The simultaneous removal of sulfur dioxide and nitrogen dioxide by the limestone slurry with addition of organic acid additives

This study investigates the effects of organic acid on the simultaneous absorption of SO2 and NO2 in the packed column. Organic acids, i.e., formic acid, acetic acid, and propionic acid, were used as additives. In the case of the absence of additives, when SO2 and NO2 were simultaneously absorbed into the limestone slurry, both SO2 and NO2 contributed to increasing the mutual absorption efficiency. In the simultaneous absorption of SO2 and NO2 with addition of additives, the SO2 removal efficiency appeared in the order of formic acid<no addition 2 absorption efficiency. In the slurry with the addition of acetic acid and propionic acid, the reactions of absorbed SO2 and NO2 predominantly took place; thus, the SO4(2-)/SO3(2-) ratio was greater than 1. In terms of formic acid, the slurry pH was maintained at approximately 4.0, which departs from the appropriate range, attributed to the small pKa value, showing a negative effect on SO2 and NO2 removal. In the slurry with formic acid added, the SO2 predominantly reacted with formic acid; hence, the SO4(2-)/SO3(2-) ratio was less than 1.