Intraparticle gas sampling during wood particle pyrolysis: Methodology assessment by means of thermofluidynamic modeling

Abstract

An intraparticle sampling technique has recently been developed revealing the evolution of chemical species during biomass decomposition. The analysis has shown that CO2 is produced up to 10% concentration at 200°C, nearly coincidental with the evolution of CO, which reaches a maximum of 24% at 325°C. Subsequent release of H2 reaches a maximum of 0.7% at approximately 300°C. The release of these gases coincides with a commensurate mass loss of almost 70% between 225°C and 350°C. Continued decomposition of the biomass results in the reduction of light gases as observed in the decline of hydrogen and CO2 concentrations and a sharp increase in higher hydrocarbons. For example at 440°C the concentrations of CO2 and H2 are 17% and 0.4%, respectively, while the CH4, C2H6 and C2H4 are 19%, 1.2% and 0.8%, respectively.To complement this sampling approach, the thermo-fluid-dynamics of the process were assessed through a numerical model based on a finite volume method (fvm). The suction force applied by the microGC pump affects the pressure distribution within the particle. Nonetheless, the model demonstrates that the perturbing effect is confined to the inner part of the particle. In fact, the absolute pressure inside the particle is lower than 0.90, 0.95 and 0.99atm in only 1.28%, 4.47% and 30.07%, respectively, of the interior volume. Therefore, the model demonstrates that utilizing a choked-flow sampling arrangement is preferred when extracting chemical species released during thermal decomposition.