The Process Simulation And Experimental Study Of Diabatic Distillation

By locating more than one heat exchanger along the column,a diabatic distillation column can redistribute the heat requirements over the whole length of the column,resulting in a lower entropy production and energy grade.The diabatic distillation can be divided into completely diabatic distillation and partially diabatic distillation,consisting of diabatic rectifying column,diabatic stripping column and diabatic distillation column.In this article,the rate-based mode of Aspen Plus was used and the separation of the propanol-isopropanol was studied.The completely diabatic operation was applied to the rectifying and stripping section together and individually,so did the partially diabatic operation.The number of stages,the reflux ratio and the product flowrate were kept constant before and after the introduction of the intermediate heat exchange.The vapor-liquid profile,transfer forces profile and its variance,separation efficiency,heat duty of condenser and reboiler,as well as the total entropy production were studied under the three different diabatic heat distributions:(1)a uniform heat supply;(2)a heat supply distribution based on the exergy loss along the column;(3)a heat supply distribution based on curve of composition.The simulation results showed that:(1)applying diabatic operation both to the rectifying and stripping section was unfavourable for a distillation column;(2)applying the diabatic operation to the rectifying section separately can influence the operation of stripping section,while,the diabatic operation of stripping section had almost no influence on the rectifying section;(3)the diabatic operation of the rectifying was unfavourable,the total entropy production increased by 19.25% while the product purity increased only by 0.42%;(4)the diabatic operation of the stripping section had great advantage in reducing the entropy production,for example,the entropy production decreased by 15.96% at the cost of the reduction of product purity by only 0.36%.The heat supply distribution based on curve of composition can produce the least entropy among the three heat distribution profiles.At last,we carried out the diabatic batch stripping experiment with propanol-isopropanol,using a packed tower of 80 cm with φ3*3mm Dixon ring as a packing.Different heat duty was introduced in the lower part of the column.Pressure drop of the tower was kept constant(146pa)before and after the diabatic operation.The experimental result showed that:(1)the more heat duty,the lower the reboiler duty;(2)after the same separating duration,the propanol concentration at the bottom reduced by 0.46% while the heat duty reduced by 15% for the diabatic duty of 40 W,however,the heat duty reduced by 27.5% at the cost of the reduction of the propanol concentration by 1.75% for the diabatic duty of 80 W.