Lime production: improved techniques in Malawi
Practical Action
The slightly moist and hot slaked lime (calcium hydroxide, Ca(OH)2) is then allowed to dry
and cool for a period of 24 hours.
The lime is then sieved into plus or minus 5mm fractions with the latter retained, and about
11 %, being waste material.
The product from sieving is then milled in a hammer mill powered by a diesel engine, of the
type normally used for milling maize. The milling is done in order to produce a fine and
uniform product.
The milled hydrated lime is then bagged by hand.
The quality of the lime produced averages 60% available lime content. (Available lime
content is the measure normally used to compare the quality of limes. It means the amount
of chemically active freelime and is expressed as the calcium oxide or CaO content. In a
hydrated lime the theoretical maximum available lime content is 75%.)
Mechanical and air classification equipment, designed for this particular plant, is currently
being tested.
Mode of operation
The kiln operates on a
continuous 24 hour per day
basis. Although it is possible
to operate a kiln of this type
in fairly short production
runs of a few days,
considerable effort and
energy is wasted every time
the kiln is allowed to cool
down and has to be
restarted.
Production should, therefore,
be continuous with only
occasional shut downs for
maintenance and repair.
Figure 3: Technical detail of improved kiln design.
The associated activities
such as quarrying, hydrating
and bagging are, in this
particular case, only
undertaken during the day-
time shift.
Comments
One of the major issues of this particular lime production unit is its location. It was decided
to site the kiln at the town of Balaka, over 15 km from the quarry site on grounds that the
advantages of being close to power, water supplies and communications would outweigh the
disadvantage of needing to transport marble from the quarry to the kiln site. While this
decision may have been correct in the short term it is likely to prove economically
advantageous to site the kiln close to the quarry once water and power facilities are provided
at Chenkumbi.
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