SPOUTED AND SPOUT-FLUIDIZED BEDS FOR GRAM DRYING

The objectives of this work are to analyze the drying performance of conical-cylindrical spouted bed (CSB) dryers for three different grains (rice, corn and wheat), and to compare the drying efficiency of CSB dryers with that of spout-fluid bed (SFB) dryers. A PC-program was developed for: (I) -optimization of the CSB dryer dimensions; (2) -simulation of drying grains in the optimized CSB dryer (including start-up period); and, (3) -analysis of the drying performance in a similar SFB dryer.

The liquid diffusion model is used to describe the falling rate drying period. Semi-empirical correlations available in the literature as well as information obtained in the authors' laboratory for spouted and spout-fluidized beds of grains are used to describe the aerodynamic parameters.

The results are presented in terms of the size of the dryer, energy consumption, air handling requirement, drying characteristics etc for different drying conditions. The drying effeciency in a CSB is compared with that in a similar SFB for different grain feed rates and drying temperatures.     

Spouted bed drying of agricultural grains

It is shown that the presence of a “slotted draft tube” results in reduced air requirements for spouting and improved drying performance. Experimental data are presented on batch as well as continuous spouted bed drying of wheat, paddy, maize and peas. The variables studied are feed moisture content (Q_o), inlet air temperature (T_o), bed mass hold-up (M_p), inlet superficial air velocity (u_o) and bed diameter (D_c) in batch drying, and the above variables and solids feed rate (F_s) in continuous drying. The data on average overall drying rate, ?_m, in kg moisture evaporated per unit time per kg bed solids, is found to be correlatable as ?_m, = k (50Q_o + 0.118T_o ? 12.5) 10^?5, and the single parameter k is presented for wheat, paddy, maize and peas for both batch and continuous modes of spouted bed drying. The correlation obtained should be useful in dryer design for the grains studied as well as for other similar materials.     

ANALYSIS OF MECHANICALLY AGITATED FLUID-PARTICLE CONTACT DRYERS

Incorporation of agitation to spouted and fluidized bed dryer result in significant increases in the drying capacity (Q_s ), although product retention persist, which is reduced by increasing the air flow. The physical phenomena occurring in these dryers with several liquid substrates was analyzed and the residence time distributions (RTD) were obtained by the use of dye tracers. The residence time (τ) was found to be a function of the rate of agitation (n) and reaches a minimum at n = n _opt, which was characteristic for each type of substrate, and where maxima also appeared for the drying capacity (Q_s = Q _{s max}) and the heat transfer coefficient (Nu _p = Nu _{p max}). The RTD can be modeled by series of consecutive dryers and a modified Vanderschuren and Delvosalle model can be employed to calculated moisture of the dry product.     

A consideration of circulating bed electrodes for the recovery of metal from dilute solutions

A comparison is made of three types of circulating particulate electrodes: spouted (circulating) bed (SBE), vortex bed (VBE) and moving bed (MBE). In applications such as metal recovery, all electrodes perform similarly in terms of current efficiency. On the basis of scale-up, it appears that the spouted bed electrode is the preferred system.Nomenclature I cell current (A) - F Faraday constant (94487 C mol^–1) - C dimensionless concentration - C _F friction factor - C ₀ Initial concentration (mol m^–3) - D pipe equivalent diameter (m) - e _b bed voidage - e _c voidage of conveying section - L bed length (m) - S _b cross section area of bed (m²) - S _T cross section area of conveying section (m²) - T dimensionless time=It/nFVC ₀ - U _f superficial liquid velocity in conveying (m s^–1) - U _i particle terminal velocity corrected for wall effects (m s^–1) - U _s particle velocity in transport (m s^–1) - U _SL slip velocity (m s^–1) - t time (s) - V electrolyte volume (m³) - V _f liquid velocity in the bed (m s^–1) - V _mf minimum fluidization velocity (m s^–1) - V _s particle velocity in the bed (m s^–1) - P pressure drop (NM^–2) - fluid density (kg m^–3) - _s particle density (kg m^–3) - Re Reynolds number     

SPOUTED AND SPOUT-FLUIDIZED BEDS FOR GRAM DRYING

The objectives of this work are to analyze the drying performance of conical-cylindrical spouted bed (CSB) dryers for three different grains (rice, corn and wheat), and to compare the drying efficiency of CSB dryers with that of spout-fluid bed (SFB) dryers. A PC-program was developed for: (I) -optimization of the CSB dryer dimensions; (2) -simulation of drying grains in the optimized CSB dryer (including start-up period); and, (3) -analysis of the drying performance in a similar SFB dryer.

The liquid diffusion model is used to describe the falling rate drying period. Semi-empirical correlations available in the literature as well as information obtained in the authors' laboratory for spouted and spout-fluidized beds of grains are used to describe the aerodynamic parameters.

The results are presented in terms of the size of the dryer, energy consumption, air handling requirement, drying characteristics etc for different drying conditions. The drying effeciency in a CSB is compared with that in a similar SFB for different grain feed rates and drying temperatures.     

Pressure drop,bed expansion and liquid holdup in a three phase spouted bed contactor

Data on the pressure drop, bed expansion and liquid holdup in a three phase spouted bed contactor with an initial bed height of 243 mm. were obtained as a function of the gas and liquid flowrate. Polyethylene spheres 10 mm. in diameter with a density of 320 kg/m³ were spouted in a 194 mm. column using a 30 mm. nozzle. The spouted bed contactor with gas and liquid mass flow-rates of 2.18 and 1.88 kg/m² sec, respectively had similar pressure drop per unit area of particle surface, total liquid holdup per unit volume of operating bed, and “active” holdup, as a fluidized contactor.     

Coal gasification in a spouted bed

Low Btu gas has been produced by gasifying coal in a spouted bed reactor. Coal of size 0.8-3.6 mm is fed continuously to a 0.15 m diameter spouted bed of inerts and gasified using mixtures of steam and air. Tests of the process with Western Canadian coals of free swelling index 0, 4 and 7 are reported. Gases of heating value to 3.61 MJ/m³ were produced at coal throughputs of 0.188 kg/m²s with the reactor operating at atmospheric pressure and temperatures to 930°C. Characteristics of the spouted bed gasifier are presented and results compared to commercial moving and fluidized bed systems. A simple mathematical model based on the two-region spouted bed model of Mathur and Lim is used to predict the effect on steam utilization of bed composition, bed height and diameter, and particle size.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

Effect of process conditions on particle growth for spouted bed coating of urea

The aim of this work was to analyze the influences of operational variables on particle growth for urea coating in a conventional spouted bed (CSB). An aqueous polymeric suspension was the coating liquid sprayed on the spouted particles. The effects of inlet air temperature, coating suspension flow rate and atomizing air pressure on particle growth were analyzed by a central composite rotatable design (CCRD) of experiments. The results showed particle growth in the range of 1.1–2.6%, therefore, some results below the expected for a film coating (2–8%). A second-order polynomial model was obtained for estimating particle growth as a function of the statistically significant variables: air temperature, suspension flow rate and atomizing air pressure, with percentage of explained variation R² = 90.72%. The urea growth kinetics during coating was analyzed for the optimal operating condition and a linear growth coefficient of 1.13 × 10⁻³ min⁻¹ was obtained. The volatilization analyses showed that the polymer film coating provided a decrease of the nitrogen loss in the range of 3–57%. And, SEM analyses demonstrated a total, uniform and homogeneous covering of the urea particles surface.     

Prediction of the maximum spoutable bed height in spout-fluid beds

A model for predicting the ratio of the maximum spoutable bed height in a spout-fluid bed to the maximum spoutable bed height in a spouted bed is presented and experimentally verified. The model is a further extension of the basic Mamuro and Hattori force balance model. The ratio H_mSF/H_m is found to be a function of the external annular fluid flowrate and a parameter C, which is the ratio of fluid velocity at the top of the annulus to that at minimum fluidization. C = 0.935 gives a best fit of our data.     

Minimum spouting velocity of dense particles in shallow spouted beds

Quantitative method is used to experimentally measure the minimum spouting velocity in shallow conical spouted bed. And a new minimum spouting correlation for shallow conical spouted beds is developed. It is based on spherical ZrO₂ particles whose density is as high as 5890 kg/m³ while the other U_ms correlations published so far are mainly based on relatively deep conical beds composed of lower density particles with density around or lower than 3000 kg/m³. The new U_ms correlation can predict U_ms of heavy particles well within the range of the experimental matrix. © 2011 Canadian Society for Chemical Engineering     

SCALE-UP OF SPOUTED BED DRYERS: CRITERIA AND APPLICATIONS

Abstract

The criteria required for reliable scale-up of the aerodynamics of spouted bed dryers of grains are stated and discussed. The dryer modeling role for effective scale-up, design and analyses of such dryers will be outlined. Suggestions are made on how small scale drying and aerodynamic data may be scaled up for spouted bed dryers. Appropriate empirical and semi-empirical correlations are listed. A flowchart is provided for design and analysis of a conventional and a two-dimensional spouted bed dryers.     

An investigation of heat transfer from a vertical tube in a spouted bed

An experimental investigation on heat transfer from a vertical tube in a gas—solid spouted bed has been conducted. Values of heat transfer coefficients (h_s) have been found to vary between 95 and 230 W/m²°C. Maximum values of h_s are always at the spout axis and decrease monotonically towards the column wall. The drop is most important at the spout-annulus boundary. Most of the effects from different parameters can be explained by the flow patterns of the gas, although particle convection still contributes to some extent to the heat transfer rate. Equations correlating h_s in the spout and the annulus have been developed.     

Spouted bed drying of cork stoppers

The spouted bed is commonly used to dry granular particles as it displays some special characteristics which render it capable of performing cyclic operations, with particles that are very difficult to fluidize under a different type of bed.Information on the characteristic drying rates of cork stoppers is still very limited in the technical and scientific literature, and until now no published data was found on the spouted bed drying of cork stoppers.The characterization of the drying performance of Port wine cork stoppers was carried out in a laboratory scale spouted bed. Characteristic drying curves were determined with 29 mm × 21 mm cork stoppers under several operating conditions. Values for the effective diffusivity were obtained in the range of 1.36 × 10⁻⁹ to 4.44 × 10⁻⁹ m²/s, with the temperature dependence represented by an Arrhenius-type relationship. The activation energy obtained was 28.72 kJ/mol.     

Study of Tire Particle Mixing in a Moving and Stirred Bed Vacuum Pyrolysis Reactor

The paper studies the motion of scrap tire shreds in a moving and stirred bed vacuum pyrolysis reactor. The reactor configuration is a novel concept. The pattern and the residence time distribution (RTD) of the particle motion in the reactor were investigated using tracers, for different feed rates and blade speeds. It was shown that the particle motion in the reactor is plug flow nature with intermediate dispersion (σ² = 0.02—0.055). The mean residence time is in the range of 7—23 min, depending on the speed of the blades and the feed rate. The ratio of mean particle speed and the speed of blades v_m/v_b varied between 0.03 and 0.07.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Application of chitosan‐entrapped β‐galactosidase in a packed‐bed reactor system

The model enzyme β‐galactosidase was entrapped in chitosan gel beads and tested for hydrolytic activity and its potential for application in a packed‐bed reactor. The chitosan beads had an enzyme entrapment efficiency of 59% and retained 56% of the enzyme activity of the free enzyme. The Michaelis constant (K_m) was 0.0086 and 0.011 μmol/mL for the free and immobilized enzymes, respectively. The maximum velocity of the reaction (V_max) was 285.7 and 55.25 μmol mL^?1 min^?1 for the free and immobilized enzymes, respectively. In pH stability tests, the immobilized enzyme exhibited a greater range of pH stability and shifted to include a more acidic pH optimum, compared to that of the free enzyme. A 2.54 × 16.51‐cm tubular reactor was constructed to hold 300 mL of chitosan‐immobilized enzyme. A full‐factorial test design was implemented to test the effect of substrate flow (20 and 100 mL/min), concentration (0.0015 and 0.003M), and repeated use of the test bed on efficiency of the system. Parameters were analyzed using repeated‐measures analysis of variance. Flow (p < 0.05) and concentration (p < 0.05) significantly affected substrate conversion, as did the interaction progressing from Run 1 to Run 2 on a bed (p < 0.05). Reactor stability tests indicated that the packed‐bed reactor continued to convert substrate for more than 12 h with a minimal reduction in conversion efficiency. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1294–1299, 2004     

Interfacial and Solution Behavior of Amphiphilic Drug and Counterion‐Coupled Gemini (COCOGEM) Surfactants

The critical micelle concentrations (cmc) of mixed systems comprising an amphiphilic drug amitriptyline hydrochloride and counterion‐coupled gemini surfactants 12‐6‐12, 14‐6‐14, or 16‐6‐16 [1,6‐bis(N,N‐alkyldimethylammonium) adipate] were determined using tensiometry. The results were analyzed in the light of different theoretical models from Rosen, Clint, Rubingh, and Motomura. The cmc values decrease with increasing mole fraction of surfactant (α₁). The cmc_id values (cmc value at ideal mixing conditions) also decrease with α₁ but remain above the experimental cmc values. This means that the mixed micelles form as a result of attractive interactions. These interactions are also seen in surface excess concentration (Γ_max) and minimum area per molecule (A_min) data: Γ_max increases and A_min decreases. Both Rosen's and Rubingh's models indicate synergistic interactions (interaction parameter, β^m and β^σ, values are negative). The β^m values are larger in magnitude than β^σ for 14‐6‐14 and 16‐6‐16 systems, whereas the reverse is the case with 12‐6‐12 because the surfactant's short chain makes adjustment in the core difficult for both components.     

Mathematical modeling of polyethylene terephthalate pyrolysis in a spouted bed

A model has been developed for pyrolysis of polyethylene terephthalate (PET) in a spouted bed reactor based on the conservation equations for heat, mass, and momentum transports. A spouted bed has been constructed and the kinetic parameters have been obtained within the temperature range of 723–833 K, using two particle size ranges, (0.1–1.0) × 10^?3 and (1.0–3.0) × 10^?3 m. The model' predictions for the radial distributions of temperature and concentration confirm the excellent mixing of particles. Thus, spouted beds are appropriate equipments for performing kinetic studies of PET pyrolysis. The inlet gas temperature and the mass of PET highly affect PET conversion. The amount of inert particles has a negligible effect on the conversion and it can be reduced as far as a stable spouting is preserved. The gas flow suffices to eliminate the external heat and mass‐transfer limitations. It can be reduced to the minimum value to decrease the energy consumption. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1900–1911, 2015     

A fluidized bed catalytic cracking regenerator model

A grid model including thermal effects is proposed. The aim is the simulation of a fluidized catalytic cracking regenerator similar to the industrial unit of Destileria La Plata, YPF, Argentina. It is demonstrated that a simple C.S.T.R. model without bypass of gas feed entering the bed provides a good approach for representing the fluidized bed including the grid region. In addition, by means of the C.S.T.R. model, it is shown that there exist two characteristic operating regions: a zone where (C^o_o – C_o) depends on the initial coke concentration and a zone where (C^o_o – C_c) is controlled by oxygen supply.