Cooling first catalyst bed exit gas

Chapter 12 shows that a first catalyst bed oxidizes less than 80% of its input SO2. It also indicates that this SO2 oxidation efficiency is increased to 98+% by passing first catalyst bed exit gas through a series of gas cooling/catalytic oxidation steps. 

This chapter describes gas cooling between first and second catalyst beds (Fig. 13.1). It sets the stage for Chapter 14 s examination of second catalyst bed SO2 oxidation. The objectives of this chapter are to  

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Figure 13.1 Schematic of first and second catalyst beds with gas cooling between the beds. The cooling system cools first catalyst bed exit gas in preparation for more catalytic SO2 oxidation in a second catalyst bed. Industrial catalyst bed arrangements are discussed in Chapters 7 and 8. Gas cooling is discussed in Chapter 21.

Boilers and superheaters also cool first catalyst bed exit gas. EcOTiomizers are typically used to cool last catalyst bed exit gas just before it goes to H2SO4 making (absorption). 

This chapter examines oxidation of the SO2 in cooled first catalyst bed exit gas—in a second catalyst bed. 

Cooling first catalyst bed exit gas and passing the cooled gas through a second catalyst bed increase SO2 oxidation efficiency from ... 

Recycle of cooled first catalyst bed exit gas is an effective way of preventing first bed catalyst degradation. It requires slightly more first bed catalyst and a slightly larger... 

It does, however, apply when cooled first catalyst bed exit gas is recycled into the first catalyst bed feed gas stream (Chapter 27). This is because recycling does not actually remove anything from the system. 

Appendix Y Cooled first catalyst bed exit gas recycle calculations... 

Metallurgical and spent acid decomposition gases are initially dehydrated and then passed through the fuel-fired air preheater because they are cool from gas cleaning/ dehydration. When SO2 oxidation has steadied, this gas heating duty is switched to heat exchange from hot first catalyst bed exit gas. 

Cooled tirst catalyst bed exit gas i Cooled first catalyst bed intercept gas 0.0692 kg mol SO, Section 12.2 0.0308 kg mol SO,... 

Oxidation of SO2 in strong SO2 feed gas tends to overheat and deactivate first bed catalyst (Figs. 1.7 and 12.8). This can be avoided by recycling cooled, S02-depleted first catalyst bed exit gas to the first catalyst feed gas stream (Fig. 27.1). 

Figure 27.2 Effect of recycling cooled first catalyst exit gas on first catalyst bed exit gas temperature. As expected, exit gas temperature decreases with increasing recycle extent. First catalyst bed exit gas temperature falls below 900 K with 8% recycle.

This means that the first catalyst bed exit gas might only be cooled to 700 K (Section 13.2). Recycle gas temperature might also be cooled to 700 K (Fig. 27.3). The latter affects the amount of recycle that is necessary to bring the first bed exit gas temperature down to 900 K. 

The acid plant has five catalyst beds arranged in a 3-2 configuration (Section 20.3). A portion of the cooled third catalyst bed exit gas is recycled at 553 K to the inlet of the first catalyst bed. Additirmal design information is provided in Tables 27.1 and 27.2 (Daum, 2009). 

Recycle of cooled first or third catalyst bed exit gas to the first catalyst bed feed gas stream lowers first catalyst bed exit gas temperature. It can be used to avoid first bed overheating and catalyst degradation while treating high SO2 concentration feed gas. The extent of gas cooling increases with ... 

As can be seen, the first catalyst bed exit gas temperature is lowered from 910 to S90 K (safely below the catalyst degradation temperature) by recycling 20% of the cooled... 

Figure 27.8 Comparison of first and third catalyst bed exit gas recycle. Third bed exit gas recycle is seen to be sUghtly more effective. However, third bed recycle gas passes through all three beds requiring aU beds, ductwork, and heat exchangers to be enlarged to accommodate the increase in gas flow. The recycle gas, whether tfom the exit of the first or third catalyst bed, is cooled to 660 K before combining with 660 K feed gas at the inlet to the first catalyst bed. The second and third catalyst bed inlet temperatures are 700 K.

Table Y.l s exit gas is cooled to 660 K. 20% of the cooled gas is recycled to the first catalyst bed feed gas stream (Fig. Y.l). The recycled gas quantities are 20% of the Table Y.l output quantities, i.e. ...

Figure 13.2 First catalyst bed heatup path, equilibrium curve, and intercept point (Fig. 12.1). The first catalyst bed s exit gas is its intercept gas (Section 12.12). It is cooled and fed to a second catalyst bed for more SO2 oxidation.

Figure 27.6 Effect of recycling cooled first catalyst exit gas on total % SO2 oxidized after each catalyst bed. Figure 27.5 s advantage is maintained in all beds, but it decreases with each successive bed.

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