PROCESS FOR TREATING THE WASHING LIQUID DURING REMOVAL OF SO2 AND NOx FROM FLUE GASES

摘要

Process as described in which the untreated gas is placed in contact with a washing liquid containing alcaline iron-II-EDTA complexes and a reducing agent. It is known to reduce SO2 and NOx in flue gases by means of washing solutions in washing plant. For this, EDTA-iron complex compounds are used in preferably alkaline washing solutions, and a strong oxidation of iron from iron-II into iron-III inevitably takes places owing to the high level of atmospheric oxygen in the flue gases. To enable reduction from iron-III to iron-II, reducing agents or electrolytic processes are employed. The necessary consumption of reducing agent or the use of electrolysis is highly cost-intensive. To reduce significantly this consumpstion it is proposed that the washing liquid is fed to a holding tank and is stored in this tank for the purpose of reduction, with a holding time in excess of 15 min. The holding time is selected according to the quantity of iron-III which is to be reduced. Furthermore the degree of NOx deposition can also be influenced by setting the density of the washing liquid in the range 1.10 - 1.20 g/l. With this invention it is also possible to add magnesium salts to the iron chelate complex solution in the washing liquid.