Although fluidized bed reactors at elevated temperatures (up to 1000deg C) have a wide field of application, there is still a lack of measurement techniques for local solids volume concentration and velocity. In this paper, a measurement technique which relies on the measurement of the local dielectricity is described. Through the application of a guard circuit and specially designed probes, an extremely high resolution and stability has been achieved. The calibration function was proved to be linear by comparison of capacitance probe signals to pressure drop measurements in a semi-technical scale circulating fluidized bed (CFB) reactor. The measurement system has been successfully operated under high-temperature conditions in an industrial-scale CFB combustor where the local time-average solids volume concentration was 0.1percent.
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