Speed of stripping & speed of spirit runs

[S-Cackalacky]

Makes perfect sense Skow and the very reason we see lower ABV with a strip run with higher heat input and a higher ABV with a spirit run with lower heat input. That lower ABV for a strip would be indicative of the water being pushed through by the higher heat input.

[skow69]

I really would like to see a rigorous scientific explanation of the mechanism(s) that cause the apparent violation of Rault's law. I have a hard time accepting just about anything that doesn't have equations and numbers attached, even if it doesn't break the rules.

[Haus]

This page seems to have a bunch of numbers on it.

http://cavemanchemistry.com/oldcave/projects/alcohol/" onclick="window.open(this.href);return false;" rel="nofollow

[Kegg_jam]

Seems logical. More heat is gonna get the higher boiling point liquids moving. Therefore more water in the vapor mix is gonna lower abv.

[Badmotivator]

I have been playing around with some models I found on demonstrations.wolfram.com in the chemical engineering section related to batch distillation. I had to install a "player" to play with the parameters. The ones which interested me were the ternary mixtures. (Ternary Batch Rectification, and Multicomponent Simple Batch Distillation especially.) These models have sliders for relative volatilities of the components, number of stages, and reflux ratio, but they do not have any variable power term in the model. I view this as circumstantial support for my hunch that power does not matter, except as it affects reflux ratio. (This is not likely a large effect in a simple pot still.)

Also, I found a guy with a doctorate in Chemical Engineering, who many years ago designed and ran refineries (petroleum distillation), and I sketched out the problem I'm having. He has promised to review the problem and respond this week.

Visually, the problem is this: using adjustments to power ONLY, can you shift the distillation from something that looks like this:

to something that looks more like this:

[raketemensch]

We need a legend for the colored lines. Or at least I do.

[Badmotivator]

We need a legend for the colored lines. Or at least I do.

I was using those lines just as a way to visualize the shape of the problem, so to speak. Ideally I would find a ready-built model that would allow me to plug in any number of chemicals and their qualities (volatility, molecular weight, I don't know what else is relevant) and then simulate the distillation from there.

For these pics I would just think of the three lines as heads chemicals (early-peaking curve), hearts chemicals (middle-peaking) and tails (late-peaking).

[skow69]

This page seems to have a bunch of numbers on it.

http://cavemanchemistry.com/oldcave/projects/alcohol/" onclick="window.open(this.href);return false;" rel="nofollow

Thanks. That's a great curriculum. I spend a lot of time at the Kahn Academy, too. It would almost make you wish you had paid more attention in high school. But education was such a low priority at that stage of life.

[S-Cackalacky]

I really would like to see a rigorous scientific explanation of the mechanism(s) that cause the apparent violation of Rault's law. I have a hard time accepting just about anything that doesn't have equations and numbers attached, even if it doesn't break the rules.

Skow, I appreciate your curiosity and inquisitiveness, but I think the OP was looking for a simpler less complicated answer - which I think you have also helped to provide.

Mark Twain wrote in his book "Letters from the Earth" that Adam's (Gods first man) greatest scientific contribution was the discovery that "water flows downhill". I accept that this is scientifically factual without the need of further research on my part. There's not much here on the forums or elsewhere on the internet that I take at face value, but practical experience and common sense tells me that running slower will improve ABV and cause less smearing. That's all that most of us need to know.

Theoretically, I suppose you COULD run a still based solely on temperature, but the science and computation speed and accuracy needed to do that would be prohibitive. You would need to identify every single element of a wash and the exact quantity of each element in order to even attempt to separate them cleanly using only heat - and what about other tangible issues like heat control, reflux, and condensation back into liquid form. It's just too frikkin' mind boggling to think about. I don't even need to know the boiling point of a mixture made up of different liquids. I can see the output and control its rate by adding or taking away heat input. It doesn't need to be any more complicated than that.

[skow69]

I have been playing around with some models I found on demonstrations.wolfram.com in the chemical engineering section related to batch distillation. I had to install a "player" to play with the parameters. The ones which interested me were the ternary mixtures. (Ternary Batch Rectification, and Multicomponent Simple Batch Distillation especially.) These models have sliders for relative volatilities of the components, number of stages, and reflux ratio, but they do not have any variable power term in the model. I view this as circumstantial support for my hunch that power does not matter, except as it affects reflux ratio. (This is not likely a large effect in a simple pot still.)

Thanks, Badmo. That is probably just what I've been looking for. I've had Wolfram alpha in my bookmarks for a long time, but I never use it. I think maybe it is so huge and comprehensive that I get intimidated, like I don't feel worthy to ask my insignificant little question. Har. Weird. I'm usually not shy like that.

CDF player is downloading now. Time to take better advantage of the available free resources. Having modelling/simulation, as powerful as this appears to be, freely available to the unwashed masses (me) just blows my mind. Imagine what you would have to go through to study that same question just 20 years ago. Or 10. It truly is a brave new world that we live in.

[skow69]

I really would like to see a rigorous scientific explanation of the mechanism(s) that cause the apparent violation of Rault's law. I have a hard time accepting just about anything that doesn't have equations and numbers attached, even if it doesn't break the rules.

Skow, I appreciate your curiosity and inquisitiveness, but I think the OP was looking for a simpler less complicated answer - which I think you have also helped to provide.

Mark Twain wrote in his book "Letters from the Earth" that Adam's (Gods first man) greatest scientific contribution was the discovery that "water flows downhill". I accept that this is scientifically factual without the need of further research on my part. There's not much here on the forums or elsewhere on the internet that I take at face value, but practical experience and common sense tells me that running slower will improve ABV and cause less smearing. That's all that most of us need to know.

Theoretically, I suppose you COULD run a still based solely on temperature, but the science and computation speed and accuracy needed to do that would be prohibitive. You would need to identify every single element of a wash and the exact quantity of each element in order to even attempt to separate them cleanly using only heat - and what about other tangible issues like heat control, reflux, and condensation back into liquid form. It's just too frikkin' mind boggling to think about. I don't even need to know the boiling point of a mixture made up of different liquids. I can see the output and control its rate by adding or taking away heat input. It doesn't need to be any more complicated than that.

Quite true, SC. You can run a still without ever having heard of partial pressures. It is only when something goes wrong, or you want to modify something, or try an innovation that you've never seen before, that some understanding of thermodynamics shows its value.

I hope I didn't muddy the waters too much.

[Badmotivator]

Believe me, friends, I never want to muddy the water. But I keep hearing people assert what look to me like mutually-incompatible truths, and I want to find out which is true.

Truth 1: you can't change the composition of the distillate at any given time by adjusting the temperature of the boiling wash. The wash will only reach its boiling point, whatever that is, and then more power just makes more vapor.

Truth 2: by adjusting the power added to the boiling wash you can separate the fractions more cleanly. High power blows a higher proportion of less-volatile fractions at any given time than low power would.

I realize that I sound like a crazy person here, but I still think that in a pot still with negligible reflux, the composition of the wash ALONE determines the composition of the vapor at any moment.

[Monkeyman88]

Believe me, friends, I never want to muddy the water. But I keep hearing people assert what look to me like mutually-incompatible truths, and I want to find out which is true.

Truth 1: you can't change the composition of the distillate at any given time by adjusting the temperature of the boiling wash. The wash will only reach its boiling point, whatever that is, and then more power just makes more vapor.

Truth 2: by adjusting the power added to the boiling wash you can separate the fractions more cleanly. High power blows a higher proportion of less-volatile fractions at any given time than low power would.

I realize that I sound like a crazy person here, but I still think that in a pot still with negligible reflux, the composition of the wash ALONE determines the composition of the vapor at any moment.

Do one run fast and one run slow. Then come back and tell us if the distillate is the same.

[skow69]

Badmo: EXACTLY!

That is the very same paradox that I have been talking about. I believe in partial pressures as well. This leaves me with the assumption that passive reflux is the main actor, an idea that makes me very uncomfortable. I would love to find theory or evidence for a different mechanism.

[IanD]

Maybe it really is the saturation temperature timelines getting smashed together.

[IanD]

We need a legend for the colored lines. Or at least I do.

I was using those lines just as a way to visualize the shape of the problem, so to speak. Ideally I would find a ready-built model that would allow me to plug in any number of chemicals and their qualities (volatility, molecular weight, I don't know what else is relevant) and then simulate the distillation from there.

For these pics I would just think of the three lines as heads chemicals (early-peaking curve), hearts chemicals (middle-peaking) and tails (late-peaking).

Yes, that's a good start but we need a better model really. Four liquids would be much better: water, ethanol, a heads contaminant and a tails contaminant.

I guess that model is the best we've got at present without learning mathaematica. If you make the quantities of heads stuff and tails stuff very small relative to the hearts stuff does that make it more sensitive to small amounts of reflux? I'm thinking that we have mostly water and ethanol. The heads and tails contaminants are very small in volume compared to either water or ethanol.

[Badmotivator]

Leaving aside for the moment the possibility that a tiny amount of passive reflux in a pot still can shift the curves meaningfully, which I doubt, does anyone else see any contradiction in the idea that power both is and is not capable of determining vapor composition? Isn't the whole point of this graph that power does not change vapor composition?

[Badmotivator]

Alright. I'm stripping 7 gal of bourbon in my stainless steel keg pot still . I tried three times to provoke a rise in the ABV by reducing power from 4 kW to 1 kW. I dumped the parrot seconds after reducing power and waited for the hydrometer to float again. Every attempt failed to support the idea that power affects ABV in a pot still with negligible reflux, as Skow69 and S-Cackalacky asserted. The ABV only ever went down, never up.

[Antler24]

I'm a believer that running fast will smear.

With my pot still (15g Keg, 2" riser, 3/4" over 1/2"x36" Liebig) in a slow spirit run its a tell tale sign I'm into tails when it slows down to only a few drips per second. When I'm stripping wash as fast as I can, I can smell the tails a quart or more before it starts to slow down.

[raketemensch]

I'm a believer that running fast will smear.

With my pot still (15g Keg, 2" riser, 3/4" over 1/2"x36" Liebig) in a slow spirit run its a tell tale sign I'm into tails when it slows down to only a few drips per second. When I'm stripping wash as fast as I can, I can smell the tails a quart or more before it starts to slow down.

Is the question being asked about ABV or smearing?

I think we're getting confused at this point, and talking about different things.

[Badmotivator]

Is the question being asked about ABV or smearing?

I think we're getting confused at this point, and talking about different things.

Those two questions are related. The Power->Smearing Hypothesis is the same as the Power->ABV Hypothesis. The larger idea that they share is that (all other things being equal) power affects vapor composition.

If the Power->Vapor Composition Hypothesis is correct, then you can run spirit runs slowly to get better separation or higher ABV. If it's false, and it turns out vapor composition is based only on wash composition at that instant, then you can run spirit runs at basically any speed and the result will be the same.

[Antler24]

I'm a believer that running fast will smear.

With my pot still (15g Keg, 2" riser, 3/4" over 1/2"x36" Liebig) in a slow spirit run its a tell tale sign I'm into tails when it slows down to only a few drips per second. When I'm stripping wash as fast as I can, I can smell the tails a quart or more before it starts to slow down.

Is the question being asked about ABV or smearing?

Neither actually. The OP's question wasn't directly about smearing or abv, it was about how run speed/heat input effects the final product. My post was in agreement with still_stirrin's explanation below as to why its better to run low and slow rather than hard and fast when doing a spirit run.

In either case my post was on topic, I think you are among those confused, and talking about different things

....In other words, why not run spirit runs at full speed?

In a word....smearing. Same as a strip....but in a strip, you're collecting for the low wines so you can blast through the strip, at least as fast as you can condense the vapor.

Now, if you're running your spirit through a column with reflux, the reflux ratio affects the purity, that is...the more reflux the higher the purity. That is where you fraction the good drop from the bad. In a potstill spirit run, you have to rely on good cuts.
ss

[muscashine]

As has been stated many times (which I'm sure you've read about even though you may not yet understand) that the heat input (power) controls the rate of boil, not the temperature of the boil. The temperature of the boil is determined by the composition of the liquids in the mixture (because the constituents all have different saturation boiling points) and because you're changing the mixture constantly throughout the boil, the boiling temperature changes as well.
ss

Took my friend and I several runs to get that through our thick heads. We put a thermometer in our pot still, and no matter what we did the temperature always crept up on us slowly. We would turn the heat down, which would slow the output, but the temperature would keep rising. Finally figured it out and just let it run, testing with the hydrometer. I still like a thermometer on my stills, it gives me something to watch other than just dripping.

[skow69]

Alright. I'm stripping 7 gal of bourbon in my stainless steel keg pot still . I tried three times to provoke a rise in the ABV by reducing power from 4 kW to 1 kW. I dumped the parrot seconds after reducing power and waited for the hydrometer to float again. Every attempt failed to support the idea that power affects ABV in a pot still with negligible reflux, as Skow69 and S-Cackalacky asserted. The ABV only ever went down, never up.

When you cut the power how did your collection rate react? Can we see a picture of your still? What was the ABV of the wash and the distillate? How do you measure the heat input?

I'm not being argumentative, I very much want to understand what makes the difference between your experience and mine.

[skow69]

Who else is making a stripping run this week? The more trials the better. I don't think I can strip anything until the weekend.

[jb-texshine]

Who else is making a stripping run this week? The more trials the better. I don't think I can strip anything until the weekend.

I've got a big wash destined to be 1.5 dist. Outline the parameters for anyone interested in participating. I got 15 gallons of clear wash.

[skow69]

The basic hypothesis is that, all else being equal, more heat will produce distillate at a lower ABV.

It's been years since I did it, but I was stripping a wash in a potstill on a gas cooktop running a pencil lead stream, barely. I had a thermometer in the headspace of the still. I turned the flame down to a slow drip to see what the effect would be. A few minutes later the temperature dropped a few degrees F and the ABV rose by a couple percent. I don't remember the details but it was definitely measurable. A few minutes later I turned the heat back up. The temp and ABV went back to where they were, or maybe a point off from the change in wash composition. The best test would be to repeat the cycle at least once for an ABAB.

[S-Cackalacky]

Skow, my guess would be that a fast boil raises the pressure in the vapor path enough to cause at least a slight increase in temp. When you lowered the output rate to a drip, there was less pressure in the vapor path and the temp dropped.

My theory (and that's all it is) is that ABV changes take place relative to takeoff rate because water is being pushed through with higher rates. My strips are usually well below 50%. I realize that this proves nothing - I collect differently depending on strip or spirit. I suppose the best comparison would be to use identical wash in identical equipment with the takeoff rate being the only variable.

[Badmotivator]

When you cut the power how did your collection rate react? Can we see a picture of your still? What was the ABV of the wash and the distillate? How do you measure the heat input?

I'm not being argumentative, I very much want to understand what makes the difference between your experience and mine.

Understood, and I appreciate your fair-mindedness.

When I cut the power the collection went from a thick fast stream to medium to low speed drips. On the last trial the parrot took about 10 minutes to refill, it was so slow. Pic of the still below. (Ignore bucket, pic was taken while filling the still.) Distillate started at 50 ABV so the wash was around 7 or 8 per the alcohol vapor curve. (Mash was goopy. No SG reading possible) My still has 2 X 2 kW elements. One is switched, the other is on an SCR controller with dial and ammeter. My low-power kW numbers are not accurate, but between what the switches and dials tell me, what my ears tell me, and what the collection stream tells me, I think they're true enough. The largest difference in power I could manage made no difference in the distillate ABV in any of three trials.

[Badmotivator]

The basic hypothesis is that, all else being equal, more heat will produce distillate at a lower ABV.

You'll want to be careful about this. Time alone will lower the ABV, so seeing a drop in ABV might not be as meaningful as you'd like. I think what you have to aim for is a rise in the ABV after lowering the power. That's a better confirmation or disconfirmation of the Power->Composition hypothesis since that would never happen with no change, so the change must have caused it.