Wood Furnace

[m_brothers]

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.

[R Funk]

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.

BE VERY CAREFUL! MAKING CHARCOAL PRODUCES CARBON MONOXIDE! AS WE ALL KNOW THIS IS A VERY TOXIC GAS.

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.

[fossilmaniac]

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

[Glenn]

fossilmaniac
Go to the top of hte forum page and click on User CP
Click on Edit profile
Go to the bottom of the page and enter your location and save.

We would like to know where in the world your located.

[Glenn]

R Funk
Your post is excellent and has been added to the wiki. Thanks.

[BeaverDamForge]

Fuel For The Fires: Charcoal Making in the Nineteenth Century

Good Luck!

[Ice Czar]

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

[JohnW]

m_brothers,
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.

[BT]

Here is another site with some info
Table of Contents

and a site with some info on the Missouri kiln

News Tribune

[m_brothers]

Okay. I will read through all of these articles and figure out where to go from there. You guys have been very helpful. Thank-You.