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43731Re: calculating heat input

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  • totallyanonymousemail18
    Apr 22, 2013
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      On that point, I'm in the same process of heat input calibration. I've got a fairly big boiler (55 gal 304SS) with 3 x 1" FPT fittings at the base: one is a ball valve for flushing, the other has a 4 KW element for heat up, and the last is for simmering/running. At first I had a 750 W element, but when I switched over, the temp in my column plummeted (neither boiler nor column are insulated right now, may be in the future, and I expect this will change my heat calcs). I went to 2 KW, and that was not quite enough to maintain a constant temp at the top of my column. So I thought that 2500 W would do it, and it did for a bit, yielding 5 drops/sec, but after only maybe 2 liters of product, it stopped. So from your response, I either need to dial down further on the reflux, or add some power during the process?

      Thanks

      --- In new_distillers@yahoogroups.com, Bob Glicksman <bobg542492@...> wrote:
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      > It is only true at the beginning of a batch distillation. Since the vapors are higher in alcohol than in the liquid, the remaining liquid in the boiler becomes stripped of alcohol as the boiling progresses. That is why you must monitor the temperature of the product vapor and increase the reflux ratio as the main run progresses and then terminate it altogether when you judge that you are at the tails of the run. So yes, you are correct that you could increase the heat input from the absolute minimum as the batch run progresses to prevent the vapor into the column from reducing with time until it is too low for your production purposes. But you don't need to increase the heat to the boiler if you can tolerate the reduction in product takeoff. There is a fairly wide range of vapor volume and speed that works well in any given packed column still and most batch distillers seem OK with this.
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      > -----Original Message-----
      > From: chris jude <vegbenz300@...>
      > To: new_distillers <new_distillers@yahoogroups.com>
      > Sent: Wed, Apr 17, 2013 11:55 am
      > Subject: Re: [new_distillers] calculating heat input
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      > Thanks for that response. With your example of 10% alc. beer, you say the vapors are 54% ethanol and 46% water. Is that a number you could use as a constant for the whole process, or are you having to overcome greater latent heat from the beginning to the end of the batch distillation?
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      > On Wed, Apr 17, 2013 at 1:44 PM, Bob Glicksman <bobg542492@...> wrote:
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      > The minimum heat that you need for distillation is the latent heat of vaporization of your vaporized beer (i.e. the heat energy carried into the distallation column). Thus, if your beer is 10% abv, the vapors are 54% ethanol and 46% water (ignoring all of the other stuff, which is small by comparison). Find the latent heat of vaporization of ethanol and of water, BY VOLUME, and factor these using the 54/46% numbers, above to give the unrecoverable energy of distillation.
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      > Note that this calculation is the minimum energy that is needed to distill. In general, you will need to put in more energy due to other factors, e.g.: imperfect insulation in the column, too few plates/low HEPT (necessitating higher than minimum reflux ratio), the "sensible heat" needed to raise the beer to the boiling point to begin with, etc. These other energy needs are, in theory, recoverable and/or avoidable, but the latent heat of vaporization of the beer is neither recoverable nor avoidable (you can recover this heat in the condenser(s) and use it elsewhere, e.g. for cooking the mash, but it cannot be recovered for distillation purposes because the temperature is the temperature of the vapors at the top of the column which is the boiling point of the distilled product and must necessarily be lower than the boiling point of the beer).
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      > -----Original Message-----
      > From: chris jude <vegbenz300@...>
      > To: new_distillers <new_distillers@yahoogroups.com>
      > Sent: Wed, Apr 17, 2013 7:46 am
      > Subject: [new_distillers] calculating heat input
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      > Hi,
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      > I'm trying to size a heater for a still. I know the calculation for raising the temperature of the wash up to boiling, but how can I calculate the heat input required for distillation? After the wash is up to the boiling point, is it just the latent heat of vaporization, and losses to atmosphere?
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      > Chris
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