Reactors catalytic gas-solid

The ordinary burning of sulfur produces SO2. This is the hrst step in the manufacture of sulfuric acid. The second step oxidizes SO2 to SO3 in a gas-solid catalytic reactor. The catalyst increases the reaction rate but does not change the equilibrium compositions in the gas phase. 

Show that the effect of axial dispersion on the conversion obtained in a typical packed bed gas-solid catalytic reactor is small. As the starting point consider the following relationship (see Chapter 2, equation 2.30). 

S. Elnashaie, S. Elshishini, Dynamic Modeling, Bifurcation and Chaotic Behaviour of Gas-Solid Catalytic Reactors, Gordon and Breach, 1996, 646 p... 

Froment, G.F., Hofmann, H., Design of fixed-bed gas-solid catalytic reactors, in Chemical Reaction and Reaction Engineering, Marcel Dekker, New York, USA, 1987... 

Gas-solid heterogeneous reactions may be noncatalytic. An example is the hydrofluorination of uranium dioxide pellets referred to in Sec. 7-1. Since one reactant is in the solid phase and is consumed, the rate of reaction varies with time. Hence such processes are basically transient, in comparison with the steady-state operation of gas-solid catalytic reactors. The process for smelting ores such as zinc sulfide,... 

As in the case of gas-solid catalytic reactors (Table 11.11), fluid-fluid reactors can also be rated in terms of ease of operation and cost. Such a rating is presented in Table 11.20. Further details about these reactors are given by Danckwerts (1970) and Doraiswamy and Sharma (1984). 

Volume 9 DYNAMIC MODELLING, BIFURCATION AND CHAOTIC BEHAVIOUR OF GAS-SOLID CATALYTIC REACTORS by S.S.E.H. Elnashaie and S.S. Elshishini... 

Radial dispersion of mass and heat in fixed bed gas-solid catalytic reactors is usually expressed by radial Peclet number for mass and heat transport. In many cases radial dispersion is negligible if the reactor is adiabatic because there is then no driving force for long range gradients to exist in the radial direction. For non-adiabatic reactors, the heat transfer coeflScient at the wall between the reaction mixture and the cooling medium needs also to be specified. 

The conventional ammonia production line consists of seven gas-solid catalytic reactors, namely desulfurization unit, primary reformer, secondary reformer, high temperature shift, low temperature shift, methanator and finally the ammonia converter. In addition the production line includes an absorption-stripping unit for the removal of CO2 from the gas stream leaving the low temperature shift converter. The ammonia converter is certainly the heart of the process with all the other units serving to prepare the gases for the ammonia synthesis reaction which takes place over an iron promoted catalyst under conditions of high temperature and pressure. 

Types of reactors a. Gas-solid catalytic reactors Fixed bed reactors... 

The design of such gas-solid catalytic reactors can be approximated by a pseudo-homogeneous model with gas phase in plug flow. In the case of very exothermic reactions accounting for radial dispersion of heat and mass might be useful to prevent excessive particle overheating. The reaction time must find a compromise with the hydrodynamic design, namely the maximum gas velocity and pressure drop. 

To measure the pressure drop in a two-phase gas-solids catalytic reactor, 1 in. diameter sonic orifices are installed. The supply nitrogen pressure is 9 atm and it is at a temperature of 20 °C ... 

The risks of using space velocity for scale-up of fixed-bed (gas-solid) catalytic reactors are well known [12]. Trickle-bed... 

This chapter covers the basic principles of multiplicity, bifurcation, and chaotic behavior. The industrial and practical relevance of these phenomena is also explained, with referenee to a number of important industrial processes. Chapter 7 eovers the main sources of these phenomena for both isothermal and nonisothermal systems in a rather pragmatic manner and with a minimum of mathematics. One of the authors has published a more detailed book on the subject (S. S. E. H. Elnashaie and S. S. Elshishini, Dynamic Modelling, Bifurcation and Chaotic Behavior of Gas-Solid Catalytic Reactors, Gordon Breach, London, 1996) interested readers should eonsult this reference and the other references given at the end of Chapter 7 to further broaden their understanding of these phenomena. 

Froment, G.F. and Hofmann, H.P.K. (1987), Design of Fixed Bed Gas-Solid Catalytic Reactors, in JJ.Carberry and A.Varma, Eds., Chemical Reaction and Reactor Engineering, 373-440 (Marcel Dekker). [235]... 

Pereira, C.J., Wang, J.B., and Varma, A. (1979) A Justification of the Internal Isothermal Model for Gas-Solid Catalytic Reactors , AIChE J. 25, 1036-1043. 

---