Refrigerated ammonia spills: Evaporation and dispersion model validation

Abstract It is well understood that storing and handling ammonia as a cold/refrigerated liquid under low pressure is inherently safer than the practice of storing, handling, and transporting ammonia in an ambient temperature, high pressure liquified state. To better understand the behavior of ammonia following a loss of containment, Air Products sponsored the conduct of Red Squirrel tests in 2022 and 2023 for releases of liquified ammonia. These included spills of refrigerated ammonia at low pressure into a concrete bund. Measurements included bund loading, thermocouple measurements, and concentration sensors. This paper validates models in DNV's Phast consequence modeling tool against these experiments. Phast gives excellent reproduction of the observed pool results. Liquid mass within the bund over the first hour closely matches the load‐cell data. Beyond this time, Phast begins to overpredict the vaporization rate. Thermocouple measurements suggest this can be explained by the formation of dry patches within the bund, and accounting for this improves agreement with load‐cell data over the second hour. For the dispersion of vapor from the pool, the noise and variability in sensor readings and the limited measurement range of the sensors necessitated careful interpretation. The Phast dispersion predictions were broadly in line with peak observed concentrations.