Self-regulation of bed temperature field of the fixed-bed reactor unit by composite-filled oxygen carriers for chemical looping combustion of methane

Abstract

Fixed-bed reactors (FBRs) are suitable for chemical looping combustion (CLC) of gaseous fuels. However, the non-uniform temperature field such as the formation of hotpots can easily lead to the deactivation of oxygen carriers (OCs), ultimately leading to the degradation of the CLC performance and the durability of the OCs. This work systematically investigates the effect of individual CuO/SiO2 and Fe2O3/Al2O3 OC-filled FBR units on the bed temperature field using a self-built experimental setup to monitor the real-time bed temperature evolution. In addition, a strategy for self-regulating the bed temperature field by composite OCs-filled FBR units is proposed based on the differences in the thermodynamic properties of different OCs, including CuO/SiO2, Fe2O3/Al2O3, Mn2O3/ZrO2 and NiO/ZrO2. It has been found that the radial bed temperature of a single CuO/SiO2 OC-filled FBR unit is significantly higher than that at the central axis, and the bed temperature fluctuates within a range of ± 50 °C throughout the CLC process. The bed temperature of a single Fe2O3/Al2O3 OC-filled FBR unit fluctuated within a range of ± 25 °C during the reduction stage, but the bed temperature increased by nearly 100 °C due to the strong exothermic reaction of the oxidative regeneration of the reduced Fe2O3/Al2O3 OCs. The use of composite OCs-filled FBR units not only improves the CH4 conversion and CO2 selectivity, but also maintains a stable bed temperature fluctuates within a range of ± 15 ℃ during the different reaction stages of the CLC process. The synergistic effect between the OCs contributes to the bed temperature field remaining in a relatively stable state. The results indicate that the rational distribution of composite-filled OCs in FBRs can achieve self-regulation of the bed temperature field to some extent by exploiting the OCs’ endothermic and exothermic properties.