How to calculate the recovery rates of light and heavy components in distillation column design
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As the title suggests, previous calculations were related to the verification of the tower’s performance. Now, I want to carry out design calculations for the tower based on the requirements regarding inlet and outlet conditions. During the design process, it is necessary to specify the recovery rates of the light components and heavy components; I’m not sure how to calculate these values. I hope someone experienced can help me. As in the example below, it is not clear how to calculate the design of a continuous tray distillation column operating at atmospheric pressure. The design parameters are as follows: 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 ； The textbook states directly that, through calculation, the recovery rate for the light key component is 0.9983, while the recovery rate for the heavy key component is 0.0029. It’s not clear how these values are calculated.
By using the mass balance equations F=D+W and 0.386F=0.995D+0.005W, it is possible to calculate the flow rates at the top and bottom of the tower; thereafter, the recovery rate can be determined.
The recovery rate of the light key component = D*XD/F×X_light. But it seems that in Aspen, a function written in FROTRAN is required
In Aspen, the formula for calculating the recovery rate is: D = F * (Xf – Xb) / (Xd – Xb). The recovery rate of the light components at the top of the tower is: Recov_l = Xd * D / (Xf * F). The recovery rate of the heavy components at the top of the tower is: Recov_h = (1 – Xd) * D / ((1 – Xf) * F) (lowercase letters indicate subscripts)
Thank you so much; it’s written in great detail, haha. I’ve learned a lot from it
Feed components: water 63.2%, methanol 38.6% (by mass)? ?
Is the title written wrong? The sum of the two mass fractions is greater than 100: L
Is the recovery rate calculated as a molar percentage?