FGD has many density measurement points with widely varying conditions: limestone slurry deals with scaling, gypsum discharge with large pipe diameters, wastewater with corrosion. Sort out the selection for these three and the whole FGD instrumentation falls into place.
Power-plant FGD density meter selection guide
Selection paths for three key FGD measurement points — limestone slurry tank, gypsum discharge, wastewater — with typical failure modes and fixes.
Steps
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Limestone slurry tank / absorber recirculation
Typical range 1.05–1.35 g/cm³, heavy scaling. Recommend PS7400 tuning fork. Install on the absorber recirculation line or in the slurry tank — fork vibration handles scaling well.
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Gypsum discharge / large-bore main
Discharge piping is usually DN200+, range 1.10–1.25 g/cm³. Recommend PS7300 differential pressure. DP is cost-effective for large bore, no moving parts, low maintenance.
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FGD wastewater
Wastewater is high-chloride and corrosive. If no tapping allowed, PS7010 clamp-on ultrasonic is first choice — no wetted parts means no corrosion problem. If tapping is OK, PS7400 works but must use Hastelloy fork tip.
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Common field issues
Issue 1: Readings swing with load → usually turbulence from sensor placed too close to pump or elbow. Relocate the install point.
Issue 2: Gypsum slurry reads low consistently → check for trapped gas; DP is especially sensitive.
Issue 3: Severe crystallization in limestone tank → check tank temperature; CaSO₃ crystallization is a process problem, not an instrument problem.