Thursday, November 11, 2021

Charcoal, Part 1: Fuel

Erin wrote several articles about activated carbon for filtering and medicinal uses a few months back. This is good information, but there are more uses for basic carbon in the form of charcoal.

Most of us have used, or at least, seen charcoal grills for cooking. Charcoal is made from wood by heating it in the absence or lack of oxygen to drive out the water and volatile chemicals, leaving fairly pure carbon. Charcoal has several advantages over wood as a fuel for cooking and heating:
  • Easier storage. Wood has to be kept off the ground, covered from the elements, and neatly stacked to provide airflow for drying. You'll only bring in what you need to burn for a day in order to cut down on the pests and debris inside. Charcoal can be stored in a box, bag, or bin about anywhere until you need it. You'll have black dust instead of bits of bark, splinters, dirt, bugs, and other debris once you empty a storage space.
  • Longer storage life. Wood rots. Insects and vermin love woodpiles, as they provide shelter and food for them until they get a chance to move into your living quarters. Unless you are very careful with your storage, raw wood will only last a few years before it has degraded to a state where it's not usable as fuel. Charcoal, however, is close to coal in shelf-life, and without the water and volatile elements of wood, insects and vermin have no resources to exploit so it won't degrade as quickly. It is a bit more fragile than wood, so repeated handling will result in smaller pieces, but they'll still burn at the same rate.
  • Higher burning temperature. Pure carbon like coal or charcoal can burn at a higher temp because of the lack of water. Water takes a lot of heat to turn into vapor, and that heat is then not available for cooking or heating. Charcoal doesn't burn quite as hot as coal so it's safer to use in woodstoves.
  • More efficient. During the production of charcoal, the voids or empty spaces created by the removal of water and volatile elements form channels for combustion. This makes for a more uniform burn in a smaller space, which makes it easy to have a more efficient fire.
  • Cleaner burning. If you're smoking or drying meat for preservation, wood will impart a taste or flavor to the meat. Sometimes that is the desired effect; the use of hickory, mesquite, apple, etc. wood to impart a flavor is common, but if all you have available are cedar, pine, or some other wood with a disagreeable taste, you'll end up making dried food that not even the dogs will eat. The process of making charcoal removes all of the volatile compounds that will provide flavor, so the source wood isn't a factor. You'll end up with about the same amount of ashes as wood, but without the clinkers that coal will produce.
  • More uniform heat generation. Wood is never uniform, so you're going to have differing heat coming from different spots at different time as it burns. Look at the end of a log and you'll see the variations in quality of fuel: bark, soft outer layers, harder inner layers, knots, rot, etc. Charcoal production takes away most of the variations, leaving a more uniform fuel for a more uniform fire.
  • Higher energy density. Since charcoal doesn't have the impurities found in wood, you can get about three times the heat out of a pound of charcoal versus a pound of wood. While less dense than wood, the higher energy content per pound of charcoal makes transportation more efficient as well. For a scholarly explanation of the numbers, here's a report out of Africa comparing the two. Reading through examples from areas that lack our infrastructure is a good source of ideas for how to deal with the failure (or lack of) said infrastructure.
There are some downsides to charcoal, though, especially if used for cooking. The main detriment to using charcoal for cooking is the same benefit it has as a filter or medicine: its adsorption capacity. Storing charcoal near a source of strong odors will allow those odors to permeate it, and those concentrated odors will be released when you burn it. I've seen some very good steaks ruined by being cooked on a charcoal grill because the charcoal was stored for a long time near petroleum products. Nobody wants a T-bone that tastes like diesel fuel. 

Charcoal has many uses, so don't get stuck on just the fuel or filtration aspects. I'll describe a few other uses in my next post.

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