The gasification reactions of solid carbonaceous particles such as biomass or coal are complex. Multiple physical phenomena and operating conditions of gasifier simultaneously govern the response of these reactions during carbon conversion. Direct or indirect coupling among the involved transport mechanisms of heat and mass transfer and the chemical kinetics at the active site of the solid impact the overall gasification performance. This study addresses a mathematical model during CO2 gasification of a spherical biomass particle subject to entrained flow condition at high temperature. An algorithm is developed to account both internal and external mass transport limitation during char conversion while devolatilization event occurs in parallel. The prediction of overall carbon conversion is compared to experimental data from a bench scale entrained flow reactor. The results show almost 60% devolatilization is completed when the char gasification reaction starts and the char conversion is <0.8% when the particle is completely devolatilized. The effect of the boundary layer is important during the devolatilization event that provides heat and mass transfer resistance. Complete carbon conversion for 90 mu m particle can be achieved at 1200 degrees C temperature and 40% concentration of CO2 with a time close to 10 s. (C) 2018 Elsevier Ltd. All rights reserved.