Making Charcoal for Biochar at Home
Charlie Sellers, November 18, 2007
I advise testing your homemade version on a small scale first, to get some experience with the various stages and important variables. I first built one abroad with a welding rod can (like a very tall, wide food can) with no top and a few rough openings around the perimeter, at the very bottom. My first batch failed because I burned up all the charcoal, so I dug a shallow pit, put the can in that, waited until all of the volatiles came off (in the form of dense smoke), put a tight pot lid on top to keep air out, then piled earth over the openings in the bottom (filling in the pit essentially). We showed the locals that useful charcoal could be made from all kinds of forest and agricultural waste - which was everywhere since they thought it too smoky to use for cooking with in homes. Nobody got very excited - they could not afford to purchase charcoal often, but it was not that expensive. In the towns, the night cafes used huge "honeycomb" briquettes for cooking, instead of wood charcoal - made from coal (and known to be a poor product for most applications) and much bigger than the ones in China.
But is "charcoal" the same thing as "biochar", since we can't control the production temperature - don't you need certain characteristics to get the best biochar structure and chemistry?
I did see that you want the fuel to be relatively consistent in density and diameter, or the product is not all "done" at the same time. And vertical stacking gives an easy way to pack densely when the fuel elongated in shape. It seemed helpful to put a crude grate in - just waded up wire screen in the bottom - but I couldn't be sure.
My next attempt to scale up the process (for charcoal to feed into gasifiers) was not so successful - similar principle and scale as Jeff's hot water heater version, but using a 55 gallon drum and an electric blower at the bottom. I even put in a good grate, stacked firebricks around the inside circumference for insulation, and added a pipe and burner head on top - I don't want all that smoke (or flame) to go to waste, I want to use it for cooking on, or at least for flaring at night. We made some good walnut shell char for Burning Man, but I could never get the gas to flare - any suggestions. It eventually proved too hard to control the process - leaks at the bottom holes (bad welds), a poorly sealing top, and maybe bad air distribution. Version 3 will be better, but I may go back to small ones just to figure out the flare situation - especially because I live in a very urban area.
Charlie
http://improvedstoves.blogspot.com/ - just R&D related to fuel efficient biomass stove issues
http://ewbappropriatetechnology4.blogspot.com/ - just posts for the ATDT of the EWB-SFP; AT for developing countries http://travelswithcharlie.blogspot.com/ - most recent travel posts http://travelswithcharlie2.blogspot.com/ - older travel posts, including Nepal travelogue
http://www.flickr.com/photos/12820147@N07/sets/ - best of my travel photos
http://huiplesofguatemala.blogspot.com/ - my textile project in Guatemala - what colors!