# Pot size to column diameter ratio

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Does anyone know about the direct relationship on the size of the pot to the size/diameter of the column on a hybrid still? I am wondering about a 4-6 plate column.

If you had a 100 gallon pot what diameter column would be the most efficient? Can you put a 12inch diameter column on a 100 gallon pot ?

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For our 600 liter column still (158 Gal) the diameter of the column is 200 mm (about 8 inches).

The column goes up 31 ft.

There is another version of the same still with two columns that maxes at 23 feet.

But on the 500 gallon pot still the column is not proportionally larger in diameter. I will measure it to get the exact numbers.

Here are some pictures for comparison purposes.

http://www.tetondistillery.com/distillery-equipment

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you are asking the wrong question.

it is not column size to amount of gallons.

It is column diameter to the surface area of the still. No pun intended but it boils down to the evaporation rate due to the surface area of the diameter of the still and the vapor velocity that the column can handle without being overrun, or dropping inefficiency.

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Generally there are fewer risks associated with oversizing a column than there are undersizing. However the risk associated with oversizing column diameter is the liquid loading capacity of each plate. Theoretically, you design a system where the liquid needed to load the trays exceeds the volume of alcohol in the boiler.

Diameter is more directly related to the power input into the boiler than the liquid capacity of the boiler. The higher the power input, the faster the potential vapor speed through the column.

Evaporation is very different from boiling, once you hit the boiling point of the liquid, the surface area is largely irrelevant. Boiler geometry is only important when we're talking about jacketed heat transfer into it.

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James- " Theoretically, you design a system where the liquid needed to load the trays exceeds the volume of alcohol in the boiler."

Is that how you meant to say that? If I needed more liquid than I had, I would never get my trays loaded. My brain might not be working properly yet? Or it might be working fine, one never really knows. Scrounge

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Oops, typo - "Theoretically you *could* design a system where the liquid needed to load the trays exceeds the volume of alcohol in the boiler."

Not that you would want to, but you could.

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you are asking the wrong question.

it is not column size to amount of gallons.

It is column diameter to the surface area of the still. No pun intended but it boils down to the evaporation rate due to the surface area of the diameter of the still and the vapor velocity that the column can handle without being overrun, or dropping inefficiency.

This couldn't be more wrong. The surface area of the top of the liquid is irrelevant to the amount of vapor that is produced. The amount of vapor that is produced is controlled by the amount of heat that is input into the still.

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This couldn't be more wrong. The surface area of the top of the liquid is irrelevant to the amount of vapor that is produced. The amount of vapor that is produced is controlled by the amount of heat that is input into the still.

Well that's an interesting theory. I wonder how that would explain all the lake effect snow we are getting in NY this week, because the entire surface of Lake Ontario is currently un-frozen.

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Well that's an interesting theory. I wonder how that would explain all the lake effect snow we are getting in NY this week, because the entire surface of Lake Ontario is currently un-frozen.

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Well that's an interesting theory. I wonder how that would explain all the lake effect snow we are getting in NY this week, because the entire surface of Lake Ontario is currently un-frozen.

Boiling and evaporation are completely different processes. With evaporation, yes the surface area drives the amount of vapor produced. That is not the case with boiling.

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Let put like this.

Vapor saturation.........

examples:

1. 20 lb LP cylinder in the middle of the winter will barely make a flame.

A giant farm LP cylinder laying on its side will run the stove, water heater, over, and the dryer, furnace.

2. Sugar in a glass of water reaches a point were you can't put and more sugar in the glass because of saturation.

3. Have you ever heard of having 150% humidity outside? O' wait its called a pool.

My point is that at a certain point you reach max amount of vapor, after that you increase pressure, and increase pressure causes a reduction in vapor and an increase in the boiling point of all the liquid in the whole system. This causes all your temperature of cuts to be off.

I just saying........

Stick with me kid, ya might learn something.

Take Care

Just my 2 cents.

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Just to be a smart @\$\$

I your theory we could just put like 100,000,000 btus to a 1000 gallon pot and distill it in like 10 min.

right??

Just sayin.

Dehner-out............

you know i love ya.....

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check this out.... i just looked this up

LP boils at -44 f

so when it is 32f outside the lp is boiling technically.

Vapor saturation baby

Dehner- out

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You obviously don't know anything about thermodynamics so it probably isn't worth arguing with you and trying to teach you anything. There is this thing called enthalpy of vaporization. It is a measure of the energy required to convert a given amount of liquid into a gas. Let's take water as an example.

Let's assume I have 100 gallons of water. 100 gallons of water will weigh about 834 lbm. Let's also assume for the moment that we are dealing with a simple pot still. The liquid in the pot should be at atmospheric pressure because it is an open system. At atmospheric pressure the enthalpy of vaporization is 970 BTU/lbm. That means that once the water is brought to 212 F, for every 970 BTU of energy that is input into the system, 1 lbm of vapor will be produced. Let's say we have gotyen the pot up to 212 F and we heat that water with 100,000 BTU/hr for 1 hour. We've input 100,000 BTU into the system and have boiled off 103 lbm of water, or about 12.4 gallons. If we heated it with 200,000 BTU/hr instead for 1 hour we would have boiled off 24.8 gallons.

That example dealt with a simple pot still. To prove your previous point wrong, let's discuss a plated column where there actually is a slight amount of pressure. The only pressure is due to the height of the liquid on the plates. If there was a whopping 28" of water combined on the plates, the pressure in the still boiler is still only 1 psi gauge. Now back to our steam tables and enthalpy of vaporization. At 1 psi our boiling point has now risen yo 215 F, but our enthalpy of vaporization is now only 968 BTU/lbm instead of 970 BTU/lbm. So if we again are boiling and heat with 100,000 BTU/hr for 1 hour we will have boiled off MORE water than we did before.

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Well, there ya go spread your knowage to the masses of the world............. run forest run............

Point being the column must be matched to the pot volume, surface area, power input, % of alcohol in solution, heat loss, efficiency, reflux ratio, liquid and vapor volume in the column, and about 5 million other factors.

****Based on a Standard rate of evaporation match the column size to the surface area of the still, you can't go wrong.*****

If the hill people can make moonshine, than we should be able to make super great products.

Just make good booze.....put great liquid in bottles...... make lots of money.......I love it...

I'll stick to what I know. You can go work with NASA. What fun right?

You know what I love about this forum, I have so much fun. We are all stubborn about our opinions, but we are all doing the same thing.

Dehner-out

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YOU need to do an experiment. A wide shallow pot with an internal heating element vs a tall skinny pot with the same internal element. They are filled with the same volume of liquid and have the same diameter column. See which one produces product faster. The answer is they'll produce at the same speed. The surface area of liquid on the top is irrelevant!

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this is point i just made with the two different size LP tanks.

LP boils at -44f so if it is 32f outside and you have a 20lb cylinder vs a big farm cylinder with both going to a 1/2 line.

And the temp "32f" would be the same amount of heat for both (76F over boiling) the larger surface area of the larger tank will always win out. The smaller tank will make a super small frame. Just ask anyone brewing beer in there garage in the winter, or should I say trying to brew beer.Look I under stand what you are trying to say. I respect your point, I do. I respect science very much, that is what we all do here whether we like it or not we are all chemical engineers sort of. But with that said I feel you are incorrect. If I get time I will do a youtube video of your experiment for you.

I don't mean to be stuck on this whole LP tank thing but I must be. If the surface area did not matter the tanks would be standing up and painted like giant corn cobs.

I have a batch of rum coming up. I'll try to shoot a video, lets see what happens. I have several stills but I just want something close in heating, and small batch size. Do you think a still that is 18" dia vs 22.5" would be ok? I might be able to put a 55 gallon drum on its side like a big farm cylinder. I could run the same batch and same volume ( lets say 35 gallons), also I can use the same tower on both. Reflux or no reflux? What do you think?

I am game, what do you think?

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i just did the math

18" vs 22.5"

22.5 is 1.562 times more surface area.

Do you think that is enough for this experiment? I would say so. Let me know.

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Your analogy you keep going back to about propane tanks is faulty too by the way. The surface area at the top of the liquid there again isn't the driving factor in how much gas is produced. The driving factor there is the wetted surface area. That is the area of the side walls of the tank in contact with the liquid propane.

The reason I'm giving you such a hard time is that you are a commercial still builder and you just demonstarted that you don't understand basic physical processes that govern a still's operation.

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There isn't a fixed ratio between the diameter of the column and the diameter of the pot because they depend on two different factors.

The diameter of the column is primarily determined by the vapor velocity up the column. If the vapor velocity is too high you get entrainment and flooding. The liquid loading does come into the diameter determination to some extent, but the main controlling factor is the vapor velocity. If this velocity were the determining factor for the diameter of the pot then it could be the same diameter as the column. And indeed this is what is done with many large continuous stills used for neutral spirit.

The vapor velocity in the column does vary over the height of the column. As dwrich1020 pointed out the latent heat of vaporization does vary with pressure, but this is a relatively small factor. Ethanol has a much smaller latent heat of vaporization per unit mass than water so on the upper trays where there is a higher proportion of ethanol a given quantity of heat will generate more pounds of vapor than it would on the bottom trays. Luckily ethanol has a much higher molecular mass than water so this counteracts the latent heat effect. In fact it is common to assume "equimolal overflow" which basically means that on a volume basis the flow rate is almost constant and the velocity remains much the same from the bottom to the top of the column (unless there is an intermediate feed or take-off). Certainly it is easy to design a bubble cap tray that will cope with the variation in velocities and the same tray design can be used for all the trays.

The factor that determines the diameter of the pot is how the pot is heated. In the large continuous stills that I mentioned as having pots with the same diameter as the column, the heating is often done in reboilers external to the pot. The reboiler can have an area of hundreds of square feet but because it is outside the pot it does not require the pot to have a larger diameter. The amount of vapor being returned from the reboiler is roughly the same as that traveling up the column, so the same diameters can be used to ensure entrainment is low. But if you are heating with electrical elements on the pot shell, or coils of tubes inside the pot, or even a direct flame the required area could be very different and then the pot may need to be a larger diameter than the column.

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I do under stand all in which you are referring to. But that all exist in a world where everybody has millions and millions of dollars to put in an ethanol plant.

I still stick to my guns in reference to the ratio between column and boiler size because this day and age where people are starting distilleries all over and lot of people don't have tons and tons of money to spend on heat source. So they buy what they can. And even that being said if someone wants to go out and buy a 500,000 BTU boiler or 1,000,000 BTU boiler the efficiency of that particular device cannot be 100% efficiency due to the fact of inefficiencies throughout the whole system. Therefore one cannot truly calculate out the precise type or boiler needed without hiring several engineers and spending lots and lots of money that they don't have. So they deal with the inefficiencies and so thus for it is easier to calculate out what people need based on the industry standard of operations.

I believe that you'll find in life that reality plays a much larger part in how the world works then how the world is supposed to work.

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• 1 month later...

This is an interesting read. Lets say I had a 60 gallon Groen soup pot. I filled the jacket with oil, had 3- 4500w elements (13500w total) installed in the pedestal base reservoir to heat the oil. The diameter of the surface of the liquid is 36" and I fill it with 50 ish gallons low wines that are 30 to 35% ABV.

I am very interested to hear your estimates on what size of hybrid column I should have put on there, and why. Thanks.

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Lots of unknowns here, what's your target ABV output, what's your product? What kind of time constraints do you have? By "hybrid" do you mean utilizing a packed column and trays? What's the packing material? If trays, how many trays? Bubble Cap or Sieve? Why are you even considering a hybrid approach (I would argue this is unnecessarily complex, since you need to engineer both the packed and tray columns to operate within the same set of design parameters for optimal efficiency).

You are going to get a half a dozen opinions, at least. The hobby community has done a lot of trial-and-error design work on packed columns, and there are a number of rules of thumb with regard to column diameter and power input, column height to diameter ratios, hetp, etc that would probably help you. In the commercial world, much of this is either trade secret or so complex you'd wear out your slide rule.

And … the diameter of the boiler is not relevant to column sizing.

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I disagree.

boiler size and power, can over take a column by having to much vapor velocity. That leads to poor separation, that leads to poor Quality.

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