Tour - Oil Processing

The oil comes from the restaurants with watery waste, food bits, and occasionally other trash. The burner requires the largest particle size to be no more than about 150 microns, so particles larger than this must be removed. The oil must also be free of water and the oil must be completely melted. Since we collect both animal fats and vegetable oils, we have to assume that our TBF will solidify at about 40F to 50F. Once it has solidified, it must be warmed to at least 110F for the all crystals to melt. The warmer the better for straining and settling. The discussion below describes the warming, straining, and settling process that we use solve these two problems. The photo on the left shows dirty oil which contains animal fat and emulsified water. The photo on the right shows the oil after processing.

Move Drums Into Greenhouse For Warming

55 gallon drums are moved with the tractor and material handling forks two at a time. The drums are set on a concrete slab, heated by hot water from the TBF boiler, in the greenhouse. Essentially, it's a little radiant floor heating pad. The drums warm to a pumpable, strainable liquid in about a day for all the vegetable oils and 2 days for animal fats. We consume as much as 60 gallons/day in 3 Clean Burn burners on a cold winter day, so the processing must be done at least every three days if left until January. We try to process as much oil during the summer as possible and then re-store the clean oil in clean 55 gallon drums. The clean oil is segregated for winter when it is most difficult to keep up. The left and middle photos below show the warming pad we use and the photo on the right shows the process and burner area with the warming pad covered with a silver colored blanket to retain heat and speed warming.

Transfer Oil To Strain Tank

Once warm the oil is cleaned in four steps:

Step 1 - Suck oil from drums by holding the suction tube just below the surface of the oil. This prevents both the floating and sinking debris from being transferred. We use a separate tube with 2 inverted openings (see left photo below) to suck the best oil off the top to minimize settling time required. We use a 1 inch gear pump and 2 HP motor (see middle photo below), both from Grainger. When we do this transfer we are careful not to suck any solid debris that might damage the transfer pump. The pumping is stopped near the bottom of the drum to avoid sucking the solids that settle there. Following this step the drums are cleaned and stored in the empty pile for reuse.

Step 2 - The strain tank was fabricated from a used ob-round No 2 oil tank by cutting off the top, replacing the shell portion of the removed top with 14 gage sheet steel perforated with 1/8" holes. The trough was then inverted and set into the reinforced open top of the tank. Oil flows into the trough of the strain tank where larger particles are collected.

Step 3 - The oil should be allowed to settle over night to allow free water and other sediment to collect at the bottom. This material is removed by opening the bottom valve in the strain tank invert and draining slowly until clear oil is observed. Follow this link to a sketch of the strain and settling tank bottom connection details. The sketch shows that the tanks is heat traced and insulated. As the oil temperature rises, sludge and bottom water settle to the bottom and the clean oil floats on the top. The photo (below left and middle) shows the valve and connection configuration for each tank. The connection and valve on the left is always the bottom water and sludge connection. The connection on the right is always the clean oil connection. The photo at right shows the process temperature of at least 120F. Note that I have not been able to install all the heat exchangers and insulation as of now. Also note that the sludge and bottom water is discharged into a pail and transferred back to a sludge drum. The bottom water and sludge is added to compost during the summer.

Step 4 - The clean oil is transferred to the burner day tanks. The same 2 HP gear pump is used to transfer the clean oil. I have 2 day tanks in each greenhouse. When a tank is empty, I reposition the valves to pull from the full tank and then transfer clean oil into the empty. This allows the oil to continue to settle. This process assures that only the cleanest oil goes to the burner. Clean oil means reliable burner operation.