Pressure Fluctuations in Jet Spouted Beds

Jet spouted beds that consisted of a transparent Plexiglas cylindrical column of 1 m high and a conical base with cone angles of 30°, 36°, and 40° were used in this study. The particles used were spherical glass beads with an average diameter of 1.7, 2.1 and 3 mm, respectively, and particle size of 2.2 – 3.1 mm, non‐spherical rice particles. The effect of size and shape of particles, and static bed height on the minimum jet spouting velocity, and standard deviation of pressure fluctuations, was investigated. The results show that the minimum jet spouting velocity and pressure drop increased as the bed height and particle size increased. The minimum jet spouting velocity could be determined from the plot of standard deviation of pressure fluctuations vs. superficial gas velocity. The results obtained were in close agreement with the results of other methods in the literature.     

Determination of Minimum Spouting Velocities in Conical Spouted Beds

Minimum spouting velocities in conical spouted beds have been obtained from pressure drops versus the superficial gas velocity curves, based on both increasing and decreasing the superficial gas velocity. It has been shown that the minimum spouting velocity from decreasing the superficial gas velocity is lower than from increasing the superficial gas velocity in most cases. This phenomenon is similar to that in conventional spouted beds and different from the early works. The experimental results also showed that there isn't significant difference in the pressure drop and U_ms under identical operating conditions between semi‐circular and circular conical spouted beds, and the same U_ms can be obtained from absolute pressure drops at any position above the gas inlet. The U_ms is found to increase with increasing the cone angle and static bed height, as well as the gas inlet diameter to a less extent.     

Liquid spouting of pulp fibers in a conical vessel

Pulp fibers can be spouted in water in a conical vessel. The entities which are spouted are fiber flocs rather than individual fibers. Synthetic fibers, which do not flocculate, cannot be spouted. For comparison, rigid spherical particles were spouted with water in the same conical vessel. Liquid spouting of rigid particles was similar to gaseous spouting. For pulp spouting, the minimum spouting velocity is proportional to the mass of fibers in the bed and inversely proportional to the diameter of the inlet. For rigid particles, the minimum spouting velocity is proportional to the height of the bed and inversely proportional to the square of the diameter of the inlet. A model for the minimum spouting velocity was developed for pulp spouting.     

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.     

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.     

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.     

Spouting characteristics of spf wood pellets

The spouting characteristics with ambient air of cylindrical wood pellets, 6.5 mm in diameter and 11.1 ± 4.1 mm long, were investigated using a transparent 152.4‐mm diameter semi‐circular cone‐based cylindrical column. Despite the previously unexplored shape of the pellets in the spouted bed mode, the measured minimum spouting velocities at different bed heights, the maximum spoutable bed height and the mean spout diameter above the conical base were all well represented by equations from the literature developed mainly for more rounded particles. Pellet attrition was found to be severe, so that the possible torrefaction of the pellets by the spouting technique without sacrifice of their integrity appears to be unlikely. © 2012 Canadian Society for Chemical Engineering     

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.     

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.     

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.     

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.     

An experimental study of spouting in large sector beds

In a sector spouted bed, fluid is introduced into the bottom at the junction of two vertical walls, the bed forming a sector in horizontal cross-section. The hydrodynamics of beds of 30° sector angle have been studied in equipment of radius up to 0.78 m. The spout radius is greater than would be predicted from standard correlations on small circular beds. The overall pressure drop can be less than 20% of that found for minimum fluidisation. The vertical pressure distribution is given approximately by a quarter cosine function. Minimum spouting velocity decreases with increasing size of bed, loss of spouting being caused by a decrease in fountain height followed by snuffing of the spout by annular solids.     

喷动流化床流动形态变化的试验研究国家

在一个可视化的半圆柱喷动流化床试验台上研究了喷动流化床的流形变化规律。研究表明：随着喷动气量和流化气量的改变,床内会呈现不同的流动形态：固定床、带射流的流化床、喷动床、充气喷动床和喷动流化床。同时研究了量小喷动速度和最小喷动流化速度随喷动管内径、颗粒粒径、静止床高的变化规律,归纳了预测量小喷动速度和最小喷动流化速度的试验关联式,绘制了喷动流化床的流形划分相图。     

Numerical simulation and experimental study of fluid-particle flows in a spouted bed

In this work, the Eulerian-Eulerian multiphase model is used in the computational simulation of fluid dynamics of spouted beds with two different geometries: conical-cylindrical and conical. For the conical-cylindrical spouted bed, the simulated results of radial velocities of particles with a 1.41 mm diameter along bed heights in the range of 0.022 to 0.318 m are compared with experimental values obtained by He et al. [Y.L. He, C.J. Lim, J.R. Grace and, J.X. Zhu, Measurements of Voidage Profiles in Spouted Beds, Canadian Journal of Chemical Engineering, 72 (1994), 229-234], and show a good agreement. The influence of static bed height on the characteristic curve is assessed through simulations using different airflow rates. The respective minimum spouting velocities are compared with experimental values and with values obtained through empirical correlations reported in the literature. The results of the CFD simulations show a deviation of 3.8% when compared with the experimental data, which is less than the aforementioned correlations. The stages of transition from the condition of static bed to spouting bed are presented through the simulation of solids volume fraction distribution and the radial profile of voidage in the spouting region. The characteristic curve and minimum spouting conditions for a simulated conical bed, with glass particles of 6 mm diameter are compared with the experimental results showing deviations of 12.1% for the pressure drop and 5.6% for the minimum spouting velocity.     

Hydrodynamics of a gas-driven gas-liquid-solid spouted bed with a draft tube

A cylindrical gas-liquid-solid spouted bed, driven exclusively by gas flow, has been developed with a high potential for use in biochemical processes, such as a biological wastewater treatment. A plexiglass column with a 152 mm inner diameter was used in combination with a 53 mm inner diameter plexiglass draft tube. Three particle types were studied with densities ranging from 1044 kg/m³-1485 kg/m³ and average particle sizes ranging from 0.7-2.5 mm. Four flow regimes were observed when increasing the gas velocity, including fixed bed, semispouted bed, full spouted bed, and internal circulating fluidized bed. The transition gas velocities between those regimes were experimentally measured and termed as minimum spouting velocity, full spouting velocity, and minimum circulating velocity, respectively. A measurement of the downward particle flux in the annulus was used to identify the minimum spouting velocity, while the particle velocity and dense phase retraction in the annulus were monitored for the full spouting and minimum circulating velocities. All regime transition velocities increased with more dense particles and longer draft tubes. The minimum spouting velocity and full spouting velocity were not affected when varying the nozzle-tube gap, while the minimum circulating velocity increased with longer nozzle-tube gaps. Experiments without a draft tube were carried, though the spouting stability was significantly reduced without the draft tube.     

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.     

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     

纳米TiO_2颗粒在声场导向管喷动流化床中的流化特性

在内径120 mm的半圆柱型声场导向管喷动流化床中,以平均粒径290 nm的TiO_2颗粒为原料,高速空气射流为喷动气,考察了操作条件、声参数(频率和声压)对纳米颗粒在声场导向管喷流床中的流态化特性的影响。结果表明:声波可以有效抑制沟流,改善环隙流化质量,防止射流旁路,从而促使粉体稳定循环,加快循环速率;同时声波可以显著地降低纳米TiO_2颗粒的最小喷动速度,声波频率一定时,最小喷动速度随声压的增加而减小;声压一定时,最小喷动速度在声波频率为80 Hz时达到最小值,低于或者高于80 Hz,最小喷动速度都会增大。     

Minimum spouting velocity of conical spouted beds

Existing correlations for predicting minimum spouting velocity in conical spouted beds have been found to give poor agreement with available literature data. A new correlation has been developed based on literature data to give much better prediction of the minimum spouting velocity for both small and pilot-scale conical-spouted beds.