Investigation on breakage behaviour of oil shale with high grinding resistance: A comparison between microwave and conventional thermal processing

Co-processing (e.g. co-combustion) of oil shale with other fuels like coal to derive energy could mitigate environmental-related problems associated with oil shale whilst enhancing thermal efficiency. However, reducing the size of oil shale particles to that similar to coal for better handling and combustion is energy-intensive given its high grinding resistance. Therefore, it is essential to improve the grindability of oil shale. In this study, two Chinese oil shales were investigated. The sieved samples were pre-treated and crushed to study the failure mechanisms, as well as changes in uniaxial peak strength and specific breakage rate in comparison to that of untreated samples; and how chemical properties were affected after either conventional or microwave-enhanced thermal processing. Results show that the uniaxial compressive strength of oil shale was significantly reduced whilst the breakage rate increased after a short exposure to microwave irradiation. The improvement was approximately 50 % higher than that observed after conventional heating. Hence, results suggest that microwave processing could lead to a more significant and rapid improvement in oil shale milling compared to conventional pre-heating, and without adversely affecting fuel quality. The simple microwave pre-treatment can potentially widen the utilization of oil shale, particularly when homogeneity is necessary during co-processing.