Those of you following the biochar-hawaii list know that i’ve stopped using my kiln, and am now focused on making biochar in a pit. This is both for reasons of scalability and wear; my 55-gal steel drum kiln/retort could only make ~23-gal of char, and the surrounding kiln blocks cracked from repeated heating.
Hence, a pit. Mine is lined with blocks for clean char and easy unloading. Continuously fed wood, pyrolysis occurs at the air-starved bottom of the pile, gradually the pit fills up, then i cover and let it cool for a day, before opening and scooping out the finished char:
That first small pit worked well, so i made it bigger and sure enough, it scales well:
|Width||Length||Depth||Gallons||Cubic feet||# of blocks||Gallons of Char|
|32||48||24||On second burn:||82|
That 82-gallon operation took 2.5 hours to do the burn, then 2.25 hours the next day to unload, crush, sort, sift, and load into buckets. That’s 82/4.75 = 17.25 gallons of char per hour of work. That’s not bad, given that i’m working with some cheap concrete blocks, a piece of old corrugated roofing, and a shovel. With more money and technology, like a continuous pyrolysis machine, you could certainly get vastly more char per hour of labor, but those machines start at $100,000. I’m feeling quite happy about my pit. The Biochar2010 album has all the pictures.
I gave a biochar talk to the Kona Coffee Grower’s Association on June 2. 10 minutes of that talk got uploaded to YouTube. I then addressed the Hawaii Tropical Fruit Growers on July 19, that time with a fancy presentation with charts and pictures. Next will probably be an evening talk in Waimea on August 8, and then a 1-day workshop on making and using biochar here at our farm, date TBA.