Portland cement when mixed with water undergoes the process of Setting & Hardening
The initial stiffening or setting of PC pastes appears to be the result of the rapid hydration taking place on the surface of the cement particles. This rapid initial setting is controlled by the presence of calcium sulfate and for this reason a small proportion of gypsum is interground with cement clinker to control the rate of initial setting. Following this the principal reaction is the formation of single calcium silicate hydrate(C-S-H) from the various anhydrous calcium silicates present in the cement particles.
Raw feed fed to kiln contains 30-40% water by weight
Semi Wet Process / Semi Dry Process
Raw feed, prepared by either the wet or dry methods according to the nature of the raw materials is formed into pellets or modules, which are fed into the kiln by way of a grate preheater in which the moving bed of nodulized material is dried and brought upto calcining temperature by heat from kiln .
Raw Material fed to kiln contains 2-4% water by weight
In this type of Separator Due to drag force of air separation of fines from coarse takes place. Fresh feed is fed to distributing plate, which disperse feed into air stream flowing up. Fines get entrained in air stream & coarse hits the wall of separator. After hitting the wall coarse gets collected into cone.
The Mill discharge material is fed on dispersion plate. The material then cascade down to separating (classifying zone) where tangential inlet air suspends feed particles against the opposing centrifugal force of the rotor.
Intense shearing force breaks apart the particle agglomerates for highly efficient classification.
Product size particles, controlled by rotor speed, pass through the rotor blades to the cyclone. Rejects fall down to the collection hopper & fed back to mill. An externally located fan sucks the fine. Air is again recirculated to the separator. Small amount of recirculated air is vented off.
Crystalization of liquid phase into mainly aluminate & ferrite
Clinkerization Overview Raw Meal Preheating Removal of Water Calcination Oxide Formation Belite formation Liquid & Phase formation CaO SiO2 Fe2O3 Al2O3 CaCO3 -> CaO + CO2 CaO + SiO2 -> CaO.SiO2 CaO.SiO2 + CaO -> (CaO)2.SiO2 (CaO)2.SiO2 + CaO -> (CaO)3.SiO2 (CaO)3.(Al2O3) ----- C3A (CaO)4.(Al2O3).Fe2O3--- C4AF Clinker Kiln Preheater Raw Meal 30 o C to 100 o C 100 o C to 300 o C 30 o C to 900 o C above 800 o C Above 1200 o C Cooling 1350 o C to 1250 o C Crystalization