We wish to know about oxygen enrichment in the cement kilns/precalciners. Please brief us about the expected merits and demerits. Are there any cement plants using this technique? If yes, then why is it not used commercially on regular basis in most of the cement plants.

This is a big question! The merit is that the output of the kiln can be boosted by up to 15 per cent, the demerit is that the oxygen is expensive and therefore the costs of producing the additional clinker are higher. If market demand exists with good prices for cement then oxygen enrichment can be a good option. There are a number of kilns in the USA using oxygen enrichment of either the main burner or the precalciner. It is worth noting that CEMEX USA consider oxygen enrichment of precalciner firing to be their technology for which they have lodged a patent. You can find papers on oxygen enrichment in the proceedings of the IEEE conference in Vancouver 2001.

Does better nodulisation mean more consistent size of nodules with less dust or with less large nodules ? What might be wrong if always getting a large portion of large nodules (4-6 inches in diameter), even at 25 per cent liquid phase, which isn't high, and ALm of kiln feed ranging from 1.55-1.75. Kiln is typically run at 3.5rpm. The large nodules are only visible on kiln stops when there is a chance to look into the cooler, before the clinker goes through the crusher.

Your chemistry does not sound abnormal and we have discussed the possibility that the large nodules are caused by MgO variation before. A further remote possibility would be Mn₂O₃ variation where slight increases cause the formation of vary large balls and also take the coating out of the burning zone. However, that is a long shot.