Inter-pass absorption towers

The temperature of circulating oleum at the inlet of the tower plays a very important role in the proper absorption of the SO3 from the gas phase. It is maintained as low as possible—and generally not allowed to exceed 52-53 °C. There is a considerable escape of acid mist from the oleum tower and hence it is almost always followed by an acid tower (the inter-pass absorption tower). 

In the earlier variants of the DCDA process, the SO2 was converted to SO3 by catalyst passes and the SO3 was then absorbed in the inter-pass absorption tower. The gases from the exit of the IPAT were again reheated to about 425 35 °C and... 

Separate acid circulation circuit for final absorption tower to avoid stripping of dissolved SO2 from the inter-pass absorption tower acid circuit which can occur if a common acid circulation tank is used. 

The following details should be separately recorded for each of the acid towers (drying tower, inter pass absorption tower, final absorption tower)... 

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