| 摘要 |
A process for extracting oxides of nitrogen from waste gases, said oxides having an average degree of oxidation corresponding at least to N2O3, by scrubbing with an aqueous suspension of Ca (OH)2 in an amount to form a solution containing not more than 65 gm./litre of nitrogen present as (NO2)- and (NO3)-, then adding at least 2, e.g. 2.2-2.5, mole H2SO4 for every 3 moles of Ca (NO2)2 whereby NO is evolved. The scrubbing should be performed below 55 DEG C., e.g. 20-30 DEG C. Alternatively H2SO4 may be added in a molar ratio to Ca(NO2)2 of 1: 1 whereby a solution of about 10 to 20% of HNO3 is produced in addition to NO, in which case the preferred nitrile solution contains 50-65 gm./litre of nitrogen present as (NO2)- and (NO3)-. The absorption may be carried out in several stages, the scrubbing solution and gases flowing in countercurrent. The solution discharged from the first scrubber preferably contains between 3 and 5 gm. of CaO per litre. The scrubbing apparatus may be columns packed with ceramic rings or grids or bubble tray columns, or spray towers. In the acidification step air may be bubbled in to facilitate release of NO. |
