Storti L., Buccoliero D., Paesani C., 2013, A Risk Based Approach on Selection of Refrigerated Ammonia Storage, Chemical Engineering Transactions, 31, 571-576.
Recently first edition of API STD 625 has been issued providing general requirements on refrigerated liquefied gas storage selection; according to this standard the selection of storage concept among the three alternatives (single containment plus dike, double containment, full containment, external or internal pumps) shall be supported by a risk-based approach analysis. The application of API STD 625 to refrigerated storage of ammonia is challenging since not practical configuration may be required to control the potential hazardous scenarios of ammonia, due to the large area affected by a huge release of liquefied ammonia in comparison with the one associated to similar release of a liquefied flammable gas. In fact the ammonia has a very low concentration limit leading to irreversible acute toxicity effect to humans. One of the main issues identified is associated to the current practice to have external pumps on refrigerated ammonia storage with respect to other applications (e.g. ethylene, liquefied natural gas) for which internal pumps are a consolidated design. A case study is presented: selection of 50,000 t Ammonia Storage inside an Ammonia Plant. The topics discussed highlight how further enhancement is required in order to make the safety performance of these facilities comparable with the ones of refrigerated liquefied flammable storage and how API STANDARD 625 provides a valid approach to identify critical issues to be discussed and improved.
