Importance of Thermal treatment in Kiln on clinker reactivity
Thermal treatment of raw mix has an important role in amount of clinker phase formation as well its reactivity.
Experts view is requested to elaborate the role of following thermal treatment.
1. Rate of heating with in the kiln
2. Maximum temperature at burning zone
3. Time spend at hotest/maximum temperature zone
4. Cooling after buurning zone
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re Importance of Thermal treatment in Kiln on clinker reactivity
The hydration reactivity of clinker minerals is determined by five main influencing factors;-
1. Heating rate in the burning zone.
2. Maximum temperature reached.
3. Residence time at max. temperature
4. Rate of cooling.
5. Amount and type of foreign ions incorporated into the clinker mineral crystal structures.
Each of these factors can influence one or more of the following clinker properties, each of which affect mineral reactivity to varying degrees;-
1. Alite, belite and aluminate crystal size
2. Crystal polymorphic type. eg cubic or orthorhombic aluminate, alpha, beta or gamma belite etc.
3. Stability (reactivity) of the polymorphic type.
4. Presence of belite and free lime clusters.
(a) A slow heating rate is likely to cause large alite size an loss of alite reactivity.
(b) Optimal time in the burning zone will promote the transition of belite to the alpha polymorph, improving its reactivity.
(c) Insufficient burning zone temperature or time in the burning zone will result in large clusters of belite and free lime, which reduce the surface area of belite available for hydration, reducing the reactivity..
(d) A slow cooling rate results in larger aluminate crystals and allows impurities in belite crystals to crystallize out along lattice planes causing inversion of alpha belite to the the beta polymorph, reducing its reactivity.
(e) Incorporation of alkali into aluminate results in a change from the cubic to orthorhombic polymorph resulting in a subsequent improvement in aluminate reactivity.
Given the same raw mix chemistry, mineralogy and particle size, the most reactive clinker is produced in a kiln having a rapid burning zone heating rate, sufficiently high maximum temperature and burning zone residence time, and a rapid cooling rate. Which is why you often hear the old saying that a kiln should always have a "short, sharp, hot flame".