Cement, Energy and Environment

80 roller or one pair of opposite rollers fails, so that at least partial-load operation of the kiln line is possible. Ball mills are still used in 12 - 13 per cent of all raw material grinding applications, such as the grinding of dry or abrasive raw materials. 4 Types of mills for raw material grinding (OneStone) However, the development potential of ball mills seems to be exhausted, even though some new concepts are under investigation, such as ball mills with a conical housing and mills with variable UD ratios. Although roller presses have so The advantage of vertical mills is grinding capacity of 745 tph. All far generally been used in their relatively low power the leading manufacturers of combination processes with ball consumption and the vertical mills now build machines mills, they have gained simultaneous grinding, drying with capacities exceeding 600 significance for the finish and separation in the mill itself, tph. Large vertical mills with grinding process in recent years, together with a wide mass flow several independent grinding partly due to new developments. control range of 30 - rollers allow grinding operation Horizontal mills have so far little 100 per cent. This mill type to be maintained even if one been able establish themselves ~----------------------~~~=-~~~~~~~ achieves a specific power requirement of below 1 0 kWh/t at a medium raw material hardness and a medium product fineness of 12 per cent R 0.09 mm. The increasing throughput rates of vertical mills kept pace with the rise in kiln line capacities. For instance, a Loesche LM 69.6 with its grinding track diameter of almost 7m, six grinding rollers (Figure 5) and a drive power of 6600 kW can achieve throughput rates up to 1200 tph for medium-hard cement raw material. The example of a grinding plant at Grasim's Tadripatri works shows that the mill capacity decreases significantly if the cement raw material is hard. At this plant, 16000 tpd of raw material is ground by two LM 69.6 mills for a clinker output of 10 000 tpd. Each mill runs at its warranted capacity of 420 tph. However, at a different plant in India the same size of mills achieves a 5 Illustration of the Loesche LM 69.6 (Loesche) 3