Small-scale Lime-burning in Namibia
Investigations into various construction materials that can be produced locally have formed part of the ongoing activities at the Clay House Project in Otjiwarongo, Namibia. The onsite team comprised of several EcoSouth experts quickly saw the connection between the devastating bush encroachment and the wide-spread lime deposits throughout the region. Gate agreed to support investigation of the use of bush encroachment as the combustion material for burning lime and to ascertain the quality of lime. Upon determination that commercial quality lime could be produced, a second phase concentrated upon constructing a simple oven to burn lime with vistas toward its commercialization.
Prof. Nolasco Ruiz of CIDEM was the project leader and was able to construct a viable oven with clay bricks. The Clay House Project technician onsite could draw upon the farmhands as a workforce. This was an integral part of the project concept, that farmers could burn lime at the beginning of the dry season, thereby providing work for their farmhands.
The lime-burning at Otjiwarongo has attracted widespread interest from other municipalities, as well as local organizations and farmers interested in using the lime.
During the trial firings Prof. Ruiz and his team were able to produce nine tons of excellent lime. During the following months some of this lime was used to plaster the walls of the newly built clay houses, as well as a kindergarten built by a group of poor local women.
The behavior of the lime upon slaking was very good and with simple sieving and some selective crushing the lime was ready for use. Only a small amount of bones (unburned rocks) were discovered, something that normally happens whenever lime production begins. Upon termination of the trial burnings, the technicians and workers were able to determine the exact percent of each size of limestone, as well as the time and temperature required for burning.
The design of the kiln has proven to be correct and its performance was good. Some small cracks did appear, which was expected as the shrinking of the clay bricks (adobe) was factored into the design. Those cracks have been filled in and will not be a limiting factor to the kiln´s performance.
The use of adobe bricks for the walls of the kiln helps reduce the price of the materials, mainly the part of the price which should be paid to foreign producers and now is going to the very poor families which are making adobe bricks.