Design of micro interconnected fluidized bed for oxygen carrier evaluation

Abstract

Oxygen carriers (OC), one of the key factors in chemical looping combustion (CLC), are regularly evaluated using thermogravimetric analysis (TGA) and batch fluidized beds with oxidizing and reducing gas streams. Nevertheless, the reaction status in these devices has a specific deviation from a real CLC process. It introduces difficulty when assessing attrition rate, thermal stability, and reactivity. In this work, a micro interconnected fluidized bed (MIFB) is designed to provide a real CLC environment to increase the accuracy of OC evaluation. The air reactor and fuel reactor are identical two-stage bubbling beds, which have 30 mm ID and 100 mm height. With stable and flexible fluidization, the amount of bed inventory in MIFB was minimized to reduce operational cost. 350 g bed inventory was required after size miniaturization, structure optimization and circulation path simplification. Synthetic NiO/Al2O3 and natural hematite are employed as OCs to give insight into MIFB performance. Reactivity of hematite was observed in MIFB with conversion efficiencies of 100%, 36.8%, and 16% for H2, CO and CH4 respectively at 900℃. Ni-based OC displayed excellent reactivity and thermodynamics, but also exhibited severe carbon deposition at low temperature. OC lifetimes of 457 h and 680 h were estimated for hematite and NiO/Al2O3, respectively. In addition, particle size distributions were employed to evaluate OC attrition behavior in MIFB. Based on this approach, the potential of MIFB as an OC evaluation device is demonstrated, accurately reflecting fluidization hydrodynamics, OC reactivity, mechanical behavior and lifetime, the influence of temperature and carbon deposition phenomenon.