Particle clusters in CFB risers were identified from the instantaneous solids holdup signals by a new sliding-window based signal processing method. By shifting the sliding time window and calculating the mean and the standard deviation within it, a non-linear threshold curve for identifying the clusters was derived instead of the conventional constant threshold. The optimal sliding window size was determined as Wb = 1024 data points based on the bisection method on the entire piece of signals. Using the proposed method, a more realistic characterization of the clusters in both the HDCFB and LDCFB was obtained by considering the bulk fluctuation of the gas-solids flow. The clusters in the HDCFB have higher solids holdup and lower velocity than that in the LDCFB. The HDCFB is also found to have a greater number of loose clusters for better gas-solids contacting and exchanges in the center of the riser.

Gas-solid fluidized beds have been widely used as reactors in the industry. Per the operations, fluidized beds can be classified as bubbling fluidized bed (BFB), turbulent fluidized bed (TFB), circulating turbulent fluidized bed (CTFB), circulating fluidized bed riser (CFB riser) and circulating fluidized bed downer (CFB downer). For fluidized beds, the instantaneous flow structure determines the overall performances. However, in the literature, the instantaneous flow structure remains lacking for TFB, CTFB, high-density CFB riser and high-density CFB downer. As a result, the evolution of the instantaneous flow structure in fluidized beds has not been well studied. In this work, instantaneous flow information in fluidized beds was acquired using an optical fiber probe. Then, according to the phase characteristics, instantaneous flow structures were demarcated as the “dilute structure” and “dense structure”. Finally, the evolution of instantaneous flow structures is, for the time, thoroughly discussed for gas-solid fluidization.