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Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner
Published on: October 25, 2017
Electronic-Oxygen Synergy at Ca-Fe Dual-Metal Interfaces for Selective Syngas Regulation in Biomass Chemical Looping
Yijie Wang1,2, Jiajie Li3,4, Sitao Zhu3
1School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Abstract:
This study reveals the efficient catalytic role of Ca-Fe-based oxygen carriers (Ca2Fe2O5) in biomass chemical looping gasification. With oxygen carrier introduction, the CO yield doubled (0.13 Nm3/kg→0.26 Nm3/kg), with 76.10% selectivity. Steam co-feeding further increased the H2 yield from 0.19 Nm3/kg to 0.72 Nm3/kg, significantly elevating the H2/CO ratio to 2.62. Combined with density functional theory (DFT), the micro-mechanism of reduced oxygen carrier surfaces activating CO2/H2O was elucidated. CO2 (adsorption charge -0.952 |e|) and H2O (adsorption charge -0.612 |e|) chemically adsorb at the CaO(111)/Fe(110) interface, where Fe atoms (charges 0.433 |e|, 0.927 |e|) act as electron donors to drive efficient molecule activation. CO2 undergoes single-step splitting (CO2→CO* + O*), with the desorption energy barrier (Ea = 1.09 eV, 105.17 kJ/mol) determining the reaction rate. H2O splits via two-step cleavage (H2O→HO* + H*→2H* + O*), which is rate-limited by the first step (Ea = 0.42 eV, 40.52 kJ/mol). Simultaneously, the reduced oxygen carrier achieves oxidative regeneration through surface O* lattice incorporation. This work atomically reveals the "electron transfer-oxygen transport" synergy at the Ca-Fe bimetallic interface, establishing a theoretical framework for the directional regulation of the syngas composition and the design of high-performance oxygen carriers.
