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

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.