Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Patent
1996-12-16
1999-04-06
Tran, Hien
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
422193, 422211, 422311, 277650, E04B 168, B01J 804
Patent
active
058914056
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to an exothermic heterogeneous catalytic synthesis reactor of the type comprising: plate for containment of the catalyst, shell.
As is known, when exothermic heterogeneous catalytic reactions are carried out within a synthesis reactor, the external shell and bottom plate of the catalytic beds arranged in the shell being subjected to a temperature increase undergo dimensional changes due to the thermal expansion of the materials which make them up. These dimensional changes can cause undesired phenomena at the connection zone between the shell and the bottom plate, such as for example outlet of the catalyst contained in the bed or damage to the bottom plate structure.
In the field of exothermic heterogeneous catalytic synthesis reactors there is an ever growing requirement for providing a device capable of ensuring between the external shell and the bottom plate of the catalytic beds an effective catalyst seal, constant and long lasting so as to avoid the drawbacks mentioned above.
2. Prior Art
In order to meet the above mentioned requirement, connection devices are provided between the external shell and the bottom plate of the catalytic beds, which comprise a compressible material, e.g. ceramic cords or braids, appropriately arranged in a space defined between the bottom plate and the shell, have become ever more widely used.
If in a reactor for heterogeneous synthesis of ammonia or methanol, the expansion coefficient of the material of the external shell, e.g. of low alloy steel, is different from that of the material of the bottom plate, e.g. of stainless steel, the high operating temperatures due to the exothermic nature of the reaction cause a dimensional variation of the shell on the order of 5 mm to 25 mm, which is much less than that of the bottom plate which is generally from 10 mm to 40 mm.
Consequently, the space between the bottom plate and the shell will be calculated at the time of installation sufficiently ample to allow for the different expansion rates of the materials.
The use of compressible material in the air space permits making a seal between the bottom plate and the shell capable of at least partially absorbing the thermal expansion of the materials.
In the terminology of the field this type of seal is generally termed stuffing box or packing box seal.
Although substantially meeting the purpose the above mentioned device exhibits a series of drawbacks as set forth below.
A first shortcoming is the fact that the device in accordance with the prior art is capable of absorbing only partially the dimensional variations caused by heat expansion of the materials. The compressible material arranged between the bottom plate and the external shell possesses indeed limited compressibility characteristics which make the stuffing or packing box seal effective only in situations of low differential expansion of the materials, such as for example if the different heat expansion between the bottom plate and the shell does not exceed 1 mm to 2 mm.
Consequently, in an ammonia or methanol synthesis reactor where, as seen above, there is a differential expansion of the materials of even 15 mm, the use of the above described device is unsatisfactory because during the various cooling/heating cycles which characterize the life of a reactor of this type, the compressible material is crushed irreversibly and thus does not ensure any longer the necessary compensation for the different heat expansions of these materials, with the risk of a leak of the catalyst contained in the bed.
A second drawback is connected with the first and lies in the fact that the compressible material tends to deteriorate rapidly in time because of the unavoidable passage of the gas through it which erodes it.
Consequently, even after a brief period of operation of the synthesis reactor it is no longer possible to ensure optimal and reliable catalyst seal by the connection device.
A third drawback of the connection device in accordance with the prior art is that
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Bianchi Luca
Rizzi Enrico
Methonal Casale S.A.
Tran Hien
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