Stilligent

Reflux column calculator

Match a reflux column to its boiler: the vapour speed your power gives in a column of a given size, the power that suits it, how many stages and how much packing it takes to reach your strength, what it will produce, and the cooling water it needs.

Units

Reflux column sizing

Whether a column suits your power - and how tall to pack it, what it will produce and how much cooling water it needs.

W
%
%
%
Vapour speed–
Power for this column–
Column for this power–
Theoretical stages–
Packed height–
Product–
Cooling water–

Engineering estimates for home columns at normal air pressure. Vapour speeds are the comfortable ranges home distillers use; packing performance varies widely with how it is made and packed, so allow some extra height. The stages assume a well-mixed boiler and steady reflux.

The background is in Pot still vs reflux still.

How to use it

  1. Choose the column. Pick a standard tube size, or set the inside diameter yourself in millimetres or inches.
  2. Enter the power. The heating power you will run at, and how much of it reaches the column (around 90% with an insulated boiler).
  3. Choose the packing. Copper or stainless mesh, structured copper packing, ceramic or glass rings, or plates.
  4. Set the strengths. The strength in the boiler - the weakest you'll run down to - and the strength you want at the top.
  5. Set the reflux ratio. How much is returned down the column for each part collected. Higher ratios give stronger, purer spirit, more slowly.
  6. Set the cooling water. How much the water warms on its way through the condensers. A smaller rise needs more water.

How it works

Vapour speed. Every joule that reaches the column boils off vapour - about one mole for every 39.5 kJ. Dividing the volume of vapour by the area of the column gives its speed. Too fast, and the rising vapour holds the reflux up until the column floods and surges; too slow, and the packing doesn't wet evenly. The calculator compares your speed with the range home columns run comfortably at, for the packing you chose.

Stages and packing. Each theoretical stage is one step of boiling and condensing. The calculator steps from the top of the column down to the boiler (the McCabe–Thiele method) at your reflux ratio, and counts how many stages it takes. It turns stages into packed height with typical figures - about 7 cm a stage for mesh, 10 cm for structured packing, 15 cm for rings, and plates at about 60% efficiency - and adds a quarter to spare.

Output and cooling. At a reflux ratio R, one part in R + 1 of the vapour is collected. All the heat that reaches the top has to be taken away by the condensers, so the cooling water needed is the power divided by how much each litre warms.

A worked example

A 2-inch column (47.5 mm inside) packed with copper mesh, on 2,000 W with 90% reaching the column, carries vapour at 0.75 m/s - comfortable, at 71% of flooding speed. It suits about 1.2–2.1 kW.

To reach 93% from a 10% boiler at a reflux ratio of 4, it needs 6 theoretical stages including the boiler - about 45 cm of mesh - and produces about 1.6 L an hour. At a reflux ratio of 8 the output falls to 0.9 L an hour. The condensers need about 1.3 L of water a minute, warming by 20 °C.

A 3-inch column on 4,000 W runs at 0.63 m/s and produces about 3.2 L an hour at the same ratio.

Where Stilligent fits

This calculator finds the power that suits your column; Stilligent holds it there. You set the power in kilowatts, and it adjusts the element as the mains voltage rises and falls, so the vapour speed - and the way the column behaves - stays the same from run to run. If the element can't reach the setting, it tells you. Larger stills can share the power across up to four elements.

Its live estimate of the strength at the head shows how well the column is holding its strength as the run goes on. It switches the condenser's cooling on and off, and watches the column-head sensor: if that fails or slips out of the column, Stilligent cuts power to the boiler and sounds the alarm, to help prevent an accident.

Power in the FAQWatch a run in the demo

Questions

What is the reflux ratio?

Of the liquid condensed at the top of the column, the reflux ratio is how much is sent back down for each part collected. At a ratio of 4, four parts go back and one is collected.

What happens when a column floods?

The vapour rises so fast that it holds the returning liquid up in the column. Liquid builds up, the still surges and gurgles, and separation collapses. Reduce the power and let it settle.

How do I know my column's power?

Use the power range this calculator gives for your column and packing, and watch the still: steady, even reflux and no surging mean you are within it.

Why does the spirit weaken towards the end of a run?

As alcohol leaves, the boiler gets weaker and the column needs more stages to reach the same strength. Raising the reflux ratio holds the strength for longer.

Is a taller or a wider column better?

Height buys strength and purity; width buys output, because it carries more vapour. Choose the width for your power, then the height for your strength.

More calculators for distilling

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Free to use, in metric or US units; your settings are remembered on this device. All results are estimates for planning: check strengths with a hydrometer or alcoholmeter. Distil only where it is legal to do so, and never leave a running still unattended.

Underlined terms are explained in the glossary - tap one for a quick definition.