FIBER OPTIC AND CAPACITANCE PROBES IN TURBULENT FLUIDIZED-BEDS

In the present study, local flow properties are investigated in pilot plant scale fluidized bed reactors using both fibre optic and capacita nces probes. Measurements are conducted at ambient as well as at 150 d egrees C. The system used is air and spent FCC particles (mean particl e diameter: 65 mu m). The static bed height is 1.6 m. Bubbling and tur bulent regimes (V = 0.40 and 0.70 m/s) are investigated in two 0.3 and 0.5 m ID columns. Bubble fraction under the bubbling regime and at ro om temperature, measured using fibre optic and capacitance probes, are in good agreement. However, in the turbulent regime, fibre optic prob es are prone to underestimate the bubble fraction while capacitance se nsors tend to overestimate it These discrepancies between fibre optic and capacitance measurements increase with temperature. Using capacita nce probes, a prevalent hat bubble rise velocity profile is measured. This is assigned to the relatively slow response, to the size and to t he geometry of the capacitance probes. Overall this gives an underesti mation of the bubble frequency and an overestimation of the bubble con tact time and the bubble contact length. Due to the high fibre optic p robe sensitivity, care should be taken in the interpretation of signal s. Overestimation of bubble frequency leads to underestimation of both bubble contact times and bubble contact lengths.