H.E. Booth
H.E. BOOTH is an authority on charcoal production. This article was edited from an FAO paper he prepared for the United Nations Conference on New and Renewable Sources of Energy, Nairobi, August 1981, of time there is a revision to traditional methods such as the earth pit.
BRICK CHARCOAL KILNS IN BRAZIL old-fashioned but with certain advantages
The portable steel charcoal kiln consists of two cylindrical steel shells, a conical lid and four chimneys. It has been tried extensively in charcoal production throughout the world for many years.
Under suitable conditions this kiln will make good charcoal. There are a number of examples in the developed world where it has been used successfully for many years producing charcoal on a fairly small scale. In the developing world, however, where these kilns have been tried, it is usually found that after a period
Meanwhile, the various kinds of brick kilns have continued to produce more and more charcoal in the developing world. This may seem surprising when it is considered that the steel kiln appeared in Europe in its present form more than 50 years ago. The reason for its failure in the developing world is that it requires certain specific conditions which either are not present or can be provided only in uneconomic ways. In Europe, on the other hand, these conditions are available, and thus the steel kiln continues to play a useful part in charcoal production. Briefly these conditions are:
· A high-price charcoal market.· Ready availability of cheap steel and corresponding fabrication and repair facilities.
· Ready availability of transport facilities, i.e., roads and vehicles and the means to process and carry small quantities of timber and charcoal in scattered locations using a mobile, highly skilled work force.
· No shortage of investment and operating capital.
The typical situation in a developing country is rather different. There, the traditional method of making charcoal is to carbonize the wood in pits dug in the ground or on the side of a hill, or to cover a pile of firewood with mud and earth - the so-called earth-clamp, or "parva". In most cases charcoal making is carried out by people without any access to investment capital. Such capital is indispensable, though it can, if necessary, be on a low level, involving people whose technological experience is limited.
A higher level of technology is available from portable steel kilns or from kilns made of bricks and set in mud mortar. While brick kilns are not mobile, they can readily be dismantled and rebuilt. In either case, there has to be a transfer of technology. The imported steel kiln has the advantage of making a whole kiln available instantly, but it requires back-up maintenance such as steel-plate welding and heavy sheet-metal working capability. These are usually quite beyond the local charcoal makers and have to be provided on a state or cooperative level, usually as a loss operation.
Brick kilns must therefore be built. Building them is a comparatively new technique requiring a supply of bricks or the ability to make simple direct-fired bricks from a sandy clay. Given these prerequisites, maintenance of brick kilns is very simple. They are virtually immune to damage from local overheating, unlike steel kilns. The only maintenance normally needed is the pouring on of mud slurry to seal cracks. Furthermore, when the kilos must be moved, say a few kilometres away, they are simply dismantled and the bricks re-assembled at the new site. However, brick kilns should be used only in cases where frequent relocations are not to be expected and where wood can be transported to the kiln.
Some types of brick kilns have no steel at all, merely mud and bricks. Others, such as the Brazilian type, have a ring of fencing wires to provide tensile reinforcement at the base of the cupola roof. The brick kiln is much larger than the steel one and hence produces ten to twenty times more charcoal at a single burn. The brick kiln has doors, a fact that makes loading and unloading simple, since wheelbarrows, carts and sometimes conveyor rolls can be used.
The steel kiln requires the wood and charcoal to be loaded and unloaded over the top rim of the bottom section of the unit, a laborious and dusty undertaking. The wood first has to be reduced to block form, typically not bigger than 30 x 10 x 10 cm. Hence, chainsaws and complex block-splitting machines are needed to make wood preparation practical. By contrast, both earth pits and clamps and brick kilns can utilize large logs of up to 50-cm diameter and 1-2 m in length. Typically, the wood is simply cut into billets about 1.8 m long.
Two problems affect the steel kiln in particular. First, since air leaks occur easily at the ground line, hot spots can crop up during a burn, leading to buckling and collapse of sections of the shell. This problem is reduced, but not eliminated, where the kiln is made of more costly heat-resisting steel. Hot spots also occur with brick kilns, but they do not damage the kiln itself. The second special problem of steel kilns arises from its low insulation value. The action of rain and wind can cause the kiln walls to become too cold. This slows down the exothermic decomposition of the wood near them and results in an excessive production of partly carbonized wood known as "brands". Brick kilos, because of their greater size and better insulation, are less susceptible.
Finally, it should always be borne in mind that the burning stage is only one small, though essential, step in charcoal production. The more important steps are the harvesting and transport of the fuelwood, and the delivery and distribution to market of the finished charcoal. The imported steel kiln gives an illusion of instant charcoal availability which tends to blur the vision of administrators and officials taking a good hard look at the real problems affecting charcoal supply in a developing country.
Advantages and disadvantages of steel kilns compared to other types
|
Factor |
Portable steel kiln |
Earth pit |
Brick kiln |
|
Cost in place ready to run (US$) |
5 000 |
- |
1000-2 500 |
|
Internal volume (m3) |
6.5 |
8-30 |
50-130 |
|
Cycle time (days) |
3-4 |
20-30 |
9-25 |
|
Maintenance |
skilled with workshop |
simple |
simple |
|
Mobility |
yes |
yes |
demolish and rebuild |
|
Life (years) |
1.5-4 |
- |
8-10 |
|
Charcoal quality |
good |
fair |
good |
|
Typical yield (percent weight basis) |
20 |
15 |
20 |
|
Ease of burning |
simple |
difficult |
simple |
|
Maximum size of fuelwood (cm) |
30x5x5 |
no limit |
200x30x30 |
|
Performance in rainy climate |
good poor |
good |
|
|
Ability to tolerate "hot spot" and accidents |
poor |
fair |
good |
PADDON & MARKER. 1979. The production of charcoal in a portable kiln. Trop. Prod. Inst. Pub. No. G119. London.
KANT, H. 1979. The development of forest energy resources in Ghana. Rome, FAO: FO:GHA/74/013.
PIOT, J., BREYSSE, G. & NANOT, R. 1980. Etude pratique de carbonisations en forêt classée de Gonse. République Haute Volta.
