My (I'm guessing Portuguese, but it could have been arabic, or Catalan, for all of me) is a little rusty, but I watched the video. I appreciate the benefits of biochar, and I'm planning on using it a lot in my projects, but I have a problem with the way they do it specifically. You see the conventional chimneystack top just coughing out this endless white cloud, which I grant might be a lot of steam, considering the colour, but I'm positive that you could feed that exhaust back into the combustion stream to burn off anything that isn't steam. I suspect that the holes on the bottom of the inner retort did serve to force any expanding volatile gasses out into the fire, so that's good. I just find it messy that they end with text overlaid onto the video of the belching chimney that suggests that you lower your carbon emmissions by making biochar.
I was thinking that a RMH would be a much better base for a kiln, and doing things this way is much closer to the bubblegum-on-a-stick end of the permaculture scale than I personally am comfortable with. There are better video examples, in English, by a guy out of Australia, using a similarly constructed device (that still leaves room for optimization) that takes the temperature much higher, and we can tell this because both laser thermometers and thermocouples are used on various models. The exhaust is still burning as it exits the chimney, and careful attention is paid to making sure the temperature exceeds that necessary for cracking the tars in the smoke, making the exhaust as clean as possible. That is much further along the scale, in my opinion. Search these fora for biochar.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein