Module 5.7 — Applied capstone: a cooling tower chemistry problem worked start to finish, using cycles of concentration, LSI, and inhibitor logic together.
| PARAMETER | RESULT | TARGET | STATUS |
|---|---|---|---|
| Recirc. Water Chloride | 460 ppm | ~250 ppm (5 cycles) | HIGH |
| Makeup Chloride | 50 ppm | — | BASELINE |
| Calculated COC | 9.2 | ~5 | HIGH |
| Calculated LSI | +1.8 | 0 to +0.5 | HIGH |
| Scale Inhibitor Residual | Low-normal | Full target | CHECK |
| Corrosion Inhibitor Residual | Normal | Full target | OK |
| Condenser Approach Temp | Rising trend | Stable | TREND |
Click a highlighted row to see how it fits the diagnosis. Cycles of concentration reads nearly double target, LSI is correspondingly far into scaling territory, and approach temperature is trending — this isn't purely a paperwork problem.
Unit B's cooling tower normally runs around 5 cycles of concentration with LSI held in the 0 to +0.5 target range using a scale inhibitor program (Module 5.3). This week's chemistry log shows chloride-based cycles of concentration calculated at 9.2 — nearly double target — with a correspondingly elevated LSI of +1.8, well into scale-forming territory. Scale inhibitor residual reads low-normal rather than fully at target. Condenser approach temperature (the gap between cooling water outlet temperature and steam saturation temperature — a standard condenser performance indicator) has been trending upward, consistent with developing scale beginning to degrade heat transfer.
Recall from Module 5.2 that cycles of concentration is calculated from a conservative tracer ion — chloride here — and that COC and blowdown rate are directly linked: less blowdown means higher cycles. A COC reading of 9.2 against a target of 5 points strongly toward inadequate blowdown, exactly the diagnostic logic Module 5.2 described: a cycles reading significantly higher than expected can indicate blowdown control isn't functioning as intended, worth checking before assuming a chemical dosing problem.
The rising condenser approach temperature trend is the practical consequence Module 5.3 predicted: LSI well above target drives active calcium carbonate scaling, and scale insulates tube surfaces, directly degrading heat transfer (Module 5.3's core point). This is why the investigation can't stop at "cycles are high" — the approach temperature trend confirms this is already producing a measurable operational impact, not just a chemistry number sitting outside target on paper.