Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Patent
1997-03-07
1998-05-12
Cain, Edward J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
B01J 804
Patent
active
057500800
DESCRIPTION:
BRIEF SUMMARY
FIELD OF APPLICATION
In a general aspect, the present invention relates to a method for in-situ modernization of reactors for the urea synthesis at high pressure and temperature.
The present invention also relates to a reactor for the urea synthesis at high pressure and temperature particularly but not exclusively achievable by means of the above said method.
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 performance and obtain e.g. greater production capacity and/or greater conversion yield and/or reduction in energy consumption.
In the terminology of the field this type of modernization is also termed "retrofitting" or "revamping".
In the field of urea synthesis at high pressure and temperature, the requirement for increasing the conversion yield of synthesis reactors to improve their Production capacity and reduce energy consumption in the urea plant is increasingly felt.
PRIOR ART
In order to satisfy said requirement, synthesis reactors comprising a vertical tubular shell in which is supported a plurality of superimposed horizontal perforated plates in mutually spaced relationship have been becoming increasingly used.
The urea is produced by intimate contact of a liquid phase and a gaseous phase comprising ammonia (NH.sub.3) and carbon dioxide (CO.sub.2) flowing co-currently in the reactor from below upward.
The perforated plates have the function of mixing together said phases to facilitate their intimate contact and hence exchange of mass and heat indispensable for conversion of the reagents, NH.sub.3 and CO.sub.2, into urea.
Synthesis reactors in accordance with the prior art are mainly of two types depending on the perforated plates used.
A first type of reactor comprises a plurality of superimposed perforated plates extending horizontally over the entire cross section of the reactor and in which is defined a plurality of holes for passage of a two-phase gas and liquid flow.
Since the liquid and gaseous phases pass through the same holes, there is alternating passage of gas and liquid with a pulsing flow which prevents intimate gas and liquid mixing. As a result there are low mass and heat transfer coefficients and hence low conversion yield.
A second type of reactor comprises a plurality of superimposed horizontal perforated plates in mutually spaced relationship. Between the peripheral edge of each of these plates and the internal wall of the reactor is defined an annular aperture.
Even in this case however it is not possible to obtain the desired intimate mixing between the liquid phase and the gaseous phase because the liquid flows preferably along said peripheral apertures while the gas tends to coalesce in the central part of the reactor.
Since they do not ensure effective intimate contact between the reagents the reactors in accordance with the prior art are not able to permit an optimal exchange of material and heat, which is the basic condition for achieving optimal conversion yield. Said reactors therefore operate far below their potential production capacity with resulting high energy consumption of the urea plant.
To overcome said drawbacks, U.S. Pat. No. 5,304,353 of this applicant describes a urea synthesis reactor capable of operating at high conversion yields thanks to the use of special perforated plates shaped in such a manner as to permit homogeneous mixing of the liquid and gaseous phases.
Replacement in the reactors according to the prior art described above of the original perforated plates by plates of new conception described in U.S. Pat. No. 5,304,353, although advantageous as regards conversion yield, necessitates a high investment cost not always economically justifiable.
SUMMARY OF THE INVENTION
The technical problem underlying the present invention is to increase conversion yield, improve the production capacity of synthesis reactors and reduce energy consumption in urea plants in accordance with the prior art mentioned a
REFERENCES:
patent: 5304353 (1994-04-01), Dente et al.
Cain Edward J.
Urea Casale S.A.
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