A three-dimensional, two-phase model of the simultaneous transfer of momentum, beat and chemical components with variable physical properties was made for a moving-bed furnace for coke combustion. Patankar’s SIMPLER method was employed for the numerical computation. The three-dimensional solutions were obtained on arbitrarily chosen horizontal and vertical cross sections of the furnace by means of a colored graphic display. The numerical experiment using this computational code provided a variety of valuable information necessary for thermal design of a practical sludge-melting furnace. This numerical simulation with the boundary condition based on test-furnace operating data was found useful for scale-up of a commercial furnace.
Vapor pressures of dimethyl, diethyl, diisopropyl and dibutyl succinates were measured in the ranges of 0.6–100, 0.6–100, 0.4–100 and 0.5–15 kPa respectively. The percent root mean square deviations of pressure of the four succinates by fitting the Cragoe equation were 0.36, 0.34, 0.28 and 0.94 respectively. When, in addition to the information for the molecular structure of a substance of interest the value of the normal boiling point, Tb, was known, the Lee-Kesler and Gomez-Thodos equations with values of θ (=Tb/Tc) and Pc obtained from the Joback method were separately applied to the estimation of vapor pressures for the succinates. The equations mentioned above were also extended successfully to the estimation of vapor pressures where only the value of any one datum point at the reduced pressure, in addition to knowledge of the molecular structure, was known.
Furfural formation from xylose is a typical successive reaction in which the furfural produced in a reactor disappears by side reactions such as polymerization and decomposition. In this work we investigated the effect of the extraction of furfural by supercritical CO2 on the selectivity and yield of the furfural. Furthermore, based on kinetic data we proposed a reaction model for farfural formation with or without supercritical CO2 extraction. Judging from the experimental results, the recovery of furfaral from the reaction mixture by supercritical CO2 extraction greatly improved the selectivity and yield of the furfural owing to the suppression of its side reactions. A simple reaction model could represent satisfactorily the change in furfural selectivity and yield with the xylose conversion for the reaction without supereritical CO2 extraction, while the model could explain fairly well the reaction accompanying supercritical CO2 extraction.
Experiments were performed to investigate the properties of a large bubble in a bubble swarm of a three-phase fluidized bed using video camera moving at the same speed as the large bubble. The rising velocity of a large bubble in a bubble swarm relative to liquid phase is extremely high compared to that of single bubbles, probably due to the wake velocity of the bubble swarm, which shows a distinct upward flow at the center and a downward flow near the column wall. Assuming that bubbles of uniform size are generated regularly from all holes in the perforated plate and that the interaction between bubbles in the lateral direction is negligible, the rising velocity of a large bubble in a bubble swarm can be roughly estimated by applying the concept of the wake velocity for in-fine bubbles. This means that the rising velocity of the coalesced bubble in a three-phase fluidized bed can be estimated from the terminal velocity of the coalesced bubble in isolation and the size of bubbles in the swarm also.
Dead-end ultratiltration with application of a d.c. electric field to reduce membrane fouling rates was conducted under constant pressure using protein (bovine serum albumin) solution. When electric fields were applied, the filtration rate was significantly increased over that in ordinary dead-end ultrafiltration by both electrophorefic motion of the solutes away from the cake surface and electroosmosis occurring in the filter cake. The improvement in filtration rate becomes more pronounced with increasing electric field strength. In addition, effects of such processing variables as the solution concentration, the pH of solutions and the applied filtration pressure on the performance of dead-end electro-ultrafiltration were examined. A mathematical model was developed to describe the processes occurring during dead-end etectro-ultrafiltration, taking both electrophoretic and electroosmotic effects into account. The model accounted well not only for the dynamically balanced filtration rate but also for the variation in filtration rate with time.
Vapor-permeation separation of water-ethanol mixtures by asymmetric polyimide hollow-fiber membrane modules was carried out in a countercurrent flow pattern and in a both-end-opened pattern to investigate membrane performance and the effects of operating factors on the membrane module responses. The specific permeability coefficient of water vapor for the fibers was about 4 × 10–7 mol/(m2·s·Pa) at 378K, which was about 500 times that of ethanol vapor. The experimental results of membrane module responses for enrichment of ethanol composition at feed outlet, XRE, up to 99.7wt% were in good agreement with the results calculated from a conventional model. The both-end-opened flow pattern was much superior to the countercurrent one, especially for high-level enrichment, because of reduced buildup of permeate pressure inside the hollow fibers. The calculation showed optimum inside diameter and length of the hollow-fibers, depending on XRE and feed-side pressure.
A new method for graphic exergy analysis of multicomponent distillation and for visualization of rate characteristics of a distillation column is proposed by applying an energy-utilization diagram, EUD. By introducing the concept of a premixing model, the exergy losses in a distillation column can be decomposed into losses caused by premixing in liquid phase and those caused by premixing in vapor phase. Also, the energy exchange in a phase change such as condensation or evaporation of each component is displayed individually. By introducing the concept of partial molar quantities, those exergy losses in liquid phase and vapor phase can be categorized into losses caused by heating and mixing in liquid phase and losses caused by cooling and mixing in vapor phase. To use this method, the energy exchanged (ΔHea) and the energy levels (Aed and Aea) are displayed systematically on EUD. As a case study, simulation of the separation of n-hexane, n-heptane and n-octane is conducted for a column with 11 plates. The effect of reflux ratio and side-cooling or side-heating is discussed by using EUDs.
A continuous rotating annular chromatograph with rotating feed nozzles and product collectors was used to separate two kinds of proteins, (myoglobin and hemoglobin). Simultaneously, both proteins could be concentrated by using two kinds of eluents. The cation exchange resin, CM-Sepharose CL-6B was used as an adsorbent. The adsorption forces of both proteins on CM-Sepharose CL-6B were dependent on the value of pH in the buffer solution. Therefore, both proteins could be separated and concentrated by changing pH in the eluent. Experimental results could be predicted by numerical solutions.
Batch kinetic experiments were performed for adsorption of nitrobenzene and benzonitrile from aqueous solution onto activated carbon, the isotherms of which were only partially expressed by Freundlich equations. The experiments were carried out with adsorbents which had been equilibrated with a certain concentration of the solution in advance, to obtain adsorption rates representing certain ranges of the amount adsorbed. The intraparticle mass transfer rate was confirmed to be dominated by surface diffusion through the determination of pore diffusivity using a non-adsorptive substance, while the external mass transfer resistance could not be neglected. The surface diffusivities thus obtained were analyzed from the viewpoint of the non-ideality of the driving factor of surface diffusion, the amount adsorbed. Introduction of mobility of adsorbed molecule, derived through a treatment similar to ordinary diffusion in liquid phase, and assumption of the change of mobility with the energy of adsorption well explained the dependence of surface diffusivity in the whole range of concentration investigated.
The present study was conducted with the aim of optimizing the filtration of mesophase pitch by determining solid impurities which are several microns in particle diameter and in very low concentration. The concentration and mean size of solid impurities in mesophase pitch were estimated by an experiment using filter aids and a filtration model of a binary-mixture cake. The filtration model consists of a porosity and specific filtration resistance estimation equations for a binary mixture of solid particles. As a result, mean diameter of solid impurities of 9.2 μm and a concentration of 690 ppm were obtained. These values closely agreed with the values obtained by using various filter aids. It was confirmed that the model can be used to estimate the concentration and mean size of solid impurities contained in mesophase pitch. Though the present experiment was carried out to determine solid impurities in mesophase pitch, the filtration model of a binary-mixture cake employed in the present study is considered applicable widely to other operations involving body filtration.
A new type of isotherm equation is presented for mobile molecules adsorbed on a heterogeneous surface of random topography. The basic idea of the adsorption model is that molecules moving around on the surface spend more time on sites interacting with lower energy; the probability on each site is determined from the energy term that pulls the system toward more stable states and the entropy term that maximizes the number of combinatorial configurations on sites. The hybrid isotherm equation was applied to single- and mixed-gas adsorptions on MS-13X and on H-mordenite by assuming two sites. The site fractions were found to be important quantities for correlating the single-gas isotherms, while the assignments of sites were crucially important for the interpretation of mixed-gas adsorptions. This theory suggests that the large negative deviations from Raoult’s law observed for systems of C3H8 + CO2 and C3H8 +H2S on H-mordenite are due to the negative site correlations, which means that the lower-energy sites do not compete with each other.
Sauter mean bubble sizes and size distributions on a number basis were determined photographically in the neighbourhood of a Rushton turbine impeller. To determine the effect of gas density, four gases of molecular weights from 4 to 131 were used and deionized water (coalescing) and water saturated with carbon dioxide (repressed coalescence) were used as the liquids. Very low gassing rates with impeller speeds just above the flooding-loading transition were used to allow an unobstructed light path for photography of a flat-bottomed vessel of 0.61 m diameter. All the bubble size distributions show positive skewness with most bubbles less than 0.2 mm in diameter. The Sauter mean is in the range of 0.35 to 0.7 mm. These sizes are smaller than have usually been reported because of the point of measurement. The Sauter mean diameters decrease with increasing impeller speed, but not as rapidly as implied by Kolmogoroffs theory of isotropic turbulence. The size also increases slightly with increasing gassing rate or molecular weight of gas.