Assessment of vapour compression for the concentration of dilute urea solutions

Vapor compression (VC) is one of the important methods for desalination and solution concentration. In this work the use of vapor compression in the recovery of urea from the industrial wastewater of urea manufacturing plants was thermally and economically analyzed. Mathematical models were formulated for both mechanical and thermo-vapor compression systems; and economic models including capital, operating and maintenance costs in addition to annual savings have been also formulated. Simulation has been performed to analyze the systems and identify the most appropriate design and operating conditions. Urea concentrations in the range of 1¯5% have been evaluated for a plant of 1000 m3 of daily effluents. Concentrations of 2¯5% could be achieved by conceptually assuming that the VC system is preceded by an RO unit. VC is designed to provide further concentration to about 35%. Results indicated that it is preferable to use a thermo-vapor compression system rather than a hybrid (RO-VC system) for economic in addition to technical considerations.