Main features of Fixed Chimney Kiln 2
The adoption of fixed chimney do not automatically results in energy savings and sometimes the performance of the fixed chimney kilns
may be comparable or even worse than a moving chimney kiln. Proper operation of the kiln is the key to achieve the energy savings.
Principle of operation of fixed chimney kilns The kiln can be divided into three zones –brick cooling, preheating and combustion zones.
In the cooling zone air picks up heat from the fired bricks while in the pre heating zone, green bricks are heated by the hot combustion
gases. In both these cases the mode of heat transfer is convection. Convective heat transfer depend on the temperature difference between
the gas and the solid as well as on the speed with which the gas passes the solid.
In the combustion zone the fuel is fed from the top through the fire holes. Most of the solid fuel drops down to the bottom of the setting and
burns on the floor of the kiln. The combustion of fuel depends on: a)the properties of the fuel; b) temperature and size of fuel particles;
c) availability of air for combustion; and d) fuel feeding rate etc. Control of air flow As mentioned above amount of air flow through the kiln
controls both combustion as well as heat distribution in the kiln. In general higher is the air flow rate higher is the fire travel in the kiln.
The air flow in the kiln is achieved with the help of chimney. The hot gases inside the chimney are lighter than the ambient air outside the
kiln, the difference in weight between the hot air column inside the chimney and outside air produces a pressure difference which is known
as draught (figure 4). This pressure difference results in air movement in the kiln. The setting in the kiln provides resistance to air flow and
therefore the quantity of air flowing through a kiln depends both on the draught produced as well as resistance provided by brick setting,
flue ducts and chimney.