CFD simulation of gas and particle flow and a carbon capture process using a circulating fluidized bed (CFB) reacting loop.

Abstract Circulating fluidized bed (CFB) loop-based reactors are widely used in the chemical and energy industries. CFB reactors are excellent candidates for chemical looping of solid sorbents for CO 2 capture and sorbent regeneration processes because they ensure a continuous carbon dioxide removal process in a relatively compact unit. Computational fluid dynamics (CFD) provides an excellent approach to model the carbonator and regenerator reactors and the entire CFB loop design in a systematic and computationally feasible way. The simulation of individual parts of the system was recently performed and provided a qualitative estimation of the system behavior. In order to use CFD to perform simulations of the CO 2 capture regenerative process, a model based on the multiphase flow equations taking into account the sorption/regeneration is needed. Therefore, in this work, a CFD approach was developed and applied to simulate gas and solid flows and CO 2 sorption and regeneration in the entire CFB loop. The CFB's geometry used in this study is the same as National Energy Technology Laboratory's experimental setup. Our calculations showed that the CFB hydrodynamic behavior reached to a statistical steady state after about 10 s in a three-dimensional domain. The time to reach statistical steady state strongly depends on the initial condition of the simulations, and the geometry and the size of the system. Three-dimensional CFD simulations demand significantly high computational time; thus, we used only the three-dimensional domain for understanding the hydrodynamics of the system and to verify the dynamics of the same system in a two-dimensional CFD domain (no reaction was included in the three-dimensional domain). The two-dimensional domain requires considerably less computational time and allowed us to ultimately add two heterogeneous reactions to the circulating fluidized bed's CFD simulation for carbonation and regeneration of MgO-based solid sorbents. The results of our simulation showed the excellent capability of our CFD approach in describing the CO 2 conversion profiles and flow behavior in a reacting CFB system that includes the entire range of solid volume fraction from very dilute (i.e., riser) to very dense (i.e., standpipe) ranges. The effect of CO 2 sorption and regeneration at elevated temperature and pressure was also studied. Graphical abstract Unlabelled Image Highlights • We modeled a circulating fluidized bed full loop. • Shrinking core model kinetics model were able to calculate the reaction rates. • 3D CFD model reached to steady after 10 s. • 2D CFD model with modified boundary condition result the same as 3D model. [ABSTRACT FROM AUTHOR]