Delivery of inert gas through a vertical borehole using inert gas generator: A theoretical study

Abstract

The delivery of the inert gas through a vertical borehole using inert gas generator or IGG is investigated. Potential limitations and/or transient effects are highlighted. During the analysis, the borehole diameter, borehole length, type of borehole and partial condensation prior to entering the borehole were varied. A choked flow will occur for a contraction exit or borehole of 0.3 m in diameter if no condensation prior to the contraction occurs. If partial condensation takes place, a borehole diameter of 0.3 m will be possible if almost 50% of the water vapour condensates. However, pressure losses along boreholes with a diameter of 0.3 or 0.4 m are significant and could pose a challenge if trying to mitigate the pressure losses. Adding a booster fan prior to the inlet of the 0.4 m lined borehole would still be a challenge. The corresponding case with a 0.5 m borehole presents much more favourable pressure losses. The 0.5 m diameter lined borehole should be regarded as the lower threshold. The rapid heating of the unlined borehole surface will increase the risk of thermal spallation and possibly imposing restrictions. Understanding the mechanisms during gas delivery will increase the likelihood of a successful inertisation.