| Urea is one of the most important nitrogen-based fertilizers andchemical material, which is widely used around the world. Since itsproduction was industrialized in 1922, urea process has attracted muchresearch from different countries. Innovation and achievement has beenmade in the synthesis mechanism, thermodynamics property andflowsheeting. This work is started with the basis thermodynamicsprinciples, and then the process flowsheeting is researched, and finally asoftware is developed in order to guide the production. The maincontents of this paper are as follows:1. NH3-CO2-H2O-Urea system, which was presented by former, issummarized. The extended UNIQUAC equation is applied tocalculate the vapor-liquid equilibrium involved in the ureaprocess system. The program to resolve this mathematics modelwas focused on and a robust algorithm was developed.2. The equilibrium stage model of urea reactor and stripper areproposed based on the former system. The calculated results areclosed to design data, and then the model is used in theflowsheeting simulation as one of the modules. Other unit modules have been based.3. Based on these unit modules, the full process is simulated.Since the urea process is a complex process with a number ofcircumfluence, it's difficult to resolve it in a lump. So firstly, themain streams are picked out and being resolved, and then theothers.4. In the need of increasing yield and decreasing energy cost, therule going with the load is analyzed. Operation temperature andNH3/CO2 are selected as optimizing variables.
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