Sulphur dioxide (SO2)
Sulphur is input into the clinker burning
process via raw materials and fuels. Depending on their respective
deposits, the raw materials may contain sulphur bound as sulphide
or sulphate. Higher SO2 emissions by rotary kiln systems
of the cement industry might be attributable to the sulphides
contained in the raw material, which become oxidised to form
SO2 at the temperatures between 370°C and 420°C
prevailing during the kiln feed preheating process. Most of the
sulphides are pyrite or marcasite contained in the raw materials.
Given the sulphide concentrations found, for example, in
German raw material deposits, SO2 emission
concentrations can total up to 1.2 g/m3 depending on the
site location. In such cases, lime hydrate may be utilised to lower
SO2 emissions.
The sulphur input with the fuels is completely converted to
SO2 during combustion in the rotary kiln. In the area of
the preheater and the kiln, this SO2 reacts to form
alkali sulphates, which are bound in the clinker.