Drag models for simulating gas–solid flow in the turbulent fluidization of FCC particles

This paper examines the suitability of various drag models for predicting the hydrodynamics of the turbulent fluidization of FCC particles on the Fluent V6.2 platform. The drag models included those of Syamlal-O＇Brien, Gidaspow, modified Syamlal-O＇Brien, and McKeen. Comparison between experimental data and simulated results showed that the Syamlal-O＇Brien, Gidaspow, and modified Syamlal-O＇Brien drag models highly overestimated gas-solid momentum exchange and could not predict the formation of dense phase in the fiuidized bed, while the McKeen drag model could not capture the dilute charac- teristics due to underestimation of drag force. The standard Gidaspow drag model was then modified by adopting the effective particle cluster diameter to account for particle clusters, which was, however, proved inapplicable for FCC particle turbulent fluidization. A four-zone drag model （dense phase, sub- dense phase, sub-dilute phase and dilute phase） was finally proposed to calculate the gas-solid exchange coefficient in the turbulent fluidization of FCC particles, and was validated by satisfactory agreement between prediction and experiment.

The effect of different Co phase structure(FCC/HCP)on the catalytic action towards the hydrogen storage performance of MgH_(2)

High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH_(2).In this study,Co particles with a face centered cubic(FCC)structure and a hexagonal close packed(HCP)structure were prepared facilely and proved to be good catalysts for magnesium hydride.Co particles with FCC structure presented better catalytic effect on MgH_(2)than that with HCP structure.Both 7%(mass)Co FCC and HCP particle modified MgH_(2)decreased the initial dehydrogenation temperature from 301.3℃ to approximately 195.0℃,but 7%(mass)Co with FCC structure modified MgH_(2)has a faster desorption rate,and around 6.5%(mass)H_(2)was desorbed in 10 min at325℃.Hydrogen uptake was detected at 70℃ under 3.25 MPa hydrogen pressure and 6.0%(mass)H_(2)was recharged in 40 min at 150℃.The hydrogen desorption and absorption activation energy for 7%(mass)FCC Co modified MgH_(2)was significantly decreased to(76.6±8.3)kJ·mol^(-1) and(68.3±6.0)kJ·mol^(-1),respectively.Thermodynamic property was also studied,the plateau pressures of MgH_(2)+7%(mass)FCC Co were determined to be 0.14,0.28,0.53 and 0.98 MPa for 300℃,325℃,350℃ and375℃.The decomposition enthalpy of hydrogen(ΔH)for MgH_(2)+7%(mass)FCC Co was(80.6±0.1)kJ·mol^(-1),5.8 kJ·mol^(-1)lower than that of as-prepared MgH_(2).Moreover,cycling performance for the first20 cycles revealed that the reaction kinetics and capacity of MgH_(2)-FCC Co composite remained almost unchanged.The result of density functional theory calculation demonstrated that cobalt could extract the Mg AH bond and reduced the decompose energy of magnesium hydride.Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.