Clinker heating rate

A major contribution came when Ono (1957) pub lished a microscopical study of the formation of port land cement clinker, tracing the changes of phase chem istry and crystal morphology as functions of raw material fineness, mixing, and heating rate. He concluded with a prophetic statement that the microscopical information might be useful in the control of clinker manufacture. 

Photograph 6-5 Amber belite crystals in 44- to 75-pm fraction of crushed clinker. Low maximum temperature, long burning time, slow heating rate, moderately slow to slow cooling. Coal-fired, wet-process kiln. (S A6620)... 

Scheubel (1988) found that the alite chord length could be used to construct a cumulative crystal size curve, the data from which were used to evaluate heating rates and retention times in various kiln systems. High-quality clinkers were said to have uniform granulometry, small silicate crystals, and easy grindability. 

Photograph 7-79 Free-lime nest colored by water etch in polished section. Chemical analysis gave clinker free-lime value of 2.69%. High maximum temperature, moderately long burning time, moderately slow heating rate, moderately slowly cooled, 31 MPa. Gas-fired, dry-process kiln, 3000 tons/day. (S A6697)... 

Burki and Braun (1988) asserted that the clinker structure from laboratory tests is principally determined by raw meal properties and to a lesser extent by the heating rate. Rapid heating was said to increase the alite formation rate, accelerated with a homogeneous raw meal made of a chalky, clayey limestone (cement rock). A coarse microstructure (large voids and large crystals) was produced from coarse meal made largely of monomineralic particles. No influence of the final size of the alite and belite was observed after variations in heating rates. 

It has been reported (Albats and Shein, 1997) that the strength of Portland cement with an elevated belite content may be increased by using a very high heating rate in the clinker burning process (as high as 20 °C/min) and by simultaneously increasing the... 

The operation of planetary and rotary coolers requires no special attendant personnel for control. The cooling air flow rate, the clinker discharge rate and the secondary air temperature automatically adjust themselves in relation to the clinker output of the kiln, the heat consumption and the temperature of the clinker on entering the cooler. Fluctuations in the discharge rate or temperature of the clinker on leaving the kiln which are caused by, for example, dislodgment of coating cannot be compensated in the cooler... 

By definition, the kinetic curve of a cement is the weighted sum of the curves for its constituent phases as they occur in that cement. The reactivities of individual clinker phases were considered in Section 4.5 and some effects of particle size distribution, which is a particularly important variable, in Section 4.1.4. Although many data relating particle size distribution directly to strength exist, much less is known about its relation to degrees of reaction. Parrott and Killoh (P30) presented data indicating that the rate of hydration, as represented by that of heat evolution, was proportional to the specific surface area during the period of hydration in which the rate was controlled by diffusion. 

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