Energy efficiency in claybrick manufacture in South Africa

The South African market for clay bricks amounts to about 3.5 billion per annum. 60-70% are produced in “clamps”, stacked air-dried green bricks that contain about 5% fuel, which reach temperatures high enough to ensure vitrification when fired. However, clamps are both polluting and thermally very inefficient, so there is increasing pressure to adopt fixed kiln technologies to replace clamps, particularly as the cost of energy increases. Studies were carried out on a variety of such kilns. For medium-sized producers, with a capacity of the order of 30 million bricks per annum, a vertical shaft kiln appeared ideal. Its energy requirements were a little over 1MJ per kg of product; clamps could require as much as 7MJ per kg. In neither case was there any accounting for the energy required to dry the green bricks, as air-drying was used in both cases. For larger production, one of several designs of tunnel kiln seemed optimal. They required over 2MJ per kg, but this included the energy necessary to dry the green brick. Some consideration is also given to changes in the design of the standard brick, particularly the use of perforations in the brick. These improve the heat transfer during firing, and require less energy per brick because they weigh less. Being lighter, they are also cheaper to transport than a solid brick of the same size.