Optimization of Distillation Separations Using Feed Splitting by a Homotopy Continuation Method.

It is a common procedure to save energy in industrial distillation towers by preheating and precooling the feed with heat transfer from the bottom and top products. An example is oil sweetening by distillation. It is shown here using simulation that if, before entering the unit, the oil feed is split into two streams and only one of them is preheated, further savings of energy (up to 50%) can be achieved. The same results are achieved by splitting the feed to an ethane-ethylene distillation column and precooling only one part of it just before entering the tower. In this study, the effects of feed splitting into hot and cold towers were investigated in order to reduce the duties of the reboiler or condenser and the total annual cost (TAC). Also, consideration was given to obtaining a common design in order to achieve greater flexibility for the required operating schemes. The investigation was carried out as an optimization problem defined by effective parameters affecting the reboiler and condenser duty and product recovery. Models for finding the best feed split-fraction ratio, optimal locations for the feeds, number of trays required for a specified separation, and best operating pressure for a distillation column with feed splitting are presented. When a homotopy continuation method was used in MATLAB and it was connected to the ASPEN HYSYS simulator, the optimal values for decision variables were calculated. It is observed that the optimal feed-splitting technique leads to a 49.2% reduction in energy demand in an oil sweetening process and a 24% reduction in reboiler duty and a 22% reduction in condenser duty in an ethane-ethylene separation process in comparison with conventional processes. [ABSTRACT FROM AUTHOR]