Problem 12.6: A tower operates at 5 cycles based on

From Chapter 12 Problem Set. Level 2: Applied Thinking.

Question

A tower operates at 5 cycles based on conductivity. Lab results show:

MAKEUP: Chloride = 48 mg/L; Calcium = 160 mg/L as CaCO₃

TOWER: Chloride = 245 mg/L; Calcium = 640 mg/L as CaCO₃

Answer

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Chloride COC = 245 ÷ 48 = 5.10. Calcium COC = 640 ÷ 160 = 4.00. The mass balance is not intact. Chloride-based COC exceeds calcium-based COC, meaning calcium is leaving the water as scale. Expected calcium at 5.10 cycles = 160 × 5.10 = 816 mg/L as CaCO₃. Actual = 640 mg/L. Calcium lost = (816 − 640) ÷ 816 = 21.6% precipitating as scale. Next steps: evaluate LSI/RSI at current conditions, check condenser approach temperature for fouling evidence, review scale inhibitor residual and dosing, and consider whether cycles need to be reduced or inhibitor chemistry adjusted.