Showing papers on "Packed bed published in 2017"

Abatement of VOCs Using Packed Bed Non-Thermal Plasma Reactors: A Review

Abstract: Non thermal plasma (NTP) reactors packed with non-catalytic or catalytic packing material have been widely used for the abatement of volatile organic compounds such as toluene, benzene, etc. Packed bed reactors are single stage reactors where the packing material is placed directly in the plasma discharge region. The presence of packing material can alter the physical (such as discharge characteristics, power consumption, etc.) and chemical characteristics (oxidation and destruction pathway, formation of by-products, etc.) of the reactor. Thus, packed bed reactors can overcome the disadvantages of NTP reactors for abatement of volatile organic compounds (VOCs) such as lower energy efficiency and formation of unwanted toxic by-products. This paper aims at reviewing the effect of different packing materials on the abatement of different aliphatic, aromatic and chlorinated volatile organic compounds.

How bead size and dielectric constant affect the plasma behaviour in a packed bed plasma reactor: a modelling study

Abstract: Packed bed plasma reactors (PBPRs) are gaining increasing interest for use in environmental applications, such as greenhouse gas conversion into value-added chemicals or renewable fuels and volatile pollutant removal (e.g. NOx, VOC, ...), as they enhance the conversion and energy efficiency of the process compared to a non-packed reactor. However, the plasma behaviour in a PBPR is not well understood. In this paper we demonstrate, by means of a fluid model, that the discharge behaviour changes considerably when changing the size of the packing beads and their dielectric constant, while keeping the interelectrode spacing constant. At low dielectric constant, the plasma is spread out over the full discharge gap, showing significant density in the voids as well as in the connecting void channels. The electric current profile shows a strong peak during each half cycle. When the dielectric constant increases, the plasma becomes localised in the voids, with a current profile consisting of many smaller peaks during each half cycle. For large bead sizes, the shift from full gap discharge to localised discharges takes place at a higher dielectric constant than for smaller beads. Furthermore, smaller beads or beads with a lower dielectric constant require a higher breakdown voltage to cause plasma formation.

A review on process intensification in HiGee distillation

Abstract: This review paper describes the state-of-the-art in the field of HiGee contactors used for gas–liquid mass transfer processes, with a special focus on distillation, and for heterogeneously catalyzed reactions. Several types of rotating beds are discussed, including single-block rotating packed-bed, split-packing rotating bed, rotating zigzag bed, two-stage counter-current rotating packed bed, blade packing rotating packed bed, rotating bed with blade packing and baffles, counter-flow concentric-ring rotating bed and crossflow concentric-baffle rotating bed. The working principles of HiGee technology, as well as the modeling, design and control aspects, and practical applications are explained and discussed. In addition, this paper addresses the advantages and disadvantages with respect to mass-transfer performance, pressure drop, rotor complexity and suitability to perform continuous distillation and to be filled with catalyst packing for heterogeneous reactions. © 2017 Society of Chemical Industry

Plasma-catalyst interaction studied in a single pellet DBD reactor: dielectric constant effect on plasma dynamics

Abstract: A novel single dielectric pellet DBD that is designed to facilitate studying the interaction between plasmas and catalysts is presented. The influence of material dielectric constant on plasma dynamics across a range of applied voltages is determined through the use of electrical characterisation combined with videos of the discharge. Different discharge modes in nitrogen are observed and their behaviour is characterised. A particular focus is given to the phenomenon known as 'partial discharging'. This is where incomplete plasma formation occurs between the electrodes of the reactor, which may have implications for the fair testing of catalysts in packed bed reactors. Additionally, the occurrence of an 'almond shaped' QV plot in the event of point-to-point discharging in PBRs is explained. This work provides easily implemented analytical techniques that can be applied to understand the behaviour of plasmas within packed bed DBD reactors.

Influence of Gap Size and Dielectric Constant of the Packing Material on the Plasma Behaviour in a Packed Bed DBD Reactor: A Fluid Modelling Study

Abstract: A packed bed dielectric barrier discharge (DBD) was studied by means of fluid modelling, to investigate the influence of the dielectric constant of the packing on the plasma characteristics, for two different gap sizes. The electric field strength and electron temperature are much more enhanced in a microgap reactor than in a mm-gap reactor, leading to more current peaks per half-cycle, but also to non-quasineutral plasma. Increasing the dielectric constant enhances the electric field further, but only up to a certain value of dielectric constant, being 9 for a microgap and 100 for a mm-gap reactor. The enhanced electric field results in a higher electron temperature, but also lower electron density. This last one strongly affects the reaction rate.

Fundamental and Practical Insights on the Packing of Modern High-Efficiency Analytical and Capillary Columns.

Abstract: New stationary phases are continuously developed for achieving higher efficiencies and unique selectivities. The performance of any new phase can only be assessed when the columns are effectively packed under high pressure to achieve a stable bed. The science of packing columns with stationary phases is one of the most crucial steps to achieve consistent and reproducible high-resolution separations. A poorly packed column can produce non-Gaussian peak shapes and lower detection sensitivities. Given the ever larger number of stationary phases, it is impossible to arrive at a single successful approach. The column packing process can be treated as science whose unified principles remain true regardless of the stationary phase chemistry. Phenomenologically, the column packing process can be considered as a constant pressure or constant flow high-pressure filtration of a suspension inside a column with a frit at the end. This process is dependent on the non-Newtonian suspension rheology of the slurry in which...

Review on the mass transfer performance of CO2 absorption by amine-based solvents in low- and high-pressure absorption packed columns

Abstract: The gas-phase volumetric overall mass transfer coefficient (KGaV) plays a key role in the assessment of an absorption packed column's performance since it determines the height of an absorber column. The effective and useable data provided by KGaV is necessary for designing and scaling up absorption packed columns. This study provides the first comprehensive review of mass transfer performance in terms of KGaV for CO2 (KGCO2aV) absorption into amine solutions for absorber columns with random and structured packing. To date, researchers associated with the KGCO2aV parameter have focused on two main fields: experimental works and developing empirical correlations. For experimental works, KGCO2aV has been evaluated in the literature for a large number of conventional and improved amines over a range of operating parameters in laboratory-scale packed columns. In addition, researchers have developed empirical correlations for KGCO2aV based on operating parameters affecting KGCO2aV and physical properties. The details of research determining the KGCO2aV have been reviewed for low- and high-pressure absorption packed columns. Finally, directions for future research of the mass transfer performance for absorber packed columns in the CO2 capture process have been discussed.

Effect of Particle Shape on Fluid Flow and Heat Transfer for Methane Steam Reforming Reactions in a Packed Bed

Abstract: Numerical simulations of a cylindrical packed bed with tube to particle diameter ratio of 1.4, containing 10 particles, were performed to understand the effect of particle shape on pressure drop, heat transfer and reaction performance. Six particle shapes namely, cylinder as the reference, trilobe and daisy having external shaping, hollow cylinder, cylcut, and 7-hole cylinder including internal voids were chosen. Methane steam reforming reactions were considered for the heat transfer and reaction performance evaluation. The present study showed that the external shaping of particles offered lower pressure drop, but lower values of effectiveness factor indicating strong diffusion limitations. The internally shaped particles offered increased surface area, led to higher effectiveness factor and allowed to overcome the diffusion limitations. The effective heat transfer and effectiveness factor of the trilobe-shaped particle per unit pressure drop was found to be the best among the particle shapes considered in the present work. © 2016 American Institute of Chemical Engineers AIChE J, 63: 366–377, 2017

Hydrodynamics of gas–liquid flow in micropacked beds: Pressure drop, liquid holdup, and two-phase model

Abstract: Hydrodynamics of gas–liquid two-phase flow in micropacked beds are studied with a new experimental setup The pressure drop, residence time distribution, and liquid holdup are measured with gas and liquid flow rates varying from 4 to 14 sccm and 01 to 1 mL/min, respectively Key parameters are identified to control the experimentally observed hydrodynamics, including transient start-up procedure, gas and liquid superficial velocities, particle and packed bed diameters, and physical properties of the liquids Contrary to conventional large packed beds, our results demonstrate that in these microsystems, capillary forces have a large effect on pressure drop and liquid holdup, while gravity can be neglected A mathematical model describes the hydrodynamics in the micropacked beds by considering the contribution of capillary forces, and its predictions are in good agreement with experimental data © 2017 American Institute of Chemical Engineers AIChE J, 63: 4694–4704, 2017

Evaluation of an activated carbon packed bed for the adsorption of phenols from petroleum refinery wastewater

Abstract: The performance of an adsorption column packed with granular activated carbon was evaluated for the removal of phenols from refinery wastewater. The effects of phenol feed concentration (80–182 mg/l), feed flow rate (5–20 ml/min), and activated carbon packing mass (5–15 g) on the breakthrough characteristics of the adsorption system were determined. The continuous adsorption process was simulated using batch data and the parameters for a new empirical model were determined. Different dynamic models such as Adams–Bohart, Wolborsko, Thomas, and Yoon-Nelson models were also fitted to the experimental data for the sake of comparison. The empirical, Yoon–Nelson and Thomas models showed a high degree of fitting at different operation conditions, with the empirical model giving the best fit based on the Akaike information criterion (AIC). At an initial phenol concentration of 175 mg/l, packing mass of 10 g, a flow rate of 10 ml/min and a temperature of 25 °C, the SSE of the new empirical and Thomas models were identical (248.35) and very close to that of the Yoon–Nelson model (259.49). The values were significantly lower than that of the Adams–Bohart model, which was determined to be 19,358.48. The superiority of the new empirical model and the Thomas model was also confirmed from the values of the R 2 and AIC, which were 0.99 and 38.3, respectively, compared to 0.92 and 86.2 for Adams–Bohart model.

About the enhancement of chemical yield during the atmospheric plasma synthesis of ammonia in a ferroelectric packed bed reactor

Abstract: We acknowledge financial support from Junta de Andalucia through the project P12–2265 MO and from the MINECO‐CSIC through the EU regional fund project RECUPERA 2020.