JOURNAL OF INTERNATIONAL ACADEMIC RESEARCH FOR MULTIDISCIPLINARY Impact Factor 1.393, ISSN: , Volume 2, Issue 4, May 2014

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1 PREDICTION OF BED PRESSURE DROP AND TOP PACKED BED HEIGHT FORMATION IN THREE PHASE SEMI-FLUIDIZED BED WITH REGULAR HOMOGENOUS BINARY MIXTURES D.K. SAMAL* Y.K. MOHANTY** G.K. ROY*** *Dept. of Chemical Engineering, Gandhi Institute of Engineering & Technology (GIET), Gunupur, Rayagada, Odisha, India **Dept. of Chemical Engineering, Gandhi Institute of Engineering & Technology (GIET), Gunupur, Rayagada, Odisha, India ***Dept. of Chemical Engineering, Gandhi Institute of Engineering & Technology (GIET), Gunupur, Rayagada, Odisha, India ABSTRACT Hydrodynamics study have been conducted in a 0.05m internal diameter Perspex column, with water and air (secondary) as fluidizing medium in gas-liquid-solid semifluidized bed with spherical two different sizes of glass beads. The study is relating to bed pressure drop and packed bed formation. Experimental parameters studied include superficial gas and liquid velocities, average particle size and static bed height and the bed expansion ratio. Empirical and semi-empirical models have been developed. The calculated values from predicted models have been compared with the experimental values and fairly good agreement has been obtained. The hydrodynamics study conducted and the correlations developed thereof can find potential applications in chemical processing. KEYWORDS: Gas-Liquid Solid Semi-Fluidization, Regular Homogeneous Particles, Binary Mixtures, Hydrodynamics, Dimensional And Statistical Analyses. 1. INTRODUCTION A semi-fluidized column is defined as the combination of fluidized and packed bed conditions coexisting in one column, which operates in series, was first initiated by Fan et al, in Hydrodynamic characteristics such as bed pressure drop and height of top packed bed are essential for designing and improving the quality of semi-fluidization. Regular binary homogenous particle mixtures are preferable due to easy formation of semi-fluidized bed at low bed pressure drop compared to that of single sized particles. The regular shaped particles are being used in the catalytic reaction engineering. Many of the catalytic reaction involved in the process industries deals with binary and ternary mixture of catalyst. Several investigators have been attempted to explain the behavior of semi-fluidized bed in gas-solid, liquid-solid or gas-liquid-solid systems with various types of particles and their mixtures. Most of the studies relate to single particle while a few studies on binary homogenous and 202

2 heterogeneous irregular mixtures have been reported [1-6]. Hydrodynamics of regular single particles of more than 2 mm diameter (glass beads) have been studied by Jena et al.[7] with initial static bed height of m to m in Samal et al. [8-9] have studied the liquid-solid semi-fluidized bed hydrodynamics of irregular homogenous ternary mixture and gas-liquid-solid semi-fluidized bed hydrodynamics of irregular homogenous binary mixture in Practically no work has been conducted on hydrodynamics of homogeneous binary mixtures of regular particles in a gas-liquid-solid semi-fluidized bed. Thus, the hydrodynamics of regular homogenous binary mixture particles have been studied in gas-liquid-solid semifluidized bed. The purposes of use of binary mixture of glass bead are to investigate the effect of particle interaction on the hydrodynamic characteristics. The objective of the present work is to study the effect of superficial liquid velocity (U sfl ), superficial gas velocity (U sfg ) average particle diameter (d pav ) (mixture composition, wt. %), initial static bed height (H s ) and the bed expansion ratio (R) on the bed pressure drop, top packed bed formation. Simultaneously, correlations have been developed for the prediction of the responses in a liquid-solid semifluidized bed using dimensional and statistical analyses. The experimental data have been compared with the values obtained from the developed correlations in this study. The unique feature of the current study is the investigations carried out in 0.05m internal diameter cylindrical columns with binary mixture of spherical glass beads of average particle size of m (-8+10 BSS), m ( BSS), as in industrial practice 20 μm to m diameter spherical catalyst particles are used for fixed and fluidized bed reactors. Various applications in different fields have been reported in literature where semifluidization plays an important role. Dynamics of Fines Deposition [10], Simultaneous Removal of Cyanide and copper Ions [11], Formation of nitrogen oxides and deposits on the heating surfaces of boilers [12], Extractive fermentation of ethanol by immobilized yeast cells [13], Thin-layer drying of high-moisture faba beans in semi-fluidized bed [14] and the treatment of palm oil mill effluent [15] are some of them. 2. Materials and Methods Schematic and pictorial representation of the experimental setup is shown in Fig. 1. The details of the set-up and the method of investigations are described in an earlier paper [9]. 203

3 The scope of the experiment is presented in Table 1. The procedure was repeated varying the initial static bed height, average particle size, and bed expansion ratio for dimensionless responses like semi-fluidized bed pressure drop (ΔP sf /ΔP mf ) and height of top packed bed (H pa /H s ). The responses ΔP sf /ΔP mf and H pa /H s respectively have been taken to be functions of sets of independent variables H s /D c, d pav /D c, G sfl /G mfl, G sfg /G mfl, R. Table 1:- Scope of the experiment for regular binary mixture (A) Properties of bed material (B) Binary mixture properties Size Particle size Composition Avg. particle (d p x 10 3, m) Mixture (wt%) (d pav x 10 3 m) d p Mixture 1 50 : d p Mixture 2 60 : Mixture 3 70 : Mixture 4 80 : Mixture 5 90 : (C) Materials Materials Glass Beads ρ s, kg/m (D) Bed expansion ratio R In this work mathematical and statistical model have been used for predicting For statistical analysis, Central Composite Design (CCD) [16-18] has been used to develop correlations for four responses (dependent dimensionless variables). The complete experimental range and the levels of independent variables are given in Table

4 Table 2:- Level of independent variables for regular binary mixture Variables Symbol - α α Aspect Ratio (H s /D c ) X Particle diameter (d pav /D c ) X Liquid mass velocity (G sfl /G mf ) X Gas mass velocity (G sfg /G mf ) X Bed expansion ratio (R) X The design of the experiment is given in Table 3 (dimensional analysis) and Table 4 (statistical analysis). For statistical analysis, a statistical software package Design-Expert , Stat-Ease, Inc., Minneapolis, USA, has been used for regression analysis of the semifluidized bed responses. Table 3:- Experimental design matrix and responses (Dimensional Analysis) for regular binary mixture. H s /D c d pav / D c G sfl /G mfl G sfg /G mfl R Expt. ΔP sf /ΔP mfl Cal. ΔP sf /ΔP mfl (Eq. 1) Expt. H pa /H s Cal. H pa /H s (Eq. 2)

5 Table 4:- Experimental design matrix and responses (Statistical Analysis) for regular binary mixture. H s /D c d pav / D c G sfl /G mfl G sfg /G mfl R ΔP sf /ΔP mfl ΔP sf /ΔP mfl

6 Results and Discussions Hydrodynamic parameters for the gas-liquid-solid semi-fluidization using homogenous regular binary viz. the semi-fluidized bed pressure drop, height of top packed bed have been found to be dependent on material property (average particle size) and system parameters (initial static bed height and bed expansion ratio). 3.1 Development of correlations by Dimensional Analysis: For dimensionless bed pressure drop, the equation is ΔP sf /ΔP mfl = (H s /D c ) (d pav /D c ) (G sfl /G mfl ) (G sfg /G mfl ) R (1) For dimensionless top packed bed height, the equation is H pa /H s = (H s /D c ) (d pav /D c ) (G sfl /G mfl ) (G sfg /G mfl ) R (2) Fig. 2 shows the comparison between the experimental and calculated values of ΔP sf /ΔP mf with a standard deviation of 1.31 and a coefficient of correlation of respectively. Fig. 3 shows the comparison between the experimental and calculated values of H pa /H s with a standard deviation of and a coefficient of correlation of respectively. 207

7 3.2 Development of correlations by statistical analysis approach For dimensionless semi-fluidization pressure drop, the equation is ΔP sf /ΔP mf = X X X X X X 1 X X 1 X X 1 X X 1 X X 2 X X 2 X X 2 X X 3 X X 3 X X 4 X X X X X X 5 (3) For dimensionless top packed bed height, the equation is H pa /H s = X X X X X X 1 X X 1 X X 1 X X 1 X X 2 X X 2 X X 2 X X 3 X X 3 X X 4 X X X X X X 5 (4) Predicted vs. Actual Predicted vs. Actual Fig. 4: Comparison of Experimental with Calculated (Eq. 3) values Fig. 5: Comparison of Experimental with Calculated (Eq. 4) values Fig. 4 shows the comparison between the experimental and calculated values of ΔP sf /ΔP mfl with a standard deviation of 3.49 and a coefficient of correlation of respectively. Fig. 5 shows the comparison between the experimental and calculated values of H pa /H s with a standard deviation of and a coefficient of correlation of respectively. 4. CONCLUSION Investigations have been carried out to study the behavior of regular homogenous binary mixtures with the superficial liquid and gas velocities in gas-liquid-solid semi-fluidized beds with particles of different size in 0.05 m column diameter. It may be concluded that the bed 208

8 pressure drop and height of top packed bed are strong functions of superficial liquid and gas velocities and the average size of particle. The initial static bed height is also important for the purpose. Correlations for the calculation of bed pressure drop and height of top packed bed have been proposed. The values calculated from the developed correlations have been compared with the experimental ones. The coefficients of correlations are found to be greater than 0.96 in both the approaches, thus emphasizing the validity of the developed correlations over the range of the operating parameters investigated. The present hydrodynamics study along with the developed correlations can find potential applications in physical and chemical processing. In the present investigation, the wide range in experimental parameters involved especially with respect to mixture particle and bed expansion ratio, makes it amenable to logical scale-up while considering design of gas-liquidsolid semi-fluidization systems. Acknowledgement The authors gratefully acknowledge the support and encouragement received from GIET, Gunupur, Odisha, India Nomenclature BSS British Standard Sieve D, d Diameter, m G Mass velocity, Kg.m -2.s -1 H, h Height, m P Pressure, N.m -2 R Bed expansion ratio Greek letters Δ Difference Subscripts av average c column f fluid g gas l liquid mf minimum fluidization p particle pa top packed bed s static sf semi-fluidization References 1. Dash. J, Roy. G. K, Liquid-Solid Semi-fluidization of Homogeneous Mixture-I, Prediction of Onset Semi-fluidization Velocity'. Indian Chemical Journal, February, p

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