TL;DR
A blocked preheater cyclone must be cleared promptly to prevent raw meal buildup and damage. Use the air cannon first, then the manual lance procedure if airflow does not restore.
What you might see
- pressure drop across one cyclone above normal
- kiln feed string interrupted to that stage
- temperature differential between preheater stages reversed
- blockage indicator air cannon not clearing the obstruction
Likely causes
Raw meal build-up accumulating in the cyclone cone from moisture-rich feed
Alkali sulfate rings forming inside the cyclone cone narrowing the throat
Feed surge overloading the cyclone capacity causing material compaction
Cooling after a kiln stop causing condensation that cements loose material
Required tools
- Compressed-air lance
- Radiant-heat PPE
- Hot-work / confined-space entry permit
- CO and O2 gas monitor
Safety first
- Preheater tower gases are above 800 degC and contain CO. Full radiant-heat PPE and gas monitor required for all access at tower height.
- Do not apply water to a hot cyclone. Violent steam generation can cause an explosion.
- Working at height on preheater towers requires fall arrest equipment at all elevated platforms.
Procedure
- 1
Notify the control room and reduce kiln feed to the affected string.
Warning: Preheater tower cyclones contain raw meal and gases above 800 degC. All work at this level requires radiant-heat PPE and a confined-space or hot-work permit. - 2
Activate the air cannons on the affected cyclone cone in sequence from top to bottom as designed.[1]
- 3
Monitor the pressure differential across the cyclone. If it decreases, the blockage is clearing.[1]
- 4
If air cannons do not clear the blockage, stop the kiln feed to that string.
- 5
Using the manual lance port, insert a compressed-air lance into the blockage area only after verifying the area is safe and PPE is worn.
- 6
Do not apply water to a hot cyclone blockage. Thermal shock can crack the refractory lining.
- 7
After clearing, inspect the cyclone cone for refractory damage before returning to full feed.
Sources
FLSmidth FLSmidth ILC / SLC-D Preheater Tower / Calciner general technical documentation, FLSmidth
FLSmidth preheater tower operation and maintenance manual, cyclone blockage clearing procedures (general)
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