The hydrodynamics of a fuel reactor in a chemical looping combustion (CLC) system is analyzed by using a multiphase two-dimensional computational fluid dynamics (CFD) model that involves solid–gas interactions and chemical reactions. The study compares the fuel reactors of two CLC systems numerically by using hydrogen with calcium sulfide as an oxygen carrier, and methane with nickel as an oxygen carrier in similar conditions. Kinetic theory of granular flow has been adopted. The model considers the conservation equations of mass, momentum and species, and reaction kinetics of oxygen carriers. The results obtained are in good agreement with the experimental and numerical results available in open literature. The bubble hydrodynamics in both the fuel reactors are analyzed. The salient features of the bubble formation, rise, and burst are more prominent in the hydrogen-fueled reactor as compared to the methane-fueled reactor. The fuel conversion rate is found to be larger for the hydrogen-fueled reactor.