Bleeding off fores early

[bt1]

Howdy,

Been watching the glass still for enough runs now to really start putting together how the columns load up, plates run etc.

In the copper girl I always did as most do ...hold it all in total reflux till she's balanced, tweaked heating down from wash heat up to approx. running level etc.

I'm kinda changing my view on that cos I can see there's a period just prior to plates fully loading where the fores are sitting up on the top plate(s) isolated from the filling plates below. By this stage leaving RC down to very low flows the column bits in the upward vapour stream are hot enough not to induce natural reflux, allowing the fores to push over into the PC.

I've been bleeding off the fores at this point. Not wide open but a reasonable flow. It seems logical as it's not mixed with upcoming heavier spirit and rely solely on weight to separate out first. I'm still taking my normal overly cautious fores throw out its just about when it's done.

I'm unsure but doubt it's applicable to all stills as the naturally occurring reflux in taller sections above the RC like say if your using a packed rock section above would induce reflux and cause fores fall back and remixing back in any case. If your on a shorter length to the turn over point to downward vapour path it may well be worth giving it a try.
By smell, its very strong fores and real distinct. The remainder of the fores throw out cut is less unique.

btw, as a side issue to plate drivers, suggest you make sure your column is level so plates are dead flat. I can say for a fact a good few mms off dead flat and your plates act differently based on vapour bath levels at the loading stage...lower acting almost like a "bypass" route for the hard charging vapour and the slightly deeper side holding everything up or notably falling down to plate below. This seems to be an present until plates load up to the normal downcomer off take bath level.

bt1

[Brendan]

Sounds kind of like what I've been doing bt1...

I find at the right power level vs. coolant flow, that the fores will push through on their own and once bled out, the output stops or just drips as the RC is holding the rest back...

[bluess57]

Thanks bt, that's how my runs have been going with the heat turned up.
The RC on slow water flow doesn't hold full reflux and the fores push over

[bt1]

You know been watching the glasser last few runs and noticed, every run, the fores just sit there in winter all piled up ready to push over but due to reducer through to the turn over point not being hot enough it induces full reflux.

I can see it trying but it floods back onto the top plate.

So here we go soln..... put a top plate drain in to draw it off.

Why not I ask... all with big sight glasses will see it happening it's closer to best practice...less smearing so I ask why don't we?

bt1

[Sam.]

Basically the same principle as bleeding off the fores with a LM.

Is there any benefit to this over just bleeding them off normally then going back into full reflux :think:

[Sam.]

You would want to do it real slow too I reckon as not to upset the equilibium of the whole rig too much :handgestures-thumbupleft:

[CH3CH2OH]

any further thoughts to this topic?

[bt1]

Howdy,

been doing this for a while now. It just seems logical as the heads sit on top plate and won't flow over until the return head /turndown of the still is hot enough.

1/4" feed seems to do the trick. Still pull normal amount off so bout 300ml for me on most common wash.

bt1

[Yummyrum]

bt1 to get this right, have you soldered a piece of 1/4" presumably with a valve on it as a drain on your top plate ?

[troglodyte]

I've been using a vm take off on my top plate for a while now, just remove the top s/g and clamp on your vm tap/condenser etc. I pull all fores/heads through this, it saves heads going through your p/c, other than that I don't think there is any "true" benefit. though it does make things more interesting when doing a run.

trog.