(43f) Application of CFD Models for the Onshore Process Industry

The evolution of technology has made the application of complex computational fluid dynamics (CFD) models practical for the onshore process industry. Previously, CFD models were extremely complex and required computing capacity in excess of the typical desktop PC and expertise beyond most skilled engineers. Creating CFD models had also been a cumbersome and time intensive task, resulting in a cost exceeding that within reach of most process industries. However, advances in computing capacity together with easier to use programs have allowed skilled engineers the ability to apply these tools to enclosed processes at onshore process plants for a reasonable cost. These enclosed processes previously had few practical means of evaluating explosion hazards. Limitations of commonly used approaches include:

? The use of external vapor cloud explosion blast curves is not a valid application, though often used due to the lack of other available means.

? The Shell Code for Overpressure Predictions in gas Explosions [SCOPE] model is a cost-effective tool, but has limitations in the available venting surface and deluge modeling, limiting its application to onshore facilities as a screening-level analysis.

? NFPA 68 calculations have also been used, but inappropriately in the process industry since congestion levels cannot be accounted for by this method.

Over the last several years, ABS Consulting has performed multiple studies evaluating process buildings for internal explosions to evaluate both dispersion and explosion and their effects on nearby structures using the FLame ACceleration Simulator (FLACS) CFD model. Significant factors that can be accounted for with the CFD models include: fan activation, natural ventilation, hydrocarbon monitoring, leak isolation, sprinkler activation and a significant amount of vent surface area from openings and frangible panels. Most of these studies had been previously evaluated using other methods that were very conservative and resulted in significant damage predictions to nearby buildings. In the majority of cases, the CFD models reduced these damage predictions and provided confidence that accurate and cost-effective modeling methods were now available to the onshore process industry. Examples presented in this paper show how CFD models were used to minimize the blast effects of internal explosions, sometimes by helping to design fire protection and other automated actions, and examples of actions that can inadvertently increase building damage predictions.