Computational Simulation of a 100 kW Dual Circulating Fluidized Bed Reactor Processing Coal by Chemical Looping with Oxygen Uncoupling

Chemical looping with oxygen uncoupling (CLOU) is a promising carbon capture technology that utilizes two interconnected fluidized-bed reactors to separate oxygen from air using a metal oxide, and then to use that oxygen to combust fuel in a nitrogen-free environment. CLOU is particularly well suited for solid fuels such as coal since released O₂ will readily combust with solid char. This study presents simulations of the University of Utah's dual fluidized bed chemical looping process development unit (PDU) operating as a CLOU system at 100 kW_th, using CPFD Software's Barracuda-VR™ CFD modeling program. A full 3D model of the PDU was used including both reactors, as well as loop seals and cyclone separators. Hydrodynamic settings and the drag model are based on previous cold-flow validation experiments. Mechanisms describing CLOU reaction kinetics for cuprous oxide oxidation in the air reactor and cupric oxide reduction in the fuel reactor were adapted from previously completed experimental work. Coal char kinetics were based on the carbon-hydrogen-nitrogen-oxygen-sulfur, CHNOS, method. Submodels for devolatilization, gasification, and homogenous gas-phase reactions used relationships from the literature. Results predict volatile burnout almost immediately, though coal combustion continues into the upper portions of the fuel reactor and cyclone. Nitrogen gas leakage into the fuel reactor is shown to be mostly carryover from the air reactor. Carbon capture was predicted to be 91.4%.