Re-boiler Within the Boiler?

[Lester]

I have a 2" x 4' packed column and I imagine that some reflux eventually finds its way back into the boiling wash below. And even though what goes back is low wines (from a 12% wash for example) the low wines will still be a lot "cleaner" than the wash below, so why contaminate it again?

Has anybody built (can't find it with google) a catch pot within the boiler itself to accumulate the drippings coming off the column? I am thinking that whatever low wines that ends up in this reboiler will boil again considering that the reflux's boiling point is lower than the wash itself. Heat comes from the wash through conduction. Please refer to cutaway drawing below.

Thanks for any inputs!

[Halfbaked]

Totally baked! Sorry

[Lester]

I have seen 2. I exactly like what you are have in your pic. I see problems with the design. This is the 2nd http://homedistiller.org/forum/viewtopi ... 6&start=20 jimbo electric conversion.

Thanks for the link Halfbaked. But I think Jimbo's intentions are different from mine. Jimbo said: ".... so I should be able to doo goopy 5 gallon plum and peach slurries now." I think his intention is really to avoid scorching his mash so he built a double boiler. But in my case I wanted to re-boil the reflux without contaminating it with the wash.

Do you mind telling what are the problems you see?

[googe]

yeah not the same half baked, it's a good idea Lester, thinking outside the square . Remindes me of larrys inline Thumper. I'm curious about how the rising vapors from the wash and the inner boiler would react, wether they would cancel each other out?.

[meatheadinc]

I agree with Google, but like the concept of recapturing reflux
Think you would be better off with a humper thumper like Larry.
A similar idea came up a while back and got me thinking, however the only way I could visualize it working was to join the catch can to the column and use a sieve plate or bubble cap.
Then thought the loss of boiler head space was to great and would be easier to make a Larry inspired humper thumper.

[LWTCS]

I think the OP is thinking very well. Especially with a short column.
As Harry pointed out a tall column would likely only be returning water however.
The other issue is that the needed temp split would not be there I don't think. The theoretically more pure liquid within the internal vessel would flash off very quickly as the surronding primary boiler temps rise during the run. It might make for poor separation as the temp gradient may never have the chance to behave.

Just thinking out loud is all.

[Halfbaked]

I guess after looking at this thing again I should have looked a little closer. I thought the inner reboiler was a cut a way view. I see it is not.. I was thinking both came out the 1 hole. I didn't read well either. I see it said a catch boiler. My bad sorry.

[Lester]

yeah not the same half baked, it's a good idea Lester, thinking outside the square . Remindes me of larrys inline Thumper. I'm curious about how the rising vapors from the wash and the inner boiler would react, wether they would cancel each other out?.

Hello Googe,

Thanks for your kind words!

Come to think of it, the reboiler need not be in contact with the wash below. The vapor contains the heat anyway, so.......

I would tend to think that the inner boiler would be acting like a condenser simply because its temperature is lower than the wash.

Rising vapors from the wash would get stripped of its heat and condense, the liquid falls back to the wash.

The liquid reflux in the reboiler would now have excess heat and would commence to boil.

I am thinking along the lines of "Latent Heat of Vaporization" and "Latent Heat of Condensation".

[Lester]

I agree with Google, but like the concept of recapturing reflux
Think you would be better off with a humper thumper like Larry.
A similar idea came up a while back and got me thinking, however the only way I could visualize it working was to join the catch can to the column and use a sieve plate or bubble cap.
Then thought the loss of boiler head space was to great and would be easier to make a Larry inspired humper thumper.

Hello Meathead,

Loss of head space is real, but may be inconsequential in some cases. What is lost in head space is compensated for by a corresponding decrease in overall height, and for those who are limited by physical constraints, e.g., low ceiling, this may be a viable option.

In my case I was looking for a means to increase takeoff rates and this idea came to mind so I posted it here. Not really sure if it is a good idea or not.

Thanks for your interest!

[Lester]

I think the OP is thinking very well. Especially with a short column.
As Harry pointed out a tall column would likely only be returning water however.
The other issue is that the needed temp split would not be there I don't think. The theoretically more pure liquid within the internal vessel would flash off very quickly as the surronding primary boiler temps rise during the run. It might make for poor separation as the temp gradient may never have the chance to behave.

Just thinking out loud is all.

Hello Larry,

I watched your videos and I think they are great! I'm a fan of yours!

Perhaps we should not expect so much out of this "pot within the boiler" idea. It was just a product of an idle mind. But I do hope the purer liquid will flash off quickly and vaporize the richer reflux in the process. I'm sure the column will be able to sort out the vapors as needed, it's the column's job anyway.

Harry's comments may not necessarily apply to all columns. Height is one thing and packing is another. In a real-world scenario we are all hoping for perfect column operation but reality is far from this. I was looking for a "crutch" for my 4-ft tall column and this reboiler came to mind. (I wanted faster takeoff rates and was looking for ways to do that)

I would like to try and build your humper thumper cuz I do see the advantages you pointed out, but that would mean major surgery to my existing column which I am not yet ready to do at the moment. Maybe later?

Thanks man!

[Lester]

I guess after looking at this thing again I should have looked a little closer. I thought the inner reboiler was a cut a way view. I see it is not.. I was thinking both came out the 1 hole. I didn't read well either. I see it said a catch boiler. My bad sorry.

No worries bro'

[Lester]

I tried this concept today and it seems to work, somewhat. I noticed that the lower 1/3 of my column would tend to hold its temperature longer, the temp took a lot longer to rise when taking off product at 1:1 RR. (I usually take product off at 4:1 RR when my boiler charge is 12% BW). If that's an indication of a purer vapor going into the column I can't say for sure. This run is subjective and may be prone to errors in my observations. It is rather unfortunate that I don't have hard data from my previous runs to compare with this run. Even my wash is different: All-bran boiler charge instead of the usual BW so no comparison is available. Sorry.

After the run I inspected the reboiler and there were several distinct liquid level marks on the inside wall of the reboiler itself. I guess these marks are due to the oils in the tails (the reboiler pot did smell of tails). I saw 4 different & distinct level marks and I think the different levels has to do with the amount of reflux dripping out of the column (indeed it is not pure water only), at different times during the run. (I do tend to fiddle with the reflux adjustment during the run especially towards the end, hoping to squeeze the remaining alcohol out from the tails). The marks were greasy (oily?) but came off easily with soap and water. I estimate my reboiler to be about 1.5 liters capacity and it is partly immersed in the wash as I have shown in my drawing. My boiler is about 29 liters (including the lid's volume), all-bran wash is around 17 liters.

If anything I think this idea saves some heat (power) and also allows for a shorter column.

More experiments ahead...... Thanks for the encouragements!

[Lester]

Revision no. 1

Drawing is scaled to my existing boiler & boiler charge. A smallish pie pan for the reboiler will be used, hung off the lid of the boiler. I will be adding a thermometer for the reboiler to get a better grasp of what's going on in there throughout the run.

If anyone has an idea on how to go about evaluating this reboiler please let me know.

Right now I tend to see this reboiler as 1 extra plate, like a thumper but internal to the boiler. It is a very simple add-on to any boiler. What benefit I get out of it remains to be seen.

[googe]

Wow, you don't waist time lol. we can theorise all we want but hands on is the only way . How did you attach the inner boiler?. Do you have any ABV comparisons?. I like the second diagram, you would think getting the reboiler out of the wash would be beneficial, just having it heated by rising vapor would give it a more stable heat sorce?. Good luck.

[Lester]

How did you attach the inner boiler?.

For the initial trial I made some fancy legs for the pot by wrapping SS screen mesh all around the pot and tied it in place with copper wire. It was temporary anyway, just wanted to see what reflux I can catch. Stinky tails were in that pot for sure.

Do you have any ABV comparisons?.

ABV stays the same (95%) but this has more to do with the way I run my still. I would tend to reflux more once I see the temp go up a little so I can't comment in that area. Please help me here. Should I leave that reflux setting alone and see what ABV I get? I imagine I will still need some reflux to get the packing to work and 1:1 RR seems to be reasonable. I have only made neutrals so I don't have any experience with the other spirits. I also could not rely on my taste buds so much because I noticed that what tastes good on one day can be entirely crap on some other days. That's me.

I have a thermometer on my boiler, plus 2 other thermometers on the column. I can "see" alcohol % in those locations. Very useful during equilibriation. I will put another thermometer on the reboiler.

I like the second diagram, you would think getting the reboiler out of the wash would be beneficial, just having it heated by rising vapor would give it a more stable heat sorce?. Good luck

Thanks. I tend to lean towards maximum surface area now. If there's more alcohol in the reflux then it would be easy to boil off. If it's only water then nothing happens, vapor just passes by as if the reboiler wasn't there..........

[lampshade]

Just thinking out loud…, but what if the reboiler was changed so that any liquid that it collected was discarded, instead of re-boiled. Might make an efficient late-tails collector for those making "pure whiskey".

[YHB]

Lester,

If you put another set of slant plates at the bottom of the column, you could divert the condensate that would normally be returned to the boiler to anywhere you like. That would tell you what the condensate was at that point, alcohol percentage wise.

If it is water, is it worth saving and reprocessing?

If it is alcohol, is it stronger than the wash or not? If it is stronger then it will flash boil, if it is weaker then it will just sit there and gradually overflow into the boiler.

It would also tell you how much condensate you are talking about, and how big a re-boiler you need to cope with the condensate from a whole run.

Just my 2p's worth

Brian

[Lester]

Hello Lampshade! Hello Brian! Good to hear from you guys!

I did think it was only water that was dripping out the column, but........ the reality is that as the run progresses the contents of the column is in a constant state of change.

Let's talk about my still for the moment, 4-ft tall column packed with scrubbies. Thermometer probes at 1/3 up, 2/3 up, and one more probe at the take of port. There's also a probe inside the boiler (immersed in the wash) so I have 4 thermometers total on my still. Assuming a 12% BW boiler charge:

At the start of equilibriation. The temperature at 1/3 up the column is close to the wash temperature, about 92-deg C. Based on the charts on this thread ----> http://homedistiller.org/forum/viewtopi ... =1&t=10158
we know that this temperature equates to about 12% ABV. That tells me the purity is low at the start of equilibriation, equal only in purity to the wash below, at 1/3 up the column. I can imagine that what is dripping back into the boiler is only water at this time. (I will confirm this later during subsequent runs, temperature will reveal the story).

As equilibriation progresses, the temperature at 1/3 up the column will gradually fall, stopping at about 85-deg C or even 80-deg C, depending on how long you are willing to wait (if you wait an entire day that might even go down to 78-deg C but I'm just guessing). At this time (and temperature) we know that the liquid at that point in the column will be full of alcohol, anywhere between 33% to 75%, or even 94% ABV. During this time I am certain that the liquid falling back into the boiler is laden with alcohol and it is this alcohol that I want to catch and hopefully reboil. No sense in letting it drip back into the wash.

So! Sometimes it's only water, but sometimes there's also alcohol dripping out from the column. Depends a lot on how you run, how much you reflux, how tall is your column, packing, etc......

I also know that if I'm getting 85-deg C at 1/3 up the column, then at 2/3 up the column the temp will be about 79-deg to 80-deg C which is good enough to get me 95% ABV at the take of port. (This is confirmed by ABV measurements after the run, 95% or better every time)

Yes the slant plates came to mind but simplicity wins every time. This is such a simple and easy mod to the boiler. Add 1 literal plate below the column and get HETP +1..... PLUS, no contamination of the dripping reflux.

I got my SS plate now, will be done with the mod in a few days' time. But I have no wash to run so.....

If we can come up with a definite evaluation plan then I can chuck my vodka back into the still and run it again. I have about 20 liters @ 40% ABV. Any suggestions? (The 20 liters is for Christmas & New Year parties, ok?

BTW I use these DIY thermometers on my still: http://homedistiller.org/forum/viewtopi ... =2&t=43379

[Edwin Croissant]

If it is water, is it worth saving and reprocessing?

If it is alcohol, is it stronger than the wash or not? If it is stronger then it will flash boil, if it is weaker then it will just sit there and gradually overflow into the boiler.

I think that the vapor from the boiler cannot reboil a condensate (that what is coming out of the bottom end of the column) lower in ABV then the ABV of the boiler content itself. The vapor temperature is simply not high enough. I found in the book “Whisky - Technology, Production and Marketing - I. Russell (Elsevier, 2003)” on page 191 in table 6 (Mass balance of continuous grain whisky distillation) a value of 10% ABV for the hot feints recycle for a 7.5% ABV wash. On the next page a 10-15% ABV is mentioned for the hot feints. The hot feints is the discharge from the bottom of the rectifier column and comparable with the discharge from the bottom of a column of a discontinuous still.

(the reboiler pot did smell of tails)

Fusel oil volatility compared to ethanol volatility is higher at low ABV values then at high ABV values. Fusel oil concentrate therefore in the lower part of the column (same book, page 196) and is flushed out by the condensate if not removed with a side stream. That is why you are finding tails in that pot.

This is just a wild idea I have but I want to share it anyhow: If you want to play with the bottom end of your column you might try to superheat the vapor (you do not need very much power to do that, 14W per kW installed heating power will heat the vapor from a 10% ABV boiler charge to 100 °C) and collect the condensate in a separate vessel. I think you will need to bleed off the fusel oil in the lower part of your column as it will certainly build up and cause column hiccups.

Just my 2 cents.

Edwin

[Lester]

Hello Edwin,

I fully agree with your statement (edited):

I think that the vapor from the boiler cannot reboil a condensate ...... (when the condensate is) lower in ABV then the ABV of the boiler content itself. The vapor temperature is simply not high enough.

However, I have already pointed out that the above condition is not always true for the entire duration of the run. Most people here on HD use batch-fed stills (not continuous). Let's keep this in mind also, ok? I think you have the wrong book for this thread:

Mass balance of continuous grain whisky distillation

As for the fusel oils I hope to keep them away from my distillate since I am making vodka.

[Lester]

I have finished installing the reboiler, pictures to follow.

Also, I have just finished running my still with the reboiler in place. Attached is the temperature log of my run this morning, lots of comments in there (sorry, HD doesn't allow .xlsx attachments). I would like to call your attention to the temperature of the reboiler relative to the temperature of the boiler itself (wash temp).

Comments please.

[Lester]

I learned a lot from this particular run. I guess I did not explain so well so here goes.......

1. Almost all throughout the run, the temperature of the reboiler was always cooler than the boiler itself. Meaning: There's more alcohol concentration in the reboiler compared to the wash, and this alcohol can only come from the drippings from the column. Conclusion: It is not only water that is dripping out of the column, the drops also contain alcohol.

2. During equilibriation and taking out foreshots & heads using lower heat (time 10:29 to 10:55), the reboiler's temp gradually became cooler relative to the boiler. Meaning: Alcohol is being accumulated in the reboiler, coming from the dripping reflux.

3. When I take product off at a fast rate (Time 10:55 to 11:14) the reboiler's temp climb faster than the boiler temp. Meaning: The reboiler is boiling & being stripped of its alcohol AHEAD of the wash below. This is the goal!!! As a result of this reboiling I can take out product faster without upsetting the column's equilibrium.

4. When I equilibriate again (Time 11:14 to 11:22), the reboiler temp falls gradually again, a smaller amount this time, yet the boiler's temp climbs up. Meaning: Alcohol is again dripping out of the column and falling into the reboiler, adding to the reboiler's alcohol content, and so the temperature of the reboiler drops lower than that of the boiler.

The reboiler can only boil off so much. If the reflux falls faster than it can be boiled off, the temperature of the reboiler goes down. This is also influenced by the temp difference between the boiler & reboiler, the bigger the difference the faster the reboiler boils off the alcohol content.

That's what I learned. If there's anything wrong with my conclusions please let me know.

Thank you all!

[Edwin Croissant]

Lester, I don't think I got the wrong book. There is clearly a bias against continuous distillation on this forum and I thing it is not wise to reject all the knowledge gained from this type of distillation as this knowledge can also be applied to batch distillation. IMHO it makes no difference for the behavior of a rectifier column to receive the vapor from a stripper or a boiler. When I tried to understand the distillation process I asked myself what the ABV of the condensate (spent reflux?) was. So I made up an assumption and found in this book a confirmation for my line of thinking. And you confirmed that assumption again with your simple and very clever experiment. Thank you, well done!

That you accumulate alcohol in your reboiler during equilibration is obvious, all vapor is returned to the boiler so the returned liquid has the same ABV as the vapor. Collecting that high ABV condensate to speed up your run is a very neat trick! (but I wonder if a bubble ball is not doing the very same thing).

Just my 2 cents.

Edwin

[googe]

Sounds like it went well mate, well done. So, if you had a reboiler big enough to hold all the alc, you could collect it in the reboiler and then run it out fast?. I'm having trouble getting my brain around it! Lol.

[Lester]

Hello Edwin,

Now I understand what you were trying to say. And I do agree with your study habits also, just took me a while to get it.

Yes we are in agreement. Thank you!



Hello Googe,

I deliberately made my reboiler small in capacity, 1.5 cups only. I imagine that once reflux starts dripping into the reboiler it will only be water initially. It is only after some time that we begin to see alcohol drops. I wanted to displace the water in the reboiler as quickly as possible so as not to dillute the alcohol. If I had used a large container it will take a long time for the ABV to go up (tne temperature will go down). With a large container I might have missed seeing the benefit of the reboiler and probably arrived at a wrong conclusion.

OK mate?

[Lester]

I've taken the temperatures and translated them into % ABV. You can now see the % ABV difference between boiler & reboiler. I think the % ABV difference is very significant. Also, notice the trend of %ABV reboiler, how %ABV increases & decreases during the run. This is what I was hoping for.

The reboiler will now be a permanent addition to my boiler.

[Lester]

Some pics.

The long copper tube beside the pencil is the temperature probe for the boiler. It is submerged in the wash. The digital thermometer is for the reboiler, mounted in a slanted manner for maximum immersion in the reflux.

[Lester]

Alcohol purity (% ABV) in the boiler & reboiler

X axis = Time
Y axis = Purity (% ABV)
Red line = Reboiler
Blue line = Boiler

A = Equilibriation + taking out foreshots, low heat
B = Taking out hearts, max heat
C = Equilibriation, max heat
E = Separation is less than 1 theoretical plate (maybe I should have waited longer?)

[Edwin Croissant]

E = Separation is less than 1 theoretical plate (maybe I should have waited longer?)

Atmospheric pressure and boiler pressure ( 2,5 cm water column?) have some influence. Fusel oil concentration in your re-boiler is higher then in your boiler and fusel oil raises the boiling temperature of a water ethanol mixture. Try to take a sample and measure the density to be sure.

Regards,

Edwin

[LWTCS]

Hi Edwin,
I believe the bubble ball (or the like) does do the same thing. Relatively more alcohol is shifted out of the primary and used to more fully enrich the rectifier.

I was afraid the close proximity to the primary heat source would be some what less than optimal (and perhaps is?). But it is good to see some data on this particular configuration.

WTG Lester.

We were trying to find out what the optimal amount of liquid would be within a secondary vessel. We did not fully conclude what that volume would be, but do now believe that there is a point where too much can offer diminished returns.