Spouted bed hydrodynamics in a 0.91 m diameter vessel

Hydrodynamic measurements were obtained in a flat-based half-cylindrical column of diameter 0.91 m and inlet orifice diameters of 76 to 114 mm. Beds of 3.5 to 6.7 mm diameter particles with static depths of 0.53 to 1.83 m were spouted with air. In agreement with measurements by earlier workers in smaller columns, it was found necessary to operate with inlet orifice diameters less than about 30 times the mean particle diameter in order to be able to achieve stable spouting. Correlations for minimum spouting velocity developed on small vessels generally gave poor predictions for the large diameter vessel employed in this work and failed to predict the observed dependence of U_ms on the static bed height. Substantial dead regions where particles were stagnant were observed in the lower outer portion of the vessel. Other aspects of behaviour studied, including spout diameters and shapes, fountain heights, pressure profiles and gas velocities in the annulus, were qualitatively similar to those in smaller columns, although equations developed for the smaller vessels did not always provide accurate predictions.     

Analysis of the dynamics of paste drying in a spouted bed

Although there are some models available in the literature for paste drying in spouted beds, few of them have focused on transient analysis of dynamical systems. Our objective was to integrate experiments and simulations of a dynamic model to investigate the transient response to disturbances and interruptions in the feed flow during paste drying in a spouted bed with inert particles. The spouted bed consisted of a cylindrical column with 50.0?cm of height and 20.0?cm of diameter. Drying tests were performed at inlet gas temperatures of 70?°C and 100?°C and inlet air flow 30% above the minimum spouting velocity. A 5% w/w suspension of calcium carbonate was used as paste material, and glass spheres of 2.2?mm were used as inert materials. Different patterns of step function changes were tested in the paste feed flow rate. A lumped parameter model was used to predict mass and heat transfer during the drying. Experiments and simulations were in good agreement.     

Batch drying kinetics of corn in a novel rotating jet spouted bed

The batch drying kinetics of corn as a test material were investigated experimentally in a novel rotating jet spouted bed (RJSB) using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, superficial air velocity, nozzle diameter, distributor rotational speed and intermittency of spouting and heat input. The results indicate that the drying kinetics are comparable with conventional spouted and fluidized beds for slow drying materials and that intermittent drying can save up to 40% of the thermal energy as well as air consumption with better quality product.     

Analysis of conical spouted bed fluid dynamics using carton mixtures

The pyrolysis has risen as an important alternative technology for generating value from waste. Among the modern solid wastes, the post-consumer carton packaging highlights due to the high value-added of the primary products obtained from pyrolysis. In an attempt to use conical spouted beds (CSBs) as a pyrolysis reactor for processing cartons, this present research aims at analyzing experimentally the air–carton mixtures flow dynamics in CSBs and stating comparisons with characteristic fluid dynamics obtained by using CFD technique. The flow behavior of air–carton disk is experimentally investigated by analyzing data of bed pressure drop, air velocity and fountain height. For the carton disk and polyethylene mixtures up to 50% cartons (in mass), and carton disks and sand mixtures comprising 5 and 10% cartons (in mass), the analysis of the experimental data shows that the stable spouted regimes are achieved. Furthermore, the simulated results demonstrate that the Eulerian approach using the Syamlal drag model is able to predict qualitatively the flow behavior in conical spouted beds comprising non-spherical particle mixtures.     

Voidage and particle velocity profiles in a spout‐fluid bed

Detailed hydodynamic measurements have been obtained for fully cylindrical spout‐fluid beds of 1.3 mm, 1.8 mm and 2.5 mm glass beads in a fully cylindrical column of diameter 152 mm using three different types of optical fibre probes. The reallocation of up to 43% of the air to auxiliary air introduced through the conical base caused some decrease in spout voidages, but remarkably little change in spout diameter compared with spouted beds where there was no auxiliary air addition. Auxiliary air led also to some decrease in particle velocities in the spout and to a modest decrease in the net solids circulation rate.     

Cold flow experimental study and computer simulations of a compact spouted bed reactor

Spouted beds are a very interesting class of gas–solid contactors that possess excellent heat transfer and mixing characteristics, while they are particularly suited to process coarse particles. Proper design of such beds requires the prediction of various hydrodynamic characteristics, such as the minimum spouting velocity and maximum spoutable height. Contrary to their typical initial applications, spouted beds have been finding recently more frequent use on the one hand at endothermic processes and on the other hand using much finer particle sizes. In the current work, the hydrodynamic characteristics of a laboratory scale spouted bed of 0.05 m diameter have been investigated via cold flow studies using olivine particles of 3.55–5.00 × 10⁻⁴ m size. Hydrodynamic parameters have been measured at this compact geometry and fine particle size and were compared with common literature correlations. An empirical correlation was derived to predict the fountain height for the studied fine particle spouted bed. Computer simulations have been further used to investigate the heat transfer characteristics of the bed under endothermic reactive conditions, using methane reforming as a case study. Given sufficient external heat supply, a spouted bed operating at a well-mixed regime can efficiently drive even highly endothermic reactions.     

HYDRODYNAMIC STUDIES IN A HALF SLOT-RECTANGULAR SPOUTED BED COLUMN

Experiments were carried out in a half slot-rectangular spouted bed to investigate the effects of slot width and lower section basal angle on column hydrodynamics. Flow regimes, minimum spouting velocity, spouting and maximum pressure drops, and maximum spoutable bed height were determined for 4?mm diameter polyethylene particles. The results are compared with those for conventional cylindrical and rectangular spouted beds. Correlations for each hydrodynamic parameter are developed and compared with equations available in the literature.     

Hydrodynamics of pressurized spouted beds

Experiments were carried out in a pressurized spouted bed with pressures up to 345 kPa. The minimum spouting velocity was found to decrease with increasing pressure. Comparison of the experimental minimum spouting velocities with the Mathur-Gishler (1955) equation gave unsatisfactory agreement. The maximum spoutable bed height, Hm, and spout diameters increased with increasing bed pressure. The McNab and Bridgwater (1977) equation consistently overestimated Hm for large or heavy particles and underestimated Hm for small particles, with the deviations between the predicted and experimental values being greater at high bed pressures. Although the McNab (1972) equation gave good predictions of average spout diameters for beds at ambient pressure, it gave poor predictions at elevated pressures, with errors up to 66%. For a given fluid-solid combination and column geometry the longitudinal pressure profile in the annulus was found to be independent of bed pressure. Five fairly distinct flow regimes were observed, and spoutability could be improved by increasing bed pressure.     

Spout Shape Predictions in Spouted Beds

A theoretical study to predict spout‐annulus interface variation with bed level for different column geometries of spouted beds is proposed. A previous mathematical model (Krzywanski et al., 1989), developed for spout shape predictions in two‐dimensional spouted beds, is here proposed to be applied also for cylindrical, conical or cone‐based cylindrical columns. Its predictions depend on the average spout diameter and on the spout expansion angle. While there exists empirical equations available to estimate the first model parameter, the second one requires a rigorous stress analysis of the particles at the entrance of the bed. To avoid this difficulty, this work proposes a simple mathematical strategy to calculate the spout expansion angle. The reliability of this approach was checked by comparison with several experimental results obtained in cone‐based cylindrical (Lim et al., 1974; Wu et al., 1987; He et al., 1998) and rectangular (Zanoelo, 1994) spouted beds.     

Aerodynamics of a novel rotating jet spouted bed

A novel rotating jet spouted bed (RJSB) is developed and tested. It consists of a rotating air distributor with two radially located spouting air nozzles. The effects of bed height, distributor rotational speed, nozzle diameter and particle properties on the flow characteristics were examined. Various flow regimes were mapped as functions of distributor rotational speed and superficial air velocity for different materials and column dimensions. Empirical correlations were developed for the minimum spouting velocity, peak pressure drop and steady spouting pressure drop.     

A comparative hydrodynamic study of two types of spouted bed reactor designs

In order to properly design and scale up spouted beds, one needs to predict the minimum spouting velocity of specific systems having different bed dimensions, and properties of particle and spouting gas. Because of inherent complexity of predicting minimum spouting velocity, the prevailing approach has been to use empirical correlations, a number of which are available in the literature. Central jet distributors are commonly used in the experimental studies reported in the literature. Circular slit distributor is a new concept in which air is supplied to the bed of particles through a circular slit. This paper presents results of an experimental study on the hydrodynamics of central jet and circular slit distributors. In this paper a fully connected feed-forward neural network model was used to predict the minimum spouting velocity of central jet and circular slit spouted beds. A neural network model was also developed to predict minimum fluidization velocity. The actual experimental data obtained from published literature and from the experiments carried out in this study were used for training and validating the models. The minimum spouting and fluidization velocities predicted using the neural network models developed in this study show a better approximation to the actual experimental values than those obtained from correlations available in the open literature. The position of flow regime of circular slit spouted bed was also established relative to the flow regimes of central jet spouted bed and fluidized bed.     

Aerodynamics and heat transfer during coating of tablets in two-dimensional spouted bed

The two-dimensional spouted bed has been pointed out in recent research works as an improved configuration of spouted beds. The main advantages in relation to the conventional spouted beds are the easy construction and scale-up. In this work we begin the study of coating of tablets in two-dimensional spouted beds. An experimental system was constructed and the data obtained were used to determine the values of maximum pressure drop, minimum spout flowrate and gas-to-particle heat transfer coefficient, for 36 process conditions. The experimental results have been correlated with process and geometrical parameters.     

Pressure distribution in spout-fluid bed reactors

The occurrence of several flow regimes in spout-fluid beds was investigated. Four different flow regimes, viz. a packed bed flow regime, a bubbling and a fluctuating spouted bed flow regime and a stable spouted bed flow regime, were found to exist. Pressure distributions in a spout-fluid bed were measured in several of these flow regimes by means of a moveable pressure probe. A theoretical model that describes the flow pattern in spout-fluid beds was developed from fundamental relationships that govern the flow of gases through porous media. Pressure distributions calculated from this model agree fairly well with measured values.     

Characterization of Gas Spouted Beds Using the Rescaled Range Analysis

Differential pressure fluctuation measurements were conducted in a gas spouted bed of 120 mm in diameter at different axial and radial positions. Hurst's rescaled range analysis of the differential pressure fluctuation signals was successfully employed to recognize different flow regimes, i.e. packed bed, stable spouting and unstable spouting, and characterize their transitions. Obvious two‐phase behaviour, as suggested by two Hurst exponents, was observed in the stable spouting regime. It had also been found that the spouting behaviour in deeper spouted beds was significantly different from that in shallow spouted beds. The influences of measurement location and bed height on the Hurst exponents were discussed.     

Characterization of spouted bed regimes using pressure fluctuation signals

This work compares time, frequency and phase space analyses of pressure measurements in different spouted beds. The experiments were carried out in different constructions of spouted bed apparatuses, operated under ambient conditions and under different spouting regimes. Spouted beds are used when the conventional fluidized beds fail to achieve a homogeneous and stable flow regime as, for example, in the case of non-spherical particles and in poly dispersed and finely dispersed systems. Different fluidization regimes in spouted beds have been characterized by the analysis of pressure fluctuation signals. Several flow regimes are found to exist as: fixed bed, channel formation, bubbling formation, stable spouting and slugging bed regimes. Analyses of standard deviation and chaotic time series on pressure fluctuation signals are conducted to determine the transition gas velocities. A treatment technique using the Fast Fourier Transformation of measured pressure fluctuations was developed to create plots describing the bed behaviour evolution from fixed to slugging bed. At the beginning of stable spouting the amplitude of pressure fluctuations is uniform and small.     

HYDRODYNAMIC STUDIES IN A HALF SLOT-RECTANGULAR SPOUTED BED COLUMN

Experiments were carried out in a half slot-rectangular spouted bed to investigate the effects of slot width and lower section basal angle on column hydrodynamics. Flow regimes, minimum spouting velocity, spouting and maximum pressure drops, and maximum spoutable bed height were determined for 4 mm diameter polyethylene particles. The results are compared with those for conventional cylindrical and rectangular spouted beds. Correlations for each hydrodynamic parameter are developed and compared with equations available in the literature.     

Local porosity in conical spouted beds consisting of solids of varying density

Local bed voidage has been measured in conical spouted beds by means of an optical fibre, for different geometric factors of the contactor (angle and inlet diameter) and under different experimental conditions (height of the stagnant bed, particle diameter and air velocity). The study has been carried out with glass beads and materials of lower density (high- and low-density polyethylene, polypropylene and extruded and expanded polystyrene). From the results, a correlation has been proposed for calculation of the local bed voidage in the spout and annular zones. The effect of the experimental conditions on the bed voidage in the solid ascent (core) and descent (periphery) regions of the fountain has been studied and the fountain has been proven to be of greater importance in the design of conical spouted beds, as solid density and shape factor are lower.     

Computational fluid dynamics (CFD) modeling of spouted bed: Assessment of drag coefficient correlations

In the computational fluid dynamics (CFD) modeling of gas-solids two-phase flows, drag force is the only accelerating force acting on particles and thus plays an important role in coupling two phases. To understand the influence of drag models on the CFD modeling of spouted beds, several widely used drag models available in literature were reviewed and the resulting hydrodynamics by incorporating some of them into the CFD simulations of spouted beds were compared. The results obtained by the different drag models were verified using experimental data of He et al. [He, Y.L., Lim, C.J., Grace, J.R., Zhu, J.X., Qin, S.Z., 1994a. Measurements of voidage profiles in spouted beds. Canadian Journal of Chemical Engineering 72 (4), 229-234; He, Y.L., Qin, S.Z., Lim, C.J., Grace, J.R., 1994b. Particle velocity profiles and solid flow patterns in spouted beds. Canadian Journal of Chemical Engineering 72 (8), 561-568.] The quantitative analyses showed that the different drag models led to significant differences in dense phase simulations. Among the different drag models discussed, the Gidaspow (1994. Multiphase Flow and Fluidization, Academic Press, San Diego.) model gave the best agreement with experimental observation both qualitatively and quantitatively. The present investigation showed that drag models had critical and subtle impacts on the CFD predictions of dense gas-solids two-phase systems such as encountered in spouted beds.     

Investigation into the viability of a liquid-film three-phase spouted bed biofilter

A variety of technologies exist for the treatment of malodorous air streams, including adsorption, absorption, catalytic combustion, biofiltration and bioscrubbing. Conventional packed bed biofiltration of malodorous substances from waste gas streams has the disadvantages of large unit surface area and relatively uncontrolled design principles. The large bed surface area leads to difficulties in maintaining even moisture and temperature profiles. In addition, the control of such biologically important parameters as pH is difficult. Novel fluidized/spouted beds were studied for biological treatment of gases because of their high specific gas flowrate and vigorous mixing which facilitates enhanced gas–biomass contact. Trials of a range of fluidized and spouted beds, with gas loadings of up to 14000 m³-gas m⁻²-bed h⁻¹, were carried out on various biofilm support media including glass ballotini, rice hulls, plastic discs and granules, silica gel, molecular sieves, vermiculite, perlite, activated carbon, cork, polystyrene and expanded clay. Severe aggregation and wall adhesion restricted the operational range of the reactors. Particle suitability was based on a combination of shape, density, size, porosity and wettability, with large, heavy clay particles performing best. Limited gas-phase bacterial studies on selected media with ammonia- and nitrite-oxidizing bacteria demonstrated the potential of fluidized/spouted beds for efficient biofiltration of ammonia (20–40 mg dm⁻³). © 1998 Society of Chemical Industry     

Energy analysis of intermittent drying in the spouted bed

Abstract

The aim of this study was to evaluate different intermittency ratios applied to a spouted bed used to dry alumina, from the energy perspective. Two types of intermittency (reduction and total interruption of the air flow) and five different intermittency profiles were evaluated, including the use of time-variant intermittency ratios. The use of intermittency provided higher energy efficiency and better use of the energy supplied, compared to the continuous process. Reductions of energy consumption in the range from 13.2% to 67.2% were obtained, relative to the continuous process. The findings showed that the use of intermittency is a promising way to optimize energy consumption in spouted beds.