Bubble Washing Biodiesel
By Rick Da Tech
Bubble washing is more aggressive than mist washing. It is done by adding a layer of water beneath the biodiesel and forming air bubbles in the water. The water is dragged up into the biodiesel in a small layer around the air bubble, which falls back down through the biodiesel when the bubble bursts at the top of the tank. The size of the bubbles and the volume of air will determine the aggressiveness of the wash. Small bubbles with low flows are not very aggressive, but large bubbles with high airflows are very aggressive. If the wash tank is not sealed and used as a first wash technique it can release significant amounts of methanol into your workspace area and create a safety issue. This method uses less water than the mist wash technique.
Bubble washing notes:
- Cheap aquarium stones will dissolve in biodiesel
- Limewood wooden air diffusers generate very tiny bubbles for less aggressive bubbles. They hold up well to biodiesel but the plastic hose barb will need to be replaced with a brass one.
- You need a way to adjust airflow to regulate the aggressiveness of the bubbles.
- An aquarium pump with a rheostat adjustment is a great way to allow adjustment of the airflow.
- Airflow can also be adjusted with a needle valve inserted in the line.
- Bubble stones can be made from grinder stones.
- Bubble stones can be made from HDPE pill bottles by using a push pin to poke lots of holes in the bottle.
- Polyethylene tubing can be made into a bubble stone by sealing the end and using a pin to poke lots of holes in the last few inches of the tubing.
- Bubble rings can be made from copper tubing by grinding a thin spot on the tubing then punching a hole using a pushpin.
- Polyethylene tubing will withstand biodiesel but requires the use of compression fittings since it will split when stretched over a hose barb.
- Weights to hold the bubble stone down in the water are best if made from stainless steel. Stainless steel nuts slid over the tubing make good weights.
Cheap Aquarium Stones tend to melt in biodiesel. You might get a couple of batches through before you have to clean out the green goo in the bottom of your wash tank.
These bubble stones are actually exhaust mufflers for compressed air tools and have lasted several years. They are available from McMaster-Carr for a reasonable price.
These Air Tool Exhaust Mufflers are available from MSC Industrial Supply and are made of polyethylene.
This is a wooden bubbler available at Utah Biodiesel Supply
This Bubbler is polyethylene tubing poked full of pin holes. If you look closely at these two videos, you can not only see the air bubbles rising to the top and bursting, but you can also see water filled bubbles falling down through the biodiesel once the air has escaped.