Abstract
A global sensitivity analysis is performed on Phast’s dispersion model for simulating jet releases of dense-phase carbon dioxide (CO2). The releases studied consist of above-ground, unconfined, horizontal, steady-state orifice discharges, with orifices ranging in diameter from ½ to 2 inch (12.8 to 50.4 mm), and the liquid CO2 reservoir maintained at between 100 and 150 bar and close to ambient temperatures. These scenarios are relevant in scale to leaks from large diameter above-ground pipes or vessels.
The sensitivity analysis is performed using a Gaussian emulator that is constructed from 100 Phast simulations. The parameters varied include the reservoir temperature and pressure, orifice size, wind speed, humidity, surface roughness and height of the release. The emulator is used to identify the input parameters that have a dominant effect on the dispersion distance of the CO2 cloud. The whole analysis (including the Phast simulations) runs on a laptop computer in less than 30 minutes.
The study demonstrates that Bayesian analysis of model sensitivity can be conducted rapidly and easily on consequence models such as Phast. There is the potential for this to become a routine part of hazard assessment.
A more limited set of results is also presented using the Computational Fluid Dynamics (CFD) software, ANSYS-CFX13, which is used to examine the effect of the solid CO2 particle size, which cannot be examined using Phast. The results show that the CO2 particle size has a relatively minor effect on the dispersion distance in the scenarios considered here.
