A study of wood pellet and waste plastics oxy-combustion with oxygen staging in a fluidized bed reactor

Abstract

This study was the first to investigate the oxy-combustion of wood pellets and polyethylene (PE) combined with secondary oxygen injection. It began with fuel property analysis and thermogravimetric evaluation, including activation energy, combustion characteristics, and synergistic effects. Co-combustion experiments were conducted in a bubbling fluidized bed, examining parameters like fuel-blending ratio (BR), oxygen concentration, and secondary oxygen ratio (SOR). Synergistic effects between wood pellets and PE were observed in three stages: promotion from 240–400 °C, inhibition from 400–480 °C, and promotion from 480–560 °C. Activation energy analysis showed it rose with O₂ concentration, except for PE. PE added to wood pellets caused tar coverage, delaying reactions and reducing combustion characteristic index. In fluidized bed experiments, higher O₂ concentrations decreased temperatures in the lean phase, while higher SOR reduced temperatures in the dense phase. Increased oxygen levels raised NO emissions, but higher SOR extended gas residence time, reducing NO levels. While CO concentrations decreased with increasing O₂ concentration, local sintering under 40 % O₂ may lead to increased CO emissions. The highest exergy efficiency without secondary oxygen was achieved at 25 % O₂/75 % CO₂ and 40 % PE, reaching 55.67 %. Exergy efficiency improved with higher SOR, peaking at 60.1 % for 30 % O₂/70 % CO₂ under 30 % BR, and 30 % SOR conditions.