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

In the present investigation, a nonlinear mathematical model is developed for the analysis of Septuple effect flat falling film evaporator (SEFFFE) system used for concentrating weak black liquor in a nearby paper mill. This model is capable of simulating process of evaporation considering variations in boiling point rise (), overall heat transfer coefficient (U), heat loss from evaporator (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, which is solved repeatedly in a predetermined sequence using generalized cascade algorithm. For development of empirical correlations for , U of flat falling film evaporators and Qloss, plant data have been collected from SEFFFE system. These correlations compute , U and Qloss within average absolute errors of 2.4%, 10% and 33%, respectively, when their results are compared with the plant data.