When a kiln is overheated, the feed starts to ball up and the coating turns into liquid in the burning zone. Within a short time, unless this condition is not drastically counteracted, the entire refractory lining in the burning zone could be lost (washed away) as soon as the protective coating starts melting.
The question automatically arises - How and Why Overheating of the Rotary Kiln happens.We have very established reasons: overheated conditions are more apt to result from erratic feed loading and advancement in the kiln rather than from any action of the kiln operator. Indirectly, it means that an irregular cycling and upset kiln operating conditions can therefore be a cause for short refractory life. Which is why, kiln operating stability is so important.
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It is not uncommon for the cement rotary kilns all of them operating within a narrow temperature range in the burning zone and having other parameters also similar, yet
Heating up of the refractory very fast can cause thermal deterioration and disintegration of the refractory lining. Generally the refractory supplier should provide a heating schedule in this regard depending on the type of refractory installed.
Here, the expansion of kiln shell should not be overlooked since depending on the thermal conductivity of the refractory the shell expansion takes place somewhat slower than the expansion of the refractories. According to a conservative figure a period of 16 hrs should elapse when heating a kiln to operating temperature. More time would be required to bring the kiln on line with thicker refractory linings and larger kilns.
with large discrepancies as far as their refractory life is concerned. The reason for this can be found in the fact that each kiln has its own specific characteristics and idiosyncrasies which greatly influence its refractory life. As in the case of kilns used in other industries, the life of refractories of a cement rotary kiln too is governed by certain key factors. This is the second part of this
continued article (First part: How to minimize Refractory Failure and wear of Refractories inside a Rotary Kiln) we are discussing such key factors with their causes and how to minimize refractory failure and wear of refractories inside a rotary kiln.
Refractory life is directly proportional to the number of shutdowns for a cement rotary kiln. The more shutdowns, the shorter is the refractory life (what is Spalling Resistance of the Refractory). The danger of damaging the refractory is directly related to the rate of cooling down of the kiln, the danger being the greatest when cooling is too rapid.
A Typical Rotary Kiln Jacking Schedule (Frequency of turns)