Loading...

Studying Mixing and Segregation Phenomena in Binary Gas-Solid Fluidized Beds by Analyzing Pressure Signals

Zeinalizadeh, Nasrin | 2024

0 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57493 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Fotovat, Farzam
  7. Abstract:
  8. Many fluidized bed reactors contain particles such as catalysts, biomass, etc. that vary in size, density, and shape. Despite the significance of these systems, the multi-component fluidized beds have been less studied compared to single-component systems. An important challenge in multi-component fluidized beds is the occurrence of particle segregation and reduced mixing, which severely diminish the reactor's efficiency. The objective of this study is seeking the relationship between the pressure signals measured in a binary gas-solid fluidized bed and the degree of particle mixing/segregation of dissimilar components at relatively low superficial gas velocities. To this end, pressure signals were acquired from a 2D fluidized bed involving single-component and binary-component systems. In the single-component experiments, glass beads with a diameter of 300 micrometers were used, whereas in the binary-component experiments a mixture of glass beads and polyethylene particles with a diameter of 4 millimeters was studied. The changes in the inlet gas velocity were such that the segregation and complete mixing of the particles could be observed in the binary system. Additionally, by image processing technique, the degree of particle mixing at different gas velocities was calculated in the binary system and compared to the results obtained from pressure signal processing. The results were evaluated using PSD, TPSD, coherency, and wavelet analysis. The results of the PSD analysis showed that the particles are segregated at a velocity of 0.138 m/s. At this velocity, the PSD plots in the upper part of the bed do not show any bubbles due to the accumulation of coarse polyethylene particles in the upper part of the bed. The energy concentration of the pressure signals in the middle of the bed is about 15 to 18 Hz, attributed to the channelization of gas caused by the segregation of the particles. Using the TPSD analysis, the stability of the bed during segregation and the effect of time on the PSD values were investigated. The results showed that when the particles are subject to segregation, the system experiences an unstable state, and it takes about 15 to 20 seconds to stabilize. The results of the wavelet and coherency analysis showed that the most influential parameter on the degree of particle mixing is the bubble size. The pattern of changes in the H index and the changes in the standard deviation of the incoherent components as a function of velocity are similar to the changes in the particle mixing versus velocity obtained from the image processing technique. The results of this study demonstrates that the analysis of pressure signals can be exploited as an effective tool for determination of mixing/segregation in binary fluidized beds
  9. Keywords:
  10. Mixing Index ; Solid-Gas Fluidized Bed ; Solids Mixing and Segregation ; Pressure Signals ; Binary Gas-Solid Fluidized Bed ; Transient Power Spectral Density (TPSD)

 Digital Object List

 Bookmark

No TOC