Boiler Operation, Combustion, and Firing Equipment
Domain 2: Boiler Operation, Combustion, and Firing Equipment
This domain tests safe startup, normal operation, and shutdown, plus combustion fundamentals: fuel/air ratio, draft, purge, ignition, flame safeguard, and firing equipment such as burners, registers, and pilots.
Core rules
- Before light-off, purge the furnace and gas passages with air for the manufacturer required time and volume; prove airflow. Never light a burner with fuel already present.
- Combustion needs fuel, oxygen, and ignition. Excess air must be enough for complete combustion without excessive stack loss; CO and smoke indicate incomplete combustion, not automatically a rich mixture.
- Draft systems may be natural, forced, induced, or balanced. Furnace pressure must stay within design; loss of induced draft can force hot gas out of openings.
- Flame scanners must prove flame at light-off and during operation. Low-water fuel cutoff, high-pressure trip, and flame failure must trip fuel.
Worked example
Methane burns as CH4 + 2O2 -> CO2 + 2H2O. One cubic foot of CH4 needs two cubic feet of O2. Air is about 21% O2, so stoichiometric air is 2/0.21 = 9.52 ft3 air per ft3 CH4. At 10% excess air, required air is 9.52 x 1.10 = 10.47 ft3. This is why a burner set for 10% excess air supplies roughly 10.5 ft3 air per ft3 natural gas.
Traps
Skipping purge; bypassing a flame scanner; reading no smoke as complete combustion; and adjusting fuel before establishing airflow.