A cement rotary kiln consists of a slightly inclined tube made from steel plate and lined with refractory brick. The refractory is used to insulate the steel structure, which becomes soft and weak above 800 C.
The kiln rotates between 30 and 250 revolutions per hour, taking in a raw mix at the upper end. The rotation of the kiln causes the mix to gradually move downhill over the burner, then drop out into a cooler. Rotary kilns run 24/7 and are stopped only for a few days for essential maintenance. This is important because of heatup and cool down thermal transients.
The process of starting a rotary kiln is complex – thermal differences between components must be carefully controlled to avoid the introduction of high thermally-induced stresses that can cause damage. During the startup of a kiln, problems with the conveyor system feeding the kiln had occurred, and the kiln heatup was suspended.
One day later, heatup resumed, but hot spots were observed on the kiln shell, indicative of problems with the refractory lining. We were asked to investigate.
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