The Simulation And Exergy Analysis Of Diabatic Distillation

Distillation, which is presently being applied to the industrial level in crude oil refine, chemical engineering and natural gas processing, is one of the most widely used separation technology in present industry and almost the largest energy consumption unit operation. Therefore, it is very important to have the investigation of the energy saving in the distillation process under the circumstance of energy source deficiency.Diabatic distillation, i.e. with heat exchangers on trays, can reduce exergy losses and increase exergy effectiveness compared to adiabatic distillation with a reboiler at the bottom and a condenser at the top. In fact, diabatic distillation has become a universally concerned subject among the field of chemical engineering. The simulation and analysis of the diabatic distillation should be regarded as a considerable issue both in theory and application. By simulating the diabatic distillation system, the influential factors of energy-saving have been analyzed and studied in detail in this paper. The following points are emphasized:(l)The operation models of adiabatic and diabatic distillation have been set up and the operation block, thermodynamics model and mathematical model in the simulation have been determined as well;(2)Based on the simulation and exergy analysis with Aspen Plus program, shortcut distillation design—DSTWU model and rigorous distillation design—RADFRAC model, the author has determined the heat duty, exergy losses and the distribution of exergy losses along the adiabatic column, which will help the simulation and optimization of the diabatic distillation;(3)Diabatic distillation under various operation conditions has been simulated by using energy balance method and exergy analysis;(4)How the different mixture and the various degree of separation, number of trays and feed location influence exergy saving in diabatic distillation have also been discussed;(5)On the basis of the total exergy losses along the column, different schema of the heat transfer distribution along the column have been compared and analyzed;they can be classified in three categories: heat duty equipartition approach, empirical approach, separation degree matching approach. In conclusion, different heat transfer distribution along the column will have effect on total exergy losses. In particular, most satisfactory results have been obtained by using separation degree matching approach. In order to diminish the exergy losses, heat transfer distribution should meet the needs of the request of separation degree.And on this premise, the author makes his suggestion in increasing the proportion of heat supplied to the tray with minimum exergy losses and decreasing the proportion of heat supplied to the tray with the maximum exergy losses.