Saturday, May 31, 2008

Bubble washing of biodiesel

Bubble washing - The bubble washing technique was developed at the University of Idaho and is the most economical way of washing biodiesel after processing. The pumps use only a few watts of electricity (your mixing motor may use 250 to 300 watts) and you need only use 50 to 75% ratio of water to biodiesel to wash, as opposed to three or four times the volume of water in the more usual mixing wash method.

You will need various items from an aquarium shop - they are not expensive and you can tailor the size to match the size of your washing tank. You will need a pump - some of them come complete with a filter, which can be used for something else. They all have a mains power cable and air line. Few have switches incorporated, as they are designed for continuous running - a plus point. They are quiet - another plus point - but they do vibrate with a low hum - 50 or 60 cycles per second, depending on your supply. You will also need an air stone. The small ones are the best, as they form many small bubbles, but some of the plastic inlet tubes (especially blue ones, for some reason) tend to be melted by the biodiesel. Some are about six inches long, with clear plastic inlets. You may choose to run with a bigger pump and two stones, using a T piece in the air line - the more bubbles the better. All you do is plug in and leave running for two to three days, checking the pH of the biodiesel periodically. Ideally, it should end up about 7.5 - neutral

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