Fluidization stability and periodic fluctuations in gas–solid separation fluidized bed using Geldart A dense medium

Gas–solid separation fluidized bed is a typical method for coal separation without water utilization.Geldart A particles is also considered as the ideal dense medium to strengthen separation efficiency.Fluidization stability reflects the bed pressure fluctuations and the distribution of bubble and emulsion phases,affecting the separation performance.And the main frequency of pressure fluctuations can directly reflect the degree of pressure fluctuations.Therefore,the detailed fluidization stability is analyzed combined the method of standard deviation of pressure fluctuations,power spectral density,etc.,for Geldart A particles.The results showed that maintaining an appropriate gas velocity resulted in an average bed pressure of around 2000 Pa.The main frequency is mainly concentrated around 1–1.5 Hz.Finally,a prediction model of the main frequency of pressure fluctuations is established,and the error can be controlled within±0.15.The investigation further proved the stable fluidization of Geldart A particles and provides a method for predicting the main frequency of pressure fluctuations in the gas–solid separation fluidized bed.

Hydrodynamic behavior of an internally circulating fluidized bed with tubular gas distributors

To better understand the hydrodynamic behavior of an internally circulating fluidized bed, solids holdup in the down-comer （Eso）, solids circulation rate （Gs） and gas bypassing fraction （from down-comer to riser y^R, and from riser to down-comer yRD） were experimentally studied. The effects of gas velocities in the riser and in the down-comer （UR and UD）, orifice diameter in the draft tube （dor）, and draft tube height （HR） were investigated. Experimental results showed that increase of gas velocities led to increase in Gs and yDR, and slight decrease in yeD. Larger orifice diameter on the draft tube led to higher 8sD, Gs and yDR, but had insignificant influence on YRD. with increasing draft tube height, both Gs and YDR first increased and then decreased, while yRD first decreased and then increased. Proposed correlations for predicting the hydrodynamic parameters agreed reasonably well with experimental values.

Local heat transfer properties in co- and counter-current G-L-S magnetically stabilized fluidized beds

Heat transfer coefficients were measured by immersed probes in co- and counter-current G-L-S magnetically stabilized fluidized beds （MSFBs） using air, water and nickel-alloy particles as the gas, liquid and solid phases. Influences of major factors, including magnetic field intensity, superficial gas and liquid velocities, liquid viscosity and surface tension, on heat-transfer properties were studied experimentally, indicating that both co- and counter-current G-L-S MSFB can provide relatively uniform radial distribution of heat transfer coefficients under appropriate operation conditions, thus controlling operation temperature for highly exothermic multi-phase reaction systems. Two correlations were provided to estimate accurately heat transfer properties in both co- and counter-current G-L-S MSFB systems, with an average error of less than 10%.