When a tumbling particle bed in a horizontal rotating drum is aerated, the particle bed can be considered as a gas fluidized bed, which may be called a fluidized bed in rotating drum (FBRD). Measurement of the residence time distribution (RTD) of gas in an FBRD of coarse particles was carried out by the stimulus-response method using a bench-scale rig. The concentration change of nonadsorbing tracer gas (methane) in the exit stream, as the response to a pulse input, was measured by a flame ionization detector connected with PC data acquisition system. The results of the experiments revealed that the RTD of gas was affected by the parameter ξ, which included aeration rate and rotation speed of drum, and aeration angle. Backmixing of gas was found for large ξ. The reactor efficiency, calculated from the real RTD functions, was close to that of the packed bed and was distinctly higher than that of the conventional bubbling fluidized bed for small ξ. Finally, the reactor efficiency of the FBRD was represented in terms of parameter ξ.
A model was proposed to describe the expansion behavior of a gas fluidized bed of fine particles by using the elastic wave velocity. The difference between the maximum bed voidage in homogeneous fluidized beds, εmb, and the emulsion-phase voidage in bubbling beds, εe could be explained by the proposed model. These voidages were calculated by comparing the voidage propagation velocity with the elestic wave velocity, the latter being represented as a function of the volume elasticity and the rigidity for uniformly expanded beds. In the emulsion phase of bubbling fluidized beds, however, the rigidity was neglected. This difference reflected the fact that εmb was larger than εe in any gas–solid system of fine particles. Since it was difficult to formulate quantitatively the value of the elastic wave velocity based on the theoretical approach, it was modified by experimental data in the literature.
The velocity and the axial dispersion of solids within a bed (50 mm in inner diameter, 3600 mm in height) with high gas velocity were analyzed by impulse response of tracer particles. FCC-particles (“group A” powder according to Geldart classification) were employed for the present investigation. Local particle velocity at the axis of the bed increased with increased gas velocity, while the fraction of solids decreased. The axial dispersion coefficient within the bed ranged from 1 to 900 cm2/s. This result suggested unsteady and random behaviour of solids within the fast fluidized bed. Local slip velocity at the axis of the bed was mostly larger than the terminal velocity of a single particle.
The flow structure and mixing characteristics of a high-viscosity fluid in an agitated thin-film evaporator with vertically aligned multiple blades were investigated by measuring the material exchange rate between the fillet and film using an electro-conductivity method. The optimum design of an agitated thin-film evaporator with multiple blades was studied. The results show that vertically aligned multiple blades can strongly promote the material exchange between the fillet and film compared with a conventional single blade. Furthermore, it is shown that the optimum distance between the vertically aligned blades can be determined by the mixing Reynolds number and the number of blades required can be estimated from the material exchange rate.
The transfer rates of Na+ , K+, Mg2+ and Ca2+ across a cation exchange membrane were investigated. Two models were examined to explain the experimental results. The first model is based on the ion exchange equilibrium at the membrane surface, the second on the nonequilibrium exchange kinetics at the membrane surface and within the membrane. The transfer rates calculated by the second model were in good agreement with the experimental results for both monovalent and divalent ions.
In recent studies of cake filtration, a new deliquoring technique called as “filtration consolidation” was proposed. It is principally based on the mechanism of non-unidimensional filtration and gives a highly compacted cake without any additional mechanical load. To investigate the deliquoring mechanism of filtration consolidation in detail, it is essential to find a relation between liquid pressure PL and solid compressive pressure PS in non-unidimensional filter cake. Accordingly, a generalized PL–PS relation applicable to any cake profile and filtrate flow pattern of complicated geometry is derived in terms of an orthogonal curvilinear coordinate system. It is also shown that, starting from the generalized equation, all the PL–PS relations already reported for non-unidimensional filter cakes of relatively simple geometries can be easily reduced.
A methodology for developing a computer-based system that can generate a sequence of operations for starting up a chemical plant is given by making use of AI technology. A computer-based system has been developed on the basis of such methodology and applied to the start-up of a practical chemical plant: a subprocess of an existing ethylene plant. To facilitate the use of heuristic knowledge at each stage of decision-making during the generation of operating procedures, where relatively higher-level knowledge is needed, another inference mechanism, called HIGH-LEVEL INFERENCE ENGINE, is introduced by using a PROLOG-like logical programming paradigm. A knowledge base is also organized in a generic fashion so that the system can be applied to chemical plants in general.
To obtain a simple method for determining filtration characteristic values as functions of the applied pressure, filtration experiments are conducted by increasing the applied pressure with time stepwise. A procedure is presented for obtaining such average values as the void ratio eav and the specific filtration resistance αav on the basis of measurements of both the hydraulic pressure within the cake and the accumulated filtrate volume. In addition, an approximate method is developed in which the characteristic values of the local void ratio e and the local specific filtration resistance α are determined as functions of the local solid compressive pressure ps from calculations based upon the overall values of eav and αav of filter cakes. The relations obtained from step-up pressure filtration are fairly consistent with those from constant-pressure filtration and C-P (compression-permeability) cell data. The filtration behavior under constant-pressure and variable-pressure conditions is well evaluated by using these relations.
The compression-permeability characteristics of a solid–liquid mixture can be obtained from the gravitational sedimentation test (in dilute region) and the C-P cell method (in concentrated region). In this paper, two new methods—the centrifugal method for the compression data and the constant-rate compression method for the permeability data—to obtain the characteristics in the intermediate concentration region between the two are presented. In the centrifugal test, the compression data in the intermediate region can be obtained by choosing suitable centrifugal acceleration and measuring the equilibrium height of a sediment. The data are in good agreement with those in the concentrated region. The gravitational sedimentation data, however, show higher porosity because of the friction between the sediment and the inner wall of a cylinder. In the constant-rate compression test, a material is compressed in a C-P cell for a given time at the rate at which the material is kept approximately homogeneous, followed by the permeability measurement. The permeability data based on this method can be combined with C-P cell data and the sedimentation data of an extremely dilute suspension.
Using an order-of-magnitude evaluation, a quantitative evaluation was performed of the natural and Marangoni convections produced in the melt during single-crystal growth by the floating zone method. The Reynolds number, which forms a standard for free interfacial velocity, was described as a function of the Grashof number, Marangoni number and Prandtl number. The results of this theoretical study showed good agreement with previous experimental works using model liquids and a glass melt.
The control of crystal-melt interface shape by crystal rotation rate during Czochralski growth of oxide single crystals was theoretically studied. Effects of the melt properties and operational conditions on the critical crystal rotation rate at which the crystal–melt interface becomes flat were clarified. A method of evaluating the dominant convection in the melt was proposed. Applying this method to previous experimental results for the crystal-melt interface, it was suggested that in most of them Marangoni convection was more dominant than natural convection in the melt. It was shown that the results obtained in this study could adequately explain the previous experimental values of the critical crystal rotation rate.
Extraction rates of zinc with ammonium chloride salts of Amberlite LA-2 in hexane were measured in a horizontal rectangular channel. The experimental results were analyzed by considering the processes of diffusion in both solutions, adsorption and desorption to/from the interface and reactions at the interface for the species related as following steps;
(BHCl)2,org + σ = (BHCl)2,ad (1)
(BHCl)2,ad + ZnCli,aq–(i–2) = (BH)2ZnCl4,ad + (i – 2)Claq– (2)
(BH)2ZnCl4,ad = (BH)2ZnCl4,org + σ (3)
(BH)2ZnCl4,org + (BHCI)2,org = (BH)4ZnCl6,org (4)
2(BH)2ZnCl4,org = ((BH)2ZnCl4)2,org (5)
The extraction rates of zinc was interpreted from the rate equation that the interfacial reaction between (BHCl)2 adsorbed at the interface and zinc chloride in the aqueous solution shown in step (2) is the rate-determining step. Some parameters of the rate equations were estimated.
The continuous demulsification of W/O emulsion under applied A.C. voltage was investigated, using a tubular coalescer. The effects of water-phase holdup, applied voltage and water-droplet size on demulsification rate were investigated, using emulsions prepared under various conditions. The rate was proportional to the –1, 0.5 and 3rd power of water-phase holdup, applied voltage and water-droplet size, respectively. The experimental equation taking these contributions into account showed satisfactory agreement with the observed values. Further, the effects of surfactant, extractant and solvent on the rate were examined and it was found that the combination of the three strongly affects the rate. The energy consumption for continuous demulsification using the present apparatus is several kWh/m3-emulsion, so this coalescer can be applied to industrial processing.
Autoxidations of oleic acid, methyl oleate and ethyl oleate were carried out in the temperature ranges of 343–393 K, 358–378 K and 383–413 K, respectively, and in the oxygen partial pressure range of 0–0.1 MPa. The accumulation and decomposition rates of hydroperoxide were measured under the reaction control condition to obtain the following results. (1) Auto-acceleration in the formation rate of hydroperoxide was clearly observed in the initial stage of the oxidation. (2) A first-order dependence of hydroperoxide formation rate on oxygen partial pressure was found at low oxygen partial pressure, but the rate was almost independent of oxygen partial pressure at comparatively high oxygen partial pressures. (3) A semi-theoretical rate equation of hydroperoxide formation with four kinetic constants was developed to explain the autoxidation behavior of oleic acid and oleates.
Measurements of the circulation time for pseudoplastic liquids in an agitated vessel of 0.128 m diameter equipped with a variety of helical ribbon impellers were carried out in a wide range of apparent Reynolds number by means of a small tracer particle. Seven impellers of different dimensions (clearance between blade and vessel wall, impeller pitch and blade width) were employed in this work. Whilst previous investigators have suggested that the dimensionless circulation time is independent of the Reynolds number, a number of data obtained in this work have proved that the dimensionless circulation time of pseudoplastic liquids with a helical ribbon impeller decreases slightly with decrease in the apparent Reynolds number in the laminar flow region. It was also found that the circulation time increases as the liquid shear-thinning property increases. These results are explained by considering the relation between the motion of a tracer particle and the non-uniformity in viscosity created in a vessel.