The radiation and convection section of a steam cracker are thermally coupled. Optimization and design requires a coupled simulation of both sections. In this work a 1D model for the convection section, CONVEC-1D, is developed. Several models for the different heat transfer phenomena are implemented and evaluated. For flow boiling, an empirical and a mechanistic model are developed and compared for both single-and multicomponent hydrocarbon feeds. The latter is performing best over a wide range of operating conditions, taking into account the different two-phase flow regimes. The coupled iterative procedure is demonstrated for an n-pentane steam cracker convection section.

To study fouling in steam cracker convection section tubes, accurate tube wall temperature profiles are needed. In this work, tube wall temperature profiles are calculated using a hybrid model, combining a one-dimensional (1D) process gas side model and a computational fluid dynamics (CFD) flue gas side model. The CFD flue gas side model assures the flue gas side accuracy, accounting for local temperatures, while the 1D process gas side model limits the computational cost. Flow separation in the flue gas side at the upper circumference of each tube suggests the need for a compartmentalized 1D approach. A considerable effect is observed. The hybrid CFD-1D model provides accurate tube wall temperature profiles in a reasonable simulation time, a first step towards simulation-based design of more efficient steam cracker convection sections.

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