Yep, the colder it is, the less vapours there will be, if you can get teh condensate and the collection vessel cold you will get no vapours in your pump. Most pumps get pretty hot when operating and the methanol will quickly boil out of the pump oil anyways so just make sure its vented outside as fabricator suggests.
Just had one of those "aha!" moments. It all clicks now, I was looking at it from the wrong angle. Thanks guys
Can any of you draw a simple plan how and where to connect the vaccum pump and the vent ?
How much vaccum is enough ?
Connect the vac pump to the output of your collection vessel, it should connect to the top of the vessel while the end of the condenser should connect below the output so that the methanol or water entering the vessel isnt falling past the input to the vac pump. The vac pump vent should just lead outside.
I use 5/8" (approx) quick connect compressor fittings for the connections and 3/4" vacuum hose for the flexible connections.
The more vac the better, particularly for dewatering, I find between 25 and 29Hg is where the majority of the dissolved water comes out of the wvo.
Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
vac.png (5 Kb, 23 downloads)
Sorry for awakening the old thread, but I finally started demething with my vac pump and found out something interesting.
1st I was demething with the vessel closed and pump runing and got nice amounts but it took forever.
Than I decided to shut down the pump and heater and I had a valve installed (at the bottom to connect the compressor) and decide to let the vac pump run and I opened up that valve just a little.
Result twice the amount of methanol in same period of time.
My guess is that the air that is drawn from the bottom of the vessel help methanol vapors to escape.
Oh, yes, absolutely. The introduced air can't condense but all the methanol vapor carried with it will. That, I think, is an error, or at least a point of improvement, that my still doesn't have. I end up with a big dead-head of methanol vapor that is not being moved out the plumbing to the condenser.
I am in the final stages of constructing a reactor (30 gal) with the intent to do WBD without vacuum. I never anticipated that cooling the condenser would take so much cold water. May be my 20 gallon batches will be less challenging. I have a flat plate heat exchanger and was wondering if it work as a condenser more efficiently than the copper tube in tube design. May be my small batches and the potential methanol recovery volumes isn't worth the effort of running the recovery side of the process. Comments and suggestions would be greatly appreciated.
I'm doing 290 L of oil and 75l of methoxide in a single batch. i am using a double condenser (tube in tube style). With the vac method I mentioned earlier I got about 20L of meth in 4 hours. To cool the condenser I have 1000L tank of cool water and that never gets hot.
I will try to get a stronger vac pump to get the time down to 2 hours or maybe less.
In my experience, the size of the pipe/condenser ID makes a big difference. I wish I had made mine of all 1" pipe, I will be upgrading to 5/8" from 3/8" at some point this year when I feel like coughing up the 150 bucks for the copper...
My outer pipe is 20mm and inner is 15mm I think.
I post some pics of my setup, but I'm currently out of the country.
I did notice a thing with settling, if I'm demething it takes a very long time to settle the soaps and glyc. If I'm not demething the glyc drops instantly, although the soap content is then much higher, and needs further cleaning.
Any suggestion how to speed up the settling after demething?
Jon you are right! Today I had a bit time to play around, so I raised the temp to 80 C and the meth was flowing out like crazy, at one point my condenser couldn't keep up and I had to shut down the vac pump for a bit so the condenser cooled of. So now I have to rethink my condenser design. Any suggestion on what design of condenser to build ? I was thinking of using a large PVC tube and insert 5 or more 15mm copper tubes. At the moment I have 2 plumbers delight condensers but I have a feeling that the volume of water between tubes is not big enough.
I made what I dubbed the "cheap and dirty" condenser. I just fished about 80' of 3/8" soft copper into a 1" black poly water line, then used a 1" tee fitting at each end of the poly pipe to terminate the water lines and the condenser tube. Its works excellent other then I wished I used a bigger copper line to speed up recovery.
I have pics of it up on Graydons biodieselpictures.com site but it is down ATM...
If your only doing 300L batches then a 1/2" pipe should be plenty big, just make sure its long enough, the longer it is the cooler the output and the less likely you will overload it.
A 50' coil of 1/2" soft copper, some poly pipe and fittings should be able to be bought for under $100. I just drilled out a couple brass ferule fittings so the copper could pass right through them to seal the water jacket around them.
It looks like existing links to Graydons site still work, you can see the condenser hanging off the right side of the tank, the black coil of pipe, the tee fitting is at the bottom where you can see the copper tube coming out, thats where I connect the vacuum...
Hi Guys. I have read these three pages with great interest. I have just managed to get a great vacuum pump. Its an Edwards two stage pump 11m3 per hour. It is capable of pumping down to 5 by 10-3 Tor with gas ballast closed.
I have a 250 liter air receiver and a 75 liter air receiver to use. My question is if you were starting from scratch How would you couple these together for de-watering and WBD and or methanol recovery??
Any thought on a schematic and what sort of condensers should I build?
The guys who dewater the transformer oil use a sort of slush pot with a cooling coils inside. A tangential feed for the vacuum in to swirl the air flow around the tubes in the pot. vacuum out is high up at the top of the pot and from there to the pump.
Any thought or ideas from your experience would be appreciated.
I demeth biodiesel at about 304 millimeters of pressure. I use ice water cooled condenser. I had a still head temperature of about 36 degrees celcius last time, at the start of distillation. I looked up, Methanol (data page) Wikipedia on the internet. It looks like the boiling point of methanol at 5 millimeters of mercury pressure is about -20 degrees centigrade. If I understand your vacuum pump pulls 5 millimeters of mercury pressure, then your condenser would need to be colder than -20 degrees centigrade, or it will go out through your vacuum pump. It might make a mess. Nice vacuum pump. My vacuum pumps are single stage, cheap ones.This message has been edited. Last edited by: WesleyB,
Your best option for chilling the condenser water would be an industrial process chiller, they are pretty spendy though. I have used a medium sized chest freezer filled with water and glycerine as an antifreeze with good success on a small 100L processor too. Currently I am just using tap water right out of my well on my big processor and that also works very well.
The longer your condenser the more efficient it will be at transferring the heat out of the methanol or water. My 80' or so condenser as described above seems to work very well. I adjust the water flow to just a trickle and the water coming out the other end of the water jacket is hot enough to burn your hand while the methanol or water coming out into my collection container is as cold as the condenser input water. The condenser I describe above works great and is very easy to make with a few fittings and coils of pipe.
The best advice I think I could give you is to use as large a pipe as you can afford for the condenser tube and associated plumbing, this will ensure your recovery time is speedy and efficient.
Is your pump a rotary vane oil bath type?
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