(30a) Ammonia Safety: Emergency Ventilation Design for Machinery Rooms

The ammonia refrigeration industry has a historically good safety record and hence there have been few instances of ammonia release resulting in ignition events. However, when such events do occur in confined enclosures, such as machinery rooms, the devastating consequences can occur. The present study uses computational fluid dynamics (CFD) to quantitatively evaluate the performance of various emergency ventilation designs and emergency ventilation rates for controlling the flammability hazard during ammonia releases in machinery rooms. A wide range of emergency ventilation rates were considered in addition to a range of leak location/direction combinations. In total, approximately 2000 CFD simulations were performed. Emergency ventilation performance was quantitatively evaluated based on the system’s ability to limit the size of the flammable ammonia/air cloud to less than 25% of the room volume during a leak. The results of this study demonstrate that the release characteristics of saturated ammonia liquid, subcooled ammonia liquid and superheated ammonia vapor differ quit substantially. Required emergency ventilation rates for ammonia machinery rooms have conventionally been provided as an equivalent 30 Air Changes per Hour (ACH) of the machinery room. However, the results of the present study demonstrate that emergency ventilation cannot be determine by ACH alone, and the ventilation must be scaled to the leak or vapor generation rate. The paper presents necessary guidance to limit the size of the flammable ammonia/air cloud to less than 25% of the room volume during an emergency unintentional release.