Retrofitting direct sequence distillation columns using driving force method

Abstract

Distillation is the primary separation process widely used in chemical processing. In retrofitting, distillation column problem can occur when it requires additional and major unit operations. Therefore, this research has been carried out in order to achieve a minimum or zero modification of unit operation and design the optimal column sequence with less energy consumption. The large energy requirement of these processes can be greatly reduced by changing the sequence of the existing direct distillation columns by using the driving force method. The objective of this research is to develop a methodology to find the best sequence that can save energy and has better economic performance which consists of four hierarchical stages. In the first stage, the design of existing direct sequence was simulated and the energy used is analysed by using a shortcut method for distillation column in Aspen HYSYS. Then, the optimum sequence was determined by using the driving force method in the second stage. In the third stage, the optimal sequence was simulated and the energy used was analysed using a shortcut method of distillation column in Aspen HYSYS. Finally, the energy requirements from both sequences were compared and the economic performance was evaluated and calculated. A maximum energy saving of natural gas liquids fractionation of 21.2% was obtained with the Return of Investment (ROI) of 6 with 2 months of payback period. The results for hydrocarbon mixture show achievement of maximum energy saving of 39.53% and the ROI of 3 was obtained with 4 months of payback period. All of this findings show that the methodology is able to retrofit the existing direct sequence of distillation columns with minimum energy distillation column sequence in an easy, practical and systematic manner.