Lime production: improved techniques in Malawi
Practical Action
The kiln's fuel efficiency, calculated at 42% is reasonably good for a kiln of this type.
The loss on ignition is between 36 -37%, meaning that approximately 86% of the calcium
carbonate entering the kiln is converted to calcium oxide. Again, this is a satisfactory
conversion rate for a vertical shaft kiln, particularly considering the difficult calcining
characteristics of coarse grained marble, the raw material used. The quality of the lime
produced is also reasonably good at around 60% available lime content and a particle size
distribution of 70% less than 150 microns. This is acceptable to the sugar processing
industry.
The main technical objectives of this kiln design have been met. These were to produce a
lime hydrate to meet the requirements of the sugar processing industry, negating the need to
import lime, and to utilize renewable fuel sources rather than the traditional use of
indigenous hardwoods, which is both costly and a major contributory factor in deforestation.
The kiln's operation provides employment for 57 people including those employed in
quarrying. This clearly demonstrates the ability of appropriate technologies to combine
labour intensive and technically efficient methods of production, thus maximising the
benefits and advantages of both systems.
Information at a glance
Type of kiln
Capital costs
Mode of production
Running costs
Type and quality of limestone
Type and quantity of fuel
Fuel efficiency
Conversion rate CaCO3 TO CaO
Hydration
Sieving/classification
Milling
Quality of lime produced
Principal market
Number of persons employed (including
quarrying)
Person shifts per 100 tonnes Ca(OH)2
produced (including quarrying)
Mixed feed vertical shaft kiln with forced
draft
Medium
Continuous at 4 tonnes Ca(OH)2
Medium
Marble, approx. 95% CaCO3
Charcoal. 30 MJ/Kg. 0.8 tonnes per day
42%
86%
Mechanical hydrator, 220Kg per batch
Manual sieving at 5mm. Air classification
system under test
Diesel powered hammer mill
Good, 60% available lime content
Sugar processing and building industries
57
1570
Postscript
This technical brief was originally written in 1991. The Balaka lime plant only continued in
production for a short time afterwards. The need to transport limestone to the kiln from the
Chenkumbi Hills added considerably to the production costs. Also, although the test
production runs indicated that high quality lime could be produced by the plant, the quality
could not be sustained under actual ongoing production conditions. The sugar industries in
Malawi decided not to use the Balaka lime in their processes and continued to use imported
lime.
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