Deep Fried Wood

[John Evans]

This is a continuation of the "Charcoal Foundry" thread.

I have spent close to a year developing a technology for producing home made charcoal. After melting a couple of crucibles of bronze with wood and charcoal, I have come to the conclusion that charcoal is an inefficient fuel. While it produces the very high temperatures needed to melt bronze it uses a lot of charcoal to do so. Making your own charcoal is very labour intensive and very wasteful of energy. I estimate that in my process I expend 20 units of energy to produce 1 unit of charcoal energy.

Much to my surprise I discovered that dry wood (I had access to Birch) can bring a furnace up to a bright orange color if you provide enough air to the bottom of the fire. But it helps to have a more concentrated source of energy to achieve the bright yellow color needed to bring bronze to a pourable temperature.

I have two sources of free energy, wood and used cooking oil. My experience is that adding oil to a very hot furnace is a dangerous activity. I needed a way to deliver wood and oil, to the hot furnace, in the same package. Watching the cook, at my local fast food restaurant, make fried potatoes gave me an idea. Why not deep fry wood?

Wood is made from many long microscopic tubules made from cellulose. These xylem tubules are glued together with a variety of flamable organic compounds. In green wood these tubules are mostly filled with water. As wood dries some of the water evapourates and leaves the tubules partially filled with air. I wanted to get rid of the air and water and fill the tubules with oil.

In my first experiment I half filled a large pot with oil and placed a 6" long by 2" diameter piece of green wood in it. About 1/3rd of the log floated above the surface of the oil. On the kitchen stove I started to heat the oil (I kept track of the temperature with a candy thermometer). When the temperature rose above 212 F tiny bubbles began to emerge from the cut ends. By the time the temperature had reached 400 F bubbles were fizzing out at a great rate. I kept this up for about an hour (until my wife returned and put an end to the experiment). Bubbles were still emerging but at a somewhat slower rate. When the oil had cooled the log had sunk to the bottom of the pot. I assume that oil had replaced the air and water within the wood.

Now I have to scale this up to a larger size. If any one else has experience with this I would be very interested.

[RWJR]

did you measure the oil, how much was absorbed? sound like the same process used in cresote lumber, I think they use pressure somehow, like a pressure cooker

I used to go to mexico for casting and the guys used old motor oil as fuel.

[Daniel]

I bought this book describing how to make a tilting furnace that uses old motor oil as fuel, and I've been toying with the idea of actually building one. The biggest problem is that I live in Los Angeles where the neighbors would completely freak out if they caught wind of what I'm doing. I would have the EPA, Fire Department, OSHA, and probably the police banging on my door.

Anyways, the website for the book is: http://stephenchastain.com/books5.htm

I'm probably going to with an electric crucible furnace instead since it is silent and won't make so many nasty fumes. I will also be able to use it to burn out small investment molds.

[fused]

The first foundry I used for pouring bronze had kerosine for fuel, gravity fed from a tank four feet off of the ground and the top of a shop vac as a blower. I've read different sources about "fuels" for foundry/kiln burners and it would seem that almost any combustable material can be incorporated into the process.

I'm thinking that the "deep fried wood" sounds like an unneccessary step and that the cooking oil should be used in a more direct way. Is this stuff a coagulated thick gunk or a thinner viscosity? The oil could be preheated with a copper tube coiled around the burner pipe ending at the top, where it is fed/dripped into the flame and maybe a soft brick under the burner to catch & burn off any excess. This style burner was designed to use old motor oil as fuel.

Another source of heat that far exceeds charcoal would be coke and might be found locally via an iron foundry. Blacksmiths also use it, but your requirements would be so small that a foundry might give you enough to try it out. Next you can thrill your wife (and neighborhood) by building an iron cupola in your backyard.

In graduate school the ceramics department built a wood fired kiln out in the country and burned nothing but pine scraps which were donated by a local truss fabricator. With two fire boxes it was remarkably efficient, after an overnight preheat that kiln would reach cone 9 by noon.

[John Evans]

Lately I have been doing a lot of experimenting with deep fried wood. So I will pass on these observations.
1) Why bother? I am looking for a cheap and effective way to melt bronze. The free sources of energy available to me are wood and waste cooking oil. In our first attempt to melt bronze we brought 104 lbs of bronze to pouring temperature (1950 F), using birch and charcoal, 2hours and 45 minutes). We burned dry birch for the first 2 hours and then switched to charcoal. From this experience we learned that charcoal is good for bringing the temperature up to pouring temperature but is totally inefficient from an energy and labour point of view. I settled on cooking oil because it was free and because coke is unavailable in Newfoundland.
2) One of you suggested adding the oil directly. We tried that but at high furnace temperatures it simply exploded without even hitting the bottom of the furnace. I think most of the energy just blew out of the hole in the furnace top as a towering 6-foot flame. We need to introduce the oil in a way that its energy would be released in a more controlled manner. Having it packaged inside wood seemed to be a valid approach.
3) I fry the wood out doors where, if the oil catches fire, it can do no harm. About 40 gallons of fat are held in a large stainless steel cauldron about a foot over a fire pit. The oil is heated with scrap wood to a temperature of between 375F and 400F. I use a candy thermometer to monitor the temperature. Over heating is prevented by raking burning wood out of the fire pit. Wood is loaded into a wire basket and lowered into the hot oil. The oil bubbles violently as the water in the wood is transformed into steam. The wood is cooked when the bubbling stops.
4) Some details. A) The wood is cut in short 4-inch chunks because the water can only escape thru the cut ends, and because I want to be able to introduce the oiled wood int the furnace without opening the top. B) Green wood bubbles violently and takes up to 6 hours to finish. By contrast dry wood bubbles gently and cooks in about two hours. C) I allow the oil to cool before removing the wood on the theory that as the wood cools it will suck oil into its pores. D) After cooking dry hard wood is impregnated with oil and increases in weight by about 25 percent. The weight of soft wood increases by 100 percent. By contrast green wood changes weight very little. I figure it simply exchanges oil for water.
5) In a few days we will be melting bronze and using oiled wood for the first time. I will post the results soon after.

[zora]

If you have access to unlimited used cooking oil, I have seen (can't remember where, probably somewhere around here: http://backyardmetalcasting.com/ ) this guy who bought an el-cheapo (harbor freight) paint gun and sprayed used motor oil through it to vaprorize it, then lit it on fire. Basically a nice blow torch, but apparently he was able to use it in his foundry and melt aluminum with it. I suspect you could probably do the same with cooking oil.

Bryon

[F.C. White]

Sounds to me like the bulk of your "free" fuel resource is used cooking oil. Why not simply create a forced air venturi burner where the oil being added to it will atomize as it reaches the burner's orifice? Navy ship foundries use a similar method using diesel fuel to this very day. You can easily get any light oil product to deliver enough heat to melt steel with the use of forced air and atomizing the fuel through the burner. Way less effort and a one time cost of make'n the burner, itself... which, in itself, isn't that costly really. Any machine shop can do it for you simple enough. Just explain what it is you're try'n to accomplish and they'll fix you right up.

[John Evans]

In reply to "Why not use straight cooking oil?" The question is valid but for a number of reasons I am going to stick with deep fried wood, for the following reasons.
1) the furnace that I have designed is set up for solid fuel.
2) I am a coward, atomized oil sounds like it could explode if improperly used.
3) Cooking oil is filled with junk and would have to be well filtered.
4) I am not technically competent to start messing around designing burners and atomized oil. It seems pointless when I know know that fried wood provides all the heat I need to heat bronze to pouring temperature.
5) I have an endless supply of wood for burning and frying.
6) Frying wood is such a simplistic process once you have built the cooker. All you need is 300 to 400 old bricks and a couple of 45 gallon barrels. (I will send pictures later in January 2007)
7) Cooking is dead simple and uses very little fuel. Once you get used to it cooking a batch of wood takes no more than an hour of attention spread through out a day.
8) I am a romantic, for 100's of years people have been burning out wax and melting bronze with solid fuel (wood and charcoal). Even though we have a big computer controlled electric kiln and a 1,000,000 BTU propane furnace I have always dreamed of building a wood fired foundry. Its fun, surely that is reason enough. But it is also cheap to build and operate. My foundry, with a capacity to pour about 130 pounds of bronze, has cost me about $1,500 dollars. Most of my cost has been for refractory cement and ceramic insulation. The rest is mostly recycled bricks, angle iron, sheet steel etc.
9) For the past month I have been reading "The Pirotechnia of Vannoccio Biringuccio: The Classic Sixteenth-Century Treatise on Metals and Metallurgy" It is amazing how similar his text is to what I have been building. Instead of cooking oil they used charcoal.
10) This is a work in progress. So far I have had 3 bronze melts and one burnout. None were total disasters nor were they perfect. After each attempt I have analysed the failings and redesigned and rebuilt the kiln and furnace. I do not want to publish pictures until I have worked most of the bugs out. One of the most important lessons I have learned is that the furnace needs to be portable. When you have flames shooting 8 feel out of the top of the furnace it is wise to melt bronze outside.
11) We are having a casting early in January.