Dynamic Analysis of Tubular Reactors

In this chapter, tubular chemical reactors will be analyzed. Reaction mechanisms considered are first order in the components. As will be shown, at isothermal conditions reactor dynamics can be described by partial dififerential equations for the component balances. If non-isothermal conditions exist, the energy balance would also be a partial differential equation. Dynamics models are considerably different from the models for ideally stirred chemical reactors under similar operating conditions. 

The previous chapter dealt with ideally mixed reactors. Tubular reactors, as shown in Fig. 13.1, oflen give a higher conversion than ideally mixed reactors for the same reaction conditions because on average the reactant concentration is higher. They are therefore, theoretically, preferred over stirred tank reactors. 

To limit complexity, let us start out by making the following assumptions  

Assumptions d, e and g mean that the flow through the reactor can be considered to be plug flow. 

Process Dynamics and Control Modeling for Control and Prediction. Brian Roffel and Ben Betlem. 2006 John Wiley Sons Ltd. 

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Dynamic analysis of tubular reactors(both packed or empty) has the following main characteristics ... 

Kinetic analysis of main reactor in dependence on used catalytic system showed (see 5.2) that under oligomerization of piperylene initiated by AICl3-0(C6H5)2 it is advisable to use tubular turbulent apparatus. Not high values of dynamic viscosity of liquid oligo-piperylene rubber at output of reactor (at 283 K, i = 1 mPa Sec) allows also perfecting of stage of catalyst deactivation by propylene oxide or water (Fig. 6.8b). 

In this work, thermal cracking reactors of ethylene plants are investigated dynamically. The main attention is given to the cracking coil. The modelling of the furnace itself is not considered.The tubular reactor is modelled by assuming the external wall temperature profile or heat flux profile of the coil. There is no report on dynamic analysis of this type of reactor in the literature except Jackman and Arises work (12). The literature is mainly interested in the steady state modelling of these reactors and control. 

Kirkbir,F. "Dynamic Analysis of a Tubular Reactor". M.Sc.Thesis Middle East Technical University, Turkey. (1984). 

This example models the dynamic behaviour of an non-ideal isothermal tubular reactor in order to predict the variation of concentration, with respect to both axial distance along the reactor and flow time. Non-ideal flow in the reactor is represented by the axial dispersion flow model. The analysis is based on a simple, isothermal first-order reaction. 

Computational fluid dynamics (CFD) approaches are emerging as alternative detailed tools for examining polymerization systems with complex mixing and reactor components. Recent examples on LDPE cases include Kolhapure and Fox [118], micromixing effects in tubular reactors Zhou etal. [119], tubular (and autoclave) reactors Wells and Ray [120], analysis of imperfect mixing effects applicable to many reactive flow systems, including LDPE autoclaves and Buchelli etal. [121], fouling effects. 

Bonvin,D., R.G.Rinker and D.A.Mellichamp. "Dynamic Analysis and Control of a Tubular Reactor at an Unstable State". Chem.Eng. Sci. v35 (1980) 603-612. 

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