Chemistry of a flue gas combined NO X and SO 2 scrubber employing ferrous cysteine additives

Use of ferrous cysteine additives in flue gas scrubbing systems creates a different and simpler scrubber chemistry compared to Japanese processes using ferrous chelates such as Fe 2+ (EDTA). Instead of being converted to nitrous oxide, nitric oxide in flue gas can be concentrated and/or reduced to nitrogen gas. Also, production of dithionate ions and nitrogen‐sulfur compounds in scrubbing systems can be avoided. Fixation of nitric oxide occurs by a rapid reaction with the ferrous cysteine complex, at pH between 7.5 and 6.5, to form solid cystinatodinitrosyl iron (II), which releases NO upon heating. Most of the NO is reduced to gaseous species, primarily N 2 , in ferrous cysteine solutions at pH 10. Cysteine can rapidly reduce ferric ion to ferrous ion while being oxidized to cystine. Cystine can be reduced back to cysteine by SO 2 .