Abstract
The biomass gasification by means of fluidized beds has become one of the most reliable and sustainable processes to produce energy, thanks to the low-impact by-products developed during the process. Recently many countries decided to invest on the Dual Circulating Fluidized Bed (DCFB) technology. Being able to optimize these reactors entails the capability to correctly model the particle motion under the fluidization regime. Although fluidized beds for gasification purposes have been widely studied from the chemical and thermal points of view, their fluid dynamic behaviour is still partially unknown. This work aims at theoretically and experimentally describing the particle motion and the segregation problem in fluidized granular bed reactors. The fluid dynamics of four, cold, lab-scale reactors will be investigated combining Particle Tracking Velocimetry (PTV), Particle Image Velocimetry (PIV) tools and Magnetic Particle Tracking (MPT) techniques. Pressure measurements will be also exploited to investigate the influence of the Particle Size Distribution (PSD) of the bed on its fluid-dynamic behaviour. The performance of the several techniques will be assessed and compared: pros and cons of the tested experimental methods will be highlighted considering the different purposes of the measurements. The experiments run with the simplest reactor will also be used to validate numerical simulations carried out with both fully Eulerian and Eulerian-Lagrangian numerical schemes. We expect to find a strong correlation between zones where particles velocity decreases and concentration increases, resulting in segregation phenomena to occur. This undesired process must be avoided since it can unexpectedly stop the chemical reactions within the reactor. The final aim of this work is then providing a very solid dataset of measurements on fluidized beds hydrodynamics that can be used in future to validate Lagrangian simulations of these complex reactors.