Chemical, thermal and dilution effects of carbon dioxide in oxy-fuel combustion of wood in a fixed bed

Experimental and numerical modeling was performed on eucalyptus wood combustion under oxy-fuel conditions using a fixed bed reactor in order to isolate the role of various carbon dioxide effects on the burning rate. Wood combustion was investigated under four different mixtures of O 2 and Ar/CO 2 /N 2 : 21 % O 2 /79 % N 2 ; 21 % O 2 /22.5 % CO 2 /56.5 % Ar; 40 % O 2 /60 % CO 2 ; and 40 % O 2 /47 % CO 2 /13 % Ar. The first three mixtures were designed to have the same peak temperatures in order to isolate chemical and dilution effects of CO 2 . This was achieved by substituting some percentage of CO 2 with Ar in O 2 /CO 2 mixture while maintaining a constant concentration of O 2 . The fourth mixture was meant to isolate the thermal effect of CO 2 . The results were obtained from both the experimental rig and numerical simulation for a fixed bed configuration. Wood combustion in the fixed bed was modeled using Lagrange-Euler method, where gas-phase was calculated using computational fluid dynamics (CFD), that is Euler phase, while solid-phase was tracked in Lagrange phase using discrete element method (DEM). The results show that ignition time in CO 2 environment decreases gradually as O 2 concentration is increased. On the other hand, burning rate and flame front speed increase as O 2 concentration is increased. It was established that dilution effect is the most influential parameter on the burning rate of wood combustion in an oxy-fuel system.