Belite size distribution
Belite size is affected by several factors ranging from raw materials, the length of the burning zone, the fuels used in the production process as well as the conditions in the cooling zone.
Figure 1: example of belite crystal size distribution
The sizes of belite crystals in Portland cement clinker depend on a number of factors that relate to the raw materials, burning zone length, fuels used and combustion efficiency.
Raw materials
The relative proportions of alite and belite in clinker are predominantly determined by the lime saturation factor (LSF) of the clinker, which relates the amount of lime in the mix to the amounts of silica, alumina and iron oxide. Usual ranges for LSF are between 96-100 per cent and reducing the LSF below this level reduces the energy required to make the high-temperature phase alite. It is often considered that a higher energy requirement would lead to the growth of larger alite and belite crystals. However, crystal growth in a cement kiln is quite a complex business and this is not necessarily the case. The effects of burning conditions on belite are discussed later, but it is not only the proportions of the materials that affect crystal sizes but also the sizes of the different constituents.
