Reaction reflux stills to Tony
A happy new year. Thanks for your reply.
Using your reaction the next 3 reasons will explain the quite large amount of heat-loss I have:
- I haven’t insulated yet my pot and column with packing.
- My column is made of copper. It is 120 mm in diameter and 1.0m high. So the surface area is quite large.
- My 80 L pot is indirecly heated by a 9 kW gas-pit. Between the outside iron pot and the inner copper boiler-still, I use glycerin because of its high boiling point without bad smells. On this way it is not possible for wash-solids to burn "in" de copper boiler-pot.
Nowadays most German stills are indirectly gas/electric heated by using water pressure between the stainless steel outside vessel and the inside copper vessel. To increase the boiling point a water pressure valve is used. The older German stills used glycerin or other oil liquids for heating indirectly without high pressure.
My column diameter (120mm) is much greater than theoretical is required by calculation (55 mm). Compare to many German 80L -stills my column diameter is O.K. Mostly the column diameter of these professional home stills is between 100 mm and 200 mm, using "clocks" instead of ceramic packing.
I will change my glass "chips-packing" by ceramic Raschig Rings. I am still hesitating whether I will use ceramic packing or stainless steel wool scubbers to get more alcohol with less cooling water.
Because of its "diabolic-form" of the copper reflux cooler in the column top, I have enough cooling surface. Because I use a AVTA-cooling-valve (Danfoss), the cooling water flow rate is very small.
On the other hand the cooling water temperature is very high. I don’t know now whether I am sub-cooling the reflux distillate?!…. Maybe I am wasting the top portion of my column as all its doing is trying to heat it back up to equilibrium temperature again, before it can start stripping the vapour of its water content.
May be you can give me some more advice ?
Peter from Poederoyen, Holland
That sounds like an interesting way of doing the indirect heating. I
haven't seen that on a hobby-still before. Yes it will explain some of the
You are quite right in not worrying about the column diameter too much -
many are oversized (compared to theory) and still work very well - and its
far better to be too wide rather than too narrow.
When you say that your cooling water is very hot, how hot is it ? From a
theoretical point of view, you don't want to cool the reflux distillate much
below its dew point (i.e. around 78-80C), but from a practical/control point
of view, and hugely from a SAFETY perspective, you want to be a bit more
below this (there is no way you want ethanol vapour getting out of the still
without condensing). You need some safety margin to allow for fluctuations
in water flowrate or temperature (e.g. someone else in the house turns on a
tap or flushes the toilet!) I personally still use the "finger test" -
making sure its not too hot to hold my finger under - e.g. around 50-60 C.
The main point being that you don't need to be cooling it to down at 15-20C.