Combustion Troubleshooting

Chapter from the Fired Heaters Design Guide.

COMBUSTION TROUBLESHOOTING

Troubleshooting Decision Framework

Symptom	Possible Causes	Diagnostic Check	Corrective Action	Safety Warning
High CO (>200 ppm)	Insufficient air, poor mixing, cold flame	Check O2, inspect flame, burner tips	Increase air, clean tips, check draft	CO indicates incomplete combustion — explosion risk
High O2 (>6% dry)	Excess air, air leaks in convection	Close dampers, check casing for leaks	Seal leaks, adjust air registers	High O2 = wasted energy
High stack temperature	Fouled convection, reduced heat transfer	Inspect fins, check convection ΔP	Clean convection section	Efficiency loss, possible stack fire if soot
Low draft	Plugged stack, wind effects, fan issue	Measure draft at multiple points	Clean stack, adjust damper, check fan	Low draft → poor combustion → CO
Smoke/soot (gas firing)	Very low air, fuel quality, burner damage	Visual, check O2, fuel analysis	Increase air, inspect burners	Soot in convection = fire hazard
Flame instability	Draft variation, fuel pressure changes	Check fuel P, draft, wind conditions	Stabilize fuel supply, windscreen	Flameout → purge required before relight
Afterburn in convection	Unburned fuel igniting in convection	Check for CO in firebox, flame carryover	Reduce firing, fix combustion issue	CRITICAL — can destroy convection tubes
Hot spots on casing	Refractory failure, hot gas bypass	IR scan casing, inspect refractory	Repair refractory at turnaround	Personnel burn hazard
Uneven tube temperatures	Maldistribution of flow or firing	Check skin TCs, inspect flames	Balance fuel, check process flow	Local overheating → tube failure
Noise/pulsation	Combustion instability	Change air/fuel slightly to break cycle	Adjust dampers, check for resonance	Structural fatigue, operator concern

Source: Fired_Heaters_Design_Guide_v1.xlsx · sheet “Combustion Troubleshooting”

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