The petrographic determination of reactivity differences of two South African inertinite-rich lump coals

Abstract

There is limited literature on the classification and characterization of chars generated from lump coals during synthesis gas production, especially from a South African perspective. Two inertinite-rich medium rank C Highveld lump coals (Coals A and B) were utilized to study their burning behaviour in a packed-bed reactor combustion unit. Seven sample increments were dissected per coal obtained from predefined zones within the reactor. Proximate analysis revealed that Coal A released 10% more of its volatile matter yield within the reactor zones when compared to Coal B. Petrographic analysis showed that Coal B had a higher content of reactive macerals when compared to Coal A. The reactive maceral content of Coal A was dominated by vitrinite and liptinite whereas for Coal B, reactive macerals were comprised of 49% vitrinite and liptinite and the other 51% is reactive semifusinite and reactive inertodetrinite. This difference leads to different reactivity behaviour when these coal samples were subjected to high temperatures. Coal B produced a greater proportion of inert chars, ran at higher temperatures in the hotter region of the reactor because of its aromatic richness thus leads to lower CO2 reactivity. This paper highlights the need for a detailed characterization of coals to fully determine their conversion performance; detailed coal petrography is one such tool that its value is frequently underplayed.