A column containing eight theoretical plates and reboiler is assumed, with the feed entering on plate 5, numbered from the column top. The feed consists of three components : benzene, toluene and xylene. The modelling approach follows closely that of Luyben (1973, 1990).
Each component of the mixture is expressed by a separate component mass balance. Using mole fractions one balance is omitted ans replaced by the condition that the sum of the mole fractions equals unity.
Assumptions
The system is assumed to be ideal, with equilibrium described by a constant relative volatility, the liquid components have equal molar latent heats of evaporation and there are no heat losses or heat of mixing effects on the plates. Hence the concept of constant molar overflow and the use of mole fractions are allowable.
The liquid hold up in the reboiler, reflux drum and on the column plates is constant and the liquid volumes are well mixed regions of uniform composition.
The reboiler provides a constant vapour boil-up rate, which remains constant with respect to time.
The column plates have 100% plate efficiency and act as theoretical plates.
Vapour phase dynamics are neglected.
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