This paper presents the effect of feed composition, xF, and feed thermal conditions on benzene-toluene distillation plant performance. An interactive computer model was developed to simulate the process using vapor-liquid equilibrium (VLE) data, mass and energy balances and McCabe-Thiele method. The feed thermal conditions studied were vaporized feed (VF), feed at its boiling point (FBP) and subcooled liquid (SCL) feed. The feed composition was varied between 0.20 and 0.45 kmol/kmol. The process was simulated at fixed feed flow rate (1000 kmol/h), reflux ratio (R = 4.0) and distillate and bottoms compositions (95 and 5%, respectively). The minimum reflux ratio, theoretical and actual number of stages, reboiler duty and steam mass flow rate, and boil-up ratio changed with increasing xF according to fourth-order polynomial functions. The condenser duty and cooling water flow rate increased linearly with xF. The effect of increasing xF on the stripping section operating line (SOL) is reported separately for different feed thermal conditions. While all q-lines for VF passed at (xB, xD) with decreasing slope; the q-lines for FBP were vertical and those for SCL feed were parallel. Graphical presentations of q-lines and SOLs for increasing xF were developed in this study.
Key words: Distillation plant performance, feed composition, feed thermal conditions, number of stages, reboiler duty, condenser duty, boil-up ratio, mass and energy balances, vapor liquid equilibrium.
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