Condenser re-evaporation of

The previous section indicates that 75 mass% H2S04( ) 25 mass% H20( ) acid condenses near the top of the condenser tubes. Yet the product of the condenser is almost always 98 mass% H2S04( ) — 2 mass% H20( ) acid. 

This strengthening is caused by re-evaporation of H20(g) from the weak acid condensate as it flows down to the hot bottom of the condenser. 

This explains the high H2S04( )-sfrength product of the condenser in spite of a high H20(g) concentration in its feed gas. 

It should be noted that with extremely low feed gas SO2 concentrations 0.2-0.4 volume% SO2, the product acid contains 94-95 mass% H2SO4 (Laursen and Jensen, 2007). This acid concentration is suitable for sale and use in most industries. 

The H2S04( )-H20( ) system has an azeotrope at 98.8 mass% H2S04( ) —1.2 mass% H20( ) (Bolsaitis and Elliott, 1990). The weak condensate from the top of the glass condenser cannot be strengthened by evaporation beyond this composition. This is 

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