After-intermediate-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. 

The after intermediate H2SO4 making equilibrium curve equation is ... 

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.

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. 

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