A MATHEMATICAL-MODEL OF ABSORPTION STRIPPING COLUMNS FOR REMOVAL OF AMMONIA FROM CONDENSATES

A mathematical model of absorption/stripping columns for removal of ammonia from condensates in the sugar industry is presented. The system consists of two packed columns through which air saturated with steam recirculates. In the first column physical stripping of ammonia from condensates to air and steam takes place, while in the other one absorption of this gas with simultaneous formation in the aqueous solution of ammonia sulphate from sulphuric acid takes place. The mathematical model of the columns include equations determining physico-chemical parameters of gas and liquid phases, equations of gas-liquid absorption equilibrium, equations for determination of phase flow rates through the columns, relations used to calculate column diameters, correlations of mass transfer coefficients in both phases and available specific mass transfer area, equations determining liquid hold-up on the packing, relations describing pressure drop, and balance equations for calculating packing height. A numerical simulation of the model was performed for typical conditions in Polish sugar factories and the effect of particular parameters on this process was evaluated. Results were used to select optimum process conditions which make it possible to apply a small-size installation.