VM output very slow even fully open.

[MartinCash]

Hi everyone,

Well, I did a full trial run, after packing the column fully with structured copper, using 40% mixed feints from rum washes, and the good news is my brand-new VM build produces azeotrope or close to it, about 95%. I'm pretty happy with that.

You can see pictures of the still here: http://homedistiller.org/forum/viewtopi ... 3#p7080633. It's 2'' pipe with a 48'' column. The product takeoff is 2'' reducing to 3/4'' for the gate, then with a reducing elbow down to 1/2'' for the liebig.

One thing I noticed was, even with the 3-ring gas burner at full blast, I was only getting about 3 drips per second out of the condenser. When I did a trial run with only 2 stainless scourers at the top and bottom of the column, I was getting 1.8L /hr of 90% (and this was at 7 degrees C., so probably closer to 92% at the callibrated temp). Do I have way too much column length? It seems like I'm getting too much inherent reflux in the design already. I will try shortening the length of packing in the column and see what the result is.

Also, other people with similar designs seem to be able to get better output. Could I improve it by adding extra 2'' length before the reduction? By adding a reducing collar above the takeoff? Maybe 2''-3/4'' so the vapour paths have a similar constriction? Any benefit in having this below the takoff? What turbulator options do I have that I can add below the takeoff to increase product rate? I spent some time reading anything I came across Googling the site for VM and turbulator, VM and slow, etc... From what I could gather, it's the opening the vapour sees that's important (2'' in the tee)...

Another option would be to have the 2'' tee horizontal, rather than vertical, at the top of the column, with one side to the liebig and the other to the reflux condenser... but that creates added centering problems. Does this design, with its added turbulence, perform better?

Any thoughts?

Thanks!

[myles]

Shortening the packed length is not a solution.

Your maximum product speed is determined by the ratio between the cross sectional areas. The entry port into the reflux condenser chamber, and the entry port into your VM branch. However there are factors that can increase or decrease your product rate.

Your packing needs to stop a few inches below your VM port so that there is an empty void in the vapour splitting chamber next to the VM branch. Also if you run your reflux condenser MUCH too cold, you can transfer a cold zone down the wall of the column and into the copper wall of the vapour splitting chamber. This can reduce your product rate.

On the positive side. If you add in a restriction below the vapour splitting chamber it increases the vapour speed. This in turn introduces turbulence that aids the split of vapour between the two exit ports. Also adding in a scrubber above your VM branch and below your reflux condenser, has the effect of introducing a bit of back pressure that also aids the vapour split.

It is my personal opinion that the offset version with a horizontal T at the top of the column is inherently better, but it does introduce other problems. You should be able to fix the inline version.

I would start with this option with a restriction both sides of the vapour splitting chamber, both matching the VM port. You can use the vertical condenser instead of the horizontal one. I like the height saving of the horizontal condenser.

head1.png (2.07 KiB) Viewed 1581 times

Your next 'tweak' is to route the reflux condensate EXTERNAL to the column so that it does not pass through your vapour splitting chamber - but that is for other reasons, not to increase your product speed. OOPS!

[MartinCash]

Thanks myles,

So would you recommend choking the vapour a bit with internal reducers (above or below the takeoff port, or both), to add turbulence (and also center the reflux), or reducing the tee with the vapour take-off to 1'', so that the 3/4'' side-arm is not proportionally that much smaller than the condenser path?

I am also thinking of adding a length of vertical 3/4'' pipe below the elbow and above the liebig to see if I can achieve some chimney effect.

MC

[myles]

The column restriction below the vapour splitting chamber introduces the turbulence as an aid to splitting the vapour. I usually make both output ports from the same size as theoretically this will give you a 50:50 split in vapour paths. However this does not factor in the restriction caused by your product valve.

I did run a 2" inline version for a while (with a short heads column) but not for long.

The product rate was faster with the restriction caused by the heads column, than without it. I tried both ways of doing things. I have used an internal orifice plate in the 2" column, but it is a lot simpler to use a smaller T. For convenience these days I just use an equal T smaller than the column.

On my current column I use a 1.4" T on a short 2" adaptor over a 3" column



I know this is offset, but the principle is the same. Column into a smaller T with 1 branch used for the VM side and the other leading to your reflux condenser.

If you wish to use the internal plates, a simple option is to cut down a reducing coupling and put it inside one of the fittings. This was an early version I tried



You just put the cut down coupling inside the fitting before you solder in the column. Shortening the male part to about 1/4" seems to work OK.

[MartinCash]

Hi,
Wow, thanks myles, love the examples you've provided.

I have no need for a horizontal condenser, as height is no issue for me in my 5m-high garage. The horizontal tee, however, would give me much more equal splitting of the vapour between reflux and take-off paths. I'll probably get tinkering on a new head as soon as I save a bit more for parts.

However I think I could improve my existing head by constricting vapour flow by using a 1'' tee instead of a 2'' one. I have temporarily welded a 2''-1'' concentric reducer above the take-off so the vapour sees similar sized apertures, and will test it to see how it does compared to the 2'' tee.

What's the word on chimney effect? Has anyone run a VM head with and without a 12'' vertical extension to the takeoff port pipe above the condenser? myles, I notice your first pictured head has one. Does it have any noticeable effect on output rates?

Thanks!

[myles]

Not sure. I think this is more applicable to the inline condenser version because it uses the vapour density of ethanol vapour vs water vapour as part of the auto shut down feature when you get to the end of the run. On the offset version with a horizontal T, I don't think it plays such a big role.

There are some folks using a VM/ LM combination that actually use the vertical tube above the VM valve for the heads removal with the product going through the LM side.

On mine I use that extension just to bring the valve within reach, but have it insulated to try and prevent pooling above the valve.



I think if you were using a basic inline condenser, with no restrictions above the vapour splitting chamber, then the vapour density issue becomes more important. However once you start messing about with back pressures etc then everything changes.

I have to say though that if I had the luxury of unrestricted head height, then I do know which column configuration I would use.

Use a full sized packed heads column, with a heads trap, and don't bother removing the heads at all. Just push them all up into the column above your take off port where they are not going to bother you. The longer void in the packing under your take off port is a buffer zone to prevent liquid droplets being blown into your VM branch at higher vapour speeds.

I think this is the best system of dealing with heads that is available. Most folks don't use it just because they don't have the space available.

[DAD300]

After looking at your build post...you have a huge reflux condenser. Try slowing the water to it. The goal would be to find the minimum water to stop vapor from bypassing the reflux condenser and then add a small safety margin. If your reflux condenser is supercooling (cooling more than necessary) your reflux it could account for the slow takeoff. It could even be cooling the takeoff port to the point of eliminating takeoff.

[maheel]

here is a pic of what i build and they make 800-1000ml of 95% per hour no drama
thats a fairly fast trickle that i describe as a "just broken stream"
the product is better in the 700-800ph range

as you can see it's nearly the same as yours
but mine are a 1" takeoff and valve then into the 1/2 liebig

i would
stick a scrubber under the coil but above the T area this helps "push" the vapour into the T
ensure the coil is not to close to the (ensuring there is a space / void at the T)

mine seem to like to run "best" at about 2000w (240V)

[MartinCash]

Thanks for the replies and ideas!

Yes, I have a large, double-wound condenser. It's probably overkill. However, I run it so the output water is warm, and have a fair headspace between the takeoff port and the condenser. The temperature at the takeoff port is spot on, around 78 degrees, so I think I must be running it ok. I've added a flow restrictor/reflux centering immediately above the tee (a 3/4'' concentric reducer), and packed a scrubber in the space between the tee and the condenser. This should theoretically allow more vapour into the takeoff. In addition I've added a 10'' piece of 3/4 below the elbow, to draw down the heavier vapour. Will try to have a go tomorrow and see what the improvement is.