Study of solids movement in pebble bed / moving bed reactors using radioactive particle yracking (RPT) technique

V. B. Khanea , M. H. Al-Dahhanb

a Chemical and Biochemical Engineering Dept., Missouri University of Science and Technology,Rolla, MO-65401, USA

b Chemical and Biochemical Engineering Dept., Mining and Nuclear Engineering Dept., Missouri University of Science and Technology, Rolla, MO-65401, USA

Abstract

Moving bed reactors are used in the chemical, petrochemical and petrochemical refining industries in situations where there is a need to replace deactivated catalysts with new or regenerated catalysts. They are also under consideration as a 4th generation nuclear reactor known as Pebble Bed Reactor (PBR). It is important to study the movement of solids in moving beds, which will provide useful information about Lagrangian trajectories, residence time distributions, velocity fields, and the presence and extent of dead zones, if any. The Radioactive Particle Tracking (RPT) technique is capable of providing a full description of three-dimensional flow field in highly dense and opaque reactors. The RPT technique is implemented around a Continuous Pebbles Recirculation experimental set-up that mimics a cold flow moving bed operation of Pebble Bed Reactor (4th Generation Nuclear Reactor concept). A Cobalt-60 based tracer having activity of 500µCi mimics the dynamics of pebble phase in pebble bed. RPT calibration experiments suggested that counts received at the detectors are not only a function of the tracer-detector distance but also of the attenuation characteristics of the medium in between the tracer and the detector. Development of cross-correlation based position reconstruction algorithm suitable for this study has been carried out and validated using the counts data for known positions. Obtained results of the RPT technique about Lagrangian trajectories, velocity field, residence time distributions etc. are serving as a benchmark data for an assessment of the contact force model used in the Discrete Element Method (DEM) based simulations.

Keywords: Moving Bed Reactor; Pebble Bed Reactor; Radioactive Particle Tracking; Discrete Element Method