JohnO's Semi-Continous Processor

By Rick Da Tech


small bird watererJohnO is an industrial engineer that has been tinkering with automation for cleaning WVO and making biodiesel for at least 15 years. At the core of this processor is his "Bird Waterer" used for drying WVO. He considers it a modular component and has used it as part of his cleaning and drying WVO for a long time.

His Semi-Continuous processor will make 1-3/4 gallon of raw BD/Glyc every 15-20 minutes, if the oil is dry to start with. That's 120 gallons/day. It adds up. Power consumption is less than 1 KWH/cycle, or roughly 500 watt-hours per gallon. More if the oil is wet, which also slows down the cycle rate.

Going small has it's advantages, it only cost JohnO a few hundred dollars to build.


The warm, dried oil from the Bird Waterer dribbles into a can that has three float switches, a stirrer motor, and an outlet pump.  Attached to the can is a solenoid valve connected to a tank and pump of pre-mixed Methoxide. The sequence is as follows:

1) Warm, dry oil reaches the second float switch (about 1.5 gallons of oil), which turns off the oil pump and starts the methoxide pump and solenoid valve, as well as the stirrer.

2) When the level reaches the 3rd float switch, the methoxide turns off, and a 2-minute mix timer starts.

3) At the end of 2 minutes of mixing the outlet pump starts to drain the can of what is now raw mixed biodiesel/glycerine.

4) When the level drops to the 1st float switch, the mixer and the outlet pump stop, and the Bird Waterer turns back on.

The 1st float switch is only an inch from the bottom of the can.  The 2nd one is 6 inches above, and the 3rd one is a carefully measured 1.2 inches above  that one, giving a fixed 20% methoxide/oil ratio.

The processor passes 3/27 with only two minutes of mixing time using the traditional single stage recipe. 3/27 tests must wait for the glycerin to mostly settle, but can be done periodically during the process to verify everything is working ok.

The Birdwater is a tube in tube heat exchanger connected to a Waring stainless steel electric skilled obtained second hand for $5. He added a few pieces of "Reflectex" insulation to reduce the heat losses, and also added the pipe sticking out of the bottom off-center - it's the vapor vent and extends up above the oil level inside the covered skillet.  This keeps rain out, plus provides an oil over-flow in case the heat exchanger gets clogged.  It's positioned over the can.




The following was extracted from an archived infopop thread:



1 What it is: The Birdwaterer is a continuous-flow oil dryer. It incorporates a set of controls, a heat exchanger, and filters.

2 What it does: It dries vegetable oil by heating to 250F while exposing a large surface area to the air, allowing ready evaporation. The hot dry oil flows through a heat exchanger to preheat arriving oil, improving the thermal efficiency. It has sensors to shut itself off when the oil is done, or when a filter plugs.

3 How it works: The wet oil (used fryer grease) is manually loaded into a 1st barrel through a rough screen. A pump draws the rough-screened oil from the 1st barrel and pushes it through the heat exchanger to the electric skillet. The pump is controlled by a temperature sensor in the electric skillet. It stops the oil flow when the skillet drops below 250F, as occurs when water is present and begins to boil. When the temperature rises above 250F, the oil is dry, and the pump starts again.

The oil flows back through the heat exchanger, pre-heating arriving oil and cooling the dried oil. It pours into a cone-filter for initial filtering (to roughly 50micron), and collects in a 2nd barrel where it settles briefly. A float switch in the 2nd barrel triggers a demand pump connected to a filter bank, automatically filtering the cool dry oil ready for vehicle use. Note that filtering is not necessary if the oil is destined for biodiesel production, in which case the warm, dry oil pumped directly into a processor.

4 What makes it work: The electric skillet has its own thermostat, set to about 275F. Another thermostat has its temperature sensor bulb submerged in the oil in the skillet. That thermostat is set to 250F, and controls the pump through a relay. The Birdwaterer needs the pump to turn OFF when the temperature of the oil is too low, so it boils the water out, then turns ON when the temperature goes high again. This is the opposite of an oven controller, so the relay reverses the action.

The skillet, pump and thermostat are the heart of the Birdwaterer, and would work for drying oil without the other parts. The other parts just make it more efficient and more convenient. You can pick and choose whatever parts you want to add.

5 What the other parts do: The coarse screen in the 1st barrel is mostly to protect the pump from debris. A friend uses a sock filter, which is much finer than my screen. He can clean his in a dish washing machine, but I don’t have one. I can clean mine with a wire brush and trowel, and have used a weed burner to melt off a thick layer of tallow. Try that with a sock filter! There’s no right way to do this; there’s just your way. If you’re really patient you can simply let the oil settle and take the unfiltered oil from the top, eliminating the screen and filter completely.

The 1st barrel is just a 55-gallon steel drum with the top cut off, insulated with Reflectex to keep the oil warm and liquid. It’s got a band heater wrapped around the bottom for cold weather use. I also used a cheap heating pad for a while, but it burned out and I was worried about fires.

The barrel has a float switch about 1/3 up from the bottom. It shuts off the whole system when the oil level drops too low. The oil is pumped from a point just below the float switch, so there’s plenty of room for junk to settle out. Once a year I have to clean out the bottom of the barrel, using a shovel. The goo that accumulates is nearly solid grease or tallow, with a lot of grit and food debris mixed in. I’ve discovered that song birds love it!

The pump is a 12-volt automotive fuel pump. I’ve used the old Facet metal cube pumps (now out of production), their new plastic pumps (very short lived in this application) and the current Carter pump.

The heat exchanger (HXC) is a ½ inch copper tube inside a ¾ inch copper tube. The hot dry oil leaving the skillet flows in the ½ inch tube, heating the wet, cold oil flowing the other direction in the ¾ inch tube. This helps recover and recycle about half the heat. The efficiency can be improved by making it longer, but then the cold oil clogs the paper grease filter. I made a 50-foot long coiled HXC that was really efficient once, but it clogged easily and eventually couldn’t be cleaned out. This shorter one works better, considering. Life’s full of compromises.

The warm oil exits the HXC and pours through a paper filter (commercial restaurant grease filter), which removes a surprising amount of grit, and a lot of tallow. It seems to average about 25 gallons or so, of my oil, before the $0.05 filter needs changing. Patience would allow your oil to settle in the 2nd barrel without the filter. I eventually added another float switch to shut down the process when the paper filter gets full.

The same float switch will also shut down the process if the barrel gets too full, since it’s now positioned below the top of the barrel (the picture is from the time before I thought about using the same float switch for both purposes).

The 2nd barrel is another insulated 55-gallon headless drum. It also has a float switch 1/3 from the bottom. It also has its outlet just below the float switch. It also gets cleaned out annually. It’s never needed a heater, yet. The oil is still a bit warm when it’s pumped out, even after settling several hours.

A note about oil settling, my WVO sources use hydrogenated soy, the kind that’s nearly solid at cool room temperature (see the "first barrel screen" picture, above. It's clogged with thick gooey tallow/oil). Then they cook meat and breaded stuff in it. Thus it’s difficult to clarify by simple settling, it’s just too thick, and the food particles are suspended in mid-tallow. After heating to 250 though, the food particles settle to the bottom very quickly. Weird! I’ve tried other settling techniques without success, but everyone’s oil will behave a little differently. Mine is a sort of worst-case oil, but the Birdwaterer handles it ok. If you’ve got better oil, you can simplify the process.

It doesn't take much imagination to think of using the 2nd barrel as a biodiesel mixer. My latest idea is to reposition the float switch to the 35-gallon height, so it will hold exactly one mixer load for the nearby sealed processor. This would allow it to run normally, but the heavy fractions and settled junk could be pumped out to make into BD anytime.

The float switch controls a 12-volt demand pump (Shur-Flow or Flojet agricultural sprayer pump) through a relay. The oil gets pumped through a bank of 5 water filters having string-wound 5- or 10-micron ratings, and on into a storage tank, ready for vehicle use. 5 filters were necessary to get an acceptable flow rate and they seem to last somewhere between 25-50 gallons each, average. I change all 5 at once, when the flow rate slows to a trickle. It’s easy to tell when they’re getting too plugged up, the pump will cycle on and off, spending longer periods off as the plugged filters take longer for the pressure to bleed down (which is set very low, about 25psi, to avoid filter collapse). With clean filters and decent oil, the pump will run continuously until the float switch shuts it off. Most of the time it cycles on and off every few seconds. It will filter 25 gallons of oil in a day even when partially plugged up.

The rack of filters has a bypass valve, allowing the unfiltered oil to go somewhere else. I connected a hose from the valve to my biodiesel processor, so it gradually fills up with warm, dry, roughly filtered oil. If the processor had a float switch, controlling the pump, it would automatically fill to the right level and stop. That would approach full automation. What a frightening thought.

Where do you get your floats and float switches from?

Filters: box of 50 costs $9.90 at Serv-U, part number SRVY-1100.

The float switches are from McMaster-Carr, McMaster-Carr part number 46515K45, $13.07 each. They need a relay since their current capacity is limited. I use 120vac Ice Cube Relays or 12-volt automotive relays, depending on application. To mount the switches I weld or braze a 1/2 inch pipe coupling into the tank side. I've also found some gasketed pipe bulkhead fittings, meant for swamp coolers. The switch has pipe threads. Use a good sealant or teflon tape. Turning it upside down makes it normally open, or normally closed if turned the other way.