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Wood Furnace

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It's winter right now and there is a lot of snow, so all of the wood is wet. Wood usually takes a year to dry out for it to be "safe" to burn in your fireplace according to some regulation. I use charcoal for my fireplace, as the nearest coal is 117 miles away and costs $22 a bag. Centaur Forge, in wisconsin. And we live on a good chunk of forest, and I've been doing some logging and make small pieces that I will use to make charcoal. What I wanted to know is if I could make a furnace out of plywood -- it's okay if it burns a little bit to -- and pile the wood up inside of it and have two vents one on each side and have two fires going with the smoke and heat being vented into the plywood furnace to dry it out and get it ready to make charcoal. Is this a crazy idea or should I dry it? Any better ways or ideas? It's oak, maple, and pine wood if anyone is wondering. Dimensions are gonna be an 8 foot cube

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Making Charcoal is just the burning of wood with little oxygen available. Nothing fancy is needed from what I have read. You can dig a hold in the yard, fill it with wood, start it on fire and cover it over. Mass production is done in large piles of wood and covered with dirt or sod after starting the center on fire.

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M-brothers........I don't know if I can help or not, but here goes.........
In the winter, with rain and snow, all wood usually is wet. Wood that has been lying on the ground will be saturated...and difficult to burn.

We heat our home with wood, and a couple of times ran out in February. Not a good time to have to find 'dry' firewood and cut it.

A dead tree that is still standing or dead limbs which have not laid on the wet ground will offer the driest wood.

The problem with using really wet wood to make charcoal is that the burn is often so slow(using the direct method), that the outside of wood chunks burn into ash while the middle of the wood is 'frying' and still spewing water. result.........little charcoal.

You mention a 'plywood furnace'........sounds sort of like a drying kiln as you desribe it.
I wouldn't know how to go about making something like that.
Sounds like a difficult project.

Hope this helps.
Be careful!

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if I could make a furnace (8 foot cube) out of plywood -- it's okay if it burns a little bit to -- and pile the wood up inside of it. have two fires going with the smoke and heat being vented into the plywood furnace to dry it out

Cut, split, and stack the firewood. Stack it two rows deep and cover it with clear plastic leaving the ends open. This will keep the wood from getting wet and acts as a solar collector to dry the wood.

Collect the limbs and cut them into 4 inch lengths or chip them. You can forge by using raw wood. It takes a lot of wood to keep a good bed of coals going the the radiant heat is a serious factor to deal with, but it can (and has) been used as a forge fuel. Not efficient, but it works.

Buy the coal and be happy.
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Hers a good link on making charcoal, lots of folks use this method.

Making Charcoal

This web link is how I made charcoal when I first started smithing. It works real good, if you can get good coal from centaur forge then what are you thinking of making charcoal for? Good smithing coal is so much superior to charcoal. You will burn up a lot of charcoal compared to coal. Charcoal is much better than bad coal though. If you are going to blacksmith full time, and use charcoal, then you should find someone to make your charcoal for you, cause you will spend a lot of time making charcoal.
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Someone mentioned in another thread that commercially charcoal is made by the starting the center of the pile of wood on fire and then putting dirt on top of it. Is this true? I posted a differnet thread about drying out wood. Right now I've got about 400lbs of chopped up wood. What I was wondering is, is there a faster way to make it or a better way to make, like the commercial way other than the indirect method.

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Charcoal is made by the controlled combustion of wood in an atomsphere with limited or no oxygen. This process is called pyrolysis and most commomly occurs between 600 F and 1200 F for wood. Simplistically pyrolysis consists of driving off all material from the wood except carbon and ash (non combustibles) via heat. The material driven off is principally moisture and hydrocarbon type materials and are referred to a volitales while the remaing material is fixed carbon and ash. The volitales results in the majority of the smoke and flames we see when we burn wood. The fixed carbon is what we generally see as the "coals" remaining after the flames are gone. However in a fire were the oxygen supply is uncontrolled, such as a campfire much of the fixed carbon is burnt along with volitales due ample oxygen supply. When we make charcoal we desire to preserve all the fixed carbon possible as this is the charcoal.


The process can be divided into to 2 basic processes, direct and indirect.

The direct process is a controlled burning process where the wood is burned in atmosphere with limited oxygen and some of the wood and fixed carbon is burnt, producing heat for the pyrolysis or charcoal making process. This process would include all processes where a fire is actually lit in the charcoal producing wood and combustine is controlled by limiting air supply (oxygen) to the wood. This is less efficient as some of the wood goes to fuel the process instead of being converted to charcoal. It is the most common method of charcoal production in most parts of the world.

The indirect process involves heating the an enclosed container such as a barrel as shown in the link included earlier in the thread. It is a superior process as none of the fixed carbon, the product we want and call charcoal is burnt if the continer is indeed air tight. The off gases from the pyrolysis can be burnt to provide heat for the process and in some commercial applications are condensed for chemical making applications.

The process of making coke from coal is pyrolysis and a very similar process to making charcoal excepting the scale of production and specialized equipment utilized for the making coke for iron blast furnaces.

Historically charcoal was made by carefully piling wood and covering with dirt and leaves leaving a vent hole in the middle. The "coaler" would start the pile on fire and live with the pile for several days carefully tending the pile, controlling the air flow into the pile by manipulating air vents (holes in the dirt/leaf cover) to control temperature. After their judgement indicated that the process was complete they would completely seal the pile from air infiltration and allow it to cool. When it was cool the charcoal was removed from the pile. This type of process is still used in 3rd world countries.

This process was improved with permant concrete bunker type structures with steel dampers replacing the dirt covered piles of wood. During the 1930's,40's & 50's the states of Missouri and Wisconsin in particular encouraged the use of this structure to produce charcoal. These structures were approximately 30' X 60' in size and 12' high. They were piled full of wood, ignited and the temperature and cumbustion process was controlled by limiting air supply. In the lower midwest they were referred to as "Missouri Kilns" They produced large amounts of pollution in the form of unburned volitales (smoke) and at one time were the largest air pollution source in Missouri.

More recent technology includes rotary kilns or hearths which converted sawdust and planer shavings to charcoal for briquetting purposes.

I would suggest that using the barrels or small concrete or brick kiln 3' x 3' x 3' or so would be the prefferred technology. Constructing a pile of wood covered with leaves and dirt would work but will require more attention and if the covering of dirt fails and air is addmitted in a uncontrolled manner, you have just created a large bonfire, not a charcoal producing system.

Building a fire and qenching with water has 2 problems.
1) Allowing the fire to burn long enough to pyrolyse the inside of the wood will result in significant loss of fixed carbon (charcoal)due to the readily available oxygen for combustion.

2) You have almost no control over temperature and burning paterns. This will result in burning much of the fixed carbon that you want for charcoal

A sealed or semi-sealed system will allow you preserve as much carbon (charcoal) as possible.

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Before I found a source of coal / coke, I acquired old pallets. Many are hardwood of some type and I just cut them into chunks with my skill saw and use them. Works great but like another one suggested, it does take alot of wood so make a big pile before firing up the forge. Many shops are happy for you to get rid of their old pallets and will gladly let you have them or if you have a silver tongue, pay you to haul them off. Never overlook the obvious and free. fossilmaniac

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first, R Funk xxxx fine answer ;)

second an expansion on your

The off gases from the pyrolysis can be burnt to provide heat for the process and in some commercial applications are condensed for chemical making applications.

Handbook of Biomass Downdraft Gasifier Engine Systems, Solar Energy Research Institute of course its now known as the National Renewable Energy Laboratory a hop skip and a jump from me ;)

employing a downdraft gasifier as a charcoal and energy generator is my ultimate goal for the home forge
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I believe jayco and Glenn are on the mark, and here's a couple other things.
-- For direct burn, split wood to 1" or 2" diameters, I would say 10" lengths (Glenn said 4") but length won't be as important. Larger diameter wood can burn for a long time and still be wood on the inside and charcoal on the outside.
-- With most versions of dirct burn, slow burn with less oxgen is no help. The key is stopping the burn after charcoal but before ashes for as much of the wood as possible.
-- Yip, wet wood is very slow to burn (with direct burn) but wet wood will dry quickly (maybe 2 weeks) when spit and stacked in a dry place.
-- Yip, as strech says, making charcoal is a time consuming thing. It's not entirely free, you need some equipment.

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well maybe not "all" of them, the one I linked is a book :P

a gasifier isnt really a charcoal "production" unit, unless its run as a batch mode and interrupted

if you are interested in it you might want to build a slightly smaller version first

this paper would help with "tuning" a gasifier for more charcoal

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Right now I've got about 400lbs of chopped up wood.

While 400lbs of wood seems like a lot, it really is not. Also, you lose some of that mass in the coaling process (I can't remember exactly how much, and I'm sure someone will call me on being to lazy to look it up). Personally, if I were going through the trouble and mess to make my own charcoal, I would take it in one fell swoop and burn down at least a full cord or so at a time (if space, supply, etc. allowed for it). As far as the charcoaling process, I CAN offer this.
Jack Daniel's charcoal filters their whiskey. When I took the tour of the distillery, they explained how their charcoal making process works, and I took the initiative to ask a few more questions of the tour guide. They cut and/or split the pieces of (I believe) maple so they are dimensioned about 1-2" by 1-2" by X length. They then rick them up log cabin style. They add a little flammable liquid (Distilled alcohol incidentally) and they light the pile up. As soon as it looks like the wood has coaled (they are professionals and know when this is), they hose it down. That simple. Split, stack, burn, hose down. From what I saw of the charcoal, it seemed to be pretty well coaled, and as far as I can figure it is the relatively small cross section that allows it to coal up so well in so short of time (my speculation).
-Aaron @ the SCF
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I know you will lose quite a bit if you just pile it up and burn it. That is why the charcoal burners put a 24 hr watch on the pile of wood for a week or 2 for the size of piles they used to do. You can't let it get away or you have ash and that doesn't work very good in a forge. In the retort you lose none of what you put in the retort. You just lose what you used to heat it with.

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