Development of Optical Techniques for Chemical Engineering Applications

The design of separation processes for nuclear spend fuel treatment, dedicated to either R&D studies or industrial applications, is currently based on a phenomenological approach, relying on Computational Fluid Dynamics, and complemented by validation tests achieved at small-scale. Indeed, most of the steps of the PUREX^® process involve multiphasic flows (dissolution, leaching, liquid-liquid extraction, precipitation, filtration, etc.). Therefore an accurate knowledge of the dispersed phase properties is required in order to assess their coupling with the flow features, to predict the process performance and efficiency and to achieve size reduction or extrapolation.Hence, the measurements of particulate flows properties, and especially the particles (or drops or bubbles) size distribution, concentration (i.e. hold-up) and velocity has become a growing issue. Relevant techniques for measuring these flow properties are multiple, from the high-speed video acquisition coupled to image processing to the laser-induced fluorescence, including the particle imaging velocimetry or interferometric techniques (digital in-line holography, rainbow refractometry, etc.). In this communication, different techniques developed at CEA Marcoule for the characterization of multiphase flows, will be introduced. The strong interaction with computational fluid dynamics, in the scope of a multiscale approach, will be discussed through typical results of gas-liquid, liquid-liquid and solid-liquid flows possibly encountered in nuclear fuel reprocessing process.