Ahmad Nafais Rahimi

Optimal Retrofit of Natural Gas Liquids Separation Direct Sequence and Feed Condition Sensitivity Analysis

The objective of this paper is to present the retrofitting analysis for the direct sequence natural gas liquids (NGLs) separation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient NGLs separation process methodology is developed. Hence, the methodology consists of four hierarchical steps. In Step 1, a simple and reliable short-cut method for distillation column design of process simulator (Aspen HYSYS) is used to simulate a base (direct) NGLs sequence. The energy used to perform the separation is obtained that will be used for comparison purpose. In the Step 2, an optimal NGLs sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. The optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the energy used in the optimal NGLs sequence is analysed. Finally, the energy and sensitivity used in the optimal NGLs sequence is compared with the base sequence in Step 4. Several case studies involving several sequences have been used to test the performance of the developed methodology. A maximum energy saving of 11.7 MW was achieved when compared with the optimal (driving force) sequence with the direct sequence. For sensitivity analysis, the results show that the driving force sequence has the best sensitivity compared to other sequences. These findings show that the developed methodology is not only able to design energy efficient distillation columns sequence but also better process sensitivity with respect to the feed conditions for NGLs separation process in an easy, practical and systematic manner.

Hydrocarbon Mixture Fractionation Direct Sequence Retrofitting and Feed Condition Sensitivity Analysis

The objective of this paper is to present the retrofit analysis for the hydrocarbon mixture (HM) direct sequence fractionation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient HM separation process methodology has been developed. The methodology consists of four hierarchical steps. In the Step 1, a simple and reliable short-cut method of process simulator (Aspen HYSYS) is used to simulate a direct HM sequence. The energy used to recover individual fractions in the base sequence is analysed and taken as a reference. In the Step 2, an optimal HM sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. Once the optimal HM sequence has been determined, the new optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the process sensitivity and energy used in the optimal HM sequence are analysed, the process sensitivity of optimal HM sequence is compared with the other three different sequences by changing their feed conditions. Better sensitivity sequence was achieved when compared optimal sequence with the other three sequences in Step 4, the sequence determined by the driving force method has better sensitivity compared to the three other sequences as well as less energy requirement. All of these findings show that the methodology is able to design better sensitivity and minimum energy distillation column sequence for HM fractionation process in an easy, practical and systematic manner.

Energy efficiency improvement in the natural gas liquids fractionation unit

The objective of this paper is to present the study and analysis of the energy efficiency for the natural gas liquids (NGLs) fractionation sequence by using driving force method. To perform the studies and analysis, the energy efficient NGLs fractionation plant methodology is developed. Hence, the methodology consists of four hierarchical steps; Step 1: Existing Sequence Energy Analysis, Step 2: Optimal Sequence Determination, Step 3: Optimal Sequence Energy Analysis and Step 4: Energy Comparison. The capability of this methodology is tested in designing an optimal energy efficient distillation columns sequence of NGLs fractionation unit. By using the driving force method, maximum of 21 % energy reduction is able to be achieved by changing the sequence of NGLs fractionation unit. It can be concluded that, the sequence determined by the driving force method is able to reduce energy used for NGLs fractionation. These findings show that the methodology is able to design energy efficient distillation columns for NGLs fractionation sequence in an easy, practical and systematic manner.