PRIOR ART
10
[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 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 15 whole endothermically or, after
overcoming the activation energy, exothermically. The present invention
relates in particular to strongly endothermic reactions.
[0003] Examples of such processes are steam cracking, various reforming
20 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 guided
through the reactor in the form of coils, which can have at least one U-bend in
the reactor, whereas tubes running through the reactor without a U-bend are
25 typically used in steam reforming.
[0004] The invention is suitable for all such processes and designs of reaction
tubes. The articles "Ethylene," "Gas production," and "Propene" in Ullmann's
Encyclopedia of Industrial Chemistry, for example the publications dated April
30 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:
2
10.1002/14356007.a22_211, are referred to here for purely illustrative
purposes.
[0005] The reaction tubes of corresponding reactors are conventionally heated
using burners. In this case, the reaction tubes are 5 routed through a combustion
chamber in which the burners are also arranged.
[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
10 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 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
15 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.
[0007] Against this background, the aforementioned DE 10 2015 004 121 A1
20 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. 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
25 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 preferably extends transversely to
the reactor tubes or along the horizontal. WO 2015/197181 A1 also discloses
a reactor whose reaction tubes are arranged in a star-point circuit.
30
[0008] It is also conceivable in principle to carry out electrical heating of
reactors by means of direct current or single-phase alternating current. In this
3
case, no star circuit with a potential-free star point can be realized; however,
in principle, the current feed can be realized in a similar manner. The present
invention is suitable for both variants of electrical heating.
[0009] DE 23 62 628 A1 discloses a tube furnace for 5 the thermal treatment of
liquid or gaseous media in metal tubes, which can be heated by means of
resistance heating, wherein the tubes to be heated by means of resistance
heating are conductively connected to current supply lines via electrical
connections at the ends of the sections to be heated.
10
[0010] US 2014/0238523 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 in each case, wherein each electrical
resistance heating element has at least one end set at a potential close to
15 ground potential and the electrical resistance heating element is remotely
connected to a connection of a direct current source or in each case to a phase
of an n-phase alternating current source.
[0011] In particular, the feed of current has proven to be challenging with such
20 electrically heated reactors due to the high current flows and temperatures.
Therefore, the object of the present invention is to improve corresponding
electrically heated reactors for carrying out chemical reactions.
DISCLOSURE OF THE INVENTION
25
[0012] 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 of the dependent
claims and the following description.
30
[0013] In the at least partially electrified furnace concept (the term "furnace" is
commonly understood to designate a corresponding reactor or at least its
4
thermally insulated reaction space), which is the basis of the present 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 an electrical
resistor in order to generate heat. This strategy has the advantage of a greater
efficiency compared to indirect heating by external 5 electric heating elements
as well as a higher attainable heat flux density. The scope of the invention
includes the possibility of also providing part of the total heat output used in
the furnace through the combustion of chemical energy carriers.
10 [0014] If, therefore, electrical heating is mentioned here, it does not preclude
the presence of additional non-electrical heating. In particular, it can also be
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 such as natural gas.
15
[0015] In the case of heating with polyphase alternating current, 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 are
advantageously also electrically connected to a star point. The number of
20 phases M is in particular 3, corresponding to the number of phases of
conventional three-phase current sources or three-phase current networks. 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. Thereby, a phase offset amounts to in particular
25 360°/M, i.e., 120° for a three-phase current.
[0016] In an electrical heating system with polyphase alternating current,
potential equalization between the phases is achieved by the star circuit at the
star point, which makes electrical insulation of the connected pipelines
30 superfluous. This represents a particular advantage of such a furnace concept,
since a break in the metallic reaction tubes for insulating certain sections is
5
undesirable, in particular because of the high temperatures used and the high
material and construction outlay thus required.
[0017] However, the measures proposed in accordance with the invention,
which are explained below, are suitable in the same 5 way for the use of direct
current, and the present invention can be used in reactors heated by both
alternating current and direct current or also in corresponding mixed forms. In
the case of a direct current arrangement, only the type of the current source
and the region of the reaction tubes opposite to the current feed or
10 corresponding sections acted upon by current are different from an alternating
current arrangement. In the latter, an electrical connection of different tube
sections is carried out only optionally. Since there is no potential-free star point
in a direct current arrangement, suitable current discharge elements, which
safely return the current flow to the outside again, are to be provided. The
15 same applies in principle also to single-phase alternating current, which can
also be used.
[0018] In the language of the claims, the present invention relates to a reactor
for carrying out a chemical reaction, which reactor comprises a reactor vessel
20 (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 run between a first region and a second region within the
reactor vessel and through an intermediate region between the first and
second regions, and wherein for the electrical heating of the tube sections, the
25 tube sections in the first region in each case are or can be electrically
connected to one or more current connections, and in the case of a direct
current arrangement to one or more direct current connections, and in the case
of a single-phase or polyphase alternating current arrangement to the phase
connection or connections ("external conductors") of the alternating current
30 source, as explained in detail below.
6
[0019] The first region can in particular lie on a first terminal end of the straight
tube sections and the second region on a second terminal end, which is
opposite the first terminal end. In particular, the first region can lie in an upper
and the second region in a lower region of the reactor or vice versa. In other
words, the first region and the second region lie in 5 particular at opposite ends
of the reactor vessel or its interior, wherein the interior of the reactor vessel
between the first and the second region corresponds in particular to the
intermediate region. The first region can, for example, represent or comprise
the terminal 5%, 10% or 20% of the interior at one end of the reactor vessel,
10 whereas the second region can represent or comprise the terminal 5%, 10%
or 20% at the other, opposite end of the interior of the reactor vessel. In
particular, during the operation of the reactor, the first region is arranged at the
bottom and the second region is located at the top.
15 [0020] As mentioned, in a polyphase alternating current arrangement, 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 present invention, for example, a
supply network or a suitable generator and/or transformer can serve as a
20 polyphase alternating current source. In this arrangement, the tube sections
form in particular a star circuit in which they are electrically conductively
coupled to one another at their respective end that lies opposite the current
feed, i.e., in the second region.
25 [0021] However, in the case of a direct current arrangement, the same or
different static electrical potentials are fed via the direct current connections,
and current extraction elements or current discharge elements are provided in
particular in each case at the end opposite the current feed. The terms "feed"
and "extraction" may refer to the physical or technical current direction. A
30 single-phase alternating current source is used in a comparable manner.
7
[0022] 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
intermediate region, wherein "substantially straight" 5 is to be understood as
meaning that an angular deviation of less than 10° or 5° is present.
[0023] In particular, the cracking reactions in steam cracking are strongly
endothermic reactions. Therefore, for the provision of the necessary energy
10 for the reaction by means of direct heating (ohmic resistance), high current
intensities, which are provided in the aforementioned reactor concept by one
or more transformers placed outside the reactor, are required.
[0024] The electrical current must be conducted from the outside into the
15 interior of the thermally insulated reactor and to the process-carrying regions
with the lowest possible losses (low electrical resistance). In the latter, the
endothermic reaction together with the very rapidly flowing process medium
on the tube inner side (high heat transfer) leads to the very effective cooling of
the reactor tubes or to a very high heat flux density on the tube inner side. The
20 desired direct heat transfer from the at least partially electrically heated tube
material to the process gas is thus achieved in the process-carrying tubes.
[0025] A particular problem relates to the above-mentioned low-loss supply of
the high current to the process-carrying tubes. Such supply must necessarily
25 be effected, provided that a current is to be fed into the tubes within the reactor,
via conductors that cannot be cooled by direct convective heat transfer to a
cooler process gas, as will also be explained below. Here, there must not be
an unacceptable increase in temperature in the less efficiently cooled regions.
Moreover, a steep temperature rise of up to 900 K (max. temperature
30 difference between the environment and the reactor) within short path lengths
(in part less than 1 meter) must also be overcome via such supply.
8
[0026] To reduce the thermal losses and thus to achieve a high system
efficiency, it is imperative to place the electrically directly heated reactor tubes
in an insulated box (referred to here as the reactor vessel). During the
penetration of the thermally insulated wall of the reactor vessel, the current
conductor must overcome a quasi-adiabatic zone 5 without impermissibly high
local temperatures occurring in such regions.
[0027] According to the invention, in order to achieve such objective in the first
region of the reactor, that is, in the region of the current feed, current feed
10 arrangements are provided, to each of which a tube section or a group of the
tube sections is electrically connected. The tube sections are provided in such
a number that in each case one or in each case one group of a plurality of tube
sections can in each case be connected to one of the current feed
arrangements and vice versa. The number of current feed arrangements is
15 based on the number of phase connections of the polyphase alternating
current source in the case of an alternating current arrangement, or such
number corresponds to the number of direct current connections. When an
alternating current arrangement is used, it can be the same as the number of
phase connections or can be an integer multiple thereof. In the latter case, for
20 example, two of the current feed arrangements can in each case be connected
to one of the phase connections of the alternating current source, etc.
[0028] The current feed arrangements each comprise one or more contact
passages, which adjoins or adjoin at least one of the tube sections in the first
25 region, and which run through the current feed arrangements. The one or more
contact passages in the current feed arrangements can, as described in more
detail below, run straight or in the form of a U-bend through the current feed
arrangements. They are then in particular formed as a wall-reinforced bend.
Reaction tubes without U-bends are in particular wall-reinforced sleeves.
30
[0029] Within the scope of the invention, the one or more contact passages in
the current feed arrangements can either be formed in one or more
9
components that are attached and firmly bonded to the tube sections in a hightemperature-
resistant manner, or alternatively in the form of, in each case, a
section or a continuous section of the reaction tubes. In all embodiments, a
design with as few components as possible is typically found to be
advantageous, 5 as also explained below.
[0030] In the former case, the tube sections that run between the first and the
second region in the reactor can be welded to a prefabricated component in
which one or more of the contact passages runs or run, or a corresponding
10 additional component can be cast onto the tube sections that run between the
first and the second region in the reactor. In the latter case, continuous tubes
that, on the one hand, run between the first and second regions in the reactor
and, on the other hand, are to form the contact passages in the respective
current feed arrangements, can be provided, and additional components of the
15 current feed arrangements can be provided by means of casting or recasting
or welding.
[0031] It is understood that, where hereinabove and hereinafter reference is
made to the fact that the current feed arrangements include one or more
20 contact passages "that in each case adjoins or adjoin at least one of the tube
sections in the first region," this means that the contact passages in the current
feed arrangements form with the respective tube sections between the first
and second regions a continuous channel for the process fluid to pass through
the tube sections.
25
[0032] In particular, a tube interior of the respective tube sections between the
first and the second regions continues in the corresponding contact passages,
in particular without a significant tapering or widening, wherein a "significant"
tapering or widening is intended to designate a tapering or widening by more
30 than 10% of the cross-sectional area. The term "contact passages" is used to
express that these are regions in which there is a conductive connection via
metallic components to a current connection, even if, in certain embodiments
10
of the invention, the "contact passages" are continuous continuations of the
tube sections in the first region.
[0033] The term "firmly bonded in a high-temperature-resistant manner" is
intended to designate a type of connection 5 by means of which two or more
metallic parts are firmly bonded to one another and the connection is
permanent at 500°C to 1,500°C, in particular 600°C to 1,200°C or 800°C to
1,000°C, i.e., does not become detached at such temperatures during regular
operation. A high-temperature-resistant firmly bonded connection can in
10 particular be formed as a metal-to-metal connection, which is designed such
that no nonmetallic material remains between the connected parts. Such a
connection can be produced in particular by welding, casting or recasting. It
can also be a connection where no structural difference can be observed at
the transition of the connected parts and in particular a connection where no
15 additional metal is used for the connection.
[0034] According to the invention, a wall of the contact passages of each
current feed arrangement is connected in each case to a current feed element
that has at least one rod-shaped section, which in each case runs at a wall
20 passage through a wall of the reactor vessel. The "wall" of the reactor vessel
can also be an intermediate wall to a separate space in which the rod-shaped
sections are contacted, and which in turn is delimited by means of a further
wall or a plurality of walls. The rod-shaped section is, for example, in contrast
to strands or the like, in particular in one piece (i.e., in particular not in the form
25 of parallel or intertwined wires) made of a current-conducting material such as
metal. It can be formed to be solid or at least partially tubular, i.e., as a hollow
rod. The rod-shaped section has a longitudinal extension perpendicular to the
wall of the reactor vessel, which is at least twice as large, in particular at least
three times, four times or five times, and, for example, up to ten times as large
30 as the largest transverse extension parallel to the wall of the reactor vessel.
The rod-shaped section can be formed to be, for example, round, oval,
triangular or polygonal in cross-section, or can have any other shape.
11
[0035] The current feed elements of the current feed arrangements can be
attached with their rod-shaped sections directly to the wall of the contact
passages or can transition into them by a single-piece fabrication. However,
one or more intermediate elements can also be 5 provided, which then in each
case form a part of the current feed elements.
[0036] According to the invention, the introduction of current into the reaction
tubes or the tube sections thereof to be heated thus takes place via the rod10
shaped section, which is preferably attached to the process-carrying tube in
vertical direction to the local process gas flow, i.e., in particular at the apex of
a U-bend or vertical to the course of the tube in the case of non-curved tubes.
Here, in particular a globally decreasing free conductor cross-section from the
outside to the reaction zone can be present in a rod-shaped section with a
15 homogeneous material composition. This relates to both the rod-shaped
section and the transition region to the reaction tube or the contact passage,
which preferably has an enlarged wall thickness in comparison with the
reaction tube away from the feed.
20 [0037] A particularly advantageous embodiment of the present invention
comprises that, for any two cross-sectional areas S1, S2 representing
insulating surfaces through the current feed element, via which the temporal
root mean square (rms) value of the electric potential Vrms,i is constant in each
case, and which are arranged at different distances from the alternating
25 voltage source, i.e., in particular a transformer, the temporal root mean square
potential Vrms,1 of the cross-sectional area S1 located closer to the
transformer is always higher than the temporal root mean square potential
Vrms,2 of the cross-sectional area S2 located further away from the
transformer, so that Vrms,1 > Vrms,2 applies. The terms "closer" and "further"
30 refer here to shorter or longer flow paths of the electrical current from the
current source to the respective cross-sectional area. The use of rms values
for the potentials refers to the reactor operation with alternating current. In the
12
case of direct current operation, the described relationships apply to
arithmetically averaged values of the electrical potential.
[0038] The entire current feed (i.e., the entire feed element with the contact
passage) is further advantageously designed in 5 such a way that, for the
explained two arbitrary cross-sectional areas S1 and S2 at different distances
from the current source and with Vrms,1 > Vrms,2, the quotient A2/A1 of the
surface area A2 of the cross-sectional area S2 located further away from the
current source and of the surface content A1 of the cross-sectional area S1
10 located closer to the current source is up to 0.5, in particular up to 0.9, up to 1
up to 1.1 or up to 2. In a particularly preferred embodiment, the quotient A2/A1
of the surface areas of any such pairs of areas is up to 1.
[0039] For example, for manufacturing reasons, deviations from this preferred
15 embodiment can occur, so that even small cross-sectional increases can be
accepted locally. For two cross-sectional areas S1* and S2* with global
extreme values of their respective surface areas A1* = Amax and A2* = Amin,
the relationship is however advantageously always Vrms,1* > Vrms,2*, i.e., the
area with the highest cross-section is closer to the current source than the area
20 with the smallest cross-section.
[0040] In the manner explained, an optimally continuous increase in the
material temperature can be ensured, wherein the maximum is particularly
preferably reached only in the reaction zone. According to a particularly
25 advantageous embodiment of the present invention, as a specification with
regard to the temperature distribution, it can be specified, analogously to the
area distributions, that for the explained two arbitrary cross-sectional areas S1
and S2 at different distances from the current source and with Vrms,1 >
Vrms,2, the temperature difference T1-T2 of the temperature T1 of the cross30
sectional area S1 located closer to the current source and the temperature T2
of the cross-sectional area S2 located further away from the current source is
up to -100 K, in particular up to -10 K, up to -1 K, up to 0 K, up to 1 K, up to 10
13
K or up to 100 K. In a particularly preferred embodiment, the temperature
difference T1-T2 of all such pairs of areas is less than 0 K.
[0041] This specification includes, among other things, the condition that, in
the entire region of the current feed, a maximum 5 local temperature increase of
-100 K, - 10 K, -1 K, 0 K, 1 K, 10 K or 100 K occurs in relation to the maximum
material temperature occurring in the adjacent tube section.
[0042] The temperature difference T1*-T2* of the temperatures T1* and T2* of
10 the cross-sectional areas S1* and S2* with the global extreme values of the
surface areas A1*=Amax and A2*=Amin in the current feed element is further
advantageously up to -500 K, up to -200 K, up to -100 K, up to 0 K or up to
100 K, i.e., the area with the highest cross-section according to this
embodiment of the invention must be located closer to the transformer and is
15 preferably cooler or at most slightly hotter than the area with the smallest
cross-section.
[0043] The current feed element is advantageously formed, from the direction
of the current source to the tube sections, initially as a solid material rod and
20 leads to the contact passage located closer to the tube sections, which can in
particular be formed as a thick-walled bend or sheath, up to the relatively thinwalled
reactor tubes or the tube sections to be heated.
[0044] In one embodiment of the present invention, the free conductor cross25
section advantageously decreases predominantly continuously or
monotonically. Since, with identical or similar materials provided in this
embodiment, the electrical resistance depends only on the available conductor
area, the specific amount of energy released also increases steadily in this
way. This results in the highest possible utilization of the supplied energy, since
30 only the amount of heat absorbed by the process gas can be effectively used
in the reaction tubes.
14
[0045] According to a particularly advantageous embodiment of the present
invention, the exact course of the conductor cross-section is moreover adapted
to the local temperature and heat transfer conditions. For example, in the
region of quasi-adiabatic wall passages through the wall of the reactor vessel
(in which no significant heat dissipation is possible 5 through the insulating
reactor wall), large cross-sections, which reduce the local heat dissipation in
such regions to a minimum, are preferably used, so that the local increase in
temperature can be limited upward. In other words, the rod-shaped section of
the current feed element advantageously has a larger cross-sectional area in
10 the region of the wall passage than in at least one remaining region. Since, as
mentioned below, the rod-shaped section is guided displaceably in the wall
passage, the region of the rod-shaped section "in the region of the wall
passage" is to be understood to mean at least one such region that is located
in the wall passage at maximum thermal expansion of the tube sections.
15
[0046] As will also be explained below, for avoiding contact resistances, at
least the rod-shaped section the current feed element and the contact section
are particularly preferably made of a one-piece component, e.g. in the form of
a standing cast part. In the case of a multi-part construction, which is
20 alternatively likewise possible, it is advantageously ensured by means of
suitable joining methods (e.g., friction welding) that the explained
specifications relating to the conductor cross-section and the maximum local
temperature increase are maintained even in the region of the joint connection.
25 [0047] Particularly advantageously, the current feed elements each have a free
conductor cross-section that, between the respective wall passage of the
current feed elements and a point of the wall of the one or more contact
passages that is closest to the wall passage and is electrically contacted by
the respective current feed elements, is at no point less than 10 square
30 centimeters, advantageously at no point less than 30 square centimeters and
in particular at no point less than 50 square centimeters. By using
15
correspondingly high conductor cross-sections, a particularly good current
transfer without resistance losses can be ensured.
[0048] Here, a free conductor cross-section is intended to designate the
proportion of the cross-section of a conductor that 5 is formed to be currentconducting.
For example, in the case of a tubular conductor or a conductor
provided with a groove or cavity, the tube interior or the region of the groove
or cavity does not count as the free conductor cross-section. By contrast, in
the case of a solid conductor made of a current-conducting material, the cross10
section corresponds to the conductor cross-section and the free conductor
cross-section.
[0049] According to the invention, the rod-shaped sections of the current feed
elements are in each case guided in a longitudinally movable manner in their
15 wall passages through the wall of the reactor vessel. A freedom of movement
ensured in this way is particularly advantageous for the mechanical behavior
of the reaction tubes, which is dominated primarily by the thermal expansion
of the tubes by several decimeters during operation of the reactor. Due to the
freedom of movement, the bending load on the reaction tubes that would occur
20 in case of a rigid fastening is reduced. On the other hand, as also mentioned
below, the reaction tubes can be fastened in the second region to a rigid star
bridge on the reactor roof, so that in this way a stable suspension is provided
even in the case of a corresponding longitudinal mobility of the rod-shaped
sections of the current feed elements. Due to their advantageous dimensioning
25 with a sufficiently high conductor cross-section, the rod-shaped sections of the
current feed elements ensure a secure lateral guidance of the reaction tubes.
[0050] Since the reactions carried out in the reactor according to the invention
require high temperatures, the electrical connection in the first region must be
30 implemented in a high-temperature range of, for example, approximately
900°C for steam cracking. This is possible by the measures proposed
according to the invention by the selection of suitable materials and their
16
adequate dimensioning. At the same time, the connection is intended to have
a high electrical conductivity and high mechanical stability and reliability at high
temperatures. Failure of the electrical connection leads to asymmetrical
potentials at the star point and consequently to an instantaneous safety-related
shutdown of the system due to undesired current 5 flow in system parts. The
present invention provides advantages over the prior art by avoiding such
situations.
[0051] The contacting of the tube sections within the reactor vessel provided
10 according to the invention, compared to a theoretically likewise possible
contacting outside the reactor vessel, for which the reaction tubes would have
to be led out of the reactor vessel, has the advantage of a clear defined section
of the electrical heat input, because in this case no electrically heated tube
sections have to be guided from the warmer interior to the colder exterior. Due
15 to the contacting according to the invention, external thermal boundary
conditions that are highly homogeneous in terms of space of the electrically
heated tube sections can be achieved due to the tube sections arranged
completely within the reactor vessel. This results in process engineering
advantages, for example, an expected excessive coke formation in heated and
20 externally thermally insulated passages can be avoided.
[0052] Outside the reactor vessel, the rod-shaped sections of the current feed
elements can be electrically connected to a transformer system, for example,
by means of connection elements such as busbars and connection bands. The
25 connection bands and busbars can be made of a different material. Such
connection elements are formed to be flexible, since lower temperatures are
present outside the reactor vessel. Switching devices can be installed in
particular on a primary side of the transformer system since there is a higher
voltage and a lower current there.
30
[0053] Within the scope of the present invention, the current feed elements,
the contact passages and the tube sections may be formed from the same
17
material or from materials whose electrical conductivities (in the sense of a
material constant, as is customary in the field) differ from one another by no
more than 50%, no more than 30%, no more than 10%, or are advantageously
the same. For example, the components mentioned can also be formed from
steels of the same steel class. The use of the same 5 or closely related materials
can facilitate casting or welding.
[0054] In a preferred embodiment, the current feed elements, the contact
passages and the tube sections have a heat-resistant chromium-nickel-steel
10 alloy with high oxidation or scaling resistance and high carburization
resistance, or are formed from such.
[0055] For example, it can be a ferrous material 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%
15 silicon, 0 to 5% tungsten and 0 to 1 wt% other components, wherein the
constituents complement each other to form the non-ferrous fraction.
[0056] For example, materials with the standard designations GX40CrNiSi25-
20, GX40NiCrSiNb35-25, GX45NiCrSiNbTi35-25, GX35CrNiSiNb24-24,
20 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", may be used. These have proven to be
particularly suitable for high-temperature use.
25
[0057] 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%,
30 or are advantageously the same. For example, the 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
18
of the connecting element and of the tube sections, for example by means of
casting or welding.
[0058] In the second region, all tube sections within the reactor vessel can be
electrically conductively connected to each 5 other by means of a rigid
connecting element ("star bridge") when heated by means of polyphase
alternating current, or such connection can take place in groups by means of
a plurality of rigid connecting elements.
10 [0059] The electrically conductive connection is made in this case, i.e., in the
case of heating by means of polyphase alternating current, in such a way that
at least extensive potential equalization of the phases connected in the first
region arises, as explained. The one or more connecting elements couple the
connected tube sections, in particular, in a non-fluid-collecting and non-fluid15
distributing manner, in contrast to a collector known from the prior art and
arranged outside the reactor. The potential equalization within the reactor
vessel proposed in the embodiment of the invention just explained has the
advantage of an almost complete absence of potential or a significantly
reduced return of current via a neutral conductor. The result is minimal current
20 dissipation via the header connections to other parts of the process system
and a high level of shock protection. In this connection as well, the advantage
of the external thermal boundary conditions that are highly homogeneous in
terms of space applies in contrast to a guidance of the reaction tubes outside
the reactor vessel through the wall of the reactor vessel, that is required for
25 potential equalization, the process-related advantages already explained
above.
[0060] The corresponding realization of a star circuit in combination with the
explained current feed via longitudinally guided current feed elements as a
30 whole creates a design that enables efficient energization with simultaneous
stable fastening, which withstands the stresses resulting primarily from the
high thermal expansion rates.
19
[0061] This likewise applies to the heating that is also possible according to
the invention by means of direct current or single-phase alternating current,
wherein, in this case, no star point is present in the reactor, as mentioned.
Nevertheless, a rigid arrangement can also be 5 provided here at the end
opposite the current feed, since the reaction tubes can expand substantially
freely due to the current feed elements provided according to the invention,
without the generation of stresses. Thus, a rigid arrangement can be provided
at the end of the reaction tubes opposite the current feed, but, if necessary,
10 elements that correspond to the current feed elements according to the
invention can also be provided here. In any case, however, a movable
arrangement can be dispensed with.
[0062] The present invention will be described below first with reference to
15 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
addressed subsequently. In general, as mentioned, the reactor proposed
according to the invention can be used for carrying out any endothermic
chemical reaction.
20
[0063] Reaction tubes, as are typically used for steam cracking, typically have
at least one U-bend. For example, these can be so-called 2-passage coils.
These have two tube sections in the reactor vessel, which pass into one
another via (exactly) one U-bend and therefore basically have the shape of an
25 (elongated) U. The sections entering and exiting the reactor vessel, which in
particular pass 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.
30
[0064] In this embodiment, the reactor can therefore be formed in such a way
that the tube sections in each case comprise two tube sections of a plurality of
20
reaction tubes which are arranged at least partially side by side in the reactor
vessel, the two tube sections of the plurality of reaction tubes in each 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 5 the others of the in each
case two tube sections in the second region are connected to an extraction
section.
[0065] In this case, the one or more contact passages in the current feed
10 arrangements can comprise or represent the U-bends. Since a plurality of
reaction tubes with U-bends is present, a plurality of U-bends can also be
provided in each of the respective current feed arrangements if there is a
corresponding number of them, and in this way can be connected to a current
connection. In this way, the mechanical fastening can be improved and the
15 number of components can be reduced. Alternatively, however, it is also
possible to provide one current feed arrangement per U-bend in each case
even when a plurality of U-bends is energized via a current connection, for
example in order to ensure an individual longitudinal mobility of the current
feed elements with a thermal expansion that may differ.
20
[0066] The embodiment of the invention just explained can also be applied to
cases in which reaction tubes having two feed sections and one extraction
section are used. With such reaction tubes, the two feed sections are each
connected to one tube section. The extraction section is also connected to a
25 tube section. The tube sections connected to the feed sections pass into the
tube section connected to the extraction section in a typically Y-shaped
connection region. Both the tube sections connected to the feed sections and
the tube section connected to the extraction section can each have one or
more U-bends or none at all.
30
21
[0067] For example, reaction tubes as illustrated in Figure 7C can be used. 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.
[0068] However, reaction tubes as illustrated in Figure 5 7B may also be used.
In these, the tube sections connected to the feed sections each have one Ubend
and the tube section connected to the extraction section has two Ubends.
10 [0069] Even the use of reaction tubes as illustrated in Figure 7A is possible. In
these, the tube sections connected to the feed sections each have three Ubends
and the tube section connected to the extraction section has two Ubends.
15 [0070] In addition to the embodiment described above with reference to 2-
passage coils, however, an embodiment suitable for use with so-called 4-
passage coils can also be used. They have four essentially straight tube
sections. However, arrangements with a higher, even number of straight tube
sections are also possible.
20
[0071] In more general terms, a correspondingly designed reactor 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
25 connected in series with one another via the U-bends, and wherein the Ubends
are arranged alternately in the first and the second regions starting with
a first U-bend in the first region.
[0072] A "U-bend" is understood here in particular to mean a tube section or
30 tube component that comprises a part-circular or part-elliptical, in particular a
semicircular or semi-elliptical tube bend. The beginning and end have cut
surfaces lying next to one another in particular in one plane.
22
[0073] Each of the U-bends, provided it is located in the first region within the
reactor vessel and is to be energized accordingly, can be designed in the form
of a contact passage in a current feed arrangement according to the invention
or represent a 5 part of such a contact passage.
[0074] As mentioned, a corresponding reactor can be designed in particular as
a reactor for steam cracking, that is in particular by the choice of correspond
temperature-resistant materials and the geometric configuration of the reaction
10 tubes.
[0075] Reaction tubes, as are typically used for steam reforming, typically have
no U-bends within the reactor vessel. In this case, the tube sections can each
comprise a tube section consisting of a plurality of reaction tubes, wherein the
15 tube sections within the reactor vessel are arranged in a fluidically
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 feed and extraction sections for fluid extend
in particular in the same direction as the tube sections or do not cause a fluid
20 flow that is deflected by more than 15° in relation to the fluid flow in the tube
sections connected 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 may, in particular, also be equipped with a
suitable catalyst for steam reforming.
25
[0076] In this embodiment, the contact passages in a current feed arrangement
according to the invention represent straight tube sections or channels. Here,
the current feed element can be attached to the reaction tubes in the second
region in particular in the manner of a sleeve.
30
[0077] In all cases, by forming the current feed elements and the contact
passages, and optionally also the tube sections, from as few individual parts
23
as possible, the number of metal-to-metal connections (e.g., welded or
soldered connections) can be reduced or even completely dispensed with.
Mechanical stability and reliability can thereby be increased. In a particularly
advantageous embodiment, the current feed elements and the contact
passages can each be implemented as a single casting, 5 or, as mentioned,
parts of the process-carrying tubes can be recast and/or parts of the processcarrying
tubes can be formed as an integral part of a corresponding casting.
[0078] Metal-to-metal connections or metal transitions, which can be reduced
10 within the scope of the present invention, could lead to a local 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
[0079] A one-piece design of as many components as possible brings
mechanical stability, reliability and a reduction of individual components. A high
degree of mechanical stability is desirable, since failure, as mentioned, can
lead to safety-critical situations. By means of the described embodiment in the
20 sense of the present invention, the principle of reaction 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.
25 [0080] 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 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 each electrically
30 connected to one or more current connections of a current source.
24
[0081] According to the invention, a reactor is used, which has current feed
arrangements in the first region to which in each case one or in each case one
group of the tube sections is electrically connected, wherein the current feed
arrangements each comprise one or more contact passages that in each case
adjoins or adjoin at least one of the tube sections 5 in the first region, and
wherein a wall of the contact passages in each case is connected to a current
feed element that has at least one rod-shaped section, which in each case
runs at a wall passage through a wall of the reactor vessel.
10 [0082] For further features and advantages of a corresponding method, in
which a reactor according to one of the previously explained embodiments of
the invention is advantageously used, reference is made to the above
explanations.
15 [0083] The invention will be further explained below with reference to the
accompanying drawings, which illustrate embodiments of the present
invention with reference to and in comparison with the prior art.
DESCRIPTION OF THE FIGURES
20
[0084] Figure 1 schematically illustrates a reactor for carrying out a chemical
reaction according to an embodiment not according to the invention.
[0085] Figure 2 schematically illustrates a reactor for carrying out a chemical
25 reaction according to an embodiment of the invention.
[0086] Figure 3 schematically illustrates a reactor for carrying out a chemical
reaction according to a further embodiment of the invention.
30 [0087] Figure 4 schematically illustrates a reactor with a current feed
arrangement according to an embodiment of the invention.
25
[0088] Figures 5A to 5C illustrate reaction tubes and corresponding
arrangements for use in a reactor according to an embodiment of the invention.
[0089] Figures 6A and 6B illustrate reaction tubes and corresponding
arrangements for use in a reactor according to an embodiment 5 of the invention.
[0090] Figures 7A to 7C illustrate further reaction tubes for use in a reactor
according to an embodiment of the invention.
10 [0091] Figure 8 shows values of thermal and electrical parameters in a current
feed arrangement according to an embodiment of the invention.
[0092] Figure 9 schematically illustrates a reactor with a current feed
arrangement according to an embodiment of the invention.
15
[0093] In the following figures, elements that correspond to one another
functionally or structurally are indicated by identical reference symbols and 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
20 to the methods carried out therewith and vice versa. The description of the
figures repeatedly refers to an alternating current heating. As mentioned,
however, the present invention is also suitable in the same way for the use of
direct current for heating. Reference is made here to the above explanations.
25 [0094] Figure 1 schematically illustrates a reactor for carrying out a chemical
reaction according to an embodiment not according to the invention.
[0095] The reactor here designated by 300 is set up to carry out a chemical
reaction. For this purpose, it has in particular a thermally insulated reactor
30 vessel 10 and a reaction tube 20, wherein a number of tube sections of the
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
26
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, the
reactor vessel can in particular have a furnace (not illustrated). It goes without
saying that a plurality of reaction tubes can be provided 5 in each case here and
subsequently.
[0096] Figure 2 schematically illustrates a reactor for carrying out a chemical
reaction according to an embodiment of the present invention, which is overall
10 designated by 100.
[0097] The zones previously designated by 11' and 12' here take the form of
regions 11 and 12, wherein the tube sections 21 for heating the tube sections
21 in the first regions 11 can each be electrically connected to the phase
15 connections U, V, W) of a polyphase alternating current source 50. Switches
and the like as well as the specific type of connection are not illustrated.
[0098] In the embodiment of the invention illustrated here, the tube sections 21
are electrically conductively connected to one another in the second regions
20 12 by means of a connecting element 30 which is integrally connected to the
one or more reaction tubes 20 and is arranged within the reactor vessel 10. A
neutral conductor can also be connected thereto.
[0099] In the reactor 100 illustrated here, a plurality of tube sections 21 of a
25 reaction tube 20 (although a plurality of such reaction tubes 20 may be
provided) are thus arranged side by side in the reactor vessel 10. The tube
sections 21 pass into one another via U-bends 23 (only partially designated)
and are connected to a feed section 24 and an extraction section 25.
30 [0100] A first group of the U-bends 23 (at the bottom in the drawing) is arranged
side by side in the first region 11 and a second group of the U-bends 23 (at the
top in the drawing) is arranged side by side in the second region 12. The U-
27
bends 23 of the second group are formed in the connecting element 30, and
the tube sections 21 extend from the connecting element 30 in the second
region 12 to the first region 11.
[0101] Within the scope of the present invention, the 5 use of the connecting
element 30 is optional but advantageous. However, embodiments of the
invention, which are explained below, relate in particular to the embodiment of
the means for feeding current in the first region 11. This is carried out by the
use of current feed elements 41, which are illustrated here in a highly simplified
10 manner and of which only one is designated.
[0102] Figure 3 schematically illustrates a reactor for carrying out a chemical
reaction according to an embodiment of the present invention, which is overall
designated by 200.
15
[0103] In the reactor 200, the tube sections – here in contrast designated by
22 – each comprise a tube section 22 consisting of a plurality of reaction tubes
20, wherein the tube sections 22 are arranged side by side in the reactor vessel
10 in a fluidically unconnected manner and are each connected to feed
20 sections 24 and extraction sections 25. For the remaining elements, reference
is expressly made to the above explanations relating to the preceding figures.
[0104] In turn, within the scope of the present invention, the use of a connecting
element 30 is optional but advantageous. Here as well, current feed elements
25 41 are illustrated in a highly simplified manner. They can have a sleeve-like
region 49, which is placed in the first region 11 around the reaction tubes 20
or the tube sections.
[0105] Figure 4 shows a detail illustration of the first region 11 of a reactor 100,
30 for example according to Figure 2, with a current feed arrangement 40
arranged in the first region 11 and a reaction tube 20 connected thereto, the
28
tube sections 21 of which, illustrated in sections here, merge into one another
via a U-bend 23.
[0106] Here, the U-bend 23 is formed in a contact passage 42 with a reinforced
wall, which adjoins the two tube sections 21 5 in the first region 11. A wall of the
contact passage 42, and thus of the U-bend 23, is connected to the already
mentioned current feed element designated as a whole by 41, which, as
indicated here between dashed lines, has a rod-shaped section 43, which runs
in each case at a wall passage 15 through a wall 14 of the reactor vessel 10.
10 Here, the wall passage 15 is shown with an exaggerated width. The rodshaped
section is accommodated in the wall passage 15 so as to be
longitudinally movable and, for example, is lined with a suitable insulation
material 16.
15 [0107] Optionally, but in no way essential to the present invention, a bellows
arrangement 44 can be provided on the outside of the wall 14 of the reactor
vessel 10 to ensure a gas-tight seal of the reactor vessel 10 against the
environment despite the longitudinal mobility of the rod-shaped sections 43.
20 [0108] In the example shown, an additional rod-shaped section 45 adjoins the
rod-shaped section 43, the temperature of which section increasingly
decreases as the distance from the reactor vessel 10 increases. The additional
rod-shaped section merges into a current feed pin 46, to which, for example,
two busbars or strands are attached to connect the phases U,V,W or
25 corresponding current connections of a direct current source or of a singlephase
alternating current source.
[0109] In cracker furnaces, in addition to the reaction tubes 20 previously
shown in Figures 1 and 2, which are commonly referred to as 6-passage coils,
30 and which comprise six straight tube sections 21 having two 180° bends, i.e.,
U-bends 23, above or in the second region 12, and three 180° bends, i.e., Ubends
23, below or in the first region 11 (the latter with corresponding current
29
feed arrangements), variants with fewer passages are can also be used. For
example, so-called 2-passage coils have only two straight tube sections 21
and only one 180° bend or U-bend 23. When applied to electrical heating, this
variant can be regarded as a combination of 6-passage cracker furnace
(Figures 1 and 2) and reforming furnace (Figure 3, 5 with reaction tubes without
U-bends 23):
[0110] The current can be fed in each case in at one point per reaction tube 21
at the lower (or only) U-bend. In each case, M reaction tubes can be electrically
10 coupled to one another, with a phase shift of 360°/M and with a common
connecting element 30. In a first alternative, a particularly large connecting
element 30 can be used per coil package or for all reaction tubes 20
considered in each case. In a second alternative, however, the use of two
smaller-sized connecting elements 30 is also possible.
15
[0111] The first alternative just explained is illustrated in Figure 5B, the second
alternative just explained in Figure 5C in a cross-sectional view through the
tube sections 21, wherein a corresponding reaction tube 20 is shown in Figure
5A in a view perpendicular to the views in Figures 5B and 5C. Reference is
20 made to Figure 1 for the designation of the corresponding elements. It goes
without saying that the connecting element or elements 30 with the U-bends
23 possibly arranged there, on the one hand, and the other U-bends 23, on
the other hand, with the connections to the phases U, V, W are arranged in
different planes corresponding to the first and second regions 11, 12 of a
25 reactor, via the current feed arrangements 40 (shown here in a highly simplified
manner). It should be emphasized again that the presence and arrangement
of the connecting elements 30 within the scope of the present invention is
purely optional or arbitrary.
30 [0112] This concept can also be applied correspondingly to coils or reaction
tubes 20 having four passages or tube sections 21 (so-called 4-passage coils),
in this case with one, two or four star bridges or connecting elements 30. A
30
corresponding example is shown in Figures 6A and 6B, four connecting
elements 3 being shown in Figure 6B. For improved illustration, the U-bends
23 are shown here by dashed lines (U-bends in the second region 12 of the
reactor) and by unbroken lines (U-bends in the first region 11). For the sake of
clarity, the elements are only 5 partially provided with reference symbols.
[0113] Reference has already been made to Figures 7A to 7C, which illustrate
further reaction tubes for use in a reactor according to an embodiment of the
invention. The reaction tubes and tube sections are here only in some cases
10 provided with reference symbols. Feed and extraction sections may be
deduced from the flow arrows shown. The current feed arrangements 40,
which can be present in particular several times and can be formed in the
manner explained above, are indicated in a highly simplified manner by
dashed lines.
15
[0114] Figure 8 illustrates values of thermal and electrical parameters in a
current feed arrangement 40 according to a particularly preferred embodiment
of the present invention, wherein the abscissa shows a value of the temporal
root mean square potential (rms value) over the designated elements 46
20 (current feed pins), 46 and 45 (rod-shaped elements), 42 (contact passage)
and 21 and 22 (tube sections), and the ordinate shows a value of the average
temperature of cross-sectional or insulating surfaces and the corresponding
surface areas. Graph 101 (solid line) illustrates the average temperatures of
the cross-sectional areas and graph 102 (dashed line) illustrates the surface
25 areas.
[0115] As can be seen, the average temperatures 101 rise and show a jump
in an intermediate zone between the contact passage 42 and the tube sections
21 and 22, in particular due to a rapid decrease in cross-section. As shown
30 with dashed or dot-dash regions 101a and 102a, a delimited local temperature
increase and a cross-sectional extension can be present in the region of the
wall passages 15.
31
[0116] Figure 9 shows a detail illustration of the first region 11 of a reactor 200,
wherein the elements shown in each case have already been explained in
connection with Figure 4. In contrast to Figure 4, however, the reaction tube
20 has no U-bend here and the tube sections 21 are arranged 5 along a common
central axis. A non-curved transition region is designated by 23a. A
corresponding embodiment can be used, for example, instead of a sleeve in
the reactor 200 according to Figure 3.
10 [0117] Here as well, the transition region 23a is formed in a contact passage
42 with a reinforced wall, which adjoins the two tube sections 21 in the first
region 11. For further explanations, reference is made to Figure 4. Here, the
wall passage 15 is also shown with an exaggerated width. Here as well, the
rod-shaped section is accommodated in the wall passage 15 so as to be
15 longitudinally movable and, for example, is lined with a suitable insulation
material 16. However, the wall passage 15 can also have a different
configuration in deviation from the illustration shown here, in particular in order
to create further movement options. This also relates to the optional bellows
arrangement 44.

I/We Claim:
1. A reactor (100, 200) for carrying out a chemical reaction, comprising a
reactor vessel (10) and one or more reaction tubes (20), wherein a number of
tube sections (21, 22) of the one or more reaction 5 tubes (20) in each case run
between a first region (11) and a second region (12) in the reactor vessel (10),
wherein for the electrical heating of the tube sections (21, 22), the tube
sections (21, 22) in the first region (11) in each case are or can be electrically
connected to current connections (U, V, W) of a current source (50), wherein
10 current feed arrangements (40) are provided in the first region (11) of the
reactor (100, 200), to which in each case one or in each case one group of the
tube sections (21, 22) are electrically connected, and which each comprise
one or more contact passages (42) that in each case adjoins or adjoin at least
one of the tube sections (21, 22) in the first region (11), wherein a wall of the
15 contact passages (42) in each case is connected to a current feed element
(41) that has a rod-shaped section (43) that runs at a wall passage (15) through
a wall (14) of the reactor vessel (10), wherein the rod-shaped sections (43) of
the current feed elements (41) are in each case guided during operation in a
longitudinally movable manner in their respective wall passages (15) through
20 the wall (14) of the reactor vessel (10), and wherein the rod-shaped sections
(43) of the current feed elements (41) outside the reactor vessel (10) are
electrically connected or connectable to the current connections (U, V, W) of
the current source (50) by means of flexible connection elements.
25 2. The reactor (100, 200) according to claim 1, in which the tube sections
(21, 22) are provided in such a number that in each case one or in each case
one group of a plurality of the tube sections (21, 22) can in each case be
connected to one of the current feed arrangements (40).
30 3. The reactor (100, 200) according to claim 1 or 2, in which the one or
more contact passages (42) are formed in one or more components that is or
are attached and firmly bonded to the tube sections (21, 22) in a high-
33
temperature-resistant manner, or in the form of, in each case, a section or a
continuous section of the reaction tubes (21, 22).
4. The reactor (100, 200) according to one of the preceding claims, in
which the rod-shaped section (43) has in each case 5 a longitudinal extension
perpendicular to the wall of the reactor vessel, which is at least twice as large
as the largest transverse extension parallel to the wall (15) of the reactor vessel
(10).
10 5. The reactor (100, 200) according to one of the preceding claims, in
which the current feed elements (41) each have a free conductor cross-section
that, between the respective wall passage (15) of the current feed elements
(41) and a point of the wall of the one or more contact passages (42) that is
closest to the wall passage (15) and is electrically contacted by the respective
15 current feed elements (41), is at no point less than 10 square centimeters.
6. The reactor (100, 200) according to one of the preceding claims, in
which the current feed elements (41), the contact passages (42) and the tube
sections (21, 22) are formed from the same material or from materials whose
20 electrical conductivities differ from one another by no more than 50%.
7. The reactor (100, 200) according to one of the preceding claims, in
which the current feed elements (41), the contact passages (32) and the tube
sections (21, 22) are formed from a chromium-nickel-steel alloy with 0.1 to 0.5
25 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% tungsten and 0 to 1 wt% other components, wherein
the constituents complement each other to form a non-ferrous fraction.
8. The reactor (100, 200) according to one of the preceding claims, in
30 which the tube sections (21, 22) are electrically conductively connected as a
whole or in groups within the reactor vessel (10) by means of one or by means
of a plurality of rigid connecting elements (30).
34
9. The reactor (100) according to one of the preceding claims, in which the
reaction tube or tubes (20) have one or more U-bends (23) in the first region
(11) of the reactor vessel (10) and the contact passages (42) in the current
feed arrangements (40) comprise or form the one or 5 more U-bends (23) in the
first region (11) of the reactor vessel (10).
10. The reactor (200) according to one of the preceding claims, in which a
plurality of reaction tubes (22) without U-bends (23) run in the first region (11)
10 of the reactor vessel (10) and the contact passages (42) in the current feed
arrangements (40) form straight tube sections.
11. The reactor (100, 200) according to claim 9, which is formed as a
reactor (100) for steam cracking, or according to claim 10, which is formed as
15 a reactor (200) for steam reforming, for dry reforming or for the catalytic
dehydrogenation of alkanes.
12. The reactor (100, 200) according to one of the preceding claims, in
which the flexible connection elements that are attached outside the reactor
20 vessel (10) are made of a different material than the rod-shaped sections (43)
of the current feed elements (41) guided in a longitudinally movable manner in
their respective wall passages (15) through the wall (14) of the reactor vessel
(10).
25 13. The reactor (100, 200) according to one of the preceding claims, in
which the wall (14) through which the rod-shaped sections (43) of the current
feed elements (41) are guided in a longitudinally movable manner is an
intermediate wall to a separate space in which the rod-shaped sections are
contacted with flexible connection elements, and which in turn is delimited by
30 means of a further wall or a plurality of walls.
35
14. A method for carrying out a chemical reaction using a reactor (100, 200)
that comprises a reactor vessel (10) and one or more reaction tubes (20),
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) in
the reactor vessel (10), wherein for heating the tube 5 sections (21, 22), the tube
sections (21, 22) in the first region (11) are each electrically connected to
current connections (U, V, W) of a current source (50), wherein a reactor (100,
200) is used, in which current feed arrangements (40) are provided in the first
region (11) of the reactor (100, 200), to which in each case one or in each case
10 one group of the tube sections (21, 22) are electrically connected, and which
each comprise one or more contact passages (42) that in each case adjoins
or adjoin at least one of the tube sections (21, 22) in the first region (11),
wherein a wall of the contact passages (42) in each case is connected to a
current feed element (41) that has a rod-shaped section (43) that runs at a wall
15 passage (15) through a wall (14) of the reactor vessel (10), wherein the rodshaped
sections (43) of the current feed elements (41) are in each case guided
during operation in a longitudinally movable manner in their respective wall
passages (15) through the wall (14) of the reactor vessel (10), and wherein the
rod-shaped sections (43) of the current feed elements (41) outside the reactor
20 vessel (10) are electrically connected to the current connections (U, V, W) of
the current source (50) by means of flexible connection elements.
15. The method according to claim 14, wherein a reactor according to one
of claims 1 to 13 is used.