An Equilibrium Stage Model With A Shortcut Gas Flow For Distillation Columns

Distillation column is the most widely used and big energy consuming separation equipment in chemical industry. It has been an important research subject to study the contact condition of gas-liquid flow and hydrodynamic performance of the trays. Optimal design and reasonable operation of the distillation column contribute to improve the separation efficiency. To use of the computer technology to establish a widely applicable distillation column model for commercial production and research use is particularly important. A modification is proposed to the conventional equilibrium stage model by including a shortcut gas flow in this paper and an actual plate model is established:1?In the actual operation, the gas streams countercurrent contact with liquid streams, but gas phase and liquid phase is not in the complete thermodynamic equilibrium state. This paper proposes a shortcut gas flow accounting for the deviation of the behavior of a real plate from the equilibrium assumption. Gas from the lower plate is divided into two parts: the immerging gas coming into close contact with the accumulated liquid, and the shortcut gas having no contact with the liquid.2?Combined with mass transfer theory and Stefan-Maxwell equation, the gas phase mass transfer is described as a first order process.In the immerging gas flow rate formula, there is one tuning parameter which depends only on the geometry of the plate and can be easily calibrated with production data. For a given plate working with a given system of substances, the proposed model is predictive in the sense that its only tuning parameter is independent of operating conditions.3?The hydrodynamic performances of the model including weeping,entrainment, pressure drop is also considered. In the simulation test with cyclohexane/n-heptane and ethanol/water distillation columns, the plate efficiency of the proposed model agrees very well with those calculated by three well-established efficiency correlations.