Application of a reflective optical probe to measure solids fractions in a circulating fluidized bed [electronic resource] /

by Seachman, Steven M.

Application of A Reflective Optical Probe to Measure Solids Fractions in a Circulating Fluidized Bed Steven M. Seachman A novel method of extracting localized solids volume fractions from reflective multi-fiber optical probes was developed. The fiber optic probes were originally designed by Vector Scientific, Inc. to measure local solids velocities. The probe measures reflected light from a particle medium which is converted into a voltage. Development of this new method yields two valuable solid flow parameters from a single probe system. The method involves a formulated model with empirical calibrations and three physical bases. The three physical bases are the Conservation Law, Beer-Lambert’s Law, and the reflected light intensity from the particle medium. A novel bed depth calibration procedure is used to find the reflected light contribution from each layer of particles. This calibration is used to find the fixed fraction, kB1B, of scattered light detected by the probe, and the factor, kB2,B to convert number concentration into a solids volume fraction. The layer-by-layer analysis of the solids fraction avoids the need to directly address the effects of beam divergence and multiple scattering. The probes were used to measure the solids volume fractions and velocities inside the riser of a cold-flow Circulating Fluidized Bed (CFB) operating under several different flow conditions. These experiments were performed with two different batches of glass spheres, with average particle diameters of 64 ?m and 180 ?m, respectively. The solids fraction measurement method was compared with other solids fraction measurement methods. The fiber optic probe method compared well with other methods including solids sampling and pressure drop measurements, with the exception of near wall measurements using a solids sampling probe. The fiber optic probe gave solids fractions varying from 1.0% to 3.1% near the center and 7.7% and 21.1% at the wall of the riser of the CFBCC, which is consistent with other solids fraction measurement methods. The fiber optic probe was used to make measurements at different angular positions near the solids inlet, in the fully developed region, and near the solids outlet of the CFB riser. The method developed allowed calculation of the solids fraction distribution at these locations. Statistical analyses were performed in order to determine if the velocities or solids fractions were azimuthally dependent. It was found that the angular dependency of solids velocity and solids fractions is functions of elevation and flow conditions.