Catalyst beds paths

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

The spatial distribution of deposited Ni and V in the reactor bed is determined by the activity of the catalyst and phenomenologically parallels that for profiles in individual pellets. Metals will tend to deposit near the reactor inlet with a highly active catalyst. A more even distribution or one skewed toward the reactor outlet is obtained for catalyst with less activity, as shown by Pazos et al. (1983). Generally with a typical small-pore (60-A), high-surface-area desulfurization catalyst, metals will concentrate near the inlet (Sato et al., 1971 Tamm et al., 1981). Fleisch et al. (1984) observed concentration maximums a short distance into the catalyst bed, as a probable consequence of the consecutive reaction path. 

Similar reactions are the hydrogenation of lubricating oils, whereby oils with a flatter viscosity-temperature curve are produced, as well as low-temperature hydrogenation of brown-coal tar, which became known as the TTH process. Although in these two processes the bulk of the feedstock remains liquid and reacts as liquid with hydrogen on the fixed-bed catalyst, the path of the reaction is the same as in the vapor-phase operation. 

In the majority of fixed-bed reactors for industrial synthesis reactions, direct or indirect supply or removal of heat in the catalyst bed is utilized to adapt the temperature profile over the flow path as far as possible to the requirements of an optimal reaction pathway. Here a clear developmental trend can be observed. 

Fig. 7.5. Heatup path for gas descending the Fig. 7.1 catalyst bed. It begins at the feed gas s input temperature and 0% SO2 oxidized. Its temperature rises as S02 oxidizes. Maximum attainable S02 oxidation is predicted by the heatup path-equilibrium curve intercept, 69% oxidized at 893 K in this case. This low % SO> oxidized confirms that efficient SO-> oxidation cannot be obtained in a single catalyst bed. Multiple catalyst beds with gas cooling between must be used.

Fig. 7.8. Heatup paths, intercepts and cooldown paths for Fig. 7.6 converter. They are described in Section 7.5. Final % SO2 oxidation after Fig. 7.6 s three catalyst beds is -98%.

Fig. 11.1. Heatup path for S02, 02, N2 gas descending a catalyst bed. The S02 and 02 in feed gas react to form S03, Eqn. (1.1). The gas is heated by the exothermic heat of reaction. The result is a path with increasing % S02 oxidized and increasing gas temperature. Notice how the feed gas s heatup path approaches its Chapter 10 equilibrium curve.

The heatup path for the Section 11.5 feed gas is prepared by re-doing the above calculation for many different levels and temperatures in the catalyst bed, Fig. 11.4. Only cells G8 to J8 in Table 11.2 are changed. 

This chapter assumes that equilibrium is attained in an acid plant s 1st catalyst bed, i.e. that a feed gas s heatup path always intercepts its equilibrium curve. 

Catalyst bed S02 + /202 — S03 oxidation is represented by heatup paths and equilibrium curves. Maximum S02 oxidation occurs where a feed gas s heatup path intercepts its equilibrium curve. 

Fig. 13.2. 1st catalyst bed heatup path, equilibrium curve and intercept point, from Fig. 12.1. The 1st catalyst bed s exit gas is its intercept gas, Section 12.12. It is cooled and fed to a 2nd catalyst bed for more S02 oxidation.

Fig. 13.3. Cooldown path added to Fig. 13.2. It is a horizontal line at the lsl catalyst bed intercept % S02 oxidized level - between the 1st catalyst bed intercept temperature and the specified 2nd catalyst bed gas input temperature. Gas composition and % S02 oxidized don t change in the gas cooling equipment.

Fig. 14.2. Sketch defining Section 14.4 s 2nd catalyst bed heatup path problem.

The 2nd catalyst bed heatup path is prepared by re-doing Section 14.9 s calculation for many different temperatures in the bed. Only cells HI5 to K15 are changed (most easily with enthalpy equations in cells, Appendix K). The results are tabulated in Table 14.3 and plotted in Fig. 14.3. 

Table 14.3. Heatup path points for Fig. 14.2 s 2nd catalyst bed. The points are shown graphically in Fig. 14.3. They have been calculated using matrix Table 14.2 with enthalpy equations in cells H15-K15, Appendix K. An increase in gas temperature from 700 K to 760 K in the 2nd catalyst bed is seen to be equivalent to an increase in % SO oxidized from 69.2% to 89.7%.

Chapter 14 describes 2nd catalyst bed heatup paths. This chapter describes 2nd catalyst bed ... 

Table 15.1. 2nd catalyst bed % S02 ox/d/zed/temperature points near heatup path-equilibrium curve intercept. They have been calculated as described in Appendices K and D. 

This chapter s 3rd catalyst bed heatup path is calculated much like Chapter 14 s 2nd catalyst bed heatup path. Differences are ... 

Fig. 16.2. Specifications for (i) 2-3 cooldown and (ii) 3rd catalyst bed heatup path and intercept calculations. The 1st and 2nd catalyst bed exit gas quantities are equivalent to ...

Appendix N shows a 3rd catalyst bed heatup path matrix with these equations. It also shows several heatup path points. Figs. 16.3 and 16.4 show the entire heatup path. 

Table 17.1. 1st catalyst bed heatup path worksheet with 0.2 volume% S03 and 9.8 volume% SO2 in feed gas. It is similar to Table 14.2 s 2nd catalyst bed... 

C02-in-feed-gas affects catalyst bed heatup paths and intercepts (but not equilibrium curves, Appendix F). The remainder of this chapter indicates how C02-in-feed-gas affects ... 

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