Numerical Study on the Hydrodynamics of a Chemical Looping Combustion System with a Binary-Particle Mixture

Chemical looping combustion (CLC) involving multicomponent particles is favorable for the purpose of capturing CO₂ with a low energy penalty. While the complex flowing behavior in terms of mixing and segregation of particles makes it a challenge to have a deep understanding of hydrodynamics as well as its application. In this paper, a multifluid model based on the Eulerian–Eulerian approach is introduced for a three-dimensional (3D) simulation of the fluidization process in a chemical looping combustion system with binary particles consisting of heavy glass beads (GBs) and light polyethylene (PE) as two model metal oxides (i.e., oxygen carriers). The multifluid model integrates the k_g – ε_g – k_s – ε_s – Θ formulations for the description of turbulence flow and the EMMS drag for the interaction between particles and gas. With this model, the distributions of pressure and phase velocity as well as the solid circulation rate can be obtained. Also, satisfactory agreements are found between the predictions and experimental data, which validates the proposed model. It is observed that a higher fluidizing velocity in the air reactor (AR) and fuel reactor (FR) results in a higher solid circulation rate with less significant segregation. Increasing the diameter of heavy GB from 98 to 138 μm with a fixed PE diameter of 231 μm leads to a continuous intensification of the segregation behavior in AR and riser as well as FR, while the difference in values of averaged binary-mixture compositions (i.e., averaged light PE weight fraction) between AR and FR shows an inflection point where a relatively equal composition within the two reactors is reached when the GB diameter is 116 μm. Higher fluidizing velocity in loop seals just leads to a higher solid circulation rate, and it almost has no influence on the composition of binary particles in AR and FR, indicating a valve-like function of the loop seals.