farmers and landless labourers. Yields (weight of charcoal/weight of wood) from pits vary from less
than 10 per cent to over 25 per cent.
Brick and concrete kilns
Kilns made of bricks can be more efficient than earth mounds, can be operated all year round and
have longer lifetimes than metal or mud kilns, and are less susceptible to poor operator practices.
However, the high-grade charcoal that they produce may not be acceptable to domestic users, since
it is difficult to ignite. Switching to large, efficient kilns, has many economic and social implications,
as most charcoal is still produced by farmers and landless peasants who, under normal
circumstances, might not be able to benefit from the switch and, indeed, might suffer from it.
Brick kilns are ideal for replacing traditional kilns when consistent high-quality charcoal is required
in large quantities. The throughput of a battery of seven "beehive" kilns, for example, is around
15,000 cubic metres per year. However, the construction of such kilns requires a relatively high
level of brick-building skills, as well as a supply of bricks. This restricts the scope of such kilns in
many countries, but in areas where they can be cheaply built and maintained, they have proved to be
a very effective method of charcoal-making. The "beehive" kilns cost approximately $200-300 with
yields of up to 35 per cent of input wood.
One of the major advantages of the brick kiln over earth kilns of similar size earth kilns is that their
carbonization cycle is much quicker. Typically, a 50 cubic metre brick kiln has a carbonization cycle
of 8-10 days, whereas that of the comparable earth kiln is, at least, twice as long. Moreover, the
labour involved in operating the brick kiln is very much less than that required to construct and
manage the earth kiln. Furthermore, the operation of the brick kiln is generally much simpler than
the earth kiln: workers can be trained in its use relatively easily and shortages of skilled labour are
not likely to be a constraint on production.
Brick kilns, however, are usually permanent structures: they are, thus, only suitable in locations
where there is a supply of wood within easy transport distance and sufficiently large to last the
working life of five or more years of the kilns.
Portable steel kilns
Portable steel kilns are in the form of a
cylinder with a conical top. A kiln breaks
down into three components which are
designed to be easily rolled along the forest
floor to new burn areas or to be transported
by truck. Portable steel kilns have a small
output: the annual production from a typical
demountable kiln with a volume of 7 cubic
metres is in the range of 100-150 tons.
They are not, therefore, particularly suitable
for areas where there is a need for high-
volume production. Their ideal application is
where the source of wood is dispersed and
charcoal-making is carried out on a relatively
Figure 2: Using a portable metal kiln in Sudan.
Photo: Practical Action Sudan.
The advantages of the portable steel kiln are that it requires less labour than the small earth kiln and
has a generally greater yield of more consistent and higher quality charcoal. It is also much quicker:
the total carbonization cycle with a 7 cubic metre demountable steel kiln is 3-4 days; with a similar
size earth mound, the cycle is likely to be 10-14 days.
The mobile steel kiln, like the brick kiln, has the substantial advantage over the earth kiln in that
training in its use is very easy. The steel kiln can, therefore, be used even in areas where there is no
tradition of charcoal-making.