Experimental and kinetic study of acetylene oxidation over CaO- and MgO-based bed materials under biomass circulating fluidized bed systems

Incomplete oxidation of light pyrolysis gases caused by locally insufficient oxygen, limited residence time, and imperfect mixing may reduce combustion efficiency in biomass circulating fluidized-bed (Bio-CFB) systems. Ca- and Mg-based materials, commonly introduced for in-furnace desulfurization and agglomeration control, have the potential to affect the oxidation of those volatile species through heterogeneous catalytic pathways. This study investigated high-temperature acetylene (C 2 H 2 , a representative intermediate of biomass-derived volatiles) oxidation over CaO and MgO in a tubular-flow fixed-bed reactor at 700–900 °C, excess oxygen ratios of 3–12, and particle sizes of 3, 45, and 120 μm. A multiscale kinetic framework including the surface-, particle-, and reactor-scale models was developed to distinguish homogeneous and heterogeneous contributions and kinetic parameters. Both CaO and MgO substantially promoted C 2 H 2 oxidation, with higher catalytic activity of CaO. Both materials exhibited a similar non-monotonic particle-size dependence. Multiscale fitting yielded activation energies of 81.58 and 96.05 𝗄 𝖩 ∙ m o l − 𝟣 for C 2 H 2 oxidation to CO 2 and CO over CaO, compared with 94.57 and 103.25 𝗄 𝖩 ∙ m o l − 𝟣 over MgO. These findings clarify the coupled effects of intrinsic catalytic activity and mass transport on C 2 H 2 conversion, providing a kinetic basis for improving volatile burnout and coordinating the use of functional bed additives in Bio-CFB combustion.