The invention describes a process whereby reactor effluent is first depressurized via a valve whereafter it is heater in a heat exchanger in co-current way. New is that the diameter of the heat exchanger tubes are smaller than usual in order to maintain high velocities and avoid crystallization problems. Downstream the heater a gas-liquid separator is installed where after the liquid (mainly urea and water) become in contact with air while heat is introduced to vaporize the water.
As it is not necessary with this invention to maintain a large volume of reactor effluent to solve the crystallization problems, this invention leads to a low biuret product.

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1941 Porter Solvay 22671133 Urea process.pdf