Calculation of component recovery rate in Aspen
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There is a case: design of a continuous tray distillation column operating at atmospheric pressure, with the following design parameters. Feed composition: 63.2% water, 38.6% methanol (by mass)； Processing capacity: 55 t/h of water-methanol mixture ； Feed thermal state: Saturated liquid phase feed ； Feed pressure: 125 kPa ； Operating pressure: 110 kPa ； Single-board pressure drop: ≤0.7 kPa ； Top distillate: Methanol content greater than 99.5% (by mass). Bottom residue: Water content greater than 99.5% ； (Mass fraction). Reflux ratio: user-defined ； Overall tower efficiency: ET=52%. Heat source: low-pressure saturated water vapor. I have formulated the equation for calculating the recovery rate of the light key component as: Recovery rate = /. By substituting the values, the recovery rate comes out to be 0.9920. However, the recovery rate given in the example is 0.9983. I’m a beginner using Aspen; I would be extremely grateful if experts could point out where my mistake lies!
I did the calculations; it’s probably the example that’s wrong. Yours should be correct.
Methanol mass balance: 0.995*D+0.005*W=55*0.386 (D is the amount extracted from the top； W is the flow rate at the bottom of the tower). Water and material balance: 0.005D + 0.995*W = 55*0.632; D can be calculated from this equation. Methanol recovery rate: 0.995*D/55*0.386
Because when performing simulation calculations, the number of plates is an integer, which means the purity of the component obtained may be higher than the value you set; therefore, first check the composition of the components being separated!
OP, why do yourXd, Xf, Xw values directly include those quality percentages? These three values should be mole fractions, right?