The Non-Steady Outflow of Propane Vapor from a Railroad Tank Car

摘要

This report discusses the venting of vapors from rail tank cars. Two particular problem areas are addressed, namely the non-steady character of the flow in the final blow-down stage and the influence of real gas effects on flow predictions. Equations are developed with which the non-steady mass flow rate, the stagnation temperature and pressure drop and the mass left in the tank as a function of time can be predicted for vapor flow out of a finite-sized tank. The influence on the predicted flow rates due to the use of different equations of state (e.g. perfect gas equation, van der Waal's equation, Starling's equation) is shown and discussed. Example calculations are carried out for propane. The developed equations and calculation methods are valid for most other vapors and gases of industrial fluids commonly shipped in rail tank cars.