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.     

Recognition of the flow regimes in the spouted bed based on fuzzy c-means clustering

Hilbert-Huang transformation has been applied to extract eigenvectors from the pressure fluctuation signals in the spouted bed. According on these eigenvectors, the flow regimes in the spouted bed could be classified into 4 clusters including ‘packed bed’, ‘stable spouting’, ‘bubbling fluidized bed’ and ‘slugging bed’ by chaos optimized fuzzy c-means clustering algorithm. The Elman neural network was used to recognize these four flow regimes, and the parameters in the Elman neural network were optimized by adaptive fuzzy particle swarm optimization algorithm. The recognition accuracies of ‘packed bed’, ‘stable spouting’, ‘bubbling fluidized bed’ and ‘slugging bed’ can reach 85%, 90%, 85% and 80% respectively.     

Stability of slot‐rectangular spouted beds: Effect of slot configuration

Experiments were carried out to determine the flow stability of slot‐rectangular spouted beds of 300 × 100 mm cross‐section with slots of different widths, lengths, and depths. The effects of slot expansion angle and diverging base were also investigated. Dependent variables included the minimum spouting velocity, bed pressure drop and standard deviation of pressure fluctuations. Based on the flow regimes and spout termination mechanisms, instability was found to be mainly due to the interaction of multiple spouts. Criteria were identified relating stable spouting to slot dimensions and particle size. Slots of limited cross‐sectional area can provide sustainable and symmetric spouting with little fluctuation, as long as the slot length‐to‐width ratio and depth are within certain limits, related to those for conventional spouted beds.     

Evaluation of flow regimes in a semi‐cylindrical spouted bed through statistical,mutual information,spectral and Hurst's analysis

Hydrodynamic studies were conducted in a semi‐cylindrical spouted bed column of diameter 150 mm, height 1000 mm, conical base included angle of 60° and inlet orifice diameter 25 mm. Pressure transducers at several axial positions were used to obtain pressure fluctuation time series with 1.2 and 2.4 mm glass beads at U/U_ms from 0.3 to 1.6, and static bed depths from 150 to 600 mm. The conditions covered several flow regimes (fixed bed, incipient spouting, stable spouting, pulsating spouting, slugging, bubble spouting and fluidization). Images of the system dynamics were also acquired through the transparent walls with a digital camera. The data were analyzed via statistical, mutual information theory, spectral and Hurst's Rescaled Range methods to assess the potential of these methods to characterize the spouting quality. The results indicate that these methods have potential for monitoring spouted bed operation.     

Hydrodynamics of a Novel Biomass Autothermal Fast Pyrolysis Reactor: Flow Pattern and Pressure Drop

A novel biomass, autothermal, fast pyrolysis reactor with a draft tube and an internal dipleg dividing the reactor into two interconnected beds is proposed. This internally interconnected fluidized beds (IIFB) reactor is designed to produce high‐quality bio‐oil using catalysts. Meanwhile, the pyrolysis by‐products, i.e., char, coke and non‐condensable gases, are expected to burn in the combustion bed to provide the heat for the pyrolysis. On the other hand, the catalysts can be regenerated simultaneously. In this study, experiments on the hydrodynamics of a cold model IIFB reactor are reported. Geldart group B and D sand particles were used as the bed materials. The effects of spouting and fluidizing gas velocities, particle size, static bed height and the total pressure loss coefficient of the pyrolysis bed exit, on the flow patterns and pressure drops of the two interconnected beds are studied. Six distinct flow patterns, i.e., fixed bed (F), periodic spouted/bubbling bed (PS/B), spouted bed with aeration (SA), spout‐fluidized bed (SF), spout‐fluidized bed with slugging (SFS) and spouted bed with backward jet (SBJ) are identified. The investigations on the pressure drops of the two beds show that both of them are seen to increase at first (mainly in the F flow pattern), then to decrease (mainly in the PS/B and SA flow patterns) and finally to increase again (mainly in the SA and SF flow patterns), with the increase of the spouting gas velocity. It is observed that a larger particle size and lower static bed height lead to lower pressure drops of the two beds.     

HYDRODYNAMICS AND STABILITYOF SLOT-RECTANGULAR SPOUTED BEDS. PART I: THIN BED

Spouted beds of rectangular cross-section with gas entry through bottom slots have been proposed as a means of overcoming scale-up difficulties of conventional spouted beds. A study was undertaken of bed hydrodynamics in a thin slot-rectangular column of width 150 mm and slot width 2 to 20 mm for four types of particles. Flow regimes and bed hydrodynamics are qualitatively similar to those in cylindrical spouted beds, but there are significant quantitative differences caused by the different geometry. Slot width exerts a strong influence on such features as flow regimes, maximum spoutable bed height, minimum spouting velocity, pressure drop and fountain height.     

HYDRODYNAMICS AND STABILITYOF SLOT-RECTANGULAR SPOUTED BEDS. PART I: THIN BED

Spouted beds of rectangular cross-section with gas entry through bottom slots have been proposed as a means of overcoming scale-up difficulties of conventional spouted beds. A study was undertaken of bed hydrodynamics in a thin slot-rectangular column of width 150 mm and slot width 2 to 20 mm for four types of particles. Flow regimes and bed hydrodynamics are qualitatively similar to those in cylindrical spouted beds, but there are significant quantitative differences caused by the different geometry. Slot width exerts a strong influence on such features as flow regimes, maximum spoutable bed height, minimum spouting velocity, pressure drop and fountain height.     

Flow Characteristics in Slot‐Rectangular Spouted Beds with Draft Plates

An experimental investigation was conducted of slot‐rectangular spouted beds with air entry slots spanning the full thickness of the column and vertical draft plates intended to help control the solids circulation rate. With increasing superficial gas velocity, the flow between the draft plates changed from bubbling to slugging and then to spouting with dilute pneumatic between the plates and moving‐bed downward motion on both sides. However, there was difficulty maintaining stability and symmetrical flow on the two sides. Once spouting is established, pressure drops and local voidages vary with gas velocity, particle size and gas entry size in broadly similar manners as for conventional spouted beds     

Flow regime recognition in the spouted bed based on Hilbert-Huang transformation

Empirical mode decomposition has been used to decompose the pressure fluctuation signals in the spouted bed into several intrinsic mode functions, and these modes were transformed from the time domain into the frequency domain by Hilbert transformation. According to the characteristic parameters extracted from these modes, flow regimes were recognized by RBF neural network, and parameters in RBF neural network were optimized by adaptive genetic algorithm. The recognition accuracy of packed bed, spouted bed, bubbly fluidized bed and slugging bed can reach 90%, 85%, 85%, 95%, respectively.     

Fluid-Dynamic Study of Deformable Materials in Spouted-Bed Dryer

The present work is concerned with a fluid-dynamic study in spouted beds using deformable dice pieces of red guava. Data are presented on structural variations of the bed due to changes of regime during drying. Variation of physical properties (size and density) results from the volumetric shrinkage of these materials. Alterations in the fluid-dynamic stability of the spouted bed were correlated with Archimedes number. Along the process, the transition from fixed bed to fluidization can be observed, followed by stable spout and slugging. Mapping of the different regimes as a function of the moisture content is also presented.     

Characterization of the pneumatic behavior of a novel spouted bed apparatus with two adjustable gas inlets

Recently the importance of spouted bed technology has significantly increased in the context of drying processes as well as granulation, agglomeration or coating processes. Within this work the fluid dynamics of a novel spouted bed plant with two adjustable gas inlets is investigated. By analysis of gas phase pressure fluctuation spectra by means of fast Fourier transformation algorithm and quantitative particle image velocimetry (PIV) measurements, different operation ranges will be identified and depicted graphically. A stable spouting range will be identified if a uniform and circulating particle motion without occurrence of dead zones is observable resulting in equal gas phase pressure fluctuations. Particle velocity vector maps as well as root mean square (rms) velocity plots provided by the PIV measurements confirm the results of the determination of the stable spouting range by analysis of the gas phase pressure fluctuations.     

Pressure drop in slotted spouted beds of grains: Comparison of data with models

Data obtained in a rectangular slot spouted bed for two different grains (wheat and oats) have been analyzed to determine the minimum spouting velocity (V_ms) and the minimum spouting pressure drop (ΔP_ms) as a function of the bed height.Three different aerodynamic regimes occur as the bed height is increased.The results are compared with the literature models for the conventional (conical-cylindrical) spouted bed.For shallow beds, the experimental minimum spouting velocity and minimum spouting pressure drop can be well represented by the Littman et al.'s two-dimensional model.     

Characterization of dynamic behavior of a spout-fluid bed with Shannon entropy analysis

Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds.     

Hydrodynamics and heat transfer of spouted beds with a two-component (gas-solid) dispersing medium

Experimental studies of hydrodynamics and interphase heat transfer in spouted beds, with aerosol as the dispersing media, have been conducted in conic-cylindrical columns. The effects of various column geometries, dust fraction concentrations, dispersed materials and operation parameters have been investigated to find new ways of using the spouting technique for treating fine dispersed materials. The qualitative spouting mechanism of two-component dispersing media is elucidated. The effect of dust concentration in the incoming gas flow and of the principal operation and design parameters on the structure, pressure drop, and dust accumulation in the bed and on the interphase heat transfer in ordinary and swirled spouted beds is shown.     

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.     

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.     

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.     

The spouting regime map,bubbling characteristics and bed expansion of deep beds of large hollow polyethylene spheres

The high velocity spouting regime of a deep bed containing 9.6 mm hollow polyethylene spheres of density 394 kg/m³ was investigated in a 152.4 mm flat bottom cylindrical half column with a 50.8 mm inlet. A bed height vs gas velocity regime diagram is presented showing the conditions under which type II spouting is observed. The transition velocity from bubbling to type II spouting is determined using the autocorrelation of the pressure fluctuations in the bed. The bubbling characteristics of the bed are described. Bed expansion in bubbling and type II spouted beds are reported.     

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.     

Intelligent identification of the flow regimes of two-component particles in a fluidized bed with the optimized fuzzy c-means clustering algorithm

Flow regime identification is important in the application of fluidized beds. This paper provides a method for deciding flow regime number by objective criterion. The optimized fuzzy c-means clustering algorithm was used to cluster the flow regime classification of two-component particles in a fluidized bed. The genetic algorithm was applied to optimize the initial center clusters of fuzzy c-means clustering. Hilbert-Huang transform was applied to analyze pressure fluctuation signals and extract the characteristic parameters. Three clusters were found and respectively ascribed to three flow regimes: bubbling bed, slugging bed, and turbulent bed. A multilayer neural network was used to train and test the identification system of the flow regimes. The identification accuracies of bubbling bed, slugging bed, and turbulent bed can reach 91.67%, 92.85%, and 91.30%, respectively.