Residence time distribution of solids in multistage fluidisation

Krisrnaiah, K.; Pydisetty, Y.; Varma, Y. B. G.

doi:10.1016/0009-2509(82)85009-4

Cited by 20 publications

(10 citation statements)

References 10 publications

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“…These experimental data were adjusted successfully to the tanks in series model (Levenspiel, 1979), obtaining as the best fit 3.7 ideal stages, while the pilot plant presented three real stages. As reported by Krishnaiah et al (1982), multistage fluidized bed reactors with downcomers present solids RTD, which can be interpretated successfully by the monoparameter tanks in series model, obtaining a higher value of ideal stages than the real ones due to the baffles placed in each stage and the effect of the downcomers, as ocurrs in this case. The increase of 0.7 stages above the three real ones indicates that the effect of the downcomers and the baffles, although significant, is small.…”

Section: Three-stage Fluidized Bed Pilot Plant With Downcomersmentioning

confidence: 83%

Steam Activation of a Bituminous Coal in a Multistage Fluidized Bed Pilot Plant: Operation and Simulation Model

Martı́n-Gullón

Asensio

Marcilla

et al. 1996

Ind. Eng. Chem. Res.

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A hydrodynamic and kinetic model was developed and applied to simulate the experimental data from a three-stage fluidized bed pilot plant with downcomers. This was used to study the activated carbon production from a Spanish bituminous coal by steam gasification. The steam gasification kinetics, considering the influence of inhibitors, were also determined in a thermobalance. With the kinetic equation and the experimental solids residence time distribution of the pilot plant, the model simulates the overall process that takes place in the reactor. The proposed model is able to reproduce the experimental results satisfactorily.

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Section: Three-stage Fluidized Bed Pilot Plant With Downcomersmentioning

confidence: 83%

Steam Activation of a Bituminous Coal in a Multistage Fluidized Bed Pilot Plant: Operation and Simulation Model

Martı́n-Gullón

Asensio

Marcilla

et al. 1996

Ind. Eng. Chem. Res.

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“…The mean residence time is influenced by air flow rate, material flow rate, and the number of stages. Raghuraman [12,13] and Krishaniah [5,14] have studied in detail the actual residence time of solids both in multistage fluidized beds with and with out downcomers using tracer techniques. The actual residence time of the solids can be predicted, if the configuration of the bed and the flow rates of the phases are known.…”

Section: Resultsmentioning

confidence: 99%

Some Drying Aspects of Multistage Fluidized Beds

Kannan¹,

Natesan

1998

Chem. Eng. Technol.

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Multistage fluidized beds with and without downcomers to the horizontal perforated plates are used to dry food materials under different experimental conditions. The influence of various operating parameters such as inlet temperature of the heating medium, flow rate of the heating medium, material flow rate, and number of stages have been investigated. The performance of multistage fluidized beds with and without downcomers is compared and the difference in performance is explained based on stagnancy and short-circuiting of materials in each stage.The performance of the multistage fluidized bed with downcomers is also compared with batch fluidized bed and found to be superior under identical operation conditions.

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“…The assumption of ideal mixing was made by Krishnaiah et al (1982) and Toei and Akao (1968) while studying RTD of solids in a multistage fluidized bed. Ideal mixing of solids can be characterized by a tanks-in-series model (Levenspiel, 1972).…”

Section: Department Of Chemical Engineering National Institute Of Tementioning

confidence: 99%

Residence Time Distribution of Solids in a Fluidized Bed

Babu

Setty

2003

Can J Chem Eng

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A continuous fluidized bed provides an intimate and large area of contact between gas and solid particles, which results in good heat and mass transfer rates between the phases. A fluidized bed is also characterized by uniform temperature throughout as compared to a fixed bed. But the fluidized bed is limited in its operation between minimum fluidization velocity and terminal velocity of solids. In addition, solid particles are subjected to attrition.With an increase in gas rate above minimum fluidization, backmixing of solids increases. Beran and Lutcha (1975) reported that the advantages found for plug flow reactors with fluids are true for the plug flow of solids in a continuous fluidized bed. Hence, the authors (1975) suggested that by using baffles inside the bed, plug flow could be approached.Several investigations were carried out by earlier workers using different types of baffles inside the bed to reduce gross irregularities and instability of the bed caused by the excess gas. But these modifications increase the complexity of the bed, rendering operation and control more difficult. The aim of the present work is to carry out experimental work on residence time distribution of solids in a single-stage fluidized bed and suggest an alternative method to reduce the non-idealities inside the bed to approach plug flow conditions which improves quality of the product. This can be achieved by using a binary solid mixture in place of uniformly sized solids, as observed in the present work. In other words, using a binary solid mixture gives more and more plug flow tendency to the particles.The earlier work on RTD (residence time distribution) of solids in a continuous fluidized bed may be classified on the basis of single-parameter and multi-parameter models. Beran and Lutcha (1975) and Reay (1978) used a dispersion model to describe the RTD of solids in a rectangular fluidized bed dryer provided with vertical baffles. Beran and Lutcha (1975) reported increased dispersion coefficient with an increase in gas flow rate, while Reay (1978) reported an increase in particle diffusivity with an increase in gas rate, and a decrease in particle size and density. Burovoi and Svetozarova (1965) reported a decrease in dispersion coefficient with an increase in the particle size. Pydi Setty (1983) used an axial dispersion model to describe the RTD of solids in a single-stage spiral fluidized bed. Morris et al. (1964) reported poor agreement between the experimental data in a single-stage fluidized bed and the axial dispersion model. They observed that solids mixing by bulk movement of solids did not occur when the bed is operated near minimum fluidization velocity. Above 1.5 U mf , they noticed that the movement of solids occurred by gross solids movement but not by diffusion. Hence, the authors concluded that representation of solids mixing by a simple axial dispersion model is inadequate. The assumption of ideal mixing was made by Krishnaiah et al. (1982) and Toei and Akao (1968) while studying RTD of solids in a multistage...

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Residence time distribution of solids in multistage fluidisation

Cited by 20 publications

References 10 publications

Steam Activation of a Bituminous Coal in a Multistage Fluidized Bed Pilot Plant: Operation and Simulation Model

Steam Activation of a Bituminous Coal in a Multistage Fluidized Bed Pilot Plant: Operation and Simulation Model

Some Drying Aspects of Multistage Fluidized Beds

Residence Time Distribution of Solids in a Fluidized Bed

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