VM still - reflux condenser position?

Reflux still design and discussion

VM still - reflux condenser position?

Postby oglennyboy » Thu Nov 28, 2019 8:13 am

heya chaps, I've been using a simple pot still with Liebig attached to my beer brewing urn for a while (pugirum & Teddy's FFV, bloody legends!) and have accumulated quite a stash of feints. I'm collecting the bits to make a VM still and after reading through a load of posts am stuck on the last bit... where precisely should the reflux coil sit in the head?
The coil I have is 160mm long, and looking at the SD short 2x2x2" tri-clamp tee it looks like there's about maybe 20-25mm from the top of the branch to the top of the tee. If I use a 200mm extension I'll have about 50-60mm gap from the bottom of the coil to the top of the offtake stub. Is this important? Likewise, a 100mm extension means lifting about 40mm of the coil out of the head, reducing the amount of cooling a little I guess.
I'd toyed with the idea of the CCVM approach but I'm a short arse ;)

The VM will be a 2" SS column made from 2x510mm triclamp tubes wit SS scrubbies as packing. To marry up to the Liebig I'm running from the 2" tee in 3/4", using a triclamp reducer rather than a taper to keep the valve close to the takeoff.

I was thinking of using one of those stainless mesh screens thats built into a triclamp seal as a centering ring, but also see that a few people think centering is not a big issue for a 2" column. What's the brains trust thoughts on that?
And one more question! When plumbing the reflux coil, does the cold water connect to the inside or outside loop?
Pics to come when the bits have arrived :) And probly more questions.... like.... a sight glass to double for gin infusion?.....
cheers!
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Re: VM still - reflux condenser position?

Postby woodduck » Fri Nov 29, 2019 9:58 am

I'd like to help mate but just not quite sure what your asking. Can you draw a diagram or post some photos so we get a better idea.
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Re: VM still - reflux condenser position?

Postby oglennyboy » Fri Nov 29, 2019 7:31 pm

Thanks for the reply WD, hopefully the chat below helps a bit...
The pic below shows the tee I bought, its a short leg one to keep the valve close to the takeoff (that seemed to come up a few times in discussions around VM's).
The other pic shows the 1/4" double helix coil which is 160mm long from the cap. Lined up against a pipe shows where the end of the coil sits in relation to either a 100mm or 200mm long riser off the tee. So the dodgy pic is a bit off as its using a long leg tee, but for the short leg tee I have:
- for 100mm riser, about 40mm of coil pokes out the top, meaning only about 120mm of coil is in the vapour path
- for 200mm riser, the coil sits about 60mm above the top of the take off branch

Is one or the other case better or worse? I had a better rummage thru the posts in the reflux forum and found some replies from Orcy & TheMechwarrior where 150-250mm of coil has enough to easily knock down a 2" column. So I'd be OK with the second case I feel (for a 2400 watt boiler), but wanted to see whether the empty space above the take off branch is an issue.
cheers
Reflux coil.jpg

Short 2in tee.jpg
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Re: VM still - reflux condenser position?

Postby RC Al » Fri Nov 29, 2019 9:48 pm

If your planning on using a 3/4 valve to regulate vm takeoff, i would strongly suggest instead adding 4-500 to the column, going ccvm and getting a step ladder, significant speed increase

What you are doing will work, but with a 3/4 valve, your setting in stone a rather high reflux ratio, which will be needed with the shorter column, but translates to a long run time

If you're going to keep going as is, put the coil in a 200 section above the T, otherwise you'll have to play with cooling rates as well as the vapor valve to regulate output if the coil overlaps into the takeoff zone
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Re: VM still - reflux condenser position?

Postby oglennyboy » Sat Nov 30, 2019 1:24 pm

Thanks for the info RC Al, yeah I went with the 3/4" valve due to the Liebig being 750mm x 3/4" over 1/2", so I thought that might be the controlling restriction.
Based on one of those calculators I expect somewhere around 750-850ml/hr, which is gonna be painful for sure. But only a bit more tedious than current spirit runs on the pot
If the reflux ratio isn't really affected once it hits the condenser, then I think I could go to a 1&1/4" valve as the calculators indicate about 1900ml/hr for the 2400W boiler. That's probly a stretch in the real world, but I know the condenser will knock down 2000ml/hr when running my pot still in stripping runs.
Would the reflux ratio based on a 1&1/4" valve apply when running into the condenser via a taper reducer? See the pic below for example....
valve to reducer.jpg


The future plan is for a nice 2" 5 Star shotty, but that's a ways off.
cheers
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Re: VM still - reflux condenser position?

Postby RC Al » Sat Nov 30, 2019 3:42 pm

Ahhh yup, I can't answer that one, pretty sure that you may have the right of it with the 1/2" being more of a determining factor, however the effect of the vapor acellerating as it cools might counteract the restriction....

Even a 2" shotty only has 5x 1/2 tubes, roughly a 1/4 of the area of 2" :think:
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Re: VM still - reflux condenser position?

Postby oglennyboy » Sat Nov 30, 2019 7:23 pm

Yeah I haven't really been able to get a solid feel on where in the system the reflux ratio is taken at. The Liebig I have is going to be positioned immediately after the valve, with a bushing to reduce. It might have a bit of acceleration as you say, making an effective ratio better than the 3/4" : 2" suggests.
To set the system up to suit future expansion with a better condenser I think I'll go with a 1&1/4" valve and a short reducer off the 2" tee, seems it might be the biggest bang-for-bucks when considering the cost of valves around that 1" - 1&1/4" - 2" range, and the big step up in ratio compared to the original idea of matching 3/4" all the way through from the tee.
Hopefully I can get something approaching 1600-1800ml/hr, at about 94.6-94.8%, which is about the take-off rate at 82% I'm getting when doing a spirit run on the pot. And this pot still spirit run can only maintain that purity for 65 mins, so I'll be way ahead when it comes to doing a feints run.
Thanks for your replies.
cheers!
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equipment: 44 litre urn for homebrew, just finished making a pot still attachment and about to get excited!


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