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.

  • Try to eliminate kiln shutdown by operating the kiln more efficiently on a continuous basis.
  • ​In case of kiln shutdown make sure that the cooling is slow and uniform. Cooling time should be at least 8 hours. A large damper in the kiln back end helps to conserve the heat and retards cooling during shutdown. To ensure a uniform cooling, the kiln has to be turned and jacked on a regular schedule, because the feed bed and the refractory underneath it will cool much slower than the refractory which is exposed to the kiln gases. A suggested schedule for turning the kiln after a shutdown on both dry and wet process  kilns of various size and diameter is given in the table below.
  • Once a shift, check the clinker loading in the cooler inlet and run this material out when the pile becomes higher than 2 ft. This is necessary because each time the rotary kiln is turned a small amount is dumped into the cooler.     
  • Another procedure to ensure slow cooling is to make sure the draft fan has been put off immediately after the fire has been taken out of the kiln (a must for kilns with internal heat exchangers) The primary air fan should be left running only for such a time as needed to protect the burner pipe from heat during the early period of kiln cooling.   

A Typical Rotary Kiln Jacking Schedule (Frequency of turns)
  1. Continuous rotation on auxiliary drive for 30 min.
  2. One-third turn every 10 min for 1 hr.
  3. One-third turn every 15 min for 1 hr.
  4. One-half turn every 30 min for 4 hr.
  5. One-half turn every hour for 4 hr.
  6. One-half turn every 2 hr for 12 hr.
  7. One-half turn once every 24 hr regardless of length of shutdown.​​

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.

Factors Responsible for Refractory Failures and Wear of Refractories of a Cement Rotary Kiln

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.  

<< Previous                                                                     Next >>

Overheating the Rotary Kiln

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 

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 

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.

Please click on the Next icon to read further.

Industry Guru (Home)  > Cement Industry (Technology / Manufacturing)


Techno-Commercial ​​​​​​​

Very Fast Heating of the Refractories

Frequency of Kiln Shutdown