Process for preparing nitric acid with a concentration in the range from 50 to 77.8 by weight

摘要

A process for preparing nitric acid by: catalytically oxidizing ammonia, to obtain a gas mixture containing NO and O₂; cooling and condensing the gas mixture, thereby further oxidizing NO with O₂, to obtain a gas stream containing NO₂/N₂O₄ and an aqueous solution containing nitric acid; and countercurrently absorbing the NO₂/N₂O₄ from the gas stream in an absorber with process water (H₂O), to obtain nitric acid and an NO_x-containing absorber offgas, wherein the water content of the nitric acid is regulated to a concentration in the range from 50 to 77.8% by weight and the NO_x content of the absorber offgas to a concentration in the range from 20 to 500 ppm, by continuously measuring the water content of the process air supplied to the catalytic gas phase oxidation and, as a function of this, adjusting the amount of process water (Q-H₂O) fed to the absorber.