## Re : Temperature range

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• ... The temperature at the top of the column is a result of the purity of the vapour you have there. eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06
Message 1 of 2 , Feb 24, 2001
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>within reason what is the allowable temperature range at the
>top of the collum And what is the ideal temperature

The temperature at the top of the column is a result of the purity of the
vapour you have there.
eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06 %, 78.74 C is
90.15 % and so on.

For me, I target around 78.2C

There is a table of these values at
http://www.geocities.com/kiwi_distiller/calc.htm (if you want the detail),
or a graph of it (easy to understand) at
http://www.geocities.com/kiwi_distiller/theory.htm#strong

You should be endevouring to control the tmperature up there by controlling
the purity of the product you're making. The way to do this is to change
the height of the column, its packing, or the reflux ratio (eg how much
liquid you return back down over the packing, compared to how much you take
off to keep).

If you're trying to control the heat input to the pot, all you're doing is
changing the amount of vapour that you're producing. Change the vapour
flowrate too roughly, and you'll get surging then periods of nothing,
really upsetting the balance in the column. Decrease it from maximum, and
you'll be distilling slower than what you can ideally.

Given that the height of the column, and its packing, don't change within
the course of a distillation run, your lever really should be the reflux
ratio.

If you've got the "pass-through" cooling tubes, like in the Still Maker
design, these will be condensing a fairly constant amount of vapour. This
is why changing the heat input will work to some degree - if you're
condensing out a fixed amount, you can change the ratio by altering the
total amount. But it's arse about face. Instead, see if you can do it by
altering the amount of cooling going on with the cooling tubes. Keep the
vapour flowrate at maximum (ie don't control heat input), and alter the
amount you're condensing with the tubes. Do this by altering the water
flowrate through the tubes. The proviso for this is that your still has
been designed to match the column diameter with the power input being
supplied to the pot (and hence vapour flowrate). If your column is too
narrow, then it will "flood" - eg there will be more vapour rising through
it than desired, and it will push the refluxing liquid back up, rather than
letting it trickle down through the packing. This is a fundamental flaw
with the design. Only in this case should you try to run at less than
maximum heat, as you'll need the lower flowrate just to get things working
ok. This is where those "lower pass-through" tubes are sometimes of
benefit - they'll knock out a lot of the vapour prematurely, before it can
enter the column, and thus reduce the amount in the column. But this is a
fundamental design problem, and should be addressed by changing the column
diameter. If you're doing things to reduce the vapour using the column,
all you're achieving is an extended distilling time.

This is where the use of pass-through tubes can be a limitation. They may
not present enough surface area to enable enough cooling to produce the
amount of reflux you require at the higher purities. There's a couple of
ways around this - make sure that the column is tall, not short, and that
you've got some really high surface area packing in there (eg stainless
steel wool pot scourers). If you've satisfied these two criteria, you
really don't need a lot of reflux to get the high purity / low temperature
situation.

eg - my column is 1.1m tall, and packed with pot scourers. I only need a
reflux ratio of about 2 (eg return 20 mL back down the column for every 10
mL kept), to keep the temperature at around 78.2 C. Having a good column
then means that the low reflux ratio keeps the collection rate fairly high
- I'm not having to slow things down. With an 1800W element, I'm
collecting 95%+ purity at around 40-50 mL/minute

If you can't directly measure the reflux ratio (like with the Nixon-Still
design), you can still estimate it using a wee calculator I've got at
http://www.geocities.com/kiwi_distiller/dtw.htm#use_fract

How high should you let it get ? Again, you can keep it fairly constant by
slowly increasing the reflux ratio during the course of the run, to deal
with the slowly decreasing alcohol content in the vapour, as the pot starts
to run out of alcohol. But there comes a point where you've slowed your
collection to a dribble, and its still climbing. Depending on your still
design, this can be an abrupt change, or a gradual one starting a lot
earlier.

Looking at the graph at
http://www.geocities.com/kiwi_distiller/theory.htm#strong , you can decide
at what lower % purity you want to stop. At it starts to lower,you'll be
getting into collecting the tails - the fusel oils. I stop collecting for
purity reasons around 79 C. At this stage I then just open up the valve
and don't bother refluxing. I'll then collect the vapour from between 79 C
to 96 C in a seperate bottle. This I'll put in with the next wash, next
time I distilling. I get about 200-300 mL of liquid in this range.

Tony
• Hello Tony From the above, you mention that your column is 1.1m tall and full of pot scrubbers. Can you remember how many pot scrubbers? Is the column packed
Message 2 of 2 , Mar 3, 2001
• 0 Attachment
Hello Tony

From the above, you mention that your column is 1.1m tall and full of pot
scrubbers.

Can you remember how many pot scrubbers?

Is the column packed everywhere including top and bottom?

I am using the plastic balls in my column and was considering a trial using

Cheers

Gary Gluyas
gluyas@...

www.pbsltd.co.nz

----------
From: Tony & Elle Ackland <Tony.Ackland@...>
To: 'Distillers newsgroup' <Distillers@yahoogroups.com>
Subject: [Distillers] Re : Temperature range
Date: Sunday, 25 February 2001 09:16

>within reason what is the allowable temperature range at the
>top of the collum And what is the ideal temperature

The temperature at the top of the column is a result of the purity of the
vapour you have there.
eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06 %, 78.74 C is
90.15 % and so on.

For me, I target around 78.2C

There is a table of these values at
http://www.geocities.com/kiwi_distiller/calc.htm (if you want the detail),
or a graph of it (easy to understand) at
http://www.geocities.com/kiwi_distiller/theory.htm#strong

You should be endevouring to control the tmperature up there by controlling

the purity of the product you're making. The way to do this is to change
the height of the column, its packing, or the reflux ratio (eg how much
liquid you return back down over the packing, compared to how much you take

off to keep).

If you're trying to control the heat input to the pot, all you're doing is
changing the amount of vapour that you're producing. Change the vapour
flowrate too roughly, and you'll get surging then periods of nothing,
really upsetting the balance in the column. Decrease it from maximum, and
you'll be distilling slower than what you can ideally.

Given that the height of the column, and its packing, don't change within
the course of a distillation run, your lever really should be the reflux
ratio.

If you've got the "pass-through" cooling tubes, like in the Still Maker
design, these will be condensing a fairly constant amount of vapour. This
is why changing the heat input will work to some degree - if you're
condensing out a fixed amount, you can change the ratio by altering the
total amount. But it's arse about face. Instead, see if you can do it by
altering the amount of cooling going on with the cooling tubes. Keep the
vapour flowrate at maximum (ie don't control heat input), and alter the
amount you're condensing with the tubes. Do this by altering the water
flowrate through the tubes. The proviso for this is that your still has
been designed to match the column diameter with the power input being
supplied to the pot (and hence vapour flowrate). If your column is too
narrow, then it will "flood" - eg there will be more vapour rising through
it than desired, and it will push the refluxing liquid back up, rather than

letting it trickle down through the packing. This is a fundamental flaw
with the design. Only in this case should you try to run at less than
maximum heat, as you'll need the lower flowrate just to get things working
ok. This is where those "lower pass-through" tubes are sometimes of
benefit - they'll knock out a lot of the vapour prematurely, before it can
enter the column, and thus reduce the amount in the column. But this is a
fundamental design problem, and should be addressed by changing the column
diameter. If you're doing things to reduce the vapour using the column,
all you're achieving is an extended distilling time.

This is where the use of pass-through tubes can be a limitation. They may
not present enough surface area to enable enough cooling to produce the
amount of reflux you require at the higher purities. There's a couple of
ways around this - make sure that the column is tall, not short, and that
you've got some really high surface area packing in there (eg stainless
steel wool pot scourers). If you've satisfied these two criteria, you
really don't need a lot of reflux to get the high purity / low temperature
situation.

eg - my column is 1.1m tall, and packed with pot scourers. I only need a
reflux ratio of about 2 (eg return 20 mL back down the column for every 10
mL kept), to keep the temperature at around 78.2 C. Having a good column
then means that the low reflux ratio keeps the collection rate fairly high
- I'm not having to slow things down. With an 1800W element, I'm
collecting 95%+ purity at around 40-50 mL/minute

If you can't directly measure the reflux ratio (like with the Nixon-Still
design), you can still estimate it using a wee calculator I've got at
http://www.geocities.com/kiwi_distiller/dtw.htm#use_fract

How high should you let it get ? Again, you can keep it fairly constant by

slowly increasing the reflux ratio during the course of the run, to deal
with the slowly decreasing alcohol content in the vapour, as the pot starts

to run out of alcohol. But there comes a point where you've slowed your
collection to a dribble, and its still climbing. Depending on your still
design, this can be an abrupt change, or a gradual one starting a lot
earlier.

Looking at the graph at
http://www.geocities.com/kiwi_distiller/theory.htm#strong , you can decide

at what lower % purity you want to stop. At it starts to lower,you'll be
getting into collecting the tails - the fusel oils. I stop collecting for
purity reasons around 79 C. At this stage I then just open up the valve
and don't bother refluxing. I'll then collect the vapour from between 79 C

to 96 C in a seperate bottle. This I'll put in with the next wash, next
time I distilling. I get about 200-300 mL of liquid in this range.

Tony

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