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48005Re: Running too hot!

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  • Harry
    Jul 1, 2011
      All the good advice you've been given so far is very useful to fix your problem.

      Building stills is not just a 'hit or miss' affair. Everything is worked out to balance.

      One thing you need to know when building a fractioning still of any sort (eg bokakob) is the vapor speed. The power input and the column diameter determine the vapor speed up the column. This in turn governs the separating capability of your column, and thus the purity of your product.

      The maximum vapor speed is around 18" per second. There's calculations you can do here in the files...

      Using Mike's figures, your 1.5" diameter column at the moment with 1500W power input is running at almost 39" per second; way too fast and hence your troubles. To bring your vapor speed down to 18" per second, you'll have to reduce your power input to 695W max, in which case you'll need a controller like was advised in an earlier reply.

      The only other way to fix it is to go to a bigger diameter column. A 2" diameter column @ 1500W input runs at almost 22" per second. To run a 2" column at 18" per second the power input needs to be about 1200W. Or you can use an un-shielded column and 1500W because the unshielded column will lose about 300W heat to the atmosphere.

      Ideal lengths for component separating capability are:
      1.5" Diam --- 2 metres
      2" Diam --- 1 metre

      So now you know the 'what' and the 'why' of the issue.


      regards Harry

      --- In Distillers@yahoogroups.com, IZbraun <izbraun@...> wrote:
      > Thank you Geoff, for a very detailed explanation.  It really help me!!
      > I’m sort of disappointed that I followed the bokakob design exactly (except the size of condensing coil) only to find the column is too short and/or too narrow. 
      > Assuming I don’t want to start from scratch and re-build my column, what can I do to improve my results?  I will try to do a better job with my heat but I’m using an electric commercial grade (1500 watt) hot plate so the temperature fluctuation can be substantial as it cycles on and off.
      > I’ve also got some leftover 3/16” tubing so I’m going to try to make a new double coil (coil inside a coil) to see if that helps.  I’ve see a few photos online but it looks difficult to make.
      > Thanks again for all your help
      > IZbraun
      > From: geoff burrows <jeffrey.burrows@...>
      > To: Distillers@yahoogroups.com
      > Sent: Wednesday, June 29, 2011 2:56 AM
      > Subject: [Distillers] Re: Running too hot!
      > Hi izbraun,
      > I can see three areas were your problems might lie I think these are:-
      > 1.      Your Column diameter and length
      > 2.      Your heat source
      > 3.      And a fundamental misunderstanding of  how different liquids boil when mixed with other liquids and at what temperature they then boil. In our case ethanol/alcohol  and water at various temps
      > Let’s deal with
      > Number 1. 
      > Your column diameter and height  is smaller than the usual 2” diameter x 1 metre long  (at least) of our hobby stills and because this 1½” is narrower the steam/ethanol mix tends to move faster up the column than in the 2” type columns and your reflux rate will be down because of the shorter column length. 
      >      So a lot of the data you have on these forums appertains to the 2” x 1 metre columns and thus rules out a lot of stuff that you would expect to happen in your still i.e. your take off rate, your condenser size which needs to knock down that steam/ethanol mix fast or you’ll be giving a bigger share to the angels.  This leads on to your next problem area your heat source
      > Number 2
      > Because you have a narrower and shorter column than usual you need to keep really good control of your flame and when you start your run just keep that flame on tick over.  
      > Keep it low and slow it’s the way to go.  That way your condenser can knock the steam /ethanol mix down easier.  Using 3/16 copper tubing is good the bigger the condenser tubing the better the separation rate.  If you were to give your column an extension of another 24”  you would find you’d have a better behaving still.  A lot of the guys on here have 1½” columns but they are considerably longer than 24”.  Having such a short column will make your still harder to control and as one member once said it’ll be squirrel-ee which brings us to
      > Number three
      > Ethanol will near as dam it boil at 78C so with a longer column and good control of your heat source i.e.  low and slow  You’ll find you don’t  need to constantly keep adjusting the flame because it’ll get to 78C and stay there throughout the entire run. One of the guys on this forum has a chart of the different boil temps of the ethanol water mixes and they’ll probably supply it if you ask.
      >      In ethanol water mix the ethanol boils first i.e.  the column temp, with the correct heat input,  will rise to and sit at  78C and as long as your condenser keeps knocking it down it’ll stay at that temp as long as you have ethanol or alcohol in the wash when the temp starts to rise there’s less alcohol and you can make your cut early depending how clean or pure you want your ethanol
      >   Bear in mind this is the way I see things but hey I might be wrong and if so I will be put right never fear
      > Geoff
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