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BioChar Stove How To: Become a Pyroneer

July 7, 2011

This is a cross post from my Personal Blog where I  detail my work in South Central Wisconsin and its focus on sustainability, appropriate technology and small scale agriculture as we seek to reskill and transition to a less energy dependent future.  

Rob's Quick & Dirty TLUD Stove. $50 and one hour of fab time. About 20-30# of char per firing, 2-3 hour burn time.

I garden for many reasons, but mostly to Be the Change I wish to see in the world.  And the more I read about our need to relocalize, the more I hear about how screwed up our climate is getting, the more I read about how very real the pressures of Peak Energy are going to be, the more convinced I am that Bio-Char is an absolutely critical component in any transitional farming system.  The hard truths of our age are that we have far too many mouths to feed, we have far too much carbon in the air, our soils are denuded to all hell, and we will need local means to produce energy cause the cheap, easy stuff is gone.  Guess what – biochar can help ALL of these.  By growing coppice biomass plantations as windbreaks around CSA farm plots or in unused/unusable portions of our farms we can tap into fast growing plant’s abilities to pull carbon from the air and “fix” it into biomass.  This biomass can then be turned into biochar, which reduces syck amounts of heat that can be captured for use in myriad ways from making maple syrup and canning tomatoes, to methane and ethanol.  Best of all, the resulting char can be run through a composting regime, charged with nutrients and micro-organisms, and added to the soil for simply incredible results that increase fertility over millenia – your yeilds go up and and your farming goes regernerative as you sequester the airborne C02 in the soil.  Congrats – your farm is now Carbon NEGATIVE.

So after reading The Biochar Revolutionand getting some great hands on tips from it, I decided to become a “Pyro-neer” and I built my own Top Lit Updraft Gasifier (TLUD) last week.  A TLUD stove is simple as all heck.  Take a metal container (gallon tin can, trash can, 30-55 gln drum), cut some holes in the bottom so it can draw air in the bottom, fill it with biomass, light it, and put a chimney stack on top.  The heat from the top lit fire will rise up the chimney, causing fresh, oxygen rich air to be drawn in through the bottom of the stove (hence the “updraft” in the name).  The flame front slowly burns down the biomass, and as it does it consumes the oxygen as it burns.  The burning results in pyrolysis – where hydrogen and carbon monoxide is released from the biomass (along with some tars and other gases) – what we know as smoke.  But as the flames have used up all the oxygen – as the flame front moves down the barrel, the char is unable to further combust and thus remains as char.  Most TLUD’s then reintroduce oxygen above the char layer by drilling holes into the base of the chimney stack or raising the consolidating area ( the lid of the barrell / can) a bit to let fresh air in.  With the O2 reintroduced into the system, the smoke can be re-ignited for a secondary burn which burns up the rest of the smoke (the emissions are clear when it works right) and returns the gases into C02 and H20.  At this point, heat can also be captured and used to do work- such as heating water, cooking, or space heating a home or greenhouse as a furnace.  If you are able to do this you rock; congratulations, you have created a CHAB stove – (Combined Heat And Biochar) which is awesome because more acronyms are always better.  Plus you are function stacking.

Now my stove is not perfect, it is easy to let it burn too much, and my secondary air inlets are not sized right so it can have imperfect afterburn (working on that).  BUT I built it for $50 and it took less than an hour to fab up.  THAT is awesome.  Before we get going, if you are not in possession of enough common sense to use proper protective equipment (safety goggles, gloves, hearing protection) and have proper skills to safely use power tools to cut metal, and if you are not comfortable around fire and all the common sense safety rules therein, you should not do this.  Don’t blame me if you get cut or burned; Darwin gives his own awards… you have been warned.  That said, this is not a complicated build if you are comfortable with tools and lighting things on fire.  If you are not, perhaps find someone to teach you – we all need to reskill.

Have drill? MAKE HOLE.

First up get yourself a 55 gln (200l) drum with a removeable top.  The used one hereabouts are $10 on Craigslist.  You can also find them free on freecycle once in awhile.  I have 2-3 laying around from various projects- this one was from the Methane Midden.  Drill a crap ton of holes in the bottom – in my case I had a 4″ hole saw from my rainbarrel building days so I grabbed my 9 amp uber drill and had’atr.  Nothing beats drilling on steel with wicked huge drills.   Put the hole low on the barrel as anything below the hole will not really burn.  I would also drill some smaller holes into the dead bottom of the drill to let water out (I quench the fire by dumping water down the chimney – that is a great way to get scalded with steam – repeat my insanity at your own risk).  At this point I attached a small 4″ pipe – about 6″ long to the hole.

6" air inlet. The inlet smooths the air flow and helps keep embers from flying out and burning your toes since you forgot to put on boots and are still wearing your flip flops. That was dumb - you are burning 75# of biomass and should wear proper footgear!

My Big Box hardware store also had a slick mounting ring for this – pretty sure this is a setup for a dryer vent.  It was like $6 total.  Make sure you don’t have any plastic bits anywhere – your a BURNING 75# of wood hear and this shit gets HOT.  Mount the bracket with some self tapping screws.  Easy, peazy.  Don’t worry about air leaks, you WANT air to get into the stove.

There are easier/better ways to do this, but you go to war with the army you have.

Next up make an 8″ hole in the top of your barrel lid.  This is MUCH easier to do with a saber saw.  My saber saw is broken.  So I drilled 3 holes with my 4″ hole saw and connected them with “precision” cuts with my reciprocating saw.  This was loud as all hell and shook my fillings out.  Plus the cut was ugly as all get out so I ended up filing it ‘smooth’ by hand.  Also wicked loud.  If I were to do this again, I would offset the hole for the chimney as much a possible to make a larger surface for heat reclamation (a.k.a. cooking).

Now its time to attach your chimney stack.  For this I used cheap stove pipe.  It is relatively heavy gauge to stand up to the heat of the secondary combustion and its not too expensive.  I bought a 24″ x 8″ piece as well as an 8″ “T” peice.  About $20 total.

I put chimney sealant around the base. DON'T. Leave the cut ragged- you want air coming in anyhow. I used 3 1" "L" brackets attached with self tapping screws to keep the chimney stack on.

After 2-3 burns I am still working on fine tuning the secondary air inlet.  This is why science meets art.  For now I can tell that the 8″ opening is wicked overkill and lets in turbulence which effs up the afterburn.  That said, I LOVE the ability to pull off the cap on the “T” and see how the burn is progressing.  Cutting out the “T” piece would save $8-10, and lower the stack which is likely overly tall.  for secondary air, I plan to play with either raising the “gas condenser” (aka barrel lid) by putting it onto a few pieces of rebar, and/or drilling some 1/2″ holes around the base of the chimney stack.  I will start with the rebar as drilling is hard to undo.

Once the 24″ chimney pipe is put on you are essentially done with the stove.  I recommend putting a grate in the bottom to allow the inlet air to disperse through the entire biomass – my first burn had a large amount of unburned biomass around the edges as it looked like the O2 wasn’t reaching all around.  Luckily, a standard BBQ grate is the PERFECT size to fit into a 55gln drum.  $8.  I also bought 6 fire bricks to put the grate on.  $10.  You could also use field stone – some rocks will explode in the heat, some won’t.  Could be fun!  Fill your stove with biomass (dry and similar sized pieces for a consistent burn) and light the top like a campfire.   I used a blow torch, but I have no patience.

Fill your TLUD with biomass- make sure it is dry and of uniform size lest the smaller, dryer bits burn faster than your larger/wetter bits.

Once the fire is burning well, put the lid on.  USE GLOVES – fire is, well, fire is hot.  The chimney stack will start the draft almost immediately and soon you will be producing syngas (CO + Hyrdrogen) which will then form a secondary combustion with the O2 from the secondary air inlets.  Here is a little video of the whole affair.

The stove is a bit testy – it is somewhat easy to over/under burn it, but on the second burn I was able to get about 20# of char (about 15 gallons). Once you think the burn is done (I  do this by checking to se when the fire is visible through the air inlet, then letting it burn for another 15 minutes or so for everything to char) I then pour 5 gallons of water down the stove pipe.  This is rather stupid as steam scalds quickly, but it does quench the fire enough to remove the top for a second quenching.  I also really need to mount some better (hell ANY) handles to the stove lid for easier/safer removal and installation. The nice thing about this stove is that it is easily converted to a retort – which is allegedly more self regulating and will likely be the next phase of this project once I am done playing with the secondary air inlets.  All in all, thrilled to pieces with the little stove – make a TON of heat, creates biochar, and was rather easy to build.  Win:Win:Win!

Be the Change


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