1156 posts
Burning Question 81
What are the possible causes of large snowballs occurring in a short precalciner kiln, which build up and eventually cross into the burning zone, and require a stoppage to break them up.
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1156 posts
Re: Burning
I can't recall any really good articles on the formation of snowballs but know they can be quite frightening. They are caused by variations in the clinkering range or flux content of the feed. Mostly they break up under the flame but I have seen monsters fall into the cooler, which is quite alarming and can cause major damage. This happened occasionally in one kiln where I was involved and we traced the problem to variations in the MgO content of the limestone and kiln feed. That might be the answer.
1156 posts
Burning Question 82
There are two kinds of alkalis contained in clinker-soluble and insoluble alkalis. Please explain about the formation processes in the kiln and the effects of two alkalis respectively on clinker quality, especially on setting and compressive strength.
1156 posts
Re: Burning
Alkalis in clinker will preferentially combine with chloride and sulphate, the alkali chloride and sulphate formed is volatile and leads to the build up of the alkali cycle in the kiln. Alkali sulphates are less volatile than chlorides and some pass out of the kiln in the clinker. These are the source of the soluble alkali in the clinker. They promote the hydration of the cement and lead to higher early strengths. If alkali is present in excess of the sulphates in clinker then it enters into the clinker minerals. These are the "insoluble" alkalis. They do affect the hydration behaviour of the cement as they affect the clinker mineralogy, however effects are not as clear as for the soluble alkalis.