Consider the following when designing a fired heater control and protection system:
(See the appropriate section of this manual for additional information.)
• Blinds on all fuel oil and fuel gas lines to or from the heater, including any fuel to the pilots, are recommended for all heaters.
• A minimum flow by-pass on fuel gas to the heater is recommended for all heaters. This is normally left open even when the heater is burning oil, thus acting as a safety pilot.
• Full flow by-passes are recommended around both oil- and gas-firing valves.
• Facilities are recommended to purge the fire box, such as a forced draft fan or a steam connection into the firebox.
• Separate block valves for gas, oil, and atomizing steam are recommended for each burner.
• A knockout drum is recommended for fuel gas to the unit.
• Low-charge-flow alarms and shutdowns are strongly recommended.
• Snuffing steam to the header boxes is recommended for heaters with plug type return headers.
• A stop device is recommended for dampers with positioners unless normally closed or specifically designed to completely close. For each such damper, the action desired in case of a furnace fire should be reviewed.
• Individual process outlet temperature measurements for each pass are recommended.
• High-temperature alarms are recommended for the flue gas above the convection section.
• An alarm to show when rotation stops is recommended for heaters with Ljungstrom type air preheaters
• An alarm is recommended for high pressure in the fire box.
• A low-oxygen alarm is recommended.
• Low RPM alarms and safety interlocks are recommended for all forced and induced draft fans.
• Low-pressure alarms are recommended in combustion air ducts downstream on any control damper or air preheater.
• If possible, any emergency should be alarmed before activating a safety interlock.
• Action on instrument air or power failure is normally the following:
Fuel control valves Close
Pass control valves Open
Stack Dampers Open
• See the next section for additional items on specific fired heaters.
Automatic shutdowns should stay tripped until manually reset.