Coal pyrolysis: Comparative evaluation of the technical performance of two Southern Hemisphere demineralized bituminous coals

Abstract

Differences in the physico-chemical properties of char can fundamentally affect the reactivity of the char during conversion processes and even the reaction pathway. Transformations from coal to char using a high heating rate have been thoroughly assessed; however, there is less information on the reactivity of this transition to chars. Two South African bituminous coals of ≤75μm were acid washed, and subjected to a slow heating rate of 25°C/min from 450 to 700°C at atmospheric atmosphere. The chars were characterized by physical, chemical and petrographic evaluations. The effect of the heat treatment conditions on the reactivity of the chars towards oxygen under chemical kinetic controlled regime was assessed. The oxygen content of the resultant chars was also measured directly by scanning electron microscope (SEM) attached with element detector sensor (EDS) technique. The coals are medium rank C bituminous (Rov=0.73 for high volatile and Rov=0.78 for low volatile). Char properties determined revealed correlations of the chemical structural changes during the coal to char transition. The findings of this study would suggest that the loss of carbon combustion reactivity cannot be assessed on the basis of its time-temperature history only, but the extent of carbon interaction with oxygen also come into play. The synergy of reactions induced by modifications of the carbon structure, oxygen uptake and the reaction between oxygen and the resultant chars is presented and discussed.