Multi-scale Analysis Of The AE Signals And Its Application In Solid-liquid Systems

The slurry concentration, minimum agitation speed and slurry suspension height, as the basic parameters in the solid-liquid system, is very important to the design and optimization of the reactors. Reliable approach to measurement is therefore expected by the people from both academia and industry.The relationship between acoustic emission (AE) signal and slurry concentration, minimum agitation impeller speed, stirred tank height was investigated systemically in this paper according to the mechanism that AE energy in a stirred tank is the function of slurry concentration and velocity. Characteristic frequency ranges of the signals representing the movement of solid particles and the characteristic parameters which indicate the relationship between AE signals and slurry concentration, minimum agitation speed, slurry suspension height was obtained by using frequency spectrum analysis, wavelet transform and R/S analysis. Then the criterion and models for measuring the minimum agitation speed, slurry suspension height and the slurry concentration was proposed respective. The results show that AE technique would achieve on-line measurement of the slurry concentration, minimum agitation speed slurry suspension height fast, non-intrusively, nature and with good accuracy. The innovative results can be summarized as following:1. According to the mechanism that AE signals with different frequency ranges were emitted when solid particles impacted the wall, characteristic frequency ranges of the signals representing the movement of solid particles were obtained and a model of the slurry concentration in a loop reactor was established to explore the quantitative relationship between acoustic emission energy, flow rate, and slurry concentration by using wavelet transform and R/S analysis. The system of water-beading was used as an example in loop reactor to investigate the relationship between characteristic AE energy and slurry concentration at the flow rate ranging from 5 m·s^-1 to 8 m·s^-1. AE signals with the frequency from 0 to100 kHz were analyzed by 9 scales wavelet transform and R/S analysis at a constant flow rate. It was found that d₁ and d₂ frequency ranges could be the characteristic frequency ranges representing the movement of solid particles. The ratio between the sum of the AE energy in the d₁, d₂ frequency range and 3^rd power of the flow rate was proportional to the slurry concentration. The results showed that the slurry concentration could be successfully predicted with the average relative errors 11.8%, which indicated AE technique would achieve on-line measurement of the slurry concentration in loop reactors fast, non-intrusively and with good accuracy.2. The minimum agitation speed in stirred tank was experimentally investigated by AE technique. The criterion of determination of minimum agitation speed in stirred tank that the impeller speed in which the characteristic value representing the collision between solid particles and the wall decreases quickly and begins to be constant was presented by analysis of the relationship between R and impeller speed. A satisfactory agreement was obtained between measurement by AE technique and visual method for beading-water system or calculated by model for beading-water system, and the AARD were 3.51% and 3.17 % respective, which indicated AE technique would measure the minimum agitation speed fast, non-intrusively and with good accuracy.3. According to the mechanism that AE signals with different frequency ranges were emitted when solid particles impacted the wall, characteristic frequency ranges of the signals representing the movement of solid particles were obtained and a model of the slurry concentration in a stirred vessel was proposed to explore the quantitative relationship among AE energy, stirring rate, Particle diameter, and slurry concentration by using wavelet transform and R/S analysis. The model was used for measuring the slurry concentration in stirred tank when all the solids are suspended and below the suspension height. The experiment in the stirred tank showed that a satisfactory agreement was obtained between measurement by calculated values and the actual values for water-beading system,and the AARD was 17.45 %. Therefore, this model could predict the slurry concentration with fairly good accuracy.4. The slurry suspension height and liquid layer height was experimentally investigated by using energy analysis, wavelet transform and R/S analysis. It was found that the characteristic R_E which is the energy ratio between measurement point and the bulk region would decreases quickly twice. So, the criterion of the slurry suspension height and liquid layer height that the location is the slurry suspension height and liquid layer height in which the R_E attend the mutation was present. The slurry suspension height and the liquid layer height were that the location is the in which the R_E=0.62 and R_E=0.12 for water-beading system respective. The experiment in the stirred tank showed that a satisfactory agreement was obtained between measurement by AE technique and observation for water-beading system, and the AARD was less than 11.8 %. So the AE approach to measuring the suspension height and liquid layer height in the stirred tank can be developed to judge the tank level precisely with good accuracy.