Cement, Energy and Environment

100 00 • ,.... 'tJ!. 60 ...... e I'll .s:: 40 VI 20 0 0 Vertical mill Other fineness requirements, because the grinding pressures and , in some cases , the grinding table speeds can be adjusted fully automatically. Important mill developments Vertical mills Mill type ~ Without lOCal Chinese ma11<et In the raw material and coal grinding sectors, vertical mills have maintained their high market shares of 89 - 90 % and have improved to almost 40 per cent in clinker grinding applications. With 41 0 vertical mills ordered, including slag grinding systems {Figures 21 ), the number of different design versions has increased. Loesche successfully transferred the 2+2 principle to larger mills 20 Types of mill for coal grinding (OneStone) on the 90 ~m screen for petroleum coke and anthracite and < 10-15% residue on the 90 ~m screen for hard coal. In each case, the required residue on the 200 ~m screen is 0%. Finer grinding of the coal reduces the NOx emissions of a kiln line, but simultaneously decreases of throughput of the coal mill and raises the specific power consumption of the grinding process. Reduction of the residue on the 90 ~m screen by two percentage points raises the electrical power intake by around 1kWh/t. While the specific power consumption for grinding depends on the required product fineness and the grindability, the amount of wear in the mills is mainly determined by the quartz and pyrites content of the coals. Figure 20 shows that in recent years only two types of mill accounted for most coal grinding applications in the cement industry. Vertical mills have meanwhile achieved a share of almost 90 per cent, while ball mill are just over 10 per cent. Ball mills are almost exclusively employed for fuels with poor grindability. Up to now, the capacities of vertical mills for coal grinding in cement works have ranged up to 50 tph. Keeping pace with the trend towards higher kiln throughput rates has presented no problems. Vertical mills can cope quite flexibly with changes in the type of fuel, different grindabilities and 21 Slag grinding plant with Loesche mill in Rouen, France (Loesche) QM Grinding tor~ =r z.soo leN 22 Development of roller modules for the Quadropol (Polysius) 9