The light components at the bottom of the distillation tower cannot be removed completely
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In the distillation column, with volatilities in the order of a, b, c, and d, at a bottom temperature of 140 degrees and a vacuum level of around 100, the mass fraction of a+b at the bottom is 0.3; however, when the bottom temperature is 137 degrees and the vacuum level is 97.4, the value of a+b at the bottom drops below 0.1. Why is that? 140 is already the maximum allowable temperature at the bottom of the tower. What efforts are needed to reduce the concentration of component A at the bottom of the tower to zero? I seek advice from experts! ! !
Increase the circulation rate of the reboiler at the bottom of the tower, if possible.
Increase the vacuum level and raise the reflux ratio
If the vacuum level is high, the temperature at the bottom of the tower can be further reduced; the separation efficiency can be controlled using the reflux ratio
In fact, the setting of the operating points is related to the selection of the evaporation rate and the condensation temperature at the top of the tower. Based on your description, when the temperatures are 97.4/137 degrees, there is less light component in the bottom of the tower, which indicates that under these operating conditions the evaporation rate is higher and the separation is more thorough.
I would like to ask how the material at the bottom of the tower is discharged
It might be sufficient to add a little bit of substance B; perhaps the temperature you need will be even lower
Do you mean the vacuum level at the top of the tower? If so, you need to examine the total pressure drop across the tower at different vacuum levels. When the vacuum level is close to 100, the gas velocity inside the tower becomes too high, which in turn reduces the efficiency of the packing. It’s not necessarily the case that a higher bottom temperature and higher vacuum level always lead to better results. The efficiency of packing is determined by various factors.