Alternative fuels > Waste Motor Oil

Conditioning waste motor oil

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MachineNLectricMan:
Waste motor oil is a good source of energy for a Lister. The only drawback is the abrasive wear that this fuel causes and the premature ring and cylinder end of life. There may be a good solution to this though and that is Vacuum Distillation. This process is a lot easier to set up than imagined, requires low temperatures and could likely be conducted using only engine coolant and/or exhaust heat. Refineries use this process a lot and old motor oil is often recycled using this method. Since the abrasive character of burning used oil comes from the "ash" produced mostly from the additives, it is likely that vacuum distillation would easily remove most of these. Only additives that form "Azeotropes" would remain but reduced if the operation uses a "reflux" bubble chamber between the boiler and the condenser.

The higher the vacuum, the lower the temperature required. Since the system is sealed, theoretically once the vacuum is pulled, it stays as long as an equal amount of distilled oil is removed for the waste oil that is added to the boiler. However, if any oil breaks down, or any molecular changes occur, additional vacuum or evacuation flow will likely be needed to maintain the correct vacuum. The product must be pumped out to keep the seal. The feed can be orifice and needle valve regulated since the vacuum will suck it into the retort, just keep the feed and pump out balanced. A fluid level glass, float, or indicator will also be needed in both ends.

Also, playing the higher vacuum lower temperature option will result in more water coming over the still if there is any in the oil. Other more volatile materials will also come over. As long as they are fuels it doesn't matter, but if destructive additives start coming over, the purpose of the whole operation becomes defeated. The key will be finding the vacuum that gives the best balance.

The vacuum process might be useful with waste veg. oil too, but probably in reverse. I.E. Using vacuum distillation to remove water and taking the purified product from the retort side of the operation using a staged retort.

Assuming most Lister users likely have welders, and since low cost flux core migs are so common now days, construction should not be an issue. Silver solder, Phos/copper and other techniques used in HVAC work would also work. It is also possible to assemble such as system without any welding or soldering, but perhaps not as efficient. Old 20 pound propane tanks for instance that may no longer be safe at 110-120 PSI in the summer would be OK in a vacuum system as long as they are not in really bad condition. Use one for the retort and one for the distillate collector. Set the retort tank in the top of that barrel you use in that thermo-syphon cooling system. You might even use two smaller barrels, one smaller top barrel that just fits around the propane tank retort, then the coolant flows into a lower barrel for more cooling. Insulate the top barrel to keep more heat for the vacuum distilling input.

Another more efficient method would be to weld or braze a DIY heat exchange coil or loop into the inside of the tank used for the retort, and circulate engine coolant through it. If designed correctly thermo-syphon would also work for the coolant flow, I.E. larger tubing and fewer coils and bends inside the retort tank. Input the coolant into the top coil and exit from the bottom coil to a radiator or barrel.

Most electric vacuum pumps sold pretty much everywhere for automotive AC work will give the proper vacuum, and there are dozens of ways to rig a mechanical vane type vacuum pump to a Lister, preferably using a clutch of some type. If you are running a generator, the electric method is easiest to set up and control. Whatever method, just rig a regulator so the vacuum pump only comes on when the vacuum is not high enough, and use a tank to "store" some vacuum between vacuum pump cycles so the system stays balanced better. If you just leave the pump running you will needlessly wear it out soon, and burn a lot more extra energy than you would like.

In summary, the idea is to set up a self distilling waste motor oil fuel feed for the Lister, not sacrifice engine life, and take advantage of a high energy fuel source that is widely available. Waste motor oil usually has more energy than diesel per gallon.

Also bear in mind that there is a close cousin to this process called Steam Distillation. While this would also likely work, it would be more complex requiring a boiler, and/or system steam circulation pumps and so forth, slightly higher temperatures, and may waste more energy. The steam serves to reduce the "partial pressure" and creates a type of "artificial" vacuum. Then you have to add a water separation stage.

I will eventually get on of those round tooits and do this myself like I eventually do with everything else. In the mean time, why withhold this from the rest of the Lister folks? Since most folks here are pretty smart and creative, here is something to experiment with!

mobile_bob:
there was much discussion about the use of waste motor oil on this forum maybe 10 years ago or so.

the general consensus was it probably was not a good idea to use it in original engines, as accelerated cylinder/ring wear results from the ash left behind along with some other byproducts.

now that the new oils, particularly those made for the new diesels are very low ash, so maybe burning such would not be a problem

i made an argument for burning waste motor oils in a changfa engine, based on a cost analysis where i could save X amount of dollars in fuel expense factored against the cost of cylinder kits needed from accelerated wear.

for the relatively low cost of parts, ease of repair (low labor cost) the rather large amount of money saved burning waste motor oil offset the repair costs by a large factor.

there are two schools of thought,

1. i don't want to damage my original antique lister engine, that might not have cylinder sleeves.  a valid argument, or

2. i expect to have to do more frequent overhauls because of my ease of access to free waste oil streams, and cheap rebuild parts.  parts needed as part of the cost of operation.  which is also a valid argument.

then we might also consider what kind of waste oil are we going to have access to? if it is from a source of low ash, low mileage oils, maybe that weighs things one way or another.
one might also factor in the cost per gallon or liter of pump diesel as well?

fwiw, the changfa will start from cold on motor oils, i have tested all the way up to 50 weight oils with no problems at all. a bit more smoke until up to operating temps and then it burns as cleanly as pump diesel.  i did not run long hours on motor oils, so i can't speak to the accelerated wear issues, but will stipulate that it is likely there would be some reduction in parts life.  which of course i am ok with given the low cost of repair parts, the run times that i anticipated being quite low, among other factors that would likely be viewed in other ways for other folks in other applications.

basically you mileage will vary

having said all that, if i had an original lister/bore type block (no sleeves) and it was a nice example that had value for its antiquity, i too probably would not want to burn anything but clean pump diesel fuel.

bob g
 

mihit:
I wonder if a vacuum system would have advantages over a centrifuge? Or if it could be added to the process, before or after, as an additional refining step.
If anyone has the gear already set up, to compare these methods side-by-side, or one before the other and compare yield and some kind of test of clarity, calorie, ph, gravity etc...  This would be very interesting, OR, I'll add it to my long list of projects!

38ac:
I think you have accessed the situation well Bob G. I burn a LOT of WMO,, but in my shop furnace. The amount of ash produced is tremendous and it doesn't matter if the oil comes from a trucking company or a hot rod shop, my two main sources.
Seems to me that using waste oil as engine fuel has many trade offs, who wants to spend half thier  life fooling around in the shop or engine shed so they can burn "free" fuel? It appears very few. None the less its some thing to talk about.

mobile_bob:
38ac:

i get where you are coming from,

i don't recall the graphic details of the analysis, and i am sure part of that was the "free" labor involved in dealing with added maintenance. i do remember at the time pump diesel was near 4 bucks a gallon which factored in heavily.

also of note, iirc my analysis was in using wmo in a 50/50 mix with pump diesel to cut the fuel cost basically in half, and also reduce the viscosity to the point that the oil could be filtered down to a micro or better.  that would get out most of the trash.

another thing that i never ran long enough to test the theory, but i wonder if under certain conditions the added ash might pass through with limited wear, such as near max loading, higher cylinder temperatures, rather than partly loaded engines where the cylinders are cooler, and where the ash might collect with partially burned fuel to make for a very good lapping compound.

my bet is higher rpms, near max loading, close cooling systems with attending higher cooling system temperatures, likely would not collect as much of the ash and mix with unburned or partially burned fuel to accelerate the wear.

during testing, i did run quite a bit of 50/50 mix, along with straight motor oils, had the head off a few times and the piston showing no signs of excess carbon buildup, but then again the unit is a closed 7psi system running between 205-214F at max loading.  the cylinder didn't seem to show signs of premature wear as the crosshatch remained intact.

but then again, only way to know for sure would be to run the engine to a point where there would be increased crankcase pressure, exhaust smoke and/or loss of power... then total the hours ran, power made, fuel burned, and overhaul cost (parts and with or without labor) to get a total cost per kw/hr, then calculate what that cost might have been with pump fuel

basically would take a lot of hours, and have to do it at least twice, once with wmo and once with pump fuel.

in my application the design was for 2 one hour runtimes per day, and at that rate i probably would not live long enough to see both tests ran to completion.  or at the very least i probably would forget what it was i was testing for in the first place.

:)

bob g

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