Lime Kiln - Carbon Dioxide Emissions

Carbon Dioxide Emissions

The lime industry is a significant carbon dioxide emitter. The manufacture of one tonne of calcium oxide involves decomposing calcium carbonate, with the formation of 785 kg of CO₂ in some applications, such as when used as mortar; this CO₂ is later re-adsorbed as the mortar goes off. Additionally, if the heat supplied to form the lime (3.75 MJ/kg in an efficient kiln) is obtained by burning fossil fuel it will release CO₂: in the case of coal fuel 295 kg/t; in the case of natural gas fuel 206 kg/t. The electric power consumption of an efficient plant is around 20 kWh per tonne of lime. This additional input is the equivalent of around 20 kg CO₂ per ton if the electricity is coal-generated. Thus, total emission may be around 1 tonne of CO₂ for every tonne of lime even in efficient industrial plants, but is typically 1.3 t/t . However, if the source of heat energy used in its manufacture is a fully renewable source, such as solar, wind, hydro or even nuclear, and depending on the ultimate use of the lime there may be no net emission of CO₂. Less energy is required in production per weight than portland cement, primarily because a lower temperature is required.