Reactor radial flow

Assuming that only the radial velocity is nonzero, but retaining two-dimensional pressure variation, we can reduce the continuity and momentum equations to the following system  

The Jeffery-Hamel analysis seeks solutions for the radial velocity u in a separable form as 

Substitution into the momentum equations, cross differentiating, and subtracting yields the following third-order differential equation, 

Note that this equation still retains the radial coordinate r. Therefore, unlike wedge case, there is not a unique ordinary differential that applies at any radius. Rather, there is an ordinary differential for every r position. Such local similarity behavior certainly represents a simplification compared to the original partial-differential-equation system. Nevertheless, the differential equation is more complex than that for the wedge case. 

The equation can be put into nondimensional form, following much the same procedure as used for the wedge case. Define nondimensional variables as 

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Catalysts intended for different appHcations may require their own unique types of reactor and operating conditions, but the key to designing a successful system is to use the same feedstock composition that is expected in the ultimate commercial installation and to impose so far as is possible the same operating conditions as will be used commercially (35). This usually means a reactor design involving a tubular or smaH-bed reactor of one type or another that can simulate either commercial multitubular reactors or commercial-size catalyst beds, including radial flow reactors. 

In most existing styrene processes, the catalyst is loaded into large, radial flow reactors, which are operated adiabaticaHy at low pressure and temperatures near 600°C. Heat is suppHed by superheated steam. During start-up, dehydrogenation begins slowly and accelerates as the Fe (HI) is reduced to Fe (II,III). The catalyst, which was red in color when fresh, turns to the characteristic black color of Fe O. ... 

More up-to-date data of this process are employed in a study by Rase (Fixed Bed Reactor Design and Diagnostics, Butterworths, 1990, pp. 275-286). In order to keep the pressure drop low, radial flow reactors are used, two units in series with reheating between them. Simultaneous formation of benzene, toluene, and minor products is taken into account. An economic comparison is made of two different catalysts under a variety of operating conditions. Some of the computer printouts are shown there. 

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

Figure 8.22. Schematic drawing of an adiabatic two-bed radial flow reactor. There are three inlets and one outlet. The major inlet comes in from the top (left) and follows the high-pressure shell (which it cools) to the bottom, where it is heated by the gas leaving the reactor bottom (left). Additional gas is added at this point (bottom right) and it then flows along the center, where even more gas is added. The gas is then let into the first bed (A) where it flows radially inward and reacts adiabatically whereby it is heated and approaches equilibrium (B). It is then cooled in the upper heat exchanger and move on to the second bed (C) where it again reacts adiabatically, leading to a temperature rise, and makes a new approach to equilibrium (D). (Courtesy of Haldor Topspe AS.)...

Fig. 7.10 A proposed radial-flow reactor to deposit a film on eight 75-mm wafers.

Figure 9. Main design concepts for adiabatic reactors. A) Adiabatic packed-bed reactor B) Disk reactor C) Radial-flow reactor.

A critical feature of packed radial-flow reactors is the shape of the upper bed closure. A simple horizontal covering is not practicable since a gap through which unreacted gas can pass is then formed due to the unavoidable settling of the packing. The arrangement... 

Explorations of new electrochemical routes to traditional as well as specialty chemicals via electro-organic synthesis have given rise to a search for more efficient electrochemical reactors. The radial flow reactors or cells show promise compared to the conventional parallel plate configurations. A typical radial flow reactor is schematically shown in Fig. 39, which includes the... 

Description The process consists of a reactor section, continuous catalyst regeneration (CCR) section and product-recovery section. Stacked radial-flow reactors (1) facilitate catalyst transfer to and from the CCR catalyst regeneration section (2). A charge heater and interheaters (3) achieve optimum conversion and selectivity for the endothermic reaction. Reactor effluent is separated into liquid and vapor products (4). The liquid product is sent to a stripper column (5) to remove light saturates from the C6 aromatic product. Vapor from the separator is compressed and sent to a gas recovery unit (6). The compressed vapor is then separated into a 95% pure hydrogen coproduct, a fuel-gas stream containing light byproducts and a recycled stream of unconverted LPG. 

The packed bed reactors section of this volume presents topics of catalyst deactivation and radial flow reactors, along with numerical techniques for solving the differential mass and energy balances in packed bed reactors. The advantages and limitations of various models (e.g., pseudo-homogeneous vs. heterogeneous) used to describe packed bed reactors are also presented in this section. 

Work on the fluid mechanics of radial flow reactors can be traced back to the calculations of radial velocity profiles by Soviet investigators (1,2). This analysis was later repeated by... 

Recently a rather unique concept was developed by a Fast Engineering Ltd. in Russia [859], The catalyst bed of the radial flow reactor is subdivided by cooling elements into several sections in a spiral-like configuration, as shown in Figure 84. In a revamp operation the existing converter of a 600 t/d ammonia plant in the Cherkassy production complex was equipped with a new basket having the innovative design filled with... 

Radial flow reactors can be used to good advantage for exothermic reactions with large heats of reaction. The radical velocity varies as... 

PS-18a Radial flow reactors are used to help eliminate hot spots in highly exothermic reactions. The velocity is highest at the inlet and then decreases as 1 /r as ihe fluid moves away from the inlet. The overall heat-transfer coefficient varies with the square root of the radial velocity ... 

Consider die flow conditions to one of the tubes for the SO oxidation described in Example 8-10. Replace the tube with a radial flow reactor I cm in height with an inlet diameter of 0.5 cm. The reactor is immersed in the same boUing liquid as in Example 8-10. Plot the temperature and conversion as a function of radius and catalyst weight for three different inlet temperatures, Study the behavior of thi.s reactor by varying a number of parameters, such as flow rate and gas composition. 

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