Condenser not knocking everything down in column...

[joeymac]

I ran my new 3" packed section yesterday but used my 2" boka head on it. I wasn't worried about the boka head (or at least I thought I shouldn't be).

When I do stripping runs, about ten now with this setup) I attach the boka head directly to the boiler and crank the heat to 5500w and the boka head spits everything out without any vapor puffing the top. It knocks all 5500W down even with the cooling input water surprisingly as warm as 105F/40C. It's a beast. 2" diameter, 12" long with a double coils over a center 1/2" coldfinger.

So I ran my first neutral on a new 3"x40" packed section the old boka head. During column stabilization at 90% power (4400-5000w) I'm smelling vapors and for the life of me, can't find the leak. I think maybe it's coming out the top, and sure enough there was a decent amount of vapors - enough to make a dime-size wet condensation spot on a cold mirror. My cooling water was flowing well at 2.5LPM and wasn't even warm yet... probably only 25C. Now logic tells me that if this thing can knock down full power monted directly to the keg with super warm cooling water... that's as bad as it should ever get.

Why can't it knock down 90% power mounted 40" higher on an uninsulated column using still cool water?!?

I couldn't figure it out, so I dialed power back to 80% and continued the run like that... but I had to swap out my cooling water about once an hour because it would get intermediately warm and my bok head would start puffing slightly.

[Lyonsie]

Im interested in this. I would have built a boka only for the take off speed. I don't understand how you are getting vapour escaping though. Your bottom plate should be flooded should it not?

[pfshine]

How packed is the column? It could be the vapor speed messing with you. The vapor may have found a small channel to go through and increase speed so much that the condenser can't knock it down due to speed.

[joeymac]

How packed is the column? It could be the vapor speed messing with you. The vapor may have found a small channel to go through and increase speed so much that the condenser can't knock it down due to speed.

5/8" Marbles - leaving 42% open column volume. That's a good point. I can try finding somewhere to stick copper mesh into to slow vapor down and give it more time. Because it's not a typical vapor leak, it's sort of "huffing" out the vent hole. And I've seen my condenser and recirculation setup handle 5500W a bunch of times in the past on stripping runs - so I know it can physically handle the power.

Which get me thinking (out loud)... I think you're right. It's got to be a vapor speed problem:
On a boiler charged with 10% wash (potstill/stripping), I'm probably looking at an initial vapor composition of 55%ABV and the other 45% is mostly water. With a packed column making 95%ABV, the other 5% is water. And the catch is that for any amount of power, the mass of ethanol vaporized is about 2.7X more than the mass of water vaporized. So it's quite possible that 5500W of 55%ABV vapor is drastically less volume (and therefore vapor speed) even 4500w of 95%ABV vapor.

Ethanol enthalpy of vaporization, +0.8370 kJ/g
Water enthalpy of vaporization, +2.256 kJ/g

[joeymac]

Im interested in this. I would have built a boka only for the take off speed. I don't understand how you are getting vapour escaping though. Your bottom plate should be flooded should it not?

The vapor is coming out the top vent hole. All LM columns should have a vent hole somewhere past the condensers so the still can "breathe" and maintain steady pressure - otherwise the liquid output would surge.

[jedneck]

Condeser water on a pump or mains pressure?

[joeymac]

Condeser water on a pump or mains pressure?

Pump, 2.5LPM steady.

I guess when I do column runs, I could hook it to my garden hose. The water would always be cold and I could really dial up the flowrate.

Alternative strategy (and much more fun) 3" Boka Head with 3 tightly spaced coils and a cold finger return

[kimbodious]

Huffing? Could it be that the RC is running too well? What are you seeing in that sight glass? Is the condensate a steady drizzle or are there surges of condensate? I would try putting some scrubbers in the coil of the RC and backing off the amount of water sent there.

[Desvio]

Imma step out on a limb and ask a dumb question, is it possible to run so hard where the condenser coil is able to knock down the most or all of the ethanol and yet still have some water vapor get past?

[Saltbush Bill]

I'm going to go with Kimbo on this one, Thats exactly whats happening, your still is huffing like a liebig condenser can, 5500W is a lot of heat.
My gut feeling is that is if you reduce the amount of water to the condenser so that the water leaving the it is quite hot you might at least lessen the problem if not fix it completely.

[Swedish Pride]

I'd go with PF on this one, deffo think it's vapourspeed.
I get some vapur bypass on my RC and I reckon it's down to vapour speed.
I've a 6" column with a 3" condenser, I always get a small drip bypassing the RC no matter how hard i run the boiler, I have to use a shit ton of water to stop the drip ( about a drip every two second)

I don't care about the drip and just let it drip until for the few min that it takes to fill the plates

[jedneck]

Condeser water on a pump or mains pressure?

Pump, 2.5LPM steady.

I guess when I do column runs, I could hook it to my garden hose. The water would always be cold and I could really dial up the flowrate.

Alternative strategy (and much more fun) 3" Boka Head with 3 tightly spaced coils and a cold finger return

At what head height? Could be that on strip runs it get plenty of flow but with colunn flow decreaces cause of head height.

[USACelt]

Sounds to Me like the boka is flooding at full power. Causing the liquid to bubble out the top vent. I also see two problems here.

[joeymac]

Jedneck, Height is +44" vs the strip runs. Flow measured at both is approx 2.5LPM so that's not it. Flow was the first thing I checked and it's basically the same as my notes from potstill mode.

I'll check my math notes when I get home, but I'm pretty sure my issue is the physical vapor volume difference of 95% abv and 55% abv. i shouldn't have assumed all power condensed was the same.

USAcelt, Not sure what's wrong with a big old collection jug for stripping runs. If your complaining about the tube, it's teflon tubing. That stuff is stupid expensive though... like $5/foot. Buts super convenient when I need a little piece to drop into a jar/bottle/jug. It slips right onto the copper tube with a leakproof tight seal.

[jedneck]

Jist spitballin ideas. Figured you checked it bit never hurts to check

[kimbodious]

Your monster RC at 2.5 lpm has massive knockdown capability, plenty enough for a stripping run (say producing 50%ABV) at full roar. Heaps and heaps more than what is required for a spirit run producing 90+% ABV . I am holding out on the vapour column is constantly collapsing and reforming again because of the strong cooling effect of your RC. Your mention of the vapour huffing reminded me of this excellent demonstration in the videtorial by Yummyrum http://tinyurl.com/jw8m9ps, enjoy!

[joeymac]

So I finally dug up my distilling thermo notes:

Ethanol:
Latent Heat of Vaporization 836.8 kJ/kg
Vaporization Energy == 1.195 g/kW-s
0.740 g/mL Liquid Density @ 78degC
0.00143 g/mL Vapor density @ 80degC

Liquid EtOH 1.615 mL/kW-s
Vapor EtOH 835.7 mL/kW-s
(approx 517:1 )

Water:
Latent Heat of Vaporization
Vaporization Energy == 0.4428 g/kW-s
0.9718 g/mL Water Density @ 80C
.000590 g/mL Steam Density @ 1bar

Liquid Water 0.456 mL/kW-s
Water Vapor 750.5 mL/kW-s
(approx 1645:1)

Stripping Run 50%ABV Vapor Volume: 793.1 mL/kW-s
Azeotrope Run 95%ABV Vapor Volume: 831.4 mL/kW-s

The last two lines are what's important. They describe the vapor volume vs. power input for a 50%ABV product (as seen for something like a 8-10% wash in a potstill) and a 95%ABV product (as seen from a neutral column). unfortunately for my hypothesis, the numbers came out alot closer than I would have guessed because even though WAY less water mass-per-kW is boiled versus ethanol... water vapor volume is HUGE compared to ethanol vapor.

So plugging in my real world boiler power input I get
Stripping Run 50%ABV Vapor Volume: 4.362 L/s @ 5500w
Azeotrope Run 95%ABV Vapor Volume: 3.741 L/s @ 4500w

In fact, it looks like my potstill mode makes 15% more vapor @ 5500w volume than my column setup at 4500w. I don't think my hypothesis holds water, here. Back to being confused again.

Your monster RC at 2.5 lpm has massive knockdown capability, plenty enough for a stripping run (say producing 50%ABV) at full roar. Heaps and heaps more than what is required for a spirit run producing 90+% ABV . I am holding out on the vapour column is constantly collapsing and reforming again because of the strong cooling effect of your RC. Your mention of the vapour huffing reminded me of this excellent demonstration in the videtorial by Yummyrum http://tinyurl.com/jw8m9ps" onclick="window.open(this.href);return false;" rel="nofollow, enjoy!

Kimbo, Thanks for that excellent video. Very interesting. It might be that, but I don't know if puffing at the a column's ventilation port is entirely comparable to a potstill huffing. When my cooling water is freshly changed out and cold on the column setup my puffing problem goes away and as the water gets medium temperature or slightly warm it slowly starts puffing. In contrast on the potstill mode, I can input anything from 16C cold water to pretty darn warm 40C water and the coils knock everything down.

I might just live with the problem and just hook a water-vapor trap up to the breather port so if it huffs hard enough, it bubbles into a small water tin and the water captures the vapor.

[still_stirrin]

...It might be that...column's ventilation port is...huffing. When my cooling water is freshly changed out and cold on the column setup my puffing problem goes away and as the water gets medium temperature or slightly warm it slowly starts puffing....

I might just live with...the breather port, so if it huffs hard enough, it bubbles into a small water tin and the water captures the vapor.

How big is the "breather port"? Do you plug it when running "potstill" configuration?

I suspect that it is too small, such that as the vapor rises, it pushes and pulls air through the orifice. And it also causes the vapor flow to stagnate in the column top, restricting the vapor flow into the condenser area. A larger orifice might be the solution. My reflux condenser is open to the atmosphere in its entirety...no cap on top at all (1-1/2" ID).
ss

[joeymac]

...It might be that...column's ventilation port is...huffing. When my cooling water is freshly changed out and cold on the column setup my puffing problem goes away and as the water gets medium temperature or slightly warm it slowly starts puffing....

I might just live with...the breather port, so if it huffs hard enough, it bubbles into a small water tin and the water captures the vapor.

How big is the "breather port"? Do you plug it when running "potstill" configuration?

I suspect that it is too small, such that as the vapor rises, it pushes and pulls air through the orifice. And it also causes the vapor flow to stagnate in the column top, restricting the vapor flow into the condenser area. A larger orifice might be the solution. My reflux condenser is open to the atmosphere in its entirety...no cap on top at all (1-1/2" ID).
ss

3/8" It's always open even during potstill configuration. The whole cap the coils are connected to just sits over the 2" pipe - it's not actually sealed, but it is a slip-fit as pipe fittings tend to be. I just have the open vent hole for easier venting if needed.

Interesting thought on the size being too small. I guess I can try to get more opening. I'll have to play with it. I should have enough feints to make a neutral run in about 3 more weeks.

[still_stirrin]

...3/8"

It's always open even during potstill configuration. The whole cap the coils are connected to just sits over the 2" pipe - it's not actually sealed, but it is a slip-fit as pipe fittings tend to be. I just have the open vent hole for easier venting if needed...

So, if you were trying to prevent "over pressure", the 3/8" vent would suffice. But, you need the vapor to be "buoyant" enough to enter the reflux condenser chamber. With the small "pin hole" opening, you've essentially made an orifice, which regulates flow by the pressure drop through the orifice. It is a "flow restrictor"

But since you're producing vapor in a 2" column, the little orfice presents a back pressure to the rising vapors. When that happens, they don't continue to "float upward" into the condenser section. And what's more, the pressure difference creates a "puffing" condition through the orifice...and even the liquid outlet if the plates are empty. You'll get surges at the liquid outlet until the reservoir is empty and then it too will puff out.

Open the top up. Let the rising vapors continue at the same velocity into the reflux condenser chamber. There, it'll collapse on your big double coil + cold finger condenser and drip back down. The full open top will allow the collapse without a noticeable "huffing" as well.

So, for a 2" boka, I would suggest your "vent" be at least....at least 1" diameter....preferably larger, if you can. If you want the cap to hold your cold water inlet and outlet lines on the top, then cut away all unnecessary copper in the cap, with enough support ONLY to hold the tubing in place.

And when you run a potstill, you'll likely need to close the opening completely and add a product condenser coming from the "fully opened" liquid outlet lines. Better yet...build yourself a potstill head and a Liebig. Get your tools in order, to make the best products you can.
ss

[kimbodious]

+1 that makes a lot of sense still_s, so too the advice about building a pot head. I'll bet there's not all that much vapour entrained with the air being forced back out that small aperture but plenty enough to emit an odour and condense on the mirror. A smaller opening would induce a higher velocity and probably greater entrainment of vapour?

[Pikey]

I ran my new 3" packed section yesterday but used my 2" boka head on it. I wasn't worried about the boka head (or at least I thought I shouldn't be).

When I do stripping runs, about ten now with this setup) I attach the boka head directly to the boiler and crank the heat to 5500w and the boka head spits everything out without any vapor puffing the top. It knocks all 5500W down even with the cooling input water surprisingly as warm as 105F/40C. It's a beast. 2" diameter, 12" long with a double coils over a center 1/2" coldfinger.

So I ran my first neutral on a new 3"x40" packed section the old boka head. During column stabilization at 90% power (4400-5000w) I'm smelling vapors and for the life of me, can't find the leak. I think maybe it's coming out the top, and sure enough there was a decent amount of vapors - enough to make a dime-size wet condensation spot on a cold mirror. My cooling water was flowing well at 2.5LPM and wasn't even warm yet... probably only 25C. Now logic tells me that if this thing can knock down full power monted directly to the keg with super warm cooling water... that's as bad as it should ever get.

Why can't it knock down 90% power mounted 40" higher on an uninsulated column using still cool water?!?

I couldn't figure it out, so I dialed power back to 80% and continued the run like that... but I had to swap out my cooling water about once an hour because it would get intermediately warm and my bok head would start puffing slightly.

I'm not entirely sure you have a problem here.

In another recent thread, people said it was normal to smell vapours early on with a boka.

During the heat up period, the air in the still top and column expand and as soon as the vapour starts to be emitted, the vapour starts to replace the air.

Now in pot still mode with your 2" top, the air has two ways to get out of the column, a) thorough the vent and b) through the discharge pipe. If it goes through the discharge pipe, it willl be going along with already condensed liquid and any small amount of residual vapour stands a good chance of being condensed in the journey.

Now when you stick a 40" x 3" diameter column in between the still and the condenser and shut ff the discharge tube, a) There is LOT more air which has to find a way out and b) it only has ONE escape route, through the vent (which is small so the air would come out at pressure and possibly take some "smell" with it.

ss's suggestion of making the vent bigger may help, or you may find that for a few minutes at that ctitical stage (starting to boil) you could reduce the power to perhaps 40% until all the air had been driven out then returning the power when the jet stream ceased, may well reduce your "smell" to a more acceptable level.

The same thread said that one member ( Odin? ) had done a smoke test when the run was under way and found that the vent was actually pulling air into the column once the run was under way.

[joeymac]

Pikey, it's not only doing it during heatup and stabilization though. It was puffing the whole 6 hour run. It's not a leak in the sense that vapor is overpowering the coil but it's light breathing. I almost can't even feel it if I cover the vent hole with my finger. Only when I use a small mirror can I see puffing and a very small dime-size spot of condensation.

Odin's observations are spot on because in all the boka's I've ever built, they sort puff in and out - and pull a slight vacuum on a water column (only about 1/4" water column though). Which is what this one is sort of trying to do but this one is just puffing a small bit of vapor out when it exhales. And I agree with still_stirrin, the more I think about it... It's a volume and hole size problem. I think with fresh cold water almost all the vapors are getting condensed on the lower 1/3 of the coils. That leaves a decent amount of room for mingling stray vapors and air to get knocked down by the excess volume surrounding the remaining 2/3 of the coil. As my recirculated cooling water gets warmer and now it takes, for example, the lower 2/3 of the coil to knock everything down, I have less and less open volume with the remaining 1/3 of the coils to capture those stray vapors. So when the when column breathes in and out because of the small hole, some vapors are carried with it. I think with a bigger hole or more head volume it wouldn't have to puff/breathe so hard.

I probably never noticed it before because it doesn't do it while strpping in potstill mode (not sure why yet, but it just doesn't), spirit runs in potstill mode are slow with only like 25-30% power, and my old 2" reflux column could never run enough power to reveal the problem. So my 2" head with its small vent works great on a 2 column as it was designed. I might just need a bigger tool for a bigger job.

I think rather than modify this 2" column head, because it's so nice, I'll just keep using it for now and start constructing a more proper 3" head. Then I can sell off this 2" head to recoup some costs. Heck, I can turn my old 2" column into a couple of boka heads and sell those too.

[Pikey]

So be it - please do let us know when you cure it