Problem 13.8: Your blowdown conductivity controller reads

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

Question

Your blowdown conductivity controller reads 2,000 µS. Your handheld meter reads 3,800 µS on a cooled grab sample. The blowdown valve has been closed for hours. (a) What has happened? (b) Estimate the actual cycles if feedwater conductivity is 80 µS. (c) Using the ASME table, is this boiler (300 psig) at risk? For what?

Answer

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(a) The conductivity sensor is fouled or out of calibration, reading artificially low. The controller believes the water is clean and has closed the blowdown valve, allowing cycles to climb unchecked. (b) Actual cycles = 3,800 / 80 = 47.5. (c) At 300 psig, the ASME TDS limit is ~3,000 mg/L. If 3,800 µS corresponds to roughly 2,500–3,000 mg/L TDS (depending on ionic composition), the boiler is at or near the carryover risk threshold. Foaming, silica deposition in the steam system, and TDS-driven carryover are all concerns. Immediate action: validate the sensor, perform manual blowdown, recalibrate the controller.