Comparison between dispersion and plug-flow models for fixed-bed enzyme reactors

AIChE Journal ◽  
1992 ◽  
Vol 38 (9) ◽  
pp. 1477-1480 ◽  
Author(s):  
Robert Lortie ◽  
Dominique Pelletier
Keyword(s):  
Plug Flow ◽  
Fixed Bed ◽  
Flow Models ◽  
Enzyme Reactors

scholarly journals Particle-Resolved Computational Fluid Dynamics as the Basis for Thermal Process Intensification of Fixed-Bed Reactors on Multiple Scales

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2913
Author(s):  
Nico Jurtz ◽  
Urvashi Srivastava ◽  
Alireza Attari Moghaddam ◽  
Matthias Kraume
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Transport ◽  
Multiple Scales ◽  
Plug Flow ◽  
Fixed Bed ◽  
Process Intensification ◽  
Transport Parameters ◽  
Flow Models ◽  
Fixed Bed Reactors

Process intensification of catalytic fixed-bed reactors is of vital interest and can be conducted on different length scales, ranging from the molecular scale to the pellet scale to the plant scale. Particle-resolved computational fluid dynamics (CFD) is used to characterize different reactor designs regarding optimized heat transport characteristics on the pellet scale. Packings of cylinders, Raschig rings, four-hole cylinders, and spheres were investigated regarding their impact on bed morphology, fluid dynamics, and heat transport, whereby for the latter particle shape, the influence of macroscopic wall structures on the radial heat transport was also studied. Key performance indicators such as the global heat transfer coefficient and the specific pressure drop were evaluated to compare the thermal performance of the different designs. For plant-scale intensification, effective transport parameters that are needed for simplified pseudo-homogeneous two-dimensional plug flow models were determined from the CFD results, and the accuracy of the simplified modeling approach was judged.

Hydrogen Production from Ethanol Steam Reforming: Fixed Bed Reactor Design

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Pablo Giunta ◽  
Norma Amadeo ◽  
Miguel Laborde
Keyword(s):  
Steam Reforming ◽  
Flow Model ◽  
Multicomponent Mixture ◽  
Plug Flow ◽  
Fixed Bed ◽  
Fixed Bed Reactor ◽  
Ethanol Steam Reforming ◽  
Heterogeneous Model ◽  
Ethanol Steam ◽  
Hydrogen Stream

The aim of this work is to design an ethanol steam reformer to produce a hydrogen stream capable of feeding a 60 kW PEM fuel cell applying the plug flow model, considering the presence of the catalyst bed (heterogeneous model). The Dusty-Gas Model is employed for the catalyst, since it better predicts the fluxes of a multicomponent mixture. Moreover, this model has shown to be computationally more robust than the Fickian Model. A power law-type kinetics was used. Results showed that it is possible to carry out the ethanol steam reforming in a compact device (1.66 x 10 -5 to 5.27 x 10 -5 m3). It was also observed that this process is determined by heat transfer.

Degradation of chlorophenols by biofilms on semi-permeable membranes in two types of fixed bed reactors

1995 ◽  
Vol 32 (8) ◽  
pp. 205-212 ◽  
Author(s):  
A. Wobus ◽  
S. Ulrich ◽  
I. Röske
Keyword(s):  
Continuous Flow ◽  
Plug Flow ◽  
Fixed Bed ◽  
Biofilm Reactor ◽  
Flow Conditions ◽  
Concentration Gradients ◽  
Batch Mode ◽  
Sequencing Batch Biofilm Reactor ◽  
Fixed Bed Reactors ◽  
Protozoan Community

Two identical fixed bed reactors containing gas-permeable tubings as carrier material were compared for the elimination of chlorophenols. Under plug flow conditions, the continuous flow operation resulted in a stratification of biomass due to concentration gradients. To achieve a homogeneous colonization, the sequencing batch mode has been applicated to one biofilm reactor (Sequencing Batch Biofilm Reactor - SBBR). Concentration gradients after filling, probably due to sorption phenomena, caused an uneven distribution of biomass in the SBBR. However, the colonization of the SBBR was more homogeneous as compared to the continuously operated reactor (CFBR). As to the elimination of a trichlorophenol (2,4,5-trichlorophenol - TCP), no significant differences between the SBBR and the CFBR were observed with regard to its sensitivity against load surges. It is to be supposed that sorption to the biofilm was included in the elimination of chlorophenols. A higher diversity of protozoan community and meiofauna is obviously to be attributed to continuous flow.

scholarly journals Hydrogenation and Dehydrogenation of Tetralin and Naphthalene to Explore Heavy Oil Upgrading Using NiMo/Al2O3 and CoMo/Al2O3 Catalysts Heated with Steel Balls via Induction

Catalysts ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 497 ◽  
Author(s):  
Abarasi Hart ◽  
Mohamed Adam ◽  
John P. Robinson ◽  
Sean P. Rigby ◽  
Joseph Wood
Keyword(s):  
Heavy Oil ◽  
Coke Formation ◽  
Plug Flow ◽  
Fixed Bed ◽  
Effect Of Temperature ◽  
Catalytic Upgrading ◽  
Heavy Oil Upgrading ◽  
Steel Balls ◽  
Surrounding Fluid

This paper reports the hydrogenation and dehydrogenation of tetralin and naphthalene as model reactions that mimic polyaromatic compounds found in heavy oil. The focus is to explore complex heavy oil upgrading using NiMo/Al2O3 and CoMo/Al2O3 catalysts heated inductively with 3 mm steel balls. The application is to augment and create uniform temperature in the vicinity of the CAtalytic upgrading PRocess In-situ (CAPRI) combined with the Toe-to-Heel Air Injection (THAI) process. The effect of temperature in the range of 210–380 °C and flowrate of 1–3 mL/min were studied at catalyst/steel balls 70% (v/v), pressure 18 bar, and gas flowrate 200 mL/min (H2 or N2). The fixed bed kinetics data were described with a first-order rate equation and an assumed plug flow model. It was found that Ni metal showed higher hydrogenation/dehydrogenation functionality than Co. As the reaction temperature increased from 210 to 300 °C, naphthalene hydrogenation increased, while further temperature increases to 380 °C caused a decrease. The apparent activation energy achieved for naphthalene hydrogenation was 16.3 kJ/mol. The rate of naphthalene hydrogenation was faster than tetralin with the rate constant in the ratio of 1:2.5 (tetralin/naphthalene). It was demonstrated that an inductively heated mixed catalytic bed had a smaller temperature gradient between the catalyst and the surrounding fluid than the conventional heated one. This favored endothermic tetralin dehydrogenation rather than exothermic naphthalene hydrogenation. It was also found that tetralin dehydrogenation produced six times more coke and caused more catalyst pore plugging than naphthalene hydrogenation. Hence, hydrogen addition enhanced the desorption of products from the catalyst surface and reduced coke formation.

Optimal Design, Modeling and Simulation of an Ethanol Steam Reforming Reactor

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Luis E Arteaga ◽  
Luis M Peralta ◽  
Yannay Casas ◽  
Daikenel Castro
Keyword(s):  
Hydrogen Production ◽  
Modeling And Simulation ◽  
Design Patterns ◽  
Plug Flow ◽  
Fixed Bed ◽  
Cell System ◽  
Fixed Bed Reactor ◽  
Effect Of Temperature ◽  
Ethanol Conversion ◽  
Renewable Hydrogen

The optimum design, modeling and simulation of a fixed bed multi-tube reformer for the renewable hydrogen production are carried out in the present paper. The analogies between plug flow model and a fixed bed reactor are used as design patterns. The steam reformer is designed to produce enough hydrogen to feed a 200kW fuel cell system (>2.19molH/s) and considering 85% of fuel utilization in the cell electrodes. The reactor prototype is optimized and then analyzed using a multiphysics and axisymmetric model, implemented on FEMLABM(R) where the differential mass balance by convection-diffusion and the energy balance for convection-conduction are solved. The temperature profile is controlled to maximize hydrogen production. The catalyst bed internal profiles and the effect of temperature on ethanol conversion and carbon monoxide production are discussed as well.

Solids Flow Models for Gas - Flowing Solids - Fixed Bed Contactors

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Nikola M Nikacevic ◽  
Milorad P. Dudukovic
Keyword(s):  
Dispersion Model ◽  
Fixed Bed ◽  
Axial Dispersion ◽  
Step Response ◽  
Model Parameters ◽  
Response Curves ◽  
Flow Models ◽  
Solids Holdup ◽  
Axial Dispersion Model ◽  
Static Zone

Three solids flow models for gas – flowing solids – fixed bed contactors are analyzed. They all presume axial dispersion in the dynamic, freely flowing zone, but they differ in the interpretation of the stagnant zone. The models have been examined and the model parameters have been optimized on the basis of two types of tracer experiments. One provides step response curves for flowing solids at the exit and the other presents the response curves of the static flowing solids holdup. The model which assumes axial dispersion and exchange between dynamic and two active static zones, most accurately describes the solids flow pattern. A simpler model which presumes exchange between dynamic and one static zone can be used if there is no need for a precise description of the behavior of stagnant particles. The most simple axial dispersion model is not realistic, as it does not explain stagnancy at all, which was experimentally observed for the gas – flowing solids – fixed bed contactors.

scholarly journals INLET TEMPERATURE INFLUENCE ON ISOTHERMAL GAS CLEANING FROM MONO-IMPURITIES BY FIXED LAYER OF ADSORBENT

2020 ◽  
Vol 63 (9) ◽  
pp. 88-92
Author(s):  
Olga N. Filimonova ◽  
Andrey S. Vikulin ◽  
Marina V. Enyutina ◽  
Alexey V. Ivanov
Keyword(s):  
Gas Flow ◽  
Physical Adsorption ◽  
Plug Flow ◽  
Fixed Bed ◽  
Initial Boundary ◽  
Gas Production ◽  
Solid Particles ◽  
Inlet Temperature ◽  
Isothermal Adsorption ◽  
Gas Cleaning

The influence of the temperature of the inlet gas containing mono-impurity was evaluated for the process of physical adsorption purification in a porous fixed bed of granular adsorbent. The theoretical analysis is based on the classical mathematical model of the isothermal adsorption dynamics in a porous stationary medium structurally made-up of the dispersed phase of solid particles, under the assumptions made: the gas to be purified contains a low-concentration mono-impurity, its motion in the adsorber is unidirectional, and the levelling effect of the velocity profile in the porous cross section environment allowed to adopt the hydrodynamic regime of plug flow; axial mixing in the gas flow  is negligible; the adsorption heat is negligible; the layer porosity is uniform; adsorption rate is determined by the sorption kinetics equation with an isotherm, obeying Henry's law. An initial-boundary-value problem is formulated for a system of first-order partial differential equations, which solution with respect to mono-impurity concentrations in the gas stream and adsorbent is obtained in an explicit analytical form using the one-sided integral Laplace transform. A comparative analysis of the computational experiment results with known experimental data showed that the proposed model with an assumptions system is quite adequate qualitatively and quantitatively describes the adsorption separation process. Using the example of an industrial adsorber functioning in the ZB-120/120 complex purification unit in a mobile gas production system, it is shown that the temperature increase by 10 K of inlet dried air after compression containing carbon dioxide reduces the working time in the adsorption stage by 45%. It has been established that the temperature change in the gas inlet flow has a significant effect on the adsorber efficiency and should be taken into account when identifying the overall characteristics of the complex cleaning unit.

A Capillary Electrophoresis Platform With “On-Chip” Electrochemical Detection: Experimental and Computational Flow Studies

2001 ◽  
Author(s):  
Thomas J. Roussel ◽  
Robert S. Keynton ◽  
Kevin M. Walsh ◽  
Mark M. Crain ◽  
John F. Naber ◽  
...  
Keyword(s):  
Capillary Electrophoresis ◽  
Electrochemical Detection ◽  
Power Supply ◽  
Electroosmotic Flow ◽  
Plug Flow ◽  
Finite Element Models ◽  
Separation Channel ◽  
Flow Models ◽  
On Chip ◽  
Electrochemical Potentials

Abstract The purpose of this study was to compare experimental electrokinetic plug flow velocities to computational flow models of microfabricated capillaries. Electroosmotic flow studies of dichlorofluorescein and electrophoretic separation of dopamine and catechol in a microfabricated capillary electrophoresis (CE) system were performed both experimentally and computationally. A “balanced cross design” consisting of a bent 2 cm long injection channel and a straight 2 cm long separation channel was used. The geometry of the capillary was 65 μm wide and 20 μm deep. For the fluorescein study, separation voltages ranging between 0.25 kV and 1 kV were applied, while voltages ranging from 100 V to 550 V were used in the separation studies. Laser Induced Fluorescent (LIF) images were obtained for flow visualization and qualitative analysis in the electroosmotic flow studies, while electrochemical potentials were acquired using “on-chip” electrodes interfaced to a custom-designed power supply and electrochemical detection (ECD) circuit. Finite element models of the experimental device were generated and flows were simulated using commercially available software. For the electroosmotic flow studies, the computational results were found to be within ± 11% of the experimentally obtained values. Similarly, the results of the computational separations of catechol and dopamine predicted plug velocities that were within ± 7.6% of the experimentally determined values.

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