A Bull’s Trench Kiln (BTK) emits black smoke that carries high quantities of particulate matter, carbon dioxide (CO2), carbon monoxide (CO), sulphur dioxide (SO2), etc. This emission pollutes the immediate surroundings of the kiln impacting the health of workers, local population, crops, trees, etc. The emission of CO2 and black carbon also contributes to global warming and climate change.
The emissions from large brick kiln clusters around cities such as the National Capital Region, Patna, Dhaka, and Kathmandu contribute to poor air quality in these cities.
The main reasons for high air pollution in BTK are:
Usually two firemen feed fuel continuously in a BTK for about 5–10 minutes, followed by a time gap of 30–45 minutes. In the case of coal, about 150–300 kg is fed by them in each session using large spoons, each having a capacity of 1.5–2.0 kg.
Such intermittent heavy feeding leads to accumulation of the fuel on the floor of the kiln. This heap of coal at the kiln floor does not get sufficient air for combustion and remains partially unburned, giving rise to emission of particulate matter and CO in the form of black smoke, thus polluting the environment.
In traditional operation of a BTK, fuel is fed in one or two rows of fuel feeding holes. The volatiles released from the fuel in the kiln do not get sufficient time for combustion. These unburned volatiles come out of the kiln in the form of black smoke, particulates, and CO.
Several of the fuels used in BTKs have high sulphur content. For instance, petroleum coke has sulphur content of 2%–6%, coal from Assam and Meghalaya has 1%–2%, and rubber tyres 1%–2%. Combustion of these fuels results in emission of SO2, which pollutes the surrounding air.