chapter - 1 introduction - Meghalaya State Pollution Control Board

Hills Cement Co. Limited.
4. Grinding
After cooling, the clinker can be stored in the clinker dome, silos, and bins
or outside. To produce powdered cement, the nodules of clinker are
ground. Grinding of clinker, together with additions (3-5% gypsum to
control the setting properties of the cement) can be done in ball mills, ball
mills in combination with roller presses, roller mills, or roller presses.
Power consumption for grinding depends on the surface area required for
the final product and the additives used. Electricity use for raw meal and
finish grinding depends strongly on the hardness of the material
(limestone, clinker, pozzolana extenders) and the desired fineness of the
cement as well as the amount of additives. Blast furnace slag is harder to
grind and hence use more grinding power, between 50 and 70
kWh/tonne. Modern ball mills may use between 32 and 37 kWh/tonne.
Modern state-of-the-art concepts utilize a high-pressure roller mill and the
horizontal roller mill that are claimed to use 20-50% less energy than a
ball mill.
Finished cement is stored in silos, tested and filled into bags, or shipped
in bulk on bulk cement trucks, railcars, barges or ships. Facilities for
testing the physical properties like sieve analysis, setting time,
soundness, fineness, CCS, grind ability, moisture content, lime reactivity
& drying shrinkage, etc. For determining the particle size distribution of
the raw mix, clinker, cements, etc. a laser diffraction type PSD analyzer
may be installed having typical particle size range of 0.3 mm – 400
micron. To ensure consistent product quality and to permit the trouble
free and cost effective operation, the quality control plan for sampling &
testing of various raw materials, in-process materials and the final product
is suggested.
Additional power for conveyor belts and packing of cement is generally
low and not more than 5% of total power use that is estimated at 1-2
kWh/tonne cement. The power consumption for packing depends on the
share of cement packed in bags.
Pollution Control Consultants (India) Pvt. Ltd. 20