Simultaneous scrubbing of SO2 and NOx having an intermediate step

摘要

It is known to purify SO2 and NOx from combustion exhaust gases by use of a wet scrubbing circulation whose scrubbing water contains iron II-EDTA or iron II-NTA complex. To retain the iron II complex within the scrubbing solution, reducing agents are added or scrubbing water treatments are carried out in the by-pass in order to reduce again the iron oxidized by the atmospheric oxygen from iron II to iron III in the chelate complex and thus to prevent the use of expensive reducing agents. In order further to improve the process according to the main application P 3525051.8 using sodium and/or calcium formate, according to the invention it is proposed that the scrubbing liquid is contacted with the SO2- and NOx-containing gas at a pH below 6, preferably between 4.3 and 4.8, and from this, a portion of the scrubbing water is reduced to a pH around 1.5 by sulphuric acid for EDTA precipitation and by introduction of SO2-containing gas, the reduction phase from FeIII sulphate to FeII sulphate is initiated. The liquid thus treated is returned to the active scrubbing circulation.