An experiment was carried out for investigating pressure behavior of catalyst powders, with a Sauter mean diameter of 63.6 lm, flowing downward in a cyclone dipleg with 150 mm inner diameter and 9000 mm high. Time mean pressure and time series of pressure fluctuations were measured at different axial positions in the dipleg with particle mass fluxes ranging from 50.0 to 385.0 kg m -2 s -1 . The experimental results showed that the time mean pressure in the dipleg increased progressively from the top section to the bottom section. The experimental phenomena displayed that the fluidization patterns in the dipleg can be divided into two types on the whole, namely the dilute-dense coexisting falling flow and the dense conveying flow along the dipleg. In the dilutedense coexisting falling flow, the dilute phase region was composed of a length of swirling flow below the inlet of dipleg and a dilute falling flow above the dense bed level. With increasing particle mass flux, the dilute-dense coexisting falling flow was gradually transformed to be the dense conveying flow, and the exit pressure of the dipleg increased considerably. The pressure fluctuations were closely related to the fluidization patterns inside the dipleg. In the dilute-dense coexisting falling flow, the pressure fluctuations in the dilute flow region originated from particle clusters, propagating downward as a pressure wave; however, the pressure fluctuations in the dense flow region originated from rising gas bubbles, propagating upward. When the dense conveying flow was formed in the dipleg, the pressure fluctuations originated mainly from instability of the feed and the compressed gas, propagating downward. The standard deviation of the pressure fluctuations indicated that the intensity of pressure fluctuations first increased and then decreased with increasing particle flux.

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A large-scale cold model experimental setup of combined riser with variable constraint exit (CRVCE) was established. The axial and radial distributions of solids holdup and particle velocity, under different operating conditions, were investigated experimentally, and the results were compared with conventional riser (CR). Experimental results showed that, the exit restrictive effect of combined riser with variable constraint exit was weak when particle circulation flux and static bed height in upper fluidized bed were lower, while it turned to be strong when superficial gas velocity and static bed height in upper fluidized bed were higher. Under the same conditions, averaged cross-sectional solids holdup of CRVCE was characterized by C type distribution when article circulation flux was higher, while that of CR with weak constraint exit was characterized by linear distribution. In axial direction, averaged cross-sectional particle velocity of CRVCE changed in order: acceleration-constant-decrease velocity, while that of CR changed in another: acceleration-constant velocity. The maximum of local solids holdup value of CRVCE appeared at the dimensionless radius position r/R=0.7, while that of CR appeared in the wall region. Their local particle velocities were similar in the core region, while local particle velocity of CRVCE was lower than that of CR in the annular region.

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