Continuous still brainstorming

[Edwin Croissant]

hey, with two peristaltic pumps it seems it would be easy to maintain a steady state in the still.

You mean with a Max_Vino take-off?



So from top to bottom:
Condenser
Max_Vino take-off for Methanol and the volatile components like Acetaldehyde, Ethyl acetate, Diacetyl and Methanol.
Methanol column
Max_Vino take-off for Ethanol
Ethanol column with take-off point(s) for fusel oil (same type of pump?)
Feed entry with peristaltic pump
Stripper column
Boiler.
Heat exchanger between bottoms and wash feed to preheat the wash.
Cooling pump - heat exchanger between cooling system and cooled down bottoms - radiator - condenser.

I think that it is possible to mount the three columns side by side, take-off for ethanol will pump reflux into ethanol column. Vapor from stripper must be heated to reduce the ethanol concentration of the condensate from the ethanol column by running the vapor line from stripper through the stripper column and the boiler into the ethanol column. Otherwise you need a hot feints pump to pump the condensate from the ethanol column to the top of the stripper column.

[dullfig]

Neat! I like that max-vino take-off. Yep, that's kinda what I was thinking of.

[Maritimer]

Here is the ratcheting metered flow that I considered.

The valves are inexpensive and electrically operated. They have a large area for the wash to flow through when they are open. A microcontroller already runs my still, so I can generate signals to operate the valves.

Here is how it works.
- The valve on the wash pipe opens, admitting liquid to the little bowl.
- The float switch tells the microcontroller that the bowl is full.
- Microcontroller closes the wash valve.
- After a measured time--which is adjustable by the microcontroller, the bottom valve is opened and the contents of the bowl fed to the continuous stripping still, where it goes into a heat exchanger. The heat exchanger is filled with hot exiting waste from the still.
- On the next cycle, the warmed wash in the heat exchanger is pushed into the still and the heat exchanger is filled with fresh wash.
- The microcontroller can use timing information from the float switch to monitor the pressure from the wash (the head) as well as the quality of the exciting wash flow.
- The liebig condenser should also be fed with wash. In fact, there would be a lot more heat available here that from the exciting waste. The liebig captures the energy of condensation, the latent heat of vapourization, which is much larger than mere heat transfer from the waste.


Wow! If the wash going into the still contains all of the heat of condensation of the exiting ethanol and water, the efficiency will skyrocket.



M

[dullfig]

I was reading somewhere that if your alcohol content is up to 10% in the wort, you would not need any cooling water, the wort is sufficient.

[flyingdutchman]

I hear Mike Nixon published an article on a simple continuous distillation apparatus. I don't suppose anyone has access to this article? I would love to see it and it may be relevant to what we are talking about here.

[dullfig]

ok, this is just brainstorming, I haven't given this next idea a great deal of thought, it is just an observation. If you split the still in two, with a stripper and a rectifier, the rectifier should get progressively heavier as more and more alcohol collects, right? maybe that would be one way of knowing how much alcohol to draw. like maybe mount it on a load cell, and draw alcohol to keep total weight steady or something like that.

Dan

[dullfig]

if you wanted to really be a purist and use no electronics, you could hang the rectifier from a balance beam, and have the balance beam operate a small valve. you could set the reflux rate by adjusting a weight on the balance beam.

[Maritimer]

Note: This is an edited version of the original. I forgot to include the density of ethanol in the original calculations.

Back to the continuous stripper http://homedistiller.org/forum/viewtopi ... 16&t=33101 .

From experience, but also from calculation http://homedistiller.org/forum/viewtopi ... 0#p7133969 , the stripped product from a 10%ABV wash is approximately 30%ABV.

For the sake of calculation, suppose that the ratcheting dispenser passes 100ml on each cycle.

So 33.3 ml of product are produced from each 100 ml of wash.

The temperature of the wash is 20*C, say.

In 100 ml of 10%ABV wash there are 90 ml of water and 10 ml of ethanol.
In grams, this is:
10 ml x 0.791 g/ml = 7.91 g ethanol and 90 g water = 97.1 g

To raise 100 ml of wash 1 K would require:
7.91 g x 0.58 cal/g + 90 g x 1 cal/g = 94.5 calories per *C (or K in Kelvins)

So, the specific heat of the wash is 94.5 cal/97.1 g = 0.973 cal/(g K)

The boiling point of the wash, from the usual phase diagram, is 93.1*C.

The product is 30%ABV. So 100 ml of product contains:
30 ml x 0.791 g/ml = 23.7 g ethanol + 70 g water = 93.7 g.
So 33.3 ml would have a mass of 31.2 g.

The LHV of the product is therefore:
23.7 g x 204 cal/g + 70 g x 540 cal/g = 42640 cal per 93.7 g
or 42640/93.7=455 cal/g

The boiling point of the product is 85.7*C, from the phase diagram.

So, we have 97.1 grams of wash going into the liebig and 31.2 g of product being condensed.

The 31.2 grams of vapour will give up 31.2 x 455 cal/g=14196 cal

Now 14196 cal put into 97.1 g of wash would raise its temperature by:

14196 cal/97.1 g/0.973 cal/(g K)=150 K (that's off by 3 K from the erroneous first calculation!)

There is actually more heat available than the wash can take.

So, instead of the usual liebig to condense the product, have two liebigs in series. The first would be cooled by the wash, which would extract as much heat as possible, raising its temperature to 85.7*C, and the second part would finish off the job using water as a coolant.

Now, if instead we had used the waste to warm the incoming wash, we would have: 0.667 x 97.1 = 64.7 grams of water at 100*C. This would result in heating the 97.1 grams of wash to an equilibrium temperature, Teq, of:

97.1 x 0.973 (Teq - 20) = 64.7 (100 - Teq)

Teq = 52.5*C

So, by using the liebig to heat the wash instead of the waste, it would be:

85.7-52.5=33.2*C hotter.

Edit: Interesting; taking into account the density of ethanol makes hardly any difference in the results. To really get accurate, the volume change with %ABV would have to be included, too.

M

[Lester]

Nice Maritimer!

The substantially-reduced power consumption would be enough motivation to go for a continuous still. Where I am, the fuel cost is responsible for about 25% ~ 30% of the total cost of the product.

As for the pulsed-feed method, how about adapting an existing automotive technology like CRDi solenoid valves? Maybe the orifice is not large enough.... then perhaps a fixed bypass in parallel with the valve itself could be used.

[Edwin Croissant]

I made some spreadsheets with macro's to assist in my calculations.
I am not satisfied with this spreadsheet, I am not sure if this is a valid model, the output looks good but from my experience these are the most dangerous models, as they show you what you expect. So use at your own risk .

If you find any errors, I would appreciate some feed back

The spreadsheets are in two flavors, OpenOffice Calc and Microsoft Excel.

For those of you that are interested in the calculations from ABV to ABW and mole fraction and vice versa I included a paper that I made to get some experience with OpenOffice.

[Lester]

I would be very pleased to have a continuous stripping column that supplies 30% ABV product at a very low fuel consumption. Maybe I can run the boiler using just heads & foreshots as fuel?

[Maritimer]

Hi Lester,

The wash is being heated to almost boiling temperature, but that only requires 0.958 cal/(g K). Vapourizing the wash takes 439 cal/g.

So bringing one gram of wash from 20*C to 93.1*C would require 70 calories.

On the other hand, you only need to vapourize 33.3% of the wash (at 10%ABV), but you have to bring all of it up to the boiling point. So 439/3=146 calories per gram of wash are required for vapourization.

Interesting how the numbers can surprise you!

M

[heartcut]

Yeah, the second law of thermodynamics is a bitch.

[Lester]

Hi Lester,

The wash is being heated to almost boiling temperature, but that only requires 0.958 cal/(g K). Vapourizing the wash takes 439 cal/g.

So bringing one gram of wash from 20*C to 93.1*C would require 70 calories.

On the other hand, you only need to vapourize 33.3% of the wash (at 10%ABV), but you have to bring all of it up to the boiling point. So 439/3=146 calories per gram of wash are required for vapourization.

Interesting how the numbers can surprise you!

M

From what I understand, the vapor contains almost all of the heat. So if there's 146 cal/g of vapor, and if I can transfer most of that heat to the wash (in the liebig), then I can save a lot of fuel in the process. I only need to supply additional heat for system losses and if that is indeed the case then a small burner would suffice (provided I have a well-insulated system). Am I getting this concept correctly?

[flyingdutchman]

I would be very pleased to have a continuous stripping column that supplies 30% ABV product at a very low fuel consumption

I absolutely would agree. If for nothing else from a safety standpoint. I would be quite happy with a continuous still that produces anything under 40%. A continuous still almost implies someone might not be watching it 24/7. It would also be easier to store as low wines. Then the cuts could be made in batch mode later. OR just couple this column to a rectifying one if so desired.


There is another discussion going on where a really good idea was presented based on Mike Nixons continuous distillation paper (which was why I asked).

Anyway part of the design (not mine) was to use the wash feed as a reflux condenser (rather than a product condenser) at the top of the column.

PS
For the heat of vaporization it might be easy to work on a per mole basis for calculations (if you are dealing with multiple concentrations of ethanol in water) since to a rough approximation they have approx. the same LHV/mol
Unfortunately I do not believe this holds true for molar heat capacity.

[Lester]

From what I understood so far, I've taken the liberty to draw what I have in mind. Please feel free to edit. I thought we needed a diagram to dispel any ambiguities that may exist in my head.

[Maritimer]

Hi Lester,

Assuming you are considering the technique I used, which is basically a pot still with four quadrants that feed into each other, there isn't really a column involved.

The wash feeds into the first quadrant, and since the extra input would put it at a higher level than the next one, the wash in the first quadrant starts to flow into the second, and so on. Each quadrant gives up some of its ethanol, until in the last quadrant there is only a small amount left. I set this last quadrant at 0.5%ABV, which I controlled by measuring the temperature of the wash in the fourth quadrant. The whole process just imitates a pot still and even produces the same %ABV that I get when I use a pot still to strip.

You could use gas to heat the still. I used 1000 watt elements in each quadrant.

I was rereading your older post.

"From what I understand, the vapor contains almost all of the heat. So if there's 146 cal/g of vapor, and if I can transfer most of that heat to the wash (in the liebig), then I can save a lot of fuel in the process. I only need to supply additional heat for system losses and if that is indeed the case then a small burner would suffice (provided I have a well-insulated system). Am I getting this concept correctly?"

That 146 cal/g for the vapourization was a little slight of math. Since only 1/3 of the wash is vapourized, where each individual gram requires 439 calories to vapourize, that comes to 146 calories per gram for the whole wash. What you save is the energy required to heat the wash up to boiling temperature (close to it, anyway).

M

[flyingdutchman]

I like the drawings.
Here is a previous take on this idea. http://homedistiller.org/forum/viewtopic.php?f=1&t=5432
Note the tube with the T goes up the column to presumably the 1/2 way point. By traveling up vapor lock hopefully isn't a problem. The overflow on the bottom is a lot like on the parent site.
I like the idea of preheating the mash. With out that a lot of energy is wasted and perhaps time as well since it would probably need to be run a lot slower.

Also attached is a simplistic lab setup with a form of metering setup.

Cont Dist Appratus lab.pdf

(655.73 KiB) Downloaded 279 times

Oh and here is some work Manu did. Might help learning from what he has already done.
http://homedistiller.org/forum/viewtopi ... s#p6736495

[Lester]

Thanks for the drawing Maritimer.

I have been staring at my still for a while and it seems very easy to modify into a continuous stripper, but configured to scavenge some of the heat from the Liebig, the work involved is just a few copper tubes here and there, a small overhead tank for initial trials, plus a needle valve.....

..... and I can dial in what % ABV I want at the output (to some extent) by varying the feed rate of the wash.

But if the math doesn't hold up then there's no point in trying. What I'm really after is fuel savings. I see that most of the fuel consumed is spent in vaporizing the wash........ and I can recover most of the heat via the Liebig........ so to some extent it should save more fuel than just "heating up the wash"? I don't understand why the fuel saved is only

What you save is the energy required to heat the wash up to boiling temperature (close to it, anyway).

Nice links FD! Thank you!

[Maritimer]

Hi there Flying Dutchman,

There is a very different method of operation between the stills you have cited and the technique I'm using. I'm not using reflux at all. The incoming wash is not injected into the column but is added to the wash in the boiler.

This is a schematic of the still. In practice, the quadrant separators are a lot taller, allowing the contents of each quadrant to boil without overflowing into their neighbours. Each quadrant holds approximately one liter of liquid.

Each separator has a tube that goes down close to the bottom of the stock pot. It rises about 2-1/2 inches, bends 90 degrees, and goes through a hole in the quadrant separator to allow liquid to get into the next quadrant.

If you pick up any book on differential equations, there will be a section on "mixing phenomena" in which liquids of various compositions are added to a tank at certain rates and the tank is drained at another rate. This is just the first one I found on Google:
http://www.math.washington.edu/~conroy/ ... ples01.pdf" onclick="window.open(this.href);return false;" rel="nofollow .

This better explains the operation than thinking of reflux.

M

[Maritimer]

Hi Lester,

A typical Birdwatcher's Wash that I make is 90 liters. The still will use the heat of condensation to heat up that 90 liters almost to boiling. That's the energy that you save.

The heat to vapourize 1/3 of the 90 liters is the energy you require.

There is still a lot of heat being thrown away in the water-cooled liebig and in the waste. Maybe you can find a use for this, say, by running a reflux still at the same time and using it to heat up the low wines.

M

[Maritimer]

Oops! I forgot to include the density of ethanol in the calculations. the numbers are off, but the general picture is the same--there is plenty of heat available to heat the wash with lots to spare.

I'll fix it tomorrow if the post is still editable.


Edit: The original post now includes the density of ethanol. The result changed only marginally.

M

[Maritimer]

Hi Lester,

Here is a use for the waste, which is leaving the still at about 99.5*C.
Refer back to the calculations post for numbers that appear out of nowhere:
http://homedistiller.org/forum/viewtopi ... 0#p7149378

If you put a heat exchanger (a liebig, say) after the wash has been heated by the LHV of the product, the temperature of the wash could be raised even more.

Call the equilibrium temperature that would be achieved Teq.

Think of a 100 ml ratcheted charge going into the still and 64.7 ml water exiting at 99.5*C. The wash has already been heated to 85.7*C.

97.1 x 0.973 (Teq - 85.7) = 64.7 (99.5 - Teq)

Teq = 91.309*C.

The boiling point of the wash is 93.1*C.

You are only 1.8*C away from boiling!

M

[dullfig]

Hey guys, how much alcohol do you suppose is in circulation in the reflux column when it's running? a lot? a little? would you be able to measure the difference in weight of the column while running as compared to when it's dry?

Does a high reflux ratio mean that there's a lot of alcohol circulating in the column?

[flyingdutchman]

Hi Maritimer,
Thanks for the post on mixing!
I did see your stripper setup and it is a great idea. I see it (like I think you pointed out) as almost 4 pot stills in series with a gradient (mole fraction ethanol)from the first to the last.

I see that those continuous stills are indeed different than your setup. Some of those links were intended to illustrate specific problems and how others had addressed them. For instance...
Avoiding vapor lock in the heated wash feed line..
Automated wash feed system
How other have preheated their wash lines and what they encountered when they did

PS
You probably already know this (perhaps some other do not?) but due to the molecular interaction between water and ethanol the total volume of the solution is not the sum of the individual components volumes. So you need to use experimentally determined density's for water ethanol mixtures.
This from Perry's
http://www.separationprocesses.com/Cour ... erty01.htm

[Maritimer]

Hi Flying Dutchman,

I'm a retired university research lab technician. I designed and built apparatuses for professors and students to do their experiments. These labs were in three quite different disciplines, but the devices I built were all "mechatronic"--everything from pure electronic to pure mechanical and all gradations of combinations in between.

From the start I avoided chemistry because of my extreme sensitivity to smells.

So, it seems that the best way to approach mixtures of chemicals is by moles and mole fractions. I'll have to make an effort to understand things that way. I understand what a mole is and a what mole fraction is, but as Edwin would say, I just haven't grokked it yet.

When I repaired my calculations in which I neglected the density of ethanol, I was surprised to find that there was very little difference between the (more) correct analyses and the erroneous ones.

Would it be permissible to use milliliters instead of grams and use the specific heat and latent heat of volumes instead? For general understanding, is the volume change with the ratio of ethanol to water important enough to include?

Or should I just learn to deal with moles?

M

[flyingdutchman]

Hi Maritimer,
I think your calcs look good and you have a firmer grasp of calculus than most organic chemists (LOL). Working in weight percent is fine. Its only volumes that cause calc. errors.

I only suggested moles for the Latent heat of vaporization because it is close enough for both water and ethanol on a per moles basis that to a reasonable rough approximation we can call it the same.
So ..
10%, 50% or even 90% ABV liquid has a LHV of ~ 40 kJ/mol. It doesn't matter what the ABV is when working in moles (unlike grams). Sometimes that makes life easier. This is exactly how Nixon came up with the commonly quoted statement that a 1kW element will produce 45 liters of vapor (at that specific temperature) regardless of the ratio of ethanol to water in that vapor.

I believe you can easily work in weight percent (like you were). Just start out by converting your ABV to ABW. Use the correct density to convert volume to grams. Now the weight percent tells you what percent of the weight (grams) is ethanol. Then work in grams to do all the calcs like you already were. Then when ready use the corrected density from say Perrys to convert back to volume.

I am not sure how much error the incorrect density would give you but it would be easy to compare.

Odessit posted an excel sheet that converts ABV to ABW here
http://homedistiller.org/forum/viewtopi ... W#p6842016

[flyingdutchman]

In the vein of calculating how much thermal energy is available to preheat the wash for a continuous distillation....
Here is another reference paper related to density of ethanol water solutions. It also gives surface tensions viscosity and molar volume.
http://link.springer.com/article/10.100 ... 9-6#page-1
Just use the look inside option to view the table without having to purchase the article

I am sorry but concentration it is in mol fraction. Perhaps Edwin could help out with an easy way to convert from ABV to ABW and Mol fraction of ethanol water solution (with say excel)?

[Edwin Croissant]

You probably already know this (perhaps some other do not?) but due to the molecular interaction between water and ethanol the total volume of the solution is not the sum of the individual components volumes. So you need to use experimentally determined density's for water ethanol mixtures.

See my paper on the conversion of alcohol

Perhaps Edwin could help out with an easy way to convert from ABV to ABW and Mol fraction of ethanol water solution (with say excel)?

Just pick my spreadsheets apart from the above mentioned post. It is all there

So, it seems that the best way to approach mixtures of chemicals is by moles and mole fractions. I'll have to make an effort to understand things that way. I understand what a mole is and a what mole fraction is, but as Edwin would say, I just haven't grokked it yet.

By using the International System of Units you do not need to convert anymore which reduces the change of mistakes considerable. All my calculations are done in mole, just pick my spreadsheet apart

I made some improvements in my spreadsheet as it was, as I expected, based on a flawed understanding. The numbers I now get are not that far of from what I did, but at least I know now what I am doing. (famous last words )
I am still improving as I want the feed, feed heating power and boiler heating power to be positive numbers and the distillate, condensate and cooling power to be negative numbers.

[flyingdutchman]

Ok for anyone interested I found FermCalc here http://web2.airmail.net/sgross/fermcalc ... sions.html
It will change ABV to ABW and vice versa.
It claims to use this in its calculations (Edwin I am guessing this is the recommendation 22 in your paper?)

FermCalc uses the general formula for calculating the densities of mixtures of ethanol and water found in International Recommendation 22: International Alcoholometric Tables by the International Organisation of Legal Metrology (OIML, 1973) to calculate the densities of alcohol ρa and water/alcohol mixtures ρm at 20ºC that are required to perform the conversion. When performing the conversion for a wine with a specified specific gravity, the actual wine density is used in place of ρm in equation (31).

Now the calcs from ABW to mol fraction are a lot simpler as Edwin's paper outlines.

However for those who still live in an analog world such as myself I have this paper which lists it all in tables.
http://136.145.83.33:8000/jspui/bitstre ... .%2019.pdf