A burner management system (BMS) sequences and protects fired equipment: heaters, boilers, thermal oxidisers. Several of its functions are safety instrumented functions.
Typical functions
| Function | Purpose | Typical design |
|---|---|---|
| Pre-ignition purge | Remove combustible gas before light-off | Air flow proven for a set time and volume; purge permissive |
| Pilot and main flame proving | Confirm ignition within a trial time | Flame scanners with timed trials |
| Flame failure trip | Stop fuel on loss of flame | Self-checking scanners, fuel double block and bleed |
| Low or high fuel pressure trip | Prevent unstable combustion | Pressure transmitters on the fuel header |
| Low combustion air trip | Prevent fuel-rich firing | Air flow measurement, fan running |
| Low process flow trip (heaters) | Protect tubes from overheating | Pass flow transmitters |
Design points
- Fuel shutdown with two valves in series and a vent between them (double block and bleed); test both valves and the vent.
- Flame scanners must be self-checking for continuous operation and see their own burner, not the neighbour's flame.
- Purge requirements come from the equipment design and applicable codes; the BMS enforces them.
- Separate the BMS safety functions from combustion control.
In First Out AI
The fired heater example (SIF-103), its LOPA scenario, the HAZOP library for heaters and the burner management C&E example show these functions working together.
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.