I make all my charcoal using Maureen the charcoal kiln . This is a transportable ring kiln , 7ft in diameter and holding around 2 tons of hardwood. The kiln,lid and chimneys all fit onto a 8ft x 4ft trailer for transport to new woods .
when the kiln is set up on a bit of roughly level ground the first bits of wood are put in radiating out from the centre .These are the bearers that will support the wood charge and keep the air flowing underneath from the inlets . Further bits of wood bridge over the bearers to form a platform for the rest of the charge . A circle about 18 inches accross is left in the centre of the platfrom and thin bits of wood bridge over this whole to support leaves , dry sticks and brown ends from a previous burn to get the kiln going well at the start .
The kiln is filled with wood about 2ft 6in long with thinner wood being near the outside and the bottom of the kiln and larger pieces near the centre and the top of the kiln . The kiln is filled to about 1ft above the top of the kiln and the lid perched on the top of the wood . The kiln is lit with a piece of rag dipped in parafin and tied to the end of a stick which is then lit and pushed in through one of the inlets to the centre of the kiln . Earth is removed from around the bottom of the kiln to ensure enough air gets to the fire to get it going well . These can be blocked up when the fire is going well . Initially huge amounts of steam are given off as the wood dries .
After around 2 hours the lid will settle onto the kiln and the chimneys can be put onto 4 of the inlets . It's a good idea to pre-warm the chimneys on the kiln before they are needed so that when they are put on the outlets the rising warm air starts the circulation within the kiln. The chimneys are moved to the inlets after about 4 hours so that the charge is burnt evenly . To further check that the burn is even accross the kiln splash water onto the side of the kiln , its then easy to see how far down the kiln that the burn has progressed as the water sizzles .
As the burn gets lower down the kiln the smoke tends to take on a yellow tinge before as the burn finally gets to the bottom of the kiln the smoke turns a bluish and more transparent .
At this point the kiln is closed off by seaking the lid with sand and blocking the inlets and outlets with socks filled with wet sand . The kiln is then left to cool for a day , and shouldn't be opened during this time or it might start burning again and burn all the charcoal and damage the kiln .
The kiln can be unloaded on the third day , with partly converted wood (brown ends ) and bits of charcoal that are covered in wood tar being discarded . The charcoal is shovelled onto a screen to seperate the dust and pieces smaller than .5 inch . The chips are good for horticultural charcoal .