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Re: My reflux column

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  • edbar44
    I m going to add my two cents to this post because I really want to share this. I ve been doing this hobby for almost five years now and that elusive 96% has
    Message 1 of 32 , May 5, 2012
      I'm going to add my two cents to this post because I really want to share this.

      I've been doing this hobby for almost five years now and that elusive 96% has been difficult, at best to get for the most part although I've managed on more than one occasion to get it.

      I could never figure out why on one run I'd be getting 96+ and the next run have trouble getting over 93 and always set everything up the same way, I THOUGHT.

      Just roaming around the boards I picked up on this because it was interesting, http://www.artisan-distiller.net/phpBB3/viewtopic.php?f=3&t=2332

      This information managed to get me the 96+ consistently for the last four runs.

      Two things I discovered in reading this article that I took for granted was the column packing and the level/plumb of the column.

      I purchased new copper packing and packed it as tight as I could and when setting up, I made sure the column and boiler were level and plumb, BINGO, 96+ every time.

      This is no real brainer, just common sense, how many of us check to make sure things are level and plumb, I never did, as little as 1 degree can cause your reflux to flow down the walls and thus not really refluxing. If anyone is getting their 94% but can't get more, check it out and see if this may be your problem.

      My thanks go out to Snuffy for writing this fine article.

      --- In new_distillers@yahoogroups.com, Gavin Flett <gavin_flett@...> wrote:
      > Ok Bob, one more for ya. Now it seems that it's the end of the run, but instead of the temperature going up..... it's going down. What's up with that?

      > If you got higher proof when your column was uninsulated, then I would say that this is a clear indication that you don't have enough heat removal capacity in your condenser(s). Remember conservation of energy -- the energy that goes into the still must all come out of the still. However, you can't just radiate heat arbitrarily out the column wall because the fractionating "magic" that causes the ethanol and water to separate requires a very specific temperature gradient to exist up the length of the packing. If the temperature gradient is not maintained exactly throughout the run, your column will fall out of equilibrium and the proof will go down (or the product rate will go down). I never fully answered your question about taking heat off of the column walls, so I will do so below. But the bottom line is that your condensor(s) is probably undersized for the heat that you are puting in.
      > Figuring out the right size for a condensor is a little tough. I forget the metric units, but in English units, 1 BTU raises one pound of water one degree F. Recall that heat transfer can only take place from a higher temperature to a lower temperature. To get azeotrope, the vapor temperature from which you are removing heat in the condenser(s) is the boiling point of the azeotrope which is something like 173 deg F. If you are using cooling water at 73 degrees F to remove heat in the condenser, then at MOST you will be able to raise the water temperature 100 degress F (below boiling), therefore absorb 100 BTU of heat for every pound of water that flows through the condenser. Convert pounds of water to liquid volume and you will know the minimum flow rate needed. If you measure the input and output coolant temperature from your condenser(s) and the coolant flow rate, you can calculate the anount of heat energy that you are removing and compare this with the heat energy that you are puting into the column. I'll bet that you don't have enough removal and need a larger condenser(s).
      > Here is why you must insulate your column. The fractional distallation process upon which your still column works requires a constant heat exchange at various plates running up the column of the still. You don't have actual plates with a packed column, but the principle is the same (you have 'theoretical plates" and the number of theoretical plates that you have depends upon the HETP of the packing material and the packing height). Each plate in the column represents a mixture of ethanol and water that corresponds to a liquid/vapor equilibrium at some specific concentration of ethanol/water in the mixture. The specifics are not arbitrary. They are absolutely dictated by physics and depend only upon the initial concentration of ethanol/water in your beer. If your beer is, say, 10% ethanol and 90% water (by volume), then physics dictates that the vapors resulting from boiling this mixture will contain 55% ethanol/45% water, by volume when condensed back to liquid. You can't change this -- it is required by the laws of physics. So your boiler, which is the first "plate" will be the the boiling point of a 10% ethanol/90% water mixture, your first theoretical plate in your column must be at the boiling point of a 55% ethanol/45% water liquid mixture, the next plate up must be at whatever the concentration ratio phsycis dictates , etc. You can compute what physics dictates from the LHV of water and ethanol and the molar concentration at each step, or simply find it in a table or graph in a book (sorry, my copy of Nixon and McCaw is loaned out right now so I can't cite you the page and figure number, but it is there for sure). In any event, each plate (real or theoretical) in your column must be maintained at the specific temperature that is the boiling point of the mixture at that plate, as required by the physics of liquid/vapor equilibrium (LVE). If the column is not held precisely in this state of equilibirum, your production and proof will change. So however you do it, you are required, by the laws of physics, to keep the column in exact equilibrium.
    • Bob Glicksman
      Gavin, If you are trying to get to the azeotrope starting with 10% abv beer, the minimum reflux ratio that you need is 2.4:1. This means that for every 1
      Message 32 of 32 , May 8, 2012
        If you are trying to get to the azeotrope starting with 10% abv beer, the minimum reflux ratio that you need is 2.4:1.  This means that for every 1 liter of product that you take off, you need to send 2.4 liters (or about 70% of the liquified vapor) back down your column.  Theoretically, to achieve this minimum you need an infinite number of plates; in practice, you can get close enough to azeotrope that you can't measure the difference with around 25 theoretical plates.  To a limited degree, you can reduce the number of plates and still get the same proof by increasing the reflux ratio.  At 100% reflux, you can get aeotrope with about 7 plates from a 10% beer (but of course 100% reflux gives you no product and is only useful as a science fair project).  Nixon and McCaw advocate short columns and around 90% reflux (10 liters down the column for even one that you take off). 
        This is all dictated by the laws of physics.  The only ways around this are:
        - increase the proof of your beer (decreases reflux for azeotropic product)
        - reduce your product purity requirement (reduce the required proof of the product)
        You can also use these same figures and increase your product production rate by increasing the boiler power, but only if you correspondingly increase your condenser heat removal capacity (to maintain the reflux ratio needed for your HETP), and making sure that your column diameter is sufficient to maintain vapor flow up the column at a resasonable rate (12 - 20 in/sec; calculated as I described in an earlier posting).
        Note that when you start your batch still off with 10% abv, it won't stay this way.  As product comes off, the %abv of the beer must reduce and therefore you need to monitor still head temperature (as a proxy for proof) throughout your run and as you see the temperature increase, you must increase your reflux rate to get back to azeptrope (or whatever proof you desire).  At some point, your reflux ratio will be so high that you decide that it isn't worth it anymore and you will stop the run and use the low wines on a subsequent run.
        I cannot emphasize enough that the "correct" way to get your still set up and going the way that you want it is to start with 100% reflux and get the column up into equilibirium.  This could easilt take a couple of hours.  If you can't achieve equlibrium with 100% reflux, you aren't removing enough heat or don't have enough HETP or have some other issue such as fugitive heat loss from the column, reflux running down the column walls, or plugged packing, etc.  If your beer was only ethanol and water, then at equilibrium the still heat temperature would be around 172.5 degrees F which is the boiling point of the azeotrope.  You would then SLOWLY start to take off product, carefully watching the thermometer, until you saw it rise to a new, higher temperature at equilibrium, and then you would slightly increase the reflux ratio back to azeotrope and keep watching and adjusting, for reasons stated earlier.  Of course you have other stuff in your beer than ethanol and water and some of it has a lower BP than the azeotrope, so your initial equilibrium temperature will be a little lower depending upon how much methanol and other stuff is in your beer.  As a spirit distiller, you probably want to very slowly bleed off this stuff (foreshots) and discard it, then start collecting the heads and the main run and stop at the tails.  I'm more interested in fuel ethanol and can afford to take this other stuff off as product, as long as I see that it is small (my engine won't get a headache :-).
        Get you column into equilibrium and keep it in equlibrium at all times!!!  This is what reflux distillation is all about.  Patience is the watchword here.  If you don't have the patience to do this, get yourself a high quality continuous still and then once you get it up into equilibirium and establish the required minimum reflux ratio, you can just leave it there without further adjustment (which doesn't mean unattended -- you are making a highly flammable fuel, regardless of what you actually intend to do with it later :-).

        -----Original Message-----
        From: Gavin Flett <gavin_flett@...>
        To: new_distillers <new_distillers@yahoogroups.com>
        Sent: Mon, May 7, 2012 10:48 pm
        Subject: RE: [new_distillers] Re: My reflux column

        Just an update on the run Bob. I have tried it with 450W, 600W and 900W of 
        power, I have tried a 2:1, 1:1 and 1/2:1 reflex ratio. Everything that I do 
        achieves 92% ABV, so I am thinking that it is my packing that is preventing 
        further purity. Or, maybe it's my alcoholometer that is faulty....
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