(117b) Boiling Ammonia Pools – Evaporation and Dispersion Models Validation

Air Products conducted Red Squirrel tests¹ for releases of liquified ammonia in 2022 and 2023, and a detailed report, raw and processed data, videos, etc. are available to the public. It is now well understood and accepted that storing and handling ammonia as a cold/refrigerated liquid under low pressure is inherently safer than the fairly common practice of storing, handling, transporting ammonia at an ambient temperature, high pressure liquified state.

The Red Squirrel data are being used by different organizations to better understand the behavior of ammonia plumes following a loss of containment. We have analyzed data from the Red Squirrel-1 (RS-1) dataset to validate models in the Phast and Safeti tools used for consequence and risk analysis, respectively. The experiments spilled cold/refrigerated ammonia at low pressure into a concrete bund (4 m x 4 m). Measurements included bund loading, thermocouple measurements and downwind concentration sensor readings.

Modeling the experiments as liquid leaks in Phast gives excellent reproduction of the observations. Liquid mass within the bund at the end of the release and the reducing mass over the first hour as the ammonia vaporizes closely match the load-cell data. Beyond around an hour, Phast begins to over-predict the vaporization rate. This divergence can be potentially explained by the formation of dry patches within the bund. Thermocouple measurements support this explanation, and introducing a faster-shrinking pool in Phast to model the emergence of such patches significantly improves agreement with load-cell data over the second hour. For the dispersion of vapor plume from the pool, the noise and variability in sensor readings and limited measurement range of the sensors necessitated careful interpretation. Generally, the Phast dispersion predictions were broadly in line with peak observed concentrations.

This paper provides detailed information on the modeling approach, model inputs and comparison of the results to Red Squirrel experimental data.

¹Red Squirrel paper link: https://aiche.onlinelibrary.wiley.com/doi/full/10.1002/prs.12454