GB636951A - Process of and apparatus for the production of nitric acid - Google Patents

Abstract

<PICT:0636951/III/1> In producing nitric acid from gases containing nitrogen oxides and free oxygen by absorbing nitrogen dioxide in water, the absorption is carried out successively in two or more stages by introducing the water at different points of the absorption process, removing the nitric acid formed from each absorption stage, passing the nitric oxide formed and unabsorbed at each absorption stage to the next and allowing the unabsorbed nitric oxide to oxidize to nitrogen dioxide by reaction with the free oxygen present prior to or upon reaching the next absorption stage. The oxidation of the nitric oxide may be assisted by the presence of dilute nitric acid, preferably of a concentration between 50 and 57 per cent by weight. According to one embodiment, the gases enter through inlet 2 into the first, b1, of a series of absorption zones of a tower 1 wherein the nitrogen dioxide content of the gases is converted by absorption in water admitted through conduits into nitric acid which is drawn off through conduit e1. The unabsorbed gases then flow upwardly through a demisting zone c1 wherein a substantial portion of the residual nitric oxide is converted into nitrogen dioxide, the water separated in the zone issues through conduit f1 as dilute nitric acid. The demisted and partially oxidized gases then enter an oxidizing zone d1 in which they are sprayed with nitric acid which issues from the tower through conduit g1. The treated gases enter further absorption stages b2 . . . b5 and the series of operations is repeated until the last stage when the residual gases after being demisted are vented at outlet 3. In another embodiment, Fig. 2 (not shown), substantial oxidation of nitric oxide takes place in each demisting zone, while further oxidation proceeds in the lower part of each adsorption zone. Specification 131,029, [Class 1 (ii)], is referred to.