In any design urea plant there is a very important pipeline connecting the High Pressure with the Low Pressure section. In this pipeline, the operating pressure reduces suddenly and there is a huge pressure drop of 130-140 bars. The high pressure drop results in flashing and thus a two-phase flow causing vibrations in this pipeline.
Solutions from process and mechanical point of view have been investigated. From process point of view there are some solutions however one has to be able to accept a somewhat more urea losses due to hydrolysis and a higher biuret content in the final product.
From mechanical point of view it is advised pay proper attention to the design and installation of the supports of this pipeline. Further sufficient bends and expansion bellows to absorb the vibrations are to be included in the design. Finally special attention has to be paid to the lay-out of the actuator in relation to the pipeline; experience has proven that a vertical installation of control valve will decrease the vibrations in comparison of a horizontal control valve.