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Problems with consecutively operating wash flooding columns
Hey,
We have a 1000L steam jacketed still with 2 12 inch columns. They are run in series meaning the vapor path of the first column enters the bottom of the second column and then exits the second column and enters the condensor. Each column has a deflegmator with the water run in parallel. Each column has a return pipe in the bottom for the reflux to return to the boiler. This return pipe dips down below the surface of the wash in the boiler.
The issue we’re having is the refulx return in each boiler pulls wash into the boiler and doesn’t allow the refulx to return to the boiler. This causes the columns to flood from the bottom up. We’ve tried reducing the steam pressure to almost zero and the issue still persists so it’s not that we’re running too hot. Anyone have any thoughts on what the issue could be? Maybe something obvious I’m missing. Thanks.
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13 Replies
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Take the reflux returns off the pot, run the reflux through a little cooler down into a sump then pump the reflux back into the pot. Make sure there is a check valve at the base of each column and on the pressure side of the pump. We had the same issue and fixed it this way. That still is actually for sale in the peer-to-peer board if you want to take a look at the piping…or what you can see of it from the pic anyway. Hope this helps.
Cheers!
Adam
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This is a common problem in still arrangements like you have. The solution proposed by @Stumpy’s will solve the problem but you may get away with a less complicated arrangement. In the photo posted by Stumpy’s the base of the second column is below the liquid level in the boiler and it was essential to use a pump in his case.
If your columns are sufficiently above the liquid in the boiler you might not need a pump. A similar problem was discussed inhttps://adiforums.com/topic/11969-return-line-to-pot-question/where the photo shows the column bases higher than the boiler. In that thread I mentioned that sometimes small holes (3 mm, 1/8 inch) are drilled into the return pipes inside the boiler but above the liquid level. This is especially necessary to prevent air locks if there are gooseneck (U-bend) seals in the return piping. Never use an S-bend seal in the return piping.
Although the return piping seems very simple there are many things that can go wrong in gravity driven drains. If you can post a photo or sketch of the piping it would likely bring out better comments.
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Thanks for the replies. @Stumpy I’ll check out the pics and solution for sure. Glad to hear I’m not just crazy and others experience this issue as well.
@meerkatThanks, I’ll read up on that thread. Our columns are above the liquid level in the boiler typically (Unless we really really fill the boiler up to the manway.)
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Here are some videos of the issues we’re having. Along with a trace of the return piping.
https://drive.google.com/folderview?id=1cpeg5V18yqvERPz2s_NdmYw26BU3Xptk
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How far do the return pipes project under the liquid level in the boiler?
Are there any U-bends or seals in the return piping inside the column skirt (i.e. in the section of pipe that cannot be seen in the video)?
How far above the boiler liquid level is the entrance point to the drain pipe at the bottom of each column?
Do you have any pressure measurements?
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The downtubes are roughly 28 inches long. So they extend about 25 inches below the liquid level (when full.)
They enter the boiler about 3 inches above the liquid level. Once the piping enters the boiler it just does a 90 degreen elbow and straight down into the liquid. Roughly 3 inches away from the sidewall.
The entrance point for the drain at the bottom of the columns is roughly another 5 inches above the return… so a total of about 8 inches over the liquid level.
We do not have any pressure measurements. Not sure how to take them.
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That all sounds fine to me. The last thing that I can think of checking is if there are anti-siphon holes drilled either in the elbows just inside the boiler or just below them. If there are anti-siphon holes but no U-bend seals in the drain pipes immediately below the columns it could cause a problem. If you have anti-siphon holes then you should also have U-bend seals.
From the spurting behavior and the vapor bubbles in the returning wash it really looks as though there is vapor getting into the return lines. If there are no anti-siphon holes or other openings above the liquid level then I am stumped.
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Hmm yeah thanks. Gives me some stuff to look at. We just had the returns redone as separate returns because they were plumbed together originally. There are no vents or traps… But it could possibly be that the connectors are not air tight. So I’ll start there at least.
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Mors9
To gravity feed correctly you must have your condensate return connections in the column bases high enough above the liquid level in the pot to overcome the back pressure created by the level of liquid in the trays (its amazing how many still builders don’t know this). If you have 23″ of liquid total in all of the trays in your columns, then the lowest that the condensate can be at the bottom of the column is 24″ above the top of the mash level in the pot. We go around 3″ higher than that for good column condensate gravity feed back into the pot.
If your column bases are too low, I have pump kits that will do the job for you and we have them on over 30 of our stills in distilleries (no sump needed) Do not pump the condensate from the last column in line back to the pot. That is not the right way to do it, in your situation. We have a method that will give you a significant proof increase and more efficiency than doing it that way. Email paul@distillery-equipment.com or call 417-778-6908 and ask for Paul.
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We also have a 2x column vodka still that we’re trying to get running correctly. 100ish gallon kettle with an 8″ packed column directly on top, deph, and then going into a 2nd 8″ packed column which is significantly above the liquid level.Originally the 2nd column just had a U-bend before dumping into the pot above the liquid level. We modified it so that there’s a 3/4″ line running below the liquid, and we added a vent hole to the 90 above the liquid level.The problem we’re having is that when running the 2nd column the still surges, probably similar to what’s happening in Mors9s still (we don’t have sight glasses). We’ve been trying multiple configurations, but so far we have not solved the problem. Running on the primary column the still is completely stable, 2 columns causes issues. Unless we find a solution we’re just going to build an enclosure on the roof and extend the primary column up about 10 feet to solve the problem for good. Obviously, if I can avoid that expense, I’m all ears.
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Something I didn’t mention before, but which will apply to both @mors9 and @Skaalvenn, is that horizontal piping that can contain vapor and liquid at the same time should always be sloped down in the direction of liquid flow and never be truly horizontal. This is well understood by civil engineers and domestic plumbers, but we process people sometimes forget it.
Ideally we want the liquid level in the base of the column to be a couple of inches above the base (which would make the drain pipe full of liquid), but because loads vary this cannot be guaranteed and at some stage the level will be in the horizontal pipe. This is always a recipe for problems and causes the spurting and cyclical behavior we often see. Even if we try to make it truly horizontal there are often high and low spots which aggravate the problem. It is best to give a generous slope of around 2% (2 cm per metre, 1/4″ per foot). This ensures that the vapor will not impede the liquid flow.
Over the last 40 years all the worst piping problems I have experienced have involved gas-liquid flow in horizontal pipes and this has caused me to rather err on the large side when sizing these pipes. An 8″ column might have a return flow of 0.6 to 1.0 gpm and a 12″ column a bit more than double that. I would prefer to use a 1″ drain on the 8″ column and a 1.5″ drain on the 12″ – even if this can only be done for the horizontal sections.
I have discussed this problem with @Southernhighlander before and I know that he understands the problem well and has a practical working solution. A self draining system is nice, but if you just want the problem to go away then get a quote from him.
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Thanks! We’re running again in a little bit with about a half dozen changes made, including adding down slope to the return pipe. The original design was ever so slightly sloped back towards the column, but that is changed now. Hopefully it works. With all the changes we made I won’t know for sure which one does the trick (if any). Fingers crossed.
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You will get better functionality, and use less coolant if you run the dephlegmator plumbing in series from your final condenser to the last dephlegmator in line then from the last dephlegmator in line to the dephlegmator before it and so on. Doing this will have little effect on column flooding but it will help keep surging from occurring and decrease the amount of coolant flow adjustments that you have to do. Plumbing your coolant this way will balance the system better and allow for better smoother operation. Of course you will want to have bypasses at each dephlegmator for when you are not using that particular dephlegmator. Also the German still designers claim that this plumbing method will give you a better flavor profile than plumbing the dephlegmators independently because the temperature differential between the coolant and ethanol vapor in the dephlegmators is much lower. They believe that a high temperature differential in the dephlegmators creates a chemical reaction in the spirit which causes subtle off flavors to occur.
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