Igloo type brick kilns in Zimbabwe
Practical Action
For industrial/engineering bricks, a pattern
called "face to face setting" is normally
employed, and the bricks are laid on their
edges/stretcher faces. "Face to face" setting
produces a much denser packing than the
"pillar" setting.
The third and final setting arrangement
employed is similar to the "face to face"
setting, but the bricks are laid on their bed
faces and their edges/stretcher faces left
exposed.
Figure6: Pillar setting (packing) inside an igloo kiln.
The bulk density in a seven metre diameter
beehive kiln would be about 120 bricks/ m2
for face bricks, whilst for industrial engineering bricks it would be 150 bricks/m2.
Operating Regime for an igloo/beehive kiln
As a matter of importance, these kilns are charged with bricks which are dry enough, ie with a
relatively low moisture content.
For a 24,000 face brick capacity kiln, the following would be typical operating regime:
1. Four days are spent on loading the kiln with a team of two setters and four loaders. After
loading, the entrance is sealed.
2. Low temperature firing would proceed for three days with one fireman per shift. At the
end of these three days, temperatures within the kiln are in the region of 850°C to
950°C. The fireman is manually feeding coal into the fire boxes, starting with a low fire
to gradually drive off the moisture content and bring the bricks to the soaking
temperatures.
3. With the addition of more coal, the temperatures are elevated to a range of about
1,000°C to 1,200°C and roughly maintained within that region. High temperature firing
proceeds for about four to five days. The condition of the bricks is constantly monitored
by checking the state and colour of the bricks through inspection holes. It is also during
this period that salt is added to the fire to achieve various colour shades of the bricks.
Dampers are used to regulate draught.
4. Cooling of the kiln takes about four to five days. It is absolutely essential that cooling
proceeds in a regulated manner. Cooling can, however, be accelerated after the initial
one and half or two days by the use of fans.
5. Finally, off-loading takes about three days.
Fuel consumption and energy efficiency aspects
Fuel consumption in igloo kilns at the brick plants studied (on the basis of quantities of coal
utilized) was found to range from 4.375 MJ/kg to 7.08 MJ/kg or from 4,375 kJ/kg to 7,080
kJ/kg.
These figures are comparable with experiences elsewhere in the world, where energy
consumption figures for similar types of kilns range from 2,160 kJ/kg to 8,500 kJ/kg (Energy use
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