The rotary kiln is 60 m long and 3 m in diameter. It rotates at 1 rpm.
Coal is ground to a fine powder, mixed with air and blown into the rotary kiln, where it ignites, producing the necessary heat.
Theoretically, to convert 1 tonne of limestone into lime, 3.17 GJ of heat energy is required, as the chemical reaction occurring is endothermic. However, due to energy losses through the process, the actual amount per tonne of limestone calcined is between 5 and 6 GJ.
The chip will be in the kiln for 2 hours. The temperature in the kiln ranges from 1200°C at the terminal end to 1000°C at the upper end.
Not all of the limestone is converted to lime. A small amount known as ‘loss on ignition’ (LOI) remains. This is about 0.5–1%.
Every hour, a sample of lime chip exiting the kiln is taken and sent to the on-site lab for analysis.
McDonald’s Lime Limited