Master of Engineering Science
Chemical and Biochemical Engineering
The intermediate phase in low-velocity gas-solid fluidized beds generally presents excellent gas-solid contact in the systems. However, no comprehensive understanding of this vital phase is available in the literature. Therefore, this study proposed a statistical method to identify this intermediate phase, named ‘mid-phase’ in this thesis, to interpret the system performance based on the analysis of solids holdup in a low-velocity gas-solid fluidized bed.
The distributions of the mid-phase are investigated along both radial and axial directions in consideration of different flow regimes. The result shows that the turbulent regime contains a higher amount of mid-phase and the spatial mid-phase distributions within this regime present to be more heterogeneous. According to the analysis of the spatial distributions, the mid-phase tends to concentrate at the medium bed heights adjacent to the wall. These results are of great significance to precisely guide the related process intensification operations.
Summary for Lay Audience
Gas-solid fluidization system plays an important role in industrial applications of Fluid Catalytic Cracking (FCC), coal gasification and particle drying due to its great gas-solid contact quality and reaction performance. Low-velocity gas-solid fluidized beds including bubbling fluidized beds (BFB) and turbulent fluidized beds (TFB) are common gas-solid fluidization systems, which operate with low gas velocity to reduce energy consumption.
In the low-velocity gas-solid fluidized bed, bubbles (voids) and emulsion phases composed of gas and solid particles will be formed respectively when the gas is blown into the bed. There is a transition region between the bubbles and the emulsion phase called ‘mid-phase’. The mid-phase is composed of the gas from bubbles and the solid particles from the emulsion phase. In the mid-phase, both gas and solid particles have more opportunities to contact with each other, which can improve the gas-solid contact of the system. Due to better gas-solid contact, the mid-phase has been studied in this research to provide guidance for improving the gas-solid contact quality in low-velocity gas-solid fluidized beds.
This study focuses on the distribution of the mid-phase in the BFB and TFB. In BFB, the mid-phase time fraction increases with increasing gas velocity. However, it remains nearly constant with increasing gas velocity in TFB. For spatial distribution, it is more uniform in BFB. Overall, TFB has better gas-solid contact and more heterogeneous spatial mid-phase distribution.
Zhang, Zhenan, "Identification and Distribution Analysis of the Mid-phase in a Low-velocity Gas-solid Fluidized Bed" (2022). Electronic Thesis and Dissertation Repository. 8774.