The Effect Of Bed Height On The Sorting Minimum In Dense Phase Gas-solid Fluidized Bed

Fluidized bed height is an important parameter of fluidization technology,which directly affects the fluidization behavior in the dense phase gas-solid fluidized bed.On the fluidized bed coal preparation technology,the bed is too shallow to sorting because of insufficient sorting space.On the contrary,the bed will produce large bubbles and slugging phenomenon to affect the stability of fluidized bed.The fine coal separation in the lower limit is seriously affected by the height of the bed.The lower limit of separation will be affected due to the increase of bed height.So this paper focuses on the research of the effect of bed height on the low separation limit in dense phase gas-solid fluidized bed.Based on fluidization,standard deviation of bed density distribution and the nonuniformity were used as evaluating indicators,then this test explored the impact of heavy particles size model,distributor pressure,two dimensional component and fluidization number on the fluidization.And based on the above factors is the best one,fluidization characteristics,porosity and density spatial distribution were explored,variation characteristics of stable fluidization zone at different bed heights was revealed,then the relationship between standard deviation of bed density distribution S and height diameter ratio H/D in fluidized bed was obtained:Starting from the angle of sorting,the relationship of the maximum feeding rate rmax of each grade coal samples and average particle size of coal sample (?) was explored firstly in the text:rmax=0.004369(?)+0.05350The actual feed rate was determined according to the slope of the relationship model.Separation tests of-10+8mm,-6+5mm,-5+4mm,-4+3mm,-8+6mm,-3+2mm,-2+1mm and-1+0.5mm coals were carried out under different bed heights and different fluidization numbers.With the analysis of ash separation degree and possible deviation,relevant conclusions were drawn: Firstly,The separation effect was better under the larger fluidization number when the feed size was major;and the separation effect was better under the smaller fluidization number when the feed size was minor.Secondly,the separation effect was worse with the decrease of particle size and the sorting effect of smaller particle size was not ideal in the same bed height.Thirdly,the separation effect of the coal samples with different grain size is getting better with the increase of the bed height.When the bed height increases to 240 mm,the lower limit of the separation can reach-4+3mm grade.Fourthly,the separation effect of the mixed coal particle size feed was same as the single coal particle size feed,and the relationship between particle size,fluidization number and bed height was similar.Finally,the separation effect of high fluidized bed was better thanthat of low bed in a relatively short period of time separation.With the increase of time,separation effect in high or low bed was getting better,but the amplitude of the former was more significant than the latter.Separation effect of high bed was weaker than that of low bed in a short period of time,and separation effect of high bed was better than that of low bed in a longer time.Starting from the analysis of the mechanism,gas velocity-pressure drop,gas-solid two-phase model,bulk fluidization region and particle sedimentation theory were used to clarify fluidization and separation process,and the results were verified by the high speed dynamic analysis.