Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Reexamination Certificate
2001-06-15
2004-03-09
Caldarola, Glenn (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
C564S067000, C564S068000, C564S070000, C564S071000, C564S072000, C422S105000, C422S198000, C422S198000, C422S198000
Reexamination Certificate
active
06702992
ABSTRACT:
FIELD OF APPLICATION
The present invention relates to a method for the modernisation of a plant for urea production according to the process with stripping with carbon dioxide.
More specifically, the invention relates to a method for the modernisation of a plant for urea production of the type comprising:
a reactor for urea synthesis;
means for feeding ammonia and carbon dioxide to the reactor for urea synthesis;
a stripping unit with carbon dioxide for subjecting a reaction mixture comprising urea, carbamate and free ammonia in aqueous solution leaving the reactor to a treatment of partial decomposition of carbamate and partial separation of free ammonia, thus obtaining a flow comprising ammonia and carbon dioxide in vapour phase and a flow comprising urea and residual carbamate in aqueous solution, respectively;
a recovery section for the flow comprising urea and residual carbamate in aqueous solution leaving the stripping unit for separating urea from the residual carbamate in aqueous solution;
at least one vertical condensation unit of the film type, comprising a tube bundle for subjecting to partial condensation the flow comprising ammonia and carbon dioxide in vapour phase leaving the stripping unit, thus obtaining a liquid flow comprising carbamate in aqueous solution and a gaseous flow comprising ammonia and carbon dioxide in vapour phase;
means for respectively feeding the flow comprising carbamate in aqueous solution and the flow comprising ammonia and carbon dioxide in vapour phase to the reactor for urea synthesis;
means for feeding a gaseous flow comprising one or more passivating agents, inert with respect to the synthesis reaction of urea, to the stripping unit and from the stripping unit to the reactor for urea synthesis through the condensation unit.
In the following description and enclosed claims, with the term “modernisation”, it is intended to mean the modification of a pre-existing plant with the purpose of improving its performance and obtaining, for example, an increase of the production capacity and/or of the conversion yield as well as a reduction of the energy consumption. In particular, the modernisation of a urea plant according to the present invention foresees to increase the capacity, maintaining the main equipment of the high pressure synthesis section (synthesis loop).
In the following description and enclosed claims, with the term “condensation unit of the film type”, it is intended to mean an apparatus wherein the condensation of the gaseous phase occurs in a liquid film, flowing downwards inside a plurality of tubes in co-current with the gaseous flow. The liquid film flows in contact with the tube wall whereas the gaseous phase flows inside the tubes.
According to a further aspect of thereof, the present invention also relates to a process for urea production as well as to a plant for carrying out such process.
As known, with respect to urea production, the need is more and more felt of having on one hand plants of always greater capacity and operation efficiency available, and on the other hand of having lower and lower investment and operation costs, as well as lower energy consumption.
PRIOR ART
To this end, methods for the modernisation of existing plants for urea production according to the stripping process with carbon dioxide have been recently set forth in the field, substantially based on the modification of the synthesis reactor, on the replacement of the apparatuses downstream the synthesis reactor with apparatuses of greater capacity and/or on the addition of new apparatuses in parallel to the existent apparatuses.
For example, in EP-A-0 796 244 a method of modernisation of a plant for urea production is disclosed, which foresees the addition of a partial decomposition step of the carbamate in aqueous solution recycled to the synthesis reactor. With this method of modernisation, it is possible to remarkably reduce the amount of water recycled to the synthesis reactor, thus permitting to obtain an increase of the conversion yield and therefore of the production capacity of the plant.
One of the main problems that is encountered when an increase of production capacity is considered in existing plants for urea production according to a stripping process with carbon dioxide, is that of increasing the capacity of the high pressure condensation section which may comprise one or more condensation units.
The methods of modernisation for increasing the capacity of said condensation section proposed to date always foresee the insertion in parallel of additional condensation units of the film type or of a unit provided with a high exchange coefficient, for example a horizontal condensation unit of the Kettle type (pool condenser).
In some instances the replacement of the existing unit(s) with new units of greater capacity must be even taken into account.
Such provisions have a very negative impact both on investment costs and on the constructional complexity relative to the modernisation of the condensation section according to the above mentioned methods of the prior art.
Because of these disadvantages, the modernisation of plants for urea production according to the stripping process with carbon dioxide has found to date a relatively reduced application, notwithstanding the ever increasing interest of industry of modifying the existing plants—instead of replacing them with new plants—with the purpose of increasing the production capacity and decreasing the energy costs.
SUMMARY OF THE INVENTION
The technical problem underlying the present invention is therefore that of providing a method for the modernisation of a plant for urea production which allows an increase of the production capacity thereof, implies low energy consumption and investment costs and is technically easy to be implemented.
According to the present invention, this problem is solved by a method of the aforementioned type, which is characterised by comprising the steps of:
providing means for feeding a minor portion of the flow comprising ammonia and carbon dioxide in vapour phase together with a minor portion of the gaseous flow comprising one or more passivating agents leaving the stripping unit directly to the reactor for urea synthesis;
providing means for feeding a major portion of the flow comprising ammonia and carbon dioxide in vapour phase together with a major portion of the gaseous flow comprising one or more passivating agents leaving the stripping unit to such at least one condensation unit;
providing in such at least one condensation unit means for subjecting to substantially total condensation the major portion of the flow comprising ammonia and carbon dioxide in vapour phase, obtaining a flow comprising urea and carbamate in aqueous solution.
As far as the term major portion is concerned, this indicates a portion greater than 50% of the total flow of ammonia and carbon dioxide in vapour phase coming out of the stripping unit. Depending on the operating conditions in the synthesis reactor, the major portion can be in a range between 65 and 85% of such flow, for example between 70 and 75%.
Advantageously, the present invention permits to remarkably increase the exchange coefficient and therefore the efficiency of the condensation section, permitting a debottlenecking of the existing plant to full advantage of the overall production capacity, which may be therefore optimally increased.
All this is attained in a simple and effective way, with minimum and quite secondary interventions in the high pressure synthesis section that is thus maintained substantially unchanged, and with low energy consumption.
Accordingly the investment, implementation and operation costs are considerably lower than the costs required by the methods of modernisation according to the prior art.
In fact, thanks to the present method, the pre-existing condensation section is not upgraded nor replaced with new apparatuses, but advantageously preserved, requiring only small internal modifications of the condensation unit(s) in such a way to obtain a substantially total condensation of t
Pagani Giorgio
Zardi Federico
Caldarola Glenn
Urea Casale S.A.
Wachtel Alexis
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