CA2175236A1

CA2175236A1 - Catalytic reactor for endothermic reactions

Info

Publication number: CA2175236A1
Application number: CA002175236A
Authority: CA
Inventors: Francesco Giacobbe
Original assignee: Individual
Current assignee: Vodafone GmbH; Technip Holding Benelux BV
Priority date: 1993-10-29
Filing date: 1994-10-26
Publication date: 1995-05-04
Also published as: ITRM930719A0; CZ117696A3; NO961114D0; NO961114L; EP0725675B1; IT1261857B; FI961746A0; DE59402559D1; BR9407895A; WO1995011745A1; ITRM930719A1; JPH09503961A; ATE152003T1; AU8057094A; GR3023315T3; DK0725675T3; EP0725675A1; CN1133570A; FI961746A; ES2100745T3

Abstract

The invention is directed to a catalytic reactor for endothermic reactions. The catalyst is located in a housing (13) which is formed of refractory material, at least one tubular catalytic vessel (10) being arranged in the interior ofthe housing (13). In order to provide a catalytic reactor in which 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, the invention proposes the following: a plurality of catalytic vessels ( 10) are arranged at a distance from one another in the housing (13), a plurality of burners (15) are arranged in the housing (13) in such a way that the catalytic vessels (10) lie between the burners (15), and the flame region ofthe burners (15) lies in the region ofthe heat distributors (16) in each instance so as to ensure nonadiabatic combustion.

Description

T~
-- 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 ", -- ~17523~

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;

., ' 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 . .
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 ., - 2~7S23~

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 i 21~ 236 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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Claims

1. Catalytic reactor for endothermic reactions having a housing (13) which is formed of refractory material, the interior of the housing (13) being heatable by hot combustion gases which can be guided out through a flue gas outlet line (22), wherein a plurality of catalytic vessels (10) are arranged at a distance from one another in the interior of the housing (13), these catalytic vessels (10) being filled, at least in the vicinity of their outer wall, with a catalytic material and having a process gas feed line (17) for the material to be processed catalytically as well as a product gas outlet line (19) for the product formed in the catalytic reaction, and wherein a plurality of burners (15) are arranged in the housing (13) in such a way that the catalytic vessels (10) lie between the burners (15), and the flame region of the burners (15) lies in the region of the catalytic vessels (10) in each instance so as to ensure a nonadiabatic combustion, characterized in that the catalytic vessels (10) are enclosed at least along a portion of their axial length by a tubular heat distributor (16), which is formed of material with good heat conducting properties, in particular metal, while leaving open a narrow annular gap (21) to allow the passage of the hot combustion gases, in that an ascending pipe (18) is provided in the catalytic vessels (10) which are tightly closed at their bottom end by a base, this ascending pipe (18) being arranged coaxially to the longitudinal axis, extending substantially along its entire axial length, and ending at a slight distance from the base of the catalytic vessel (10) so as to leave a through-gap, wherein an annular space (11) is formed between the ascending pipe (18) and the outer wall of the catalytic vessel (10), this annular space (11), through which the process gas can flow from top to bottom, being filled with the catalytic material, and wherein the product gas outlet line (19) adjoins at the top of the ascending pipe (18).

2. Reactor according to claim 1, characterized in that the catalytic vessels (10) are arranged vertically and substantially parallel to one another, in that directly adjacent catalytic vessels (10) are spaced equidistantly, and in that the burners (15) are arranged symmetrically with respect to the catalytic vessels (10).

3. Reactor according to claim 2, characterized in that the longitudinal axis of at least some of the catalytic vessels (10) lies in a common plane, and in that the burners associated with these catalytic vessels (10) are arranged adjacent to one another in two rows in a mirror-symmetrical manner with respect to the plane of the longitudinal axes of the catalytic vessels (10).

4. Reactor according to one of claims 2 or 3, characterized in that the burners (15) are arranged so that their flame direction is vertical, in particular with their flame being directed from top to bottom.

5. Reactor according to one of claims 3 to 4, characterized in that the catalytic vessels (10) and burners (15) are provided alternately in a plurality of parallel adjacent rows.

6. Reactor according to one of claims 2 to 5, characterized in that the longitudinal axes of the burners (15) associated with a row of catalytic vessels (10) are offset with respect to the longitudinal axes of the catalytic vessels (10) in such a way that a burner (15) of one row of burners is, in each instance, located opposite a burner (15) of the other row of burners in the intermediate space formed between the catalytic vessels (10).

7. Reactor according to one of claims 1 to 6, characterized in that the heat distributors (16) extend substantially along the entire axial length of the catalytic vessel (10) to form an isothermal reactor.

8. Reactor according to one of claims 1 to 6, characterized in that the heat distributors (16) extend only along a portion of the axial length of the catalytic vessel (10), in particular only along the lower portion of the catalytic vessel (10), and in that the catalytic vessels (10) are enclosed by the refractory material of the housing (13) along the remaining portion of their axial length accompanied by a continuation of thenarrow annular gap (21).

9. Reactor according to one of claims 1 to 8, characterized in that a helical baffle (24) is arranged in the annular gap (21) and displaces the combustion gas flowing through the gap (21) into a helical flow rotating externally about the catalytic vessel (10).

10. Reactor according to one of claims 1 to 9, characterized in that a heat exchange promoter (23) in the form of a preferably tubular flow displacement body is arranged in the ascending pipe (18) and extends coaxially substantially along the entire length of the ascending pipe (18) so as to leave open a second annular space (25) through which the product gas flows from the bottom to the top.

11. Reactor according to one of claims 1 to 10, characterized in that the catalytic vessel (10) is provided at its upper end at the end side with a tightly closing cover (12) located outside the housing, through which cover (12) the catalytic material can be introduced, and in that the process gas feed line (17) and the product gas outlet line (19) are guided laterally out of the upper portion of the catalytic vessel (10) below the cover (12).

12. Reactor according to one of claims 1 to 11, characterized in that the catalytic vessels (10) and the heat distributors (16) are fitted to the upper part of the housing (13) so as to be freely suspended, wherein their lower end ends in each instance at least at a distance from the base of the housing (13) such that a free suspension is ensured while allowing for thermal longitudinal expansions during operation and a sufficiently large entrance gap (20) remains to allow the combustion gases to flow into the annular gap (21).

13 . Reactor according to one of claims 1 to 12, characterized in that the heat distributors (16) have slots in their wall at their lower ends, the combustion gases entering into the annular gap (21) through these slots.