Lime production: traditional techniques in Patarra, Costa Rica
Practical Action
The size of the fuelwood used varies from 50mm diameter for kindling, to 400mm diameter
logs which can be up to 3m long. Lime producers experience considerable difficulty in
obtaining suitable fuelwood and often need to bring wood from distant places.
There would be enough wood from cuttings from plantations, but preparation and transport
of this material is more expensive than fuelwood from traditional sources.
Agricultural production in the country is growing rapidly, and there are plenty of residues of
crops that can be used as fuel. Many lime producers are considering using this waste, even
though the cost of wood is still low.
Stone is extracted by hand from small surface excavations using picks, crowbars, hammers
and dynamite. When large rocks need to be broken, a hole is dug and dynamite is used, but
much of the rock taken straight from the quarry face is of suitable size for putting in the kiln.
The kiln and firing methods
The kiln is cylindrical in shape, it is lined with stone blocks, and is usually placed in the
slope of a hill. The internal dimensions of the cylinder vary but an average size would be
approximately 3m in diameter and 4m in height. The kiln has two ramps, one to the top of
the kiln, and one to
the base. It has one
firing opening in its
front side, which leads
into one trench
running to the centre
of the kiln.
To build up the stone
in the kiln an arched
vault is first built over
the trench using large
boulders.
Figure 1, Sketch of traditional kiln
Other large rocks are
then piled on top of
these boulders and
then stones are added
which gradually
decrease in size from
40cm near the bottom
to 2.5cm in the top.
The kiln is fed with
fuelwood through the
opening at the bottom.
Approximately 30 tonnes of marble and 24 tonnes of wood are required for each batch. The
kiln is ignited and fed with wood for two or three days. A change of colour of the stone at the
top of the kiln indicates when to stop adding fuel. Usually a layer of recently hydrated lime is
then placed over the top of the kiln to seal it. This allows the hot kiln gases to circulate
round other areas of the kiln apart from the top because there the conversion of stone to
quicklime has already taken place. This stage in the process lasts a few hours.
Usually lime producers obtain one batch per week, spending 10 hours charging the kiln, 60
hours burning and two or three days allowing the kiln to cool down before discharging. The
firing hole is used to discharge the kiln directly into a truck. Finally a man goes inside the
kiln to finish the discharge.
The kiln always has a shed for storing the firewood and sometimes this area is used to store
and bag the lime as well.
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