Civil Engineering Reference
In-Depth Information
Figure 8.11: Section through a tunnel kiln.
The tunnel kiln came into use after the Second World War. The kiln can be up
to 120 m long and is divided up into a warming-up zone, a firing zone and a
cooling zone. The unburned clay bricks are placed on a truck which moves slow-
ly through the kiln. The energy source can be coal, gas, oil or electricity.
In the brick industry there is a big difference in the energy consumption of differ-
ent kilns. The open charcoal kiln uses approximately twice as much energy as the
circular kiln, while the circular kiln uses slightly less energy than the tunnel kiln.
Energy consumption during firing in the circular kiln and the tunnel kiln varies a
great deal depending upon the product being fired, and falls considerably with
lower firing temperatures, to about 60 per cent for medium fired products.
Sorting
There is an uneven distribution of heat in an open charcoal kiln. The bricks at the
outside are usually less well fired than those in the middle. There is some shrink-
age in the circular kiln, but much less than that occurring in the open kiln. Tunnel
kilns give the most even heat distribution and shrinkage is minimal, even if the
outermost bricks have a tendency to sinter.