Time-series analysis of the characteristic pressure fluctuations in a conical fluidized bed with negative pressure

The negative pressure conical fluidized bed is widely used in the pharmaceutical industry.In this study,experiments based on the negative pressure conical fluidized bed are carried out by changing the material mass and particle size.The pressure fluctuation signals are analyzed by the time and the frequency domain methods.A method for absolutely characterizing the degree of the energy concentration at the main frequency is proposed,where the calculation is to divide the original power spectrum by the average signal power.A phenomenon where the gas velocity curve temporarily stops growing is observed when the material mass is light,and the particle size is small.The standard deviation and kurtosis both rapidly change at the minimum fluidization velocity and thus can be used to determine the flow regime,and the variation rule of the kurtosis is independent of both the material mass and particle size.In the initial fluidization stage,the dominant pressure signal comes from the material movement;with the increase in the gas velocity,the power of a 2.5 Hz signal continues to increase.A method of dividing the main frequency by the average cycle frequency can conveniently determine the fluidized state,and a novel concept called stable fluidized zone proposed in this paper can be obtained.Controlling the gas velocity within the stable fluidized zone ensures that the fluidized bed consistently remains in a stable fluidized state.

Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor

Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor （SAB） were performed based on bed expansion ratio （E）, maximum bed sludge content （Vpmax）, and maximum bed contact time between sludge and liquid （Tmax）. Bed expansion behavior models were established under bed unfluidization, fluidization, and transportation states. Under unfluidization state, Ewas 0, Vprnax was 4867 ml, and rmax was 844-3800 s. Under fluidization state, E, Vpmax, and Tmax were 5.28%-255.69%, 1368-4559 ml, and 104-732 s, respectively. Under transportation state, washout of granular sludge occurred and destabilized the SAB. During stable running of SAB under fluidization state, E correlated positively with superficial gas and liquid velocities （Ug and ul）, while Vpmax and Tmax correlated negatively. For E and Vpmax, the sensitivities of ug and ul were close to each other, while for Tmax, the sensitivity of ur was greater than that of Ug. The prediction from these models was a close match to the experimental data.