Feed stage rigorous simulation

The easiest way to use a shortcut distillation model is to start by estimating the minimum reflux and number of stages. The optimum reflux ratio is usually between 1.05 and 1.25 times the minimum reflux ratio, Rmm, so 1.15 x Rmin is often used as an initial estimate. Once the reflux ratio is specified, the number of stages and optimum feed stage can be determined. The shortcut model results can then be used to set up and initialize a rigorous distillation simulation. 

Liquid-liquid extraction unit (Fig. 3.16) simulates a counter-current extraction device consisting of equilibrium stages. Multiple feeds, side products and heaters/coolers may be considered. Accurate modelling of liquid-liquid equilibrium is essential, particularly when the unit is involved in a recycle. If the thermodynamics is not reliable, a simple black box unit is recommended for closing the recycles. The analysis and design of a selected equipment type can be done as stand-alone unit by using rigorous models. 

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