Mass-flow measurement of solids using electrodynamic and capacitance transducers

Mass-flow measurement of gas/solids flow is a common requirement in many industrial processes. The authors present a case study dealing with the measurement of returned fines in the recycle line of a fluidised-bed gasifier pilot plant. The problem is solved by measuring two parameters, namely the solids velocity and the volumetric concentration. The former is measured by cross correlating the electrostatic charge fluctuations generated by the conveyed solids, and the latter by using an inherently stray-immune capacitance transducer. The two measurements are then combined to give the solids mass-flow rate. The effects of solids flow characteristics (Reynolds number, flow regime) on the measurement errors of solids velocity and concentration are experimentally investigated. Possible measures to reduce these errors are discussed.