Building a charcoal kiln #4

Part 4 of,

"More than you ever wanted to know about building a kiln for making bladesmithing charcoal."

I've got a few more things that I'd like to try.

For starters, my burn chamber is just a horizontal tube of tin. Once the draft gets established, the heat and smoke gets drawn into the coaling chamber nicely. It works OK, and you can't get much more simple than that, but when I look at the diagrams of the traditional earth berm kilns, you can see that the burn chamber is much more enclosed within the body of the kiln. 

The metal drum Iwasaki kilns that I've repeatedly referenced use a separate partial drum to serve as a burn chamber, and that's great. Mine could be improved though. See, the reason that I like the more enclosed fire chamber is that it looks like a smaller fire could be used, since the heat and smoke are more tightly directed into the coaling chamber. By reducing the size of the fire, we are trading a possibly longer coaling time, with the lessening of heat and the force of the flames.......At least that's my thinking.

The second thing that I've been wanting to test out.

The traditional kiln shows the wood being tightly packed and VERTICAL. I did the best that I could, and the back has a higher proportion of vertical, but.....This was a huge PITA, and I doubt that I'll do it this way again. Maybe with a rectangular coaling chamber it wouldn't be so difficult. We'll see what the charcoal looks like.

So here is my quick and dirty improvement to the burn chamber. That's not parallax error, it really is tilted.

The end that abuts the barrel lid has a mating flange that it sort of hangs from and also seals the join a bit, point being that it forms a tighter fit than before. Towards the center of the burn "tube" is the feed door, a 3-sided cut, bent down at about a 45 degree angle. The end of the tube at the left is still fully open. If it bears repeating, I'll take better photos next time. The description is hard to follow.

What I've made here is closer to being a top loading, horizontal draft "rocket stove", and it works so much better it's surprising. The separate air channel on the left let's you pack the fuel port totally full, without starving the fire of air. The burn chamber creates good air turbulence as well, contributing to better combustion. These simple mods make the fire much easier to start, it burns hotter, and it's easier to load the fuel charge (meaning you can cram it full and then just check back every 30 minutes or so to refuel). The slight incline to the chamber might help induce a properly directed draft too. It seemed that way, despite the visible flames occasionally shooting out the fuel port. 

It's still ugly and cheesy looking, but remember, I need to be able to whip this whole assembly out of the way in seconds, when it's time to shut down the coaling process. I can grab a stick and lift this nasty mess out of the way in two heartbeats. Also, don't forget that the galvanized metal that I am using gives off extremely poisonous fumes as the zinc burns off. Don't sit too close, not before making peace with your gods.

And the third thing.......

Right after my last firing, I was sitting around reading about Sumi-yaki (Google : 炭焼き ), looking for more tips and improvements I can make to the process. I found a couple of good ones. 

This is from a site making bamboo charcoal, slightly different, but essentially the same.

Charcoal making process according to the drum charcoal kettle is as follows.
1. pilot flame to burn and raise the temperature of
2. smoke up to 85-95 degrees and make sure that "it was deliberately fart" (strong smell) (0.5 to 1 hour)
3. fired to stop the pilot flame, to limit the supply of air, keep the temperature of the smoke (4 hours)
4. temperature of the smoke if promoted carbide begin to rise (2 hours)
5. temperature of the smoke misses the thermometer When equal to or greater than 180 degrees (one hour) is
6. smoke Open the internal cover Once colorless, do "Nerashi" (about 10 minutes)
7. Exit to close the air inlet and the chimney outlet (total of 8 hours)

When you get to the "Fart-smelling, yellow smoke phase", stop firing and cut back the air supply......huh.

I don't think that I've ever seen that referenced before, stopping the fire (the fart smell....everyone knows that. The yellow smoke has a large sulfer component, I think). The thought behind this is that once you get the yellow smoke going, the wood inside the drum has established a kind of oxygen deprived combustion, so any additional heat input only would be causing potential damage to the coal.
When you get into making traditional bladesmithing charcoal, you quickly realize that there is something missing in our body of knowledge, some little detail. Nearly everyone out there is making nasty, overcooked char. It's fine for the garden, but not as good in the forge. Everything that I've read has you firing the burn, right up until it's time to shut 'er down. Maybe this simple thing is one of the details?

Cutting back on the air supply will further slow the process of coaling, but it also gives greater control. Once you get to the yellow smoke phase, things start to happen ever more quickly. During my last burn, from YS phase to done only took a little over an hour. This time.....closer to 2 hours, but the rate of change towards the end of the process felt much more relaxed. I'm hoping that the charcoal felt the same too, nice and relaxed. We'll see.

So the yellow smoke for me and this Guava I'm coaling went on for quite a while, but essentially, I stopped fueling the fire and cut back the air a bit.

The yellow smoke phase is around 350*F at the stack. 

The partial brick at the front can be bumped either way to give enough air to keep the stack temperature rising.

 

I didn't really need to do anything though, just sat and watched the smoke.

We are getting close to shut down time. The stack temp reads around 500*F and there is still quite a bit of "white" in the smoke.

The amount of finishing time is one of the more important aspects that determine the qualities of the charcoal. Because I am using this for bladesmithing, I don't want to cook everything out. If I was using this for an indoor hibatchi or a charcoal heater, I would try to cook the charcoal until it was as clear as possible.

I guess that it goes to show just how divorced from the mainstream I am but.....it just occurred to me, the number one use for real charcoal is likely to be for grilling a barbecue, haha. Would you believe that I've not tried that yet?!

Wow! Get a life, kid!

Here is where I shut down, nearly 800*F at the stack.

If you compare the smoke to the prior pic, you can see that most of the "white" is gone. The time interval between the two was approximately 15 minutes.

I dragged the firebox out of the way, piled up bricks and dirt to shut down combustion, capped the stack and called it a night. 

So what do we get this time? Trash or treasure?

Hmmmmm......

I'm thinking trash. Where does all of the wood go?! The barrel was packed as tightly as I could get it. Lots of ash......

Overcooked.

Oh well.....it all burns, right?

I grab the shovel and sieve to start cleaning up, but this stuff doesn't shovel. Just past the overcooked stuff are sticks of solid carbon, and they aren't falling apart like the other charcoal that I've made.

Almost the entire burn looked like this......sticks, magically shrunken and transformed. 

It's too bad that the bark is still on the sticks, because that thin outer layer affects the resonant qualities. I've finally made the "hard" charcoal, paradoxically known as "white" charcoal, or electrolytic charcoal. These carbon sticks are now conductive to electricity. The light was pretty flat, but you can see that the charcoal looks silver, not black. Cool, huh?

I don't think that this would be considered true "white" charcoal, but it's getting close. This charcoal kiln is definitely capable of getting up to the 2000*F needed for complete carbonization, and I've been wanting to attempt the making of the "white" charcoal, but to get it right, I would need to open the barrel at the finish, then quickly smother the charcoal. Scary! The burning charcoal gets buried in old wood ashes.....ironically, something that I don't really have much of, haha.

This charcoal is really starting to exhibit the resonant qualities that I find so interesting. The water being completely driven out of the wood, making the carbonized cells ring like bells, each stick like part of a strange looking wind-chime.....I don't know, but it's neat to experience, charcoal that sings.

The resonance is dampened by both the outer bark layer and the amount of wood shrinkage within the stick itself. These didn't ring well.

As you'd expect, a solid bar of carbon rings clean and loud, while one that is covered in tiny plates of carbonized bark – which also resonate, but at different rates/frequencies– sounds flat or muddy.

These sound like tuning forks.

You only get a couple of whacks before some fracture occurs and the stick breaks in two. Some of the smaller stuff must've been fairly dry when they went into the kiln, because they showed no shrinkage splits at all, just solid carbon. When they break, it's with a super high pitched *TINK* that hurts my ears a bit. Some of them shattered forcibly, like a candy cane.

Towards the rear of the kiln, in the area of the vent stack, the wood barely even looks like charcoal. It has a brown hue, but it's not undercooked. There was also an iridescent blue in spots, some strange chemical compound flaring off, I guess.

 

So, at the very bottom of the barrel I laid four sticks full length, and of the entire load, it was only these sticks that didn't fully carbonize. Everything else was fully cooked, through and through. 

The verdict is in. 

I deem the charcoal kiln a success, though my firing procedure could still use some refinement. This kiln design is far and away the easiest and most reliable way to make high quality blacksmithing charcoal, at least compared to what I've done in the past. I'm having a hard time restraining myself from burning all the time, I just love opening the kiln up, seeing what has been created. Maybe it's because good charcoal is such a rarity? I don't know, but I just love it. 

A big question remains......is this charcoal any good? I am following my interests here, doing this just for fun. I mean....I still need to build a fuigo and small forge, I'm not even prepared to test this stuff properly. Right now, I'm learning the art, getting to know the kiln itself. I'm just seeing what *kinds* of charcoal I can make, and I'm not worried about whether or not the stuff burns hot/cool/too slow/fast, whatever. This batch ended up very "hard".... fun, but not what you want for forging, exactly. 

For forging you want the softer "black" charcoal, not this hard "white" charcoal, at least that's my understanding. When I was using my home made charcoal before, I was using the soft, crummy, and overcooked charcoal for lower temperature work like quenching and tempering, and saved the best hard pine charcoal for welding. It was soooo much nicer to work with, but it was also touchy, too. Get my timing off, forget what I was doing for just a moment and I'd start to hear the metal breath....then hiss, the sound of the steel burning. The charcoal that I made from rotten cedar deck boards could also reach welding heat, but it took MUCH more effort. Not beter/worse, just different. It should be a relatively simple matter to make a variety of slightly differing charcoal that will be task specific. 

Hopefully when Mark Grable reads this, he will be able to comment on what the charcoal was REALLY like, the charcoal that Yataiki preferred for forging his saws. I've got so many questions.......

• Red pine for forging, so I've heard, but were there different qualities that were used to differentiate? I can imagine opening a bag o' charcoal, sorting through the sticks and making different piles.....Chopping into ever smaller pieces.
• Is there anything that must be avoided, when choosing? Different species would burn differently, but also might introduce a chemical component that would be good....or bad.
• What am I obviously missing here? I mean....this is what I've come up with after watching a handful of YouTube videos, written anecdotes and allusions that I've found, and my own slight experience. But mostly this is the product of inference, experiment, and some guessing, haha.

And of course, there is the question of tree species. For all I know, guava might be a terrible bladesmithing charcoal.....I guess that I'll find out. This wood is still fairly wet, but surprisingly, it doesn't seem to matter much. Using dry wood must speed the operation some, but that might not be a completely good thing. This wet wood is shrinking dramatically, and shows many cracks and fissures. That keeps it from being used as part of a totally kickass Halloween themed windchime, true, but it also means that it is easier to split. The hard and solid ones are harder to break.....kind of loud too.

That a person can make a simple little charcoal kiln out of an old paint can, make some char, then start burning steel.....needing only a armfull of bricks and an old bathroom fan (and the paint can).....That's freakin' cool.

I've already got the kiln started on the next batch, this time loaded with all of the sticks lying flat, easy as can be. If anything strange happens, I'll let you know. If you know something that I don't......you let me know, OK?

Build a charcoal kiln part 3....The first results.

 

 

So I built this charcoal kiln to make proper bladesmithing charcoal.....If you want to see it from the beginning:

• Part 1
• Part 2

It's ugly, I'll grant you that, haha.

 

 

 

How did yesterday's burn work out?

 

Not the greatest I've made....

 

 

.....but not the worst, either. It looks badly overcooked. The barrel is only half full, but started out being packed.

 

 

Given that this was a newly constructed kiln, surrounded by wet grass/clay insulation (didn't work, BTW), and filled to the brim with wood that was far from dry....my expectations were low. I was anticipating a lot of undercooked stuff though, so go figure. This was probably a worst case scenario, so the results are encouraging.

 

My only real successes in the past have been using a 5 gallon retort style kiln. I've cooked in 55 gallon drums a few times before, but that only resulted in badly overcooked or badly undercooked charcoal. Certainly nothing approaching a consistent result, anyways. What did I get this time?

 

 

The first shovels don't look so hot (no pun intended). This ashy, shrunken and fractured look is overcooked. Too much heat, over too long a time period.

 

 

 

 

I sift out the fines using a nominal 1/2" mesh.

 

When I first opened the barrel, it looked to me as though much of the wood had been reduced to ashes –generally that's due to having an air leak somewhere– but as I am sifting, I'm not really finding as much ash as I had thought.

 

 

I do find a couple of pieces that aren't fully cooked. This chunk is 1/2 charcoal, the other 1/2 still a little bit brown.

 

 

You can still see the holes in the wood, tunnels left by beetle larvae. So cool!

 

 

Here is a perfect example of overcooked charcoal. Spongy looking, soft rounded edges, and a gray cast to it.

 

 

This is charcoal that has had all of the volatile elements burned from it, not really what we want for the forge. It's great for the garden though. I am surprised how little there is of this. Only 4-5% of the total, if that. I got similar results when using my 5 gallon retort.

 

 

Most of the charcoal came out looking like this. A perfect piece is on top, a slightly overcooked piece below.

 

 

The perfect charcoal breaks cleanly with a crisp *snap*. You can see how fine grain this Guava is. That is another variable to this attempt, I've never cooked a hardwood species, much less Guava. I've only used softwoods in the past.

 

 

A before and after comparison.

 

 

 

 

One of the aspects that I love the most is how little the wood is affected by a proper coaling process. If done well, the charcoal product will look exactly like the original, just shrunken and black after having all of the liquid components removed. The Japanese have turned this into an art of sorts, converting all sorts of things into charcoal themed displays.

 

 

I recognize a pineapple and a sea urchin, but the other stuff? Is that a lufa sponge?

 

 

My guava charcoal isn't that pretty, but you can see how many of the sticks had fissured, peeling bark when they went into the kiln and still have it upon coming out.

 

 

 

You can see evidence of the larvae tunneling underneath the bark. I just love this stuff.

 

 

It's hard to tell from the photos, but the charcoal itself has a silvery sheen to it, and it rings slightly when tapped. Pouring the charcoal into the bag, it has a musical sound to it.

 

 

And here is the yield. A small 4 lb bag of fines (mostly the small fragments of bark that fell off of the sticks), and a large bag of decent charcoal.

 

 

This Guava charcoal is MUCH heavier than the pine and cedar charcoal that I am used to. I would guess that the bag weighs around 70lbs, more than the bag can withstand in any event, so somewhere around there.

 

The small bag of fines can be crushed further and used for the bed of my forge, added to the clay for yaki-ire, used as a component of the welding flux, or just spread in the garden. Nothing is wasted.

 

 

Here is the barrel after shoveling out the interior. I took no special care here, just scooped out the charcoal, but my point is that there was actually very little ash produced, far less than I was expecting.

 

 

So in retrospect, the yield wasn't as poor as I had initially thought. The cooked charcoal is dramatically reduced in diameter after losing all its water, and also had settled quite a bit. It's hard for me to guess at a yield, but based primarily on the amount of ash I saw.....jeez, 80% maybe? 

Another good thing about proper charcoal.....it's clean. Well, kinda clean.

 

 

Despite having shoveled out a whole drum of char, screening it all and bagging it, my hands are barely dirty. My feet are still clean! It's nice stuff.

 

 

This particular batch of charcoal doesn't have the clear pure *ring* of some charcoal, but had I started with dry sticks to begin with, I suspect it would. The next batch (I'll probably start today....I'm a charcoal junky, haha) I will shut down sooner, earlier in the blue smoke phase, so we'll see how that affects things. The kiln is dry now too, not buried in wet mud. That should help. This charcoal will be fine to use, but I still want to do better.

 

Another improvement will be to construct the fire chamber to be more like a self feeding rocket stove, with a tilted or vertical entry for the fuel sticks. Put gravity to work for you, right? Nothing too fancy though, because you need to be able to seal the coaling chamber quickly.

 

So, a success! If you are into traditional blacksmithing and need some fuel, this works well. We've got tons of downed trees sitting here that I need to clean up, nearly all of it being thin, invasive guava that everyone else hates. I haven't used the guava charcoal in the forge yet (still haven't built my forge even, so I guess that I better hurry up, huh?), but this should work fine. There is a never ending supply of free guava here.

 

This is a great way to use what many people view as waste, and that's a huge positive in my book. Cut the tree, and what isn't suitable for lumber gets turned into charcoal. The smallest twigs and twistiest branches are used to actually make the charcoal, while the leaves go into the garden compost.

 

The only real problem that remains is the noxious smoke thing. Maybe we can devise a scrubber for the vent stack. One of the more common uses for the Iwasaki kiln is to capture the "Wood vinegar" distillate, used for lots of different things but I'm not really familiar with that side of stuff. Essentially, the smoke gets funneled into a long cooling pipe, then condenses back into a liquid which then is collected. Something to think about. It might be worth a shot.

 

 

My charcoal producing kiln is not really an original idea (nothing is, right?), but is loosely based on a traditional Japanese coaling kiln.

 

http://blogs.yahoo.co.jp/okakawa2/62354573.html

 

The fire never actually touches the wood that will be turned into charcoal, and the blue line presumably represents the liquid distillate. The traditional kiln is packed with wood as tightly as possible, but much of the wood is stacked vertically, and there doesn't appear to be an air channel underneath the wood, only a small space that runs just under the ceiling. I might try this next firing.

 

The 55 gallon drum that the design is based around has a limited service life, so perhaps I will make the real version one day. That a fun class that would be!

 

 

So there you have it. Now you can make awesome charcoal too. It's pretty easy and might even be called fun. If the neighbors get fussy, have them come talk to me.

 

 

Now if only I had a forge......

 

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Building a charcoal kiln #2..."FIRE!"

More about making a kiln to produce blacksmithing charcoal.......Installment #1 here.

OK, where was I?

I toss on a few more sheets of tin to serve as a roof and it's time to give it a try.

I first lay a perpendicular floor of sticks, to keep the wood slightly elevated and to give an air path for the initial stages of burning.

I fill the barrel with short 15" lengths of cut Guava branches, trying to fit them as tightly as possible. Here's half full.

 

 

Now, as tightly as possible might not be the best choice, but being the curious sort that I am.........

See, the problem is that:

• The insulating grass/mud mix is wet as hell still, and will likely never dry completely, given that it rains here so frequently.
• The sticks that I am coaling were cut 6 months ago, but have been sitting out in the elements. They are far from being dry.
• By nature, I am sometimes perversely contrary (just ask my wife), so what the hell. Fill it to the brim! Bring it on!!!

 

I've got two remnant circles of roof tin staring at me, so I trim one down to fit inside the barrel, forming a baffle. Notice that the corrugations run vertically and there is an air-gap at the top of the divider. I want about 2" of clearance between the baffle and the very front of the lid. Hopefully that will be doesn't restrict the airflow too much.

 

 

 

 

I had cut an 8" square opening on the lid, three tabs that I bent over to give rigidity to the thin steel.

 

I also built up a soil platform to get the firebox up where it belongs.

 

 

I bent a small sheet of tin into a box-like shape that will serve as the firebox. I support the tin with dirt, rocks and bricks, whatever is close to hand.

 

I forgot to take pics, but it's nothing special. This is an area that I want to improve some. V#2 will probably be a rocket stove variant. More on that to come....

 

 

 

 

 

Grab a healthful breakfast of leftover seaweed salad, snag the fire extinguisher and the propane torch and......let's see what happens!

 

 

 

We've got smoke! The white smoke phase is relatively cold, and nearly all of the smoke produced is water vapor/steam. The guava that I'm burning smells nice, just perfect for smoking meat!

 

You can see that I've got a chunk of broken CMU restricting the opening at the front of the firebox. You need to balance the amount of air that gets to the fire, enough air for combustion, but not so much that you lose the draft. It's tempting to build something fancy, but I'll think about that later.

 

 

 

For a baseline measure, the firebox is at 200F.....

 

 

 

....and the lid temp is 236F.

 

 

 

 

The all important stack temp reads 134F.

 

 

I'm psyched, the 134F means that hot air is being drawn through the tightly packed sticks, no problem.

 

 

 

The amount of time required to convert a drum full of wood into blacksmithing charcoal will vary. I started this burn rather late in the day and given that I packed the kiln full to the gills with only superficially dry wood, leaving little room for air to flow, this batch should take quite awhile. Between searching out dry twigs to get the fire established (you'd think I'd have a pile of already dry wood set aside, wouldn't you, haha) doing dishes/laundry/cooking dinner, changing the brakes on my car and ten other things......6 hours later it was getting dark, right when the kiln really started pumping out the smoke. Bad timing, because the nightime's cooling air will hold the smoke right at ground level. I capped the vent stack, blocked the air intake, then called it a night.

 

 

The next day the fire was much quicker to take, given that the wood in the kiln was now partially cooked. The stack was pumping white smoke for a good hour before the color of the smoke began to shift to the yellow. The yellow smoke phase is the nasty part of the process, as this is when the more interesting volatile compounds are being released from the wood. The yellow smoke stinks, plain and simple.

 

 

Your neighbors won't thank you for this.

 

 

Is it any wonder that I need to live in the country, haha?!

 

As I mentioned before, the yellow smoke is volatile, and quite combustible. Clever people channel the smoke back to the burn chamber and harvest those otherwise wasted BTU'S, but this is right about the time where the process starts to speed up, so extra heat isn't what's needed. Still, my sense of economy is offended.

 

People ask whether you can just burn straight wood in the forge instead of charcoal, and the answer is yes, BUT.......All of that white smoke we saw is water vapor that pulls huge numbers of BTU's from your forge, so a straight wood fire isn't very hot. Also, the yellow smoke is exactly what you get from a smoldering fire, virtually guaranteeing that everyone you meet will ask if you were recently at a bonfire party. Sure thing, the smoke goes right in your eyes and because the wood burns with a visible flame, you'll be doubly blind. In comparison, good charcoal burns with a nearly invisible flame, gives off almost no smoke and very little scent. Apples and oranges.

 

 

The yellow smoke phase sees elevating temperatures everywhere.

 

 

 

I love the double wall vent pipe. Warm to the touch, that's all.

 

 

 

And the vent gasses themselves.....nearly 400F.

 

 

 

So, things start to happen more quickly now and it's time to be attentive. From yellow smoke to finish took about 1.5 hours but again, this was wet wood, packed tight. A loose or cross stacked pile would produce only 1/2 the amount of charcoal, but might only take a few hours if you use dry wood.

 

 

1 hour or so of billowing yellow clouds of smoke, but now the smoke is getting thinner, less yellow, more gray.

 

 

You see how the air is getting clear, right where the gasses exit the stack?

 

 

462 degrees Fahrenheit.

 

 

 

 

 

Remember my clever grass and mud insulation? That's not just steam from it drying out, haha.

 

117F is great, but that's due to the insulative effects of the lava. The grass has turned into char, and the only reason that it didn't burst into flame is that the lava cinder kind of smothered it, deprived it of air. More clay might have helped, but the drum temperature gets extremely hot, so maybe straight dirt/rocks is just the way to go.

 

 

You need to have *some* flame pics, right?

 

 

Once the draft is established, nearly all of the flames and smoke from the heat fire get drawn into the kiln. The flames hit the baffle then travel up and over. I assume that by that time there isn't enough oxygen to support true combustion, just what we want. You can also see how wet this wood is. I'm actually surprised that it burns this well!

 

 

Another 15 minutes goes by, and the flue gasses are even more clear. Almost all the water and other stuff has been expelled from the wood.

 

 

 

Almost 500F.

 

 

 

Another 10 minutes, gasses are clear at the exit, and the smoke is developing a distinct bluish cast. Almost done.

 

 

 

Almost 600F, a rise of 100 degrees in just a few minutes time.

 

 

 

5-7 minutes more and it's time to shut it down. There volume of smoke is drastically reduced and the smoke exiting the pipe is blue, not gray.

 

 

 

Almost 800F.

 

 

 

I pull the firebox away from the mouth....

 

 

...and pile up some bricks and dirt to shut off the oxygen. I cap the vent using an old coffee can topped with a rock, should the breeze kick up.

 

 

Tomorrow I'll open it up.

 

Fun, right?!

 

 

 

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