(255a) How Intrusive Are Our Intrusive Probes?

Many of the probes used to understand hydrodynamics in risers are intrusive. In other words, these probes are interacting with the very environment being measured. Pitot tubes, extraction probes, optical fiber probes, γ-ray densitometer probes, capacitance probes, etc. are all intrusively inserted into the riser flow stream to obtain radial profiles. Yet, the assumption they are not intrusive is almost always made. PSRI has found that this could be a poor assumption. Fiber optic probe measurements were found to consistently over predict the solids concentration compared to local ΔP/L values obtained from differential pressure measurements in the fully developed flow region of a 12-inch (0.3-meter) diameter by 60-foot (18-meter) tall riser containing FCC catalyst powder. The magnitude of this difference was sensitive to both superficial gas velocity and solids circulation rates. Barracuda? CFD simulations confirmed this, and suggested that particle momentum is lost at the bottom of the probe and particles are spilling over (deflecting) to the sensor face. Based on these observations, new probe designs are proposed.