what are the differences between charcoal made from different species of wood?

[Ericcc]

I watched a youtube video from an English guy that was making charcoal for a wood gasifier engine -- if anyone is interested I can find the name -- and recently more or less imitated his set-up for making charcoal, and it's working very well for me. Basically I got a friend to cut the top of a 5 gallon propane tank out and cut a lid out from a second tank cut a little bit wider (i.e. larger diameter) so that it sits on top of the first one with a little overlap all the way around. And since I already have a water stove, I've just put that propane tank filled pretty tightly with chunks of dried oak in my firebox and kept a good fire going for a few hours straight, and then after the fire has died down I've had really nice looking charcoal. So that process is working very well for me.

What I'm wondering now is how charcoal from different species of trees would differ. What differences would there be and would charcoal from some trees be better for some uses and charcoal from other trees be better for other uses? I'm mostly just thinking of grilling at this point, but I'd be interested in other uses of charcoal, too. I hewed a few yellow pine (shortleaf) beams this winter, so I have a bunch of chunks of pine that would be a nice size for turning into charcoal, but I imagine yellow pine would be very different from oak charcoal. Anyone know what to expect from different species?

 

[Isaac Carlson]

I have never made charcoal before on purpose, but I would imagine the density would be different. I know some charcoal smells better, so species might be a factor there too.

 

[SpaceBus]

If you have a blower handy you could make a charcoal forge or crucible. After I finish a hundred other priorities I'd like to make some aluminum bronze using only charcoal as fuel.

 

[Ericcc]

Here's the set-up I've been using that's working great, by the way. It's a limited quantity I can make at a time, but I'm still making more than enough charcoal for my own use and to give away to friends that grill with charcoal, all just as part of heating my house and hot water.

 

[Stinkpickle]

I have never made charcoal before on purpose, but I would imagine the density would be different. I know some charcoal smells better, so species might be a factor there too.

Agreed. If it’s properly carbonized, density should probably be the only thing left.

 

[ABMax24]

I'm intrigued, I wonder how that would work with pine? Softwoods are generally avoided for direct contact with food because of the off flavours the high lignin content imparts. Now if that was burnt off in the process of making charcoal maybe it would be useable as cooking fuel. Assuming there was enough mass energy left in the charcoal to be worthwhile doing.

 

[Isaac Carlson]

I'd rather use the pine/softwood to cook off the hardwood rather than the other way around.

 

[SpaceBus]

I'm intrigued, I wonder how that would work with pine? Softwoods are generally avoided for direct contact with food because of the off flavours the high lignin content imparts. Now if that was burnt off in the process of making charcoal maybe it would be useable as cooking fuel. Assuming there was enough mass energy left in the charcoal to be worthwhile doing.

There absolutely is. Softwoods charcoal has been used for centuries to forge weld iron, fire ceramics, and other things. However, hardwood charcoal is usually the choice for cooking. Probably for the same reason we like it in the stove, long slow heat release.

 

[Ericcc]

I don't really know what tar is, but I wonder if even if the charcoal were the same once it was fully carbonized no matter what species of wood it was made from, whether tar or anything else would collect in the bottom of the tank my charcoal is in if I were to use pine. In other words, even if wood species doesn't make any difference in the charcoal other than density, I wonder if everything that comes out of the wood will be gasified and burnt up regardless of species. Does anyone know how to make tar on a small scale? Are there other useful wood extractives that might potentially be made together with charcoal (that would either collect in the bottom of my tank or that I could potentially be collected somehow from the gases if I could collect and condense those gases instead of burning them off?

And if the only difference between charcoal made from different species is density, I wonder how that affects different uses. Does less dense charcoal burn faster and hotter? I don't know enough about grilling to even know why that would be undesirable (other than the charcoal simply needing to be replaced more often), and I'd assume the heat could be adjusted by simply adjusting the total quantity of charcoal at any one time.

And if the only difference is density, there's potentially a bigger difference between some oaks -- I'm using some kind of red oak now -- and a really dense hardwood like apple or persimmon than there is between oak and pine. (Southern red oak has a typical density of 42 lbs/cu3 compared to 35 for shortleaf pine and 52 for apple or persimmon, for example.) So if oak is that much better for grilling than pine, maybe I should be making all my charcoal from persimmon instead of oak. I obviously have lots of questions and hardly any understanding of what I'm doing yet.

And if the least dense hardwood is best for some uses (like forging), would paulownia charcoal (density of 18 lbs/cu3) be far superior to yellow pine for those other uses? I guess I'm assuming that the density of the charcoal corresponds to the density of the dry wood, but maybe that's not even true.

 

[SpaceBus]

I do know how to dry distill tar. You make a setup like Ericc has posted in his photo, but there are a few differences. You would first need a large steel can, like a coffee can or large tomato can. Some cans have a liner, so best to burn it out before hand. Dig a hole and place the large open top can inside. Fill up a retort like the one Eric made, but instead of having the hole in the lid, put a small hole in the bottom. Place the retort hole side down on top of the buried canister. You want the hole a bit larger and deeper than the can so the retort is also mostly buried. Build a fire on top of the retort and burn it hot and fast for many hours. Let the hot coals build up on top of the retort if you can. let everything completely cool and dig it all up. The cannister at the bottom should have collected the VOCs as they condensed after the fire went out. Many native peoples used similar processes to produce various tars for glues and antiseptics. If you use all pine, you will get a raw turpentine type material. Birch bark will produce birch tar, and so on and so forth.

My description is probably lacking, but merely meant to give an idea of how it works. I'm sure there are tons of videos on youtube. If your goal is to produce only charcoal the system Ericc has made is hard to beat. The hot gasses come out of the lid and create a decreasing O2 environment inside the retort where the wood is. I have a few smokeless firepits that would probably work in a similar way, just need to find some cheap pots with lids!

 

[Ericcc]

@SpaceBus So, if I'm interpreting what you said correctly, tar is made by condensing the gases that I'm currently burning off. Have I got that right?

 

[SpaceBus]

@SpaceBus So, if I'm interpreting what you said correctly, tar is made by condensing the gases that I'm currently burning off. Have I got that right?

Yes, that is the idea. I found a thread on the Bushcraft USA forum on the topic and the process they use is the one I described above. @peakbagger posted about a company a while back that uses a more refined process to make liquid biofuels from woody plant stock.

 

[peakbagger]

Wood is mix of cellulose fibers held together with lignin with some alcohol and water mixed into the lignin. Back when the US was a colony the British wanted our tall trees for masts but they also wanted pipe tar from southern pines. The "tar" was used for waterproofing and other things. They called the products naval stores https://www.britannica.com/technology/naval-stores. Once oil started getting pumped most o f the pine based naval stores were replaced with petroleum based products.

Cellulose wants to burn if there is oxygen around so if you keep the oxygen out the picture and heat the wood it will break into its parts. The cellulose turns to carbon which is the coals. If you take the cloud of vapor, it will condense at different temperatures and different constituents will separate. If you heat it further with the right process, pressures and catalysts you end up with cloud of elements and you can reform them into a lot of different end products. That is what the Germans had to do to make synthetic fuels in WW2.

A typical backyard retort will give off the cloud of vapors, usually the wood alcohol leaks out so the result is mixture of lignin and water. The alcohol is usually the source that goes boom if the vapors get sparked off by the fire. Boil off the water and you get "tar". Getting rid of the water in the first place is the way to go with dry wood as it take a lot of energy to get rid of it afterwards.

The Ensyn renewable fuel oil is basically the "tar" stabilized with other chemicals to keep it stable. It had a relatively short shelf life and we constantly needed to recirculate it to keep it blended. If it leaked out, it fairly quickly turned into a sticky molasses like product. I think it was made with pre dried woody feedstock. It just could not compete with cheap oil so its a niche product.