Home Distillation of Alcohol (Homemade Alcohol to Drink)

Reflux Still Design

Summary
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.


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 donít allow enough mingling (equilibrium), then you wonít achieve a full step, but end up a little shy of the target. You get the first step free - its the boiler/pot.

Basically, off a 10% wash
1 = 53%
2 = 80%
3 = 87%
4 = 90%
5 = 92%
6 = 92.6%
7 = 93.3%
8 = 93.8%
9 = 94.2%
10 = 94.4%

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 Ė its all happening only between 78.1 C and 82.2 C Ė quite a tight band to walk between.

Mike Nixon explains in a bit more detail ...


This is where the various designs that have cooling tubes running through their columns at all different heights (eg Labmaster) come adrift Ė they donít allow the required sequence of temperatures to develop fully, and thus wonít work at their full potential. They also donít allow all the refluxed liquid to do its job over the packing Ė 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):

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) - theyíre 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).

Jim adds:

Phil suggests a cheap supply of ceramic packings though ... More about using plates (rather than packed columns ... Hennie writes:

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 HETPís 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 donít have an exact number of plates, thatís still OK; youíll end up somewhere proportionally between the two.

So an empty column, with no packing, ainít 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:

Typical HETPs for common packings are :

PackingHETP
Stainless Steel Wool Scrubbers0.13 m
Marbles (10mm diameter)0.33 m
6mm Ceramic Raschig Rings0.24 m
13mm Ceramic Raschig Rings0.38 m
Zoran suggests that in some cases marbles may be as effective as a 0.2m HETP.

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 & Nixonís where all the vapour is condensed separately, and you control the amount withdrawn vs returned (refluxed). Itís 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 ...

Select Packing Type
(note: the values these selections generate are only approximate guesses)
MaterialDiameterSurface AreaSurface Tension
Marbles 0.010 m 50 m2/m3 0.061 N/m
6 mm Raschig rings 0.006 m 140 m2/m3 0.061 N/m
13 mm Raschig rings 0.013 m 40 m2/m3 0.061 N/m
Stainless Steel Wool 0.001 m 800 m2/m3 0.075 N/m
or your own values ... m m2/m3 N/m
Still Characteristics
Column Diameter
m
Packing Height
m
Reflux Ratio
Power Input
W

Estimate of Packed Column Performance
Height Equivalent of Packing (HETP): m
Number of Theoretical Plates :   = (height/HETP) + 1 for pot
Approx Vapour Purity : %

See http://www.raschig-rings.com for more information on other column packing details. Note also that when real plates are used in a column, you also need to do a similar calculation - they are often far from ideal in operation, and you may need several to achieve one HETP.

Jan Willem of http://www.geocities.com/homedistilling/ experimented with this ...

The improvement isnít 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;


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. The following diagram is based on the calculations - unfortunately the sizes are about 50% smaller than what appears the actual limit, so scale up the calculated result if you plan on following them.


SS = Stainless Steel Wool Scrubbers, RR6 = 6mm Ceramic Raschig Rings,
RR13 = 13mm Ceramic Raschig Rings, M = 10mm Marbles


Instead, I scale up/down for what I know works for me ... using scrubbers for packing, a 1.5" diameter column can handle 1800W. So .. for constant vapour rate per cross-sectional area ...

Maximum Power for a Given Column Diameter

1.00" = 800 W
1.25" = 1250 W
1.50" = 1800 W
1.75" = 2450 W
2.00" = 3200 W
2.25" = 4050 W
2.50" = 5000 W
Note that these figures are roughly the maximum power that you would want to use for any given column diameter. Mike argues that you should use quite a lot less power ...
Generally, a 2" (50mm) diameter is an ideal size to use. This will happily run from 750W up to 2500W without any trouble. If in doubt, go for 2".

Its this amount of energy that you put in which will determine the rate at which you make and collect the distillate. If collected at the condenser at say 95%, it works out roughly to the following figures. If you run a reflux ratio of 4 (e.g. return 40 mL for every 10 mL you keep - typical for SS scrubbers) - then the second figure is the flowrate you'd expect to collect at ...

1000 W = 52 mL/min (max, no reflux) or 10 mL/min (if RR=4)
1500 W = 78 mL/min (max, no reflux) or 16 mL/min (if RR=4)
2000 W = 105 mL/min (max, no reflux) or 21 mL/min (if RR=4)
2500 W = 131 mL/min (max, no reflux) or 26 mL/min (if RR=4)
3000 W = 157 mL/min (max, no reflux) or 32 mL/min (if RR=4)
3500 W = 183 mL/min (max, no reflux) or 36 mL/min (if RR=4)
4000 W = 209 mL/min (max, no reflux) or 42 mL/min (if RR=4)

Note though that you are probably going to be limited in how much power you can deliver to the still. Many homes only run 10 amp fuses in their fuseboxes. This will limit you to 240 V x 10 A = 2400 W before you have to have a safety chat with your electrician about upgrading the wiring.

The risk of making the column diameter too small is that the column will "flood", as discussed in "Chemical Engineering - June 2002" pp 60-67 by Simon Xu and Lowell Pless about flooding in distillation columns. These guys have been using "gamma scanning" to work out where abouts various distillation columns are flooding, and why. I'll quote a few paragraphs about "packed columns" for ya (they also did a fair bit on trayed columns) ....

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 ...

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 OK with a 1800W element. Roughly, lets say to use 1.5 inch for 1000W - 1500W and 1.75 - 2 inch for 1500W - 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. 2" is a well used, very reliable diameter that works under most circumstances.

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 120 to 150cm. 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://www.Moonshine-Still.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.

An excellent variation on that is Alex's (Bokakob) mini-still:

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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