Cement, Energy and Environment

8 World's largest ball in high regard due to easy operation and high availability (Figure 8). Secondly, conversions to high-efficiency separators in closed circuits are often undertaken, often involving the purchasing of replacement ball mills or the modernization of existing ball mills. Sometimes, ball mills are purchased as stand-by mills for vertical mills. Furthermore, ball mills offer price advantages in comparison to other mill types, particularly if supplies from China are considered (Figure 9). In recent years, a number of developments have dealt with the improvement and optimization of ball mills. Such efforts are prompted by the fact that ball mills are still widely used and by the increasing specific grinding costs. Studies by the VDZ or, by CRH, show that existing cement mills possess a high optimization 10 Combination grinding system with roller press at Ladce Cement (Koeppern) potential. One significant field is improvement of the grinding ball grading, which can reduce the energy requirement by around 10 per cent. Specific material transfer diaphragms and discharge diaphragms with material flow regulation bring a significant additional improvement. Modern noise sensors on the rotating mill shell can accurately measure the filling levels of the first and second grinding compartments independently of each other. The Flexibility of the HPGR!roller press allows it to be used in various system configurations as a "combi-mill" (Figure 10) together with ball mills for primary grinding and semi-finish grinding, or as a single-stage grinding process for finish grinding. Particularly in the last few years, a trend towards finish grinding has become discernible. Three points are viewed as the main reasons for this: 1. Significantly improved grinding element service lives, 2. New separator technology with static-dynamic separators (Figure 11 ), 3. The quality characteristics of cements from grinding machines other than the ball mill are no longer regarded as negative. 5