Double-packed bed absorption tower

A second key feature of Fig. 24.8 s HRS is its double-packed bed absorption tower— through which  

S03-bearing gas ascends H20(f)-bearing sulfuric acid descends 

The bottom-packed bed is fed with 450 K, slightly diluted return acid from the steam-from-acid heat boiler. H20( ) in the descending acid reacts with the ascending gas SO3 to form hot H2S04( ) by exothermic reaction (1.2). Input acid composition and flow rate are controlled to give hot ( 500 K) absorption tower product acid. 

The top-packed bed is fed with cool ( 350 K) acid from the acid plant s final absorption tower (Fig. 9.6). Its principal purpose is to absorb SO3, H20(g), and H2S04(g), rising from the hot bottom bed. The vapor pressures of all these gases are all lower with cool acid than with hot acid. 

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