Reduction of NOx in Low Pressure Nitric Acid Plants

NOx emissions of low pressure nitric acid plants are difficult to reduce economically. This paper describes a system to reduce NOx emissions by absorbing them with sulphuric acid at low pressure and low temperature. Part of the NOx react with sulphuric acid to form nitroxil-sulphuric acid and another part are dissolved in the liquid phase. The resulting liquid is heated and the NOx are stripped by air and steam and reintroduced in the nitric acid plant. Investment and operating data of a 300 MTD plant operating at 2 kg/cm²are shown. NOx reduction over 90% is achieved. Economics of the process seem very promising.