26th - 27th January 2015 CCECP, Singapore 3rd Annual International Conference on Chemistry, Chemical Engineering and Chemical Process (CCECP), 26th - 27th January 2015, Singapore Keynote Address by Prof. G.P. Rangaiah on Improving Energy Efficiency of Chemical Processes by Heat Exchanger Network Retrofitting G. P. Rangaiah* and B. K. Sreepathi Department of Chemical and Biomolecular Engineering National University of Singapore, Singapore 117585 *Corresponding Author’s Email: [email protected] Abstract Chemical processes involve reactions and separations for converting raw materials into valuable products required by the society. These processes often occur at elevated temperatures whereas raw materials are at ambient temperature and products should be stored at about room temperature. Hence, energy is required for heating material/process streams before reaction and also for separation such as by distillation, and then outlet streams have to be cooled using cold utilities such as water and air. There is potential to recover thermal energy from hot process streams and to reuse it for heating cold process streams. For this, heat exchanger networks (HEN) are employed in process plants. Thus, energy/heat integration and HEN help to improve energy efficiency of chemical processes. This led to numerous studies on synthesis and design of HEN in the last four decades after the oil crisis of 1970’s. The existing plants were designed and established many years ago according to the then prevailing economic and technological conditions. Energy resources are depleting, and environmental concerns and energy prices are rising. Hence, improving energy integration in existing process plants is essential for enhancing energy efficiency of chemical processes since most of their energy requirement is for heating and cooling of process streams. Energy integration can be increased by retrofitting (also known as revamping) of HEN in existing process plants; it involves area addition, relocating existing heat exchangers and/or installing new exchangers to reduce hot and cold utilities (i.e., energy) required. Methods for HEN retrofitting can be broadly classified into three categories: pinch analysis based methods, mathematical programming based methods and hybrid methods (which selectively combine the pinch analysis and mathematical programming methods). In this keynote presentation, these methods and their applications reported in about 60 journal papers will be outlined. Then, application of multi-objective optimization (MOO) for HEN retrofitting will be discussed for a typical case study. MOO provides many optimal solutions showing the trade-off between conflicting objectives. The decision maker can choose one of them for implementation considering available budget, required investment and ease of changes to be made to the existing HEN. Reference: Sreepathi B.K. and Rangaiah G.P., Review of Heat Exchanger Network Retrofitting Methodologies and their Applications, Industrial & Engineering Chemistry Research, vol. 53, p. 11205-11220 (2014).