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

The combustion reactivity of char obtained by devolatilization of Sout h African bituminous coal has been investigated by thermogravimetric a nalysis in the temperature range of 653 to 733 K at oxygen partial pre ssures 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 a nd of their volume and size distribution of pores. Different experimen tal techniques, namely mercury porosimetry and adsorption of either ca rbon dioxide or nitrogen, and models for the interpretation of porosim etric data have been used. Analysis of meso- and macropore size distri butions, and of adsorption isotherms in the low relative pressure regi on, has been directed to check whether the topological structure of th e porous matrix of the char might be described as a fractal.