LM Reflux Sight glass, what do we want to see?

[mashins]

Hi, I am new to all this but been reading on here and elsewhere about distilling and fermentation. A few books, Designing and building by Riku, Home distillers workbook, The complete distiller, Artisan distiller etc etc.

Currently leaning towards building a 3" Boka style reflux still. Now the point about sight glasses. To some its is pointless having a sight glass at all, to others its vital, but why?

So If we want to drive the still for optimal extraction, what will seeing inside the column give us that temp, sound and ABV is not already providing? Why have em and what do we really want to see? Should the sight glass be at the top of the packing or elsewhere? What do we really want to use the sight glass for and where do we best place it? Do we need more than one? I would guess that depends on what we really want to see and why we want to see that?

A few points:

• Should we see the top of the packing and why?
  Should we be able to see the level of condensate/reflux above the packing and why?
  What about the bottom part of the condenser and why?
  Or the takeoff of the liquid and why do we want to see that?
  How can seeing the reflux help us manage the ratio?
  What about flooding?
  What about the fogging of the glass, what does that indicate? Its water vapor after all.

Will this help in driving us to better manage the heat input to the boiler? Can seeing inside assist with the reflux management? Or can it help in adjusting the valve as to not upset the reflux ratio? So things like this then should really help in finding out if I need sight glass at all and where to place it, no? So this is to help me solidifying my ideas for the build.

As is most likely clear from this, I am a noob at this

Thank yaall

[Euphoria]

Many members on here don't use one, or feel the need for one, but I like having it on my setup for a couple of reasons. Besides just being cool to watch the activity in your column, I find it useful for keeping an eye on my still column to head off a "puking" situation by getting an earlier indication of running it to hard. This is more useful if you are doing an AG run, as they are more prone to the possibility of puking. The other reason I like having it is that it gives me a visual indication of when I start to hit tails during the run. When the glass starts fogging up, it's telling you that you are past your hearts. I mount mine right on top of the boiler at the bottom of my column. YMMV

[kimbodious]

As a novice distiller being able to monitor for flooding is reassuring. My sight glass is set at the top of the packing just below the takeoff. I can tell when tails are iminent by when the condensate level at the top of the packing suddenly disappears; a bit later the glass fogs. The glass also fogs when the vapour initially reaches that part of the column; this is useful if you need to quickly reduce the power from heat-up to operating level

[StillerBoy]

Thanks mashins for raising this point.. Now this thread has my attention..

Mars

[skow69]

I spent considerable time fretting over a related issue a couple years back.

I believe the most efficient way to run a reflux column is as hot as you can without flooding. Put your sight glass at the top of the packing so you can monitor the top of the liquid reflux/flood level. What you will see is a column of liquid rising through the packing. This is the famous "aquatic environment." If you have the right packing you may also achieve the equally famous "fluidized bed". But we won't open that can of worms.

When the top of this column rises above the packing it will be a boiling surface, throwing drops or blobs of liquid up two or three inches. This will be the limiting factor on your boka. Keep the rolling boiling liquid well away from your slant plates. If you go too high you will get entrainment, where reflux liquid from the column comes out your product take off. This is also the first stage of flooding. By staying as high as possible without entraining you are maximizing vapor production and, it seems to me, creating maximum opportunity for vapor to mingle with reflux, which amounts to maximum distillation going on.

In practice this all adds up to: Heat it up until you see the flood and then back it off a little bit.

[kimbodious]

I uploaded this video to YouTube to demonstrate was Skow69 is referring to. Sorry about wobbly foitage; I had to stand on a stool to record this. https://youtu.be/jAP21_wocvQ

[skow69]

Publish it on you tube and use the "utube" button on the reply page

[greggn]

By staying as high as possible without entraining you are maximizing vapor production and, it seems to me, creating maximum opportunity for vapor to mingle with reflux, which amounts to maximum distillation going on.

By following that process, how do you create a vapor-temperature gradient in the column ?

[skow69]

I'm not sure I understand the question. The vapor mingles with the reflux, causing multiple stages of redistillation in the column, and, over time, the different fractions stack up with the most volatile on top. Every part of the column will stabilize at the boiling point of the local mixture so the top is cooler than the bottom. You know it is stacked when the head temp stops dropping, and you get a little jump in temp when you bleed off the foreshots. Is that what you mean?

[greggn]

> The vapor mingles with the reflux, causing multiple stages of redistillation in the column,

If, for example, I run a 40" column with 36" of packing and I've flooded/fluidized the column close to the top of the packing then hasn't the effective height of the column been shotened from 40" to 4" ? By flooding the column hasn't the the area in which vapors can segregate and stack been reduced ?

I run a CM column, packed with raschig rings, so I can tell from the rattling anytime (and how high) it floods. In my experience, the only times I've had trouble stacking vapors during and after equalizing is when it's in a flooded state.

[kimbodious]

I perceive flooding to be where vapour pressure and the restriction posed by the packing material are such that the condensate is being kept from returning to the boiler until the level of condensate above the packing extends past the offtake even up in to the reflux chamber. I don't perceive flooding as the whole column being full of condensate - I could be wrong?

[skow69]

If, for example, I run a 40" column with 36" of packing and I've flooded/fluidized the column close to the top of the packing then hasn't the effective height of the column been shotened from 40" to 4" ? By flooding the column hasn't the the area in which vapors can segregate and stack been reduced ?

I don't think so. I think the fractions all still exist in the same locations and the same temperature but in liquid phase rather than vapor. And the vapor above it is composed of the same stuff as the top layer, like always. As I understand it this idea came from the Russians experimenting with SPP, but I don't know why it wouldn't apply to other packing, at least random packing, as well.

I will try to find one of their videos and post it.

[skow69]

Here is one to start with. This one is kind of neat because it shows 2 sections. If you look around they have some that are ridiculously tall, some packed with weird shit like seashells.



Their website is pretty entertaining, too. Once you figure out what a cube and nozzles are. Lol.

http://www.homedistiller.ru/

[StillerBoy]

At this stage of the exchange, I am with greggn on this.. except, as I ponder this while doing a reflux run this afternoon, using my flute column packed with lava rocks.. that there is different of abv levels.. in the boiler the abv is say in the range of 35% at the start, and you reflux hard to fill some of the column, that fluid level in the column will have a much higher level of abv.. that I take is a given.. but flooding the whole pack area of the column, would somewhat eliminate the refluxing and then it would be behaving more like a 1 plate setup..

Mars

[skow69]

Mars, if it does, then I can make 95% ABV with a 1 plate setup. Lol. I can see how you would develop that opinion from the mental image of a flooded column. Did you look at any of the Russian videos?

Also, we might be taking this idea of the flooded column too literally, here. With my still, even when I've got the entire column flooded, with the boiling going on way above the packing, I can still find places where discrete drops form and drip, so the entire volume can't really be inundated with only liquid.

EDIT: here is a Russian vid that is easy to see how the mingling goes on. My still doesn't appear to be that active because the packing is way tighter, but the mechanism is the same.

I won't be running my column for awhile, but when I do, I will run some trials and record some data on performance for comparison. You, or anyone else, could do the same thing. All I can say with certainty right now is that I can make 95% ABV with the column dry or with it flooded. Although I have never timed it, I believe the aquatic environment (gotta love that phrase) does it faster.

'Course I been wrong before.

[kimbodious]

Flooding occurs if the volume of vapour being pushed up the column is so great that it is limiting the amount of condensate that can flow back down; that vapour bubbles through the condensate reaches the RC and it too condensates building up more and more. It is like blowing out a drinking straw while someone is pouring liquid down the orher end; keep blowing hard enough and no water reaches your mouth,

[mashins]

Now here is my thought process now. Since there is no easy way to get the takeoff from within the sight glass, it must be above or below. The sight glass I am eying is the 6" tall ala Stilldragon/Moonshine type that is a tube with Tri Clover ends. For a 3" pipe column we need the slant plate a certain height above the top of the packing. My question now would be, if the sight glass is 6" tall from flange to flange, the slant plate bottom would be at least 6" above the packing if the packing stops at the bottom flange of the sight glass.

Now most of the documents/designs show the slant plates only about 1/2" to 1.5" above the packing (entrainmen). My deduction is this is no way high enough?? What would be to high, if there is such a thing?

Would it be OK for the packing to stop somewhere inside the sight glass? But then if you add or remove the sight glass the packing will not be contained/fall out or some such... It may also damage the glass casing causing stress fracturing, no? One can not set the slant plate below the sight glass, as then the "boiling reflux" action will be hidden. Then what will you see??

Thankin yaall

[kimbodious]

Yeah, chuck some scrubbies part way up the sight glass, you won't hurt anything. How high? I guess you'll have to experiment but at least you 'll be able to see when you need to wind back on the vapour flow by how close th condensate is splashing up near the slant plate take off!

[skow69]

Standard advice for a boka is usually like one to two diameters of open space between the packing and slant plate. What kind of packing are you using? Random packing in the sight glass sounds messy but a scrubby or roll of mesh wouldn't be bad. So 6 inches open space would be in spec, but if you end up at 9 inches, all you have lost is three inches of packed height. How tall is your column? If it's 50 inches, you'll never notice the lost three. If it's 24 inches, I would stuff a scrubbie in the bottom of the sight glass.

[mashins]

Ok thank you Skew69. It kind of makes sense, tall will be 46" with the sight glass on top and then the condenser I thinks. Trying for copper scrubbers but so far not finding with copper all, only plastics or normal steel. Not yet knows what else to use for now, still looking. I will experiment with packing when I can start the build, real soon to hope.

Thankin yaall

[greggn]

I think the fractions all still exist in the same locations and the same temperature but in liquid phase rather than vapor.

I can accept that in principle though I'm somewhat skeptical of how stable those fractions remain given the violent turbulence we see in those videos. I just recently purchased a digital thermometer from Auber with what they claim to be a precision RTD probe. I'll give another shot at running an "aquatic environment" and see if I can still pull well-defined fractions.


(it is curious that given some of the innovative techniques developed by the Russian distillers they still collect output with plastic hoses)

[mashins]

Hey, those videos show nice why how the gas liquid interchange happen....

[skow69]

Ya. You'll never make another centering ring, huh? Lol.

I can accept that in principle though I'm somewhat skeptical of how stable those fractions remain given the violent turbulence we see in those videos.

Oh I don't know. Maybe they'd be more stable in liquid phase than vapor. Suppose you want to collect 5 oz. of foreshots. In liquid phase that will occupy about 150 ml of volume. As a vapor it needs over (gulp) 200 liters of volume. {Can that be right? Somebody please check my math here.} So I'm thinking it must be a combination of liquid and vapor, and mostly liquid or we would never get anything to stack. I'm just thinking out loud here, and be glad to listen to anyone who disagrees..