Boiler Auxiliaries, Feedwater Systems, and Piping
Domain 3: Boiler Auxiliaries, Feedwater Systems, and Piping
This domain tests the equipment between the water source and the steam header: feedwater pumps, deaerators, economizers, air preheaters, water treatment, valves, traps, and piping layout.
Core rules
- Feedwater flow must equal steam flow plus blowdown. A boiler evaporating 20,000 lb/hr with 5% blowdown needs 21,000 lb/hr feedwater.
- Deaerators heat feedwater to saturation and strip oxygen and carbon dioxide; the vent must remain open, and the storage tank must maintain the required pressure.
- Economizers recover heat from flue gas to feedwater; they must not be run dry or allowed to boil in a cold state without bypass protection.
- Piping must allow expansion, support weight, and drain at low points. Check valves prevent backflow; steam traps remove condensate without losing live steam.
Worked example
A boiler produces 20,000 lb/hr steam. Blowdown is held at 5% of steam flow. Blowdown = 0.05 x 20,000 = 1,000 lb/hr. Feedwater = steam + blowdown = 21,000 lb/hr. If a flow meter reads 20,000 lb/hr at the feedwater inlet, the boiler is losing water inventory or the meter/blowdown rate is wrong.
Traps
Sizing feedwater supply on steam flow alone; closing the deaerator vent to save steam; ignoring economizer bypass during startup; and using a steam trap that fails open, which wastes live steam.