How is a typical boiler start-up sequence controlled?

• A. Pre-purge, ensure safety interlocks, ignite fuel, light off, purge to remove combustibles, and then gradually heat up and bring feedwater online before loading.
• B. Ignite fuel first, then pre-purge.
• C. Load full feedwater before ignition.
• D. Start with maximum load and adjust.

Answer: (A)

Safe, controlled light-off and gradual heating is what this startup sequence is about. The first step is a pre-purge that blows out any combustibles or fuel vapors from the furnace with air. This creates a clean, safe ignition environment. While purging, safety interlocks—such as flame safeguards, proper ventilation, and critical sensors—must be satisfied so fuel is only admitted when conditions are safe.

Once those conditions are confirmed, fuel is introduced and ignition is established, providing a stable light-off. After ignition, a purge is often continued to remove any residual hydrocarbons and ensure the furnace remains safely lit. Then the system is gradually heated and feedwater is brought online in a controlled way before loading, so the boiler can ramp up without sudden thermal or pressure stress.

Starting the boiler any other way—igniting without purging, loading full feedwater before ignition, or jumping to full load—risks explosions, thermal shock, improper water level control, and equipment damage. This orderly sequence protects personnel and equipment while delivering a reliable start-up.