why charcoal burns so hot even though it’s already been burned
In: Physics
Because it’s already been burned. It just hasn’t been burned all the way. When you ignite charcoal, you’re finishing the job after all the hard work has been done
Wood is mostly made up of long complex hydrocarbons molecules. This is pretty good for a tree since it’s what makes wood so tough, but long complex hydrocarbons don’t burn very efficiently. In order for them to act as fuel, they need to break down into shorter hydrocarbons, which is a process that happens as the molecules heat up from the fire.
As well wood, even dry wood, as a lot of moisture in it. Sap etc. Light it on fire and that moisture also needs to heat up and boil off, which take heat away from the fire.
This is OK and wood isn’t that bad fuel source, but both those facts limit the amount of heat that can be produced. The reaction can only break down those long molecules into nice burnable short ones so quickly and you can only boil off the moisture so fast.
If you want to make wood into a hotter burning fuel you need to drive off as much of that moisture as possible, and ideally break down those hydrocarbons into shorter ones. You can do both by heating the wood up, but not letting all of it burn away. Very conveniently fire is good at heating things up and wood is pretty flammable. When you burn wood in a charcoal kiln, you burn much of it as fuel to convert the remainder into charcoal. If you don’t manage the temperature inside the kiln well, it either wont turn into charcoal (to cold), or it’ll all just burn away on you (to hot).
After letting it burn, you smother the fire and once it’s cooled down whats left is a bunch of wood that’s gone partway through the process of burning. All those long hydrocarbons that make wood so tough have broken down leaving a much more brittle material, and all the moisture boiled away making it both bone dry, much lighter, very porous and unable to rot.
All the stuff that slows down the reaction has been done so when you reignite the remaining charcoal it can burn much more quickly, and thus produce much more heat.
Also while the charcoal burns much hotter, producing charcoal is not very efficient. Even in a really good kiln with good dry wood to start with, more than half the possible energy you could have gotten out of the wood is spent in producing the charcoal. A poor kiln with bad material will lose north of 80%.
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