While designing my processor, I decided that I will have a methanol condenser and probably do whole batch demething. I liked Graham Laming's approach, using a venturi to actively pull the vapors from the headspace through the condenser. I also read everything I could about eductors.
I see five jobs for my venturi:
1. Remove the water from the oil before adding methoxide.
2. Pull in and mix the methoxide from the oil cube.
3. Perform active mixing during the reaction (eductor function).
4. Recover the unreacted methanol from the finished bio/glycerine.
5. After draining glycerine, remove any remaining water.
After some effort and luck, I found this eductor for $6.42
It has 3/4" NPT threads on both ends. The suction connector is 3/8 NPT with an adapter for 1/4 NPT and a barb. The orifice is about 0.18, just slightly smaller than the 3/16i (0.1875) that Rick used in his
"High Velocity Nozzle Testing" page:
Also be sure to read "Using a Venturi to Inject Methoxide"
I also bought the smaller (1/2 inch blue) and larger (1 inch black) for testing and comparison:
I tested all three side by side with the "little black 3/4HP pump" from Harbor Freight, and found that the blue venturi is just too small, and the black venturi is too large. The orange is just right.
The orange (3/4 inch) venturi moves 6 gallons per minute with a backpressure of 27 PSI. In my 30- gallon processor, this gives a nominal turnover of 5 minutes. At that pressure, the stream into the processor should give good mixing.
The venturi sucks 2 liters of liquid per minute, so my nearly 18 liters of methoxide will load in 9 minutes (almost 2 turnovers).
If I decide to modify the system for vacuum distillation, I can set up a second pump, venturi, and water barrel, and the venturi will supply 20 inches of vacuum. My pressure is around 660mm, and reducing the pressure to 150mm should give me a boiling temp of 33C for methanol and 61C for water. The vacuum setup should cost less than $60 and would have the pump well separated from any methanol vapors, even if some did get in the vacuum line. I would have to use a vacuum-proof container for the methoxide, methanol, and water though.
I hope this information is helpful. If anyone is interested in the blue or black venturis, I have the vacuum and flow tests for those too.
Good information and a great post.
can you provide a link to that black 3/4 hp pump?
Right now, it is listed on sale for $45, and the 20% off coupon (16073090) might apply.
I forgot to mention that I measured the power draw was around 400 watts.
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