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.

Fluid dynamic study of mixtures of sugarcane bagasse and sand particles: Minimum fluidization velocity

“…V mf increases because the fine bagasse particles tend to become entangled, forming a network with a high cohesive force which must be broken to achieve fluidization. This interlacement of biomass particles mixed with sand has been reported in previous studies by Pilar et al [18] and Chok et al [19], using other types of biomass with physical characteristics very similar to those of the sugarcane bagasse particles.…”

“…Cook et al [19] studied binary mixtures of palm shell particles with different size and of different types and sizes of sand, showing that the (V mf ) remains practically constant for different fractions of biomass/sand when the particle diameters are too small (particles of palm shell between 1.18 and 2.36 mm with 2e10% of biomass in the mixture and sand of 0.196 mm of diameter). Rao and Reddy [13] also studied the fluid-dynamic characteristics of mixtures of rice husk, sawdust, and groundnut shells and sand with different sizes, making comparisons between experimental and theoretical values obtained from different correlations.…”

Experimental Comparisons of Anchovy Drying using Centrifugal and Gravitational Fluidized Bed Techniques

“…Products dried by solar power may be contaminated with dust, dirt, rainfall, animals, birds, rodents, insects and microorganisms and also take longer (Travis et al, 2013). Fluidized bed dryers are one of the hot air dryers that show a high rate of heat and mass transfer (Chok et al, 2010). They consist of a vertical drying chamber and the products are dried in high velocity hot air which is supplied by a blower (Ghaly et al, 2012).…”