Thermodynamic Model And Simulation For Desorber And Hydrolyzer Of Urea Process

Based on the comprehensive analysis of the existing thermodynamic model of NH₃–CO₂–H₂O–Urea (ACWU) system, this paper collected the vapor-liquid equilibrium experiment data and diagrams under different temperature and pressure of ACWU system. Its vapor-liquid equilibrium thermodynamic model is established with the activity coefficient method.While establishing the system of ACWU vapor-liquid equilibrium in which the hydrolysis reaction can be neglected at the conditions of temperatures from 60℃to 160℃, pressures up to 3.0MPa and the mole fraction of NH₃ up to 0.3, the activity coefficients of the real species in liquid phase was described by the extended UNIQUAC equation and the fugacity coefficients of vapor phase was calculated by the SRK equation of state. To describe vapor-liquid equilibrium better, experimental data at the same condition is added up, but the mole fraction of NH₃ is up to 0.2. The temperature was taken into account in describing the interaction energies'contribution to the excess Gibbs energy, and the interaction energy parameters were regressed by the simplex method. The model can also be used for the simulation and calculation of desorber.The average relative error between calculations of pressure from 37 groups'data of ACWU system and literature data is 9.14%, and that between calculations of pressure from 390 groups'data of ACW system and literature data is 2.77%. It turns out that the model can predict vapor-liquid equilibrium of ACW and ACWU system under wider range of tempreture, pressure and concentration. It also provides a solid theoretical basis for simulation, calculation and optimizing of the equipments in the recovery system at mesolow pressure.