Boiler Operation, Startup, Shutdown and Load Control
Pre-start and light-off
Walk the unit systematically: water level at the normal line, vents and drains in the correct position, burner and fan free to turn, fuel pressure and temperature normal, limits and interlocks proven, and the furnace purged with the outlet damper open. Light the burner on a low firing rate and warm a cold boiler slowly; a bottom blowdown during warm-up equalizes drum and shell temperatures and limits differential expansion.
Bringing on line and load changes
Raise pressure gradually, warm the steam header with drains cracked, then open the main stop slowly. Drum level behaves counter-intuitively: a sudden load increase causes swell (level rises) followed by shrink as pressure falls. Operators who chase the apparent level with the feed valve cause oscillation and trips. Control firing rate in small steps and let the feed regulator follow.
Shutdown and lay-up
Reduce firing gradually, blow down as required while the boiler is still warm, and let the unit cool at a controlled rate - no cold-water shock. Decide between wet and dry lay-up and follow the procedure, including desiccant or nitrogen blanketing for dry storage.
Traps and rule of thumb
Common wrong answers: firing before a complete purge, slamming the main stop open on a cold header, and shutting every valve on a hot boiler so it cools under vacuum. Rule of thumb: never change firing rate or load faster than the boiler can absorb thermally, and log every startup and shutdown.