Comparison of Various Methods of Mitigating Over Pressure Induced Release Events Involving Ammonia Refrigeration Using Quantitative Risk Analysis(QRA)
Author: Donald Fenton and Tyler Hodges
The objective of this project was to determine the effectiveness of different methods of mitigating ammonia releases through a pressure relief device in an ammonia refrigeration system. A literature review was conducted and among the methods discovered, five were selected for further study and include: discharge into a tank containing standing water, discharge into the atmosphere, discharge into a flare, discharge into a wet scrubber, and an emergency pressure control system. All the methods were compared applying quantitative risk analysis where failure rates of each system were combined with ammonia dispersion modeling and with the monetized health effects of a system’s failure to contain an ammonia release.
It was determined that the ammonia release height had the greatest influence on the downwind cost impact relative to the other variables, including weather conditions and release from multiple sources. While the discharge into a tank containing standing water was determined to have the lowest failure rate, the other discharge methods can be designed to have comparable failure rates and comparable release consequent cost. The emergency pressure control system, now required by codes, used in conjunction with the other ammonia release mitigation systems, was determined to be very effective.