>Thanks for the refluxdesign calculations.
>Using the different parameters of my own still-equipment, I find out
>that the ignored cooling water & heat loss must be quite much. I had to
>reduce my "gas-power-input" from 9000 Watt to 2200 Watt to match the
>"time to heat up" match with my still-experiences.
Glad to hear that http://www.geocities.com/kiwi_distiller/reflux_calc.htm
has been of use to you. That seems to be quite a large amount of heat loss
you are having. Have you been able to insulate your pot & column in any
way ? Some of the "heat losses" ignored by the calculation are also those
required to heat up all the pot, column, packing, etc (all the metal &
ceramic bits) too - the bulkier the still the longer it will take to heat
up, but it should be fine once at temperature (eg more like the 9000W
performance). As you would have seen from the calculations, this amount of
loss will affect your design & operation quite a bit; a 9000 W heat input
will require a column of approx 50-55 mm diameter, whereas 2200 W is best
suited with approx 25-30 mm diameter.
>Can somebody give me some tips to measure the amount of cooling water
>and the the amount of alcohol very quickly, without disturbing the
>destilling-proces ? Then its easier to calibrate the different
>parameters used in the calculations.
I'm a bit of a "bucket chemist" when it comes to this. I just use a small
measuring cylinder, marked off in 10 mL increments, and time how long it
takes to fill say 100 mL to get the flowrates.
You only have to do this rigourously once to understand your stills
operation. Treat this one run as an experiment, and spend the time on it.
Measure & write down the temperatures every 5 or 10 minutes, and graph
them as you go. Collect the distillate into 200 mL or so containers, and
note how long it took to fill them. Once they're each cool, measure their
%. Measure the cooling water flowrate & temperature, and work out how much
it needs to be increased near the end of the run to keep it cool.
This will allow you to get an accurate idea of the heat input to the still,
so that you can then optimise its diameter (you may need to widen it if too
small, or decrease it (by stuffing it with some stainless steel rods or
suchlike) if too large) if too far from that desired.
By understanding the flowrate of distillate you are collecting, you can
determine the reflux ratio that you are getting from your cooling coils
etc. Once you know this, you can work out the HETP for your packing, and
thus the number of "theoretical plates" your still has. This will
determine the maximum purity that you can achieve - if close to it, you're
doing well, if miles away from it then something aint working right. If
the maximum is less than what you want, then you'll need to make the column
taller or change the packing (or both !).
The cooling water temperature will tell you if you're sub-cooling the
reflux distillate. If this is happening, then you're wasting the top
portion of your column as all its doing is trying to heat it back up to
equilibrium tempeature again, before it can start stripping the vapour of
its water content. If the cooling water flowrate is really large (eg more
than about 2/3L per minute) then your cooling isn't as efficient as it
could be - see if it needs more surface area to work over.
Once you understand how your temperatures & distillate flowrate changes at
the end of a run, you can predict more accurately when you're starting to
receive the tails. Compare the total distillate collected, and its purity,
against what is theoretically possible. There's no point is trying to
wring too much out of the still, or else you'll just be into collecting
those tails and ruining your whole batch. (This is where the table of
"amount collected over time" might be usefull to you - as a guide to when
As always, I've put heaps of disclaimers around the calculations on
; they're not the
complete picture, but should be usefull as a guide along with
in terms of
understanding and getting the best from your still.