One Pass Oil Cleaning and the Automatic Controller

Our tests show that waste motor oil or WMO, typically contains between 3 to 5 percent solids. When cleaning WMO, the solid particulates become concentrated next to the bowl wall and clean oil floats to

Particulates in Waste OIl

the center of the bowl, spilling over the top edge and going out of the centrifuge through the clean oil output port.  As the solid particles move to the bowl wall, some of the solid matter sticks to the sides of the bowl, however much of it is concentrated as a slurry of solid particulates in oil. If you feed the WMO or oil slow enough for long enough time so that all the particulates move to the wall, you could remove all the particulates as solid matter stuck to the sides of the bowl. However, such a slow feed rate and the amount of time spent scraping solid matter from the centrifuge bowl are too impractical and labor intensive for actual production.  Much of the solid matter can be removed before the bowl fills up. Draining the slurry from the centrifuge before the bowl fills up allows a higher feed rate without sludge spilling over into the cleaned oil. This greatly extends the run time between bowl cleanings and also reduces or eliminates the sludge that spills into the cleaned oil.

The amount of WMO sludge concentrated in the centrifuge bowl depends upon 1. The G force with higher G force having a higher rate of concentration 2. The feed rate, the feed rate must be low enough for the centrifuge to do its job and settle the sludge to the outer wall (again, higher G force = faster and higher concentration of sludge). At some point, the bowl will fill with sludge and spill over into the cleaned oil. At this point, the centrifuge is removing very little if any contaminants as they spill over into the cleaned oil as fast as they are removed. Two remedies for this situation are 1. Slow the feed rate so low that all the particulates move to the outer wall and only cleaned oil is discharged, but we have already seen that this is impractical. 2. Stop the centrifuge and drain the sludge before it spills over, contaminating the cleaned oil.

The size of the bowl dictates the volume of oil processed between draining.

How often should the centrifuge be stopped and the bowl drained? An approximate starting point is determined by the bowl size. The US Filtermaxx WMO centrifuge has about 165 cubic inches sludge capacity.

5% =.05  

3%= .03

1 gallon = 231 cubic inches

165 cubic inches / .05 = 3300 cubic inches of oil

3300 cubic inches / 231 in3/gal = 14.3 gallons

165 cubic inches / .03 = 5500 cubic inches

5500 cubic inches / 231 in3/gal = 24 gallons

So the optimal range of oil fed to the US Filtermaxx centrifuge between bowl draining is between 14 and 24 gallons. Running any centrifuge longer that the bowl capacity is like trying to put 10 gallons of sludge in a 5 gallon bucket.

Run time between draining will vary by G force, viscosity of the oil and percent contamination, however; volume between draining will remain about the same.

The volume between draining for other sized bowls is calculated in a similar manner.

A centrifuge bowl capacity of 1 pint = 28.875 cubic inches

28.875 / .05 = 577 cubic inches

577cubic inches / 231in3/gal = 2.5 gallons

For a bowl capacity of 1 quart = 5 gallons

Nobody wants to sit around and wait to drain their centrifuge bowl, so here at US Filtermaxx, we design a variety of programmable automatic centrifuge controllers to remove the burden of manually draining the sludge from the centrifuge, allowing automatic one pass cleaning.US Filtermaxx Dual Centrifuge Controller