Waste Oil Burners » Technical Notes
This page contains detailed technical information about waste oil burners and was designed in response to
the frequent inquiries i get from other potters interested in implementing a similar system in their kilns.
It was not intended to be a step-by-step series of instructions but rather a list of essential details that
must be considered by anyone attempting to do this. Five years of research and development can be saved by anyone
who reads this page because i am currently one of the only full-time production potters firing entirely with waste
oil and a lot of this information is posted in the form of responses to questions i have received via email.
I occasionally design systems for other potters on a consultation basis, for a modest donation that is generally re-invested back into this firing system so to keep improving on it, thereby having more information to share with others. I can provide sources for quality used components and part numbers for necessary off-the-shelf items at the best prices available on the market. I can plan out a customized system based on your needs and the consultation fee i charge will be made back before you even do the first firing; and the systems i develop now are actually more cost effective to implement and efficient to use than mine since they begin with what i know now and eliminate all the trial and error involved with my system.
At the start of 2009 i redesigned the pre-filtration system to significantly reduce the amount of time and maintenance involved.
Previously, i was transferring the oil into a 55 gallon drum on wheels which had two pipe fittings welded near the bottom: one of them
had a drain valve mounted and the other had a hot water heater element. The process was to heat the oil enough to make it easy to
filter, and then connect a hose to the drain valve and pump the oil through a 20 micron household water filter. With fairly clean oil
this worked fine but i found that some kinds of oil were nearly impossible to filter this way. Plus that type of filter was much finer than
needed so the extra time and energy it took was rather wasteful. I replaced the steel drum with the tanks pictured to the right.
The oil is collected in a 60 gallon air compressor tank converted by drawing a vacuum on it, turning it into a
suction tank that pulls oil into it from collection barrels. Then compressed air is used to pump it
into 275 gallon tanks (often available on craigslist for $0 - $100, i paid $50/each for mine). An old
pneumatic diaphragm pump i got on a trade and fixed up (which requires a good shop compressor to use)
pumps from the tanks, through a pipeline across the kiln shed and into the main supply tank for
burners, which is a 55 gallon drum with a 3/4" pipe fitting welded near the bottom.
Along with way it passes through a "hydraulic return line filter" made by Lenz in Dayton, OH and sold for about $120. It has a cleanable, stainless steel 200 mesh filter inside (other meshes are available) with 1" NPT ports and a pipe thread adapter (also purchased from Lenz) with a 1/2" ball valve for easy draining. It is heated with a flexible silicon blanket heater, purchased for about $55 from Tapco in Cincinnati and controlled with a 320F thermal switch. This reduces the viscosity of the oil, making it easier to filter, especially important when filtering WVO. A pressure gauge must be located at the inlet of the filter so you know when to clean it - once the pressure gets up to around 20 psi i know that the filter is getting clogged and it is time to remove it and soak it in kerosene, and brush the pleated surface with a toothbrush, continually dipping both back it the kerosene. When i am done i use an air chuck to blow all along the inner surface toward the outside to get the remaining particles out. If too much pressure builds up the filter element will collapse (i ruined a few, no big deal but about $30 for a new one).
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The burners were originally used on residential oil furnaces and are made by Beckett in the "AF" or "AFG" series. If you have a local oil furnace technician in your area he can probably provide you with some old ones because whenever furnaces are replaced the burners are as well, even though they generally work fine. Other aspects of the furnace, like the heat exchanger, are usually the reasons for replacement. It is best to start with two burners of the same make and series, and if possible with the same size blast tubes (but not absolutely needed). If you can't find anything locally you can try ebaying "beckett AF burner" and see what comes up but i would not advise on spending more than $50/each, especially because a lot of the stock parts are removed and older ones work just as well as newer ones. It's just not worth a bidding war - and if you get creative with searching you may find some (like i did for $10) listed by folks who are just trying to get rid of their old ones for a few dollars and not are totally into the savvy ebay seller thing trying to make their living selling them. One day my next door neighbor junked his and the works "Beckett" just seemed to jump out off the white burner casing as i drove by so i stopped and he gave it to me. Basically, you should be able to come up with a pair of Becketts somehow without spending too much, and it will make it a lot easier to get this project started. They require "sipon nozzles", "siphon nozzle adapters" and the "Kagi flame retention head" available at Kagi Heating in Spokane, WA (google them to find their site). I think i paid about $125 for these parts for each burner, including shipping and also some extra 0-rings which you will need. I am not sure of the exact prices at the moment but probably not that much more.
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The lines going to each individual burner need to be 3/8" soft copper so you can back them in and out of the kiln as needed and move them around for servicing. VERY IMPORTANT: although you can use black iron pipes going from the tank to the soft copper lines, they must stop wherever the final filter is. If you use a common filter for both burners mounted just before the soft copper, they must end there. All pipe and fittings from the final filter to the burner nozzle must be copper or brass (or stainless/aluminum but only if you have them around). Otherwise the oil will eventually form a polymerized skin along the inside of the fittings which will peel off and clog nozzles. It happened to me numerous times over the course of a few firings before it took things apart and found the cause.
The burners are started by turning on the blower, ignitor, fuel heater and compressor (at a very low pressure at first) but the needle valve for the oil is closed. The radial air band should be all the way closed. As the oil heats up it will expand and push enough out the tip to get a small flame going. Starting them this way minimizes the amount of oil that will drip down the burner and onto the floor. The tip of the burner is pushed as far into the kiln as it will go (before the kiln reaches red heat it will be backed out so that only 1/4" or so goes into the ports). Once the flame starts (or as soon as you know the oil is hot) the valve is open enough to get a good flame out and then the radial air band can be opened just enough to get an oxidizing flame. The air pressure can be increased as needed: not enough and you get smoke, but too much and it will blow the flame right out (this can also happen if the radial air band is opened to much, especially early in the firing).
It is very important to back the burner tip out of the ports some time before red heat because if they are left all way inside the thin slots inside the nozzles (called "spinners") will gradually get coked and restrict the fuel flow. Once the kiln reaches red heat you can turn of the ignition transformer because it serves no purpose - the heat from the kiln will instantly ignite the oil.
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