The main problems that you face in a Bull’s Trench Kiln (BTK) are:
Some of these are inherent problems of a BTK and, to a large extent, they will remain so. The better way would be to shift from BTK to Zigzag Kiln technology or to other efficient kiln technologies. However, there are several ways to improve the performance of your existing BTK.
Some of the ways to improve the performance of your BTK are listed below.
The current practice in a BTK is that the fuel is fed for 5–10 minutes continuously every 30–45 minutes. During this 5–10 minutes session, about 150–300 kg of coal is fed by two firemen using large spoons, with each spoon having a capacity of 1.5–2.0 kg of coal.
Such heavy intermittent feeding of coal results in large quantities of coal getting accumulated at the base of the kiln. This pile of fuel does not get sufficient air for combustion and thus does not burn completely, leading to wastage of coal and high air pollution.
The combustion of coal can be improved by improving fuel-feeding practices as suggested below.
Improvement in fuel combustion will result in reduction in fuel consumption and air pollution.
Air is required in the kiln for the combustion of fuel to produce heat and for heat recovery. Heat recovery means the transfer of heat from the brick-cooling zone to the firing zone and from the firing zone to brick preheating zone. Ideally, all the air should enter the kiln from the brick unloading end and should flow through the cooling zone, the firing zone, the preheating zone, and the flue gas ducts before coming out through the chimney.
The inside of the kiln is at a lower pressure compared to the atmospheric pressure. Therefore, wherever there is an opening, air from the surroundings will enter the kiln. Hence, only the brick unloading end is kept open for entry of air. However, there is a possibility of cold air from the surroundings leaking into the kiln through wicket gates, kiln roof, flue gas ducts, kiln walls, and tarpaulin (tirpal).
Any leakage of air into the kiln will reduce the amount of air entering the kiln from the brick unloading end, and hence will reduce the extent of heat recovery. Also, combustion efficiency is reduced due to lesser amount of air being available for the combustion of fuel. Leakage of cold air near to the firing zone will also create difficulty in maintaining high temperatures and will eventually increase the fuel intake.
Preventing air leakages will reduce fuel consumption and improve the product quality.
In a BTK, heat losses take place through the kiln roof, side walls, wicket gates, and covers of the fuel feed holes. You can reduce these heat losses by:
Reducing heat losses in the kiln will result in lesser fuel consumption.
Good housekeeping and operational practices can help a long way in improving the performance of your BTK. A few such best practices are listed below.