Increased coal grindability as a result of microwave pretreatment at economic energy inputs

Five coals from different parts of the world were ground and sieved into four size fractions (3.35–4.7, 6.7–9.5, 9.5–19, 19–22.4 mm), respectively. The vitrinite reflectance of the coals ranged from 0.35 to 0.76% and the vitrinite content ranged from 55 to 96% (on a volume percent basis). Approximately 300 grams of each size fraction were heated in a TE010 single mode microwave cavity operating at 8 kW with an exposure time of 0.1 s. These settings were chosen to represent industrially viable operating conditions, i.e. sufficient microwave power density power and low residence times. The paper reports quantitative data which assesses for the first time the influence of the microwave pretreatment on grindability in a batch Bond ball mill at potentially economic microwave energy inputs. The paper demonstrates that grindability increases significantly as a result of pretreatment with the specific rate of breakage (Si) increasing by an average of 100%.