Operation, Startup, Shutdown and Load Management
Operation, Startup, Shutdown and Load Management
This domain tests safe sequential operation: pre-start checks, purge, warm-up, cut-in, load changes, blowdown, normal and emergency shutdown, and layup. Expect questions on sequence and on the consequences of skipping a step.
Core rules and concepts
- Before startup, verify water level, vent and drain positions, fuel supply, draft, interlocks, and all inspection openings. Prove purge airflow before ignition.
- Warm up slowly to limit thermal stress in drums, tubes, and headers. Follow manufacturer limits for pressure and temperature change rates.
- On load changes, coordinate fuel, air, and feedwater. Increasing firing rate without enough air causes incomplete combustion; increasing air too fast can cool the flame or trip flame scanners.
- Bottom blowdown removes sludge and controls solids. Open slowly, confirm valve movement, and avoid water-level loss.
- Normal shutdown includes reducing load, stopping fuel, purging, and controlling cooldown. Emergency shutdown may isolate fuel immediately, but the furnace must not be reopened to air while hot.
Worked example
A boiler fires at 50,000 lb/hr steam with 5% blowdown, so blowdown is about 2,500 lb/hr. The blowdown valve passes about 10,000 lb/hr when wide open. Required open time is 2,500 ÷ 10,000 = 0.25 hr, or 15 minutes, if flow were constant. In practice, open the valve briefly, observe level, and repeat rather than leaving it unattended. The reasoning is mass balance: solids removed equal solids entering, and the valve capacity sets how long flow must occur.
Traps that cost marks
- Lighting a burner without a proven purge.
- Raising pressure faster than the boiler can tolerate thermally.
- Blowing down without watching drum level.
- Opening a hot furnace to air after an emergency fuel trip.