Packed beds, H2SO4 production

Fig. 1.3. Top of H2S04-making ( absorption ) tower, courtesy Monsanto Enviro-Chem Systems, Inc. www.enviro-chem.com The tower is packed with ceramic saddles. 98.5 mass% H2SO4, 1.5 mass% H2O sulfuric acid is distributed uniformly across this packed bed. Distributor headers and downcomer pipes are shown. The acid flows through slots in the downcomers down across the bed (see buried downcomers below the right distributor). It descends around the saddles while S03-rich gas ascends, giving excellent gas-liquid contact. The result is efficient H2SO4 production by Reaction (1.2). A tower is 7 m diameter. Its packed bed is 4 m deep. About 25 m of acid descends per minute while 3000 Nm of gas ascends per minute.

Another approach is to strip the chlorine from the acid in a packed column. This should reduce the consumption of air by providing a richer off-gas. lypical liquid flow rates are close to 10,000kghr with L/G between 1.5 and 3. Ceramic saddles typically are used, in beds between 3.5 and 5 m deep. At normal scales of operation, the saddles measure 25 mm or less and result in a pressure drop of 1-2 mmHg m. Chlorine is least soluble in acid of 70-80% H2SO4, and the waste product will have its dissolved chlorine content reduced to less than 100 or 150 ppm. 

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