KINETICS OF CO2 GASIFICATION OF FAST PYROLYSIS BLACK LIQUOR CHAR

The CO2gasification rate of black liquor char (BLC) was studied in a thermogravimetric analysis setup at temperatures between 600 and 800°C. The BLC was prepared via fast pyrolysis of dry solids of spent liquor of the kraft wood pulping process. BLC gasification by CO2is well described by Langmuir-Hinshelwood type kinetics. The gasification rate of BLC is 1 order of magnitude larger than that of a high surface area activated carbon impregnated with 12% Na2CO3. Also, the gasification rate of BLC remains high at sodium/carbon ratios where the rate of Na2CO3impregnated chars would normally be strongly reduced. The rate of BLC gasification was also influenced by the drying method and pyrolysis heating rate. Using a scanning electron microscope and energy dispersive spectroscopy (SEM-EDS) mapping and line scan techniques, it is shown that the unique gasification properties of BLC are caused by a very fine distribution of sodium in the carbon matrix. The present data suggest that internal surface area measurements rather than swelling tests might be more appropriate to characterize combustion properties of black liquors. © 1990, American Chemical Society. All rights reserved.