A Comparison of the RANS and LES Turbulence Models in the Simulation of Emissions from Flares to the Environment

Purpose: This study attempts to simulate wake-stabilized flares in the petroleum and gas industry using mathematical equations governing the flow, turbulence and combustion in flames as encoded in the ANSYS-HYSYS simulation software package. The work compares the RANS and LES turbulence models in conjunction with the partially premixed combustion model. The model uses the mixture fraction approach to predict the flame appearance and the thermochemical properties of the wake-stabilised cross-flow flame. Design/Methodology/Approach: The research strategy involves using the RANS (Reynolds Averaged Navier Stokes) and the LES (Large Eddy Simulation) mathematical Models to simulate and study the physical structure and the thermochemical properties of natural gas flares in the presence of crosswind. The wind tunnel geometry was built and meshed using the ICEM software, the calculations were carried out in the ANSYS-Fluent CFD software, and the computational data generated was processed and analysed using the Tecplot CFD post-processing software package. The results of the simulation were then validated against the experimental work of Huang and Wang. Findings: The findings demonstrated that the LES turbulence model outperformed the RSM turbulence model in terms of predicting temperature trends and pollutant species. However, the peak temperatures at the analysed measurement locations were accurately predicted by both models. The LES model also improved CO2 concentration predictions. In general, the LES turbulence model predicts more accurately than the RANS model, but the RANS model still provides a respectably accurate forecast of the thermo-chemical characteristics of the flame, making it a viable substitute for the more expensive LES. Research Limitation: The findings from simulations using RANS and LES models may be case-specific, with limited scalability and generalizability to different flare configurations or operating conditions. Each flare system may require tailored modelling approaches, limiting the broad applicability of the research results. Practical Implications: The work's practical implications are that simulation can be used in place of experiments to save money on some of the more expensive experimental projects since the simulation results agree fairly well with the experimental data. Social Implications: Gas flaring has caused a lot of environmental damage in the Niger Delta area of Nigeria and other parts of the third world where the gas flaring menace has been a concern. The availability of simulation codes to investigate the pollution from the flares will go a long way in mitigating the effects of this pernicious industrial practice. Originality and Value: Previous work with gas flares has focused mainly on methane, but this work focuses on propane, which is also an important constituent of natural gas.