Methods to lower sulfur emissions

Section 19.8 showed that removing SO3 and sending the gas through one additional catalyst bed increase SO2 oxidation. Maximum industrial SO2 oxidation for a four bed single contact acid plant is 99%. Greater than 99% SO2 oxidation often requires double contact or scrubbing of single contact acid plant tail gas (Fig. 29.2). 

In some cases, the required SO2 emission levels are so low that scrubbing of the double contact acid plant tail gas is required (Smith, 2012). 

Cesium-promoted catalysts and the new catalysts LEAPS (Christensen and Polk, 2011) and GEAR (Felthouse et al., 2011) are used to maximize SO2 oxidatimi. They are more costly than conventional catalysts (potassium promoted), but give appreciably better SO2 oxidation performance. Table 29.3 provides industrial design data which show the benefits of using cesium-promoted catalyst in a four pass single coti-tact type metallurgical acid plant. 

The feed gas contams 10 volume% SO2, 14 volmne% O2, and 76 volume% N2. In this example, the use of cesium-promoted catalyst results in a 21 % decrease in SO2 emissions. Case 1 uses all conventional (potassium promoted) catalyst. Defined below Table 28.1. 

Chapter 28 described industrial acid plant tail gas scrubbing. Typical achievable tail gas SO2 concentrations for various technologies are shown in Table 29.5. The key advantage of tail gas scrubbing is that its performance does not inherently decrease in time as with catalyst. 

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Equilibrium SO2 oxidation is never achieved in an industrial acid plant, resulting in slightly higher than optimum SO2 emissimis. Methods to lower sulfur emissions from the acid plant mainly focus on decreasing SO2 emission and include ... 

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