Amongrotary kiln operators, refractory failure is considered the most critical upset in a rotary kiln operation. Refractory failure inside the rotary kiln is indicated when the rotary kiln shell becomes red hot because the refractory lining has either been entirely lost or has become so thin in an area that the rotary kiln shell becomes overheated. Such a condition is dangerous because once the protection supplied by the refractory has been removed, the steel shell could easily be warped to such an extent that replacement of an entire rotary kiln shell section becomes necessary. In most instances, however, damage can be avoided if the rotary kiln is shut down for lining replacement as soon as the shell starts to show a large red spot. Because of the importance of such a situation, remedial procedures for hot shell conditions are described in other articles.

Replacement of the rotary kiln lining,especially in the burning zone,  is unfortunately a frequent necessity, exerting a large strain on the operating budget and on production schedules. For example, replacement of an entire burning zone lining over a length of 50 ft in a 16-ft diameter rotary kiln costs in excess of $80,000. This figure represents only the cost of the refractory itself and does not include the added expense of installation, nor the hidden cost resulting  from loss of production and the extra fuel required to bring the rotary kiln back to operating temperatures.

Ideally, one would like to obtain a service life on the burning-zone lining that would extend through a continuous operation cycle from one tum-around to the next.  In other words, the optimum service life would be a period of either 11 or 23 months. In most rotary kilns, however, this is more the exception than the rule. Although  linings in the upper, cooler regions of the Iciln can show lives of 5-20 years, in the intensely hot burning zone the life ranges from as little as 30 days to as much as two years. Regardless of the fact that all cement Icilns operate within a narrow temperature range in the burning zone there still exists  that  large discrepancy between rotary kilns in matters of refractory service life. The reason for this can· be found in the fact that each rotary kiln has its own specific characteristics and idiosynchrasies which  are discussed in the following section.