The Theory Behind Boiler Design (1)


A warning up front: this is going to be a rather technical post. On boiler design. How cool can that be, right? I mean, it’s not like we are discussing goodies like packing or automation or robotized needle-valve action. Boilers … boilers .. dull in a way, but – hey – we need them. Well, keep on reading. You might yet change your opinion about boilers being dull!

Distillation equals evaporation and condensation

Distillation is evaporation and then condensation. When the same amount of water (or beer or wine) is spread over a bigger, wider area, we get faster evaporation. Imagine a muddy pool with an amount X of water. The wider more shallow pool will dry out (evaporation) sooner. Or imagine you put an Y amount of water in two glasses, one wide the other narrow. The wider one will dry out sooner. And there is more, but more on that later. How does this translate to what we do and how we design iStill boilers? We like making them wider and low rather than narrow and high.


The way in which we distill, as Master Distillers making alcoholic beverages, is what’s actually called a “controlled environment distillation”. It’s not just about pool or glass evaporation rates. Instead, we want to control both evaporation and condensation.

With most distillation equipment, there’s controls for power in, for column management systems, as well as there are column and/or product coolers. The more control we get, the better drinks we can make in a more efficient way.

Boiler design is most of the time overlooked. But not by iStill. Since boiler shapes have a huge impact on the first part of distillation (evaporation), a well designed boiler is essential. If you want more control and better performance during your distillation runs, start with a good boiler design.

Boiler design

The wider instead of more narrow boiler design creates many advantages:

  1. More surface area means more evaporation, so you create a bit more gasses at the same energy input;
  2. A wider boiler, with more surface area, means the energy input is dispersed (evaporation!) over a wider area, so the liquid bath doesn’t rock & roll so much;
  3. As a result a wider boiler, with the same total content as a more narrow, higher design, can contain more liquids: 80 to 90% instead of 60 to 70%. Ergo: with the same amount of material you can do bigger runs;
  4. Because of the bigger fill, the gas bed above the liquid bath in the boiler is smaller, creating a more stable run that allow for higher production rates in a more controlled manner, and:
  5. Because the wider liquid bath does not rock & roll as much as a smaller diameter boiler does, the gas bed above it is much more stable, giving you even more stability in terms of constant gas pressure and stable gas speeds, again upping total system performance.

In short, our wider boiler design allows you to run bigger charges in a more controlled and therefore faster way.

From philosophy to practice

You will find this philosophy reflected in our boilers, which are much wider than other designs by other manufacturers. The iStill 50 boiler is 60 liter gross, but can be filled with 50 liters of liquids. That’s over 80%. The iStill 250 boiler is 300 liter gross, yet can hold up to 250 liters. That equals 83%. The boiler to the iStill One can even be charged up to 85%.

We can turn this around and state: with a wider boiler design, you need less total gross capacity to distill a certain set amount of wash. Ergo: you can build a smaller still. A smaller still has less material to it, so it is both cheaper to make and cheaper to run, since there is no need of heating up material we actually don’t need.

So, our boiler design allows you to run bigger charges in a more controled manner, at a higher pace, and with less energy losses! And less energy lost to materials heating up means there’s more energy you can put into the actual distillation process. More energy to play with translates to yet more (1) control ; (2) speed.

Positive feedback for better total system integration and performance

By starting our designs with the boiler, we create a positive feedback loop, where the total system benefits. For instance:

  1. More gasses are created;
  2. Allowing for faster runs in Potstill Mode and more reflux in Pure Mode;
  3. More reflux (in Pure Mode) boosts packing performance;
  4. So you get more redistillations for higher output and better Heads & Tails control;
  5. Gases are fed to the column in a more stable manner;
  6. Allowing for a run with less fluctiations, so the column management system can optimize easier (and faster);
  7. The upped control allows for higher power inputs again;
  8. Thus creating a situation where the complete system is used to its maximum performance potential.

The unique control, versatility, and performance of our rigs starts with designing a great boiler.


Why don’t others use wider boiler designs? How does boiler design effectively influence taste? There’s more to boiler design. I will keep you posted!


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