Steam, Feedwater, and Water Treatment Systems
Core concepts
Understand feedwater chemistry: pH, conductivity, dissolved oxygen, silica, hardness, and alkalinity. Know external treatment (softening, demineralization, reverse osmosis) and internal treatment (oxygen scavengers, amines, phosphate, chelants). Grasp blowdown - continuous and bottom - and its role in controlling dissolved solids. Learn deaerator operation and why it removes oxygen both mechanically and chemically.
Traps
Questions confuse conductivity types (cation vs specific) and their meaning. Watch for items that treat silica as harmless - it volatilizes and deposits on turbine blades. Distinguish scale (hardness) from sludge (suspended solids) and from corrosion products. Also beware of pH targets: too low causes corrosion; too high causes caustic embrittlement or foaming.
Worked example
If boiler water chloride is 300 ppm and feedwater chloride is 30 ppm, allowable cycles of concentration ≈ 10. Blowdown fraction ≈ 1/10 = 10% of feedwater. Rule of thumb: blowdown is set by the most limiting chemistry parameter (often silica or conductivity), not by a fixed percentage.