Dense-phase riser transport

The transport velocity can also be evaluated from the variations of the local pressure drop per unit length (Ap/Az) with respect to the gas velocity and the solids circulation rate, Jp. An example of such a relationship is shown in Fig. 10.4. It is seen in the figure that, along the curve AB, the solids circulation rates are lower than the saturation carrying capacity of the flow. Particles with low particle terminal velocities are carried over from the riser, while others remain at the bottom of the riser. With increasing solids circulation rate, more particles accumulate at the bottom. At point B in the curve, the solids fed into the riser are balanced by the saturated carrying capacity. A slight increase in the solids circulation rate yields a sharp increase in the pressure drop (see curve BC in Fig. 10.4). This behavior reflects the collapse of the solid particles into a dense-phase fluidized bed. When the gas... 

The fast fluidization regime is represented by a dense region at the bottom of the riser and a dilute region above it. The inter-relationship of the fast fluidization regime with other fluidization regimes in dense-phase fluidization and with the dilute transport regime is... 

Dense phase transport lines should have gradual curvatures to prevent rough operation. Aeration should be provided to ease the flow of solids in dense phase transport lines and in risers. Blast connections should be available to clear them in case of plugging. Technique should be developed to weld patches on eroded lines during operation. 

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