The waste acids come from Nitration and esterification processes in the plastics and production of energetic material industries such as, for example, the production of nitrocellulose, nitroglycerine, dinitroluene and nitroglycol. The residues of these organic substances and their intermediate products, and nitrous acid also have to be removed during the denitration.
During denitration of nitroglycerine or nitroglycol waste acid the organic constituents are decomposed with the consumption of nitric acid and are passed to an NOx absorber as nitrous gases.
3NO2+ H2O>>2HNO3+ NOThe nitrogen monoxide formed during this reaction and that already present in the exhaust gas must be oxidized:
2 NO + O2>> 2 NO2Both reactions are strongly exothermic and are pressure and temperature dependent. The result is that at normal pressure and with the use of cooling water at approx. 25 deg C it is possible to produce nitric acid at a concentration of approx. 50% and the exhaust gas leaves the column with an NOx content of about 1000 to 2000 ppm. For relatively small quantities of exhaust gas this is mixed with air to achieve permitted waste gas contents for example, 200ppm.
As well as absorption at normal pressure the following processes have proved effective in industrial use:
Acid Concentration Plants