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PID controlled methanol recovery

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http://biodiesel.infopop.cc/eve/forums/a/tpc/f/4441089311/m/3537029563

January 09, 2013, 01:56 PM
Nick Duden
PID controlled methanol recovery
I'll have a PID on my new setup to control oil heating, how do you guys use them to control methanol recovery? The one I saw on here used the thermocouple at the head of the still to measure the vapor temp, can I get methanol the same purity from measuring the temp of the fuel/glycerin mix Im heating?
January 09, 2013, 05:13 PM
Ryan P.
I use a thermocouple at the head of the still to measure the vapor temp, indirectly through the wall of the copper pipe, so its set a bit cooler than what would be expected in an "ideal" direct measurement.

I would think if you were measuring the temperature of the pot it would be a much more variable temperature, and you would have to figure out what temp to even try to hold there. What's important is maintaining the head temp going into the condenser, so typically you would measure right where its important, or as close as is feasible.
January 09, 2013, 05:24 PM
Nick Duden
What sort of head temp do you shoot for?
January 09, 2013, 05:44 PM
Ryan P.
I think I set it to 135F early and as the flow slowed I crept it up to 140F. That was the range where my condenser could keep up.

I plan to add better condenser cooling before spring, so maybe I can hold it at 140F right from the start.
January 11, 2013, 02:59 PM
Jon Heron
I only measure the pot temp, for dewatering I bring it up to about 220F and for WBD maximum 175F to prevent a back reaction. This is also while under vacuum not sure what your setup is?
Check out Grahams site for more information on the topic...
Cheers,
Jon


___________________________

Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
January 11, 2013, 06:18 PM
Nick Duden
Jon I've got a pretty close copy to what you have. It's a 500 gallon propane tank stood upright, and it will be under vacuum. I thought I remembered seeing that you measured the temp at the head of the still (maybe on a previous setup or someone else's), that's why I started looking into it. I plan on doing WBD, I was just curious as to how the pro's were doing it
January 11, 2013, 09:47 PM
Jon Heron
Hi Nick,
I am no pro, just a backyard hack!
Your probably thinking of the heated reflux pipe I have on the top of the reactor, I use a PID controlled heat tape to heat the pipe thats on a 45 degree angle from the top of the tank to the top of the condenser. The TC for the pipe is at the 90 on the top of the pipe right where it turns down into the condenser. This arrangement is not really necessary with how I set it up though. I made a mistake with the size of the pipe and the size of my condenser, its all too small for my vac pump.
If I was to do it again (which I am Smile )I would use a minimum 2 or 3" pipe to the top of the condenser and the condenser would be a minimum of 5/8" tubing. I am going to make these changes in the spring and will let you know how it works out...
With my old setup, the heated pipe allowed me to get 99 to 100% purity recovered methanol using a 1/2" condenser and the same 3/4" heated pipe from the top of the tank to the top of the condenser. With my setup now the best I can get is 98%. At 98% it has caused no issues on the next batch anyways but my 3/8" condenser just takes way to long to demeth 1425litres and if I have it apart to fix the condenser I figure I might as well try a larger heated pipe to give more room for reflux.
My pot temp is controlled via the simple aquastat on my boiler.
I do WBD so its important to not overheat the batch thus why I monitor the pot.

Here is a pic of the heated pipe before I insulated it, the heat tape is taped on with high temp tape along either side of the pipe.

Here is a close up of the TC and the fitting where the 3/8" condenser attaches.


http://biodieselpictures.com/viewtopic.php?t=743
Cheers,
Jon
Edit: Its hard to see in the pic but the tip of the TC is just gear clamped to the top of the 90.


___________________________

Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
January 12, 2013, 01:32 PM
Nick Duden
You havent had any issues with draining the glycerin after its been distilled? I plan on starting to do WBD when I get this going, but in my previous experience I know the glycerin gets pretty thick after the methanol is gone. Some of the stuff Ive distilled is barely fluid even at 185*F, but it did sit for awhile before that. I know switching to KOH makes a difference, but I don't want to do that unless I really have to.
January 12, 2013, 01:50 PM
Jon Heron
Nope, no problems. You have to drain it right away though.
Once the WBD is done the glycerin settles out right away so you dont have to wait overnight for it to settle like you would with a standard batch with the methanol intact.
Once I shut down the boiler I suck all the boiler and plumbing contents into the reactor, wait 10 to 15 minutes and drain the glycerin, then pump the hot fuel into my tote to bubble off the remaining methanol overnight. Any glycerin left in the fuel ends up in the bottom of the tote in a solid layer the next morning and causes no problems, you just have to clean out the glycerin in the bottom of the settling totes every year. I did mine this fall, I half filled the totes with water and agitated with a stick for a couple days till it was all dissolved then spread the soapy water all over my gravel driveway.
Cheers,
Jon


___________________________

Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
January 14, 2013, 09:23 PM
Nick Duden
Do you circulate while you're demething?
January 14, 2013, 10:40 PM
Jon Heron
Yes, I have to always circulate whether dewatering or demething because I use a boiler (you have to add heat as you distill) and it must have circulation to be able to fire.
Besides that when doing WBD you have to circulate, pumping from the bottom of the reactor to keep the glycerin moving and from settling out. I pump into the head space, as the liquid exits the pipe the pressure drops and the water or methanol flashes off.
Cheers,
Jon


___________________________

Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
July 13, 2014, 05:08 PM
dkenny
I use the temp at the top of the column to control the
the heating..a second pid it shut down everything when the pot
temp hits 205F..pump seal limit..otherwise 240-260 would be
a good upper limit time vs energy vs recovered amount

I limit the top to 151F..
148.9 is boiling for per methanol..if I remember correctly..
but I get pure enough methanol for use in AE..

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile