Flow Characterization in Bubbling Fluidized Beds with Solids Crossflow

Licentiate thesis, 2024

The present study focuses on the application of bubbling fluidized beds with solids crossflow, which is relevant in processes such as drying, iron ore reduction, pharmaceutical production, and waste incineration. While a uniform distribution of temperature and reactants across the beds can be achieved in a stationary bubbling fluidized bed, the introduction of solids crossflow is typically driven by the need for significant throughput of mass and/or heat transfer across the bed. Moreover, cross flow can aid in stabilizing the fluidization behavior, which is essential for consistent process performance and the scaling up of operations. Despite the critical role of fluidized beds in various industries, understanding their flow characteristics remains a significant challenge for the design and scale-up of new processes. This study aims to explore the behavior of solids flow within a bubbling fluidized bed featuring horizontal crossflow. The research is organized around four key objectives: 1. elucidating the interaction between solid convection and lateral dispersion, 2. analyzing fluidization quality, 3. evaluating the impact of bed-wall friction on solid flow, and 4. assessing the efficiency of solid convection by testing various conveying configurations.

The study employs a cold flow model designed and operated according to the simplified Glicksman scaling laws, using Geldart B-type solids for the investigations. The study evaluates four measurement methods (integral mass accumulation, differential mass accumulation, thermal tracing, and magnetic solids tracing) to assess the solids circulation. Magnetic solids tracing emerges as the preferred technique, as it enables a non-intrusive, continuous, and detailed study of solids transport dynamics. Through this measurement method, a linear correlation was observed between the horizontal solids dispersion coefficient and the mean solids velocity, attributed to the enhanced horizontal mixing due to the backmixing induced by the shear flow friction. Rheological analyses confirmed the non-Newtonian, shear-thinning properties of the bed. Lastly, conveying the solids under a controlled bubbling fluidization regime emerged as the most efficient configuration for solids transportation in the studied unit.