Packed beds, flow

The pressure is higher at the bottom of the sohds draw-off pipe due to the relative flow of gas counter to the sohds flow. The gas may either be flowing downward more slowly than the solids or upward. The standpipe may be fluidized, or the solids may be in moving packed bed flow with no expansion. Gas is introduced at the bottom (best for group B) or at about 3-m intervals along the standpipe (best for group A). The increasing pressure causes gas inside and between... 

In Fig. 1, a comparison can be observed for the prediction by the honeycomb reactor model developed with the parameters directly obtained from the kinetic study over the packed-bed flow reactor [6] and from the extruded honeycomb reactor for the 10 and 100 CPSI honeycomb reactors. The model with both parameters well describes the performance of both reactors although the parameters estimated from the honeycomb reactor more closely predict the experiment data than the parameters estimated from the kinetic study over the packed-bed reactor. The model with the parameters from the packed-bed reactor predicts slightly higher conversion of NO and lower emission of NHj as the reaction temperature decreases. The discrepancy also varies with respect to the reactor space velocity. 

The kinetic parameters estimated by the experimental data obtained frmn the honeycomb reactor along with the packed bed flow reactor as listed in Table 1 reveal that all the kinetic parameters estimated from both reactors are similar to each other. This indicates that the honeycomb reactor model developed in the present study can directly employ intrinsic kinetic parameters estimated from the kinetic study over the packed-bed flow reactor. It will significantly reduce the efibrt for predicting the performance of monolith and estimating the parameters for the design of the commercial SCR reactor along with the reaction kinetics. 

Fig. 1. Prediction of the model for 10 and 100 CPSI honeycomb reactors extruded with the ViOs/sulfated Xi02 catalyst. (—, prediction with the parameters estimated from the experimental data over a packed-bed flow reactor —, prediction with the parameters estimated from the experimental data over a honeycomb reactor).

C. Packed Bed CFD Simulation Issues 1. Packed Bed Flow Regimes... 

The catalyst may be held in a packed bed and the reactants passed over the catalyst. A packed bed flow reactor is commonly called a fixed bed reactor and the term plug-flow is also used to indicate that no attempt is made to back-mix the reaction mixture as it passes through the catalyst bed. The main modes of operation of a flow reactor are differential involving a small amount of reaction so that the composition of the mixture is approximately constant throughout the catalyst bed, or integral involving a more substantial amount of reaction such that the composition of material in contact with the final section of the catalyst bed is different from that entering the bed. 

Hsiao YL, Nobe K. Hydroxylation of chlorobenzene and phenol in a packed bed flow reactor with electrogenerated Fenton s reagent. J Appl Electrochem 1993 23 943-946. 

The molar balance equation for a packed bed-flow catalytic reactor is given by [126]... 

Separative flow often occurs in a packed bed—typically a tube filled with a granular material. Chromatography in packed columns is the most important example of packed-bed flow. Similar flow is found in porous membranes used for membrane separation. The fluid flowing through such media can be a gas, a liquid, or a supercritical fluid. 

In terms of organization, the text has two main parts. The first six chapters constitute generic background material applicable to a wide range of separation methods. This part includes the theoretical foundations of separations, which are rooted in transport, flow, and equilibrium phenomena. It incorporates concepts that are broadly relevant to separations diffusion, capillary and packed bed flow, viscous phenomena, Gaussian zone formation, random walk processes, criteria of band broadening and resolution, steady-state zones, the statistics of overlapping peaks, two-dimensional separations, and so on. 

Column efficiency is mainly dependent on the kinetic factors of the chromatographic system such as molecular diffusion, mass-flow dynamics, properties of the column packing bed, flow rate, and so on. The smaller the particles and the more uniform their packing in the column, the higher the efficiency. The faster the flow rate, the less time analyte molecules have for diffusive band-broadening. At the same time, the faster the flow rate, the further analyte molecules are from the thermodynamic equilibrium with the stationary phase. This shows that there should be an optimum flow rate that allows achievement of an optimum efficiency for a given column. Detailed discussions of the... 

For three-phase fluidization systems, two distinct phenomena pertaining to macroscopic hydrodynamic behavior—bed contraction and moving packed bed flow—are noted below. 

In packed-bed, flow-through electrodes, concentration and potential variation within the bed can also give more than one steady state. The convective transport equation with axial dispersion, coupled with Ohm s law for the electrode potential, was solved recently (418) by polynomial expansion and orthogonal collocation within the bed, to determine multiplicity regions. 

For this, the use of a liquid barrier stream is particularly useful, as its latent heat helps remove the heat of reaction developed in the downcomer. The barrier stream is fed and easily distributed in the moving packed bed. The reaction heat and the solid sensible heat vaporize the barrier liquid, which is fed slightly in excess to the theoretical intergranular amount of gases moving downwards, so that a net gas flow upwards is created in the upper point of the downcomer. Thus, the polymer level above the injection point forms a seal that prevents contamination between the two reaction zones as long as the packed bed flow regime is maintained. 

Niiyama and Suzuki (1982) studied hydrogenation of ethylene over Ni—A1203. Oscillations in particle temperature were observed. Similarly in a packed bed flow reactor, a multiple-particle system, the temperature of the catalyst bed and the... 

The third major factor in dynamics is packed bed flow behavior. The pressure drop in the adsorbent media is caused by drag due to fluid flowing through the interstices. For slow flow, the pressure drop, AP, across a bed of length Az and superflcial velocity v, can be represented by Darcy s equation ... 

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