Introduction of VSBK firing kiln
Specific coal consumption corresponds to gross calorific value of coal as 18.8MJ/kg ( 4500 kcal/kg ) and for a fired
brick weight of 3 kg ** discussed later in detail, the BTK is the continuous Bull’s Trench Kiln
firing zone: the fresh air com¬ing from below cools the fired bricks before unloading.
The kiln works as a counter-current heat exchanger, with heat transfer taking place between the upward moving air
and downward moving bricks ( inter¬mittent movement ). The maximum temperature is achieved in
the middle of the shaft where fire is maintained. At in¬tervals of 2 to 3 hours, a batch of fired bricks is unloaded
at the bottom. A batch of bricks chas four to six layers.
To understand why the VSBK is the most efficient kiln, we will have to understand that in a brick kiln only a small
part of the heat is utilised for the firing and drying opera¬tions and most of the heat is lost. Efficient heat
transfer process and lower heat losses makes VSBK more efficient.
There are thus excellent reasons to promote such an energy-efficient kiln. However, the VSBK also has its
lim¬itations and it may not be the best solution for all situ¬ations. Its relatively short firing period of around
24 hours means that the green brick must be suitable to withstand quick heating and cooling to produce high
quality bricks and the firing process requires skilled personnel. BTK and intermittent kilns are much less
sensitive to green brick quality as the bricks take several days to be fired.