A case study in lime production ~ Sri Lanka
Practical Action
Raw materials and quarrying techniques
In Sri Lanka limestone occurs in various forms, including:
Miocene limestone (over 95% CaCO3)
Coral (over 95% CaCO3)
Shell (over 95% CaCO3)
Dolomite (MgO (variable 8% -21%))
Calcite (CaCO3 (100% pure))
Miocene limestone is mainly consumed in the cement industry. Calcite: is limited in its
occurrence and is used in the ceramic industry. Shell, coral and dolomite are used for lime
production. However, it is estimated that coral and shell deposits will be exhausted in 8 to 10
years time. Dolomite deposits and the Miocene limestone would eventually have to be the raw
materials for lime manufacture.
Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which
is used in the hill country, is readily accessible, but needs to be quarried and broken down to
lumps of the required size. It is extracted manually using crowbars, picks and hammers.
Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer
to a kiln feed size of 50-80mm diameter. This part of the activity is mostly done by women.
In recent years lime and brick producers have experienced very great difficulties in obtaining
suitable fuelwood for burning in their kilns. The State has imposed a series of rules and
regulations on the transport of fuelwood due to rapid deforestation in all parts of the island.
The scarcity of fuelwood and calcareous raw materials (coral and shell) has resulted in
considerable increases in the price of lime.
The kiln and firing methods
The main type of fuelwood used is the trunk of the coconut palm cut into lengths of about
75cm. Coconut palm leaves, husks and coconut shells are normally used to start the fire in
the kiln.
One of the largest concentrations of the lime industry is at Akurala located 88 km south of
Colombo. Coral is used as the raw material. A typical kiln at Akurala has a cylindrical inner
wall which ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0
meters. The kiln is constructed with normal cottage type clay engineering bricks set in a lime
clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with
alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other
materials to rapidly initiate a fire. For each batch about 1.5 to 3 tons of coral are used
together with around 0.75 to 1.5 tons of
fuelwood. The kiln is ignited and allowed to
burn for approximately 48 hours and then
cooled to recover about 0.75 to 1.5 tons of
quicklime (CaO). Discharging is carried out
from the bottom. Batch type kilns are
normally used to burn coral and shell.
Depending on capacity, the output of the
kilns varies considerably.
In the hill country the greatest
concentration of the lime industry is in the
Matale area, with dolomite as the raw
material. The kilns are of the continuous
type and are taller than the kilns in the
coastal area. They are 3.0 to 3.5 metres
high with an inner diameter of 1 to 1.5
metres. About 2 tons of dolomite is loaded
into these kilns alternating with fuelwood
(coconut palm trunks), and daily a ton of
2