automatic reflux ratio
- I've tested an idea I have had, how to control the reflux ratio
automatic. Check files area -> johan -> self tuning head.png
Explanation to the picture:
A normal column with for instance an sr head, total packing height
about a metre. (1) reflux runs down into a 6 mm tube that is
soldered onto the column and is about 30 cm. Then down to a liquid
lock (4) up in a tube 2 that ends a bit below the head. Product
comes out in 3.
The column is insulated including pipe 1. pipe 2 is uninsulated.
From the start when you heat up the still and vapour condense onto
the cold packing you get separation. even at the start it has high
strength when it reach the top. that runs down in the tube 1.
a bit down in the column the strength is lower and temperature is
higher. If the distillate that comes down in 1 have higher strength
the distillate will boil since it is heated through the column wall.
When it does so the pressure in tube 1 is lower than tube 2, product
stop. Reflux ratio increase and ethanol is accumulated at the top of
the column. Temperature decrease in the column and the distillate
stops to boil. Product is coming out. If it comes out to fast temp
start to rise at the bottom again and product stop.
The nice thing with this is that it reacts to the strength a bit
down in the column so the top strength isn't changed. And it doesn't
disturb the column too much.
I tested it, in practice tube 1 is winded around the column in a
spiral, it gets better contact that way. To my big surprise it
actually worked at first test without any valve. Strength was 96 %
But I used low strength mash then. It's a different story with high
strength mash (or normal 14%) The reflux ratio to achieve 96% with
good strength in the boiler is rather low, so the temperature
difference inside the column isn't as pronounced then. The temp a
bit down in the column isn't much higher than the top. Little heat
pass through to the tube, also the flow in the tube is high and
require a lot of heat to make it boil. So it reacts a little to
late. When it finally reacts it does it wildly. In worst case
pushing out all liquid, even that in 2.
With a valve on 2 to limit the flow some the idea works. At the end
it regulates itself to produce top strength even though the needle
valve is set for rather big flow. (and stops automatic)
I'm not pleased with it yet, I don't want any valves, the idea
should work without any valve. Why? alright add a valve for heads so
that can be removed slowly, but then open it full and let the still
adjust by itself, making it run at high speed but with high quality,
if the column is tall enough and the pipe 1 is low down, it should
produce good quality. It has to do it foolproof, I hate almost
working things =)
Another approach to this would be to have a tube along the column
that fills up with some distillate to begin with and then stays
there. That'll give it plenty of time to heat up. When it boils it
somehow prevent output. Another idea is to use air that heats up and
expand and prevent output. Or capsulated 96% that builds up pressure
and stops flow somehow easy.
Or simply the same idea but with better heat transfer, smaller tube
or longer, or pipes through the column or... well.. it cost money to
test and I don't have the time.
We'll see if I continue with this experiment further on.
It has potential especially for fuel stills or vacuum stills or lazy