Boiler Operation, Startup, and Shutdown
This domain tests safe routine operation, controlled startup, putting a boiler on line, and shutdown without thermal damage. Expect pre-start checks, purge, warm-up, pressure raising, parallel operation, and cooling and preservation procedures.
Startup sequence
- Confirm the boiler is inspected, isolated drains and vents are positioned correctly, and the drum has the correct water level.
- Verify the fuel train, draft system, flame scanner, and interlocks are functional. Purge the furnace and gas passages before light-off.
- Light off at low fire, prove flame, then increase firing gradually. Open superheater drains and vents as required.
- Raise pressure slowly. Uneven heating creates differential expansion between the drum and headers.
On line and shutdown
Bring the boiler on line gradually and match pressure and temperature before opening the main steam stop. When paralleling, adjust firing so the boiler picks up load smoothly. For shutdown, reduce load, stop firing, purge, and allow controlled cooling. Drain only when the boiler is cool enough to avoid thermal shock; use proper layup if it will be idle.
Worked example: During a cold start, the upper drum metal is 140 degrees F hotter than the lower drum metal. That exceeds a practical 100 degrees F differential limit. Reduce firing rate, hold pressure, and allow equalization before continuing. The reason is differential thermal expansion, which can overstress drum-to-tube connections and cause leakage or cracking.
Traps: skipping purge; firing with low water; raising pressure too fast; adding cold feedwater to a hot, low-water boiler too quickly; opening the main steam stop before matching conditions; cooling a hot boiler with cold water.