The influence of force and inertinite on pore development in coke and its implications on coke strength
U.P. Eyibio, Hammad Aziz, Karen M. Steel
Abstract
• Applied force determines coke’s pore size and porosity. • Inertinites act as a buttress against applied force which increases pore sizes. • Temperature plays an important role in the size distribution of semi-cokes. This study investigates the effect of force on the porosity and pore size distribution (PSD) of the plastic phase during pyrolysis for a vitrinite-rich coal, as well as the influence of inertinite and high temperatures on pore development. A bituminous coal from Australia was separated into vitrinite and inertinite concentrates using a handpicking method and crushed. The effect of force was studied on the vitrinite concentrate and on an 80:20 (vitrinite: inertinite) blend to ascertain the role of inertinite in pore development. A decrease in the mean pore size (MPS) of the interconnected pores from 75 µm to 59 µm occurred when the force applied to the expanded plastic phase was increased from 0.1 N to 2 N (equivalent to 0.2 and 4 kPa, respectively). This reduction in pore size indicates that during coking in a coke oven, internal gas pressure in the plastic layer might directly cause a reduction in the size of pores in the adjacent resolidifying layer. This reduction is expected to have implications for coke making, as small pore sizes are preferred and are generally associated with stronger cokes. When the vitrinite concentrate was blended with inertinite the MPS of the interconnected pores was greater than for the vitrinite alone, suggesting that the inertinite may act as a buttress against the applied force, thereby restricting pore contraction. As expected, heating coke samples from 525 to 900 °C caused reductions in the overall porosity from 47 to 41 %, and the MPS from 77 to 70 µm. Also, a reduction in porosity from 56 to 43 % and MPS from 82 to 69 µm was observed in the 80VC:20IC coke sample when the temperature was raised from 525 to 700 °C. The high-temperature shrinkage behaviour of coke played an important role in both scenarios.