Experimental Study On The Functions Of Horizontal Baffles In Gas-solid Fluidized Beds

Gas-solid fluidized bed has been widely applied in process industry.Bubbling is an inherent disadvantage in dense fluidized beds.The existence of large bubbles will affect the gas-solid contact efficiency,cause severe fluctuation of operation parameters of fluidized bed,and affect production efficiency and equipment stability.The simplest and most common way to break bubbles is to add internal baffles in the bed.Although the applications of internal components in fluidized bed have been deeply studied,the understanding of the functions of baffles in fluidized beds and the inner mechanism are not deep enough.Usually,researchers measure the changes of local parameters of the free fluidized bed and baffle fluidized bed.The commonly used measuring instruments are optical fiber probes,pressure probes,high speed framing camera and so on.As a relatively new non-invasive measurement method,electrical capacitance tomography(ECT)has been widely used in gas-solid fluidized bed,which can measure the fluidization parameters in the fluidized bed.Especially,there is no literature report on the use of electrical capacitance tomography(ECT)technology to measure baffled fluidized bed.The aim of this study is to use the new non-invasive ECT combined with the traditional pressure difference measurement technology,the new chaotic time series processing method combined with the traditional fluidization quality evaluation method,systematically measure and analyze the influence of different baffle in fluidized bed.The bed expansion height,bed local void fraction,heterogeneity index,power spectral density,R/S analysis and Lyapunov exponent are employed to obtain a new understanding of the mechanism of the baffle.Through the intensive experimentation in this study,the following results are obtained:(1)By comparing the R/S analysis results of ECT and pressure difference measurement technology,the feasibility of the application of R/S analysis in fluidized bed signal and the feasibility of the application of ECT in fluidized bed are proved,the addition of baffle significantly reduces the jet diameter and jet cycle,and the Hurst exponent of baffle fluidized bed at the high-speed jet process is slightly larger;(2)The baffle can suppress the solids backmixing under the baffle,and the change trend of void fraction of different structural types is similar;(3)The ability of the porous baffle to suppress the growth and coalescence of bubbles under the baffle is greater than that of the louver baffle.The emulsion internal circulation phenomenon may occur above the baffle,resulting in the increase of the heterogeneity index;(4)The power spectral density of ECT has a similar peak value to that of pressure difference signal at 0 Hz;(5)R/S analysis can identify the bubble period of fluidized bed.Baffle can reduce the bubble period,and the porous baffle has stronger ability to reduce the bubble period,and the broken bubbles of baffle may lead to the decrease of Hurst exponent;(6)The baffle fluidized bed system is still a chaotic system,and the broken bubbles of baffle may lead to the increase of Lyapunov exponent.