Investigation of the dynamics of a high-flux CFB riser using chaos analysis of pressure fluctuations

The dynamics of a high-flux circulating fluidized bed riser (10 m high with i.d. of 76.2 mm) were studied using a chaos analysis technique with differential pressure signals sampled at 400 Hz. Spent FCC particles (d_p = 67 μm) were used as the solid phase. The solids flux ranged between 50-400 kg/m²s while the gas velocity was varied between 4.0-10.0 m/s. Using the measured signals, the complexity and predictability of the gas-solids flow were characterized using correlation dimension and Kolmogorov entropy. The axial profiles of the dimension and entropy revealed a more complex and less predictable gas-solids flow in the transition section of the riser. Both dimension and entropy decreased with increasing solids holdup and solids flux. Moreover, the correlation dimension increased exponentially with decreasing average absolute deviation (AAD), at a power of 0.3. On the other hand, the entropy was observed to decrease exponentially with increasing average cycle time (ACT) of the pressure fluctuations at a characteristic power ranging between 0.95 and 1.10. Also, a comparison was made between low- and high-flux conditions based on the dynamic properties of the riser.