Minimum and Complete Fluidization Velocity for Sand-Palm Shell Mixtures, Part II: Characteristic Velocity Profiles, Critical Loading and Binary Correlations

Abstract

Problem statement: In Part I of this research, the main features of the fluidization behavior and characteristic velocities had been reported. Approach: In the present research, the mixtures characteristic velocity profiles for various sand sizes, palm shell sizes and weight percents were presented. It was recognized that there are instances where the characteristic values remain nearly unchanged from its pure sand values. This regime of constant values can be observed in both compartments and can be established depending on the bed properties. The term "Critical loading" is then selected to define the maximum palm shell content (size and weight percent) that can be present in the mixtures where the characteristic velocities remain absolutely of pure sand values. Results: The critical loading increases with the increase of sand size but decreases with the increase of palm shell size. Moreover, it can be observed that the critical loading generally decreases with the increase in particle size ratio, although exception is sighted in the combustor for the mixture with the largest sand size. Overall, the largest sand size has the highest critical loading. Meanwhile, the selected correlations are able to describe the qualitative variation in the characteristic velocities. However, quantitatively, these correlations are unsatisfactory as they are either over-estimate or under-estimate. Conclusion/Recommendations: It is desirable to establish the regime of critical loading since the mixture characteristic velocities can be pre-determined using bed material properties made up from pure sand (inert) values. Within this regime, a single operational velocity can be set for respective compartment that is independent from variation of palm shell size and weight percent in the mixtures (especially during combustion or gasification). Ultimately, the state of fluidization (e.g., bubbling or vigorously fluidized) and mixing/segregation condition that depend on relative magnitude of operational and characteristic velocities can be identified and maintained.