Enhanced oil agglomeration separation of coal gasification fine slag by ultrasonic cavitation-fluid shear

Coal gasification fine slag (CGFS) has high utilization value, but the low recovery rate of residue carbon greatly restricts its resource utilization. The oil agglomeration separation method has obvious advantages in the CGFS separation process, but its separation efficiency is severely limited by the symbiotic structure of carbon and ash. In order to break through the bottleneck problem of residue carbon separation and enrichment technology by oil agglomeration method, the effects of ultrasonic time, ultrasonic power, fluid shear time and their interaction on oil agglomeration and separation were investigated in this paper. Combined with BET, particle size distribution, FT-IR, XPS and SEM-EDS analysis methods, the strengthening mechanism of ultrasonic cavitation and fluid shear (UC-FS) pretreatment on oil agglomeration separation was revealed. The results show that when the ultrasonic power is 270 W, the ultrasonic treatment time is 29 min, and the fluid shear time is 23 min, the concentrate with ash content of 9.55% and the tailings with ash content of 91.51% can be obtained, and the combustible recovery rate can be increased to 90.54%. Ultrasonic cavitation gradually loosens the original dense carbon ash structure, and promotes the development of the pore structure of CGFS in coordination with the scouring effect of fluid shear, which increases the dissociation degree of carbon ash particles and thus reduces the ash content of concentrate. UC-FS pretreatment can effectively increase the proportion of hydrophobic groups such as C—C, C= C and C—H on the surface of carbon residue, increase its contact angle from 110.34° to 121.16°, and further expand the difference of hydrophilic and hydrophobic properties on the surface of carbon and ash particles, thus improving the effect of oil agglomeration separation. The mechanism of UC-FS synergistic pretreatment to improve the efficient separation of carbon ash particles is mainly attributed to the micro-abrasive effect generated by the coupling of ultrasonic cavitation bubbles and fine-grained microspheres. This study can provide theoretical basis and technical guidance for the separation and utilization of CGFS. © 2024 China Coal Society. All rights reserved.