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Dan O'Connor

Making Charcoal

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I thought I had it figured out years ago. Making charcoal that is.

 

I even told the world about it here.

 

Get a barrel. Run pipe out of it and back under it. Build a big fire under the barrel. Cook off the volatile gases until they ignite and continue cooking the wood with its own gases until it stops. Let it cool and Voila! charcoal.

 

Everybody else thought it was pretty cool as well. People even started cottage industries in South Africa using my method.

 

But guess what. There is more to charcoal making than cooking it with its own gases with a big fire.

Now ain't that a surprise. :rolleyes:

 

Turns out there are quality specifications for charcoal.

 

Things like retained volatiles, carbon content, friability, percentage of fines etc.

 

This first came to my attention last November when I visited a swordsmiths shop in Nagano.

 

His apprentice was cutting charcoal and it twern't nuthin' like the stuff I had been making. It was made from pine same as mine but that is where the similarity ended.

It looked just like the section of log it came from only black. There was a metallic shininess to it and it had a ring to it when I rapped it on my knuckle. As he cut, the pieces came off in one piece with very few little bits and no fines flying everywhere. When I rubbed it on my hand it left almost no dust.

 

I could not crush it between my fingers and when the pieces where jostled together there was, for want of a better word, a crystal sound (TINK)

 

In contrast the stuff that came out of my barrels was barely recognizable as wood with big cracks and lots of small pieces and fines. It had a dull color to it. There was no resonance when struck. Just a dull "thunk". I could easily crush it between thumb and forefinger. Hell sometimes it fell apart just picking it up. And dust-Holy Moly what a mess.

 

When I cut it sometimes 10% or better was lost to little bits and fines.

 

The real proof of the pudding was that his fire seemed much hotter and BIGGER with a hint of blue flame to it when air was pumped in.

 

So after a bunch of research and then a week and half in Chicago this month at the IMTS trade show, I started testing this week.

 

Tell ya what I found out tomorrow. Kind of sleepy right now.

 

No surprise-it is all about temperature and air control.

 

testburn2.jpg

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that sounds very interesting..

- if you were into smelting, i'd think it would affect that area, awell

 

do you have pictures of your current apparatus

 

 

thanks

Greg

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that sounds very interesting..

- if you were into smelting, i'd think it would affect that area, awell

 

do you have pictures of your current apparatus

 

 

thanks

Greg

Greg

 

Smelting is indeed in the picture but a bit of a road to go before I get there. Orishigane at the least.

 

Here are some pictures of what I have been using. The pictures don't show it but a lid was put on to close up the barrels.

 

barrel2.JPG

 

kilnfront.JPG

 

staterfire.JPG

 

kilnfire.JPG

 

allchar.JPG

 

frontclose.JPG

 

Now that I know what I am looking at I can tell that the charcoal got way too hot and the the air was not properly shut off before it cooled down allowing it to burn inside the barrel after it finished "cooking".

 

This is why I went through charcoal so quickly when forging.

 

It was mostly air and carbon only.

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I wanted as controlled environment as I could get so I used a paint can, flue thermometer to 1800F, and an ash bucket.

 

I used way more fuel that I created but the point was to gather information.

 

setup.jpg

 

setuploadcan.jpg

 

1st66C2.jpg

 

This first burn I overloaded the fuel and it got too hot.

 

1stsmoke.jpg

 

1st700C.jpg

 

1stpegged.jpg

 

I don't know if you can see it but in the last picture the temperature is pegged at over 1800 degrees.

 

In the end I had flames coming out around the temperature gauge so I pulled it.

 

Resulting in this picture.

 

1stflames3.jpg

 

So, I have no idea what the temperature was.

 

Whatever it was it was too much too fast as can be seen by the resulting charcoal pieces.

 

1stand2ndcharcoals2.jpg

 

1stcharcoal.jpg

 

It is similar to what I had already been making .

 

Soft, dull, crumbly charcoal that looked like it had been blown up.

 

One thing I did notice was that there was definitely a correlation between the internal temperature and whether or not the gases ignited.

 

I always thought that you needed an external ignition source to light the gas.

 

Not true. at least not in these tests. If the internal temperature is hot enough the gas will ignite when hitting the air.

 

Seems to be about 1200F. Below that even though I passed a propane torch through the gas it would flame but go our as soon as I took away the torch.

 

Definitely at 1400F the flame ignited on its own with no external ignition.

 

One way of gauging the temperature.

 

Tomorrow-results of a low temperature burn

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I wanted as controlled environment as I could get so I used a paint can, flue thermometer to 1800F, and an ash bucket.

 

Dan,

 

These pictures and tutorial are very well done and for the right circumstances describe an ideal way of making charcoal. I will continue to use the pit making method..I am not recommending it to anyone. I see people ( including myself) in general ( particularly in smelting ) hanging on to the methods they learned or developed.. .even when a "better" method is at hand. Probably just human nature.

Thank you for taking the time to make that tutorial.

Jan

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Thanks for this, Danocon. Fuel and its provenance and quality is not the most glamorous of subjects, but it is so important.

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Dan,

 

These pictures and tutorial are very well done and for the right circumstances describe an ideal way of making charcoal. I will continue to use the pit making method..I am not recommending it to anyone. I see people ( including myself) in general ( particularly in smelting ) hanging on to the methods they learned or developed.. .even when a "better" method is at hand. Probably just human nature.

Thank you for taking the time to make that tutorial.

Jan

 

Jan,

 

I agree-For the most part.

 

But each of us make our own series of complex decisions to arrive at our "art". Here in the US and maybe elsewhere-Jeep has come up with what I consider a brilliant tag line.

"The things we make-Make us"

So the decisions we make are not always entirely practical-at least in my case anyway.

 

But in your case I think using a pit to make charcoal is pretty practical. Smelts are voracious consumers of charcoal. Setting up a large enough retort system to supply the needs of smelting would be horrifically expensive I think.

Plus, my pursuit of the perfect piece of charcoal may or may not further my bladesmithing. As I have said before I sometimes get so caught up in the processes I don't actually produce anything.

 

 

Thanks for this, Danocon. Fuel and its provenance and quality is not the most glamorous of subjects, but it is so important.

 

Dan,

You guys are more than welcome.

There is a tremendous amount of good information on this forum. Too be brutally honest I am a mediocre bladesmith. However, my 30 years as a machinist, process engineer and later a teacher have left me with a talent to dig into the core of something and then explain it in simple terms.

 

If I can use that to contribute something here in exchange for all that I receive- I am happy.

 

Dan

Edited by Danocon
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So I decided to go to the other extreme. To see what the result would be at the lower end of the temperature scale.

 

Wood starts to carbonize at 270C or about 520F. I am going to stick with Celsius from here on out. I live in a Fahrenheit world but all the research I have read is in Celsius and I have come to think in Celsius for making charcoal anyway.

 

Please note the temperature gauge is in Fahrenheit.

 

I cut way back on the fuel-Reused what I had extinguished from the previous test in fact.

 

2nd350Cwide.jpg

 

2nd350C.jpg

 

I was able to maintain around 350C pretty consistently.

 

The problem with this setup was that the heat was only at the bottom.

 

Only about the bottom 2/3rds of the sample carbonized fully.I believe it all would have carbonized if I had left I longer but about 1-1/2 hours was all I was willing to devote to any one burn.

 

This piece did not Carbonize fully. The inside was still wood.

 

2ndcharcoal.jpg

 

These did

 

2ndcharcoal3.jpg

 

My four tests are color and reflectivity, breakability and friability (How does it break and how easy is to crush) and how much dust does it create. And of course the real test-how does it burn.

 

 

 

The color was a dull black and even thought pictures show some reflectivity there was in fact not much.

 

They were difficult to break and the was no crushing or any give for that matter between my thumb and forefinger even when I used both hands.

 

No dust at all.

 

During the burn there were no flames coming out of the lid and when I held a lit propane torch to the smoke it ignited but went out as soon as I took it away.

 

It burned with a lot of yellow flame (I only used the fully carbonized pieces). This meant that there were still a lot of volatiles in the charcoal. Not good for a hot consistent forge fire.

Edited by Danocon

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Most of the research says that 550C is the optimum temperature.

 

OK lets give it a shot. Trying to control temperature with my rig is a challenge.

 

I decide to not heat the bottom and only pile fuel around the diameter of the can.

 

3rdsetup.jpg

 

However with some judicious loading of the fuel, fanning the fire and shielding it when the wind blew to much I was able to get it to around 550C and keep it there for maybe 45 minutes. During this time there was lot of smoke under pressure. You could hear it hissing as it exited the vent holes,but only sporadic flaming.

 

 

3rd550C.jpg

 

That is until about 50 minutes into the burn. With no change in what I was doing the temp when to 760C. Whoop we got flames now!

 

 

3rd750C.jpg

 

3rdreheat.jpg

 

It stayed at 760C for around 10 minutes then the flames subsided and died and temperature dropped rapidly. As I had been doing all along to kill the burn I pulled the can and turned it upside down on a pile of dirt to cut off the oxygen so that the hot charcoal would not ignite inside the can.

 

This was some nice charcoal.

 

550CCharcoal.jpg

 

Nice color, Broke cleanly with little or no dust. And it had a really cool crystal sound.

 

It burned with almost no flame and when it did the flame was a blue color.

 

I think we have a winner. But the sudden rise in temperature bothered me. So I tried one more time and was shooting to keep it at around 720C.

 

One paper said this was the optimal temperature for metallurgical charcoal.(steel making) resulting in around 85% carbon and 12-15% volatiles.

 

So one more time. Kept it at around 720C for again about 45 minutes and then again a temperature spike. This time off the scale 950C+ like the very first burn.

 

Surprisingly this was some pretty nice charcoal as well. More friable than the previous burn but pretty good. and the sound was really cool kind of musical. Don't know if that translates to good forging fuel but cool none the less.

 

 

720Cburn3.jpg

 

720Cends.jpg

 

It burned similar to the last batch with maybe more blue flame to it.

 

testburn.jpg

 

testburn2.jpg

 

(BTW-The new fuigo and forge are working great-on these small fires anyway.)

 

So what about these temperature spikes.

 

The official name for this process is pyrolysis. Turns out that pyrolysis CAN be an Exothermic reaction. Where the reaction generates more heat (energy) than is put into it. But it can also be Endothermic-where it absorbs more heat than it generates. There are a lot of variables involved but the big one is how much energy is put into it. So in the 350C burn there was not enough heat energy put into it so it remained Endothermic. In the 550C and 720C burns the applied energy passed the threshold and the reaction went exothermic.

 

Even the scientific papers I have read-the ones i could understand that is say that there are so many variables in the pyrolysys of wood that it is almost more art than science.

 

Now ain't that cool. :D

 

So with this info I have a staring point. I have a new charcoal kiln design drawn up. The weather has cooled off in Texas-time to get serious.

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Dan, thank you for taking the time to present your experiments like this. I really enjoy reading about it. Right now I use a propane forge, but I have not forgotten about the virtues of (and joy using) a charcoal forge.

 

Using pre cut wood like the one you use in the small can is a good idea. That would make chopping quicker work afterwards, I assume.

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I am reading this thread with interest and I am looking forward to see how you translate your research into a larger scale model.

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Dan, thank you for taking the time to present your experiments like this. I really enjoy reading about it. Right now I use a propane forge, but I have not forgotten about the virtues of (and joy using) a charcoal forge.

 

Using pre cut wood like the one you use in the small can is a good idea. That would make chopping quicker work afterwards, I assume.

Peter,

 

Yea there is certain romance using charcoal.

 

In this case I used pre-cut wood so that I would get consistent results. I am of mixed feelings about pre-cutting for more bulk processes.

My raw material is construction scraps. The leftover ends of 2x4s 2x6s etc. So it is already somewhat precut.

 

My general procedure is anything under 12 or so inches goes into the kiln. Longer stuff (if any) fires the kiln.

 

This stuff I have been making this past week cuts like a dream. So I think it is more expedient to a split 12 inch 2x4 and then cut it cross ways with my cleaver after it has been charred.

 

I don't think I will spend the time and electricity to precut it on my table saw. If I start using sawmill slabs that are available not too far away that may be a different story.

 

That would add precutting and probably drying to the process. As long as somebody is building a house though there is more than enough material available for my needs.

 

Later down the road as I try my hand at smelting that will change.

 

Thanks for looking and taking the time to comment.

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I appreciate your work as well, Dano. My last attempt at coaling was a dismal failure, but then it was just a 55 gallon drum full of not-entirely seasoned branches in the middle of the burn pile. If I ever get serious about it this thread will be invaluable! :)

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I am reading this thread with interest and I am looking forward to see how you translate your research into a larger scale model.

 

Me too Jesus :lol:

 

I have set some ambitious criteria for this setup.

 

1) It must be controllable. Unlike my previous setup that once the candle was lit, it was pretty much a runaway train.

 

inkiln.JPG

 

2) It must recover the volatile gas and use it to carbonize the wood.

3) It must separate out the tars and turpentine's. These elements in the pine were a contributing factor to the runaway train effect. Plus, there is bound to be some use for this stuff. They also send a lot of ugly smoke into the atmosphere when they burn-Not good for the environment and more importantly my relationship with my not too close but close enough neighbors.

4) Be build-able by some one with intermediate skills with metal (welding etc.) It will not be dead simple like my pipes out of a barrel but reproducible by someone with some mechanical and building ability.

5) Be at least semi automatic. That is you don't need to constantly fuss with it to produce good results.

 

I have material list in hand. will start collecting it on Friday after returning from Houston.

 

I spend way too much time in hotels

Edited by Danocon
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Dan,

 

I see you are using concrete block to contain the heating fire..how does that hold up at firing temperatures? I am considering lining my pit with those and an inner layer of brick. Will it last for 20 hrs at high temperature?

 

Jan

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Jan,

 

Under the intense heat generated by the volatile gases burning the concrete blocks eventually failed.

 

I had one reader say that they used the 4" wide solid blocks instead of the 8" wide hollow block with good result.

 

My understanding of the pit method is that the temperatures are not so extreme. My opinion is that since you are also going going to use a fire brick lining the CMUs would be protected from any real heat and add the structural support that you need.

 

Dan

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I have some interesting information (Well to me anyway), but I have no idea what it is telling me.

 

I am in the process of building my charcoal kiln. Much of it involves welding and my welding skills make the going slow.

 

I took a break today and was playing around with some of the charcoal I made in the testing. How does it break how does it cut, how does it burn etc.

 

There is not really enough of it to get good data on how it burns but I like the fire.

 

 

I accidentally dropped a piece on my anvil and there was a definite musical tone.

 

This was from the batch where I tried to keep it a 720C and it went off the scale at the end of the burn.

 

I tried some others and over half of the batch had basically the same tone. The ones that did where always solid pieces with no splits or breaks. One that I dropped broke at the split and when I dropped it again it now had the same tone as the others. :huh:

 

So I tested some other and there was correlation between temperature and tone.

 

Here they are in descending order from high tone to low or no tone (thunk)

 

720C spike to 950C +

550C spike to 760C

These two had very pleasant sounds just one was a little lower than the other.

 

350C

Not really a tone more of a solid sound

1st burn that remained at 950C+ and looked like it had been blown up

Almost no sound. Like dropping a pillow on the floor.

Plus stuff broke of of it in little pieces and dust.

 

 

Any acoustical engineers out there that can shed some light on this phenomenon? It may not mean anything but something about the structure is resonating or not.

Seems to me that it is telling us something about its chemical and structural properties.

 

I warned you that this may be more than you wanna know :D

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I have some interesting information (Well to me anyway), but I have no idea what it is telling me.

 

I

Dan,

Interesting...I strike every piece of scrap I handle...usually with a wooden stick..i know nothing about music but have heard some sweet tones.

 

jan

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Dan,

Interesting...I strike every piece of scrap I handle...usually with a wooden stick..i know nothing about music but have heard some sweet tones.

 

jan

Jan,

I find that interesting as well.

Why do you strike every piece of scrap (steel?) you handle? Is there something in particular your listening for?

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Hi Danocon

This may seem totally unrelated, but do you think those retorts of yours could be adapted/used to make coke from slack (small pieces of bituminious coal used to bank up a fire overnight)? I want to build my first furnace and will probably go with oil as coke is unobtainable in may neck o the woods, but if I can make my own thats a different story. :D A book of mine says that meturilogical coke needs to be heated to 1000 degrees C. Could your barrel retorts get that high?

 

Any input apprieciated!!

Neil

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Neil, charcoal is the original fuel for iron and steel making. You'd need a lot of it, but the raw materials for producing met coke aren't necessarily easy to get in some parts of the country.

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Hi Danocon

This may seem totally unrelated, but do you think those retorts of yours could be adapted/used to make coke from slack (small pieces of bituminious coal used to bank up a fire overnight)? I want to build my first furnace and will probably go with oil as coke is unobtainable in may neck o the woods, but if I can make my own thats a different story. :D A book of mine says that meturilogical coke needs to be heated to 1000 degrees C. Could your barrel retorts get that high?

 

Any input apprieciated!!

Neil

Hey Neil,

 

The short answer is yes. When I was making charcoal in my retorts I have no doubt that it was above 1000C when all the gas was flowing under pressure.

The long answer is I have no idea how long you have to cook the coal to get coke. If it must remain at temp for hours then the barrels will burn out in a short time. The wood gives of volatile gases so is pretty much self sustaining. I don't know but I assume coal does not give off these gases in the volume required to self cook. That would mean that you have to supply external energy (wood, gas fire) to cook it.

 

What I am saying that in regards to making coke in a retort it is untread ground for me. My gut feeling is that it would not be an economically sound endeavor.

 

If you try it let us know.

 

Dan

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Well,

 

Work, design issues, and welding skills all conspired to slow things down but here is what I have so far on the new charcoal kiln.

 

This is a much more complex idea than the barrel retort I used before. And it is a huge leap of faith that it will actually work.

 

All the science is there but theory and actual don't always meet in the middle

 

It is a semi-production system and based on a car system where "cars" are loaded with wood and placed in the kiln. When the process is complete the cars are pulled to cool and new cars are placed in the hot kiln. This kiln will hold 4 cars made from 55 gallon drums.

 

The tricky part of the system is the recovery of the distillable products and only use the gas to power the kiln. I wanted to do this for a few reasons.

 

Seems like a waste to burn off something that can be useful

The distillables burn with a lot of toxic smoke-Not good for me or the environment.

They make temperature control more difficult.

 

I wanted to make this semi-production so that I can set aside a weekend in the cool part of the year to make my charcoal supply.

 

The idea is to spend one weekend collecting pine scraps and another making charcoal that hopefully will last me the year since I am a weekend smith anyway.

 

A few of the unknowns

1) Will the separate combustion chamber generate enough heat to cook the 4 cars?

2) Can I get the volatile gases back to the combustion chamber to ignite?

3) Will I be able to control the temperature?

 

Anyway here are few pictures

 

kiln1.jpg

 

kiln2.jpg

 

kiln3.jpg

 

This is a trial assembly. Today I am taking it apart and pouring perlite concrete in the exterior cavities for insulation. Another unknown quantity as to how it will work.

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Well,

 

Dan,

Why not just perlite or "dry stall" rather than making a concrete ( I think even vermiculite will work at that temp)....I hope you are hiding these numbers from the family accountant...or ( heaven forbid ) she may clarify the data for you. Couldn't you have just built her a nice BIG pizza or bread oven and put all that wasted heat to use. Good luck, it is an interesting post. I am enjoying the swordbuilder post as well..and plan to participate in the discussion. First, I have to finish this wootz stuff ( this Winter ) and get these darn crucibles to stop cracking on me. Tamahagane is a by-product of the cast iron I make, when you get down the road a bit I will be glad to share some with you.

 

Jan

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Well,

 

Dan,

Why not just perlite or "dry stall" rather than making a concrete ( I think even vermiculite will work at that temp)....I hope you are hiding these numbers from the family accountant...or ( heaven forbid ) she may clarify the data for you. Couldn't you have just built her a nice BIG pizza or bread oven and put all that wasted heat to use. Good luck, it is an interesting post. I am enjoying the swordbuilder post as well..and plan to participate in the discussion. First, I have to finish this wootz stuff ( this Winter ) and get these darn crucibles to stop cracking on me. Tamahagane is a by-product of the cast iron I make, when you get down the road a bit I will be glad to share some with you.

 

Jan

 

 

Jan,

 

Nope, no hiding from the family accountant. B) Another reason for a lack of progress-Perlite is kind of expensive. Best I could do was a 4 cu/ft bag for $43.00. looks like I will need 3-4 bags. I bought all the steel at a wholesale place but still I've got $300.00 in the steel.

 

Then of course I needed one of those little gasless flux core mig welders :lol:

 

To use loose perlite I need some way to contain it. I am pouring the concrete in the open side of the frame then tilting it up and bolting it together again. Then I will wire it and then stucco the whole thing to protect it and seal it. That's the plan anyway.

 

Tamahagane would great. :)

 

Dan

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