Law Of Gas-solid Flow In A Fluidized Bed With Baffles

For the operation of gas-solid dense phase fluidization,the phenomenon of stagnation is likely to occur,which in turn reduces the gas-solid contact efficiency and the operational stability in the bed.It is expected to reduce the tendency of occurrence of stagnation by adding baffle to suppress bubble growth or break up bubbles,thereby improving the quality of gas-solid fluidization in the bed.Under the operating conditions of apparent gas velocity(Ug)ranging from 0.04 m/s to 1.14 m/s and initial loading heights(H)being 650 mm,550mm,450 mm and 350 mm,the change of two-phase flow state and the scope of rotating sieve tray type gas-solid baffle effectively suppressing and breaking bubbles were established by analyzing characteristics of gas-solid two-phase flow and comparing and analyzing standard deviation of pressure fluctuation,standard deviation of pressure difference pulsation,pressure pulsation power spectral density and other parameters in free fluidized bed,single-rotary sieve tray type gas-solid baffle fluidized bed and dual-rotation sieve tray type gas-solid baffle fluidized bed.The results show:When the initial loading heights(H)is 650 mm,there will be four different stages in the gas-solid two phase in the free fluidized bed with the increases of apparent gas velocity.When0.04 m/s≤U_g≤0.57 m/s,the two phases are in the bubbling-throttle transitional fluidization stage and the range of the main frequency of the pressure pulsation power spectrum is 0.40Hz≤f≤0.70 Hz at this time;When 0.57 m/s<U_g≤0.74 m/s,two phases are in the bubble coalescence stage dominated by bubble aggregation and the range of the main frequency of the pressure pulsation power spectrum is 0.70 Hz≤f≤1.10 Hz at this time;When0.74 m/s<U_g≤0.83 m/s,the two phases are in the bubble fluidization stage dominated by the size of the split bubble and the range of the main frequency of the pressure pulsation power spectrum is 0.70 Hz≤f≤1.10 Hz at this time;When 0.83 m/s<U_g≤1.14 m/s,the two phases begin to transform into turbulent fluidization and tend to stabilize and the range of the main frequency of the pressure pulsation power spectrum is f≥1.1 Hz.The scope of rotating sieve tray type gas-solid baffle effectively suppressing and breaking bubbles is 0.04 m/s≤Ug≤0.57m/s and at this time,the gas-solid two-phases in the corresponding free fluidized bed is in bubbling-sugging transitional fluidization;The gas velocity scope of effectively breaking the bubble narrows as the height of the static bed decreases.The scope of axial space is the area below the rotating sieve tray type gas-solid baffle and the area containing rotating sieve tray type gas-solid baffle;In addition,the axial spatial extent of the broken air bubbles of the inner member is independent of the static bed height.Increasing the number of rotating sieve tray type gas-solid baffle helps to strengthen the effect of breaking bubbles and broadening its axial spatial extents,but it does not broaden the gas velocity range of broken bubbles.For the free bed,the standard deviation of the pressure pulsation increases with the increase of the initial loading height over the all bed and the entire research gas velocity range.For single-layer baffle bed,the standard deviation of the pressure pulsation is expressed as follows when the axial height is less than 0.6 m(below the baffle and the area containing the baffle):At low gas velocity,it increases with the increase of the initial loading height;There are two situations in high gas velocity,and the standard deviation curve is similar when the initial loading height is lower than the baffle installation height,and the standard deviation curve is similar when the initial loading is higher than the baffle installation height,but the latter is larger than the former as a whole.When the axial height is greater than 0.6 m,the change trend is the same as that of the free bed.The standard deviation of the pressure pulsation increases with the increase of the initial loading height in the whole research gas velocity range.For the double-layer baffle bed,the variation of the standard deviation of the pressure pulsation with the initial loading height is similar as that of the single-layer baffle bed which is less than 0.6 m in the entire axial range.