High-temperature reactor

Abstract

In a tube bundle reactor for carrying out catalytic gas phase reactions, comprising reaction tubes (3) which are made of a material having a first thermal coefficient of expansion α1, and comprising tube bases (5), (8) and a reactor casing (11) which are made of a material having at least one second thermal coefficient of expansion α2, where α2 > 1.13 * α1 or α2 < 0.88 * α1, the reactor casing (11) is formed in the axial direction by three casing portions (12, 13, 19), the first (12) of which is connected to the gas-inlet-side tube base (5) and the second (13) of which is connected to the gas-outlet-side tube base (8) and both (12), (13) are made of a material having the at least one second thermal coefficient of expansion α2, wherein between the first casing portion (12) and the second casing portion (13) a third casing portion (19) made of a material having a third thermal coefficient of expansion α3 is provided, where α3 <= 0.99 * α2 if α2 > 1.13 * α1, or where α3 >= 1.01 * α2 if α2 < 0.88 * α1. The invention also relates to methods for operation and uses of such a tube bundle reactor.

Description

[0001] PB06196

[0002] “High-temperature reactor”

[0003] The present invention relates to a tube-bundle reactor according to the preamble of claim 1, as well as to a method for operating such a tube-bundle reactor and to uses of such a tube-bundle reactor. It particularly relates to the production of carbon monoxide using a catalytic reverse water gas shift (RWGS) reaction.

[0004] It is known that tube bundle reactors for high temperature processes such as the RWGS reaction

[0005] CO2+ H2CO + H2O AHR = + 41 kJ / mol

[0006] (with carbon dioxide (CO2), hydrogen (H2), carbon monoxide (CO), water (H2O), and the reaction enthalpy (AHR)). This process in particular can lead to corrosion on the gas side due to metal dusting. Corrosion on the heat transfer side can also occur due to aggressive heat transfer media. These attacks can be counteracted by materials adapted to the specific corrosion mechanisms. These different materials often have different thermal expansion coefficients, which can lead to critical material stresses even when heating the reactor from ambient temperature to operating temperature.

[0007] Typically, the reaction tubes and the reactor shell are made of similar materials with similar thermal expansion coefficients. With good flow, the heat transfer salt in the shell of the tube-bundle reactor achieves good heat transfer, so that the temperature of the reaction tubes and the shell deviates only slightly from the temperature of the heat transfer medium. The mechanical stresses on the tube-bundle reactor due to different expansions resulting from different temperatures are thus minimal.

[0008] Application US4559207A relates to a boiling water tube bundle reactor for the production of methanol with reaction tubes made of a catalytically inactive metallic material with respect to the reactant gas. Another feature of this material is that its thermal expansion coefficient almost matches that of the reactor shell material. Mixed ferritic-austenitic chromium steels are proposed as suitable materials for the reaction tubes, which can also be inertly coated or plated if necessary.

[0009] Similarly, GB724452A describes a tubular reactor in which the oxidation of olefins is particularly favored by the use of reaction tubes made of nickel-free chromium steel with a thermal expansion coefficient slightly lower than that of the carbon steel from which the reaction vessel is made.

[0010] The situation is different when the reaction tubes and the reactor shell are made of materials with different thermal expansion coefficients. This can occur if the reaction tubes must be made of a particularly resistant material due to the corrosive properties of the reaction gas, but the reactor shell is not exposed to these conditions and can therefore be made of a more cost-effective material that has a different thermal expansion coefficient.

[0011] In EP 1 113 238 A2, different expansions of the reaction tubes and the reactor shell are accommodated by a compensator in the reactor shell. A similar design is known from WO 2004 / 052525 A1, with a compensator in the reactor shell in the area of ​​an annular channel. However, these designs are only possible at lower pressures or with smaller reactor dimensions. Using similar materials can also solve the problem, but this is expensive.

[0012] In US2003 / 0173062A1, the adverse effects of thermal expansion in a heat exchanger reactor are minimized through various measures such as flow baffles through which the tubes are guided, insulation layers, and fins. The baffles have a lower thermal expansion coefficient than the tube sheets.

[0013] WO 2009 / 092724 A1 relates to a tubular reactor with nickel-containing platings of the tube sheets and designs of the reaction tubes made of a nickel-based material, in which the outer shell of the reactor has a thickness that is sufficient to absorb tensile forces occurring in the event of a different expansion due to a temperature difference between the tube and the outer shell.

[0014] WO 2008 / 115933 A1 describes a multi-stage process for producing hydrocarbons and alcoholic fuels using renewable energy sources, preferably using tube-bundle reactors for a RWGS process and a Fischer-Tropsch process. The RWGS tube-bundle reactor is preferably heated with a liquid heat transfer medium consisting of a liquid alloy, molten salt, or an organic heat transfer medium. Design details of these tube-bundle reactors are not disclosed. Examples of appropriate catalysts are given for the various processes. A similar process is published in WO 2022 / 263384 A1. This process concerns the production of CO only and is operated in a single stage with recycle gas. The recycle gas is treated in a known manner by condensing out water and separating the target components.The RWGS reactor preferably consists of a tube bundle reactor operated with molten salt. The feed gas generally has a temperature between 5°C and 150°C and a pressure in the range from 1 to 200 bar. The pressure is preferably between 5 and 70 bar. The pressure stated is to be understood as absolute pressure, as are all other pressure statements in the context of this publication. After heating, the feed gas typically has a temperature between 200 and 700°C, preferably between 450°C and 600°C, before entering the RWGS reactor. The reaction temperature is preferably in a range between 500°C and 600°C. Catalysts that suppress methanation are preferably used. The RWGS reactor preferably contains two catalyst beds, whereby the gas can be heated between them. The heat transfer medium is preferably conducted countercurrently to the reaction gas and is electrically heated outside the reactor.The advantage is that, compared to known high-temperature processes, metal dusting or methanation are largely avoided due to relatively low operating temperatures, so that more cost-effective materials can be used.

[0015] WO 2007 / 108014 A1 presents a process for producing liquid fuels from CO2 and water. The RWGS reaction forms an intermediate step for producing a reaction gas containing CO2 and H2, which is then used to produce liquid fuels via intermediates such as methanol and DME (dimethyl ether). The RWGS process uses a catalytic tube-bundle reactor operating at 400°C and 5 bar. Conversion increases with other operating modes, such as 500°C and 50 bar with an H2 / CO2 ratio of 2:1 in the feed gas. The reaction heat for the RWGS process comes from exothermic subprocesses.

[0016] Further RWGS methods are known, for example, from WO 2022 / 129338 A1 , WO 2021 / 062384 A1 , WO 2003 / 070629 A1 or WO 2021 / 225643 A1.

[0017] The study "Conceptual and Technical Design of a Development Platform for Power-to-Liquid Fuels," available at https: / / www.now-gmbh.de / wp-content / uploads / 2021 / 08 / EPP_Abschlussbericht.pdf, proposes a demonstration plant for the production of electricity-based liquid fuels. The RWGS reactor used there is designed using known technology as a natural gas / biogas-fired reformer including a waste heat and steam generator system, thus representing a plant configuration otherwise common for steam reforming of natural gas / biogas. The process is to be carried out at temperatures in the range of 700°C to 1000°C and at pressures of up to 30 bar using standard catalysts. An inlet pressure of 27 bar and a temperature of 900°C are preferred. Electrically heated reactors are considered immature.

[0018] A central problem with the RWGS process is the material attack caused by "metal dusting." The mechanism of this type of corrosion is not yet fully understood. In any case, a highly carburizing gas composition is required, which is characterized by carbon activity "a cThe critical temperature range is between approximately 400°C and 900°C. From approximately 800°C to 900°C, metal dusting decreases again. Metal dusting is intensified by high pressure from approximately 5 to 10 bar or only occurs above these conditions. The effect has been observed in various processes in petrochemical plants, e.g. in catalytic reforming, ammonia and methanol production, in reduction plants and others. Synthesis gas is a typical corrosive gas for metal dusting. Synthesis gas, also called syngas, is a basic raw material in the chemical industry with which a variety of synthesis reactions are carried out. Syngas essentially consists of hydrogen (H2), carbon monoxide (CO) and possibly smaller amounts of other substances such as carbon dioxide (CO2), methane (CPU) or water vapor (FhOg). During the corrosion process caused by metal dusting, elemental carbon and fine metal particles are formed.Iron, low- and high-alloy steels, as well as cobalt or nickel-based alloys are susceptible, although nickel-based alloys are more resistant. Particularly resistant nickel-based alloys have a high proportion of chromium (Cr) and aluminum (Al), as well as smaller proportions of silicon (Si) and sometimes copper (Cu). These alloy components form protective oxide layers. Furthermore, such alloys have a low iron content and defined grain sizes. Recent developments include duplex steels. New alloys resistant to metal dusting are continually being developed.

[0019] The article “Metal Dusting”, https: / / www.corrosionguru.com / wp-content / uploads / 2017 / 12 / metal- dusting.pdf, describes various mechanisms of metal dusting and materials that are resistant to it.

[0020] The article "Development of Materials Resistant to Metal Dusting Degradation," Argonne National Laboratory, 2005, https: / / doi.org / 10.2172 / 890559, describes the corrosion mechanisms of various iron-based and nickel-based alloys. It discusses in detail the carbon activity of cas a function of gas composition, temperature, and pressure. The tests are carried out on various alloys at 482°C, 593°C, and 704°C. The metal dusting rate is highest at 593°C. It also increases with increasing pressure and exposure time. At atmospheric pressure and 593°C, almost no alloy exhibits metal dusting, but it does at 14.3 bar. At this increased pressure, the degree of corrosion depends heavily on the alloy quality but also on the exposure time. The susceptibility of the materials decreases with increasing alloy proportions of nickel, chromium, and aluminum. These alloy components form protective layers of chromium and aluminum oxide. Very good resistance to metal dusting has been found for nickel-based materials from Alloy 602CA onwards. Alloy 693 shows better resistance. Alloy 601 is comparatively less resistant.

[0021] These results are confirmed in publication WO 2013 / 182177 A1, which presents a similar nickel-chromium-aluminum alloy with good processability, creep strength, and corrosion resistance. WO 2006 / 121561 A2 presents another resistant alloy.

[0022] WO 2022 / 253963 A1 relates to a process for converting a feed gas containing CO2 and H2 into syngas in a two-zone endothermic heat exchange reactor with exothermic reactions in the first reaction zone and endothermic reactions in the second reaction zone. Methane is formed in the first reaction zone and reacts back at the high temperatures in the second reaction zone. The feed gas can optionally be preheated before entering the RWGS reactor. The heat transfer medium for introducing the reaction heat is preferably a gas. The application assumes that metal dusting occurs with gases containing CO2, particularly when the gas is cooled. To avoid metal dusting, the reaction temperatures are therefore chosen to be as high as possible. The reaction temperature in the first reaction zone is preferably above 500°C (800°C, 900°C - 1000°C) and in the second reaction zone above approximately 600°C and up to 800°C.The syngas can be combined directly with the heat transfer medium in various ways. The reaction heat to be introduced is provided by an electric, fired, or autothermal RWGS reactor. The pressure in the shell space is between 2 bar and 50 bar or between 50 bar and 200 bar. In the exemplary embodiments, the pressure is between 9.5 and 11.5 barg. When the heating gas from the shell side is combined with the reaction gas, the same pressure is present throughout the reaction space. The reactor design can be, for example, a conventional steam reformer. Materials resistant to metal dusting are not discussed in WO 2022 / 253963 A1.

[0023] It is therefore known that in shell-and-tube apparatus, different linear expansions of the tubes and the apparatus shell can occur due to different thermal expansion coefficients and / or due to different temperatures on the tube side and the shell side. These different linear expansions lead to material stresses in the apparatus, which must be compensated for by appropriate measures such as sufficient wall thicknesses, compensators, or suitable materials. However, there are applications in which certain materials with different thermal expansion coefficients are absolutely necessary for reasons of corrosion resistance and strength at high temperatures, and in which state-of-the-art measures are no longer applicable if the different linear expansions exceed a certain level.

[0024] The invention is therefore based on the object of designing a tube-bundle reactor according to the generic term in such a way that it can be operated at temperatures between 450°C and 650°C and at pressures between 5 bar and 50 bar, such that the material stresses caused by different thermal expansions resulting from different thermal expansion coefficients of the reaction tubes and reactor shell remain within a permissible range, and such that the tube-bundle reactor can be manufactured economically. A further object is to design the tube-bundle reactor in such a way that it can be used to conduct endothermic gas-phase reactions, specifically RWGS reactions and, in particular, gas-phase reactions in which the reaction gas has strong carburizing properties and can lead to corrosion mechanisms such as metal dusting.

[0025] According to the invention, this object is achieved by the characterizing features of claim 1 as well as by the method and use claims. The subclaims further specify advantageous embodiments.

[0026] Due to process-technical requirements, a tube bundle reactor according to the invention fulfills one of the conditions 02 > 1.13 * ai or 02 < 0.88 * ai.

[0027] The reactor shell of the tube bundle reactor according to the invention is formed in the axial direction from three shell sections, the first of which has an axial length L1A and is connected to the gas inlet-side tube sheet, and the second of which has an axial length L2A and is connected to the gas outlet-side tube sheet, and both of which are formed from a material with at least one second thermal expansion coefficient O2. A third shell section with an axial length L3 made from a material with a third thermal expansion coefficient O3 is arranged between the first shell section and the second shell section, with O3 < 0.99 * O2 for the case that O2 > 1.13 * cu or with as > 1.01 * O2 for the case that O2 < 0.88 * ai.

[0028] If O2 is greater or smaller than ai, the reactor shell and the reaction tubes expand differently with increasing temperatures. This results in stresses on the apparatus components that can be controlled using various state-of-the-art methods, for example, by appropriately thick shell walls or by compensators. These methods reach their limits when the ratio of the thermal expansion coefficients exceeds a certain limit, which for practical large tube bundle reactors with apparatus diameters in the range of 6 m to 8 m is O2 > 1.13 * ai or O2 < 0.88 * en. Above these ratios, designs that are uneconomical or technically impractical are produced using known design methods.

[0029] The measures according to the invention make it possible to manufacture tube-bundle reactors in which the materials used are resistant to metal dusting on the gas side and resistant to salt corrosion on the shell side, thus enabling, for example, high conversion in the lower temperature operating range of the RWGS reaction. The different materials required for the reaction tubes and the reactor shell for reasons of corrosion and cost-effectiveness lead to different axial expansions with correspondingly high material stresses. However, these stresses can be reduced to a permissible level by using different shell sections made of materials with different thermal expansion coefficients. This results in optimal possibilities with regard to process conditions and material usage, because the tube-bundle reactor can be operated at high temperatures and pressures with minimized material usage.A tube bundle reactor according to the invention can be manufactured in sizes that are uneconomical or technically not feasible using the known design methods.

[0030] In a preferred embodiment, the reactor shell and the tube sheets together have an average axial thermal expansion coefficient am = (a2* (L1 A + L1 B + L2A + L2B) + a3* L3) / (L1 A + L1 B + L2A + L2B + L3) with a ratio Om / ai which is in a range from 0.88 to 1.13, preferably in a range from 0.90 to 1.10 and particularly preferably in a range from 0.92 to 1.09. By choosing a material with a corresponding thermal expansion coefficient 03 and the ratio of the sum of the axial lengths L1A, L1 B, L2A, L2B to L3, an average expansion coefficient am is obtained which satisfies the condition Om / ai <= 1.13 or am / ai >= 0.88.

[0031] The ideal value for the ratio Om / ai is exactly 1.0. However, this is often not possible due to design limitations and the selection of available materials. If the ratio Om / ai remains within the specified range limits, the material stresses resulting from the different axial expansions within the tube bundle reactor are smaller than the permissible material stresses at any point and at any time. The material stresses can occur if all parts of the tube bundle reactor have the same temperature at any time during heating up to the operating temperature or if different parts of the tube bundle reactor have different temperatures during heating up as a result of different heating. The respective linear expansions are calculated using the relationship

[0032] AL = a * AT * L0 with

[0033] AL [mm] Linear expansion a [1 ZK] Thermal expansion coefficient

[0034] AT [K] Temperature change

[0035] L0 [mm] respective reference length

[0036] The resulting material loads are determined using calculation methods familiar to the expert. Examples include DIN EN 13445-3:2021-12, 13.5.9 or ASME BPVC.VIII.1-2021, UHX-13, particularly Part UHX-13.6.

[0037] In practical designs, the aim is to use as few materials as possible. Accordingly, it is advisable to use the same material for the tubesheets and the adjoining shell sections for the reactor heads. However, if different materials are used, possibly with different thermal expansion coefficients, the calculation equation for a m to be expanded accordingly.

[0038] A well-known problem when welding dissimilar materials is that welded joints made of high-strength carbon steel require post-weld heat treatment. This is not necessary for stainless steel. Since heat treating the entire tube-bundle reactor is very complex, this is avoided whenever possible.

[0039] When welding high-strength carbon steel to stainless steel, a buffer layer of stainless steel is applied to the weld edges of the middle shell section and then heat-treated if necessary. Heat-treating this spatially confined area requires little effort. The weld edges of all shell sections are now made of stainless steel and no longer need to be heat-treated after welding. Details of such processes are known, for example, from US2963129, W02000 / 032350A1 or WO2015 / 091681 A1 for various applications. They are also described, for example, in the ASME BPVC Sec. IX, QW-283 standard. In an advantageous embodiment of the invention, O2 > 1.13 * cu and O3 <= 0.99 * O2 and O3 <= ai.

[0040] Since stainless steel generally has a high thermal expansion coefficient, the thermal expansion coefficient Δ2 of the first and second shell sections is usually greater than the thermal expansion coefficient ai of the reaction tubes: Δ2 > Δcu. To compensate, the thermal expansion coefficient Δ3 of the third shell section must be smaller: Δ3 < Δ2. In a preferred embodiment, this is at most as large as the thermal expansion coefficient ai of the reaction tube material: Δ3 <= ai.

[0041] By inserting a third shell section with O3 <= 0.99 * O2, the overall axial expansion of the reactor shell is reduced. On the other hand, the stainless steel of the first and second shell sections also expands more in the radial direction than the third shell section made of carbon steel. These effects are taken into account in a corresponding strength calculation, and the required wall thicknesses are determined.

[0042] At certain temperature and pressure ranges, syngas leads to metal dusting in some materials. Another prerequisite is the so-called carbon activity. If the carbon activity is significantly higher than one, metal dusting must be expected. This prerequisite is generally met under the preferred operating conditions considered here. In a preferred embodiment, the reaction tubes are therefore made of a material that is more resistant to the corrosion properties of the process gas at the selected gas composition, pressure, and temperature. For safety reasons and reasons of manufacturability, the reaction tubes are preferably made entirely of this corrosion-resistant material.

[0043] In a favorable development of the invention, the reaction tubes are made of a nickel-based alloy. Many different materials are known from this material class and can in principle be used for the reactor according to the invention. Alloys selected from the materials Alloy 601, Alloy 602CA, Alloy 693 or Alloy 699XA or comparable are particularly suitable. A "comparable material" within the meaning of this document is one that is classified as equivalent in other designation systems. For example, the UNS material N06025 or material no. 2.4633 - NiCr25FeAIY are comparable to the material Alloy 602 CA used here according to the German designation, whereby this designation is a shortened designation in common usage for the full designation "VDM® Alloy 602 CA".While equivalent materials from other designation systems have essentially the same composition and mechanical properties, these may differ slightly from those of the reference material. The corrosion resistance of these materials increases in the order listed. These materials represent a selection of the most advantageous materials currently available. The reaction tube material is preferably selected according to a defined selection procedure in which the required material quality is determined based on the key parameters. This procedure ensures that only the material quality actually needed for the specific application is used. In this way, costs can be kept to a minimum. The materials listed are by no means to be understood as exclusive.They are merely a preferred choice when there is a risk of metal dusting. For other applications, other materials may be used.

[0044] In many cases, the material Alloy 602CA is used. This represents a good compromise between corrosion resistance and price. In certain cases, the material Alloy 601 can also be used when the risk of material attack by metal dusting is low, for example, when only low pressure is present or the expected operating time of the reactor is short, as in a laboratory test reactor. Materials with high corrosion resistance such as Alloy 683 or Alloy 699XA are used when this is required due to the boundary conditions. The selection is not exclusive. New alloys are constantly being developed that can equally be used in the tube bundle reactor according to the invention.

[0045] In a preferred embodiment of the invention, the tube sheets, the gas inlet hood, the gas outlet hood, and the first and second shell sections are made of a high-temperature-resistant stainless steel, e.g., material SS316 or comparable, and the third shell section is made of a high-temperature-resistant, low-alloy carbon steel, e.g., material SA387 Gr. 22 CI.2 or comparable. The material SS316 or comparable is particularly characterized by its combination of the properties of good high-temperature strength, freedom from heat treatment, corrosion resistance, and price.

[0046] The thermal expansion coefficient of the material SA387 Gr. 22 CI.2 or comparable for the third shell section is smaller than that of the first and second shell sections and even smaller than that of the reaction tube material. Furthermore, it has good strength properties even at high temperatures and is comparatively inexpensive. Therefore, the aim is to maximize the shell length L3 portion. On the other hand, the lengths L1A and L2A must be large enough to accommodate the annular channels. To compensate for expansion, sufficient clearance must be maintained in the direction of the intermediate shell section. This creates a smooth transition that can compensate for radially varying expansions in the weld area. The relevant regulations must also be observed.

[0047] An approximation to the ideal state can therefore be achieved, for example, by the following material combination:

[0048] Nickel-based material Alloy 602CA for reaction tubes: O602CA = 14.8 * 10- 6 * K' 1

[0049] Stainless steel SS316 for tube sheet etc.: asssie = 18.64 * 10- 6 * K- 1

[0050] Carbon steel SA387 Gr. 22 CI.2 for the third shell section: as387 = 14.48 * 10- 6 * K- 1

[0051] In a non-inventive embodiment, a third shell section is not present. Assuming equal lengths for the reaction tubes on the one hand and for the reactor shell and tube sheets together on the other hand, for this material combination, ai = C(602CA and a m = 02. Thus, a m / ai = 1.26 and thus outside the range of thermal expansion coefficient ratios according to the invention. Under this boundary condition, the permissible material properties are exceeded when the tube bundle reactor is started up to operating temperature and, at the latest, during operation under pressure load, resulting in plastic deformation and even fracture.

[0052] In the embodiment according to the invention, a third shell section made of carbon steel is therefore used. In this example, this third shell section has a thermal expansion coefficient that is smaller than that of the first and second shell sections and even smaller than that of the reaction tubes.

[0053] However, the other case can also occur, in which the second thermal expansion coefficient Δ2 is smaller than the thermal expansion coefficient Δcu of the reaction tubes and the third thermal expansion coefficient Δ3 is greater than the second thermal expansion coefficient Δ2. This can be the case if the reaction tubes are made of stainless steel and the reactor shell is made of carbon steel. In this case, for example, the third shell section with the length L3 is preferably made of a material with a similar thermal expansion coefficient to that of the reaction tubes, whereby in this case, a material from the group of stainless steels is suitable.

[0054] Advantageously, the tubesheets, gas inlet hood, and / or gas outlet hood are clad on the gas side with a nickel-based material from the group of materials used for the reaction tubes. The type of nickel-based material is determined analogously to the selection process for the reaction tube material. For example, stainless steel is specified as the material for the gas inlet hood, gas outlet hood, and tubesheets. A subsequent test is carried out to determine whether this material is susceptible to metal dusting under the operating conditions. The feed gas temperature is generally lower than the reaction temperature. Under these conditions, the reaction equilibrium of the RWGS reaction lies more on the reactants side, i.e., CO2 and H2. Susceptibility to metal dusting is thus reduced.Depending on its properties, the selected material can either be used without additional protective measures or protected with a metal dusting-resistant plating. This resistance may be lower than that of the subsequent tube-bundle reactor components, which are exposed to higher carbon activity due to higher temperatures, higher pressures, and more aggressive gas compositions. One plating process is explosive plating. The tubesheet is usually always clad, preferably with the same material as the reaction tubes. This allows for easy welding of the reaction tubes to the tubesheet.

[0055] Preferably, the third shell section is clad with a material that is corrosion-resistant to the heat transfer medium, wherein this clad extends over an axial length in a range between 1 and 100 mm into the adjacent first and second shell sections and is tightly connected to each of them. The use of molten salts made of carbonate salts allows process control at high temperatures. However, in the range of the upper application limit, the molten salt becomes highly corrosive due to decomposition reactions to oxides in combination with many materials at the specified temperature. Although the material of the third shell section has good strength values ​​at high temperatures, it is generally not corrosion-resistant to molten carbonate salts and is therefore protected from the heat transfer medium by a clad. The material used is generally the same as the first and second shell sections.The preferred material is SS316 or a higher grade. Plating is performed using a state-of-the-art process.

[0056] In tube bundle reactors for the most important exothermic gas-phase reactions, the inner tube diameter is usually in a range between 21 mm and 26 mm. These tube diameters result in a cooling surface density at which the reaction heat can be safely dissipated, particularly in the hot spots that often occur in exothermic gas-phase reactions. In endothermic gas-phase reactions, such hot spots do not exist, so in this case the heating surface density can be reduced to a certain extent by increasing the inner tube diameter. This reduces the number of tubes and the manufacturing costs for the tube bundle reactor. In another embodiment of the invention, the reaction tube inner diameter is therefore in a range of 30 to 60 mm. Larger reaction tube inner diameters are also possible, but care must be taken during process design to ensure that heat transfer is still sufficient.In an advantageous embodiment, a tube bundle reactor according to the invention has at least one modular electric heater for heating the heat transfer medium, where the term "electric heater" is understood to mean an electrically operated heater. This electric heater is preferably arranged parallel to a circulation pump of the tube bundle reactor. The heat transfer medium is fed from the pressure side of the circulation pump to the electric heater and from there to a point upstream of the circulation pump. The heat transfer medium flow through the electric heater is regulated by an optional control valve. If required, at least one further electric heater is arranged downstream of the at least one first electric heater. The modular design of the electric heater enables a simple power expansion. These further electric heaters are preferably arranged parallel to the first electric heater.This facilitates accessibility for assembly and maintenance work, especially with regard to the heating elements. All electric heaters are preferably powered by renewable electricity to achieve emission-free operation.

[0057] In a preferred embodiment, the reaction temperatures are in a range from 450°C to 650°C. In an even more preferred embodiment, they are in a range from 500°C to 550°C. This temperature range is sufficiently high to achieve the highest possible conversion, but at the same time it is still low enough to allow for a sufficient selection of permissible and economical materials. At lower temperatures, the tendency to corrosion decreases on both the gas side and the heat transfer medium side, and the thermal and mechanical stress on the tube bundle reactor decreases, but this also reduces the conversion and product yield. The opposite effects occur at temperatures that exceed the upper temperature limit.

[0058] The pressure in the gas chamber is advantageously in a range from 5 bar absolute to 50 bar absolute, and even more preferably in a range from 10 bar absolute to 35 bar absolute. These pressure ranges offer an optimum in terms of the highest possible mass throughput and high conversion on the one hand, while also limiting design effort on the other. The design effort results primarily from the mechanical stress, which requires corresponding wall thicknesses. On the other hand, the requirements for material quality increase, as the corrosive properties of the process gas increase with increasing pressure.

[0059] In another preferred embodiment, a melt of a mixture of carbonate salts or of a mixture of nitrate and nitrite salts, preferably solar salt, is used as the heat transfer medium. A molten salt mixture of a mixture of nitrates and nitrites has proven successful in many cases as a heat transfer medium in tube-bundle reactors. A ternary eutectic salt mixture known as HITEC™, consisting of 7% NaNO3, 53% KNO3, and 40% NaNO2, is known. It has a melting point of 142°C and a service temperature range of up to approximately 540°C. Decomposition processes begin in the upper temperature range. Solar power plants often use "solar salt," a mixture of 60% NaNO3 and 40% KNO3. The melting point here is approximately 240°C, and the application limit is approximately 600°C. The decomposition can be mitigated with protective gas and additional pressure.

[0060] It is known that hydrogen diffuses through metals. The diffusion flow depends on pressure, temperature, and the type of metal. If the nitrates / nitrites of a heat transfer salt decompose to form oxygen, the gas atmosphere above the heat transfer salt must be sufficiently purged to prevent the formation of an explosive atmosphere. Nitrate salt mixtures are therefore generally suitable as heat transfer media for the tube-bundle reactor according to the invention, as long as no process gases containing hydrogen are used and as long as the operating temperatures are not too high.

[0061] For higher operating temperatures, a melt made from a mixture of carbonate salts is preferred as the heat transfer medium due to its higher thermal stability. However, any other compositions can also be used if appropriate for the application. The carbonate salt melt is advantageously blanketed with a protective gas of CO2.

[0062] A tube bundle reactor according to the invention is particularly suitable for processes in which the reactor shell and the reaction tubes are exposed to different loads, resulting, for example, from high operating pressures in the process gas, high temperatures, or materials with different physical properties. It is particularly suitable for endothermic catalytic gas-phase reactions.

[0063] A tube bundle reactor according to the invention is preferably used to carry out a catalytic gas-phase reaction selected from the group consisting of the production of styrene, formaldehyde, methyl ethyl ketone (MEK), hydrogen cyanide, the dehydrogenation of alkanes, the dehydrogenation of alcohols, the reverse water gas shift (RWGS) reaction, the steam reforming of methane or ethanol, the cracking of ammonia, methane, or methanol, the catalytic naphtha reforming to a mixture of the aromatic hydrocarbons benzene, toluene, and the three xylene isomers (BTX aromatics), the oxidative coupling of methane (OCM), and the production of acetaldehyde, benzene, acrylonitrile, nitric acid, methyl mercaptan, the oxidation of sulfur dioxide to sulfur trioxide, and the production of kerosene from methanol via olefin synthesis. In endothermic reactions, the required reaction heat has so far been provided primarily by the combustion of fossil fuels.In the tube bundle reactor according to the invention, the required reaction heat is supplied to the process gas preferably by regeneratively generated electrical current via an electric heater and a heat transfer medium as an intermediate medium.

[0064] A tube bundle reactor according to the invention is particularly suitable for a process in which the catalytic gas phase reaction is formed from the reverse water gas shift reaction to produce CO. The CO2 required for this reaction can be obtained to a certain extent from biogenic sources such as biogas, carbon-containing waste or from the by-products of many industrial processes. Another possibility is capture from the ambient air. Although this process is more complex, this source is widely available and practically unlimited. The hydrogen required for this purpose is preferably obtained using an electrolyzer, which splits water into hydrogen and oxygen. Renewable electricity, e.g. from wind power or photovoltaics, is preferably used to operate the systems for capturing CO2 and producing H2.

[0065] The invention is explained in more detail below using the figures as examples. Herein:

[0066] Fig. 1 shows a longitudinal section through an embodiment of a tube bundle reactor according to the invention;

[0067] Fig. 2 a plan view of the embodiment from Fig. 1 , with circulation pumps and electric heaters

[0068] Fig. 3 shows a longitudinal section along line A - B in Fig. 2 through a circulation pump and two electric heaters.

[0069] Fig. 1 shows a longitudinal section through a preferred embodiment of a schematically illustrated tube bundle reactor 1 for carrying out catalytic gas-phase reactions. For reasons of clarity, conventional peripheral units such as circulating pumps, coolers, heaters, and the like are not shown here. The tube bundle reactor 1 has a tube bundle 2 of catalyst-filled reaction tubes 3, which are made of a material with a first thermal expansion coefficient cu and through which a process gas 4 flows. In this example, the process gas 4 is guided from top to bottom through the tube bundle reactor 1. A flow guidance from bottom to top is equally possible. The following designations, which depend on the flow direction, change accordingly in this case. The reaction tubes 3 open at their gas inlet-side ends into a gas inlet-side tube sheet 5 and are tightly connected to this at their ends.The tubesheet 5 is spanned by a gas inlet hood 6 with a gas inlet line 7 and is tightly connected to the gas inlet hood 6. The type of connection depends on the specific application. For higher pressures, approximately 10 bar and above, or when a hermetic seal is required, the tubesheet 5 and gas inlet hood 6 are preferably welded together, but a flanged connection is also possible. The reaction tubes 3 open at their gas outlet ends into a gas outlet side tubesheet 8 and are tightly connected to this at their ends. The gas outlet side tubesheet 8 is spanned by a gas outlet hood 9 with a gas outlet line 10 and is tightly connected to the gas outlet hood 9. The statements for the gas inlet side apply analogously to the types of connection on the gas outlet side as for the gas inlet side.

[0070] The tube sheets 5, 8, the gas inlet hood 6, the gas inlet line 7, the gas outlet hood 9 and the gas outlet line 10 are plated on the gas side with a nickel-based material from the group of materials for the reaction tubes 3 (5a, 8a, 6a, 7a, 9a, 10a).

[0071] The tube bundle 2 is surrounded by a multi-part reactor shell 11, which is tightly connected to the upper, gas inlet-side tube sheet 5 and the lower, gas outlet-side tube sheet 8. All parts of the tube bundle reactor 1 are preferably connected to one another by welded joints.

[0072] A highly heat-resistant stainless steel is preferably used as the material for the tube sheet 5, 8, the gas inlet and gas outlet hoods 6, 9 and for the directly adjoining shell sections 12, 13.

[0073] The reactor shell 11 is formed from a first shell section 12 with an axial length L1A, which is connected to the upper tubesheet 5, and a second shell section 13 with an axial length L2B, which is connected to the lower tubesheet 8. The upper tubesheet 5 has a thickness L1B, and the lower tubesheet 8 has a thickness L2B. The first and second shell sections 12, 13 are formed from a material with a second thermal expansion coefficient α2. The first shell section 12 is surrounded by a first, upper annular channel 14 near the upper tube sheet 5 for discharging a heat transfer medium from the shell space 15 of the tube bundle reactor 1 through openings 16 in the first shell section 12. Analogously, the second shell section 13 is surrounded by a second, lower annular channel 17 near the lower tube sheet 8 for introducing the heat transfer medium into the shell space 15 through openings 18 in the second shell section 13.The heat transfer in the shell space 15 from the heat transfer medium to the reaction tubes 3 is optimized by known flow guidance devices (not shown here). Flow guidance from top to bottom is equally possible. In this case, the units connected to the tube bundle reactor must be designed accordingly.

[0074] Between the first and the second jacket section 12, 13, a third jacket section 19 with an axial length L3 and a third thermal expansion coefficient as is inserted.

[0075] The second thermal expansion coefficient θ2 of the first and second shell sections 12, 13 is greater than the thermal expansion coefficient ai of the reaction tubes 3 and the third thermal expansion coefficient θ3 is smaller than the thermal expansion coefficient θ2 of the first and second shell sections 12, 13 and preferably even smaller than the thermal expansion coefficient ai of the reaction tubes 3.

[0076] The ratio a m / ai is in a range from 0.88 to 1.13, preferably in a range from 0.90 to 1.10 and most preferably in a range from 0.92 to 1.09. Where a m the average thermal expansion coefficient of sections L1A, L1B, L2A, L2B and L3 with am = (a2* (L1A + L1B + L2A + L2B) + a3* L3) / (L1A + L1B + L2A +L2B + L3).

[0077] By the specified ratio a m / ai the individual linear expansions are smaller than predetermined maximum values ​​at which the material loads within the tube bundle reactor 1 at any point and at any time are smaller than the permissible material loads.

[0078] The first linear expansions occur when the tube bundle reactor 1 heats up from ambient temperature to operating temperature. During the heating process, care must be taken to ensure that the temperature change over time does not exceed a specified maximum value to prevent material damage due to excessively varied linear expansions. Further varying linear expansions occur when the pressure in the gas space is increased to the operating pressure. Such load cases are taken into account in the strength calculation.

[0079] The third shell section 19 is plated 19a with a material that is corrosion-resistant to the heat transfer medium, this cladding 19a extending over an axial length 19b in a range between 1 and 100 mm into the adjacent first and second shell sections 12, 13 and being tightly connected to each of them.

[0080] The plan view shown in Fig. 2 shows the gas inlet line 7, which leads into the gas inlet hood 6. On the right-hand side, a connecting line 20 leads from the upper annular channel 14 to a first circulation pump 21. From this, a connecting line 22 shown in Fig. 3 leads to a first electric heater 23, which in turn is connected to a second electric heater 25 by a connecting line 24. This electric heater 25 is in turn connected to the circulation pump 21 by a connecting line 26. A third electric heater 27 and a fourth electric heater 28 are connected in mirror images to these two electric heaters 23, 25. In the same way, four further electric heaters 30, 31, 32 and 33 are connected to an opposite circulation pump 29. The number of electric heaters depends on the heat requirement of the respective tube bundle reactor 1. It can be decreased or increased.The electric heaters 23, 25, 27, 28, 30, 31, 32, and 33 are fundamentally identical in their design, i.e., they have a modular construction. This simplifies the design and construction effort and reduces costs. All electric heaters 23, 25, 27, 28, 30, 31, 32, and 33 are connected to the tube bundle reactor 1 by supports (not shown here).

[0081] Fig. 3 shows a longitudinal section along the section line AB shown in Fig. 2. The circulating pump 21 conveys the heat transfer medium 34 coming from the upper annular channel 14 downwards into the lower annular channel 17. A connecting line 22 leads from the lower pump housing 35 to the first electric heater 23. In this, the heat transfer medium 34 is heated by electrically operated heating elements 36 and flows upwards, if necessary under the influence of guide plates. The heat transfer medium 34 flows downwards via a vertical connecting channel 24 into the inlet of the second electric heater 25, through which the flow is analogous to the first electric heater 23. The electric heaters 23, 25 are preferably of identical construction, so that a modular construction according to Fig. 2 is easily possible. The heat transfer medium flow through the electric heater unit is regulated by an optional control valve 37. To accommodate the change in length of the reactor, the pump housing 35 preferably contains a compensator 38.The arrangement shown is by no means limiting. Depending on the application, the design can be modified within the meaning of the invention by a person skilled in the art. For example, the control valve can be arranged between the first and second electric heaters, or the electric heaters can be arranged in a triangular configuration, for example, rather than along a line in plan view. Furthermore, the electric heaters can be arranged in parallel, in series, or in combinations thereof, depending on the practicality.

[0082] List of reference symbols

[0083] 1 tube bundle reactor

[0084] 2 tube bundles

[0085] 3 reaction tubes

[0086] 4 Process gas

[0087] 5 gas inlet tube sheet

[0088] 6 Gas inlet hood

[0089] 7 Gas inlet line

[0090] 5a, 6a, 7a Cladding of the gas inlet tube sheet, the gas inlet hood and the gas inlet line

[0091] 8 gas outlet side tube sheet

[0092] 9 Gas outlet hood

[0093] 10 Gas outlet line

[0094] 8a, 9a, 10a Cladding of the gas outlet tube sheet, the gas outlet hood and the gas outlet line

[0095] 11 Reactor shell

[0096] 12 first mantle section

[0097] 13 second shell section

[0098] 14 first, upper ring canal

[0099] 15 jacket space

[0100] 16 openings in the first shell section

[0101] 17 second, lower ring channel

[0102] 18 openings in the second shell section

[0103] 19 third mantle section

[0104] 19a Cladding of the third shell section

[0105] 19b Overlap of the cladding 19a

[0106] 20 connecting line

[0107] 21 first circulation pump

[0108] 22 connecting line

[0109] 23 first electric heater

[0110] 24 connecting line

[0111] 25 second electric heater

[0112] 26 connecting line

[0113] 27 third electric heater

[0114] 28 fourth electric heater

[0115] 29 second circulation pump ,31,32,33 further electric heaters heat transfer medium lower pump housing heating elements control valve compensator

Claims

PB06196 Claims 1. A tube bundle reactor for carrying out catalytic gas-phase reactions, comprising a bundle (2) of reaction tubes (3) which are formed from a material having a first thermal expansion coefficient cu and which are catalyst-filled in the operating state, through which a process gas (4) flows and around which a heat transfer medium flows, a gas inlet-side tube plate (5) with the axial dimension L1 B, which is tightly connected to the gas inlet-side ends of the reaction tubes (3) and through which the reaction tubes (3) open into a gas inlet hood (6) with a gas inlet line (7), wherein the gas inlet hood (6) spans the gas inlet-side tube plate (5) and is tightly connected to it, a gas outlet-side tube plate (8) with the axial dimension L2B,which is tightly connected to the gas outlet-side ends of the reaction tubes (3) and through which the reaction tubes (3) open into a gas outlet hood (9) with a gas outlet line (10), wherein the gas outlet hood (9) spans the gas outlet-side tube plate (8) and is tightly connected thereto, further comprising a reactor jacket (11) which surrounds the bundle (2) of reaction tubes (3) and is connected to the gas inlet-side tube plate (5) and the gas outlet-side tube plate (8), wherein the tube plates (5), (8) and / or the reactor jacket (11) are formed from a material with at least a second thermal expansion coefficient O2, characterized in that, 02 > 1.13 * ai or 02 < 0.88 * ai, the reactor shell (11) is formed in the axial direction from three shell sections (12, 13, 19), the first (12) of which has an axial length L1A and is connected to the gas inlet-side tube sheet (5) and the second (13) of which has an axial length L2A and is connected to the gas outlet-side tube sheet (8) is connected and both (12), (13) are formed from a material with the at least one second thermal expansion coefficient α2, wherein between the first shell section (12) and the second shell section (13) there is a third shell section (19) made of a material with a third thermal expansion coefficient αs and an axial length L3 with αs <= 0.99 * α2 for the case α2 > 1.13 * ai or with α3 >= 1.01 * α2 for the case α2 < 0.88 * ai.

2. Tube bundle reactor according to the preceding claim, characterized in that the reactor shell (11) and the tube sheets (5), (8) together have an average axial thermal expansion coefficient am = (a2* (L1 A + L1 B + L2A + L2B) + a3* L3) / (L1 A + L1 B + L2A + L2B + L3) with a ratio Om / ai which is in a range from 0.88 to 1.13, preferably in a range from 0.90 to 1.10 and particularly preferably in a range from 0.92 to 1.

09.

3. Tube bundle reactor according to one of the preceding claims, characterized in that O2 > 1.13 * ai and O3 <= 0.99 * O2 and O3 <= ai.

4. Tube bundle reactor according to one of the preceding claims, characterized in that the reaction tubes (3) are formed from a material which is resistant to the corrosion properties of the process gas at the selected gas composition, the selected pressure and the selected temperature.

5. Tube bundle reactor according to one of the preceding claims, characterized in that the reaction tubes (3) are formed from a nickel-based alloy selected from the materials Alloy 601, Alloy 602CA, Alloy 693, Alloy 699XA or comparable.

6. Tube bundle reactor according to one of the preceding claims, characterized in that the tube sheets (5), (8), the gas inlet hood (6), the gas outlet hood (9), the first and the second shell section (12), (13) are formed from a high-temperature-resistant stainless steel, e.g. material SS316 or comparable, and that the third shell section (19) is formed from a high-temperature-resistant, low-alloy carbon steel, e.g. material SA387 Gr. 22 CI.2 or comparable.

7. Tube bundle reactor according to one of the preceding claims, characterized in that the tube sheets (5), (8), the gas inlet hood (6) and / or the gas outlet hood (9) are plated (5a, 8a, 6a, 9a) on the gas side with a nickel-based material from the group of materials for the reaction tubes (3).

8. Tube bundle reactor according to one of the preceding claims, characterized in that the third shell section (19) is plated with a material which is corrosion-resistant to the heat transfer medium (34), said cladding (19a) extending over an axial length (19b) in a range between 1 and 100 mm into the adjacent first and second shell sections (12), (13) and being tightly connected to each of these.

9. Tube bundle reactor according to one of the preceding claims, characterized in that the reaction tube inner diameter is in a range of 30 to 60 mm.

10. Tube bundle reactor according to one of the preceding claims, characterized by at least one modular electric heater (23) for heating the heat transfer medium.

11. Method for operating a tube bundle reactor (1) according to one of the preceding claims, characterized in that the reaction temperatures are in a range from 450°C to 650°C.

12. Method according to the preceding claim, characterized in that the pressure in the gas space is in a range from 5 bar absolute to 50 bar absolute.

13. Method according to one of claims 11 or 12, characterized in that a melt of a mixture of carbonate salts or of a mixture of nitrate and nitrite salts, preferably solar salt, is used as the heat carrier (34).

14. Use of a tube bundle reactor (1) according to one of claims 1 to 10 for carrying out a catalytic gas phase process selected from the production of styrene, Formaldehyde, methyl ethyl ketone (MEK), hydrogen cyanide, the dehydrogenation of alkanes, the dehydrogenation of alcohols, the reverse water gas shift reaction (RWGS), the steam reforming of methane or ethanol, the cracking of ammonia, methane or methanol, the catalytic naphtha reforming to a mixture of the aromatic hydrocarbons benzene, toluene and the three xylene isomers (BTX aromatics), the oxidative coupling of methane (OCM), as well as the production of acetaldehyde, benzene, acrylonitrile, nitric acid, methyl mercaptan, the oxidation of sulfur dioxide to sulfur trioxide and the production of kerosene from methanol via olefin synthesis.

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