Boiler Operations, Startup, and Shutdown
Core concepts
Operators must know pre-start checks, purge requirements, light-off sequencing, warm-up rates, drum level control, and controlled cooldown. Understand why a pre-purge (typically five volume changes or the manufacturer's requirement) is mandatory, and why warm-up is slow: thermal stress in thick-walled drums and headers. Learn the difference between hot, warm, and cold starts and how each affects allowable ramp rates.
Traps
Questions often test sequence order - purge before light-off, prove flame before opening fuel valves, and never bypass interlocks. Drum level traps: low water can cause carryover and tube overheating; high water can cause priming and water hammer. Watch for items that treat "increasing firing rate" as a way to raise drum level - it temporarily lowers it (swell). Also distinguish normal shutdown from emergency trip actions.
Worked example
A cold drum should be warmed so metal temperature rises no faster than about 100°F/h; thicker sections require slower rates. If a drum starts at 100°F and saturation at operating pressure is 480°F, plan at least ~4 hours of warm-up. Rule of thumb: never exceed manufacturer ramp limits, and hold at saturation during light-off to avoid quenching.