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I Forge Iron

About charcoal

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All through my village everyone who ever owned a plow or went to the smithy to get a tool fixed or made said that the blacksmiths always asked for charcoal made out of plum trees (the trees that grow plums - not sure if there's an English name for it). The blacksmiths here always required that the client bring his own charcoal.

I recently made a batch of charcoal out of plum wood by surrounding a cylinder made of random tins with earth and lighting a huge fire in it. It was about the size of half of an oil drum and had an air intake at the bottom. When the fire was going strong ..I covered it and sealed every hole with wet earth and let it smoke away for 3 hours. 70% of the wood turned to charcoal.
It burned good but after 5 hours of forging I got and amount of clinker out similar to 3 baseballs.

Does anyone have any recommendations on how to improve my system?
And has anyone here heard of cherry and plum tree wood as being good for charcoal?
Do you think that the incomplete charring of the wood made my forge produce so much clinker?
And what is clinker anyways? How can one stop it from forming ?

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clinker in all the impurities burning. i got about the same ammount when i used homemade charcoal. there is really no way of stoping it either.

i think that homemade charcoal may be durty or somptinh for it to do that but i am not shure.

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Was it clinker? I've never had any of my homemade charcoal do that, although it isn't from plum trees, just random pieces of wood on the farm. Was the wood charred all the way through? Were there any metal that would have melted, such as nails in the wood? Was it hard like strong glass, such as clinker gets, or just packed ash?

Any wood will make good charcoal, hardwoods work the best because they are denser so you get hotter with a smaller fire and use less fuel, but I've welded smaller pieces (~1/4"-7/16") with softwood charcoal. Just went through a bit more fuel in the time to do it.

Edited by easilyconfused
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If you can find one a 55gl. drum with the removable lid makes an excellent charcoal retort.

any clinker you got was probably dust and dirt from your coaling method. A clean retort will cure that problem, however there is a VERY small possibility dust collected as the wood grew might be doing it.

There are a couple possibilities for why all the wood didn't convert (pyrolize) the first that comes to mind is it was too thick. The rule of thumb is at least one dimension no larger than 3" or 75mm. for example a 2 x 12" x 6' long is fine because one dimension is under 3". A 4" x 4" x 4" is too big.

What happens if you use wood that's too thick is too much burns completely before all of it is converted to charcoal. For this reason, another rule of thumb is to use wood that's all about the same size so it all gets finished at the same time or the small pieces will burn away before the larger ones are done.

The other thing for incomplete combustion that comes to mind is you closed the air off too soon or too tight, it needs a little air or it just goes out and cools.

The method you're using is called "semi-direct" and is half way between the "direct" and "indirect" methods.

Direct means the wood you're converting is used as fuel to provide heat for the process. For example, raking the coals out of a campfire and quenching them is the simplest way to make charcoal there is.

The "indirect" method calls for putting the wood for conversion in an air tight container and heating it with an outside source. For example packing split wood in a sealed drum and putting it on a fire till it stops smoking is about the simplest indirect or retort method.

The drum can't be perfectly air tight of course, the volatiles being driven off have to have a way to escape and when conversion is complete pressure has to be able to equalize or air pressure will crush the drum as it cools.

I pull the 2" bung from the drum for the vent and when it stops smoking I stuff ah wad of fiberglass insulation in it to stop the air from getting in.

Another method is to roll the drum out of the fire and turn it over on loose dirt or sand and bury the rim to keep air out.

The most efficient method is the self sustaining indirect method. For this you need a double chamber, the second one has to be a couple inches larger than the drum (for example) with several inches clean under the drum.

You remove the 2" bung and using pipe fittings plumb the vent so it's aimed back into the air draft. Then you pack scrap wood under the drum and light it up and keep the fire going till the gasses from the vent start burning. Once that happens the volatiles being driven out of the wood will provide heat to keep the process going.

When it stops burning from the vent close the air draft and stack so no air can enter and burn up your charcoal.

Once the drum is cool you can open it up and collect your charcoal. Be VERY CAREFUL how you store the fresh charcoal, the smallest ember will light the whole pile once it gets a little air. Just because the drum is cool does NOT mean it's out! Charcoal can keep burning for days with almost no air and you do NOT want the pile to start burning after you've gone to bed.

Keeping it in an air tight drum outdoors is probably your safest bet.


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I would say dry wood works better, but that's not a necessary condition. It's better to have consistency in the wood as much as possible so that it all gets done at the same time, at least in direct burn methods. Smaller, dryer pieces of wood will burn to ash while larger wetter pieces still aren't charcoal.

Efficiency isn't everything. Burn enough wood and you'll get some charcoal.

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Yes, like all wood burners dry is better. Peeled is sometimes better, say if you have birch like we do.

On the other hand wood that produces a lot of volatiles from the bark make a better self sustaining reaction.

On the other other hand you could stuff the bark under the container for the initial heat and not have to cook it out of the retort.

It is a simple process but it's time consuming, requires constant attention and a good dose of common sense. Of course your results will improve with experience too.

Remember, process and practice aren't necessarily the same thing. Simple in principle like an atomic bomb can be much more difficult in practice. It goes the other way too, some technically difficult things turn out to be really simple in practice, like sourdough bread. Fortunately coaling isn't technically difficult, it just requires a lot of attention and work.


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Boy, I got into this thread at the right time. Since we are talking Charcoal, I do have a question. My shop is not considered air tight. Can I burn wood charcoal in my forge without a chimney while inside the shop ? When I tried a little of the charcoal out, I dont see much smoke at all and it seems to burn clean.

PS: Good post Frosty I just got my 55 gallon drum and am getting ready to try my first charcoal burn.

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If by, "not considered air tight," you mean three walls, sure why not. If on the other hand you do have four walls and a roof you'll kill yourself in short order.

First it'll deplete the oxygen quickly and oxy is good.

Then there are the combustion by-products like CO2 which will quickly screw up your respiration reflex leading to unconsciousness and worse eventually.

Then there's the big KILLER, CO "carbon monoxide." While not directly toxic it does attach itself to the hemoglobin in your blood more readily than oxygen does, leading to death by anoxia.

Of course you can pump enough air through the fire to prevent CO production but then you get to breath other wonderful things like nitrous oxide and nitric acid. Of course in the case of nitrous oxide you'll die laughing and the nitric will drive you out of the shop very quickly.

No, there's no safe way to run a combustion forge of any kind indoors without adequate ventilation. A couple CO monitors are a good idea too no matter how well ventilated the shop is.


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You need a fairly large volume of air moving through the shop if you don't have a chimney. There is more to burning fuel than smoke. The is carbon dioxide and carbon monoxide both of which will kill you if built up to enough concentration. And the carbon monoxide will bind to the hemiglobin in your blood and reduce the amount of oxygen your body recieves for hours or days. There are other products of incomplete combustion (such as if you have a reducing fire) that are harmfull. If you've ever got dizzy or a headache when forging you may be getting poisoned from the fuel burning (other possibilities are heat exhaustion or dehydration). And many of these products are colorless and odorless, you don't know you're breathing them untill you get sick or die.


edited to add: Frosty you beat me to it :)

Edited by son_of_bluegrass
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