True or False: You make charcoal by heating organic matter such as wood in an oxygen poor environment?

Charcoal Pit
Charcoal pit. Image credit: sarahemcc
Charcoal Pit

True. Charcoal can be made from anything containing carbon. Traditionally wood has been the raw material used to make charcoal. Wood consists of three main components: cellulose, lignin and water.  These compounds are composed almost entirely from atoms of hydrogen, oxygen and carbon.  Charcoal is made by removing the hydrogen and oxygen in the wood while leaving just the carbon.

Making charcoal consists of 4 steps.

1.)    Drying the wood to be made into charcoal.

2.)    Heating the wood in an oxygen limited environment.   Limiting the oxygen keeps the process from turning into full combustion which would reduce the wood  to ash. As the wood heats the following changes occur:

  • At 100°C the chemical bonds begin to break.
  • 100° to 200°C, noncombustible products, such as carbon dioxide, traces of organic compounds and water vapor, are produced.
  • Above 200°C the celluloses break down, producing tars and flammable volatiles.  If these are mixed with air and heated to the ignition temperature, combustion reactions occur.  That is why it is important to keep the environment oxygen poor.
  • Above 200°C the lignin in the wood starts to breakdown in an exothermic reaction. This releases additional energy which can cause the temperature of the wood to rise to 400°C or more. 

3.)    The wood should continue to be heated to between 450- 500°C.  A temperature of 500°C gives a typical fixed carbon content of about 85% and a volatile content of about 10%. The yield of charcoal at this temperature is about 33% of the weight of the oven dry wood. 

4.)    The wood is allowed to cool in an oxygen limited environment to prevent the oxidation (combustion) of the remaining carbon.

 

Charcoal pit sketch by Nancy Aldrich
Charcoal Pit

Traditionally this was done by piling dry wood into a dome shaped mound.   The mound was then covered with smaller branches, leaves and finally dirt.  Covering the mound limited its exposure to oxygen. A flue was left open in the middle of the mound to introduce hot coals and start the mound to smoldering.  The shape of the mound is important because as the wood transforms to charcoal it shrinks in size.   This shrinking inevitably causes holes in the outer covering of dirt which allows more oxygen into the mound.  These holes have to be plugged quickly or the mound will catch fire and all the potential charcoal will go up in smoke.  Planning for the shrinking of the mound helps to minimize the work in plugging holes as they appear.   The key is to keep the entire mound smoldering but not burning.  This requires constant attention.  If there isn’t enough oxygen the mound will cool too much and if there is too much oxygen the mound will catch fire.  The Swiss have been making charcoal this way since the Middle Ages. It might take two men three weeks to build the mound of 700kg (1500lbs) which will then burn for 12-18 days.  The charcoal burner must spend the entire time by the mound tending to it as it smolders.

 

Charcoal Barrel
Charcoal barrel

A more modern method (and one that requires less attention) is to seal up the wood in a fireproof container with a small hole in it so that it can vent the gasses that are produced and then place the container in a fire or kiln.   This allows more attention to be paid to the fire that is providing the heat without having to worry that the wood being charred is being exposed to too much oxygen.  Here a steel barrel has been converted to a charcoal kiln.  The wood would be loaded into the barrel and then it would be sealed up.  A fire would be lit underneath the barrel to provide the necessary heat.  Note how it vents the gasses from the barrel back into the fire with the tube that comes out of the barrel.  This set up could be made much more efficient if the barrel were surrounded by earth or bricks to help trap the heat.   (Photo from http://www.instructables.com/id/How-to-Make-some-Charcoal/)

 

Odd Notes: The process of driving off the hydrogen and oxygen by thermal decomposition is called pyrolysis.  Pyrolysis is the same process that is used to turn coal into coke. It is also used to make carbon fiber. When carried to an extreme so that it leaves mostly carbon residue it is called carbonization.

 

References:

http://www.reuters.com/article/2008/09/03/us-swiss-charcoal-idUSLQ29563720080903

http://www.fao.org/docrep/X5328e/x5328e05.htm#TopOfPage

http://www.fpl.fs.fed.us/documnts/pdf1989/levan89a.pdf

What secret don’t survival books teach you about making fire with friction?

Hand Fire Drill
Example of fire by friction image by Steve Sanford for Field and Stream. 
Hand Fire Drill

Answer: The type of wood used for the spindle and hearth board is crucial to making an ember. This is an often overlooked fact in many descriptions of making fire by friction.

What you are trying to do is create a very fine wood dust and then heat it to between 371-426°C (700-800°F). When that occurs, the wood dust starts to glow and it forms an ember much like the tip of a lit cigarette. That glowing ember can then be coaxed into a flame by adding it to a bundle of very dry tinder and blowing.

There are several ways to try to accomplish this; bow drill, hand drill, fire plow, or fire saw. They all have one thing in common. The type of wood used is crucial to making an ember. It comes down to the quality of the wood dust formed during friction and the ability of the wood to retain the heat where the dust is forming. Low density woods (softwoods) don’t transmit heat as well as hardwoods and therefore they keep the heat concentrated near the wood dust.

Storm from Primitive Ways has personally made hundreds of embers by method of the hand drill using various combinations of wood. He has created a chart of the combinations (PDF) and the effort it took to create an ember (if it was possible at all). It is important to note that not every combination of wood will successfully create an ember.  So if you are not having success it could be that the combination of wood you have chosen won’t work.

 

References:

Storm's guide to using the hand drill should get you started http://stoneageskills.com/articles/handdrill1.html