Experiments were conducted in a liquid-solid circulating fluidized bed (LSCFB) to study the flow regimes, operational instability, critical transitional velocity to circulating fluidized bed (CFB) regime, solids holdup and solids circulation rate by three experimental methods. The results indicate that the operational instabilities such as arch formation, liquid-solid separator blockage and solids return pipe blockage were observed in two of these methods at large primary and auxiliary liquid velocities. The critical transitional velocity that demarcates the expanded bed from CFB regime was observed to be different by these three methods. Each of these methods has its own merits and demerits in terms of operating range of CFB regime, solids holdup, solids circulation rate and application. © 2008 Elsevier B.V. All rights reserved.

P Sesha Talpa Sai

Department Of Chemical Engineering

K. Krishnaiah

CIRCULATING FLUIDIZED BED

CRITICAL TRANSITIONAL VELOCITY

SOLIDS CIRCULATION RATE

SOLIDS HOLDUP

STABLE OPERATING REGIME

FLUID DYNAMICS

Fluidization

Fluidized bed process

Liquids

velocity

Fluidized beds

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Chemical Engineering and Processing: Process Intensification

We present a modeling framework for the simulation of the hydrodynamic features of a liquid solid circulating fluidized bed (LSCFB) using computational fluid dynamics (CFD). Using an Eulerian-Eulerian approach to deal with the two-phase flow aspects and the kinetic theory of granular flow (KTGF) approach to deal with the solid-fluid interaction, we simulate the complete flow loop of an LSCFB using three-dimensional, time-dependent CFD calculations. We show that the essential features of the two-phase flow in the riser, the downcomer, the liquid-solid separator at the top and in the solids return feed pipe at the bottom are captured well in these simulations. The role of the flow distributors in establishing circulation is critically analyzed with the aid of post-processing tools. Comparison with literature data shows qualitative agreement with known trends of important hydrodynamic parameters and highlights the need for calibration of the constitutive equations for LSCFB applications. © 2013 Elsevier B.V.

Powder Technology

Numerical simulation of the hydrodynamics of a liquid solid circulating fluidized bed

Experiments were conducted in a liquid-solid circulating fluidized bed to study the effect of liquid viscosity and solids inventory on pressure gradient, critical transitional liquid velocity, onset average solids holdup, axial solids holdup distribution, average solids holdup and solids circulation rate in circulating fluidization regime with riser operated in fixed inventory mode. The results indicate that critical transitional liquid velocity decreases with increase in liquid viscosity. The onset average solids holdup, on the other hand, increases with increase in either auxiliary liquid velocity or solids inventory. The variation of axial solids holdup distribution, average solids holdup and solids circulation rate with liquid viscosity when solid inventory was 0.15. m was dissimilar with either 0.25. m or 0.35. m solid inventory. Correlations were proposed for estimating the average solids holdup and are satisfactorily compared with experimental values. © 2010 Elsevier B.V.

Macroscopic properties of liquid-solid circulating fluidized bed with viscous liquid medium

AbstractCirculating fluidized beds (CFB) play a major role in the chemical industry especially as heterogeneous catalytic reactors. Research on hydrodynamic properties of Liquid – Solid CFBs (LSCFB) is significantly under-reported as compared to Gas – Solid CFBs (GSCFB). Steadily, prominent research is being established in fields like food industry (whey protein recovery), waste management (removal of heavy metals from radioactive wastes) and others, which use LSCFBs. In this context, it is important to have significant knowledge about the changes occurring in hydrodynamic properties like solid hold-up, rate of solid circulation etc., on changing certain critical physical properties such as inventory height. An LSCFB of height 2.95 m and riser outer diameter 0.1 m was chosen and the effect of inventory height on the properties was studied by taking the initial inventory heights as 15 cm, 25 cm and 35 cm. The hydrodynamic studies concentrated on axial solid holdup, average solid holdup, solid circulation rate and slip velocity. On increasing the inventory, uniformity of axial solid holdup was confirmed along with studying holdup patterns. Solid flux was seen to follow an inverse relationship to holdup, as expected. The change in slip velocity with varying inventory was also checked, and was found to decrease with inventory. The distribution parameter, Coof the drift flux model was used to determine the extent of non-uniformity in solid distribution. Cowas calculated to be less than unity in the range of 0.983–0.994, suggesting non-uniformity in solid distribution, with higher solid concentration by the walls compared to the core.

Fulltext

Chemical Product and Process Modeling

Effect of Inventory Change in a Liquid – Solid Circulating Fluidized Bed (LSCFB)

Experiments were conducted in a liquid-solid circulating fluidized bed with different viscous liquids and particles to study the hydrodynamics, average solid hold up and solid circulation rate. The effects of operating parameters, i.e., primary liquid flow rate in the riser, auxiliary liquid flow rate, total liquid flow rate and viscosity of the liquid were studied for solids of different density and particle size. Results show that the circulating fluidization regime starts earlier for more viscous solutions because of the decrease in critical transitional velocity. The onset of solid holdup increases with an increase in liquid viscosity for sand and for glass beads. The solid circulation rate increases with an increase in total velocity and auxiliary velocity, and also increases with increasing viscosity.

Brazilian Journal of Chemical Engineering

SOLID HOLDUP AND CIRCULATION RATE IN A LIQUID-SOLID CIRCULATING FLUIDIZED BED WITH VISCOUS LIQUID MEDIUM

Average solid holdup in the axial direction was investigated in a liquid solid circulating fluidized bed riser (LSCFB), with liquids of different viscosities. The effect of operating parameters including; primary, secondary and total velocity, particle diameter and density was studied. Experiments were conducted using water and glycerol at different concentration having viscosities in the range 1-1.36 cp. The results indicated that the solid holdup in the riser was axially uniform for viscous liquids and increases with increase in auxiliary velocity. The average solid holdup decreases with increase in total velocity and increases with increase in viscosity for sand-glycerol, glass bead-glycerol system. The experimental measurements were compared with the existing holdup model prediction that varied linearly with viscosity. Further, a correlation was developed to estimate average solid holdup in the riser, and the performance of the expression was compared with the present experimental data. © 2014 Production and hosting by Elsevier B.V.

Journal	Chemical Engineering and Processing: Process Intensification
ISSN	02552701
Open Access	No