The fluidized bed reactors can operate in different flow regimes. The reactor performance can change significantly as a result of flow regime change. It is very important to know how to identify the boundaries of the different flow regimes since reactor volume productivity, mixing, mass and heat transfer are affected by the prevailing flow regime. In this work pressure transducer and optical probe were used to identify the main flow regime transitions in two different plexiglas fluidized beds (0.14 m and 0.45 m in ID). By means of statistical and autocorrelation analyses applied to gauge pressure fluctuations (pressure readings above the atmospheric pressure) and optical probe signals the boundaries of the main hydrodynamic regimes were derived. Such information is needed for preparing a flow regime map.
The gauge pressure fluctuations were measured at a sampling frequency of 67 Hz and the optical probe readings were recorded at 5 kHz. The measurements were performed at three different axial positions. Air was used as a gas phase and glass beads (solid density ρs=2500 kg/m3, mean particle size dp=150-210 μm) were used as a solid phase in both columns. The same type of gas distributor (made of a porous polyethylene sheet with a pore size of 15-40 mm) was used in both columns.
In the case of small fluidized bed the autocorrelation function showed that the minimum fluidization velocity occurred at 0.12 m/s and the transition velocity to bubbling fluidization regime occurred at 0.38 m/s. The profile of variance was capable of identifying the onsets of both turbulent fluidization regime (0.91 m/s) and fast fluidization regime (1.6 m/s). In the case of bigger fluidized bed the profile showed that the minimum fluidization velocity occurred at 0.1 m/s and the transition velocity to bubbling fluidization regime occurred at 0.29 m/s. We confirmed these results by applying the same statistical methods to the optical probe data.
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