The main factors affecting entrainment in fluidized beds

The article presents design of a fluidized bed grain dryer, which allows grain recirculationinside the dryer with alternating heating-cooling cycles and makes it possible to feed adrying agent with an elevated temperature into the drying chamber without any risk ofoverheating and deterioration of grain quality, which in turn will increase the drying speed.The proposed grain dryer allows to clean simultaneously the grain heap from light impurities.The regularities and mechanisms of entrainment of small particles in the fluidized bed havebeen studied. The degree of entrainment is significantly influenced by the characteristics ofthe grain layer and the air as a drying agent: linear velocity of the air flow in the layer, size ofthe fine fraction particles, grain size. The degree of entrainment increases sharply when theair velocity increases above the hovering speed of the component to be carried away. Themethod and quality of air distribution at the base of the apparatus depend on the design ofthe gas distribution sieves and affect the efficiency of phase contact in general. Since thequality of air distribution deteriorates in the higher parts of the grain layer, the degree ofentrainment should be inversely proportional to some function of the height of the layer undercertain conditions. The diameter of the drying chamber affects the fluidization mode, so thedegree of entrainment depends on the diameter of the working chamber. To confirm thecorrectness of theoretical studies to substantiate the design parameters of the dryingchamber and establish their possible values, experimental studies were conducted thathelped determine the limits of variation in the degree of entrainment of fine impuritiesdeposited in the cyclone filter of the fluidized bed dryer. The influence of changes in thediameter of the holes of the gas distribution grid of the drying chamber, the ratio of height tothe diameter of the grain layer on the removal of a fine fraction from the fluidized grain layerhas been studied. The conducted research makes it possible to increase the efficiency of thetechnological process of drying the grain heap by improving the design of the dryer withfluidization of the grain layer.