[0001] The invention relates to a reactor and a method for carrying out a
chemical reaction according to the preambles of the independent claims.
5
PRIOR ART
[0002] In a number of processes in the chemical industry, reactors are used
in which one or more reactants are passed through heated reaction tubes
10 and catalytically or non-catalytically reacted there. The heating serves in
particular to overcome the activation energy required for the chemical
reaction that is taking place. The reaction can proceed as a whole
endothermically or, after overcoming the activation energy, exothermically.
The present invention relates in particular to strongly endothermic reactions.
15
[0003] Examples of such processes are steam cracking, various reforming
processes, in particular steam reforming, dry reforming (carbon dioxide
reforming), mixed reforming processes, processes for dehydrogenating
alkanes, and the like. During steam cracking, the reaction tubes are routed
20 through the reactor in the form of coils which can have a reversal point in
the reactor, whereas tubes running through the reactor without a reversal
point are typically used in steam reforming.
[0004] The invention is suitable for all such processes and designs of
25 reaction tubes. The articles "Ethylene," "Gas production," and "Propene" in
Ullmann's Encyclopedia of Industrial Chemistry, for example the
publications dated April 15, 2009, DOI: 10.1002/14356007.a10_045.pub2,
dated December 15, 2006, DOI: 10.1002/14356007.a12_169.pub2, and
dated June 15, 2000, DOI: 10.1002/14356007.a22_211, are referred to here
30 for purely illustrative purposes.
2
[0005] The reaction tubes of corresponding reactors are conventionally
heated using burners. In this case, the reaction tubes are routed through a
combustion chamber in which the burners are also arranged.
5 [0006] However, as described, for example, in DE 10 2015 004 121 A1
(likewise EP 3 075 704 A1), the demand for synthesis gas and hydrogen
which are produced with or without reduced local carbon dioxide emissions
is, for example, currently increasing. However, this demand cannot be met
by processes in which fired reactors are used due to the combustion of
10 typically fossil energy carriers. Other processes are ruled out, for example,
due to high costs. The same also applies to the provision of olefins and/or
other hydrocarbons by steam cracking or the dehydrogenation of alkanes.
In such cases, too, there is a desire for processes that at least on site emit
lower amounts of carbon dioxide.
15
[0007] Against this background, the aforementioned DE 10 2015 004 121
A1 proposes an electrical heating of a reactor for steam reforming in
addition to a firing. In this case, one or more voltage sources are used which
provide a three-phase alternating voltage on three external conductors.
20 Each external conductor is connected to a reaction tube. A star circuit is
formed in which a star point is realized by a collector into which the pipelines
open and to which the reaction tubes are conductively connected. In this
way, the collector ideally remains potential-free. In relation to the vertical,
the collector is arranged below and outside the combustion chamber and
25 preferably extends transversely to the reactor tubes or along the horizontal.
[0008] A corresponding electrical heating of a reactor can be problematic in
cases in which no collector of the type explained is present, e.g., in reactors
in which the reaction tubes have, within the reactor, a reversal point at which
30 they are to be connected to the star point, as is also the case, for example,
in WO 2015/197181 A1. Due to the high current flows and temperatures in
3
the reactor, it is difficult to find a solution for electrically connecting the
reactor tubes at the star point with satisfactory current transition values in
order to reduce excessive power losses and to ensure that current flow is
uniformly distributed and the star point is thus potential-free.
5
[0009] US 2014/02338523 A1 relates to a device for heating a pipeline
system for a molten salt, comprising at least two pipelines along which an
electrical resistance heating element extends, wherein a potential close to
ground potential is set at at least one end at each electrical resistance
10 heating element, and the electrical resistance heating element is connected
remotely therefrom to a connection of a direct current source or in each case
to a phase of an n-phase alternating current source.
[0010] WO 2015/069762 A2 discloses a chemical reactor system
15 comprising a chemical reactor having an inlet and a manifold in fluidic
connection with the inlet, the manifold comprising a manifold housing, the
manifold housing defining a manifold chamber and having at least one
additional component that may comprise a heater in thermal connection
with the manifold chamber and a cavity, wherein the manifold housing
20 defines the cavity and a seal is provided in a specific arrangement.
[0011] A fixed-bed reactor disclosed in US 2015/010467 A1 has an inflow
path for raw gas for a catalytic reaction and an outflow path for reformed
gas, a catalytic reaction vessel which is connected to the inflow path and
25 the outflow path and contains a catalyst, catalyst holders which have a
ventilation property and hold the catalyst, and a drive mechanism which
moves the catalyst up and down by moving the catalyst holders up and
down.
US 6 296 814 B1 discloses a fuel reformer which serves to produce a
30 hydrogen-enriched process fuel from a raw fuel. The catalyst tube
arrangement preferably comprises a plurality of catalyst tubes which are
4
arranged in a hexagonal arrangement. A housing contains internal
hexagonal thermal insulation in order to ensure uniform heating of the
catalyst tubes. The diameter of the tubes is dimensioned such that the
distances between adjacent tubes in the arrangement can be minimized for
5 efficient heat transfer.
[0012] The object of the present invention is therefore to improve electrically
heated reactors for carrying out chemical reactions.
10 DISCLOSURE OF THE INVENTION
[0013] Against this background, the present invention proposes a reactor
and a method for carrying out a chemical reaction according to the
preambles of the independent claims. Embodiments are the subject-matter
15 of the dependent claims and the following description.
[0014] In the mostly partially electrified furnace concept (the term "furnace"
is commonly understood to denote a corresponding reactor or at least its
thermally insulated reaction space) which is the basis of the present
20 invention, at least one of the reaction tubes or corresponding tube sections
thereof (hereinafter also referred to for short as "tubes") is itself used as
electrical resistors in order to generate heat. This approach has the
advantage of a greater efficiency compared to indirect heating by external
electric heating elements as well as a higher attainable heat flux density.
25 The scope of the invention includes the possibility of also providing part of
the total heating output in the furnace by firing other energy carriers, e.g.,
fossil energy carriers, such as natural gas, or even energy carriers such as
so-called bio natural gas or biomethane.
30 [0015] If, therefore, electrical heating is mentioned here, it does not preclude
the presence of additional non-electrical heating. In particular, it can also be
5
provided that the contributions of electrical and non-electrical heating are
varied over time, e.g., as a function of the supply and price of electricity or
the supply and price of non-electrical energy carriers as mentioned above.
5 [0016] The current is fed into the directly heated reaction tubes via M
separately connected phases. The current-conducting reaction tubes
connected to the M phases must also be electrically connected to a star
point. The number of phases M is in particular 3, corresponding to the
number of phases of conventional three-phase current sources or networks.
10 In principle, however, the present invention is not restricted to the use of
three phases but can also be used with a larger number of phases, e.g., a
number of phases of 4, 5, 6, 7, or 8. A multiple of 3, e.g., 6, 9, 12 etc. is
particularly preferred. A phase offset in this case is in particular 360°/M, i.e.,
120° in the case of a three-phase current.
15
[0017] Potential equalization between the phases is achieved by the star
circuit at the star point, which makes electrical insulation of the connected
pipelines superfluous. This represents a particular advantage of such a
furnace concept, since a break in the metallic reaction tubes for insulating
20 certain sections is undesirable, in particular because of the high
temperatures used and the high material and construction outlay thus
required.
[0018] In the language of the claims, the present invention relates to a
25 reactor for carrying out a chemical reaction, which reactor has a reactor
vessel (i.e., a thermally insulated or at least partially insulated region) and
one or more reaction tubes, wherein a number of tube sections of the one
or more reaction tubes in each case runs between a first region and a
second region within the reactor vessel and through an intermediate region
30 between the first and second regions, and wherein for the electrical heating
of the tube sections, the tube sections are or can in each case be electrically
6
connected in the first region to the phase connections ("external
conductors") of a polyphase alternating current source, for example, by
means of busbars and connecting strips. Switching devices can be installed
in particular on a primary side of an employed transformer system since
5 there is a higher voltage and a lower current there.
[0019] As mentioned, an alternating voltage is in each case provided via the
phase connections and the alternating voltages of the phase connections
are phase-shifted in the manner explained above. Within the scope of the
10 present invention, for example, a supply network or a suitable generator
and/or transformer can serve as an AC power source. The tube sections
form a star circuit in which they are electrically conductively coupled to one
another at their respective opposite end to the current supply, i.e., in the
second region.
15
[0020] In the intermediate region, the tube sections run through the reactor
vessel in particular freely, i.e. without mechanical support, without electrical
contacting, and/or without fluidic or purely mechanical cross-connections to
one another. They in particular run substantially or entirely straight in the
20 intermediate region, wherein "substantially straight" is to be understood as
meaning that an angular deviation of less than 10° or 5° is present.
[0021] According to the present invention, the tube sections are electrically
conductively connected to one another overall in the second region by
25 means of a single rigid connecting element ("star bridge") which is integrally
connected to the one or more reaction tubes and is arranged inside the
reactor vessel, or this connection is effected in groups by means of a
plurality of such rigid connecting elements. The one or more connecting
elements fluidically couple the respective electrically connected tube
30 sections to each other at most in pairs. In this case, "at most in pairs" is to
be understood as meaning that at most one tube section entering the
7
connecting element is fluidically coupled to at most one other tube section
entering the connecting element (or in the sense of the direction of flow,
exiting therefrom) or that, in other words, the tube sections in each case
fluidically connected in pairs via the connecting element in each case carry
5 or are designed to carry substantially the same quantities of fluid per time
unit. In this specific context, "substantially the same quantities of fluid"
should be understood to mean a difference of not more than 10%, 5%, or
1%. The one or more connecting elements therefore couple the connected
tube sections in a non-collecting and non-distributing manner, in contrast to
10 a collector known from the prior art and arranged outside the reactor.
[0022] This measure proposed according to the invention has the
advantage that a maximum potential equalization can take place via one or
more star bridges formed by one or more connecting elements. This results
15 in almost complete freedom from potential or a significantly reduced current
return via a neutral conductor which may be connected thereto. The result
is minimal current dissipation via the header connections to other parts of
the process system and a high level of shock protection.
20 [0023] A further advantage of the one or more connecting elements
proposed according to the invention in comparison to one or more collectors
which is or are arranged outside the reactor vessel and optionally likewise
provides or provide an electrical connection at a star point, consists in a
more clearly defined distance of the electrical heat input (e.g., over all tube
25 sections, which is not the case with a star point on a collector because
electrically heated tube sections must here be guided from the warmer
interior space to the colder exterior space) and spatially very homogeneous
external thermal boundary conditions of the electrically heated tube sections
(no electrical heating in the thermally insulated passages through the
30 reactor vessel to the collector operated at low temperature). This results in
process engineering advantages, for example, an expected excessive coke
8
formation in heated and externally thermally insulated passages can be
avoided.
[0024] Since the underlying reactions require high temperatures, the
5 electrical connection in the second region must be realized in a hightemperature range of, for example, approximately 900°C for steam
cracking. This is possible through the measures proposed according to the
invention by the selection of suitable materials. At the same time, the
connection is intended to have a high electrical conductivity and high
10 mechanical stability and reliability at high temperatures. Failure of the
electrical connection directly prevents potential equalization and
consequently leads to an instantaneous safety-related shutdown of the
system due to undesired current flow in system parts. The present invention
provides advantages over the prior art by avoiding such situations.
15
[0025] In conventional burner-heated reaction tubes for steam cracking,
there is no need for a connection between the U-bends of the reaction tubes
arranged in the reactor, which here are suspended with a certain freedom
of movement. In particular, the lower U-bends can hang freely in the reactor
20 vessel, while the upper ones have less, but nevertheless some, freedom of
movement. The freedom of movement is advantageous for the mechanical
behavior of the reaction tubes, this being dominated primarily by the thermal
expansion of the tubes. The present invention is based accordingly on the
finding that a rigid connection, which is considered negative in the context
25 mentioned, offers advantages which outweigh the possible disadvantages
of a lack of freedom of movement.
[0026] In the realization of a star circuit of reaction tubes, it is necessary to
provide a construction which provides an adequately dimensioned
30 electrically conductive cross-connection between the tube sections and at
9
the same time which withstands the stresses resulting primarily from the
high thermal expansion rates.
[0027] According to the prior art, it has not been as yet possible for the
5 required electrical connection between the U-bends (star bridge) to be
flexibly embodied in this temperature range. There are no materials with
sufficient long-term temperature stability or sufficient processability (e.g.,
weldable) from which flexible electrical connections can be made.
Moreover, there is hardly any connection technology available in this field
10 of application for the metal-to-metal transition.
[0028] The invention is based accordingly on the surprising finding that,
despite a lack of freedom of movement, a rigid star bridge connection which
has a cross-section sufficient for the required electrical potential
15 equalization is capable of absorbing the mechanical stresses occurring in
high-temperature use over the operating times relevant to practical
application. The currents flowing here lie in the kiloampere range and
therefore require considerable design effort.
20 [0029] The present invention will be described below first with reference to
reaction tubes and reactors as used for steam cracking. However, as
explained afterwards, the invention can also be used in other types of
reactors, as subsequently mentioned. In general, as mentioned, the reactor
proposed according to the invention can be used for carrying out any
25 endothermic chemical reaction.
[0030] In a first development of the present invention, the reactor can be
used in particular with so-called 2-passage coils. These have two tube
sections in the reactor vessel, which pass into one another via (exactly) one
30 U-bend and therefore basically have the shape of an (elongated) U. The
sections entering and exiting the reactor vessel, which in particular pass
10
seamlessly or without a flow-relevant transition into the heated tube
sections, are here referred to (also with reference to the reaction tubes
described below) as "feed section" and "extraction section". There is always
a plurality of such reaction tubes present.
5
[0031] In this development, the reactor can therefore be designed in such a
way that the tube sections each comprise two tube sections of a plurality of
reaction tubes which are arranged at least partially side by side in the
reactor vessel, the two tube sections of the multiple reaction tubes in each
10 case passing into each other in the first region in each case via a U-bend.
In particular, as mentioned, one of the in each case two tube sections in the
second region is connected to a feed section and the others of the in each
case two tube sections in the second section are connected to an extraction
section.
15
[0032] In the development of the present invention just explained, it can be
provided in one variant that the one tube section of each of the two tube
sections of the multiple reaction tubes in the second region is connected to
a first one of the connecting elements and the other tube section of the
20 respective two tube sections of the multiple reaction tubes in the second
region is connected to a second one of the connecting elements. In this way,
a plurality of in each case potential-free star points can be formed, with the
advantage that, due to increased flexibility of narrower, multiple connecting
elements, smaller mechanical stresses occur, in particular due to thermal
25 expansions.
[0033] In the development of the present invention just explained, in another
variant it can in contrast be provided that in each case both tube sections of
the multiple reaction tubes, and in particular all tube sections in the second
30 region, are connected to a common connecting element. In this way, a
11
potential-free star point is formed overall, with the advantage that, for
example, a further intermediate connectiion can be dispensed with.
[0034] The development of the invention just explained can also be
5 transferred to cases in which reaction tubes having two feed sections and
one extraction section are used. In such reaction tubes, the two feed
sections are in each case connected to one tube section. The extraction
section is also connected to a tube section. The tube sections connected to
the feed sections pass into the tube section connected to the extraction
10 section in a typically Y-shaped connection area. Not only the tube sections
connected to the feed sections but also the U-bend connected to the
extraction section can each have one or more U-bends or none at all.
[0035] For example, reaction tubes as illustrated in Figure 10C can be used.
15 In these, the tube sections connected to the feed sections have no U-bend,
whereas the tube section connected to the extraction section has a U-bend.
[0036] In this case, in particular tube sections, which are each formed by the
tube sections connected to the feed sections, can be connected in the
20 second region to a first one of the connecting elements and a tube section
which is formed by the tube section connected to the extraction section is
connected to a second one of the connecting elements. In this way, a
plurality of respectively potential-free star points can be formed as above
with the advantages likewise already explained above.
25
[0037] Alternatively, however, it can also be provided here in another variant
that the tube sections, which are each formed by the tube sections
connected to the feed sections, and the tube section, which is formed by the
tube section connected to the extraction section, and in particular all tube
30 sections in the second zone, are connected to a common connecting
element. In this way, a potential-free star point is also formed overall here,
12
with the advantage that, for example, a further intermediate connection can
be dispensed with.
[0038] However, reaction tubes as illustrated in Figure 10B may also be
5 used. In these, the tube sections connected to the feed sections each have
a U-bend and the tube section connected to the extraction section has two
U-bends.
[0039] Even the use of reaction tubes as illustrated in Figure 10A is possible.
10 In these, the tube sections connected to the feed sections each have three
U-bends and the tube section connected to the extraction section has two
U-bends.
[0040] In the last two cases, any of the tube sections in the second region
15 can also be connected to different connecting elements or to a common
connecting element, as a result of which the advantages already explained
above can likewise be achieved. A multiplicity of further configurations with
branched or Y-shaped combined reaction tubes is also possible.
20 [0041] Alternatively, however, it can also be provided here in another variant
that the tube sections, which are each formed by the tube sections
connected to the feed sections, and the tube section, which is formed by the
tube section connected to the extraction section, and in particular all tube
sections in the second zone, are connected to a common connecting
25 element. In this way, a potential-free star point is also formed overall here,
with the advantage that, for example, a further intermediate connection can
be dispensed with.
[0042] In addition to the development described above in particular with
30 reference to 2-passage coils, however, a development suitable for use with
so-called 4-passage coils can also be used. These have four essentially
13
straight tube sections. However, arrangements with a higher, even number
of straight tube sections are also possible.
[0043] In more general terms, a correspondingly designed reactor
5 comprises one or more reaction tubes, each of which has an even number
of four or more tube sections connected in series with one another via a
number of U-bends, the number of U-bends being one less than the number
of tube sections connected in series with one another via the U-bends, and
wherein the U-bends are arranged alternately in the first and the second
10 regions starting with a first U-bend in the first region.
[0044] A "U-bend" is understood here in particular to mean a tube section or
pipe component which comprises a part-circular or part-elliptical, in
particular a semicircular or semi-elliptical pipe bend. The beginning and end
15 have cut surfaces lying next to one another in particular in one plane.
[0045] In a first example, in which a 4-passage coil is used, the tube sections
mentioned include a first, a second, a third and a fourth tube section of a
reaction tube or in each case of one reaction tube of several reaction tubes,
20 wherein the first tube section passes via a first U-bend into the second tube
section, the second tube section passes via a second U-bend into the third
tube section and the third tube section passes via a third U-bend into the
fourth tube section. The first tube section is in particular connected in the
second zone to a feed section and the fourth tube section is in particular
25 connected in the second zone to an extraction section. The first and third
curved sections are arranged in the first region and the second curved
section is arranged in the second region. These explanations
correspondingly also apply to six tube sections, wherein a first, third and
fifth curved section are then arranged in the first region and a second and
30 fourth curved section are arranged in the second region.
14
[0046] In the developments just explained with one or more U-bends, the Ubends arranged in the second region can be formed in the connecting
element and the tube sections can extend from the connecting element in
the first region to the second region.
5
[0047] In this case, the connecting element can here be cast onto the
formed tube sections previously joined to the U-bend(s) in the second region
(for example, welded thereto) or connected to it or them (for example, by
bending). In other words, a reaction tube can thus be formed beforehand
10 with corresponding tube sections and one or more U-bends and then
encapsulated in corresponding regions. This results in a simpler design of
the reaction tubes.
[0048] Alternatively, however, it is also possible to form (for example, to
15 cast) the U-bend(s) in the second region within the connecting element and
to weld the tube sections to the connecting element. In this way, a
corresponding reactor can be produced in a simplified and modular manner,
and only the straight tube sections need be welded on. The use of the
connecting element as a standard part results in lower production costs.
20
[0049] To summarize once again, a corresponding reactor can have any
reaction tubes known from the prior art, such as are also described in
particular in the above-mentioned article "Ethylene" in Ullmann's
Encyclopedia of Industrial Chemistry. Corresponding reaction tubes are
25 designated, for example, by SC-1, SC-2, SC-4, USC-U, Super U, USC-W,
FFS, GK-1, GK-6, SMK, Pyrocrack 1-1, Pyrocrack 2-2 or Pyrocrack 4-2.
[0050] As mentioned, a corresponding reactor can be designed in particular
as a reactor for steam cracking, that is in particular by the choice of
30 temperature-resistant materials and the geometric configuration of the
reaction tubes.
15
[0051] In a further alternative, however, the tube sections can each
comprise a tube section consisting of a plurality of reaction tubes, wherein
the tube sections within the reactor vessel are arranged in a fluidically
5 unconnected manner and at least partially side by side and in each case
are connected to a feed section (for fluid) in the first region and an extraction
section (for fluid) in the second region. The latter extend in particular in the
same direction as the tube sections or do not cause any fluid flow deflected
by more than 15° in relation to the fluid flow in the tube sections connected
10 thereto. The feed sections and extraction sections are in particular likewise
formed integrally with these, i.e. in particular in the form of the same tube.
The reaction tubes are designed here in particular without U-bends. In this
way, a reactor is created, as is suitable, for example, in particular for carrying
out steam reforming. This can also be effected in particular by equipping the
15 reaction tubes with a suitable catalyst.
In this embodiment, the connecting element in the second region is cast, in
particular, onto the reaction tubes. In particular, it can surround the reaction
tubes in the manner of a cuff.
20 [0052] In all of the cases explained above, the connecting element and the
tube sections can be formed from the same material or from materials
whose electrical conductivities (in the sense of a material constant, as is
customary in the field) differ by no more than 50%, no more than 30%, no
more than 10%, or are advantageously the same. For example, the
25 connecting element and the tube sections can also be formed from steels
of the same steel class. The use of identical or closely related materials can
facilitate the one-piece design of the connecting element and of the tube
sections, for example by means of casting or welding.
30 [0053] In all cases, by forming the connecting element from as few individual
parts as possible, the number of metal-to-metal connections (e.g., welded
16
or soldered connections) can be reduced or even completely dispensed
with. Mechanical stability and reliability can thereby be increased. In a
further embodiment, the connecting element can be implemented as a
single casting, or, as mentioned, parts of the process-carrying pipes can be
5 cast into the connecting element and/or parts of the process-carrying pipes
can be formed as an integral component of a corresponding casting.
[0054] Metal-to-metal connections or metal transitions, which can be
reduced within the scope of the present invention, could lead to a local
10 change in electrical resistance, and therefore to hot spots. Hot spots in turn
lead to a reduction in service life due to elevated local temperatures or to
mechanical stress peaks due to steep local temperature gradients. This is
avoided within the scope of the present invention.
15 [0055] A one-piece connecting element provides mechanical stability,
reliability and a reduction in individual components. A high mechanical
stability of the star bridge is desirable since, as mentioned, failure of the star
bridge will lead to safety-critical situations. By means of the described
embodiment in the sense of the present invention, the principle of reaction
20 tubes resistively heated with polyphase alternating current in a star circuit
is technically realizable in the high-temperature range, i.e. in particular at
more than 500°C, more than 600°C, more than 700°C or more than 800°C.
[0056] A desired increased conductance of the connecting element can be
25 achieved in the case of equal conductivities by an increase in the crosssectional area according to R = ρ (l/A), where R is the resistance of the
conductor in ohms, ρ is the specific electrical resistance, i.e. the reciprocal
of the conductivity, l is the length of the conductor and A is its cross-sectional
area.
30
17
[0057] Possible materials for the reaction tubes and therefore also for the
connecting element are, for example, highly alloyed chrome-nickel steels,
such as are also used in fired furnaces. Advantageously, these are alloys
with high oxidation or scale resistance and high carburizing resistance.
5
[0058] For example, it may be an alloy with 0.1 to 0.5 wt% carbon, 20 to 50
wt% chromium, 20 to 80 wt% nickel, 0 to 2 wt% niobium, 0 to 3 wt% silicon,
0 to 5 wt% tungsten and 0 to 1 wt% other components, wherein the
constituents complement each other to form the non-ferrous fraction. A
10 corresponding alloy may also, for example, contain 20 to 40 wt% chromium,
20 to 50 wt% nickel, 0 to 10 wt% silicon, 0 to 10 wt% aluminum and 0 to 4
wt% niobium.
[0059] For example, materials with the standard designations
15 GX40CrNiSi25-20, GX40NiCrSiNb35-25, GX45NiCrSiNbTi35-25,
GX35CrNiSiNb24-24, GX45NiCrSi35-25, GX43NiCrWSi35-25-4,
GX10NiCrNb32-20, GX50CrNiSi30-30, G-NiCr28W, G-NiCrCoW,
GX45NiCrSiNb45-35, GX13NiCrNb45-35, GX13NiCrNb37-25, or
GX55NiCrWZr33-30-04, according to DIN EN 10027 Part 1, "Materials",
20 may be used. These have proven to be particularly suitable for hightemperature use.
[0060] In a further embodiment, the connecting element can be thermally
insulated from the hot environment in order to reduce thermal stress
25 resulting from steep temperature gradients. For example, a radiation
protection shield arranged within the reactor vessel can be provided, which
shields the region of the connecting element from an excessive heat input
from the region of the tube sections.
30 [0061] In a further embodiment, a part of the connecting element may
consist of the material of the reaction tubes and a part (or further parts) of
18
the connecting element may consist of a material having a higher specific
electrical conductivity. In this case, a solid metal-to-metal connection (e.g.,
a weld seam) is not necessarily provided. The electrical contact can also be
ensured by a different thermal expansion. For example, a casting consisting
5 of one of the previously specified materials could be inserted into a matching
molybdenum U-profile.
[0062] In this development, therefore, in the language of the claims, the
connecting element is surrounded at least in part by a conducting element
10 made of a material rich in molybdenum, tungsten, tantalum, niobium and/or
chromium or formed therefrom. In particular, the material has a higher
specific electrical conductivity than the material from which the connecting
element is formed. As a result, the potential equalization in the star point
can be significantly improved or a corresponding connecting element can
15 be constructed to be correspondingly lighter.
[0063] The invention also relates to a method for performing a chemical
reaction using a reactor having a reactor vessel and one or more reaction
tubes, wherein a number of tube sections of the one or more reaction tubes
20 in each case run between a first region and a second region in the reactor
vessel, and wherein the first regions for heating the tube sections are in
each case electrically connected to the phase connections of a polyphase
AC power source.
25 [0064] According to the invention, a reactor is used here in which the tube
sections in the second regions are connected to one another in an
electrically conductive manner by means of a connecting element which is
integrally connected to the one or more reaction tubes and is arranged
inside the reactor vessel.
30
19
[0065] For further features and advantages of a corresponding method, in
which a reactor according to one of the previously explained developments
of the invention is advantageously used, reference is made to the above
explanations.
5
[0066] The invention will be further elucidated below with reference to the
accompanying drawings, which illustrate developments of the present
invention with reference to and in comparison with the prior art.
10 DESCRIPTION OF THE FIGURES
[0067] Figure 1 schematically illustrates a reactor for carrying out a chemical
reaction according to a non-inventive development.
15 [0068] Figure 2 schematically illustrates a reactor for carrying out a chemical
reaction according to a development of the invention.
[0069] Figure 3 schematically illustrates a reactor for carrying out a chemical
reaction according to a further development of the invention.
20
[0070] Figure 4 schematically illustrates a connecting element for use in a
reactor according to a development of the invention.
[0071] Figure 5 schematically illustrates a connecting element for use in a
25 reactor according to a development of the invention.
[0072] Figure 6 schematically illustrates a connecting element in crosssection for use in a reactor according to a development of the invention.
30 [0073] Figure 7 illustrates resistors in an arrangement for use in a reactor
according to a development of the invention.
20
[0074] Figures 8A to 8C illustrate reaction tubes and corresponding
arrangements for use in a reactor according to a development of the
invention.
5
[0075] Figures 9A and 9B illustrate reaction tubes and corresponding
arrangements for use in a reactor according to a development of the
invention.
10 [0076] Figures 10A to 10C illustrate further reaction tubes for use in a
reactor according to a development of the invention.
[0077] In the following figures, elements that correspond to one another
functionally or structurally are indicated by identical reference symbols and
15 for the sake of clarity are not repeatedly explained. If components of devices
are explained below, the corresponding explanations will in each case also
relate to the methods carried out therewith and vice versa.
[0078] Figure 1 schematically illustrates a reactor for carrying out a chemical
20 reaction according to a non-inventive development.
[0079] The reactor here designated 300 is set up to carry out a chemical
reaction. For this purpose, it has in particular a thermally insulated reactor
vessel 10 and a reaction tube 20, wherein a number of tube sections of the
25 reaction tube 20, which are designated here by 21 only in two cases, run
respectively between a first zone 11' and a second zone 12' in the reactor
vessel 10. The reaction tube 20, which will be explained in more detail below
with reference to Figure 2, is attached to a ceiling of the reactor vessel or to
a support structure by means of suitable suspensions 13. In a lower region,
30 the reactor vessel can in particular have a furnace (not illustrated). It goes
21
without saying that a plurality of reaction tubes can be provided in each case
here and subsequently.

I/We Claim:
1. Reactor (100, 200) for carrying out a chemical reaction, which has a
reactor vessel (10) and one or more reaction tubes (20), wherein a number
5 of tube sections (21, 22) of the one or more reaction tubes (20) in each case
run between a first region (11) and a second region (12) within the reactor
vessel (10), and wherein the tube sections (21, 22) in the first region (11)
for the electrical heating of the tube sections (21, 22) in each case are or
can be electrically connected to the phase connections of a polyphase
10 alternating current source (50), characterized in that the tube sections (21,
22) are used as electrical resistors in order to generate heat and in that the
tube sections (21, 22) in the second region (12) are electrically conductively
connected to one another as a whole by means of a single rigid connecting
element (30) or in groups by means of a plurality of rigid connecting
15 elements (30), which is or are integrally connected to the one or more
reaction tubes (20) and is or are arranged within the reactor vessel (10) as
one or more star bridges effecting a potential equalization, wherein the one
or more connecting elements (30) is or are configured for operation at a
temperature of more than 700°C.
20
2. Reactor (100, 200) according to Claim 1, wherein the chemical
reaction is an endothermic chemical reaction.
3. Reactor according to Claims 1 or 2, wherein the tube sections (21) in
25 each case comprise two tube sections (21) of a plurality of reaction tubes
(20) which are arranged at least partially side by side in the reactor vessel
(10), wherein the respective two tube sections (21) of the plurality of reaction
tubes (20) pass into one another in the first region (11) in each case via a
U-bend (23).
30
27
4. Reactor according to Claim 3, wherein in each case the one tube
section (21) of in each case the two tube sections (21) of the plurality of
reaction tubes (20) is connected to a first of the plurality of connecting
elements (30) and the other tube section (21) of the respective two tube
5 sections (21) of the plurality of reaction tubes (20) is connected to a second
of the plurality of connecting elements (30).
5. Reactor according to Claim 3, wherein in each case both tube
sections (21) of the plurality of reaction tubes (20) are connected to the one
10 connecting element (30).
6. Reactor (100) according to Claims 1 or 2, in which the tube sections
(21) are an even number of four or more tube sections (21) of a reaction
tube (20) or in each case one of a plurality of reaction tubes (20) serially
15 connected to one another via a number of U-bends (23), wherein the
number of U-bends (23) is one less than the number of tube sections (21)
serially connected to one another via the U-bends (23), and wherein the Ubends (23), beginning with a first U-bend (23) in the first region (11), are
arranged alternately in the first region (11) and in the second region (12).
20
7. Reactor (100) according to Claim 6, in which the U-bend or U-bends
(23) arranged in the second region (12) is or are formed in the rigid
connecting element (30) and in which the tube sections (21) extend from
the connecting element (30) in the second region (12) to the first region (11).
25
8. Reactor (100) according to Claims 6 or 7, in which the connecting
element (30) is cast onto the formed tube sections (21) previously provided
with the U-bend or U-bends (23) in the second region (12) or connected
thereto.
30
28
9. Reactor (100) according to Claims 6 or 7, wherein the U-bend or Ubends (23) in the second region (12) are formed in the connecting element
(30) and the tube sections (21) are welded to the connecting element (30).
5 10. Reactor (100) according to any one of the preceding claims, which is
designed as a reactor for steam cracking.
11. Reactor (200) according to Claim 1, wherein the tube sections (22)
in each case comprise a tube section (22) of a plurality of reaction tubes
10 (20), wherein the tube sections (22) are arranged side by side in the reactor
vessel (10) in a fluidically unconnected manner and are in each case
connected to a feed section (24) in the first region and an extraction section
(25) in the second region.
15 12. Reactor (200) according to Claim 11, which is designed as a reactor
for steam reforming, dry reforming or the catalytic dehydrogenation of
alkanes.
13. Reactor (100, 200) according to any one of the above claims,
20 wherein the connecting element (30) and the tube sections (21, 22) are
formed from the same material or from materials whose electrical
conductivities differ from one another by not more than 50%, preferably not
more than 30%, particularly preferably not more than 10%, in particular from
chrome-nickel steels which comprise 0.1 to 0.5 wt% carbon, 20 to 50 wt%
25 chromium, 20 to 80 wt% nickel, 0 to 2 wt% niobium, 0 to 3 wt% silicon, 0 to
5 wt% tungsten and 0 to 1 wt% other constituents, preferably 20 to 40 wt%
chromium, 20 to 50 wt% nickel, 0 to 10 wt% silicon, 0 to 10 wt% aluminum
and 0 to 4 wt% niobium, wherein the contents of the specified constituents
in each case complement one another to form the non-ferrous fraction.
30
29
14. Reactor (100, 200) according to any one of the preceding claims,
wherein the connecting element (30) is surrounded at least in part by a
conducting element (31) made of a material rich in molybdenum, tungsten,
tantalum, niobium and/or chromium or formed therefrom and/or which has
5 a higher specific electrical conductivity than the material from which the
connecting element is formed.
15. Method for carrying out a chemical reaction using a reactor (100,
200), which has a reactor vessel (10) and one or more reaction tubes (20),
10 wherein a number of tube sections (21, 22) of the one or more reaction
tubes (20) in each case run between a first region (11) and a second region
(12) within the reactor vessel (10), and wherein the tube sections (21, 22)
in the first region (11) for the heating of the tube sections (21, 22) in each
case are electrically connected to the phase connections of a polyphase
15 alternating current source (50), characterized in that a reactor (100-500)
is used, in which the tube sections (21, 22) are used as electrical resistors
in order to generate heat and in which the tube sections (21, 22) in the
second region (12) are electrically conductively connected to one another
as a whole by means of a single rigid connecting element (30) or in groups
20 by means of a plurality of rigid connecting elements (30), which is or are
integrally connected to the one or more reaction tubes (20) and is or are
arranged within the reactor vessel (10) as one or more star bridges effecting
a potential equalization, wherein the one or more connecting elements (30)
are operated at a temperature of more than 700°C.