Keywords: Nitric acid, Azeotropic, N2O reduction, NOx abatement.
The main contemporary issues for the nitric acid industry are having environmental friendly plants even during start up and shutdown conditions and boosting the product strength of normal plants to azeotropic concentration for non-fertiliser use.
The paper describes the state of the art in the manufacture of nitric acid (fertiliser and azeotropic grades) and the abatement of NOx and N2O emissions to the atmosphere.
Special attention is given to reduction techniques for emissions of nitrous oxide (N2O) which has been identified as a contributor to the greenhouse effect. Some countries have already limited the admissible levels of nitric acid plant emissions of N2O to the atmosphere, while others will do in the future.
Techniques for reducing emissions of oxides of nitrogen during plant start up and shutdown are reviewed.
The reasons behind the actual trend to acid concentrations close to azeotropic are described and the technological conditions to be achieved for a conventional nitric acid process to manufacture 68% HNO3 acid are detailed with special emphasis to the plant water balance.
Finally the paper shows how Espindesa has addressed the above in its design of azeotropic nitric acid plants. Specific consumptions of raw materials and utilities are provided.
Luis M Marzo, Espindesa, Madrid, Spain.
28 Pages, 7 figures, 4 Tables, 23 References.