GB481629A - Process and apparatus for the production of nitric acid - Google Patents

Abstract

<PICT:0481629/III/1> In obtaining nitric acid from gases containing nitrogen oxides and oxygen by oxidising the oxides to the tetroxide stage and absorbing the tetroxide in water and aqueous nitric acid, the gases, after initial oxidation substantially completely to the tetroxide stage, are treated in a series of small chambers, in each of which the gases remain for a maximum period of about 10 seconds, for absorption by nitric acid of progressively decreasing strength whereby the concentration of the tetroxide is progressively diminished until it is completely extracted, and are thereafter passed into a larger chamber for the oxidation of nitric oxide formed during absorption to tetroxide for further complete absorption treatment, so that the gases as they enter the oxidation chambers contain practically no tetroxide. Gases, containing nitrogen, oxygen and nitrogen tetroxide (say ammonia oxidation gases) pass in succession through a series of small absorption chambers 2-8, an oxidation chamber 9, a second series of small absorption chambers 10-12, an oxidation chamber 22, a third series of small absorption chambers 13-15, an oxidizing chamber 23, and a final series of small absorption chambers 16-18, the spent gases issuing from the plant at 19. The successive oxidation chambers 9, 22 and 23 are gradually increased in size. Water or a weak acid solution is admitted at 21 to the final absorption chamber 18 and after circulation by a pump 26 overflows into the absorption chamber 17. The acid is circulated jointly in the chambers 15 and 17 by a pump 27, overflows into the absorption chamber 14, is circulated jointly in the chambers 14, 16, 12 and 8 by a pump 28, overflows into the absorption chamber 7, is circulated jointly in the absorption chambers 7, 11 and 13 and the oxidation tower 23 by a pump 29, overflows into the absorption chamber 6, is circulated jointly in the absorption chambers 6 and 10 and the oxidation chamber 22 by a pump 30, overflows into the absorption chamber 5, is circulated jointly in the absorption chamber 5 and oxidation chamber 9 by a pump 31, and thereafter the acid passes successively through the absorption chambers 4, 3 and 2 to issue from the plant at its maximum concentration at 20. According to another modification a battery of seven small absorption chambers is directly succeeded by five large towers of progressively increasing size which serve as combined absorption and oxidation towers. Water or weak acid enters the last combined tower and passes successively through circulations embodying the fourth combined tower and the seventh small absorption tower, the third combined tower and the sixth small absorption tower, the second combined tower and the fifth small absorption tower and so on, finally issuing from the first absorption tower.