Cement, Energy and Environment

GRINDING TRENDS IN THE CEMENT INDUSTRY Summary: The main trends concerning grinding processes in the cement industry are still higher efficiency, reduction of the power consumption and system simplicity. In the case of new orders, vertical mills have increased their share to over 60 per cent and ball mills have fallen to less than 30 per cent. It is somewhat surprising that the number of different grinding processes and mill types used by the industry have increased rather than decreased. The throughput capacities of the employed mills have risen, but in some cases this has brought machines, e.g. gear units, to the limit of their capabilities. In the cement industry, the use of separate grinding plants is currently showing a two-digit annual growth rate. The number of mill vendors has also increased and the competitive pressure has intensified. Dr. Joachim Harder OneStone Consulting Group GmbH, Buxtehude/Germany Introduction Worldwide , there are around 600 separate grinding plants in the cement industry. These receive their feed materials, such as clinker, slag, fly ash and other pozzolanas and intergrinding materials from various sources and are not preceded by an integrated clinker production line. This principle, known as the "split grinding" or "hub and spoke process", is a practical method in cases where the raw materials for clinker manufacturing are only available locally, and particularly not at the locations where the cement is consumed. For this reason , the TECHNOLOGY TREND market for split plants has grown especially strongly in China, India, Vietnam, Brazil and Turkey. However, numerous split plants also exist in countries like Italy, Germany, France, Spain, South Korea, South Africa and Australia. One reason for this is that existing integrated plants often remain in operation only as grinding plants after clinker production has been discontinued, and the reason is that grinding plants enable newcomers to quickly establish themselves on a market. The two foremost cement manufacturers, Lafarge and Holcim, increased the number of their grinding plants by 11 and 16 respectively in the period 2005 to 2008. Taken together, this makes up 16 per cent of all new grinding plants installed during this period. The variety of employed grinding processes already mentioned can already be seen in the case of the separate grinding plants (Figure 1). Today, approx. 70 per cent of the installed mills are ball mills. This statistic includes the figures for China. In the case of new plants, the number of ball mills is even lower, at less than 50 per cent, and energy– efficient grinding processes are preferred. This trend is even clearer in integrated cement plants, where the world wide percentage of new ball mills for raw material and coal grinding is now only approx. 10 per cent (excluding China) or 15 per cent (including China). The figures for clinker grinding are again comparable with those for separate grinding plants. Overview of grinding processes and applications The cement industry makes use of four mill types: the ball mill, the vertical mill, the roller press (also known as high– pressure grinding roll) and the horizontal mill. However, it also has to be taken into consideration that the different mill feed raw material, coal, clinker and slag have different grindabilities, feed particle size ranges and moisture contents and also demand different throughput rates, fineness data and other quality parameters. Each of the mill types and the associated grinding process are therefore more suitable for some 1 Tilbury grinding plant. owned by Cemex UK (Cemex)