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In this paper, the minimum fluidisation velocity ( u m f ) of activated carbon particles in a gas–solid fluidised bed was experimentally determined using dry air as the fluidising medium. The effect of particle size and temperature on the minimum fluidisation velocity of the fluidised activated carbon particles was analysed. The particle sizes 212, 425, and 710 µm and bed temperatures of 30°C, 100°C, 200°C, and 300°C were studied. From the experimental results, it was found that the u m f decreased with a decrease in particle size of the activated carbon particles and decreased with an increase in the temperature. Based on the experimental results, a new correlation was developed to predict u m f at higher temperatures, since at higher temperatures, the deviation of experimental u m f values was higher when compared with the values estimated using previously published correlations. The present study will be useful for the design of an experimental system to study the continuous adsorption and desorption of organic vapours at higher temperatures in the fluidised bed of activated carbon particles. The details of the experimental study and analysis of results are discussed in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Packed fluidization is a novel technique, in which small particles are allowed to fluidize in the interstices of relatively large and stationary packing to enhance heat transfer rates of a unary packed bed of same size pebbles. In the present study, heat transfer in unary packed bed and binary packed fluidized bed were investigated and compared in terms of the effective thermal conductivity. In the experimental works, large pebbles (size: 3–10mm) of two different materials viz. lithium titanate and alumina and small particles (size: 231–780μm), also of two different materials viz., lithium titanate and silica were used. It was found that the heat transfer in unary packed bed is enhanced due to the packed fluidization and in terms of the effective thermal conductivity; the enhancement was up to 260%. It was found that the volume fraction of small particles, operating gas velocity, particle to pebble size ratio and the type of materials have a significant effect in enhancing the effective thermal conductivity and heat transfer rates. It was also found that 60% (v/v) of small particles in the interstitial voids of packing pebbles can give much improved effective thermal conductivity keeping all other operating parameters same. Possible mechanism for heat transfer enhancement due to packed fluidization has been proposed. Based on the results for different particle and pebble sizes, materials and process variables viz. particles to pebble size ratios, operating gas velocity ratios, volume fraction of small particles in the interstices and bed wall temperatures, we could arrive at optimum conditions for determining effective thermal conductivity and a correlation to estimate the same. [Copyright &y& Elsevier]

Abstract: Uniformly sized particulate solids often fluidize poorly with bubbling and slugging. Slugging is a phenomenon associated with the geometry of the vessel, gas flow rate and properties of gas solid particles. It is severe with Geldart Group B particles especially in bed with high aspect ratio and beyond the minimum bubbling velocity. Geldart B particles fluidize well, but bubbles appear as soon as the operating gas velocity exceeds the minimum fluidization velocity. Fluidization of small Geldart B particles in the interstitial void space of large and stationary particles, called packing, overcomes these drawbacks and changes the hydrodynamic characteristics of the bed. Experiments were carried out to investigate these characteristics as a function of the size of the small particles, fraction of voids of packing filled by the small particles and bed wall temperature. Small particles in the voids of packing start to fluidize at a lower superficial velocity (flow-rate divided by empty bed cross-sectional area) than small particles in unary beds. This velocity decreases with increase in wall temperature. A correlation is proposed to estimate the minimum fluidization velocity of the small particles in the voids as a function of measurable variables. [Copyright &y& Elsevier]

Abstract: Quality of fluidization is an important criterion for efficient heat and mass transfer in gas–solid fluidized beds. Knowledge of voidage distribution in fluidized bed is essential when exothermic reactions are carried out in fluidized beds. Quality of fluidization is often expressed in terms of time average local void-faction distribution. Gamma ray transmission technique is one of the techniques used to study the quality of fluidization. In the present study, Gamma ray transmission technique was explored to study the quality of fluidization in a unary fluidized bed and packed fluidized bed, in which small particles are fluidized in the interstitial void space of relatively large and stationary pebbles. Gamma ray photons were allowed to pass through a unary fluidized bed of silica and lithium–titanate particles at different angular and axial positions of the bed. Experiments were conducted in packed-fluidized bed of silica particles in the interstices of large size alumina pebbles and lithium–titanate particles in the interstitial void space of large size lithium titanate pebbles. It was observed, that packed fluidized bed provides better quality of fluidization or more homogeneous fluidization compared to that of a unary fluidized bed. Operating principle, experimental details and results are discussed in this paper. [Copyright &y& Elsevier]

Abstract: Experiments were conducted to investigate the hydrodynamic behaviour of lithium titanate (Li2TiO3) in gas-solid fluidized bed. The objective of the study was to study the fluidization properties of Li2TiO3 particles. These studies will be useful to find the applicability of fluidization to increase the effective thermal conductivity and wall to bed heat transfer coefficient of Li2TiO3 particulate bed in test blanket module of fusion reactor. Li2TiO3 was synthesized by solid state reaction process and different particle sizes were classified. Experiments were conducted in a cylindrical column of 90mm diameter and 650mm height in perspex material with metallic distributor plate. Dry compressed air was used as fluidizing medium. From the experiments it was observed that Li2TiO3 is fluidizable, but severe slugging and bubbling were observed in the fluidized bed. Minimum fluidization and bubbling velocity of Li2TiO3 particles were determined and compared to that of white sand of similar particle size and density. The experimental details and observations are discussed in this paper. [Copyright &y& Elsevier]

It is often important to know minimum fluidization velocity of particles in gas-solid fluidized bed at different temperatures and with different fluidizing gases. Generally, carrying out such experiments are often time consuming as well as very expensive. Computational fluid dynamic (CFD) modeling is presently an important tool that can be extended to solve these problems. The present work demonstrates the use and advantages of CFD modeling to study the effect of temperature on fluidization velocity for lithium titanate (Li 2 TiO 3 ) particles which fall under Geldart B type and air as fluidizing media. 2D simulation of fluidized bed was performed using Eulerian-Eulerian approach. The inlet superficial air velocity was varied and pressure drop across the bed was predicted at different temperatures from 30 to 600 °C for spherical particles of diameter from 231 to 780 μm. Minimum fluidization velocity was also determined using experiments for validation for different temperatures and diameter of particles. CFD predicts the minimum fluidization velocity with 95% accuracy when compared to experimental observations. The minimum fluidization velocity decreases with increase in temperature which is confirmed with validated model. The data from simulations was also compared with correlations reported in literature. [ABSTRACT FROM AUTHOR]