimensioned. In this way, a level above atmospheric pressure can be set in the reactor vessel 1 with the advantages described. One or more gases for providing the required oxygen content in the reactor vessel 1 can be premixed or fed in separately, as shown by dashed arrow 4.3 in the figure only for illustration. Undetermined gas losses of the reactor vessel 1 are shown by curved arrows.

[0145] exist Figure 4 In the other embodiment of the reactor device 400 shown, no permanently open gas extraction device is included, so that flow cannot be established here, and the reactor vessel 1 can preferably be pressurized with a suitable gas atmosphere at the beginning or at regular time intervals. As mentioned above, the reactor vessel 1 is particularly operated at a level above atmospheric pressure.

[0146] Figure 5An operating mode according to one embodiment of the present invention is shown, by which a method of adjusting a specific oxygen content in a gas atmosphere in a reactor vessel (such as reactor vessel 1) in the aforementioned embodiments is explained.

[0147] exist Figure 5 In the diagram, the maximum temperature 501 of the heating elements (such as the aforementioned heating element 3), the average temperature 502 of these heating elements, the maximum temperature 503 of the reaction tubes (such as the aforementioned reaction tube 2), the average temperature 504 of these reaction tubes in ° C. (left vertical axis), and the heating power 505 absorbed by the reaction tube 2 in kW (right vertical axis) are shown compared to the operating time of the corresponding reactor device in days (horizontal axis). The heating power absorbed by the reaction tube is closely related to the power input of the heating element, because the power absorbed by the heating element is converted into heat and is transmitted to the reaction tube as absorbed heating power almost completely (i.e., in a proportion of at least 85%, 90%, 95% of the power input) only after deducting the heat loss to the environment. The values ​​of absorbed heating power given here refer to a group of three reaction tubes heated by a plurality of heating elements. The invention also relates to cracking furnaces with different numbers of reaction tubes and different amounts of absorbed heating power. In particular, the invention is also intended for large electrically operated cracking furnaces having a cumulative absorbed thermal power exceeding 3 MW, 5 MW, 10 MW, 20 MW.

[0148] The illustration of the exemplary sequence from standby 510 (herein understood as the "second" operating mode) to cracking operation 520 ("first" operating mode) to decoking operation 530 ("second" operating mode) to standby operation 510 to cracking operation 520 to decoking operation 530 to standby operation 510 is simplified, in particular only one decoking step is shown here, corresponding to the partial steps listed as an example in Table 1, and the maximum temperature of the reactor tube during the cracking operation is shown as a linear growth curve. In practice, if the control system is designed to operate with a product gas composition that is as constant as possible, for example a constant ratio of propylene to ethylene in the product gas, the maximum temperature generally increases monotonically, but not at a constant rate over time. The illustration of a constant rate of heat absorption of the reactor tube during such operation is also simplified, because minor adjustments can occur here depending on the selected control strategy and the growth of the coke layer on the inside of the reactor tube. In addition, the transition from cracking operation 520 to decoking operation 530 may also include an intermediate temporary or intermittent operation period, which may be similar to the standby operation 510, although it is preferred to decoke the process tubes promptly after the cracking operation period ends to reduce the risk of coil damage associated with the existing coke layer inside.

[0149] It is also possible to adjust the control during the cracking operation to keep the product gas temperature as constant as possible, resulting in greater variations in the product gas composition over time and thus in greater adjustments in the heating power absorbed by the reaction tubes.

[0150] Depending on the operating mode of the furnace ("first" or "second" operating mode), when the operating mode of the furnace is switched from a mode with hydrocarbons or other reactants flowing through the reaction tubes (reaction operation 520, "first" operating mode) to a mode without hydrocarbon flow (standby mode 510 or decoking mode 530 or other startup or shutdown mode, "second" operating mode), or within a short time interval after the transition, both the upper and lower limits of the oxygen content in the gas atmosphere in the reactor vessel may change significantly.

[0151] In particular, it is advantageous if the upper limit value of the oxygen content is lowered to at least the maximum permissible oxygen content for hydrocarbon operation (i.e., the maximum value to prevent a possible coil rupture situation) before switching to the reaction operating mode 520. Preferably, the lower limit value is changed at the same time, for example, to continue to maintain a sufficiently large control window for setting the gas atmosphere regulation. Therefore, when the upper limit value is lowered before switching to the reaction mode 520, the lower limit value is preferably also lowered.

[0152] On the other hand, both limits are preferably increased in the reverse transition from reaction operation 520. The upper limit may be increased to correspond to the oxygen content of the ambient air, and the lower limit is preferably increased to a value sufficiently far above the lowest oxygen content that is favorable for the (transient) operation of the heating element.

[0153] In this context, the increase in oxygen content in hydrocarbon-free operation can be advantageously utilized, since drastic changes in the temperature of the heating elements also occur primarily during the switching operation that is performed after a shutdown or before the hydrocarbon supply is turned on. This is true in particular, since the required heating power during hydrocarbon-free operation is significantly reduced, which has a significant influence on the heating element temperature. Figure 5 As shown, when switching between the reaction mode 520 and other modes 510, 530, the heating power 505 and the maximum temperature 503 of the reaction tube are significantly reduced. The temperatures 501, 502 of the heating elements are determined by complex relationships (such as the geometric arrangement of the reaction tube and the heating element). However, it can be generally believed that the temperature difference between the heating element (heat source) and the reaction tube (heat sink) is closely related to the heating power required for the reaction tube. Therefore, the heating element temperature difference between the reaction mode 520 (high temperature and high heating power lead to extremely high heating element temperature) and other hydrocarbon-free flow modes 510, 530 (reduced coil temperature and reduced heating power lead to significantly reduced heating element temperature) is large. The actual heater temperature can fluctuate up and down depending on the geometry of the furnace and the design of the heater, but does not limit the scope of this application.

[0154] Table 1 gives Figure 5 An overview of representative conditions for the three main operating modes 510, 520, 530 described.

[0155] Table 1

[0156]

[0157] In particular, the atmospheric conditioning, ie the setting of the oxygen content, and other process settings can be changed in a targeted, even short-term manner before or after the switching process.

[0158] To prepare the reactor vessel for entering reaction mode 520 for hydrocarbon feeding, possible options include, for example in a special hot steam standby in operating mode 510, bringing the heating elements to the highest possible temperature (low reaction tube inlet temperature and high outlet temperature), thereby setting a high target range for the oxygen content and then gradually adjusting the target range downward to at least reduce the upper limit value to a level below the safety-related limit value that allows hydrocarbon operation or reaction operation 520.

[0159] After switching directly from cracking operation 520 to hydrocarbon-free operation, the oxygen content can be increased quickly (preferably in less than 1 h, 30 min, 10 min or 1 min), in particular after closing the hydrocarbon valve, for example during the transition at the end of a cracking cycle or cracking operation 520. Preferably, after the subsequent decoking operation 530 is completed, a special hot steam standby for increasing the heating power can be set again in the operating mode 510 in order to achieve the maximum temperature of the heating element at least intermittently in the case of an increased oxygen concentration in the reactor vessel.

[0160] As described in detail above, within the scope of the invention, the regulation of the oxygen content can be based on instantaneous measured values ​​and / or target values ​​and, additionally or alternatively, on the temporal variation or temporal fluctuation of these measured values ​​and / or target values.

[0161] In particular, non-monotonic control relationships can also be provided, such as hysteresis control, i.e. different types of control are applied during heating or cooling of the heating element (because the risk of defect formation in the outer oxide layer may be different during heating and cooling). Such hysteresis control can be applied in particular to the temperature of the heating element or other components, the process gas temperature, and the flow rate of the partial flow and / or the total flow, the electric heating power / voltage / current.

[0162] In particular, such regulation can also be carried out during transient changes, such as during load changes during intervals, standby or decoking operations. An important example is the gradual increase in the hydrocarbon flow rate after the start of the feed, during which the heating power and thus the heating element temperature also rise sharply. The invention proposes that during the gradual increase in the hydrocarbon load, although the oxygen content range is always below the hydrocarbon operating upper limit specified by the safety regulations, the oxygen content range is still kept at a relatively high level. This transient increase process can be detected by the increase in data of heater temperature, heater power, hydrocarbon flow rate, etc. over time, and can be used accordingly as a control influencing variable for changing the gas atmosphere regulation. In addition, the instantaneous flow rate, for example when the normal design value is reached, can be used to detect when a transient change of the above type occurs or has been completed.

[0163] It is therefore preferred in practice that during a gradual increase in load the regulation is first set to a value which tends to be higher for the oxygen content and then this value is reduced continuously, stepwise or immediately.

[0164] This is of particular concern when gradually heating up "clean" reactor tubes to the start of the respective cracking or reaction operating cycle. The risk of coil rupture is particularly low when gradually heating up uncoked reactor tubes. For this reason, a relatively high upper limit of the oxygen content can be selected in this case and then replaced by a lower upper limit of the oxygen content after stable and continuous cracking operation has been achieved and a new coke layer has begun to form in the tubes. This allows for safe optimal regulation during continuous full-load operation.

[0165] Furthermore, the oxygen content can be further reduced towards the end of the operating period, since the risk of tube rupture tends to increase as the coke layer builds up. At the same time, the temperature of the heating elements also rises, but not suddenly, so the risk of defects forming in the protective oxide layer is low and there are no particularly strict requirements for the oxygen content in relation to the life of the heating elements.

[0166] Preferably, in particular at all times during the cracking operation it is ensured that the regulating gas stream added in a controlled manner has an oxygen content below the upper limit value. This is to prevent, for example, during an intermittent increase in the average oxygen content in the reactor vessel, the oxygen content in regions of the reactor vessel with slow mixing from rising locally and exceeding the upper limit value currently specified.

[0167] Analogously to the variation of the regulation parameters in the cracking operation described above, similar regulation can also be performed for the standby or decoking operation. For example, in particular in the decoking operation, a variable regulation of the regulation can be performed in parallel with the time-dependent process control (as mentioned above, the decoking cycle consists of different steps which provide, among other things, different flow rates and heating capacities). The same applies, for example, to the heating of the reactor vessel during commissioning. In this context, the time-dependent gas atmosphere regulation can be performed, for example, according to a specified heating temperature ramp.

Claims

1. A method for performing a chemical reaction using a reactor assembly (100 to 400), wherein a reaction tube (2) arranged in a reactor container (1) is provided in the reactor assembly (100 to 400), wherein - during one or more first operating modes, one or more reactants are supplied to the reaction tube (2) at a first mass flow rate, and during one or more second operating modes, the one or more reactants are not supplied to the reaction tube (2), or during the one or more second operating modes, the one or more reactants are supplied to the reaction tube (2) at a second mass flow rate, at least on a time-averaged basis, being lower than the first mass flow rate, wherein - during the one or more first operating modes, radiant heat is supplied to the reaction tubes (2) by means of one or more electrical heating elements (3) in the reactor vessel (1) at a first heat flow rate, and during the one or more second operating modes, the radiant heat is not supplied to the reaction tubes, or during the one or more second operating modes, the radiant heat is supplied to the reaction tubes (2) at a second heat flow rate, which second heat flow rate is lower than the first heat flow rate, at least on a time-averaged basis, It is characterized in that - in at least a portion of the reactor vessel (1) provided with the one or more heating elements (3), providing a gas atmosphere in which the oxygen content is adjusted to a predetermined volume fraction, wherein - during said one or more first operating modes, said volume fraction of oxygen is regulated between a first limit value of not less than 500 ppm and a second limit value of not more than 10%, and - during said one or more second operating modes, said volume fraction of oxygen is set to a higher value than during said one or more first operating modes, at least on a time-averaged basis.

2. The method according to claim 1, wherein: The gas atmosphere is provided in at least a portion of the reactor vessel (1) provided with the one or more heating elements (3), the gas atmosphere being separated from the one or more reactants supplied to the reaction tube (2) by the wall of the reaction tube.

3. The method according to claim 1 or 2, wherein: The amount of the radiant heat supplied to the reaction tube (2) by the one or more electric heating elements (3) in the reactor vessel (1) accounts for more than 90% of the total amount of heat supplied to the reaction tube (2) in the reactor vessel (1).

4. A method according to any one of the preceding claims, wherein: During the one or more second modes, the volume fraction of oxygen is adjusted between a third limit value and a fourth limit value, wherein the third limit value is higher than the first limit value and the fourth limit value is equal to or higher than the second limit value, and / or wherein the third limit value is higher than the second limit value.

5. A method according to any one of the preceding claims, wherein: During the one or more second operating modes, the volume fraction of oxygen varies over time at least intermittently.

6. The method according to claim 5, wherein: During the one or more second operating modes, the second mass flow rate of the one or more reactants varies with time at least intermittently, and / or wherein the second heat flow rate of the radiant heat varies with time at least intermittently.

7. The method according to claim 6, wherein: During the one or more second operating modes, the at least intermittent variation of the volume fraction of oxygen is performed taking into account the at least intermittent variation of the second mass flow rate of the one or more reactants and / or taking into account the at least intermittent variation of the second heat flow rate of the radiant heat.

8. A method according to any one of the preceding claims, wherein: During the one or more first operating modes, at least a portion of each of the reaction tubes (2) is maintained at a reaction tube temperature within a first temperature range and during the one or more second operating modes, at least a portion of each of the reaction tubes (2) is maintained at a reaction tube temperature within a second temperature range lower than the first temperature range, wherein the first temperature range is particularly 400°C to 1500°C or 500°C to 1200°C.

9. The method according to claim 7 or 8, wherein: During the one or more second operating modes, the reaction tube (2) operates in at least one of the following modes: - operating in a steam standby mode, wherein the reaction tube (2) is maintained at a predetermined temperature or within a predetermined temperature range by passing steam through the reaction tube (2), - operating in a decoking mode, wherein the reaction tubes (2) are decoked by passing steam and air through the reaction tubes (2), and - Operation in transient cracking mode, wherein the reaction feed load through the reaction tube (2) and / or the process gas temperature at the outlet of the reaction tube (2) are varied over time.

10. A method according to any one of the preceding claims, wherein: - one or more gases or gas mixtures for providing the gas atmosphere are continuously or discontinuously fed into the reactor vessel (1), and in particular, - at least partially simultaneously or at least partially delayed withdrawing at least a portion of the gaseous atmosphere from the reactor vessel (1).

11. A method according to any one of the preceding claims, wherein: A subatmospheric pressure level or a superatmospheric pressure level is provided in the reactor vessel (1).

12. The method according to claim 1, wherein: The gas atmosphere is provided using one, two or more gases or gas mixtures, wherein, when using the two or more gases or gas mixtures, the two or more gases or gas mixtures in particular comprise 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, the first gas or gas mixture and the second gas or gas mixture being introduced into the reactor vessel simultaneously or at different times, in particular wherein at least a portion of the first gas or gas mixture is introduced into at least a first region of the reactor vessel (1), and wherein at least a portion of the second gas or gas mixture is introduced separately into at least a second region of the reactor vessel (1), and / or wherein a gas or gas mixture is used and introduced into the second region of the reactor vessel without introducing a gas or gas mixture into the first region of the reactor vessel, wherein the heating element (3) is arranged in at least one first region of the reactor vessel (1) and the reaction tube (2) is arranged in at least one second region of the reactor vessel (1).

13. The method according to claim 12, 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 reactor vessel (1) and are introduced into the reactor vessel (1) in a mixed state.

14. The method according to claim 12 or 13, wherein: During the reaction and / or at the start of the reaction and / or at the end of the reaction, and / or during the heating and / or at the start of the heating and / or at the end of the heating, and / or during the cooling and / or at the start of the cooling and / or at the end of the cooling, and / or during the decoking and / or at the start of the decoking and / or at the end of the decoking, and / or during the standby and / or at the start of the standby and / or at the end of the standby, the actual volume fraction of oxygen is detected in at least one area of ​​the reactor vessel and / or a chimney, a bypass or a purge line connected to the reactor vessel, and the feed of the one or more gases or gas mixture for providing the gas atmosphere is adjusted or controlled based on the detection.

15. A reactor device (100 to 400) for performing a chemical reaction, the reactor device (100 to 400) comprising a reactor vessel (1), a reaction tube (2) arranged in the reactor vessel (1), and a device arranged for: - during one or more first operating modes, one or more reactants are supplied to the reaction tube (2) at a first mass flow rate, and during one or more second operating modes, the one or more reactants are not supplied to the reaction tube (2), or during the one or more second operating modes, the one or more reactants are supplied to the reaction tube (2) at a second mass flow rate, at least on a time-averaged basis, being lower than the first mass flow rate, wherein - during the one or more first operating modes, radiant heat is supplied to the reaction tubes (2) by means of one or more electrical heating elements (3) in the reactor vessel (1) at a first heat flow rate, and during the one or more second operating modes, the radiant heat is not supplied to the reaction tubes, or during the one or more second operating modes, the radiant heat is supplied to the reaction tubes (2) at a second heat flow rate, which second heat flow rate is lower than the first heat flow rate, at least on a time-averaged basis, The device provided is configured to: - in at least a portion of the reactor vessel (1) provided with the one or more heating elements (3), providing a gas atmosphere in which the oxygen content is adjusted to a predetermined volume fraction, wherein - during said one or more first operating modes, said volume fraction of oxygen is regulated between a first limit value of not less than 500 ppm and a second limit value of not more than 10%, and - during said one or more second operating modes, said volume fraction of oxygen is set to a higher value than during said one or more first operating modes, at least on a time-averaged basis.

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