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In the radiant section of cracking furnace,the thermal cracking process is highly coupled with turbulent flow,heat transfer and mass transfer.In this paper,a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme,combined with a comprehensive rigorous computational fluid dynamics(CFD)model.The eddy-dissipation-concept(EDC)model is introduced to deal with turbulence-chemistry interaction of cracking gas,especially for the multi-step radical kinetics.Considering the high aspect ratio and severe gradient phenomenon,numerical strategies such as grid resolution and refinement,stepping method and relaxation technique at different levels are employed to accelerate convergence.Large scale of radial nonuniformity in the vicinity of the tube wall is investigated.Spatial distributions of each radical reaction rate are first studied,and made it possible to identify the dominant elementary reactions.Additionally,a series of operating conditions including the feedstock feed rate,wall temperature profile and heat flux profile towards the reactor tubes are investigated.The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.
In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics (CFD) model. The eddy-dissipation-concept (EDC) model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Cautions of the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Larger scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of op erating conditions include the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used scientific guidelines for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.