Free lime reduction

Published 08 October 2012

The occurrence of high free lime can result in poor clinker quality and inefficient burning. Chemical variance in the raw materials and changes to the burning conditions can also upset the kiln balance, which can lead to other problems such as the formation of snowballs. So what are the main factors that will help to reduce high free lime?

Figure 1: cluster of early-formed C2S crystals

(field of width 750µm)

As in most walks of life, cement manufacturing has developed a degree of mythology over the years which sometimes clouds discussions on how to deal with incidents. It is frequently necessary to question ‘known’ solutions to various issues and look deeper into what the root cause might be.

High free lime

Very often the first sign of a problem is an unexpected increase in the free lime of clinker and frequently the immediate response is to put more fuel on the main burner. This is only one solution of many as to why the free lime cannot be reduced and it relies on the fact of there being insufficient fuel in the first place. If the kiln has been operating for some time this is unlikely.

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