Chemical reactor modeling effectiveness factor

This involves knowledge of chemistry, by the factors distinguishing the micro-kinetics of chemical reactions and macro-kinetics used to describe the physical transport phenomena. The complexity of the chemical system and insufficient knowledge of the details requires that reactions are lumped, and kinetics expressed with the aid of empirical rate constants. Physical effects in chemical reactors are difficult to eliminate from the chemical rate processes. Non-uniformities in the velocity, and temperature profiles, with interphase, intraparticle heat, and mass transfer tend to distort the kinetic data. These make the analyses and scale-up of a reactor more difficult. Reaction rate data obtained from laboratory studies without a proper account of the physical effects can produce erroneous rate expressions. Here, chemical reactor flow models using matliematical expressions show how physical... 

As with continuous processes, the heart of a batch chemical process is its reactor. Idealized reactor models were considered in Chapter 5. In an ideal-batch reactor, all fluid elements have the same residence time. There is thus an analogy between ideal-batch reactors and plug-flow reactors. There are four major factors that effect batch reactor performance ... 

An extension of this one-dimensional heterogeneous model is to consider intraparticle diffusion and temperature gradients, for which the lumped equations for the solid are replaced by second-order diffu-sion/conduction differential equations. Effectiveness factors can be used as applicable and discussed in previous parts of this section and in Sec. 7 of this Handbook (see also Froment and Bischoff, Chemical Reactor Analysis and Design, Wiley, 1990). 

The objective of Chaps. 10 and 11 is to combine intrinsic rate equations with intrapellet and fluid-to-pellet transport rates in order to obtain global rate equations useful for design. It is at this point that models of porous catalyst pellets and effectiveness factors are introduced. Slurry reactors offer an excellent example of the interrelation between chemical and physical processes, and such systems are used to illustrate the formulation of global rates of reaction. 

The dusty gas model is often used as the basis for the calculation of a catalyst effectiveness factor in chemical reactor analysis. The extension to non-ideal fluids noted above and its application in RD modeling has not been used as often, partly because of the somewhat greater uncertainty in the parameters that appear in the equations [1, 11]. 

Mathematical analysis of chemical reactors is based on mass, energy, and momentum balances. The main features to be considered in reactor analysis include stoichiometry, thermodynamics and kinetics, mass and heat transfer effects, and flow modeling. The different factors governing the analysis and design of chemical reactors are illustrated in Figure 1.3. In subsequent chapters, all these aspects will be covered. 

Understanding and modelling the effects of various factors governing the stability of two-phase dispersions systems is vital since it influences the process design of appropriate chemical reactors, their subsequent downstream processing, storage and transportation. Central to this is the ability to make direct measurement of the sedimentation kinetics of such dispersions in an on-line manner. 

Various aspects of the effect of process scale-up on the safety of batch reactors have been discussed by Gygax [7], who presents methods to assess thermal runaway. Shukla and Pushpavanam [8] present parametric sensitivy and safety results for three exothermic systems modeled using pseudohomogenous rate expressions from the literature. Caygill et al. [9] identify the common factors that cause a reduction in performance on scale-up. They present results of a survey of pharmaceutical and fine chemicals companies indicating that problems with mixing and heat transfer are commonly experienced with large-scale reactors. 

ABSTRACT The optimisation of charcoal production in a retort kiln calls for control of the carbonization mass and energy flows. These depend essentially on three types of factors the physico-chemical characteristics of the raw material, the operational parameters and the reactor parameters. Carbonization experiments have been conducted to assess and to model the effect of four physical characteristics moisture content (two levels 0 %, 37 % dry basis), density (two levels beech wood (650 - 740 kg/m anhydrous basis) and poplar wood (398 - 426 kg/m anhydrous basis)), dimension and shape (two levels cubes of 4 cm side and blocks of 4x4x 16 cm, length parallel to the fibres orientation). The carbonization final temperature was 500° C, the residence time at this temperature was 100 min. The heating rates were 2 and 20°... 

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