Reactor adiabatic beds

Nonisothermal reactors with adiabatic beds. Optimization of the temperature profile described above assumes that heat can be added or removed wherever required and at whatever rate required so that the optimal temperature profile can be achieved. A superstructure can be set up to examine design options involving adiabatic reaction sections. Figure 7.12 shows a superstructure for a reactor with adiabatic sections912 that allows heat to be transferred indirectly or directly through intermediate feed injection. 

Optimal adiabatic bed reactors for sulfur dioxide with cold shot cooling (with K.-Y. Lee). Ind. Eng. Chem. Proc. Des.-Dev. 2, 300-306 (1963). 

The resulting equations are linear in the unknown variables, so an analytical solution is easily obtained. For example, for the case with three adiabatic beds (NR = 3) in the reactor vessel, there are six equations and six unknowns (T ci r(2, 7 c3> Fj, Fos,2 and Fes,3) ... 

In ammonia synthesis, high temperatures correspond to small reactor volumes. For exothermic reactions, the equilibrium conversion Xe decreases as the temperature increases. Therefore, these reactions are often carried out in a series of adiabatic beds with either intermediate heat exchangers to cool the gases or bypass the cold feed to decrease the temperatures between the beds. Some compromise can be achieved between high temperatures involving small reactor volumes and high equilibrium conversions. 

In most applications of trickle-flow reactors, the conversions generate heat that causes a temperature rise of the reactants, since the industrial reactors are generally operated adiabatically. In the cocurrent mode of operation, both the gas and the liquid rise in temperature as they accumulate heat, so there is a significant temperature profile in the axial direction, with the highest temperature at the exit end. When the total adiabatic temperature rise exceeds the allowable temperature span for the reaction, the total catalyst volume is generally split up between several adiabatic beds, with interbed cooling of the reactants. In the countercurrent mode of operation, heat is transported by gas and liquid in both directions, rather than in one direction only, and this may increase the possibility of obtaining a more desirable temperature profile over the reactor. 

Leitenberger s work (1939) is concerned with the oxidation of sulfur dioxide in adiabatic beds and tubular reactors. Using the Boresskow-Slinko kinetic equation he calculated the optimal tem-6... 

The search continues for better and more economical processes for the production of ethylene. Those processes include catalytic thermal cracking, methanol to ethylene, oxidative coupling of methane, advanced cracking technology, adiabatic cracking reactor, fluidized bed cracking, membrane reactor, oxydehy-drogenation, ethanol to ethylene, propylene disproportionation, and coal to ethylene. Much work is still needed before any such process can compete with current processes. 

This suggests a useful graphical presentation of the design of an adiabatic tubular reactor. In Fig. 8.8 the equilibrium line Fe and the curve of maximum reaction rate in an adiabatic bed, are shown. The broken lines are adiabatic paths. Let and be the extent and temperature at a point on Then the adiabatic path through such a point is... 

J. P. Malenge and J. Villermaux, Optimal Adiabatic Bed Reactor with Cold Shot Cooling, Ind. Eng. Chem. Process Design and Develop., 6, 535 (1967). 

Fixed-bed reactors (multi-tubular and staged adiabatic), fluidized-bed reactors (bubbling bed, turbulent bed, fast, and transport or pneumatic), radial flow reactor, gauz reactor... 

The temperature-composition relation in such a multibed adiabatic reactor is illustrated in Fig. 11.3-4 for ammonia synthesis [3]. The F, curve in this diagram represents the equilibrium relation between composition and temperature. The maximum ammonia content that could be obtained in a single adiabatic bed with inlet conditions corresponding to A would be 14 mole % as indicated by point B, and this would theoretically require an infinite amount of catalyst. The five-bed quench converter corresponding to the reaction path ABCDEFGHIJ permits... 

In Eq. (d) is a function of temperature and composition. The third term on the right-hand side is zero for adiabatic beds. For the nonadiabatic bed T represents the temperature of the feed that is preheated inside the tubes. For this part of the reactor another equation has to be added to those written above ... 

Case Study Optimal Adiabatic Bed Reactors for SuHiir Dioxide with Cold Shot Cooling... 

The problem was to design a reactor with N adiabatic beds and, for the sake of definitiveness, N = 3, as reported in Figure 1.1. 

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