Liang Qiang， Liu Shu， Li Xiaolong， Yan Cuiping， Lin Longyuan
Key Laboratory of Solid Waste Treatment and Resource Recycle （Ministry of Education）， College of Environment and Resources， Southwest University of Science and Technology， Mianyang， Sichuan 621010， China
Abstract
Objective Plant-derived activated carbon for supercapacitors （PAC） requires an appropriate particle size distribution and sufficient specific surface area to ensure slurry dispersion， coating uniformity， and subsequent application performance. In an opposed-jet fluidized-bed jet mill， high-speed jet milling， centrifugal classification， axial conveying， and coarse-particle recirculation occur simultaneously， making it difficult to fully reveal the mechanisms of particle size regulation and particle transport through experiments alone. This study aims to optimize the jet-milling and classification process parameters of PAC by using biomass-based activated carbon as the feedstock， with emphasis on analyzing the effects of classifier wheel speed on airflow structure and particle transport stability in the classification zone.
Methods A staged single-factor experimental method was adopted to investigate the effects of classifier wheel speed， induced-draft fan frequency， and nozzle inlet pressure on the particle size distribution and specific surface area of PAC. D10， D50， D90， and D100 were used to characterize the particle size features. The experimental system mainly consisted of two opposed Laval nozzles， a centrifugal classifier wheel， a pleated cartridge dust collector， a product collection device， and a centrifugal induced-draft fan. Based on the relatively optimal experimental conditions， a three-dimensional numerical model of the opposed-jet fluidized-bed jet mill was established using ANSYS Fluent. The shear-stress-transport （SST） k-ω turbulence model was used to describe the continuous gas phase， and the discrete phase model （DPM） was used to track particle motion and concentration distribution. In the numerical simulation， the nozzle inlet pressure and outlet diameter were fixed at 0.6 MPa and 3 mm， respectively. The classifier wheel speeds were set to 3 000， 4 800， 6 000， 7 200， and 8 000 r/min， and the particle size range was set to 0.217-27.7 μm. Velocity streamlines， cross-sectional streamlines， axial and tangential velocity distribution， and DPM particle concentration fields were analyzed to characterize the coupling between centrifugal classification and axial conveying.
Results and Discussion Classifier wheel speed had the most significant effect on coarse-particle retention and recirculation for further milling. Increasing the classifier wheel speed generally reduced D10， D50， D90， and D100， although the benefit of further increasing the speed for particle refinement gradually diminished at high speeds. Increasing the induced-draft fan frequency strengthened axial suction and particle conveying， but excessively strong negative-pressure suction shortened the effective residence time of particles in the milling and classification zones， causing some insufficiently milled coarse particles to enter the collection system prematurely. The effect of nozzle inlet pressure on medium and coarse particle fractions was non-monotonic. At low to intermediate pressures， increased gas flow rate and axial drag enhanced particle transport， while the jet energy was still insufficient for complete deagglomeration and breakage. At higher pressures， relative velocity， collision intensity， and shear increased， and particle deagglomeration and breakage gradually became dominant. Under the relatively optimal operating conditions of 0.6 MPa nozzle inlet pressure， 3 mm nozzle outlet diameter， 7 200 r/min classifier wheel speed， and 20 Hz induced-draft fan frequency， the D10， D50， and D90 of the obtained PAC were 2.39， 6.42， and 16.75 μm， respectively. Its specific surface area increased from 876 m²/g of the raw material to 1 021.37 m²/g， representing an increase of approximately 16.6%. This indicated that jet milling and classification promoted particle refinement， aggregate deagglomeration， and exposure of effective surface area. Numerical simulation results showed that classifier wheel speed substantially altered the flow-field structure in the classification zone. At 3 000 and 4 800 r/min， pronounced streamline deflection， local backflow， and axial-velocity fluctuations occurred near the classifier inlet and the transition between the milling and classification zones， indicating insufficient upward-flow induction at low speeds and unstable particle transport. When the speed increased to 6 000 r/min， streamline continuity improved and circumferential flow became better developed. At 7 200 r/min， the flow formed a relatively continuous spiral upward structure from the milling zone to the classification zone. The circumferential streamlines around the classifier wheel became more complete， the axial velocity increased steadily， and the tangential velocity distribution was comparatively uniform. These characteristics indicated favorable coordination between centrifugal classification and axial conveying. DPM particle concentration results further showed that， with increasing wheel speed， particle distribution evolved from local enrichment to circumferential enrichment and then to a continuous annular concentration band. At 7 200 r/min， particles formed a continuous annular distribution at the outer edge of the classifier wheel and were transported relatively uniformly along the blade passages， suggesting stable feeding， classification， and fine-particle discharge. When the speed was further increased to 8 000 r/min， excessive tangential centrifugal effect drove high-concentration particles toward the wheel rim and near-wall regions， while the particle concentration in the central region decreased. Particle retention， backflow， and circulating load therefore increased， showing that simply increasing the classifier wheel speed could not continuously improve classification performance.
Conclusion Stable PAC milling and classification in an opposed-jet fluidized-bed jet mill are governed by the coordinated action of jet milling， centrifugal classification， and axial airflow conveying rather than by any single operating parameter. An appropriate classifier wheel speed provides sufficient centrifugal action to retain coarse particles while maintaining stable transport of fine particles toward the interior of the classifier wheel and the outlet. Excessively high speed shifts the balance toward centrifugal retention， suppressing the passage of fine particles， and aggravates particle accumulation and recirculation near the wheel rim. The agreement between experimental results and CFD-DPM simulation results shows that a dynamic balance between centrifugal classification capacity and axial conveying capacity is essential for improving the stability of PAC particle size regulation and the classification performance of fine powder. These findings provide a theoretical basis for optimizing the operating parameters of opposed-jet fluidized-bed jet mills and for the continuous PAC preparation.
Keywords：activated carbon； fluidized bed； particle size distribution； milling and classification； two-phase flow； numerical simulation； particle processing； classifier wheel speed
Get Citation: Liang Qiang， Liu Shu， Li Xiaolong， et al. Particle size regulation and particle transport characteristics of activated carbon in opposed⁃jet fluidized⁃bed jet mills［J］. China Powder Science and Technology， 2027， 33（3）： 1-14.
Received：2026-06-20， Revised： 2026-08-24， Online： 2026-11-网上出版日期:12。
Funding：The research was supported by the National Natural Science Foundation of China (Grant No. 52463026) and the Science and Technology Plan Project of Sichuan Province (Grant No. 2024ZHCG0121).
DOI：10.13732/j.issn.1008-5548.2027.03.014
CLC No.: TB44；TD989
Type Code：A
Serial No.：1008-5548（2027）03-0001-14
