A Study on Preventing Thermal Runaway of Contaminated Ammonium Nitrate Prill in Bulk Storage

ABSTRACT Ammonium nitrate (AN) prills are widely used to manufacture mining explosives and fertilisers. They exothermally decompose when exposed to certain pollutants during storage generating catalytic NOx species. Heat and the catalysts generated can cause a spreading thermal runaway in bulk prill, which can pose a significant safety risk by causing fires, explosions, and poisonous NOx gas emissions. This study aimed to understand the causes of thermal runaway spreading beyond its origin and propose methods for its prevention. The rate of heat generation during a runaway reaction in an adiabatic calorimeter was determined by contaminating AN with FeS 2 . The effect of mixing hydrotalcite (HT), an NOx scavenger, with AN to halt the decomposition was tested. The impact of bulk prill ventilation on the runaway was explored theoretically. The simulations showed that improving interstitial ventilation can reduce the runaway spreading. It was proposed that the prill storage containers be fitted with an NOx‐switchable ventilation system so that if NOx generation begins, the prill can be vented interstitially. The thermal runaway was eliminated by adding 6% HT powder to AN. These discoveries are useful for the development of safer AN explosives and fertilisers, as well as for enhanced safety in the AN prill storage systems.