At 9 p.m. on December 27, the nitric acid unit of Nylon Technology Company entered the critical stage of startup. Before igniting the oxidation furnace, A “milligram-level” battle has been raging in the inspection room for several hours now. The protagonists are two employees from the central laboratory and a seemingly minor yet critically important indicator—the ammonium salt content.

For the nitric acid plant, in the process materials... When the ammonium salt content (ammonium nitrate, ammonium nitrite) is too high, This can directly affect catalyst activity and the quality of the final product, and even clog pipeline equipment, leading to plant shutdown. Therefore, before starting up the plant, reducing the ammonium salt content within the system to a safe range (with a process control target of ≤18 mg/L) is an indispensable “iron threshold” for ensuring a safe and successful startup.

Fully aware of the critical importance of their service and production responsibilities, the central laboratory promptly entered “combat readiness” mode. “Nitric acid is about to start up—please have Zhonghua cooperate closely in monitoring ammonium salts!” Upon receiving the production order, the night-shift staff immediately hopped onto a tricycle, loaded it with equipment, reagents, and glassware, and headed straight for the nitric acid unit, braving the cold winter winds. In the somewhat rudimentary on-site inspection room, they swiftly set up a temporary “field laboratory.”

As the driving process progresses step by step, ammonium salts circulate throughout the system along with the materials. Each sampling and analysis serves as a “diagnostic confirmation” of the system’s safety status.

21:45, First analysis, The ammonium salt content was 146 mg/L—far exceeding the target level! This indicates that the initial flushing stage of the system contained a high concentration of impurities, and continuous purging and replacement are essential. At 22:00, the second analysis showed an ammonium salt content of 89 mg/L, a significant drop from the previous reading, confirming that the flushing and replacement process is effective. However, there’s still a substantial gap to reach the safety threshold. At 22:10, the ammonium salt content had dropped to 15 mg/L, below the control target of 18 mg/L—the first time the safety threshold has been reached. At 22:20, the fourth analysis revealed an ammonium salt content of 12 mg/L. The data has stabilized within the safe range and continues to decline steadily.

“The ammonium salt content analysis has passed inspection!” The news quickly spread to the nitric acid workshop. The leap from 146 to 12—a shift of four digits—demonstrates the close collaboration between laboratory analysts and process engineers, as well as their professional competence and service-minded attitude in helping to accelerate the start-up process.

As the on-site operators of the nitric acid plant were carrying out the follow-up work to ensure a successful startup, two Sinochem personnel had already packed up their “field laboratory” and quietly departed into the night.