Routine Operation, Startup, and Shutdown Procedures
Operation questions ask for the correct order of steps and the reason behind each one.
Pre-start checks
Confirm water level in the gauge glass, verify all isolation valves are in the correct position, open air cocks and superheater vents, check the fuel train and burner for leaks, confirm the low-water cutoff and flame safeguard are in service, and purge the furnace before any light-off.
Cold start and warm-up
Bring pressure up slowly. Warm-up rate is limited (commonly about 100 deg F per hour for thick-walled drums, slower for large units) to avoid thermal stress. Vent air through the air cocks until steam appears, then close them. Bottom blow the boiler once pressure is established (about 15 to 30 psig) to remove sediment and promote circulation. Drain superheater and warm the main steam header before opening the main stop valve.
Cutting in a second boiler
Warm and drain the header, equalize pressure across the stop valve, open the stop valve slowly, and place the feedwater regulator and firing controls in automatic after level and pressure are stable.
Normal operation
Maintain level in the middle of the glass, control blowdown on conductivity, watch stack temperature and flue gas analysis, and log readings.
Shutdown
Reduce firing gradually, blow down as required, cool slowly, and drain only when pressure is zero and metal temperature is low enough to permit it. Hot draining or admitting cold water to a hot boiler causes differential contraction and cracked tubes.
Traps
Questions offer to top up a boiler quickly by wide-open feedwater - wrong on a hot, low boiler. Questions also reverse purge and light-off.
Worked rule
Never blow down a boiler that is low on water, and never blow down two boilers at once. Short, frequent blows beat one long blow, and watch the gauge glass the entire time.