I receive rather few inquiries on the subject why I chose to place thermometer in my still columns in the top third of the column packing. This post will try to explain my point of view and hopefully to answer many questions in one sitting.
Here is a short answer what I usually write:
I have a certain view for the location of the thermometer. In short, when "equilibrium" process just started, the 78*C temperature is maintained at the top of the packing.
As "equilibrium" achieves a steady state, 78*C temperature descends down the packing and maintained approximately in the top 12''~16'' of the packing depending on power, geometry, losses and ambient conditions.
If this state is altered, then temperature will rise above 78*C starting at the bottom. If the thermometer is placed closer to the bottom of this "equilibrium" region, it will indicate change of conditions earlier compared to the thermometer placed at the top of this region.
This will give you a chance to correct the "equilibrium" with minimal nasties breaking through the packing toward the take off.
For those who are not bored yet, here is the cut-paste copy of the write-up I have in my files sections. It is called "Reasoning behind design principle of short distillation column." Again this is only my observation. Others may have a different point of view.
This write-up is only for understanding my motifs behind the actual construction dimensions.
Customary and historically home made reflux distillation columns vary in length from two, two-and-a-half feet through four-five feet long in majority of projects.
The description below description corresponds to the stage when foreshots and heads had been separated from the main run body.
The temperature gradient along the column length would change from somewhere near water boiling point of the mix at the bottom and to the boiling point of alcohol at the top of the column. This change is not linear. At the bottom of the column temperature is higher. When temperature permits, tail fractions would get carried over to the height when temperature falls and does not allow these fractions to be carried upward anymore. This section is not very beneficial to the distillation process. (There is a picture in the original article).
At the higher column section the packing is completely saturated with condensing and precipitating vapors thus maintaining alcohol boiling point temperature of around 78* throughout the upper portion of the column length.
This section of the rectifying column is doing most of the cleaning work. The section below, where the temperature is significantly higher is not doing its work effectively.
The idea was to use the upper part of the distillation column, not the whole length of three to four feet. The only thing that ensures working regime of this portion of the column is that packing must be completely saturated with condensing alcohol.
One of the only possible indicators of this condition is the sound of overflow distillate falling back in the boiler. Other methods are possible as well, a looking sight glass for example. Temperature in the middle of the rectifying column is another indicator. Yet the third indicator of constant temperature would be condensation of vapors at the top of the column.
The bottom indicator of completely saturated column being the sound of falling back distillate might not be very correct if there is some channeling in the column. However, I see no current easy for home distiller solution to that.
As the result, we have a short fully saturated reflux column with three points where temperature is checked top, middle and the bottom.
Practical tests showed good agreement with this hypothesis. Resulting alcohol from short column was compared to the output of a regular four foot column. I could not detect any difference in taste, smell or color.
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
[Non-text portions of this message have been removed]