Capacitance measurements of solid concentration in gas-solid flows

Several methods of solid concentration measurement were implemented in a gas-solid multiphase flow to validate an electrically based solid concentration measurement device called a bulk impedance ring. Spatially averaged gamma-densitometry tomography and differential pressure measurements are compared and contrasted with the electrically based method. Experiments were performed on the riser of a pilot-scale circulating fluidized bed at Sandia National Laboratories, which circulates equilibrium fluid catalytic cracking particles with air. It was found that the mixture model used to convert the electrical impedance obtained by the bulk impedance ring to solid concentration must be applied carefully. Use of the Maxwell-Hewitt relation requires that the continuous and dispersed phases in the multiphase flow be identified correctly for the mixture model to work. Temporally averaged solid concentrations obtained from gamma-densitometry tomography and differential pressure measurements agree with solid concentrations obtained from the bulk impedance ring. Temporally resolved data from the bulk impedance ring and differential pressure measurements show good correlation. These results have validated the bulk impedance ring and show the feasibility of building a multiple-electrode electrical-iinpedance tomography system. (C) 2004 Elsevier B.V. All rights reserved.