Catalyst flow model

Thus the ECCU always operates in complete heat balance at any desired hydrocarbon feed rate and reactor temperature this heat balance is achieved in units such as the one shown in Eigure 1 by varying the catalyst circulation rate. Catalyst flow is controlled by a sHde valve located in the catalyst transfer line from the regenerator to the reactor and in the catalyst return line from the reactor to the regenerator. In some older style units of the Exxon Model IV-type, where catalyst flow is controlled by pressure balance between the reactor and regenerator, the heat-balance control is more often achieved by changing the temperature of the hydrocarbon feed entering the riser. 

Fig. 2 compares the experiments (at 50 C) with the calculations by using the plug-flow model without adjusting the kinetic parameters. The predictions are quite satisfactory except for large catalyst loading. This is an indication that in this reaction more than one elementary... 

To summarize, to properly model liquid water transport and ensuing flooding effect on cell performance, one must consider four submodels (1) a model of catalytic surface coverage by liquid water inside the catalyst layer, (2) a model of liquid water transport through hydrophobic microporous layer and GDL, (3) an interfacial droplet model at the GDL surface, and last (4) a two-phase flow model in the gas channel. Both experimental and theoretical works, in academia and industry alike, are ongoing to build models for the four key steps of water generation, transport, and removal from a PEFC. 

The kinetic analysis of the whole set of transient data collected over the powdered SCR catalyst has been addressed using the dynamic ID isothermal heterogeneous plug-flow model of the test microreactor (Chatterjee et al., 2005 Ciardelli et al., 2004a) described in Section IV. 

There are numerous applications that depend on chemically reacting flow in a channel, many of which can be represented accurately using boundary-layer approximations. One important set of applications is chemical vapor deposition in a channel reactor (e.g., Figs. 1.5, 5.1, or 5.6), where both gas-phase and surface chemistry are usually important. Fuel cells often have channels that distribute the fuel and air to the electrochemically active surfaces (e.g., Fig. 1.6). While the flow rates and channel dimensions may be sufficiently small to justify plug-flow models, large systems may require boundary-layer models to represent spatial variations across the channel width. A great variety of catalyst systems use... 

The Munakata study utilized an upflow packed bed column filled with 0.1-2.0 g of 1% w/w Pd/alumina catalyst crushed to a 0.3-0.8 mm size fraction. (Munakata et al. 1998) The influent water stream consisted of deionized water containing 1.5-25 mg/L ofTCE. Hydrogen was supplied by purging the influent water supply with hydrogen gas and pressurizing it to 0.5 atm. As in the Yu study, a plug flow model was used and an apparent first order rate constant with respect to TCE was calculated. 

Riser Model. The riser is represented by a steady state adiabatic plug flow model with no slip between oil and catalyst (18). The material and energy balances give ... 

An additional and important advantage of the recycle reactor, compared to the differential packed bed reactor, is that here flow uniformity through the bed is not required, so channeling is not a problem and one layer of catalyst or even separate particles can be used in the reactor. For packed bed reactors, flow nonuniformity would inhibit the application of the plug flow model. 

All these results indicate that although, as predicted by both the holdup and the effective catalyst-wetting models, the conversions in pilot-scale hydroprocessing reactors depend upon the liquid flow rate, and log-log plots of ln(Ci/Cc) versus either l/LHSV or L are straight lines, the slopes of these plots depend upon the nature of the feed, temperature, and the catalyst size. 

In the previous section, it was recognized that for perfect fluid distribution flow direction has only a second order effect on conversion. In this section, the effects of maldistribution are investigated. In order to eliminate the influence of flow direction, a pseudo-homogeneous plug flow model is used with purely radial flow through the catalyst basket. The governing equation is thus Eqn. (14), which in more convenient form is... 

In the Multigrain model, fractured catalyst microparticles are produced during the polymerization and uniformly dispersed in the polymer each of these particles behaves as a micro Solid core and diffusion within them, as well as in the interstices between them, can take place. In the Polymeric flow model the catalyst microparticles are dispersed in a polymer continuum and move outward in proportion to the volumetric expansion due to polymerization only one value of diffusivity is considered. Both these models predict significant MWD broadening due to mass transfer limitations (Q , 9 for polypropylene in the Polymeric flow model) on the basis of mathematical calculations carried out assuming reasonable values of the kinetic and physical parameters. 

The influence of longitudinal dispersion on the extent of a first-order catalytic reaction has been studied by Kobayashi and Arai (K14), Furusaki (F13), van Swaay and Zuiderweg (V8), and others. They use the one-dimensional two-phase diffusion model, and show that longitudinal dispersion of the emulsion has little effect when the reaction rate is low. Based on the circulation flow model (Fig. 2) Miyauchi and Morooka (M29) have shown that the mechanism of longitudinal dispersion in a fluidized catalyst bed is a kind of Taylor dispersion (G6, T9). The influence of the emulsion-phase recirculation on the extent of reaction disappears when the term tp defined by Eq. (7-18) (see Section VII) is greater than about 10. For large-diameter beds, where p does not satisfy this restriction, their general treatment includes the contribution of Taylor dispersion for both the reactant gas and the emulsion (M29). 

It is, however, necessary to ensure that elimination of the shroud does not lead to flow mal-distribution by proper redesign of the screens. The support screens for the catalyst added in zone C also need to be properly designed to ensure uniform flow through the catalyst bed. It is, therefore, essential to develop a detailed flow model to evaluate these possibilities. 

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