Dephleg preferential condensing

[tubbsy]

I've searched but haven't been able to find anything, but does a dephleg preferentially condense components of the vapour?

I'm planning on using my boka head on my new plated still and was curious how or if it would be any different to a dephleg at forcing reflux. All I could think of was a dephleg letting some components through easier than others.

[Yummyrum]

This my take on it . A Deflag is a partial condenser . It is a Reflux condenser that is operating right on the brink . Usually we run it so that it is condensing say 4/5 of the vapour but 1/5 sneaks through it up and over into the product condenser .

Consider that a reflux still is normally operating in a state of equilibrium , so at the top where the Deflag is , the vapour is of a very similar composition.

Now some seem to think that a Deflag lets certain ABV components past due to its critical temp , the heavier fractions condensing , the lighter ones getting through .

Seriously ,

There are Deflags made with coils and tube and shell etc , all will have hotter bits and cooler bits depending where coolant enters and leaves . The Deflag body is not at one temp but many ..... so this .... in my opinion debunks the theory about lighter fractions passing while heavier ones condense .

You can successfully use them counterflow or contraflow.

It is just a condenser that is running with not quite enough coolant flow to fully condense all the vapour passing up to it .



Anyway , getting back to your question , yes you can use an LM or VM ( as I have done) or CCVM and the plated still will work in my opinion just the same as if you were using a Deflag . (CM )

I changed to VM after running CM ( deflag) for a few years and now find it so much more pleasurable to run . No more variations in output flow and ABV due to increasing coolant tank temp , wind gusts , gas bottle pressure and touchy regulator issues .

[Saltbush Bill]

but does a dephleg preferentially condense components of the vapour?

Thats a big can of worms to open Tubbs.
Short answer imo yes.
http://thermopedia.com/content/691/
Quote:" Vapor leaving the device has become concentrated in the more volatile components, while the condensate is richer in the less volatile components."

[shadylane]

I'm thinking, the action of the column controls what components of the vapor gets to the top.
The job of the dephleg is to condense a percentage of that and the rest sneaks past as vapor.

[Saltbush Bill]

As I said this is a can of worms, hoping some one like LWTCS might jump in on the subject. Lets leave coil condensers and the rest out of this for the moment ,they are not true Dephlegs imo.
I look at it this way ..a well made dephleg that is functioning correctly should have a temperature gradient as do all condenser type apparatus when run at optimum.
Cooler at the bottom and hottest at the top.
Volatile components within the column that have boiling points that are below the highest temp at the top of that dephleg cant get past it and have to get knocked down as reflux. How efficient this process is depends on many things I would imagine, length of dephleg, vapour speed within the column, vapor contact to surface area within the dephlegs tubes, the list goes on.
Aint a brain surgeon or rocket scientist but that's how I see it.

[Yummyrum]

Lets leave coil condensers and the rest out of this for the moment ,they are not true Dephlegs imo.

Why not Salty , I’m interested what you define as a true Dephlegamator . ( however that link you gave was interesting )

Maybe be we all been using the wrong name for our partial condensers .

Seems no matter what we use , they all do the same job at the end of the day .
T

I'm thinking, the action of the column controls what components of the vapor gets to the top.
The job of the dephleg is to condense a percentage of that and the rest sneaks past as vapor.

Thats my thinking too Shady .

But like Salty said , its a big can of worms .

[shadylane]

Lets leave coil condensers and the rest out of this for the moment ,they are not true Dephlegs imo.

What about a coil condenser used on a CM rig as a dephlegmator?
They seem to work real good at getting the job done

I look at it this way ..a well made dephleg that is functioning correctly should have a temperature gradient as do all condenser type apparatus when run at optimum.
Cooler at the bottom and hottest at the top.

I've tried running cooling water through a dephleg both ways
It didn't appear to make any real difference.
Other than due to gravity, it's easier to fill from the bottom up

[Saltbush Bill]

What about a coil condenser used on a CM rig as a dephlegmator?
They seem to work real good at getting the job done

Very true Shady ..and something for me to give some consideration.

[tubbsy]

There are Deflags made with coils and tube and shell etc , all will have hotter bits and cooler bits depending where coolant enters and leaves . The Deflag body is not at one temp but many ..... so this .... in my opinion debunks the theory about lighter fractions passing while heavier ones condense .

When you say warmer bits, just how warm/cool are they? It needs to become warm enough to let some vapour pass through, but is it just fast travelling vapour that gets through before cooling too much to condense, or those preferentially condensed, lower boiling/dew point vapours?

The link from SaltbushBill was helpful. I'd imagine though that was a precisely designed part of a thoroughly controlled process. Also, the components that pass through are very light. Cant get any lighter than hydrogen!

It seems from the other comments that it probably doesn't happen in our hobby scale.

[Saltbush Bill]

When you say warmer bits, just how warm/cool are they? It needs to become warm enough to let some vapour pass through, but is it just fast travelling vapour that gets through before cooling too much to condense, or those preferentially condensed, lower boiling/dew point vapours?

Just one of many of the possibility's that present them selves Tubbs.

[DetroitDIY]

As I understand it, a dephlegmator provides a function, rather than describes a specific design (though I have seen a lot of information that a dephleg is typically a short, fat, tube in tube, with converging and diverging cones to neck from the outer tube in to the inner tube and then back out to the outer tube). The function is to partially condense a vapor (and let part of it to bypass). If this is a reasonable description of the function, then most any condenser I can think of could work as a dephleg or as a perfect condenser (product condenser), it mostly depends on the operation, and possibly some on the design about the condenser.

Regarding the preferential separation, I can't think of a physical way this wouldn't happen. The lower boiling point compounds will get through preferentially to the higher boiling point compounds. That's the principle on which our stills work. But I think the point that some are thinking here is that the preferential separation is dominant in the column and negligible in the dephleg itself... and that perhaps each individual's design and execution of their dephleg build is a huge noise factor on this already negligible preferential separation and thus, don't worry about it.

And while I don't doubt that each of our systems runs a bit differently, and allow slightly different ratios to bypass our dephlegs (those of us that use them), that we would be hard pressed to tell the difference even if we had access to each others rigs, and that many of the other variables in our ingredients, fermenting, distilling, cuts, and aging decisions have much more significant affects on what we're drinking so... don't worry about it.

[shadylane]

Regarding the preferential separation, I can't think of a physical way this wouldn't happen. The lower boiling point compounds will get through preferentially to the higher boiling point compounds. That's the principle on which our stills work. But I think the point that some are thinking here is that the preferential separation is dominant in the column and negligible in the dephleg itself...

I'm one of the folks that think the separation happens in the column and is negligible in the dephleg.
Try running a potstill with a dephleg and see what happens.
At best, the abv will increase a tiny amount
And the output will slow way down.

The dephleg isn't doing any preferential separation
It's just condensing a portion of the vapor that passes through it.

On a side not
I hate the word dephlegmator
How about calling it a PRC. Partial Reflux Condenser

[Bushman]

As I understand it, a dephlegmator provides a function, rather than describes a specific design

I agree with this statement. I use a shotgun style dephlagmater which most people think of when dealing with a more modern CM still for their PC. I know that PrairiePiss ran a coil design for his.

Shady wrote: On a side not
I hate the word dephlegmator
How about calling it a PRC. Partial Reflux Condenser

This was true when we had poorly designed CM stills I can get 100% reflux on my shotgun style condenser until I am ready to collect. However unlike my VM still my CM is harder to regulate once collecting.

[DetroitDIY]

I hate the word dephlegmator

I agree. It does not roll off the tongue, nor does in conjure a pretty image.

[shadylane]

I hate the word dephlegmator

I agree. It does not roll off the tongue, nor does in conjure a pretty image.

The word is also too long, difficult to spell and hard to abbreviate.

[LWTCS]

I hate the word dephlegmator

I agree. It does not roll off the tongue, nor does in conjure a pretty image.

The word is also too long, difficult to spell and hard to abbreviate.

Hahaha, I'm sure if Harry were still around he would be lecturing how important it is to use correct terminology so that we can be sure we are all talking about the same thing. He used to get pissed off at me for saying "Dee-fleg".

[LWTCS]

As I understand it, a dephlegmator provides a function, rather than describes a specific design (though I have seen a lot of information that a dephleg is typically a short, fat, tube in tube, with converging and diverging cones to neck from the outer tube in to the inner tube and then back out to the outer tube). The function is to partially condense a vapor (and let part of it to bypass). If this is a reasonable description of the function, then most any condenser I can think of could work as a dephleg or as a perfect condenser (product condenser), it mostly depends on the operation, and possibly some on the design about the condenser.

Regarding the preferential separation, I can't think of a physical way this wouldn't happen. The lower boiling point compounds will get through preferentially to the higher boiling point compounds. That's the principle on which our stills work. But I think the point that some are thinking here is that the preferential separation is dominant in the column and negligible in the dephleg itself... and that perhaps each individual's design and execution of their dephleg build is a huge noise factor on this already negligible preferential separation and thus, don't worry about it.

And while I don't doubt that each of our systems runs a bit differently, and allow slightly different ratios to bypass our dephlegs (those of us that use them), that we would be hard pressed to tell the difference even if we had access to each others rigs, and that many of the other variables in our ingredients, fermenting, distilling, cuts, and aging decisions have much more significant affects on what we're drinking so... don't worry about it.

This sounds about right to me.

With respect to design considerations, the defleg simply needs to allow for two way traffic flow. Vapor traveling upward and liquid traveling downward.
With the shot gun design, if the through tubes are too narrow liquid can pile up and cause crappy surging behavior.

As far as the ability so separate volatile compounds? Yes it does.

[LWTCS]

http://thermopedia.com/content/691/

This bit here speaks specifically to that assertion:

In contrast, a particular instance where the importance of the dephlegmator as a heat and mass transfer device is clear (the word is thus used without dispute) is in the separation and recovery of ethene from a cracked gas feed, which contains a significant proportion by volume of light components (hydrogen, carbon monoxide and methane). The heavy component of the feed, ethene, is separated from the light components in a dephlegmator, and the ethene-rich condensate is passed on to a distillation column to remove any remaining methane. An earlier method of recovering ethene involved fractionation of the entire feed stream in a conventional adiabatic distillation column. The introduction of the dephlegmator, constituting a preseparation stage, resulted in vast savings in energy costs. A substantial part of the heat removed in the dephlegmator is transferred to the coolant at a higher temperature than was possible when the fractionation was done entirely in the conventional column.

[LWTCS]

I think the issue at the hobby scale is that we really don't have sophisticated enough instrumentation or consistently available cooling capacity to fully utilize the dephlegmator as a preseparation unit and measure the impact of the work it does.

[LWTCS]

Here on this continuous system, there are 3 preseparation condensers.
The one closest to the reboiler kettle is intended to keep tails in the kettle.

The one at the very top is intended to allow heads to escape.

The middle unit allows for fine tuning the whiskey take off profile.

[Birrofilo]

Regarding definition, a dephlegmator is anything which makes a partial reflux of the alcoholic vapour.
In Italy the helm of a pot still (variously called capitello, elmo, duomo) is also called a deflemmatore.

Confusingly enough, but maybe not, flemma is the non-definitive product of a distillation, what would be low wines in English parlance.

For what I understand, a proper dephlegmator selectively lets vapour pass through. Vapours which are more volatile pass through, vapours which are less volatile are refluxed.

It's the other side of the distillation coin: in the pot you apply heat, and high-volatility substances boil first (with the usual caveat that they bring with them all the friends and family): the boil is "selective". In the dephlegmator, you subtract heat, and low-volatility substances fall back first: the dephlegmator is also selective. This is not surprising as the various substances have different behaviours with different temperatures and as they behave differently in the pot, so also they must behave differently in the dephlegmator.

In the column there should be "equilibrium" and vapours are ideally ordered according to their boiling point. Ideally, water is on the bottom, and the higher volatility component is at the top, and they are all ranked like the woman of a matrioska, the smaller ones (most volatile, "thinner") at the top, the larger ones at the bottom.

When the dephlegmator status is changed from 100% reflux to "let someone pass the gate", i.e. when the temperature of the dephlegmator is slightly raised, a little chink is opened. Thin people like high-volatility gases can pass through the chink. Fat people beyond a certain threshold are bounced back. (But they will be able to pass later on, when the chink will be opened a bit more).

If the dephlegmator is kept at constant state, at a certain point the thin people have all passed through and the still stops producing (sufficient proof the dephlegmator is selective).

An analogy comes to my mind at the moment: a dephlegmator is like a final condenser which doesn't work well and fills your room with explosive vapour. The vapours that are not condensed are the higher-volatility ones. In order to condense them you have to "increase coolness" in your final condenser. This is exactly what you would do in your dephlegmator when you want to restore a 100% reflux state.

[Saltbush Bill]

What about a coil condenser used on a CM rig as a dephlegmator?
They seem to work real good at getting the job done

Been thinking on this , Shady can you clarify what you mean by CM rig here ..are you talking plated columns or referring to CM packed column reflux stills as one might use to make a neutral or vodka?

use correct terminology so that we can be sure we are all talking about the same thing.

Its also a bug bear of mine, how the hell can we all be on the same page in discussions if people decide for them selves what they think they will call something. Ive noticed the problem creeping into this forum more and more, people calling things alsorts of weird arse names.
We have a glossary around here somewhere for a reason. We all had to learn a new language when we first started distilling, just to add to the brain overload, why should today's newbies be any different ? , 99% of the names and terms we use for things are used because they are the industry standard, its that simple.

With respect to design considerations, the defleg simply needs to allow for two way traffic flow. Vapor traveling upward and liquid traveling downward.
With the shot gun design, if the through tubes are too narrow liquid can pile up and cause crappy surging behavior.

Quick hypothetical question Larry , If you made a longer exaggerated version of the deflegs that we use, 2-3 foot for arguments sake , and ran it with a gentle heat gradient , would it do a better job of the separation of the lower boiling point wash components. its something that Ive thought about experimenting with at times.

[LWTCS]

[/quote]
Quick hypothetical question Larry , If you made a longer exaggerated version of the deflegs that we use, 2-3 foot for arguments sake , and ran it with a gentle heat gradient , would it do a better job of the separation of the lower boiling point wash components. its something that Ive thought about experimenting with at times.
[/quote]

You know what Bill, that is a totally legit question and I think I'd bet money that it would.

[LWTCS]

Yeah I bet it would work really well!

I think one of the issues is the height needed.
Fact on the continuous rig I posted I went with the horizontal design so we couldd get plenty of knockdown power under the ceiling. But in retrospect I bet establishing a longer gradient within the space tasked with condensing would work so much better.

[Saltbush Bill]

That in turn makes me wonder if people are seeking ease of use over function by building short tuna can length deflegs to reduce response times when they adjust water flow? There for not getting the full benefit of a defleg to begin with.

[LWTCS]

Bill, talk about how you would conduct that experiment and confirm your results.

[LWTCS]

That in turn makes me wonder if people are seeking ease of use over function by building short tuna can length deflegs to reduce response times when they adjust water flow? There for not getting the full benefit of a defleg to begin with.

Yeah maybe true Bill.
Course there will always be a trade off with respect one's interpretation of "user friendly " I suppose?

[LWTCS]

Shoot I think I touched a crazy mod button or sumpin?

[Saltbush Bill]

Shoot I think I touched a crazy mod button or sumpin?

Sorry no that was me I think .....lol wrong button ..still learning

Bill, talk about how you would conduct that experiment and confirm your results.

Just a thought bubble in my head at this stage ...life is busy enough without experimenting with things like that.

[LWTCS]

Kk so my thinking is to install a "preseparation" condenser at the base of a column (rather than the top) and run with no coolant In order to establish a typical base line for an otherwise normal short plated column.
Monitor temps at each plate level.

Then run with coolant flowing to the "preseparation" condenser. But doing so with coolant discharge temps that are equal to what would ordinarily be the plate temp above. So basically a single run with coolant discharge temps that are equal to each plate. In other words 4 plates= four separate runs.

Also, making notes as to how well the column gradient behaves for each run.
Noting how long tails could be held off.

Power input uniformly consistent for each run.