Engineering Chemistry S Datta

SILICATE TECHNOLOGY 421
1250°C Commencement of liquid formation Endothermic
– 1280°C
> 1280°C Further formation of liquid Endothermic
and compounds
*Main reactions between lime and clay.
Lime produced combines with main
constituents of clay viz. Al 2
O 3
and SiO 2
.
Crushed
shale
limestone
Mills
Oversize
Screen
Correcting
tank
Slurry
mixers
Water
Filtrate
Filter
Kiln
Fuel
Hot air
Gypsum
Cooler
Shale – 500 lbs
Limestone – 2400 lbs
Gypsum–70lbs
Air Clinker
storage
Water – 750 gal
Coal – 600 lb
Power – 90 kwh
Labour – 2.1 man hr
Per ton
of
cement
Mills
Storage, bagging
Fig. 19.6 Wet process for cement manufacture.
The analysis of typical samples of cement gives the following composition:
Lime ⇒ 55.06%; SiO 2
⇒ 22.92%; Al 2
O 3
⇒ 8%
Fe 2
O 3
⇒ 5.46%; MgO ⇒ 0.77%; Potash ⇒ 1.13%
Soda ⇒ 1.7%; CaSO 4
⇒ 1.75%; Unchanged clay and sand ⇒ 2.27%.
The final product formed consists of hard grannular masses from 1/8 to 3/4 inches in
size, called clinker. The clinker falls through openings in the stationary firing ring of the kiln
into rotating coolers, which simultaneously preheat the combustion air. Pulverising followed
by the fine grinding in tube ball mills and packaging complete the steps to the finished cement.
During fine grinding the following materials are added to the finished cement.
• Retarders such as gypsum
• Plaster or calcium lignosulphate
• Air entraining agents
• Dispersing agents and
• Waterproofing agents