Measuring stripping column yield with temperature

[tommysb]

I have been doing some recent some experiments with a continuous stripping column, and the performance initally seemed 'too good'. I was measuring temperature at the base of the column, and making the assumption that if this temperature is 100c, then there is no alcohol vapor present, and so all alcohol has been stripped/removed. Wash was being fed with a perastaltic pump, so I had fine-grained control over input feed rate and it increases very close to linearly with increasing RPM, e.g. double the pump RPM, double the was litres/hour.

I was increasing the wash input feed speed, and expecting to see that temperature drop at a certain point, where the power of the steam was no longer enough to properly strip the incoming wash.

In the first setup, I had the probe below column packing, as shown in this diagram:

drawing2.jpg

In this setup, I was always measuring 100c, regardless of feed speed. Like I said, it seemed 'too good'. Thinking about it a bit more, there is very little interaction between steam and wash at this point. I would guess that it would almost ALWAYS read 100c, as it's essentially just in the steam coming out of the boiler.

I blocked off the outflow with some copper mesh, allowing liquid to still pass through, and packed the lower part of the column too, having a setup essentially like this:

drawing3.jpg

In this setup, i was able to see a change, (and drop!) in temperature when the feed rate exceeded a certain point. The question in my mind is, in the second scenario, if I read 100c on the thermometer, am I extracting all the alcohol from the wash?


I feel it was working accurately and quite sensitive to feed speed changes exceeding the threshold for extraction - Going from 200rpm to 230rpm would drop the measured temp from 100c to 99.9c and up to 250rpm would drop to somewhere like 99.7c.

For reference this was with about 4600w-4800w (230v on a 20A breaker), and 200RPM equates to about 45l/Hour, which i think is consistent with the figure I've seen here of something like 400w/gal/hour. - roughly 100w/litre/hour.

Who has some thoughts on extraction efficiency? I know Larry likes to measure temp at the top of the column!

P.S. I don't have an exact ABV for the incoming wash, but did measure output, something like 3.6LPA/hour., 8.2 litres at 44% at 200rpm.