Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1999-03-23
2000-07-25
O'Sullivan, Peter
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564 67, 564 69, 564 70, 564 71, 564 72, C07C27304
Patent
active
060938501
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improvement in an urea synthesis process in which unreacted ammonia and carbon dioxide contained in the urea synthesis solution are separated as a gaseous mixture of ammonia, carbon dioxide and water at a pressure substantially equal to the urea synthesis pressure, the gaseous mixture is condensed under cooling in a condenser having a multi-tubular cooler, and the condensate thus-obtained is recycled to the urea synthesis.
BACKGROUND ART
Urea synthesis processes, which comprise reacting ammonia and carbon dioxide in an urea synthesis column at a urea synthesis pressure and a urea synthesis temperature, separating ammonium carbamate from the thus-obtained urea synthesis solution at a pressure substantially equal to the urea synthesis pressure as a gaseous mixture of ammonia and carbon dioxide, causing an absorption medium to absorb said gaseous mixture so as to recycle the absorbed medium to the urea synthesis column, and separately providing an urea solution from the urea synthesis solution from which said ammonium carbamate has been separated, are well known, and a variety of proposals have been made with regard to the processes. In the processes, since liquid is allowed to flow down from the condenser to the urea synthesis column and from the urea synthesis column to the stripper by head difference, it is necessary to place the condenser and urea synthesis column at high grounds.
It is well known that the above-described processes employ corrosion-preventive oxygen supplied to the urea synthesis column, condenser and stripper as a countermeasure to corrosion. The oxygen, being dissolved in the urea synthesis solution, is supplied onto anticorrosive films in the interior of the equipments, and therefore the interior of the equipments was protected from corrosion.
As described above, even if the interior was immersed in a highly corrosive recovery solution or urea synthesis solution, corrosion prevention was possible as far as corrosion-preventive oxygen was supplied, although it depended on the operating pressure and temperature, liquid conditions and other conditions.
By reasons of much time and labor taken to install and repair the equipments, there have been developed urea synthesis processes wherein urea synthesis column and other equipments are placed on the ground.
The applicant previously proposed, in Japanese Patent Application No. 234364/1997, a urea synthesis process which permits placing the synthesis column and other equipments on the ground.
The proposal relates to a urea synthesis process and an apparatus therefor in which a urea synthesis column is installed in a lower part and a vertical condenser is installed thereon or thereabove, a first downpipe is provided to make the condenser communicate with the urea synthesis zone, the condensate is allowed to flow down by gravity from the top part of the condenser through the down pipe to the bottom part of the urea synthesis zone, and the condensate thus having flowed down is allowed to flow down by gravity through a second down pipe having an opening in the top part of the urea synthesis column to the top part of a stripper, or to a process in which the condensate from a vertical condenser is sucked by an ejector using heated feed liquid ammonia as a driving fluid and introduced into the bottom part of the urea synthesis column where it is subjected to urea synthesis, and an apparatus therefor.
In the above processes, a recovery solution is supplied to the shellside of the condenser. The operating conditions in the condenser in the former process are such that the pressure is the same as that of the urea synthesis, the molar ratio of ammonia to carbon dioxide (referred to as N/C hereunder) is controlled at 2.5-4.5, the molar ratio of water to carbon dioxide (referred to as H/C hereunder) at 0.0-1.0, the residence time at 10-30 minutes, and the operating temperature is controlled to be 170-190.degree. C., so that a urea synthesis rate of 20-60% is achieved.
In the latter process, the pressure is s
REFERENCES:
patent: 3720548 (1973-03-01), Barake et al.
Fujii Hidetsugu
Kojima Yasuhiko
O'Sullivan Peter
Toyo Engineering Corporation
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