A FRACTAL APPROACH TO THE ANALYSIS OF LOW-TEMPERATURE COMBUSTION-RATE OF A COAL CHAR .1. EXPERIMENTAL RESULTS

The combustion reactivity of char obtained by devolatilization of South African bituminous coal has been investigated by thermogravimetric analysis in the temperature range of 653 to 733 K at oxygen partial pressures from 0.21 to 1 bar. Samples of the same char, either unreacted or preburned in a fixed bed reactor to given levels of carbon burn-off, have been characterized from the standpoints of their surface area and of their volume and size distribution of pores. Different experimental techniques, namely mercury porosimetry and adsorption of either carbon dioxide or nitrogen, and models for the interpretation of porosimetric data have been used. Analysis of meso- and macropore size distributions, and of adsorption isotherms in the low relative pressure region, has been directed to check whether the topological structure of the porous matrix of the char might be described as a fractal.