Pulses of microwave radiation to improve coke grindability

► Coke grindability is improved by MW treatment. ► Short pulses of MW produce better results than continuous heating. ► The presence of moisture in cokes has a negative effect on MW treatment. ► An energy saving of up to 40% can be achieved at laboratory scale. Metallurgical cokes are made by destructive distillation of bituminous coals and they have a high content in elemental carbon; however, the inorganic elements that were part of the original bituminous coal remain trapped in the resultant coke, having very different capacities for absorbing microwave radiation. Therefore, when cokes are irradiated with microwaves, some parts of the particle will undergo rapid heating, while others parts will heat up slowly. Moreover, due to the electrical conductivity exhibited by metallurgical cokes, microwave radiation gives rise to electric arcs or microplasmas, producing hot spots. As a result of the expansion and the stresses caused by thermal shock, small cracks and micro-fissures appear on the surfaces, leading to a weakening of the coke particles and facilitating their grindability. This paper studies, at laboratory scale, the microwave-assisted grinding of metallurgical coke and assesses the improvement in grindability and the amount of energy saved. It was found that treatment consisting of short pulses of microwave irradiation produces better results than the continuous heating used in previous studies.