Clinker poorly burned

Burning too near the discharge end of the kiln, where the temperature change is 1400°C to 1000°C, also produces small alite, and the clinker is usually poorly burned. Alite sizes of less than 15 pm in a 1000 tons-per-day kiln can be indicative of poor burning a 20-pm alite size is typical of poor burning in a 4000 tons-per-day kiln (Ono, 1980c). A well burned clinker (f-CaO < 0.6%) does not have alite crystals under 20 pm (Ono, 1995). 

Ono (1995) characterized the alite in raw (poorly) burned clinker in relation to the occurrence of the alite (1) next to free lime and (2) next to a belite nest. Where alite is next to a free lime cluster, the alite is small, isolated and dispersed, separated from free lime, con tains a large amount of melt, is strongly etched, and is heterogeneous and zoned. Alite next to a belite nest is relatively large, connected and welded, touching the belite, contains a small amount of melt, is weakly etched, and is homogeneous and flat (not zoned). 

Poorly burned clinker frequently contains many small belite clusters. If the raw mix contains coarse quartz grains, belite clusters appear even in well-burned clinker, and the alite size has a wide range. 

Ono (1991) listed some of the characteristics of poorly burned clinker free lime greater than 4.5%, tightly packed large free lime nests, belite nests with a surrounding of small alites, high porosity, a loose framework of free lime and alkali aluminate, and a flow pattern of matrix into the free-lime nest. Well-burned clinker was said to contain small free lime and octahedral periclase from dolomite and coarse aluminate and ferrite, resulting from equilibrium crystallization. 

Dusty clinker, coarsely crystalline silicates, low-porosity nodules, poor grindability Slow temperature rise, higher clinkering temperature, longer time in burning zone and transition zone (Wolter, 1985)... 

The clinker produced itsually has a low alkali content, which is due to the more intensive alkali volatihzation caused by the higher burning temperature employed. It also may contain increased amoimts of free lime, owing to the relatively poor bumability of the raw meal. The reactivities of the alite and behte phases may be relatively low, owing to the reduced amoimts of foreign ions incorporated into their crystalline lattices. 

---