Heat Transfer And Energy-saving Performance Investigation Of Internally Heat Integrated Distillation Column

Distillation one of the most preferred unit operations in liquid phase separation.Meanwhile,it is one of the most energy consumption unit operation,its energy consumption accounts for up to about 40% in the chemical industry with the drawback of low thermodynamic efficiency which is only 5~20%.Compared with the conventional distillation column(CDiC),the heat integrated distillation column(HIDiC)has the advantage of high thermodynamic efficiency and low energy consumption,hence wide concern has been aroused by scientists of domestic and abroad about HIDiC at the current international situation that energy is becoming increasingly intense.The separation of ethanol-water mixture with a self-made pilot-plant concentric structured internally heat integrated distillation column is systematically investigated experimentally in the condition of total reflux and continuous feed respectively to obtain the parameters with respect of its function and energy saving performance.Temperature profiles at different compression ratios are obtained,the preliminary analysis of experimental data shows that with the increase of compression ratio,the temperature difference between rectifying section and stripping section increase,the amount of internal heat exchange first increase then become steadily,the overall heat transfer coefficient decreases.Therefore,among all the affecting factors of internal heat exchange,the influence of temperature difference is bigger than that of overall heat transfer coefficient.Heat transfer model of HIDiC is built,then a series of adiabatic simulation is carried out,it shows that the temperature profile in adiabatic simulation is correlated with that in the experiment.As a result,a more reasonable heat distribution is proposed,in which the heat transfer coefficient of each section is calculated through convectional heat transfer empirical formula before the experiment.This calculation method is proved credible through the comparison of total amount of heat exchange between the two sections.Operating lines of ethanol-water system under different compression ratio indicate that when internal heat integration take place,the mass transfer driving force of rectifying section increases while the mass transfer driving force of stripping section decreases.Based on the second law of thermodynamics,the thermodynamic deduction of internal heat integrated distillation process is carried out by using entropy method,it demonstrates that HIDiC shows obvious improvement on entropy production and thermodynamic efficiency and could reduce energy consumption.Based on the first law of thermodynamics,the comparison of CDiC and HIDiC under different compression ratio shows that the average reboiler heat duty saving of HIDiC is 25.36% and average condenser heat duty saving is 62.25%.Thermodynamic efficiency and entropy production of HIDiC arecalculated,results show there is an average increase of 35.47% in thermodynamic efficiency and an average decrease of 24.53% in entropy production.Meanwhile,the optimal operating zone of compression ratio is decided to be 2.2 to 2.5,where the average energy saving parameters are better than that of the whole operating zone.