Home Distillation of Alcohol (Homemade Alcohol to Drink)
Reflux Still Design
Summary
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To increase the purity of the alcohol, and hence reduce the amount of
"off-flavours" in it, you need to use a taller column, packed with something
which has a large surface area (scrubbers are best), and have some of the vapour condensing
and being returned back down over the packing as a liquid (reflux).
For a certain height of packing (called the HETP), the purity will
improve - roughly 1x = approx 85% purity, 3x = 90%, 5x = 93%, and 7-9xfor 95%+.
Just make it as high as what you want pure. For scrubbers the HETP is about
10cm (4 inches), whereas it is 24-38 cm (10-16 inches) for raschig rings or marbles.
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See my Detail of the Equations used
if you want to get into the detail of this.
Purity is improved during distillation by allowing the rising vapour
to mingle with some liquid at a slightly cooler temperature. In doing
so, some of the water rich vapour will condense, supplying
a bit of energy to allow some alcohol rich vapour to form from the liquid
, and join the existing vapour. Each time this "mingling" is sufficient
to reach equilibrium, the purity takes a "step" on the graph
below:
Thanks to Chris Noonan for helping do this Applet.
This graph is of the "ethanol-water equilibrium"
eg a liquid of 15% alcohol will be in equilibrium with a vapour
at 65% alcohol. If this 65% vapour is then cooled to form a liquid
(it will remain at 65%), the new liquid would then be at equilibrium with a 84%
vapour, and so on. If you have a pot still, just set the plates to one.
You can see that due to the shape of the curve, most of the gains
are early on; to get to the really high % purity, you need to take lots
of steps later on. There is no way around this. If you want high purity,
you have to work hard for it. Also note (particularly for inefficient columns
with the equivalent of only 1-2 plates) that the starting % can also affect the
final % achieved - hence a good idea to use the better yeasts.
Each of these "steps" represents an "ideal plate"
where enough mingling of liquid & vapour allows them to come to
equilibrium. If you don’t allow enough mingling (equilibrium), then you
won’t achieve a full step, but end up a little shy of the target.
You get the first step free - its the boiler/pot.
One way of doing these steps is to do many single distillations,
collect the vapour that comes off, condense it, clean out the still, and
run it through the still again. This why pot stillers do double &
triple distillations to get into the 80+ % range. But a Reflux column
allows this to happen continuously; if given enough surface area to
equilibrate on, the vapour can have gone through multiple distillations
by the time it gets to the top of the column.
For each plate to work, it has to be at a particular temperature,
slightly cooler than the one below, and warmer than the one above. Only
then will it achieve its equilibrium and an increase in the alcohol purity.
The differences are really fine too – its all happening only between 78.1 C
and 82.2 C – quite a tight band to walk between.
This is where the various designs that have cooling tubes running through
their columns at all different heights (eg Labmaster) come adrift – they don’t
allow the required sequence of temperatures to develop fully, and thus won’t
work at their full potential. They also don’t allow all the refluxed liquid
to do its job over the packing – the less liquid/vapour contact the poorer the
"polishing" of the vapour will be.
This is why you should also (see my interactive
Heat & Mass Balance page to play with these and see it for yourself):
- Insulate the column well (don’t want breezes causing additional
cooling out of sequence),
- Let the column run at total reflux for a while (to allow the packings
to heat up to their equilibrium temperature). This is also important
so that the methanol is given a chance to all work its way to the top of
the column, so that it will all come off in the first off-take,
- Only have condensors for reflux above the packing, and
- Use a stable/continuous heat source (you don’t want it switching off
& on all the time causing surges of vapour going up the column
then periods of nothing; it has to be a steady continuous flow of vapour & liquid)
So you can easily work out what is required to get a particular %
purity; just look up the number of ideal plates needed, eg 2 plates = 87%,
3=90%, 4=92% and so on. Remember you get the first one free - its the pot.
A pot still is the equivalent of a single plate; if it has "thumpers"
attached to it, each of these can act as an extra plate.
Why call them plates ? In large distillation columns, they are exactly
that; large metal plates or trays, which the liquid flows over, and the gas
bubbles up through holes in them. However they are quite tricky to design
& build, and not really suited for small column diameters (say less
than 1 ft diameter) - they’re just too fiddly. Below this size, its easier
to use a Packed Column; where the packing can be random (eg just dumped in
there and given a shake), or carefully positioned & stacked . For any
particular type of packing, we can estimate how much of it is required to
make one of these "ideal plates". See
http://www.5continentsusa.com/cer-pack.htm for examples of different commercially available
types of packing. These commercial packings are quite difficult to source, then
expensive to purchase. They're designed for an industrial operation, where they're
expected to be run continuously 24/7 for weeks or months at a time without fouling up.
For a hobby distiller it is far easier, and with higher performance (%purity), to
use common pot scourers (non-rusting stainless steel or copper) instead for packing, as
we'll be cleaning them frequently (like after every 20L run).
The height of packing needed in order to do the same job as an ideal
plate is called the HETP -
Height Equivalent
to a Theoretical Plate. Smaller HETP’s are better than large ones,
as it means that for a given column height (say 1m) you end up with more
ideal plates, eg only 2 plates (87% purity) if the HETP= 0.5m, but 4 plates
(92% purity) if HETP = 0.25 m. If you don’t have an exact number of
plates, that’s still OK; you’ll end up somewhere proportionally between
the two.
So an empty column, with no packing, ain’t going to do a lot.
Sure, you might get a little liquid running down the sides of it, but this
has got nowhere near the same surface area as using packing.
The HETP for a packing depends on its:
- Size (smaller objects pack together better). The size also needs to be in proportion to the column diameter too
- Voidage (need to allow room for the gas & liquid to flow around them, don’t want to block the column off)
- Surface area (eg how many square meters of surface you have per cubic meter of packing – the more surface area, the more places for the liquid & vapour to mingle)
- The amount of liquid & vapour flowing around it
Typical HETPs for common packings are :
Packing | HETP |
Stainless Steel Wool Scrubbers | 0.13 m |
Marbles (10mm diameter) | 0.33 m |
6mm Ceramic Raschig Rings | 0.24 m |
13mm Ceramic Raschig Rings | 0.38 m |
These HETPs change depending on how much liquid & vapour are
flowing around them. This ratio can be described by the Reflux Ratio -
the ratio of Liquid flowing down the column over the amount of distillate
drawn off :
R = L / D = (V-D) / D
This can be easily measured if
the still design is like Stone & Nixon’s where all the vapour is
condensed separately, and you control the amount withdrawn vs returned
(refluxed). It’s a little harder with the Stillmaker design where the
refluxing liquid is determined by the amount of cooling done by the first
condensers, and you never get to single it out, but you should be able to
estimate the amount of vapour from the amount of heat you apply.
As the reflux ratio increases, so the HETP improves. Generally though,
you can see that choosing the right packing to start with does the greatest
improvement; increasing the Reflux ratio only squeezes the last extra bit
out of it (at the cost of having to wait longer too). Where you will notice
it is when the design is poor to start with - increasing the reflux ratio
will help out quite a bit.
Calculate the HETP for your still ...
Jan Willem of http://www.geocities.com/homedistilling/
experimented with this ...
I get 94% at a rate of ~ 500mL/hour. My column is 115cm long and 42mm wide
Filled with potscrubbers from the undersite to just under the
precooling coil. (Tony - ie its of a good design already - heaps of HETP)
At my latest distilling escapade I turned the reflux ratio up.
Just as a test that would show me how pure it could get AND if there
was a taste diffirence (after dilluting ofcourse)
Collected the good stuff at 100mL/hour (a long wait)
Then the score was initialy 95.?% and was going down a bit to 94.5%
(Dunno if it was 94.3 or 94.8 so I say 94.5%)
After the taste test I noticed NO difference, but I'm no expert at
wodka tasting.
The improvement isn’t linear either - you can halve the HETP for
Stainless Steel Wool (SS below) by going from "bugger-all" reflux
to "some" reflux, but there is little improvement winding it up
too far past there.
SS = Stainless Steel Wool Scrubbers, RR6 = 6mm Ceramic Raschig Rings,
RR13 = 13mm Ceramic Raschig Rings, M = 10mm Marbles
So, put these together to work out your still performance;
- Determine the HETP for the packing you are using, then
- Work out for the height of packing you have, how many Ideal
Plates you have, then
- Look up the purity expected for that number of plates.
SS = Stainless Steel Wool Scrubbers, RR6 = 6mm Ceramic Raschig Rings,
RR13 = 13mm Ceramic Raschig Rings, M = 10mm Marbles
But what diameter should the column be ? This needs to be worked out
from the amount of heat you are putting in. The more heat, the more vapour
you generate. If the vapour rate is too great, then instead of having
your refluxing liquid flowing down the column, it will be blown out the
top. You also need to consider how much space the packing is taking up
too.
SS = Stainless Steel Wool Scrubbers, RR6 = 6mm Ceramic Raschig Rings,
RR13 = 13mm Ceramic Raschig Rings, M = 10mm Marbles
Stainless Steel Wool Scrubbers/Scourers
From the above analysis, I figure that Stainless Steel Wool Scrubbers (pot scourers)
are 2-3 times better than rachig rings with the typical small diameter columns we
use in this hobby.
Using these as the best type of packing will allow you to use a smaller column or a lower
reflux ratio to get the same purity. Or keep the same height & reflux
ratio, and have improved purity. Are you happy with the existing purity, or
do you want cleaner alcohol ?
The stainless steel scrubbers are probably only good however up to about 2-3 inch
diameter columns. Beyond this, they will be difficult to keep in place &
have even liquid flow over them (e.g. don't want areas where they are really
packed tight or spread too thin - it has to be uniform). It is at the
larger diameters that the more regular packings like rachig rings come into
their own (as they won't compact up or seperate to leave holes),
and for even larger diameters, that you'd consider structured
packings (i.e. carefully stacked into a regular pattern). One rule of thumb
I've heard of for raching rings is to size them 1/10th the diameter of the
column; e.g. the small 6mm rachig rings are really only suitable down to
about 60mm (2.4") diameter columns (and they're expensive!).
So for columns up to 2-3 inches in diameter (50-75mm), you might as well
go for the better performing, cheaper option of scrubbers. Bigger than this though,
and you might need to start using what commercial units do.
David comments ...
I use 3M ones
myself as I have found them the best quality. Use a good quality one
preferably. On a 1.5 or 2" column each should fill 55mm to 75mm (max) of
column (less on 2"). Even less if you prefer. I tend to work in the vicinity
of each filling somewhere between 55 and 63mm. At 55mm on a 36" column this
equates to almost 17 from which I deduct 1 to allow for space at the top ie.
=16. Allow at least 2" to 2.5" of clear space between the top of the
scrubbers and the takeoff point for the vapour to expand into and so the
reflux falls back into the scrubbers.
Do not unravel but tease them out by hand a bit so they fill the whole
column diameter rather than just a part of it. Most of the ones I have seen
in NZ do not have rubber bands around them. Place them into the column from
the bottom one at a time using some sort of restriction at the top and
bottom to prevent them going further or dropping out back into the boiler..
I use a 2" pall ring which works well.
On a slightly longer column (1m = 39.37" ) I use 19 off memory so 17 is
probably around the right number. You dont want them too loose or too tight.
If too tight they will compact more. The main thing is to have an even
constant heat so you dont get surging. Surging causes compaction.
Calculations
I've developed a couple of interactive pages which do all these
calculations for you :
Designing Your Own Still
So how do you put all this together to make your own still ?
Say you're looking at wanting to make 90%+ purity, off a 20L wash.
Pot
To hold 20L you want at least another 1/4 spare for foam, etc.
So go for something in the 25-30L range. I'd suggest something
where you can easily lock the lid down, but also be able to get
into it fully to clean it out. Suggestions include paint tins as
seen in :walt or
AV25L or a preserving pan
with a clipped lid like Teds at http://mwci.s5.com/.
These all have pretty thin lids, so to support the column,
you may need a small flange to help hold it all up, or a stiffening
plate/oversized washer to help strengthen the lid.
Heating Element
Probably in the 1000-1500 W size. Whats cost-effective for you ?
A 1500W element will heat up the contents to begin in around 65
minutes, but a 1000W will take 98 minutes. If time is crucial, you
could add a second element to act as a boost during the initial heat up.
Column Sizing
The diameter is based on the amount of heat you're using, whereas
its length determines what purity you'll get. Its a hobby
still, so I've assumed that the packing will be stainless steel or
copper scourers - they only take about 1/2 the height that marbles do
to get the same purity. You will also need to insulate the whole
length of column too - plumbing suppliers sell slip-on piping
insulation for around NZ$8/m
Diameter : 1 inch is too narrow for a 1380W element, but
1.5 inch is fine with a 1800W element. Roughly, lets say to use
1.25 inch for 1000W, 1.5 inch for 1500W and 1.75 inch for 2000W.
If in doubt, go up in size by say 0.25 inch. Too narrow will lead
to all manner of problems & difficult operation, but too wide will
only give a minimal reduction in purity.
Height : This is the purity. Use the wee interactive
applet at the start of this page
to see how the number of stages or HETP's improves the purity.
Its easy to get the first gains up to 90%, but then more difficult
to squeeze out the last improvements towards 95%+ Lets assume
(we'll come back to this) that each HETP for scrubbing pads is around
15cm... then for a 15% wash,
No packing, purity = 62% , 15cm packing = 82%, 30cm = 88%, 45cm =
90%, 60cm = 92%, 75cm = 92.8%, 90cm = 93.4%, 105cm = 93.9%.
These won't be exact, and depend on a number of different factors,
but it shouldn't be too far off. So, if height is a problem, and
you're happy with low 90's, then 60cm should do ya. If you want
to make a perfect vodka, go for 120cm. Normally I'd recommend at
least 100cm, but the choice is yours, as it depends on the type
of product you want to make.
These numbers assume that we've reached equilbrium nicely for
each 15cm of packing. To do so, we need to provide heaps of surface
area for the liquid and vapour to mingle over (done - using scrubbers),
and that we're refluxing a large proportion of the vapour back down
as liquid, rather than keeping it. But this means that our take-off
will be rather slow. Eg we may be able to start out with a reflux
ratio of say 3-4 (ie return 30-40mL for every 10 mL we keep) when the
pot is very rich in alcohol, but later on, when its getting down in
alcohol, we may need to increase this up to 5-10 to keep the high purity.
A reflux ratio of 4, with a 1500W element means that we're collecting
at around 20 mL/min. Thus a 20L 15% wash will take a minimum of 2.5 hours to
collect (20 mL/min), up to 5 hours at a reflux ratio of 8 (10 mL/min). The
actual time will be somewhere between these, depending on what ratio you end up
needing in order to deliver the purity you're after.
If the distilling time is taking too long, we can make the column taller,
and then run at a slightly smaller reflux ratio, to get the same purity.
The collection rate is directly proportional to the element size, so if a
1500W element with reflux ratio of 4 takes 3 hours to distill, then 1000W will
take 4.5 hours, or a 2000W 2.25 hours.
Making the Reflux
Theres a couple of different options for how to provide the refluxing liquid.
The choices come down to how much control you want over it.

The first, simplest and cheapest, is just to have a cooling coil in the head
of the column, which is fed cooling water direct from the condensor. Provided
you have sufficient coil surface area available (eg > 1-2 m), you should be able to increase
and control the reflux ratio to give you the high purity. If you only have a couple
of coils inside the column (like I've drawn), then you wan't be able to make enough reflux, and
you're in for mediocre results.
Second - plumb the cooling coil with its own water supply - say a T joint
off the main line, with a couple of valves to be able to regulate the water to
the coil seperately from the main condensor. This would allow you to say turn off the coil if you want
to do a stripping run, without affecting the performance of the main condensor.
For excellent instruction on fitting a coil, see Homers diagram or a couple of Phils
photos.
If the main column is too narrow to have a coiling coil inside it, you can
always use a cold collar around the outside of it. Another, but less effective
method is to coil around the outside of the column.
There are excellent instructions for making the external condensor in the
"StillMaker" pdf, or at http://stillmaker.dreamhost.com.
Basically just use a couple of T fittings, or if you're a dab hand at welding, just
build it up yourself. Another (easier) option is the "Euro" still condensor, where
the cooling water is simply fed in a tube up through the outlet pipe.
See a photo of it.
Third (my preferred option) is to do the Nixon style of condensor, as seen in the
photos, where all the vapour is condensed (with an oversized
coil - thus minimal water required), and then you proportion off the amount of
liquid you keep vs return. This gives you maximum control over the reflux ratio,
being able to dial it up from "total reflux", essential for getting a column into
equilbrium before taking off the heads, through to "no reflux" if you want to do
a stripping run, or only a low reflux run say for a flavourful rum or the like.
The disadvantage of this design is that it adds to the height - say another
30 cm. But I reckon well worth it.
Controls
I prefer to only control the reflux ratio. If the column is wide enough, then you
don't need to worry about metering the heat input via the element. Either up the
water flowrate, or close down the take-off valve, in response to the vapour
temperature measured at the top of the column. Use this graph below
to compare temperature to purity. Cheap (NZ$28 at www.dse.co.nz ) digital thermometers are
excellent for reading this temperature.
Summary
So, in summary, to make a very cheap, short still, how about a 1500W element, with a 1.5 inch
by 60-70cm column, scrubber packing, and simple external condensor (Euro style) & internal
cooling coil of say 4-5 turns, directly plumbed between the two.
To make a more high performance still with more options on how to run it & what products
you can make from it, first make it taller, and then consider using the Nixon condensor.
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