Operating parameters analysis of a nitric acid plant to increase production and reduce NOx gases emission

Abstract

In this work the influence of some operating parameters of a medium pressure nitric acid plant producing 54,000 t/year was studied in order to evaluate its influence over the absorption column efficiency. The target is to increase nitric acid production and reduce NOx emissions. The nitric acid plant was simulated using ProSimPlus HNO3. The parameters considered in the analyses were: secondary air molar flow rate; absorption column operating pressure; cooling water temperature and absorption water molar flow rate. Parameters were evaluated individually and the best results were combined in a multi-parameter analysis evaluating different optimized scenarios, including the possibility of increasing the amount of ammonia injected in the system and the addition of a plug flow reactor (PFR), which is a new approach to improve NO oxidation. Considering a base case, the best scenario obtained was able to reduce NOx emissions in 55 % while increasing nitric acid production in 18 %, using the following set of parameters: 20 kmol.h − 1 of additional ammonia; a 40 m3 PFR; cooling water at 5 °C; 172 kmol.h − 1 of absorption water and 345 kmol.h − 1 of secondary air. The results obtained in this work contribute to provide practical insights for optimum absorption stage operation in a real nitric acid plant.