Cement, Energy and Environment

18 MPS BC mill at ACC in India (GPAG) grinding have been designed for capacities of up to 300 tph. Roller presses are employed for finish grinding and in combination grinding processes together will ball mills. Due to their high grinding pressures and short material compression time, the greatest energy savings are achieved in finish grinding. Finish grinding plants of the latest generation (Figure 19) are very compact. Due to improved separator technology and longer grinding element service lives, roller press finish grinding plants have become an alternative to vertical mills. The separator technology and drying in an air stream allow the mill to be fed with GGBFS with moisture contents of up to 15 per cent. Depending on the system configuration, the dried material from the external material circuit and the coarse material from the finished material separator can be mixed into the fresh feed material for the roller press. It is sensible to have a minimum feed material moisture content >2% in order to improve the material pull-in conditions for roller press. Coal grinding Today, the product fineness demanded when grinding solid fuels is approx. <0.5-5% residue The main advantage of vertical mills (Figure 18) is their process simplicity with drying, grinding, separation and material conveyance all taking place in one unit, combined with their very good energy utilization and low wear rates. In the meantime they achieve and equally high fineness of grinding >6000 g/cm 2 (Blaine) as ball mills. In slag-grinding systems, the external circulating material quantities are higher than those of raw material and clinker grinding systems because of the lower gas velocities in the mill. Tramp metal is removed from the circulating material by magnetic drum separators and other separating devices. Vertical mills can handle a maximum moisture content of 20 per cent. Moist materi al has the effect of a grinding aid and actually assists in the grind ing bed stabilization . Throughput rates depend greatly on the mill feed material and on the required product finenesses. Up to now, vertical mills for slag 19 Comflex grinding system with roller press (KHD Humboldt Wedag) 8