Nonlinear analysis of bed density fluctuation characteristics in gas-solid fluidized bed using micron-scale composite dense medium

This study proposes a Variational Mode Decomposition (VMD) method optimized by the Subtraction Average-Based Optimizer (SABO) and tailored for gas-solid fluidized beds, using the minimum permutation entropy as the fitness function. Combined with time-domain analysis and chaos analysis, the study systematically investigates the effects of varying ultrafine coal powder content on the stability of bed density fluctuations in micron-sized composite dense medium gas-solid fluidized beds. The research shows that adding a small fraction of ultrafine coal powder (w=1 %-w=3 %) suppresses the formation and coalescence of large bubbles and enhances operational predictability and stability. However, it can also promote channel blockage, leading to poor local fluidization and larger density fluctuations. A moderate amount of ultrafine coal powder (around w=6 %) significantly improves the uniformity of gas-solid distribution, reduces density fluctuations, thereby optimizing coal separation efficiency and precision. Conversely, an excessive dosage (w=8 % and above) increases system complexity and chaos, introducing new forms of instability. These results provide valuable theoretical guidance and practical recommendations for the design and operation of gas–solid fluidized beds, particularly in dry coal-separation applications.