On Experimental And Simulation Analysis For Distillation Systems With Internal Heat Integration

Internally heat integrated distillation column (HIDiC) is not only one of theenergy efficient distillation structure, which combines the advantages of direct vaporrecompression and the diabatic operation, but also provide a new configurationaloption for heat integration of distillation systems. Unfortunately, such a configurationhas not yet been widely used in the industrial practice because of its complicatedstructure and difficulties in operation.In the present work, the heat exchange coefficient and separation efficiency of anannular structured HIDiC were experimentally measured to provide the necessary datafor the HIDiC column design. In the experiment, the overall coefficient for theinternal heat exchange was shown to decrease with the pressure ratio, but not affectedby the F-factor. The internal heat exchange obviously affected the separationperformance of the outer column.Secondly, the heat integrated two diabatic binary distillation columns under totalreflux operation as above experiment was simulated for the aim to investigate thedistribution of the heat load along the column in the present work. The simulationresults showed that, only if the heat load distribution along the column axis wasuniform, the overall heat exchange coefficient can be used for each stage to calculatethe internal heat transfer; otherwise, the calculation error could be appreciably large.Thirdly, the reversibility of HIDiC was analyzed for its optimization design.HIDiC needs heat transfer between the two column sections. The intermediatecondensing and reboiling of the rectifying and stripping sections increase thereversibility of the separation process and lead to the increase in energy efficiency ofthe process, but can rise the need for more heat loads for the two sections or,equivalently, for more theoretical stages. The increase in heat loads can provide majordifficulties in locating enough heat exchange areas in the design. At the same timeincreasing stage numbers can increase the investment cost. In this part ot thedissertation the influence of increasing stage number to the operating cost and capitalinvestment of HIDiC was analyzed through two HIDiC design cases, and the stagenumbers (or equivalently the heat loads) were optimized to achieve the balancebetween the two kinds of cost. Finally, a configuration of an intermediate heat-integrated sequence ofdistillation columns (IHISDC) is proposed in this dissertation. The proposed IHISDCconfiguration is analyzed by applying it into a direct sequence of distillation columnsfor ternary mixture separation. In this configuration, heat is transferred form therecifying section of the high pressure column to the stripping section of the lowpressure column through intermediate heat exchangers. Comparing to theconventional heat integrated sequence of distillation columns (HISDC), the proposedIHISDC system was shown to have smaller pressure difference between the twoheat-integrated columns in the sequence, and consequently the energy cost for thereboiler of the high pressure column or for the condenser of the low pressure columncan be saved. It was also found that the heat duties of the reboiler of the high pressurecolumn and the condenser of the low pressure column were increased, and that theinvestment cost was increase due to the increase in the number of heat exchangers.The IHISDC needs to be optimized in order to lower its total annualized cost.