Compact VM head, coil in a box

[manu de hanoi]

Hi all,

I have to follow the VM hype, making 1/2 a millimeter adjusments to the liquid output valve (2 meters high) every 10 minutes is annoying indeed. So, the column is 3 inches, the output is 2 inches, using a valve with screw fittings.

Here are the design constraints :
- the 2 inches stainless screw fittings are expensive, at least 2 males are required for the pipes on each end of the valve (already equipped with female screw fittings). the fittings will be welded on 2 pieces of a 2 inch pipe one connecting to the column the other to the cooling section
- Cooling: I want to use a copper coil because it's much smaller than a stainless jacketed cooler, the problem is that for maintenance, one must be able to disassemble the coil, and that make things much more complex
- distillate liquid output : 10 mm pipe
- My current design so far is in the picture, I am not really satisfied because the coil will touch the bottom of the pipe and retain/slow distillate evacuation. If the coil was vertical then it would require one more screw fitting in order to let the coil be disassembled

I need some suggestions on how to improve the design

[Nykter]

A traditional VM needs to have the product condenser significantly lower than the exit from the column in order to get the siphoning effect, but since you use a really large one you might not need it that badly.
Its this effect that shuts down the still when there's no more ethanol in the mash.

[minime]

Hey Manu, you might want the coil to lay on the bottom and cool your distillate before it heads to the collection jar. if you wrapped it in copper gauze it wouldn't slow it enough to back up down the column. Your idea might work like a champ.

[manu de hanoi]

This head is used on top of a continuous still.

A traditional VM needs to have the product condenser significantly lower than the exit from the column in order to get the siphoning effect, but since you use a really large one you might not need it that badly.
Its this effect that shuts down the still when there's no more ethanol in the mash.

Can you explain how the siphoning you mention works on a batch still ? i'd like to understand. Now that you mention it, since there will be a long, 8 mm pipe connected to the distillate output, i'm afraid the vapors will be pulled in the condenser too hard ..... Perhaps drilling a vent would help...Could close the vent if output is too weak.

Hey Manu, you might want the coil to lay on the bottom and cool your distillate before it heads to the collection jar. if you wrapped it in copper gauze it wouldn't slow it enough to back up down the column. Your idea might work like a champ.

Actually the condensate is heading to the rectifying column (i use 2 continuous columns) and I need it liquid but not chilled for energy saving purposes.
If i let the coil touch the bottom, i'm afraid the liquid flow would be blocked and go back to the main column. But thanks for the idea, some scrubbers will do the trick of lifting the coil.....if i manage to coil the pipe to something smaller than 2 inches....

[decoy]

you could just wrap 2 lengths of 1.6+ mm of copper electrical wire around the coil so its like a sled...

[DestructoMutt]

Nykter wrote-

A traditional VM needs to have the product condenser significantly lower than the exit from the column in order to get the siphoning effect, but since you use a really large one you might not need it that badly.
Its this effect that shuts down the still when there's no more ethanol in the mash.

what siphoning effect? are you implying that the condensing of the vapor in the product takeoff arm is causing a vacuum? if thats the case, how does the pressure balance counter effect (for every action there is an equal, but opposite reaction) "know" not to come in from the product take-off output opening? is there supposed to be a one way valve installed on the product take-off that i haven't heard about?

my understanding of the mechanics (fluid dynamics, heat transfer, gas flow, etc.) involved in a compound reflux column does not include a "siphon effect". the effect may well be present in a potstill and a reflux column (no induced reflux and sealed at the top), where the take-off could be completely filled with liquid and stop air from going in through the take-off tube. then the condensing of the vapor in the take-off tube could cause a vacuum.....if the production of vapor in the boiler was not keeping up with the condensing of the vapor. so if there was a vacuum created....the boiling point of the liquid in the boiler would drop and there would be a surge of vapor created which would fill the vacuum. would this then create a slight over pressurization, forcing uncondensed vapor out the product take-off?

this "siphon effect" theory is intriguing....could someone please explain how it works (while not breaking any laws of physics). or is it like a jack-a-lope, actually being just an urban legend for those that don't really want to think?

[DestructoMutt]

manu wrote-

Actually the condensate is heading to the rectifying column

why?

[Nykter]

Can you explain how the siphoning you mention works on a batch still ? i'd like to understand. Now that you mention it, since there will be a long, 8 mm pipe connected to the distillate output, i'm afraid the vapors will be pulled in the condenser too hard ..... Perhaps drilling a vent would help...Could close the vent if output is too weak.

Hmm well on a classic VM batch still the flow of product vapour is is pulled down through the product condenser by gravity, since ethanol vapour is heavier than air. At the end of the run, when vapour finally contains enough water, it will be lighter than air, reducing this effect, minimising product takeoff, until it finally stops if the still is properly tuned.

I think you won't need an extra vent to minimise output, use the valve instead.

DestructoMutt, this effect is only present in a classic VM which is enough open in the top and in the end of a (tall) Leibig condenser not to allow for any pressure differences. The law of physics i call is a simple one, gravity.

Imagine a vertical tube, filled with a gas heavier than air, open in both ends. What will happen? The gas will slowly flow down through the tube. Now imagine the same tube fillled with a gas lighter than air. The gas will rise.

Now, add a condenser in each one of the ends, still very open, and a connection to a boiler/column somewhere in the middle of this tube adding more gas. The amount of gas has to be less than or equal to the gravity forced flow in the tube. Make sure the condensate from the upper condenser flows back into the column, also by gravity.
If the gas is lighter than air (steam) it will condense in the upper condenser and reflux into the column. If its heavier (ethanol) it will flow down and condense as product.

And please note I'm _not_ suggesting that a mixture of water and ethanol vapour will separate, they wont.

Now, here's the tricky part:

Add a valve in the tube right below the inlet. Close this valve just enough to let the flow of vapour pulled down by gravity be approximately 1/10 of the total vapour entering the tube. Now 9/10 of the vapour will be forced to rise to the reflux condenser, condense and return to the column as reflux.

Now imagine, with the same power and valve settings, the vapour containing more and more water, and less and less ethanol, it will finally be lighter than air. What will happen?

Since the path up to the reflux condenser is in practice unrestricted, all vapour will head to it, and no vapour will be pulled down, by gravity, to the restricted (by the valve) path to the product condenser. Full reflux.

Of course if the amount of vapour leaving the column is large enough, the tube and reflux condenser will act as a restriction, killing this effect by introducing an overpressure just above the valve.

So, a poorly contructed or run VM vill not have this effect.





I think.

[DestructoMutt]

Nykter wrote-

Hmm well on a classic VM batch still the flow of product vapour is is pulled down through the product condenser by gravity, since ethanol vapour is heavier than air. At the end of the run, when vapour finally contains enough water, it will be lighter than air, reducing this effect, minimising product takeoff, until it finally stops if the still is properly tuned.

gravity is good. but that's not why vapor goes into the product take-off arm.

you are neglecting:
-the boiler is constantly producing vapor - a gas - gasses expand to fill their container. if you look at a container full of a single gas, at a consistent temperature - the density of the gas will be the same at all points in the container and so will the pressure of the gas (not vapor pressure, but force exertion).
-convection - warm gases are less dense than cooler gases - thus rise. if you heat the bottom of the container, the warmed gas will rise to the top, the cooler gas will sink. [if the container is closed, the pressure will increase because the gas is more energized. if the container is open to the atmosphere, gas will escape. just trying to show i'm not ignoring other factors and reactions.]
-the flow of a gas filling a container is dependent on the physical characteristics of the container, the existing contents of the container and the introduced gas, not just gravity.

ethanol vapor that is at the same temperature as the surrounding air is denser and thus heavier than air. however, if you heat the ethanol vapor sufficiently above the temperature of the surrounding air, you can and will make the ethanol vapor lighter and less dense than air. it will rise, it will also expand to fill its container, if enclosed, such as in a column. (as it cools it will sink/settle, but it cools before sinking/settling, hence it's density is increasing as it sinks/settles.)

addressing just one physical characteristic of the system is inappropriate. gravity is just one part of the total equation, you must consider the effect of the constantly produced vapor from the boiler - this produces an over pressuritzation in the column - gases expand, especially warmed gases. the production of a dense gas from the boiler also forces out/expels lower density gases (atmoshperic air). we then end up dealing with system containing ethanol, water and the other byproducts of fermentation, but lacking atmospheric air. the ethanol vapor splits into two streams in the vapor management head (top part of the column) not because of gravity, but because the vapor is doing what a gas does - it's expanding to fill its container. gravity is pulling the condensed liquid down the condensors, but has fairly little effect on the movement of the gas/vapor.

additionally you must consider the flow of heat in the system, and how the heat affects the flow of gas/vapor and liquids. heat flows from hot to cold. warmed air rises, but can transfer its heat to something else and then sink again. water vapor gives up its heat faster than ethanol (a characteristic that is exploited in distillation), thus condenses out of gas form faster than ethanol.

if you want to think of an effect that might have some play in the column, consider the venturi effect - a gas or liquid flowing in a pipe, past a small opening in a pipe, gat generate a vacuum in the small pipe such that the contents of the small pipe are sucked into the larger pipe. but this doesn't happen in the column of a still, just ask anybody who has leak in their column. for the effect to come into to play, the large pipe needs to shrink in diameter at the point of the small pipe, such that the gas/liquid in the large pipe has to speed up as it passes the small pipe.

[manu de hanoi]

meanwhile a 2 inches 2nd hand valve was aquired for 9 usd.

[snuffy]

I think you need to move the two condenser coils much farther away from the valve.

The valve has to be at vapor temperature or the vapor will start condensing in the valve itself. Conduction through the walls of the takeoff chamber and valve will cause the vapor to collapse too soon and severely limit the amount of output.

The reflux condenser needs to be at least two feet above the vapor takeoff so there is sufficient head to the height of the vapor column. Too short and there will be little or no pressure to drive the vapor into the valve and product condenser.

Also, you can probably use a valve much smaller - 3/4" or smaller. The valve opening is very small compared to the cross-sectional area of the reflux column.

Maybe minime can tell us the cross sectional area of his valve openings at various stages of the run and the height of his vapor column above the takeoff? I think his reflux column is 3" diameter, yes? These ratios are very important to getting VM working properly.

[decoy]

id like to hear more on your theory about alcohol vapor going down the tube to condensor because its heavyer..
it dosent sound right... im inclined to think its more so presure related...

is there a source i could perhaps have a read of..?