Using a Venturi to Inject Methoxide
By Rick Da Tech
One issue I have with the Appleseed biodiesel processor is that you have to add the methoxide slowly or quality will suffer. Since it does not mix inside the tank, we have to make sure the methoxide is evenly distributed through out the tank. To do that we add the methoxide slowly. How slowly depends on how fast you can turn over the oil in the tank. The typical pump used on an Appleseed is either the Harbor Freight or Northern Tool Clear Water Pump. These pumps will flow hot oil at about 7.5 gallons per minute. That means for a 40 gallon water heater making 25 gallon batches, you will pump all the oil through the pump once every three minutes or so. We want to inject the methoxide over four passes. That gives us a ratio of 18:1 oil to methoxide when injecting. What we find out is that this 18:1 ratio holds no matter what size water heater you have. I started off talking about the problem being that we have to inject the methoxide slowly. Well to be correct the problem is that until now we have not had an inexpensive way to consistently inject the methoxide at the proper rate.
Having heard that there was a venturi available on the market that would give us our 18:1 ratio using the Northern Tool Clear Water Pump, we went on the search. It took a while but we found the Mazzei 584 Venturi Injector that was made of methanol and biodiesel resistant material with a maximum temperature rating of 200F. At least it worked by the books. We did a lot of testing on the venturi and found that it had a methoxide injection rate of 15:1. That's not quite our ideal 18:1 but close enough for the job. It will load all the methoxide in about 3 and a half passes through the pump.
One of the nice things about the venturi was that it really pulled a serious vacuum. It maxed out my vacuum gauge with 29" on the gauge. It had no difficulty pulling up the tubing three feet from the floor to the venturi. The venturi will load down the pump enough to slow the flow rate from 7.5 gpm down to 6 gpm when being used to draw methoxide. It loads it down when not in use as well. Not quite as much as when it's in use, but enough that we want to look at using a bypass for mixing.
A bypass lets the biodiesel go around the venturi when it's not in use. This eliminates the head pressure on the pump and increases the flow in the circulation line. It's a simple device that with a ball valve and union being the main components. Open the ball valve when the venturi is not in use, and close it when you want to inject the methoxide.
Mazzei 584 Venturi from Amazon.com