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Cold flow simulation of gas flare auxiliary air

University of British Columbia

Flaring in oil and gas production is the controlled burning of unwanted exhaust gases to enhance safety. During flaring, there are two important concerns. The first is to prevent the flame from accumulating on the flare tip, which occurs during periods of high crosswinds. Such flame accumulation, which is known as flame capping, can cause premature failures and structural damage of the flare tip if sustained for long period of time. Excluding the combustion physics, a gas flare can be simplified as a jet in a crossflow (JICF). To avoid the considerable complexity associated with simulating a combusting flow, cold flow modeling can be used to investigate the critical flow conditions that would result in flame capping. The second concern is to avoid excessive smoke during combustion, which is important to meet the environmental regulations. Saudi Aramco has therefore developed a flare system that ameliorates both concerns. The system uses supersonic air nozzles that are distributed evenly around the flare exit. Besides preventing flame capping, the high-speed jets of these nozzles introduce extra oxygen and improve mixing in the combustion zone, which reduces flare smoking. The focus of this thesis is the cold (non-combusting) flow in one of these flare systems. Computational Fluid Dynamics (CFD) was used to study the flow within a gas flare. The capabilities of different turbulence models to simulate the flare flow field, particularly Large Eddy Simulation (LES) and Shear Stress Transport (SST) k-ω model, were tested by reproducing previous JIFC experimental data. The flow within the auxiliary air nozzles was studied by computing several parameters such as the mass entrainment, axial velocity, turbulent kinetic energy and Mach number in different flow regimes. Additionally, the differences between the results from different Reynolds-Averaged Navier–Stokes (RANS) models (including the SST k-ω and the Realizable k-ε) are investigated. For fixed mass flow rate, the detailed geometry of these nozzles is shown to have little impact on the mass entrainment rate, and therefore is expected to have little impact on the flare combustion characteristics. Finally, this work presents a preliminary study of a simplified full flare system.

Text

2018-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/67049

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/