Urea synthesis process with liquid carbamate recycle, in which the reactor effluent is divided into major and minor streams. The major stream is reduced in pressure and subjected to heating and substantial carbamate decomposition to ammonia and carbon dioxide decomposer off gas, either directly or after preliminary ammonia separation. The minor stream is reduced in pressure and is contacted with decomposer off gas and fresh make up carbon dioxide, either directly or after preliminary ammonia separation, and in indirect heat exchange with a relatively colder fluid, whereupon ammonium carbamate is formed from the mixture of the minor stream, fresh make up CO.sub.2 and decomposer off gas in an aqueous solution of urea and the resulting solution is recycled to the urea synthesis reactor.
Disclosed herein is a process of synthesizing urea including reacting ammonia and carbon dioxide at a urea synthesis pressure and temperature in a urea synthesis zone, separating excess ammonia and unreacted ammonium carbamate from the thus-obtained urea synthesis melt as a gaseous mixture containing ammonia and carbon dioxide, recirculating the gaseous mixture to the urea synthesis zone, and, on the other hand, obtaining urea from an aqueous urea solution which has been obtained by separating the excess ammonia and unreacted ammonium carbamate. The above process features ingeniously combined conditions of various process steps. It produces urea using less high-pressure steam and recovers less low-pressure steam. A stripping operation making use of carbon dioxide can be effectively incorporated in the above process. The above process permits to cut the construction cost of a urea synthesis plant.
Ammonium carbamate, in solution with urea, water and ammonia and under high temperature and pressure is cooled to below its crystallization temperature while being subjected to an elevated pressure. The crystallized substance formed is then dried, crushed, and pelletized with the aid of a binding agent to produce pellets having substantial strength and stability, and having particular utility as a deicer for roadways.
In a process for decomposing a carbamate aqueous solution coming from a urea recovery section of a urea production plant at a predetermined temperature by indirect heat exchange with a heating fluid having a different predetermined temperature, the temperature difference between said carbamate aqueous solution and said heating fluid is reduced to a value not higher than 70.degree. C.
