(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
AIChE Annual Meeting
Thursday, November 1, 2018 - 8:21am to 8:42am
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.