Hydrodynamics and optimum conditions of a solid recycle system have been determined in a circulating fluidized bed (0.1m I.D. × 5.3m high) of FCC particles ($d_p = 65 ㎛, ρ_s = 1720 kg/㎥$) and silica sand particles ($d_p = 125 ㎛, ρ_s = 3055 kg/㎥$).
The solid recycle system consists of a downcomer ($0.08 m I.D. × 4.0 m high$) and a loop-seal as a solid feed device (nonmechanical valve).
The effects of aeration gas rate ($0.054 - 0.264 N㎥/hr$) and aeration locations (0.1 - 0.8 m) on the solid flow rate through loop-seal, and the consequent pressure balance around the circulating fluidized bed (CFB) loop have been determined. The solid flow rates through loop-seal increase linearly with increasing aeration rate, and the maximum solid flow rates are obtained at the location where the ratio of height to diameter above horizontal section is 2.5. The controlling pressure drop across the loop-seal decrease with increasing solid circulation rate.
The effect of solid inventory on the maximum solid flow rate through loop-seal has been determined. The maximum solid flow rate increases with increasing solid inventory in the CFB.
The effects of solid inventory, solid circulation rate and superficial gas velocity on the pressure balance around the CFB have been determined. At the constant gas velocity and solid circulation rate, the pressure drop across the downcomer and loop-seal increase linearly, but the pressure drop across the riser do not change with increasing solids inventory in the downcomer. At constant solid inventory in the system, the pressure drop across the riser and the downcomer increase with increasing solid circulation rate and decreasing gas velocity in the riser.
The improved loop-seal with the downward tangential aeration system has been developed. The effect of actual aeration rate considering voidage on solid flow rate has been determined. The maximum solid flow rate was enhanced by 2.5 times by using the improved loop-seal compared to the existing loop-seal in FCC particles. At the same aeration rate, the solid flow rate is enhanced by 1.8 times. In sand particles, the solid flow rate is enhanced by 1.7 times at the same aeration rate. Also, a stable solid flow through the improved loop-seal is obtained compared to the existing loop-seal.
The obtained voidage above the aeration point in the downcomer has been correlated with the pertinent dimensionless groups as:
◁수식 삽입▷(원문을 참조하세요)
The obtained solid flow rate has been correlated considering slip factor with the experimental variables as :
◁수식 삽입▷(원문을 참조하세요)
