LM with Flow Independent reflux ratio?!?!

[plamrock]

OK so I am new to the world of distillation but I have taken the advice for this forum and read and re-read article after article. And I probably have a lot more reading to go so please feel free to send me back to reading if need be!

Looking at reflux designs and from what I have read (emphasised in kiwistiller's basic overview article) the real benefit of VM over LM is the ability to control (or set) the reflux ratio once for the duration of the distillation, whilst in LM requires alteration of a valve to control (with a little guessing) the ratio as condensate diminishes.

The question I have is if you could set the split ratio of the condensate from the reflux condenser (rather than the obviously easier vapour ratio) do you end up with the same benefits of a VM system? ie is it just that the valving on an LM is limited to flow rate control independent of supply. Or are there a multitude of other reasons for a VM over LM other than RR that I am missing?

I was thinking about ways of controlling reflux ratios from a LM perspective that are (1) flow independent (2) allow better calculated ratios and (3) can provide more than 1:1 (or as per build hardware) if required. Really just a modified Bokakob or slant plate with ratio option replacing the flow control.

Ok so feel free to start correcting me now!

[Coaster]

@ plamrock,

Welcome to the Forum

Perchance have you considered a LM/VM Combination Still? There are numerous LM/VM Combination Stills threads throughout the Forum. Suggest reading up on the design function of a correctly designed LM/VM Combination Still and believe you will find that LM/VM Combination Still will meat your needs.

Regards,
Coaster

[rad14701]

The reason that VM requires less run time adjustments is due to the fact that there is always a constant rain of reflux whereas with LM the amount of reflux in relation to the spirits removed diminishes... There is another form of LM, called Reverse Liquid Management (RLM), where the needle valve is used to regulate the amount of reflux and the spirits take off slowly diminishes instead... This helps keep the column in equilibrium longer without the need for adjustments... The Nixon Stone style offset head valved reflux column can actually be run in this manner if built with both needle valves instead of only one, or if built specifically for RLM...

[plamrock]

Thanks rad14701,

Hmmn I might have to get my head around RLM a bit more as from what I understand this simply puts the reflux into a constant rate instead of the product. Hence at initial take off product is highest and dimishes over time. Doesn't this suggest a change in ratio over time? I notice you mention keeping to column in equilibrium longer would this actually be the preference then?

Thanks for your advice. My initial question I suppose was a theoretical one whether a constant ratio split of reflux condensate (if it could be done) would be equivalent outcome to a VM.

[plamrock]

Hi coaster,

I'll have to look up the VM/LM options. As I mentioned to rad I suppose I was trying to better understand the theory by asking whether a constant ratio split of reflux condensate (if it could be done) would be equivalent outcome to a VM. Rad has mentioned the column equilibrium issue which I will read into further.

Thanks for the advice. Plenty to read which as a scientist I am loving!!!

@ plamrock,

Welcome to the Forum

Perchance have you considered a LM/VM Combination Still? There are numerous LM/VM Combination Stills threads throughout the Forum. Suggest reading up on the design function of a correctly designed LM/VM Combination Still and believe you will find that LM/VM Combination Still will meat your needs.

Regards,
Coaster

[rad14701]

plamrock, yes, the reflux ratio does increase over the course of the run when using RLM because the reflux remains the same while the product take off rate diminishes... The only time you might need to adjust the reflux rate is if the column temperature begins to rise because it is the amount of reflux that helps maintain that equilibrium... Another potential option, albeit sometimes not effective, is applying more heat to increase the amount of vapor produced... This can be a double-edged sword, however, because of the proportionately increased amount of water to alcohol in the vapor...