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Columns lower than the Pot

A message from @marcus that I found in our Activity feed and reposted here on his behalf:

@marcus said: I am building a still but the columns are lower than the pot. Is it just a case of adding a pump? Any help would be great, thanks.

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  • edited May 2015

    @marcus, I can only guess you mean to pump the liquid from the bottom of the columns back into the boiler? I'm not a pump expert, so someone else with more knowledge on that matter may be able to help on what's the best solution for that problem.

    StillDragon Europe - Your StillDragon® Distributor for Europe & the surrounding area

  • what i was concerned about is when the condensate gathers at the bottom of my column when its pumped away will it cause a vacuum and empty the plates

  • edited May 2015

    First off, pumping reflux is a potentially dangerous endeavor. In a standard boiler mounted column, or a high side mount column, you have a very safe gravity feed to ensure the reflux returns to the boiler. For what you are describing, you need a pump, and with pumps come a risk of leaks and the other risks of pumping highly flammable liquids (electrics, sparks, etc). Assume your reflux is near your output abv, which means you are potentially pumping very high abv compared to the wash in the boiler.

    The safest solution is probably a small air-powered diaphragm pump and a pneumatic liquid level switch in the column base. No electrics. But, this is all very expensive. You would be looking at a stainless/teflon pump, or a teflon/teflon pump, easily hundreds in parts depending on how much reflux you are pumping. The pneumatic level switches are pretty specialized - when the float is tripped, it opens the airway passage to the diaphragm pump. I'd also recommend plumbing it in stainless. You could even use a small regulator to balance the flow rate and get away without a level valve.

    Easiest solution is probably a peristaltic pump, but it's very hard to find an explosion proof peristaltic. Probably easy to do something with a smaller adjustable speed peristaltic for a small column, with a larger column it's going to be tough. For this approach, I would suggest manually balancing the drain pump speed, and not using any kind of float or switching, you don't need it. A good adjustable peristaltic is going to be a couple hundred bucks as well (Masterflex, etc). Other issue here is that you'll need to size it before you buy it.

    I would advise unless you have some overwhelming need, it's probably easier to cut a hole in the ceiling than spent upwards of $1000 on specialized gear needed to pump reflux safely.

    You don't need to worry about the pump draining the plates, it won't. However when you run you need to be sure you are balancing the reflux rate. Just turning the thing on and letting it rip isn't the way to go. With a centrifugal pump, you'll just end up killing the pump.

  • @marcus: how many plates did you have in mind and how is the whole setup of your still? Maybe someone comes up with a better idea, if more details are available. People here are very skilled in having creative and fantastic solutions! B-)

    StillDragon Europe - Your StillDragon® Distributor for Europe & the surrounding area

  • There is another option that might work depending on how you are going to run the still.

    You can include a secondary boiler. Either to just capture the required volume of column bottoms, or to act as a reboiler. You can also drain off column bottoms for storage and subsequent re-processing. As i mentioned above a lot depends on how you intend to run the still.

    Easiest option has to be to avoid the issue. There are some 3x columns out there that were built to deal with restricted head height, so it is do-able.

  • we are looking at 10 buble plates on a 8" column with a condenser on top this gives a column 3meers tall our concern was the condensate to the pot should it run into a seperate pot with float switches not to cause a negative pressure in the column

  • Two 5 plate columns draining back to the boiler. ;)

  • we intend to add another column of 10 in time we have seen it done on large comercial stills

  • @marcus said: we are looking at 10 buble plates on a 8" column with a condenser on top this gives a column 3meers tall our concern was the condensate to the pot should it run into a seperate pot with float switches not to cause a negative pressure in the column

    Tundish/air break? it could be vented to a safe location

  • By the sound of the size if your column, it sounds like the boilers going to be permanently installed, so If you can't go up, go down, may sound crazy but dig a hole!

  • I've seen boilers installed below ground level! I think I'd just go more shorter columns, it sounds cheaper.

  • what i think i will do is raise the column by 300mm and add a pot to the side with float switches on/off for a pump and with the second column do the same but pump that run off back into the top of the first column as it should be 80% proof uk not us

  • @marcus said: what i think i will do is raise the column by 300mm and add a pot to the side with float switches on/off for a pump and with the second column do the same but pump that run off back into the top of the first column as it should be 80% proof uk not us

    80% is the same the world over buddy, it's a fraction of 100.
    80 proof however is half that and slightly different tween UK and US.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • edited May 2015

    Wouldn't having the columns separate like the commercial dudes be easier and cheaper?. On my configuration I can't see much improvement to ABV, end product, speed by changing anything. Does larger size change things with separate configurations?.

  • edited May 2015

    @marcus said: what i think i will do is raise the column by 300mm and add a pot to the side with float switches on/off for a pump and with the second column do the same but pump that run off back into the top of the first column

    If I'm reading this right. The reflux from the second column will be pumped to the top of the first column, and the reflux from the first column pumped back into the pot?

    The typical approach would be to use two separate reflux condensers, one per column, and return the drains for both back to the pot. I would think that this approach will run more consistently than trying to use a float switch and pump to return reflux to the top. Not to mention that a reflux condenser is less expensive than the second pump setup you'll need.

    This approach also risks flooding depending on pump sizing, it's very possible that when the float trips, a large slug of reflux is pumped into the column, and it will overcome the downcomer's ability to drain. You'll have a wavering/cycling going on because of it.

    To work properly your design would need to use a peristaltic pump to return reflux to the top of the column, and you'll need to have the ability to adjust the pumping speed to match your column reflux rate, no float switches, always pumping. As you progress through the run, you'll likely need to keep adjusting the reflux pump speed.

    Again I'll caution, this is no place for cheap electric equipment, you are pumping a class IB liquid, not pumping wash. If it leaks, and gets on the pump, you'll have a fire. If a hose connection comes lose, it will probably be spraying too, so you'll need to watch out for what will be a flamethrower in your shop. Your hoses will need to be specialized, as hot ethanol will do a number on any plastic. Better yet, stainless tubing.

    It really makes much more sense to try to squeeze more plates in your setup using gravity drain than it does to try to use pumped reflux. Or, why not try to find a squatter pot that sits right on the floor, no legs. Perhaps mounting a vertical tank on it's side.

  • I dont have the hight to put it above the pot .you say that liquid is flamable but its not like petrol as i often see stills with a fire box underneath and they seam to manage .as with the flooding isuxe with a continuous still product is put in at the top .the reason I want to put back in at the top of the first column from the second column is because all the work has been done going through those plates then you just dump it back in the pot seams a shame.all the pipework will be in stainless.there will be a condenser on both columns and a one meter gin basket/rum doubler

  • edited May 2015

    Well be safe about it. Your pump will need to be constructed of materials like stainless, with ceramic, teflon, or kynar seals. At a minimum stainless with teflon seals, alcohol and solvent resistant. At least a 250F temperature rating. This pump will be very expensive. Review Telluride's stripper thread for more information on using a peristaltic (which I'd recommend here), it will still be expensive, but for another reason). I can easily see each pump setup running upwards of $750-1000usd, even more if you want XP.

  • I don't want to be the mean one, but some buildings just are not made for housing a vodka still... especially when you consider all that work and expense to take flavor out and that you can buy good quality neutral cheaply... even 'ideal buildings' need ceiling stretchers and cutters.... at some point you have to be willing to say that a location is just not good for what you want to do.

  • edited May 2015

    StillDragon Europe - Your StillDragon® Distributor for Europe & the surrounding area

  • i think we have wandered from the original subject

  • Do you have any drawing for your plans? It would be interesting to see, how the setup in the room might look like. I am still sure, that there can be an easier, cheaper and safer solution.

    StillDragon Europe - Your StillDragon® Distributor for Europe & the surrounding area

  • i am waiting for some parts to be welded and i can show you our small still built, this will have 10 x 8" bubble sections which reaches 3 meters from the floor it will have a seperate 350 litre pot so we can strip and rectify to 95% our solution to the condensate is a seperate vessel with float switches to switch the pump on/off i dont think any body has built a still like this before, the excise in our country are keen to see it as it was difficult to get a licence, but in the end we have 5 to run this still, the first in the uk. we are also building a larger still similar. but with 40 trays so no problem reaching over 96% this has a 3000 litre pot and 600mm columns split into 2 each column is 5 meters so if these were all together on the pot it would be 15 meters tall, so with the small one we can hopefully find any problems

  • @marcus, you can solve the height and pump concerns by "simply" splitting your 2 columns into 3. They can all then freely drain back under gravity. Is this something you think might work for you?

  • edited May 2015

    +1
    I am in favour of letting gravity do the work for you.

  • edited May 2015

    Beautiful looking rig, can't wait to see it. Since you are still in design, you might also reconsider some of your vapor plumbing, as there seem to be very many ways to dead-head your plumbing, which can potentially cause a dangerous situation. Electrically actuated valves fail all day long, and you appear to have a good number of them in a complex arrangement. Also keep in mind that vapor will take the easiest path, the paths that need valves/closures, are the ones that represent an easier flow path for the vapor.

    There is a thread floating around here somewhere (I can't seem to find it) that has a very elegant plumbing arrangement for 2 side mount columns.

  • edited May 2015

    its not cost effective to build another column when you have condensers like this on top

    image

  • Some of the split column rigs actually use a single condenser and then split the condensate stream. Some of this is to meter the condensate flow to each column to balance it to the vapour speed. However, there is a condition at higher power levels where you can produce TOO MUCH condensate for the columns. The excess can be returned directly to the boiler.

  • I think it would be cheaper than a pump failure or a valve failure.

    Have you done a HAZOP on your design?

    Let's for a moment assume a 100% chance that one of your pumps will fail in the first year. What safety mechanisms do you have in place to prevent this failure from becoming catastrophic?

    I'd like to echo the comments of @grim with respect to valves and ensuring no possibly dead heading of the system. I know you can have your valves set to any fail state desired but I'm seeing opportunities in your design for removing 2 valves and replacing with a single L port 3-way.

    Before spending more money on expensive items like these condensers, pass your design through a critical HAZOP study. Only then should you look to spend any more money. Just my opinion, not my money.

    Also keep in mind, the more safety systems you build in to manage the inherent design risks the more money it all costs. You are pumping an explosive class substance, you need an IECEx rated motor and your electrical valves and electrical pressure/temperature safety systems will also all need to be IECEx rated. BIG BIG dollars.

    An air pump is one way to reduce your costs but air pumps also fail ALL the time, so you need to be able to handle all fail modes. There are multiple modes of failure with an air pump, you need safety systems in place to detect a failure.

    I could go on but hopefully you get the picture, it will cost you more to use pumps. Gravity is free and requires no safety systems in the event of a failure. If gravity fails we have bigger issues to deal with.

    PS, nice condensers, where did you get them?

    Cheers,

    Mech.

  • the pot has a presure relif valve so any problems down the line this will vent, regarding pump failure we will hold a spare and its all triclamp so easy to change. position of the valves is not set in stone once all the component parts are made the piping will be made to fit, this will be 4".

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