TL;DR
Crown refractory wear shows as a hot spot on the external scan. Track hot spot temperatures and schedule a crown repair or full rebuild based on the remaining crown thickness and hot spot growth rate.
What you might see
- furnace crown hot spot on thermal scan
- crown temperature above the alarm threshold
- increased heat loss from the furnace top
- refractory dust dropping into the glass melt
Likely causes
Normal refractory wear from furnace gas stream erosion and batch carry-over over the campaign
Flame impingement on the crown from incorrect burner angles
Batch carryover from high pull rate depositing aggressive materials on the crown surface
Thermal cycling from temperature fluctuations cracking the refractory
Required tools
- Thermal camera
- Aluminized radiant-heat PPE
- Crown repair refractory material
- LOTO kit for cold repair
Safety first
- Crown access above an operating or recently stopped glass furnace involves extreme thermal radiation. Aluminized PPE and strict time limits are mandatory.
- Glass furnace gases contain CO and SO2. Use a personal gas monitor near any furnace opening.
- Never allow moisture near the crown repair zone. Water contacting hot refractory or glass melt is violently steam-reactive.
Procedure
- 1
Conduct a thermal scan of the furnace crown with a thermal camera at least weekly. Log all readings and track hot spot growth rate.[1]
- 2
If a hot spot exceeds the alarm threshold, increase scan frequency to daily.[1]
- 3
Review burner angles for the zone below the hot spot. If the flame is impinging on the crown, adjust the burner firing angle.
- 4
Review pull rate and batch composition. Reducing the pull rate can slow crown erosion near the end of a campaign.
- 5
Plan a cold repair (patch from above during a short campaign stop) if the hot spot growth rate allows. Cold repair requires the crown to be accessible from above and at below 200 degC at the patch zone.
Warning: Crown access above a glass furnace involves extreme thermal radiation from the furnace openings below. Full aluminized radiant-heat PPE and strictly limited exposure times are required. - 6
If the hot spot temperature approaches the structural integrity threshold, consult the furnace refractory engineer about a campaign end decision.
Sources
Sorg Sorg LoNOx Melter Glass Tank Furnace general technical documentation, Sorg
General glass tank furnace crown refractory inspection and campaign management procedures (general)
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