This technical paper features a review of Root Cause Analysis (RCA) of poor performance in nitric acid plants. Johnson Matthey has assisted in root cause analysis for several customers in recent years, working in conjunction with the plant engineers to improve plant performance.
Johnson Matthey was supplying the primary pgm ammonia oxidation gauze for these plants, when they began to experience performance issues, typically seeing a reduction in both conversion efficiency and increase in N2O emissions. In most of these cases, the initial conversion efficiency started high before rapidly dropping several percent during the campaign.
In all these cases, a combined team of engineers, from JM and the customer plant, proceeded with a detailed RCA to identify the possible causes of the problem and to prepare and implement the corrective actions to solve this issue.
By following the RCA process, a fault tree analysis was developed from an identification exercise, which highlighted potential cause factors to the problem. A range of root causes have been identified in different plants over the last few years, including catalyst contamination from poor gas filtration and boiler leaks. The most common cause, typically resulting in the worst drop in performance, has been a structural problem with the basket within the burner, resulting in ammonia by-passing the catalyst.
As part of any investigation into poor performance Johnson Matthey used its proprietary kinetic model to simulate the performance of the gauzes and to determine the reaction profile within the catalytic packs installed in the burner. The paper describes describe how the systemised design and modelling applies to the technology systems offered to the nitric acid industry.