(617b) Numerical Investigation of Scale-up and in-Bed Heat Exchanger on the Hydrodynamic Characteristics of the Fluidized Bed Combustor of Coal Direct Chemical Looping System

Coal Direct Chemical Looping (CDCL) for electricity generation is as an energy efficient carbon capture technology with a capability of capturing 99% of the CO2 from fossil fuels. The CDCL system developed by the Ohio State University uniquely uses counter-current moving bed with Geldart group D particles for its reducer. The technology is ready for the scale up to pilot and industrial scales. However, achieving a fundamental understanding of the mechanisms governing the hydrodynamic behavior of the combustor operated under a fluidized bed mode, particularly under industrial operating conditions, still presents a major scientific and engineering challenge. For Geldart Group D particles using in the system, slugging fluidization normally occurs in sub-pilot scaled units whose combustors are with small diameters and large height-to-diameter ratio. While, when the system is scaled-up, the geometry and the height-to-diameter ratio will change, which will change the hydrodynamic characteristics dramatically. The installation of the in-bed heat exchanger tubes inside the combustor may also change the hydrodynamic characteristics. Thus, hydrodynamic characterization on the sub-pilot scaled cold flow model is not enough for understanding the hydrodynamics of pilot and commercial sized combustors. In this study, a two-fluid model (TFM) imbedded in the MFIX model was used to investigate the effect of scale-up and in-bed heat exchanger on the hydrodynamic characteristics of the combustor. Appropriate drag models and wall boundaries were selected for the simulation and validated with experimental data from sub-pilot scale cold flow models. The model and the boundaries are then applied to industrial scaled simulation with the consideration of in-bed heat exchangers.