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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Building a charcoal kiln #1

 

Yeah, pretty it's not.

 

Charcoal making, be it for forge or the garden....it's a messy business and the kiln itself is no exception. Charcoal is made by cooking all of the moisture and -some- of the volatile organic compounds from wood, leaving behind the pure carbon. There are a variety of ways to go about this, but essentially there are two different means of driving the moisture out, direct fire and indirect fire.

 

Direct fire is the traditional and most familiar method. You make a big pile of wood, then bury it under a mound of soil. You leave various small opening to start the fire and allow in air for combustion, then as the pile begins to take, you gradually close off the holes until the entire mound is sealed. The fire buried in the mound will gently smolder for the next few days, leaving behind pure, carbonized wood.

Back in the day, charcoal makers would head off into the woods for the entire season, collecting the leftovers from timber harvest, then making mounds of charcoal and filling the sky with clouds of smoke. The direct fire process is the only efficient way that I know of to make huge amounts of charcoal, but this scale is far beyond my needs. And it's smoky. And messy.

Direct fire is viable on a small scale if you use a 55 gallon steel drum as a containment vessel. Take a drum with a lid, cut 6-8 1" holes around the perimeter at the bottom, then pack the drum full of *VERY DRY* wood. Try for as uniform a size as possible, nothing too big, and pack it clear to the top. Light a fire of small sticks and twigs right on the top of the pile, then keep feeding the fire until you can see that combustion has reached the very bottom of the barrel. When that happens, seal the top, then cover the holes at the bottom by shoveling dirt around the base, cutting off all oxygen to the fire. By the next day, the charcoal should've cooled and you can open up the barrel. It will probably be about 1/2 full of mostly overcooked charcoal, if your results are similar to mine.

This could be called a "top-down" burn, and the nice thing here is that by having the fire on top, much of the smoke of coaling gets consumed in the process. You need to mind the fire, and it's not smoke free (a smoke free burn is the Holy Grail for us charcoal makers, BTW). While not perfect, this is one of the simplest ways to make charcoal, and would be excellent for making basic blacksmithing charcoal.

 

Here is a much better description of the process.......

 

http://iron.wlu.edu/reports/CharcoalBarrel.htm

 

 

You can do a "bottom up" burn too, but I find that it results in greater amounts of both waste and smoke. The bottom up method seems to generate higher heat, leading to more overcooked charcoal and lower yields, maybe >15% less than a top down burn, but the process is even easier. The burn requires less monitoring, just start a fire, then keep piling on the wood. When the fire is clear to the top and raging hot, cap it and give it a day to cool. Perfect for making biochar for the garden, super easy. Great fun on a cold fall day, bonfire in a can! Bring hotdogs!

 

 

 

Indirect burn is where the wood that is being reduced to charcoal never actually touches the fire. This could be called the "retort" method of coaling. When I was making charcoal for the forge back in Oregon, that was the method I was using.

 

 

http://mypeculiarnature.blogspot.com/2014/08/charcoal-for-forge.html

 

 

Long story short.....Take a big can, punch some holes in the bottom, then fill it full of wood. The same parameters apply here, use dry wood of as small and consistent a size/diameter as possible. Seal the lid. This is your retort. Start a fire in a bigger can, then place the wood packed retort into the fire, placing more burning wood around the sides and top. As the wood in the retort give up its moisture, you will see jets of smoky water vapor coming from the little holes, then later when the wood gives off its volatile gasses, the jets turn into tiny flamethrowers. At this point the retort sounds a little like a jet engine, very fun stuff.

 

 

 

The retort method of coaling is easy, and most of the smoke gets consumed in the process, so this is a good option for those who have neighbors. The only complaints that I have are that in my case, the process didn't scale up very well, and it's difficult to know when to remove the retort from the fire. My forays into larger retorts resulted in larger batches of overcooked charcoal —perfect for biochar, but not so good for the forge. The retort method is just too darn hot.

 

The seduction of the retort method is that it comes tantalizingly close to being efficient. The gasses that get expelled from the wood during the coaling process are very combustible, and the Internet is rife with excellent examples of retorts that channel this gas to good use, creating a self fueling charcoal kiln. You start a fire to get the process going, but by the halfway mark, the volatile gasses from coaling are doing all the work, a positive feedback loop.

 

So....The retort method uses the least amount of fuel, and it's the least smoky, two strong positives in its favor. If I was making biochar for agriculture use, this is the method that I would use. The retort gets extremely hot, so if you are using a barrel as your containment vessel, it burns up pretty quickly.

 

 

There is another, lesser known method of indirect heat charcoal making, and that is the Iwasaki style barrel kiln. Based on traditional Japanese coaling methods, the Iwasaki kiln is an insulated horizontal chamber packed with the wood to be coaled, then a separate fire chamber with a baffle in between the two. The baffle serves to keep the flames of the heating fire isolated, but still allowing the hot gasses to pass into the coaling chamber.

 

 

http://iwasaki-sumiyaki.com/esub2.htm

 

You fill the main chamber with wood, then start a small fire in the smaller burn chamber. As with the other charcoal methods, you watch the smoke to determine when to seal the kiln (or if you're feeling flush, a temperature probe). First you get the white steam of water vapor that is expelled from the wood. Next will be an acrid white/yellow plume, the volatile compounds. When most of the volatiles have been driven off, the smoke will turn blue-ish for a short period, then go nearly clear. That's your signal to seal off all openings. Let the kiln sit for a day to ensure that the coaling process is finished, then open it up.

 

 

 

Dave Friesen, the "Island Blacksmith" outside of Vancouver, BC has gone through the charcoal evolution process as well, and it was from his blog posting that I learned of the Iwasaki kilns. You can follow his charcoal journey here (and check out his work as well.....beautiful and extremely skilled. I LOVE his forging videos!)

 

http://islandblacksmith.ca/2013/03/charcoal-kiln-v-3-0/
 

If your kiln was well insulated, you'll be left with some wonderful blacksmithing charcoal! The difference between using well made pine (the traditional blacksmithing charcoal, East and West, has always been made from pine) charcoal and overcooked mediocre char is notable. By all means, use what you got, but the nice stuff is clean burning, nearly smoke free, and produces very little ash. It also burns fast and hot, so if you leave your blower running in between heats, you're gonna burn up a lot of charcoal for no good reason. That's yet another reason to build a traditional fuigo Japanese box bellows.

 

 

The kiln that I am building is similar in spirit to the Iwasaki kilns, but more simple. I have seen a couple of YouTube videos of this basic design, but I have some ideas that I've been wanting to try out. I am building a side by side pair of kilns, but a single unit would be great too. I figure that if you need to be sitting there tending the small heat fires anyways, you might as well be tending two.

 

 

So.

 

If you stuck with me this long, here are the pics.

 

 

I bought a couple of used barrels with removable lids, then traced and cut out two holes in a piece of old roofing tin.

 

 

 

 

How did I cut the holes in the steel, when we have no electricity?

 

 

My hot cut chisel that I forged from a cheap wrecking bar worked great, slicing through the steel with little difficulty. MUCH faster (and easier) than using tin-snips, and resulted in a neater job, too.

 

 

At the rear of the barrel I cut a 4" hole to receive a 90* elbow fitting for the smoke vent. For this kiln I am using a double wall vent pipe for both the ease of attachment –I slit the outer jacket to form tabs to attach the elbow to the barrel– and also to keep the stack temperature as high as possible. A double wall or insulated vent should contribute to forming a better draft, not so important here in balmy Hawaii, but might be a good idea in areas that see more cold weather. Single wall would be fine as well, cheaper too, but here in Hawaii the price was nearly the same, go figure.

 

Two elbows, before slitting and after.

 

 

 

 

To seal the joint, I mix up a little clay paste, then fasten the elbow in place with sheet metal screws.

 

The 90 degree outlet will be at the bottom of the horizontal barrel.

 

 

So here is the enclosure itself, with two holes for side by side barrels.

 

 

Four corner poles and some old roofing tin. All of the rock around here is lava, the most perfect insulating/refractory brick that you could hope for. Try to get good even support for the barrels, and lay a slight slope towards the front so that when you forget the stack cap off, the rain will drain out on its own. More importantly, the liquid that condenses inside the kiln will flow towards the front where the heat is most intense, and so get consumed.

 

What's that? You don't have lava kicking around because don't live on a volcanic island? Sand would make an excellent bed, as would most anything really. A material that offers some insulative quality is preferred, but again......use what you got. Don't buy anything, just use dirt.

 

 

I want to insulate the barrels as much as possible, so I am going to try making a straw /mud slurry. Except I don't have any straw laying around. I've got lots of weeds though. Time to trim the driveway!

 

 

I also don't have any clay –few areas in Hawaii do– but I found a bag of fire-brick mortar clay at Home Depot, in the torn/damaged pile....50% off.

 

 

I mix a slurry, then plunge handfuls of grass into the soup. My mix is much thinner than I would like. I would rather it coated thicker, more like thick cream than my skim milk.

 

 

50# of powdered clay doesn't go very far, so if at all possible, find a local source for something that will work. You don't need sticky stuff, you just need something that will coat the grass and prevent it from catching fire. Soaking clumping, non scented cat litter in a bucket of water was my second option, something that I've wanted to try out but haven't yet.

 

 

You can see here that I am once again killing two birds with one stone. When I weed the walkway, the weeds pull up little clumps of nice red lava cinder as well.

 

 

I first lay some gloppy grass/mud mix against the wall of the barrel, then bury it in lava rock and cinder. Since my mud mix was so thin, I'm half expecting the whole thing to catch fire on the first use, but hopefully the lava rock insulation keeps the blaze under control.

 

 

 

 

I add a 5' extension to the smoke pipe, also double wall stuff, then keep burying.

 

 

 

 

I'm just doing one side for now, so we'll stop here. There's more a comin'.

 

 

 

 

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