Even though from a technical point of view the Portland cement production process is well defined worldwide, there is still an increased demand for high quality and high performances cements. This is mainly due to the urgent needs of cost and energy savings, both for economical and environmental reasons. In order to comply with the most advanced standard, during the last years the use of grinding aids has been spreading in several countries.
The grinding process of cement absorbs 60-70% of the total energy employed. Finish grinding accounts for about 38% of specific electric power consumption. The quantity of energy required by the process to obtain the correct fineness is only partially employed for the creation of new surface: in fact most of the total energy is lost as heat. Grinding efficiency rapidly decreases as fineness increases, mainly due to the agglomeration between the finest particles.
Grinding aids are organic substances that are strongly adsorbed on the surface of ground particles, so that preventing agglomeration and coating on ball and mill lining. Thanks to their dispersing effect, grinding aids also increase the efficiency of air separators because the finest particles are not carried along with the largest. The result is a reduction of circulating load and an improvement of particle size distribution. The advantages obtained by the use of grinding aids are the following:
- significant mill output increase at the same fineness. The increase in production can be used to reduce production costs or to cover market demand.
- Fineness increase at equal output, or both effects. In some cases very high fineness may only be obtained by using grinding aids.
- Improved particle size distribution at equal fineness. It is well known that the particle size fraction between 3 and 30 μm is directly related to the strengths development, and the fractions below 3 μm contributes to the early strengths . The use of grinding aids allows higher mechanical strengths to be obtained thanks to a positive influence on particle size distribution.
- Higher separator efficiency.