Chemical-looping combustion characteristics in an annular circulating fluidized bed reactor

Abstract

The chemical-looping combustion (CLC) has the advantage of no energy loss for separation of carbon dioxide ( $CO_2$ ) without nitrogen oxides ( $NO_x$ ) formation. This system consists of oxidation and reduction reactors where metal oxides particles as oxygen carriers are circulating through these two reactors. The metal oxide particles are reduced by fuel gas in a fuel reactor. i.e., the fuel is burned, and the reduced metal oxide particles are oxidized with air in an air reactor. At complete conversion of the fuel gas (e.g. methane, natural gas etc.), the exit gas stream from the fuel reactor contains only $CO_2$ and $H_2O$ thereby, pure $CO_2$ can be obtained with $H_2O$ condensation. The flue fas from the air reactor will contain only $N_2$ and unreacted $O_2$ . The CLC reactors could be designed by interconnecting fluidized beds that have an advantage over the other alternative designs since the process requires good contract between gas and solid phases and continuous smooth flow of solid materials between the two reactors. The reactivity of Ni-, Fe-, and Mn-based oxygen carrier particles supported on bentonite has been determined by alternating the reduction ( $CH_4$ and $H_2$ +CO) and oxidation ( $O_2$ ) reactions in thermal gravimetric analyzer (TGA). The kinetic parameters for reduction and oxidation of each oxygen carrier particle were determined by the solid-state reaction rate models. The phase-boundary-controlled model was applied to predict conversion of the reduction and oxidation of the oxygen carrier particles and the activation energy for each reaction were determined from the Arrhenius plots and compared with the literature data. Before and after the reactions, no significant variation of size and pore of particles were observed so that this result also supports that the overall reaction rate should be controlled by the chemical reaction rate at the interface. Based on the reactivity data, the design values of the reactor, solid circulat...