Showing papers on "Packed bed published in 2000"

Impact of tube-to-particle-diameter ratio on pressure drop in packed beds

Abstract: Discussions in the literature about the influence of (1) the operating parameters Re 0 (Reynolds number) and D/d p (tube-to-particle-diameter ratio), and (2) the physical phenomena of wall friction and flow maldistribution on the pressure drop in packed tubes are in conflict. This influence is analyzed by applying the extended Brinkman equation to cylindrical beds of particles of nearly (but not perfectly) spherical shape and moderate-size dispersity.

Packed column reactor for continuous atom transfer radical polymerization: Methyl methacrylate polymerization using silica gel supported catalyst

Abstract: A continuous column reactor packed with silica gel supported CuBr-HMTETA catalyst has been successfully developed for ATRP of MMA. The reactor had a good catalytic stability up to 100 h. The MMA conversion decreased with an increasing feeding flow rate. The polymerization kinetics was first order with respect to the monomer. The molecular weight increased linearly with conversion, demonstrating the living character. Possible flow back-mixing and polymer trapping in the pores of silica gel caused some broadening in the molecular weight distribution. This type of packed column reactor is believed to be a significant development for possible commercial exploitation of the ATRP process.

Process development of continuous hydrogen production by Enterobacter aerogenes in a packed column reactor

Abstract: Hydrogen bioproduction from agro-industrial residues by Enterobacter aerogenes in a continuous packed column has been investigated and a complete reactor characterization is presented. Experimental runs carried out at different residence time, liable of interest for industrial application, showed hydrogen yields ranging from 1.36 to 3.02 mmolH 2mmol−1 glucose or, in other words, from 37.5% to 75% of the theoretical hydrogen yield. A simple kinetic model of cell growth, validated by experimental results and allowing the prediction of biomass concentration profile along the reactor and the optimization of superficial velocity, is suggested. By applying the developed approach to the selected operative conditions, the identification of the optimum superficial velocity v 0,opt of about 2.2 cm h−1 corresponding to the maximum hydrogen evolution rate H˙ 2 g , max, was performed.

Local transitions in flow phenomena through packed beds identified by MRI

Abstract: Magnetic resonance imaging (MRI) velocity measurement techniques are used to investigate flow of water and a glucose solution, of viscosity 3.89 × 10−3 Pa·s, within the interparticle space of a cylindrical packed bed of 5 mm diameter glass ballotini. The experiments were performed over a range of Reynolds numbers from 0.84 to 14.52, spanning the regime where inertial effects begin to play a significant role relative to viscous forces. A transition from creeping to inertial flow occurs in isolated pores at a local Reynolds number, defined for each pore within the interparticle space, of approximately 30. Despite this transition in flow behavior in some pores, the gross features of the flow pattern scale approximately with flow rate, which can be explained by considering the volume of the void space in which the flow is nearly stagnant as largely determining the pressure distribution within the bed.

The Chemistry of Dichloromethane Destruction in Atmospheric-Pressure Gas Streams by a Dielectric Packed-Bed Plasma Reactor

Abstract: The destruction of dichloromethane by a nonthermal plasma in atmospheric-pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrati...

Enantiomeric separation of amino acids and nonprotein amino acids using a particle-loaded monolithic column

Abstract: A solution is prepared of 5 μm silica particles modified with (S)-N-3,5-dinitrobenzoyl-1-naphthylglycine (particle 1) or (S)-N-3,5-dinitrophenylaminocarbonyl-valine (particle 2) suspended in liquid tetraethylorthosilicate, ethanol, and aqueous hydrochloric acid. This solution is injected under pressure into a 30 cm long, 75 μm inner diameter capillary column and heated for 1 h at 120°C after which the modified particles are embedded in a monolithic column of sol gel. The packed column measures approximately 15 cm from the inlet to the window used to view the laser-induced fluorescence. Thirteen different amino acids and three nonprotein amino acids are derivatized with the fluorogenic reagent 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) before injection onto the column for capillary electrochromatographic separation. The enantiomeric separation of the monolithic column packed with particle 1 results in a resolution ranging from 1.14 to 4.45, whereas that packed with particle 2 results in a resolution ranging from 0.79 to 1.17. On the basis of resolution and amount of chiral packing material the enantiomeric separation obtained by capillary electrochromatography is judged to be superior to that obtained previously with high performance liquid chromatography (HPLC).

Mathematical modeling as a tool to investigate the design and operation of the zymotis packed-bed bioreactor for solid-state fermentation.

Abstract: Zymotis bioreactors for solid-state fermentation (SSF) are packed-bed bioreactors with internal cooling plates This design has potential to overcome the problem of heat removal, which is one of the main challenges in SSF In ordinary packed-bed bioreactors, which lack internal plates, large axial temperature gradients arise, leading to poor microbial growth in the end of the bed near the air outlet The Zymotis design is suitable for SSF processes in which the substrate bed must be maintained static, but little is known about how to design and operate Zymotis bioreactors We use a two-dimensional heat transfer model, describing the growth of Aspergillus niger on a starchy substrate, to provide guidelines for the optimum design and operation of Zymotis bioreactors As for ordinary packed-beds, the superficial velocity of the process air is a key variable However, the Zymotis design introduces other important variables, namely, the spacing between the internal cooling plates and the temperature of the cooling water High productivities can be achieved at large scale, but only if small spacings between the cooling plates are used, and if the cooling water temperature is varied during the fermentation in response to bed temperatures

Biological Decolorization of Textile Dyestuff by Coriolus Versicolor in a Packed Column Reactor

Abstract: Biological decolorization of textile dyestuff Everzol Turquoise Blue G, a phthalocyanin type reactive dyestuff, by white-rot fungi Coriolus versicolor MUCL was studied in a packed column reactor. Decolorization performance of fungi immobilized on different support particles such as metal mesh, sponge, stone, wood ash, polyurethane and wood particles were investigated in shake flasks. Metal mesh particles was found to be superior to the other immobilization matrices resulting in 97% decolorization efficiency. The packed column reactor containing fungi immobilized on metal mesh particles was operated in repeated-batch mode. The reactor was loaded 7 times with fresh colored media in every 24 hours. The reactor was gently aerated by a diffuser from the bottom of the column. Environmental conditions were adjusted to T= 28 °C and pH= 4.5–5.0. TOC, glucose and dyestuff concentrations were determined throughout the experiments. During the course of repeated batch operation, decolorization efficiency decreased fro...

On the effective heat transfer parameters in a packed bed

Abstract: Comprehensive numerical simulation model was developed to describe the structural changes in the iron ore sintering bed by using the discrete element method (DEM). The heat wave propagation through the sintering bed was incorporated by combining the solutions of the various reaction rates and gas-granule heat transfer with the calculation of the granule movement by DEM. Simulations were conducted under different conditions, i.e., different carbon content and melting temperature of the granules. Results show that both carbon content and melting temperature of the granule influence the final structure of the sintering bed. The obtained structural change of the sintering bed show that the proposed model is a potential tool to analyse the agglomeration phenomena occurring in the iron ore sintering process under various conditions.

Numerical simulation model of the iron ore sintering process directly describing the agglomeration phenomenon of granules in the packed bed

Abstract: Comprehensive numerical simulation model was developed to describe the structural changes in the iron ore sintering bed by using the discrete element method (DEM). The heat wave propagation through the sintering bed was incorporated by combining the solutions of the various reaction rates and gas-granule heat transfer with the calculation of the granule movement by DEM. Simulations were conducted under different conditions, i.e., different carbon content and melting temperature of the granules. Results show that both carbon content and melting temperature of the granule influence the final structure of the sintering bed. The obtained structural change of the sintering bed show that the proposed model is a potential tool to analyse the agglomeration phenomena occurring in the iron ore sintering process under various conditions.

Pressure Drop of Centripetal Gas Flow through Rotating Beds

Abstract: The pressure drop across packed beds that are rotating differs in significant and unexpected ways, compared to the pressure drop behavior across conventional packed beds. For a wide range of operating conditions, (1) the pressure drop across an irrigated bed can be significantly lower than that across a dry bed and (2) for a fixed outer diameter, increasing the depth (i.e., more transfer units) of a rotating bed can result in a reduction in the pressure drop across the bed. Furthermore, the power required to spin the rotor diminishes as the vapor flow rate increases. Previously published correlations on the pressure drop across rotating beds do not explain or predict these phenomena. Here, a semiempirical sectional pressure drop model is presented, where all of these phenomena are related to the gas phase conserving its angular momentum as it flows from the shell through the rotating bed toward the centrally located exit.

Enhancement of heat and mass transfer in silica-expanded graphite composite blocks for adsorption heat pumps. Part II. Cooling system using the composite blocks

Abstract: Cooling systems using graphite/silica-gel composite blocks were built and their performances were compared with that of the silica gel packed bed. Spatial and temporal profiles of temperature in the composite blocks were obtained in axial and radial directions. The amount of adsorption and specific cooling powers for each composite block were also measured. It was shown that the axial profile of temperature was affected mainly by mass transfer while the radial distribution of temperature was largely due to poor heat transfer. When compared with a pure silica gel packed bed, both heat transfer and mass transfer were enhanced by using the composite blocks. As a result, the good mass and heat transfer of the composite blocks led to enhancement of performances of the cooling systems.

CFD modeling of mass-transfer processes in randomly packed distillation columns

Abstract: The volume-averaged equations for velocity and concentration fields have been used to simulate the hydrodynamics and mass-transfer processes in randomly packed distillation columns. This approach is regarded as a second-generation computational fluid dynamics (CFD) based model, and a significant departure from the traditional one-dimensional, first-generation models. The model has ability to capture radial and axial variations in flow and mass-transfer conditions. The spatial variation of void fraction has been included to take into account the effect of bed structures. The simulation results have been compared with experimental data reported by Fractionation Research, Inc. (FRI) which performed their tests in a 1.22-m-diameter column with a packed bed height of 3.66 m. For validation, we have used data obtained with 15.9-, 25.4-, and 50.8-mm metal Pall rings at various operating conditions. Good agreement between CFD predictions and published experimental data has been obtained. This is regarded as an en...