Si Daorun， Lu Feigan， Yan Zihan， Lu Chunxi
State Key Laboratory of Heavy Oil Processing， China University of Petroleum， Beijing 102249， China
Abstract
Objective To resolve the severe secondary back-mixing issues in industrial turbulent fluidized bed reactors， the specific effects of an anti-back-mixing cone on the complex internal flow fields and the discharge loads of an axial flow cyclone separator are systematically investigated. The effects of different cone dimensions and their installation positions on the macroscopic separation characteristics and internal aerodynamics are thoroughly analyzed to provide a theoretical basis for highly efficient primary gas-solid separation designs.
Methods A comparative experimental study was conducted utilizing a large-scale cold model apparatus. The three-dimensional flow fields， overall pressure drops， and separation efficiencies of a standard short cyclone （SC） and modified short cyclones equipped with varying anti-back-mixing cones （SCC） were measured. An L-shaped five-hole probe was employed to capture aerodynamic data across multiple axial cross-sections. All experiments were performed using ambient air and 325-mesh silicon micro-powder， with inlet gas velocities ranging from 8 to 30 m/s and a constant inlet dust concentration of 20 g/m³.
Results and Discussion At the vortex finder inlet， the large-sized cone （SCC⁃big） deepened the negative pressure center to below -6.5 kPa， whereas the small-sized cone （SCC⁃small） raised it to -5.1 kPa， compared to -6.1 kPa in the standard SC. At the bottom of the separation space， the standard SC exhibited an extremely deep negative pressure center dropping below -7.1 kPa. Notably， the small-sized cone effectively mitigated the vacuum state in this bottom zone. Consequently，the integral average static pressure at the dipleg inlet was drastically reduced from -6 601 Pa in the standard SC to -2 215 Pa in the SCC-small. A classic Rankine vortex structure with an “M-shaped” radial tangential velocity distribution was maintained at the vortex finder inlet. However， the SCC⁃big increased the peak tangential velocity from 56.9 m/s to 59.0 m/s， whereas the SCC⁃small reduced it to 49.0 m/s. At the bottom of the separation space， overall gas rotation intensity was weakened by the cones.Peak tangential velocities decreased by 2.8% and 23.2% for the SCC-small and SCC⁃big， respectively， compared to the SC baseline of 54.3 m/s. Conversely， the tangential velocity near the cyclone wall enhanced by up to 16% with the large-sized cone. Analysis of the axial velocity revealed that the small-sized cone accelerated the central upward airflow to a peak of 20.0 m/s due to a localized throttling effect， while the large-sized cone severely disrupted the main upward flow， inducing an intense downward flow with a peak velocity of 41.7 m/s. At the very bottom， small-sized cones triggered a localized upward airflow of up to 52 m/s at the cone edge. Furthermore， the small-sized cone induced a strong centripetal radial airflow of 25~30 m/s， which promoted secondary back-mixing. Macroscopically， while the small-sized cone successfully reduced the total working pressure drop across all operating conditions， the separation efficiency was highly velocity-dependent. For inlet velocities below 11.5 m/s， high separation efficiency was maintained. However， once the inlet gas velocity exceeded 11.5 m/s， a severe “cone-impacting” effect was triggered by the downward-extending natural swirl core hitting the cone surface. This aerodynamic collision generated the aforementioned extreme localized upward and inward flows， causing a precipitous drop in separation efficiency. To address this issue， an optimized configuration was proposed by extending the cylinder length to three times its diameter and lowering the cone. The extended model successfully circumvented the direct swirl impact， yielding a measured separation efficiency increase of over 20% compared to the baseline lengthened cyclone within the high-velocity range of 19.2 to 26.9 m/s.
Conclusion Flow field and performance analyses establish the complex mechanisms by which anti-back-mixing cones influence axial flow cyclone separators. It is concluded that different dimensions of anti-back-mixing cones exert distinctly diverse interventions on the central flow field. A small-sized anti-back-mixing cone exhibits a highly beneficial “flow-guiding and throttling” effect. This stabilizes the strong central vortex core and eliminates turbulent dissipation caused by localized chaotic flows， translating into excellent drag reduction and pressure drop characteristics. Moreover， the physical obstruction provided by the small cone effectively intercepts the intense suction exerted by the central vortex core on the bottom section. By drastically weakening the negative pressure at the dipleg inlet， the driving force for gas reverse flow is minimized， providing a critical safeguard for smooth dust discharge and source-level suppression of secondary re-entrainment in industrial applications. Conversely， large-sized cones are considered unsuitable， as their excessive physical blockage severely disrupts the primary upward airflow structures， induces intense localized downward flows， and fails to achieve any systemic drag reduction. Importantly， a critical operational bottleneck is identified under high inlet gas velocity conditions （exceeding 11.5 m/s）. The natural downward extension of the high-speed main swirl core results in violent aerodynamic collisions with the cone surface， defined as the “cone-impacting effect”. This collision is the root cause of the abnormal localized upward and centripetal radial airflows that sweep settled dust back into the vortex， culminating in severe secondary back-mixing and efficiency degradation. By structurally extending the separator cylinder and correspondingly lowering the cone installation position， sufficient buffering space is provided for the natural reverse of the extending swirl core. This optimized structural design fundamentally eradicates the direct vortex impact， effectively broadens the high-efficiency operational range to 8~25 m/s， and offers a robust theoretical and engineering foundation for the advanced design of industrial gas-solid primary separation systems.
Keywords： axial cyclone separator； anti-back-mixing cone； flow field； secondary back-mixing； pressure drop； dipleg draft
Get Citation:Si Daorun， Lu Feigan， Yan Zihan， et al. Effects of anti-back-mixing cones on performance of axial flow cyclone separators［J］. China Powder Science and Technology， 2026， 32（6）： 1-16.
Received：2026-03-14，Revised： 2026-05-24，Online： 2026-07-10。
Funding： The research was supported by the National Key R&D Program of China (Grant No.2021YFA1501304) and the PetroChina Innovation Foundation (Grant No.2024DQ02-0203).
CLC No.：TQ051.8； TB4
Type Code：A
Serial No.：1008-5548（2026）06-0001-16
