TLUD Biochar Stove

TLUD = top loading up draft. It's one of the many stove concepts out there. 

I use a homemade TLUD stove for making biochar out of the scads of windblown twigs that accumulate around here. My latest stove has reached the end if it's life, so I'm building a new one. I'm making a few modifications to the new replacement to see if it works better for me with the fuel that I have. 

I picked up a metal trash can. Yes, I actually paid cash for something! But I found a piece of discarded stove pipe at the metal recycling, and snagged that for free. 

I flipped the trashcan upside down and proceeded to cut a 6" diameter rough hole in its bottom. I used a hammer and old chisel. Pretty crude but effective. 

3/4 the way around the metal no longer cooperated, so I just folded the flap inside to finish the hole making process. My previous stove didn't have a large opening like this. I was seeing problems with smoking if I wasn't ultra careful in using ultra dry fuel. So I am hoping that adding more air will correct that. We'll see. 

I then set the stove pipe inside the trashcan, over the hole. Looking down the pipe, it looks like a proper fit. By the way, if this hole proves to be too large, I can block part of it with a piece of metal. 

Looking down the stovepipe I realized that something was wrong. I forgot to install a grate so that the fuel and fire would stay inside my stove. 

So I picked up the trashcan and slid a BBQ grate under the hole. Good so far. 

I did a very brief test fire and realized that I need more holes. So I flipped the trashcan over, and using my trusty old chisel, clobbered more air holes. These holes will provide the secondary air source for igniting the gases given off by the burning.....sometimes called a second burn. This prevents smoke. 

Ok. Here's how it looks so far. Trashcan with holes. Pipe inside running inside, and up to two inches below the top lip of the trashcan. That two inch gap is important. It could be more but I've found that two inches works with past stoves. I'm hoping it works for this one too, otherwise I will need to cut the stove pipe down in height. 

The trashcan stove is set atop two cinder locks sitting on a concrete slab, with metal guards around it. Nothing combustable in the vicinity. 

I put an old metal pot beneath the opening for catching the embers. This turned out to be too small so I later switched to using jumbo steel pan that had once been used in a restaurant. It holds about four times what this pot does. 

The stove isn't quite ready to run yet. It needs a flame constrictor in order to help it run fairly smokeless. "Smokeless" is a goal that I have. No need to frighten the neighbors with billowing smoke. 

So again the old chisel and hammer gets used to make a hole in a piece of old roofing. I guessed at the diameter for the hole, figuring that I could make it bigger if the stove smoked. But it turned out to be fine. 

Now to test the stove. I packed the interior stove pipe with broken up twigs. (I break them up by running over them with the vehicles in the driveway. I just spread them out on an old tarp and drive the truck over the twigs in my routine comings and goings. As they become small enough pieces....1" to 3", I scoop them up and store them in old feed bags.) I packed it tightly, which means no empty spaces but still little gaps between the twigs for air flow. Twigs work fine with this kind of stove, but sawdust wouldn't. Air needs to run up through the fuel from the bottom. 

I use some cardboard pieces for lighting the fuel from the top. A couple of torn up pieces of cardboard and a squirt of 90% alcohol gets it going. 

Once the fire seems well lit, I'll add the flame constrictor. I should see flames not smoke. If it smokes then the fire isn't ready.........or something needs to be modified on this particular stove design. But happily I got a nice clean flame. 

On top of that I'll add a chimney. The chimney gets the fire roaring because the gases being given off get ignited via the secondary air source (that is, the holes in the bottom of the trashcan.)  I use a briquette starter as a chimney, because it's so easy to use and lasts forever. Without a chimney I don't get good second combustion. 

The test burn went well. The stove worked exactly like I wanted. 

So what about the biochar? How do I know when it's done? 

I want to stop the burning process when flame disappears. People would say that means when the fire has died back, no flames coming out the top, and just burning embers inside the stove. It's important to stop the burning process at that point. If not, then the embers will continue burning all the way down to ash. With twigs that happens quickly. Now if it's ashes I wanted, well just it burn until the fire goes out. But if it's biochar that I'm looking for, then I need to stop the burning process. I still get some ash along with the biochar, but that's not a problem. 

The easiest way I've found to stop the embers from burning is to quench them. With this stove I simply pull out the grate from under the trash can and allow the embers to drop into a pan of water below. Now you understand why the original pot was too small. There were more embers than it could hold. The restaurant pan holds all the embers easily, plus enough water to quench them. Perfect. 

PS- No photos of the end product because I somehow screwed up my phone camera. It's now taking monster sized photos in some weird mode. I need hubby to fix it. I'm no good with these techy electronic gadgets. I'll get photos for you later.