Implementation and Optimization of a Multiphase, Transient Release Rate Model for Consequence Estimation

Abstract The life safety consequences of CO2 pipelines and those carrying other toxic chemicals, unlike natural gas pipelines, are affected to a great extent by the outflow’s response to time and phase behaviour over a long timescale. Therefore, a critical part, of evaluating the hazard of releases is outflow modelling. To bridge this technical gap, as well as to produce a general model suitable for evaluating a range of product types, including natural gas and natural gas-hydrogen blends, a multiphase, transient release rate model is required. This paper outlines the enhancements applied to a method of characteristic-based flow solver, described by the University College of London, to facilitate its practical application to repeated simulations. These improvements include an adaptive grid and locally defined timestep; a REFPROP-derived equation-of-state property lookup table; a 1D wall heat-transfer treatment; a domain-extending boundary condition; and a numerical construct that uses a steady-state approximation of the conservation equations to extrapolate beyond the calculation domain to better approximate a semi-infinite pipeline.