For what it's worth, a simple way to make biochar. Take one galvanised dustbin and drill about 50, 10 mm holes roughly equidistant in the base. Obtain 3 house bricks or similar and stand on edge, to act as feet but leaving as much space as possible in the middle to allow air to enter through the base of the dustbin which is placed on top. Get two iron bars to put across the top of the bin to make a gap of about half an inch when the top is put on. Make a hole 5 inches in diameter in the centre of the lid. Make cuts approximately 1 inch deep and 1 inch apart all around the cut, then bend the results upwards at right angles. This will stop the 3 ft length of 8 inch stove pipe from sliding off. Additional needs, one pair fire fighters heat resistant gloves and one container to hold at least 25 litres your choice of liquid fertiliser. 25 litres will hold 20 litres of biochar without much visible expansion. Also a metal hand size shovel with long handle to start putting the HOT biochar into the liquid fertiliser.. A hosepipe with a spray will start the quenching procedure. Next step, fill the bin to within 3 inches with dry wood chip/shavings of one sort or another. Put the two iron bars across the top of the bin. sprinkle some paraffin over the chips and ignite. When well lit put on the lid (evenly all around the rim) and then place the stove pipe over the hole in the lid.. It is important that the heat can circulate through the wood chip so avoid having any fine sawdust in it. The burn should take roughly half an hour so at that point watch out for any red hot ash falling out of the holes at the bottom of the bin. Dismantle the top and using the hose pipe briefly quench the flames to just stop the burn. Using the shovel transfer the very hot biochar into the liquid fertiliser, or if you are brave enough, pick the bin up to tip it in. You will probably find some unburned fuel in the bottom centre of the bin but that wont notice when you come to put it on the garden. For those who try, GOOD LUCK

One think l forgot to mention, when you place the shavings into the burner, DO NOT compress them. Interferes with the air and heat flow. If you have drying facilities, shreddings from the garden, e.g. corn stalks runner bean stems, hedge clippings, can all be turned into biochar, but l tend to incorporate them with the wood chips.