Water Treatment and Steam/Water Chemistry
Core concepts
Understand the sources of boiler water problems: scale, corrosion, carryover, and foaming. Know the key chemistry parameters - pH, conductivity/TDS, alkalinity, hardness, dissolved oxygen, silica, and iron. Study external treatment (softening, demineralization, reverse osmosis) and internal treatment (oxygen scavengers, scale inhibitors, amines for condensate pH). Understand blowdown control and the role of continuous vs. bottom blowdown. Know how dissolved oxygen causes pitting and how deaeration and chemical scavengers prevent it.
Traps to watch
- Confusing scale (hardness deposits) with corrosion (oxygen, low pH).
- Assuming high pH is always good - too high causes caustic embrittlement.
- Forgetting that silica limits depend on pressure.
- Overlooking condensate return chemistry (low pH from CO₂).
- Mixing TDS control (blowdown) with hardness control (softener).
Worked example / rule of thumb
If feedwater TDS is 200 ppm and the boiler limit is 2,000 ppm, cycles of concentration = 2,000/200 = 10. Blowdown fraction ≈ 1/10 = 10% of feedwater. Rule of thumb: cycles of concentration = boiler limit ÷ feedwater TDS; blowdown % = 100/cycles.