METHOD AND APPARATUS FOR DECOMPOSING NITRIC ACID

PURPOSE: To decompose nitric acid of relatively high concentration into harmless water by using an economical, safe method and apparatus by decomposing nitric acid in mixed gas into nitrogen oxides by the use of a catalyst and reducing the nitrogen oxides into nitrogen and water using ammonia as a reducing agent. CONSTITUTION: A waste nitric acid aqueous solution is introduced from an injection pump 1 into a nitric acid gasification unit 4 while being adjusted to keep the level of the gasification unit 4 constant by a level control valve 2 interlocked with a level gauge 3. The gasified nitric acid, with entrainments separated by a flow straightener 10, is sucked from a pump 21 while being adjusted by a flow rate meter 20 and heated with part of air which passed through a heat exchanger 17 by a burner 12. The heated gasified nitric acid is decomposed into NOX by a nitric acid decomposition reactor 13 filled with a nitric acid decomposition catalyst 14. Gas from the reactor 13, with the amount of part of air which passed through the heat exchanger 17 adjusted by a carrier gas control valve 18, is controlled to temperature necessary for the reduction and reduced by the reaction with NH3 in a reduction reactor 18 into harmless N2 and H2 O.