Computational Fluid Dynamics Analysis of Local Heating of Propane Tanks

This report describes a three-dimensional, time transient computational fluid dynamics (CFD) analysis of liquefied petroleum gas tanks with various types of local heating by fire. The analysis, conducted using the commercial CFD code by Fluent Inc., was performed as part of a larger study of the effects of thermal protection defects. Thermal protection systems are used to protect dangerous goods tank-cars from accidental fire impingement. They are designed so that a tank will not rupture for 100 minutes in a defined engulfing fire, or 30 minutes in a defined torching fire. Recent inspections have shown that some tanks have significant defects in these thermal protection systems. If a tank has thermal protection defects, it will heat up more rapidly in a fire. This means the tank will experience higher wall temperatures, lading temperatures and tank pressure, all of which increase the risk of tank failure. Testing shows that when a tank is heated in a fire, the liquid near the wall is heated first. This warm liquid then rises to the liquid surface, where it generates vapour to pressurize the tank. This rising of the warm liquid is called temperature stratification. The CFD analysis was conducted to quantify this process for the case of local tank heating due to thermal protection defects. It was used to study the effect of defect size and location on the transient heating of the liquid lading in the tank. The results show that heating near the tank ends or near the liquid level on the tank sides causes the most rapid rise in liquid temperatures on the liquid surface. Heating near the tank bottom results in the slowest rise in liquid surface temperature.