multi column reflux pump tank question

[Brian Morton]

I must have posted this in the wrong place previously. I'm not the best with forums. Would like to hear your ideas. Thanks again!

So I am running a 600 gallon pot with column. Its a multi column/gin setup. Do to height restrictions I have a reflux pump and holding tank. This allows reflux to fall and empty column/'s to holding tank and then pump up to still. I have done a couple runs and found that the column fills properly, stacks, and after pulling heads it runs about five gallons out and the the temp rises in the column. It is acting like it is at the end of a run. I then noticed that during the runs the reflux pump wasn't being triggered to empty the tank. Next I shut things down and then let it cool and the reflux fell and still no pump action... I checked the tri clamp the holds the pipe to the tank and as undo it starts to act like it has an air lock or some pressure issue. As soon as that stops the reflux floods the tank and pump works fine and empties the reflux into the still. This same thing happens on the next run.

So I am assuming that the column temp goes up due to water/alc content in the column going down and that the new vapor from still isn't able to enter into column in normal amounts due to some air lock or vapor pressue issue that has to do with the pump back.

Is there a needs relief valve for the holding tank? Or am I completely nuts and need more beer.

I hope someone has a bit of wisdom that they can share. This is the first time I have ever really posted like this. I know a lot of you and thank you in advance. -Brian

[John McKee]

Brian,

Your still OEM should be able to answer these questions.

Cheers,

McKee

[Brian Morton]

John ,

This is a still that I have had and added new parts to. It simply isn't a manufacture direct set up. This is one of my first stills that I bought back in '09 and was trying to set up strictly for GNS. I got about 50-60,000 gallons of fruit wash to go through. I have built (installed,designed,Not fabricated. I am no welder) and installed several stills but this seems a bit different. I just thought there might be another distiller out there that has a similar set up. I know a lot of people deal with height issues and have columns. I was hoping someone might use a similar pump back system. Do you know of anyone that pumps reflux back to the still? Thanks John. -Brian

[PeteB]

Brian, from the way you have described your problem I suspect you are getting a significant pressure buildup in your system

DO NOT FIRE IT UP AGAIN UNTIL YOU HAVE DEFINITELY ELIMINATED THIS POSSIBILITY

You asked if you should have a pressure relief on the holding tank, I say yes. I see no reason it cannot be an open top tank, but maybe I don't understand your design.

DO YOU HAVE PRESSURE RELIEF VALVES ANYWHERE IN THE SYSTEM??

What type of device activates the pump?

If it is a small float, and if I correctly recall school physics experiments done 50 years ago, an increase in air pressure above the float will cause it to sink.

There are at least another couple of possible causes for a float switch not to work. A float that is sized to only just large enough to float in water will not float in high proof alcohol.

Also if the float arm goes through the side of your tank via some type of mechanical seal then that seal could tighten and stop it operating if there is internal pressure.

Post us a photo of your setup.

Again, I would not operate that still until you are certain you have eliminated pressure buildup.

EDIT

******** A very likely cause of increase in column temperature that early in the run is a pressure buildup ******

[meerkat]

This is a very insightful analysis by PeteB. The drain piping from the condenser to the reflux tank can be problematic and if the design is wrong it can entrain air into the tank and pressurise it. My experience is that poor design usually leads to cyclical surging rather than the steady over-pressure you are getting, but it could be a factor. A photo as requested by PeteB or a sketch showing pipe sizes, relative heights, vents and flow rates would be helpful in understanding the behaviour.

[Brian Morton]

Thanks guys for taking the time to read my post. I do have pressure relief valves on my tank and also a open parrot with product coming out. But I had not put one on the reflux tank. It is a closed tank, due to vapor I would believe you would have to in order to be safe. I thought the same thing about the float sinking. The float used is a 24 volt mechanical pencil style float. It is connected to a 24 volt switching system. Pumps are switched via the switch with 110v. That was my first thought (pressure building and holding it down). I just was trying to figure out how it was happening and how to eliminate it. But I'm not positive. I hadn't thought about the proof causing it to sink. That's a good idea, but it should not have that high of proof in the reflux unless a vacuum was pulling vapor down. At least that is how my non engineer brain thinks. Each column is 12in, each has a 3/4 in reflux piping and individual p traps with inline one way swing valves ( non spring loaded, flapper style). On the holding tank the reflux enters in through the top and the pump inlet is always submerged. The pump outlet also has a one way valve in the return line. The switch is a mounted via a tri clamp through the side. It has a short throw (up and down float level may 2.5 inch.) so to eliminate any chance of creating a hydrolic cylinder when triggering the pump. I have verified that everything's does function. Just not correctly during the run.

For now I am putting a one inch blowoff line on the tank with a bucket of water ( simple air lock like a fermenter) to see if that will fix the problem. I wish I could run a vent line but I can't get it to the roof without major work. I plan on running it tomorrow and I will post if that works along with pics.

Any ideas are greatly appreciated! Thank you again for taking the time to reach out. - Brian

[Southernhighlander]

Brian,

This is a little off subject, but I am curios. Is your float switch and pump explosion proof?

[PeteB]

I am afraid you have lost me with the description of your plumbing.

I might wait for the pictures.

to quote you " It has a short throw (up and down float level may 2.5 inch.) so to eliminate any chance of creating a hydrolic cylinder when triggering the pump"

I do not understand the "hydrolic cylinder"

A longer arm on the float will have more leverage to overcome any friction through the seal (assuming that is how it works)