(68d) The Screened Waveguide for Intrusive Acoustic Emission Detection and Its Application in Circulation Fluidized Bed

Passive acoustic emission (AE) has been widely used in various chemical industries, as it has the characteristics of real time, on-line and environmental-friendly. However, most of the acoustic signals are only collected from the surface of measured device, which are superimposed signals of the acoustic wave from the detection area of the sensor. Besides, the flowing state near the wall is usually quite different from that inside the reactor due to wall effects. It is undeniable that the information near the wall is important, however, detailed information inside the system is definitely more significant for the whole system. Therefore, in order to achieve local information detection and obtain the spatial distribution of particle motions inside systems, a new waveguide with screening structures was proposed based on the theory of sound wave generation and propagation. Subsequently, an intrusive acoustic emission detection based on the screened waveguide was developed to detect the particle flow patterns inside a circulating fluidized bed. Results showed that the noise energy accounted for only 2.1% of the total signal energy received by the waveguide, indicating that under real experimental conditions, the designed waveguide had a good shielding effect. Radial acoustic energy distribution detected via the waveguide was highly consistent with the radial solid flux distribution measured by extraction probe, validating the feasibility of this method. Furthermore, the radial flow pattern of Geldart D particles in a riser of circulating fluidized bed was systematically investigated based on this method, which was also an important supplement to the experimental study of the riser.