Using Pure Oxygen in a Nitric Acid Plant to Increase Production and Reduce NOx Emissions

Abstract

Nitric acid is a strong acid and a powerful oxidant. It is very important for the production of fertilizers, pharmaceuticals, dyes, synthetic fibers, and explosives. The objective of this work is to explore the usage of pure oxygen as an additional raw material for a nitric acid plant to optimize its production while reducing NO_x losses, considering a medium pressure plant (operation range between 230 and 600 kPa), trying to increase the efficiency of the plant by intensifying the absorption column. The analysis was performed using ProSim Plus HNO₃ simulator. After simulation and validation, an optimization procedure was performed using other operational parameters besides the amount of pure oxygen fed into the system, such assecondary air molar flow, absorption column cooling water temperature, and absorption water molar flow rate. The results obtained were also analyzed considering their effectivity over the production increase, and an economic analysis of how much oxygen can be injected was performed, comparing the amount of nitric acid produced. Using the proposed methodology, the nitric acid production rate could be increased by 32%, and it has shown to be profitable for various scenarios without exceeding NO_x losses of the base case scenario. The best scenario considering raw material and product prices has increased the production by 25%, without the necessity of changing process configuration. Results obtained in this work show that process intensification of a nitric acid plant is possible without changing any equipment or layout of a current nitric acid plant in operation.