Static Washing
Static or gravity washing is the least aggressive and least likely to generate an emulsion. It is simply placing water and biodiesel in the same tank without any mixing. Contaminates migrate from the biodiesel to the water through the boundary layer over time. This process takes anywhere from 4 hours to 24 hours to saturate the water with contaminates. Most homebrewers will let the static wash continue over night before draining and starting a different technique. It is particularly effective as a first wash for biodiesel from high FFA oils.
Static washing Tips:
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Use hot water directly from the tap or from any other source.
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Introduce the biodiesel onto the top of the water by pumping the biodiesel into the tank through the standpipe.
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Insulate and cover the drum to keep the heat in.
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Consider using a sealed and vented wash tank to reduce methanol vapors in the workspace.
Mist Washing
Mist washing is the spraying of water over the top of the biodiesel and letting it settle down through the biodiesel collecting contaminates as it goes. It is more aggressive and therefore more effective at removing contaminates that static washing. It is also effective at removing methanol vapors from the air over the biodiesel, making it a safer first wash technique. It uses more water than most of the other techniques unless you re-circulate the water. It can also cause the biodiesel to overflow the wash tank if left running without using overflow prevention equipment. In places where water is abundant and wastewater disposal is not a problem, a continuous mist wash can be implemented allowing very long wash times.
High flow, agressive mist washing is a variation on mist washing that requires high conversion fuel, low soap content, extended settling to remove all the glycerin, hard water, and a heated wash. Not everyone is able to use high flow agressive mist washing because if not all the conditions are met, it will form heavy emulsions. If all the conditions are met, then the wash cycle can be completed in just a few hours.
Mist washing notes:
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The size of the droplet can have an effect on mist washing
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Very small droplets can cause a cooling effect due to evaporation and require the addition of a heat source to compensate for the heat lost due to evaporation. This effect is more pronounced in dry climates. If the tank is sealed the cooling effect goes away as soon as the air over the biodiesel is saturated with water vapor.
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Large droplets can increase agitation and cause emulsions if the source of the spray is too close to the biodiesel. Raising the source to at least a foot above the biodiesel will reduce this effect.
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In summer, a black garden hose laid out in the sun can raise the temperature of the water used for mist washing and improve the wash, although people report mixed results from heating the mist water, not everyone notices an improvement.
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A continuous mist wash is an inexpensive way to prevent tank overflows or run your mist washer for extended periods of time.
Continuous Mist Washing
Mist washing has one problem. If you don't stop it in time, your wash tank will overflow and spill biodiesel everywhere. This simple drain system will limit how high the biodiesel will go in the tank.
Click Here to see more pictures of this continuous mist washing tank being built.
Be sure you connect the "Water Out" to a suitable drain or tank to catch the water. A steel riser pipe would sturdier than a PVC or tubing. It would be a bad idea to use the pipe as a handle to move your wash tank because of the risk of breaking off the pipe. If your drain is kinked or pinched the water will back up and flow spill out the vent pipe.
One note of warning: If you create a big emulsion, it will want to flow out the drain taking your biodiesel with it. It could also stop up the drain and overflow the tank anyway. So you still need to keep an eye on the wash and stop it if you see an emulsion forming.
The water will drag along some biodiesel with it. Best practice is to drain the wash tank into a drum to give the biodiesel time to rise to the surface where it can be removed. If you add epsom salt to the spent wash water, it will react with the soap, making the soap insouble in water and releasing the biodiesel.
  An often overlooked upgrade to the continuous mist wash tank is the addition of a timer and overflow shutoffs. The only solenoid valve that will work with low flow misting systems is the direct acting solenoid valve. One place to purchase an inexpensive direct acting solenoid valve is www.omega.com. The 1/8" valve (SV31050) is plenty big for most misting systems and comes with a 110V coil standard. For a timer, a lamp and appliance timer with non removable push pins at 15 minute intervals lets you turn the water on and off every 15 minutes for water conservation. Available online is the Sylvania SA110 15 Amp Heavy Duty Appliance Timer for under $20. Then use float switches on the wash tank and water catch tank with normally closed contacts that open when the float rises to shut off the water if either drum fills for any reason.
Bubble Washing
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:
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Cheap aquarium stones will dissolve in biodiesel
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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.
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You need a way to adjust airflow to regulate the aggressiveness of the bubbles.
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An aquarium pump with a rheostat adjustment is a great way to allow adjustment of the airflow.
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Airflow can also be adjusted with a needle valve inserted in the line.
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Bubble stones can be made from grinder stones.
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Bubble stones can be made from HDPE pill bottles by using a push pin to poke lots of holes in the bottle.
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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.
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Bubble rings can be made from copper tubing by grinding a thin spot on the tubing then punching a hole using a pushpin.
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Polyethylene tubing will withstand biodiesel but requires the use of compression fittings since it will split when stretched over a hose barb.
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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.
Stir Washing
Stir washing is a very aggressive technique for washing. Stir washing is accomplished by placing water and biodiesel in the same tank and aggressively mixing to form an emulsion. The emulsion then separates over time. However, it sometimes creates a stable emulsion that does not settle out with time. This is best used on high conversion biodiesel with very little soap using hot, hard water and is primarily used on commercially made biodiesel where new oil is used as a feedstock and very little soap is made.
Rick
-no I don't do the five % pre wash, but all my washes use only 5 - 7% warm/hot(45C) Soft water
use of cold or hard water will result in extra washes
-I don't prop wash anymore, and haven't for several years, but when I did i transfered the biodiesel to a plastic garbage can and added water and mixed using a 3.5" dia paint mixer turned by an air drill. it really got the job done, but this prop technology was more difficult to incorporate into the fixed wash tank. Now I use the NT blue pump.
-static wash is done in a tank specially for that purpose, it has a shower head in the top, I vacuum this tank to 29"hg then suck in 8 lts of warm water, let sit for one hour and repeat.
-no to batches are really the same unless, the water and ffa content of the wvo are controlled.
-I don't take any credit for the minimal amount of water I use now, that credit has to go to Jim the biodiesel chemist I email regularly I was really skeptical at first, I swithched from cold hard water at a rate of 40% to soft warm water at a rate of 5 - 7% Let me put it this way, I'm never going back!!!! Tom
More details please.
Are you doing this at any specific temperature?
Do you do a 5% prewash?
Are you using a pump or a prop?
How long are your static wash and how much water are you using in them?
Rick
-Stir washing or prop washing is as stated above an aggresive method of washing biodiesel. That said, it is also very fast, the emulsion breaks and the water is ready for draining 1 hour after mixing.
-stir washing should only be done after two or three static washes to remove as much byproduct as possible. With the amount of methanol we use there will always be byproduct suspended in the biodiesel, and this can cause big trouble with an agressive wash.
-advantages of prop washing
-1) it is fast
-2) there is no oxidization of the fuel
-3) only 5% water/oil required per wash (more is NOT better)
-disadvantages I can't think of any!
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