Process for the continuous treatment of reaction products from flue gas scrubbers with simultaneous removal of sulphur dioxide and nitrogen oxides

摘要

The invention relates to a process for the continuous treatment of reaction products, essentially sulphate, sulphite, dithionate and nitrogen sulphonates, which are formed in the metal-complex-catalysed reduction of nitrogen oxides by sulphur dioxide in an absorptive scrubbing solution. In order further to improve such a process, according to the invention it is proposed that a part-stream is taken off from this scrubbing solution, which part-stream is then heated to a temperature of 80 to 180, but preferably 100 to 120 DEG C, as a result of which nitrogen sulphonates, with reduction of the pH, decompose to give ammonium hydrogen sulphate and dithionate simultaneously disproportionates to give sulphite and sulphate, the sulphite present in the acid medium then being converted to sulphur dioxide, and that this digestion solution is then, after stripping of the sulphur dioxide, adjusted to a pH of 7 to 11, but preferably 8 to 9, with an alkalising agent, ammonia then forming from ammonium sulphate, which ammonia can be driven off in the heat, while a sparingly soluble sulphate can be precipitated from the remaining solution, depending on the choice of the alkalising agent, with or without cooling, after which the mother liquor, except for a small effluent stream to be purged, is returned to the scrubber solution.