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Jun 08, 2022 View:

Column Plates Flooding During Run

I attempted my first vodka run today on my 20 plate Vendome (4 plates and a dephlegmator above the pot and two side mounted columns each with 8 plates and a dephlegmator).

I stacked each column in order before finally letting the vapor out of the last one into the condenser. In the beginning of the run the furthest column from the pot began to fill with condensate. I was finally able to correct it after fiddling with the steam input, the dephlegmator water and the individual plate valves. The condensate return lines from each column back to the pot were open the entire time. Midway through the run the same thing happened again and I wasn't able to correct it. I shut everything down and at that point the plates drained back into the pot. I tried again three more times, immediately had the same problem, and was unable to correct without shutting everything down.

Again, the condensate return line that drains the condensate from the side columns back into the pot was open for both side columns the whole time. Opening the individual plate drains did not help at all.

Anyone experienced this before or have any ideas what might be happening?

Flooded Plate Vid.MOV


Reply:

Is it possible that the dephlegmator on your final column is turned up too high? You might just have to dial it back a bit so you're not getting so much reflux.


Reply:

Assuming there are no obvious design flaws (highly unlikely on a Vendome), it's one of two things:

Steam pressure too high on the kettle, too much power input causing vapor speeds in excess of design. This causes entrainment flooding which is commonly associated with top plate flooding (tiny droplets of distillate get carried upwards with the vapor).

Dephlegmator/Reflux condenser temperature too low - this would increase the volume of reflux being generated and can overwhelm the ability for plates to drain (mentioned above).

There is a kind of balancing act that you need to get a feel for. If your dephlegmator temperature is too low, you might find yourself needing to increase the kettle pressure to compensate for the higher reflux ratio. But, if you don't need the higher reflux ratios, it would be much easier to adjust by running a higher dephlegmator temperature.

Do you have any kind of dephlegmator temperature monitoring or control (thermostatic valves)? If you did not, your system might be impacted by changes in your cooling water or flow rates.


Reply:

I haven't been able to reach anyone at Vendome but they sent me a very brief email this morning suggesting I drill a "weep hole" in the side column condensate return/ drain (see attached diagram). They want me to drill the hole in the elbow inside the pot where the drain makes the 90° angle downward.

I've spoken with several people this morning who advise against this as it could potentially cause vapor to enter the side columns from the pot.

Any thoughts? Anyone with a similar setup have this "weep hole"?

Weep Hole.pdf


Reply:

This:

>> Assuming there are no obvious design flaws (highly unlikely on a Vendome),

Followed by:

>> they sent me a very brief email this morning suggesting I drill a "weep hole" in the side column condensate return/ drain

Made me chuckle!


Reply:

It looks like they believe an airlock is forming in your condensate return pipe. Would that suggest pressure in the pot is too high for the condensate to "push" back into the pot. Wouldn't a better fix be a bigger return pipe or lower heat/pressure in the pot? Not suggesting you get to work on that, more of a general design question.

What kind of rake angle is in that return pipe?


Reply:

Thanks, Patrick.

I do believe it's a vapor lock/ back pressure issue.

The weep hole they had me drill seemed to fix the problem but I'm worried it doesn't address the larger issue.

The condensate return line is pretty much level until it enters the pot and angles 90° downward where it ends just above the bottom of the pot. Do you think that angling it more downward toward the pot could help to overcome the back pressure?


Reply:

Although I have not come across the specific problem that you have experienced, this sort of vapor lock in gravity driven piping is common. In general, any pipe that runs by gravity should be sloped rather than level. This allows the liquid to run down, while the vapor or air can rise in the opposite direction. As soon as a pipe is made "level" there is a risk of high points being created, and this is where the vapor gets trapped. Very little vapor will short-circuit through the 1/8" weep hole and it should not affect your distillation run with the current set up, but it seems that you have a flexible set up and when you re-arrange the order of the columns (or when they are taken out of line) keep this weep hole in mind as it may have an effect in other arrangements.


Reply:

Good info meerkat.


Reply:

Thanks for the helpful info, Meerkat!


Reply:

Agreed Meerkat! We had a slight issue with this. It was in fact vapor lock, and with a small relief hole drilled into the pot return line 90 deg elbow on the interior of the pot we have never again suffered flooding.


Reply:

I say cut the pipe off completely, flush with the inside of the still. Put a "P" trap between the still and the column. Proof problem solved.


Reply:

@Dehner - moving the seal from inside the pot to in the drain pipe does not remove the potential of vapor locks unless the drain line is sloped downwards from the column to the P-trap. There must be a way to let any air or vapor trapped in the line either flow back up to the column, or be pushed forward into the pot (as will happen with the vent hole suggested by Vendome).

@patrick260z - on rereading the thread I see that you had already queried the slope on the pipe. You had also suggested a larger drain pipe. Agreed. This is just as important as the slope on the pipe. If the pipe is too small the velocity of the liquid will prevent the vapor from flowing back to the column. A safe combination would be to keep the theoretical velocity in the pipe below 1 ft/s, and the slope at least 5% (1" drop per 20" run). This gives 2.5 GPM in a 1" pipe, 6 GPM in a 1.5", and 10 GPM in a 2". In all of these 3 cases the pipe will not run full, so it is important to seal the end with a dip pipe into the pot, or with a P-trap as suggested by Dehner. Without a seal some vapor will bypass the first column and flow directly up the drain line into the second column.


Reply:

Meerkat; I believe, per the illustration provided by StonesRyan their still has the dip pipe design.


Reply:

@Dehner - moving the seal from inside the pot to in the drain pipe does not remove the potential of vapor locks unless the drain line is sloped downwards from the column to the P-trap. There must be a way to let any air or vapor trapped in the line either flow back up to the column, or be pushed forward into the pot (as will happen with the vent hole suggested by Vendome).

@patrick260z - on rereading the thread I see that you had already queried the slope on the pipe. You had also suggested a larger drain pipe. Agreed. This is just as important as the slope on the pipe. If the pipe is too small the velocity of the liquid will prevent the vapor from flowing back to the column. A safe combination would be to keep the theoretical velocity in the pipe below 1 ft/s, and the slope at least 5% (1" drop per 20" run). This gives 2.5 GPM in a 1" pipe, 6 GPM in a 1.5", and 10 GPM in a 2". In all of these 3 cases the pipe will not run full, so it is important to seal the end with a dip pipe into the pot, or with a P-trap as suggested by Dehner. Without a seal some vapor will bypass the first column and flow directly up the drain line into the second column.


Reply:

I agree with you that the P-trap will prevent vapor from sneaking up the return line. That is why I wrote in my comment to partick260z "it is important to seal the end with a dip pipe into the pot, or with a P-trap as suggested by Dehner." If the P-trap is installed immediately below the column then it will not have the vapor lock problems I was warning against.


Reply:

Good Talk!

Awesome.

Take Care!!