Electrical dehydration performance of shale oil: From emulsification characteristics to dehydration mechanisms

Abstract

Shale oil, as a successor to ordinary crude oil, has received extensive attention. However, the high-stability shale oil emulsions are still challenging for electrical dehydration systems. In this work, the differences between shale oil and ordinary crude oil were compared in terms of emulsion droplet size, physical properties and components to clarify the emulsification characteristics of shale oil and reveal its electrical dehydration mechanism. To this end, comprehensive electrical dehydration experiments were carried out under different parameters and transformers. The results showed droplet diameters of shale oil emulsions less than 10 µm, a value much smaller than that of crude oil. Shale oils with high viscous contained lots of natural emulsifiers, promoting the formation of the rigid asphalt film and wax crystal network structure. The synergistic adsorption of surfactant and paraffin molecules and the film formation of asphaltenes promoted by resins make shale oil display lower interfacial tension and higher interfacial film pressure. The above characteristics were the main reasons behind the formation of shale oil stable emulsions. Factors, such as electric field frequency, dehydration temperature, dehydration time, and demulsifier concentration influenced the emulsification characteristics and dehydration performance of shale oils at variable degrees. The dehydration performances of high-frequency transformer (Transformer B) and ultra-high-frequency transformer (Transformer C) on shale oil emulsion SH-1 were better than that of low-frequency transformer (Transformer A) due to tensile breakup or oscillatory coalescence of droplets under different electric field conditions. Considering energy consumption and economy comprehensively, Transformer C has excellent application potential. The analyses also show that high-frequency, heating and adding demulsifier are the key and necessary factors in the electric dewatering treatment of shale oil. In sum, these results look useful for future design optimization of shale electrical dehydration devices.