Radial flow fixed-bed reactor

The foregoing summary can be understood better by seeing how the procedure is applied to a particular case, namely a radial-flow, fixed-bed reactor. Such reactors appear in a variety of processes, including... 

An analysis of radial flow, fixed bed reactor (RFBR) is carried out to determine the effects of radial flow maldistribution and flow direction. Analytical criteria for optimum operation is established via a singular perturbation approach. It is shown that at high conversion an ideal flow profile always results in a higher yield irrespective of the reaction mechanism while dependence of conversion on flow direction is second order. The analysis then concentrates on the improvement of radial profile. Asymptotic solutions are obtained for the flow equations. They offer an optimum design method well suited for industrial application. Finally, all asymptotic results are verified by a numerical experience in a more sophisticated heterogeneous, two-dimensional cell model. 

Figure 1. Schematic of radial flow, fixed bed reactor operation...

V. Balakotaiah and D. Luss, Effect of flow direction on conversion in isothermal radial flow fixed-bed reactors. AlChE J, 27 442 (1981). 

H.-C. Chang, M. Saucier, and J.M. Calo, Design criterion for radial flow fixed-bed reactors, AIChEJ. 29 1039 (1983). 

In a fixed bed reactor, gas phase reactions are generally carried out using a stationary bed of solid catalyst. In a typical reactor, suitable screens support the bed of catalyst particles, through which the gas phase flows. Gaseous reactants adsorb on the catalyst surface, reactions occur on this surface and reaction products desorb back to the gas phase. Two major types of fixed bed reactor are the conventional axial flow fixed bed reactor and the radial flow fixed bed reactor. These types are shown... 

FIGURE 13.1 Types of fixed bed reactors, (a) Axial flow fixed bed reactor Up or down flow, single or multi-stage, with or without inter-stage cooling, single or multi-tubular, (b) Radial flow fixed bed reactor Radially inward or outward flow, straight or reverse flow (direction of inlet and outlet is same or opposite to each other). 

Radial flow fixed bed reactors were developed to handle large gas flow rates with minimum pressure drop and are most suitable for processes in which fluids need to be contacted with solid particles at high space velocity (Chang and Calo, 1981). Radial flow fixed bed reactors are used for a variety of processes including catalytic synthesis of ammonia, xylene isomerization and desulphurization. 

The typical radial flow fixed bed reactor configuration shown in Fig. 13.1b is considered here. The reactor configuration is axis symmetric. Details of reactor construction are shown in Fig. 13.2 (only half of the reactor is shown since it is symmetric). The annular catalyst bed is supported by permeable cylindrical screens (inner and outer) and impermeable top and bottom cover plates. The top cover plate also comprises of a shroud as shown in Fig. 13.2. Such a shroud is generally provided to compensate for possible shrinkage in catalyst bed height with time. Reactants are fed to the reactor from the top end. The flow changes direction after hitting the cover plate. The feed enters the catalyst bed from the annular space between the catalyst bed and the... 

FIGURE 13.2 Details of considered radial flow fixed bed reactor (from Ranade, 1997). 

For a radial flow fixed bed reactor, capacity enhancement will involve the following two aspects ... 

Calo JM. Cell model studies of radial flow, fixed bed reactors. In Weekman Jr VW, Luss D, editors. Chemical Reaction Engineering—Houston. ACS Symposium Series, Vol. 65. Washington, DC American Chemical Sodetyt 1978 550-561. 

Ponzi PR, Kaye LA. Effect of flow maldistribution on conversion and selectivity in radial flow fixed-bed reactors. AIChE Journal 1979 25 100-108. 

MALDISTRIBUTION IN THE RADIAL-FLOW FIXED BED REACTOR C-.S. YOO AND A.G. DIXON... 

Ponzi, P,R, and L.A, Kaye, Effect of Flow Maldistribution on Conversion and Selectivity in Radial Flow Fixed-Bed Reactors, AIChE J. 25 (1979) 100-108. 

Chang, H. C,M, Saucier and J,M, Calo, Design Criterion for Radial Flow Fixed-Bed Reactors, AIChE J, 29 (1983) 1039-1041,... 

Cell Model Studies of Radial Flow, Fixed Bed Reactors... 

Can the Dispersion model be used for the analysis or design of a radial-flow, fixed-bed reactor, based on the existing intensity of dispersion correlations ... 

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