(52i) Atmospheric Discharge Screening for Hydrogen-Rich Streams from Pressure Relief Valves

At each facility in oil & gas, petrochemical, and chemical industries, it is not cost effective to route all pressure relieving devices with potentially hazardous substances to a disposal system such as a flare or effluent treatment system. Hence, it is important to have a sufficient method to determine which pressure relieving devices need to discharge to a disposal system and which devices can discharge safely directly to the atmosphere. This determination can be made by doing detailed dispersion modeling for each pressure relieving device; however, a semi-qualitative, simplified method provides a more accessible and cost-effective analysis to screen out unsafe discharge to atmosphere. Currently, API STD 521 provides a simplified method to make this determination. However, the API STD 521 screening method has a limitation in that it can under-predict the extent of the vapor cloud for some hydrogen-rich streams, common in petroleum and renewable refineries. The purpose of this paper is to address that limitation and provide recommendations for evaluating safe discharge of hydrogen-rich streams.