CA2833055A1

CA2833055A1 - Fixed-bed reactor

Info

Publication number: CA2833055A1
Application number: CA 2833055
Authority: CA
Inventors: Manfred Lehr; Wolfgang Schuster; Edmund Bohm; Joachim Engelmann
Original assignee: CHEMIEANLAGENBAU CHEMNITZ GmbH; MAN Diesel and Turbo SE
Current assignee: CHEMIEANLAGENBAU CHEMNITZ GmbH; MAN Energy Solutions SE
Priority date: 2012-11-15
Filing date: 2013-11-13
Publication date: 2014-05-15
Also published as: AU2013257470A1; DE102012220926A1; CN103816840A; EA201301166A1

Abstract

The invention relates to a radial-flow reactor (1) for carrying out chemically catalytic reactions with an isothermal reaction regime. According to the invention, the reaction space (7) of the reactor (1) is penetrated by a plurality of heat exchange tubes (9), the heat exchange tubes (9) being arranged as parallel to the centre axis (6) as possible and in a plurality of groups, such that the groups form full rows (38) which are arranged in the radial direction in the reaction space (7), the outer contours of adjacent heat exchange tubes (9) of a row (38, 39) being so close to one another that radial flow ducts (40) are formed.

Description

Fixed-bed reactor The invention relates to a radial-flow fixed-bed reactor.
Fixed-bed reactors are reactors for carrying out chemical reactions, a fluid flowing axially or radially through a catalyst located in a fixed bed.
A wide variety of fixed-bed reactors are known from the prior art. Of particular interest are radial-flow fixed-bed reactors. With this construction it is possible to create a large flow surface with little pressure loss. Heat exchange devices are often provided in the reactors in order to remove or supply heat so as to create uniform reaction conditions in the case of exothermic and endothermic reactions.
For example, EP 2 165 755 A1 describes an isothermal chemical reactor comprising heat exchange elements comprising a plurality of heat exchange elements which are arranged around the reactor axis and each consists of a radially oriented row of a plurality of heat exchange ducts extending axially in parallel. The ducts of a heat exchange element are each connected to a distributing tube and to a collecting tube having a continuously variable cross-section. The heat exchange ducts have an elongate cross-section having an approximately oval or rectangular shape and a varying lateral orientation within a heat exchange element. The integration of each individual duct having a non-circular cross-section to the distributing or collecting tube which is perpendicular thereto is technically challenging, and thus in turn cost-intensive. In addition, for structural reasons, only a limited heat exchange surface density can be achieved.
DE 100 31 347 A1 presents a cylindrical reactor comprising radially arranged heat exchanger plates, it also being possible for the heat exchanger plates to be wedge-shaped.
For structural reasons, maintenance and repair work on such apparatuses is complex. The uniform distribution of the heat exchange medium into the heat exchanger plates requires particular care. The production of heat exchange plates, in particular when pressure stability is required or in the case of variable plate thickness, is complicated and thus cost-intensive.
EP 2 363 203 A1 also discloses a reactor comprising heat exchange plates which comprise a plurality of adjacent ducts for transporting the heat transfer medium. Owing to their complicated construction, these heat exchange plates are cost-intensive to produce and, I

owing to their delicate structure, vulnerable to mechanical stress, in particular compressive stress.
DE 10 2009 031 765 A1 discloses a cylindrical converter for carrying out exothermic catalytic reactions, in which converter wedge-shaped heat panels are used to remove the reaction heat. The heat panels are specifically adapted to a cooling system comprising an evaporating medium. In this system, the evaporated heat transfer medium delivers its heat in a heat exchanger located in the converter itself to a heat transfer medium of a secondary heat transfer medium circuit. These heat panels are also cost-intensive to produce owing to their complicated construction for ensuring pressure stability.
The object of the present invention is to propose a radial-flow fixed-bed reactor for chemically catalytic reactions, even under increased pressure, with heat tone, which reactor is inexpensive to produce and can be tailored very easily to different reaction profiles and different amounts of released or required reaction heat to create reaction conditions which are as isothermal as possible.
According to the invention, the object is achieved by a reactor having the features of the main claim. The dependent claims relate to preferred configurations of the invention.
The reactor according to the invention is suitable for carrying out chemical catalytic reactions with heat tone with reaction conditions which are as isothermal as possible, although adiabatic areas of the reactor can be advantageous for some reactions and hence the invention relates also to reactors having a mainly isothermal reactions space with adiabatic zones. In the adiabatic zones no cooling or heating of the reaction gas is carried out.
In principle, the shape of the reactor is cylindrical with a cross-section which is as circular as possible, such that this shape defines an axial (in the longitudinal direction of the cylinder) and a radial direction (in the circular cross-sectional area from the centre outwards). The centre axis of the reactor is arranged centrally in the circular cross-section in the axial direction. During use, the reactor is upright, that is to say the axial direction is oriented vertically.
The reactor comprises a cylindrical reactor shell which is arranged about the centre axis, is preferably pressure-stable and is closed at its upper end by an upper head and at its lower end by a lower head. The entirety of the reactor shell and the upper and the lower head is referred to in this document as the pressure shell.
Inside the reactor shell there is a substantially annular reaction space which surrounds a perforated central tube. The wording "substantially" expresses the fact that a circular shape is preferred, but slight deviations, for example owing to production tolerances, are admissible.
The annular reaction space is surrounded by an outer cavity, the outer cavity and the reaction space being separated by an outer wall which is perforated at least in part. For use of the reactor, a catalyst bed is filled in the reaction space. An inner cavity is defined inside the central tube.
The outer cavity and the central tube are provided for supplying the feed gas and for removing the product gas, whether the supply takes place via the central tube and the removal via the outer cavity or vice versa depending on the specific reaction to be carried out. The feed gas is supplied and the product gas removed through the perforated regions of the inner and the outer wall defining the reaction space. The supply and removal allow the radial gas flow.
In this context, perforated expresses the gas permeability of the outer wall of the reaction space and of the central tube (the inner wall of the reaction space), such that the reaction gas can penetrate these, but the catalyst located in the reaction space is retained. The perforation can be ensured in a wide variety of ways, for example by a wall having discontinuities, for example in the form of holes or slots, or a wire grid.
The hole size must be tailored to the particle size of the catalyst to be filled. it must also be ensured that catalyst particles do not block the perforation. A multilayer wall can optionally be provided for this purpose, the layers of which are also advantageously spaced apart by spacers.
The dimensions of the reactor according to the invention are not particularly limited and are determined according to the production output required in each case. In commercial use, for economic reasons it is generally desirable to make the reactor as large as possible. In a first step, the radial and axial dimensions of the reaction space are determined on the basis of the reaction requirements. The external dimensions of the reactor then result from the space requirement of the corresponding apparatus parts for supplying the reaction gas and the heat transfer medium and from design requirements.

The outer diameters of such reactors are generally in a range between 2 m and 9 m, preferably between 3 m and 5 m. The overall height is generally in a range between 3 m and 30 m, preferably between 15 m and 25 m. However, reactors having smaller dimensions are also possible, for example for decentralised solutions or for test purposes.
The central tube generally has a diameter of between 0.3 m and 1.5 m. Preferred diameters are in a range between 0.6 m and 0.9 m. As a result, the central tube is accessible for assembly, maintenance and repair purposes. Depending on the porosity and length of the porous wall of the central tube, a uniform radial flow of the gas over the face of the porous wall is possible. The radial dimension of the outer cavity is preferably in a range between 0.05 m and 0.5 m, preferably between 0.1 m and 0.3 m.
In addition, the reaction space is penetrated by a plurality of heat exchange tubes, the heat exchange tubes being arranged as parallel to the centre axis as possible and in a plurality of groups. Each group forms a full row which is oriented in the radial direction in the reaction space. The outer contours of adjacent heat exchange tubes of a row are so close to one another that radial flow ducts are formed by the full rows. in this context, full row means that the rows cover virtually the entire reaction space in the radial direction. In this context, radial flow ducts are understood to mean ducts in which the catalyst is located when a reaction is carried out and which divide the reaction space into radially extending sections, the tube rows, as duct limitations, preventing transverse flows to adjacent ducts to the greatest possible extent. Although the flow is mainly in a radial direction caused by a pressure difference between the central tube and the outer cavity, transverse flows can occur due to differences in the mass density of the reaction gas caused by temperature differences between areas closer to the heat exchange tubes and areas distant from the heat exchange tubes. Transverse flows can make the reaction less efficient as they result in an undefined time period, during which the reaction gas remains in the reactor. By placing the adjacent heat exchange tubes close to each other to form full rows as explained above transverse flows are advantageously reduced to a minimum.
In this context, radial direction of the flow ducts or of the full rows is understood to mean not only the exact radial direction from the centre axis outwards. For particular reactions it may be advantageous for reaction gas to cross the reaction space not by the shortest path, but rather for example slightly obliquely or in a serpentine manner. The wording "radial flow through the reactor" means flows which flow through the reactor in the radial direction, but these may also be directed slightly obliquely, that is 10 say with an axial component.

Large distances between the heat exchange tubes lead to a temperature distribution between the middle in between to neighbouring heat exchange tubes of one row and the outer surface of the heat exchange tubes resulting in pressure differences and transverse flows. The outer contours of adjacent heat exchange tubes of a row preferably have a spacing of less than 5 mm, preferably less than 3 mm, more preferably less than 2 mm and particularly preferably less than 1 mm, direct contacting adjacency being particularly advantageous. A reason for the spacing can be conditional of manufacturing.
The withdrawal of the product gas or the supply of the feed gas can take place laterally through the reactor shell or in the region of its axial ends, that is to say the upper and the lower head, and there in particular in the region of the centre axis.
In principle, the cross-sectional shape of the heat exchange tubes is unlimited. However, circular tubes are preferred, since these can be obtained inexpensively as semi-finished products and are easy to process, and in addition cost-effective automated methods for welding the tubes are available. In addition, a circular cross-section allows the smallest wall thickness at a given pressure difference.
The outer diameters and wall thicknesses of the heat exchange tubes are selected according to the process requirements and flow considerations. The flow cross-sections are selected to be of a size such that a flow speed of the medium is achieved which ensures sufficient heat transfer in exothermic and endothermic reactions, that is to say that the reaction heat can be removed safely in exothermic reactions and the heat required for the reaction is supplied in endothermic reactions and the pressure losses remain within economic limits. Conventional outer diameters of such heat exchange tubes are in a range between 15 mm and 40 mm, preferably between 20 mm and 30 mm. The wall thicknesses are generally between 1.0 mm and 4.0 mm, preferably between 1.5 mm and 2.5 mm.
The material is selected primarily according to the maximum temperatures during the entire operation and the chemical resistance. In general, non-alloy or low-alloy boiler tube steels and in special cases also stainless steels are used.
The spacing between the full rows and their arrangement in relation to one another are dependent on the desired reaction conditions. For instance, the styling of the arrangement of the rows of heat exchange tubes in the reaction space depends on the progress of the reaction in the flow direction and on the degree of heat tone. Adapting the arrangement of the heat exchange tube rows to a reaction ensures isothermal conditions in the reaction space. The heat exchange surface density is adapted to the reaction conditions. The heat exchange surface density can be increased by laying intermediate rows or using different tube diameters.
The heat exchange tubes are suitable for the flow of different heat transfer media, for example water, oil, steam or molten salts, and are in a circuit with a further heat exchanger, which is preferably arranged outside the reactor shell.
The reaction process is dependent on a plurality of influencing variables. it is influenced significantly by the pressure, the temperature and the composition of the reaction gas, the residence time of the reaction gas in the catalyst bed and by the composition, size and form of the catalyst. The residence time is dependent on the volume flow of the reaction gas and on the cross-sectional area of the flow duct. The temperature is determined by the heat transfer at the duct wails, the heat transfer in turn being dependent on the flow speed in the duct and the type of wall surface. Thus, an optimum reaction process is adjusted by setting the size and arrangement of the heat exchange tubes according to the invention appropriately.
Advantageously, a reactor which can be adapted particularly flexibly to the required reaction conditions of very different reactions is thus created. For instance, only the arrangement of the heat exchange tubes in the reaction space must be adapted. The heat exchange surface density can thus also be adjusted flexibly and easily. Owing to the structured surface of the radial flow ducts formed, turbulence of the reaction gas is also produced in this region and advantageously assists the heat exchange. Further advantageously, (in particular circular) tubes are pressure-stable, and therefore this requirement is also met inexpensively.
A person skilled in the art can without difficulty undertake the configuration of the reactor, in particular the adaptation of the above-mentioned factors to the reaction conditions planned for a particular reaction.
Preferably, at least one heat exchange tube of a group is bent once or preferably twice at at least one tube end and fixed in a tube sheet at least at one end. Preferably, the tubes are bent twice in opposite directions, such that the bending results in an axial offset without changing the entry angle into the tube sheet, such that the connection in the tube sheet still takes place in the axial direction.
The heat exchange tubes are passed through holes in the tube sheet and the tube ends are connected in a sealing manner, in particular welded, to the tube sheet. The welding is preferably done in automated methods by means of arc welding or laser welding.
The heat exchange tubes are thus fixed in their position and location in the tube sheet.
Preferably, all the heat exchange tubes are fixed in a tube sheet at one end, more preferably in a tube sheet at each end. Preferably, two tube sheets are provided.
Owing to the lateral offset of the tube ends resulting from the bending, these tube ends can be connected in the tube sheets to the heat transfer medium circuit without being constrained, despite the small spacings between the outer contours of the heat exchange tubes. There are various options for styling the bending; for instance, the tubes of a group can be bent alternately to the right and left, or alternately bent to the left (or right) and straight (without bending).
A further advantageous effect of the bending is the increased stability of the tube sheet. For instance, fixing the heat exchange tubes without bending results in segmentation of the sheet by the holes. Owing to the bending, the holes are advantageously spaced apart and the tube sheet is thus not segmented and also the holes do not transition into one another and thus form a comb-shaped slot.
Although the tubes are preferably fixed in a single tube sheet at their respective ends, this does not exclude the possibility that the tube sheets of each end can also be in multiple parts, as presented in DE 20 2007 006 812 U1 for example.
In an alternative configuration, the tubes can also have a relatively small tube diameter at their ends, such that between the outer contours a spacing is provided which allows proper con nectability.
Further preferably, further groups of heat exchange tubes are arranged between the full rows of heat exchange tubes and form relatively short intermediate rows.
Preferably, the intermediate rows start on a radius between the central tube and the outer wall and extend I

up to the outer wall. Advantageously, owing to the intermediate rows the heat exchange effect can be increased in the outer region of the reactor.
In a preferred configuration of the invention, a plurality of full rows of heat exchange tubes is arranged in a star shape and symmetrically about the central tube. These preferably extend from the central tube to the outer wall.
In the region of the central tube and/or in the region of the outer wall, adiabatic zones can be provided, in the region of which no heat exchange tubes are arranged, the proportion of the catalyst volume in these adiabatic zones depending on the process.
Alternatively or additionally, an adiabatic intermediate zone which is positioned in an annular manner in a middle region of the reaction space can also be provided. The proportion of the catalyst in the adiabatic zone in the region of the central tube and in the annular adiabatic intermediate zone should preferably be no more than 5 % of the total catalyst volume in each case. In the adiabatic zone in the region of the outer wall this proportion may be up to 10 %, depending on the reaction.
Preferably, the heat exchange tubes have a continuously circular cross-section. Tubes of this type are inexpensively and very readily available as semi-finished products. In an alternative configuration, the heat exchange tubes have a circular cross-section at their ends and an elongate (for example oval or n-cornered) cross-section in the middle region. Owing to the circular cross-section, the connection and fixing in the tube sheet can thus take place as described above. The elongate cross-section in the middle region of the heat exchange tubes is very well suited to particular processes. If the transverse axes of these tubes in the radial direction are large enough, in the case of straight tubes the spacings between the tubes in the tube sheet can be large enough that the weld seams of adjacent tubes no longer influence one another. Bending of the tubes can be omitted in this case.
Further preferably, the heat exchange tubes within a group have varying cross-sections. In this context there are a wide variety of alternatives, which are selected on the basis of the process-specific conditions, for example: alternately large and small circular diameters within a group or relatively large diameter in the outer region and relatively small diameter in the inner region of the reaction space.

The geometry of the radial flow ducts (catalyst gaps through which gas flows) is predefined by the arrangement of the rows of the heat exchange tubes (full rows and intermediate rows).
Preferably, the spacing between the outer contours of adjacent full rows or adjacent full and intermediate rows increases from the central tube outwards. Styling of this type is particularly suitable for petrol synthesis.
In the case of a reaction process with decreasing conversion in the flow direction (for example synthesis of hydrocarbons from methanol or from a dimethyl ether/methanol mixture or from a mixture of alcohols), the radial flow ducts are configured such that they become wider in the flow direction. As a result, the cooling effect is greatest in the inlet region of the gas and lessens in the flow direction towards the outlet. In this type of reaction, discontinuity at the inner start of an intermediate row (relatively small tube diameter at the beginning of the intermediate row) has an advantageous effect, since as a result the space between the full rows is used optimally to accommodate heat exchange surface.
Other reactions, such as reactions having a reaction process with constant conversion in the flow direction (for example methanol synthesis from synthesis gas), require parallel flow ducts which are obtained for example via tube cross-sections which become larger towards the outside. As a result, the cooling effect is constant in the flow direction of the reaction gas.
The heat removal in each region of the reaction space is thus adapted to the reaction process by the targeted distribution of the heat exchange surfaces. This results in the following advantages:
damage to the catalyst owing to overheating is avoided;
undesirable side reactions owing to local overheating in the reaction space are avoided;
the intermediate regeneration cycles become longer in the case of regenerative catalysts;
- the life of the catalyst is significantly increased;
- the product selectivity and yield are increased.
In order to allow good filling of the reactor with the catalyst, the minimum spacing between two (full or intermediate) rows is at least 15 mm, preferably 20 mm.

Preferably, the axes of the heat exchange tubes of at least one full or intermediate row are located on a straight line directed radially outwards.
In an alternative configuration, the axes of the heat exchange tubes of at least one full or intermediate row form a serpentine line. This arrangement promotes turbulent flow components in the region of the heat exchange tubes.
To increase the turbulence of the flow of the gases through the reaction space, the heat exchange tubes can have turbulence generators on their outer contour. The turbulence generators are arranged only in regions of the outer contour such that the turbulence generators project into the flow duct. No turbulence generators are provided between the heat exchange tubes. Turbulence generators can also be provided inside the heat exchange tubes to increase the turbulence when heat transfer medium flows through and thus also to increase the heat exchange.
The heat exchange tubes are connected by at least one end, preferably both ends, to a distributing device or a collecting device. The collecting device collects the heat transfer medium exiting the heat exchange tubes and the distributing device distributes the heat transfer medium to the heat exchange tubes. These distributing and collecting devices are preferably formed from the tube sheet to which the heat exchange tubes are fixed and from a head which spans these tube sheets.
In most cases, the collecting device (also referred to as a heat transfer medium collector or collecting head) is connected to a heat exchanger, which is preferably arranged outside the reactor. Advantageously, the heat exchange circuit thus formed can be used for cooling and heating. For instance it is possible, for example when starting up the reactor, to supply heat in order to reach the process temperature more rapidly. When the reaction starts, a transition to cooling can then take place in order to maintain the optimum process temperature for the exothermic reaction.
The heat transfer medium is preferably conveyed to/from the heat exchanger to/from the reactor via a ring line which is preferably also located also the reactor. The ring lines have a plurality of connections to the distributing or collecting device. Preferably, four connections are provided.

The distributing device can optionally also comprise a device for flow homogenisation, for example a perforated plate, upstream of the tube sheet.
The specific configurations of distributing and collecting devices, the ring line and the heat exchanger are dependent in particular on the heat transfer medium used. The reactor according to the invention is suitable for most heat transfer media, which are in particular water, oil, steam and molten salts.
For example, for a reactor for petrol synthesis, molten salt having the following composition is provided as heat transfer medium: potassium nitrate (53 `)/0 by weight), sodium nitrite (40 % by weight) and sodium nitrate (7 % by weight).
During operation, there are differing thermal expansions of the reactor shell and of the heat exchange system located therein, consisting of heat exchange tubes, distributors and collectors and the corresponding passages from the reactor. To avoid inadmissible stresses between these apparatus groups, compensators are provided, preferably at the upper passages of the heat transfer medium from the reactor. Corrugated compensators are preferred. The compensators may in principle be located outside or inside the reactor, an arrangement outside the reactor being preferred.
Preferably, the perforation of the central tube and/or of the outer wall of the reaction space can vary over the axial length of the reactor, with the aim of uniform distribution of the feed gas into the reaction space at each axial point of the catalyst bed.
A catalyst, preferably in the form of a granular bed, is filled between the heat exchange tubes in the reaction space. In the case of petrol synthesis, the ratio of the heat exchange surface of the heat exchange tubes to the catalyst volume preferably decreases in the radial flow direction of the reaction gas (from the central tube to the outer cavity). In the case of methanol synthesis, this ratio preferably remains constant in the flow direction of the reaction gas. The ratio of the heat exchange surface of the heat exchange tubes to the catalyst volume generally behaves as 10 m2/m3 to 200 m2/m3, preferably as 50 m2/m3 to 110 m2/m3.
The catalyst volume identifies the total space filled with catalyst particles, including the space in between the catalyst particles, excluding the volume of the heat exchange tubes. In contrast the reaction space defines the total space in between the central tube and the outer cavity and hence the catalyst volume plus the volume of the heat exchange tubes.
Preferably, an inert material is filled in the upper and the lower region of the reaction space.
The inert material prevents a reaction in these regions and avoids bypass flows of the reaction gas, by providing a high flow resistance. In the case of bent tube ends, the structure of the flow ducts is distorted by the bending in this region, such that a defined reaction process in these regions hardly seems possible. In addition, for the most part the heat exchange tubes extend axially out of the catalyst bed, such that a dead space is formed in the uppermost region of the reaction space. The central tube and outer wall are preferably not perforated in the region of the inert material and also of the dead space.
Since the catalyst particles tend to settle during the use of the reactor, the dead space contains reserve catalyst particles, which compensate the volume of catalyst particles lost by the settling. It is recommended to fill the whole space between the perforated central tube and the outer wall with catalyst particles to avoid the possibility that gas can pass through the reactor without contacting the catalyst. ,The reserve catalyst particles in the dead space are very advantageous. Hence the catalyst volume decreases during usage. However, the influence on the above mentioned ratio of heat exchange surface to the catalyst volume is insignificant and can be neglected.
Preferably, the catalyst to be filled is an extrudate having a particle size of between 1 mm and 2 mm diameter and a length of between 3 mm and 15 mm, more preferably between 3 mm and 6 mm length. Particularly preferred are approximately spherical particles having a diameter of 1 mm to 3 mm, preferably 1.5 mm to 2 mm. Advantageously, the required size of the reactor can thus be reduced by a relatively high packing density of the catalyst, with associated material and energy savings. In addition, a small particle size facilitates the filling of the reactor with catalyst and not least also advantageously homogenises the gas flow.
Preferably, at least one support grid which fixes the position of the tubes in relation to one another and within the reactor, and thus also sets the width of the flow ducts, is arranged at the heat exchange tubes between the upper and the lower end. This support grid consists of an annular system of spokes. Particularly preferably, the support grid consists of at least two concentric rings, connected by rods which extend parallel to the tube rows and thus as radially as possible, such that closed cassettes are formed around the rows of heat exchange tubes, the spacings between the spokes being variable in order to hold heat exchange tubes of different diameters. The rods are particularly preferably flat bars, and connected by welding. The flat bars can comprise interlocking grooves to facilitate mounting.
Particularly preferably, the flat bars have oblique and/or rounded upper and lower edges so as not to hinder filling and removal of the catalyst and thus to avoid associated dead zones.
Advantageously, the annular adiabatic layer in the middle region can coincide with the ring of a support grid.
Preferably, the reactor can be accessed for maintenance and repair work. This can take place in particular via one or more manholes in the upper and/or the lower head of the pressure shell or via the supply line of the reaction gas or the outlet line of the product gas.
Particularly preferably, a releasable connection, for example a flange, is provided for this purpose in the supply or outlet line in order to open the line for entry.
Preferably, the reactor comprises a filling device for the catalyst filling.
A particularly preferred filling device is described in claim 15 and comprises at least one catalyst distributor and a plurality of filling tubes which are connected thereto. The filling device is arranged above the reaction space. The at least one catalyst distributor is arranged outside the bundle of heat exchange tubes. A plurality of filling tubes, which each open into the at least one catalyst distributor with their upper ends, extend into a dead space formed by the uppermost region of the reaction space and open into this space with their lower ends, the profiles of all filling tubes being tailored to one another in the dead space such that all of their lower ends are distributed over the entire cross-section of the catalyst space.
The filling device takes advantage of the knowledge that, when filling the catalyst space with catalyst particles, firstly the time interval between two catalyst particles impinging on the same point should be sufficiently great that the impinging catalyst particles do not cant or jam each other, but rather each have enough time to rotate and slide into their own stable positions, and as a result they are packed as tightly as possible, and secondly these time intervals should be as uniform as possible in order to obtain packing which is vertically homogeneous. Using the filling tubes, preferably arranged as a bouquet, which extend from a catalyst distributor into the clearances between the heat exchange tubes into the catalyst-free dead space (that is to say the unfilled reaction space) between the lower side of the upper tube sheet and the upper side of the catalyst bed to be filled, a stationary filling device can be formed which, despite a lack of rotary and vertical movement, can fill catalyst material such that the resulting catalyst bed is homogeneous in the horizontal and the vertical direction and tightly packed. Since the profiles of all the filling tubes in the dead space are tailored to one another such that all their lower ends are distributed over the entire cross-section of the catalyst space, uniform filling with catalyst material over the cross-section of the catalyst space is ensured.
The upper ends of the filling tubes open into a catalyst distributor such that an uninterrupted, uniform flow of catalyst material to each filling tube and thus an outflow of catalyst material from the lower ends of the filling tubes which is uniform over time (hereinafter also referred to as flow speed) is ensured. The amount of catalyst material which flows through the filling tubes per unit time is determined via the size of the opening cross-section of the filling tubes or of the inlet opening at the upper ends of the filling tubes. The inlet openings or the inner dimensions of the filling tubes can be determined according to the desired flow speed. The catalyst distributor is arranged outside the groups of heat exchange tubes such that it firstly can be styled and positioned freely and secondly is freely accessible, whereby the catalyst distributor can easily be refilled with catalyst material by an operator during the filing of the catalyst space. A filling device according to the invention is preferably rigidly installed in the fixed-bed reactor and is preferably not removed therefrom after the filling process, such that the freedom of design is also not limited by a removal option which is to be provided.
After completion of the filling, the upper side of the catalyst bed touches the lower ends of the filling tubes. Since the filling device preferably remains in the fixed-bed reactor, the filling tubes and the catalyst distributor can remain filled with catalyst material such that, during reactor operation, in the event of settling of the catalyst bed, further catalyst material automatically flows into the catalyst space until the target height of the catalyst bed is reached again, that is to say until the upper side of the catalyst bed has reached the lower ends of the filling tubes again. It is thus also always ensured that the optimum height of the catalyst bed is maintained.
The capacity of the filling device and the dimensions and spacings of the relevant apparatus parts are preferably dimensioned such that, even in the event of settling, the upper side of the catalyst bed is always reliably over a preset minimum catalyst height. To limit bypass flows in the upper region of the catalyst bed and above, it is expedient to fill the region above the minimum height of the catalyst bed with an additional inert bed. The inert bed can also be supplied via the filling device when the amount of catalyst is sufficient, or through the = 15 clearance between heat transfer medium collector and reactor shell or through an opening in the heat transfer medium collector. For this purpose, the gas-impermeable upper closure of the central tube can be removed temporarily, for example. Similarly, openings can be made in the impermeable region in the outer wall of the reaction space for this filling process. The dead space below the heat transfer medium collector can be minimised effectively by an upper inert bed produced in this manner.
Preferably, the reactor shell forms the catalyst holder. An additional component for holding the catalyst bed horizontally is thus avoided.
In another, also preferred embodiment of the invention, the groups of heat exchange tubes and the catalyst bed are formed annularly with a tube- and catalyst-free inner cavity, the catalyst bed being held by a radially outer and a radially inner catalyst holder and an outer cavity being arranged between the reactor shell and the radially outer catalyst holder. The inner and the outer cavity can be used for supplying the feed gas and for removing the product gas. In addition, reactions in the edge region of the fixed-bed reactor, in which the reaction conditions may be subject to disruptive influences, are avoided.
Advantageously, the catalyst support is the surface of a bed in the lower reactor head. The construction of the fixed-bed reactor is simplified as a result, since no separate component needs to be provided as a catalyst support.
Preferably, the catalyst distributor is arranged horizontally outside the groups of heat exchange tubes. In this way, the space vertically above the heat exchange tubes can be used for other components, such as a heat transfer medium distributor or collector.
In a favourable development of the invention, only one catalyst distributor is formed and extends annularly along the inside of the reactor shell over the entire circumference. By these measures, the catalyst distributor is arranged in the fixed-bed reactor in a space-saving and also freely accessible manner.
The catalyst distributor is preferably trough-shaped in cross-section, into the base of which trough the filling tubes open and the walls of which extend in an inclined manner to the mouths of the filling tubes. In another embodiment, the walls can also extend in a perpendicular manner. In this way, the catalyst distributor can be formed in a structurally i I

simple manner and it is ensured that all the catalyst material present in the trough reaches the mouths of the filling tubes.
In a preferred embodiment of the invention, a heat transfer medium distributor or collector (depending on the flow direction of the heat transfer medium) is arranged over the cross-sectional area of the groups of heat exchange tubes (full or intermediate rows) and the catalyst distributor is arranged over the dead space between the heat transfer medium distributor or collector and the reactor shell. Such an arrangement of heat transfer medium distributor or collector and catalyst distributor uses the space over the heat exchange tubes in a space-saving manner.
Advantageously, the upper ends of the heat exchange tubes are tightly welded in respective through holes of an upper tube sheet and the tube sheet is the base of the heat transfer medium distributor or collector and the heat exchange tubes open into this heat transfer medium distributor or collector. As a result, a fixed-bed reactor according to the invention can be produced even more economically, since a separate component is not required for the base of the heat transfer medium distributor or collector.
Particularly preferably, the filling tubes each comprise a first portion which extends from the catalyst distributor, between the heat transfer medium distributor or collector and reactor shell, vertically downwards into the dead space, and a second portion which extends radially inwards from the first portion. In this configuration, the first portions of the filling tubes extend in a space-saving manner in a bundle between the heat transfer medium distributor or collector, that is to say the upper tube sheet, and the reactor shell and only thereafter are the second portions thereof distributed in the form of a bouquet over the catalyst space.
In the case of multipart heat transfer medium distributors and/or collectors, the filling tubes can also be passed between two heat transfer medium distributors or collectors. It is also possible to pass filling tubes through heat transfer medium distributors or collectors.
In an advantageous configuration of the invention, the lower ends of the filling tubes are distributed such that they each fill equal volume components of the catalyst bed. As a result, a density of the catalyst bed which is as uniform as possible over the entire cross-section thereof is achieved. The catalyst bed extends in the vertical direction preferably exclusively over the region in which all heat transfer tubes have straight portions, that is to say not into the regions in which the heat exchange tubes located radially further out are bent.
Preferably, the filling tubes have an oval cross-section. Filling tubes shaped in this manner can readily extend with the relatively small cross-sectional dimension even in narrow clearances between heat exchange tubes and, owing to the relatively large cross-sectional dimension in the direction perpendicular thereto, still have a tube cross-section large enough to achieve a sufficient flow speed and/or avoid blocking of the tubes.
It is advantageous when, in the operating state of the fixed-bed reactor, the catalyst space, the filling tubes and each catalyst distributor are filled with catalyst material. As a result, catalyst material can automatically flow into the catalyst space and refill the catalyst bed in the event of settling of the catalyst bed, even during ongoing reactor operation. Reactor operation thus takes place uniformly with the optimum height of the catalyst bed.
Preferably, each filling tube comprises a throttle. In this way, the inner dimensions of the filling tubes can be selected such that blocking thereof with catalyst material is ruled out, and the entry cross-section for each filling tube can be selected by means of the throttle so as to produce the desired flow speed.
Particularly preferably, the size of the throttle openings is adjustable. As a result, the size of the throttle openings and thus the flow speed can readily be adapted to altered conditions even during an ongoing filling process.
The invention also relates to the use of a reactor comprising heat exchange tubes which are arranged in groups as directly adjacent to one another as possible and form radial flow ducts, using molten salt as heat transfer medium in the heat exchange tubes to achieve an approximately isothermal reaction regime. An approximately isothermal reaction regime is understood to mean a reaction regime which has a virtually constant temperature with a variation in temperature of at most 10 C, preferably at most 5 C, more preferably at most 2 C. Particularly preferably, the reactor according to the invention is used to carry out an exothermic or endothermic reaction with an approximately isothermal reaction regime using molten salt as heat transfer medium inside the heat exchange tubes.

. 18 Further preferably, the reactor according to the invention is used for gas phase reactions, preferably exothermically catalytic or endothermically catalytic reactions.
Particularly preferably, the reactor according to the invention is used for oxidation, hydrogenation, dehydrogenation, nitration, alkylation reactions or to produce hydrocarbons from alcohols or dimethyl ethers, in particular for petrol synthesis from methanol and methanol synthesis from synthesis gas.
In the case of use for petrol synthesis, the reaction partners are preferably supplied via the central tube and the reaction products removed via the outer cavity. As heat transfer medium a molten salt is preferably used, which in the heat transfer medium circuit is pushed via a heat transfer medium distributor arranged at the bottom through the heat exchange tubes and into the heat transfer medium collector arranged at the top and fed from the collector to a heat exchanger.
The invention will be described below with reference to embodiments and figures, in which:
Fig. 1 is a longitudinal section through a reactor according to the invention, Fig. 2 is a cross-section through a reactor according to the invention, Fig. 3a, 3b show different arrangements of tube rows, Fig. 4 shows a detail of a support grid, Fig. 5a, 5b show the connection of bent and non-bent tubes in the tube sheet in two sectional views, Fig. 6 is a longitudinal section through an axial-flow isothermal fixed-bed reactor which comprises a catalyst filling device according to the invention, Fig. 7 is a longitudinal section through a radial-flow isothermal fixed-bed reactor which comprises a catalyst filling device according to the invention, and Fig. 8a, 8b are two sections through a filling device according to the invention.

Fig. 1 shows an isothermal reactor 1 according to the invention in a sectional view. This reactor comprises a pressure shell 2, consisting of a cylindrical reactor shell 3 which is closed at its upper end by an upper reactor head 4 and at its lower end by a lower reactor head 5. The reactor 1 is oriented vertically, that is to say the centre axis or reactor axis 6 extends vertically. Inside the reactor shell 3 there is a reaction space 7 which is defined by a perforated outer wall 10 and a central tube 13 which surrounds an inner cavity 11. The perforated outer wall 10 separates the reaction space 7 from an outer cavity 12. A catalyst bed 8 is filled in the reaction space 7. The reaction space 7 is penetrated by a plurality of heat exchange tubes 9 in the axial direction (that is to say in the direction of the centre axis 6).
The axis of the gas-permeable central tube 13 is the centre axis 6. The catalyst bed 8 thus extends in an annular manner between the outer wall of the reaction space 10 and the central tube 13.
In the embodiment shown in Fig. 1, the lower region of the reactor 1 is filled up to the start of the catalyst bed 8 with a lower inert bed 14a on which rest the catalyst particles of the catalyst bed 8. An upper inert bed 14b is located above the catalyst bed 8.
The reaction gas 15 referred to in general flowing through the reactor 1 has a different composition depending on where it is within the reactor 1 and is accordingly referred to differently. As feed gas 16 it enters the reactor 1 as fresh, unreacted gas via a gas inlet line 17 located centrally in the lower reactor head 5. Pressure, temperature and composition of the feed gas 16 are optimally adjusted according to the specific process. The feed gas 16 flows from the gas inlet line 17 into the directly adjoining perforated central tube 13. From there it enters the catalyst bed 8 located in the annular reaction space 7 through the openings 18, formed by the perforation, in the wall of the central tube, passes through said catalyst bed in the radial direction as reaction gas 15 and reacts to form the desired reaction products. Afterwards, it enters the outer cavity 12 through the gas-permeable outer wall of the reaction space 10 as product gas 19, flows from said outer cavity into the upper reactor head 4 and from there leaves the reactor 1 via a gas outlet line 20 passing through the upper reactor head 4.
A constant radial outlet speed from the central tube 13 into the reaction space 7 is achieved by careful configuration and mutual adaptation of all flow portions which generate pressure =

losses. In this context, the ratio of the flow cross-section of the central tube 13 to the total flow surface of the central tube wall, the axial porosity distribution of the central tube wall and the pressure loss coefficients of the catalyst bed 8 and of the gas-permeable outer wall 10 of the reaction space are available as relevant design parameters. During operation, settling of the catalyst bed 8 is always to be anticipated. To avoid bypass flows in the upper region of the catalyst bed 8, the central tube 13 has a gas-impermeable region 21 at the top. The outer wall 10 likewise has a gas-impermeable region 22 at the top. Moreover, the catalyst is filed into the reactor 1 in a sufficient amount such that the fill level of the catalyst does not fall below the impermeable region 21 of the central tube 13 or below the impermeable region 22 of the outer wall 10.
The reaction temperature in the catalyst bed 8 is controlled by a plurality of heat exchange tubes 9 through which heat transfer medium 25 flows. The ends of the heat exchange tubes 9 are inserted into an upper tube sheet 23 and a lower tube sheet 24 where they are welded thereto in a sealing manner. In this connection, the heat transfer medium 25 flowing through the heat exchange tubes 9 is fed into the heat transfer medium distributor 28 via a heat transfer medium supply line 26. The distributor head 27 is tightly connected to the lower tube sheet 24. Before entering the heat exchange tubes 9, the heat transfer medium 25 is uniformly distributed over the flow cross-section inside the distributor 28 by means of a homogenisation device 29, in this case designed as a perforated plate. After flowing through the heat exchange tubes 9, the heat transfer medium 25 reaches a heat transfer medium collector 30. This is constructed in an identical or similar manner to the heat transfer medium distributor 28. The collector 30 accordingly has a collector head 31. Via a heat transfer medium discharge line 32 the heat transfer medium 25 is removed from the reactor 1 and fed to a cooling device (not shown). For maintenance and repair work the collector 30 is accessible via a collector manhole 33. The interior of the reactor 1 is accessed for example via a releasable connection 34 in the gas outlet line 20 or via a manhole (not shown) in the upper reactor head 4. Different thermal expansions of the reactor shell 3 and all the elements of the heat exchange system located inside the reactor are accommodated by compensators 35, which in this case are in the form of corrugated compensators arranged outside the upper reactor head 4.
According to the invention, the heat exchange tubes 9 laid in the catalyst bed 8 are arranged in groups 36 (see Fig. 2) as parallel to the centre axis as possible. For production and transport of the tube bundle, the heat exchange tubes 9 are fixed in position by a plurality of horizontal support grids 37.
Fig. 2 shows a cross-section of the reactor showing the distribution of the heat exchange tubes 9 inside the catalyst bed 8. The heat exchange tubes 9 are grouped into groups of full rows 38 and intermediate rows 39 which form radial flow ducts 40. If the radial extension of the intermediate rows 39 does not reach the outermost extension of the full rows 38, this results in radial flow ducts 40 having an enlarged flow cross-section. Thus, if necessary, radial flow ducts having a reduced cooling surface density 41 can be created.
In addition, catalyst zones without cooling, that is to say adiabatic reaction zones 42, are provided radially outside the heat exchange tube regions. These adiabatic reaction zones can be arranged radially inwards, that is to say towards the reactor axis, and radially outwards, that is to say leading away from the reactor axis.
Fig. 3a and 3b show alternative configurations of the rows of heat exchange tubes 9. In Fig.
3a these are arranged with their axes on straight lines, heat exchange tubes 9 of different diameters alternating.
Fig. 3b shows a serpentine arrangement of the axes of the heat exchange tubes 9, which thus form a serpentine radial flow duct 40.
Fig. 4 shows a support grid 37 for the heat exchange tubes (not shown in Fig.
4). This basically consists of radial support elements 43 and circular support elements 44. The support grid 37 can also be reinforced by additional cross struts 45. The support elements 43, 44, 45 are preferably produced from rectangular semi-finished products.
They also preferably have rounded upper and lower sides so as not to prevent the catalyst from falling down when the reaction space 7 (see also Fig. 1) is filled therewith and to avoid dead spaces. The radial support elements 43 support the rows of heat exchange tubes 9 (see also Fig. 1) on either side, the flat bars being adaptable to different tube diameters for example by changes in thickness. They thus fix the heat exchange tubes 9 of a row to one another. The circular support elements 44 in turn fix the different tube rows to one another, these being connected by the radial support elements 43.
Fig. 5a shows a sectional view of the arrangement of bent heat exchange tubes 9 in a tube sheet 23 in the alignment of two tube rows. The tubes 9.01, 9.02 and 9.03 are positioned directly side by side in a row. The tube 9.01 is bent twice in opposite directions to the right and penetrates the tube sheet 23 in a position offset to the right in relation to the straight linear arrangement. The tube 9.02 is passed straight through the tube sheet 23. The tube 9.03 located behind is also bent twice in the same way as the tube 9.01, but to the left and is also passed through the tube sheet 23 with an offset to the left. The procedure is exactly the same for the adjacent tube row comprising the tubes 9.11, 9.12 and 9.13.
Fig. 5b is a plan view of the tube sheet with the tube ends described in Fig.

5 visible from above. The dashed circles indicate the position of the bent tubes located below the tube sheet 23.
In the embodiment shown in Fig. 6, the catalyst space 49 or the catalyst bed 8 filled therein extends in the horizontal direction over the entire cross-section inside the reactor shell 3, that is to say the horizontal cross-section through the catalyst bed 8 is a circular area, the edge of which forms the inner wall of the reactor shell 3. The heat exchange tubes 9 in the catalyst bed 8 are accordingly also distributed over a circular area, that is to say a horizontal cross-section through the bundle of heat exchange tubes 9 substantially also takes up a circular area. The radially innermost heat exchange tubes 9 are arranged in an approximately circular manner about the reactor axis 6 and the radially outermost heat exchange tubes 9 are arranged in an approximately circular manner with a predefined spacing from the inner wall of the reactor shell 3.
The terms "substantially" and "approximately" are intended to indicate that, for design-related reasons, the radially innermost and outermost heat exchange tubes 9 may not be positioned precisely on a circular line but may be radially offset from one another by at most two tube axis spacings.
The catalyst bed 8 rests against the outsides of the heat exchange tubes 9 and reaction gas 15 flows through said bed when the reactor 1 is in the operating state.
In this embodiment, reaction gas 15 and heat transfer medium 25 flow in counter-current in the catalyst bed 8, the reaction gas 15 from the top down and the heat transfer medium 25 from the bottom up.

The gas entering the reactor 1 is referred to as feed gas 16, the reacting gas flowing through the catalyst bed 8 as reaction gas 15, and the gas exiting the reactor 1 as product gas 19.
In this embodiment, the feed gas 16 is fed into the upper reactor head 4 through a gas inlet line 17 and the product gas 19 is removed from the lower reactor head 5 through a gas outlet line 20.
The lower ends of the heat exchange tubes 9 are tightly welded in through holes of a lower tube sheet 24 and open into a heat transfer medium distributor 28, the base of which forms the lower tube sheet 24.
The upper ends of the heat exchange tubes 9 are tightly welded in through holes of an upper tube sheet 23 and open into a heat transfer medium collector 30, the base of which forms the upper tube sheet 23.
The lower reactor head 5 spans the heat transfer medium distributor 28 and the upper reactor head 4 spans the heat transfer medium collector 30.
In an embodiment which is not shown, the heat transfer medium distributor 28 and/or the heat transfer medium collector 30 can also be formed in multiple parts.
In the embodiment shown, the heat transfer medium distributor 28 and the heat transfer medium collector 30 are ring-shaped, the reactor axis 6 extending through the centre of the ring in each case. The inner diameter of the rings is selected such that the radially innermost heat exchange tubes 9 can extend in a straight line between heat transfer medium distributor 28 and heat transfer medium collector 30. The outer diameter of the rings is smaller than the outer diameter of the bundle of heat exchange tubes 9, such that heat exchange tubes 9 located radially further out have bent ends in order to be able to open into the heat transfer medium distributor 28 or collector 30. Halfway between heat transfer medium distributor 28 and heat transfer medium collector 30, the heat exchange tubes 9 pass through a horizontal support grid 37 which stabilises the heat exchange tubes 9 in the horizontal direction.
In an embodiment which is not shown here, a plurality of support grids 37 can also be arranged in the vertical direction.
/ I

The heat transfer medium distributor 28 is connected to at least one heat transfer medium supply line 26. In the embodiment shown, there are two heat transfer medium supply lines 26, which extend vertically through the lower reactor head 5 from outside the reactor 1.
The heat transfer medium collector 30 is connected to at least one heat transfer medium discharge line 32. In the embodiment shown, there are two heat transfer medium discharge lines 32, which extend horizontally outwards through the reactor shell 3.
The catalyst bed 8 extends in the vertical direction exclusively over the region in which all heat exchange tubes 9 have straight portions, that is to say not into the regions in which the heat exchange tubes 9 located radially further out are bent.
A bed of inert material ¨ hereinafter also referred to as a lower inert bed 14a ¨ is arranged below the catalyst bed 8 and fills the lower region of the reactor 1, that is to say the lower reactor head 5 and the lower part of the reactor shell 3, up to the start of the straight heat exchange tube portions in the case of the bent heat exchange tubes 9 and thus up to the start of the catalyst bed 8. The upper side of the inert bed 14a therefore forms a catalyst support for vertically supporting the catalyst bed 8 and thus downwardly limiting it.
The upper limit of the catalyst space 49 and thus the target height of the catalyst bed 8, that is to say the upper side thereof, has a predefined spacing from the lower side of the upper tube sheet 23 or the heat transfer medium collector 30. The space formed by this spacing is referred to as dead space 50.
The filling device 51 is arranged above the catalyst space 49 and comprises a catalyst distributor 52 and a plurality of filling tubes 48/53.
The catalyst distributor 52 is annular and arranged above the heat transfer medium collector 30 in the reactor 1. The cross-section of the catalyst distributor 52 is trough-shaped with a base 54 and walls 55 which taper towards the base 54.
The upper ends of the filling tubes 48/53 are tightly fixed in through holes 56 (see Fig. 8a) in the base 54 of the catalyst distributor 52 and open into this, see detailed view in Fig. 8a.
They extend outwards from the catalyst distributor 52 initially as a bundle in the direction of the reactor shell 3 and then downwards between the outer edge of the heat transfer medium collector 30 and the inner wall of the reactor shell 3 into the dead space 50.
There they branch and extend in different directions and with different lengths into the clearances between the heat exchange tubes 9, all of the lower ends of the filling tubes 48/53 being distributed substantially uniformly over the entire cross-section of the catalyst space 49. The filling tubes 48/53 have over their entire length a minimum inclination, which ensures unobstructed flow of the catalyst material in the filling tubes 48/53.
In an embodiment which is not shown, filling tubes 48/53 in the case of multipart heat transfer medium distributors 28 and/or collectors 30 can be passed through between two heat transfer medium distributors 28 and/or collectors 30. It is also possible to pass filling tubes 48 through heat transfer medium distributors 28 or collectors 30.
The inner diameters of the filling tubes 48/53 are configured such that only a predefined amount of catalyst material can pass through each filling tube 48/53 per unit time, that is to say a predefined flow speed is produced.
The filling device 51 remains permanently in the reactor 1. The heat transfer medium distributors 28 and/or collectors 30 can therefore be designed more freely, for example in terms of easier access to the heat exchange tubes 9 and without regard for a removal option.
The upper reactor head 4 comprises a catalyst filler pipe 57 through which the catalyst distributor 52 can be filled with catalyst material by means of a suitable device.
The lower reactor head 5 comprises a catalyst emptying pipe 58 through which the lower inert bed 14a, the catalyst bed 8 and optionally the upper inert bed 14b can be removed from the reactor 1.
A manhole 59 is also formed in the upper reactor head 4, through which manhole an engineer can enter the upper region, that is to say above the heat transfer medium collector 30, for maintenance and repair work. The manhole 59 can also be used to supply the catalyst.
Moreover, the heat transfer medium supply line 26 and/or the heat transfer medium discharge line 32 can be configured such that the reactor interior is accessible therethrough.

Unless described differently below, the embodiment according to Fig. 7 corresponds to the embodiment according to Fig. 6.
In the embodiment shown in Fig. 7 of a reactor 1 according to the invention, the catalyst space 49 or the catalyst bed 8 is formed in an annular manner with a catalyst-free inner cavity 11 and a catalyst-free outer cavity 12 along the inner wall of the reactor shell 3. On its radially outer side, the catalyst bed 8 is surrounded by a cylindrical gas-permeable outer wall 10. To avoid bypass flows, an impermeable region 22 adjoins the gas-permeable outer wall 10. The outer cavity 12 is formed between the outer wall 10 and the inner wall of the reactor shell 3. At its radially inner side the catalyst bed 8 rests against or is limited by a gas-permeable central tube 13, the axis of which is located on the reactor axis 6.
In accordance with the annular design of the catalyst bed 8, the bundle of heat exchange tubes 9 is also annular. The radially innermost heat exchange tubes 9 are arranged with a predefined spacing from the radially inner limit of the catalyst bed 8 and the radially outermost heat exchange tubes 9 are arranged with a predefined spacing from the radially outer limit of the catalyst bed 8.
In this embodiment, the gas flows from the bottom up, it being fed as feed gas 16 into the lower end of the gas inlet line 17, and in the region of the catalyst bed 8 flowing through the wall of the central tube 13, which wall is gas-permeable there, into the catalyst bed 8, flowing substantially radially through said catalyst bed as reaction gas 15 and then flowing vertically upwards in the outer cavity 12 to a gas outlet line 20 and exiting this as product gas 19.
Since the heat transfer medium 25 also flows from the bottom up, in this respect a co-current of heat transfer medium 25 and gas is provided in this embodiment.
In this embodiment, all the heat exchange tubes 9 extend in a straight line over their entire length. As in the embodiment according to Fig. 6, the lower ends of the heat exchange tubes 9 are tightly fixed in through holes of a lower tube sheet 24 and open into a heat transfer medium distributor 28, the base of which forms the lower tube sheet 24. The heat transfer medium distributor 28 further comprises a distributor head 27 which spans the lower tube sheet 24 and is tightly connected thereto.

I I

The upper ends of the heat exchange tubes 9 are tightly fixed in through holes of an upper tube sheet 23 and open into a heat transfer medium collector 30, the base of which forms the upper tube sheet 23 and which further comprises a collector head 31, which in this embodiment is dome-shaped, which spans the upper tube sheet 23 and is tightly connected thereto.
A collector manhole 33 is formed in the collector head 31 in order to allow an engineer to access the heat exchange tubes 9 for maintenance and repair work_ The heat transfer medium distributor 28 and the heat transfer medium collector 30 are annular, each having a central through opening through which the central tube 13 passes in the case of the heat transfer medium distributor 28 and a predefined distance into which the central tube 13 extends in the case of the heat transfer medium collector 30.
The radially outer edge of the heat transfer medium distributor 28 and the heat transfer medium collector 30 is located between the radially outermost heat exchange tubes 9 and the radially outer limit of the catalyst bed 8, such that between the radially outer edge of the heat transfer medium distributor 28 (and also of the heat transfer medium collector 30) and the inner wall of the reactor shell 3 an annular gap is formed, the radial extension of which is greater than that of the outer cavity 12.
The heat transfer medium distributor 28 is connected to at least one heat transfer medium supply line 26. In Fig. 7, two heat transfer medium supply lines 26 are shown, which extend vertically and outwards through the lower reactor head 5.
The heat transfer medium collector 30 is connected to at least one heat transfer medium discharge line 32. In Fig. 7, two heat transfer medium discharge lines 32 are shown, which extend vertically outwards through the upper reactor head 4 and for their part are connected to an outer, annular heat transfer medium collector 60. The outer heat transfer medium collector 60 is in turn connected to a horizontal heat transfer medium discharge line 61.
The vertical heat transfer medium discharge lines 32 between the heat transfer medium collector 30 located in the upper reactor head 4 and the outer heat transfer medium collector 60 each comprise, within the upper reactor head 4, a compensator 35 for compensating different thermal expansions.

For horizontal stabilisation of the heat exchange tubes 9, a horizontal support grid 37 through which the heat exchange tubes 9 pass is arranged halfway between the lower and the upper tube sheet 24 and 23 or between the heat transfer medium distributor 28 and the heat transfer medium collector 30.
The central tube 13 extends downwards through the lower reactor head 5 and outwards beyond this and forms a gas inlet line 17 for the feed gas 16. From the lower end, that is to say from the inlet opening for the feed gas 16, to the lower start of the catalyst bed 8, the wall of the central tube 13 is impermeable to gas.
At its upper end, the central tube 13 extends into the central opening of the annular heat transfer medium collector 30. In its upper end region, the central tube 13 also has a gas-impermeable wall 21 which extends from the upper end of the central tube 13 a predefined distance into the catalyst bed 8. The upper end of the centrai tube 13 is sealed in a gas-tight manner.
In this case, too, the lower part of the reactor 1 ¨ that is to say the lower reactor head 5 and the lower part of the reactor shell 3 up to the lower end of the catalyst bed 8 ¨ is filled with a lower inert bed 14a. The upper side of this lower inert bed 14a thus forms the lower limit and vertical support for the catalyst bed 8.
In the embodiment shown in Fig. 7, the catalyst distributor 52 of the filling device 51 extends in an annular manner along the inside of the reactor shell 3 over the entire circumference thereof. It is arranged above the clearance or annular gap between the outside of the heat transfer medium collector 30 and the inner wall of the reactor shell 3, such that the filling tubes 53 extend vertically from the base 54 of the catalyst distributor 52 to below the upper tube sheet 23 or the heat transfer medium collector 30 and then, as in the embodiment according to Fig. 6, branch in the form of a bouquet into the bundle of heat exchange tubes 9.
Fig. 7 shows the state after complete filling of the catalyst space 49 with catalyst material, that is to say the upper side of the catalyst bed 8 touches the lower ends of the filling tubes 53. The filling tubes 53 and the catalyst distributor 52 are still filled with catalyst material, such that the catalyst space 49 is automatically refilled with catalyst material in the event of settling of the catalyst bed 8, even during reactor operation. In this embodiment, there is still an upper inert bed 14b over the catalyst bed 8.
As in the embodiment according to Fig. 6, the upper reactor head 4 comprises a catalyst filler pipe 57 and a manhole 59.
Similarly, as in the embodiment according to Fig. 6, the lower reactor head 5 comprises a catalyst emptying pipe 58.
The reactor 1 shown in Fig. 7 also comprises a fluidisation device 62 for emptying the reactor 1. Said device includes distribution lines 63 for a fluidisation gas which extend between the catalyst bed 8 and the heat transfer medium distributor 28 in the lower inert bed 14a. The distribution lines 63 comprise a ring line 64 which extends around the bundle of heat exchange tubes 9 and is connected to a gas supply line 65 which extends horizontally outwards through the reactor shell 3 and comprises a compressor 66 outside the reactor shell 3. The gas can be fed in a dehumidified state at increased pressure and continuously or with pressure surges in a pulsed manner. The distribution lines 63 further comprise radial branch lines 67 which are in fluid communication with the ring line 64 and extend within the lower inert bed 14a into the bundle of heat exchange tubes 9 and from which the fluidisation gas exits. Optionally there are further, preferably separately operable, lower branch lines 68 which are arranged below the bundle of heat exchange tubes 9.
Fig. 8a shows the connection of the upper end of a filling tube 53 to the base 54 of the catalyst distributor 52 on an enlarged scale. The upper end of the filling tube 53 comprises a radially widened shoulder portion 69 which is tightly connected to the base 54 of the catalyst distributor 52. The base 54 slopes towards the mouth of the filling tube 53, such that catalyst material slides from the side regions of the catalyst distributor 52 towards the mouth. A
throttle 70 comprising a throttle opening 71 is arranged in the shoulder portion 69 at the upper end of the filling tube 53, by means of which throttle the amount of catalyst material entering the filling tube 53 per unit time and thus the flow speed of the catalyst material exiting the filling tube 53 is defined.
The filling tube 53 has an oval cross-section (Fig. 8b). The smaller cross-sectional dimension 72 is determined by the size of the clearance between adjacent heat exchange tubes 9, through which clearance the filling tube 53 passes. The size of the largest cross-, 30 =
sectional dimension 73 is defined such that the free passage cross-section 74 of the filling tube 53 is large enough in relation to the dimensions of the catalyst particles to avoid jamming of catalyst particles and thus blocking of the filling tubes 53.

. 31 List of reference numerals 1 reactor 2 pressure shell 3 reactor shell 4 upper reactor head lower reactor head 6 centre axis / reactor axis 7 reaction space 8 catalyst bed 9 heat exchange tubes outer wall of the reaction space 11 inner cavity 12 outer cavity 13 central tube / inner wall of the reaction space 14a lower inert bed 14b upper inert bed reaction gas 16 feed gas 17 gas inlet line 18 openings in the central tube '19 product gas gas outlet line 21 impermeable region in the central tube 22 impermeable region in the outer wall of the reaction space 23 upper tube sheet 24 lower tube sheet heat transfer medium 26 heat transfer medium supply line 27 distributor head 28 heat transfer medium distributor 29 homogenisation device heat transfer medium collector 31 collector head 32 heat transfer medium discharge line , , = 32 33 collector manhole 34 releasable connection 35 compensator 36 group of heat exchange tubes 37 support grid 38 full rows 39 intermediate rows 40 radial flow duct 41 radial flow duct with reduced cooling surface density 42 adiabatic reaction zone 43 radial support elements 44 circular support elements 45 cross struts 48 filling tubes through the heat transfer medium collector 49 catalyst space 50 dead space 51 filling device 52 catalyst distributor 53 filling tubes 54 base of the catalyst distributor 55 walls of the catalyst distributor 56 through holes 57 catalyst filler pipe 58 catalyst emptying pipe 59 manhole 60 annular heat transfer medium collector 61 horizontal heat transfer medium discharge line 62 fluidisation device 63 distribution lines 64 ring line 65 gas supply line 66 compressor 67 branch lines 68 lower branch lines 69 shoulder portion 70 throttle 71 throttle opening 72 relatively small cross-sectional dimension 73 relatively large cross-sectional dimension 74 passage cross-section I I

Claims

1. Radial-flow reactor (1) for carrying out chemically catalytic reactions with an mainly isothermal reaction regime, comprising a cylindrical shell (3) which is arranged substantially about a centre axis (6) and inside which a substantially annular reaction space (7) is formed, which reaction space surrounds a perforated central tube (13) and is surrounded by an outer cavity (12), the outer cavity (12) and the reaction space (7) being separated by a perforated outer wall (10), and the outer cavity (12) and central tube (13) being provided for supplying the reaction gas (15) and for removing the product gas (19), characterised in that the reaction space (7) is penetrated by a plurality of heat exchange tubes (9), the heat exchange tubes (9) being arranged as parallel to the centre axis (6) as possible and in a plurality of groups, such that the groups form full rows (38) which are arranged in the radial direction in the reaction space (7), the outer contours of adjacent heat exchange tubes (9) of a row (38, 39) being so close to one another that radial flow ducts (40) are formed.

2. Reactor (1) according to claim 1, characterised in that at least one heat exchange tube (9) of a group is bent once or preferably twice at at least one tube end and fixed in a tube sheet (23, 24) at least at one end.

3. Reactor (1) according to either of the preceding claims, characterised in that further groups of heat exchange tubes (9) are arranged between the full rows (38) of heat exchange tubes (9) and form relatively short intermediate rows (39).

4. Reactor (1) according to any of the preceding claims, characterised in that adiabatic reaction zones (42) are located in annular spaces between the perforated central tube (13) and the full rows (38) of heat exchange tubes (9) and/or between the perforated outer wall (10) and the full rows (38) of heat exchange tubes (9) and/or the full and intermediate rows are interrupted by at least one annular adiabatic intermediate zone.

5. Reactor (1) according to any of the preceding claims, characterised in that the heat exchange tubes (9) have a continuously circular cross-section or have a circular cross-section at their ends and an elongate cross-section in the middle region.

6. Reactor (1) according to any of the preceding claims, characterised in that the heat exchange tubes (9) within a group have varying cross-sections.

7. Reactor (1) according to any of the preceding claims, characterised in that the spacing between the outer contours of adjacent full rows (38) or adjacent full and intermediate rows (39) increases from the central tube (13) outwards or remains as uniform as possible.

8. Reactor (1) according to any of the preceding claims, characterised in that the axes of the heat exchange tubes (9) of at least one full or intermediate row are located on a straight line directed radially outwards.

9. Reactor (1) according to any of claims 1 to 7, characterised in that the axes of the heat exchange tubes (9) of at least one full or intermediate row are located on a serpentine line.

10. Reactor (1) according to any of the preceding claims, characterised in that a distributor (28) or collector (30) for heat transfer medium (25) is arranged at at least one end, preferably at both ends, of the heat exchange tubes (9).

11. Reactor (1) according to claim 10, characterised in that the heat transfer medium supply line (26) and/or the heat transfer medium discharge line (32) are connected via compensators (35) to the reactor shell (3) or the upper (4) or lower reactor head (5).

12. Reactor (1) according to any of the preceding claims, characterised in that the perforation of the central tube (13) and/or of the outer wall (10) of the reaction space (7) varies in the axial direction of the reactor (1).

13. Reactor (1) according to any of the preceding claims, characterised in that a catalyst (8) in the form of a granular bed is filled between the heat exchange tubes (9) in the reaction space (7) and the ratio of the heat exchange surface of the heat exchange tubes (9) to the catalyst volume decreases or remains constant in the radial flow direction and behaves as m2/m3 to 200 m2/m3, preferably as 50 m2/m3 to 110 m2/m3.

14. Reactor (1) according to claim 13, characterised in that the catalyst (8) to be filled has a particle size of between 1 mm and 2 mm diameter and 3 mm to 15 mm length, preferably between 3 mm and 6 mm length, or more preferably comprises spherical particles having a diameter of 1 mm to 3 mm, preferably 1 5 mm to 2 mm

15 Reactor (1) according to any of the preceding claims, characterised in that in the reactor (1) a filling device (51) for filling the reaction space (7) with catalyst bed (8) is arranged above the reaction space (7) and comprises.
at least one catalyst distributor (52) which is arranged outside the bundle of heat exchange tubes (9), and a plurality of filling tubes (53) which each open into the at least one catalyst distributor (52) with their upper ends, extend into a dead space (50) formed by the uppermost region of the reaction space (7) and open into this space with their lower ends, the profiles of ail filling tubes (53) being tailored to one another in the dead space (50) such that all of their lower ends are distributed over the entire cross-section of the catalyst space (49)

16 Use of a reactor according to any of the preceding claims comprising heat exchange tubes which are arranged as directly adjacent to one another as possible and form radial flow ducts and using molten salt as heat transfer medium in the heat exchange tubes to achieve an approximately isothermal reaction regime

17. Use of a reactor according to any of claims 1 to 15 to carry out a reaction with heat tone with an approximately isothermal reaction regime using molten salt as heat transfer medium inside the heat exchange tubes

18 Use of a reactor according to any of claims 1 to 15 for gas phase reactions, preferably exothermically catalytic or endothermically catalytic reactions.

19 Use of a reactor according to any of claims 1 to 15 for oxidation, hydrogenation, dehydrogenation, nitration, alkylation reactions or to produce hydrocarbons from alcohols or dimethyl ethers, in particular for petrol synthesis from methanol and methanol synthesis from synthesis gas