Acoustic emission(AE) technique

based on Hilbert-Huang transform(HHT) analysis

was used to analyze the AE signal received from the wall of a multi-layer slurry stirred tank

in which cation exchange resin was dispersed in water by agitation.IMF 1—5

which considered the characteristic scale(20—230 kHz)

was obtained by empirical mode decompositon(EMD)

representing the slurry system. A reconstructed AE signal was acquired by IMF 1—5.The energy of the reconstructed signal was found changing regularly with increasing impeller speed in the stirred tank.Then

a criterion to determine the critical suspension speed was presented.When energy began to remain constant after rapidly increasing

the corresponding impeller speed was the critical suspension speed.It was shown that the average absolute relative deviation(AARD) was about 3.83% compared with visual observation. Furthermore

external loop could diminish the critical suspension speed by intensifying axial flow in the tank

which meant that solid suspension was promoted.A predictive equation for calculating the critical suspension speed in a stirred tank with an external loop was proposed

which gave an AARD of 5.78%.Therefore

multi-scale analysis of acoustic signals based on HHT analysis was feasible for determining the critical dispersion speed and had the merit of being sensitive

non-intrusive and accurate.