Evaluation of mass transfer correlations applying to cryogenic distillation process with non-equilibrium model

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Reliable heat and mass transfer model plays a significant role on design and calculation of the distillation process. Since the cryogenic fluids of oxygen, nitrogen and argon have obviously different thermal physical properties compared to the room temperature ones, it is of great necessity to evaluate the feasibility of the existing heat and mass transfer models in the cryogenic distillation calculation. In this study, a non-equilibrium model (NEM) based on the FORTRAN compiler is implemented to investigate the actual cryogenic distillation process in a structured packing column (SPC) of the air separation unit (ASU) with capacity of 17,000 Nm3/h. The complete conservation equations for materials, mass and energy in the phases are numerically solved based on the Thomas algorithm. The commonly used mass transfer coefficient models with different diffusion coefficients, as well as the heat transfer model, are evaluated in the performance prediction of the cryogenic SPC. The multiple imports and exports of the model are validated by the limited available measurements, while the calculated distributions of the component molar fraction, temperature, pressure and flow rates along the column are compared with those from the Rate-based module of Aspen plus simulation. The comparisons verify the solving strategy and help to understand the reliability of the existing basic transfer correlations for future cryogenic distillation calculation.