Catalyst beds H2SO4 making

Catalyst beds before intermediate H2SO4 making + beds after intermediate H2SO4 making. 

The latter causes S02+ /202 — SO3 oxidation to go almost to completion in the after intermediate H2SO4 making catalyst bed, Chapter 19. 

H2SO4 making by contact of cooled 3 catalyst bed exit gas with strong sulfuric acid, Fig. 16.1. 

Fig. 16.1. Schematic of single contact, 3 catalyst bed sulfuric acid plant. It is a single contact plant because it has only one H2SO4 making step. Note gas cooling between catalyst beds. It permits additional SO2 oxidation in the next catalyst bed.

See Table 19.3 (end of this chapter) for industrial after H2SO4 making catalyst bed data. 

Fig. 19.2. Double contact acidmaking flowsheet with numerical values used in this chapter s calculations. The plant consists of 3 catalyst beds followed by intermediate H2SO4 making and a 4 catalyst bed. The gas from the last catalyst bed goes to cooling and final H2SO4 making (not shown). All kg-mole values are per kg-mole of D catalyst bed feed gas. Gas pressure = 1.2 bar, all beds.

Calculate the equivalent SO2 oxidation efficiency with 4 catalyst beds but no intermediate H2SO4 making. Use the technique described in Appendix S with all of Prob. 19.1 s temperatures and pressures. 

Fig. 20.3. SO2 oxidation efficiency of acid plants with 1 catalyst bed after intermediate H2SO4 making. Oxidation efficiency increases with increasing number of before-intermediate-H2S04-making beds. However, the difference between 3 -1 and 4 - 1 plants is very small.

Fig. 20.5. 3 - 1 acid plant with one Cs catalyst bed (660 K gas input) and three K, Na catalyst beds (690 and 720 K). Maximum SO2 oxidation is obtained with the Cs catalyst in bed 4, i.e. after H2SO4 making. Bed 3 Oust before H2SO4 making) is nearly as good. The calculations are all based on Table 20.1 s values - except for gas input temperature. 

The most efficient double contact plants have one catalyst bed after H2SO4 making, remainder before. 3 - 1 plants are more efficient than 2-2 plants. 4 - 1 plants are more efficient than 2-3 and 3-2 plants. 

Cs catalyst is costly so many acid plants use it in only one catalyst bed. From the SO2 oxidation efficiency point of view, it is best used after intermediate H2SO4 making. 

These values pave the way for Chapter 22 s examination of catalyst bed and H2SO4 making temperature control. 

Fig. 21.1. Heat transfer flowsheet for single contact, suliiir burning sulfuric acid plant. It is simpler than industrial plants, which nearly always have 4 catalyst beds rather than 3. The gaseous product is cool, SO3 rich gas, ready for H2SO4 making. The heat transfer product is superheated steam. All calculations in this chapter are based on this figure s feed gas composition and catalyst bed input gas temperatures. All bed pressures are 1.2 bar. The catalyst bed output gas temperatures are the intercept temperatures calculated in Sections 12.2, 15.2 and 16.3.

So, per kg-mole of 1 catalyst bed feed gas, 8.46 MJ must be removed from 721.1 K 3 catalyst bed exit gas to cool it to the specified 470 K H2SO4 making input gas temperature. The heat is, of course, transferred to water in Fig. 21.1 s economizer. 

The next chapter builds on this information to show how catalyst bed and H2SO4 making input gas temperatures are controlled by bypassing gas around the cooling devices. 

Use your Prob. 16.1 3 catalyst bed output quantities and Eqn. (21.3) to calculate H2SO4 making s input gas enthalpy. 

Calculate the rate, MJ/hour, at which heat must be transferred from 3 catalyst bed exit gas to economizer water to obtain the above specified 470 K H2SO4 making gas. 100 000 Nm per hour of catalyst bed feed gas is entering the 1 catalyst bed. 

What fraction of Prob. 22.1 s 3 catalyst bed exit gas will have to be bypassed around Prob. 22.1 (b) s economizer to give 470 K H2SO4 making input gas when the economizer input gas is ... 

Mass SO3 into H2SO4 making tower, kg per I catalyst bed feed gas... 

H2SO4 production increases with increasing SO3 mass in H2SO4 making tower input gas, both per kg-mole of dry 1st catalyst bed feed gas. Acid plant water requirement increases commensurately. 

The H2SO4 making tower input gas (i.e. cooled catalyst bed exit gas) contains ... 

Fig. 24.5. Effect of S03(g)-in-input-gas concentration on H2SO4 making output acid temperature. Output acid temperature decreases slightly with increasing SOs(g) concentration. The volume% SO3 values have been calculated as described in Chapter 16 starting with 8, 9, 10, 11 and 12 volume% SO2 in 1 catalyst bed feed gas.

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