Hans-Peter Schmidt and Paul Taylor have invented a new version of the cone kiln they call the Kon-Tiki Kiln. Here's a picture:
The tap at the bottom is for draining the quenching water.
Here are some specs from Hans-Peter:
Kon-Tiki I
volume: 850 liters
Production capacity: 700 l biochar in 4 to 5 hours
yield: 25 to 30% (Dry Matter)
Here is the kiln in operation. He uses prunings and waste from his vineyard:
Lots more information in this great video: