A nonlinear model is developed for a SEFFFE system employed for concentrating weak black liquor in ail Indian Kraft Paper Mill. The system incorporates different operating strategies such as condensate-, feed- and product-flashing, and steam- and feed-splitting. This model is capable of simulating a MEE system by accounting variations in tau, U, Q(loss), physico-thermal properties of the liquor, F and operating strategies. The developed model is used to analyze six different F including backward as well as mixed flow sequences. For these F. the effects of variations of input parameters. T-0 and F, on output parameters such as SC and SE have been studied to select the optimal F for the complete range of operating parameters. Thus. this model is used as a screening tool for the selection of an optimal F amongst the different F. An advantage of the present model is that a F is represented using an input Boolean matrix and to chan e the F this input matrix needs to be changed rather than modifying the complete set of model equations tor each F. It is found that for the SEFFFE system, backward feed flow sequence is the best as far as S E is concerned. (c) 2007 Elsevier Ltd. All rights reserved.