Tail Gases from Nitric Acid Manufacture

5 Tail Gases from Nitric Acid Manufacture 

Various processes can be used for cleaning the tail gases of older nitric acid plants or newer medium pressure plants, but often give rise to problems. 

Final emission values of 100 ppm can be achieved by alkali scrubbing e.g. with sodium hydroxide, ammonia or urea solutions, but disposal of the nitrites and nitrates formed is problematic. 

Removal of NOx from tail gases is often more difficult than improving the absorption technology 

Alkali scrubbing is encumbered by disposal of tbe nitrite and nitrate formed. 

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The acid is degassed by blowing out with secondary air and distilled (the head product consisting of highly concentrated acid and the sump product of the azeotropic acid). The azeotropic acid is recycled. The concentration of nitrous gas in the tail gas is <100 ppm. In the Sabar process the manufacture of low or medium concentration acid is possible in addition to highly concentrated acid. These are obtained by adding acid condensate from the combustion of ammonia to the sump of the nitric acid tower. 

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