2017 08 Lines Graham Coping with Vacuum
In urea industry, the evaporation process is used to increase the concentration of urea/water solution by vaporizing the water under certain conditions of vacuum and temperature, these conditions are essential to avoid urea crystallization and formation of any undesired substance.In operation, a high-pressure motive steam enters the steam chest at low velocity and expands through the converging-diverging nozzle. This results in a decrease in pressure and an increase in velocity. Meanwhile, the suction fluid enters at the suction inlet. The motive fluid, which is now at high velocity, entrains the suction fluid and combines with it. The two fluids are then recompressed through the diffuser. Potential energy is converted to kinetic energy; thus, velocity increases and pressure decreases. While the ejector itself can be quite simple, specifying the optimum system to meet specific needs is not simple. Important parameters involved in ejector sizing and staging include pressure of motive gas, required discharge pressure, suction pressure and relative mass flow rates of motive fluid to suction fluid.This paper provides a deeper review of ejector systems and highlights the importance of ejector systems in urea plants.