Discussion on the distillation limit
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Binary distillation, methanol and water solution, feed methanol molar fraction 30%. Discussion: 1. Can separation by column distillation be achieved to obtain methanol at a concentration of over 99.5% at the top of the column, and water at a concentration of over 99% at the bottom? In another scenario, two columns are used for separation: the first column ensures the concentration at its top, and the liquid from that column enters the second column; the second column ensures the concentration at its bottom, with the vapor from its top being recycled back as feed to the first column. 2. Of these two methods, which one is better, which one is more optimal? Which is less, the equipment cost or the operation cost? I earnestly ask for your valuable advice from the friend who designed Haichuan! ! Thank you.
A single tower isn’t entirely impossible, but it’s difficult to operate; a dual-tower setup is better as it’s easier to use, though the investment is higher
It’s hard to say; software simulation is needed to calculate it.
I remember that methanol and water are azeotropic, so a single column would work as well, but the costs associated with the reflux ratio might be too much for you to accept
I think operating with two towers is better; the investment isn’t necessarily higher, as the height of the towers is reduced. The quality requirements for the top of the tower are quite high, but those for the bottom of the tower are not as strict; therefore, it is possible to handle this with a single tower. It’s better to carry out calculations for each of the two options separately and compare them; it’s not wise to draw conclusions rashly
One tower can achieve this, but if high purity is required, the reflux volume must be large. Methanol recovery tower referring to MTBE
Personally, I think it’s no problem to achieve the aforementioned separation purity from a design perspective； However, in terms of operation and control, it is generally difficult to maintain stability at both ends, but it is not impossible; as long as there are no significant disturbances in the feed flow composition, this should be achievable.
Personally, I think one tower is feasible; specific calculations need to be done. As for the costs, they will have to be compared after the calculations are completed
It is recommended that the original poster use software to do the calculations, or perform them manually; there is ample data available on the phase equilibrium of the methanol-water system, so it should not be too difficult. For methanol and water alone, it is not difficult to achieve a purity of 99.5% on both ends, meaning that two pure products (with a purity of over 99%) can be obtained from one column. . In a typical methanol recovery tower, the methanol feed concentration is around 5–20%, the reflux ratio is 3–4, and the number of theoretical plates is between 15–20; these conditions are sufficient to achieve a recovery rate of over 99% at both the top and bottom of the tower. Since your feed concentration exceeds 40% (by weight), the task becomes even easier. A reflux ratio of 3–4, 20 theoretical plates (with the actual number of plates being around 30–40; packed columns are quite effective – about 10 meters of packing is sufficient in such cases). Distillation at atmospheric pressure – is it very difficult? Here are the actual operational data for this process: Methanol concentration in the feed stream: 30% (wt%); reflux ratio: 3.5–4; methanol concentration at the top of the tower: >99.7% (wt%); methanol concentration at the bottom of the tower: 99.5%. If one tower is sufficient to carry out this process, then why use two towers? ? And the difficulty of one tower isn’t that high.