Fluidization characteristics of supercritical fluidized beds: A comprehensive review

Abstract

Fluidized beds (FBs) are widely used in many industrial applications, and continuous improvement of their performance is imperative. However, the inherent limitations of gas-solid FBs, particularly concerning fluidization characteristics, mass transfer efficiency, and operational stability, cannot be adequately addressed solely through structural optimization. Accordingly, fluidized bed reactors using supercritical fluids (SCFs) as fluidizing agents have attracted considerable attention in recent years due to their unique physicochemical properties. Supercritical fluidized beds offer higher fluidization uniformity, reduced bubble diameter, improved particle mixing, and greater bed expansion compared to conventional gas-solid FBs. This review comprehensively examines the advancements in supercritical fluidization technology, with emphasis on supercritical water and carbon dioxide. The main findings indicate that operational parameters, including temperature, pressure, and superficial fluid velocity, exert a substantial influence on fluidization characteristics by modulating the properties of the SCF. Particle properties, including diameter, shape, and size distribution, significantly affect minimum fluidization velocity, bubble dynamics, and bed homogeneity. Predictive correlations for critical parameters are discussed, highlighting their role in reactor design and optimization. Despite notable progress, challenges persist, such as limited experimental data and the limited applicability of traditional fluidized bed testing methodologies to the supercritical domain. This review is of considerable significance for the optimized design of supercritical fluidized beds and provides direction for future applications of supercritical fluidized beds across a wider range of fields.