Charred!

It's been about a month and a half since the Seattle crew was here and we made the big pile of brush to burn for biochar. I had actually thought the burn would be an activity while they were here, but instead we got a foot of snow. 

Since then, I added to the pile, and kept looking for a day with a convergence of several things: 1) It had been dry for a day or two (at least) to dry out the brush; 2) It wasn't windy; and 3) I had time. Many times we had a day or two of sun, and then when I thought I could do the burn it would start raining again, or be very windy. 

Sunday turned out to be perfect. It hadn't rained for two days, the afternoon and evening winds were under 10 knots, and I had time after supper with the long daylight hours we have now. I was pleasantly surprised at how quickly the brush caught fire. I had used just a couple of pieces of newspaper crumpled up. This was a one match start. 

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Here's about two hours later - though the picture looks about the same, notice the missing brush pile - it has all been used. I even brought some of the juniper branches from the pile beyond the fence to use in finishing up. At this point everything underneath the flames is dense, packed in (to exclude oxygen) coals. Note that there's almost no smoke. There were times after I added new material that there was smoke, but the goal is to feed the fire in a way that produces little smoke. 

After I stopped adding material, I tamped it down and let it finish for about half an hour. 

Here you can see ash starting to form on top. Now it's time to quench the fire with a lot of water, to stop the combustion process. If I didn't do that, the coals would slowly burn all the way to ash. By stopping it at this point, I get charcoal. 

I started the quench by dumping three 5 gallon buckets of water in, and then spraying with a hose. After a few minutes, I was able to work free the metal ring (you can see the overlap joint near the top center of the picture above. The ends were just overlapped and held in place by contact with one of the metal posts. Once the ring began to open up, I could rake out the coals and douse with more water. Eventually I had the ring fully removed, which you can see below along with the black locust pole I used to tamp down the pile (this is about 4" diameter at the big end and 7 feet long), the sheet metal is about 12' long. 

Here's the finished pile this morning. For scale, you can see 3 of the 4 (I pulled one out in the process) metal posts where the ring was. There's a lot of really good charcoal (close to pure carbon), along with a few bigger chunks that didn't get fully burned, which is normal. Some I thought were way too big when I put them in, but I wanted to see what would happen. 

So this worked out very well. I turned a huge pile of brush into a good amount of charcoal which, when crushed, is a great soil amendment. This is also a stable carbon form that will persist for centuries in the soil. I started at 5:30 pm and was done by 9:30. Burning the pile, feeding the kiln, took 2.5 hours; then I let it burn down for about half an hour, and the quenching process took another half hour.