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

Abstract 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 ( Q loss ), 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 Q loss , plant data have been collected from SEFFFE system. These correlations compute τ , U and Q loss within average absolute errors of 2.4%, 10% and 33%, respectively, when their results are compared with the plant data.

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