Minimum fluidization velocity at elevated temperature in tapered fluidized bed

Very little data of minimum fluidization velocity at elevated temperatures of tapered bed are available in the literature. This study was undertaken to provide some data under elevated temperature conditions in tapered bed. Data on minimum fluidization velocity have been obtained experimentally for temperature up to 800 °C in case of 0.5 mm diameter of sand particles and up to 500 °C in case of 1 mm diameter of glass beads in tapered bed. An equation valid for the bed has been developed in terms of Archimedes number and Reynolds number. The experimental values for minimum fluidization velocity at elevated temperatures have been compared with the calculated values obtained from present equation and from earlier equations developed by other authors for ambient conditions in conventional (cylindrical) bed and tapered bed. Fairly good agreement was found to exist between the calculated (from present equation) and the experimental values.     

Pressure and temperature effects on the hydrodynamic characteristics of ebullated-bed systems

Experiments were performed to study the hydrodynamic characteristics of ebullate-bed systems operated under conditions of high pressure and temperature. The effects of these variables on bed porosity and the liquid minimum fluidization velocity were determined and a correlation has been proposed as a criteria for determining flow regime transitions between the dispersed and coalesced bubble flow regimes. The bed porosity has been described with the pseudo-fluid model. The minimum fluidization velocity data were contrasted with predictions from empirical correlations reported in the literature.     

Modification and re-interpretation of Geldart's classification of powders

In developing his powder classification, Geldart [D. Geldart, Powder Technol. 7 (1973) 285.] employed fluidization data obtained only at ambient temperature and pressure and from beds fluidized only with air. Unfortunately, industrial applications of fluidized bed technology invariably are at elevated pressure and temperature and with fluidizing gas other than air. Geldart classification of powders does not apply at elevated pressure and temperature. There are ample evidences reported in the literature indicating that normally Geldart Group B powders at ambient conditions, such as polymer particles, can behave like a Group A powder under polymerization conditions at elevated pressure and moderate temperature with substantial emulsion-phase expansion, relatively small bubbles, smooth fluidization, and reduced gas bypassing [J.R. Grace, Can. J. Chem. Eng. 64 (1986) 353; I.D. Burdett, R.S. Elsinger, P. Cai, K.H. Lee, Gas-phase fluidization technology for production of polyolefins, in Fluidization X, Eds. M. Kwauk, J. Li, W.C. Yang, 2001, pp. 39-52; P.N. Rowe, P.U. Foscolo, A.C. Hoffmann, J.G. Yates, X-ray observation of gas fluidized beds under pressure, in Fluidization IV, Eds. D. Kunii, R. Toei, 1983, pp. 53-60]. Similar findings were also reported for Geldart Group B powders fluidized by supercritical carbon dioxide at elevated pressures [C. Vogt, R. Schreiber, J. Werther, G. Brunner, Fluidization at supercritical fluid conditions, in Fluidization X, Eds. M. Kwauk, J. Li, W.C. Yang, 2001, pp. 117-124; C. Vogt, R. Schreiber, G. Brunner, J. Werther, Powder Technol. 158 (2005) 102; D. Liu, M. Kwauk, H. Li, Chem. Eng. Sci. 51 (1996) 4045; M. Poletto, P. Salatino, L. Massimilla, Chem. Eng. Sci. 48 (1993) 617; A. Marzocchella, P. Salatino, AIChE J. 46 (2000) 901].The original Geldart's classification is modified and re-interpreted in this paper by plotting a dimensionless density against the Archimedes number. The new parameters allow powders with different properties fluidized at different pressures and temperatures with gases of different properties to be plotted in the same graph. The proposed modification successfully transforms the normally Geldart Group B particles at ambient conditions to Group A classification when fluidized at elevated pressure and temperature. The selection of these two parameters, the dimensionless density and the Archimedes number, for plotting is not arbitrary, however. The experimental and theoretical development is discussed.     

Vapor-liquid equilibrium behavior of the ethane—n-butane—n-hexane system

A high pressure visual cell was designed and constructed for the study of vapor-liquid equilibria of rnulticomponmt systems at elevated temperatures and pressures. One of the unique features of this vapor-liquid equilibrium cell facility resides in the ability to measule pressures using a transducer connectcd directly to the equilibrium chamber of this cell. In addition, the design of this cell, incorporated the capability to permit the withdrawal of vapor and liquid microsamples from the respective phases in equilibrium. The composition of these microsamples was established with a gas chromatographic facility provided with a thermal conductivity detector. The overall performance of this vapor-liquid equilibriiini facility was tested on the system ethane-n-butane for which reliable vapor-liquid equilibrium data are already available in the literature. Five different charges of the ethane-n-butane-n-hexane system were investigated with this facility for temperatures ranging from 48.3 up to 143.5°C and pressures up to 7619 kPa (75.19 atm). For these conditions, K-values were established from the experimental measurements on this ternary system. K-values calculated using the BWR-method for conditions corresponding to the experimental measurements produced K-constants that were in good agreement with the measured values. For these calculations, the original BWR-equation, constants and mixing rules were employed.     

On the relationship between operating pressure and granular temperature: A discrete particle simulation study

Low density polyethylene and polypropylene are produced at large scale via the UNIPOL™ and SPHERIPOL™ process. In this process catalyst particles are fluidized with monomer gas that reacts with the catalyst particles to form polymeric particles up to a size of 1 mm. The process is typically operated at pressures of 20 to 25 bar. Pressure impacts the hydrodynamics of the fluidized bed as it influences the bubble behaviour, particle mixing and heat transfer characteristics. Despite decades of research on fluidized beds these effects are not completely understood.In order to gain more insight in the effects of operating pressure on the fluidization behaviour we have performed full 3D discrete particle simulations. We used a state-of-the-art discrete particle model (DPM) to simulate fluidization behaviour at different pressures. In our model the gas phase is described by the volume-averaged Navier-Stokes equations, whereas the particles are described by the Newtonian equations of motion. The DPM accurately accounts for the gas-particle interaction, which is necessary for capturing the pressure effect.In order to study the pressure effect on the granular temperature, we analysed seven simulations with operating pressures ranging from 1 to 64 bar. It was found that the granular temperature increases with pressure. This is mostly caused by the increased porosity at elevated operating pressures. The granular temperature is anisotropic: it is larger in the vertical direction. Also the pressure dependency of the granular temperature is larger in the vertical direction.     

Hydrodynamics of a superheated steam vacuum fluidized bed

Hydrodynamics of a superheated steam vacuum fluidized bed was experimentally studied. In these experiments, eight different types of large particles (1970–7430 μm) were used. In all cases, a behavior similar to that found in an air fluidized bed was observed. The minimum fluidization velocity was found to be increasing with decreasing operating pressure. In the case of employing superheated steam, the minimum fluidization conditions are established at a lower velocity than using air as the fluidizing medium. These tendencies are attributed to the variation of the mean free path of molecules. On the other hand, the experiments showed that the bed voidage in the minimum fluidization conditions is almost insensitive to the variation of the operating pressure. Several equations were developed to predict the minimum fluidization velocity. The values provided by these equations were compared with the experimental data as well as with the predictions of the correlations presented in the technical literature.     

Minimum fluidization velocity at elevated temperatures and pressures

A procedure based on the Ergun equation to predict the minimum fluidization velocity at elevated temperatures and pressures and for different gaseous fluidizing agents has been discussed and shown to be applicable for practical purposes.     

Effect of elevated temperature and silica sand particle size on minimum fluidization velocity in an atmospheric bubbling fluidized bed

The impact of temperature and particle size on minimum fluidizing velocity was studied and analyzed in a small pilot scale of bubbling fluidized bed reactor. This study was devoted to providing some data about fluidization to the literature under high temperature conditions. The experiments were carried out to evaluate the minimum fluidizing velocity over a vast range of temperature levels from 20℃ to 850℃ using silica sand with a particle size of 300-425 μm, 425-500 μm, 500-600 μm, and 600-710 μm. Furthermore, the variation in the minimum fluidized voidage was determined experimentally at the same conditions. The experimental data revealed that the U_mf directly varied with particle size and inversely with temperature, while ε_mf increases slightly with temperature based on the measurements of height at incipient fluidization. However, for all particle sizes used in this test, temperatures above 700℃ has a marginal effect on U_mf. The results were compared with many empirical equations, and it was found that the experimental result is still in an acceptable range of empirical equations used. In which, our findings are not well predicted by the widely accepted correlations reported in the literature. Therefore, a new predicted equation has been developed that also accounts for the affecting of mean particle size in addition to other parameters. A good mean relative deviation of 5.473% between the experimental data and the predicted values was estimated from the correlation of the effective dimensionless group. Furthermore, the experimental work revealed that the minimum fluidizing velocity was not affected by the height of the bed even at high temperature.     

Modeling viscosity of methane,nitrogen, and hydrocarbon gas mixtures at ultra-high pressures and temperatures using group method of data handling and gene expression programming techniques

Accurate gas viscosity determination is an important issue in the oil and gas industries. Experimental approaches for gas viscosity measurement are time-consuming, expensive and hardly possible at high pressures and high temperatures (HPHT). In this study, a number of correlations were developed to esti-mate gas viscosity by the use of group method of data handling (GMDH)-type neural network and gene expression programming (GEP) techniques using a large data set containing more than 3000 experimen-tal data points for methane, nitrogen, and hydrocarbon gas mixtures. It is worth mentioning that unlike many of viscosity correlations, the proposed ones in this study could compute gas viscosity at pressures ranging between 34 and 172 MPa and temperatures between 310 and 1300 K. Also, a comparison was performed between the results of these established models and the results of ten well-known models reported in the literature. Average absolute relative errors of GMDH models were obtained 4.23％, 0.64％, and 0.61％for hydrocarbon gas mixtures, methane, and nitrogen, respectively. In addition, graph-ical analyses indicate that the GMDH can predict gas viscosity with higher accuracy than GEP at HPHT conditions. Also, using leverage technique, valid, suspected and outlier data points were determined. Finally, trends of gas viscosity models at different conditions were evaluated.     

大差异双组分混合颗粒的最小流化特性

在一套f260 mm′2000 mm的有机玻璃实验装置中,对大差异双组分混合颗粒的最小流化特性进行了实验研究,得到了混合颗粒的流化曲线,由此给出了其起始流化速度、最小流化速度、临界分离速度、完全流化速度等特征速度. 实验结果表明,流化过程可分为4个阶段,即完全流化、大小颗粒分离、大颗粒静止小颗粒流化、固定床阶段,对应混合颗粒的3个状态：完全混合、部分混合部分分离、完全分离状态;混合颗粒的特征速度随小颗粒质量分率的增加而减小,且在小颗粒质量分率达到0.4~0.5后其减小的趋势减缓;混合颗粒的固定床阶段和完全流化阶段的床层空隙率及混合颗粒的体积收缩比在小颗粒质量分率为0.4时达到极值.     

Gas-liquid equilibria in mixtures of hydrogen and thianaphthene

Gas-liquid equilibrium conditions in binary mixtures of hydrogen and thianaphthene were experimentally determined at temperatures of 190 to 430°C and pressures to 250 atm in a flow apparatus. The same apparatus was also employed to measure the vapor pressure of thianaphthene. Comparisons of the new mixture data with Chao-Seader and Grayson-Streed correlations show that both correlations predict the thianaphthene equilibrium ratios well but are in error by up to about 45 and 35% respectively for K-values of hydrogen.     

Minimum Fluidization Velocity At High Temperatures Based on Geldart Powder Classification

The minimum fluidization velocities of sand, ilmenite, limestone and quartz magnetite were determined at temperatures ranging from 373–973 K. A best fit of the Wen and Yu type of equation was obtained for the experimental data. This correlation was extended to all experimental data obtained by various workers at high temperatures and was also compared with the existing correlations. However, a very high error percentage was obtained (> 50 %). The Geldart Powder Classification was made use of in classifying all materials used by different workers, as A, B and D, based on the material properties i.e., density and particle size. According to Geldart, C type powders are highly cohesive and hence cannot be subject to normal fluidization. Separate correlations were fitted for A, B and D type powders. Fitting separate correlations reduced the error by a considerable amount. Thus, the usage of separate correlations to predict the minimum fluidization velocity for A, B and D type powders was substantiated.     

Vapor-liquid equilibrium behavior for the propane-acetone system at elevated pressures

The vapor-liquid phase behavior of the propane-acetone system under equilibrium conditions has been established experimentally at 325, 350, 375, 400 and 425 K. Under these conditions pressures up to 4666.4 kPa (676.8 psia) were obtained. The composition of the vapor and liquid phases in equilibrium, in conjunction with data available in the literature for the critical state behavior of this system, has permitted the establishment of the complete vapor-liquid equilibrium behavior of the propane-acetone system for temperatures ranging from 325 K up to the critical temperature of acetone (T_c = 508.1 K). The K-constants resulting from this experimental study when related to pressure produced isothermal relationships that follow a normal behavior and which do not exhibit any azeotropic tendencies.     

Characteristics of fluidization at high pressure

Experiments were conducted to investigate fluidization fundamentals at pressures up to 6485 kPa using nitrogen as the fluidizing gas. The particles under study were coal, char and Ballotini. Both a three-dimensional bed (10.16-cm-i.d.) and a two-dimensional bed (1.9x 10.16cm) were used in the experiments. The fundamentals of high pressure fluidization examined in this study include minimum fluidization velocity, bed voidage at minimum fluidization, bed expansion, and bubbling behavior. An empirical correlation was developed for determining minimum fluidization velocity. The effects of pressure upon bed voidage at minimum fluidization and expanded bed height were analyzed for several types of particles. High speed photographs were studied to describe bubbling behavior in a fluidized bed over a range of pressures.     

液固流化床中铜颗粒流化特性的研究

以球形铜颗粒为原料,水为流化介质,在横截面为50mm×15mm的液固流化床中,考察不同平均粒径铜颗粒的流化特性。并基于Richardson-Zaki的关联式,提出符合本实验条件计算空隙率方程中指数n的关联式。     

Hydrodynamics of Reduced Pressure Fluidization Employing Particles with Variable Density

A series of experiments was carried out to study the hydrodynamics of a fluidized bed operating at reduced pressure and employing particles with variable moisture content; that is, of variable density. In these experiments, four different types of particles were used and fluidization characteristics very similar to the ones encountered in atmospheric pressure operations were observed. A novel method to measure the minimum fluidization velocity of particles with varying density was proposed. The experimental results demonstrated that the minimum fluidization velocity increased with decreased operating pressure, increased operating temperature, and increased particle moisture content. However, the bed voidage under minimum fluidization conditions showed very little sensitivity to variations in operating pressure. Two equations were developed to predict the minimum fluidization velocity and the results were compared with the experimental data as well as with the predictions of equations available in the technical literature.     

Minimum fluidization velocity and gas holdup in gas–liquid–solid fluidized bed reactors

Experiments were performed to study the hydrodynamics of a cocurrent three‐phase fluidized bed with liquid as continuous phase. Based on the 209 experimental data (with four liquid systems and five different particles) along with 115 literature data from six different sources on minimum fluidization velocity, a unique correlation for the estimation of minimum fluidization velocity in two‐phase (u_g = 0) as well as in three‐phase systems is developed. A data bank consisting of 1420 experimental measurements for the fractional gas phase holdup data with a wide range of variables is used for developing empirical correlations. Separate correlations are developed for two flow regimes observed in this present work. The proposed correlations are more accurate and simpler to use. © 2002 Society of Chemical Industry     

Fluidization and mixing of solids distributed in size and density

This article presents a study of the fluidization of solids dispersed in size and density simultaneously. Minimum and complete fluidization velocities of these solids are measured and compared with their U_mf distribution. Extensions of some correlations established for binary mixtures are also proposed. The axial mixing state of the beds near these two velocities is then evaluated by sampling, and expressed in terms of several indices: size index, density index and the combined U_mf index. In contrast with U_mf, the axial profile of the bed is mainly controlled by the density distribution of the materials. An index based on the pressure drop along the bed height gives an on-line indication of that segregation.     

Gamma-Ray method for measuring liquid expansion coefficient at high temperatures and pressures

Expandable vessels were designed to measure the density and thermal expansion coefficients of liquid at elevated temperatures and pressures by the gamma-ray attenuation method. Light Arabian vacuum bottoms was tested from 70°C to 300°C at 13.8 MPa. Results agree well with literature data.     

Effect of elevated temperature and silica sand particle size on minimum fluidization velocity in an atmospheric bubbling fluidized bed

The impact of temperature and particle size on minimum fluidizing velocity was studied and analyzed in a small pilot scale of bubbling fluidized bed reactor. This study was devoted to providing some data about fluidization to the literature under high temperature conditions. The experiments were carried out to evaluate the minimum fluidizing velocity over a vast range of temperature levels from 20 °C to 850 °C using silica sand with a particle size of 300–425 μm, 425–500 μm, 500–600 μm, and 600–710 μm. Furthermore, the variation in the minimum fluidized voidage was determined experimentally at the same conditions. The experimental data revealed that the U_mf directly varied with particle size and inversely with temperature, while ε_mf increases slightly with temperature based on the measurements of height at incipient fluidization. However, for all particle sizes used in this test, temperatures above 700 °C has a marginal effect on U_mf. The results were compared with many empirical equations, and it was found that the experimental result is still in an acceptable range of empirical equations used. In which, our findings are not well predicted by the widely accepted correlations reported in the literature. Therefore, a new predicted equation has been developed that also accounts for the affecting of mean particle size in addition to other parameters. A good mean relative deviation of 5.473% between the experimental data and the predicted values was estimated from the correlation of the effective dimensionless group. Furthermore, the experimental work revealed that the minimum fluidizing velocity was not affected by the height of the bed even at high temperature.