While the cement manufacturing process has a long history and the machinery and controls that now exist on modern precalciner kilns enable stable production of consistent product, it is not so uncommon for some peculiarities to arise over time, such as unexpected mineral build-ups. Dr Clark is asked to explain the presence of such occurrences in kilns. This prompts distant memories of other incidents when mineral accumulations have strangely appeared in cement plants without obvious explanations.
A few days ago an intriguing question arose concerning deposits of build-up in the tertiary air duct of a cement kiln. The chemical and mineral composition of these build-up deposits had been investigated with spurrite, 2C2S.CaCO3, having been found to be present. On one occasion the deposits were greyish-black in colour and contained a high level, about six per cent, of organic carbon. How could such minerals be present in build-up formed in a tertiary air duct?
