Water Treatment, Feedwater, and Steam Systems
Water Treatment, Feedwater, and Steam Systems
This domain tests water chemistry, feedwater equipment, blowdown, and steam distribution. The goal is to prevent scale, corrosion, carryover, and water hammer.
Chemistry and treatment
Raw water contains hardness, dissolved solids, oxygen, and carbon dioxide. Softeners remove hardness; deaerators strip oxygen and heat feedwater; chemical treatment controls scale, corrosion, and pH. Boiler water must be held within limits for conductivity, alkalinity, silica, and dissolved solids. High dissolved solids cause foaming and carryover; low pH causes corrosion; oxygen pitting attacks feed lines and economizers.
Feedwater and steam
Feedwater pumps must overcome boiler pressure and maintain level. Steam traps remove condensate without losing steam; failed-open traps waste steam, failed-closed traps cause water hammer. Air vents remove noncondensables. Priming is carryover of boiler water with steam; it can be caused by high water level, high solids, or sudden load.
Worked example
Boiler water chloride is 300 ppm and feedwater chloride is 30 ppm. The concentration ratio is 300/30 = 10. Blowdown fraction = feedwater solids/(boiler solids − feedwater solids) = 30/(300−30) = 0.111, or about 11%. That means roughly 11% of feedwater must be blown down to hold chlorides at 300 ppm; if the limit is lower, blowdown must increase.
Traps
Do not use a gauge glass alone to judge water quality. Do not skip bottom blowdown because the water looks clear. Do not confuse a failed-open steam trap with a failed-closed one. Do not add treatment without testing; overfeed can cause foaming or caustic attack.