Feedwater Systems, Water Treatment, and Internal/External Boiler Care
What this domain tests
This domain covers feedwater equipment, water chemistry, blowdown, and the internal and external care that prevent scale, corrosion, carryover, and fireside fouling. The exam expects you to recognize how a deaerator, feedwater regulator, check valve, softener, oxygen scavenger, and blowdown program work together.
Core rules and concepts
- Feedwater system: feedwater passes through a deaerator or heater, feed pump, regulator, check valve, and stop valve into the boiler. The check valve prevents backflow; the stop valve isolates the boiler. An economizer recovers heat from flue gas.
- Water treatment: hardness causes scale; dissolved oxygen causes pitting; low pH promotes corrosion; high alkalinity or silica can cause carryover. Treatment commonly includes softening, dealkalization, oxygen scavenging, pH/amine control, and TDS control by blowdown.
- Blowdown: bottom blowdown removes sludge and sediment; surface or continuous blowdown controls dissolved solids. Blowdown too little and carryover or scale results; blowdown too much wastes energy and water.
- Internal and external care: inspect waterside surfaces for scale, pitting, and cracking; clean fireside surfaces for soot and slag; keep openings, gauges, and relief valves accessible; use wet or dry lay-up for idle boilers.
Worked example
Feedwater TDS is 200 ppm and the boiler-water limit is 2,000 ppm. Maximum cycles of concentration = 2,000 ÷ 200 = 10. Blowdown as a fraction of feedwater = 1 ÷ 10 = 10%. If feedwater flow is 10,000 lb/hr, blowdown is about 1,000 lb/hr and steam output about 9,000 lb/hr. Exceeding 10 cycles risks carryover and scale.
Traps that cost marks
Treating the low-water cutoff as a normal level control; omitting the feedwater check valve; operating a deaerator poorly and then adding more oxygen scavenger; and blowdown based only on “how it looks” instead of tested chemistry.