Simulation of flat falling film evaporator system for concentration of black liquor

In the present investigation, a non-linear mathematical model is developed for the analysis of Septuple effect flat falling film evaporator (SEFFFE) system used for concentrating black liquor in a nearby paper mill. This model is capable of simulating process of evaporation considering variations in boiling point rise (τ), overall heat transfer coefficient (U), heat loss (Qloss), flow sequences, liquor/steam splitting, feed, product and condensate flashing, vapor bleeding and physico-thermal properties of the liquor. Based on mass and energy balance around an effect a cubic polynomial is developed and solved repeatedly in a predetermined sequence using generalized cascade algorithm.For development of empirical correlations for τ, U and Qloss, plant data have been collected from SEFFFE system. These correlations compute τ, U and Qloss within average absolute errors of 2.4%, 10% and 33%, respectively, when their results are compared with the plant data.