39 Gasification of char particles with CO 2 AND H 2O

Abstract

Gasification of large char particles with CO 2 and H 2O has been investigated both experimentally and with model studies. A local volumetric rate model is derived that takes into account the chemical reaction rate and the effective diffusivity being a function of the local carbon conversion and therefore a function of time and position within the particle. The model includes shrinking unreacted core and homogeneous reaction as extreme cases. Chemical reaction rates of powdered deal wood char were measured for different CO 2 and/or H 2O concentrations (0.05 - 2 mol/m 3) and as a function of the carbon conversion and temperature (1073 - 1273 K) by means of a modified thermobalance. In separate single particle tests the effective diffusivity has been determined for different carbon conversions. A specially designed single particle reactor has been used for local carbon conversions. measurement within 0,04 m particles. Carbon conversion profiles obtained differ from those predicted by the shrinking core and homogeneous reaction extremes but could be very well explained by the local volumetric rate model. As an example results obtained from a 3 kg/h co-current moving bed wood gasifier are presented. Char conversion, particle diameter and temperature profiles agree well with the reduction zone model based on the local volumetric-rate particle model.