A Review on the Application of Microwave Absorbents in Oil Shale

The analysis of the current in situ oil shale mining technology shows that oil shale has the characteristic of poor thermal conductivity. Too solve the problems of low efficiency and high cost of traditional heat conduction mining methods, the microwave mining of oil shale has good production prospects. By microwave heating, electromagnetic energy is directly converted into heat energy by acting on medium molecules. Its transmission property makes the material inside and outside the medium simultaneously heated. No heat transfer is required. This paper summarizes the mechanism of the microwave pyrolysis of oil shale, pyrolysis parameters, and changes in the structure of oil shale in microwave pyrolysis, and how the addition of a microwave absorber endows the microwave with a better heating effect. At present, the absorbents used in microwave heating of oil shale are ferrite absorbents, nanometal absorbents, semicoke, and graphite. The research of ferrite microwave absorbents has been developing toward modification and nanocrystallization by adding trace elements. Among them, the microwave of nanoparticles leads to good absorption performance, which can help microwaves realize high-temperature conversion of oil shale. Microwaves can also be used with fracturing fluids. In the future, the structure and absorption relationship can be improved to achieve better results. Semicoke produces a strong eddy current in the microwave field and has a high-temperature rise rate. Using semicoke as a microwave absorbent can make semicoke waste into a treasure with efficient comprehensive utilization. In addition, the numerical simulation of oil shale microwave pyrolysis is also of great significance. Simulation can create reservoir conditions that experiments cannot reach. At present, it mainly simulates temperature field, decomposition, and product distribution of kerogen, and porosity and permeability evolution of oil shale. In the simulation of adding absorbent, the heating effect of adding nano-Fe3O4 absorbent is better than that of not adding absorbent, and its microwave heating range is also larger. But at present, there are few simulations for this aspect. The experimental research and numerical simulation of oil shale microwave pyrolysis absorbent need further exploration in the future.