Problem 13.9: A technician reports sulfite residual is zero

From Chapter 13 Problem Set. Level 3: System Integration.

Question

A technician reports: sulfite residual is zero in the boiler, scale inhibitor is depleted, and condensate pH has dropped to 5.5. Instead of increasing all three chemical pumps, describe the diagnostic sequence you would follow to identify the root cause. What single failure could explain all three symptoms?

Answer

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Do not increase chemical pumps. Diagnose the circuit. Step 1: Check deaerator temperature (explains sulfite consumption if DA is cold - elevated dissolved oxygen is overwhelming the scavenger). Step 2: Check softener output and brine tank (explains inhibitor depletion if hardness is breaking through - the scale inhibitor is being consumed by calcium instead of maintaining a residual). Step 3: Check condensate return rate (explains elevated CO₂ and low condensate pH - increased makeup alkalinity means more bicarbonate entering the boiler, more CO₂ in the steam, more carbonic acid in the condensate). A single root cause - loss of condensate return - explains all three symptoms simultaneously, exactly as in the Perfect Storm scenario. The circuit reveals the cause; the chemical tests only showed the symptoms.