Double contact acidmaking making

Fig. 19.2. Double contact acidmaking flowsheet with numerical values used in this chapter s calculations. The plant consists of 3 catalyst beds followed by intermediate H2S04 making and a 4th catalyst bed. The gas from the last catalyst bed goes to cooling and final H2S04 making (not shown). All kg-mole values are per kg-mole of 1st catalyst bed feed gas. Gas pressure = 1.2 bar, all beds.

This is called double contact acidmaking because it contacts gas and acid twice, steps (b) and (d). The advantage of double contact acidmaking is that it makes S03 and H2S04(f) more efficiently than single contact acidmaking. 

Double contact acidmaking is more efficient than single contact acidmaking. This has made it the most used industrial process. The reason for its high efficiency is its efficient oxidation of S02 in its after-H2S04-making catalyst bed(s), Chapter 19. 

Figure 19.7 Four catalyst bed single contact acid plant. The third catalyst bed heatup path and intercept are the same as in Figs. 16.3 and 16.4. The fourth bed is new (Table S.4 in Appendix S). Note that (a) the fourth bed oxidizes less than half of the third bed s exit SO2 whereas (b) Fig. 19.6 s after-H2S04-making bed oxidizes 98.9% of the third bed exit SO2 (Section 19.6). This explains the greater efficiency of double contact acidmaking.

---