Continuous Still: Could two strippers do it better?

[Pissed up]

I have been mulling over the idea of a continuous column still. It seems like people are resigned to the stripper functioning only to purify total alcohols/volatiles and then batch distilling the resultant product to cut heads and tails. I don't want to have to use another pot still. It takes the sexiness out of the continuous nature of the still. It hit me then. Replace the potstill at the end with another stripper. Two strippers (and a bit of rectifier): one bottomless and one topless.... or one stripper to remove water and tails (bottom) and a second to remove heads (top). But how? If we use the second stripper as a methanol/heads stripper we can remove these from the batch. I drew a picture, it is crude but the idea is what matters.

First column is a stripper in the classical form - steam in the bottom and wash above that. End result is hot volatile vapor (heads, hearts, tails and some water) leaving the stripper and entering the second column which is the rectifier. Packed column which cuts out the tails and water with some ethanol loss. Could send this back to stripper or just put the rectifier on top of the stripper. I hate the idea of the tails just hanging out their in the stripper though. From the top of the rectifier column the heads and hearts are condensed and fed into the third column, the methanol stripper.

This is acting just like the first stripper but in reverse. We feed in hearts and heads higher in the column which falls and meets warm rising pure (well 95%) ethanol vapor (I imagine from some small electric boiler). This rising vapor at 78c contacts hearts and heads and vaporizes the heads. Hearts continue falling and will eventually pass the EtOH vapor which is acting as a stop gate to the heads. Heads rise through the column and meet a condenser. Partial reflux partial collection. It doesn't seem like this will require too much energy just enough to evaporate heads and build the temperature gradient in the column.

The biggest problem would be optimizing two columns at the same time. I imagine that one could do the whole run with the stripper and rectifier and then clean the setup and run it again (or a smaller stripper) with the results of the first run but collecting the spent "wash" and throwing out the heads. That would wreck the fun of the continuous still theme though and I expect that the first stripper is rather scummy from all the wash. I am imagining that if one kept the steam and ethanol vapor (and thus temperature) constant, managing the columns would not be crazy.

Any ideas? I would love some criticism.

[olddog]

Do you mean like this? http://homedistiller.org/forum/viewtopi ... 2#p6821012




OD

[Pissed up]

Wow. That is quite beautiful and I am afraid that I am getting lost in the later reincarnations without a diagram. There is some similarity in the columns but you are running a pot still with columns and I am not suggesting that. Just columns with the stripper, no boiler (other than a steam generator and straight steam not wash vapor). Did you have a reverse stripper? Or just tails reboil?

[Prairiepiss]

It seems to me the condenser on column 2 would collapse the vapors to a liquid. So column 3 would do nothing but draining liquid out the bottom? So how would you make cuts?

[olddog]

There is some similarity in the columns but you are running a pot still with columns and I am not suggesting that. Just columns with the stripper, no boiler (other than a steam generator and straight steam not wash vapor). Did you have a reverse stripper? Or just tails reboil?

As most of us ferment in manageable size quantities, there is no need for continious columns unless you are distilling commercial quantities, as far as removing the need for stripping runs followed by spirit runs is concerned, I already have designed my Flute columns that will deliver 90+ABV with a single run.


OD

[Prairiepiss]

There is some similarity in the columns but you are running a pot still with columns and I am not suggesting that. Just columns with the stripper, no boiler (other than a steam generator and straight steam not wash vapor). Did you have a reverse stripper? Or just tails reboil?

As most of us ferment in manageable size quantities, there is no need for continious columns unless you are distilling commercial quantities, as far as removing the need for stripping runs followed by spirit runs is concerned, I already have designed my Flute columns that will deliver 90+ABV with a single run.


OD

Um uh! I didn't say that OD.

It was Pissed up.

[olddog]

Sorry PP, I was quoting Pissed Up


OD

[Pissed up]

It seems to me the condenser on column 2 would collapse the vapors to a liquid. So column 3 would do nothing but draining liquid out the bottom? So how would you make cuts?

This is exactly the plan but you might be missing my point. There are no cuts with a continuous system as that is a concept that only a batch system can have. Column 1 strips all volatiles. Column 2 removes remaining water and tails. The condenser on two condenses heads and hearts, which feeds into column 3. Traditionally this is the problem with a continuous still: heads and hearts can not be separated. Column 3 is a modified stripper with second small heat source producing ethanol vapor. Liquid heads and hearts are stripped in column 3 but only heads are vaporized and thus clean ethanol is obtained at the bottom without heads. Think of a normal stripper but collecting only the spent wash (ethanol) and removing the more volatile component (heads). This is just running at a lower temp as the 'steam' is ethanol vapor.

OldDog, Why a continuous? I have room for only a small boiler but I can ferment large batches. Generating steam (and using heat recovery) I expect a two gallon boiler to act like a fifteen gallon boiler. I guess people could ask 'why a flute?' 'why a column?' 'Why not buy rum from walmart like everyone else?' Dreamers keep dreaming and thinkers keep thinking.

[Bagasso]

I like the idea and I think it has been thrown out there at least a couple of times but I don't recall anyone posting any success stories. This one is different. The only thing I don't understand is where the ethanol vapor is coming from in the 3rd column?

[Pissed up]

Thanks for the interest Bagasso.
The ethanol vapor: The problem with every other small continuous still design is that taking off at a certain plate above the stripper means catching some of the rising heads. Thus the only solution is to have a second column with no rising heads through the take off point. We can't use steam except at the loss of abv. Also boiling azeotrope keeps the temperature at the bottom of the still at 78 allowing ethanol, water and some flavoring tails to pass (if they are allowed through the column). For the vapor I was thinking of a small hot plate boiler of previous batch. Even if this wasn't heads free, the heads would boil off first and escape through the top of the column.I don't think it will take all that much power to boil off the heads and set up some reflux in the stripper column.

Sticking a element in there could cause over heating. The other way was to make a drain from a plate above enter a heated tube which produced EtOH steam which is injected back into the column.Probably a bad design but you get the idea.

[Bagasso]

I've posted this idea around here before but I guess I wasn't very clear. One of the things that stood out about how flutes seem to work was that they did a good job at keeping the tails in the pot. So in a continous still it should be the same. So, running it just right, a single column should give you heads and hearts coming off the top and water and tails flowing from the bottom.

OK now you add a second column. If you take off near the top you will have heads flowing through what your taking off so you can't really do cuts. But what is coming off at the bottom? If it works the same as other flutes shouldn't this be hearts?

I think we are stuck with the focus on taking from the top but to me it makes more sense if you are getting rid of tails in the first column then the bottom of the second column is where the prize should be.

[Pissed up]

I went through this line of thinking when I was trying to come up with a design for a continuous still. I wanted to make multiple columns after the stripper and take off of the bottom of each one. I could never come up with an iteration where the rising steam did not contain heads until I added a second heater. One flute feeding into a second flute would be rather similar to stacking them. The entry point of the vapor would be the hottest point and even including plates under the vapor entry in the second column a good separation could not be achieved.

Every time I needed a second heat source. I just collapsed the multi-column down to one column and put a stripper after it. I don't think that more columns would be easy or efficient without a second heat source. Can you think of one? I like a little heads flavor but want to remove ones that are particularly nasty. Maybe you could get the percentage of heads down to a safe point. I think a second element at a very low wattage would improve it though. One would need to have a system where very little of the finished hearts got back to the second heater for vapor generation. I drew a crude picture. The columns from left to right are Stripper, Flute, Flute with heat. I imagine vapor from the first flute ought enter the middle of the second flute. Three plates under the entry point should give enough separation to remove heads. Then take at a plate above the reboiler or some system to only allow a small portion to enter the boiler and the rest flow past.

[Pissed up]

One could put something like this at the bottom of the second column. It returns a portion for reboil and the remaining hearts leave the column for collection. There is a heater coil in the second tube.

[Prairiepiss]

How much wash are you planning to run through this thing at a time?

[Husker]

Your thoughts and design are interesting. However, I think there is a huge hole in the logic and actual runtime properties of the third still:

This is acting just like the first stripper but in reverse. We feed in hearts and heads higher in the column which falls and meets warm rising pure (well 95%) ethanol vapor (I imagine from some small electric boiler). This rising vapor at 78c contacts hearts and heads and vaporizes the heads. Hearts continue falling and will eventually pass the EtOH vapor which is acting as a stop gate to the heads. Heads rise through the column and meet a condenser. Partial reflux partial collection. It doesn't seem like this will require too much energy just enough to evaporate heads and build the temperature gradient in the column.

It looks like you are basing the working of this column on this concept:

> This rising vapor at 78c contacts hearts and heads and vaporizes the heads

Not going to work that way. Yes, you will get a 'plate' equivalent of heads vaporization, but a lot of heads are still going to be in there. If distillation worked this way, then we could simply slowly bring the temp of the boiler up, keeping it under 78c, and boil off all of the heads without losing any ethanol. Well, it simply don't work that way.

I think your concept is good, you certainly are thinking outside the box. However, I think reality will set in, shortly after you start to design this. Now, that is not to say that you can not find someway to rectify the problem, and get the results you want. However, I have yet to see a continuous still, which did not also draw off heads in some form. You can continue to add additional columns which tap off a plate or 2 under the 'heads', feeding that into the next column, and get to where the heads have been pretty well eliminated. However, each column built like that will be drawing off product with some heads progressing their way through the takeoff point, up to the heads point.

I do like your driving the column with ethanol vapor. But I do not think you will end up driving out all of the heads using that as a heat source.

H.

[Bagasso]

I think you are making things more difficult then they need to be. The heat from the first column should be enough to drive the second column. Your really only looking to keep the temp high enough to keep the heads vaporized while the hearts condense and fall to the bottom. No need for other heat sources or ethanol vapor made up somewhere else.

The key is to inject into the middle of the second column and just take off of the bottom. A condensor and take off at the top of the second column would be needed to take heads because you don't want them coming off as vapor and any kind of reservoir would eventually overflow.

[mash rookie]

Several of us have kicked this around on more than one occasion

I like your thinking as well. Interesting. More than one column will give a greater opportunity to separate alcohols at temperature gradients. I am not seeing how you intend to manage temperature for correct take off. Your design will critically hinge on perfect temperature control.

The reason I stopped perusing the concept is that in a continuous still you will always have fresh heads mingling with your hearts. Trying to separate them at the last stage is difficult at best. Commercial distilleries that use continuous distillation have very tall multi plate systems, exacting controls and expert craftsmen. As much as I believe that there a lot of smart guys here, I don’t disrespect the expert distillers. I believe that commercial guys would remove all heads if they could. Particularly on top shelf products.

Batch distillation is the exact reason we can make better stuff for our consumption.
MR

[Pissed up]

PrairiePiss, no idea yet on what throughput I wanted to get. I have been messing around with calculations but nothing solid yet. I have a 1000W element (stove) for steam generation. Might not use stove. Would be really excited with 15 gallons a day stripped.

Bagasso, I am still afraid that some heads would condense at the vapor entry point of the second column.

So does anyone have qualms about using a stripper and column to produce a mixture of heads and hearts? If so the only question that remains is if the reverse stripper will function to remove/sufficiently reduce heads in the final product. I was thinking of testing the reverse stripper alone and then incorporate it into a full design. The heads stripper is completely independent from the other parts of the still so I should work the same in isolation as when run at the same time.
So here is my idea of a concept test. 4' of 2" copper pipe with a reboiler/collector like I drew previously at the bottom. Liquid entry 2.5 feet from the bottom and condenser slant plate take off at the top. Valve to control take off and reflux the rest. Reboiler (100W or so) run full open. Make a mix of heads and hearts and see what conditions (cooling water rate, reflux/heads take off, liquid addition rate) give good separation. Being able to separate heads from hearts will be the real test. I calculate that 2 foot of packed column should give the equivilant of 4 theoretical plates or so. No idea how it will react to the liquid coming down the column.

[mash rookie]

PrairiePiss, no idea yet on what throughput I wanted to get. I have been messing around with calculations but nothing solid yet. I have a 1000W element (stove) for steam generation. Might not use stove. Would be really excited with 15 gallons a day stripped.

Bagasso, I am still afraid that some heads would condense at the vapor entry point of the second column.

So does anyone have qualms about using a stripper and column to produce a mixture of heads and hearts? If so the only question that remains is if the reverse stripper will function to remove/sufficiently reduce heads in the final product. I was thinking of testing the reverse stripper alone and then incorporate it into a full design. The heads stripper is completely independent from the other parts of the still so I should work the same in isolation as when run at the same time.
So here is my idea of a concept test. 4' of 2" copper pipe with a reboiler/collector like I drew previously at the bottom. Liquid entry 2.5 feet from the bottom and condenser slant plate take off at the top. Valve to control take off and reflux the rest. Reboiler (100W or so) run full open. Make a mix of heads and hearts and see what conditions (cooling water rate, reflux/heads take off, liquid addition rate) give good separation. Being able to separate heads from hearts will be the real test. I calculate that 2 foot of packed column should give the equivilant of 4 theoretical plates or so. No idea how it will react to the liquid coming down the column.

Pissed up, at post 7

Have you built a still or distilled yet?

[Bagasso]

Theres always a certain amount of the chemicals that constitute heads in the hearts. It's just a question of how much.

Now the second column may need a heat source if it is going to be a flute because it needs the pressure to keep the liquid on the plates but a plain column with packing and a condenser take off at the top might just do the trick.

In any case I think taking from below the entry point is worth looking at. Keep us informed.

[olddog]

This concept has been done before, I researched many of these designs prior to building my Flute designs.
It's called a Coffey still, the design is well over 100 years old.

OD

[Kerry]

I don't think any of those actualy make cuts. A continous fractional still will make cuts... but... it's not going to happen under normal operating conditions.

[Pissed up]

Mash rookie, I don't know how you guys on this forum answer that question, but the fictitious character "pissed up" has run both pot and pot with column. Messed around with freeze fractionating too. Likes molasses and sugar washes (and a little pineapple juice) with good yeast and keeping the abv low. so heads are not a huge problem. +75% from pot and column.

I don't like how pot distilling scales or a large number of batches. Coffey stills are the inspiration but the size is impractical. A steam powered stripper could use a 1 gallon boiler and strip 15 gallons of wash.

[Odin]

In order to get rid of higher & lower alcohols, I think azeotropic seperation levels need to be obtained. For ethanol this is reached after a theoretical 13 distillations. In practice 15 are needed to compensate for drawing of and turbulence created taking out azeotropic (96.5%) ethanol. Now I guess that is what is needed. And some more plates/caps above, feeding mash in the lower part (about 1/3 up, if I remember). Then, and only then can you take of fractions at various levels in the column. One section would be azeotropic ethanol, on other levels the other alcohols can be drawn off. I think it was Bols who had (past tense) an continuous column in Zoetermeer, some 30 kilometers from where I live. Some 25 meters tall, if I rememeber correctly.

Anyhow, I think that with anything under azeotropic seperation (for ALL of the different alcohols, actually), a continuous still cannot be used for perfect heads/tails seperation. Smearing will take place at anything lower than that (number of plates/redistillations) and finding equilibrium is needed to draw off heads. And waiting for that means you do batches instead of continuous stillin', right?

Odin.