Impact of temperature approach on the behavior of the rectification heat and mass exchanger under fouling constraints

Abstract

In industrial applications, thermal separation of substances is carried out in rectification and distillation columns and each one of them is equipped with condenser and reboiler. Such technology is energy-consuming, i.e. it requires high heat supply to the reboiler, and significant waste heat discharge through the condenser, to the environment. The new approach assumes thermal separation carried out in a system of channels where heat distribution is sustained through a diaphragm, i.e. channel walls and the number of reboilers and condensers is reduced to minimum. This type of apparatus serves for heat transfer and simultaneous thermal separation of substances, thus mathematical model of rectification heat and mass exchanger (HME) exercises the concept of heat-integrated distillation column (HIDiC) in a channel-type geometry. As it has been shown in previous studies, such technology has a potential of reducing energy consumption by 40%–60% compared to rectification columns currently used in industry. The model of the channel-type exchanger uses a theoretical tray model for describing mass transfer, combined with our in-house mathematical description of diaphragm heat transfer that takes fouling resistance into account.Numerical calculations carried out in this work were focused specifically on the impact of fouling on the operation of channel-type heat and mass exchanger. Key issues covered in this work included the impact of fouling on the purity of collected fractions (which have to meet guidelines given by process designer) and the intensity of internal heat streams (which are decisive for energy-saving). In the parametric study, the minimum temperature difference between mixture streams in the stripping and rectifying sections was also included.The simulation results showed that for considered mixture of fractions, assuming a realistic range of fouling thermal resistances, the sensitivity of channel-based heat and mass exchanger to fouling is negligible, and the purity of distillate is hardly affected.