Probabilistic analysis of the performance of barriers controlling the ignition of combustible gas in gas turbine air intakes

Nowadays, the frequent occurrence of hydrocarbon leaks underlies the need for investigating every possible contribution to the fire and explosion risk in the oil and gas industry. Hence, controlling the potential ignition sources is paramount for ensuring tolerable risk levels. Among potential ignitors, gas turbines (GT) are regarded as one of the main contributors when employed for mechanical-drive in the process area of offshore facilities even though their behaviour when acting as live sources has never been analysed in detail. This study aimed at investigating both the role that GTs play on the fire and explosion risk and the effect of further controlling ignition barrier elements by examining a real case of study. The Kamaleon FireEx™ – Risk and Barrier Management tool was used since this couples a CFD-based description of transient releases dispersion to the ignition probability modelling. After a first optimisation of the grid resolution, a selection procedure was developed to define a base case risk level. This result was analysed to highlight the time-window where ignitions occur and used as terms of comparison in the following sensitivity studies. First, the contribution that the installation of a GT carries along was quantified. The effect of an alternative ignition probability modelling, which underlies either a detailed representation of the GT behaviour when acting as an ignition source or the activation of an inert gas injecting system, was investigated thereafter. Results show the need for a quick response to obtain a risk reduction. Then, the influence of a shield wall that was built around the GT air-intakes was analysed. A covering effect was observed, which involved a reduction in the risk. Finally, since the wall introduced even a delaying effect, it was investigated whether this may combine with the alternative ignition model. Results showed a further risk reduction and the dominant role that physical barriers play in this context.