Using CFD to Optimize Flow Distribution in Gas Flare Piping

Paper from the AFRC 2017 conference titled Using CFD to Optimize Flow Distribution in Gas Flare PipingDesign techniques for flare piping which includes the manifold headers, runners, and risers going to the tips themselves has traditionally centered around one-dimensional flow theory combined with empirical pressure-drop correlations. With increasingly complex staging and runner systems being employed in gas flaring systems such as with multi-point ground flares (MPGFs) and totally enclosed ground flares (TEGFs), CFD should play an important role in investigating and optimizing the piping system design.; This paper will provide results from a study where CFD was used to investigate the flow distribution in the original piping of an EGF and an air-assisted MPGF. Variation of flow to tips of less than 10% was desired but the CFD results indicated maximum variations that exceeded the maximum specification. For the MPGF, the flare gas headers tended to exhibit more variation than the air headers. Using only standard piping reducers and standard pipe sizes, modification to the piping system was performed to improve flow distribution uniformity for three different MPGF headers. Maximum variations for the MPGF were reduced to within the specification for the flare design. The EGF piping system was also optimized reducing maximum flow variation. An incompressible RANS version of Fluent was used for the study and was checked against using the compressible version since tip exit velocities approach sonic conditions. Results of the comparison of compressible and incompressible versions of Fluent indicated no measurable difference for this study as most of the piping system is in the incompressible flow regime