Problem 12.10: You are called to evaluate a cooling tower
From Chapter 12 Problem Set. Level 3: Optimization.
Question
You are called to evaluate a cooling tower that is consuming significantly more water than expected. The conductivity controller is functioning and holding its setpoint. Tower water conductivity reads 2,400 µS/cm; makeup conductivity is 600 µS/cm. However, the makeup meter shows water consumption approximately 30% higher than your mass balance predicts for the calculated COC. Identify at least three possible explanations for the discrepancy and describe how you would investigate each one.
Answer
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Three possible explanations: (1) System leaks – piping leaks, valve weeping, overflow events, or basin cracks allow concentrated tower water to leave the system without being metered as blowdown. This requires additional makeup to maintain basin level. Investigate by performing a basin-level hold test with all known outflows closed and checking for unexplained level drop. (2) Drift losses higher than assumed – drift eliminators may be damaged, missing, or improperly seated, allowing entrained water droplets to escape with the exhaust air. Investigate by visually inspecting drift eliminators during operation and checking for excessive visible plume or wet surfaces near the tower discharge. (3) Unmetered water draw – another system or process (basin washdown, makeup to a secondary system, landscape irrigation) may be connected to the same makeup supply upstream of or bypassing the meter. Investigate by tracing the makeup piping and confirming that no branch connections exist between the meter and the tower. Additional possibility: the makeup meter itself may be reading high due to calibration drift or mechanical wear – verify by comparing meter reading against a timed bucket test or a secondary flow measurement.