Increase in energy efficiency and enhancement of cement properties by means of separate ultra-fine grinding

摘要

The past 15 years have seen a continual increase in the fineness of cements in Germany [1]. Accordingly these now contain larger proportions of fine particles, which significantly determine the cement properties. In absolute terms, the fine range only accounts for a small part of the cement, but it is of crucial importance with regard to quality, for example the early strength of the cement. With the conventional process, the entire product is ground and classified, so that it is scarcely possible to specifically influence the proportion of fine fractions in the particle size distribution. The ball mills predominantly used in Germany generally produce the desired particle size ranges, but are not particularly energy-efficient. Vertical roller mills and high-pressure grinding rolls operate far more efficiently. Broad particle size ranges can however not be produced in all cases, and usually also not with optimum efficiency. A study was therefore conducted to establish how the missing ultra-fine fractions of the products from high-pressure comminution can be produced in a separate ultra-fine grinding unit (stirred media mill) by means of separate multi-stage grinding and subsequent mixing, and the effect this has on cement quality. The cement properties of the mortar samples produced by separate ultra-fine grinding do not essentially differ from those of a reference material, provided that there is no significant difference in the particle size distributions. It is possible to specifically influence the cement properties by adjusting the particle size distribution, in particular by altering the proportion of the ultra-fine fraction. Separate ultra-fine grinding can thus provide a further means of regulating cement properties to suit requirements. Furthermore, it can also reduce the specific energy demand for cement grinding as compared to a ball mill.