It is preferable to maintain the Kiln on one site as this increases the yield of Charcoal and the size of the kiln over a number of burns. To explain; each time the kiln is fired and emptied a small amount of soil is removed this leads to a hollow forming under the kiln hence larger capacity. And as moisture is removed from the soil a more even burn is achieved. Never site the kiln on concrete as you will never get a good seal and will most likely damage the concrete. As we are not a commercial concern we will most likely keep shifting the Kiln.
The eight vents should be spaced out equidistantly around the kiln and the intervening gaps filled and packed with Soil. Only about four inches should protrude into the kiln any more and the area above the vent will not burn, any less and the heat build up may buckle the kiln wall.
Never let the vents angle down to the centre of the kiln, as this will restrict chimney access. It is better to have them angle away or stand level.
After firing the kiln will produce a lot of smoke most of this is steam as water is forced out of the wood, ground and Kiln which should dissipate quickly even more so from within woods. If in the open half a mile from a major road it may not be advisable to start a burn. When sitting a kiln for the first time it is often an advantage to have a bonfire in the kiln on the site to dry out the ground beneath. (Hot Tip remember the kiln acts like a chimney and will burn very quickly and vigorously be careful).
This is the most important stage of preparing the kiln more time spent here will improve productivity. This is a two person job one in the kiln the other supplying him with wood.
Spokes. From inside the kiln place spokes either side of each vent to the middle of the kiln leaving an 18-inch working space. These should be about 3 inches high and are there to let Air flow all around the kiln.
Wheel. This is a ring of timber around the kiln which should cone outwards try to start with the thinnest timber at the base circa 3 inches diameter working up to 5or 6inches at the top. When the stacking reaches half to 3 quarters full it is then best to stack from the outside up to the level of the lid. The reason for stacking like so can be best explained if you look at a diagram of heat distribution in the kiln. Any further stacking should now be left until after the kiln is alight. (Hot Tip beware of bridging. This is where timber in the upper area of the kiln supports its self and does not fall leading to an uneven burn and brown ends. This is due to poor stacking in the kiln.)
This is best achieved using an old rag some used oil and a little petrol or diesel to soak the rag. (Hot Tip do not use a lot of diesel or petrol as this will taint the charcoal and is unnecessary to light the kiln.) tie the rag to a long piece of timber then pour on some oil and soak with fuel light the rag and place into the centre of the kiln. Then add some dry timber around the flame and let the fire take. (Hot Tip do not stack the rest of the kiln until after the fire has taken, as it is a pig to unstack).
When the fire is alight you can then stack the centre with timber of any size but try to keep it tight. Stack till the timber is proud of the top of the kiln and then place the lid on so that as the wood below burns the lid will drop a few inches in to place. (Hot Tip the smoke coming off as the lid is placed on will be steam beware of steam burns).
Give the Kiln half an hour for the fire to get a hold and the lid to drop.
When down you can begin to seal the lid. Use sand around the top to seal the
edge of the lid of the kiln. Then place the four chimneys on four opposite
vents and block up all the Ports with soil. The Vents will work out for them
selves whether they are chimneys or air inlets. After a few minuets all chimneys
should be blowing steam. (Hot Tip if a chimney is not drawing it is possible
to help it draw by swapping it for a hot one, which is drawing. Use gloves
or a dry wool jumper to protect your hands from the heat). You can then decide
dependent on the conditions how much air flow to allow through the kiln and
there by the speed of burn. Placing bricks or tiles over the vents to close
them off and leave an opening of a third or two thirds does this. Place the
bricks to the side of the vent, which is directly in the wind, as wind directly
on one vent will cause that side to draw more air and therefore burn faster.
Generally if the weather is colder a slow burn is desirable to allow all the
timber to cook at the same rate. The kiln is now safe to leave for the night
but remember the sides and lid will become very hot please ensure that there
is no public access and that no timber is left to close.
The new day or half way through the burn brings the time of the hot chimney shuffle. Basically this involves changing all chimneys to vents and vice versa to ensure that no area in the kiln misses the burn. (Hot Tip use a dry wool jumper to remove the chimneys as this gives better heat protection than gloves alone.)
The burn has finished when the smoke is tinged blue, When charcoal is it self burning, from all chimneys. It is now time to end the burn, this is achieved by removing the chimneys and filling all the vents with soil to stop any air flow into the kiln, No air no fire. (Hot Tip old socks filled with soil or tins of the right size, e.g. SMA milk tins, make emptying the vents for a new burn much easier).
Let it cool.
Again at least a two man job. First draw lots; the loser goes in the kiln with a shovel the other stay out side to grade and bag. Break up large pieces and shovel the charcoal on to the grader. The grader can be a timber framed chicken mesh sieve hung on the side of the kiln, charcoal is required in lumps no bigger than 5 inches and no smaller than 1 inch. Fines below 1 inch could be used as fertilizer or in mesh bags as a water filter instead of hay or straw in streams. The charcoal should be bagged in plastic bags, as it is bone dry and will draw moisture, and stored out of the rain and off the floor. As you empty the kiln look out for Brown ends these are part burnt pieces of wood that appear brown and will not break when tapped sharply. Put them to one side as they are great for restarting a new burn but must not go into the charcoal. (Hot Tip Wear a dust mask when emptying and not your best clothes. You may want to wear goggles but I found no irritation when I was emptying the kiln. Get a shower you look scary!). Once empty scrape the tar from the inside of the kiln and clear out the vents. If this tar is left it builds up and solidifies and is a pig to clean out your better doing it now.
To store the kiln place it on its side on blocks and the lid on it side, protect the outside with old oil or vegetable oil. Store the vents and chimneys indoors also protected with old oil or vegetable oil. (Hot Tip If the lid gets out of shape it can be reshaped on a flat area of say concrete with one person stood in the middle and another going round the rim with a hammer)