Modeling of Ground Flare Pits

摘要

Some new LNG liquefaction facilities have been configured to include large ground flares toallow for the safe combustion of large volumes of combustible gasses in the event of extremelyrare, short duration, facility upset conditions. A recent example is the planned INPEX LNGdevelopment near Darwin, Australia. Ground flares can exceed the size of football fields,measuring greater than one hundred yards in length. A typical ground flare consists of severalhundred burners, surrounded by porous (slotted) radiation protection fences. Questions havebeen raised as to whether the plumes of hot combustion gasses may impact the facility, the workforce, or nearby roadways in the event that the wind happens to be blowing in the wrongdirection at the wrong speed.This study examines the use of Computational Fluid Dynamics (CFD) to model plumes fromground flares and the downwind temperature distribution. The CFD model is first validated bycomparing its results with commonly used dispersion models such as PHAST (Process HazardAnalysis Software Tool) and CALPUFF. The flow features of a ground flare plume rising in acrosswind are then discussed. In particular the plume acts as what is commonly referred to as a“jet in cross flow.” In this type of flow, counter rotating vortices are known to form. Thesevortices are not represented in commonly used Gaussian plume models.The use of two adjacent flare pits is then investigated. The interaction of the two pairs ofcounteracting vortices is discussed, as it influences the downwind temperature distribution. Theresults show that the distance between adjacent flare pits is of importance when planning multiflarepit operations.