Process for the purification and treatment of nitrous exhaust gases containing at least one additional acid compound

摘要

The invention relates to a process for purifying and working up nitrous exhaust gases which contain at least one additional acidic compound, such as hydrofluoric acid, sulfur oxides, hydrochloric or phosphoric acid, individually or in combination. Starting from the disadvantages of the known prior art, a method is to be provided with which an exhaust gas of high purity and a mixed acid which can be used again for pickling or etching are obtained. The following procedure is proposed for this: The exhaust gas is gradually, in at least three washing stages with washing columns K1, K2, K3 connected in series with a packed bed FS with a surface area of 180 to 980 m2 / m3, a space load of 30 to 180 m3 / m3h each Washing column in countercurrent brought into contact with fresh water as a washing solution with a temperature of 5 to 30 ° C, with the addition of an oxidizing agent. In the first washing stage K1, at least 60% of the NOx components contained in the exhaust gas and 90% of the further acid components contained in the exhaust gas are washed out. The washing cycle is continued until a concentration ratio of mixed or thin acid in the sequence K1: K2: K3 of 500: 50: 5 to 500: 10: 0.2 is established in the column bottoms KS of the washing columns K1, K2, K3 , Immediately thereafter, mixed acid is removed from the first column K1, and then, in each case, thin acid from the second column K2 is metered into the first column K1 and from the third column K3 into the second column K2, and fresh water is fed to the third column K3 as compensation. The space load of the individual wash columns K1, K2, K3 among one another is set so that the ratio of the space load of the first wash column K1 to that of the subsequent wash columns K2, K3 is from 1: 1.5 to 1:10.