Study of the hydrodynamics within a draft tube spouted bed system

Two dimensional Darcy and Ergun models are used to describe the hydrodynamics within the annulus of a spouted bed equipped with a draft tube. Experimental pressure and stream function data for water spouting are shown to be in good agreement with theoretical predictions. Verification of a general spout-annulus interfacial boundary condition is also established and it is shown that the entry region below the draft tube functions as a classical spouted bed. In addition, an experimental procedure for determining the location of the spout-annulus interface is presented. Fluid residence time distributions are calculated for a few cases of practical interest.     

喷动床内气固二相流动行为的计算模拟

采用双流体模型结合颗粒动理学理论对喷动床内气固二相流体流动行为进行了计算模拟研究。模型中运用颗粒动理学理论描述颗粒相应力封闭流体控制方程,使用Gidaspow曳力模型描述气固相间作用。喷动床内颗粒在浓相区的体积分数很大,采用Schaeffer′s模型描述颗粒间的摩擦应力。模拟计算结果表明,喷动床内分喷射区、喷泉区、环隙区3个区域,在射流入口处形成一个瓶颈。模拟计算得到的颗粒速度和空隙度分布与实验数据进行比较,计算结果与实验结果吻合较好。     

A mathematical model of a spouted bed gasifier

A mathematical model of the spouted bed gasifier has been constructed based on simplified first order reaction kinetics for the gasification reactions and the stream tube hydrodynamic model of Mathur and Lim. This two region model treats the spout as an isothermal plug flow reactor with cross flow into a series of streamtubes forming the annulus. Each streamtube is considered as a plug flow reactor. The effects of kinetic and hydrodynamic parameters on model predictions are illustrated, and a comparison made with experimental gas composition profiles obtained in a 0.30-m dia. gasifier.     

双喷嘴矩形喷动床流动性能实验研究

在120 mm×240 mm的双喷嘴矩形不锈钢床内,对新型双喷嘴矩形导流管喷动床的最小喷动速度和喷动高度进行了研究,考察了喷动气速、粒径、静床层高度、导流管直径、导流管安装位置对最小喷动速度和喷动高度的影响。结果表明:最小喷动速度随颗粒直径、导流管直径、导喷距的增大而增大,随静床层高度的增大而减小;喷动高度随喷动气速的增大而增大,随导流管直径的增大而减小,受静床层高度和导喷距的影响不大,并得出了最小喷动速度的关联式。     

The maximum spoutable bed heights of fine particles spouted with air

The maximum spoutable bed heights of systems of fine glass spheres spouted with air are studied in flat based semi circular columns of 80 and 152.4 mm diameters using particles with average diameters ranging from 0.3 to 1.3 mm. New correlations are proposed to predict the maximum spoutable bed heights of air spouted fine particle systems. It is concluded that the influence of the column diameter on the maximum spoutable bed height is significantly decreased compared to coarse particle systems and that it further varies with particle size within the fine particle spouting regime. Data reported in the literature agree with the proposed correlations.     

Spouted bed and spout-fluid bed behaviour in a column of diameter 0.91 m

Hydrodynamic measurements were obtained in a half-column of diameter 0.91 m equipped with a conical base using particles of diameter 3.3 to 6.7mm with operation both as pure spouted beds and in the spout-fluid bed mode. Comparison of the experimental results for minimum spouting velocity with equations in the literature generally gave unsatisfactory agreement. On the other hand, the correlations of McNab (1972) and Had?isdmajlovi? et al. (1983) gave reasonable predictions of spout diameters in spouted and spout-fluid beds respectively. Hydrodynamic regimes with auxiliary air present were broadly similar to those determined in smaller columns. However, there were substantial dead regimes at the bottom of the column. A finite difference model based on the vector form of the Ergun equation gave good predictions of air flow distribution and longitudinal pressure profiles.     

Side-outlet spouted bed with draft tube: Effect of varying the position of the outlet

The vector form of the Ergun equation was used to numerically predict gas phase streamlines, residence time distributions, chemical conversions and pressure drops in the annulus of a side-outlet spouted bed with an internal draft tube. By varying the position of the side-outlet, it was demonstrated that there exists an optimum location for this outlet at which conversion is a maximum and which shows a greatly improved gas phase residence time distribution in the annulus compared with a conventional spouted bed unit.     

Flow in the annulus of a bed of fine particles spouted with water

The flow in the annulus of a water spouted bed of glass particles (275 to 774 μm) was studied experimentally in a cylindrical half-column 50.8 mm in diameter. An axisymmetric model, which assumes Darcy flow in the annulus and uses the experimental spout pressure distribution, predicts the flow and pressure fields in the annulus. The substantial differences between this flowfield and that for coarse particle beds that are observed are caused by differences in the normalized interfacial pressure profile. The model predicts that both the fluid velocity and the normalized fluid velocity at the top of the annulus decrease as the particle size and bed height are reduced. Particles are observed to enter the spout primarily near the spout inlet in agreement with predictions of the axial spout voidage distribution. The residence time distribution of the fluid in the annulus is relatively broad and the measured residence times are about 25% higher than those calculated.     

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.     

Oxygen-steam gasification of coals in a spouted bed

A bituminous and a sub-bituminous coal from Western Canada have been gasified in oxygen-steam and air-steam mixtures in a 0.30-m diameter, 50 kg coal/h continuous spouted bed reactor. Results are presented to show the effects of the blast composition and reactor temperature on gas heating value and carbon conversion. Operation in the ash agglomeration mode is illustrated, and the role of K₂CO₃ as catalyst explored. Results from a wide range of experimental gasification conditions are compared with predictions of an equilibrium model.     

喷动流化床造粒实验研究

喷动流化床用于粉体造粒，是一种新型的造粒方法。与其它几种造粒方法相比．具有设备投资省、能耗低、设备结构简单等优点。作者经过实验发现，气流雾化器安装于底部或侧部，或是二者结合。可实现对多种粉体的造粒和包衣。气流雾化喷嘴是喷动流化造粒装置的主要部件。为此对气流雾化喷嘴作了一些实验研究。     

Ash-agglomerating gasification of coal in a spouted bed reactor

Australian bituminous coal (Hoskisson) was gasified with oxygen and steam in a 0.4m diameter spouted bed reactor at atmospheric pressure and temperatures of 1050–1170 °C to produce medium calorific value gas. High-ash agglomerates fell through the throat of the spouted bed under restricted gasification conditions, with no simultaneous loss of coal. The effects of temperature, steam-oxygen ratio, coal feed rate and coal size on carbon conversion, production of ash agglomerates, gas composition and decompsition of steam were established.     

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.     

A model for gas flow in jet spouted beds

A model of general application that is based on the definition of streamlines and that is in agreement with the bed geometry has been proposed in order to describe the gas flow in a jet spouted bed in conical contactors. The model quantifies the dispersion in the direction of the streamlines by using a characteristic modulus. The validity of the model has been experimentally proven on the basis of the measurement and analytical correlation of gas velocity profiles at different radial and longitudinal positions in the contactor, and of the application of the stimulus response technique for the calculation of the residence time distribution function.     

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.     

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     

Hydrodynamics of shallow,conical spouted beds

Experiments were conducted with shallow beds, in the presence of atomizing air injected into the base, under the following conditions: Particles — urea, sulphur coated urea, polyethylene, polyformaldehyde and polystyrene; particle diameters (d_p) – 2.1 to 2.8 mm; cone angle – 60°; cylindrical bed diameter (D) – 0.24 and 0.45 m; bed height (H) – 0.24 to 0.40 m; orifice diameter (d_i) – 21 to 35 mm; main spouting air (Q_s) ≤ 37 L(actual)/s; atomizing air (Q_a) ≤ 0.87 L(actual)/s. The minimum spouting velocity is well represented by: U_ms = 13.5 (2gH)^0.5 (d_p/D')^1.17 (D'_i/D')^0.372 (H/D')^?0.148 [(τ_p - τ)/τ]^0.289 where D' and D'_i denote the modified column and orifice diameter, respectively. Q_a, which affects D'_i, significantly influenced the air velocity in the spout, but not the pressure profiles in the annulus. Morgan and Littman's (1980) correlation could be adapted to predict the experimental pressure profiles in the annulus.     

循环喷动流化床颗粒抛射高度的计算

通过对循环喷动流化床顶部封闭空间气体射流及气固运动的理论分析 ,得出了循环喷动流化床中颗粒出循环管后抛射高度的计算方法 ,所得计算结果与实测结果误差小于 8% ,为循环喷动流化床的设计提供理论依据     

双喷嘴矩形导流管喷动床喷动压降

引言 传统的柱锥形喷动床(CSBs)的应用受到一些因素的限制,例如处理物料能力、起始压力大及难以放大等,为此,Romankov等[1]最早提出了长方形截面的矩形喷动床结构,来克服CSBs的缺点.此后,Rocha等[2]用矩形喷动床进行了片剂包衣的研究.