TL;DR
Riser duct coating forms gradually from alkali sulfate condensation. Remove it during a planned kiln stop using mechanical lances. Monitor with pressure drop trending to schedule the next clean-out.
What you might see
- riser duct pressure drop increasing over weeks
- kiln back-pressure rising
- coating detected by access port inspection
- gas velocity alarm in riser duct
Likely causes
Alkali sulfate and chloride compounds cycling in the preheater condensing on cooler duct walls
Insufficiently bypassed alkali allowing buildup concentration to increase
Wet feed or high moisture in the raw meal raising condensation risk
Duct refractory surface roughness acting as nucleation sites for coating growth
Required tools
- Mechanical lance for coating removal
- Dust mask and full PPE
- IR thermometer for duct surface temperature
- LOTO kit
Safety first
- Riser duct contains high-temperature gases and CO. Full lockout and gas clearance required before opening any access.
- Coating material contains alkali compounds. Use respiratory protection and skin protection.
Procedure
- 1
Schedule the coating removal with the next planned kiln stop. Do not attempt removal during operation.
- 2
Allow the riser duct to cool. Verify the duct refractory surface temperature is below 60 degC before opening access doors.
Warning: The riser duct contains high-temperature gases and potential CO during kiln operation. Full lockout is required before opening any access. - 3
Lock out the kiln drive, raw mill feed, and ID fan before opening any riser duct access panel.[1]
- 4
Open the riser duct access doors and use mechanical lances to chip and dislodge the coating from the walls.[1]
- 5
Remove the fallen coating through the access opening. Do not allow large chunks to fall into the cyclone below.
- 6
Inspect the refractory behind the removed coating for erosion or cracking. Document damaged areas for repair.
- 7
After closure, trend the riser duct pressure drop over the next month to establish the recurrence rate for scheduling the next clean-out.
Sources
FLSmidth FLSmidth ILC / SLC-D Preheater Tower / Calciner general technical documentation, FLSmidth
FLSmidth preheater and calciner system maintenance documentation, riser duct inspection and coating removal procedures (general)
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