Combustion of spherically shaped large wood char particles

This paper examines the effects of temperature and oxygen enrichment on conversion of large wood char particle under non-isothermal conditions. Combustion air and its combination with oxygen are examined at temperatures of 800 and 850 °C for identical initial char weight, diameter and reaction time. One-film ash segregated core and random pore models are used to characterize the combustion condition. The combustion regimes for these particles are found to be near kinetic-diffusion controlled based on the ash segregated core model. Diffusion and reaction rate relationships are also characterized. Oxygen enriched conditions provided greater reactivity as compared to non-enriched oxidation conditions. For the ash segregated core model, the lowest and highest estimated activation energy values are 123 kJ/mol and 180 kJ/mol, respectively. The activation energies obtained with the random pore model showed inconsistencies. Thiele modulus values varied from 500 to 1000, indicating that the surface reaction rates are significantly faster than pore diffusion rates with oxygen being mostly consumed at the particle surface.