Velocity Measurement of Pneumatically Conveyed Solids Based on Signal Frequency Spectrum

The velocity of solids in air-solids two-phase flow is a very important parameter. For inferential flow rate measurement, the solids mass flow rate is derived from the velocity and the concentration of solids; and in "lean-phase flow", because the proportional factor between conveying air velocity and the velocity of the solids is relatively constant, so that the velocity of solids can be used to calculate the velocity of conveying air for optimising the overall air to fuel ratio. The cross-correlation method has been successfully adopted for the solids velocity measurement in muli-phase flow over a decade. A cross correlator requires two electrodes installed at up and down stream with known distance apart. The method used in this paper which is based on signal frequency spectrum analysis needs only one electrode. This electrode can provides both concentration and velocity information to calculate solids flow rate. Hence this method can be an alternative to crass correlation method with a simplified sensor construction. This paper discusses the principle of this method, and compares the signal peak frequency with the signal frequency bandwidth approaches. The tests have been conducted and the results support the theoretical analysis.