Note: Descriptions are shown in the official language in which they were submitted.
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-- l:E~T T~A ~ 1 ~T!Q~ 2 1 7 5-2 3
CATALYTIC REACTOR FOR ENDOTHERMIC REACTIONS
Description
The invention is directed to a catalytic reactor for endothermic reactions according to
the preamble of patent claim 1. Examples of such reactions are the production of hydrogen by
steam reformation of hydrocarbons and dehydrogenation processes such as are carried out,
e.g., for the production of styrene from ethylbenzene or of propylene from isobutane.
A catalytic reactor having an external cylindrical shape and a reaction chamber with a
circular cross section is known from EP 0 380 192 B1. The input material to be catalyzed is
introduced from the bottom into the reaction chamber which is filled with a catalytic material,
while the obtained catalytically converted product is extracted from the upper end of the
reaction chamber. This known reactor is heatable by means of a burner which is arranged
below the base level of the reaction chamber and enclosed in the region of its combustion zone
by a refractory shell, its flame direction being oriented coaxially to the longitudinal direction of
the reaction chamber. The asc~nding combustion gases of the burner are guided along
virtually the entire length of the reaction chamber in a heat distributor which is formed as a
tubular body from a material with good heat conduction and directly adjoins the refractory
combustion chamber wall. An annular gap remains open between the tubular heat distributor
and the inner defining wall of the annular reaction chamber. The occurring hot combustion
gases are therefore first guided upward by the heat distributor and are deflected into the
annular gap at the upper end of the heat distributor. The combustion gases then flow
downward through the annular gap and, in so doing, give off heat into the reaction space
through the inner defining wall. At the same time, however, the combustion gases flowing
downward past the wall of the heat distributor also absorb heat from the hot combustion gases
flowing upward in the interior of the heat distributor so that the temperature of the gases in
the annular gap remains virtually constant. In this way, the known device can be operated as
an isothermal reactor in practice.
In another embodiment form, the reactor known from EP 0 380 192 Bl has a plurality
of parallel heat distributors arranged in place of a central heat distributor. There is also only
one burner provided in this device, this burner being arranged with its combustion space below
the base level of the reaction chamber. Since practically no heat is given off externally in the
combustion space itself, the combustion of the fuel used in each case takes place under
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adiabatic conditions so that, depending on the fuel, undesirably high flame temperatures are
reached. In order to decrease the temperature of the combustion gases, the conventional
amount of approxilllately 10% excess air can be considerably increased, e.g., to 50%.
However, this leads to a compulsory corresponding increase in the amount of exhaust gas with
the consequent heat losses, which is also undesirable. As an alternative to a reduction in
temperature, EP 0 380 192 B 1 proposes a return of exhaust gas to the combustion zone. This
has the particular disadvantage of additional construction costs.
Another endothermic reactor is known from EP 0 369 566 B1. The reaction chamber
of this reactor which is filled with a catalyst is designed as a tubular shell or ~heathing tube
which is closed at the bottom end, an ascçndin~ pipe being inserted into the latter in such a
way that the material to be processed can flow in opposite directions through the annular
space between the sheathing pipe and ascending pipe on the one hand and through the
ascçn~ling pipe on the other hand in order to pass the reaction space. In this apparatus, the hot
combustion gas is generated for heating the reaction space in a separate part of the in~t~ tion
under adiabatic conditions and is subsequently introduced laterally into the refractory housing
in the lower end region of the reaction space, this housing enclosing the reactor externally at a
dist~nce. In order to prevent hot combustion gas from striking the wall ofthe reaction space
directly and causing damage as a result of the high temperature, the combustion gas is fed in
the housing in such a way that the hot gases first strike a tubular barrier of refractory material,
are deflected upward, and guided down again from the upper end of the refractory barrier
along a second tubular barrier formed of a material with good heat conducting properties. The
combustion gas can only flow up again at the bottom end of the second barrier and come into
a heat-exch~nging contact with the wall of the reaction space. At the same time, a heat
transfer takes place between the combustion gases flowing in opposite directions through the
heat conducting wall of the second barrier. As in the device known from EP 0 380 192 B 1,
these steps bring about an appreciable reduction in the temperature of the combustion gas so
that the wall of the reaction chamber is protected from impermissible thermal loading. The
reaction space of this reactor is limited to a single reactor vessel so that the reactor vessels in
in~t~ tions having di~eren~ output capacities must be provided with new dimensions as
appropliate. Further, it is disadvantageous that the barriers which are exposed to high
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temperatures constitute closing or sealing parts which must be exchanged after a certain
period of operation.
The object of the present invention is to improve a catalytic reactor for endothermic
reactions of the type mentioned above in such a way that the reactor vessel is protected
against thermal damage without the drawbacks of costly construction steps, unwanted
increases in exhaust gas quantities or disadvantages in the utilization of energy of the fuels
employed.
This object is met for a reactor of the generic type by the characterizing features of
patent claim 1. Advantageous further developments of the invention are indicated in subclaims
2to 14.
The essential element of the solution according to the invention consists in that the
combustion is carried out under nonadiabatic conditions, that is, heat is guided out of the
flame zone already during combustion so that the maximum flame temperature which occurs is
subst~nti~lly decreased. This is achieved by providing not only a plurality of burners, but also
a plurality of catalytic vessels which penetrate into the flame space of the burners. The
catalytic vessels are enclosed within the region of the flame space in each instance by a barrier
which will be referred to hereinafter as a heat distributor, since it is formed of a material with
good heat conduction and absorbs the heat and distributes it again in the most uniform manner
possible. The catalytic vessels are arranged between the burners, respectively.
The invention is explained more fully in the following with reference to the
embodiment examples shown in Figs. 1 to 7.
Fig. 1 shows a longitudin~l section through a reactor according to the invention;
Fig. 1 a shows detail X from Fig. l;
Fig. 2 shows cross section A from Fig. l;
Fig. 3 shows cross section B from Fig. l;
Fig. 4 shows a longitu-lin~l section of a modified reactor;
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Fig. 4a shows an enlarged view of the bottom end of the reactor vessel from Fig. 4;
Fig. 5 shows a longit~ in~l section through an isothermal reactor according to the invention;
Fig. 6 shows cross section C from Fig. 5;
Fig. 7 shows an enlarged detail section of the reactor from Fig. 5.
In the catalytic reactor which is shown in different sections in Figs. 1 to 3, a total of
five tubular catalytic vessels 10 are arranged parallel to one another in the vertical longitudinal
direction. Their longitudinal axes lie in a common plane H. The catalytic vessels 10 are
preferably equidistant with respect to the directly adjacent catalytic vessels 10 (Fig. 3). A row
of four burners 15 is arranged, in each instance, on both sides of the plane H at a distance from
the catalytic vessels 10, these burners 15 being spaced from one another in the same way as
the catalytic vessels 10. The longit~l~in~l axes ofthe burners 15 are offset with respect to the
longit~l-lin~l axes ofthe catalytic vessels 10 in such a way that the burners 15 ofthe two rows
of burners are advantageously located opposite one another in the region of the intermediate
space between two catalytic vessels 10.
Arrangements of burners 15 and catalytic vessels 10 other than the mirror-symmetrical
arrangement can also be selected. For example, the rows of burners can be positioned
concentrically in and around a circular arrangement of the catalytic vessels 10, which would
also result in a symmetrical arrangement. A less uniformly ordered distribution of the burners
15 and catalytic vessels 10 would also be possible in principle. However, the symmetrical
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arrangement has considerable advantages with regard to the most uniform possible thermal
effect.
The burners are preferably oriented vertically with respect to their flame direction,
specifically so as to be directed from top to bottom. It would also be possible in principle to
,!, arrange the burners diagonally to the longitudinal axis ofthe catalytic vessels 10 or even at
right angles from the side thereof, although the parallel arrangement is preferable because of
.~ the more uniform temperature distribution. In a further development of the invention, a
',~ plurality of rows of catalytic vessels 10 arranged parallel to one another so as to alternate with
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the rows of burners could also be provided instead of a single row. In this way, it is possible
to adapt to the required reactor capacity in virtually any manner desired without having to
alter the construction of the individual catalytic vessels 10.
As is shown by the longitu~lin~l section in Fig.. 1, the reactor according to the
invention, which is shown by way of example, has a housing 13 which is formed of refractory
material. The lower portion ofthe housing 13 widens to form a radiation chamber 14 which
receives the burners 15 in wall openings in its roof. The catalytic vessels 10, only one of
which is shown in longitudin~l section, penetrate into the radiation chamber 14 from above by
approximately one third of their length. Every catalytic vessel 10 has a product gas feed line
17 for the input material which is to be catalytically converted. In this example, the product
gas feed line 17 is arranged laterally at the upper end ofthe housing 13. Since an ascending
pipe 18 which extends practically along the entire axial length of the catalytic vessel 10 is
installed concentrically in the catalytic vessel 10 in each instance, the product gas outlet line 19
through which the products generated in the catalytic reaction are removed can likewise be
arranged laterally in the upper part of the catalytic vessel 10. This has the advantage that each
of the catalytic vessels 10 can be fitted at their upper end in the housing 13 so as to be freely
suspended. Since a sufficiently large distance is allowed for between the bottom end of the
catalytic vessel 10 and the base of the housing 13 in the nonoperational state, the catalytic
vessels 10 can expand freely downward in the operating state when heated. If the product gas
outlet line 19 were to be connected to the end of the catalytic vessel 10 located opposite the
process gas feed line 17, costly design steps would have to be undertaken to compensate for
thermal expansion so as to prevent damage to the pipelines.
Since the process gas feed line 17 and the product gas outlet line 19 are not arranged
at the extreme upper end ofthe catalytic vessel 10, but rather close below it, the upper end
face could be provided with an easily accessible, removable cover 12 through which the
catalytic material can be introduced and exchanged when required. The catalytic vessels 10
are enclosed at a ~lict~nce along their entire length penetrating into the radiation chamber 14
by a tubular heat distributor 16 which is formed of a material with good heat conducting
properties, preferably a heat-resistant steel, so that an annular gap 21 is formed between the
wall of the catalytic vessel 10 and the heat distributor 16. This is shown more fully in Fig. 1 a
which shows a detailed enlargement of detail X from Fig. 1. It will be seen that the catalytic
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vessel 10 is tightly closed at its lower end side by a base. The product gas flowing downward
through the catalytic mass 10 located in the annular chamber 11 is deflected in the region of
the end side and can flow through an annular through-gap into the ascending pipe 18 and can
be extracted at the bottom. This gap passage is formed in that the ascending pipe 18 ends at a
short distance from the base of the catalytic vessel 10. The product gas outlet line 19 is
connected with the j~ecen~1ing pipe 18 (Fig. 1) and guided out through the wall ofthe catalytic
vessel 10. The tubular heat distributors 16 are fitted to the roof of the radiation chamber 14.
The length of the heat distributors 16 is so dimensioned that a suff1ciently large distance is
m~int~ined between the base of the housing 13 and the end side of the heat distributor 16
while taking into account the thermal lon~it~l~lin~l expansion during operation, so that the hot
combustion gas can flow upward into the annular gap 21 between the heat distributor 16 and
the catalytic vessel 10 via the entrance gap. In many cases, it is advisable to provide slots in
the wall of the heat distributors 16 so that the combustion gases can enter the gap 21. This
has the advantage that the flow conditions of the combustion gases can be adjusted in a
directed manner exclusively by the selection of the quantity and dimensions of these slots
without having to change the external geometry ofthe heat distributors 16 and catalytic
vessels 10.
The heat needed for the endothermic reaction is fed to the process gas flowing through
the catalytic vessel 10 from the partial flow of the combustion gases entering through the gap
21. However, since the heat distributor 16 conducts heat, this combustion gas flow, at the
same time that it gives offits heat, absorbs heat again from the radiation chamber 14 through
the wall ofthe heat distributor 16 so that it retains virtually the same temperature until
reaching the height ofthe roofofthe radiation cllamber 14. But this temperature lies
substantially below the adiabatic flame temperature, since heat is constantly given offto the
process gas for the endothermic catalytic reaction during combustion.
Above the roof of the radiation chamber 14, the catalytic vessels 10 are enclosed at a
slight distance by the refractory material of the housing 13 similarly to the manner in which
they are enclosed by the heat distributor 16 so that the gap 21 is continued upward. Of
course, it would also be possible to continue the heat distributors 16 until the upper end of the
housing 13 and to arrange the housing wall only around the upper portion of the heat
distributors. In the upper portion ofthe catalytic vessel 10, i.e., along approximately 2/3 of its
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length in the example shown in Fig. 1, the temperature of the combustion gases drops
continuously due to the constant delivery of heat and the absence of any possibility of
absorbing heat. The cooled combustion gas leaves the reactor through the flue gas outlet line
22 and can be reused in a convection portion of a more complex overall inst~ tion, not
shown.
Figs. 4 and 4a show a modified embodiment form of the reactor according to the
invention. Parts pe~o~ ng functions identical to those shown in Figs. 1 to 3 are provided
with the same reference numbers and need not be discussed again. In contrast to the first
embodiment example, this reactor has a helical baffle 24 within the annular gap 21, this baffle
24 displacing the through-flowing combustion gas flow in an addi~ional rotational movement
about the longit~l~in~l axis ofthe catalytic vessel 10 so that a particularly uniform temperature
distribution is achieved in the heating of the reactor due to the helical overall movement of the
combustion gas flow which is brought about in this way.
The lower end of the catalytic vessel 10 with the heat distributor 16 iS shown as an
enlarged detail in Fig. 4a. As in Fig. 4, an installation which acts as a heat exchange promoter
23 and is constructed in the form of a preferably tubular flow displacement body which
extends coaxially subst~nti~lly over the entire length of the ascending pipe 18 can be seen in
the ascending pipe 18. Its outer diameter is smaller than the inner diameter of the ascending
pipe 18 so that an annular space 25 is formed between the two diameters. The tubular body of
the heat exchange promoter 23 is tightly sealed on the inside (e.g., in the lower portion) so
that the product gas formed by catalysis can only flow up through this annular space 25 to the
product gas outlet line 19 after leaving the annular space 11 which is filled with the catalytic
material. In this way, the product gas is compelled to an intimate heat exchange with the
downward flowing process gas to be heated, which is effected through the wall of the
ascentling pipe 18. Of course, a flow displacement body formed of solid material could also
be used instead of a tubular heat exchange promoter 23.
Figs. 5 to 7 show another embodiment form of the invention, the construction of the
housing 13 and the arrangement ofthe burners 15 and catalytic vessels 10 being shown
schematically in Figs. 5 to 6? while Fig. 7 shows a more detailed view of the catalytic vessel
10. Again, parts having the same function are provided with identical reference numbers.
This embodiment example differs from the first embodiment example in that the radiation
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chamber 14 practically occupies the entire housing 13 and the heat distributors 16 extend in
each instance substantially along the entire axial length of the catalytic vessels 10. In this way,
the combustion gas flowing upward through the gap 21 can give offheat to the process gas
along its entire path and can absorb heat at the same time through the wall of the heat
distributor 16 so that its temperature is m~int~ined practically constant along this path. An
isothermal catalytic reactor is formed in this way. Consequently, the product gas flowing
upward through the ascending pipe 18 has the same temperature as the process gas flowing
downward through the annular space 11 so that there is no transfer of heat between these two
gas flows. The in~t~ tion of a flow displacement body in the ascending pipe can therefore be
omitted.
A particular advantage of the invention consists in that the output of a catalytic reactor
can be changed within wide limits in the planning stage simply as a result of the quantity of
catalytic vessels 10 and burners 15 without ch~nging the individual catalytic vessels 10. As a
result of the nonadiabatic combustion, the flame temperatures are appreciably reduced so that
no complicated and accordingly expensive refractory constructions are required. Further, the
thermal loading of the tubular heat distributor remains comparatively low.
. A construction corresponding to the embodiment forms in Figs. 1 to 4 is suitable
particularly for the steam reformation of hydrocarbons, while an isothermal reactor such as
that shown in Figs. 5 to 7, is advantageous particularly for dehydrogenation processes such as
those mentioned in the introduction.
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