Oxidation of SO2 to SO3—Equilibrium curves

This chapter describes the equilibrium thermodynamics of Reaction (1.1). Its objectives are to  

This is the basis of all industrial acid plant designs. 

All industrial SO2 oxidation is done in contact with V, alkali metal, S, O, Si02 catalyst. Chapters 7 and 8. 

O2 and SO3 approach equilibrium as the gas descends the catalyst bed (left graph). % SO2 oxidized at equilibrium is the maximum extent to which the feed SO2 can be oxidized. As will be seen, this maximum depends on  

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Fig. 11.1. Heatup path for SO2, O2, N2 gas descending a catalyst bed. The SO2 and O2 in feed gas react to form SO3, Eqn. (1.1). The gas is heated by the exothermic heat of reaction. The result is a path with increasing % SO2 oxidized and increasing gas temperature. Notice how the feed gas s heatup path approaches its Chapter 10 equilibrium curve.

The flow needs to be cooled at the outlet of each bed if a high final conversion is to be achieved. In this example, we optimize the inlet temperatures of each bed to maximize the final conversion of the reactor. The SOj entering the reactor is 10% of the total inlet feed, the pressure is assumed to be 1 atm, and the temperature, 600 K. We start with sulfur as the initial raw material, which is burned with dry air and later oxidized. We need to dry the atmospheric air in order to avoid any corrosion due to early formation of sulfuric acid. For 1 kmol of air, the mass balance for the combustion of sulfur and the formation of SO3 is given in Table 11.1, where a is the molar fraction of SO2 in the feed to the converter. We first determine the equilibrium curve. The amount of moles at equilibrium is given by... 

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