Chemistry of inorganic compounds – Nitrogen or compound thereof – Ammonia or ammonium hydroxide
Reexamination Certificate
1998-03-19
2001-10-09
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Ammonia or ammonium hydroxide
C422S148000, C422S198000, C422S198000, C422S198000, C423S360000, C423S659000, C518S707000
Reexamination Certificate
active
06299849
ABSTRACT:
DESCRIPTION
1. Application Field
The present invention relates to a method for in-situ modernization of a heterogeneous exothermic synthesis reactor, including an external shell in which a plurality of superimposed catalytic beds in mutually spaced relationship are supported.
More specifically, the invention relates to a modernization method of the type comprising the preliminary step of:
providing at least a first catalytic bed in an upper portion of said shell and at least a second catalytic bed in a lower portion of said shell;
said first and said second bed being loaded with a first catalyst having a predetermined activity.
In the description given below and in the following claims, the term:“in-situ modernization”, is understood to mean the on-site modification of a pre-existing reactor in order to improve its performances and obtain e.g. a production capacity and/or a conversion yield comparable to those of a newly-built reactor.
In the terminology of the field, this type of modernization is also termed retrofitting or revamping.
In the description given below and in the following claims, the term:“upper portion respectively lower portion of the shell”, is understood to mean the space within the shell that is defined in the upper respectively lower half of the same. More precisely, the upper portion takes up generally about 20-50% of the internal space of the shell, while the lower one takes up about 50-80% of the same.
As is known, in the field of heterogeneous exothermic synthesis in general and, more particularly, in ammonia and methanol production, a double requirement must be satisfied, namely to increase, it is necessary to satisfy a two-fold need, i.e. the one hand increase the production capacity of pre-existing synthesis reactors and, on the other hand, achieve an improvement of conversion yield and a reduction of the reactor energy consumption.
2. Prior Art
For the purpose of satisfying the above-identified need, the so-called technique of modernizing the pre-existing reactors, aiming at avoiding a costly replacement of the latter and achieving at the same time the maximum conversion compatible with the available catalyst volumes, has become increasingly accepted.
For instance, in U.S. Pat. No. 5,585,074 a modernization method is described based on the replacement of the catalytic bed(s) of the pre-existing reactor with new beds of the high-yield radial or axial-radial type, and wherein the intermediate cooling of the gases flowing between the various catalytic beds are effected in the modernized reactor by indirect heat-exchange in two gas-gas heat exchangers located between the first and the second bed, respectively in the third catalytic bed.
Although advantageous in some ways, the modernization methods according to the prior art do not allow to achieve conversion yields comparable to those that are obtainable with the latest synthesis reactors which use a special ruthenium-based catalyst at high reaction activity.
In fact, such methods do not take into consideration the possibility of modernizing the pre-existing reactors by realising a structure than can contain effectively and at low investment costs the aforesaid high activity catalyst.
This is mainly due to the fact that the arrangement and the volumes of the catalytic beds of the modernized reactor are conceived for a conventional catalyst and therefore poorly suitable for use with a high activity catalyst.
In particular, the kinetic and thermodynamic characteristics of conventional catalysts require reaction spaces that are substantially greater than those required if a high activity catalyst is utilised.
Accordingly, the total reaction space of a reactor modernized according to the methods of the prior art, is markedly oversized for a utilisation with a high activity catalyst or, should one wish to exploit as much as possible said reaction space, the amount of high activity catalyst to be loaded in the beds would be such as to require prohibitive investment costs.
With regard to this aspect, it is worth stressing that the ruthenium-based catalyst has had till now—because of its extremely high costs—a very limited application in the practice, even though its particular reaction activity has been known for over ten years and the need of increasing the conversion yield of heterogeneous exothermic synthesis reactors is increasingly felt in the field.
Anyway, the use of such catalyst is nowadays limited to newly built reactors, whose realisation involves therefore very high investment costs, in addition to the cost of the catalyst.
SUMMARY OF THE INVENTION
The problem underlying the present invention is that of providing a method for modernizing a heterogeneous exothermic synthesis reactor, which allows to markedly increase the conversion yield over that obtainable by the modernization methods in accordance with the prior art, with low investment and operating costs and with low energy consumption.
Said problem is solved by a method of the type set forth above, which is characterised by the fact of comprising the steps of:
providing a lowermost catalytic bed in said lower portion of the shell having a reaction volume smaller than the reaction volume of said second catalytic bed;
loading said lowermost catalytic bed with a second catalyst having an activity higher than the one of the first catalyst loaded in the other beds.
In the description given below and in the following claims, the term:“reaction volume”, is understood to mean the volume of a catalytic bed taken up by the catalyst, and therefore the space in the bed where the synthesis reaction actually takes place.
Advantageously, the method according to the present invention allows to obtain—while keeping the external structure unchanged—a more effective reactor from the point of view of the conversion yield and thus an increase in the production capacity, by loading a high yield catalyst in a suitably sized lowermost catalytic bed.
In particular, thanks to the present method it is possible to effectively integrate in a pre-existing reactor the utilisation of conventional type catalyst with high activity catalyst, improving in this way radically the performances of the reactor, while keeping the investment costs substantially unchanged with respect to those necessary for the modernization of a reactor according to the methods of the prior art.
Moreover, being in condition of utilising high activity catalyst it allows to operate in the lowermost bed at temperatures lower than the conventional ones, obtaining in this way also savings in the operating costs and in the energy consumption, with respect to the aforementioned methods of the prior art.
Preferably, the lowermost catalytic bed is loaded with a catalyst based on graphite-supported ruthenium, such catalyst having a high reaction activity and at the same time a long working life, as it does not deteriorate and has an excellent resistance at the temperature and pressure operating conditions in the inside of the reactor.
Particularly satisfactory results have been obtained by providing within the shell a lowermost catalytic bed having a reaction volume comprised between 5% and 50% the reaction volume of said second bed, preferably between 10% and 25%.
Additionally, according to a particular and advantageous embodiment of the present modernization method, three catalytic beds are provided in said shell, said first catalytic bed in said upper portion of the shell, said second catalytic bed and said lowermost catalytic bed in said lower portion of the shell, respectively.
In this way, both the kinetic and thermodynamic configuration of the reactor and the utilisation of the available reaction volumes are optimized, so as to drastically increase the conversion yield, while minimizing the investment costs.
In a preferred embodiment of the invention, the present method further comprises the step of:
equipping said lowermost catalytic bed with means for feeding to the same a radial or axial-radial flow of reagent gases.
In so doing, the pressure drops caused by the reaction mixture passing through the c
Filippi Ermanno
Pagani Giorgio
Ammonia Casale S.A.
Langel Wayne
Sughrue Mion Zinn Macpeak & Seas, PLLC
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