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Cultivating Project of Strategic Priority Research Program of Chinese Academy of Sciences
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The critical role of scale resolution in CFD simulation of gas-solid flows: A heat transfer study using CFD-DEM-IBM method
No full textThe surface-to-bed heat transfer coefficient is an important engineering parameter for quantifying the heat transfer capability of fluidized beds. In this study, computational fluid dynamics-discrete element method-immersed boundary method (CFD-DEM-IBM method) is used to simulate the velocity and tem-perature fields around the immersed tube in two fluidized beds, the heat transfer coefficients of fluid-wall, particle-wall, and particle-fluid-wall are then analyzed and compared with experimental data. It is shown that in order to quantitatively predict the surface-to-bed heat transfer coefficient without using empirical correlations, the thermal boundary layer of gas phase that is of the order of particle diameter needs to be explicitly resolved by refining the fluid grid around the immersed tube up to 1=16 of particle diameter, whereas an empirical correlation is necessary to correctly calculate it in the state-of-the-art CFD studies which have used coarse grids. Present study highlights the critical role of scale resolution (specifically, the explicit resolution of the thermal boundary layer) in the study of surface-to-bed heat transfer in gas-solid fluidized beds.(c) 2022 Elsevier Ltd. All rights reserved
The simultaneous removal of NO and SO2 over MnO2 material via the multi-stage fluidized bed process at low temperatures
No full textTo overcome the easy poisoning and deactivation of denitrification catalysts by SO2 at low temperatures, the bench-scale multi-stage fluidized bed (MSFB) process with the active MnO2 medium (feeding rate of 0.3-1.2 kg/ h) is designed and applied to simultaneously remove the NO and SO2 from flue gas of medium/small industrial boilers in the low-temperature range of 100 - 200 degrees C, which demonstrates excellent and stable removal efficiency of both NO and SO2 even in the presence of 10 vol% water. In the MSFB system, the fluidized MnO2 particles in different layers flow against the simulated flue gas stage by stage, and the deactivated MnO2 will be continuously discharged and replaced with fresh MnO2 to keep the system effective and steady. The MnO2 medium acts as both denitrification (DeNOx) catalyst and desulfurizer, and the limited backmixing and layered arrangement of the MSFB system ensure the high removal capacity and sufficient utilization of MnO2 material. The multiple structural characterizations further reveal that the active MnO2 is gradually consumed by SO2 to form MnSO4 stage by stage with decreased specific surface and pore volume, accounting for its gradually decreased removal efficiency of both NO and SO2 stage by stage. And the deactivated MnO2 can be easily regenerated by aqueous ammonia with the conversion of MnSO4 to active MnO2. The demonstrated advantages of the MSFB system with MnO2 will provide a promising technical route for the simultaneous removal of NO and SO2 from low-temperature flue gas in industry