Double Contact H2SO4 Making

Double contact acidmaking oxidizes its SO2 more completely to SO3 than single contact acidmaking. For this reason it  

The more efficient SO2 oxidation is due not only to Fig. 9.6 s extra catalyst bed, but also to the fact that  

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

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Fig. 9.1. Single contact H2SO4 making flowsheet. SO3 rich gas from catalytic SO2 oxidation is reacted with strong sulfuric acid, Reaction (1.2). The reaction consumes H20(f) and makes H2S04(f), strengthening the acid. Double contact H2SO4 making is described in Fig. 9.6. A few plants lower the SO2 content of their tail gas by scrubbing the gas with basic solution (Hay et al., 2003).

Fig. 9.6 is a flowsheet for double contact H2SO4 making. It shows ... 

Figure 9.6 Double contact H2SO4 making flowsheet. The two absorption towers are notable. The left half of the flowsheet oxidizes most of the S02-in-feed-gas and makes the product SO3 into strengthened sulfiiric acid. It makes about 95% of the plant s new H2SO4. The right half of the flowsheet oxidizes almost all the remaining SO2 and makes its product SO3 into strengthened sulfuric acid. The final exit gas is very dilute in SO2 and SO3. Industrially, all the catalyst beds are in the same converter (Fig. 7.7). Table 23.2 gives industrial final H2SO4 making data.

Fig. 1.4. Double contact sulfuric acid manufacture flowsheet. The three main S02 sources are at the top. Sulfur burning is by far the biggest source. The acid product leaves from two H2SO4 making towers at the bottom. Barren tail gas leaves the final H2S04 making tower, right arrow.

The data are for FINAL H2SO4 making in double contact plants. ... 

Most of the mathematical chapters analyze catalytic S02+ /202—> SO3 oxidation in single and double contact acid plants. The remainder examine temperature control and H2SO4 making. 

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.

This is somewhat above industrial total SO2 oxidation (99.5-99.9% Hansen, 2004), but it confirms the high SO2 oxidation and H2SO4 making efficiencies of double contact acid plants. 

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. 

Table 23.1 Details of packed bed H2S04-from-S03 plants for FINAL H2SO4 making in double contact plants. The water requirement is also determined. All numerical values are per kg mol of dry first catalyst bed feed gas. The solution to the matrix is given below it.

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