Strange temperature rises without the heater on. (latent heat issue?)

[julianf]

Its to do with the pump im using, i know that.  Or rather the pump, pipework combo.

But its odd -

Last night i had the setup to about 85c.  In the past ive been happy to go to bed, leaving the job turning over (i know others would not like this)

Id had my suspicions with the pump causing temperature rise with the last batch, so, this time, i turned off the heater, and left for an hour or so - went back, and the temp was about 2c lower.

All good, i thought - temp falling, so ill sleep on it.


Checked in the morning - 110c.


Then this evening (a new batch) - 64c at the end of stage 2.  Open up the air the venturi, go in for dinner.  Check the temp again, and its 56c.

This is too low for demeth, so ive turned the heater back on.  Id like to leave it overnight, but the temperature is inconsistant.


Could it be that the evaporating meth is just enough to keep the temp down (latent heat and all that) and, as soon as its gone, the temp starts to climb?

That would make sense, but im surprised it would be that close.

[Julian]

Haven't you posted this before?

Yes, I get the same effect with Frankinpump, my contorted pipework and the jet breaker combo.

It's fairly predictable (I assume you're talking about leaving the pump running over night To demeth) early on in the process it needs additional heat which is held constant by the PID, but as the methanol is removed the temperature climbs and the PID stops heating.

I set the PID for 75°C during demeth and the pump cn, on occassions take it up to circa 80°C ... (I don't try and wring every last drop of methanol out).

That said, I think you're brave leaving a processor unattended over night!

[julianf]

I posted about the pump increasing the temp before - i should have found the thread, but i forgott...

but, what i did not mention / know before was that it only increased the temp under certain circumstances.  Again, last night i left it for a while, and went back to check - the temp had fallen.

And again tonight, the temp fell. 

But i bet that if i leave it going over night (which im not going to) itll rise again.


I guess at least i can run it tomorrow, and when the temp starts shooting up, it will be a real indication of demeth completion.


When i leave the job on overnight, its generally with the heater off, just the pump running.  Ie i get it up to temp on demeth, and then shut off the heater, and leave the venturi going over night.  I dont use an air pump at all, just run the venturi as it cools (or did cool, with the old pump) and then to the settling drum.



I hope that, when i increase the bore of the pipework, this issue will resolve itself.  Im currently running a new pump on old pipework, as the old pumps impeller blocked (again) and i got sick of cleaning it.

[Tony]

Certainly when boiling water off I notice that the temp rises to about 100C, sticks there and then shoots up once the water has gone, demething seems to behave differently though, I don't get any start to come off until the mix is 75C+ and then it seems to rise at a linear rate.

But that aside your explanation of the temp rising as the volatiles boil out would make sense.

I'm just surprised your pump is delivering that much energy - how powerful is it and what batch size are you using?

[julianf]

Jgs 110 LPM
Why waste 400ltr vessel

But...

22mm pipework
Jrl tam style venturi
Jrl tam style eductor

I run both venturi and eductor on full to try and reduce restriction, but it will still be constricted.

Anyhow, its done now.  I made two batches back to back so as I wouldn't be rushed rebuilding the reactor in the comming weeks.

I just hope the issue vanishes with more sensible pipework.