Showing papers on "Packed bed published in 1988"

Thermal Radiation in Packed and Fluidized Beds

Abstract: Etude du transfert radiatif dans les lits fluidises ou a garnissage. Presentation des techniques experimentales existantes pour la determination des proprietes radiatives. Analyse de l'interaction du rayonnement avec d'autres modes de transfert de chaleur

Non-Darcian Convection in Cylindrical Packed Beds

Abstract: Non-Darcian transport describes the nonuniform flow and thermal anomaliesoften found in flow through packed beds These effects include the high-flow-rate inertial pressure loss, near-wall porosity variation, solid-boundary shear, and thermal dispersion Inclusion of these effects significantly alters the velocity and temperature profiles from those predicted by models using uniform or Darcian flow In this paper, the non-Darcian formulation is used to predict the heat transfer rates for cylindrical packed beds such as chemical reactors Traditional analyses of chemical reactors assume slug flow and must include a temperature-slip boundary condition to predict the measured temperature profiles The present analysis predicts similar temperature variations by allowing the velocity and diffusivity to vary across the bed The results agree with experimental relations needed in conventional reactor models

Wall and particle-shape effects on heat transfer in packed beds

Abstract: The effective radial thermal conductivity and apparent heat transfer coefficient for a packed bed were experimentally determined for beds of spheres, full cylinders and hollow cylinders, for flow rates giving particle Reynolds numbers in the range 100-1000, and for tube to particle diameter ratios of 5-12. Over these ranges the radial Peclet number Per showed significant dependence on solid conductivity, gas flow rate and particle shape, while the wall Biot number Bi showed significant dependence on tube to particle diameter ratio, gas flow rate and particle shape. These dependencies were predicted well by equations incorporating the effects of these variables into individual gas and solid phase parameters, which were then combined to give the effective or lumped parameters

Fast Kinetics of Fe2+ Oxidation in Packed-Bed Reactors

Abstract: Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe2+ oxidized per liter per h (1,400 mmol of Fe2+ oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.

Reactor design for the ABE fermentation using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar

Abstract: Cells of Clostridium acetobutylicum were immobilized by adsorption onto bonechar and used for the production of solvents (ABE fermentation) from whey permeate When the process was performed in packed bed reactors operated in a vertical or inclined mode, solvent productivities approximating 6 kg/(m3h) were obtained However, the systems suffered from blockage due to excess biomass production and gas hold-up These problems were less apparent when a partially-packed bed reactor was operated in the horizontal mode A fluidized bed reactor proved to be the most stable of the systems investigated, and a productivity of 48 kg/(m3h) was maintained over a period of 2000 h of operation The results demonstrate that this type of reactor may have a useful future role in the ABE fermentation

Modifier effects on packed and capillary columns in supercritical fluid chromatography

Abstract: The separation of polar thermally labile solutes is one of the potentially most rewarding fields of SFC application. A presupposition for such applications is, however, mobile phases having relatively high solvent strengths. A promising approach to achieve this is the use of mobile phases consisting of carbon dioxide with a polar additive. In this work, the chromatographic effects of different concentrations of an additive, isopropanol, in carbon dioxide have been studied on capillary and packed columns. A series of antibiotics was used as test substances. Best results were obtained with carbon dioxide/8% isopropanol as mobile phase on a capillary column coated with a cyanopropyl-substituted polysiloxane stationary phase.

Model for continuous production of solvents from whey permeate in a packed bed reactor using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar

Abstract: A mathematical model has been developed to describe the operation of a packed bed reactor for the continuous production of solvents from whey permeate. The model has been used to quantitate the amounts of different physiological/ morphological types of biomass present in the reactor. The majority of biomass is inert, i.e. it neither grows nor produces solvent. Only relatively small amounts of biomass actively grow (vegetative, non-solvent-producing cells), while even smaller amounts are responsible for solvent production (clostridial, solvent-producing cells).

Packed column supercritical fluid chromatography using deactivated stationary phases

Abstract: A new cross-linked cyanopropyl bonded phase silica (Delta-bond) has been studied as a stationary phase for packed column supercritical fluid chromatography of basic nitrogen-containing compounds. The bonded phase impedes access to uncapped silanol sites, thereby giving rise to better peak shapes and more rapid elution without the necessity of a polar modifier in the mobile phase. Experiments both at elevated temperature and in the presence of a methanol modifier revealed that there is no short- or long-term deleterious effect on the column as opposed to the conventional cyanopropyl phase.

Effectiveness of moisture removal for an adiabatic counterflow packed tower absorber operating with CaCl2-air contact system

Abstract: In the open cycle desiccant cooling system, the room air or the room air mixed with ambient air is drawn through the desiccant dehumidifier where water vapor is absorbed. Then the dry air is cooled by a sensible heat exchanger by passing the air through an evaporative cooler. The desiccant may be either solid or liquid. Liquid desiccant systems are not as well developed as solid desiccant systems. Any attempt to improve the performance of a liquid desiccant should include a performance analysis of the dehumidifier. One of the efficient dehumidifiers for the liquid desiccant system is the packed bed dehumidifier and shown schematically. Because of the abundance of variables involved with the packed bed dehumidifier, the analysis becomes increasingly complex and is achieved at very high computational cost. Hence there is a need to define the performance of a packed bed quantitatively. A definition of air moisture removal effectiveness is presented based on the rigorous heat and mass transfer calculations for an adiabatic counterflow packed bed dehumidifier. This note also studies the influence of relevant parameters on tower performance quantified by the moisture removal effectiveness.

On‐line extraction and separation by supercritical fluid chromatography with packed columns

Abstract: The application of fluid extraction in combination with fluid chromatography with packed column and flame ionization detection is described. Fluid chromatographic equipment is shown. Applications of this system to drug characterization are demonstrated.

Review of Liquid Mixing in Packed Bed Biological Reactors

Abstract: The use of residence time distribution analysis to characterize the liquid phase hydrodynamics in bioreactors is reviewed, with special emphasis on packed bed bioreactors. The importance of tracer selection, the method of data analysis and other uses for the data collected in RTD measurements are discussed.

Modeling and design method for internal heat-integrated packed distillation column

Abstract: A mathematic model for an internal heat-integrated packed distillation column (IHIPAC) is developed on the basis of interphase mass transfer theory. A new method for design of an IHIPAC is proposed using the newly developed model. The binary system of methanol-water is adopted for the simulation work. The results show that an IHIPAC can be operated at a reflux ratio smaller than the minimum reflux ratio of a conventional distillation column, and that an energy saving of approximate 30% can be achieved under various operating conditions.

Combined Heat Transfer in a Semitransparent Multilayer Packed Bed

Abstract: Combined radiative, conductive, and forced convective heat transfer through a packed bed composed of two spectrally dissimilar slabs of particles is analyzed on the basis of the two-flux model. Taking into account the variation of absorption and scattering of the layers in the visibles and infrared spectral ranges, the selectivity of such a system is proved theoretically. Experiments are run using a bed composed of glass and silicon carbide particles as a solar absorber for gas heating. Good agreement is shown in comparison of predictions with experimental data.

Liquid deaerating apparatus

Abstract: A liquid deaerating apparatus comprises a deaerating tank housing a spray-type deaerator The latter has a spray nozzle means for spraying the liquid to be deaerated horizontally against a surrounding liquid spray impingement absorbing and contacting means Below the latter there is disposed packed bed means through which the liquid passes to a collection area within the deaerating tank The packed bed through whcih the liquid percolates to the collection area comprises a high flow rate system to assist such downward flow of the liquid and release of air and gas

Wall-to-liquid mass transfer in packed and fluidized beds with gas-liquid concurrent upflow

Abstract: The wall-to-liquid mass transfer coefficient, kw, was measured for both surfaces of a coaxially immersed tube and a column wall in packed and fluidi/ed bed systems with gas-liquid concurrent upflow. Supplementary measurements of kw were carried out in openpipe liquid flow, gas-liquid two-phase upflow and packed and fluidized beds with single liquid flow. The value of kw in the three-phase fluidized bed increased with increasing gas flow rate, deviating from the value in the liquid-solid fluidized bed and approaching the value in the gas-liquid two-phase upflow, while it passed through a maximum value with respect to the liquid flow rate. The value of kw in the packed-bed operation increased with increasing liquid flow rate and with increasing gas flow rate. The values of kw for the inner tube and the column wall were shown to agree with each other. The values of kw in all the gas-liquid, liquid-solid and gas-liquid-solid systems examined were correlated well by a unified equation in terms of the energy dissipation rate per unit mass of liquid. An analogy existed between wall heat transfer and wall mass transfer in all the multiphase flow systems examined.

The evolution of capillary columns for liquid chromatography

Abstract: The most recent interest in liquid chromatography (LC) is the trend of column miniaturization, i.e., in reducing the diameter of the columns. Capillary columns used in LC can be classified into three types, based on the flow resistance factor ϕ defined by Knox as $$\phi = d^2 /K_0 = \Delta Pd^2 /\eta \mu L$$ where d is a characteristic dimension of the column (the internal diameter of the tube of the mean particle diameter of the packing), Ko is the specific column permeability, ΔP is the pressure drop along the column, η is the viscosity and μ the linear velocity of the mobile phase, and L is the column length. The first type of LC capillary columns have a ϕ value of about 30. These are theopen-tubular columns, with a retentive film or layer on the inside wall of the column tubing the diameter of which should be as small as possible. The second type of LC capillary columns (ϕ≃100) is made by losely packing a glass tube which is then drawn to smaller diameter. During the drawing process the particles will be partially inbedded into the tube wall. Finally the third type of LC capillary columns (ϕ≃500–1000) are made by slurry-packing 0.2–0.5 mm ID fusedsilica capillary tubes under high pressure. These columns are well packed. In the paper various aspects of these columns are reviewed and their relative performance discussed.

Direct sample injection in supercritical fluid chromatography with packed fused silica column

Abstract: A direct sample injection technique was developed for supercritical fluid chromatography in a packed capillary column, with carbon dioxide as mobile phase and a flame ionization detector. The method allowed solutions, neat liquids, and even solids to be introduced as samples. Also, extraction with supercritical carbon dioxide was combined with this method to separate polymer additives.

A unified model for non-Newtonian flow in packed beds and porous media

Abstract: A generalized equation describing the flow of any time-independent purely viscous non-Newtonian fluid in packed beds and porous media is proposed. The equation, which is expressed in terms of the Kozeny constantk i and the bed tortuosityT, unifies the three well-known packed bed models due to Blake, Blake-Kozeny and Kozeny-Carman within a general framework which also brings out their differences. The accuracy of each of the three bed models is assessed by comparing the predictions with existing experimental results, and is found to depend on the rheological properties of the fluid. The Kozeny-Carman model appears to give the best overall description of the flow of pseudoplastic (shear-thinning) fluids in packed beds and porous media although the Blake-Kozeny model gives a better representation for the high shear-thinning fluids.

Comparison of packed and capillary columns for practical SFC separations

Abstract: A newly developed polysiloxane-type packing material shows promise for use in SFC. Relatively polar compounds were eluted from a microbore column with good peakshape using a mobile phase consisting of CO2 modified with formic acid and water. The latter combination is an effective modifier suitable for use with pressure programming and FID detection.

Direct on-line coupling of small subcritical and supercritical fluid extractors with packed column supercritical fluid chromatography

Abstract: A mini extractor of 85 μL void volume and a micro extractor of 3–4 μL void volume have been coupled directly with a packed column SFC and used under sub- and supercritical conditions. The mini extractor is suitable for holding adsorbates which can be on-line extracted and the extract chromatographed (direct SFE-SFC). The micro extractor can be used for direct sample introduction of liquid and solid materials under SF conditions. Thus any solvent interference with the sample and the chromatographic conditions is excluded. Standard samples of wood tar residue, engine oil, and metal organic compounds have been tested.

Possibilities for the development of large-capacity methanol synthesis reactors for synfuel production

Abstract: Future synfuel production schemes may call for methanol synthesis reactors larger than those in use today. Methanol may be produced in a number of quite different reactor types, and for each type some kind of practical scale-up limit exists. This investigation involves exploring the features of seven kinds of reactors, and a kinetic modeling approach is used where appropriate to determine the maximum methanol production for a unit 6 m in diameter. Reactor types discussed include the Lurgi tubular packed bed system, the ICI quench system, and the Casale mixed flow system. Other variations considered are the conventional fluidized bed, the high-velocity circulating fluidized bed, a tube-cooled radial flow system, and a high-viodage version of the four-stage quench reactor. Of the types discussed, four appear to be capable of producing an excess of 5000 ton of methanol per day in a single, 6-m-i.d. unit: the Cassale system, the tube-cooled radial flow reactor, the circulating fluidized bed, and the high-voidage quench system.

Alkaloid formation by Catharanthus roseus cells in a packed column biofilm reactor

Abstract: Catharanthusroseus cells producing indole alkaloids were grown on surfaces of Ca-alginate beads within the interspacial volume of a packed column. Production media was circulated through the packed column in an upflow mode. Growth and indole alkaloid formation were quantified and compared with suspension culture of cells. Final alkaloid concentration and alkaloid yield obtained in the packed bed was superior to those obtained in suspension culture. This is thought to be due to improved cell-cell contact and interaction in the packed column.