Conical Fluidized Bed CFD: Introduction to Particle Mixing Simulation

The Conical Fluidized bed is a highly efficient type of reactor used in many industrial processes. From a chemical engineering viewpoint, its main advantage is superior particle mixing. This project provides a detailed Conical Fluidized bed CFD Simulation. The unique conical shape creates a velocity gradient in the fluidizing gas; the gas slows down as it moves up through the expanding cross-section. This design helps prevent common problems like slugging and ensures smoother fluidization. The primary goal of a Fluidized bed CFD analysis is often to study how different types of particles mix or segregate. In this Fluidized bed Fluent simulation, we investigate a binary system with two different solid particles, coke and TiO2. We use the Eulerian multiphase model because it is designed to treat each solid phase and the gas phase as interpenetrating continua, making it perfect for modeling this complex gas-solid interaction. This study is based on the methods in the reference paper “CFD simulations of particle mixing in a binary fluidized bed [1]”.

• Reference [1]: Cooper, Scott, and Charles J. Coronella. “CFD simulations of particle mixing in a binary fluidized bed.” Powder Technology 151.1-3 (2005): 27-36.

Figure 1: Schematic of conical fluidized bed [1]

Conical Fluidized Bed CFD Simulation Process

The process for this Conical Fluidized bed CFD Simulation began in ANSYS Design Modeler, where the geometry was designed with blocking to create a high-quality structured grid. This structured mesh was then generated in ANSYS Meshing. For the solver setup in ANSYS Fluent, the Eulerian multiphase model was selected to handle the three distinct phases: the gas phase and two granular solid phases (TiO2 and Coke).

A key step in a particle mixing CFD simulation is defining the granular properties for each solid phase, such as particle diameter and density. It is important to note that the coke particles are much larger than the TiO2 particles. In a particle mixing Fluent simulation using the Eulerian model, defining the interactions between the phases (phase pairs) is also critical. This includes specifying drag models that govern the momentum exchange between the gas and each solid particle, as well as models for solid-solid interaction. This detailed setup is necessary to accurately predict the fluidization behavior and subsequent mixing patterns.

Particle Mixing CFD Analysis: Post-processing Conical Fluidized Bed Results

The post-processing results provide a deep insight into the complex particle mixing dynamics within the reactor. The contours of volume fraction, obtained from our Conical Fluidized bed CFD analysis, clearly show the distribution of coke, TiO2, and the gas phase. A key finding is the clear evidence of particle segregation and mixing zones. For instance, the smaller, less dense TiO2 particles (Figure 4) are more easily carried by the gas and show greater dispersion throughout the bed. In contrast, the larger, denser coke particles (Figure 2) tend to be more influenced by gravity and show different circulation patterns. This behavior is a direct result of the difference in their properties, which is a core focus of a particle mixing Fluent investigation.

Figure 2: Coke & Gas volume fraction contour of Particle Mixing in a Conical Fluidized Bed CFD Simulation

Figure 3: Tio2 volume fraction contour of Particle Mixing in a Conical Fluidized Bed CFD Simulation

The conical geometry plays a crucial role in the reactor’s performance. As the gas flows upwards, the increasing cross-sectional area causes the local gas velocity to decrease. This natural velocity gradient creates a distinctive flow pattern that promotes mixing and prevents “dead zones” where particles could become stagnant. The contours show that denser particles tend to move towards the walls where gas velocity is lower, while lighter particles remain more distributed in the central, higher-velocity region. This internal circulation is fundamental to the efficiency of a Conical Fluidized bed. The animation mentioned in the report shows this dynamic process clearly: initial pockets of segregated particles gradually break down and blend into a more uniform mixture, especially in the core of the bed where the gas-solid interaction is most intense. The bed expansion can also be clearly observed as the gas lifts and fluidizes the solid particles. This detailed Fluidized bed CFD and Fluidized bed Fluent analysis confirms the reactor’s effective design for achieving a well-mixed state, which is vital for uniform reaction rates and efficient heat transfer.