What on Earth have you been reading?

[stilly_bugger]

If you're like me, you enjoy reading about distilling almost as much as you like the hobby itself. So I thought I'd start a thread where people could discuss what they've been reading.

While it would be good if everything discussed was relevant to the hobby, if you want to tell us about your time wading through Fifty Shades of Grey, the Twilight series or the latest Mills & Boon, go for it.

However, if you're more into books and articles on spirits, still construction and the distillation process, speak up, tells us what you're reading, what you've learnt and any points that may be of interest.

If it proves popular, maybe a few of us could shoot the breeze about a particular piece in the new 'Tech Talk' section of chat.

:handgestures-thumbupleft:

s_b

[Frank]

http://distillers.tastylime.net/library/IslayFacts/Islay_Distilleries_Factfiles.htm

:handgestures-thumbupleft: (for those who love their peaty Scotch, a good place for reference IMHO)

[stilly_bugger]

That's a very interesting find, Frank. I'm surprised at how short the various fermentation times are. 2-4 days (during the week) doesn't seem very long.

For the design nerds, there's a plethora of technical papers and slideshows on industrial distillation column and packing design, troubleshooting, etc. available for free through Fractionation Research, Inc.

[stilly_bugger]

I've been doing a bit of reading on plated columns, trying to suss out which I'd build if and when I get around to building one. The reading has been on industrial column design, and some of the issues that occur at industrial scale may not be experienced in a hobby sized stills. Nevertheless, the industrial columns research gives you a sense of what these columns are actually doing.

So, to the point: the following diagram, showing the performance range of a sieve tray, gives a sense of the importance of balancing vapour and liquid rates in plated columns. (I've reproduced the diagram from an article that discusses what happens inside a trayed distillation column. You should be able to access a copy at your local library. ;-) )

Sieve-tray-performance.gif

The F, E, M, W, L & D points on the gray line depict changes in column performance when you hold the liquid rate constant but change the vapour rate.

So, at M your column's operating normally, although the amount of liquid on your tray or passing across your tray is low to moderate. If you keep the liquid rate where it is but increase the vapour rate — turn up the boiler heat — you'll eventually push the tray to point E, where excessive entrainment (or carry over of liquid-rich vapour from a lower to a higher plate) occurs. Apparently it's here that the column becomes less efficient as the plate loses sufficient head room to allow the proper interaction between rising vapour and downcoming and cross flowing liquid. Pump more vapour into the column and you'll reach point F, where the column (or a couple of trays in the column) flood.

Now, what happens when you go the other way and reduce the vapour rate below M? Well, in a sieve tray there's insufficient upcoming vapour to keep the downcoming/crossflowing liquid on the tray. At point W the tray begins to weep onto the lower tray(s). Tray efficiency drops (marginally) as the amount of time the liquid spends on the tray interacting with vapour is reduced. Reduce the vapour rate further and you'll reach the lower operating limit of the tray, where the upcoming vapour is sheared off by the crossflowing liquid: point L. (This 'shearing' only seems to be a problem for industrial sized columns that are run at higher pressures than hobby columns and with greater tray crossflow.) Reduce the vapour rate even further and a sieve tray will dump its liquid load onto the tray below: Point D.

This, hopefully, gives a sense of the effects of vapour and liquid rates on sieve column performance.

But so what? Well, one thing seems to come from all this, if the analysis of industrial column performance applies to hobby columns. Bubble cap trays should avoid the lower vapour rate problems that you may get in a sieve tray. Each bubble cap acts as a weir, holding liquid on an unperforated tray. Unlike sieve trays, they don't rely on upcoming vapour to keep liquid on the tray. Therefore, a sieve tray will drop out of its normal operating range at a higher vapour rate than a bubble cap tray will. That is, you could keep a bubble cap column functioning at much lower heat than a sieve tray column. Why you would want to be able to do this, I haven't the faintest idea. One of the perks of a trayed column seems to be the speed at which you can collect distillate, and you're going to need to keep the vapour rate up to do that.

Anyway, I thought this might interest others.

Cheers. :handgestures-thumbupleft:

[crow]

I will see if i can find a Link I found on another forum to industry (alcohol industry) studies of a hole range of trayed columns how they work and their advantages and disadvantages . Might be hard to find as I'm not sure what thread I found it in of who posted it (got an idea) and it was a couple of months ago I read it , fucking with I had just copied it

[stilly_bugger]

This it? [0.7MB]

[crow]

No but it has alot of the same imfo between the 2 they'd cover almost everything , jeez now I really will have to look for it :doh: . Its in a post of one of the more active members of HD which narrows it down to half a dozen blokes and less than a trillion posts

[cereal_killer]

What have I been reading.... the thousand odd pages uploaded to the library by Stilly.... Thanks again mate!!!

[stilly_bugger]

Good to see you getting into it, CK. There are some goodens in there, many of which came from Chocaholic.

[stilly_bugger]

No but it has alot of the same imfo between the 2 they'd cover almost everything...

Just read this article* before bed, which, unfortunately, is not freely available for download. Although many of the equations escape me, the conclusions are clear enough:

The efficiency of the sieve tray was found to increase significantly by adding a layer of mesh packing on the tray which can be attributed to a higher interfacial area [from smaller bubble sizes], longer vapour/liquid contact time (i.e. higher froth height) and a lower liquid backmixing.

This conclusion was drawn from experiments on a 153mm (~6") and a 300mm (~12") diameter column using 25.4mm (1") or more of "knitted mesh packing" (the small stuff in the pic below) and running, among other things, a methanol/water wash.

DEMISTER_family_large.jpg

The addition of knitted mesh packing "much improved" efficiency in both diameter columns. The efficiency improvements were greater in the 300mm column that the 153mm column. And there was also a noted improvement in tray efficiency when each tray was loaded with 3" of packing rather than 1". So, the authors argue, it follows that such improvements in tray efficiency mean that you need fewer trays in a packed tray column to achieve the same result as an unpacked tray column.

What's going on here? Sieve columns are the most common (and cheapest) type of industrial distillation column. So you can see why researchers look for ways to make them more efficient — here, essentially by making them into hybrid packed-sieve columns. The experimental trayed column used in this research just got better and better as more and more packing was added. Not surprising when tray efficiency is your measure of "better".

But if you're building a sieve or perf plate hobby distillation column, chances are that your aim may not be to make each tray or plate as efficient as possible. Chances are that you may want a certain amount of flavour or "impurity" to carry over. And if you don't, then I suppose this piece of research shows that the best way to increase a trayed column's efficiency at separating out the ethanol in a wash from everything else is to turn it into a packed column. But if that's your aim, why wouldn't you just build a packed column?
__________
* Z.P. Xu, A. Afacan, K.T. Chuang 1996, 'Prediction of Packed Sieve Tray Efficiency in Distillation', Chemical Engineering Research and Design, vol. 74, no. 8, pp. 893-900

[R-sole]

I knew it :handgestures-thumbupleft:

SPP on a plated column still for neutral.