Abstract
The design of heat exchanger networks (HEN) in the process industry has largely focused on minimisation of operating and capital costs using techniques such as pinch analysis or mathematical modelling. Aspects of operability and flexibility, including issues of disturbances affecting downstream processes during the operation of highly integrated HEN, still need development. This work presents a methodology to manage temperature disturbances in a HEN design to achieve maximum heat recovery, considering the impact of supply temperature fluctuations on utility consumption, heat exchanger sizing, bypass placement and economic performance. Key observations have been made and new heuristics are proposed to guide heat exchanger sizing to consider disturbances and bypass placement for cases above and below the HEN pinch point. Application of the methodology on two case studies shows that the impact of supply temperature fluctuations on downstream heat exchangers can be reduced through instant propagation of the disturbances to heaters or coolers. Where possible, the disturbances have been capitalised upon for additional heat recovery using the pinch analysis plus-minus principle as a guide. Results of the case study show that the HEN with maximum HE area yields economic savings of up to 15% per year relative to the HEN with a nominal HE area.
Highlights
Heat integration has been a well-established energy saving technique for the chemical process industry since the global energy crisis in the 1970s [1]
Heuristics are proposed for each disturbance scenario that necessitates bypass placement and final stage explains the effect of total sites (TS) fluctuation on utilities based on the plus-minus principle
Since the TS of stream Hot 1 (H1) is located above the pinch, based on the plus-minus principle, the of heat exchanger HE2 is not high enough to achieve the final target temperature of Cold 2 (C2), the hot utility of heater HU1 is increased in order to satisfy the remaining heat
Summary
Heat integration has been a well-established energy saving technique for the chemical process industry since the global energy crisis in the 1970s [1]. Onishi et al [20] proposed an optimisation model to enhance the work and HENs energy efficiency and cost-effective synthesis considering the unclassified process streams. It combined the methods of mathematical programming and pinch location while adjusting the pressure and temperature of unclassified streams. Chew et al [23] applied the plus-minus principle for process modification aimed at maximising energy savings for total site heat integration (TSHI) This methodology enabled designers to identify the potential process changes to maximise energy recovery and reduce utility consumption. The proposed methodology provides a simple technique of rapidly assessing the effect of supply temperature (TS ) fluctuations in heat recovery and utility reduction without the need for detailed process simulation
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