single condenser vm still 2nd attempt

[guerrila distilla]

hey there again guys. i'm at it again (uh oh i hear you all say).

here's a second attempt at a vm still using one condenser:-

inline vm still 3.jpg (26.13 KiB) Viewed 3407 times

it basically uses a shotgun condenser in the form of a water shell with 12-14 10mm 30cm tubes passing through it. the product tube will pass through the middle of the condenser using 2-4 of the same type tube.

i was told by hookline and harry that the problem with my first designs (which was very similar to this design), was that there was no way the vapour would travel up to the top of the condenser and so the still would just be in a permanent state of 100% reflux all the time even with the product valve wide open (damn the laws of physics ). a have tried to overcome this problem by using the problem to my advantage. instead of having a valve on the product tube, the valve has been put above the shotgun condenser. my theory is that when the valve is fully open the still will be at 100% reflux. when you start to close the valve, this will restrict the vapour flow to the reflux condenser and the vapour will have no option but to travel through the product tube. even with the reflux control valve completely shut the still is completely safe as the vapour will all travel through the product tube( excellent for stripping runs).

basically instead of controlling the reflux by the controlling the product outlet, you are controlling the reflux rate directly. i cant recall seeing this method before, especially direct reflux control and a single condenser (maybe there is a good reason for this). has anybody seen any other vapour management stills that are controlled in this way? i would love to see some pics if anyone has any

thanks guys and all feedback is very welcome (even the "what were you thinking!!!) ones

guerrila distilla

[Harry]

instead of having a valve on the product tube, the valve has been put above the shotgun condenser. my theory is that when the valve is fully open the still will be at 100% reflux. when you start to close the valve, this will restrict the vapour flow to the reflux condenser and the vapour will have no option but to travel through the product tube. even with the reflux control valve completely shut the still is completely safe as the vapour will all travel through the product tube( excellent for stripping runs).

basically instead of controlling the reflux by the controlling the product outlet, you are controlling the reflux rate directly.

guerrila distilla

Now it's becoming an interesting concept. There's a lot of different physics at work here. Things like 'partial vacuum' induced in the tubes due to the phase change from vapour (30x vol) back to liquid (1x vol). This will have a bearing on what amount of vapour escapes via your 'riser' tube to the liebig configuration for collection as product. But as yet I don't see any real advantage over a simple slant-plate LM ministill. However it is a novel approach. Whether it works or not is now a matter of conjecture.

I think it's time for you to build and test a prototype. Please report your findings back here. Good or bad results, the info is valuable. And who knows? You may have come up with something quite useful to hobbyists, if it can produce similar or better results to what we now use.

[HookLine]

my theory is that when the valve is fully open the still will be at 100% reflux. when you start to close the valve, this will restrict the vapour flow to the reflux condenser and the vapour will have no option but to travel through the product tube. even with the reflux control valve completely shut the still is completely safe as the vapour will all travel through the product tube( excellent for stripping runs).

Interesting.

However, it seems to me that the valve is redundant, it will not have any effect at all. You want the reflux condenser to condense all the vapour, so that none escapes into the atmosphere. But this means that the air space above the reflux tubes (inside the condenser unit, before the valve) will not be experiencing any pressure change. Therefore having the valve open or shut (or anywhere in between) will not make any difference (if the condenser is knocking all the vapour down, as it should).

If you ditch the valve and seal the top on the condenser unit shut, then maybe you can control the amount of vapour being condensed by controlling coolant flow. A new version of coolant management. However, when you are trying to condense only some of the vapour it is unclear to me how the back pressure from the vapour in top of the condenser will effect the condenser operation. I suspect that if this design does work then the pressure balance point in the head will be extremely fine and difficult to control accurately.

Also, the vapour product tube rising on the outside of the condenser will experience some reflux through heat loss from the tube, though this can probably be overcome by good insulation.

[DestructoMutt]

guerrila distilla wrote-

i was told by hookline and harry that the problem with my first designs (which was very similar to this design), was that there was no way the vapour would travel up to the top of the condenser and so the still would just be in a permanent state of 100% reflux all the time even with the product valve wide open (damn the laws of physics ).

i believe if you make the top of your condensor higher than the top side of the product arm, you will get vapor to flow in the product arm, without having to resort to putting a valve on the outlet side of the condensor.

instead of having the product arm go up and over the top of the condensor, have it go into the condensor at the midpoint (or any point lower than the top of the codensor). fluid dynamics is a branch of physics and gases are considered fluids. the point being that ethanol vapor will expand to fill its container, like any other gas, and like a fluid or any other gas it will take the path of least resistance. so, if both "outlets" are at the same height, they will have the same resistance. (for this discussion regarding the actions of the vapor/gas, the top of the arm is the height of the outlet on the product side, not the opening where the product comes out.)

[Dnderhead]

he cant do that I believe he is making vapor tube not a water tube . he has to feed in and out ends . I not in to making things complicated but why not just mount the condenser on the side

[DestructoMutt]

Hookline wrote-

However, it seems to me that the valve is redundant, it will not have any effect at all. You want the reflux condenser to condense all the vapour, so that none escapes into the atmosphere. But this means that the air space above the reflux tubes (inside the condenser unit, before the valve) will not be experiencing any pressure change. Therefore having the valve open or shut (or anywhere in between) will not make any difference (if the condenser is knocking all the vapour down, as it should).

a pressure change in the air above the condensor is not the important point, the important point is that the condesor is open to the atmosphere on one end and sealed to the boiler on the other. the vapor/gas being produced from the liquid in the boiler is expanding and under pressure because once its created new vapor is created pushing the old stuf up and out of the way. don't confues vapor pressure with pressure of the vapor. the condensor, being open to the atmosphere, gives the ethanol vapor/gas the illusion that it is making a break for freedom. it is trying to achieve pressure balance/equilibrium with the outside atmospheric pressure.

if the condensor were not open to the atmosphere, the vapor/gas would not flow into it. you would get a slight pressure build up in the condensor, equal to the resistance of any other path that you gave the vapor (hopefully you haven't completely sealed your aparatus (i like harry's word for still)) to travel.

[guerrila distilla]

destromutt has hit the nail on the head with what i'm trying to achieve. by closing the valve this should force the vapour to follow the product tube where it will be outlet as liquid. the pressure caused by the vapour being produced continiuously has to go somewhere. if it can't flow through the reflux tubes it will be forced to find the path of least resistance, i.e the product tube, which is completely open to the atmosphere and unrestricted. when the valve is being closed, hopefully this will restrict the flow of vapour to the reflux condenser which means the only other route is the product tube.

the valve can be adjusted to control how much vapour will be pushed through the product tube. i guess the valve would work in the exact opposite way to a normal vm still. instead of the valve being opened to control vapour flow through the product tube, the valve is closed to restrict the flow of refluxed vapour, which in turn will push vapour through the product tube instead.

this is all "in theory", and as i said i'm no expert when it comes to physics, so keep the discussion flowing and we'll see what happens

[Dnderhead]

ok I see what you are trying to do wish you all the luck but do not thank you will make it . trying to cook a egg and a roast in the same oven

[manu de hanoi]

no way this will will work. The valve wont change anything. Your condenser is the path of least resistance, not the product output. All the vapor will rise to the condenser, and all the vapor will be condensed creating void sucking in (if the valve is closed) more vapor.

[guerrila distilla]

manu, if the valve is closed, the vapour cannot travel through the condenser as there is no path to atmosphere. as vapour will always take the easiest route to atmosphere, it will be forced to take the product tube. if you refuse the vapour a path to flow(i.e. by closing the valve), it cannot flow through the condenser.

it's exactly the same principle as putting your thumb on top of a straw and putting it in a glass of water(i.e. the closed valve). the water will not enter the straw. but, if you take your finger off the straw (i.e. opening the valve), liquid will fill the straw. vapour cannot travel through the condenser if there is no place for it to flow. another example. take a piece of pipe and attach a valve to it. place it in a bucket of water and slowly open the valve. the air will escape and the pipe will fill with water. this is because air pressure prevents the water from travelling through the pipe. the same thing will prevent vapour from travelling through the reflux condenser when the valve is closed.

[manu de hanoi]

the column is not filled with air, it's filled with vapor, when vapor condenses, there is nothing left but void.

[HookLine]

GD, I agree with Manu, you are failing to take account of the 30 fold reduction in volume of the vapour when it is condensed and returned to the column. The volume/pressure balance is inside the still, not with the outside atmosphere.

If the reflux condenser is condensing all the vapour flowing into it (as it should be), then there is no vapour flow out of the top of the condenser, so the pressure does not change in the air gap above the condenser reflux tubes regardless of whether the valve is open or not.

It is possible to seal the top of a conventional VM or LM still above the reflux condenser and it will still work, but it will also be a potential pressure bomb if the reflux condenser fails (and the output valve is closed, ie during equilibration). Having the still open to the atmosphere above the reflux condenser is for safety reasons, not to make the still work.

There can only be a pressure from the vapour in the air gap above the condenser tubes if the condenser does not condense all the vapour, which in your design is definitely not a good thing because some vapour will be escaping past the condenser to the atmosphere (if the valve is open). Or (like I said before) if the valve is closed I am not certain what will happen, it may push vapour up the product tube, or the reflux condenser may not work properly, or both.

I cannot see how you will get the vapour to flow up the product pipe using the valve, it will make no difference at all (provided all the vapour entering the reflux condenser is being condensed, which it should be).

[guerrila distilla]

i've only just caught on to what your saying hookline, of course, as the vapour has allready condensed in the reflux condenser, even with the valve fully closed there is no pressure to send the vapour up the product tube. aah well, back to the drawing board. one possibility i was thinking of would be to put the valve before the condenser instead of after. this would make the inline design very difficult to build though. here's a possibility:-

inline vm still 4.jpg (20.58 KiB) Viewed 3195 times

as you can see, the valve now directly controls the flow of reflux to the condenser. surely, if the vapour flow to the condenser is slowed by adjusting the valve, the vapour will have no choice but to flow up the product tube. i'm pretty well out of ideas on this subject so hopefully this may be a possibility.

thanks for you're patience here guys

[DestructoMutt]

from "Single condensor vapor management still" thread

Harry wrote:
2. Vapour Pressure - Alcohol vapour is heavier than air. The principle of the VM still is that some rising vapour finds its way into the side product takeoff tube and by virtue of the fact it is heavier than air, it falls DOWNWARD through an attached condenser and is heat exchanged to liquid product (phase change). Your design is trying to go against that truism. Your split-off vapour attempts to go UPWARD against its own weight. It will not pass over into your downtube unless the still is driven pretty hard to force it up. That automatically cancels your carefully planned separation and your purity potential. Thus the still is not capable of producing a high-proof clean product.

Harry - i believe you are overlooking the effect of the continuous production of vapor on the action of the rising vapor - the vapor being created in the boiler needs someplace to go, and that place is away from the surface of the liquid in the boiler (more vapor is constantly being made....etc., etc...) which pushes the vapor up the column and towards lower pressure areas. with the aparatus being vented to the atmosphere, anywhere along the path towards the atmosphere (and away from the surface of the liquid in the boiler) is going to be a lower pressure area, with the pressure continuously falling as the "outside" is approached. so, when the vapor comes across a side product takeoff tube and proceeds to follow it, it is not following the tube (going into the tube) solely because of it's "mass", it is being pushed by the new vapor and also trying to achieve the same pressure as the atmosphere on the other end of the tube. additionally, it is expanding to fill its container. think of the experiment where liquid nitrogen is poured into a cup, the liquid changes to gas and proceeds to fill the cup, and eventually the nitrogen gas "runs" over the top of the cup and down the sides and "pools" around the cup in an ever widening "puddle". it is seeking to achieve the same pressure as the surrounding atmosphere. clearly the nitrogen gas has gone upwards against its own weight. similarily, ethanol vapor expands to fill its "container" (the aparatus), and it will fill the vapor takeoff tube.

now this is where fluid dynamics comes into play; if there were a side arm (take off tube) on the cup, and if that takeoff tube was upturned, you could get the nitrogen vapor to flow to the top of the tube, but only if the top of the tube were at the same height as the top of the cup.

too bad distilling alcohol is illegal in the states, as it would make a fascinating way to tie together physics, fluid dynamics, thermodynamics and chemistry into one class for the college types.

Hookline wrote-

you are failing to take account of the 30 fold reduction in volume of the vapour when it is condensed and returned to the column. The volume/pressure balance is inside the still, not with the outside atmosphere.

Hook - i believe you are wrong, as is Manu. there is no condensing of the vapor if the vapor can't get into the condensor. no condensing equals no reduction in volume / phase change.

Hookline wrote-

It is possible to seal the top of a conventional VM or LM still above the reflux condenser and it will still work

please elaborate - do you mean that you will leave the product take-off line open while the top is sealed? or do you actually mean that you can seal the top of your condensor (close it off completely to the atmosphere), turn on your boiler, close off your product take-off line, turn on your reflux condensor and that your still will equilibrate? if the former, yeah, we call that a pot still. if the lattter, the only way you will get ethanol vapor to enter your condensor is through the buildup of pressure, not because the condensor is "working". and as the pressure rises, so will the boiling point of the liquid. hopefully when you try to prove me wrong by actually doing what you suggest, you will use flour paste seals so that you don't hurt yourself or anything.

Manu wrote -

the column is not filled with air, it's filled with vapor, when vapor condenses, there is nothing left but void.

how exactly do you evacuate all of the air from your column before you turn on/start your boiler? i ask, because my column is full of atmospheric air before my boiler starts producing vapor. and then once your boiler starts producing vapor, how do you keep the vapor that is constantly being produced from filling the "void"?


i do believe you are overlooking the fact that GD has the product takeoff tube inlet below the condensor, just as in a vapor management head. vapor seems to find it's way out the take-off tube in those set-ups, so why not here (in GD's 2nd{?} sketch) where the valve is on top of the condensor? it should and act just like a potstill with an icecube sitting on the top - minimal reflux, with an uncontrollable reflux rate.

[Freedave]

I am no expert around here but i do posses the ability to read a drawing and some words and apply some common sense.

i think guerrilla did not quite draw his idea well enough for us to fully understand the concept. i think destructo is filling in some blanks (rightly or wrongly) and responding to comments about a design that is not fully explained by the drawing.

every one has misunderstood the other because the drawing just does not make sense. i think.

[Harry]

Hmmm...I kinda knew this was going to develop into a debate on "what-ifs & maybe's". That's why I suggested to GD that he build a prototype & test it to prove or disprove the theory of operation.

I still see the original concept as being an attempt to make one condenser do the job of two condensers. I see no other advantage than that. Anyone disagree with that? GD?

If my reading of this is correct, then I can put you all out of your misery and provide a really simple solution. Pics being worth a thousand words, I dug out an old NS condenser concept and gave it a spit & polish and a couple of tweaks. Here's the results...

Dual Purpose Multi-tube Condenser Configuration for Pot Still or Reflux Still Operation

Swivel_Condenser.JPG (50.99 KiB) Viewed 2691 times

Because it's based on the Nixon-Stone concept (proven) and the product condenser from a Christian Carl still (also proven) there's really no doubt that it will work right out of the gate. Comments?

[Rudi]

I understand this condensor can be used as a LM or a pot still but how do you configure it to run as a single condensor VM ?

[Harry]

I understand this condensor can be used as a LM or a pot still but how do you configure it to run as a single condensor VM ?

You don't.

No advantage in trying to (run VM) either. VM shines only when doing the hearts run or cut. What comes out of any properly adjusted reflux still in either VM or LM mode, is azeotrope (or near) ethanol. One is liquid, the other is vapour yet to be made liquid. The advantage of VM stills is it's easier to control purity. If you have any fluctuation in temp (can happen), then only 1/30th of the impurities can get through as vapour compared to a liquid takeoff (this is in the hearts cut). Purity personified.

Conversely, liquid takeoff is easier to concentrate than vapour. It's easier to measure and do cuts for heads or tails. There's advantages and disadvantages to any distillation system.

Yes I could draw up a VM & potstill using a single condenser. However it will be a tad complicated. But would there be any practical advantage, other than an academic exercise? Methinks not, for the reasons I stated above.

Building better mousetraps is one thing, but ethanol is a LION to be tamed. It ain't no mouse.

[guerrila distilla]

i think your right harry, the original aim was only to make a vm still with a single condenser. other than that i saw no other advantages to the design. i guess the only way to solve the debate and what if's is to build a prototype and see if it works. if it works, great, if not, i've still got all the components to make a good still. i'll give it a try and see what happens. as the parts can be used in a standard vm or lm still i can always take it apart and rebuild. thanks for all the feedback and watch this space.

[BW Redneck]

I know that this probably won't contribute much to the discussion, but I had to point something out that bothers me a little. In the offset head position pic, shouldn't the cooling water flow in the top and out the bottom to take advantage of countercurrent exchange? Or am I missing something? It just bothered me, that's all.

[Harry]

I know that this probably won't contribute much to the discussion, but I had to point something out that bothers me a little. In the offset head position pic, shouldn't the cooling water flow in the top and out the bottom to take advantage of countercurrent exchange? Or am I missing something? It just bothered me, that's all.

That's a very valid query, BW. In terms of efficient heat exchange, the best coolant flow direction is indeed counter-current. Justas it is in this situation, as you will see. Mike Nixon and I had discussions on this years ago.

A Liebig condenser is a pass-through condenser, meaning that the two fluids exchanging heat (gas and water) both pass right through from one end to the other in a single pass. A Shotgun condenser (aka Multi-tube) does the same if it is used as a multi-tube Liebig condenser like you see above in this thread.

However when a Shotgun is used in the overhead position, only coolant fluid (water) passes through. The other fluid (the gas or vapour) does a double-pass of the condenser. It passes into the tubes as vapour, undergoes phase-change (to liquid) and then travels back out the same end where the vapour was fed. So the product feed to this condenser (the vapour) runs firstly co-current to the coolant, then (as liquid) it runs down the tubes, running counter-current to the coolant.

Fluids (water & ethanol vapour/liquid). How they flow in a Overhead multi-tube (shotgun) condenser.

fluid_in_multi-tube.JPG (34.77 KiB) Viewed 2588 times

This type of double-pass actually reduces the efficiency of this style condenser somewhat. When it comes to phase-change type condensers i.e. steam condensers, the object of the game is to have the vapour touch the cooling surface, exchange heat to form liquid droplets, then get away from the cooling surface as quickly as possible to prevent sub-cooling which reduces condenser efficiency (more coolant at faster flow rate is necessary meaning more energy used to drive the condenser). This is why the Cross-flow condenser configuration is such a good performer for its size (just stating facts, not asking anyone to use my other condenser design).

Another very important point to note is this: In an upright condenser, if you were to feed the coolant (water) from the top, you would need to have sufficient pressure to keep the condenser shell (water chamber) full at all times. If the pressure drops, the shell will run dry (gravity will empty out the water). Of course this means the condenser is no longer doing anything and the vapour (your ethanol product) will pass straight through and out the top to atmosphere (not good).

Even if you DO have sufficient pressure, over time (several hours runtime) you will get an air-bubble in the top of the coolant shell. This is a tendency in all upright style condensers. This because dissolved air in the water tends to separate if pressure is applied. Small air bubbles collect at the top of the chamber, creating a big bubble, eventually insulating the topmost parts of the tubing (air is a GREAT insulator) and prevent heat transfer in that section. Thus the condenser loses part of its efficiency, sometimes as much as 25% loss.

The remedy for this situation is to place the coolant inlet & outlet as close as possible to the ends of the condenser coolant chamber(refer again to my drawings, compare to GD'd drawings). This will naturally force any air bubbles out of the chamber as they form, providing the coolant is flowing in that direction. If the coolant is flowing DOWN (as you suggested) then the bubbles will stay in the top of the shell, reducing the condenser's efficiency.

I do apologise for the length of this post, but sometimes a simple innocent question requires a very detailed answer so that the explanation actually makes sense.

[BW Redneck]

No need to apologize for a long post. I don't see too many shotgun condensers on here, so I don't know much about them. The more info on here, the better.

Another lesson for me, I suppose!