[Stoves] FW: pot skirt efficiency estimates, scale-up

Frank Shields frank at compostlab.com
Wed Sep 19 11:23:04 CDT 2012


Hi All,

 

I've done this type of test a lot in the past. I don't think you can get
better than 95% ethanol via distilling even with the right glassware to
separate out the fractions. Its easier than it seems to distill out the 95%
as you just keep track of the temperature at the top (as Crispin mentioned).
It stays constant until the ethanol is gone and water takes over then raises
quickly to 100c. I think it goes from around 76c to 100c when it is
completed. 

Our glassware is a reflexing system with a straight wall about 90cm tall
having many 'fingers' of  along the wall that are made of glass and stick
out about a cm then point down. This picks up the condensed liquid from the
gas. I think these fingers are not needed. 

 

In the past we used sodium metal to remove water from solvents (benzene) and
think it might work for ethanol. Not sure I would try it as those were the
'exciting' days in the lab. There must be better methods. 

 

Frank

 

 

 

 

 

From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Wednesday, September 19, 2012 8:00 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] FW: pot skirt efficiency estimates, scale-up

 

Dear Jed and All

 

First, indirect greetings to Alexis - he will be a big asset for you.

 

Looking over the interchange with Kevin this morning I am reminded of a
setup I saw once that was distilling ethanol so I am adding this suggestion
that is worth experimenting with. Might not work but you never know, so.

 

When you have the pipe coming out of the centre, you can run it vertically
and if possible a bit larger than the normal 'still' pipe. The idea is to
get the water to condense and fall back into the 'mash'. If you have a
bubbling pot with the lowest heat needed to keep it in that condition, it is
inevitable that you will get a lot of water droplets and vapour in the gas
mix.

 

The idea is to keep the bubbling pot going while reducing the amount of
water that is expelled into the condenser. So, the plan is to cool the
rising gas in a vertical column before it is liquefied in the condenser. The
use of a vertical metal pipe, possibly cooled a bit, but not much, will
achieve the higher ethanol and lower water content you are seeking.

 

If you have a thermometer at the top of the pipe, run the fire so the
temperature at the top is a little below the local boiling point of water.
This will help the water vapour condense and drop back into the mash without
taking much of the ethanol vapour with it. It is basically a very simple
form of fractional distillation.

 

There is no reason it cannot be done horizontally however there is more
natural cooling available on a vertical pipe than a nearly horizontal pipe
of the same length.

 

Under ideal conditions you can get 95% ethanol with this method. As long as
there is some cooling and the exit temperature is below water boiling, and
above ethanol boiling, you will get the fraction you want.

 

I understand from the guys at the Simunye Sugar Estate in Swaziland that
there are a large number of other 'alcohols' which are present in the
ethanol - more than a dozen of them - but I am not sure if you will ever be
able to separate them, or get the 'cut' you want except by watching the exit
temperature at the top of the vertical/slanted tube.

 

It may be that eventually after experimenting you will have a 2 metre copper
pipe travelling upwards from the top of the pot before it turns down to the
condenser. This trick is probably how distillers got a high ethanol content
in a single pass.

 

Doing a second pass with the ethanol alone can give 99% with similar control
on the exit temperature. The guys doing this told me the highest they can
get in one pass is 95% and that is why (because of energy cost) ethanol sold
for stoves is never higher than that - it is made by the 'cheap method'.

 

We are of course interested to hear how this goes! It is certainly an
unusual application.

 

Regards
Crispin

 

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