TL;DR
A hot spot on the kiln shell means the refractory brick has failed in that zone. Stop the kiln immediately if the shell temperature exceeds the maximum safe value to prevent shell distortion.
What you might see
- hot spot visible on the kiln shell from the outside
- kiln shell temperature above the safe limit
- kiln feed chemistry upset from dilution
- brick fall-out detected in the clinker cooler
Likely causes
Thermal shock from rapid kiln start or stop cracking the brick
Brick wear from long operating campaigns without refractory inspection
Coating spall from kiln upsets exposing the brick to direct flame
Misfire or incorrect flame shape impinging directly on the brick surface
Required tools
- Kiln shell scanner or IR thermometer with data logging
- Confined-space entry equipment
- LOTO kit
- Refractory repair materials
Safety first
- Confined-space entry into a rotary kiln requires a permit, lockout of all drives, atmospheric testing, and a rescue standby team.
- Extreme thermal radiation from a hot kiln shell. Maintain maximum safe distance and use radiant-heat PPE.
- Do not spray water on a hot kiln shell hot spot. Thermal shock can cause further shell distortion.
Procedure
- 1
Monitor the kiln shell scanner or conduct a manual shell temperature survey with an IR thermometer during every shift.[1]
- 2
If a shell hot spot above 350 degC is detected, alert the kiln operator immediately.
- 3
Mark the hot spot position by the kiln rotation degree and distance from the feed end.[1]
- 4
If the hot spot exceeds 400 degC or is growing, initiate a controlled kiln stop following the kiln stop procedure.
- 5
During cooling, continue monitoring the hot spot temperature. Reducing temperature trend confirms no further refractory loss.
- 6
After the kiln is cooled, enter the kiln using the confined-space entry procedure to inspect the failed zone.
Warning: Confined-space entry into a rotary kiln requires full lockout of all drives including the slow-drive, a rescue plan, CO and O2 monitoring, and thermal cool-down verification. - 7
Repair or re-line the failed zone before restarting the kiln.
Sources
FLSmidth FLSmidth ROTAX-2 Rotary Kiln general technical documentation, FLSmidth
FLSmidth rotary kiln operation manual, refractory monitoring and emergency stop procedures (general)
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