Fluidization dynamics of wet Geldart D particles by pressure fluctuation analysis

Abstract

The increase of liquid saturation badly affects the fluidization dynamics, even resulting in the failure of fluidization. Nevertheless, few researches focus on characterizing the flow pattern transition of wet particles. In this work, we discuss the effects of the liquid saturation, gas velocity and the particle size on the global fluidization dynamics of Geldart D particles by analyzing the pressure fluctuations in the fluidized bed. The results show that the bubble dynamics is intensified with the increasing liquid saturation and decreasing particle size. When the superficial gas velocity increases, the fluidization regimes change from expanding regime, to multi-bubbling regime and slugging. During the normal fluidization and slugging, the liquid bridge forces prevent the growth of large bubbles and promote the probability of bubble break-up. Thus, the average bubble size decreases and the number of bubbles increases, which lead to the intense bubble behavior. With the decreasing particle size, the effect of liquid bridge forces is enhanced, contributing to the intensified bubble dynamics, including fast rising, frequent coalescence and eruption of a large number of bubbles. Compared to dry particles, wet particles are easily to cause defluidization when the gas velocity is small. The PSD patterns have the sharp narrow peaks at frequency lower than 0.8 Hz. When the liquid saturation is increased to 30%, a gas channel forms in the bed, which resists the normal works of the fluidized bed. Basically, reducing the liquid saturation is a reasonable way to avoid defluidization.