Showing papers on "Packed bed published in 1987"

Effects of the column pressure drop in packed-column supercritical-fluid chromatography

Abstract: Columns packed with small particles (i.e. 3 to 10µm) may be used for fast separations in supercritical-fluid chromatography (SFC). The analysis times required for such packed columns are typically an order of magnitude smaller than what may be achieved with contemporary open-tubular (capillary) columns (25 to 100µm i.d.).

Analysis of flow channeling near the wall in packed beds

Abstract: The phenomenon of flow channeling in packed beds is investigated in the present analysis. A closed-form solution is obtained from the volume-averaged second-order momentum equation with the no-slip condition at the wall, using an exponential porosity distribution typical of packed beds. The predicted velocity profile shows the most important features of flow channeling: the sharp peak in the velocity near the wall, and the approach to the Darcy velocity far from the wall. The predictions are consistent with previous numerical results and with velocity measurements made downstream of a packed bed. The compact expression for the velocity given here is shown to be convenient for analyzing other packed-bed characteristics, such as the effective permeability of a finite-sized bed.

Mathematical modelization of a packed-bed reactor performance with immobilized yeast for ethanol fermentation.

Abstract: The performance of a continuous vertical packed-bed reactor with yeast immobilized in carrageenan gel beads is reported. The study focuses on the mathematical modelling of the steady-state fermentor behavior by means of a tanks-in-series model which includes the intrinsic kinetic model and the external mass transfer and internal diffusion-reaction conditions in the beads.

Optimization of a Packed Bed Thermal Energy Storage Unit

Abstract: The optimization of the design of a packed-bed thermal energy storage unit is presented. A one-dimensional, transient, two-phase model is chosen for the packed bed which assumes uniformity at each cross section within the packing. The governing equations for the time dependent temperature distributions in both the solid and fluid phases are solved using a fully implicit formulation. The accuracy of the numerical method is demonstrated by comparison with experimental measurements of temperature distribution in a randomly packed bed of uniform spheres. The goal of the optimization is to achieve maximum utilization of the thermal energy storage and recovery capabilities of the storage medium for a given set of operating conditions. The optimum combination of bed length, size of the packing particles, and relative size of the bed cross section to the particle diameter is determined, subject to constraints on the maximum allowable pressure drop across the packing, the maximum outlet fluid temperature, and the total amount of supplied energy. The thermodynamic availability is examined as the measure of storage utilization. The monotinicity method is utilized for the optimization process. This method identifies a global optimum without any special computations, and prevents acceptance of false optimum solutions, as could bemore » generated by numerical techniques. The results of the study provide guidelines for choosing the size of the packing and the packing particle subject to the constraints for a practical operating system.« less

Performance of tapered column packed-bed bioreactor for ethanol production.

Abstract: A tapered column type of bioreactor system packed with immobilized Saccharomyces cerevisiae was used to study the bioreactor performance as a function of design and operating variables. The performance of tapered column bioreactor system was found to be better than that of the conventional cylindrical column reactor system for the ethanol fermentation. The new bioreactor design alleviated problems associated with carbon dioxide evolution and provided a significantly better flow pattern for both liquid and gas phases in the bioreactor without local channelling. A mathematical simulation model, which takes into account of the axial convection and dispersion, interphase mass transfer, and apparent kinetic design parameters, was developed. The effect of radial concentration gradients on the bioreactor performance was found to be insignificant. For the reactor system studied, the maximum ethanol productivity obtained was 60 g ethanol/L gel/h, and the maximum glucose assimilation rate was 140 g glucose/L gel/h. One of the most important findings from this study was that the apparent kinetic parameters change at the glucose concentration of 2 g/L This change was found to be due to the changes in yeast physiology and metabolism. The values of V(m) (') and V(m) (') decreased from 0.8 to 0.39 g ethanol/g cell/h and from 97mM to 11mM, respectively. The substrate inhibition constant was estimated as 0.76M and the product inhibition constant was determined as 113 g ethanol/L The degree of product inhibition showed practically a linear relationship with an increasing ethanol concentration. Based on the hydro-dynamic analysis of the bioreactor system, it was found that the Peclet number, N(Pe) was not a strong function of the flow velocity at low flow rates through the bioreactor system, but its value decreased somewhat at an interstitial velocity greater than 0.03 cm/s. The tapered column bioreactor system showed a much better flow pattern of gas and liquid phases within the reactor, thereby providing a more homogeneous distribution of gas-liquid-solid phases in the reactor without any phase separation.

Affinity Separations in Magnetically Stabilized Fluidized Beds: Synthesis and Performance of Packing Materials

Abstract: A magnetically stabilized fluidized-bed separator designed to test the use of pellicular, ferromagnetic affinity chromatography packing materials has been developed. A wire wound solenoid was used to produce the magnetic field. The ferromagnetic packing material is comprised of a magnetite-containing, poly-urethane gel coated onto polystyrene beads. The gel contains free carboxyl groups. These were carbodiimide-coupled to soy-trypsin inhibitor and the material, used for trypsin purification. Narrow-band affinity chromatography was carried out in packed-bed, fluidized-bed and magnetically stabilized, fluidized-bed separators. Pressure drop, capacity, dilution, and peak asymmetry were evaluated for each type of separator. The three types provide comparable efficiency but the fluidized separators exhibit a much lower pressure drop. As might be expected, fluidized-bed separators perform well for affinity chromatography Oarge k') but poorly for size exclusion chromatography.

Mathematical modeling of ethanol production by immobilized Zymomonas mobilis in a packed bed fermenter

Abstract: A mathematical model which describes ethanol production in a packed bed fermenter containing. Zymomonas mobilis entrapped in small spheres of calcium alginate within a packed bed fermenter has been developed. The equations combine simultaneous diffusion and reaction as well as a complex flow pattern to calculate glucose and ethanol profiles in the column type reactor. As part of the study, diffusivity values for glucose and ethanol in cell-loaded calcium alginate were determined. Also a freecell kinetic expression for Z. mobilis at 33 degrees C and ph 6.0 was developed. Comparison of the model with actual experimental results were made showing average deviations of ca. 30-40%.

Evaluation of packed columns in supercritical extraction processes

Abstract: The purpose of the present work is to add to the base of knowledge in the use of packed columns when used in supercritical extraction service. Experimental studies were performed on a 2·54 cm diameter supercritical fluid extraction column operated in both spray and packed column arrangements. The packing used was 6· mm Raschig rings with a surface area of 722 m2/m3. The supercritical systems studied were carbon dioxide/ethanol/water and carbon dioxide/isopropanol/water at 102 atmospheres and 35°C and 102 atmospheres and 40°C, respectively. In order to compare supercritical with conventional extraction, similar data were obtained in the same column with the toluene/acetone/water system at one atmosphere and 24°C.

Mass transfer at packed-bed, gas-evolving electrodes

Abstract: Mass transfer rates were measured for the cathodic reduction of potassium ferricyanide at a H2-evolving electrode consisting of a packed bed of spheres. Variables studied were bed height, H2 discharge rate and ferricyanide concentration. It was found that the mass transfer coefficient (K) is related to the H2 discharge rate (V) by the equation $$K = aV^{0.325} $$ Bed height and electrolyte concentration were found to have little effect on the mass transfer coefficient. A mathematical model based on the surface renewal theory was formulated to explain the mechanisms of mass transfer at gas-evolving electrodes.

Modeling of fixed bed heat storage units utilizing phase change materials

Abstract: A computer model has been developed for the calculation of the heat exchanged and temperature profiles in a packed bed containing a phase change material. The packed bed is intended as a heat storage unit in which an inert fluid flowing through the bed exchanges heat with an encapsulated spherical shot of the phase change (melting and freezing) material. Examples of predicted bed temperature profiles during heat storage and utilization cycles are given. For A1-12 wt pct Si and Al-30 wt pct Si shot, a sequence of storage and utilization cycles with cyclic cocurrent fluid flow was found to utilize the high latent heat of fusion of the shot efficiently and permit the utilization of the bed as a near isothermal (577°C) heat recuperator.

Mathematical Modeling of Packed Bed Reactors: Numerical Solutions and Control Model Development

Abstract: Publisher Summary This chapter presents an analysis of the development of dynamic models for packed bed reactors, with particular emphasis on models that can be used in control system design. The method of approach formulates a comprehensives, relatively detailed packed bed reactor model. The chapter also considers the techniques available for numerical solution of the model; and utilizes one such numerical solution to examine simplifications of the model based on its underlying physics. It then describes how the model may be reduced mathematically to one useful for control system design. Mathematical models of packed bed reactors are needed for the description of steady-state and dynamic behavior for process design, optimization, and control. Although insufficient detail can lead to a model incapable of accurately representing the reactor's response to changes in operating variables, excessive detail can lead to a model that is computationally impractical or contains parameters the values of which cannot accurately be determined from operating data. Thus, although the development is intended to be generally applicable to packed bed reactor modeling, all numerical results are obtained for the methanation system. As a result, some approximations that are found to apply in the methanation system may not in other reaction systems, and, where possible. The chapter discusses approaches to numerical solution of the model with a detailed exposition of one approach, orthogonal collocation. Common physical assumptions made in packed bed reactor modeling are evaluated.

Method for stripping of residual solvent

Abstract: A method for stripping adsorbed organic solvent from a solid comprising feeding a slurry of the solid containing the adsorbed solvent into a packed column and countercurrently contacting the slurry with stripping gas, removing an overhead stream comprising desorbed solvent and a bottom stream comprising a solvent stripped solids slurry. A preferred embodiment uses a vertical packed column, an aqueous slurry of the solid, and steam as the stripping gas. The method is particularly suitable for stripping extraction solvents from spent tar sands or spent diatomite resulting from bitumen extraction methods. The vertical packed-bed stripping column has two separate zones: (a) a hot stripping zone where the feed enters at the top and the hot stripping gas enters at the bottom of the hot stripping zone; (b) and a cold stripping zone where the depleted feed from the hot stripping zone enters at the top and a cold stripping gas is introduced at the bottom of th cold stripping zone. The lower stripping zone is maintained at a temperature less than the upper zone of the same stripping column.

Continuous asymmetric reduction of 4-oxoisophorone by thermophilic bacteria using a hollow fiber reactor

Abstract: Continuous asymmetric reduction of 4-oxoisophorone by the thermophilic bacterium Thermomonospora curvata JTS321 was examined using three reactor systems: packed bed, fluidized bed and hollow fiber. T. curvata was immobilized in polyacrylamide-hydrazide gels when used in the packed and fluidized bed reactors. Of the three reactor systems, the highest productivity (964 mg.1-1.h-1) was observed in the fluidized bed reactor. However, many cells grew outside of the gel matrix, causing product contamination. The productivity of the hollow fiber reactor was 504 mg.1-1.h-1; the problem of cell contamination of the product was avoided, as the molecular cut-off of the hollow fibers (400 000) was of an appropriate size to prevent cell leakage to the product stream. We therefore consider that the hollow fiber reactor is most suitable for continuous microbial conversions.

Remarks upon thermokinetic parameters of the one-and two-dimensional mathematical models of heat transfer in a tubular flow apparatus with a packed bed

Abstract: Considerable discrepancies have been observed between the published correlations concerning the overall heat transfer coefficient α, as well as the effective thermal conductivity λe,r and the wall heat transfer coefficient αw, which are the respective thermokinetic parameters of the one- and two-dimensional mathematical models of heat transfer in a tubular flow apparatus with a packed bed. A precise method has been elaborated for evaluation of these parameters using the data collected in the same experiment. This method has allowed us to point out the reasons for the scatter of the empirical correlations published by several authors, and to verify the coincidence of the experimentally determined and theoretically predicted values of the model parameters for various beds; the best fitting of the data was observed for beds packed with spherical pellets. The theoretically developed relation between the values of the parameters of both the mathematical models has been verified experimentally and it was proved that, if the experiment is performed correctly, no correlation factor is needed in that relation, as has been proposed by several investigators.

The Effect of Pressure on Dryout of a Saturated Bed of Heat-Generating Particles

Abstract: The results of an experimental investigation of pressure effects on dryout heat flux in a volume-heated porous bed are reported. Several porous beds of near-uniform-sized particles were studied at pressures up to 5 atm. The beds were saturated with water, Freon-113, acetone, and methanol. Simple scaling of the Freon-113 results is used to yield results valid for water pressures from 1 atm to 37.3 atm.

Intraparticle diffusion coefficients in packed columns: Measurement by arrested-flow gas chromatography

Abstract: Arrested-flow chromatography was used to determine intraparticle diffusivities of large-pore particles packed in columns. Particle and column tortuosity factors were determined for helium tracer in nitrogen carrier gas at 40°C and atmospheric pressure. Semiempirical modifications of Maxwell's, Burger's, Jeffrey's, and Rayleigh's relations for the composite diffusivity of spherical particles in a stationary medium are proposed for the effective composite diffusion coefficient for a packed bed of porous particles. The equations, modified to represent accurately the extraparticle void diffusion based on measurements for beds of nonporous particles, are used to evaluate intraparticle diffusivities from experimental data obtained by arrested-flow chromatography.

Electro-oxidation rate ofp-tert-butyltoluene in a bipolar packed-bed electrode cell

Abstract: The side chain methoxylation ofp-tert-butyltoluene was carried out in a bipolar packed-bed electrode cell in which graphite pellets of diameter 4.74 mm and length 5mm were randomly packed in nine layers separated by inert mesh spacers. The reaction consisted of main consecutive reactions leading top-tert-butylbenzyl methyl ether andp-tert-butylbenzaldehyde dimethyl acetal (TBDA) and polymerization reactions. Overall reaction rate coefficients for each reaction step, current efficiency and energy consumption were determined on the basis of a reactor model. The selectivity and the current efficiency for TBDA increased with increasing current, but the energy consumption began to rise when the current exceeded 0.8 A. An addition of supporting electrolyte suppressed the overall reaction rate coefficients, although it decreased the energy consumption.

System for conversion of methanol to gasoline

Abstract: A methanol-to-gasoline (MTG) catalytic conversion system in which the conversion is conducted in a fixed bed catalytic reactor. A C3 -C4 hydrocarbon diluent is generated from pressurized liquid effluent and recycled to the fixed bed reactor in order to dissipate the heat of reaction.

Method for dephosphorization of sewage containing phosphorus

Abstract: PURPOSE:To efficiently remove phosphorus, by packing a column with a porous treatment material having a specific void ratio and containing calcium silicate as a main component and contacting phosphorus-containing sewage with said porous treatment material CONSTITUTION:A foaming agent such as an aluminum powder is added to a slurry containing a silicious stock material and a carcareous stock material as main stock material and the resulting mixture is subjected to hydrothermal reaction treatment under a high temp and high pressure condition to obtain a porous body with a void ratio of 50-90% A column is packed with the porous treatment agent and phosphorus-containing sewage is passed through the packed column to perform contact reaction By this method, the removal of phosphorus can be efficiently performed The porous treatment material reduced in phosphorus removal effect can be utilized as phosphorus fertilizer