Pressure And Solid Concentration Fluctuations In Pressure Gas-solid Fluidized Bed

Pressurized oxygen-enriched fluidized bed combustion is a very promising CO₂ capture technology.It is critical for the design of a pressurized fluidized bed combustor to explore the influence of the pressure on fluidization characteristics.On the other hand,pressurized fluidized bed has been widely used in the chemical and energy industry because it enhances the mass transfer of gas-solid.In this paper,the characteristics of pressure and particle volume fractionfluctuations in the pressurized fluidized bed are studied.Therefore,it is meaningful to studythe fluidization characteristics in elevated gas-solid fluidized bed on engineering and academic fields.In general,the current research on the atmospheric fluidized bed is very extensive and well-understood.There has been some reports in the literature about the study of pressurized fluidization,but not very much.There has been consensus on the general law of pressurized fluidized bed,such as the critical fluidized velocity decreases with the increase of pressure.However,the understanding of dynamic characteristics and quantification of pressurized fluidization is still insufficient.In this paper,a experiment platform of pressurized bubbling fluidized bed was constructed to research the influence of pressure on the critical fluidized velocity,the bed pressure difference and the variation of partial voidage.The main conclusions are as follows:?1?The devices with high and low particle concentration are designed separately to lay the foundation of calibration for optical-fiber solid concentration probes in a wide range of particle volume fractions.?2?The critical fluidized velocities of three materials?glass beads particle diameters of637m,373m and 252m?have been measured under difference pressures?0.1MPa-0.6MPa?.Critical fluidized velocities decrease with the increasing pressure,but its gradient decreases with increasing pressure.The larger the particle diameters,the more obvious the influence of pressure on critical fluidized velocities.For example,with the same increase of pressure,the critical fluidized velocity of the particle with the largest diameter reduces by 0.123m/s while that f the particle with the smallest diameter reduces by 0.028m/s.?3?Based on the determination of the critical fluidized velocity of the three materials under the different pressure,experiment on gas-solid flow characteristics in the pressurized fluidized bed has been carried out.The operation pressures are 0.1MPa?0.3MPa?0.5MPa,and the fluidized velocities are in the range of 1.5₈1))to 5.0₈1))(increasing 0.5₈1))for each operating conditions and 72 working conditions in total).Differential pressure transmitters and fiber probes were used to measure differential pressure and particle concentration in the bed of each operating condition.Subsequently,the time series data of differential pressure and particle concentration were analyzed in detail.?4?For the fluidization under different particle diameters,critical fluidized velocities and pressures,the fluctuation of differential pressure increases with the increase of the fluidized velocity,increases slightly with the increase of the particle diameter of the material,and decreases with the increase of the pressure.The intensity of bubble motion can be reflected from the characteristics of differential pressure fluctuation.?5?Increasing the pressure helps to increase the voidage of the emulsion phase,reduces the frequency of bubble's occurrence at the same time,suppresses the movement of the bubble to some extent.The peak frequencies of the fluctuation of particle volume fraction mostly near 3Hz.The fluctuation of the frequency and amplitude of particle volume fraction shows a decreasing trend with increasing fluidized gas velocity.