Configurations And Their Comparison For Internal Heat Integration In Distillation Columns

As a novel energy-efficient configuration, the internally heat-integrateddistillation was studied by means of both experiment and simulation in this paper. Theenergy-saving performance and economic feasibility of the internally heat-integrateddistillation column (HIDiC) and its various simplified configurations wereinvestigated and compared with heat-pump-assisted distillation.A concentric experimental set-up of HIDiC with random packing was constructed,and its performance in heat transfer between the inner and outer column sectionstogether with the influence on mass transfer by heat exchange was studied for thebinary system of ethanol/water. The measured overall heat transfer coefficient liesbetween750to1000W/(m2·K), and decreases with increasing temperature differencefor heat transfer. The separation efficiency of the inner column (being cooled) showslittle change, while that of the outer column (being heated) drops sharply as more heatis transferred.Simulation studies on HIDiC’s performance for the separation of propane andpropylene were carried out using Aspen Plus11.1in combination with MicrosoftExcel2003. Simplified configurations of HIDiC were also studied, in which theinternal heat integration between the whole rectifying and stripping sections issimplified to several external heat exchangers. The heat transfer locations and thedistribution of heat loads were optimized to achieve minimized energy consumption.After comparison with the original HIDiC, such an approach was proved to be able toreduce capital costs significantly while retaining the original reversible advantages tothe greatest extent possible, and thus is a more practical solution. Two novelheat-integrated configurations, i.e., VRC combined HIDiC and inversely integratedHIDiC, were developed. It was found that the former scheme could be an alternativesolution to a HIDiC with excessively large heat exchanger area requirement, while thelatter one suffers from strict requirements on the mixture to be separated as well as theproduct specification.Comparisons were made among HIDiC, simplified HIDiC andheat-pump-assisted distillation on the basis of the same minimum temperature difference for heat transfer, and the total annual cost (TAC) was selected as thecriterion. It was found that the results depended strongly on the basis selected forcomparison. If compared under their optimal total number of stages and the sameminimum temperature approach, the VRC scheme would have the lowest utility costand total annual cost, while those of the HIDiC scheme are the highest.