Energy integrated distillation column sequence

Abstract

Recently, energy consumption has become a crucial consideration especially for energy-intensive distillation process. This issue becomes worse for a multi-component process which will involve a series of distillation columns for one process. Furthermore, the absence of a reliable process to cater for a big production with desired product purity would be the reason to maintain this distillation process. Hence, the only way to solve the issue is to improve the energy efficiency of the distillation process. For that, this study aimed to develop a new holistic, systematic and comprehensive framework for a feasible energy integrated distillation column sequence (EIDCS). The feasibility aspects in this study can be divided into process/design feasibility and economic feasibility. The proposed framework consists of six stages. It started from the formulation and extraction of the feed information in stage 1 before moving on to the step of column sequencing in stage 2 which is based on the number of the components; either in a manual energy analysis for all possible sequences for less than 5 components or straightaway to the implementation of the driving force method for the vice-versa case. In stage 3, simulations for the selected sequences were carried out and the results were brought to stage 4 for application of the thermal pinch analysis via problem table algorithm (PTA) for a range of ?Tmin from 5 to 40 °C. Then the total energy requirement (TER) was obtained and the heat exchanger network (HEN) in a form of a grid diagram (GD) was developed to meet the proposed design. The process/design feasibility was then obtained based on the value of the ft correction factor for each heat exchanger in the process. Then, the design(s) underwent an economic analysis in stage 5 involving the calculation of capital costs (CC) and annual operating costs (AOC). Lastly, an optimal solution in terms of the arrangement of the sequence and the ?Tmin was obtained from the calculation of the multi-objective functions in stage 6. Five case studies had been selected to evaluate and verify the proposed framework. It successfully recorded a range of energy saving from 30 to 42% compared to the existing sequence. The optimum sequence for case study 1 is split sequence with ?Tmin value from 5 to 30 °C. split-1D sequence from 5 to 20 °C is regarded as the optimum sequence for case study 2 and case study 3. For case study 4 and 5, the optimum sequences are split-1-split (?Tmin from 5 to 25 °C) and split-1-D-split-2-D (?Tmin from 5 to 20 °C). All optimum designs can be regarded as process feasible whereby all heat exchangers in the process recorded a value of ft correction factor of 1.0. Besides, the methods also reduced the CC and AOC of the process to $870,000 and $4.28 M for case study 3. The same costs have been reduced approximately 45% for the CC and 10% for the AOC for case study 4. Case study 5 also followed the same trend with a cost saving at $476,000 for CC and around $2.78 M for the AOC compared to the existing sequence. Overall, the results suggested that the framework has successfully produced a feasible EIDCS for all cases in a holistic, systematic and comprehensive manner.