Abstract
This paper presents the development of a passive ultrasonic monitoring system for the detection of acoustic emission (AE) created by chemical particles striking the inner wall of a reactor vessel. The finite element (FE) code PZFlex was used to analyze the complex interactions between chemical particles and the vessel wall. A 4-layer 2D model was developed comprising a liquid load medium and a glass-oil-glass combination corresponding to the jacketed vessel reactor. The model has been experimentally validated with excellent correlation achieved. The excitation function was derived from Hertz's theory and used as the model stimulus corresponding to particles striking the inner glass wall. Analysis of the FE simulations provided the transducer specifications for a passive ultrasonic monitoring system. The system comprises two transducers with complementary characteristics: narrow bandwidth/high sensitivity; wideband/low sensitivity. Importantly, the sensitivity of the resonant transducer provides discrimination of particle concentration. Moreover, the broader bandwidth of the off-resonant device demonstrates potential for in situ estimation of particle size. The performance afforded by this approach has considerable potential for real-time process monitoring in the chemicals and pharmaceutical industries.
Highlights
Acoustic monitoring techniques offer a significant advantage over optical techniques such as near infrared and Raman spectrometries for process monitoring in that they can be applied to samples that are optically opaque without the need for any sample preparation
The approach undertaken to analyze the complex interactions between the chemical particles and the vessel wall used finite element (FE) modelling techniques based on PZFlex software
A model-based approach has been described through which the acoustic emission characteristics associated with particle–wall impacts in a reactor vessel have been analyzed to provide a transducer design specification for a non-invasive passive acoustic monitoring system
Summary
Acoustic monitoring techniques offer a significant advantage over optical techniques such as near infrared and Raman spectrometries for process monitoring in that they can be applied to samples that are optically opaque without the need for any sample preparation. The ability of acoustic waves to penetrate optically opaque media such as stainless steel enables acoustic techniques to be configured to operate in a non-invasive mode of operation, e.g. by sensor attachment or location of a microphone close to the outer vessel wall, without the need for incorporation of a window in the vessel. While there are only a few reports of the use of non-invasive active acoustic techniques for in situ process monitoring [1], passive acoustics has been used more widely for the non-invasive monitoring of particulate processes. Passive acoustic monitoring techniques use the acoustic emission (AE) generated by collisions of particles primarily with the inner surface of vessel or pipe walls [2], collisions with any internal structures or between particles may contribute, to determine information related to the status of the process. Tramontana et al / Sensors and Actuators A 228 (2015) 159–169
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