(22i) Nonequilibrium Modeling of Heat and Mass Transfer with Partial Condensation in a Tube-Type Interface for Heat Integrated Distillation Column

This is a fundamental study running on the governmental project line of energy-saving distillation technology for reduction of carbon dioxide gas emission in chemical industry. The present study pays attention to design of built-in interfaces for large-diameter commercial-scale plate-type heat integrated distillation columns, that is, design of built-in tubes for internal heat exchange between the higher-temperature rectifying section pressurized and the lower-temperature stripping section operated at normal pressure. The heat transfer tube having a U-tube-shaped flow passage inside is protruded from the rectifying section into the stripping section, so that the vapor mixture supplied from the rectifying section pressurized by a compressor flows through the flow passage of the tube inside with partial condensation of less-volatile components whereas the bubbling liquid on a tray of the stripping section undergoes partial vaporization of more-volatile components on the outside tube surface due to the latent heat of condensation released inside the tube. The purpose of the present study was to construct a thermal design model based on simultaneous heat and mass transfer with condensation inside a heat transfer tube. A non-equilibrium model was constructed with an assumption that the heat transfer coefficient is proportional to local mass flux of the partial condensation. This model was based on local phase equilibrium between the vapor and its condensate but did not assume equilibrium in the counter-current contact of vapor and bulk liquid flow. The simulation analysis was made for a binary system of benzene and toluene with various operation pressure and vapor supply conditions to determine local variation of the following variables inside the tube: (1) temperature and concentration of each component in vapor and liquid flow; (2) mass-flux of partial condensation, (3) heat-flux, and (4) vapor and liquid flow rates. It has been confirmed that the temperature difference between the rectifying section and the stripping section should be determined as the key control parameter taking into consideration the power consumption of compressor installed in-between the stripping section and the rectifying section. The model was generalized to analyze the internal heat exchange capacity as the key technology for plate-type heat integrated distillation column (HIDiC) systems from various engineering viewpoints. It has been assured that this model gives various important information of heat and mass transfer useful for design of internal heat exchange interfaces.