Key words: root cause analysis, nitric acid, nitrous oxide, catalysts.
This technical paper features a review of root cause analysis of poor performance in nitric acid plants. Johnson Matthey (JM) 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 platinum group metals (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 nitrous oxide (N2O) emissions.
In these cases, a combined team of engineers, from JM and the customer plant, proceeded with a detailed root cause analysis (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, which are discussed in this paper. 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.
J. Ashcroft, Johnson Matthey, Royston, UK.
15 pages, 4 figures, 2 tables.