2" or 3" shotgun dilemma

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2" or 3" shotgun dilemma

Postby Talix » Mon Nov 27, 2017 9:30 pm

Hi guys, thanks for a great community.

I've decided to upgrade my liebig to a shotgun, since my trusty liebig is having issues coping with my burner... Further more I'm in the process of upgrading to 5500w electric, it'll just have to give up during strips... And the plated column on the horizon will be complete with a super oversized condenser...

Ok, it's not all sillyness - I'm from Cairns, Au. Distilling with a liebig can be a pain here in the summer, especially since my water pipes run through the roof and often will provide 80C hot water during the day, unless I run it continuously... Even then, it's never below 35C.

I was considering the benefits of going 3" (76.2mm OD, 72.94 ID) vs 2" (50.8mm OD, 48.36mm ID) and came up with a few combinations when using (AU standards) DN15 (12.7mm OD), DN18 (15.88 mm OD) and DN20 (19.05mm OD) copper pipe. I'm not sure about the length yet, but I think I'll choose the length of the bigger pipe so that I can use one or two whole 6m lengths of the smaller copper pipe. I'll use baffles every five-eight centimeters for added efficiency.

I really like idea number 4, but I think the middle pipe might get really hot since it has little clearance... What do you think?


EDIT: For reference on AU copper standards if needed (http://www.cranecopper.com.au/downloads/wCRN_AS1432_Tube_2010.pdf)
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Re: 2" or 3" shotgun dilemma

Postby KingE » Mon Nov 27, 2017 9:52 pm

Mine Is like number two, 2 feet long. I adjust water flow to just keep the exit water pretty warm but not boiling during a strip run (5500watts). Even then the condenser is completely cold 6-8 inches down. This takes very little water flow, but mine is 45 F. Hopefully others can fill in the gaps in my knowledge of this.
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Re: 2" or 3" shotgun dilemma

Postby Twisted Brick » Mon Nov 27, 2017 11:42 pm

Nice drawings, Talix.

The 3" plans look like serious overkill, IMHO. I run a 3" pot into a 2" shotty (plan #3) and it performs like a beast. In fact, it's efficiency during a strip has exposed my 30gal reservoir as the weak link in my cooling system.

Also, a 2" promises to be easier and cost less to build, not to mention place less stress on your rig due to reduced weight.

I am a big believer in baffles, here's a look at my build: viewtopic.php?f=87&t=67972

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Re: 2" or 3" shotgun dilemma

Postby zapata » Tue Nov 28, 2017 12:20 am

Your drawing doesnt have the dimensions to easily check, but the pitch (space between tubes) should be 1.25 - 1.5 times their diameter. That is a center to center spacing for DN15 of 15.875 - 19.05 mm, DN18 19.85 - 23.82, DN20 23.8125 - 28.575.
Ideally baffles are equally spaced no less than 50mm apart and no further than shell diameter. See the following link to cut the perfect baffle:
viewtopic.php?f=87&t=67493
I personally can't see the need of the larger shell unless you just have it ready or like the aesthetics. It would be overkill for anything I can imagine running.
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Re: 2" or 3" shotgun dilemma

Postby still_stirrin » Tue Nov 28, 2017 5:51 am

I too, like the #2 design. My shotgun product condenser is 7 x 3/8” ID inside of a 1-1/2” ID shell and is 24” long with 5 internal baffles. It was designed to handle 4.5kW and does so very well even with a very slow coolant flow (great efficiency).

The 3” shell is overkill for your needs and would be expensive to build and heavy to operate.

I suggest the #2 option with a 24” jacketed section to maximize the vapor tube conducting surface area (pi x the diameter of the vapor tubes x length of the jacketed section x the number of tubes).

Vapor flow velocity should be as slow as possible to maximize dwell time. The flow area is defined by the area of the vapor tubes (pi/4 x tube diameter x tube diameter x number of tubes).

Similarly, you’ll want to keep the inlet to the shotgun as large as possible for th same reason. Therefore, it should be 2” ID or larger if possible and minimize flow restrictions (sharp bends or reducers, if possible). Thinking about the upcoming flute design, keep the shotgun’s inlet in mind.
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Re: 2" or 3" shotgun dilemma

Postby Talix » Mon Dec 04, 2017 7:30 pm

Hi guys

Thanks so much for the good advise, I will take them to heart - Perhaps 3" is just too much... From your posts it's clear that cooling power is definitely enough even with a 2".

However, what about vapor speed or possible vapor pressure in an open system? If I am to use it on a 4" CCVM column (or any column with an opening to the atmosphere apart from the vapor output) it was my understanding that reducing the size of the output after the 4" takeoff on the tee would increase my reflux ratio and reduce my possible output rate considerably (Source DAD300)... With a big 4" (8171mm2) opening to the atmosphere where the reflux coil goes in, and the product output reduced to 2" (2042mm2) and then further reduced to the 7 DN15 tubes (each approx 98mm2 = 685mm2), couldn't I have problems maintaining a good output rate? I guess I just have trouble understanding how the vapor (or gas) can travel quickly through a small output while a massive opening is present earlier in the path...

I understand that this issue is non-existant on a flute as all vapor pressure is directed towards the product output. But I was planning on making a packed column as well, since my wife likes the neutral... Would I perhaps be better off skipping the CCVM design (with the opening where the reflux coil goes in) altogether and instead rely on the flute dephlag to create reflux in my packed column? I guess that's a CM still. Then I would only have a single opening to the atmosphere through the dephlag and product condenser...

The price of the build is of little concern as I can get 4" for practically nothing, $10AUD/kg.

I apologize if the above is a bit hard to understand - English is not my first language :crazy:
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Re: 2" or 3" shotgun dilemma

Postby zapata » Mon Dec 04, 2017 11:29 pm

I hear your concern. Lets eliminate the CC part for a second and just think VM for a minute. The overwhelming factor influencing how the vapor splits is the cross section of the 2 paths at the split, with much less influence by what happens further on either path.

Look at many "traditional" VM designs where the vapor splits in an equal T, but the vapor side product condenser after the downturn is much smaller. For example a 1/2" inner tube liebig works fine on a 2" VM, at least near a 1:1 reflux ratio with a wide open valve. In terms of reflux area : product condenser area this would be about 16, where your 4" reflux area : 7 tube condenser would be about 12. So your shotgun could be less restrictive than a proven VM design.

If you read a lot of VM threads you'll find a lot of theory involving vapor density, gravity, vaccuum etc describing why the smaller condenser doesnt seem to screw up the rate too much as long as the place the vapor splits is 1;1 and depending on where the reduction happens (and a fair amount of argument about whether all of those words are technically accurate).

But more importantly for a second, lets talk about what does affect the ratio, and that is the packed heads column I added above my VM head. This no doubt causes a restriction that makes more vapor go out the VM than the 1:1 vapor split should do. Which makes sense if you think about it. Blow throw an open 1/2" tube, an open 1" T, an open 2" tube, and a packed wet 2" column. All the open tubes will feel like there is no resistance, while the packed section clearly has some resistance. I think this gives an idea of how much resistance is needed to significantly affect the ratio set by the vapor split. By the way the russians take advantage of this by simply having a smaller cheaper lighter VM takeoff instead of an equal T, the restriction of the heads column effectively "pushes" more vapor out the VM than the area ratio alone would allow.

With all that, I think it's possible to make a 4" CCVM with a 7x1/2" tube shotgun and get pretty close to a 1:1 reflux rate. I would use a 4" T, a 4" 90, and maybe a short drop of 4" before reducing to 2" and the shotgun. This is different from the OP Dad was responding to. OP there had a 2" valve coming off a 4" column giving him a minimum reflux rate of 4:1 right off the bat based on area where the vapor slits.
Now, it must be the SPP, but Dad seems to get by with much lower reflux rates (and thus much higher takeoff rates) than I've ever been able to achieve. For a neutral only still, I wouldnt mind a 4:1 minimum reflux rate, because I'd never use less. Stripping, pot runs, even refluxed rums and whiskies a minimum RR of 1:1 or less is useful, but you're already going to have a plated column none of that should matter. Unless you use SPP, you will almost never run less than 4:1.

I feel like I wrote a book, hope it makes sense.
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Re: 2" or 3" shotgun dilemma

Postby Twisted Brick » Tue Dec 05, 2017 1:23 pm

zapata wrote:
With all that, I think it's possible to make a 4" CCVM with a 7x1/2" tube shotgun and get pretty close to a 1:1 reflux rate. I would use a 4" T, a 4" 90, and maybe a short drop of 4" before reducing to 2" and the shotgun.


Very helpful post, Zapata. Do you think a 2" x 21" shotty (4 x 1/2") would get to 1:1 if the column is only ~30"?

For a neutral only still, I wouldn't mind a 4:1 minimum reflux rate, because I'd never use less.


That's good to know. I was worried 30" would be a tad bit light on the reflux, (SS scrubbies or lava rock) but I figure I could always add a 24" spool and more packing. Either that or use my spare 3" x 10" length of copper and add a single perf plate to it (and a boil ball!).
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Re: 2" or 3" shotgun dilemma

Postby bluefish_dist » Tue Dec 05, 2017 1:29 pm

To further expand on the reflux rates needed for a VM, when doing a neutral I run a 1" valve off a 2" T on a 4" column. I have never run the valve wide open. In fact if you look at how far the valve is open, it's a tiny opening.

The lower reflux rates are only needed when running whiskeys. Then I have run a 2" valve all the way open, but only for short periods during the run. Usually the first part of the hearts, then I have to start closing it. I have used the same 2" valve on the 4" head for my 6" column and it works fine except for whiskey. I have a 3" valve to try next run.
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Re: 2" or 3" shotgun dilemma

Postby zapata » Tue Dec 05, 2017 4:35 pm

Twisted, I'd guess the still in that pic should hit 1:1 with the coil all the way up. It has nothing to do with the column. And the point I was trying to make above is that it probably has llittle to do with the condenser.

What you're trying to make will determine if 30" is a tall enough column, I really dont know but would guess it'd be good for a single run whiskey or rum, but insufficient for neutral.
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Re: 2" or 3" shotgun dilemma

Postby Twisted Brick » Wed Dec 06, 2017 2:57 pm

Thanks Zapata. I understand the secondary role of the RC to the area ratio, (and how the russians manipulate it). For some reason I was thinking that the higher the ABV (taller column), the more takeoff would be realized.

Still, at 30" I'm under the 15:1 minimum for column length/width ratio, and will need to adjust accordingly.
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Re: 2" or 3" shotgun dilemma

Postby bluefish_dist » Wed Dec 06, 2017 3:17 pm

For a neutral you may be able to get a faster takeoff rate with more column height. I am planning on adding 18" to my column to make it easier to hit azeo and/ or be able to take off faster. If you are shorter than optimal then adding the height helps as you can run a lower reflux rate and achieve the same abv.
When I ran a 2" column I ran 60" packed and was able to hold azeo at 2l per hour at the start of the run.
On 4" I am at 72" now and going to 90". I can hold a true temp corrected 190+ at about 1 gal/hr. It takes a pretty high reflux rate to hold a true 190+ even at 72" packed. I have a 2" T for the split, going to a 1" valve that is only open 4 to 5 turns out. It takes 2 turns to crack the valve open.
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Re: 2" or 3" shotgun dilemma

Postby Twisted Brick » Wed Dec 06, 2017 3:51 pm

Thanks, John. The way I understand a VM to work, lower than expected ABV is adjusted by reduced takeoff/increased reflux, effectively sending a controlled percentage of vapor back through another round of reflux. By supplying the takeoff split with a higher ABV to start with (taller column), the re-cycling of vapors isn't required, thus reducing the time required to achieve the desired ABV.

Then again, maybe I have this backwards and the takeoff rate and associated ABV can only be optimized to match the maximum a column can produce.
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Re: 2" or 3" shotgun dilemma

Postby bluefish_dist » Wed Dec 06, 2017 6:09 pm

There is a max abv for a given column height. You can detune it some, but if you want lower abv it's easier to run shorter than try and detune a lot.
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Re: 2" or 3" shotgun dilemma

Postby KingE » Thu Dec 07, 2017 4:34 pm

All this sort of talk had me wondering what sense I would be able to make of it when I started running stuff. Review this discussion once in a while after you get started. It will come into focus and begin to relate to what you actually see happening with the still!
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Re: 2" or 3" shotgun dilemma

Postby zapata » Fri Dec 08, 2017 12:06 am

Talix wrote:Would I perhaps be better off skipping the CCVM design (with the opening where the reflux coil goes in) altogether and instead rely on the flute dephlag to create reflux in my packed column? I guess that's a CM still.

Just reread the thread and missed this. Yes, no doubt I would start there if you are building a flute. Put a column over the plates (or at least 1 or 2 of them depending on how modular your flute will be) and under the dephlag. Gain the benefit of a hybrid column with no need to buy the T, coil, and short head for a CCVM. Also experience running it as a flute or hybrid would translate back and forth to you just knowing how to run your rig a lot better. VM is cool, but if you have a flute I can't think of a reason to not go with a hybrid CM.
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Re: 2" or 3" shotgun dilemma

Postby bluefish_dist » Fri Dec 08, 2017 11:46 am

The real advantage that I see of a VM over CM is that the VM doesn't care if the cooling water temp changes. That works better if you recirculate water. The down side of a VM is that valves become the limiting factor as you get bigger. Not really an issue for home use, but it is for commercial.
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