Showing papers on "Packed bed published in 2008"

Characteristics of Superficially-Porous Silica Particles for Fast HPLC: Some Performance Comparisons with Sub-2-µm Particles

Abstract: Columns of 2.7-microm fused-core (superficially porous) Type B silica particles allow very fast separations of small molecules at pressures available in most high-performance liquid chromatography instruments. These highly-purified particles with 1.7-microm solid silica cores and 0.5-microm-thick shells of 9 nm pores exhibit efficiencies that rival those of totally porous sub-2-microm particles but at one-half to one-third of the column back pressure. This presentation describes other operating features of fused-core particle columns, including sample loading characteristics and packed bed stability. The superior mass transfer (kinetic) properties of the fused-core particles result in much-improved separation efficiency at higher mobile phase velocities, especially for > 600 molecular weight solutes.

Review of Packed-Bed Plasma Reactor for Ozone Generation and Air Pollution Control

Abstract: Packed-bed plasma reactors, constructed by packing noncatalytic dielectric pellets inside nonthermal plasma reactors, have been demonstrated to effectively alleviate the major bottleneck encountered by nonthermal plasma, i.e., the energy efficiency needs to be further improved. As far as the environmental issues are concerned, packed-bed plasma reactors are mainly applied to ozone generation and gaseous pollutant removal. According to the available experimental data, for a given specific energy density, the energy efficiency for ozone generation and gaseous pollutant abatement obtained with packed-bed reactors, if compared to that of nonpacked reactors, could be 1.1−4.3 and 1.1−12 times higher, depending on the type of pollutant, the reactor geometry, and the packing pellets used. Nevertheless, it is worth noticing that the packing pellets suitable for ozone generation and pollutant removal are quite different. The influences of material, dielectric constant, size, and shape of the packing pellets on the ...

Production of Very Pure Hydrogen with Simultaneous Capture of Carbon Dioxide using the Redox Reactions of Iron Oxides in Packed Beds

Abstract: A chemical looping process, which uses a packed bed of the various oxides of iron, has been formulated to produce separate, pure streams of H2 and CO2 from syngas. The process has the following stages: (1) Reduction of Fe2O3 to Fe0.947O in the syngas from gasifying coal or biomass. This stage generates pure CO2, once the water has been condensed. (2) Subsequent oxidation of Fe0.947O to Fe3O4 using steam, to simultaneously produce H2. (3) Further oxidation of Fe3O4 to Fe2O3 using air to return the oxide to step 1. Step 1 was studied here using a mixture of CO + CO2 + N2 as the feed to a packed bed of iron oxide particles, while measuring the concentrations of CO and CO2 in the off-gas; step 2 was investigated by passing steam in N2 through the packed bed and measuring the quantity of H2 produced. The third step simply involved passing air through the bed. Reduction to Fe, rather than Fe0.947O, in step 1 gave low levels of H2 in step 2 after 10 cycles of reduction and oxidation and led to the deposition of ...

Prediction of Breakthrough Curves for Sorptive Removal of Phenol by Bagasse Fly Ash Packed Bed

Abstract: Sorptive removal of phenol from synthetic aqueous solutions by bagasse fly ash (BFA) was investigated at 303 K under dynamic conditions in a packed bed. The effects of sorbent bed length (Z = 40−90 cm), flow rate (Q = 0.01−0.04 dm3/min), bed diameter (D = 2−4 cm), and initial concentration (C0 = 50−500 mg/dm3) on the sorption characteristics of phenol were investigated at an influent pH of 6.5. More than 99.5% of phenol was removed in the column operated at C0 =100 mg/dm3 of phenol. The column performance improved with increasing Z and decreasing Q. The Bohart−Adams, Thomas, Yoon−Nelson, Clark, and Wolborska models were applied to the experimental data to represent the breakthrough curves and determine the characteristic design parameters of the column. The bed depth service time (BDST) model at 50% breakthrough provided a good fit to the experimental data, and the sorption capacity of the adsorbent was close to the value predicted from a batch study. The sorption performance of the BFA columns could be w...

Solar-Driven Coal Gasification in a Thermally Irradiated Packed-Bed Reactor

Abstract: Coal gasification for high-quality synthesis gas production is considered using concentrated solar energy as the source of high-temperature process heat. The solar reactor consists of two cavities separated by a radiant emitter plate, with the upper one serving as the solar absorber and the lower one containing the reacting packed bed that shrinks as the reaction progresses. A 5 kW prototype reactor with an 8 cm depth, 14.3 cm diameter cylindrical bed was fabricated and tested in a high-flux solar furnace, subjected to solar flux concentrations up to 2600 suns and packed-bed temperatures up to 1440 K. The reactor is modeled by formulating the 1D unsteady energy conservation equation that couples conductive−radiative heat transfer with the reaction kinetics and solving it by the finite volume technique for a transient shrinking domain. The overall reaction rate was determined experimentally by thermogravimetry, while the effective thermal conductivity was determined experimentally in a radial heat flow ove...

Selectivity study of H2S and CO2 absorption from gaseous mixtures by MEA in packed beds

Abstract: In this work, an experimental and theoretical investigation of selectivity was performed for simultaneous absorption of H2S and CO2 from gaseous streams into an aqueous mono-ethanol amine (MEA) solution in a packed bed. The operating parameters playing a vital role and have been considered here, are amine concentration and pressure, while the structural and hydrodynamic parameters such as packing size and L/G ratio were found to be important as well. The qualitative effects of these parameters on absorption performance were analyzed via evaluating of absolute and relative removal efficiency. In the proposed mathematical model for theoretical investigation of the absorption performance, the two-film theory of mass transfer was used. In order to check the validity of the proposed model, in experimental section, a pilot-scale plant was constructed and variety of experimental data were obtained in a wide range of operating conditions. In this plant, construction of packed beds in several sections of the column, gives the possibility of changing the structural and hydrodynamic parameters in a flexible way. Also the proposed mathematical model is able to consider the effects of vital parameters on the selectivity of absorption. The predicted results by the proposed mathematical model were compared to the experimental data. This comparison shows a good agreement between these data and so verifies the validity of the proposed model. The results reveal that the effects of pressure, amine concentration, packing size and L/G ratio on the selectivity performance of H2S absorption into an MEA solution are significant. Results show that, the relative efficiency could be increased near 20% when L/G is manipulated properly. As a side effect it reduces the absolute efficiency. Using the packing size 1 in. instead of 0.5 in., relative efficiency could be increased more than 5% while absolute efficiency is reduced. Then the experimental results testified the benefit of any operating procedure appropriately involving these parameters for selective H2S absorption. In general, since CO2 is a weak competitor against H2S in being absorbed by MEA solution, under difficult conditions for absorption process, the weakness of CO2 is more pronounced. Therefore, the selectivity of absorption is increased, while the absolute efficiency is decreased. In particular, increasing the gas flowrate and decreasing the L/G ratio, increases the selectivity. Also when higher packing size is used, selectivity is increased. In contrast, when large amount of amine are contacted with a special quantity of acid gas in the unit volume of packed bed (generally lower packing size and higher L/G ratio), due to the strength of MEA, the amine solution absorbs nearly all gaseous acidic compounds and reduces the selectivity.

Optical measurements of pore geometry and fluid velocity in a bed of irregularly packed spheres

Abstract: Imaging methods are proposed for the characterisation of liquid flows through transparent porous media of matched refractive index. The methods are based on the analysis of laser-illuminated slices, and specialized for the case in which the porous medium is composed of irregularly packed spheres. They include algorithms for the reconstruction of the three-dimensional (3D) sphere arrangement based on a laser scan of the packed bed, particle tracking velocimetry applied to the motions of micro-tracers in a laser-illuminated plane, and techniques for the co-registration of geometry and velocity measurements acquired from different slices. The methods are applied to a cylindrical flow cell filled with mono-sized spheres and operated at Reynolds number Re = 28. The data produced include the full 3D geometry of the packed spheres assembly, the 2D fluid velocity field in the axial centre-plane of the flow cell, and the corresponding porosity and velocity distributions.

Application of CFD in the study of supercritical fluid extraction with structured packing: Dry pressure drop calculations

Abstract: Liquid phase SFE has been carried out in extraction columns, with structured packings particularly of the gauze type. Structured packing performs very well during extractions under these conditions, mainly due to their relatively large surface area and free volume. Nevertheless, there are also important disadvantages such as high cost, low capacities at high flow rates, and premature flooding. The assessment of the real efficiencies of these packings poses extreme difficulties related to the moderately high pressures involved in these processes. Computational fluid dynamics (CFD) can be used to characterize the complex single and multiphase flow inside the packed bed and evaluate the influence of the shape and geometry of the packing on the hydrodynamics and mass and heat transfer rates in the SFE packed column. In this first study, and with a very detailed modelling of the packing geometry, the dry pressure drop is calculated for both laminar and turbulent flow conditions. Results are seen to agree well with the experimental data in the literature.

Influence of surface tension on effective packing area

Abstract: Effective packing areas of Sulzer Mellapak 250Y and 500Y structured packings were determined in a 0.46-m OD packed column. A chemical method (absorption of CO2 from air using 0.1 kmol/m3 NaOH) was employed for the measurements. The packing performance was reported as fractional area, defined as effective area normalized by specific packing area. Under high surface tension conditions (∼72 mN/m), the fractional area decreased by approximately a factor of 2 in going from the 250Y to the 500Y packing. When similar tests were conducted at reduced surface tensions (∼35 mN/m, achieved by the addition of surfactant), the fractional area of the 250Y was unchanged, whereas that of the 500Y increased by 50% relative to the base case. The results indicate that, at high surface tension, access to the surface of the 500Y packing was being inhibited. Lowering the surface tension served to maximize the effective area of the packing.

A Simple Experimental Technique to Measure Tortuosity in Packed Beds

Abstract: In this article, a simple and inexpensive experimental technique easy to build in laboratory, for the measurement of tortuosity of a packed bed of inert particles, is described. Experimental values of the tortuosity were obtained with four different packed beds of sand. The experimental results obtained are in good agreement with the theoretical values of tortuosity in a porous media; and the data reported showed the tortuosity to increase with decrease in the void fraction of the packed bed as expected.